The Environmental Control of the Hyperbaric Facilities R. Ktos*, A

The environmental control of the hyperbaric facilities R. Ktos*, A. Majchrzycka*>

^Department of Diving Gear and Underwater Work Technology, The Naval Academy, 81-919 Gdynia, Smidowicza, Poland

^Faculty of Thermal Engineering, Technical University of Szczecin,

Abstract

The presented paper relates to the problems of control and the maintenance of the lifeable hyperbaric environment during simulated diving up to the depth 100 m of sea water.

1 Introduction

The most important technical requirements which should be considered before the beginning of the simulated saturation diving are: - to provide for the pressure-tight of the hyperbaric facility, - to provide for rapid and reliable manufacturing, the maintenance and correction of the mixed gas,

- to provide for the accurate measurements of the total pressure, the temperature, relative humidity and the composition of the breathing gas, - to provide for good communication with the divers. Manufacturing and the maitenance of the hyperbaric atmosphere need the preparatory and the operational skills. The preparatory skills involve manufacturing and storage of the proper amount of the mixed gases, which are used for the pressunzation of the hyperbaric facility and for the emergency respiration systems. The operational skills involve: the maintenance of the mixed gas homogemity, rapid, accurate and efficacious correction of the gas during diving and removal of the contaminants Both, the preparatory and the operational skills are concerned with the measurement technique; that needs sampling of the gas from the different places of the habitat and the proper measurement instruments.

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The presented paper will describe the properties of the hyperbanc research complex and the environmental control problems related to the saturation diving.

2 The breathing gases and the contaminants

The saturation diving is not uniform operation and can be divided into five intervals: I - The initial interval in which the hyperbanc atmosphere is formed and its parameters are established. II - Saturation of the divers. The total pressure of the breathing gas and the

partial pressure of oxygen are kept on the required level in necesarry time for the body tissues saturation with the inert gases which are the components of the breathing gas. Ill - Preparation to decompression. A few hours before decompression the

partial pressure of oxygen is increased to the required level, while the total pressure is kept constant; at the previous level. IV - Decompression at the constant level of the oxygen partial pressure, while the total pressure is decreasing to the required level.

V - Further decompression at the constant percentage of oxygen, while the total pressure of the mixed gas is decreasing.

TIME

Fig I The generalized profile of the molar fraction and the partial pressure of oxygen during the saturation diving.

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Figure 1 shows the variability of the molar fraction and the partial pressure of oxygen during the saturation diving.

In order to support the saturation diving the emergency breathing gases and the mixed gas for the pressurization of the hyperbanc chamber are needed; specially in the first interval of diving. During the pressurization of the chamber the divers breathe with the emergency breathing gas which is inhaled from the oral-nasal masks. When the pressurization of the chamber is over and the parameters of the gas are established then the divers can safety breathe with the gas directly from the chamber. The rapid establishment of the hyperbanc atmosphere parameters and the simple method of the chamber pressurization can be achived by using the mixed gases with the special composition. That procedure is used during the saturation diving up to the depth plateau 100 m of sea water. At the greater depths the hyperbanc chamber is alternately pressurized with the pure gaseous components of the breathing gas. Because of the preparation a large amount of the homogenous breathing mixtures with the required composition is laborious. Several different breathing mixtures are in common use for the saturation diving e.g. air, nitrogen-oxygen, helium-oxygen and helium-mtrogen- oxygen. The oxygen is of the special requirements. The partial pressure of oxygen should be maintained, Reimers [3], within the range Po^ = 20,3-^ 162,0 kPa with an accuracy of ±5% of indicated atmospheric level. For long - duration saturation dives the partial pressure of oxygen is generally maintained within the range Po, = 21 + 33kPa, Shilling &Werts& Schandelmeier [4]. The experimental breathing mixtures which are not in routine use may contain hydrogen, Neon 75, argon or heavy gases: A7\,(V^. The addition of the small amounts of SF^ or CP\ improves the voice intelligibility, Shilling & Werts & Schandelmeier [4]. Purity standards are established for the gaseous components of the breathing gas and the diver's breathing air in Polish Standards. The oxygen purity is determined by PN-70/-84910, the compressed medical oxygen is tested for acidity or alkalinity, carbon dioxide, carbon monoxide, halogens, oxidizing, substances, they both must contain not less than 98% by volume of oxygen. The nitrogen purity is determined by PN-71/C-84912, nitrogen 97-99,8% by volume depends on the grade: I- 0,2% by volume of oxygen, II- 2,0% by volume of oxygen, III- 3% by volume of oxygen. Helium 45 purity is determined by BN-80/6017-15; 89,995% by volume of helium, nitrogen, methane, oxygen, carbon monoxide, hydrogen less than 0,001% by volume for each of them. Diving gases supplied by the cylinder from a reputable manufacturer are free of the contaminants. The contaminants can be introduced in handling. In the hyperbanc facilities the main sources of the contaminants are the divers themselves. The table 1 presents the main contaminants emitted by "the standard man" at medium activity level, Hummer & Torbus [1]. The model of" the standard man" is very useful in designing of the life support systems.

