OFFSHORE STANDARDS
DNVGL-OS-E402 Edition July 2019
Diving systems
The electronic pdf version of this document, available free of charge from http://www.dnvgl.com, is the officially binding version.
DNV GL AS FOREWORD
DNV GL offshore standards contain technical requirements, principles and acceptance criteria related to classification of offshore units.
© DNV GL AS July 2019
Any comments may be sent by e-mail to [email protected]
This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of this document. The use of this document by others than DNV GL is at the user's sole risk. DNV GL does not accept any liability or responsibility for loss or damages resulting from any use of this document. CHANGES – CURRENT
This document supersedes the January 2017 edition of DNVGL-OS-E402 Diving systems. Changes in this document are highlighted in red colour. However, if the changes involve a whole chapter, section or subsection, normally only the title will be in red colour.
Changes July 2019
Topic Reference Description
Clarification of surface system Ch.2 Sec.1 [2.1] A requirement to submit treatment tables has been added, requirements. with operational times redefined accordingly. The ability to add
additional components to a system (LDC/differing mobilisation Changes - current arrangements) is now considered as well.
General updates. Ch.2 Sec.2 [4.1.5] Guidance to allow the use of small industrial sourced gas bottles without a corrosion allowance added.
Ch.2 Sec.3 [1.9.12] Temperature shut downs based on lubricant added.
Ch.2 Sec.6 [3.1.1] Over the side/stern operation for surface supplied diving is now restricted to a maximum significant wave height of 2 meters..
Ch.3 Sec.1 [9.2.1] Removal of the minimum hydro test value for windows which conflicted with ASME PVHO.
Ch.3 Sec.1 [9.3.9] Environmental control testing has been expanded to reflect current practice.
Ch.3 Sec.1 [2.2.4] Typical areas to be considered during the risk analysis for evacuation have been added including the impacts of split level diving.
Ch.3 Sec.1 [2.2] Requirements have been added within the systematic review (FMEA) to collate findings that require actions in operation. Testing requirements for the systematic review (FMEA) added.
Ch.3 Sec.1 [2] The purpose and content of the safety objective is rewritten, primarily to be more descriptive of expectations toward the document. Appendix A has been deleted.
Ch.3 Sec.2 [2.1.10] Requirements for the use of expansion joints (bellows) has been added.
Ch.3 Sec.2 [4.1.4] A method to allow ancillery pressure vessels to follow the same inspection frequency as the chambers has been added.
Ch.3 Sec.3 [5.1.6] Limitation on NPT thread size added.
Ch.3 Sec.3 [5.3.1] Equalisation lines are removed.
Ch.3 Sec.3 [6.1.4] Requirements to the performance of bell insulation added.
Ch.3 Sec.3 [6.7.1] Guidance on treatment for bacteria within chamber gas reclaim added.
Ch.3 Sec.4 [5.4.1] Volume within gas analysis pipelines is now considered for time delays. A timed option instead of analysis for emergency bell CO2 control added.
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DNV GL AS Topic Reference Description
Ch.3 Sec.5 [2.1.3] A description of how to handle items that cannot be certified with respect to limiting ignition risk within chambers is added based upon USN.
Ch.3 Sec.5 [4.1.5] Fixed fire fighting capacity in the SPHL is now differentiated from DDCs.
Ch.3 Sec.6 [2.1.6] Line out counter now specified as a requirement.
Ch.3 Sec.6 [2.3.3] Requirements for bell buoyancy materials added based upon UWT rules.
Ch.3 Sec.8 [1.19] Launch requirements for HRCs added. Changes - current Ch.3 Sec.8 [1.6] The interpretation regarding use of the bell as an evacuation method has been copied to this document.
Simplification of redundancy Ch.2 Sec.1 [4] Base redundancy case clarified while the safety objective is requirements for surface moved to [4.6]. This should allow simple systems to just follow systems. the base redundancy concept.
Ch.2 Sec.6 [2.3.8] Requirements to safety interlocks within LARS systems have been added. The needed Interlocks for coordinating A frame and winch movements is also clarified.
Ch.2 Sec.6 [2] The required arrangement of LARS is clarified in [2.1] and the required minimum redundancy specified in [2.2.2].
Update requirements for air Ch.2 Sec.1 [4.3.2] Essential services are now required to last the entire treatment dive equipment. table.
Ch.2 Sec.1 [4.6] The safety objective has been rewritten to try and clarify intent. Requirements have been added within the systematic review (FMEA) to collate findings that require actions in operation. Testing requirements for the systematic review (FMEA) added.
Ch.2 Sec.1 [5.2.3] Temperature ranges redefined, particularly for ventilated chambers that have internal temperatures linked to ambient temperature.
Ch.2 Sec.2 [2.2.3] Testing of the PVHO may now be based upon actual cycles experienced. Where chambers are not used operationally but in a standby function, acceptance of records is accepted. A means to include ancillary pressure vessels within the same testing as the chamber is described.
Ch.2 Sec.3 [2.3.3] Emergency gas stored within the basket/wet bell now specified as 20 min duration.
Ch.2 Sec.3 [2] Primary, secondary and emergency gas supplies have been defined and gas storage requirements are based upon the treatment table specified.
Ch.2 Sec.3 [4.2.1] Hot water for the divers is expected for systems operating below 3oC.
Ch.2 Sec.3 [4.3.2] Where heating and cooling is provided temperature requirements have been added.
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DNV GL AS Topic Reference Description
Ch.2 Sec.3 [4.6.1] Requirements to ventilated chambers have been added which will govern gas storage and operating temperatures.
Ch.2 Sec.3 [4.6.2] All systems will now test environmental control including ventilated chambers in order to confirm ventilation rates.
Ch.2 Sec.3 [4] It is recognised that there is no clear temperature cut offs for surface supplied diving and the concept of applying a temperature rating has been revised. Only systems with active heating and cooling will now get a definative operating temperature range. Others will be based upon deviation from ambient temperature.
Ch.2 Sec.5 [3.1] Position on what constitutes the outer area and the Changes - current requirements that apply for surface systems is clarified and based on evacuation time.
Ch.2 Sec.8 While requirements remain essentially with the shelf authorities the following requirements have been added. Evacuation time, the need to supply O2 within the normal lifeboats and the ability to recover from the water.
Editorial corrections
In addition to the above stated changes, editorial corrections may have been made.
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DNV GL AS CONTENTS
Changes – current...... 3
Chapter 1 Introduction...... 10 Contents Section 1 General...... 10 1 Introduction...... 10 2 References...... 11
Chapter 2 Surface diving systems...... 27 Section 1 Design philosophy and premises...... 27 1 Introduction...... 27 2 Documentation...... 27 3 Safety philosophy...... 28 4 Surface diving system philosophy...... 29 5 External and internal environmental conditions...... 33 Section 2 Pressure vessels for human occupancy, gas storage and other purposes...... 36 1 Introduction...... 36 2 General principles for design of chambers...... 40 3 Welded pressure vessels, materials, fabrication and strength...... 44 4 Gas cylinders...... 45 5 Acrylic plastic windows...... 46 Section 3 Life support systems including piping, hoses, valves, fittings, compressors, filters and umbilicals...... 49 1 Introduction...... 49 2 Gas distribution and control system...... 53 3 Gas storage...... 57 4 Diver’s heating and environmental conditioning in chambers...... 58 5 Piping systems...... 60 6 Hoses...... 61 7 Valves...... 62 8 Fittings and pipe connections...... 63 9 Pressure regulators...... 63 10 Compressors for breathing gas systems...... 63 11 Purification and filter systems...... 63 12 Umbilicals...... 64 Section 4 Electrical systems...... 65 1 Introduction...... 65
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DNV GL AS 2 System design...... 67 3 Equipment in general...... 70 4 Miscellaneous equipment...... 71 5 Cables...... 72 Section 5 Fire prevention, detection and extinction...... 73 1 Introduction...... 73 Contents 2 Fire protection...... 74 3 Fire detection and alarm system...... 74 4 Fire extinguishing...... 75 5 Miscellaneous equipment...... 75 Section 6 Launch and recovery systems (LARS)...... 77 1 Introduction...... 77 2 Design principles...... 79 3 Strength...... 83 Section 7 Instrumentation and communication...... 85 1 Introduction...... 85 2 Instrumentation...... 86 3 Communication...... 90 Section 8 Evacuation systems...... 92 1 Introduction...... 92
Chapter 3 Saturation diving systems...... 94 Section 1 Design philosophy and premises...... 94 1 Introduction...... 94 2 Safety objective/redundancy specification...... 94 3 General premises...... 98 4 System design principles...... 99 5 Diving system arrangement and layout...... 100 6 Environmental conditions...... 101 7 External and internal system condition...... 103 8 Documentation...... 105 9 Inspection and testing...... 107 10 Marking and signboards...... 110 Section 2 Pressure vessels for human occupancy, gas storage and other purposes...... 112 1 General...... 112 2 General principles for design of chambers and bells...... 114 3 Welded pressure vessels, materials and fabrication...... 117 4 Strength of welded pressure vessels...... 119 5 Gas cylinders...... 120
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DNV GL AS 6 Acrylic plastic windows...... 122 Section 3 Life support systems...... 124 1 General...... 124 2 Gas storage...... 125 3 Gas distribution...... 127 4 Oxygen systems...... 129 Contents 5 Piping systems...... 129 6 Environmental conditioning in bell and chambers...... 130 7 Gas control systems...... 132 8 Closed circuit breathing systems (CCBS)...... 133 9 Diving crew facilities...... 134 Section 4 Electrical, instrumentation and communication systems...... 136 1 General...... 136 2 System design...... 138 3 Equipment selection and installation...... 141 4 Communication...... 142 5 Instrumentation...... 145 Section 5 Fire prevention, detection and extinction...... 149 1 General...... 149 2 Fire protection...... 149 3 Fire detection and alarm system...... 150 4 Fire extinguishing...... 150 Section 6 Launch and recovery systems...... 152 1 General...... 152 2 Design principles...... 153 3 Strength...... 156 Section 7 Pipes, hoses, valves, fittings, compressors, filters and umbilicals...... 158 1 General...... 158 2 Components and hoses for oxygen services...... 159 3 Pipes and hoses...... 160 4 Valves and pressure regulators...... 161 5 Fittings and pipe connections...... 161 6 Compressors...... 161 7 Purification and filter systems...... 161 8 Umbilicals...... 162 Section 8 Hyperbaric evacuation systems...... 164 1 Introduction...... 164
Appendix A Dynamic loads in bell handling systems..... 175
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DNV GL AS 1 General...... 175 2 Loads on negative buoyant bell...... 176 3 Loads on a positive buoyant bell (at surface)...... 179 4 Design loads...... 179
Changes – historic...... 181 Contents
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DNV GL AS CHAPTER 1 INTRODUCTION
SECTION 1 GENERAL
1 Introduction Section 1
1.1 Objectives
1.1.1 The objectives of this standard are to give criteria and guidance on design, fabrication, installation, testing and commissioning of diving systems.
1.1.2 Further objectives of this standard are to: a) provide an internationally acceptable standard of safety for diving systems by defining minimum Chapter 1 requirements for the design, materials, fabrication, installation, testing, commissioning, operation, repair, and re-qualification b) serve as a technical reference document for classification and verification services c) serve as a technical reference document in contractual matters between purchaser and contractor d) serve as a guideline for designers, purchaser, and contractors.
1.1.3 General guidance is provided as to the use and interpretation of the standard and text from IMO code of safety for diving systems, 1995 resolution A.831 (19) is included for reference. In the IMO text, this code is referred to as the code.
1.1.4 The text from IMO code of safety for diving systems, 1995 resolution A.831 (19) is included as normative reference.
1.2 Scope
1.2.1 The scope is defined in each section for the various disciplines and may refer to standards that apply to the discipline in general, such as for electrical systems. In these cases this document only contains requirements that are particular to diving systems, whereas the generic requirements are given in the referred rules, standard or code. The combined requirements shall then constitute the scope.
1.2.2 Requirements for the diving support vessels, such as the requirements for floatation and positioning ability, are not given in this standard but provided in DNVGL-RU-SHIP Pt.5 Ch.10.
1.2.3 Where the code requires that a particular fitting, material, appliance, apparatus, item or type of equipment should be fitted or carried in a system, or that any particular provision should be made, or any procedure or arrangement complied with, the administration may allow alternative arrangements in that system, provided that the administration is satisfied that such alternatives are at least as effective as the requirements of the code. (See IMO code of safety for diving systems Ch.2 design, construction and survey 1.5 equivalents.)
1.2.4 This standard is not applicable to SCUBA diving, submersibles including atmospheric diving suits or submarines.
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DNV GL AS 1.3 Application
1.3.1 Where reference is made to codes other than DNV GL documents, the valid revision shall be taken as the revision that was current at the date of issue of this standard.
1.3.2 In case of conflict between requirements of this standard and a reference document, the requirements Section 1 of this standard shall prevail.
1.3.3 For use of this standard as basis for classification including the relevant procedural requirements see DNVGL-RU-OU-0375 Diving systems
1.4 Document structure
1.4.1 Besides this introduction chapter, this standard consist of two technical chapters: Chapter 1 — Ch.2 describing design philosophy and all technical and procedural requirements for surface diving systems — Ch.3 Sec.1 describing design philosophy and all technical and procedural requirements for saturation diving systems
1.4.2 General applicable procedural requirements, including documentation and survey and testing are included in the sub-section [1] of the relevant sections both chapters.
1.4.3 Ch.2 is completed with an appendix providing guidance on the selection of a safety objective.
1.4.4 Ch.3 Sec.1 is completed with an appendix providing guidance on dynamic loads in bell handling systems.
2 References
2.1 Normative references The latest revisions of the following documents apply as normative references:
Table 1 Rules and standards for certification
Reference Title
DNVGL-RU-SHIP Rules for classification: Ships
DNVGL-RU-OU Rules for classification: Offshore units
DNVGL-ST-0378 Standard for offshore and platform lifting appliances
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DNV GL AS Table 2 Offshore standards
Reference Title
DNVGL-OS-A101 Safety principles and arrangements
DNVGL-OS-D201 Electrical installations
DNVGL-OS-D202 Instrumentation, safety and telecommunication systems Section 1
DNVGL-OS-D301 Fire protection
Table 3 Class programme
Reference Title
Type approval DNVGL-CP-0183 Flexible hoses, non-metallic materials Chapter 1 Type approval DNVGL-CP-0184 Flexible hoses with permanently fitted couplings, metallic materials
Table 4 Class guidelines
Reference Title
DNVGL-CG-0169 Quality survey plan for offshore class new building surveys
Table 5 Recommended practices
Reference Title
DNVGL-RP-E403 Hyperbaric evacuation systems
Table 6 Other normative references
Reference Title
ASME VIII div.1 or div.2 ASME boiler and pressure vessel code rules for construction of pressure vessels
ASME PVHO-1 Safety standard for pressure vessels for human occupancy
ASME PVHO-2 Safety standard for pressure vessels for human occupancy: in service guidelines
ASTM G93-03 Standard practice for cleaning methods and cleanliness levels for materials and equipment used in oxygen-enriched environments
API 17E Specification for subsea production control umbilicals
ISO 9000 Quality management systems - Fundamentals and vocabulary
EN 13096 Transportable gas cylinders, condition for filling gases into receptacles, single component gases
EN 13099 Transportable gas cylinders, condition for filling gas mixtures into receptacles
EN ISO 10524-1 Pressure regulators for use with medical gases
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DNV GL AS Reference Title
EN ISO 9809-1 Gas cylinders, refillable seamless steel gas cylinders, design, construction and testing, part 1: quenced and tempered steel cylinders with tensile strength less than 1100 MPa
EN ISO 9809-2 Gas cylinders, refillable seamless steel gas cylinders, design, construction and testing, part 2: quenced and tempered steel cylinders with tensile Section 1 strength greater or equal to 1100 MPa
ISO 18119 Gas cylinders-Seamless steel and seamless aluminium-alloy gas cylinders and tubes, Periodic inspection and testing
EN 10204 Metallic products, types of inspection documents
EN ISO 11120 Gas cylinders, refillable seamless steel tubes for compressed gas transport, of water capacity between 150 l and 3000 l, design construction
and testing Chapter 1
EN 16753 Gas cylinders, periodic inspection and testing, in situ (without dismantling) of refillable seamless steel tubes of water capacity between 150 l and 3000 l, used for compressed gases
EN 13445 Unfired pressure vessels
EN 12021 Respiratory equipment compressed gases for breathing apparatus
ISO/IEC/17065 Conformity assessment, requirements for bodies certifying products, processes and services
EN 1708-1 Welding, basic weld joint details in steel, part 1 pressurized components
IMO resolution A.831 (19) Code of safety for diving Systems, 1995
IMO resolution A.692 (17) Guidelines and specifications for hyperbaric evacuation systems, 1991
IMO MSC.1/Circ.1580 (16 June 2017) Guidelines for vessels with dynamic positioning systems
IMO Res. MSC 149 (77) See SOLAS reg. III/6.2.1
IMO Res. MSC 307 (88) (FTP code)
IMO Res. MSC337 (91) Code on noise levels on-board ships
IEC No.79-10 International Electro technical Commission's publication No.79-10, and IMO (MODU) code Ch.6
ISO 6385 Ergonomic principles in the design of work systems
ISO 9000 Quality management
ISO 10013 Guidelines for quality management system documentation
ISO 10380, BS 6501 Pipework, corrugated metal hoses and hose assemblies
ISO 10474 Steel and steel products, inspection documents
ISO 13628-5 Petroleum and natural gas industries, design and operation of subsea production systems, part 5: subsea control umbilicals
PD 5500 Specification for unfired fusion welded pressure vessels
Note: see also Appendix C list of sources to assist in obtaining reference documents
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DNV GL AS 2.2 Informative references
Table 7 Informative references
Reference Title
NORSOK Standard U-100 Manned underwater operations Section 1
ISO 10297 Gas cylinders, cylinder valves, specification and type testing
Gas cylinders, compatibility of cylinder and valve materials with gas ISO 11114-3 contents, part 3: autogenous ignition test in oxygen atmosphere
Part 1: pressure regulators for use with medical gases, part 1: pressure ISO 10524-1 regulators and pressure regulators with flow-metering devices Chapter 1 (NFPA) Codes National fire protection agency
SOLAS 1974 , Consolidated edition International convention for the safety of life at sea
Guidance note: The latest revision of the DNV GL documents may be found in the publication list at the DNV GL website www.dnvgl.com.
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2.3 Terminology and definitions
2.3.1 Verbal forms
Term Definition
shall verbal form used to indicate requirements strictly to be followed in order to conform to the document
verbal form used to indicate that among several possibilities one is recommended as particularly suitable, should without mentioning or excluding others
may verbal form used to indicate a course of action permissible within the limits of the document
Note: in the cases where text from the IMO code of safety for diving systems Ch.2. design, construction and survey is used, the IMO use of should shall be interpreted as shall.
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DNV GL AS 2.4 Definitions
Term Definition
Administration The government of the state whose flag a ship or floating structure which carries a diving system is entitled to fly or in which the ship or floating structure is registered
(see IMO code of safety for diving systems Ch.2 design, construction and survey Section 1 1.3.1)
Agreement, by agreement Unless otherwise indicated, accepted/agreed in writing between manufacturer/ contractor and purchaser. When the standard is applied as basis for certification or classification by DNV GL, the terms shall mean approved upfront in writing by DNV GL.
As-built survey Survey of the installed and completed diving system, which is performed to verify that the completed installation work meets the specified requirements, and to Chapter 1 document deviations from the original design, if any.
Basket A divers basket (sometimes known as a stage) is a frame and mesh construction designed to accommodate divers whilst they are lifted in and out of the water
Bell A diving bell is a frame incorporating a dome, and including appendages, for transfer of divers between the underwater work site and the deck or the surface chamber (TUP or DDC). In the context of this standard, bell is defined as an open bell/wet- bell. (See open bell, closed bell and wet bell)
Bottle A pressure container for the storage and transport of gases under pressure (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.2)
Breathing gases All gases and gas mixtures which are used during diving missions respectively during use of breathing apparatus. Depending on the grade of oxygen, complimentary rules may be taken into consideration. The most common breathing gases used for diving are air, nitrox, HeMix, Trimix and pure oxygen.
Builder Signifies the party contracted to build a diving system in compliance with this standard
Built in breathing system (BIBS) A system of gas delivery to masks, located in the decompression chambers, baskets and wet-bells. This system facilitates breathing in the event of a contaminated atmosphere, and allows for the use of therapeutic gases during decompression. BIBS may in rare cases be closed circuit breathing systems (see CCBS definition) but are normally open circuit systems where the exhaled gas is dumped to atmosphere.
Category A machinery spaces Those spaces and trunks to such spaces as defined in the international convention for the safety of life at sea, 1974, as amended (See IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.20)
Chamber Surface decompression, pressure or compression chambers (see also DDC), hereafter called the chambers, and are pressure vessels for human occupancy.
Closed bell A sealed submersible diving chamber (SDC) that locks on and off the chamber where the divers decompress (DDC). Pressure differentials are retained by way of a closed door sealing the divers in at pressures, elevated or lowered compared to the surrounding pressure.
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DNV GL AS Term Definition
Closed circuit breathing system A system for supply of breathing gas to the diver and saving of his exhaled gases for (CCBS) re-circulation after scrubbing and replenishing
Commissioning In relation to diving systems, refers to activities which take place after installation and prior to operation, comprising the tests and trials
Compact umbilical Umbilical consisting of composite bundles of hoses, cables and strength members in Section 1 a braiding or sheathing
Compartment Part(s) of a chamber sufficiently large to contain at least one person and which may have an internal pressure different from adjacent compartments
Competent body/competent In this context defined as a company, organisation or person recognised as fit to person carry out specified inspections or tests. The recognition may be by DNV GL or by a statutory agency. Chapter 1 Compressor A mechanical device that increases the pressure of a gas by reducing its volume. The increase of pressure may be carried out by pistons, screws or diaphragms. A compressor designed with inlet (suction) pressure above atmospheric is defined as booster. Depending on the application medium, purification and/or filter systems may be provided downstream.
Construction phase All phases during construction, including fabrication, installation, testing and commissioning, up until the installation or system is safe and operable for intended use. In relation to diving systems, this includes procurements, manufacture assembly, rectification, installation, testing, commissioning and repair.
Contractor A party contractually appointed by the purchaser to fulfil all, or any of, the activities associated with design, construction and operation
Control stations Normally as defined in reg.3 and referred to in regulation 20, Ch.II-2 of the International Convention for the Safety of Life at Sea. Control stand or control station is a control station in which one or more of the following control and indicator functions are centralized: a) indication and operation of all vital life support conditions, including pressure control b) visual observation, communication systems including telephones, audio- recording and microphones to public address systems c) disconnection of all electrical installations and Insulation monitoring. d) provisions for calibration of and comparison between gas analysing e) indication of temperature and humidity in the inner area f) alarms for abnormal conditions of environmental control systems g) fixed fire detection and fire alarm systems h) ventilation fans i) automatic sprinkler, fire detection and fire alarm systems j) launch and recovery systems, including interlock safety functions k) operation and control of the hyperbaric evacuation system.
Corrosion allowance Extra wall thickness added during design to compensate for any reduction in wall thickness by corrosion (internally and externally) during operation
Demobilised Diving system is stored on shore and requires a full maintenance regime for mobilisation
Deck decompression chamber Deck mounted pressure vessel for human occupancy used for decompression (DDC)
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DNV GL AS Term Definition
Depth The water depth or equivalent pressure to which the diver is exposed at any time during a dive or inside a surface compression chamber or a diving bell (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.6)
Design All related engineering to design of the diving system Section 1
Design life The initially planned time period from initial installation or use until permanent decommissioning of the equipment or system. The original design life may be extended after a re-qualification.
Design load For PVHOs see Ch.2 Sec.3, Ch.3 Sec.2. For LARS see Ch.2 Sec.6and Ch.3 Sec.6.
Design phase An initial phase that takes a systematic approach to the production of specifications, drawings and other documents to ensure that the diving system meets specified requirements (including design reviews to ensure that design output is verified Chapter 1 against design input requirements). See ISO 9001.
Design temperature, minimum The lowest possible temperature to which the equipment or system may be exposed to during installation and operation, irrespective of the pressure. Environmental as well as operational temperatures shall be considered.
Guidance note: For LARS the design temperature is defined in DNVGL-ST-0378 standard for offshore and platform lifting appliances.
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Design temperature, maximum: The highest possible temperature to which the equipment or system may be exposed to during installation and operation. Environmental as well as operational temperatures shall be considered.
Diver heating A system for actively heating the divers in the water or in the inner area
Divers Personnel subjected to higher ambient pressure than one atmosphere
Diving bell A submersible compression chamber, including its fitted equipment, for transfer of diving personnel under pressure between the work location and the surface compression chamber (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.7)
Diving system The whole plant and equipment necessary for the conduct of diving operations (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.8)
Diving system (in DNV GL terms) The whole plant and equipment necessary for safe conduct of diving operations where compression and decompression of divers are taking place
dmax Maximum operating depth of the surface diving system. This is the depth corresponding to the maximum pressure for pressurizing divers. (For Classified systems this may be specified in the certificate and data sheet).
ECU Environmental control unit. Maintains Temperature, reduces humidity and may include removal of carbon dioxide.
Enriched Air Nitrogen oxygen mixtures with elevated oxygen content (see NITROX)
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DNV GL AS Term Definition
Equipment lock A pressure tight independent lock mounted on the shell of the chamber providing the means for locking in equipment necessary for the divers and the operation of the system (see also medical lock)
Evacuation system A system whereby divers under pressure can be safely evacuated from a ship or floating structure to a position where decompression can be carried out Section 1 (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.9)
Fabrication Activities related to the assembly of objects with a defined purpose. In relation to diving systems, fabrication refers to e.g. deck decompression chambers, wet-bells, and pressure vessels for gas storage, environmental control systems, launch and recovery systems etc.
Fabricator The party performing the fabrication (in this context, normally of windows for Chapter 1 PVHOs)
Failure An event affecting a component or system and causing one or both of the following effects: — loss of component or system function — deterioration of functional capability to such an extent that the safety of the installation, personnel or environment is significantly reduced.
Fatigue Cyclic loading causing degradation of the material
Flag administration The maritime administration of a vessel's country of registry
Gas See breathing gas
Gas containers Cylinders, bottles and pressure vessels for storage of pressurized gas
Guidance notes Contain advice which is not mandatory for the assignment or retention of class, but with which the Society, in light of general experience, advises compliance
Handling system The plant and equipment necessary for raising, lowering and transporting the diving bell between the work location and the surface compression chamber (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.10) (see launch and recovery system (LARS))
Hazard A deviation (departure from the design and operating intention) which could cause damage, injury or other form of loss (chemical industries association HAZOP guide).
Hazardous areas Those locations in which an explosive gas-air mixture is continuously present, or present for long periods (zone O); in which an explosive gas-air mixture is likely to occur in normal operation (zone 1); in which an explosive gas-air mixture it not likely to occur, and if it does it will only exist for a short time (zone 2). (See IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.11)
HAZOP (hazard and operability The application of a formal systematic critical examination to the process and study) engineering intentions of new or existing facilities to assess the hazard potential of inadvertent operation or malfunction of individual items of equipment and their consequential effects on the facility as a whole (chemical industries association HAZOP guide)
Hydro-test or hydrostatic test See pressure test
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DNV GL AS Term Definition
Hyperbaric evacuation system System for evacuating divers under pressure. This includes the hyperbaric (HES) evacuation unit (HEU), the launch and recovery and control systems.
Hyperbaric rescue vessel (HRV) IMO uses the term hyperbaric evacuation unit (HEU) see above
Inner area The areas which are inside the chambers. Interconnecting trunks are considered
part of the inner area when the door is opened into the chamber. Section 1
Inspection Activities such as measuring, examination, testing, gauging one or more characteristics of a product or service and comparing the results with specified requirements for determine conformity
Installation (activity) The operations related to installing the equipment, diving system or support structure, e.g. mounting chambers and handling systems etc., including final testing and preparation for operation Chapter 1 Installation manual (IM) A document prepared by the contractor to describe and demonstrate that the installation method and equipment used by the contractor will meet the specified requirements and that the results can be verified
Launch and recovery system The system and equipment necessary to launch and recover the divers, the diver’s (LARS) basket or wet-bell to the chambers as well as transport the divers between the surface support unit and the underwater working site, including any guide rope systems and cursor systems
Lay-up A terminology used for diving systems that are out of commission. In this state the diving system may be installed on board or permanently stored on shore.
Life support system The gas supply, breathing gas system, decompression equipment, environmental control system and equipment required to provide a safe environment for the diving crew in the diving bell and the surface compression chamber under all ranges of pressure and conditions they may be exposed to during diving operations (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.12)
Life support systems (in DNV GL The systems comprising gas supply systems, breathing gas systems, pressure terms) regulating systems, environmental control systems, and systems required to provide a safe habitat for the divers, in the basket, the wet-bell and the chamber compartments under normal conditions during diving operation
Living compartment The part of the surface compression chamber which is intended to be used as the main habitation for the divers during diving operations and which is equipped for such purpose (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.13)
Living compartment (in DNV GL A compartment which is intended to be used as the main habitation for the divers terms) and which is equipped as such
Load Any action causing stress, strain, deformation, displacement, motion, etc. to the equipment or system
Load effect Effect of a single load or combination of loads on the equipment or system, such as stress, strain, deformation, displacement, motion, etc.
Load effect factor The partial safety factor by which the characteristic load effect is multiplied to obtain the design load effect
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DNV GL AS Term Definition
Lot A number of components from the same batch. E.g. same heat, the same heat treatment batch and with the same dimensions.
Main components Main components of a diving system include the surface compression chamber, diving bell, handling system and fixed gas storage facilities
(see IMO code of safety for diving systems Ch.2 design, construction and survey Section 1 1.3.14)
Manufacture Making of articles or materials, sometimes in larger volumes. In relation to diving systems, refers to activities for the production of pressure vessels, distribution panels and other components, performed under contracts from one or more contractors.
Manufacturer Signifies the entity that manufactures the material or product, or carries out part production that determines the quality of the material or product, or does the final Chapter 1 assembly of the product
Mating device The equipment necessary for the connection and a disconnection of a diving bell to a surface compression chamber (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.15)
Maximum operating depth Maximum operating depth of the diving system is the depth in metres or feet of seawater equivalent to the maximum pressure for which the diving system is designed to operate (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.16)
Medical lock A pressure tight independent lock mounted on the shell of the chamber providing the means for locking in provisions, medicine and equipment necessary for the divers and the operation of the system (see also equipment lock)
NDT level The extent and acceptance criteria for the NDT of the components
NITROX Nitrogen oxygen mixtures with elevated oxygen content (see enriched air)
Nominal outside diameter The specified outside diameter. This shall mean the actual outside diameter.
Nominal wall thickness The specified non-corroded wall thickness, which is equal to the minimum steel wall thickness plus the manufacturing tolerance
Normal cubic meters (Nm3) is taken as cubic meters of gas at standard conditions of 0°C and 1.013 bar.
Open bell (also known as wet bell) A suspended canopy chamber, open at the bottom like a moon pool structure that is lowered underwater to operate as a stage for the divers with the advantage of providing an air pocket for refuge and a space for communication outside the mask/ helmet
Operation, incidental Conditions that are not part of normal operation of the equipment or system. In relation to diving systems, incidental conditions may lead to incidental pressures.
Operation, normal Conditions that arise from the intended use and application of equipment or system, including associated condition and integrity monitoring, maintenance, repairs etc. In relation to diving systems, this should include, start and finish of dives (pre- and post-dive checks), treatment of decompression-related incidents, gas transfer and changing out of consumables.
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DNV GL AS Term Definition
Operations (phase) The phase when the diving system is being used for the purpose for which it was designed
Pressure, system test In relation to diving systems, this is the internal pressure applied to the component or system during testing on completion of installation work to test the diving system for tightness (normally performed as hydrostatic testing) Section 1 Organization Organization means the International Maritime Organization (IMO) (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.17)
Out of roundness The deviation of the perimeter from a circle. This can be stated as ovalisation (%), or as local out of roundness, e.g. flattening, (mm).
Outer area Those areas of the diving system that are exposed to atmospheric conditions during operation, i.e. outside the inner system and the room or area that surrounds or Chapter 1 contains the diving system.
Ovalisation The deviation of the perimeter from a circle. This has the form of an elliptic cross section.
Owner Signifies the registered owner or manager of the diving system or any other organization or person who has assumed the responsibility for operation of the diving system and who on assuming such responsibility has agreed to take over all the duties and responsibilities. See DNVGL-RU-OU-0300 Ch.1 Sec.1 [4].
Oxygen systems Systems intended for a gas with a higher oxygen percentage than 25
Personal diving equipment Equipment carried by the diver on his person including his tools, diving suit, diving helmet and self-contained breathing apparatus with gas bottles. This is normally not included in the diving system specified in the standard
Plan approval Signifies a systematic and independent examination of drawings, design documents or records in order to verify compliance with the rules or statutory requirements. Plan approval will be carried out at the discretion of the Society, which also decides the extent and method of examination.
Planned maintenance system A system for planning and recording of maintenance activities (PMS)
Pressure, collapse Characteristic resistance against external over-pressure
Pressure control system In relation to diving systems, this is the system for control of the pressure in the various systems, comprising the pressure regulating system, pressure safety system and associated instrument and alarm systems
Pressure, design In relation to diving system assemblies, this is the maximum internal pressure during normal operation, referred to a specified reference point, to which the component or system section shall be designed. The design pressure shall take account of the various pressurised components in the adjoining systems, and their relative design pressures.
Pressure regulating system In relation to diving systems, this is the system which ensures that, irrespective of the upstream pressure, a set pressure is maintained downstream (at a given reference point) for the component
Pressure safety system The system which, independent of the pressure regulating system, ensures that the allowable set pressure is not exceeded
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DNV GL AS Term Definition
Pressure test The hydrostatic pressure test initially performed at the manufacturer of the pressure vessel in accordance with requirements in the design code
Pressure vessel A container capable of withstanding an internal maximum working pressure greater than or equal to 1 bar
(see IMO code of safety for diving systems Ch.2 design, construction and survey Section 1 1.3.18)
Purchaser The owner or another party acting on his behalf, who is responsible for procuring materials, components or services intended for the design, construction, installation or modification of a diving system
Purification and filter systems Purification and filter systems are used to remove contaminants from breathing gases after compression has taken place
Quality assurance (QA) Planned and systematic actions necessary to provide adequate confidence that a Chapter 1 product or service will satisfy given requirements for quality
Quality plan (QP) The document setting out the specific quality practices, resources and sequence of activities relevant to a particular product, project or contract. A quality plan usually makes reference to the part of the quality manual applicable to the specific case.
Quality system Signifies both the quality management system and established production and control procedures
Reliability The probability that a component or system will perform its required function without failure, under stated conditions of operation and maintenance and during a specified time interval
Re-qualification The re-assessment of a design due to modified design premises and or sustained damage
Resistance The capability of a structure, or part of a structure, to resist load effects
Risk The qualitative or quantitative likelihood of an accident or unplanned event occurring, considered in conjunction with the potential consequences of such a failure. In quantitative terms, risk is the quantified probability of a defined failure mode times its quantified consequence.
Risk reduction measures Those measures taken to reduce the risks to the operation of the diving system and to the health and safety of personnel associated with it or in its vicinity by: a) reduction in the probability of failure b) mitigation of the consequences of failure.
Guidance note: The usual order of preference of risk reduction measures is:
a) inherent safety b) prevention c) detection d) control e) mitigation f) emergency response.
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Safety objectives The safety goals for the construction, operation and decommissioning of the diving system including acceptance criteria for the level of risk acceptable to the owner
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DNV GL AS Term Definition
Saturation diving Once a diver becomes saturated with the gases that make decompression necessary, the diver does not need additional decompression. When the blood and tissues have absorbed all the gas they can hold at that depth, the time required for decompression becomes constant. As long as the depth is not increased, additional time on the bottom is free of any additional decompression. Section 1 Self-propelled hyperbaric lifeboat See HEU [2.3.55] (SPHL)
Significant wave height When selecting the third of the number of waves with the highest wave height, the significant wave height is calculated as the mean of the selection
Specified minimum tensile The minimum tensile strength prescribed by the specification or standard under strength which the material is purchased
Specified minimum yield stress The minimum yield stress prescribed by the specification or standard under which Chapter 1 the material is purchased
Statement of compliance A statement or report signed by a qualified party affirming that, at the time of assessment, the defined phase, or collection of activities, met the requirements stated by the customer
Submersible decompression Closed bell chamber (SDC)
Suitable breathing gas A gas or gas mixture that is breathable to divers for the pressure and duration they are exposed to it
Supplementary requirements Requirements for material properties of component that are additional to the basic requirements, and that are intended to apply to components used for specific applications
Surface compression chamber A pressure vessel for human occupancy with means of controlling the pressure inside the chamber (see IMO code of safety for diving systems Ch.2 design, construction and survey 1.3.5)
Survey planning document As described in DNVGL-RU-OU-0375 Ch.3 Sec.2 [1]document describing the diving system and the requirements to survey and testing throughout the lifetime of the diving system
Top Maximum operation time, i.e. the time from start of pressurization of the diver, until the diver is back to atmospheric conditions
Transfer compartment Compartment that is intended to be used for a lock-in or -out operation of divers between other compartments or outer area. Also known as TUP (transfer under pressure). The diving system should be capable of allowing the safe transfer of a person under pressure from the diving bell to the surface compression chamber (and vice versa). (See IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.7)
Transferable diving system A diving system designed to be easily transferable in one or more units and which may be installed on-board a ship, barge or offshore platform for a short period of time not exceeding one year. A transferable diving system may be assembled from different units into a particular configuration suitable for a specific working operation.
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DNV GL AS Term Definition
Ultimate tensile strength The measured ultimate tensile strength
Umbilical The link between the diving support unit and the diving bell and may contain surveillance, communication and power supply cables, breathing gas and hot water hoses. The hoisting and lowering strength member may be part of the umbilical.
(See IMO code of safety for diving systems Ch.2 design, construction and survey Section 1 1.3.19)
Umbilical (in DNVGL terms) A link between support vessel and the divers, or the diving wet-bell, which may contain gas hoses, hot water hose, power supply cables and communication cables
Verification A service that signifies a confirmation through the provision of objective evidence (analysis, observation, measurement, test, records or other evidence) that specified requirements have been met
Wet bell See open bell Chapter 1
Work All activities to be performed within relevant contract(s) issued by owner, builder or manufacturer
Working weight Of the basket or wet-bell shall be taken as the maximum weight of the fully equipped basket or wet-bell, including each fully equipped diver (150 kg for SAT and 200 kg for Surface). The load from this weight applies to: a) launch and recovery in air b) launch and recovery submerged, combining the maximum negative buoyancy of the wire rope, umbilical and basket or wet-bell at maximum operating depth.
Yield Stress The measured yield tensile stress
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DNV GL AS 2.5 Abbreviations and symbols
Abbreviation Definition
AE Acoustic emission testing
API American Petroleum Institute Section 1
ASME American Society of Mechanical Engineers
ASTM American Society for Testing and Materials
AUT Automatic ultrasonic testing
BS* British Standard
C-Mn Carbon manganese Chapter 1 CE Conformité Européene (European Conformity)
CRA Corrosion resistant alloy
DP Dynamic positioning
EBW Electronic beam welded
ET Eddy current testing
FMEA Failure mode effect analysis
HAZ Heat affected zone
HAZOP Hazard and operability study
HFW High frequency welding
HPIC Hydrogen pressure induced cracking
IACS International Association of Class Societies
IM Installation manual
IMO International Maritime Organisation
ISO International Organisation for Standardisation
KV Charpy value
LBW Laser beam welded
LDC Light diving craft
MPQT Manufacturing procedure qualification test
MPS Manufacturing procedure specification
MSA Manufacturing survey arrangement
NACE National Association of Corrosion Engineers
NDT Non-destructive testing alternatively NDE is used with the same meaning
NPD Norwegian Petroleum Directorate
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DNV GL AS Abbreviation Definition
P Production
Q Qualification
QA Quality assurance
QC Quality control Section 1
QP Quality plan
QRA Quantitative risk analysis
ROV Remotely operated vehicle
UTS Ultimate tensile strength
WPS Welding procedure specification Chapter 1
YS Yield stress
*Note: now PD: public document
2.6 Symbols A = cross section area D = nominal outside diameter Dmax = greatest measured inside or outside diameter Dmin = smallest measured inside or outside diameter Di = D-2tnom = nominal internal diameter E = young’s modulus f = 0 ovality,
H = wave height Hs = significant wave height ID = nominal inside diameter
O = out of roundness, Dmax - Dmin OD = nominal outside diameter T = operating temperature Tmax = maximum design temperature Tmin = minimum design temperature Tnom = nominal thickness
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DNV GL AS CHAPTER 2 SURFACE DIVING SYSTEMS
SECTION 1 DESIGN PHILOSOPHY AND PREMISES
1 Introduction Section 1
1.1 Objectives
1.1.1 The objectives of this section are to present the safety philosophy applied in this chapter, to identify and provide a basis for definition of relevant system design characteristics. These are, key issues required for design, construction, operation and re-qualification of surface diving systems.
1.1.2 This section also refers to minimum requirements for documentation for design, manufacture, Chapter 2 installation and some operational aspects.
1.2 Scope The scope of this section is to outline the requirements for planning and documenting system philosophy, safety philosophy and quality management.
1.3 Marking and signboards Labels (name plates) of flame retardant material bearing clear and indelible markings shall be placed so that all equipment necessary for operation (valves, detachable connections, switches, warning lights etc.) can be easily identified. The labels shall be permanently fixed.
