ST5.1 08/02 Breathing Gas Planning & Systems Breathing Gas Planning & Systems

Breathing Gas Planning & Systems

Deeper, decompression stop or more challenging dives? Failure of gas supply - life- threatening!! ! Divers need sufficient gas to carry out planned dives ! Have a sufficient reserve for emergencies ! Carry an alternative gas supply Depending on the type of diving being undertaken ! Equipment configurations ST5.2 08/02

Breathing Gas Planning & Systems Sufficient Gas for the Dive

Rule of Thirds ! One Third Gas supply for descent, to half way or turn 1 /3 around point. ! One Third Gas supply for second half of dive or 1 1 /3 / return including surfacing 3 ! One Third Gas supply for reserve How much gas is required for the Dive? What size cylinder is needed?

ST5.3 08/02

Breathing Gas Planning & Systems Gas required for the Dive

Amount of gas required depends on ! Personal breathing rate # Fitness # Energy output # Temperature # Nervousness # Safe Rule of Thumb - 25 litres/minute ! Depth of Dive # Use more gas at depth ! Duration of dive (minutes)

Amount of gas = 25 l/min x Abs. Pressure (bar) x Time (mins.)

ST5.4 08/02

Breathing Gas Planning & Systems Cylinder Size for the Dive

Cylinder capacity ! Size of cylinder in litres x bar pressure ! E.g. 10L cylinder at 230bar = 2300 litres air

Dive to 20m for 20 mins. - 10L Cylinder OK? Breathing rate x absolute pressure x dive time (mins) 25 l/min x 3 bar (20m) x 20 mins = 1500 litres 1 This represents two thirds (750 litres = /3) Reserve third (750 litres) needs to be added = 750 litres Total Air required = 2250 litres 10L Cylinder will be suitable for this dive

ST5.5 08/02

Breathing Gas Planning & Systems Calculating Reserve Gas

Dive to 20m for 20 mins Breathing rate x absolute pressure x dive time

! 25 l/min x 3 bar (20m) x 20 mins = 1500 litres ! This represents gas for dive (Two Thirds) ! Add reserve third - 1500 x 1.5 = 2250 litres Total

! Reserve judged against type of diving undertaken

ST5.6 08/02

Breathing Gas Planning & Systems Gas Calculation Example

Dive Plan 10L cylinder at 220bar = 2200 litres 25m for 20mins. 12L cylinder at 220bar = 2640 litres

! Breathing rate x absolute pressure x dive time 25 l/min x 3.5 (25m) bar x 20mins = 1750 litres

One third reserve (875 litres) = 875 litres

Total required = 2625 litres OR Reserve = 1750 litres x 1.5 = 2625 litres

ST5.7 08/02 12L Cylinder needed for this dive Breathing Gas Planning & Systems Emergency Gas Planning

Gas Consumption - a Function of: ! Depth ! Time to ascend (and ‘settle’ time) ! Any decompression stops required ! Stress under water # End of dive to first stop/check depth # Out of gas - sharing single system ! Accelerated breathing rates > 25l/min

ST5.8 08/02

Breathing Gas Planning & Systems Alternative Supply - AS

Why have an AS? ! Gas supply loss - life threatening ! Urgent need to re-establish air supply # Alternative supply carried by diver # Alternative supply carried by buddy Sharing techniques stressful and have poor record of success All divers should carry an AS!

ST5.9 08/02

Breathing Gas Planning & Systems AS Configurations

No one configuration of AS suitable for all circumstances Configuration must be appropriate to diving conditions Types of Configuration ! Advantages ! Disadvantages ! Practicalities

ST5.10 08/02

Breathing Gas Planning & Systems BC Demand Valve

Advantage ! Minimises number of hoses Disadvantages ! No protection against first stage failure ! Cannot be used by buddy ! Restricts diver’s head movement ! Divers must remain very close together ! Both divers consume gas from the same cylinder (1st stage)

ST5.11 08/02

Breathing Gas Planning & Systems ‘Octopus’ demand valve

Should be visible & easily accessible Advantages ! Easy access for buddy ! Diver retains own regulator ! Long hose # Buddy use easier # Can also be used by wearer Disadvantages ! No protection against first stage failure ! Both divers breathing from same cylinder ! Both divers breathing from the same 1st stage ! 1st stage performance not assured

ST5.12 08/02

Breathing Gas Planning & Systems Two Independent Regulators

Pillar valve with two independent outlets Advantages ! All the advantages of an ‘octopus’ ! Can protect against some primary first stage failures Disadvantages ! No protection against massive leak or free-flow ! Both divers breathing gas from the same cylinder

ST5.13 08/02

Breathing Gas Planning & Systems Pony Cylinder & Regulator

Comprises ! Additional cylinder, usually of 3 litre capacity ! Dedicated second regulator Advantages ! True emergency back-up to diver’s own gas supply ! Additional gas capacity ! Fairly light Disadvantage ! Capacity inadequate for deeper dives involving decompression

ST5.14 stops 08/02

Breathing Gas Planning & Twin Cylinders with Systems Independent Regulators

Advantages ! Same as pony cylinder ! Greater gas capacity ! Balanced trim underwater Considerations ! Monitoring two supplies ! Regulator switching Disadvantages ! Regulator failure loses access to gas in that cylinder ! Requires extra buoyancy

ST5.15 08/02

Breathing Gas Planning & Twin Cylinders with Isolation Systems Manifold

Isolation valve closes connection between cylinders Advantages ! No need for regulator switching ! Monitoring one supply Considerations ! Isolator must be accessible to wearer Disadvantages ! Additional ‘O’ rings ! Requires extra buoyancy

ST5.16 08/02

Breathing Gas Planning & Systems AS is a Back-up System

Gas consumption must be planned with any kit configuration Gas back up/reserve should : ! Always be kept for emergency use (Emergency Gas Consumption) ! Not used to extend dive duration ! Be adequate for dive depth or conditions ! Be adequate for self and buddy at worst point in the dive

ST5.17 08/02

Breathing Gas Planning & Systems Maintenance

Equipment is your lifeline Ensure ! All equipment is washed in fresh water after use # To remove dirt # Prevent build up of salt crystals Equipment is regularly serviced by competent technician Equipment treated with respect

ST5.18 08/02

Breathing Gas Planning & Updating or Buying New Systems Equipment

Is the system right for you? ! For the diving you are beginning to do? ! For the diving you intend doing in the future? ! Can you upgrade gradually? Consider complete system ! Overall weight of equipment ! Check buoyancy changes ! Shallow water check out dive Skills

ST5.19 Practice - Practice - Practice! 08/02

Breathing Gas Planning & Systems Summary

Gas Planning ! Adequate size of cylinder for dive ! Calculating reserves Alternative Supply ! All divers should carry an AS ! Have suitable equipment configuration for planned dive ! Maintenance and care New Equipment ! Updating or new - implications ! Become familiar in safe, confined conditions ST5.20 08/02 Practice - Practice - Practice Breathing Gas Planning & Systems

ST5.21 08/02