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Table 1 The contaminants emitted by " the standard man" at medium activity level, related to standard conditions, Hummer & Torbus |1]

The contaminants Emission per 24 hours carbon dioxide - CO, 550 dw/

methane - CH^ 3 6/m' carbon monoxide- CO 0,7 dm acetone 0,0005 dm"

water vapor 2000 dm Latent heat 5600 kJ

Dry heat 6300 kJ

The table 2 presents the maximum permissible concentration of the contaminants in the hyperbaric facilities

Table 2 The maximum permissible concentration of the contaminants in the

hyperbaric facilities, Shilling & Wert & Shandelmeier, [4]

Substance Source Maximum premissible concentration of the contaminants for exposures Ih 24h 90 days Carbon dioxide metabolic 2,5 kPa 1,0 kPa 0,5 kPa Carbon monoxide smoking 200 ppm 200 ppm 0.1 ppm Aromatic hydrocarbons solvents - - 10 mg/nf except benzen Aliphatic hydrocarbons solvents - - 10 mg/nf except methane Methane sanitary tanks 1,3% 1,3% 1,3% Nitrogen dioxide compressors 10 ppm 1,0 ppm 0,5 ppm Nitrogen compressors 10 ppm 1,0 ppm 0,5 ppm monoxide Ammonia metabolic 400 ppm 50 ppm 25 ppm

The hyperbaric maintenance and control systems should provide for maintaining the oxygen partial pressure and for removal carbon dioxide which is the main contaminant, moisture and heat generated inside the chamber They must control temperature, humidity and the homogeinity of the breathing gas

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3 The hyperbaric facility

The land-based hyperbaric complex built at The Naval Academy of Gdynia in

Poland, consists of three chambers with wet-pot. The chambers are designed as living and working space for research, training and for development of equipment and procedures during simulated saturation diving.

The specification for the hyperbaric complex: - the maximum working pressure: p = 1,25 MPa - the rate of ascend: up to 100 kPa/min

- the minimum projected rate of descend: 0,2 kPa/min - the maximum rate of the oxygen supply (for one chamber): 60 g/min - working time of the purge system without removal of absorber: 120 h - the number of the divers for long-duration simulated saturation dives: 3 - the number of the oral-nasal mask in each chamber:4

The most important criteria for choice of the measurement instruments are: the continuity, accuracy, reliability of the measurements, labour diemant at exploitation, resistance of disturbance

The table 3 presents the control requirements for the breathing gas during simulated saturation diving, up to the depth 100 m of sea water

Table:

The control requirements for the breathing mixtures used during saturation dives

Gas 0, 0, N, CO,

Measurement The partial + 4- pressure Percentage + + Surface equivalent + The range 20*140kPa l4-22%(v) 7-^SO^a ().05-5-0.5%(v) ±(0.02 * 0.6)A-/'a Accuracy ±OJ%(v) ±4kPa ±0,005%(v) The continuous + - - - measurment The doubled measurements + 4- The periodical measurements + Ih Ih 30 min + The measurements - 4- + on the request Relative humidity (p - 40 -j- 90%; accuracy k

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Figure 2 presents the gas control system of the hyperbaric complex.