2 Documentation
2.1 Documentation of arrangement a) maximum operating depth dmax b) maximum operation time for chamber during normal operation Top c) maximum operation time for chamber during treatment Ttr d) maximum number of divers in the basket(s) or wet-bell(s) e) maximum number of divers in the chamber(s) f) maximum operational sea-state g) details of planned treatment table h) the safety objective/redundancy specification, as basis for the design see [4.6]. Plans showing general arrangement of the diving system, location and supporting arrangement i) plans showing the lay-out of control stand(s) j) proposed programme for tests and trials of systems for normal operation and for emergency use. k) where a system is based upon a chamber with different configurations of support equipment e.g. with LDC or various other support equipment, these configurations shall be described.
2.2 Documentation of installation Where the system is planned to be permanently installed, detailed plans, drawings and procedures shall be prepared for all installation activities. The following shall as a minimum be covered: a) diving system location overview (planned or existing) b) other vessel (or fixed location) functions and operations
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DNV GL AS c) list of diving system installation activities d) alignment rectification e) installation of supporting structure f) installation of interconnecting services g) installation of protective devices h) hook-up to support systems
i) as-built survey Section 1 j) final testing and preparation for operation. For portable systems this may be pre approved if vessel(s) are known or handled prior to mobilisation.
2.3 Documentation for systems in operation
2.3.1 Plans for diving system operation, inspection, maintenance and repair shall be prepared in a Survey Planning Document prior to start of operation. See DNVGL-RU-OU-0375 Ch.3 Chapter 2
2.4 Filing of documentation
2.4.1 Maintenance of complete files of all relevant documentation during the life of the diving system is the responsibility of the owner.
2.4.2 The engineering documentation shall be filed by the owner or by the engineering contractor for the lifetime of the system.
2.4.3 Design basis and key data for the diving system shall be filed for the lifetime of the system. This includes documentation from design to start-up and also documentation from possible major repair or modification of the diving system.
2.4.4 Files to be kept from the operational and maintenance phases of the diving system shall, as a minimum, include final in-service inspection reports from start-up, periodical and special inspections, condition monitoring records, and final reports of maintenance and repair.
3 Safety philosophy
3.1 Quality management systems Adequate quality management systems shall be implemented according to requirements in DNVGL-RU- OU-0101 Ch.1 Sec.4 [1.2] to ensure that gross errors in the work for diving system design, construction and operations are limited.
3.2 Inspection and test plans The tabular description of the inspections and tests to be carried out during the work is frequently known as the inspection and test plan (ITP).The following items shall be checked for inclusion within the inspection and test plan: a) each inspection and test point and its relative location in the production cycle shall be shown b) the characteristics to be inspected and tested at each point shall be identified c) the use of sub-contractors shall be indicated and details of how the verification of sub-contractor’s quality shall be carried out shall be shown d) hold points established by the constructor, the operator or a third party, where witness or review of the selected inspection or test is required, shall be shown. e) testing in service is to described within the survey planning document.
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DNV GL AS 4 Surface diving system philosophy
4.1 General As far as reasonable and practicable, a diving system should be designed to minimize human error and constructed so that the failure of any single component (determined, if necessary, by an appropriate risk
assessment) should not lead to a dangerous situation. Section 1 (IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.1.) Interpretation: Whereas this is a general requirement for the systems, it is recognised that certain components cannot fulfil this requirement in and of themselves. A typical example of this is the pressure vessel for human occupancy, acrylic windows and umbilicals. In these cases the applicable standards will specify stringent safety factors. For other cases a formal safety assessment may be required. It should also be noted that static components are not exempted and human error is included (which is taken as a single user error or process of operation). Chapter 2 ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n--- This standard provides redundancy requirements that meet this objective for typical systems and conditions namely: a) Manual control and operation of the system. b) Essential and emergency services are arranged as required in the relevant sections of this chapter. Additional equipment, requirements stemming from the safety objective, alternative or novel designs shall be assessed additionally as per [4.6] and [4.7].
4.2 System integrity
4.2.1 surface diving systems shall be designed, constructed and operated in such a manner that they: a) fulfil the specified operational requirements b) fulfil the defined safety objective and have the required support capabilities during planned operational conditions c) have sufficient safety margin against accidental loads or unplanned operational conditions d) consider the possibility of changes in the operating conditions and criteria during the lifetime of the system.
4.2.2 Any re-qualification deemed necessary due to changes in the design conditions shall take place in accordance with provisions set out in each section of the standard.
4.3 Essential services
4.3.1 Essential services are herein defined as those services that need to be in continuous operation for maintaining the diving system's functionality with regard to sustaining the safety, health and environment of the divers in a hyperbaric environment. This includes services required by the crew monitoring the divers.
4.3.2 Essential services shall be maintained for the period required to safely terminating the surface diving operation, including time for decompression of the divers or to complete the treatment table Ttr [2.1] whichever is greater.
4.3.3 For services supporting divers in the water, all services are essential. 20 minutes is considered to be the minimum time required ensuring that the divers are safely recovered to the wet-bell/basket, or to the surface.
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DNV GL AS 4.3.4 For services supporting divers in a wet-bell, all services are essential. 20 minutes is considered to be the minimum time required ensuring that the divers are safely recovered into the decompression chambers or to the surface.
4.3.5 For services supporting divers in the decompression chambers, all required services are essential. The specified maximum decompression schedule is considered to be the minimum time required ensuring that the divers are safely brought to the surface. Section 1
4.4 Emergency services
4.4.1 Emergency services are herein defined as those services that are essential for safety in an emergency condition. Examples of equipment and systems for emergency services include: a) emergency lighting, including external strobe lighting on basket/wet-bell b) emergency communication Chapter 2 c) emergency life support systems involving pressure containment, oxygen supplies and CO2 scrubbing d) emergency heating/cooling systems e) condition monitoring of emergency batteries f) alarm systems for the above emergency services g) emergency launch and recovery of the wet-bell(s)/basket(s)/diver(s) (if electrical).
4.4.2 For services supporting divers in the water, all the above services may be considered emergency services and 20 minutes is considered to be the minimum time required to ensure that the divers are safely recovered in the wet-bell or basket or to the surface.
4.4.3 For services supporting divers in a wet-bell, all the above services may be considered emergency services and 20 minutes is considered to be the minimum time required to ensure that the divers are safely recovered in the decompression chambers or to the surface.
4.4.4 For services supporting divers in the decompression chambers, all the above services may be considered emergency services with the exception of launch and recovery systems.
4.4.5 Services supporting hyperbaric evacuation system are considered statutory scope and therefore reviewed on a case by case basis according to instructions from the applicable administration.
4.5 Non-important services Non-important services are those which are not essential/emergency according to the above.
4.6 Safety objective/redundancy specification This standard is based around the concept of preventing single failures, the use of dive profiles that do not risk divers entering saturation and the base requirement of being able to provide treatment (via changes in pressure and provision of treatment gas via masks) according to the specified treatment table. However, by its nature diving equipment and the required performance of this equipment is based upon operational needs and these are often assessed on a project basis along with statutory authorities (e.g. a safety case). Such needs may have impacts on the detailed requirements of this chapter and could lead to dangerous situations falling under [4.1]. As an example this standard does not provide requirements to the working environment for personnel outside of the chamber (such as temperature control at the panel) or the ability to support different medical requirements during a treatment. Both of which may be required in certain regions.
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DNV GL AS It is the purchaser/owners responsibility to review all phases from conceptual development until demobilisation, scrapping and define and describe all safety requirements that are affected by any equipment (or lack thereof) within the diving system. The safety objective shall address the main safety goals before establishing a redundancy specification, that provides a level of risk acceptable to the owner. The result should be a description of the various subsystems in the diving system giving:
— the performance requirement of each system to meet the operational need (e.g. supply rate of hot water) Section 1 — whether the sub system is essential/emergency/non important — the redundancy of the subsystem and the acceptable time before the back up system is available (e.g. immediate one hour etc.) — a description of the subsystem and any intended means of operation that impact the arrangement/ performance of the subsystem (e.g. compressors only filling offline gas banks). Guidance note: FMEAs often provide much of the above in the written text, however, they often describe what exists, not what is needed from a Chapter 2 safety point of view. Differing mitigations can have vastly different operational impacts (e.g. stop operation and move to a safe state or a full back up system coming online). This information is also required earlier in the project than when the typical FMEA is prepared.
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4.7 Systematic review
4.7.1 All work associated with the design, construction and operation of the diving system shall be such that it ensures that the requirements in the safety philosophy are met. As a minimum, it shall ensure that no single failure shall lead to life-threatening situations for any person or to unacceptable damage to the facilities or the environment.
4.7.2 Where the complexity of a subsystem prevents the assessment of possible single failures by inspection, a systematic review or analysis shall be carried out. The systematic review may be carried out to differing methodologies dependent upon applicability to the system or subsystem (e.g. fault tree analysis or FMEA). The review shall show that the redundancy specification/safety objective above is fulfilled. This review shall also consider any risk to the health and safety of personnel associated with the dive system or in its vicinity. The extent of the review or analysis shall reflect the criticality of the diving system, the criticality of a planned operation and previous experience with similar systems or operations. This review shall identify the risk to the operation of the diving system and to the health and safety of personnel associated with it or in its vicinity. Where risks are identified and managed by mitigation within a FMECA: — Mitigation by low probability only is not in accordance with the principles in IMO and may only be applied to items such as PVHOs that cannot be redundant. Increased safety factors shall be used in these cases — Any mitigations that are repair reliant shall be assessed/tested against time assumptions. The following tables shall be added as an appendix to the systematic review: — Any mitigations requiring special operational procedures/equipment requiring drills to be followed up in the owners PMS system. — Any mitigations requiring spare parts to be followed up in the owners PMS system. — A list of parts such as shear pins, spring pins and valves with specified properties (e.g. cracking pressure) that are critical to redundancy. — Any mitigations/hidden failures that are controlled by inspection/test to be followed up in the owners PMS system, required inspection periods shall be given by the manufacturer. — Any failures that allow essential systems to operate in a non redundant state or remove emergency safeguards shall be highlighted as terminate the dive.
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DNV GL AS Guidance note: This appendix is to be available for the survey planning document, see DNVGL-RU-OU-0375 Ch.3 Sec.2 [1].
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4.7.3 Testing of the systematic review A test programme shall be developed and approved in order to verify that the system behaves as expected and assumptions within the review are valid. Section 1 The test programme shall test all safety critical failures and the systems response. — The expected behaviour after failure shall be clearly described. — The system status after failure shall be assessed. — Failures that are not purely related to design and may change with the condition of the system shall be identified and the test procedures entered into the survey planning document. — Testing relating to confirming the performance of software shall also be identified and test procedures
entered into the survey planning document. Chapter 2
4.7.4 Special attention shall be given to the risk of fire and launch and recovery operations, and ensuring the divers are able to evacuate using the vessels normal lifeboats (should hyperbaric evacuation be specified requirements of Ch.3 apply as relevant).
4.8 Layout and arrangement of the surface diving system
4.8.1 All components in a diving system should be so designed, constructed and arranged as to permit easy cleaning, disinfection, inspection and maintenance. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.6)
4.8.2 The layout of the diving system shall ensure protection from accidental damage and accessibility for safe operation, maintenance and inspection. Ventilated chambers shall be protected from direct sunlight where heat gain is a concern. The diving system shall be so designed that the divers and assisting personnel are provided with safe and comfortable operating conditions. Ergonomic principles shall be applied in the design of working systems. (I.e. in accordance with DNVGL-OS-D202 Ch.2 Sec.5 and ISO 6385.)
4.8.3 The elements of the surface diving system shall be configured in such a way as to ensure that a clear access route is available from the LARS to the decompression chamber, with a distance as short as practicable and not more than that which provides enough time according to the maximum allowable surface interval stipulated in the applied decompression tables.
4.9 Wet-bell – if installed
4.9.1 If wet-bells are employed, they shall meet the requirements for bells given in this standard.
4.9.2 A diving bell should provide a suitable environment and facilities for the persons who use it, having regard to the type and duration of the diving operation. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.3.3)
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DNV GL AS 4.9.3 Diving bells should be so designed as to provide adequate space for the number of occupants envisaged, together with the equipment. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.3.5)
5 External and internal environmental conditions Section 1
5.1 General
5.1.1 Diving systems and components thereof should be designed for the conditions under which they are certificated to operate.
(IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.2) Chapter 2
5.1.2 Systems and components shall be designed for the environmental conditions given in the diving system specifications. Bells and baskets shall meet the environmental requirements for surface and submerged components. The specifications shall state the limitations on roll, maximum current etc. in order to avoid the basket/bell impacting the ships side or getting trapped under bilge keel.
5.1.3 Environmental phenomena that might impair proper functioning of the system or cause a reduction of the reliability and safety of the system shall be considered in the PMS (including fixed and land-based installations) as follows: a) wind and tide b) waves and currents c) air and sea temperatures and ice.
5.2 External operational conditions
5.2.1 Materials for diving system components should be suitable for their intended use. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.3)
5.2.2 Design inclinations shall be assumed according to Table 1 unless otherwise specified in the system specifications.
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DNV GL AS Table 1 Design inclinations
Location Roll Permanent list Pitch Trim
Chambers and other surface installations +/-22.5° +/-15° +/-10° +/-5° on a ship
On a mobile offshore unit +/-15° +/-15° Section 1
Components in a basket or wet-bell +/-45° +/-22.5°
Guidance note: For launch and recovery systems the operational design sea-state is given in Sec.6.
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5.2.3 Storage conditions for both outer and inner area shall be taken as -10°C to 52°C. Chapter 2 For systems with active heating and cooling the range of operating ambient temperature shall be taken as 4°C to 52°C, unless otherwise specified. For more extreme temperature ranges, special consideration is required. For systems that have only ventilated control of the environment the temperature range shall be established from Sec.3 [4.6.1]. The suitability of the chambers temperature range shall be assessed by the owner before each dive. The highest internal temperature under cold conditions the chamber can maintain is given as (ambient + x °C). The highest temperatures that may be experienced during a treatment table is given as (ambient + x°C). For dive systems where hot water is not considered an essential service the lowest operational external temperature is 4°C .
5.2.4 Humidity: 100%.
5.2.5 Atmosphere contaminated by salt (NaCl): up to 1 mg salt per 1 m3 of air, at all relevant temperatures and humidity conditions.
5.3 Internal operational conditions (inner area)
5.3.1 Range of ambient pressure is given by the design code or as a minimum range of 1 bar to 1.3 times the pressure corresponding to dmax with pressurisation and depressurisation rates as specified in Sec.3 [2.4.1], whichever is the greater range. This shall be applicable to materials and components installed in the pressure vessels for human occupancy.
5.3.2 Relative humidity: up to 100%.
5.3.3 Atmosphere contaminated by salt (NaCl): up to 1 mg salt per 1 m3 of air, at relevant temperatures and humidity conditions.
5.3.4 There shall be a limitation on maximum oxygen atmosphere content of 23.5% in manned diving chambers to ensure that the effects from fire-extinguishing systems/extinguishers have the intended effect.
5.3.5 A description of the internal conditions during storage, construction, installation, pressure testing and commissioning shall be prepared. The duration of exposure to seawater or humid air, and the need for using measures to control corrosion shall be considered.
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DNV GL AS When choosing materials, paints etc. the potential for emission of hazardous compounds shall be considered.
5.3.6 Statutory requirements apply for determination of exposure limits such as: a) American Conference of Governmental Industrial Hygienists, documentation of the threshold limit values and biological exposure. b) European Commission Directive on occupational exposure limit values. c) Health and safety executive occupational exposure limits. Section 1 d) NASA. Spacecraft maximum allowable concentrations for airborne contaminants (SMAC), 1999. e) ACGIH. TLVs and BEIs. Ohio: American Conference of Governmental Industrial Hygienists. f) Segadal K, Djurhuus R, Roseth I. Implementation of a standard procedure for routine surveillance of chemical contamination of diving atmosphere during diving operations in 1995. Bergen: Norwegian Underwater Technology Centre AS, 1995; NUTEC report no. 27-95. g) Djurhuus R, Jakobsen K, Sundland H, Lindrup AG, Solheim E. Procedure for testing for off gassing from materials used in diving systems. (In Norwegian). Bergen: Norwegian Underwater Technology Centre AS, 1994; NUTEC report no. 5-94. Chapter 2 h) Ahlen C. Cleaning and disinfection of operational saturation diving systems. Recommendations for an industrial standard. (In Norwegian). Trondheim: SINTEF, 1999; STF78 A99123. i) Ahlen C, Zahlsen K. FUDT-Bacteriology 1991. Disinfecting in hyperbaric environments. (In Norwegian). Trondheim: SINTEF, 1992; STF23 F92015. Note that the exposure limits need to be translated into a form relative to the depth exposure and atmosphere.
5.4 Submerged components
5.4.1 Range of ambient temperature for material selection: -2°C to 30°C. Guidance note: Ambient temperature may in this case fall outside the range stipulated. This shall be agreed on a case-by-case basis and stated in the certificates.
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5.4.2 Range of ambient pressure: 1 bar to 1.3 times the pressure corresponding to maximum operating depth. Environmental requirements apply to submerged materials and components.
5.4.3 Salinity of ambient water: 35 parts per thousand.
5.4.4 The pressure equivalent to depth of seawater at 0°C with 3.5% salinity may be taken as 1.006 bar per 10 msw (meter seawater), as a mean value. For saltwater, the density may be taken to vary as follows: — 0.05% increase for each 100 m of depth increase — 0.4% increase for an increase in salinity from 3.5% to 4.0% — 0.3% decrease for an increase in temperature from 10°C to 20°C.
5.4.5 For the selection and detailed design for external corrosion control, the conditions relating to the environment shall be defined.
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DNV GL AS SECTION 2 PRESSURE VESSELS FOR HUMAN OCCUPANCY, GAS STORAGE AND OTHER PURPOSES
1 Introduction
1.1 Objectives Section 2 Pressure vessels are designed and manufactured to internationally recognised codes and standards. The objectives of this section are to give additional requirements that relate to the function of these pressure vessels in a diving system.
1.2 Scope
1.2.1 The following scope of work is included in the requirements of this section: Chapter 2 a) conceptual and detailed design of pressure vessels for human occupancy, for gas storage and for other purposes b) manufacturing of such pressure vessels c) quality control during manufacturing and fabrication of such pressure vessels including documentation requirements d) load conditions e) interlock arrangements for doors and hatches.
1.2.2 ASME PVHO-1 safety standard for pressure vessels for human occupancy shall be used for design of acrylic plastic windows, regardless of which standard is used for the design of the pressure vessel.
1.2.3 Welding of pressure vessels and general workmanship requirements are given in the relevant rules, codes and standards.
1.3 Application
1.3.1 This section applies to all pressure vessels in surface diving systems designed to comply with this standard. Note that in addition to this standard, and the applied design standards, further national requirements may apply.
1.3.2 Closed bells are not required for surface diving systems and consequently not included in the application of this standard. If closed bells are employed, the complete diving system shall comply with the relevant requirements given in Ch.3 Sec.2.
1.4 References
1.4.1 For quantitative design parameters and functional requirements, see relevant standards and guidelines, including normative references given in Ch.1 Sec.1 [2] and DNVGL-RU-SHIP.
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DNV GL AS 1.4.2 All pressure vessels for human occupancy shall be designed, constructed and tested according to one of the following codes and standards: a) EN 13445 unfired pressure vessels. b) ASME PVHO-1, see ASME VIII div.1 or div.2 boiler and pressure vessel code.
1.4.3 Pressure vessels for human occupancy shall be classified in the highest category in the applied code or Section 2 standard.
1.4.4 All windows in pressure vessels for human occupancy shall be certified in accordance with ASME- PVHO-1.
1.4.5 Gas cylinders shall be designed, constructed and tested according to one of the following standards, norms or directives: Chapter 2 a) EN ISO 9809-1 gas cylinders, refillable seamless steel gas cylinders, design, construction and testing, part 1: quenched and tempered steel cylinders with tensile strength less than 1100 MPa. b) EN ISO 9809-2 gas cylinders, refillable seamless steel gas cylinders, design, construction and testing, part 1: quenched and tempered steel cylinders with tensile strength greater or equal to 1100 MPa. c) EN ISO 11120 gas cylinders, refillable seamless steel tubes for compressed gas transport, of water capacity between 150 l and 3000 l, design construction and testing.
1.5 Documentation Pressure vessels shall be documented as follows: Plans showing structural arrangement, dimensions, welding seams, attachments and foundations of the chamber and other pressure vessels, with details of doors, locks (medical locks and equipment locks), view ports, penetrations, flanged and welded connections. Plans showing expansion allowances under working conditions for interconnected multi-vessel systems, if applicable. Documents stating: a) grade of material b) welding methods, type and size of filler metal c) design pressure d) particulars of heat treatment e) fabrication tolerances f) extent and type of non-destructive testing of welded connections g) type of thermal insulation materials and particulars, i.e.: flammability and specific heat conductivity h) Drawings and specifications of all windows with detailed drawings and specifications of the penetration the appropriate window fitting. It shall be determined that the tolerances are sufficient including gaskets, O-rings and retainer rings i) calculations of thicknesses and or stresses j) fatigue evaluation and if necessary fatigue analysis k) Plan for simplified inspection, see [2.2.3]. For seamless steel gas cylinders and vessels: a) plans showing proposed dimensions and details such as valves and safety devices shall be made for each type and size of vessel. Details shall include: a) production method b) heat treatment.
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DNV GL AS Material specifications for the completed vessel with information on the following: a) chemical composition b) tensile strength c) yield strength d) elongation e) impact test values f) brinell hardness. Section 2 The following particulars shall be provided for information: a) type of gas b) filling pressure at 15°C c) safety relief valve setting d) weight of empty vessel and volumetric capacity e) material protection. Chapter 2 1.6 Survey and testing requirements during and after manufacture
1.6.1 For welded pressure vessels the following tests have to be carried out in addition to the tests specified in the applied design code or standard: a) all butt welds in diving chambers shall be radiographed over their full length b) branches and reinforcement of openings, including all weld connections to the shell, shall be subjected to 100% magnetic particle testing.
1.6.2 When the applied code or standard for welded pressure vessels requires heat treatment of dished ends after hot or cold forming, mechanical testing may be required after the final heat treatment.
1.6.3 The details between intermediate heads and cylindrical shells of chambers may be done in accordance with requirements given in: a) EN 1708-1 welding, basic weld joint details in steel Table 9: internal diaphragms and separators b) ASME Sec.VIII div.I Fig.UW-13.1.
1.6.4 Welded pressure vessels and seamless steel gas containers for internal pressure shall be hydrostatic tested to an internal pressure in accordance with the design code. Each compartment in chambers shall be tested separately. In addition pressure test shall be performed with test pressure in each chamber simultaneously.
1.6.5 Pressure vessels for external pressure shall, in addition to the internal pressure testing, be hydrostatic tested to an external pressure in accordance with the design code.
1.6.6 Acrylic plastic windows shall be tested in accordance with ASME PVHO-1 Sec.2 [2.7].
1.6.7 For seamless gas cylinders production tests shall be carried out in accordance with the requirements given in the applied code or standard. Further production tests, and required attendance during testing, may be given in the specifications.
1.6.8 Gas cylinders shall be cleaned and sealed according to accepted industry standards.
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DNV GL AS 1.7 Survey and testing requirements during and after assembly The gas storage and chambers shall be tested for leakage at low pressures and the maximum working pressure.
1.8 Marking and signboards Section 2 1.8.1 All gas containers shall be marked with a consistent colour code visible from the valve end, showing the name, chemical formula of the gas it contains and the percentage of each gas. Piping systems shall be marked with a colour code, and there shall be a chart posted in the control room explaining the code.
Table 1 For piping systems and gas storage bottles/pressure vessels the following colour code should be used:
Name (Symbol) Colour code Chapter 2
Oxygen (O2) White
Nitrogen (N2) Black
Air (Air) White and black
Carbon dioxide (CO2) Grey
In addition, each bottle/pressure vessel should be marked with the name and symbol given above of the gases it contains. The marking and colour coding of the gas storage bottles should be visible from the valve end. (See IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.9.)
1.8.2 Each gas container shall be permanently and legibly marked on the collar or neck ring (where the thickness of the material is greater than the design minimum) as follows: a) the design code b) the manufacturer's mark or name c) the manufacturer's serial number d) the test pressure (bar) and date of hydrostatic test e) surveyor's mark and identification f) settled pressure (bar) at 15°C g) volumetric capacity of the container, in litres h) tare weight, i.e. the mass of the container including valve, in kg. In addition marking of gas content shall be carried out according to Table 1.
1.8.3 Other pressure vessels shall be permanently and legibly marked at a suitable location in accordance with the requirements in the design code. As a minimum the following information shall be present: a) the design code b) the manufacturer's mark or name c) the manufacturer's serial number d) the test pressure (bar) and date of hydrostatic test e) the maximum working pressure f) the inspection body’s mark and identification g) the maximum set pressure of the safety relief valves.
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DNV GL AS 1.9 Materials
1.9.1 Material specifications and selection associated with the production of pressure vessels are given in the applied codes and standards (EN/ASME).
1.9.2 Areas of steel pressure vessels that can be subjected to corrosion shall be protected by approved Section 2 means. The surface of the window seats cavity shall be protected against corrosion.
1.9.3 Windows mounted on chambers shall be protected to avoid damage by impact and to prevent chemicals, which can deteriorate the acrylic plastic, to come in contact with the window from the outside. Guidance note: Many solvents for paints, acetone and other agents will deteriorate the acrylic plastic and reduce the strength significantly.
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1.9.4 All penetrators in pressure vessels for human occupancy shall be designed to minimise corrosion from any fluid passing through them. Guidance note: In some cases this requirement may best be met by the use of a sleeve passing through the hull penetration.
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1.9.5 Paints, cabling and other materials shall be considered for toxic or noxious properties.
2 General principles for design of chambers
2.1 General
2.1.1 A diving system should, as a minimum, include either one surface compression chamber with two separate compartments, or two interconnected separate chambers so designed as to permit ingress or egress of personnel while one compartment or chamber remains pressurized. All doors should be designed so that locking mechanisms, if provided, can be operated from both sides. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.1)
2.1.2 Where a surface compression chamber is to be used (-omitted, non-applicable text-), it should be so arranged as to allow most divers to stand upright and to stretch out comfortably on their bunks. The smaller of the two compartments should be large enough for at least two persons. One of these compartments should be a living compartment. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.2) Interpretation: For surface diving systems the minimum inner dimensions measured as free height above the deck plates in the middle of the chamber, shall be 170 cm. This may be less if national regulations allow it. Statutory requirements may also require larger dimensions. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
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DNV GL AS 2.1.3 A surface compression chamber should provide a suitable environment and facilities for the persons who use it, having regard to the type and duration of the diving operation. (-Omitted, non-applicable text-). (IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.6)
2.1.4 All pressure vessels for human occupancy shall be certified. Section 2
2.1.5 Wet-bells, if employed, and surface diving baskets shall be of adequate size, be equipped to cater for the number of divers intended to man them and be equipped for handling unconscious or injured divers.
2.2 Design loads
2.2.1 The design pressure for pressure vessels shall not be less than that corresponding to the maximum Chapter 2 operating pressure as defined in the specifications given in the MPS.
2.2.2 Fatigue evaluation and, if necessary, fatigue analysis shall be carried out for the number of full pressure cycles as defined by the designer. The evaluation and analysis shall be carried out according to the applied design code. Guidance note: NDT of the surface of the external weld of the large openings such as windows and locks to detect surface breaking defects shall be carried out at the renewal survey.
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2.2.3 Design for non-destructive testing inspection of PVHOs Fatigue checks (NDT) of PVHOs in service are required after 20% of the design cycles have been experienced. The use of diver monitoring systems to record the elapsed cycles may be used for timing these inspections for the PVHOs instead of after a set number of years. For surface chambers not used for surface decompression during operation, cycling shall be primarily dependent on leak/function testing during operation. For these chambers a register of testing/treatments may be added to the survey planning document/PMS system and used in lieu of pressure monitoring. At the design stage the worst case actual stress relative to the allowable stress within the design code for the defined cycle life shall be calculated. This may be used to assign the fatigue contribution of each actual cycle seen in service. The worst case chamber will then dictate inspection intervals. Ancillary pressure vessels connected to the chamber system such as scrubber pots which experience the same cycles may be included in the same regime as long as the design standards are compatible. A list of pressure vessels included in this inspection plan tabulating actual stress versus the limit as per design code shall be submitted. A plan shall also be developed marking the locations and extent of NDT testing. Should it be preferable to carry out inspections based upon traditional inspection schedules, only the NDT plan is required to be submitted. Guidance note: NDT of the surface of the external weld of the large openings such as windows and locks to detect surface breaking defects should be carried out. Insulation and fit out should allow access to the marked areas for NDT.
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2.2.4 The effects of the following loads shall be considered and shall be taken into account, if significant. a) dynamic loads due to movements of the support vessel b) local loads
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DNV GL AS c) loads due to restrictions in expansions d) loads due to weight of content during normal operation e) loads due to rough handling f) the stress evaluation shall apply the distortion theory (von Mises’ criterion). Guidance note: Multipurpose vessels may carry relatively heavy deck loads, which can cause stresses and strains on the mountings of the diving
system components. If this cannot be avoided through design of the installed diving system, it should be monitored during such Section 2 operations.
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2.3 Foundations for pressure vessels for human occupancy and for gas storage
2.3.1 The pressure vessels with foundations shall be designed for a static inclination of 30° in any direction without exceeding the allowable stresses as specified in the design code. Chapter 2
2.3.2 Suitable foundations and supporting structures shall be provided to withstand a collision force acting on the pressure vessels corresponding to one half the weights of the pressure vessels in the forward direction and one quarter the weight of the pressure vessels in the aft direction. Guidance note: The loads mentioned in [2.3.1] and [2.3.2] need not to be combined with each other or with wave-induced loads.
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2.4 Doors, hatches, windows, branches etc.
2.4.1 The living compartment and other compartments intended to be used for decompression should have a lock through which provisions, medicine and equipment may be passed into the chamber while its occupants remain under pressure. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.3)
2.4.2 Doors and hatches for human transportation shall in general be a minimum diameter of 600 mm. Guidance note: For doors and hatches in between chambers, standard pipe with nominal bore 24" may be acceptable.
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2.4.3 The medical locks shall be large enough to allow lock-in and lock-out of CO2 absorption material and necessary supplies for the divers. Guidance note: National rules and requirements may be more stringent and thereby take precedence (i.e. Norwegian Petroleum Directorate).
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2.4.4 Means enabling the doors shall be opened from either side shall be provided. Guidance note: As the above requirement also applies to the internal doors in chambers, it does follow that locking devises are not allowed on the pressurised side of these doors unless they can be operated from the other side. Clip locks are frequently used on these doors to prevent slamming due to the vessels movement in the sea. However, the clip setting should be such that they can be pushed/ pulled open from either side without the use of excessive force.
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DNV GL AS 2.4.5 Locks should be designed to prevent accidental opening under pressure and, where necessary, interlocks should be provided for this purpose. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.4) Interpretation: Interlocks shall be provided on locks. Section 2 ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
2.4.6 For: a) doors b) hatches
c) mating arrangements Chapter 2 d) pressurised locks and trunks e) pressurised containers f) accompanying equipment under pressure where opening or unintentional pressure drop may entail danger or cause injury, the closing mechanisms shall be physically secured by locking mechanisms (interlocks). This applies to units which do not seal by pressure and includes, but is not limited to: a) equipment locks b) medical locks c) soda lime (CO2 scrubber) containers for external regeneration of the chamber environments (if fitted).
2.4.7 The closing mechanisms with accompanying locking mechanisms shall be arranged so that: a) opening cannot take place unless the pressures are equal on both sides or unless the pressures in the units are at ambient level b) correct position of the closing mechanisms and the locking mechanisms shall be ensured before it is possible to apply pressure c) the pressures in the units, shall directly control the locking mechanisms, and d) the penetrators and piping for pressure sensing shall be arranged so that blockage is avoided. Guidance note: See ASME PVHO-1 with sub reference to ASME VIII D1 UG-35.2(b)(1) and EN 13445-5 C.5.7.3.2.
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2.4.8 Trunks between doors shall be equipped with pressure equalising valves. Penetrators for pressure equalising shall be arranged so that blockage is avoided.
2.4.9 Each pressure compartment should have view ports to allow observation of all occupants from the outside. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.2.5)
2.4.10 Windows shall be protected against impact. Impact protection may be provided by: a) recessing the external surface of the window at least 50 mm below the surrounding structure b) one or more external bumpers extending across the window
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DNV GL AS 2.4.11 Where mountings are secured by studs, these shall have full thread holding in the shell for a length of at least one diameter. Holes for studs shall not penetrate the shell.
2.4.12 Damage control plugs may be provided to enable the divers to seal off windows to prevent damage or leakage developing. Section 2 2.4.13 For pressure vessels where fatigue can be a possible mode of failure, attention shall be given to the possible adverse effects of the following design features: a) pad type reinforcement of openings b) set-on branches c) partial penetration welds of branches.
2.4.14 For structures that are not covered by the pressure vessel design code, the butt weld and filled weld Chapter 2 shall be designed to take shear based on 1.5 times the maximum differential pressure that can exist. The allowable stress value for the butt weld shall be 70% of the nominal design stress for the shell material and that of the fillet weld 50%. The area of the butt weld in shear shall be taken as the width at the root of the weld times the length of the weld. The area of the fillet weld shall be taken as the minimum leg dimension times the length of the weld.
3 Welded pressure vessels, materials, fabrication and strength
3.1 Materials
3.1.1 Steel grades shall comply with the applied design code and standard.
3.1.2 Other material grades may be acceptable after special consideration. In such cases, additional testing may be required and qualification procedures shall be reconsidered.
3.1.3 Materials for main pressure retaining parts shall be certified.
3.1.4 Stainless steel cladding, stainless steel tubes, fittings etc. which are welded to pressure vessels of non-stainless steel shall be of a stabilised or low-carbon grade. Acceptable grades are given in the applicable standards or in DNVGL-RU-SHIP Pt.2 Ch.2 Sec.4.
3.2 Fabrication
3.2.1 Pressure vessels for diving systems shall be manufactured by works approved by a recognised body, for the production of the type of pressure vessels being delivered.
3.2.2 Welding shall be carried out according to approved drawings. Qualification of welders, welding procedure specifications, welding procedures and testing shall be according to the applied design code or standard.
3.2.3 The outside diameter of the head skirt shall have a close fit to the cylinders.
3.2.4 The surface dimensions and finish of seals for hatches and windows are generally to comply with the tolerances specified by the manufacturers of the windows and the sealing systems. The fitting and installation of the window to the flange shall be according to the requirements given in ASME PVHO-1.
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DNV GL AS 3.3 Fabrication tolerances
3.3.1 Fabrication tolerances shall meet the requirements in the applied codes and standards.
3.3.2 Local tolerance requirements for ring frames are given in Ch.3 Sec.2 [3.3] for vessels subject to
external pressure, if applicable. Section 2
3.4 Structural analysis to determine strength
3.4.1 In the design of pressure vessels including accessories such as doors, hinges, closing mechanisms and penetrators, the effects of rough handling and accidents should be considered in addition to design parameters such as pressure, temperature, vibration, operating and environmental conditions. Chapter 2 (IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.5)
3.4.2 Pressure vessels shall be documented by structural analysis for specified design conditions according to the applied codes and standards.
3.4.3 For details not covered by the applied codes and standards, finite element analysis may be acceptable if properly planned, modelled and documented. Alternatively, by applying strain gauges, stress measurements may be carried out according to an approved programme and shall be properly documented. The tests shall be planned, and carried out during the first pressure test.
3.4.4 Fatigue evaluation and, if necessary, fatigue analysis shall be carried out for the number of full pressure cycles and non-pressure loads given in the specification. The evaluation and analysis shall be carried out according to the applied design code and standard.
3.5 Strength of vessels subjected to external pressure If applicable Ch.3 Sec.2 [4.2] applies.
4 Gas cylinders
4.1 General
4.1.1 Gas cylinders shall be produced by manufacturers authorised for such production and certified by a competent inspection body when:
where: p = design pressure in bar. V = volume in m3. The certification level shall as a minimum be manufacturer's works certificates (W). Other levels of certification may be required by the terms of delivery. Smaller gas cylinders shall be certified if they provide an essential function in the system.
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DNV GL AS Guidance note: Cylinders on-line in a system providing breathing gas to the divers will be considered essential.
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4.1.2 The materials applied in the manufacture of gas cylinders shall be certified.
4.1.3 Section 2 Special attention should be paid to the design and choice of material for the construction of pressure vessels containing oxygen. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.4.1)
4.1.4 Shell thickness shall meet the criteria given in the applied code or standard for test pressure. The working pressure for a given geographical area is given by reference to a standard such as EN 13096
transportable gas cylinders, conditions for filling gas into receptacles, single component gases and EN 13099 Chapter 2 transportable gas cylinders, conditions for filling gas mixtures into receptacles.
4.1.5 Corrosion allowance shall be specified in the terms of delivery reflecting the intended use of the gas cylinder, but shall not be less than 1 mm. Guidance note: Gas cylinders without any corrosion allowance may be accepted based on the limitation that no repair will be allowed in case of internal or external corrosion. The use of such cylinders requires acceptance by the end user.
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4.2 Heat treatment Heat treatment shall follow the requirements given in the applied code or standard, and shall be documented.
4.3 Tolerances and surface conditions Tolerances and surface condition shall meet the criteria given in the applied code or standard, and shall be documented in the design documentation. If the applied code or standard does not specify requirements for tolerances and surface conditions, then it may be necessary to specify this in the diving systems specifications.
5 Acrylic plastic windows
5.1 General The following requirements apply to windows made from cast stock of unlaminated polymethyl methacrylate plastics, in the following denoted acrylic plastic, with a design life of 10 years, suitable for: a) 10.000 load cycles b) sustained temperatures in the range specified by the end user and not less than specified by ASME PVHO-1 c) pressurisation or depressurisation rates not exceeding 10 bar/second d) use in environments that cannot cause chemical or physical deterioration of the acrylic plastic (i.e. resistant against saltwater and gases used in life support systems).
5.2 Materials Materials for acrylic plastic windows shall be manufactured and tested in accordance with ASME PVHO-1 Safety Standard for Pressure Vessels for Human Occupancy.
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DNV GL AS 5.3 Manufacturers of cast material Manufacturers wishing to supply cast acrylic plastic for diving systems, shall be approved for such production. The material shall have an approved chemical composition and to be produced, heat treated and tested according to the ASME PVHO-1 safety standard for pressure vessels for human occupancy. Approval shall be granted on the basis of a thorough test of material from the current production and a report after inspecting the works, and verification of QA and QC against requirements given in ASME PVHO-1. Section 2
5.4 Certification of cast material
5.4.1 Each delivery of cast material shall be accompanied by a certificate issued by the manufacturer (PVHO-1 forms VP-3 and VP-4). The certificate shall (as a minimum) contain the following: a) name and address of manufacturer b) certificate number and date Chapter 2 c) designation of product d) numbers and dimensions of the pieces covered by the certificate e) material test results and properties f) signature.
5.4.2 The cast material shall be marked with the manufacturer's name and with the number and date of the certificate.
5.4.3 If a later edition of the ASME standard requires further documentation and markings, the ASME requirements shall be met.
5.5 Certification of windows
5.5.1 Each batch of acrylic plastic windows used in diving systems shall have a certificate issued by the approval body, showing the test results and the annealing conditions according to the applicable forms given in ASME PVHO-1.
5.5.2 Each window shall have an identification marked on it for traceability. Identification of each window shall include; design pressure, maximum temperature, initials for P.V.H.O., window fabricator's identification mark, fabricators serial number and year of fabrication.
5.5.3 For ease of viewing, the above information shall be located on the windows seating surface with an indelible marker. Acceptable marking methods are given in ASME PVHO-1.
5.5.4 Stamping or marking that can cause crack propagation is not permitted.
5.6 Geometry and thickness
5.6.1 Windows shall be of the standard designs according to the ASME PVHO-1 safety standard for pressure vessels for human occupancy.
5.6.2 O-ring grooves shall not be located in window bearing surfaces serving primarily as support or in the acrylic window itself.
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DNV GL AS 5.7 Fabrication
5.7.1 The included conical angle of the seating surface of a window shall be within +0.25/-0,00 degrees of the nominal value.
5.7.2 The deviation of a spherical window from an ideal sphere shall be less than 0.5% of the specified Section 2 nominal external radius of the spherical section.
5.7.3 Each window shall be annealed after all forming and polishing operations are completed. The annealing process shall be according to the annealing schedule in ASME PVHO-1.
5.7.4 During the manufacturing process each window shall be equipped with identification and a manufacture process rider for recording of all pertinent data. Chapter 2
5.8 In service inspection In service inspection and testing shall be carried out in accordance with requirements given in ASME PVHO-2 guidelines.
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DNV GL AS SECTION 3 LIFE SUPPORT SYSTEMS INCLUDING PIPING, HOSES, VALVES, FITTINGS, COMPRESSORS, FILTERS AND UMBILICALS
1 Introduction
1.1 Objectives Section 3 The objectives of this section are to specify requirements for life support systems, including pipes hoses valves, fittings, compressors and umbilicals, serving surface diving systems. General requirements for piping systems are given in DNVGL-RU-SHIP Pt.4 Ch.6.
1.2 Scope
1.2.1 This section is giving guidance on: Chapter 2 a) conceptual and detailed design of life support systems b) manufacturing of life support systems c) quality control during manufacturing and fabrication of components and subsystems for life support systems.
