BSAC Sports Diver Training

1. BSAC Sports Diver Training Breathing Gas Planning & Systems

2. 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

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

4. 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.)

5. 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/minx 3 bar (20m) x 20 mins =1500 litres This represents two thirds (750 litres = 1/3) Reserve third (750 litres) needs to be added = 750 litres Total Air required = 2250 litres 10L Cylinder will be suitable for this dive

6. Calculating Reserve Gas • Dive to 20m for 20 mins • Breathing rate x absolute pressure x dive time • 25 l/minx 3 bar (20m) x 20 mins = 1500 litres • This represents gas for dive (Two Thirds) • Add reserve third - 1500 x 1.5 = 2250 litresTotal • Reserve judged against type of diving undertaken

7. Gas Calculation Example Dive Plan 25m for 20mins. = 2200 litres = 2640 litres 10L cylinder at 220bar 12L cylinder at 220bar • 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 12L Cylinder needed for this dive

8. 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

9. 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!

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

11. 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)

12. ‘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

13. 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

14. 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 stops

15. Twin Cylinders with 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

16. Twin Cylinders with Isolation 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

17. 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

18. 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

19. Updating or Buying New 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 Practice - Practice - Practice!

20. 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 Practice - Practice - Practice