TO PURGE SYSTEM

FROM HYPERBARIC COMPLEX

OUTLET TO ATMOSPHERE

Fig.2 The gas control system of the hyperbaric complex. 1 - The dew- point temperature analyzer; 2 - The thermoconductometric analyzer of helium "Mescalyt"; 3 - The paramagnetic analyzer of oxygen "Permolyt"; 4 - The infrared analyzer " Infralyt"; 5 - The gas

chromatography; 6 - The oxygen analyzer - "Oxycom"; 7 - The double measurement system for the analyzers 2,3,4; 8 - The flow regulator of decompressed gases; 9 - The valves; 10 - The shutt - of valves; 11 - The regulation valves

The atmospheric control systems allows to sample the breathing gas from the different places of the hyperbaric chamber and carefully analyze It also allows to make percentage adjustment, if it is necessary. Presented system was built on assumption that the gas chromatography is the basic instrumental method in relation to the other measurement instruments. The total pressure of the gas inside the chamber was controlled up to p=l, 1 MPa within an accuracy of &p = 100fa by the resonator pressure gauge.

In order to control the partial pressure and the percentage of oxygen within required limits; the gas chromatogrphy and analyzer "Permolyt" which

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works on the paramagnetic detection principle and electrochemical cells,and "Oxycom" analyzer were used.

The level of carbon dioxide was measured with the gas chromatography and infrared analyzer " INFRALYT" and electrochemical cells, and chemical testers. The level of carbon dioxide sholud be maintained within 0,05-^0,5% by volume. The percentage of helium was determined with thermoconductometnc analyzer " Mescalyt". The percentage of the other contaminants was determined by the gas chromatography. Relative humidity was determined by the dew-point temperature method with psychrometers because there are no measurement instruments available that are known to be accurate under pressure. The common method of removing carbon dioxide and the other contaminants is by passing the gas through the loop regeneration system which is automatically operated After that operation, percentage adjustment of oxygen is necessary.

Oxygen can be added to the mixed gas with the automatic systems with the constant or periodical dosage These systems are not in general use on account of lack of the permanent control of the oxygen dosage. During failure in the automatic dosage system or inhomogemity of the mixed gas, the quantity of oxygen may be not carefully controlled. To much oxygen can be poisonous to the body, while too little leads to suffocation. Consequently, oxygen is still added manually or semi-automatically.

During our research the method of oxygen level adjustment was verified. The adjustment of the percentage and the partial pressure of oxygen is based on the theoretical model presented by Klos & Kochanek [2 ].

The model allows to compute the pressure difference caused by the addition of oxygen. The adjustment procedure consists of three stages: - the pressure is established at the constant level, - the addition of oxygen which causes the computed increase of the pressure, - the correction of the total pressure.

The method is based on very precise measurements of the total pressure with the resonator pressure gauge. This procedure was used for rapid and precise increasing of the oxygen partial pressure before the beginning of decompression (interval III).

Since that procedure causes the instantenous (20s) disturbance in the maintenance of the total pressure level, therefore it was decided that the single permissible correction of the total pressure should be 1 kPa. A larger amounts of the gas should be added in repeated failure procedure. It comes from our experimental research that r< lOmin is the best time between the adjustment of the partial pressure of oxygen Time required for the change of the breathing gas composition ( time of reaction) is 1^2 min. Thanks to that method of oxygen adjustment it was possible to maintain the partial pressure of oxygen within an accuracy of A£>O - ±(0,02 + 0,6)kPa during steady exploitation of the hyperbaric complex (without lock and water removing from the sanitary system) The method allows to determine the safety amount of oxygen that must

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be added to the mixed gas without exceeding the permissible oxygen partial pressure.

It comes from the theoretical analysis Klos & Kochanek [2] that developed method can be used to the depth up to 600 m

Conclusions

The methods of maintaining and control of the breathing gas composition were experimentally verified during simulated saturation diving and the operational dives up to 100 m of sea water The most important technical problem is to provide for the homogenization of the breathing mixture. Ensuring of the homogeneity of the gas and the proper environmental control system are therefore absolutely essential for safety diving.

References

1. Hummer,!.&Torbus,J. The project of the system of preparing the gas mixtures simulating the organic and technical contaminants inside the

hyperbaric chamber. The Naval Academy, Gdynia Poland , 1980 2. Klos,R. & Kochanek,W. The preparation and manufacturing of the breathing gases. The Fourth Symposium on Underwater Technology, The Naval Academy of Gdynia, pp. 111-122, 13-14 October, Gdynia, Poland,

1994. 3. Reimers,S.D. Atmosphere control in the hyperbaric environment, Naval Engineers Journal, 1971, Juni, 50^-5 4. Shilling,C.W.&Werts,M.F.&Schandelmeier,N.R.77?e underwater handbook,

Plenum Press, New York and London 1976.