1.2.2 Key issue requirements for gas distribution capacities, environmental conditioning and oxygen systems.
1.2.3 Design and acceptance criteria including capacities for gas storage, choice of valves and fittings for certain applications, environmental control parameters and breathing resistance for CCBS (if fitted).
1.2.4 Requirements for the design of oxygen systems aimed at reducing the hazards posed by flash fires.
1.2.5 Limitations on the use of hoses except hoses used in umbilicals are given.
1.2.6 Requirements to ensure safe arrangements in pressurised systems and control stations and requirements for pipes, hoses, valves and fittings are given.
1.2.7 Requirements for shut off valves, pressure relief and drainage aimed at ensuring the safeguard of personnel and plant, as are the requirements for alarm systems.
1.3 Application This section applies to all systems essential for the safe operation of the diving system.
1.4 References
1.4.1 Manufacturing standards applicable to individual components shall be supplementary to this standard.
1.4.2 Further references are given to: a) DNVGL-RU-SHIP Pt.4 Ch.6 Sec.3 b) DNVGL-RU-SHIP Pt.5 Ch.10 Sec.3 c) ISO 10524-1 Pressure regulators for use with medical gases, pressure regulators and pressure regulators with flow metering devices
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DNV GL AS d) EN 10297-1 Seamless circular steel tubes for mechanical and general engineering purposes, EN ISO 11114-3 and EN ISO 10297 (informative) e) EN ISO 4126-1 safety devices for protection against excessive pressure Part 1: Safety valves f) ASTM G93-03 standard practice for cleaning methods and cleanliness levels for materials and equipment used in oxygen-enriched environments.
1.5 Documentation requirements Section 3 Life support systems shall be documented as follows: a) Plans showing schematic arrangement of all piping systems. b) Documents stating: i) material specifications ii) maximum working pressure iii) dimensions and thickness
iv) contained fluids Chapter 2 v) type of valves and fittings vi) specifications of flexible hoses vii) gas quantity arrangements/calculations based upon treatment table. c) Component lists, with specifications on make and type and documentation on any tests carried out on all equipment used in the life support system. Plans showing cross-section and giving particulars on materials and dimensions of umbilical. d) Plans (diagrams) showing arrangement and giving specifications of the gas storage and supply (gas banks, compressors, boosters etc.). e) Plans showing the arrangement and giving specifications on environmental control systems and equipment (heating, CO2-absorption, circulation), diving crew facilities and drainage systems. f) Determination showing the heat and cooling consumption for the system under specified environmental temperatures. g) Description of proposed cleaning procedure for breathing gas system. Pipes, hoses, valves, fittings, compressors and umbilicals shall be documented as follows: i) Plans and specifications showing suitability of the flexible hose in relation to its intended use. For information, documentation of tests which have been carried out, as required. ii) Plans and specifications giving particulars of umbilical conductors, minimum breaking load and minimum diameter of pulley and drums. For information, specification of max. design loads, elastic properties and weight per unit length. iii) Documentation of tests verifying the properties listed above and as required by K.
1.6 Survey and testing requirements during and after manufacture
1.6.1 In addition to the test requirements here, detailed requirements are found in DNVGL-RU-OU-0375.
1.6.2 Testing during manufacture shall be in accordance with applicable manufacturing codes for the particular component.
1.6.3 In systems conducting oxygen, all materials in contact with this gas shall be oxygen shock tested according to ISO 10524-1, pressure regulators for use with medical gases, pressure regulators and pressure regulators with flow-metering devices or equivalent standard applicable to the particular component. (See EN 10297-1, EN ISO 11114-3 and EN ISO 10297 in informative references.)
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DNV GL AS 1.6.4 For piping systems of copper, copper alloys and austenitic steels with chromium-nickel content above 22%, the test can be waived.
1.6.5 Compressors shall be tested for the gas types and pressure intended. The tests shall incorporate measurements of humidity and possible, contaminants in the gas delivered. Section 3 1.6.6 Compressor components subjected to pressure shall be hydrostatic tested in accordance with the design code.
1.6.7 Closed circuit breathing system (CCBS, if fitted) shall be tested according to DNVGL-RU-OU-0375.
1.6.8 Flexible hoses shall be tested as specified in [6]. Chapter 2 1.6.9 Umbilicals shall be tested as specified and as follows: a) Each hose for use in umbilical shall be pressure tested to 1.5 times the design pressure before fitting in the umbilical. After hose end fittings have been mounted, a gas leakage test to design pressure shall be performed. b) A pressure test to the design pressure of all hoses simultaneously and verification of the specified properties by insulation tests of electrical conductors as well as impedance measurements of signal cables to specified properties shall be carried out. c) Samples of the completed umbilicals shall be tested according to a manufacturer’s test programme complying with relevant requirements in the design code. d) The test programme shall as a minimum include tensile testing and fatigue testing to 5000 load cycles without the umbilical showing any sign of permanent deformation of electrical conductors and or significant permanent deformations of other parts.
1.7 Survey and testing requirements during and after assembly
1.7.1 Hydrostatic testing of piping systems shall be in accordance with the technical requirements and as for corresponding pipe class in breathing gas systems pertaining to class I piping systems.
1.7.2 Piping for the life support systems shall be pressure tested to 1.5 times the maximum working pressure. Hydraulic systems may, however, be tested to the smaller of 1.5 times the maximum working pressure, or 70 bar in excess of the maximum working pressure.
1.7.3 Piping systems conducting gas in life support systems shall be cleaned in accordance with an approved cleaning procedure conforming to requirements given in ASTM G93-03 standard practice for cleaning methods and cleanliness levels for materials and equipment used in oxygen-enriched environments.
1.7.4 Piping systems intended to be used in breathing gas and oxygen systems shall be tested for purity in accordance with requirements given in ASTM G93-03. The tests shall comprise: a) measurement of contamination of the cleaning agent used at the last stage of the cleaning b) tests for possible traces of cleaning agents left in the piping system.
1.7.5 The gas storage and life support systems for gas shall be tested for leakage at low pressures and the maximum working pressure.
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DNV GL AS 1.7.6 Test of environmental control [6].
1.7.7 Life support systems for normal and emergency operation shall be tested for proper functioning, This includes: a) sanitary if fitted b) diver heating and cooling Section 3 c) CO2 and O2 control.
1.8 Survey and testing requirements during and after installation
1.8.1 Support systems on-board the surface installations, significant for the safety of the diving system, are also to be tested. Chapter 2 1.8.2 During the sea trials the normal launch and recovery system will be tested to the maximum depth. For surface diving systems employing a wet-bell the life support systems shall be checked for leakage.
1.9 Materials, including components for gases containing elevated oxygen levels
1.9.1 The use of high-pressure oxygen piping should be minimized by the fitting of pressure reducing devices, as close as practicable to the storage bottles. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.8) Interpretation: The pressure in the oxygen systems shall be reduced at storage to the minimum pressure necessary for proper operation. A maximum pressure of 40 bar will normally be accepted. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n--- Piping systems containing gases with more than 25 per cent oxygen should be treated as systems containing pure oxygen. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.15) All materials used in oxygen systems should be compatible with oxygen at the working pressure and flow rate. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.7) Interpretation: Materials and components fitted in oxygen systems shall be of types especially designed and tested for this purpose. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
1.9.2 Oxygen and gases with an oxygen volume percentage higher than 25 per cent should be stored in bottles or pressure vessels exclusively intended for such gases. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.4.2)
1.9.3 Materials used in the breathing gas system shall not produce noxious, toxic or flammable products.
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DNV GL AS 1.9.4 All components used in oxygen system shall be designed and oxygen shock tested based on EN ISO 10297 (internal diameter of the test equipment shall be in line with the internal diameter of the test object) or other acceptable international standard.
1.9.5 The minimum acceptable cleanliness level for components used in oxygen systems shall be ASTM Level B (33 mg/m2) for nonvolatile residue (see DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6). Section 3
1.9.6 The metallic materials used in oxygen system shall be copper, copper alloys with copper content above 55% and austenitic steels with chromium-nickel content above 22%.
1.9.7 The nonmetallic materials used in oxygen systems shall be oxygen shock tested for the applicable pressure range acc. EN ISO 15001. Chapter 2 1.9.8 Shut of valves shall be of the types which need several turns to close. On chamber penetrators, ball valves may be accepted for emergency use only.
1.9.9 Pressure gauges in oxygen systems shall be designed and cleaned in accordance with EN 837-1.
1.9.10 Flexible metallic hoses made of austenitic steels with chromium-nickel content above 22% can be used for oxygen systems needs to be type approved. The oxygen shock test can be waived.
1.9.11 Flexible synthetic hoses can be used in systems with maximum pressure of 40 bar. Guidance note: The material of the inner liner of the hose should be oxygen shock tested (as required in [1.9.3]) to the applicable working pressure of 40 bar. The length of the flexible hose installed in the system may be longer than the length of the tested hose
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1.9.12 If a lubricant is necessary to permit assembly operations or the functioning of a component, it shall be selected from lubricants that have been found acceptable for use with oxygen and breathing gases for applicable pressure range. Where lubricants may break down under heat and pose a contamination risk appropriate shut downs to prevent overheating shall be provided.
2 Gas distribution and control system
2.1 General
2.1.1 Gas supply Each surface compression chamber and diving bell should be fitted with adequate equipment for supplying and maintaining the appropriate breathing mixtures to its occupants at all depths down to maximum operating depth. When adding pure oxygen to the chamber, a separate piping system should be provided. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.1) In addition to the system mentioned in 2.6.1 each surface compression chamber (omitted, non applicable text) should contain a separately controlled built-in breathing system for oxygen, therapeutic gas or bottom mix gas with at least one mask per occupant stored inside each separately pressurized compartment and means should be provided to prevent any dangerous accumulation of gases. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.2) Interpretation:
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DNV GL AS Text applicable to surface systems is retained and requirements met by compliance with this section. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n--- In addition to the above stipulated masks, there shall be one spare mask installed in each compartment. Gas supplies shall allow for primary, secondary and emergency sources of gas, as described below. Where compressors are used as a supply source, volume tanks and filtration packs with CO shutdown prior to filtration shall be in place unless gas is stored and tested prior to being put online. Other possible contaminants that may represent a hazard based on area of operation, such as H2S shall also cause Section 3 compressor shut down. Volume tanks should provide 10 minutes of gas supply upon compressor shut down before change over is required and a visual audio alarm provided locally and at the control stations
2.1.2 Primary supply Primary supply shall supply as a minimum all gases required for the planned dive including running a possible treatment table including possible extensions. Chapter 2 Supply is considered to be both gas required for breathing and also gas required to maintain environmental conditions where ventilation is used to control temperature and CO2 . Primary supply may be either compressor or storage based.
2.1.3 Secondary supply Secondary supply shall supply all gases required to terminate a dive including running a possible treatment table including possible extensions. Supply is considered to be both gas required for breathing and also gas required to maintain environmental conditions where ventilation is used to control temperature and CO2 . Secondary supply may be either compressor or storage based. Secondary supply should be fed from a different switchboard or source of electrical power than the primary supply and also be connected to an emergency power source.
Emergency supply 2.1.4 The emergency supply is as per [3.1.2] and shall be provided from stored gas. Where the volume tanks are used with the secondary supply and are of sufficient size these may be utilised as the emergency supply. For chamber atmospheres normally controlled via ventilation with emergency scrubbing fitted and complying with the requirements in [4.6.1] ventilation requirements as per primary and secondary may be omitted.
2.1.5 The gas distribution system consists of all components and piping necessary for distribution of gas for normal and emergency operations.
2.1.6 Piping for gas and electrical cables shall be separated.
2.1.7 Filters and automatic pressure reducers shall be so arranged that they can be isolated without interrupting vital gas supplies.
2.1.8 Valves in piping systems to masks, and divers in water shall be so arranged that: a) leaking valves cannot cause unintentional gas mixtures b) oxygen cannot unintentionally be supplied to other piping systems than that intended for oxygen.
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DNV GL AS 2.1.9 Gases vented from the diving system should be vented to the open air away from sources of ignition, personnel or any area where the presence of those gases could be hazardous. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.13) Interpretation: Section 3 Ventilation containing high O2 should not be lead toward areas with hydrocarbons. Chamber ventilation on open deck should extend away from the chamber itself where people may be present and noise should not hamper operation or communication. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
2.2 Control stands
2.2.1 Requirements for instrumentation are given in Sec.7. Chapter 2
2.2.2 The control stands shall have means for: a) choice between supplies and indication of status of supplies as required b) pressurising and pressure regulation of each compartment independently c) decompression of each compartment independently d) equalising the pressure between compartments e) controlling oxygen and mix gas supply to masks in each individual compartment f) controlling gas supply to the divers and the wet-bell if applicable.
2.3 Basket and wet-bell (if wet-bell is employed)
2.3.1 The diving bell should be designed with a self-contained breathing gas system capable of maintaining a satisfactory concentration of breathing gas for the occupants for a period (ommited non applicable text) at its maximum operating depth. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.3)
2.3.2 There shall be two independent supplies of gas to the divers and, if applicable, the wet-bell umbilical.
2.3.3 The diver(s) shall have, in addition to their normal umbilical supply, an independent self-contained emergency supply (20 minutes duration) from the basket or wet-bell. The emergency supply in a basket may be by means of reduced air from a cylinder mounted in the basket.
2.3.4 The breathing gas system supplying the personal umbilical to the stand-by diver in the wet-bell, when wet-bell is employed, shall be arranged for an alternative supply, independent of the lock-out diver(s)'s normal supply. The wet-bell’s onboard gas supply may be accepted for this purpose.
2.3.5 The wet-bell shall be equipped with a spare mask connected to both normal supply and emergency supply alternatively.
2.4 Chambers
2.4.1 The distribution system to each compartment shall facilitate:
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DNV GL AS a) two independent alternatives for pressurisation with a minimum pressurisation rate of 2 bar/minute to 2 bar and at 1 bar/minute thereafter b) depressurisation with a decompression rate in accordance with specified decompression tables (e.g. US Navy diving tables) c) maintenance of a suitable breathing atmosphere in the inner area d) supply of suitable breathing gas for masks e) exhaust from masks intended for oxygen if a closed circuit breathing gas system is not used. Section 3
2.4.2 Each compartment shall be equipped with breathing masks corresponding to the maximum number of divers for which the chamber is rated plus one. Other compartments shall have at least two masks.
2.4.3 The masks shall be permanently connected or easily connectable to piping systems for supply of the gases according to [3.1.3].
2.4.4 The exhaust sides of the masks intended for oxygen shall be connected to external dump, or shall be Chapter 2 of a closed circuit type.
2.4.5 The mask systems shall be secured against inadmissible pressure drop on the exhaust side.
2.4.6 The gas supply system shall be arranged to ensure homogenous gas content in the inner area.
2.5 Stand-by diver at surface A system for supply of life support to a stand-by diver at surface shall be arranged independent from the divers' supply, and shall meet the requirements for the normal diver’s supply.
2.6 Nitrogen/oxygen mixing systems for direct supply for breathing
2.6.1 Systems for mixing of nitrogen and oxygen for subsequent direct supply for breathing shall be automatic, to have an automatic control system, an automatic alarm system and an automatic safety system.
2.6.2 The safety system shall be independent of the control system and shall incorporate changing of the supply automatically to a premixed suitable breathing gas if tolerances are exceeded. The safety system shall ensure a constant delivery of suitable breathing gas to the diver during all operating conditions, taking into account the characteristics of components in the systems such as response time for gas analysers etc.
2.6.3 As an alternative to [2.6.2], the inclusion of a large volume tank is considered to provide an equivalent level of safety as that prescribed by the requirements for 'automation' and 'independence'. The remaining requirements shall be met. The volume tank shall be such that the prescribed tolerances for partial pressures downstream are not deviated from within the first hour after the analysers have alerted the operator that the upstream mixture is out of the tolerated range. The alarm shall be audio-visual at a manned control station.
2.6.4 The control system shall keep the mixture at a pre-set value within prescribed tolerances. Maximum tolerances: +/- 0.03 bar, partial pressure O2.
2.6.5 If the mixing system is arranged as a closed circuit breathing system (CCBS), it shall meet the requirements for such systems given in Ch.3 Sec.3 [8].
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DNV GL AS 3 Gas storage
3.1 Capacity
3.1.1 There shall be either a permanently installed gas storage plant or suitable space for portable gas containers. The size of the containers or space shall be sufficient to provide the divers with adequate Section 3 quantities of gases for operation at maximum operating depth for both primary, secondary and emergency modes, see [2.1].
3.1.2 For emergency supply the minimum gas storage capacity shall be sufficient to: a) Pressurise the inner area twice and the transfer compartments once more to maximum depth, dmax, with suitable breathing gas, and ventilate the chamber as required, see [4.6.1]. b) maintain a proper oxygen partial pressure in the inner area and supply for masks for at least 24 hours. Chapter 2 For pure oxygen, the minimum volume may be taken as 2 Nm3 for each diver where 1 Nm3 is given as 1 cubic metre of the gas at 0°C and 1.013 bar standard condition. c) Conduct two emergency dives to dmax.
3.1.3 For emergency use of masks required by [3.1.2] b) there shall be sufficient facilities to supply adequate quantities of gases. The facilities shall be capable of providing a relevant delivery rate both at maximum depth and during decompression. Adequate quantities shall be determined for the applicable operation, but not less than 2 m3 at the pressure of the inner area with an oxygen partial pressure between 0.18 and 1.25 bar for each diver.
3.1.4 If applicable, the wet-bell shall have self-contained emergency gas storage with a minimum capacity to supply the divers for the duration of their in-water stops prior to surfacing.
3.2 Shut-off, pressure relief and drainage
3.2.1 All surface compression chambers and diving bells which may be pressurized separately should be fitted with overpressure alarms or pressure relief valves. If pressure relief valves are fitted, a quick-operating manual shut off valve should be installed between the chamber and the pressure relief valve and should be wired opened with a frangible wire. This valve should be readily accessible to the attendant monitoring the operation of the chamber. All other pressure vessels and bottles should be fitted with a pressure relief device. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.5)
3.2.2 Pressure vessels shall be fitted with over pressure relief devices and shut off valves.
3.2.3 Pressure vessels without individual shut-off valves and with: pV < 50, installed in groups with a total pV < 100, can have a common overpressure relief device and shut-off valve. p = design pressure in bar V = volume in m3 (standard conditions)
3.2.4 For gas storage of breathing gases and oxygen, the pressure relief device shall be a safety valve. Safety valves shall be set to open at a pressure approx. 3% above the developed pressure at 55°C, based on filling the cylinders at 15°C to maximum filling pressure. The total relieving capacity shall be sufficient to maintain the system pressure at not more than 110% of design pressure. Developed pressure under above- mentioned conditions may be taken as given in reference to a standard such as EN 13096 transportable gas
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DNV GL AS cylinders conditions for filling gases into receptacles single component gases or EN 13099 transportable gas cylinders conditions for filling of gas mixtures into receptacles.
3.2.5 Containers where water can accumulate shall be provided with drainage devices. (E.g. volume tanks and filters).
4 Diver’s heating and environmental conditioning in chambers Section 3
4.1 General A diving system should include adequate plant and equipment to maintain the divers in safe thermal balance during normal operations. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.6.7) Interpretation: Due to the relatively short duration and lower heat losses to both different breathing gas and lower pressure Chapter 2 of surface diving compared to saturation techniques it is difficult to define a safe temperature for all systems. The approach therefore is to quantify what temperature range each system is capable of operating in to allow suitability to be assessed for each job. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
4.2 Heating of divers in the water
4.2.1 Divers may employ insulated suits and not require active heating. Where systems are rated to operate under 3 °C a risk assessment for diver safety and against freezing of equipment shall be performed if active heating is not employed.
4.2.2 When required for safety reasons this heating shall be redundant and be able to provide 20 minutes of supply under emergency conditions. Non redundant heating may be provided for comfort where loss of supply does not pose a safety risk.
4.3 Heating and cooling of chambers
4.3.1 Systems for heating and cooling of the living compartments shall be arranged when required according to environmental criteria given in the specifications.
4.3.2 Heating/cooling systems shall be redundant with one supply from emergency power. The cooling system shall be capable of maintaining a chamber temperature below 29°C with the max. number of divers and tenders within the chamber under the worst external temperature within the temperature rating. Heating systems should be able to maintain a temperature of 25°C with the minimum number of divers and tenders within the chamber under the worst external temperature within the temperature rating. Temperature control for ventilated chambers is limited by the ambient temperature during operation, see [4.6.1]. Where heating/cooling systems are non redundant and installed for comfort only, temperature ratings shall be as per ventilated systems.
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DNV GL AS 4.4 Noise reduction
4.4.1 Pipe systems should be so designed as to minimize the noise inside the diving bell and surface compression chamber during normal operation.
(IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.1) Section 3
4.4.2 Silencers shall be fitted and the system shall be so designed that the divers cannot be exposed to harmful noise levels. Guidance note: IMO resolution A.468 (XII) code on noise levels on-board ships.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e--- Chapter 2 4.4.3 Silencers shall be fitted with shields which provide protection against possible fragmentation but which do not affect the gas flow.
4.5 Gas circulation systems for chambers
4.5.1 Internal circulation systems for gas in the chambers shall be such that homogeneous gas content is ensured.
4.5.2 Pressurising and exhaust systems shall be arranged to ensure an even mixing of gas.
4.5.3 The circulation system shall have sufficient capacity to maintain a homogenous gas mix at the set operational parameters.
4.5.4 Materials shall be considered for toxic or noxious properties.
4.6 Removal of carbon dioxide Carbon dioxide removal systems shall be arranged for each living compartment and shall have the capacity to maintain the partial pressure of carbon dioxide below 0.005 bar continuously based on a production rate of 0.05 Nm3 per hour per diver. For two divers’ occupancy, this requirement may be met by flushing the chamber atmosphere providing the maximum noise levels are not exceeded.
4.6.1 Ventilated systems For ventilated systems diving shall not commence when there is a risk that ambient temperature is unsuitable for a treatment table until the post dive bends watch has been completed plus the time of the specified treatment table. Allowable values may be taken from USN Diving manual rev 7 Table 17-5 based upon the treatment treatment table considered. In no cases shall temperatures exceed 40°C. Ventilated systems shall establish their ability to hold ambient temperature by testing. The means to control ventilation rate in practice shall be described. Where visual valve marking is used, the markings shall be sufficient to accurately set the flow. A ventilation bill shall be developed at differing depths for the required minimum flushing rate for maximum chamber occupancy.
Where ventilated systems utilise internal chamber scrubbers to control CO2 under emergency gas supply conditions, the temperature rise in these conditions shall be considered.
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DNV GL AS 4.6.2 Life support testing For systems fitted with active environmental control testing is as per methods for saturation diving. For ventilated systems, a test within a stable environment shall be performed. Heaters representing the maximum number of divers and tenders shall be installed in the chamber. For chambers whose emergency CO2 removal system is an internal scrubber, ventilation should be off. The chamber should be allowed to run for the duration of the of the specified treatment table. CO injection
2 Section 3 should also be confirmed. The temperature reached at the end of the treatment table duration shall be used to establish temperature rise in the case of no ventilation and forms the (ambient + x°C) rating for the chamber given in Sec.1 [5.2.3]. Where chambers have heating systems intended to allow diving at temperatures significantly below ambient, chamber temperature should be stabilised to establish heat loss characteristics. Ventilation should then be started to demonstrate that the temperature rise due to shut in, can be reduced back toward ambient. Max. ventilation (flush rates) may be used. Chapter 2
CO2 should be injected after temperature is controlled and ventilation adjusted to a level at which both CO2 and temperature are stable at acceptable levels. The ventilation rate at this point shall be taken as the minimum ventilation rate for gas storage requirements. For heated systems the ability to increase the temperature shall be demonstrated. The final temperature increase forms the (ambient + x°C) rating for the chamber given in Sec.1 [5.2.3]. In warm climates where this test would result in impractical internal chamber temperatures, a smaller temperature rise may be shown and adjusted via calculation based on the measured heat loss characteristics. Flow rates and required gas shall be modified according to this testing, see [3.1] and Sec.1 [5.2].
5 Piping systems
5.1 General
5.1.1 All high-pressure piping should be well protected against mechanical damage. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.14)
5.1.2 Piping systems shall comply with the technical requirements for class I piping systems in DNVGL-RU- SHIP Pt.4 Ch.6.
5.1.3 Welding of joints shall be carried out by qualified welders using approved welding procedures and welding consumables. Technical requirements are given in DNVGL-RU-SHIP Pt.2 Ch.2.
5.1.4 Threaded pipe penetrations are only acceptable for internal diameters less than 20 mm.
5.1.5 Where applicable the following requirements given in DNVGL-RU-SHIP Pt.4 Ch.6 Sec.3, shall be followed: a) bending and welding procedures b) welding joint particulars c) preheating d) heat treatment after welding and forming e) non-destructive testing and production weld testing f) bracing of copper and copper alloys.
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DNV GL AS 5.1.6 Piping systems which may be subjected to a higher pressure than designed for should be fitted with a pressure relief device. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.6)
5.1.7 Low-pressure systems supplied from high-pressure system shall be provided with pressure relief Section 3 valves. The total relieving capacity shall be sufficient to maintain the system pressure at not more than 110% of design pressure. The relief device shall be located adjoining, or as close as possible, to the reducing valve.
5.1.8 All systems shall be provided with means of manually relieving the pressure.
5.1.9 Filters shall be provided on the high-pressure side of gas systems. Chapter 2
6 Hoses
6.1 General
6.1.1 Flexible hoses, except for umbilicals, should be reduced to a minimum. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.9)
6.1.2 Flexible hoses shall not replace fixed piping.
6.1.3 In addition to umbilicals, short lengths (up to 2 m) of flexible hose may be used when necessary to admit relative movements between machinery and fixed piping systems. For assemblies incorporating specially approved hoses and securing arrangements, lengths up to 5m may be permitted if fixed piping is not practicable. In such cases, securing arrangements shall be in place at 1m intervals of the length of the hose. In addition to the couplings, the hoses shall be secured in such a way as to prevent the hose from whip lashing in the event that the coupling fails. When applicable, couplings shall incorporate bends so that kinks in the hoses are avoided.
6.1.4 Flexible hoses with couplings shall be certified.
6.1.5 Flexible metallic hoses with permanently fitted couplings shall be certified.
6.1.6 Bursting pressure of synthetic hoses shall be at least: a) Hoses for fluids: 4 times the maximum working pressure. b) Hoses for gases: 5 times the maximum working pressure.
6.1.7 Hot water hoses shall be designed for conveyance of fluids of temperatures not less than 100°C.
6.1.8 Flexible metallic hoses shall not be installed in systems subject to excessive vibrations or movements.
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DNV GL AS 7 Valves
7.1 Valve design
7.1.1 Pressure ratings for valves shall be in accordance with a recognised national standard. Section 3 7.1.2 Design and arrangement of valves shall be such that open and closed positions are clearly indicated.
7.1.3 Valves are normally to be closed by clockwise rotation.
7.2 Chamber valves
7.2.1 Chapter 2 Exhaust lines should be fitted with an anti-suction device on the inlet side. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.12)
7.2.2 All pipe penetrations on chambers should be fitted with two shut off devices as close to the penetration as practicable. Where appropriate, one device should be a non-return valve. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.4)
7.2.3 All pipe penetrations in the chambers shall be fitted with external and internal shut-off valves mounted directly on the shell plating. Valves may be mounted close to chamber shells, provided that the piping between the chamber and valve is well protected and has a minimum thickness according to DNVGL-RU- SHIP.
7.2.4 In addition to the requirements in [7.2.3] all penetrations for lines designed for gas distribution (e.g. supply, exhaust and equalisation) shall be fitted with non-return valves or flow fuses as appropriate for the direction of gas flow. Lines specifically designed for non-distribution purposes (e.g. analysis) shall be kept to the minimum internal diameter possible and limited to a maximum of 5 mm.
7.2.5 The piping between externally mounted non-return valve or flow-fuse and the external shut-off valve shall be well protected and have minimum thickness according to [5].
7.2.6 The compartments shall be fitted with a safety relief valve or a visual and audible overpressure alarm alerting the operators at the control station. National standards and/or regulations may stipulate requirements for safety relief valves, and shall be followed in these cases.
7.2.7 Penetrations for safety valves shall be provided with shut-off valves on both sides of the shell plating. These shut off valves shall be sealed in the open position. Any safety valves shall be set to open at a pressure of approx. 3% above the design pressure.
7.2.8 Valves in chambers designed for holding water (i.e. hyperbaric training centres) shall be considered in each case.
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DNV GL AS 8 Fittings and pipe connections Bite and compression type couplings and couplings with brazing, flared fittings, welding cones and flange connections are only allowed for piping up to 25 mm (1") and shall be designed according to a recognised standard.
9 Pressure regulators Section 3
9.1 General
9.1.1 Pressure regulators shall have more than one full rotation from fully closed to fully opened position.
9.1.2 Automatic pressure reducers for breathing apparatuses shall be fitted. Chapter 2 10 Compressors for breathing gas systems
10.1 General
10.1.1 Compressors shall be certified.
10.1.2 Compressors shall be equipped with all the accessories and instrumentation which are necessary for effective and dependable operation.
10.1.3 Compressors shall be designed for the gas types and pressure rating as specified by the operation and so designed that the gas is protected against contamination by lubricants.
10.1.4 Suitable protection shall be provided around moving parts, and the safety relief valves shall exhaust to a safe place.
11 Purification and filter systems
11.1 General
11.1.1 Purification and filter systems shall be certified, see DNVGL-RU-SHIP Pt.4 Ch.5 Sec.4.
11.1.2 The content of contaminants in the breathing gas after the filter system shall not exceed the acceptance criteria given in EN 12021 or equivalent standards. National requirements remain unaffected hereby.
11.1.3 Where breathing gas is supplied directly from running compressors, an automatic shut off device for the compressor shall be installed to shut it down when the purification/filter system have reached an unacceptable level of contamination.
11.1.4 Where breathing gas is supplied directly from running compressors, a mean of analysing the breathing gas for carbo monoxide shall be provided for continuos monitoring, incorporating an audio/visual alarm.
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DNV GL AS 11.1.5 Filter housings, casings, breathing gas receivers and other parts subject to pressure shall be hydrostatically tested in accordance with national and international design codes.
11.1.6 Additional requirements to external environment in terms of toxic (H2S and hydro carbon) gas (see DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6 [2.1]). Section 3 12 Umbilicals
12.1 General Umbilicals shall be designed, tested and certified in accordance with relevant sections of the most recent edition of ISO 13628-5 petroleum and natural gas industries, design and operation of subsea production systems, part 5: subsea umbilicals. The relevant sections of the standard shall be agreed in a compliance matrix when the signed request for certification of the umbilicals is received by DNV GL. Chapter 2
12.2 Hoses Hoses for umbilicals shall comply with the requirements given in [6]. Hoses intended for operation with a larger external pressure than the internal pressure, shall be able to withstand 1.5 times this pressure difference without collapsing or shall be able to collapse without signs of permanent deformation.
12.3 Electrical cables
12.3.1 Electrical cables for umbilicals shall comply with requirements given for cables in Sec.4.
12.3.2 The minimum average thickness of insulating walls and temperature classes shall be in accordance with DNVGL-RU-SHIP Pt.4 Ch.8.
12.4 Sheathing Any sheathing of a compact umbilical shall be of a design which avoids build-up of an inside gas pressure in the event of a small leakage from a hose.
12.5 Strength members The strength members of umbilicals shall have sufficient stiffness to avoid plastic yielding of electrical conductors at design load, and shall be properly secured.
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DNV GL AS SECTION 4 ELECTRICAL SYSTEMS
1 Introduction
1.1 Objectives
The objectives of this section are to emphasise the special needs associated with the design and manufacture Section 4 of surface diving systems. General requirements for electrical systems and components are given in DNVGL- OS-D201.
1.2 Scope
1.2.1 The key issues are identified in:
a) the service definitions by defining essential, emergency and non-important services in Sec.1 [4] Chapter 2 b) the power supply systems and capacity by specifications for emergency supply c) cables and penetrators d) documentation requirements.
1.2.2 Material specification is included for insulation of cables in the inner area.
1.2.3 Design criteria for electrical penetrators are outlined. Philosophy on earthing is specified, in that hull return is not allowed.
1.3 Application
1.3.1 This section applies to all surface diving systems.
1.3.2 This section bears impact on Sec.3, Sec.5, Sec.6, Sec.7 and Sec.8.
1.4 References
1.4.1 Recognised production standards include those provided by the International Electro technical Commission (IEC).
1.4.2 The following codes and standards are applicable: a) DNVGL-OS-D201 b) relevant IEC equipment construction and design standards referred to c) IMCA code of practice for the safe use of electricity underwater.
1.5 Documentation
1.5.1 A system philosophy with general arrangement and where the equipment is placed shall be submitted early on in the project.
1.5.2 Single line distribution system diagrams for the whole installation. The diagrams shall give information on full load, cable types and cross sections, and make, type and rating of fuse- and switchgear for all distribution circuits.
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DNV GL AS 1.5.3 Calculations on load balance, including emergency consumption and battery capacities.
1.5.4 Complete multi-wire diagrams, preferably key diagrams, of control and alarm circuits for all motors or other consumers.
1.5.5 A list of ALARMS and monitoring parameters shall be submitted for information. Section 4
1.5.6 Plans showing arrangements of batteries with information about their make, type and capacity.
1.5.7 Plans showing arrangement and single line diagrams of the communication system.
1.5.8 Complete list of components and documentation on any tests carried out on all electrical equipment to be permanently installed within the chamber, and the wet-bell (if applicable). Chapter 2
1.6 Survey and testing requirements during and after manufacture
1.6.1 A test for insulation resistance shall be applied to every circuit between all insulated poles and earth, and between individual insulated poles. A minimum value of 1 mega-ohm shall be attainable.
1.6.2 Main and emergency power supplies shall be tested.
1.6.3 Electrical penetrators shall be tested at the manufacturers as specified below. Tests shall be made between each conductor and screen and tests shall be carried out on penetrators from the same production batch. The tests shall be carried out in the sequence they are listed. The penetrators shall show no sign of deficiency during and after the testing.
1.6.4 Tests to be carried out include: a) a voltage test, by applying 1 kV plus twice the design voltage for 1 minute between each conductor and screen separately b) a hydrostatic test to a pressure of twice the design pressure, repeated 5 times c) a gas leakage test with the cables cut and open with air to twice the design pressure d) an insulation test to 5 Megaohms at the design pressure, applying saltwater.
1.7 Survey and testing requirements during and after assembly Survey and testing during and after assembly shall be carried out according to an approved inspection and test procedure proposed by the builder in compliance with applicable requirements in DNVGL-OS-D201 Ch.2 Sec.10 [4] inspection and testing.
1.8 Survey and testing requirements during and after installation
1.8.1 Survey and testing during and after installation shall be carried out according to an approved inspection and test procedure proposed by the builder in compliance with applicable requirements in DNVGL- OS-D201 Ch.2 Sec.10 [4] inspection and testing.
1.8.2 During the sea trials the normal launch and recovery system will be tested to the maximum depth. For surface diving systems employing a wet-bell the electrical systems shall be checked for proper function.
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DNV GL AS 1.9 Markings and signboards Markings and signboards according to DNVGL-OS-D201 Ch.2 Sec.3 [5].
1.10 Materials Materials shall comply with DNVGL-OS-D201. Section 4
2 System design
2.1 Design principles
2.1.1 The electrical systems and installations supplying essential, emergency and normal services related to the divers and or the diving operation, shall meet the requirements for such services as defined in Sec.1 [4], Chapter 2
2.1.2 Electrical circuits and equipment used in water shall be considered in each separate case and in accordance with IMCA D 045, R015 code of practice for the safe use of electricity underwater. Provisions shall be made to reduce the possible fault currents, to which a diver can be exposed, to a harmless level.
2.1.3 The location of rechargeable battery installations are considered a hazardous area and shall be carefully considered during the conceptual design of the diving system lay-out early in the project, in compliance with DNVGL-OS-D201 Ch.2 Sec.2 [9.4].
2.2 System voltages For installations within the inner area (see definitions under Ch.1 Sec.1 [2.4]), the following maximum system voltages are permitted: a) The chamber: i) For power and heating equipment: max. 250 V A.C. if protected against accidental touching or insulation failures and fitted with a trip device. ii) For lighting, socket outlets, portable appliances and other consumers supplied by flexible cables and for communication and instrumentation equipment: max. 30 V D.C. These systems shall be supplied by isolating transformers. b) The wet-bell (when applicable): i) For all electrical equipment, voltages will be accepted up to max 30 V D.C., and shall be supplied by isolating transformers. ii) Higher voltages than specified above may be acceptable upon special consideration, provided additional precautions are taken in order to obtain an equivalent safety standard, e.g.: by use of earth fault circuit breakers.
2.3 Main electric power supply system The electrical systems and installations supplying essential services related to the divers and or the diving operation as defined in Sec.1 [4.3], shall be supplied from a main and an emergency or transitional source of power as required by DNVGL-OS-D201.
2.4 System functionality and design
2.4.1 The distribution system shall be such that, the failure of any single component cannot influence or set other services out of function for longer periods.
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DNV GL AS The capacity of the main source of power shall be able to provide power to all normal and essential services according to Sec.1 [4], and shall be included in the services to be supplied by the main source of power as described in DNVGL-OS-D201 Ch.2 Sec.2 [2] and interpreting SOLAS reg. II-1/40.1.1.
2.4.2 The capacity of emergency source of power shall be able to provide power to all emergency services according to [5], and shall be included in the services to be supplied by the emergency source of power as described in DNVGL-OS-D201 Ch.2 Sec.2 [3] and interpreting SOLAS reg. II-1/43.2. Section 4
2.4.3 The emergency source of power and the emergency power distribution shall be capable of handling peak loads.
2.4.4 Power supplies required for the operation of life support systems and other essential services shall be sufficient for the life-support duration in order to cater for safe termination of the diving operation.
2.4.5 Each compression chamber shall be provided with a main and emergency source of lighting sufficient Chapter 2 for the life-support time and of sufficient luminosity to allow the occupants to read gauges and operate essential systems within the chamber. Ingress of adequate light through the windows may be accepted as emergency lighting when appropriate.
2.5 Emergency power supply system
2.5.1 In the event of failure of the main source of electrical power supply to the diving system an independent source of electrical power should be available for the safe termination of the diving operation. It is admissible to use the ship's emergency source of electrical power as an emergency source of electrical power if it has sufficient electrical power capacity to supply the diving system and the emergency load for the vessel at the same time. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.10.2)
2.5.2 The alternative source of electrical power should be located outside the machinery casings to ensure its functioning in the event of fire or other casualty causing failure to the main electrical installation. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.10.3)
2.5.3 The diving system shall have a source of emergency power and an emergency power supply system independent of the main source of power and the main power supply system, as required by DNVGL-OS- D201 that outlines the SOLAS reg. II-1/43 part D requirements.
2.5.4 The emergency source of power shall be a self-contained, independent source of power. It shall immediately supply at least those services specified as emergency consumers in Sec.1 [4.4] and shall be either: a) a generator, driven by a suitable prime mover, or b) an accumulator battery, or c) the ship's emergency switchboard, or d) a combination of the above.
2.5.5 Where this source of power is a generator, it shall be started automatically upon failure of the electrical supply from the main source and shall be automatically connected within 45 sec., thereby providing emergency services.
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DNV GL AS 2.5.6 Where this source of power is an accumulator battery, it shall be automatically connected to an emergency power supply system in the event of failure of the main source of electrical power. It shall be capable of carrying the maximum emergency load for a time specified under [5] without excessive voltage drop, carrying the emergency electrical load without recharging while maintaining the voltage of the battery throughout the discharge period within 12% above or below its nominal voltage.
2.6 Transitional source Section 4
2.6.1 The following consumers shall be provided with transitional power (uninterrupted power supplies): a) condition monitoring of emergency batteries b) emergency lighting, including external strobe lighting on basket/wet-bell c) emergency communication d) alarm systems for the emergency services. Chapter 2
2.6.2 If other emergency consumers must be available in the switchover period from main to emergency power, either for operational reasons or to avoid malfunction of the service, a transitional power source (battery backup) for these consumers shall be provided. The capacity of this transitional power shall be minimum 30 minutes. (See SOLAS reg. II-1/43 part D para.4.)
2.7 Battery systems
2.7.1 Batteries shall not normally be installed within the inner areas in the chambers.
2.7.2 Battery housings shall be provided with adequate and unobstructed ventilation to open air in accordance with DNVGL-OS-D201 Ch.2 Sec.2 [9.4], so that an accumulation of generated flammable gases is avoided. The ventilation intake shall be fed into the lower parts and the outlet arranged in the uppermost part of the housing.
2.8 Electric power distribution
2.8.1 All switchboards shall be designed, constructed, tested and certified in accordance with the requirements given in DNVGL-OS-D201.
2.8.2 If the main power to the diving system is supplied from a distribution board, this board shall have two independent supply circuits from different sections of the main switchboard or separate power supplies.
2.8.3 Control gear in the inner area shall normally not be fitted. However, special arrangement may be acceptable after consideration in each case, based on special precautions.
2.8.4 Devices for easy disconnection of all electrical installations in the decompression chambers in an emergency situation shall be fitted. These devices shall be located on the control stand. It shall be possible to disconnect each chamber separately.
2.8.5 Emergency circuits wiring is considered to be an essential component in the diving system and shall therefore be fire proofed in accordance with the requirements in DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6 [8] when supplies are sourced from outside the outer area.
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DNV GL AS Guidance note: Allowances are given to IEC 60331 cables protected by A0 division trays or piping.
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2.8.6 Fuses or circuit breakers shall not be installed within chambers and wet-bells, except for emergency battery powered supply circuits.
Guidance note: Section 4 Installation inside may be arranged as mentioned above, however, fuse-gear shall not be operable by divers
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2.9 Lighting Each surface compression chamber and diving bell should have adequate means of normal and emergency lighting to allow an occupant to read gauges and operate the system within each compartment. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.10.4) Chapter 2
3 Equipment in general
3.1 General requirements
3.1.1 All electrical equipment and assemblies shall be designed and arranged in order to minimise the risk of fire, explosion, electrical shock, emission of toxic gases to personnel, and galvanic action of the surface compression chamber or wet-bell.
3.1.2 The electric power supply arrangement shall be designed to minimise the risk of electrical capacity depletion as a result of a fault.
3.2 Environmental requirements
3.2.1 All electrical equipment and installation, including power supply arrangements, should be designed for the environment in which they will operate to minimize the risk of fire, explosion, electrical shock and emission of toxic gases to personnel, and galvanic action of the surface compression chamber or diving bell. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.10.1)
3.2.2 The electrical equipment and installations, including power supply arrangements, shall be constructed and installed to operate satisfactorily under all environmental conditions for which the diving system is designed. See DNVGL-OS-D201 Ch.2 Sec.2.
3.2.3 Electrical equipment within the compression chamber shall be designed for hyperbaric use, oxygen- enriched atmospheres, high humidity levels and marine application. See: a) DNVGL-OS-D201 b) NFPA53M (National Fire Protection Agency) manual on fire hazards in oxygen-enriched atmospheres 1990 c) IMCA D 045 code of practice for the safe use of electricity underwater d) IMCA D 041 use of battery operated equipment in hyperbaric conditions.
3.2.4 All materials of submerged systems shall be such that their electrical and mechanical properties are not influenced by water absorption.
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DNV GL AS 3.3 Termination and cable penetrations
3.3.1 All electrical penetrators in pressure containing structures shall be purpose designed, certified and shall be arranged with separate fittings.
3.3.2 Penetrators in pressure vessels shall be gas and water-tight even in the event of damage to the Section 4 connecting cables.
3.4 Earthing
3.4.1 Electrical systems with hull return shall not be applied. Electrical distribution systems shall have insulated neutral (IT).
3.4.2 All pressure vessels for human occupancy (PVHOs) shall be provided with earthing connection devices Chapter 2 for external main protective earth bonding.
3.4.3 In the water, all metal enclosures shall be earthed by means of a copper earth conductor incorporated in the supply cable, with cross-section at least of the same size as the supply conductors and not less than 1 mm2. For cables having metal wire braid or armour this may alternatively be used as earth conductor, provided that the braiding cross section is sufficient.
3.5 Insulation
3.5.1 Each insulated supply system, including the secondary side of step-down or isolating transformers (or converters) shall be provided with an automatic insulation monitoring device, actuating switch-off and alarm by insulation faults. Alarm only may be used if a sudden switch-off of the equipment may cause danger for the divers. This insulation monitoring shall be continuous.
3.5.2 The indicator shall be located at the control stand. Guidance note: Protection against insulation failures may be achieved by double insulated apparatus or earth fault circuit breakers.
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4 Miscellaneous equipment
4.1 General
4.1.1 Electric motors placed in the inner area shall be provided with overload alarms or be inherently safe. The alarms may be initiated by over current, or by temperature detector in the motor itself. The normal over current protections (short circuit protection) on the motors shall also be in place. Guidance note: The requirement provides safety against overheating, with the possible development of toxic gasses, and or danger of flash fire in oxygen enriched environments. In special cases there may be other risks involved in overheating of the motors. However, if the motor is considered inherently safe, the requirement for the overload alarms may be revoked. This is considered preferable in cases where the number of alarms should be kept at a minimum so as to avoid stressful operating conditions and or confusion.
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DNV GL AS 4.1.2 Pressure resistant enclosures in the inner area or on the wet-bell shall be designed for 1.3 times the design pressure of the diving system. Tests shall be carried out with gas or water as applicable.
4.2 Lighting equipment – inner area Protection against possible bursting of electrical bulbs shall be in place. Section 4 5 Cables
5.1 Application
5.1.1 Cables for use in the outer area shall comply with DNVGL-RU-SHIP Pt.4 Ch.8. All cables shall have an earthed braiding or screen around the conductors and be equipped with an insulating outer sheet. Chapter 2 5.1.2 Cables for use in the inner area shall comply with the requirements in [5.1.1] above, with exception to the materials used. The materials shall be designed for the purpose of being installed into a hyperbaric atmosphere. The cables in the inner area shall be halogen free and shall not give off toxic, noxious or flammable gases even when overheated. Dismantled ends of insulated conductors shall be protected with sleeves of a non-combustible material (e.g. glass fibre weave). Ordinary ship cables with insulation of a halogenated material (e.g. P.V.C.) shall not be accepted. Synthetic insulation materials based on P.T.F.E. (Polytetrafluoroethylene) may be accepted.
5.1.3 Flexible cables for transmission of electrical power and signals from the surface support to the divers in the water and the wet-bell shall be constructed as dry-core cable (i.e. water shall not reach the insulation of the individual conductors).
5.1.4 The submerged cables shall be able to withstand an external hydrostatic pressure of 1.3 times the actual external pressure.
5.1.5 Unless installed in pipes, electrical cables shall be readily accessible for visual inspection.
5.1.6 Tensile loads shall not be transferred to the electrical cables.
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DNV GL AS SECTION 5 FIRE PREVENTION, DETECTION AND EXTINCTION
1 Introduction
1.1 Objective
The objectives of this section are to specify additional requirements for fire protection serving surface diving Section 5 systems. General requirements for fire protection are given in DNVGL-OS-D301.
1.2 Scope Key issues are identified through requirements for materials, insulation and separation from adjacent spaces, sprinkler systems and extinction agents. Reductions of hazards are ensured through these issues.
1.3 Application Chapter 2
1.3.1 These requirements apply to all surface diving systems. However, some systems may be located on open deck. In these cases the requirements for insulation against adjacent spaces and requirements for sprinkler systems may be more lenient.
1.3.2 This section bears impact on Sec.4 (build-up of static electricity, degree of protection provided by enclosure IP for equipment on chambers covered by sprinkler systems, power to alarms) and Sec.8.
1.4 References
1.4.1 For quantitative design parameters and functional requirements, see relevant standards and guidelines, including DNVGL-OS-D301.
1.4.2 In addition supplementary information is found in the National Fire Protection Agency codes' chapters on hyperbaric systems and oxygen enriched environments.
1.4.3 Requirements applicable to the support vessel are given in SOLAS.
1.4.4 See: a) IMO res. MSC.61(67) (FTP code) b) DNVGL-OS-A101 Ch.2 c) IMO res. MSC/Circ.848 MSC.98(73) (FSS code).
1.5 Documentation requirements Fire prevention, detection and extinction shall be documented as follows: a) A List of all materials to be installed in the inner area, where possible with data on and or evaluation of flammability in conditions under which the materials can be used. b) Plans and specifications of fire detection, fire alarm and fire extinction equipment for both the inner and outer area.
1.6 Survey and testing requirements during and after assembly The fire detection, fire alarm and fire extinction systems in the inner areas shall be tested for proper function according to specifications.
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DNV GL AS 1.7 Materials
1.7.1 All materials and equipment used in connection with the diving system should be, as far as is reasonably practicable, of fire-retardant type in order to minimize the risk of fire and sources of ignition.
(IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.1) Section 5
1.7.2 The use of combustible materials shall be avoided wherever possible. Combustible materials include materials which may be brought to explode, or burn independently in the resulting gas environment, applicable to the outer area air at a pressure of 1 bar or the inner area at applicable gas mixtures and maximum pressure.
1.7.3 Structural components, furniture and knobs, paints, varnishes and adhesives applied to these, shall be of non-hazardous materials., i.e. they shall be tested in accordance with relevant parts of IMO Chapter 2 res.MSC.61(67) (FTP code) or other acknowledged standard. Guidance note: In order to comply with [1.5], materials for use in inner area should be tested at an elevated pressure. Where such materials are not available, fitting a fixed fire extinguishing system in the inner area may be considered as an alternative.
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1.7.4 Materials and arrangements shall, wherever possible, be made so as to avoid build-up of static electricity and to minimise the rise of spark production due to electrical failures or combination of materials. In inner areas without electrical equipment, the furniture and floors of electrically conductor materials may be used. For inner areas where electrical equipment is used, the materials and arrangements shall be made so as to minimise faulty contact with earthed metalwork.
2 Fire protection
2.1 Arrangement When applicable, control rooms for surface diving systems located in hazardous zone 2 shall comply with the requirements given in DNVGL-OS-A101 Ch.2 Sec.3 safety principles and arrangements. Other control stands, essential to the function of the diving system, shall be protected such that the controls may be maintained whilst the divers are being evacuated in the event of a fire.
3 Fire detection and alarm system
3.1 Outer area
3.1.1 Interior spaces containing diving equipment such as surface compression chambers, diving bells, gas storage, compressors and control stands should be covered with an automatic fire detection and alarm system and a suitable fixed fire-extinguishing system. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.3) Interpretation: Where emergency decompression as per the owners procedure or USN and transition to the lifeboats takes longer than 15 minutes, the areas of the diving system within interior spaces critical to evacuation shall be protected by A 60 divisions and control stations shall have breathing apparatus.
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DNV GL AS Decompression chambers are not required to have object protection, however, gas storage shall be protected when stored internally. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
3.2 Inner area The inner area shall be equipped with automatic fire detection and alarm system complying with DNVGL-OS- D301. The section or loop of detectors covering the inner area shall not cover other spaces. Section 5
3.3 Fault detection Provisions shall be made for warning of faults, e.g. voltage failure, broken line, earth fault, etc., in the fire alarm and detection system.
4 Fire extinguishing Chapter 2
4.1 Inner area
4.1.1 Each compartment in a surface compression chamber should have a suitable means of extinguishing a fire in the interior which would provide rapid and efficient distribution of the extinguishing agent to any part of the chamber. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.6)
4.1.2 The inner area shall be equipped with a fixed, manually actuated fire extinguishing system with such a layout as to cover the compartments. It shall be possible to actuate the extinguisher both from within the compartments and from outside.
4.1.3 The extinguishing agent for the inner area shall be rechargeable without depressurising, and provisions shall be made for possible discharge of less than the total supply of extinguishing agent
4.1.4 The extinguishing agent shall be water, unless an approved alternative exists.
4.1.5 Where fixed water-mist systems for inner area are not supplied by a pump for continuous operation, stored charges shall have minimum capacity of 2 shots of 2 min. duration with the required application rate. Response time upon activation shall follow NFPA99, maximum 3 sec.
5 Miscellaneous equipment
5.1 Portable fire extinguishers
5.1.1 Portable fire extinguishers of approved types and designs should be distributed throughout the space containing the diving system. One of the portable fire-extinguishers should be stowed near the entrance to that space. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.4)
5.1.2 Portable fire extinguishers shall be of approved type and comply with FSS code Ch.4. If provided, inner area hyperbaric extinguishers shall be of approved type, containing non-toxic medium and certified for the maximum depth rating of the chamber in which they are placed.
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DNV GL AS 5.1.3 Spare charges or extinguishers shall be provided on-board, 100% for the first 10, and 50% for remaining extinguishers. Section 5 Chapter 2
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DNV GL AS SECTION 6 LAUNCH AND RECOVERY SYSTEMS (LARS)
1 Introduction
1.1 Objectives
The objectives of this section are to specify additional requirements for lifting appliances serving surface Section 6 diving systems. General requirements for lifting appliances are given in DNVGL-ST-0378 Sec.12 standard for offshore lifting appliances, incorporating specific requirements for lifting of personnel.
1.2 Scope
1.2.1 Key issues are identified through requirements for alternative recovery of divers. Chapter 2 1.2.2 Limitations are given in the rating of the launch and recovery systems with respect to a given, specified, sea-state.
1.3 Application
1.3.1 These requirements apply to all surface diving systems.
1.3.2 This section applies to all launch and recovery systems. However, requirements for launch and recovery of diver’s baskets may be more lenient with respect to emergency recovery, if it is possible for the surface supplied divers to ascend independent of the diver’s basket.
1.3.3 This section has impact on the requirements for strength with respect to deck loading on the support vessel and to the services from the support vessel.
1.4 References For quantitative design parameters and functional requirements, see relevant standards and guidelines, including DNVGL-ST-0378 Standard for offshore lifting appliances. See: a) App.A or equivalent b) DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6.
1.5 Documentation Launch and recovery systems shall be documented as a lifting appliance in accordance with DNVGL-ST-0378 standard for offshore lifting appliances. In addition, plans and supplementary documentation shall be made available as follows: a) Plans showing the arrangement of the launch and recovery system with specifications of loads, and dimensions of strength members. b) Plans showing the function of the systems, and giving particulars of the systems. The plans shall show a schematic arrangement of the hydraulic or pneumatic piping systems and specification of controls and power supply. c) Calculation of the design load according to [3]. d) Calculation of necessary design load for umbilical and guide ropes. e) Plans and specification of structural parts, ropes, sockets, blocks, sheaves, winches, and emergency ascent arrangement for the basket or wet-bell.
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DNV GL AS f) Specifications of materials and welds, and extent of non-destructive testing. g) Specifications of wire ropes and their end connections. h) Specification of safety devices and the logic of interlocks fitted (limit switches, automatic stop of operating handle, automatic locking of winch in case of power failure, etc.). i) Plans and specifications for systems used for emergency ascent of the divers and retrieval of the basket or wet-bell. j) Information on specification of working weight, displacement and stability of the basket or wet-bell, with all hydrostatic properties accounted for. Section 6
1.6 Survey and testing requirements during and after assembly
1.6.1 Basket/wet-bell a) The working weight shall be ascertained. b) The stability in normal and emergency modes shall be tested. Chapter 2
1.6.2 Launch and recovery systems shall be subjected to tests for structural strength and for function and power.
1.6.3 A static load test to a load equal to the design load shall be carried out.
1.6.4 Functional and power testing of normal and emergency systems shall be carried out with a functional test load of 1.25 times the working weight in the most unfavourable position. It shall be demonstrated that the systems are capable of carrying out all motions in a safe and smooth manner.
1.6.5 Monitoring of functional parameters during the tests, e.g. pressure peaks in hydraulic systems may be required.
1.7 Survey and testing requirements during and after installation
1.7.1 During the sea trials the normal launch and recovery system shall be tested with the working weight of the basket or wet-bell to the maximum depth.
1.7.2 A recovery test of the basket or wet-bell shall be carried out simulating emergency operations conditions.
1.8 Marking and signposts
1.8.1 The launch and recovery system shall, in an easily visible place, be fitted with a nameplate giving the following particulars: a) identification number b) static test load c) functional test load d) working weight e) surveyor's mark and identification.
1.8.2 The above loads shall be specified for each subsystem involved.
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DNV GL AS 1.9 Materials Materials shall be compliant with the requirements given in DNVGL-ST-0378 standard for offshore lifting appliances.
2 Design principles Section 6 2.1 General
2.1.1 Where the following IMO requirements refer to bell they shall also apply to divers’ baskets in the context of this standard.
2.1.2
A diving system should be equipped with a main handling system to ensure safe transportation of the diving bell Chapter 2 between the work location and the surface compression chamber. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.1)
2.1.3 Connection of the main lift wire to basket (or wet bell) shall have two retaining means for the removable pin.
2.1.4 For diving operations where there are no hull obstructions near the diving site, and the freeboard is less than 2 metres, one of the following options shall be utilised: a) diving basket(s) including equipment for the deployment of a surface standby diver b) ladder which extends at least 2 metres below the surface in calm water. The ladder shall have sufficient holds under and above water and on deck level to allow the diver to step easily onto the deck. In addition a dedicated arrangement e.g. a crane, A-frame or davit, certified for lifting of personnel, with sufficient reach shall be present to recover an incapacitated diver from the water by a safety harness onto the deck (this additional device shall be manually powered or be supplied by emergency power). Where a basket is utilised under a) it shall comply with [2.4.2] and the divers umbilical shall be easily released allowing the diver to do a swim to surface. The LARS shall have two HPUs and be supplied from two sources and emergency power. Wet-bells may be used, however, the requirements of [2.1.5] apply as to arrangement.
2.1.5 For diving operations where there are obstructions at the diving site, and/or a freeboard of more than 2 metres, the following shall be utilised: a) Two separate launching appliances equipped with either wet-bell or basket. b) Both shall be arranged with primary and secondary recovery as described in [2.4.2]. In operation only one shall be used while the other is reserved for launch of the standby diver and for tertiary recovery as per [2.4.3]. c) As a minimum two HPUs shall supply both LARS provided each are powered separately and can operate either LARS. Emergency power shall be provided to one HPU. Alternatives may be considered based upon Sec.1 [4.6].
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DNV GL AS 2.2 Divers basket and wet-bell (when installed)
2.2.1 A diving bell should: .1 be provided with adequate protection against mechanical damage during handling operation
.2 be equipped with one extra lifting point designed to take the entire dry weight of the bell including ballast and Section 6 equipment as well as the weight of the divers staying in the bell. .3 be equipped with means whereby each diver using the bell is able to enter and leave it safely as well as with means for taking an unconscious diver up into a dry bell. .4 (Omitted text not applicable for surface diving). (IMO code of safety for diving systems Ch.2 design, construction and survey 2.3.1) Interpretation: The above IMO requirements for bells shall also apply to divers’ baskets in this case. Chapter 2 Note that the design and location of the extra lifting fastening shall be considered in view of the need to bring a basket or wet-bell close to the surface decompression chamber. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
2.2.2 The basket/wet-bell shall be recovered to a location where the divers can safely exit the basket. Safely exiting the basket is considered to be where the basket is mechanically secured from falling independent from the lifting wires as well as secured from relative movement to the vessel due to vessel motions. Protection from falling shall be as per vessel regulations. All LARS operations until reaching this point shall be redundant with emergency power or manually operable. Internally there shall be an attachment for lifting of divers into the wet-bell or basket, if assisted recovery is required in the particular design.
2.2.3 Each diving bell should have view ports that as far as practicable allow an occupant to observe divers outside the bell. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.3.4) Interpretation: The canopy of wet-bells shall be provided with windows that as far as practicable allow the occupants to observe diving and lifting operations outside the wet-bell. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
2.3 Function
2.3.1 The handling system should enable smooth and easily controllable handling of the diving bell. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.3) Interpretation: The normal handling system shall be designed for a safe, smooth and easily controllable transportation of the divers in the design sea-state. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
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DNV GL AS 2.3.2 The lowering of diving bells under normal conditions should not be controlled by brakes, but by the drive system of the winches. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.4)
2.3.3 Section 6 If the energy supply to the handling system fails, brakes should be engaged automatically. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.5) Interpretation: Manoeuvring systems shall be arranged for automatic stop when the operating handle is not operated (dead man’s handle). ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n--- Chapter 2
2.3.4 Hoisting winches shall be fitted with two independent mechanical brakes, each capable of holding the design load. Brakes shall be engaged automatically when the hoisting motor stops.
2.3.5 The launch and recovery system shall be designed so that the systems are locked in place if the energy supply fails or is switched off.
2.3.6 If the hoisting rope can enter the drum with an angle exceeding 2° from the right angle to the drum axis (the fleet angle), a spooling arrangement shall be fitted. The rope launch and recovery system shall not permit ropes to squeeze in between, or introduce permanent deformation to ropes in underlying layers on the drum.
2.3.7 The hoisting system shall be equipped with a line-out device showing the amount of wire that is spooled off the drum and a device which stops the basket or wet-bell at its lowermost and uppermost positions. The device shall also stop the movement of the A-frame if luffing out of A-frame causes the basket to be lifted into the sheave. Guidance note: Line-out monitoring is also needed when diving in certain adverse conditions, such as zero visibility. In such conditions it will be necessary to monitor line-out in order to safely carry out surface diving operations. When the diver is out of the stage, it should be possible to match the diver’s depth with the depth of the stage.
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2.3.8 Safety interlocks/limit switches Electrical safety switches/location proximity sensors/interlocks and solenoids, such as the limit switch mentioned in [2.3.7] should be designed to fail to safe in the event of failures such as wire break and also be able to operate under emergency power situations. In case of any failures that would prevent hoisting of the basket or wet-bell, it shall be possible to override the device to safely terminate the dive operation. This shall be possible without the use of secondary or tertiary recovery described in [2.4].
2.3.9 Travelling cranes and trolleys shall be equipped with mechanical stops at their end positions. The system shall be equipped with limit switches preventing the launch and recovery of the wet-bell or basket outside of the launch and recovery area. A-frames shall be arranged with stops to prevent luffing-out beyond the maximum design angle. The launch angle for A frames should be such that loads during launch and recovery hold the frame against these stops.
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DNV GL AS 2.3.10 Precautions shall be taken to avoid exceeding the design load in any part of the launch and recovery system including hoisting ropes and umbilical due to: a) large capacity of the power unit b) motions of the supporting vessel when the basket/wet-bell or weights are caught or held by suction to the sea floor
c) failure on umbilical winch during launching of wet-bell. Section 6
2.3.11 Structural members of the launch and recovery system might be subjected to forces imposed by separate operations of the handling system (e.g. A-frame tilted by hydraulic actuator on each leg.). The structural members of the winching system shall be strong enough to withstand unintended movements of the A-frame/davit system (including mechanically deployed umbilical systems) without damage and vice versa. Hydraulic pressure relief with an automatic alarm and stop system shall be implemented when this is not possible structurally. Such safety interlocks shall be fail to safe but bypassable in order to allow dive
termination. Chapter 2
2.3.12 Hydraulic power units shall be dedicated to the lifting appliance and not shared with other consumers, such as hydraulic driven tools.
2.3.13 Where direct visual monitoring of the winch drums from the winch control station is not practical, TV monitoring shall be fitted.
2.3.14 Primary and emergency lighting in all critical launch and recovery areas shall be provided.
2.4 Recovery
2.4.1 In the event of single component failure of the main handling system, an alternative means should be provided whereby the bell can be returned to the surface compression chamber. In addition, provisions should be made for emergency retrieval of the bell if the main and alternative means fail. (-omitted, non-applicable text-). (IMO code of safety for diving systems Ch.2 design, construction and survey 2.7.6) Interpretation: There shall be at least one normal system (primary) and two (secondary and tertiary) mutually independent emergency means for recovery of the divers with return to the chambers. The alternative means shall comply with the same requirements for load strength as the main system if the basket/wet-bell is part of the recovery. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
2.4.2 The two emergency means shall be arranged as follows: a) One emergency system (secondary) may be made for recovery by aid of the normal hoisting or guide rope(s). This system shall be independently powered from the normal system, and shall incorporate all transportation necessary to transport the divers to the surface chamber. b) One system (considered secondary) shall also provide an arrangement for stopping the basket or wet- bell from falling or descending, in the event of failure in the primary lifting wire.
2.4.3 Another emergency system, (tertiary), may be that the diving system is equipped with a separate launch and recovery system and a second basket or wet-bell. Provisions shall be available for recovery of the divers to the chambers.
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DNV GL AS Alternatively this other emergency system (tertiary) may consist of an arrangement that permits the divers free ascend and shall incorporate all means necessary to transport the divers to the chamber. Where appropriate, the emergency recovery may incorporate a ladder if the freeboard and distance to the chamber allows for this.
2.4.4 The time taken to bring the diver(s) from 10 msw in the water until 10 msw equivalent in the chamber should not exceed 5 minutes in any of the three modes of recovery. Section 6
2.4.5 Guide wire equipment may, in addition to ensuring controlled movements of the basket or wet-bell in the water, function as a secondary means of recovery.
2.5 Power
2.5.1 The hoisting power system shall be designed and tested to lift and manoeuvre a load of 1.25 times the working weight of the basket or wet-bell. Chapter 2 Guidance note: This requirement is to ensure there is enough power to handle the basket or wet-bell under normal wave conditions.
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2.5.2 The power of horizontal transportation systems shall be designed and tested for safe launch and recovery at list and trim as specified in [3.1.4] and Sec.1 [5.2].
2.5.3 The strength of each of the two mechanical brakes for the hoisting system shall be based on holding of the design load. This shall be verified by static load testing, holding the design load.
2.6 Umbilical
2.6.1 The length of the umbilicals, shall, as a minimum, allow an excursion of the basket or wet-bell to: a) dmax plus 5%, or b) actual bottom depth plus 5%.
2.6.2 The termination points, where the umbilicals enter connectors and/or penetrators, shall not be subjected to significant loads or flexing.
2.6.3 The ultimate tensile strength of the umbilicals shall not be less than twice the maximum load expected during normal and emergency operations.
3 Strength
3.1 Design loads
3.1.1 The minimum design load shall be taken as 2.0 times the working weight of the basket or wet-bell in air for launching over the side or stern with a maximum significant wave height of 2 meters.
3.1.2 The working weight of the basket or wet-bell shall be taken as the maximum weight of the fully equipped basket or wet-bell, including each fully equipped diver of 200 kg. The load from this weight applies to: a) launch and recovery in air, and
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DNV GL AS b) launch and recovery submerged, combining the maximum negative buoyancy of the wire rope, umbilical and basket or wet-bell at maximum operating depth.
3.1.3 For launch and recovery through a moon pool and with significant wave height higher than 2 meters, the design load should be calculated using App.A.
3.1.4 In locked positions on a vessel, the launch and recovery system shall have a structural strength Section 6 at least sufficient for the environmental conditions described in Sec.2. In addition to the motions and accelerations in the operational design sea-state, the minimum inclinations given in Table 1 shall be taken into account:
Table 1 Permanent inclinations
Vessel type Permanent list Permanent trim
Ship 5° 2° Chapter 2
Semi-submersible 3° 3°
3.2 Dimensions
3.2.1 The minimum safety factor for steel wire ropes shall be 4 compared to design load defined in [3.1]. Guidance note: Note that a SF of 4 times the minimum design load of 2.0 gives a SF of 8.0.
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3.2.2 Blocks, sheaves, shackles etc. shall comply with recognised national codes. Drums and pulley diameters shall correspond to the type of rope. For steel wire ropes this diameter shall not be taken less than specified by the rope manufacturer, and normally not less than 18 times the rope diameter. In the case of cross hauling, such equipment shall fulfil the same requirements for strength as the rest of the launch and recovery system.
3.2.3 Structural members shall be fabricated from certified materials and shall be designed with safety against: a) excessive yielding b) buckling c) fatigue fracture, and d) shall be in accordance with technical requirements in DNVGL-ST-0378 or equivalent accepted standards.
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DNV GL AS SECTION 7 INSTRUMENTATION AND COMMUNICATION
1 Introduction
1.1 Objective
The objectives of this section are to emphasise the special needs associated with the design and manufacture Section 7 of diving systems. General requirements for instrumentation and communication systems and components are given in DNVGL-RU-SHIP Pt.4 Ch.9.
1.2 Scope
1.2.1 Recognised production standards include those provided by the International Electro Technical Commission (IEC). Chapter 2
1.2.2 Material specification is included for insulation of cables in the inner area.
1.3 Application
1.3.1 These requirements apply to all surface diving systems.
1.4 References The following codes and standards are applicable: — DNVGL-OS-D202 Automation, safety and telecommunication systems — DNVGL-OS-D201 Ch.2 Sec.2 [6.3] electrical power requirements for control and monitoring systems — relevant IEC equipment construction and design standards.
1.5 Documentation
1.5.1 The following document requirements assume a non-complex system. For complex instrumentation and/or communication systems, scope shall be agreed on a case by case basis at the start of the project.
1.5.2 For instrumentation and communication systems the following shall be documented: a) Complete key diagrams, of control and alarm circuits for all motors or other consumers. b) Plans showing arrangements of batteries with information about their make, type and capacity. c) Plans showing arrangement and single line diagrams of the communication system. d) Complete list of components and documentation on any tests carried out on all equipment to be permanently installed within the chamber and the wet-bell.
1.6 Survey and testing requirements during and after manufacture The correct calibration of all essential instrumentation (compartment pressure gauges, gas analysis instruments etc.) shall be checked.
1.7 Survey and testing requirements during and after assembly
1.7.1 Communication shall be tested after assembly, for proper function.
1.7.2 Control and monitoring system shall be tested according to an approved test procedure.
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DNV GL AS 1.8 Survey and testing requirements during and after installation During the sea trials the normal launch and recovery system will be tested to the maximum depth. For surface diving systems employing a wet-bell the communication system shall be tested.
1.9 Markings and signboards Markings and signboards shall be posted according to the relevant requirements in DNVGL-OS-D201 Ch.2 Section 7 Sec.3 [5] and DNVGL-OS-D202 Ch.2 Sec.4 [1.5].
1.10 Materials Equipment, including enclosures, shall meet the environmental requirements given inDNVGL-RU-SHIP Pt.4 Ch.9 Sec.5.
2 Instrumentation Chapter 2
2.1 General
2.1.1 A diving system should include the control equipment necessary for safe performance of diving operations. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.7)
2.1.2 In general, instrumentation shall comply with the relevant requirements in DNVGL-OS-D202.
2.2 Power supply to control and monitoring systems
2.2.1 Power supply requirements for control and monitoring systems shall comply with the principles given in DNVGL-OS-D202.
2.2.2 Where instrumentation requires power supplies, this shall be designed on the basis of the system philosophy and redundancy philosophy as applicable. Requirements for essential, emergency and normal services are given in Sec.1 [4].
2.3 Monitoring and inspection during operation
2.3.1 Parameters that could jeopardise the safety of the divers, and or violate the integrity of a diving system, shall be monitored and evaluated with a frequency that enables remedial actions to be carried out before personal harm is done or the system is damaged. Guidance note: As a minimum the monitoring and inspection frequency should be such that the diving system, and consequently the surface diving operation, shall not be endangered due to any realistic degradation or deterioration that may occur between two consecutive inspection intervals.
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2.3.2 Instrumentation may be required when visual inspection or simple measurements are not considered practical or reliable, and available design methods and previous experience are not sufficient for a reliable prediction of the performance of the system.
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DNV GL AS 2.3.3 The various pressures in a diving system shall not exceed the design pressures of the components during normal steady-state operation.
2.4 Pressure control system
2.4.1 The set pressures of the pressure regulating system shall be such that the local operational pressures Section 7 are not exceeded at any point in the diving system. Due account shall be given to the tolerances of the pressure regulating system and the associated instrumentation. Guidance note: A pressure control system is used to prevent the internal pressures at any point in the diving system rising to excessive levels, or falling below prescribed levels. The pressure control system comprises the pressure regulating systems, pressure safety systems and associated instrumentation and alarm systems. The purpose of the pressure regulating system is to maintain the operating pressures within acceptable limits during normal operation. The purpose of the pressure safety systems is to protect the systems
during abnormal conditions, e.g. in the event of failure of the pressure regulating systems. Chapter 2
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2.4.2 The pressure safety systems shall operate automatically in accordance with the fail safe principles and with set pressures such that there is a low probability for: a) the internal pressure at any point in the diving system to exceed the design pressure (maximum operating pressure), and for b) the unintentional loss of pressure at any point in the diving system to fall below set values.
2.4.3 The diving system may be divided into sections with different design pressures provided the pressure control system ensures that for each section, the local operational pressure cannot be exceeded during normal operations and that the design pressure cannot be exceeded during abnormal operation. The pressure control shall also ensure that unwanted loss of pressure in one section does not occur as a result of an abnormal condition in another section.
2.5 Control stands
2.5.1 With reference to requirements in Sec.4 and DNVGL-OS-D202 Ch.2 Sec.5, the design of control rooms shall consider ergonomics such as communication and a systematic arrangement of equipment, according to a documented traffic flow chart. Further, it shall be ensured that noise or other disturbance when working does not occur. Control stands for diving operations shall therefore be separated from the control stations associated with the other operations on board.
2.5.2 The diving system should be so arranged as to ensure that centralized control of the safe operation of the system can be maintained under all weather conditions. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.11.1)
2.5.3 Indication and operation of all vital life support conditions to and from the divers, the chamber(s) and the wet-bell(s) shall be arranged at a single control stand. The control stand shall be equipped for easy operation and control of the diving system. There shall be schematic indication of gas flow lines.
2.5.4 A surface compression chamber should be equipped with such valves, gauges and other fittings as are necessary to control and indicate the internal pressure and safe environment of each compartment from outside the chamber at a centralized position.
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DNV GL AS (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.2)
Table 1 As a minimum, facilities should be provided at the central control position to monitor the values of the following parameters for each occupied compartment:
Compartments Parameters Surface compression chamber Wet-bell (if applicable) Section 7
CO2 partial pressure Yes Yes
Humidity Yes
Oxygen partial pressure *1 Yes Yes
Pressure or depth *1 Yes Yes *2
Temperature *1 Yes Chapter 2 *1/ These parameters should be indicated continuously. *2/ Pressure or depth (omitted non-applicable text) outside bell should be indicated. (See IMO code of safety for diving systems Ch.2 design, construction and survey 2.11.2.)
2.5.5 The control stands shall also have indicators showing continuously: — the pressure in the surface mounted gas containers connected — the pressure after all pressure reducers — the pressure in each chamber compartment — the pressure (depth) at each divers location — the pressure at the wet-bell (if employed).
2.5.6 Pressure indicators on the control stand for the divers, the wet-bell and chamber compartments shall be arranged for a possible comparison between each other or with a permanently installed master indicator. If cross-connections are incorporated, these shall be arranged in such a way as to give the operators an indication when cross-connection is being conducted.
2.5.7 Instrumentation for pressure measuring for the divers, the wet-bell and chamber compartments shall have an accuracy of +/-0.3% of full scale. In addition, to facilitate accurate decompression, pressure indicators for the chambers shall facilitate depth measurements with an accuracy of +/-0.25 msw. in the depth range from 30 msw. to 0. The accuracy of other instruments for pressure measuring shall be +/-1% of full scale.
2.5.8 Pressure indicators used on gas containers and pressure reducers, shall have an accuracy of min. 1.6% of the full scale.
2.5.9 The control stands shall also have a system for continuous indication of: a) oxygen content in each compartment individually b) oxygen content in the supply to the: i) umbilicals ii) compartments iii) masks in compartments.
2.5.10 The monitoring systems shall be fitted with audible and visual high and low level alarm.
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DNV GL AS 2.5.11 A list of the essential gauges in the system shall be posted at the control stand.
2.5.12 Permanent provisions for calibration of, and comparison and back-up between, oxygen analysing instruments shall be arranged on the control stand.
2.5.13 There shall be an audio-visual gas flow indicator in the oxygen supply to the chambers, when Section 7 applicable.
2.5.14 The control stands shall have a system for regular indication of carbon dioxide content in each compartment individually.
2.5.15 There shall be systems for indication of temperature and humidity in the inner area displayed at the control stand. Chapter 2
2.5.16 Alarms for abnormal conditions are required at the control stand, if automatic environmental control systems are arranged for regulation of gas composition, pressure and temperature in the inner area.
2.6 Pressure indicators in wet-bell and chambers
2.6.1 Valves, gauges and other fittings should be provided outside the bell as necessary to control and indicate the pressure and safe environment within the diving bell.(omitted text) (IMO code of safety for diving systems Ch.2 design, construction and survey 2.5.3)
2.6.2 A wet-bell shall contain local equipment to monitor important parameters in all situations, such as depth, pressure of gas supply from surface, pressure of on-board emergency gas supply.
2.6.3 The chamber compartments shall be fitted with indicators visible to the divers inside, showing internal pressure.
2.6.4 Means shall be provided for isolating all pressure indicators without interrupting vital functions in the gas distribution system. If isolation is incorporated, these shall be arranged in such a way as to give the operators an indication when isolation is being conducted.
2.7 Oxygen and carbon dioxide analysing systems in wet-bell and chambers
2.7.1 Provision should be made within the bell for an independent means of monitoring oxygen and carbon dioxide levels. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.11.3) Interpretation: In the case of diving in a wet-bell, this is only required when risk evaluation according to given locations and operations reveal a need for monitoring these parameters locally in the wet-bell. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n---
2.7.2 Oxygen analysing systems shall have an accuracy of at least +/-0.015 bar partial pressure oxygen.
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DNV GL AS 2.7.3 The chamber compartments shall have independent oxygen analysers inside.
2.7.4 Carbon dioxide analysing systems shall have an accuracy of +/-0.001 bar partial pressure.
2.7.5 Carbon dioxide gas mixture for calibration shall be available. Section 7 2.8 Other gases
2.8.1 Where breathing gas is supplied directly from running compressors, a means of analysing the air for Carbon Monoxide shall be provided for continuous monitoring - incorporating audio/visual alarm.
2.8.2 The instrumentation for systems intended for other gases than air and oxygen mixes shall be
considered in each case, including hydrogen sulphide. Chapter 2
2.8.3 Diving shall not take place if CO and/or H2S are present, and there shall be a system for shutting down intakes of air into the diving system in cases where these gases may be present. Guidance note:
Operations in connection with exploration of oil may require instrumentation for the analysis of hydrocarbon gases and H2S.
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2.8.4 Calibration gases shall be available for each relevant gas mix.
2.9 Automatic environmental control systems (if employed)
2.9.1 The following requirements apply when systems for automatic regulation of gas composition, pressure and temperature in the inner area are installed.
2.9.2 The design principles given in DNVGL-OS-D202, apply on a general basis.
2.9.3 The most probable failure in the systems shall result in the least critical of any possible new conditions (fail to safety).
2.9.4 Automatic control systems shall keep process variables within the limits specified during normal working conditions and the alarm systems shall be activated when the limits are exceeded.
2.9.5 Alarm at the control stand is required for abnormal conditions. The alarm system is also to be activated by failures in the alarm system circuitry. The alarm system shall be independent of the automatic control system so that failure in one of the systems cannot inhibit operation of the other system.
2.9.6 A manual back-up system for the automatic control system is required.
3 Communication
3.1 General Communications systems shall comply with the relevant requirements given in DNVGL-RU-SHIP Pt.5 Ch.10.
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DNV GL AS 3.2 Visual observation of divers Visual observation of divers in each compartment shall be possible.
3.3 Voice communication systems
3.3.1 Voice communication should be hard-wired, especially when critical operations are coordinated. Section 7
3.3.2 The communication system should be arranged for direct two-way communication between the control stand and: — diver in water — diving bell — each compartment of the chambers Chapter 2 — diving system handling positions — dynamic positioning room — bridge, ship's command centre or drilling floor. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.12.1)
3.3.3 Communication systems shall be arranged for direct voice communication between the control stand and other control stations as needed. If a crane is employed during diving operations, there shall be direct communications with the crane operator.
3.3.4 Alternative means of communication with divers in the surface compression chamber and diving bell should be available in emergency. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.12.2)
3.3.5 The control stand for the divers in the water shall be provided with equipment for audio-recording of all communications with the divers.
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DNV GL AS SECTION 8 EVACUATION SYSTEMS
1 Introduction
1.1 Objectives
The objective of this section is to inform on requirements for evacuation systems as regulated by the Section 8 maritime administrations and/or shelf state authorities.
1.2 Scope The scope of work is according to instructions from the maritime administration.
1.3 Application This section applies to all surface diving systems where SOLAS requirements may be applied if practicably Chapter 2 possible. These requirements may also be applicable as flag state, or shelf state, requirements. The authorities are then contacted as part of the ISM audits or the safety case.
1.4 References a) SOLAS b) IMO guidelines for hyperbaric evacuation c) DNVGL-RP-E403 hyperbaric evacuation systems.
1.5 Documentation Contingency plans with details of responsibilities, equipment, systems and escape routes. — Test plan to establish time for emergency decompression and evacuation. — List of required treatments and equipment for lifeboats. — Ventilation guidance.
1.6 Evacuation time Evacuation time shall be established based upon worst case operational surface decompression or treatment. The emergency procedures should be followed, USN Diving Manual Rev 7 17-11.2 (or latest revision) may be used if no operator defined procedure is available. The unoccupied chamber shall be taken to the surface from deepest depth and timed. A simulation of moving the max. possible number of chamber occupants to the designated lifeboats including one injured diver is also to be timed. The movement of any required supplies for diver treatment under evacuation and not permanently stored within the designated lifeboats are also to be included in the trial. Should time from the start of emergency decompression to entering the lifeboat exceed 15 minutes outer area requirements apply in order to allow evacuation and the effects upon the evacuation of other ship personnel assessed, see also Sec.5 [3.1.1].
1.7 Life boat equipment Medical supplies for the treatment of divers during evacuation shall be available for designated lifeboats on each side of the vessel.
The ability to administer O2 treatment shall be available.
Where the designated diver lifeboats are enclosed, plans to ensure O2 build up ventilation shall be in place. Normally running the life boat engine will provide sufficient ventilation, however, guidance on minimum engine run times relative to O2 use shall be provided and clearly displayed within the designated life boats.
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DNV GL AS The impact on treating a diver with interrupted decompression upon the space requirements of the existing lifeboats shall be assessed.
1.8 Diver recovery A means shall be available to recover divers from the water during an evacuation, eg fast rescue craft or LDC. Section 8 1.9 Survey and testing requirements Trials demonstrating emergency decompression and evacuation to the lifeboat including moving an injured diver shall be carried out. Chapter 2
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DNV GL AS CHAPTER 3 SATURATION DIVING SYSTEMS
SECTION 1 DESIGN PHILOSOPHY AND PREMISES
1 Introduction Section 1 This section presents the safety philosophy applied in this chapter. It also identifies and provides a basis for definition of relevant system design characteristics. Further, key issues required for design, construction, operation and re-qualification of diving systems are identified. In addition, it list minimum requirements for documentation for design, manufacture, installation and some operational aspects. Conclusively some general guidance is given, such as safety philosophy and design premises.
2 Safety objective/redundancy specification Chapter 3 2.1 General As far as reasonable and practicable, a diving system should be designed to minimize human error and constructed so that the failure of any single component (determined, if necessary, by an appropriate risk assessment) should not lead to a dangerous situation. (IMO code of safety for diving systems Ch.2 design, construction and survey 2.1.1.) Interpretation: Whereas this is a general requirement for the systems, it is recognised that certain components cannot fulfil this requirement in and of themselves. A typical example of this is the pressure vessel for human occupancy with acrylic windows and the umbilicals. In these cases the applicable standards will specify stringent safety factors. For other cases a formal safety assessment may be required. It should also be noted that static components are not exempted and human error is included which is taken as a single user error or process of operation. ---e-n-d---o-f---i-n-t-e-r-p-r-e-t-a-t-i-o-n--- This standard is primarily equipment-based and built around the concept above of preventing single failures in accordance with [2.1]. It does not cover operational issues and assumes the use of well proven dive tables and other accepted operational practice within the industry. However, by its nature diving equipment and the required performance of this equipment is based upon operational needs and these are often assessed on a project basis along with statutory authorities (e.g. a safety case). Such needs may have impacts on the detailed requirements of this chapter where they could lead to dangerous situations as per the above. Examples of this are: — Requirements to monitor position relative to fixed subsea installations. — Requirements to communicate with other vessels/fixed assets. — Requirements to withstand more than one failure where diving operations cannot safely be terminated. As such, it is the purchaser/owners responsibility to review all phases from conceptual development until demobilisation and scrapping and define and describe all safety requirements that are effected by any equipment (or lack thereof) within the diving system. The safety objective shall describe the main safety goals before establishing a redundancy specification, that provides a level of risk acceptable to the owner. The result should be a description of the various subsystems in the diving system giving : — the performance requirement of each system to meet the operational need e.g. supply rate of hot water — whether the sub system is essential/emergency/non important — the redundancy of the subsystem and the acceptable time before the back up system is available (e.g. immediate, one hour etc.)
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DNV GL AS — a description of the subsystem and any intended means of operation that impact the arrangement/ performance of the subsystem (e.g. compressors only filling offline gas banks). Guidance note: FMEAs often provide much of the above in the written text, however, they often describe what exists, not than what is needed from an operational safety point of view. Differing mitigations can have vastly different operational impacts (e.g. stop operation and move to a safe state or a full back up system coming online). This information is also required earlier in the project than when the typical FMEA is prepared and should be considered during FEED studies. A safety philosophy will be the overarching basis for Section 1 approval on the basis of this standard and as such should be completed prior to formal submission of documentation at the earliest concept stage.
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2.2 Systematic review
2.2.1 All work associated with the design, construction and operation of the diving system shall be such that it ensures that the requirements in the safety philosophy are met. As a minimum, it shall ensure that Chapter 3 no single failure shall lead to life-threatening situations for any person or to unacceptable damage to the facilities or the environment.
2.2.2 Where the complexity of a subsystem prevents assessment of the possibility of single failures by inspection a systematic review or analysis shall be carried out. The systematic review may be carried out to differing methodologies dependent upon applicability to the system or subsystem (e.g. fault tree analysis or FMEA). The review shall show that the redundancy specification/safety objective above is fulfilled. This review shall also consider any risk to the health and safety of personnel associated with the dive system or in its vicinity. The extent of the review or analysis shall reflect the criticality of the diving system, the criticality of a planned operation and previous experience with similar systems or operations. This review shall identify the risk to the operation of the diving system and to the health and safety of personnel associated with it or in its vicinity. Where risks are identified and managed by mitigation: — Mitigation by low probability only is not in accordance with the principles in IMO and can only be applied to items such as PVHOs that cannot be redundant. Increased safety factors shall be used in these cases. — Any mitigations that are based on repairs shall be assessed/tested against time assumptions. The following tables shall be added as an appendices to the systematic review: — Any mitigations requiring special operational procedures/equipment requiring drills to be followed up in the owners PMS system. — Any mitigations requiring spare parts to be followed up in the owners PMS system. — A list of parts such as shear pins, spring pins and valves with specified properties (e.g. cracking pressure) that are critical to redundancy. — Any mitigations/hidden failures that are controlled by inspection/test to be followed up in the owners PMS system, required inspection periods shall be given by the manufacturer. — Any failures that allow essential systems to operate in a non redundant state or remove emergency safeguards shall be highlighted as terminate the dive. Guidance note: These appendices are to be available for the survey planning document, see DNVGL-RU-OU-0375 Ch.3 Sec.2 [1]
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2.2.3 Testing of the systematic review A test program shall be developed and approved in order to verify that the system behaves as expected and assumptions within the review are valid. The test program shall test all safety critical failures and the systems response:
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DNV GL AS — The expected behaviour after failure shall be clearly described. — The system status after failure shall be assessed. — Failures that are not purely related to design and may change with the condition of the system shall be identified and the test procedures entered into the survey planning document. — Testing relating to confirming the performance of software shall also be identified and test procedures to confirm upgrades entered into the survey planning document. Section 1 2.2.4 Risks during evacuation or emergency conditions Special attention shall be given to the risk of bell handling, fire and evacuation either as a sepearate document or as part of the systemic review and shall as a minimum consider: — How to recover the bell with a listing vessel that is in a survivable condition, see DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6 [4]. — Ventilation and pressurisation requirements to evacuate in a timely manner given the mode of operation including planned split level dives. Chapter 3 — The ability to operate with emergency power only over the entire decompression period (e.g. after grounding).
2.3 System integrity
2.3.1 Diving systems shall be designed, constructed and operated in such a manner that they: a) fulfil the specified operational requirements b) fulfil the defined safety objective and have the required support capabilities during planned operational conditions c) have sufficient safety margin against accidental loads or unplanned operational conditions d) consider the possibility of changes in the operating conditions and criteria during the lifetime of the system.
2.3.2 Any re-qualification deemed necessary due to changes in the design conditions shall take place in accordance with provisions set out in each section of the standard.
2.4 Essential services
2.4.1 Essential services are herein defined as those services that shall be in continuous operation for maintaining the diving system's functionality with regard to sustaining the safety, health and environment of the divers in a hyperbaric environment. This includes services required by the crew monitoring the divers.
2.4.2 Essential services shall be maintained for the period required by safely terminating the surface diving operation, including time for decompression of the divers.
2.4.3 For services supporting divers in the water, all services are essential. 20 minutes is considered to be the minimum time required ensuring that the divers are safely recovered to the bell/basket, or to the surface.
2.4.4 For services supporting divers in a wet-bell, all services are essential. 20 minutes is considered to be the minimum time required ensuring that the divers are safely recovered into the decompression chambers or to the surface.
2.4.5 For services supporting divers in the decompression chambers, all required services are essential. The specified maximum decompression schedule is considered to be the minimum time required ensuring that the divers are safely brought to the surface.
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DNV GL AS 2.5 Emergency services
2.5.1 Emergency services are herein defined as those services that are essential for safety in an emergency condition. Examples of equipment and systems for emergency services include: a) emergency lighting, including external strobe lighting on basket/wet-bell
b) emergency communication Section 1 c) emergency life support systems involving pressure containment, oxygen supplies and CO2 scrubbing d) emergency heating/cooling systems e) condition monitoring of emergency batteries f) alarm systems for the above emergency services g) emergency launch and recovery of the bell.
2.5.2 For services supporting divers in the water, all the above services may be considered emergency Chapter 3 services and 20 minutes is considered to be the minimum time required to ensure that the divers are safely recovered in the bell.
2.5.3 For services supporting divers in the bell, all the above services may be considered emergency services and 20 minutes is considered to be the minimum time required to ensure that the divers are safely recovered in the decompression chambers or to the surface.
2.5.4 For services supporting divers in the decompression chambers, all the above services may be considered emergency services.
2.5.5 Services supporting hyperbaric evacuation system are considered statutory scope and therefore reviewed on a case by case basis according to instructions from the applicable administration.
2.6 Non-important services Non-important services are those which are not essential/emergency according to the above.
2.7 Quality assurance
2.7.1 The safety format within this standard requires that gross errors (human errors) shall be controlled by: a) requirements for organisation of the work b) competence of persons performing the work c) verification of the design d) quality assurance during all relevant phases.
2.7.2 For the purpose of this standard, it is assumed that the owner of a diving system has established a quality objective. The owner shall, in both internal and external quality related aspects, seek to achieve the quality level of products and services intended in the quality objective. Further, the owner shall provide assurance that intended quality is being, or shall be, achieved.
2.7.3 A quality system shall be applied to assist compliance with the requirements of this standard. Guidance note: ISO 9000 gives guidance on the selection and use of quality systems, and ISO 10013 gives guidance on developing quality manuals.
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DNV GL AS 3 General premises
3.1 Concept development
3.1.1 Data and description of system development and general arrangement of the diving system shall be established. Section 1
3.1.2 The data and description shall include the following, as applicable: a) safety objective b) locations, foundations and interface conditions c) diving system description with general arrangement and system limits d) functional requirements including system development restrictions, e.g. significant wave height, hazardous areas, fire protection Chapter 3 e) installation, repair and replacement of system elements and fittings f) project plans and schedule, including planned period for installation g) design life including specification for start of design life, e.g. final commissioning, installation h) data of contained liquids and gases i) capacity and sizing data j) geometrical restrictions such as specifications of diameter, requirement for fittings, valves, flanges and the use of flexible hoses k) second and third party activities.
3.2 Execution plan An execution plan shall be developed, including the following topics: a) general information, including project organisation, scope of work, interfaces, project development phases and production phases b) contacts with purchaser, authorities, third party, engineering, verification and construction contractors c) legal aspects, e.g. insurance, contracts, statutory requirements.
3.3 Plan for manufacture, installation and operation
3.3.1 The design and planning for a diving system shall cover all development phases including manufacture, installation and operation.
3.3.2 Manufacture For a documentation overview, see [8] documentation.
3.3.3 Installation Detailed plans, drawings and procedures shall be prepared for all installation activities. The following shall as a minimum be covered: a) diving system location overview (planned or existing) b) other vessel (or fixed location) functions and operations c) list of diving system installation activities d) alignment rectification e) installation of foundation structures f) installation of interconnecting services g) installation of protective devices
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DNV GL AS h) hook-up to support systems i) as-built survey j) final testing and preparation for operation.
3.3.4 Operation Plans for diving system operation, inspection, maintenance and repair shall be prepared prior to start of operation. Section 1 All operational aspects shall be considered when selecting the diving system concept. The diving system operational planning shall as a minimum cover: a) organisation and management b) start-up and shut-down (pre and post dive) c) operational limitations d) emergency operations
e) maintenance Chapter 3 f) corrosion control, inspection and monitoring g) general inspection h) special activities.
3.3.5 Demobilisation Demobilisation shall be planned and prepared. Evaluation shall include the following aspects: a) safety aspects, during and after demobilisation b) environmental aspects, e.g. pollution c) impact on other structures d) possible reuse of equipment at a later stage (re-qualification and certification).
4 System design principles
4.1 System integrity
4.1.1 Diving systems shall be designed, constructed and operated in such a manner that they: a) fulfil the specified operational requirements b) fulfil the defined safety objective and have the required support capabilities during planned operational conditions c) have sufficient safety margin against accidental loads or unplanned operational conditions.
4.1.2 The possibility of changes in the operating conditions and criteria during the lifetime of the system.
4.1.3 Any re-qualification deemed necessary due to changes in the design conditions shall take place in accordance with provisions set out in each section of the standard.
4.2 Monitoring and inspection during operation
4.2.1 Parameters that could jeopardise the safety of the divers, and or violate the integrity of a diving system, shall be monitored and evaluated with a frequency that enables remedial actions to be carried out before personal harm is done or the system is damaged.
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DNV GL AS Guidance note: As a minimum the monitoring and inspection frequency should be such that the diving system, and consequently the diving operation, should not be endangered due to any realistic degradation or deterioration that may occur between two consecutive inspection intervals.
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4.2.2 Instrumentation may be required when visual inspection or simple measurements are not considered Section 1 practical or reliable, and available design methods and previous experience are not sufficient for a reliable prediction of the performance of the system.
4.2.3 The various pressures in a diving system shall not exceed the design pressures of the components during normal steady-state operation.
4.3 Pressure control system Chapter 3
4.3.1 A pressure control system is be used to prevent the internal pressures at any point in the diving system rising to excessive levels, or falling below prescribed levels. The pressure control system comprises the pressure regulating systems, pressure safety systems and associated instrumentation and alarm systems.
4.3.2 The purpose of the pressure regulating system is to maintain the operating pressures within acceptable limits during normal operation. The set pressures of the pressure regulating system shall be such that the local operational pressures are not exceeded at any point in the diving system. Due account shall be given to the tolerances of the pressure regulating system and the associated instrumentation.
4.3.3 The purpose of the pressure safety systems is to protect the systems during abnormal conditions, e.g. in the event of failure of the pressure regulating systems. The pressure safety systems shall operate automatically in accordance with the fail safe principles and with set pressures such that there is a low probability for: a) The internal pressure at any point in the diving system to exceed the design pressure (maximum operating pressure) (see Sec.3 [2.2]). b) The unintentional loss of pressure at any point in the diving system to exceed set values (see Sec.3 [5.3]).
4.3.4 The diving system may be divided into sections with different design pressures provided the pressure control system ensures that; for each section, the local operational pressure cannot be exceeded during normal operations and that the design pressure cannot be exceeded during abnormal operation. The pressure control shall also ensure that unwanted loss of pressure in one section does not occur as a result of an abnormal condition in another section.
5 Diving system arrangement and layout
5.1 General
5.1.1 The systems shall be so designed that the effect of a single failure cannot develop into hazardous situations for the divers.
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DNV GL AS Guidance note: Whereas this is a general requirement for the systems, it is recognised that certain components cannot fulfil this requirement in and of themselves. A typical example of this is the pressure vessel for human occupancy with acrylic windows. In these cases the applicable standards will specify stringent safety factors. For other cases a formal safety assessment may be required.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e--- Section 1 5.1.2 The diving system shall be so designed that the divers and assisting personnel are provided with safe and comfortable operating conditions. Ergonomic principles shall be applied in the design of working systems. (i.e. in accordance with ISO 6385.)
5.1.3 The diving system shall contain a minimum of two compartments. The smaller of the two compartments shall be large enough for two persons. One of the compartments shall be a living compartment. For saturation diving systems, a minimum of two compartments shall be designed for keeping the pressure independent of the pressure in the other compartment(s). Chapter 3
5.1.4 When the diving system is taken onboard and mobilised for use, equipment related to the diving system shall be permanently attached to the hull structure (e.g. by welding, screwed connection or similar). Fitting by means of lashing is not considered as permanent fitting.
5.2 Layout of the diving system The layout of the diving system on board shall ensure protection from accidental damage and accessibility for: a) safe operation b) maintenance c) inspection.
6 Environmental conditions
6.1 General
6.1.1 Systems and components shall be designed for the environmental conditions expected at their installed location (on the vessel or otherwise) and their geographic site of operation.
6.1.2 All systems and components shall be able to operate satisfactorily and safe in accordance with their specifications at the environmental conditions stated in [7].
6.1.3 Additional requirements for various systems and components may, however, be given elsewhere in the Standard.
6.1.4 The effects of environmental phenomena relevant for the particular location and operation in question shall be taken into account.
6.1.5 Environmental phenomena that might impair proper functioning of the system or cause a reduction of the reliability and safety of the system shall be considered, (including fixed and land-based installations): — temperature — wind, tide, waves, current — ice, earthquake, soil conditions — marine growth and fouling.
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DNV GL AS 6.2 Collection of environmental data The environmental data shall be representative for the geographical areas in which diving systems may be operated. Estimates based on data from relevant locations may be used. Guidance note: Environmental parameters may be described using characteristic values based on statistical data or long-term observations.
Statistical data may be utilised to describe environmental parameters of a random nature (e.g. wind, waves). The parameters Section 1 should be derived in a statistically valid manner using recognised methods.
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6.3 Wind
6.3.1 Where appropriate, wind effects shall be considered in the design of handling systems, including the
possibility of wind induced vibrations of exposed free spans. Chapter 3
6.3.2 For spans adjacent to other structural parts, possible effects due to disturbance of the flow field shall be considered when determining the wind actions. Such effects may cause an increased or reduced wind speed, or a dynamic excitation by vortices being shed from adjacent structural parts.
6.4 Tide
6.4.1 Tide effects shall be considered when this is a significant parameter, e.g. handling systems on shore based installations.
6.4.2 The assumed maximum tide shall include both astronomic tide and storm surge. Minimum tide estimates should be based upon the astronomic tide and possible negative storm surge.
6.5 Waves
6.5.1 Maximum sea-state, defined by maximum significant wave height, shall be specified and used in the design calculations. Calculations may be done in accordance with specifications in App.A.
6.5.2 The wave data to be used in the design of handling systems are in principle the same as the wave data used in the design of the structure supporting the system.
6.5.3 Direct and indirect wave effects shall be taken into consideration.
6.5.4 When appropriate, consideration shall be given to wave refraction and shoaling, shielding, and reflecting effects.
6.5.5 Where the handling system is positioned adjacent to other structural parts, possible effects due to disturbance of the flow field should be considered when determining the wave actions. Such effects may cause an increased or reduced velocity, or dynamic excitation by vortices being shed from the adjacent structural parts.
6.5.6 Where appropriate, consideration should be given to wave direction and short crested waveform.
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DNV GL AS 6.6 Current
6.6.1 The effect of current shall be taken into consideration.
6.6.2 Current velocities shall include contributions from positioning systems, tidal current, wind-induced
current, storm surge current, and other possible current phenomena. For near-shore fixed installations, long- Section 1 shore current due to wave breaking shall be considered.
6.6.3 The variations in current velocity magnitude and direction as a function of water depth may need to be considered. For fixed installations, the current velocity distribution shall be the same as the one used in the design of the offshore structure supporting the system.
6.7 Ice Chapter 3 For areas where ice may develop or drift, consideration shall be given to possible effects, including: a) ice forces on the system (added loads may be due to increased diameters or surface area) b) impacts from drifting ice c) icing problems during construction and installation.
6.8 Air and sea temperatures
6.8.1 Air and sea temperature statistics may be provided giving representative design values specified in the terms of delivery.
6.8.2 Monitoring of temperature may be required during construction, installation and commissioning phases if the effect of temperature or temperature variations has a significant impact on the safety of the diving system.
6.8.3 The interactive effects of temperature and humidity shall be considered.
6.9 Marine growth
6.9.1 The effect of marine growth on diving systems shall be considered, taking into account both biological and other environmental phenomena relevant for the location.
6.9.2 The estimation of hydrodynamic loads shall be considered in the cases where marine growth might have an impact on the effective surface area or surface roughness.
7 External and internal system condition
7.1 External operational conditions and outer area
7.1.1 Design inclinations shall be according to Table 1.
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DNV GL AS Table 1 Design inclinations
Permanent Location Roll Pitch Trim list
Chambers and other surface installations: +/-22.5° +/-15° +/-10° +/-5° on a ship Section 1 On a mobile offshore unit +/-15° +/-15°
Components in a bell +/-45° +/-22.5°
Guidance note: For handling systems the operational design sea-state is given in Sec.7 [3.1].
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e--- Chapter 3 7.1.2 Range of ambient temperature: -10°C to 55°C, unless otherwise specified. For greater temperature ranges, temperature protection shall be provided.
7.1.3 Humidity: 100%.
7.1.4 Atmosphere contaminated by salt (NaCl): up to 1 mg salt per 1 m3 of air, at all relevant temperatures and humidity conditions.
7.2 Submerged components
7.2.1 Range of ambient temperature: -2°C to 30°C.
7.2.2 Range of ambient pressure: 1 bar to 1.3 times the pressure corresponding to maximum operating depth.
7.2.3 Salinity of ambient water: 35 parts per thousand.
7.2.4 The pressure equivalent to depth of seawater at 0°C with 3.5% salinity may be taken as 1.006 bar per 10 msw (meter seawater), as a mean value between 0 and 200 m depth. For saltwater, the density may be taken to vary as follows: — 0.05% increase for each 100 m of depth increase — 0.4% increase for an increase in salinity from 3.5% to 4.0% — 0.3% decrease for an increase in temperature from 10°C to 20°C.
7.2.5 For the selection and detailed design for external corrosion control, the conditions relating to the environment shall be defined.
7.3 Internal conditions
7.3.1 Range of ambient pressure: 1 bar to 1.3 times the pressure corresponding to dmax with pressurisation and depressurisation rates as specified in Sec.3 [3.1].
7.3.2 Range of ambient temperature: 5°C to 55°C, unless otherwise specified.
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DNV GL AS 7.3.3 Relative humidity: up to 100%.
7.3.4 Atmosphere contaminated by salt (NaCl): up to 1 mg salt per 1 m3 of air, at relevant temperatures and humidity conditions.
7.3.5 A description of the internal conditions during storage, construction, installation, pressure testing and Section 1 commissioning shall be prepared. The duration of exposure to seawater or humid air, and the need for using measures to control corrosion shall be considered. When choosing materials, paints etc. the potential for emission of hazardous compounds shall be considered. Statutory requirements apply for determination of exposure limits such as: a) American Conference of Governmental Industrial Hygienists, documentation of the threshold limit values and biological exposure
b) European Commission Directive on occupational exposure limit values Chapter 3 c) health and safety executive occupational exposure limits.
7.4 Internal operational conditions In order to assess the need for internal corrosion control, including corrosion allowance and provision for inspection and monitoring, the following conditions shall be defined: a) maximum and average operating temperature and pressure profiles of the components, and expected variations during the design life b) expected content of dissolved salts in fluids, residual oxygen and active chlorine in sea water) c) chemical additions and provisions for periodic cleaning d) provision for inspection of corrosion damage and expected capabilities of inspection tools (i.e. detection limits and sizing capabilities for relevant forms of corrosion damage) e) the possibility of wear and tear, galvanic effects and effects in still water pools shall be considered.
8 Documentation
8.1 General
8.1.1 This section specifies the requirements for documentation during diving system design, manufacturing, fabrication, installation, commissioning and operation.
8.1.2 In accordance with quality system requirements, design output shall be documented and expressed in terms that can be verified and validated against design input requirements. The supplier shall establish and maintain documented procedures to control all documents and data. This may in part be done in accordance with the DNV GL document requirements lists (DOCREQ).
8.1.3 All documentation requirements shall be reflected in a document register. The documentation shall cover design, manufacturing, fabrication, installation and commissioning. As a minimum, the register shall reflect activities from the start of design to operation of the diving system.
8.1.4 The documentation shall be submitted to the relevant parties for acceptance, verification or information as agreed in ample time before start of fabrication.
8.1.5 Verified documentation shall be available at the work site before manufacturing commences.
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DNV GL AS 8.2 Documentation of arrangement etc. a) plans showing general arrangement of the diving system, location and supporting arrangement b) plans showing the lay-out of control stand(s) c) proposed program for tests and trials of systems for normal operation and for emergency use.
8.2.1 List stating the following particulars for the diving system: Section 1 a) maximum operating depth dmax and maximum observation depth for the bell b) maximum operation time Top c) maximum number of divers in the bell d) maximum number of divers in the chamber(s) and bell(s) e) maximum operational sea-state f) extract from the operation manual, stating the operational procedures, as basis for the design. Chapter 3 8.3 Documentation for systems in operation
8.3.1 In order to carry out periodical surveys, the minimum documentation shall include: a) personnel responsible for the operation of diving system b) history of diving system operation with reference to events which may have significance to design and safety c) a log of the total number of dives and hours of saturation in the periods between annual surveys d) records of new equipment installed and old equipment removed e) installation condition data as necessary for understanding diving system design and configuration, e.g. previous survey reports, as-built installation drawings and test reports f) inspection and maintenance schedules and their records.
8.3.2 In case of mechanical damage or other abnormalities that might impair the safety, reliability, strength and stability of the diving system, the following documentation shall, as a minimum, be prepared prior to start-up of the diving system: a) description of the damage to the diving system, its sub-systems or components with due reference to location, type, extent of damage and temporary measures, if any b) plans and full particulars of repairs, modifications and replacements, including contingency measures c) further documentation with respect to particular repair, modification and replacement, as agreed upon in line with those for the manufacturing or installation phase.
8.4 Filing of documentation
8.4.1 Maintenance of complete files of all relevant documentation during the life of the diving system is the responsibility of the owner.
8.4.2 The engineering documentation shall be filed by the owner or by the engineering contractor for a minimum of 10 years.
8.4.3 Design basis and key data for the diving system shall be filed for the lifetime of the system. This includes documentation from design to start-up and also documentation from possible major repair or modification of the diving system.
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DNV GL AS 8.4.4 Files to be kept from the operational and maintenance phases of the diving system shall, as a minimum, include final in-service inspection reports from start-up, periodical and special inspections, condition monitoring records, and final reports of maintenance and repair.
9 Inspection and testing Section 1 9.1 General
9.1.1 When a diving system is built according to this standard, an inspector or surveyor shall verify that: a) the design and scantlings comply with the approved plans and the requirements in this standard and other specified recognized standards, codes, and national regulations b) that the materials and components are certified according to this standard and the terms of delivery c) that the work is carried out in accordance with the specified fabrication tolerances and required quality of Chapter 3 welds etc. d) that piping systems conducting gas in life support systems are cleaned in accordance with an approved cleaning procedure conforming to requirements given in ASTM G93-03 standard practice for cleaning methods and cleanliness levels for materials and equipment used in oxygen-enriched environments e) that gas cylinders are clean and sealed f) that all required tests are carried out.
9.1.2 The inspection shall be carried out at the manufacturers, during the assembly and during installation. The extent and method of examination shall be agreed in the terms of delivery.
9.1.3 The tests to be carried out are stated in [9.2] and [9.3]. Additional tests may, however, be required. The testing after completed installation shall be in compliance with an approved program.
9.2 Testing at the manufacturers
9.2.1 Pressure tests a) Welded pressure vessels and seamless steel gas containers for internal pressure shall be hydrostatic tested to an internal pressure in accordance with the design code. Each compartment in chambers shall be tested separately. b) Bells and pressure vessels for external pressure shall, in addition to the internal pressure testing, be hydrostatic tested to an external pressure in accordance with the design code. c) Acrylic plastic windows shall be tested in accordance with ASME PVHO-1-2012 Sec.2. d) Compressor components subjected to pressure shall be hydrostatic tested in accordance with the design code.
9.2.2 Compressors a) Compressors shall be tested for the gas types and pressure. b) The tests shall incorporate measurements of humidity and possible contaminants in the gas delivered.
9.2.3 Closed circuit breathing system (CCBS) CCBS shall be tested according to an approved test program incorporating the following: a) breathing resistance at work b) simulation of the most probable failures and recording of the resulting system responses c) performance of the system with regard to gas composition, pressure and temperature as function of the variables
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DNV GL AS d) The results of the tests shall be made available for approval.
9.2.4 Flexible hoses Flexible hoses shall be tested as specified in Sec.7.
9.2.5 Umbilicals
Umbilicals shall be tested as specified in Sec.7. Section 1
9.2.6 Electrical pressure vessel penetrators Electrical penetrators shall be tested as specified in Sec.4.
9.2.7 Bell a) the working weight and the buoyancy shall be ascertained b) the stability in normal and emergency modes shall be tested Chapter 3 c) a shallow water ballast release test shall be carried out if fitted d) emergency release systems for hoisting rope and umbilical shall be tested.
9.3 Testing after completed installation
9.3.1 Pressure tests Piping for the life support systems shall be pressure tested to 1.5 times the maximum working pressure. Hydraulic systems may, however, be tested to the smaller of 1.5 times the maximum working pressure, or 70 bar in excess of the maximum working pressure.
9.3.2 Purity tests Piping systems intended to be used in breathing gas and oxygen systems shall be tested for purity in accordance with requirements given in ASTM G93-03 standard practice for cleaning methods and cleanliness levels for materials and equipment used in oxygen-enriched environments. The tests shall comprise: a) measurement of contamination of the cleaning agent used at the last stage of the cleaning b) tests for possible traces of cleaning agents left in the piping system.
9.3.3 Gas leakage tests a) The gas storage, chambers, bell and life support systems for gas shall be tested for leakage at the maximum working pressure. The test shall be carried out with the gas type the system is supposed to contain and which has the highest leakage rate properties, or a gas with equivalent properties. Chambers and bells may be tested for leakage using a test gas with only 10% Helium providing a thorough inspection of all penetrations is carried out using leak detection ('snooper') liquid recommended by the industry. b) A leakage rate up to 1% pressure drop in 24 hours for the whole chamber system can be accepted. The gas leakage test time shall be minimum 6 hours. Guidance note: Note that for systems with max. pressure between 20 bar and 30 bar and chamber temperatures between 20°C and 30°C, a temperature drop of about 3°C will cause a pressure drop of about 1%. (See BS 5355 Specification for filling ratios and developed pressures for liquefiable and permanent gases).
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9.3.4 Handling systems Handling systems shall be subjected to tests for structural strength and for function and power.
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DNV GL AS a) A static load test to a load equal to the design load (see Sec.6 [3.1]) shall be carried out b) Functional and power testing of normal and emergency systems shall be carried out with a functional test load of 1.25 times the working weight in the most unfavourable position. It shall be demonstrated that the systems are capable of carrying out all motions in a safe and smooth manner c) Monitoring of functional parameters during the test, e.g. pressure peaks in hydraulic systems may be required. d) A recovery test of the bell shall be carried out simulating emergency operations conditions. Section 1
9.3.5 Life support systems Life support systems for normal and emergency operation shall be tested for proper functioning.
9.3.6 Various systems The following systems shall be tested for proper functioning: a) sanitary b) communication Chapter 3 c) fire detection d) fire alarm e) fire extinction f) evacuation systems g) diver heating h) environmemtal control and CO2 removal. Other systems onboard the surface installations, significant for the safety of the diving system, are also to be tested.
9.3.7 Electrical systems a) A test for insulation resistance shall be applied to every circuit between all insulated poles and earth, and between individual insulated poles. A minimum value of 1 megaohm shall be attainable. b) Main and emergency power supplies shall be tested.
9.3.8 Instrumentation The correct calibration of all essential instrumentation (compartment and bell pressure gauges, gas analysis instruments etc.) shall be checked.
9.3.9 Environmental control systems Environmental control systems should be tested to ensure a stable temperature can be maintained at both shallow and max. depths. The tests shall include checks on redundant and emergency capacity. Monitoring system: a) Failure conditions shall be simulated as realistically as possible, if practicable by letting the monitored parameters pass the alarm and safety limits. Alarm and safety limits shall be checked. Automatic control systems: a) Some variation in heat load shall be applied to test the control system. Any functional modes that vary heat inputs significantly, such as high humidity reduction or blowers generate differing heat over their rpm range shall be considered. b) Heat shall be injected for both the number of divers and to simulate external temperature loads. For hypothermia the minimum number of divers shall be simulated and for hyperthermia the maximum. c) A test simulating complete failure to determine time to unsafe temperatures may be required if repair procedures are specified from the risk assessment. d) The behaviour of control systems shall be tested during switch-overs to back up systems and different supplies.
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DNV GL AS 9.3.10 CO2 removal CO2 removal shall be tested for both normal and emergency systems.
Emergency systems shall prove their ability to maintain CO2 levels for the full 24 hours with the permanently stored scrubber material.
Normal systems shall prove the ability to hold a CO2 at a stable level prior to scrubber material exhaustion. While there is no required duration time until exhaustion, the required stored quantities should be Section 1 considered.
9.3.11 Sea trials The normal handling system shall be tested with the working weight of the bell or basket to the maximum depth. For saturation diving systems the bell shall be checked for leakage, and the communication system shall be tested.
10 Marking and signboards Chapter 3
10.1 General Labels (nameplates) of flame retardant material bearing clear and indelible markings shall be placed so that all equipment necessary for operation (valves, detachable connections, switches, warning lights etc.) can be easily identified. The labels shall be permanently fixed. All gas containers shall be marked with a consistent colour code visible from the valve end, showing the name, chemical formula of the gas it contains and the percentage of each gas. Piping systems shall be marked with a colour code, and there shall be a chart posted in the control room explaining the code. Guidance note:
Table 2 MO code of safety for diving systems :
Name of gas Chemical formula Colour code
Oxygen O2 White
Nitrogen N2 Black Air White and black Helium He Brown Oxygen/Helium
mixed gas O2/He White and brown
Carbon dioxide CO2 Grey
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10.2 Gas containers Each container shall be permanently and legibly marked on the collar or neck ring (where the thickness of the material is greater than the design minimum) as follows: a) the design code b) the manufacturer's mark or name c) the manufacturer's serial number d) the test pressure (bar) and date of hydrostatic test e) surveyor's mark and identification f) settled pressure (bar) at 15°C g) volumetric capacity of the container, in litres
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DNV GL AS h) tare weight, i.e. the mass of the container including valve, in kg. In addition marking of gas content shall be carried out according to [10.1].
10.3 Other pressure vessels than gas containers Each pressure vessel shall be permanently and legibly marked at a suitable location in accordance with the requirements in the design code. As a minimum the following information shall be present: Section 1 a) the design code b) the manufacturer's mark or name c) the manufacturer's serial number d) the test pressure (bar) and date of hydrostatic test e) the maximum working pressure f) the inspection body’s mark and identification g) the maximum set pressure of the safety relief valves. Chapter 3 10.4 Handling system The handling system shall, in an easily visible place, be fitted with a nameplate giving the following particulars: a) identification number b) static test load c) functional test load d) working weight e) surveyor's mark and identification. The above loads shall be specified for each transportation system involved.
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DNV GL AS SECTION 2 PRESSURE VESSELS FOR HUMAN OCCUPANCY, GAS STORAGE AND OTHER PURPOSES
1 General
1.1 Objectives Section 2
1.1.1 This section aims to give general guidance on: a) conceptual and detailed design of pressure vessels for human occupancy, for gas storage and for other purposes b) manufacturing of such pressure vessels c) quality control during manufacturing and fabrication of such pressure vessels including documentation requirements d) load conditions Chapter 3 e) interlock arrangements for doors and hatches.
1.1.2 For quantitative design parameters and functional requirements, see relevant standards and guidelines, including normative references given in Sec.1 [3] and DNVGL-RU-SHIP.
1.1.3 Further requirements for piping and pipe connections can be found in Sec.7.
1.2 Application and scope
1.2.1 This section applies to all pressure vessels in diving systems designed to comply with this standard. Note that in addition to this standard, and the applied design standards, further national requirements may apply.
1.2.2 ASME PVHO-1 safety standard for pressure vessels for human occupancy, shall be used for design of acrylic plastic windows, regardless of which standard is used for the design of the pressure vessel.
1.2.3 Material specifications are given in the applied codes and standards (EN/ASME).
1.2.4 Welding of pressure vessels and general workmanship requirements are not specified herein. Further requirements for welding and workmanship are given in the relevant codes and rules.
1.2.5 This section has impact upon Sec.8, insofar as it provides the basis for design of the pressure vessels in the hyperbaric evacuation system.
1.3 Documentation Pressure vessels shall be documented as follows: Plans showing structural arrangement, dimensions, welding seams, attachments and supports of the bell, the chamber and other pressure vessels, with details of doors, locks (medical locks and equipment locks), view ports, penetrations, flanged and welded connections. Plans showing expansion allowances under working conditions for interconnected multi-vessel systems. Documents stating: a) grade of material b) welding methods, type and size of filler metal
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DNV GL AS c) design pressure d) particulars of heat treatment e) fabrication tolerances f) extent and type of non-destructive testing of welded connections g) type of thermal insulation materials and particulars, i.e.: flammability and specific heat conductivity h) type of buoyancy materials and particulars, i.e. maximum permitted water depth, specific weight, specific water absorption and buoyancy dependent on water depth and exposure time Section 2 i) drawings and specifications of all windows with detailed drawings and specifications of the penetration fitting the appropriate window is to fit. It shall be determined that the tolerances are sufficient including gaskets, O-rings and retainer rings j) calculations of thicknesses and or stresses k) fatigue evaluation and if necessary fatigue analysis. For seamless steel gas cylinders and vessels: a) plans showing proposed dimensions and details such as valves and safety devices shall be made for each Chapter 3 type and size of vessel. Details shall include: a) production method b) eat treatment. Material specifications for the completed vessel with information on the following: a) chemical composition b) tensile strength c) yield strength d) elongation e) impact test values f) brinell hardness. The following particulars shall be provided for information: a) type of gas b) filling pressure at 15°C c) safety relief valve setting d) weight of empty vessel and volumetric capacity.
1.4 Testing and marking after completion
1.4.1 The required testing and marking of pressure vessels are specified in Sec.1 [10.1] and the applied standard found in [2.1.2].
1.4.2 Materials selection associated with the production of pressure vessels is covered in the applied standard. Requirements and guidance on inspection and monitoring associated with the production of pressure vessels can be found in the applied standard and DNVGL-RU-OU-0375.
1.5 Material protection
1.5.1 Areas of steel pressure vessels that can be subjected to corrosion shall be protected by approved means. The surface of the window seats cavity shall be protected against corrosion.
1.5.2 Windows mounted on chambers shall be protected to avoid damage by impact and to prevent chemicals, which can deteriorate the acrylic plastic, to come in contact with the window from the outside.
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DNV GL AS Guidance note: Many solvents for paints, acetone and other agents will deteriorate the acrylic plastic and reduce the strength significantly.
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1.5.3 All penetrators in pressure vessels for human occupancy, shall be designed to minimise corrosion from any fluid passing through them.
Guidance note: Section 2 In some cases this requirement may best be met by the use of a sleeve passing through the hull penetration.
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1.6 Design loads
1.6.1 The design pressure for chambers and bell shall not be less than that corresponding to the maximum operating depth as defined in Ch.1 Sec.1 [2.4]. The effects of the following loads shall be considered and Chapter 3 shall be taken into account if significant: a) dynamic loads due to movements of the support vessel b) local loads c) loads due to restrictions in expansions d) loads due to weight of content during normal operation and pressure testing e) loads due to rough handling f) loads due to bell and escape tunnel clamped on to the chamber g) the stress evaluation shall apply the distortion theory (von Mises criterion). Guidance note: Multipurpose vessels may carry heavy deck loads, which can cause stresses and strains on the mountings of the diving system components. If this cannot be avoided through design of the installed diving system, it should be monitored during such operations.
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1.6.2 The design life with respect to fatigue shall be defined by the designer.
2 General principles for design of chambers and bells
2.1 Chambers
2.1.1 The dimensions of the living compartment shall be sufficient for the diving crew facilities required by [3]. Guidance note: Statutory requirements may require larger dimensions.
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2.1.2 All pressure vessels for human occupancy shall be designed, constructed and tested according to one of the following codes and standards: a) EN 13445 unfired pressure vessels. b) ASME VIII div.1 boiler and pressure vessel code.
2.1.3 Diving bells and chambers shall be classified in the highest category in the applied code or standard.
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DNV GL AS 2.1.4 Other codes and standards may be evaluated and accepted on a case by case basis.
2.1.5 All pressure vessels for human occupancy shall be certified.
2.1.6 For diving systems with an operational period exceeding 12 hours, the living compartment is normally to have a size sufficient for installation of bunks with length and breadth equal to 200 x 70 cm (see Sec.3 Section 2 [9.1.1]). The minimum inner dimensions measured as free height above the deck plates in the middle of the chamber, shall be 200 cm.
2.1.7 All windows in pressure vessels for human occupancy shall be certified. VL certificates will be required.
2.1.8 All compartments shall be fitted with windows, which allow internal areas to be viewed from outside. Chapter 3
2.1.9 For diving systems, the living compartment and other compartments that can be used for decompression including the bell, shall be provided with means for locking in provisions, medicine and equipment necessary for the operation of the system. The divers in each living compartment shall have access to toilet facilities. Paints, cabling and other materials shall be considered for toxic or noxious properties as specified in Sec.1 [8.3].
2.1.10 Expansion joints (bellows) Expansion joints shall be considered on a case by case basis but should only be utilised where a traditional trunk is not practical. Bellows shall be designed and manufactured by a EJMA (Expansion joint manufacturers association) member to their latest standards. The manufacturer shall: 1) Be made aware of the safety requirements for use as a PVHO and design the bellows accordingly under section 3 (EJMA 10th edition). It is expected that a redundant ply design with leakage alarms as per EJMA 3.1 d, c or similar is utilised. 2) Account for accidental and usage loads (internally and externally) based upon the movement of divers and possible tools and equipment. 3) Be involved in installation. 4) Create an expansion joint record system including details of the required in service inspection requirements (these shall be included in the PMS system). In addition to the documentation required to approve the expansion joint structurally the above shall also be documented and submitted for approval. Guidance note: VL certificates will be required.
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2.2 Bell
2.2.1 The bell shall be provided with proper protection against mechanical damage.
2.2.2 The bell shall be provided with windows that as far as practicable allow the occupants to observe divers outside the bell.
2.2.3 The bell shall be equipped with one extra external lifting fastening.
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DNV GL AS Guidance note: Note that the design and location of the extra lifting fastening needs to be considered in view of the need to bring the bell back to a mating trunk on the decompression chambers as required by Sec.6 [2.2.1].
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2.2.4 Internally there shall be an attachment at the top for lifting of divers. Section 2 2.2.5 Bells shall have possibilities for entry and exit when landed on the seafloor in an arbitrary manner, in an emergency. When the bell is fitted with drop weights, release of these in two stages may be accepted, when the first stage allows the bell to rise sufficiently for entry and exit. (Note guidance to Sec.6 [2.3.1])
2.3 Doors, hatches, windows, branches etc.
2.3.1 Minimum dimensions of doors, hatches and medical locks. Chapter 3 Doors and hatches for human transportation shall in general be: a) minimum diameter 600 mm, and b) minimum diameter 800 mm for lock-out and lock-in hatches on the bell. The length of the bell hatch trunk shall not exceed the diameter. Guidance note: For doors and hatches in between chambers, standard pipe with nominal bore 24" may be acceptable.
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2.3.2 The medical locks shall be large enough to allow lock-in and lock-out of CO2 absorption material and necessary supplies for the divers. Guidance note: National rules and requirements may be more stringent and thereby take precedence (i.e. Norwegian Petroleum Directorate).
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2.3.3 Means enabling the doors to be opened from either side shall be provided. Guidance note: As the above requirement also applies to the internal doors in chamber complexes, it does follow that locking devises are not allowed on the pressurised side of these doors unless they can be operated from the other side. Clip locks are frequently used on these doors to prevent slamming due to the vessels movement in the sea. However, the clip setting should be such that they can be pushed/pulled open from either side without the use of excessive force.
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2.3.4 For: a) doors b) hatches c) mating arrangements d) pressurised locks and trunks e) pressurised containers f) accompanying equipment under pressure where opening or unintentional pressure drop may entail danger or cause injury, the closing mechanisms shall be physically secured by locking mechanisms (interlocks). This applies to units which do not seal by pressure and includes, but is not limited to: a) mating arrangements between bells and transfer compartments
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DNV GL AS b) mating arrangements between hyperbaric lifeboats and escape trunks where these are installed c) equipment locks d) medical locks e) soda lime (CO2 scrubber) containers for external regeneration of the chamber environments.
2.3.5 The closing mechanisms with accompanying locking mechanisms shall be arranged so that: a) opening cannot take place unless the pressures are equal on both sides or unless the pressures in the Section 2 units are at ambient level b) correct position of the closing mechanisms and the locking mechanisms shall be ensured before it is possible to apply pressure c) the pressures in the units, shall directly control the locking mechanisms, and d) the penetrators and piping for pressure sensing shall be arranged so that blockage is avoided.
2.3.6 Trunks between doors shall be equipped with pressure equalising valves. Penetrators for pressure equalising shall be arranged so that blockage is avoided. Chapter 3
2.3.7 Where mountings are secured by studs, these shall have full thread holding in the shell for a length of at least one diameter. Holes for studs shall not penetrate the shell.
2.3.8 Windows with a diameter above 500 mm and thickness less than 90 mm shall be protected against impact. Impact protection may be provided by: a) recessing the external surface of the window at least 50 mm below the surrounding structure b) one or more external bumpers extending across the window.
2.3.9 Damage control plugs may be provided to enable the divers to seal off windows to prevent damage or leakage developing. One plug for each size window in each compartment may be sufficient.
2.3.10 For pressure vessels where fatigue can be a possible mode of failure, attention shall be given to the possible adverse effects of the following design features: a) pad type reinforcement of openings b) set-on branches c) partial penetration welds of branches. Guidance note: Provided that the external peak loads does not exceed the strain that can be taken by the pressure vessel flanges, global fatigue analysis may be omitted by the following action: NDT is carried out to detect surface breaking defects on the external surface of the external welds of all the interconnecting trunks and locks in the system as per the survey planning document.
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3 Welded pressure vessels, materials and fabrication
3.1 Materials
3.1.1 Steel grades shall comply with the applied design code and standard.
3.1.2 Other material grades may be acceptable after special consideration. In such cases, additional testing may be required and qualification procedures shall be reconsidered.
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DNV GL AS 3.1.3 Materials for main pressure retaining parts are normally to be delivered with the manufacturer's works certificates (W), as a minimum. Guidance note: Product certificates, PC, may be required in the contract or the terms of delivery.
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3.1.4 Stainless steel cladding, stainless steel tubes, fittings etc. which are welded to pressure vessels of non-stainless steel shall be of a stabilised or low-carbon grade. Acceptable grades are given in the applicable standards or in DNVGL-RU-SHIP Pt.2 Ch.2 Sec.4 and DNVGL-RU-SHIP Pt.2 Ch.2 Sec.5.
3.2 Fabrication
3.2.1 Pressure vessels for diving systems shall be manufactured by works approved by a recognised body, Chapter 3 for the production of the type of pressure vessels being delivered.
3.2.2 Welding shall be carried out according to approved drawings. Qualification of welders, welding procedure specifications, welding procedures and testing shall be according to the applied design code or standard.
3.2.3 The following tests have to be carried out in addition to the tests specified in the applied design code or standard: a) all butt welds in diving bells and chambers shall be radiographed over their full length b) branches and reinforcement of openings, including all weld connections to the shell, shall be subjected to 100% magnetic particle testing.
3.2.4 When the applied code or standard requires heat treatment of dished ends after hot or cold forming, mechanical testing may be required after the final heat treatment. The details between intermediate heads and cylindrical shells of chambers may be done in accordance with requirements given in, a) EN 1708-1:2010 welding, basic weld joint details in steel Table 9: internal diaphragms and separators b) ASME Sec.VIII div.I Fig. UW-13.1. The outside diameter of the head skirt shall have a close fit to the cylinders. The butt weld and filled weld shall be designed to take shear based on 1.5 times the maximum differential pressure that can exist. The allowable stress value for the butt weld shall be 70% of the nominal design stress for the shell material and that of the fillet weld 50%. The area of the butt weld in shear shall be taken as the width at the root of the weld times the length of the weld. The area of the fillet weld shall be taken as the minimum leg dimension times the length of the weld.
3.2.5 The surface dimensions and finish of sealings and seals for hatches and windows are generally to comply with the tolerances specified by the manufacturers of the windows and the sealing systems.
3.2.6 Flat disc windows shall have a bearing gasket between the window and its seat. This gasket shall serve as a secondary seal. The gasket shall be bonded to the seat. The retainer ring shall provide adequate initial compression of the sealing arrangement to compensate for the displacement of the window due to the pressure. The minimum seating diameter in relation to window dimensions shall be specified. The included conical angle of the seating surface of conical flanges shall be within + 0.00 or -0.25 degrees of the nominal value.
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DNV GL AS The surface finish of seats of metallic materials for conical-, double bevelled disc and spherical shell windows shall have an average roughness less than R. = 1.5 μm.
3.2.7 Before installation of a window in its flange, complete cleanliness of the seating surfaces shall be ensured. The seating surface and any o-ring grooves shall be lubricated with an oxygen compatible lubricant. Mineral oil lubricants shall, under no circumstances, be used for this purpose. Section 2 3.3 Fabrication tolerances
3.3.1 Fabrication tolerances shall meet the requirements in the applied codes and standards.
3.3.2 Local tolerance requirements for ring frames are given in Figure 1, for vessels subject to external pressure.
Chapter 3
Figure 1 Maximum deviations for ring stiffeners.
4 Strength of welded pressure vessels
4.1 Structural analysis
4.1.1 Pressure vessels shall be documented by structural analysis for specified design conditions according to the applied codes and standards.
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DNV GL AS 4.1.2 For details not covered by the applied codes and standards, finite element analysis may be acceptable if properly planned, modelled and documented. Alternatively, by applying strain gauges, stress measurements may be carried out according to an approved programme and shall be properly documented. The tests shall be planned, and carried out during the first pressure test. Section 2 4.1.3 Fatigue evaluation and, if necessary, fatigue analysis shall be carried out for the number of full pressure cycles as defined by the designer [1.6.2]. The evaluation and analysis shall be carried out according to the applied design code and standard.
4.1.4 Design for non-destructive testing inspection of PVHOs Fatigue checks (NDT) in service are required when 20% of the design cycles have been experienced. The use of diver monitoring systems to record the elapsed cycles may be used for timing these inspections for the
PVHOs. Chapter 3 At the design stage the worst case actual stress relative to the design codes allowable stress for the defined cycle life shall be calculated. This will be used to assign the fatigue contribution of each actual cycle seen in service. The worst case chamber (normally the bell) will then dictate inspection intervals. Ancillary pressure vessels connected to the chamber system such as scrubber pots which experience the same cycles may be included in the same regime as long as the design standards are compatible. A list of pressure vessels included in this inspection plan tabulating actual stress versus the limit as per design code shall be submitted. A plan is also to be developed marking the locations and extent of NDT testing. Should it be preferable to carry out inspections based upon traditional inspection windows only the NDT plan is required to be submitted. NDT of the surface of the external weld of the large openings such as windows and locks to detect surface breaking defects shall be carried out. Insulation and fit out should allow access to the marked areas for NDT.
4.2 Vessels subjected to external pressure
4.2.1 Frames and panels supporting pressure-retaining parts shall be designed for a force of minimum 1.2 times the actual load.
4.2.2 Additional stresses shall be within the limits given in the applied design code or standard, for combined stresses.
4.3 Flanges for windows Flanges for windows with conical seating shall have dimensions preventing the flange deformations to exceed the following limits when window and pressure vessel is subjected to the design pressure : — radial: 0.002 times the smaller diameter of the acrylic plastic window, and — angular: 0.5°.
5 Gas cylinders
5.1 General
5.1.1 Gas cylinders shall be produced by manufacturers authorised for such production and certified by a competent inspection body when:
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DNV GL AS where: p = design pressure in bar. V = volume in m3. The certification level shall as a minimum be manufacturer's works certificates (W). Other levels of certification may be required by the terms of delivery. Smaller gas cylinders shall be certified if they provide an essential function in the system. Section 2 Guidance note: Cylinders on-line in a system providing breathing gas to the divers will be considered essential.
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5.1.2 The materials applied shall be certified as a minimum by the manufacturer's works certificates (W). Other material certificates may be required by the terms of delivery. Chapter 3
5.1.3 They shall be designed, constructed and tested according to one of the following standards, norms or directives: a) EN ISO 9809-1 gas cylinders, refillable seamless steel gas cylinders, design, construction and testing, part 1: quenched and tempered steel cylinders with tensile strength less than 1100 MPa. b) EN ISO 9809-2 gas cylinders, refillable seamless steel gas cylinders, design, construction and testing, part 2: quenched and tempered steel cylinders with tensile strength greater than or equal to 1100 MPa. c) EN ISO 11120 gas cylinders, refillable seamless steel tubes for compressed gas transport, of water capacity between 150 l and 3000 l, design construction and testing. Guidance note: For permanent installations within EU, the directives apply as regulations. (See EU directive 2010/35/EU.)
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5.1.4 Shell thickness shall meet the criteria given in the applied code or standard for test pressure. The working pressure for a given geographical area is given by reference to a standard such as EN 13096 Transportable gas cylinders - Conditions for filling gases into receptacles and EN 13099 transportable gas cylinders, conditions for filling gas mixtures into receptacles, single component gases.
5.1.5 Corrosion allowance shall be specified in the terms of delivery reflecting the intended use of the gas cylinder, but shall not be less than 1 mm.
Guidance note: Gas cylinders without any corrocion allowance may be accepted based on the limitation that no repair will be allowed in case of internal or external corrosion. The use of such cylinders require acceptance by the end user.
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5.2 Heat treatment Heat treatment shall follow the requirements given in the applied code or standard, and shall be documented.
5.3 Tolerances and surface conditions Tolerances and surface condition shall meet the criteria given in the applied code or standard, and shall be documented in the design documentation. If the applied code or standard does not specify requirements for tolerances and surface conditions, then it may be necessary to specify this in the terms of delivery.
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DNV GL AS 5.4 Production tests Production tests shall be carried out in accordance with the requirements given in the applied code or standard. Further production tests, and required attendance during testing, may be specified through the terms of delivery.
6 Acrylic plastic windows Section 2
6.1 General. The following requirements apply to windows made from cast stock of unlaminated polymethyl methacrylate plastics, in the following denoted acrylic plastic, with a design life of 10 years, suitable for: a) 10.000 load cycles b) sustained temperatures in the range specified by the end user but not less than specified by ASME
PVHO-1 Chapter 3 c) pressurisation or depressurisation rates not exceeding 10 bar/second d) use in environments that cannot cause chemical or physical deterioration of the acrylic plastic (i.e. resistant against saltwater and gases used in life support systems).
6.2 Materials Materials for acrylic plastic windows shall be manufactured and tested in accordance with ASME PVHO-1 safety standard for pressure vessels for human occupancy.
6.3 Manufacturers of cast material Manufacturers wishing to supply cast acrylic plastic for diving systems, shall be approved for such production. The material shall have an approved chemical composition and to be produced, heat treated and tested according to the ASME PVHO-1 safety standard for pressure vessels for human occupancy. Approval shall be granted on the basis of a thorough test of material from the current production and a report after inspecting the works, and verification of QA and QC against requirements given in ASME PVHO-1.
6.4 Certification of cast material
6.4.1 Each delivery of cast material shall be accompanied by a certificate issued by the manufacturer (PVHO-1 forms VP-3 and VP-4). The certificate shall (as a minimum) contain the following: a) name and address of manufacturer b) certificate number and date c) designation of product d) numbers and dimensions of the pieces covered by the certificate e) material test results and properties f) signature.
6.4.2 The following text shall be printed in the right uppermost corner of the certificate: this certificate will be accepted by (approval body) on the basis of completed approval tests and the (approval body’s) surveillance of production control and products. The manufacturer guarantees that the product meets the requirements of (approval body) and that inspection and tests have been carried out in accordance with (code or standard)
6.4.3 The cast material shall be marked with the manufacturer's name and with the number and date of the certificate.
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DNV GL AS 6.4.4 If a later edition of the ASME standard requires further documentation and markings, the ASME requirements shall be met.
6.5 Certification of windows
6.5.1 Each batch of acrylic plastic windows used in diving systems shall have a certificate issued by the Section 2 approval body, showing the test results and the annealing conditions according to the standard.
6.5.2 Each window shall have an identification marked on it for traceability. Identification of each window shall include: design pressure, maximum temperature, initials for P.V.H.O., window fabricator's identification mark, fabricators serial number and year of fabrication. For ease of viewing, the above information shall be located on the windows seating surface with an indelible marker. Acceptable marking methods are given in ASME PVHO-1. Stamping or marking that can cause crack propagation is not permitted. Chapter 3
6.6 Geometry and thickness
6.6.1 Windows shall be of the standard designs according to the ASME PVHO-1 safety standard for pressure vessels for human occupancy.
6.6.2 Windows for two-way pressurisation shall meet the requirements applicable to one-way windows in both directions. For double bevelled disc windows, not more than 50% of the thickness shall be utilised in determination of short term critical pressure.
6.6.3 O-ring grooves shall not be located in window bearing surfaces serving primarily as support or in the acrylic window itself.
6.7 Fabrication
6.7.1 The included conical angle of the seating surface of a window shall be within +0.25/-0,00 degrees of the nominal value.
6.7.2 The deviation of a spherical window from an ideal sphere shall be less than 0.5% of the specified nominal external radius of the spherical section.
6.7.3 Each window shall be annealed after all forming and polishing operations are completed. The annealing process shall be according to the annealing schedule in ASME PVHO-1.
6.7.4 During the manufacturing process each window shall be equipped with identification and a manufacture process rider for recording of all pertinent data.
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DNV GL AS SECTION 3 LIFE SUPPORT SYSTEMS
1 General
1.1 Objectives Section 3 1.1.1 This section aims to give general guidance on: a) conceptual and detailed design of life support systems b) manufacturing of life support systems c) quality control during manufacturing and fabrication of components and subsystems for life support systems.
1.1.2 The section presents key-issue requirements for gas distribution capacities, environmental conditioning and oxygen systems. Documentation requirements are identified. Chapter 3
1.1.3 Design and acceptance criteria include capacities for gas storage, choice of valves and fittings for certain applications, environmental control parameters, breathing resistance for CCBS and diving crew facilities.
1.1.4 Requirements for the design of oxygen systems are aimed at reducing the hazards posed by flash fires.
1.1.5 This section contains requirements to ensure safe arrangements in pressurised systems and control stations.
1.1.6 Further requirements for pipes, hoses, valves and fittings are given in Sec.7.
1.1.7 Requirements for shut off valves, pressure relief and drainage are aimed at ensuring the safeguard of personnel and plant, as are the requirements for alarm systems.
1.2 Application and scope
1.2.1 For quantitative design parameters and functional requirements, see relevant standards and guidelines, including DNVGL-RU-SHIP.
1.2.2 Requirements for testing are given in Sec.1 [9].
1.2.3 Requirements for installation are only rudimentary.
1.2.4 This section has an impact on all other sections in this chapter.
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DNV GL AS 1.3 Documentation Life support systems shall be documented as follows: a) Plans showing schematic arrangement of all piping systems. b) Documents stating: — material specifications Section 3 — maximum working pressure — dimensions and thickness — contained fluids — type of valves and fittings — specifications of flexible hoses. c) Plans (diagrams) showing arrangement and giving specifications of the gas storage and supply (gas banks, compressors, boosters etc.). Chapter 3 d) Plans showing the arrangement and giving specifications on environmental control systems and equipment (heating, CO2-absorption, circulation), diving crew facilities, sanitary and drainage systems. e) Component lists, with specifications on make and type and documentation on any tests carried out on all equipment used in the life support system. Plans showing cross-section and giving particulars on materials and dimensions of umbilical. f) Calculations showing the heat and cooling consumption for the system under given environmental temperatures. g) Description of proposed cleaning procedure for breathing gas system.
2 Gas storage
2.1 Capacity
2.1.1 There shall be a permanently installed gas storage plant or suitable space for portable gas containers. The size of the containers or space shall be sufficient to provide the divers with adequate quantities of gases for operation at maximum operating depth for both normal and emergency modes.
2.1.2 The minimum gas storage capacity of fixed installed containers or space for portable containers intended for emergency operations shall be sufficient to: a) Pressurise the inner area once and the bell(s) and transfer compartments once more to maximum depth, dmax, with suitable breathing gas, and b) For diving systems with an operational time exceeding 12 hours it shall provide suitable gas to pressurise the largest compartment once, to dmax. c) Maintain a proper oxygen partial pressure in the inner area and supply for masks for at least: i) 24 hours, diving systems with an operational time not exceeding 12 hours or ii) 48 hours, diving systems with an operational time exceeding 12 hours. d) For pure oxygen, the minimum volume may be taken as: i) 2 Nm3 for each diver for a diving system with an operational time not exceeding 12 hours or ii) 4 Nm3 for each diver for diving systems with an operational time exceeding 12 hours. 1 Nm3 is given as 1 cubic metre of the gas at 0°C and 1.013 bar standard condition.
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DNV GL AS 2.1.3 For emergency use of masks there shall be sufficient facilities to supply adequate quantities of gases. The facilities shall be capable of providing a relevant delivery rate both at maximum depth and during decompression. The containers required by 102 may be used also for these emergency purposes. Adequate quantities may be taken as a minimum of: a) 2 m3 at the pressure of the inner area with an oxygen partial pressure between 0.18 and 1.25 bar for
each diver, and in addition Section 3 b) 15 m3 at the pressure of the inner area with an oxygen partial pressure between 1.5 and 2.5 bar at depths greater than 18 m, to each of the maximum number of divers in one of the living compartments for diving systems with an operational time exceeding 12 hours.
2.1.4 The storage capacity for emergency gas shall be provided in separate containers, and shall not be included in the containers for current gas supply.
2.1.5 The bell shall have a self-contained emergency gas storage with minimum capacity to supply the Chapter 3 following: a) 1 Nm3 oxygen for each diver b) suitable breathing gas mixtures. The capacity shall be the greater of the two:
— that which is sufficient to empty a bell filled with 40% water at dmax — that which is sufficient to supply each of the bell divers with suitable breathing gas for 15 minutes. The gas volume respirated by one diver in 15 minutes may be taken equivalent to 0.8 m3 at ambient pressure dmax. 3 The minimum gas storage volume, Vg (m ), of deep mix on the bell considering a minimum overpressure in the containers, and sufficient time for the operations to avoid significant temperature differences, may be estimated as follows:
where V = volume (m3) at ambient pressure dmax of the supply to the divers or 0.4 times the internal volume of the bell. pg = pressure (bar) in gas storage containers. pb = pressure (bar) in the bell corresponding to the depth.
2.2 Shut-off, pressure relief and drainage.
2.2.1 Pressure vessels shall be fitted with over pressure relief devices and shut off valves except as provided for in [5.2] and [5.3].
2.2.2 Pressure vessels without individual shut-off valves and with: pV < 50, installed in groups with a total pV < 100, can have a common overpressure relief device and shut-off valve. p = design pressure in bar V = volume in m3 (standard conditions)
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DNV GL AS 2.2.3 For gas storage of breathing gases and oxygen, the pressure relief device shall be a safety valve. Safety valves shall be set to open at a pressure approx. 3% above the developed pressure at 55°C, based on filling the cylinders at 15°C to maximum filling pressure. The total relieving capacity shall be sufficient to maintain the system pressure at not more than 110% of design pressure. Developed pressure under above-mentioned conditions may be taken as given in reference to a standard such as Section 3 a) EN 13096 transportable gas cylinders, conditions for filling gases into receptacles, single component gases. b) EN 13099 transportable gas cylinders, conditions for filling gas mixtures into receptacles.
2.2.4 Containers where water can accumulate shall be provided with drainage devices (e.g. volume tanks and filters)
3 Gas distribution Chapter 3
3.1 General
3.1.1 The gas distribution system consists of all components and piping necessary for distribution of gas for normal and emergency operations. Piping for gas and electrical cables shall be separated.
3.1.2 The distribution system to each compartment shall facilitate: a) two independent alternatives for pressurisation with a minimum pressurisation rate of 2 bar/minute to 2 bar and at 1 bar/minute thereafter b) depressurisation c) decompression rate of minimum 1 bar/minute at pressures exceeding 2 bar for saturation diving systems d) maintenance of a suitable breathing atmosphere in the inner area (when adding pure oxygen to the compartments, a separate piping system shall be provided) e) supply of suitable breathing gas for masks (for saturation diving systems this supply shall be independent for each living compartment) f) exhaust from masks intended for oxygen if a closed circuit breathing gas system is not used.
3.1.3 There shall be two independent supplies of gas to the bell umbilical.
3.1.4 Filters and automatic pressure reducers shall be so arranged that they can be isolated without interrupting vital gas supplies.
3.1.5 Valves in piping systems to masks, bells and divers in water shall be so arranged that: a) leaking valves cannot cause unintentional gas mixtures b) oxygen cannot unintentionally be supplied to other piping systems than that intended for oxygen.
3.1.6 The discharge from overpressure relief devices and exhaust shall be led to a location where hazard is not created.
3.2 Bell
3.2.1 The bell and the lock-out diver(s) shall have a normal supply and an independent self-contained emergency supply from the bell.
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DNV GL AS 3.2.2 The breathing gas system supplying the personal umbilical to the stand-by diver in the bell shall be arranged for an alternative supply, independent of the lock-out diver(s)'s normal supply. The bells onboard gas supply may be accepted for this purpose.
3.2.3 The bell shall be equipped with two alternatives for exhausts. One shall be arranged so that a diver who intends to aid his entering by a partial flooding of the bell can operate it from the lower part inside the bell. The exhaust systems shall not permit a flooding above electrical equipment when the bell is in an Section 3 upright position.
3.2.4 The exhaust system shall be designed to enable removal of the water in case of a tilted bell with closed hatch and trapped water inside. Guidance note: The degree of tilt envisaged may vary from one bell design to another and will therefore need to be considered in each case. Side
mated bells will most likely tilt more than bottom mated bells. As this requirement is normally simple to fulfil by means of a flexible Chapter 3 hose, it is thought that a 60° list should be considered minimum.
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3.2.5 The exhaust system not intended for partial flooding of the bell shall be fitted with a spring-loaded valve that closes when the valve handle is released.
3.2.6 The bell shall be equipped with masks corresponding to the number of divers plus one. The masks shall be arranged for supply from normal and emergency supply alternatively. Diving masks and diving helmets with gas supply are accepted as masks.
3.2.7 The emergency oxygen supply system shall be designed to enable the maintaining of a proper partial pressure of oxygen inside the bell by a dosage system.
3.2.8 Automatic pressure reducers for breathing apparatuses shall be fitted.
3.2.9 Bell shall be fitted with an emergency manifold at a suitable point close to the main lifting attachment which shall include connections for the following services: a) 3/4 inch NPT (female) - for hot water b) 1/2 inch NPT (female) - for breathing mixture. The manifold shall be clearly marked and suitably protected.
3.3 Chambers
3.3.1 Each living compartment shall be equipped with breathing masks corresponding to the maximum number of divers for which the chamber is rated plus one. The masks shall be arranged for breathing from each bunk. For diving systems with an operational time exceeding 12 hours, transfer compartments to the bell(s) shall be equipped with a number of masks at least corresponding to the maximum number of divers in the bell plus one. Other compartments shall have at least 2 masks.
3.3.2 The masks shall be permanently connected or easily connectable to piping systems for supply of the gases according to [2.1.3].
3.3.3 The exhaust sides of the masks intended for oxygen shall be connected to external dump, or to be of a closed circuit type.
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DNV GL AS 3.3.4 The mask systems shall be secured against inadmissible pressure drop on the exhaust side.
3.3.5 The gas supply system shall be arranged to ensure homogenous gas content in the inner area.
3.4 Stand-by diver at surface A piping system for supply of breathing gas to a possible stand-by diver at surface shall be arranged Section 3 separated from the divers' supply.
4 Oxygen systems
4.1 General
4.1.1 Oxygen shall be stored and distributed in containers and piping systems exclusively intended for Chapter 3 oxygen systems.
4.1.2 Containers for oxygen shall be stored in open air or in rooms exclusively intended for oxygen. The rooms shall be separated from adjacent spaces and ventilated according to Sec.5 and shall be fitted with an audio-visible oxygen alarm, at a manned control station.
4.1.3 The pressure in the oxygen systems shall be reduced from storage pressure to the minimum pressure necessary for proper operation. The pressure reduction shall be arranged as close as possible to the storage containers. Guidance note:
A maximum pressure of 40 bar will normally be accepted when dmax is less than 350 m.
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4.1.4 Oxygen shall not be stored or ducted in any form close to combustible substances or hydraulic equipment.
4.1.5 Oxygen dumped from the diving system shall be ducted to a safe dumping place.
5 Piping systems
5.1 General
5.1.1 Low-pressure systems supplied from high-pressure system shall be provided with pressure relief valves. The total relieving capacity shall be sufficient to maintain the system pressure at not more than 110% of design pressure. The relief device shall be located adjoining, or as close as possible, to the reducing valve.
5.1.2 All systems shall be provided with means of manually relieving the pressure.
5.1.3 Filters shall be provided on the high-pressure side of gas systems.
5.1.4 Pipe ends in chamber and bell shall be arranged so that injuries due to suction are avoided.
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DNV GL AS 5.1.5 All pipe penetrations in the chambers and bells shall be fitted with external and internal shut-off valves mounted directly on the shell plating. Valves may be mounted close to chamber shells, provided that the piping between the chamber and valve is well protected and has a minimum thickness according to the rules.
5.1.6 Threaded pipe penetrations are only acceptable for external diameters equal to or less than M30 (1" NPT threads/1" BSP treads). Section 3
5.2 Bell Bells shall be fitted with an overpressure alarm.
5.3 Chambers
5.3.1 In addition to the requirements in [5.1.5] all penetrations for lines designed for gas distribution (e.g. Chapter 3 supply, exhaust ) shall be fitted with non-return valves or flow fuses as appropriate for the direction of gas flow. Lines specifically designed for non distribution purposes (e.g. analysis) shall be kept to the minimum diameter possible and limited to a maximum of 5 mm.
5.3.2 The piping between externally mounted non-return valve or flow-fuse and the external shut-off valve shall be well protected and have minimum thickness according to Sec.7.
5.3.3 The compartments shall be fitted with a safety valve or a visual and audible overpressure alarm alerting the operators at the control station. Penetrations for safety valves shall be provided with shut-off valves on both sides of the shell plating. These shut off valves shall be sealed in the open position. Any safety valves shall be set to open at a pressure of approx. 3% above the design pressure.
5.3.4 Valves in chambers designed for holding water (i.e. hyperbaric training centres) shall be considered in each case.
6 Environmental conditioning in bell and chambers
6.1 Heating of bell
6.1.1 Bells shall have a normal heating system with controls and capacity sufficient to maintain a comfortable temperature for the divers in the bell and in water. The heating system shall be fitted with a temperature indicator.
6.1.2 For deep diving, provision for heating the divers' gas shall be provided.
6.1.3 For diving systems with an operational time exceeding 12 hours, the heating supply systems shall be provided with full redundancy. This includes full redundancy in the event of a possible loss of main power (Sec.4 [2.4.1]).
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DNV GL AS 6.1.4 Bells shall have emergency means of preventing excessive heat loss by the divers for a period of 24 hours at dmax., and shall be independent of the main umbilical. When using thermal insulation to achieve this, the performance of the insulation on the actual bell shall be calculated. Special attention should be given to modelling flanges/trunks and other uninsulated surfaces. Acceptance will be based upon achieving a better cooling profile than field tests (e.g. Polar Bear III). Guidance note: Section 3 This can be achieved by heating the bell environment, the divers directly by heated suits, or by passive thermal insulation as well as heating the divers' breathing gas by active or regenerative methods.
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6.2 Heating and cooling of chambers
6.2.1 Systems for heating and cooling of the living compartments shall be arranged. Chapter 3
6.2.2 For saturation diving systems, all compartments shall have an arrangement for heating. The living compartments shall be provided with a system for heating and cooling, enabling temperature regulation within +/- 1°C from set point under stable pressure conditions. Heating and cooling systems shall be provided with full redundancy.
6.2.3 Heating coils on the outside of the chambers shall have a minimum of two independent temperature controls of the power circuit.
6.3 Humidity reduction in chambers A system to reduce the humidity in the living compartments shall be provided. For saturation diving systems, a relative humidity of 50% shall be maintainable under steady conditions. Guidance note: For certain geographical regions this requirement is hard to fulfil unless additional coolers supplement the regular environmental control systems or some other compensation is provided for. This needs to be considered in each case.
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6.4 Noise reduction
6.4.1 Silencers shall be fitted and the system shall be so designed that the divers cannot be exposed to harmful noise levels. Guidance note: IMO resolution A.468 (XII) code on noise levels onboard ships.
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6.4.2 Silencers shall be fitted with shields which provide protection against possible fragmentation but which do not affect the gas flow.
6.5 Gas circulation systems for chambers
6.5.1 Internal circulation systems for gas in the chambers shall be such that a homogeneous gas content is ensured.
6.5.2 Pressurising and exhaust systems shall be arranged to ensure an even mixing of gas.
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DNV GL AS 6.5.3 The circulation system shall have sufficient capacity to avoid stratification of gas layers in the chambers and maintain a homogenous gas mix at the set operational parameters.
6.5.4 Materials shall be considered for toxic or noxious properties as specified in Sec.1 [9.3.5].
6.6 Removal of carbon dioxide Section 3
6.6.1 Carbon dioxide removal systems or atmospheric renewal systems shall be arranged for the bell and each living compartment. For saturation diving systems, all compartments shall be arranged with redundancy in carbon dioxide removal systems.
6.6.2 Carbon dioxide removal systems or atmospheric renewal systems for normal operation shall have the capacity to maintain the partial pressure of carbon dioxide below 0.005 bar continuously based on a production rate of 0.05 Nm3 per hour per diver. Chapter 3
6.6.3 The bell shall have a self-contained, self-powered emergency absorption system with a capacity to keep the partial pressure of carbon dioxide below 0.02 bar for 24 hours.
6.7 Regeneration of pure helium
6.7.1 Systems for regeneration of pure helium for further use in the system shall ensure only a limited content of contaminants. The system shall be capable of maintaining the nitrogen content below a partial pressure of I bar at the maximum operating depth of the diving system. For welding operations the collective argon and nitrogen content shall be considered. The system for regeneration shall move gas to clean storage directly after treatment for bacteria. The method of controlling bacterial content shall be approved. Guidance note: Normally utilising compressor temperature, membranes or antibacterial metals is sufficient.
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6.7.2 Water traps for gas reclaim shall be designed for simplicity of cleaning, disinfecting and drying.
7 Gas control systems
7.1 Control stands
7.1.1 Requirements for instrumentation are given in Sec.4.
7.1.2 The control stands shall have means for: a) choice between gas storage containers b) pressurising and pressure regulation of each compartment independently c) decompression of each compartment independently d) equalising the pressure between compartments e) controlling oxygen flow to compartments independently f) controlling oxygen and mix gas supply to masks in each individual compartment g) controlling gas supply to bell.
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DNV GL AS 7.2 Helium and oxygen mixing systems for direct supply for breathing
7.2.1 Systems for mixing of helium and oxygen for subsequent direct supply for breathing shall be automatic, to have an automatic control system, an automatic alarm system and an automatic safety system. Section 3 7.2.2 As an alternative to [7.2.1], the inclusion of a large volume tank is considered to provide an equivalent level of safety as that prescribed by the requirements for automation and independence in [7.2.4]. The remaining requirements shall be met. The volume tank shall be such that the prescribed tolerances for partial pressures downstream are not deviated from within the first hour after the analysers have alerted the operator that the upstream mixture is out of the tolerated range. The alarm shall be audio-visual at a manned control station. Guidance note:
Prescribed tolerances is normally understood to be gas having an oxygen partial pressure in the range 0.21 bar to 1.7 bar as Chapter 3 required by NPD whereas the dive control alarm will be a tolerance of +/-0.03 bar about the desired set point.
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7.2.3 The control system shall keep the mixture at a pre-set value within the prescribed tolerances. Maximum tolerances: +/- 0.03 bar, partial pressure O2.
7.2.4 The safety system shall be independent of the control system and shall incorporate changing of the supply automatically to a premixed suitable breathing gas if tolerances are exceeded. The safety system shall ensure a constant delivery of suitable breathing gas to the diver during all operating conditions, taking into account the characteristics of components in the systems such as response time for gas analysers etc.
8 Closed circuit breathing systems (CCBS)
8.1 General
8.1.1 Installation of CCBS is not required as a condition for the standard. If such system is installed, it is, however, to comply with the following requirements. See: guidelines for minimum performance requirements and standard unmanned test procedures for underwater breathing apparatus by: U.K. Department of Energy and Norwegian Petroleum Directorate. Tests may be carried out in accordance with the guidelines.
8.1.2 System particulars a) The maximum work of breathing (w) shall not exceed 3.0 Joules/litre measured at a standard breathing rate, respiratory minute volume (RMV) of 62.5 litres/minute. Guidance note: Work of breathing should be as low as possible. A preferred level would be below 1.75 Joules/litre at an RMV of 62.5 litres/ minute.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e--- b) The system shall be able to work satisfactorily over a range of RMV's up to 75 litres/minute. For test purposes the system should function to 90 litres/minute. c) The variation in respiratory pressure (ΔP) should be limited to 1.5 kPa and shall not exceed 2.5 kPa relative to the reference pressure (PR). Reference pressure(PR) is the equilibrium pressure measured at the level of the divers mouth when there is no gas flow. Respiratory pressure (ΔP) is the differential pressure measured at the divers mouth, during inhalation and exhalation, measured relative to the system reference pressure.
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DNV GL AS d) The hydrostatic imbalance (PR- PLC) varies with the orientation of the diver and the position of the demand valve (or equivalent device) and has an effect on the work of breathing. The hydrostatic imbalance shall not be outside the range of -3.5 kPa to + 2.0 kPa. Guidance note: Ideally, the hydrostatic pressure imbalance should be between -2.0 kPa and + 1.0 kPa. PR is the reference pressure at the divers mouth and PCL is the lung centroid pressure, which is defined as the pressure which restores the lungs to their normal resting volume. PCL is measured at a position 19 cm inferior and 7 cm posterior to the suprasternal notch. Section 3 ---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e--- e) The system shall be designed so as to minimise the build up of carbon dioxide. Dead space volume should be as low as possible. The partial pressure of carbon dioxide (ppCO2) shall be limited to 1 kPa. Guidance note: The volume of oronasal mask or equivalent device should be less than 200 ml.
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8.1.4 If the equipment fails, the lung over or under pressure should be as low as possible, but shall not exceed 6.0 kPa relative to the lung centroid pressure.
8.1.5 CCBS shall have an emergency mode by free exhalation, i.e. without the use of the exhaust line.
8.1.6 CCBS shall incorporate temperature regulation system for inhaled gases. Guidance note: 1 kPa = 1000 Pascal 1 Pascal = 1 N/m2 = 10-5 bar
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9 Diving crew facilities
9.1 General
9.1.1 One bunk shall be provided for each diver in the living compartment permitting the diver to rest comfortably. For DSV-SAT systems the bunks shall measure at least 200 x 70 centimetres .
9.1.2 Proper lighting shall be provided in all compartments and bell.
9.1.3 The bell shall be fitted with emergency lighting.
9.1.4 If flush type toilets are installed, the systems shall be designed so that drainage cannot take place during sitting use. (See also the requirements for safety locks given in Sec.2 [2.3.4] and Sec.2 [2.3.5]).
9.1.5 Sanitary systems connected to external systems shall be designed to avoid an unintentional pressure rise in the external system in case of malfunction or rupture of the diving systems' sanitary systems.
9.1.6 One toilet and one shower with hot and cold water are required per pressure level. The toilet may be flush type or disposable bag type. In connection with the toilet there shall be a scavenging or cleaning facility
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DNV GL AS to get rid of bacteria and odour. The shower and the toilet shall be located in a room separated from the living compartment.
9.1.7 The living compartment shall provide space for a table.
9.1.8 One toilet and one shower with hot and cold water are required per pressure level. The toilet may be
flush type or disposable bag type. In connection with the toilet there shall be a scavenging or cleaning facility Section 3 to get rid of bacteria and odour. The shower and toilet shall be located in a room separated from the living compartment. Chapter 3
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DNV GL AS SECTION 4 ELECTRICAL, INSTRUMENTATION AND COMMUNICATION SYSTEMS
1 General
1.1 Objective Section 4
1.1.1 The purpose of this section is to specify additional requirements for electrical systems and equipment serving diving systems. Emphasis is placed on the special needs associated with the design and manufacture of diving systems, whereas general requirements for electrical systems and components are given in DNVGL- OS-D201 electrical installations and DNVGL-OS-D202 instrumentation and telecommunication systems.
1.1.2 The key issues are identified in: Chapter 3 a) the service definitions by defining essential, emergency and non-important services b) the power supply systems and capacity by specifications for emergency supply c) cables and penetrators d) documentation requirements.
1.1.3 Specific references to other relevant standards are given.
1.1.4 Design criteria for electrical penetrators are outlined. Philosophy on earthing is specified, in that hull return is not allowed.
1.2 Application and scope
1.2.1 Material specification is included for insulation of cables in the inner area.
1.2.2 Some testing is included in this section. For further requirements for testing, see Sec.1 [9].
1.2.3 Recognised production standards include those provided by the International Electro technical Commission (IEC).
1.2.4 This section bears impact on Sec.3, Sec.6, Sec.7 and Sec.8.
1.3 Documentation For electrical systems the following shall be documented: — Single line distribution system diagrams for the whole installation. The diagrams shall give information on full load, cable types and cross sections, and make, type and rating of fuse- and switchgear for all distribution circuits. — Calculations on load balance, including emergency consumption and battery capacities. — Complete multi-wire diagrams, preferably key diagrams, of control and alarm circuits for all motors or other consumers. — Plans showing arrangements of batteries with information about their make, type and capacity. — Plans showing arrangement and single line diagrams of the communication system. — Complete list of components and documentation on any tests carried out on all electrical equipment to be permanently installed within the chamber and the bell.
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DNV GL AS 1.4 Codes and standards The following codes and standards are applicable: a) DNV GL offshore standard DNVGL-OS-D201electrical installations b) DNV GL offshore standard DNVGL-OS-D202automation, safety and telecommunication systems c) A.O.D.C.'s code of practice for the safe use of electricity underwater d) relevant IEC equipment construction and design standards. Section 4
1.5 Service definitions a) Essential services are herein defined as those services that need to be in continuous operation for maintaining the diving system's functionality with regard to sustaining the safety, health and environment of the divers in a hyperbaric environment. This includes services required by the crew monitoring the divers.
Essential services shall be maintained for the period required by safely terminating the diving operation, Chapter 3 including time for decompression of the divers. For services supporting divers in the water, all services are essential. 20 minutes is considered to be the minimum time required ensuring that the divers are safely recovered in the bell or basket, or to the surface. For services supporting divers in a bell, all services are essential. 24 hours is considered to be the minimum time required ensuring that the divers are safely recovered into the decompression chambers or to the surface. For services supporting divers in the decompression chambers, all required services are essential. The normal decompression schedule is considered to be the minimum time required ensuring that the divers are safely brought to the surface. b) Emergency services are herein defined as those services that are essential for safety in an emergency condition. Examples of equipment and systems for emergency services include: i) condition monitoring of emergency batteries ii) emergency lighting iii) emergency communication iv) emergency life support systems v) emergency heating systems vi) emergency handling of the bell(s)/basket(s)/diver(s) (if electrical) vii) alarm systems for the above emergency services. For services supporting divers in the water, all the above services may be considered emergency services and 20 minutes is considered to be the minimum time required to ensure that the divers are safely recovered in the bell or basket or to the surface. For services supporting divers in a bell, all the above services may be considered emergency services and 24 hours is considered to be the minimum time required to ensure that the divers are safely recovered in the decompression chambers or to the surface. For services supporting divers in the decompression chambers, with the exception of handling systems, all the above services may be considered emergency services and the capacities given in [2.4.2] apply. Services to the hyperbaric evacuation system are considered separately in accordance with the IMO guidelines given in Sec.8. c) Non-important services are those which are not essential according to the above.
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DNV GL AS 2 System design
2.1 System voltages and distribution systems types
2.1.1 Types of distribution systems Electrical systems with hull return shall not be applied. Electrical distribution systems shall have insulated Section 4 neutral (IT).
2.1.2 System voltages For installations within the inner area (see definitions under Ch.1 Sec.1 [2.4]), the following maximum system voltages are permitted: a) The chamber:
i) For power and heating equipment: max. 250 V A.C. if protected against accidental touching or Chapter 3 insulation failures and fitted with a trip device as outlined in [2.3.7]. ii) For lighting, socket outlets, portable appliances and other consumers supplied by flexible cables and for communication and instrumentation equipment: max. 30 V D.C. These systems shall be supplied by isolating transformers. b) The bell: i) For all electrical equipment, voltages will be accepted up to max 30 V D.C., and shall be supplied by isolating transformers. ii) Higher voltages than specified above may be acceptable upon special consideration, provided additional precautions are taken in order to obtain an equivalent safety standard, e.g.: by use of earth fault circuit breakers. (See guidance note to [2.3.7].) Electrical circuits and equipment used in water shall be considered in each separate case and in accordance with IMCA code of practice for the safe use of electricity underwater (see [3.2.2]). Provisions shall be made to reduce the possible fault currents, to which a diver can be exposed, to a harmless level.
2.2 Power supply systems
2.2.1 General The electrical systems and installations supplying essential services related to the divers and or the diving operation (as defined in [1.5] a)), shall be supplied from a main and an emergency or transitional source of power as required by [2.3.2], DNVGL-OS-D201 and by DNVGL-OS-D202.
2.2.2 Emergency supply a) The diving system shall have a source of emergency power and an emergency power supply system independent of the main source of power and the main power supply system, as required by DNVGL-OS- D201 Ch.2 Sec.2 [1.1.1]. b) The emergency source of power shall be a self-contained, independent source of power. It shall immediately supply at least those services specified as emergency consumers in [1.5] b). It shall be either: i) a generator, driven by a suitable prime mover ii) an accumulator battery iii) the ship's emergency switchboard iv) a combination of the above. Where this source of power is a generator, it shall be started automatically upon failure of the electrical supply from the main source and shall be automatically connected within 45 sec., thereby providing emergency services.
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DNV GL AS Where this source of power is an accumulator battery, it shall be automatically connected to an emergency power supply system in the event of failure of the main source of electrical power. It shall be capable of carrying the maximum emergency load for a time specified under A501b without excessive voltage drop, carrying the emergency electrical load without recharging while maintaining the voltage of the battery throughout the discharge period within 12% above or below its nominal voltage. If emergency consumers must be available in the switch over period from main to emergency power, either for operational reasons or to avoid malfunction of the service, a transitional power source (battery back up) for these consumers shall be provided. The capacity of this transitional power shall be minimum 30 minutes. Section 4 (See SOLAS reg. II-1/43 part D para.4.)
2.3 Distribution systems
2.3.1 General, arrangement The distribution system shall be such that, the failure of any single circuit cannot influence or set other
services out of function for longer periods. Chapter 3
2.3.2 If the main power to the diving system is supplied via a distribution board, this board shall have two separate supply circuits from different sections of the main switchboard.
2.3.3 Control gear in the inner area shall normally not be fitted. However, special arrangement may be acceptable after consideration in each case, based on special precautions (e.g. the equipment may be pressurised with pure helium (purging) or there may be other explosion protection concepts).
2.3.4 Devices for easy disconnection of all electrical installations in the decompression chambers in an emergency situation shall be fitted. These devices shall be located on the control stand. It shall be possible to disconnect each chamber separately.
2.3.5 Fuses or circuit breakers shall not be installed within the chamber and the bell, except for emergency battery power-supply circuits. Guidance note: Fuse-gear may be installed outside the bell or chamber. Installation inside may be arranged as mentioned above in [2.3.3], povided the fuse-gear isn't operable by divers
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2.3.6 Insulation monitoring a) Each insulated supply system, including the secondary side of step-down or isolating transformers (or converters) shall be provided with an automatic insulation monitoring device, actuating switch-off and alarm by insulation faults. Alarm only may be used if a sudden switch-off of the equipment may cause danger for the divers. This insulation monitoring shall be continuous. b) The indicator shall be located at the control stand, except that indication in the bell may be accepted for equipment in the bell. Guidance note: Protection against insulation failures may be achieved by double insulated apparatus or earth fault circuit breakers.
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2.3.7 Electric motors placed in the inner area shall be provided with overload alarms or be inherently safe. The alarms may be initiated by over current, or by temperature detector in the motor itself. For motors in the bell, alarms in the bell may be accepted. The normal over current protections (short circuit protection) on the motors shall also be in place.
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DNV GL AS Guidance note: The requirement provides safety against overheating, with the possible development of toxic gasses, and or danger of flash fire in oxygen enriched environments. In special cases there may be other risks involved in overheating of the motors. However, if the motor is considered inherently safe, the requirement for the overload alarms may be revoked. This is considered preferable in cases where the number of alarms should be kept at a minimum so as to avoid stressful operating conditions and or confusion.
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2.4.1 Capacity of main source of power All services for normal operations are according to [1.5]a. defined as essential services, and shall be included in the services to be supplied by the main source of power as described in DNVGL-OS-D201 Ch.2 Sec.2 [2].
2.4.2 Capacity of emergency source of power
All services for emergency operations are according to A501b defined as emergency services, and shall be Chapter 3 included in the services to be supplied by the emergency source of power as described in DNVGL-OS-D201 Ch.2 Sec.2 [3]. Also: a) Power supplies required for the operation of life support systems and other essential services shall be sufficient for the life-support duration in order to cater for safe termination of the diving operation. b) Each compression chamber shall be provided with a main and emergency source of lighting sufficient for the life-support time and of sufficient luminosity to allow the occupants to read gauges and operate essential systems within the chamber. c) The emergency source of power and the emergency power distribution shall be capable of handling peak loads.
2.5 Environmental requirements
2.5.1 General. All electrical equipment and installations, including power supply arrangements, shall be constructed and installed to operate satisfactorily under all environmental conditions for which the diving system is designed. See DNVGL-OS-D201 Ch.2 Sec.3 [2], DNVGL-OS-D201 Ch.2 Sec.3 [3] and DNVGL-OS-D201 Ch.2 Sec.3 [4].
2.5.2 Electrical equipment within the compression chamber shall be designed for hyperbaric use, oxygen- enriched atmospheres, high humidity levels and marine application. See: a) DNVGL-OS-D202 instrumentation and telecommunication systems b) NFPA53M (National Fire Protection Agency) manual on fire hazards in oxygen-enriched atmospheres 1990 c) A.O.D.C. 043 code of practice for the safe use of electricity underwater d) A.O.D.C. 062 use of battery operated equipment in hyperbaric conditions.
2.5.3 All materials of submerged systems shall be such that their electrical and mechanical properties are not influenced by water absorption. Guidance note: See A.O.D.C.'s code of practice for the safe use of electricity underwater, DNVGL-OS-D201 and DNVGL-OS-D202.
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DNV GL AS 2.6 Inspection and testing requirements.
2.6.1 All switchboards shall be designed, constructed and certified in accordance with the requirements given in DNVGL-OS-D201 Ch.2 Sec.4.
2.6.2 Testing shall be carried out in accordance with the requirements given in DNVGL-OS-D201 Ch.2 Sec.10 Section 4 [4].
3 Equipment selection and installation
3.1 General
3.1.1 Arrangements Chapter 3 a) All electrical equipment and installation shall be designed and arranged in order to minimise the risk of fire, explosion, electrical shock, emission of toxic gases to personnel, and galvanic action of the surface compression chamber or diving bell. b) The electric power supply arrangement shall be designed to minimise the risk of electrical capacity depletion as a result of a fault, fire or explosion, electric shock, the emission of toxic gases and galvanic action.
3.2 Enclosures
3.2.1 Pressure resistant enclosures in the inner area or on the bell shall be designed for 1.3 times the design pressure of the diving system. Tests to be carried out with gas or water as applicable.
3.2.2 In the water, all metal enclosures shall be earthed by means of a copper earth conductor incorporated in the supply cable, with cross-section at least of the same size as the supply conductors and not less than 1 mm2. For cables having metal wire braid or armour this may alternatively be used as earth conductor, provided that the braiding cross section is sufficient.
3.3 Earthing All pressure vessels for human occupancy (P.V.H.O. chambers and bells) shall be provided with earthing connection devices for external main protective earth bonding.
3.4 Batteries
3.4.1 Batteries shall not be installed within the inner areas (chamber or bell).
3.4.2 Battery housings shall be provided with adequate protection in accordance with DNVGL-OS-D201 Ch.2 Sec.2 [9.4], so that an accumulation of generated flammable gases is avoided.
3.5 Cables and penetrators
3.5.1 Cables a) Cables for use in the outer area (see definition under Sec.1 [4]) shall comply with DNVGL-OS-D201 Ch.2 Sec.9 [2], DNVGL-OS-D201 Ch.2 Sec.9 [2] and DNVGL-OS-D201 Ch.2 Sec.10 [3]. All cables shall have an earthed braiding or screen around the conductors and be equipped with an insulating outer sheet.
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DNV GL AS b) Cables for use in the inner area (see definition under Sec.1d)) shall comply with the requirements given in [3.5.1]a, with exception to the materials used. The materials shall be designed for the purpose of being installed into an hyperbaric atmosphere. c) Electrical cables in the inner area shall be halogen free and shall not give off toxic, noxious or flammable gases even when overheated. Dismantled ends of insulated conductors shall be protected with sleeves of a non-combustible material ( e.g. glass fibre weave). Ordinary ship cables with insulation of a halogenated material (e.g. P.V.C.) shall not be accepted. Synthetic insulation materials based on P.T.F.E.
(Polytetrafluoroethylene) may be accepted. Section 4 d) Flexible cables for transmission of electrical power and signals from the surface support to the bell shall be constructed as dry-core cable (i.e. water shall not reach the insulation of the individual conductors). e) The submerged cables shall be able to withstand an external hydrostatic pressure of 1.3 times the actual external pressure. f) Unless installed in pipes, electrical cables shall be readily accessible for visual inspection. g) Tensile loads shall not be transferred to the electrical cables.
3.5.2 Electrical penetrators for pressure vessels Chapter 3 a) All electrical penetrators in pressure containing structures shall be purpose designed and bear a manufacturer's certificate (the terms of delivery may require a higher level of certification) and shall be arranged with separate fittings. b) They shall be gas and water-tight even in the event of damage to the connecting cables. c) Electrical penetrators shall be tested at the manufacturers as specified below in d. Tests shall be made between each conductor and screen and tests shall be carried out on penetrators from the same production batch. The tests shall be carried out in the sequence they are listed. The penetrators shall show no sign of deficiency during and after the testing. d) Tests to be carried out include: — a voltage test, by applying 1 kV plus twice the design voltage for 1 minute between each conductor and screen separately — a hydrostatic test to a pressure of twice the design pressure, repeated 5 times — a gas leakage test with the cables cut and open (testing with air to twice the design pressure or with helium to 1.5 times the design pressure.) — an insulation test to 5 Megaohms at the design pressure, applying saltwater.
3.6 Lighting, inner area Protection against possible bursting of electrical bulbs shall be in place.
4 Communication
4.1 General Communications systems shall comply the relevant requirements given in DNVGL-OS-D202instrumentation and telecommunication systems.
4.2 Visual observation of divers
4.2.1 Visual observation of divers in each compartment shall be possible.
4.2.2 For saturation diving systems, suitable means (e.g. TV) shall be arranged for visual observation of the divers in the bells from the control stand for the bells and for the divers in the chamber compartments at the control stand for the chambers.
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DNV GL AS 4.3 Voice communication systems
4.3.1 Communication systems shall be arranged for direct voice communication between the control stand and: a) divers in the water
b) divers in the bell Section 4 c) each compartment d) other control stands e) the bridge (operational command centre).
4.3.2 Alternative means of communication with the divers in the chamber compartments and the divers in the bell shall be available in an emergency. Chapter 3 4.3.3 Diving systems intended for use of helium shall be provided with helium unscramblers. The sound quality shall be of such a level that the breathing pattern of the diver in water can be easily recognised. The control stand for the bell shall be provided with equipment for audio-recording of all communications with the divers in the bell and in the water.
4.3.4 The bell shall be fitted with a self-contained emergency through-water communication system.
4.3.5 A diving bell shall have an emergency-locating device, preferably with a frequency of 37.5 kHz, designed to assist personnel on the surface in establishing and maintaining contact with the submerged diving bell if the umbilical to the surface is severed. This is in accordance with the IMO code of safety for diving systems, 1995 (resolution A.831(19)). The device includes the following components: 1. Transponder 1.1 The transponder should be provided with a pressure housing capable of operating to a depth of at least dmax containing batteries and equipped with salt-water activation contacts. The batteries should be of the readily available alkaline type and, if possible, be interchangeable with those of the diver and surface interrogator or receiver. 1.2 The transponder should be designed to operate with the following characteristics:
Table 1
Common emergency reply frequency 37.5 kHz
Individual interrogation frequencies: - channel A 38.5 +/-0.05 kHz - channel B 39.5 +/-0.05 kHz
Receiver sensitivity +15 dB referred to 1 μ bar
Minimum interrogation pulse width 4 ms
Turnaround delay 125.7 +/-0.2 ms
Reply frequency 37.5 +/-0.05 kHz
Maximum interrogation rates: — more than 20% of battery life remaining once per second — less than 20% of battery life remaining once per 2 seconds
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DNV GL AS Minimum transponder output power 85dB referred to 1 μ bar at 1 m
- 6 dB at +/-135° solid angle, centred on the Minimum transducer polar diagram transponder vertical axis and transmitting toward the surface
Minimum listening life in water 10 weeks
Minimum battery life replying at 85 dB 5 days Section 4
2. Strobe light 2.1 The strobe light on the bell shall have a batterycapacity sufficient for 24 hours duration. 2. Diver-held interrogator or receiver 2.1 The interrogator or receiver should be provided with a pressure housing capable of operating to a depth of at least dmax with pistol grip and compass. The front end should contain the directional hydrophone array and the rear end the 3 digit LED display readout calibrated in metres. Controls should be provided for on and Chapter 3 off receiver gain and channel selection. The battery pack should be of the readily available alkaline type and, if possible, be interchangeable with that of the interrogator and transponder. 2.2 The interrogator or receiver should be designed to operate with the following characteristics:
Table 2
Common emergency reply frequency 37.5 kHz
Individual interrogation frequencies: - channel A 38.5 kHz - channel B 39.5 kHz
Minimum transmitter output power 85 dB referred to 1 μ bar at 1m
Transmit pulse 4 ms
Directivity +/-15°
Capability to zero range on transponder
Maximum detectable range More than 500 m
4.3.6 In addition to the communication systems referred to above, a standard bell emergency communication tapping code should be adopted as given below for use between persons in the bell and rescue divers. A copy of this tapping code should be displayed inside and outside the bell and also in the dive control room.
Table 3 Bell emergency communication tapping code
Tapping code Situation
3.3.3 Communication opening procedure (inside and outside)
1 Yes or affirmative or agreed
3 No or negative or disagreed
2.2 Repeat please
2 Stop
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DNV GL AS Tapping code Situation
5 Have you got a seal?
6 Stand by to be pulled up
1.2.1.2 Get ready for through water transfer (open your hatch)
2.3.2.3 You will not release your ballast Section 4
4.4 Do release your ballast in 30 minutes from now
1.2.3 Do increase your pressure
3.3.3. Communication closing procedure (inside and outside)
5 Instrumentation Chapter 3
5.1 General In general, instrumentation shall comply with the relevant requirements in DNVGL-OS-D202.
5.2 Control stands
5.2.1 In the design of control rooms, attention shall be given to ergonomic matters such as communication and a systematic arrangement of equipment, according to a documented traffic flow chart. Further, it should be ensured that noise or other disturbance when working does not occur (see guidance note to Sec.3 [6.4.1]).
5.2.2 Indication and operation of all vital life support conditions to and from the chamber(s) and the bell(s) shall be arranged at a single control stand or divided between suitably located control stands. The control stands shall be equipped for easy operation and control of the diving system. There shall be schematic indication of gas flow lines. For saturation diving systems the control stand for the bell shall be separated from other control stands.
5.2.3 The control stands shall have indicators showing continuously: a) the pressure in the gas containers connected b) the pressure after all pressure reducers c) the pressure in each chamber compartment d) the pressure externally and internally of the bell. Pressure indicators on the control stand for the bell and compartments shall be arranged for a possible comparison between each other or with a permanently installed master indicator. If cross-connections are incorporated, these shall be arranged in such a way as to give the operators an indication when cross- connection is being conducted. Instrumentation for pressure measuring for bell and compartments shall have an accuracy of +/-0.3% of full scale. In addition pressure indicators for the chambers shall facilitate depth measurements with an accuracy of +/-0.25 msw. in the depth range from 30 msw. to 0. For other instrumentation for pressure measuring, +/-1% of full scale. Pressure indicators used on gas containers and pressure reducers, shall have an accuracy of min. 1.6% of the full scale.
5.2.4 The control stands shall have a system for continuous indication of:
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DNV GL AS a) oxygen content in each compartment individually b) oxygen content in bell for saturation diving systems c) oxygen content in the supply to the: i) umbilical ii) compartments iii) masks in compartments.
The monitoring systems shall be fitted with audible and visual high and low level alarm. Section 4
5.2.5 Permanent provisions for calibration of and comparison between oxygen analysing instruments shall be arranged on the control stand.
5.2.6 There shall be a system for continuous monitoring of oxygen content in supply to the bell's umbilical and masks in the bell. The monitoring systems shall be fitted with audible and visual high and low level
alarm. There shall be an audio-visual gas flow indicator in the oxygen supply to the chambers. Chapter 3
5.2.7 The control stands shall have a system for regular indication of: a) carbon dioxide content in each compartment individually b) carbon dioxide content in the bell for saturation diving systems.
5.2.8 There shall be systems for indication of temperature and humidity in the inner area. For saturation diving systems, temperature and humidity indicators for the living compartments shall be located at the control stand.
5.2.9 Alarms for abnormal conditions are required at the control stand, if automatic environmental control systems are arranged for regulation of gas composition, pressure and temperature in the inner area.
5.2.10 It shall be possible to carry out work and to communicate effectively in the control room even if there is no normal breathable atmosphere in the room. Release of dangerous quantities or mixtures of gas from chamber or gas plant shall never take place in the control room.
5.3 Pressure indicators in bell and chambers.
5.3.1 The bell shall be fitted with indicators visible to the divers inside, showing: a) external pressure b) internal pressure c) pressure of gas stored on the bell.
5.3.2 The chamber compartments shall be fitted with indicators visible to the divers inside, showing internal pressure.
5.3.3 Means shall be provided for isolating all pressure indicators without interrupting vital functions in the gas distribution system.
5.4 Oxygen and carbon dioxide analysing systems
5.4.1 Analysis systems should be of a volume where any necessary reduction to atmospheric pressure at the analysers does not introduce significant time lags. Should this be unavoidable (e.g. bells) pressure should be reduced as early as possible to limit the volume of gases to be vented at the surface. An indication of time
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DNV GL AS lag at different depths should be provided and an ability to vent the line at a faster rate than through the analyser considered. Calibration pipelines should also be designed with minimal volume and details of flushing times from the cylinder.
5.4.2 Oxygen analysing systems shall have an accuracy of at least +/-0.015 bar partial pressure oxygen. Section 4 5.4.3 The bell and the living compartments shall have separate oxygen analysers inside.
5.5 Carbon dioxide analysing systems
5.5.1 Carbon dioxide analysing systems shall have an accuracy of +/-0.001 bar partial pressure.
5.5.2 Carbon dioxide gas for calibration shall be available. Chapter 3
5.5.3 The bell shall have self-contained carbon dioxide analysing systems or have a timed changeout of cannisters with capacity for the full 24 hours emergency duration. Guidance note: Tube based analysers are normally not designed for use in hyperbaric conditions and give unreliable results.
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5.6 Other gases
5.6.1 The instrumentation for systems intended for other gases than air or helium and oxygen mixes shall be considered in each case. Guidance note:
Operations in connection with exploration of oil, may require instrumentation for the analysis of hydrocarbon gases and H2S.
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5.6.2 Calibration gases shall be available for each relevant gas mix.
5.7 Contaminants For DSV-SAT diving systems, a system for sampling and analysing of trace contaminants shall be arranged. Analysing by test tubes may be acceptable.
5.8 Automatic environmental control systems
5.8.1 The following requirements apply when systems for automatic regulation of gas composition, pressure and temperature in the inner area are installed.
5.8.2 The design principles given in DNVGL-OS-D202 apply on a general basis.
5.8.3 The most probable failure in the systems shall result in the least critical of any possible new conditions (fail to safety).
5.8.4 Automatic control systems shall keep process variables within the limits specified during normal working conditions and the alarm systems shall be activated when the limits are exceeded.
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DNV GL AS 5.8.5 Alarm at the control stand is required for abnormal conditions. The alarm system is also to be activated by failures in the alarm system such as broken connections to measuring elements. The alarm system shall be independent of the automatic control system so that failure in one of the systems cannot inhibit operation of the other system.
5.8.6 A manual back-up system for the automatic control system is required. Section 4 Chapter 3
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DNV GL AS SECTION 5 FIRE PREVENTION, DETECTION AND EXTINCTION
1 General
1.1 Objective Section 5 1.1.1 The purpose of this section is to specify additional requirements for fire protection serving diving systems. Emphasis is placed on the special needs associated with the design and manufacture of diving systems, whereas general requirements for fire protection are given in DNVGL-OS-D301 fire protection.
1.1.2 Key issues are identified through requirements for materials, insulation and separation from adjacent spaces, sprinkler systems and extinction agents. Reductions in hazards are ensured through these issues.
1.1.3 For quantitative design parameters and functional requirements, see the relevant standards and Chapter 3 guidelines, including DNVGL-OS-D301.
1.2 Application and scope
1.2.1 In addition to the basis requirements in DNVGL-OS-D301 supplementary information is found in the national fire protection agency codes' chapters on hyperbaric systems and oxygen enriched environments.
1.2.2 Further requirements applicable to the support vessel are given in SOLAS.
1.2.3 Requirements for testing are given in Sec.1 [9].
1.2.4 This section bears impact on Sec.4 (build-up of static electricity, degree of protection provided by enclosure IP for equipment on chambers covered by sprinkler systems, power to alarms) and Sec.8.
1.3 Documentation Fire prevention, detection and extinction shall be documented as follows: a) A list of all materials to be installed in the inner area, where possible with data on and or evaluation of flammability in conditions under which the materials can be used. b) Plans and specifications of fire detection, fire alarm and fire extinction equipment for both the inner and outer area.
1.4 Control stands Control rooms for diving systems located in hazardous zone 2 shall comply with the requirements given in DNVGL-OS-A101 Ch.2 Sec.2 Arrangements. Other control stands, essential to the function of the diving system, shall be protected such that the controls may be maintained whilst the divers are being evacuated in the event of a fire.
2 Fire protection
2.1 Materials
2.1.1 The use of combustible materials shall be avoided wherever possible. Combustible materials include materials which may be brought to explode, or burn independently in the resulting gas environment, applicable to:
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DNV GL AS a) the outer area: air at a pressure of 1 bar b) the inner area: air at applicable maximum pressure.
2.1.2 Structural components, furniture and knobs, paints, varnishes and adhesives applied to these, shall be of non-hazardous materials, i.e. they shall be tested in accordance with relevant parts of IMO 2010 FTP Code or other acknowledged standard. Guidance note: Section 5 In order to comply with [2.1.1], materials for use in inner area should be tested at an elevated pressure. Where such materials are not available, fitting a fixed fire extinguishing system in the inner area may be considered as an alternative.
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2.1.3 Materials and arrangements are wherever possible to be made so as to avoid build-up of static electricity and to minimise the rise of spark production due to electrical failures or combination of materials. In inner areas without electrical equipment, the furniture and floors of electrically conductor materials may be used. For inner areas where electrical equipment is used, the materials and arrangements shall be made Chapter 3 so as to minimise contact with earthed metalwork. A specific electrical resistance between 107 and 1010 ohm-1 is considered to be suitable for avoiding build-up of static electricity. Where electrical equipment cannot be assessed against the above and is required for operation it shall be de-energised while combustion can be supported in the chamber. This shall happen automatically before the chamber atmosphere can support combustion and be set at the worst case ppO2 that may be encountered by the system. See USN Diving Manual Rev 7 13-17 for depth settings for deactivation based upon ppO2. For medical equipment overrides may be permitted based upon a risk assessment of using the equipment. Overrides shall automatically reset to the worst case level after a set time or when the chamber reaches surface conditions in order to allow uninterrupted treatment but minimise the chance of accidental operation at incorrect settings.
3 Fire detection and alarm system
3.1 Inner area The inner area should be equipped with automatic fire detection and alarm system complying with IMO FSS Code. The section or loop of detectors covering the inner area should not cover other spaces.
3.2 Fault detection Provisions shall be made for warning of faults; e.g. voltage failure, broken line, earth fault, etc. in the fire alarm and detection system.
4 Fire extinguishing
4.1 Inner area
4.1.1 Each compartment in a surface compression chamber should have a suitable means of extinguishing a fire in the interior which would provide rapid and efficient distribution of the extinguishing agent to any part of the chamber. (See IMO code of safety for diving systems Ch.2 design, construction and survey 2.9.6)
4.1.2 The inner area shall be equipped with a fixed, manually actuated fire extinguishing system with such a layout as to cover the compartments. It shall be possible to actuate the extinguisher both from within the compartments and from outside.
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DNV GL AS 4.1.3 The extinguishing agent for the inner area shall be rechargeable without depressurising, and provisions shall be made for possible discharge of less than the total supply of extinguishing agent.
4.1.4 The extinguishing agent shall be water, unless an approved alternative exists.
4.1.5 Fixed water-mist systems for inner area shall have minimum capacity of 2 shots of 2 min. duration Section 5 with the required application rate. For a chamber within a SPHL, a capacity of 1 shot of 2 minutes is regarded as acceptable. Response time upon activation shall follow NFPA99, maximum 3 sec. Chapter 3
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DNV GL AS SECTION 6 LAUNCH AND RECOVERY SYSTEMS
1 General
1.1 Objectives Section 6 1.1.1 Launch and recovery systems shall be certified by a competent person as lifting appliances in accordance with the procedures applicable for the issue of an ILO form 2 certificate (International Labour Organisation) or equivalent. Operational limitations shall be stated in an appendix to the certificate. The purpose of this section is to specify additional requirements for lifting appliances serving diving systems. Emphasis is placed on the special needs associated with the design and manufacture of diving systems, whereas general requirements for lifting appliances are given in DNVGL-ST-0378.
1.1.2 Key issues are identified through requirements for alternative recovery of divers. Further, requirements Chapter 3 for interlocking of the mating system between bell and transfer compartment shows the emphasis placed on these essential systems. As this standard allows for the use of buoyant ascent, emphasis is placed on the secure arrangement of such systems.
1.1.3 If the maximum allowable significant wave height is to exceed 2 m, the load conditions shall be defined through the use of App.A.
1.2 Application and scope
1.2.1 This section applies to all systems. However, requirements for handling of divers baskets may be more lenient with respect to emergency recovery, if it is possible for the surface supplied divers to ascend independent of the divers basket.
1.2.2 For quantitative design parameters and functional requirements, see relevant standards and guidelines, including DNVGL-ST-0378.
1.2.3 Limitations are given in the rating of the handling systems with respect to a given, specified, sea-state.
1.2.4 Requirements for testing are given in Sec.1 [9].
1.2.5 This section has impact on the requirements for strength with respect to deck loading on the support vessel and to the services (see Sec.4) from the support vessel.
1.3 Documentation
1.3.1 Handling systems shall be documented as a lifting appliance in accordance with the applied code or standard. In addition, plans and supplementary documentation shall be made available as follows: a) Plans showing the arrangement of the handling system with specifications of loads, and dimensions of strength members. b) Plans showing the function of the systems, and giving particulars of the systems. The plans shall show a schematic arrangement of the hydraulic or pneumatic piping systems and specification of controls and power supply. c) Calculation of the design load according to [3.1]. d) Calculation of necessary design load for umbilical and guide ropes.
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DNV GL AS e) Plans and specification of structural parts, ropes, sockets, blocks, sheaves, winches, and emergency ascent arrangement for the diving bell and mating arrangement. f) Specifications of materials and welds, and extent of non-destructive testing. g) Specifications of wire ropes and their end connections. h) Specification of safety devices (limit switches, automatic stop of operating handle, automatic locking of winch in case of power failure, etc). i) Specification of buoyancy of the bell at dmax and correction formulas when the buoyancy is measured at the surface. Section 6 j) Plans and specifications for systems used for emergency ascent and retrieval of the bell. k) Information on specification of working weight, displacement and stability of the bell, with all hydrostatic properties accounted for.
2 Design principles
2.1 Function Chapter 3
2.1.1 The normal handling system shall be designed for a safe, smooth and easily controllable transportation of the bell in the design sea-state. The lowering of bells is, under normal conditions, to be controlled by the drive system for the winches, and not by mechanical brakes. Bell and guide-wire winches used for dry transfer into a habitat shall include a heave compensation and constant tension system. Guidance note: Care should be taken when designing handling systems with heave compensation and constant tension systems incorporated, as the added systems often contribute to the increase in the stiffness of the overall system.
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2.1.2 Manoeuvring systems shall be arranged for automatic stop when the operating handle is not operated (dead man’s handle).
2.1.3 Hoisting systems shall be fitted with a mechanical brake, which shall be engaged automatically when the hoisting motor stops. In the event of failure of the automatic brake a secondary means shall be provided to prevent the load from falling. This may be manual in operation and should be simple in design.
2.1.4 The handling system shall be designed so that the systems are locked in place if the energy supply fails or is switched off.
2.1.5 If the hoisting rope can enter the drum with an angle exceeding 2° from the right angle to the drum axis (the fleet angle), a spooling arrangement shall be fitted. The rope handling system shall not permit ropes to squeeze in between, or introduce permanent deformation to ropes in underlying layers on the drum.
2.1.6 The hoisting system including the umbilical shall be equipped with a line-out device showing the amount of wire that is spooled off the drum and a device which stops the bell at its lowermost and uppermost positions. Travelling cranes and trolleys shall be equipped with mechanical stops at their end positions. The system shall be equipped with limit switches preventing the handling of the bell, wet bell or basket outside of the handling area.
2.1.7 Precautions shall be taken to avoid exceeding the design load in any part of the handling system including hoisting ropes and umbilical due to: a) large capacity of the power unit
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DNV GL AS b) motions of the supporting vessel when the bell or weights are caught or held by suction to the sea floor c) failure on umbilical winch during launching of bell.
2.1.8 Structural members of the handling system might be subjected to forces imposed by separate units of a power system. (e.g. A-frame tilted by hydraulic actuator on each leg.) The structural members are therefore either to be strong enough to sustain the resulting forces when one of the power units fails, or the power units shall be synchronised and an automatic alarm and stop system shall be activated when the synchronising is out of set limits. Section 6
2.1.9 A locking arrangement shall be fitted to the mating system between the bell and the transfer compartment in accordance with the requirements given in Sec.2 [2.3.4] and Sec.2 [2.3.5].
2.1.10 Where direct visual monitoring of the winch drums from the winch control station is not practical, TV monitoring shall be fitted. Chapter 3 2.1.11 Primary and emergency lighting in all critical handling areas shall be provided.
2.2 Alternative recovery
2.2.1 There shall be at least one normal system and two independent emergency systems for recovery of the divers with return to the chambers. The alternative systems shall comply with the same requirements for load strength as the main system. One of the emergency systems shall be independent of the hoisting and guide ropes, as well as the umbilical. Guidance note: The requirement for an emergency recovery system independent of the hoisting ropes, guide ropes and umbilical is a reminder of the fatal incidents where all these regular means of lifting the bell were severed due to snagging by anchor wires or other obstructions. More recent systems are fitted with two bells, enabling emergency recovery by wet transfer if necessary.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e--- a) One emergency system may be made for recovery by aid of the normal hoisting or guide rope(s) or umbilical. This system shall be independently powered from the normal system, and shall incorporate all transportation necessary to mate the bell to the transfer chamber. b) One system shall also provide an arrangement for stopping the bell from falling or descending, in the event of failure in the primary lifting wire. c) The other emergency system may consist of an arrangement on the bell that permits the divers inside to activate a buoyant ascent of the bell, (see [2.3.1]) and shall incorporate all transportation necessary to mate the bell to the transfer chamber. d) Alternatively, the diving system may be equipped with a separate handling system and a second bell or submersible. Provisions shall be available for recovery of the divers to the chambers.
2.2.2 Guide wire equipment may, in addition to ensuring controlled movements of the bell in the water, function as an alternative handling facility.
2.3 Emergency arrangements
2.3.1 Bells equipped for buoyant emergency ascent shall be specially considered. They shall be fitted with emergency release of hoisting rope(s), guide wires, umbilical and ascent system, that shall be activated in sequence from inside the bell.
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DNV GL AS Guidance note: Although this standard allows buoyant ascent as a means of emergency retrieval, it should be chosen only as a last resort when all alternatives have been considered and abandoned.
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2.3.2 Release mechanisms for hoisting rope, guide wires, umbilical and ascent system shall be so designed
that two separate operations shall be necessary to activate them. If hydraulic or pneumatic actuation Section 6 systems are used, possible penetration of helium into the systems shall be taken into account. Primary strength members shall be designed for a load not less than 3 times the expected maximum load during operation. Secondary strength members such as securing mechanisms shall be so designed that they cannot activate the release system in the event of their failing.
2.3.3 Bells equipped for emergency ascent shall have positive buoyancy without ballast of minimum 3% of the displacement with working weight (the trunk filled with water) at maximum depth. Chapter 3 where foam is used as a buoyancy material: — buoyancy of the foam under operating conditions shall be specified — representative foam elements shall be accessible for inspection — safe fixing to the bell — syntactic foams shall not prevent access to necessary inspection areas, e.g. pressure hull — to avoid seawater intake coating is recommended — large foam elements shall be supported to avoid concentrating the loads within the foam at the elements attachment point — the crush pressure shall be suitable for 1.3 times the diving depth. The following material properties shall be documented: — density (e.g. according to EN ISO 845) — tensile strength — uniaxial compressive strength (e.g. according to ASTM D695-15) — buoyancy variation in regard to nominal diving pressure — seawater intake (e.g. according to ASTM D2735) — hydrostatic crush pressure. A test block of insulation and a buoyancy block that is easily handled and of known properties (e.g. a cube 1dm3) should be fixed to the bell should testing be planned as per DNVGL-RU-OU-0375 Ch.3 Sec.2 [3.3.2.4]
2.3.4 The bell shall have means enabling it to be located when submerged, and in the case of a buoyant bell also at the surface (see Sec.4 [4.3.5]).
2.4 Power
2.4.1 The bell hoisting powersystem shall be designed and tested to lift a load of 1.25 times the working weight.
2.4.2 The power of horizontal transportation systems shall be designed and tested for safe handling at list and trim as specified in Table 1.
2.4.3 The strength of the mechanical brake for the bell hoisting system shall be based on holding of the design load. After the static test, however, the brake may be adjusted to the working weight of the bell plus 40%.
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DNV GL AS 2.5 Umbilical
2.5.1 The length of the umbilical if separated from the hoisting rope is at least to allow an excursion of the bell to: a) dmax plus 5%, or
b) actual bottom depth plus 5%. Section 6
2.5.2 The termination points, where the umbilical enters connectors and penetrators, shall not be subjected to significant loads or flexing.
2.5.3 The ultimate tensile strength of the umbilical shall not be less than twice the maximum load expected during normal and emergency operations. The design load of the umbilical shall be sufficient for the maximum loads expected during normal operation. Chapter 3
3 Strength
3.1 Design loads
3.1.1 If the handling system is designed for operation in sea-states with significant wave heights (see definitions in Ch.1 Sec.1 [2.3]) not exceeding 2 metres, the design load may be taken as the load resulting from the following: a) 2 times the working weight in air of bell and attachable members, b) weight of structural members of the handling system multiplied by a factor of 1.3 in the vertical direction and 0.3 in the horizontal direction, c) list and trim during operation as given in Table 1, d) list and trim in locked position as given in Sec.1 [7.1].
3.1.2 Alternatively to [3.1.1], or for sea-states with significant wave heights exceeding 2 metres, the design load shall be taken as the largest most probable, resultant load over 24 hours in the operational design sea- state due to the following: a) working weight of bell and structural members of the handling system, b) dynamical amplification due to list, trim and motion of the vessel, c) operation and response of the handling system, d) hydrodynamic forces, e) jerks in the hoisting ropes and impact on the system.
3.1.3 The working weight of the bell shall be taken as the maximum weight of the fully equipped bell, including each fully equipped diver of 150 kg. The load from this weight applies to: a) handling in air b) handling submerged, combining the maximum negative buoyancy of the wire rope, umbilical and bell at maximum operating depth.
3.1.4 In locked positions on a vessel, the handling system shall have a structural strength at least sufficient for the environmental conditions described in Sec.1. In addition to the motions and accelerations in the operational design sea-state, the minimum inclinations given in Table 1 shall be taken into account:
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DNV GL AS Table 1 Permanent inclinations
Vessel type Permanent list Permanent trim
Ship 5° 2°
Semi-submersible 3° 3° Section 6
3.1.5 Dynamic loads due to start, stop, or a slack wire rope followed by a jerk, and hydrodynamic loads shall be determined. This may be done as stated in App.A.
3.2 Dimensions
3.2.1 The minimum safety factor for steel wire ropes shall be 4 compared to design load defined in [3.1].
Minimum safety factor for synthetic fibre wire ropes shall be 5 compared to design load defined in [3.1]. Chapter 3
3.2.2 Blocks, sheaves, shackles etc. shall comply with recognised national codes. Drums and pulley diameters shall correspond to the type of rope. For steel wire ropes this diameter shall not be taken less than specified by the rope manufacturer, and normally not less than 18 times the rope diameter. In the case of cross hauling, such equipment shall fulfil the same requirements for strength as the rest of the handling system.
3.2.3 Structural members shall be fabricated from certified materials and shall be designed with safety against: a) excessive yielding b) buckling c) fatigue fracture. in accordance with technical requirements in DNVGL-ST-0378 or equivalent accepted standards. Safety factors at design load shall be taken as specified for case 1 (safety against yield: 1.5) in this reference.
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DNV GL AS SECTION 7 PIPES, HOSES, VALVES, FITTINGS, COMPRESSORS, FILTERS AND UMBILICALS
1 General
1.1 Objectives Section 7
1.1.1 The purpose of this section is to specify additional requirements for pipes, hoses, valves and fittings serving diving systems. Emphasis is placed on the special needs associated with the design and manufacture of diving systems, whereas general requirements for such systems are given in DNVGL-RU-SHIP Pt.4 Ch.6 Sec.7.
1.1.2 Key issues include the requirements for oxygen systems and to the limited use of hoses except hoses used in umbilicals. Chapter 3
1.1.3 This section does not cover general requirements given in manufacturing codes and standards for particular components, such as API codes for hoses etc.
1.2 Application and scope
1.2.1 This section applies to all systems essential for the safe operation of the diving system.
1.2.2 Manufacturing standards applicable to individual components shall be supplementary to this standard.
1.2.3 Testing after completion is included here and in Sec.1, but testing during manufacture shall be in accordance with applicable manufacturing codes for the particular component.
1.2.4 This section has impact on Sec.2, Sec.3, Sec.5, Sec.6 and Sec.8.
1.3 Documentation
1.3.1 Pipes, hoses, valves, fittings, compressors and umbilicals shall be documented as follows:
Plans and specifications showing suitability of the hose in relation to its intended use. Flexible hoses For information, documentation of tests which have been carried out, as required.
Plans and specifications giving particulars of conductors, minimum breaking load and minimum diameter of pulley and drums. Umbilical For information, specification of max. design loads, elastic properties and weight per unit length.
1.3.2 Documentation of tests verifying the properties listed above and as required by [8].
1.4 Materials
1.4.1 Materials used in the breathing gas system shall not produce noxious, toxic or flammable products.
1.4.2 Precautions shall be taken to avoid galvanic corrosion.
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DNV GL AS 1.4.3 Non-metallic materials retaining pressurised gas shall be considered for gas-permeability.
1.5 Protection Piping systems shall be well protected against mechanical damage.
2 Components and hoses for oxygen services Section 7
2.1 General
2.1.1 All components used in oxygen system shall be designed and oxygen shock tested based on EN ISO 10297 (internal diameter of the test equipment shall be in line with the internal diameter of the test object) or other acceptable international standard. Chapter 3 2.1.2 The minimum acceptable cleanliness level for components used in oxygen systems shall be ASTM Level B (33 mg/m2) for nonvolatile residue (see DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6).
2.1.3 The metallic materials used in oxygen system shall be copper, copper alloys with copper content above 55% and austenitic steels with chromium-nickel content above 22%.
2.1.4 The nonmetallic materials used in oxygen systems shall be oxygen shock tested for the applicable pressure range acc. EN ISO 15001.
2.1.5 Shut of valves shall be of the types which need several turns to close. On chamber penetrators, ball valves may be accepted for emergency use only.
2.1.6 Pressure gauges in oxygen systems shall be designed and cleaned in accordance with EN 837-1.
2.1.7 Flexible metallic hoses made of austenitic steels with chromium-nickel content above 22% used for oxygen systems needs to be type approved. The oxygen shock test can be waived.
2.1.8 Flexible synthetic hoses can be used in systems with maximum pressure of 40 bar. Guidance note: The material of the inner liner of the hose should be oxygen shock tested (as required in [2.1.4]) to the applicable working pressure of 40 bar. The length of the flexible hose installed in the system may be longer than the length of the tested hose.
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2.1.9 If a lubricant is necessary to permit assembly operations or the functioning of a component, it shall be selected from lubricants that have been found acceptable for use with oxygen and breathing gases for applicable pressure range.
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DNV GL AS 3 Pipes and hoses
3.1 General
3.1.1 Piping systems shall comply with the technical requirements in DNVGL-RU-SHIP Pt.4 Ch.6. Section 7 3.1.2 Welding of joints shall be carried out by qualified welders using approved welding procedures and welding consumables. Technical requirements are given in DNVGL-RU-SHIP Pt.2 Ch.3.
3.1.3 The following requirements given in DNVGL-RU-SHIP Pt.4 Ch.6, shall be followed: a) bending and welding procedures b) welding joint particulars c) preheating Chapter 3 d) heat treatment after welding and forming e) non-destructive testing and production weld testing f) bracing of copper and copper alloys.
3.1.4 Hydrostatic testing shall be in accordance with the technical requirements and as for corresponding pipe class in breathing gas systems pertaining to class I piping systems.
3.2 Hoses
3.2.1 In addition to umbilicals, short lengths (up to 2 m) of flexible hose may be used when necessary to admit relative movements between machinery and fixed piping systems. For assemblies incorporating specially approved hoses and securing arrangements, lengths up to 5m may be permitted if fixed piping is not practicable. In such cases the securing arrangements shall be in place at 1m intervals of the length of the hose. In addition to the couplings, the hoses shall be secured in such a way as to prevent the hose from whip lashing in the event that the coupling fails. When applicable, couplings shall incorporate bends so that kinks in the hoses are avoided.
3.2.2 Flexible hoses shall not replace fixed piping.
3.2.3 Flexible hoses with couplings shall be certified.
3.2.4 The bursting pressure of synthetic hoses shall be at least: a) for hoses for liquids: 4 times the maximum working pressure b) for hoses for gases: 5 times the maximum working pressure.
3.2.5 Hot water hoses shall be designed for conveyance of fluids of temperatures not less than 100°C
3.2.6 Each hose for use in umbilical shall be pressure tested to 1.5 times the design pressure before fitting in the umbilical. After hose end fittings have been mounted, a gas leakage test to design pressure shall be performed.
3.2.7 Flexible metallic hoses shall comply with DNVGL-CP-0184. These types of hoses shall not be installed in systems subject to excessive vibrations or movements.
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DNV GL AS 3.2.8 Flexible synthetic hoses shall comply with DNVGL-CP-0183. In addition to the testing required in DNVGL-CP-0183 the requirements in [1.4.3] and [3.2.4] applies. The internal oil resistance test may be omitted for hoses intended for gas and water only.
4 Valves and pressure regulators Section 7 4.1 Valve design
4.1.1 Pressure ratings for valves shall be in accordance with a recognised national standard.
4.1.2 Design and arrangement of valves shall be such that open and closed positions are clearly indicated.
4.1.3 Valves shall normally be closed by clockwise rotation. Chapter 3
4.1.4 Pressure regulators shall have more than one full rotation from fully closed to fully opened position.
5 Fittings and pipe connections
5.1 Detachable connections
5.1.1 Bite and compression type couplings and couplings with brazing, flared fittings, welding cones and flange connections are only allowed for piping up to 25 mm (1") and shall be designed according to a recognised standard.
6 Compressors
6.1 General
6.1.1 Compressors shall be certified.
6.1.2 Compressors shall be equipped with all the accessories and instrumentation which are necessary for effective and dependable operation.
6.1.3 Compressors shall be designed for the gas types and pressure rating as specified by the operation and so designed that the gas is protected against contamination by lubricants.
6.1.4 Suitable protection shall be provided around moving parts, and the safety relief valves shall exhaust to a safe place.
7 Purification and filter systems
7.1 General
7.1.1 Purification and filter systems shall be certified.
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DNV GL AS 7.1.2 The content of contaminants in the breathing gas after the filter system shall not exceed the acceptance criteria given in EN 12021 or equivalent standards. National requirements remain unaffected hereby.
7.1.3 Where breathing gas is supplied directly from running compressors, an automatic shut off device for the compressor shall be installed to shut it down when the purification/filter system have reached an unacceptable level of contamination. Section 7
7.1.4 Filter housings, casings, breathing gas receivers and other parts subject to pressure shall be hydrostatically tested in accordance with national and international design codes.
7.1.5 Additional requirements to external environment in terms of toxic H2S and hydro carbon gas (see DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6 [2.1]). Chapter 3 8 Umbilicals
8.1 General Umbilicals shall be designed, tested and certified in accordance with the most recent edition of one of the following codes: a) ISO 13628-5 petroleum and natural gas industries, design and operation of subsea production systems, part 5: subsea control umbilicals b) API specification 17E specification for subsea production control umbilicals.
8.2 Hoses Hoses for umbilicals shall comply with the requirements given in [2.1]. Hoses intended for operation with a larger external pressure than the internal pressure, shall be able to withstand 1.5 times this pressure difference without collapsing or shall be able to collapse without signs of permanent deformation.
8.3 Electrical cables
8.3.1 Electrical cables for umbilicals shall comply with requirements given in Sec.4.
8.3.2 The minimum average thickness of insulating walls and temperature classes shall be in accordance with DNVGL-OS-D201.
8.4 Sheathing Any sheathing of a compact umbilical shall be of a design which avoids build-up of an inside gas pressure in the event of a small leakage from a hose.
8.5 Strength members The strength members of umbilicals shall have sufficient stiffness to avoid plastic yielding of electrical conductors at design load, and shall be properly secured.
8.6 Testing of mechanical properties Samples of the completed umbilicals shall be tested according to a manufacturer’s test programme complying with relevant requirements in the design code. The test programme shall as a minimum include tensile
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DNV GL AS testing and fatigue testing to 5000 load cycles without the umbilical showing any sign of permanent deformation of electrical conductors and or significant permanent deformations of other parts.
8.7 Tests after completion A pressure test to the design pressure of all hoses simultaneously and verification of the specified properties by insulation tests of electrical conductors as well as impedance measurements of signal cables to specified
properties shall be carried out. Section 7 Chapter 3
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DNV GL AS SECTION 8 HYPERBARIC EVACUATION SYSTEMS
1 Introduction
1.1 Introduction
These guidelines and specifications for hyperbaric evacuation systems have been developed with a view Section 8 to promoting the safety of all divers in saturation and achieving a standard of safety for divers which corresponds, so far as is practicable, to that provided for other seagoing personnel, and which will satisfy Ch.3 of the code of safety for diving systems (resolution A.536(13), as amended by resolution A.583(14)).
1.2 Objectives
1.2.1 The purpose of this section is to outline general requirements for hyperbaric evacuation systems serving diving systems. Emphasis is placed on the special needs associated with the design and manufacture Chapter 3 of such systems, including requirements given by IMO. Specific requirements for pressure vessels, life support systems etc. are given in each applicable chapter preceding this.
1.2.2 Key issues are identified by specifically adding to the IMO text in relation to self-propelled hyperbaric evacuation lifeboats, equipment for connection to support and rescue vessels and launch and recovery systems.
1.3 Application and scope
1.3.1 SOLAS requirements shall be applied as far as practicably possible. This is particularly relevant to the launch and recovery systems.
1.3.2 These requirements may also be applicable as flag state requirements.
1.3.3 Some testing requirements are given, limited to those specified in the original IMO text. Additional testing may be relevant depending on the type of evacuation system installed.
1.4 Documentation See the relevant chapters in this offshore code for documentation requirements to the applicable equipment and systems. For type approved lifeboats, relevant to SPHLs, particular document requirements are issued in connection with the type approval.
1.5 General requirements and preamble
1.5.1 The requirements in this subsection are in compliance with the IMO guidelines and specifications for hyperbaric evacuation systems, resolution A.692(17), in the following referred to as the IMO guidelines. Much of the text in this Ch.9 is IMO text. If any parts of the rules are subject to discussion or misunderstanding, the IMO text shall prevail.
1.5.2 Hyperbaric evacuation units that are permanently connected to a certified diving system will, as a minimum, be regarded as deck decompression chambers and shall be certified as such. (See Sec.2). However, the minimum size requirements given in this standard shall be considered in each case.
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DNV GL AS Guidance note: For split level diving, and diving operations deeper than 200 m, two hyperbaric evacuation systems may be required to cover the various pressure levels.
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1.6 Hyperbaric evacuation methods
It is recognised that there are various methods available for evacuating divers in an emergency and that the Section 8 suitability of the various options for a safe hyperbaric evacuation depends on a number of factors including the geographical area of operation, environmental conditions, and any available offshore or onshore medical and support facilities. Options available to diving contractors will include: 1) hyperbaric self-propelled lifeboats 2) towable hyperbaric evacuation units
3) hyperbaric evacuation units which may or may not be towable suitable for offloading on to an attendant Chapter 3 vessel 4) transfer of the diving bell to another facility in the event of the bell(s) not being recoverable to the mothership due to the casualty 5) transfer of the divers from one diving bell to another when in the water and under pressure 6) negatively buoyant unit with inherent reserves of buoyancy, stability and life support capable of returning to the surface to await independent recovery. The Guidelines and Specifications do not therefore attempt to specify which particular type of hyperbaric evacuation system should be employed and recommend that clients and diving contractors examine and identify the option most suited for the area and type of operation in which they are engaged. Consideration may have to be given to the provision of separate evacuation facilities for divers in saturation at significantly different depths, see Sec.1 [2.2.4].
1.7 Contingency planning and emergency instructions A potentially dangerous situation can arise if a floating unit, from which saturation diving operations are being carried out, has to be abandoned with a diving team under pressure. While this hazard should be reduced by pre-planning, under extreme conditions consideration may have to be given to hyperbaric evacuation of the divers. The hyperbaric evacuation arrangements should be studied prior to the commencement of the dive operation and suitable written contingency plans made. Where, in the event of diver evacuation, decompression would take place in another surface compression chamber the compatibility of the mating devices should be considered. Once the hyperbaric evacuation unit has been launched, the divers and any support personnel may be in a precarious situation where recovery into another facility may not be possible and exposure to seasickness and accompanying dehydration will present further hazards. It is, therefore, necessary that diving contractors ensure that any such contingency plans include appropriate solutions. It should be emphasised that hasty or precipitate action may lead to a premature evacuation situation, which could be more hazardous in the final analysis. In preparing the contingency plans, the various possible emergency situations should be identified taking into consideration the geographical area of operation, the environmental conditions, the proximity of other vessels, and the availability and suitability of any onshore or offshore facilities. The facilities for rescue, recovery and subsequent medical treatment of divers evacuated in such circumstances should be considered as part of the contingency plan. In the case of unattended hyperbaric evacuation units, consideration should be given to providing equipment to transfer the towline to an attendant vessel before launch of the evacuation unit. Such an arrangement would enable the unit to be towed clear immediately after launching. Copies of contingency plans should be available on board the parent vessel, ashore and in the hyperbaric evacuation unit.
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DNV GL AS 1.8 Purpose The purpose of these guidelines and specifications is to recommend design and construction criteria, equipment, survey standards and contingency planning for the evacuation systems referred to in Ch.3 of the code of safety for diving systems (resolution A.536(13)).
1.9 Application Section 8 The guidelines and specifications apply to new hyperbaric evacuation units which are constructed more than twelve months after the date on which the Assembly of the International Maritime Organization adopts these guidelines and specifications for units which can be mated to a surface compression chamber. However, any existing system which, complies with the provisions of these guidelines and specifications may be considered for endorsement of the safety equipment certificate in accordance with 4.2. (I 2502).
1.10 Definitions Chapter 3
1.10.1 Self-propelled hyperbaric lifeboats are in this text understood to mean hyperbaric evacuation units installed in self-propelled lifeboats operated by crew members and life support technicians located outside the hyperbaric environment.
1.10.2 Definitions For the purpose of these guidelines and specifications the terms used have the meanings defined in the following paragraphs unless expressly provided otherwise:
Table 1
Means the government of the state whose flag a ship or floating structure which carries Administration a diving system is entitled to fly or in which the ship or floating structure is registered
Bottle Means a pressure container for the storage and transport of gases under pressure
means air or any other mixture of gases used for breathing during evacuation and, if Breathing mixture applicable, during decompression
The pressure, expressed in metres of seawater, to which the diver is exposed at any Depth means time during a dive or inside a surface compression chamber or a diving bell
Means a submersible compression chamber, including its ancillary equipment, Diving bell for transfer of divers under pressure between the work location and the surface compression chamber, and vice versa
Means the whole plant and equipment necessary for the conduct of diving operations Diving system using transfer-under-pressure techniques
Means the whole plant and equipment necessary for the evacuation of divers in saturation from a surface compression chamber to a place where decompression can Hyperbaric evacuation system be carried out. The main components of a hyperbaric evacuation system include the hyperbaric evacuation unit, handling system and life-support system.
Means a unit whereby divers under pressure can be safely evacuated from a ship or Hyperbaric evacuation unit floating structure to a place where decompression can be carried out
Means the plant and equipment necessary for raising, lowering and transporting the Handling system hyperbaric evacuation unit from the surface compression chamber to the sea or on to the support vessel, as the case may be
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DNV GL AS Means those locations in which an explosive gas-air mixture is continuously present, or present for long periods (zone 0), in which an explosive gas-air mixture is likely to Hazardous areas occur in normal operation (zone 1), in which an explosive gas-air mixture is not likely to occur, and if it does it will only exist for a short time (zone 2)
Means the gas supplies, breathing gas system, decompression equipment, environmental control system, heating or cooling and other equipment required to
Life-support system provide a safe environment for the divers in the hyperbaric evacuation unit under all Section 8 ranges of pressure that they may be exposed to during evacuation and, if applicable, during the decompression stages
Means the equipment necessary for connecting and disconnecting a hyperbaric Mating device evacuation unit and a surface compression chamber
(Of the diving system) is the depth in metres of seawater equivalent to the maximum Maximum operating depth pressure for which the diving system is designed to operate
Means a container capable of withstanding an internal maximum working pressure Chapter 3 Pressure vessel greater than or equal to 1 bar
Means a pressure vessel for human occupancy with means of controlling the differential Compression chamber pressure between the inside and outside of the chamber
1.11 Design and construction principles 1) The design and construction of the hyperbaric evacuation system should be such that it is suitable for the environmental conditions envisaged, account being taken of the horizontal or vertical dynamic snatch loads that may be imposed on the system and its lifting points particularly during evacuation and recovery. 2) The hyperbaric evacuation unit should be capable of being recovered by a single point lifting arrangement and means should be provided on the unit to permit a swimmer to hook on or connect the lifting arrangement. Guidance note: This standard interprets single point lifting as applicable to the lifting appliance and not the hyperbaric evacuation unit. Further, it is interpreted to imply that only one hook-up is required to secure the load.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e--- 3) In the design of pressure vessels including accessories such as doors, hinges, door landings, closing mechanisms, penetrators and view ports, the effects of rough handling should be considered in addition to design parameters such as pressure, temperature, vibration, operating and environmental conditions. In general, piping penetrations through the chamber should have isolating valves on both sides. 4) Materials used in the construction of hyperbaric evacuation systems should be suitable for their intended use. 5) Component parts of a hyperbaric evacuation system should be designed, constructed and tested in accordance with standards acceptable to the administration. 6) Components in the hyperbaric evacuation system should be so designed, constructed and arranged as to permit easy inspection, maintenance, cleaning and, where appropriate, disinfection. 7) The hyperbaric evacuation system should be provided with the necessary control equipment to ensure its safe operation and the well-being of the divers. 8) Special arrangements and instructions should be provided externally to enable the hyperbaric evacuation unit to be recovered safely. The instructions should be located where they will be legible when the hyperbaric evacuation unit is floating. 9) Hyperbaric evacuation systems should not be located in zone 0 or zone 1; hazardous areas and high fire risk areas should be avoided as far as is reasonably practicable.
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DNV GL AS 1.12 Equipment for connection to support and rescue vessels (HEU)
1.12.1 The hyperbaric evacuation unit (HEU) shall have an arrangement for a possible connection of umbilical to the support vessel. The umbilical connection shall enable maintenance of proper environmental conditions in the chamber for an unlimited time, and contain aids for communication. Section 8 1.12.2 Additional or emergency life support facility shall be provided for the HEU. The owner shall ensure that the facility is ready for use at all times during diving.
1.12.3 This may be in the form of a life support package (LSP) that shall be kept at a suitable location from where it can reach the HEU within reasonable time. A contingency plan, with risk analysis if necessary, shall be performed for verification. Compatibility of the LSP to the HEU shall be verified.
1.12.4 Procedures for use of the LSP shall be included in the contingency plan and shall be available with the Chapter 3 LSP and inside the HEU.
1.12.5 Relevant emergency procedures shall be available in the HEU chamber, in the HEU control and with the LSP.
1.13 Crew facilities (HEU)
1.13.1 The chamber shall be equipped with one seat and one seatbelt for each diver.
1.13.2 In case the HEU crew has to leave the HEU, it shall be possible to secure the chamber system in a way that makes it possible for the divers inside to take over the control of O2 make-up and gas supply.
1.14 Hyperbaric evacuation units 1) The hyperbaric evacuation unit should be designed for the rescue of all divers in the diving system at the maximum operating depth. The compression chamber should provide a suitable environment and adequate facilities, including, where appropriate, seat belts, for the maximum number of persons for which the unit is designed. The seating or other arrangements provided should be designed to provide an adequate degree of protection to the divers from impact collisions during launch and while the unit is afloat. Where the chamber is intended to be occupied for more than 12 h, arrangements for the collection or discharge of human waste should be provided. Where discharge arrangements are provided they should be fitted with suitable interlocks. 2) The means provided for access into the compression chamber should be such as to allow safe access to or from the surface compression chambers. Interlocks should be provided to prevent the inadvertent release of the hyperbaric evacuation unit from the surface compression chamber while the access trunking is pressurised. The mating flange should be adequately protected from damage at all times including during the launch and recovery stages. 3) Arrangement should be provided to enable an unconscious diver to be taken into the unit. 4) Compression chamber doors should be so designed as to prevent accidental opening while pressurised. All doors should be so designed that, where fitted, the locking mechanisms can be operated from both sides. 5) Arrangements should be provided to allow the occupants to be observed. If view ports are provided they should be situated so that risk of damage is minimised. 6) Where it is intended to carry out decompression of the divers after hyperbaric evacuation in another surface compression chamber, then consideration should be given to the suitability of the mating arrangements on that surface compression chamber. Where necessary, a suitable adapter and clamping arrangements should be provided.
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DNV GL AS 7) A medical lock should be provided and be so designed as to prevent accidental opening while the compression chamber is pressurised. Where necessary, interlock arrangements should be provided for this purpose. The dimensions of the medical lock should be adequate to enable essential supplies, including CO2 scrubber canisters, to be transferred into the compression chamber, and be of such dimensions as to minimize the loss of gas when the lock is being used.
1.15 Life-support system Section 8 1) Means should be provided to maintain all the occupants in thermal balance and in a safe and breathable atmosphere for all environmental conditions envisaged - air temperature, sea temperature and humidity - and with the maximum and minimum number of divers likely to be carried. In determining the duration and amount of life support necessary, consideration should be given to the geographical and environmental conditions, the O2 and gas consumption and CO2 generation under such conditions, the heat input or removal and the emergency services that may be available for the decompression of the divers. Gas losses as a result of using toilet facilities which discharge to outside the hyperbaric evacuation unit and medical lock operation should be taken into account in determining the amount of gases required. The effects of hypothermia should be considered and the effectiveness of the Chapter 3 arrangements provided should be established as far as is reasonable and practicable under all conditions envisaged. However, in no such case should the duration of the unit's autonomous life-support endurance be less than 72 h. 2) In addition to any controls and equipment fitted externally, compression chambers should be provided with adequate controls within for supplying and maintaining the appropriate breathing mixtures to the occupants, at any depth down to the maximum operating depth. The persons operating the chamber, whether they are within or outside it, should be provided with adequate controls to provide life support. As far as practicable, the controls should be capable of operation without the person who operates them having to remove his/her seat belt. 3) Two separate distribution systems should be provided for supplying oxygen to the compression chamber. Components in the system should be suitable for oxygen service. 4) Adequate equipment should be provided and be suitably situated to maintain oxygen and carbon dioxide levels and thermal balance within acceptable limits while the life-support equipment is operating. 5) In addition to any instrumentation necessary outside the compression chamber, suitable instrumentation should be provided within the chamber for monitoring the partial pressures of oxygen and carbon dioxide and be capable of operation for the duration of the available life-support period. 6) Where it is intended that divers may be decompressed within the hyperbaric evacuation unit, provision should be made for the necessary equipment and gases, including therapeutic mixtures, to enable the decompression process to be carried out safely 7) An adequate supply of food and water should be provided within the hyperbaric evacuation unit. In determining, in particular, the amount of water to be provided, consideration should be given to the area of operation and the environmental conditions envisaged. 8) A breathing system should be provided with a sufficient number of masks for all the occupants under pressure. 9) Provision should be made external to the hyperbaric evacuation unit, and in a readily accessible place, for the connection of emergency hot or cold water and breathing therapeutic mixture. The dimensions of the connections provided should be as follows: — 3/4 in. NPT (female), hot or cold water — ½ in. NPT (female), breathing mixture. The connections should be clearly and permanently marked and be suitably protected. 10) In hyperbaric evacuation units designed to pass through fires, the breathing gas bottles and piping systems and other essential equipment should be adequately protected. In addition, thermal insulation should be non-toxic and suitable for this purpose. 11) First-aid equipment, sickness bags, paper towels, waste disposal bags and all necessary operational instructions for equipment within the compression chamber should be available within the chamber, on board the parent vessel and ashore.
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DNV GL AS 1.16 Electrical systems and arrangements 1) All electrical equipment and installation, including the power supply arrangements, should be designed for the environment in which they will be required to be operated and designed to minimize the risk of electrical capacity depletion as a result of a fault, fire or explosion, electric shock, the emission of toxic gases and galvanic action. Electrical equipment within the compression chamber should be designed for hyperbaric use, high humidity levels and marine application. Section 8 2) Power supplies required for the operation of life-support systems and other essential services should be sufficient for the life-support duration. The battery charging arrangements should be designed to prevent overcharging under normal or fault conditions. The battery storage compartment should be provided with means to prevent over-pressurisation and any gas released be vented to a safe place. 3) Each compression chamber should be provided with a source of lighting sufficient for the life-support time and of sufficient luminosity to allow the occupants to read gauges and operate essential systems within the chamber. Chapter 3 1.17 Fire protection and extinction 1) Materials used in the construction and installation should so far as is possible be non-combustible and non-toxic. 2) A fire-extinguishing system should be provided in the hyperbaric evacuation unit which should be suitable for exposure to all depths down to the maximum operating depth. 3) In hyperbaric evacuation units that are designed to float and may be used to transport divers through fires, consideration should be given, where practicable, to providing an external water spray system for cooling purposes. 4) Hyperbaric evacuation units on ships required to be provided with fire-protected lifeboats should be provided with a similar degree of fire protection. Areas where hyperbaric evacuation systems are located shall be protected so that effective evacuation can take place in the event of a fire. Control stands for hyperbaric evacuation shall be protected as specified in DNVGL-RU-SHIP Pt.5 Ch.10 Sec.6.
1.18 Launch and recovery systems general
1.18.1 The launching system shall comply with a recognised national code.
1.18.2 An interlock system shall be fitted to the mating system between the evacuation unit and the evacuation-tunnel with functions as stated in Sec.2 [2.3.3], Sec.2 [2.3.4] and Sec.6 [2.1.9].
1.19 Launch and recovery of hyperbaric evacuation units Where appropriate: 1) Means should be provided for the safe and timely evacuation and recovery of the unit and due consideration should be given to the environmental and operating conditions and the dynamic snatch and impact loadings that may be encountered. Where appropriate, the increased loadings due to water entrainment should be considered. Where the primary means of launching depends on the ship's main power supply, then a secondary and independent launching arrangement should be provided. 2) If the power to the handling system fails, brakes should be engaged automatically. The brake should be provided with manual means of release. 3) The launching arrangements provided should be designed to ensure easy connection or disconnection of the hyperbaric evacuation unit from the surface compression chamber and for the transportation and removal of the unit from the ship under the same conditions of trim and list as those for the ship's other survival craft. 4) Where a power-actuated system is used for the connection or disconnection of the hyperbaric evacuation unit and the surface compression chamber, then a manual or stored power means of connection or disconnection should also be provided.
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DNV GL AS 5) The means provided for release of the falls or lift wire after the unit is afloat should provide for easy disconnection, particular attention being given to units not provided with an attendant crew. 6) Where the hyperbaric evacuation unit is designed to be recovered from the sea, or from a ship in a seaway, consideration should be given to the mode of recovery. Adequate equipment to enable a safe recovery of the unit should be provided on the unit. Permanently marked clear instructions should be provided adjacent to the lifting equipment as to the correct method for recovery, including the total weight of the hyperbaric evacuation unit. Consideration should be given to the effect which
entrained water and any bilge water may have on the total weight to be lifted by the recovery vessel. Section 8 Consideration should also be given to any means that can be provided for the absorption of the dynamic snatch loads imposed during the recovery of the hyperbaric evacuation unit from the sea. 7) Should launch be from a ramp under free fall conditions, accelerations imposed on the occupants shall be considered accordingly and installation height specified. The HEU shall be test launched from that height and should leave the ramp cleanly without tumbling or significant rotation. Where the release angle is not gravity controlled (i.e. at a set angle relative to the deck) a test corresponding to both angles of heel after damage shall be performed (this may be done by varying the launch angle of the ramp). Chapter 3 1.20 Fittings Fittings shall comply with Sec.7.
1.21 Communications 1) If breathing mixtures containing helium or hydrogen are used, a self-contained primary communication system fitted with an unscrambler device should be arranged for direct two-way communication between the divers and those outside the compression chamber. A secondary communication system should also be provided. 2) In addition to the communication system, a standard bell emergency communication tapping code should be provided which meets the requirements of that specified in the amendments to the code of safety for diving systems (resolution A.583(14)). Copies of the tapping code should be permanently displayed inside and outside the hyperbaric evacuation unit.
1.22 Location systems 1) Hyperbaric evacuation units designed to be waterborne should be provided with a strobe light and radar reflector. 2) Hyperbaric evacuation units designed to be placed on the sea-bed to await independent recovery should be provided with an acoustic transponder. The transponder should be suitable for operation with a diver- held interrogator-receiver which will be retained on board the parent ship. The equipment provided should meet the requirements specified in the amendments to the code of safety for diving systems (resolution A.583(14)).
1.23 Markings 1) Dedicated hyperbaric evacuation units should be coloured orange and be provided with retro-reflective material to assist in their location during hours of darkness. 2) Each hyperbaric evacuation unit designed to be waterborne should be marked with at least three identical signs as shown below. One of these markings should be on top of the unit and be clearly visible from the air and the other two be mounted vertically on either side and as high as possible and be capable of being seen while the unit is afloat.
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DNV GL AS Section 8
3) Where applicable, the following instructions and equipment should be clearly visible and be kept readily available while the unit is afloat: Chapter 3 1) towing arrangements and buoyant towline 2) all external connections, particularly for the provision of emergency gas, hot/cold water and communications 3) maximum gross weight of unit in air 4) lifting points 5) name of the parent ship and port of registration 6) emergency contact telephone, telex and facsimile numbers. 4) Warning instructions. Where appropriate, the following instructions should be permanently displayed on every hyperbaric evacuation unit in two separate locations so as to be clearly visible while the unit is afloat: Unless specialised diving assistance is available: 1) do not touch any valves or other controls 2) do not try to get occupants out 3) do not connect any gas, air, water or other supplies 4) do not attempt to give food, drinks or medical supplies to the occupants 5) do not open any hatches.
1.24 Stability and buoyancy 1) Hyperbaric evacuation units designed to float should be provided with adequate stability for all envisaged operating and environmental conditions and be self-righting. In determining the degree of stability to be provided, consideration should be given to the adverse effects of large righting moments on the divers. Consideration should also be given to the effect which equipment and rescue personnel, required to be placed on the top of the system to carry out a recovery from the sea, may have on the stability of the hyperbaric evacuation unit. 2) Towing attachment points should be so situated that there is no likelihood of the hyperbaric evacuation unit being capsized as a result of the direction of the tow line. Where towing harnesses are provided they should be lightly clipped or secured to the unit and, so far as is possible, be free from snagging when pulled free. 3) Hyperbaric evacuation units designed to float should have sufficient reserves of buoyancy to enable the necessary rescue crew and equipment to be carried. 4) Where hyperbaric evacuation units are designed to be placed on board a rescue vessel, attachment points should be provided on the unit to enable it to be secured to the deck.
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DNV GL AS 1.25 Self-propelled hyperbaric evacuation lifeboat
1.25.1 If self propelled hyperbaric evacuation lifeboats are required by statutory regulations or installed to comply with operational criteria, the following requirements apply:
1.25.2 The hyperbaric evacuation lifeboat's hull, machinery, equipment, manoeuvrability and seagoing Section 8 properties shall comply with SOLAS 1974 (international convention for the safety of life at sea) and a relevant recognised national code. Guidance note: Lifeboats may be type approved.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---
1.25.3 The hyperbaric evacuation lifeboat shall be fitted with seating arrangement sufficient to carry the Chapter 3 maximum number of divers and crew members in a sitting position.
1.25.4 The hyperbaric evacuation lifeboat shall have a sheltered area for at least 3 crew members in addition to the divers in the chamber. In this sheltered area the controls for the hyperbaric evacuation unit shall be located.
1.25.5 The system shall be designed such that the time necessary to disconnect and launch the hyperbaric evacuation lifeboat shall not exceed 10 minutes, counted after all divers and crew members have entered the hyperbaric evacuation lifeboat and until it is free floating with the engine running.
1.25.6 The chamber shall have windows towards the sheltered part in the lifeboat.
1.25.7 The hyperbaric evacuation lifeboat shall have a self-contained support system with capacity for at least 72 hours.
1.25.8 The hyperbaric evacuation lifeboat shall have emergency radio communication and location systems complying with requirements given in IMO Res. MSC 149 (77), see SOLAS reg. III/6.2.1.
1.25.9 The propulsion unit shall have sufficient power for 10 minutes running without using air from the atmosphere outside the boat. (Depending on the required level given in the safety certificate of the support vessel, this may also be a requirement for the HEU.)
1.25.10 Masks for breathing or breathing apparatus shall be available for the crew members and life-support technicians at atmospheric pressure. The masks shall be connected to air storage sufficient for 30 minutes breathing.
1.26 Testing, surveys and drills - general Testing of the hyperbaric evacuation system with hyperbaric evacuation unit and the handling system shall be carried out to the maximum possible extent to SOLAS requirements and to Sec.2.
1.27 Maintenance and testing The availability of any hyperbaric evacuation system provided is dependent on the regular testing and maintenance of the system. A planned maintenance and testing programme shall be devised with the responsibility for carrying out the maintenance tasks being allocated to specific crew members. Maintenance
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DNV GL AS and testing schedules shall be available for recording the execution of the tasks and the signatures of the persons allocated the tasks. Such schedules shall be maintained on board and be available for inspection.
1.28 Surveys
1.28.1 DNV GL scopes for surveys of diving systems are given in DNVGL-RU-OU-0375. Section 8 1.28.2 1) Each hyperbaric evacuation system should be subject to: 1) an initial survey before being put into service. This should comprise a complete and thorough examination of the hyperbaric evacuation system, equipment, fittings, arrangements and materials including functional tests which should be such as to ensure they are suitable for the intended service and in compliance with these guidelines and specifications 2) a survey at intervals specified by the administration but not exceeding 2 years Chapter 3 3) an annual inspection within 3 months of each anniversary date of the survey to ensure that the hyperbaric evacuation system, fittings, arrangements, safety equipment and other equipment remain in compliance with the applicable provisions of the guidelines and specifications and are in good working order. 2) Where a hyperbaric evacuation system complies with the provisions, as applicable, of the guidelines and specifications and has been duly surveyed, it may be recorded on the supplement to the cargo ship safety equipment certificate as providing the life-saving appliances and arrangements for divers in compression.
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DNV GL AS APPENDIX A DYNAMIC LOADS IN BELL HANDLING SYSTEMS
1 General
1.1 General Approximate estimates of expected dynamic loads during handling of diving bell and any connected cursor
from a vessel which is stationary and heading in the main direction of incoming waves in the design sea-state Appendix A are given in [2] and [3]. The specified methods for calculation of hydrodynamic forces are limited to the cases in which the vertical motions of the suspended bell may be taken equal to the corresponding motions of the support vessel. The conditions permitting such assumptions are specified in [2.1.2]. Other approximate or more accurate methods may be acceptable upon consideration in each case. See DNVGL-RP-C205 Environmental conditions and environmental loads.
1.2 Definitions and abbreviations
1.2.1 Parameters applied for calculation of the forces. m = mass of bell in air corresponding to its working weight including trapped water {kg}. ρ = mass density of seawater = 1030 kg/m3. V = volume of displaced water {m3}. A = cross sectional area of bell with appendices projected on a horizontal plane {m2}. Cm = coefficient for added mass (water). (For typical -diving bells with appendages such as gas containers, bumper structure etc. the coefficient may be taken as Cm = 1.0). Above water Cm = 0. Cd = drag coefficient. (For typical diving bells with -appendages the coefficient may be taken as Cd = 1.5). a = maximum expected vertical acceleration of the bell {m/s2}. 2 ar = maximum expected vertical relative acceleration between bell and water particles {m/s }. v = maximum expected vertical velocity of the bell {m/s}. vr = maximum expected vertical relative velocity between bell and water particles {m/s}. fw = reduction factor for the wave action on the bell, depending on the submerged depth z of the bell, given by:
z = submerged depth of the bell {m} when larger than hs. hs = significant wave height {m}. Guidance note: Significant wave height: when selecting the third of the number of waves with the highest wave height, the significant wave height is calculated as the mean of the selection.
---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e--- e = 2.72 fa and fv = reduction factors due to wave action (see [2.1.2]) under the heading motions of ship shaped support vessels. k = stiffness of the handling system {N/m}. CB = block coefficient of vessel.
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DNV GL AS Rp = horizontal distance from centre of mass (i.e. bell) to the axis of rotation, which may be taken at 0.45 L from the after perpendicular of the vessel {m}. Aw = cross sectional area of moon pool. sr = maximum expected relative amplitude (+/-) of motion between sea surface and support vessel in way of moon pool {m}. g = acceleration of gravity = 9.81 m/s2 d = draught of vessel at bottom of opening for moon- pool for d > hs {m} Appendix A
1.2.2 Parameters applied for correction of units in empirical formulae: -1 h1 = 1 m -1 L1 = 1 m u1 = 1 m/s u2 = 1 m
2 Loads on negative buoyant bell
2.1 Loads on bell clear of support vessel
2.1.1 Forces In a free flow field the maximum vertical hydrodynamic load Fn acting on a negative buoyant bell in the design sea-state may be taken as the smaller of the values obtained from the two following formulae:
Faw = force due to the combined acceleration of bell and water particles, given by:
Faw = (m – ρV)a + ρV(1 + Cm)faar {N} Fv = force due to the relative velocity between bell and water particles, given by: 2 Fv = 0.5 ρ A Cd(fvvr) {N} Fa = force due to acceleration of bell, given by:
Fa = (m + Cmρ V)a {N} Fw = force due to acceleration of water particles in the -deepest wave, given by:
Fw = 0.4(1 + Cm)fwρ V g {N} The parameters and principles applied for calculation of the forces are given in [2.1.2].
2.1.2 Motions of ship shaped support vessels The vertical motions of the bell may be taken equal to those of the support vessel when the natural oscillating period of the handling system is less than 3 seconds, as given by:
For calculation of the forces from the formulae given in [2.1.1] the launching or retrieval velocities should be added to v and vr.
The estimation method for a and ar as well as v and vr given in the following may be used for vessels with length between perpendiculars L {m} in the range: 50 < L < 150,
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DNV GL AS operating in sea-states with significant wave heights hs {m}of magnitude:
2 < hs < 8
The heave acceleration az of the support vessel is given by the smaller of:
or az as obtained from the rules for classification of ships. Appendix A The pitch acceleration ap of the support vessel is given by:
The combined vertical acceleration from heave, pitch and roll is given by:
r = coefficient of roll = 1.0 at centreline of vessel = 1.2 at sides of vessel
The relative acceleration ar between vessel and water particles at surface is given by: q = coefficient for position of bell. = 1.3 at stern. = 1.1 at sides amidship. = 1.0 at vessel's centreline amidship. The vertical velocity of the vessel may be taken as:
The relative vertical velocity between vessel and water particles at surface is given by:
fa = reduction factor for vertical relative acceleration of bell due to wave action, given by:
fv = reduction factor for vertical relative velocity of bell, given by:
2.2 Hydrodynamic loads on bell in moon pool
In the flow field of a moon pool (narrow well) the maximum vertical hydrodynamic load Fm acting on a negative buoyant bell may be taken as derived from [2.1], when Cm and Cd are substituted by fm · Cm and fd · Cd respectively, where: 2.25 fm = 1 + 1.9 (A / Aw)
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DNV GL AS The factors fm and fd obtained from the above apply to moon pools of constant cross section and for the ratio A/Aw < 0.8
The relative accelerations ar and velocities vr refer to the flow field above the bell.
When A/Aw approaches 1, the hydrodynamic load on the bell approaches the dynamic part of the bottom pressure, and may be taken as: Appendix A
For a moon pool at the centerline of the support vessel sr may be taken as:
where ar is obtained from [2.1.2]. Symbols, see [1.2].
2.3 Impulse loads
2.3.1 Impulse loads Fi caused by sudden velocity changes in the handling system by start, stop and snatch loads in hoisting ropes may be taken as :
vi = impulse velocity {m/s} obtained from [2.3.2] or [2.3.3]. Symbols defined in [1.2].
2.3.2 Impulse velocity The impulse velocity vi during start and stop may be taken as the maximum normal transportation velocity.
2.3.3 Slack Slack hoisting rope may be expected when
|Fn| > (m – ρ V) g
When Fn (obtained from [2.1]) is mainly wave induced and a snatch load is of short duration relative to the wave period i.e. when the natural oscillating period of the handling system is less than 3 seconds as given in [2.1.2] , then the impact velocity vi may be taken as: vi = v1 + v2 Ci v1 = free fall velocity {m/s} in calm water
v2 = vrfv as obtained from [2.1.2] for tight hoisting ropes Ci = probability coefficient obtained from the table below
Offshore standards — DNVGL-OS-E402. Edition July 2019 Page 178 Diving systems
DNV GL AS Table 1 Ci versus v1/v2
Ci
1 Appendix A
0
3 Loads on a positive buoyant bell (at surface)
3.1 Impulse loads
3.1.1 Impulse loads Fi caused by sudden velocity changes in the handling system by start, stop and snatch loads in hoisting ropes may be taken as follows:
Ve = volume of displaced water of the floating bell vi = impulse velocity {m/s} is taken to be as follows:
vr = from [2.1.2] {m/s} vhoist = normal transportation speed
4 Design loads
4.1 Maximum load
4.1.1 The maximum load P in the vertical direction may be taken as follows: In water: P = (m – ρV)g + F where F is the larger of Fn and Fi obtained from [2.1], [2.2] and [2.3]. In air:
4.1.2 The design load in the vertical direction may be obtained from the following table.
Offshore standards — DNVGL-OS-E402. Edition July 2019 Page 179 Diving systems
DNV GL AS Table 2 Design loads
Design load
P Appendix A
0.75P
Offshore standards — DNVGL-OS-E402. Edition July 2019 Page 180 Diving systems
DNV GL AS CHANGES – HISTORIC
January 2017 edition
Changes January 2017, entering into force 1 July 2017
• General The following main changes were implemented in this document: — Combination of the content of the superseded documents referred above. — Updating of (design) references to DNV GL service documents incl. DNV GL rules for classification: Ships. Changes – historic — Focusing of the scope of the document on diving systems by removal of content related to diving support vessels/unit arrangements and outer areas. — Removing procedural descriptions and requirements related to classification. In addition to the above, the following detail changes were made:
• Ch.2 Sec.2 Life support systems including piping, hoses, valves, fittings, compressors, filters and umbilicals — Ch.2 Sec.2 [5.1.4]: Restrict the use of threaded pipe penetrations to max. thread size M30. — Ch.2 Sec.2 [8]: Restrict the use of detachable connections to max 25 mm (1”).
• Ch.3 Sec.1 Design philosophy and premises — Ch.3 Sec.1 [9.1.2]: Removed reference to specific parts of ISO 9001.
• Ch.3 Sec.2 Pressure vessels for human occupancy, gas storage and other purposes — Ch.3 Sec.2 [1.6.2], Ch.3 Sec.2 [2.3.10] Guidance note, Ch.3 Sec.2 [4.1.3] and Ch.3 Sec.2 [4.1.3]Guidance note, design life with respect to fatigue to be defined by the designer. — Ch.3 Sec.2 [5.1.5]: Added guidance note.
• Ch.3 Sec.3 Life support systems — Ch.3 Sec.3 [5.1.6]: Restrict the use of threaded pipe penetrations to max. thread size M30.
• Ch.3 Sec.6 Launch and recovery systems — Ch.3 Sec.6 [3.2.1]: Text related to safety factors revised to be in line with Ch.2 Sec.6 [3.2.1].
• Ch.3 Sec.7 Pipes, hoses, valves, fittings, compressors, filters and umbilicals — Ch.3 Sec.7 [4.1.1]: Restrict the use of detachable connections to max 25 mm (1”). — Ch.3 Sec.7 [5.1.4]: Updated and more specific requirements to the compressor/filter pack.
Offshore standards — DNVGL-OS-E402. Edition July 2019 Page 181 Diving systems
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