Presentation on theme: "BSAC Sports Diver Training"— Presentation transcript:
1BSAC Sports Diver Training Breathing Gas Planning & Systems
2Breathing Gas Planning & Systems Deeper, decompression stop or more challenging dives?Failure of gas supply - life-threatening!!Divers need sufficient gas to carry out planned divesHave a sufficient reserve for emergenciesCarry an alternative gas supplyDepending on the type of diving being undertakenEquipment configurations
3Sufficient Gas for the Dive Rule of ThirdsOne Third Gas supply for descent, to half way or turn around point.1/3One Third Gas supply for second half of dive or return including surfacing1/31/3One Third Gas supply for reserveHow much gas is required for the Dive?What size cylinder is needed?
4Gas required for the Dive Amount of gas required depends onPersonal breathing rateFitnessEnergy outputTemperatureNervousnessSafe Rule of Thumb - 25 litres/minuteDepth of DiveUse more gas at depthDuration of dive (minutes)Amount of gas = 25 l/min x Abs. Pressure (bar) x Time (mins.)
5Cylinder Size for the Dive Cylinder capacitySize of cylinder in litres x bar pressureE.g. 10L cylinder at 230bar = litres airDive to 20m for 20 mins. - 10L Cylinder OK?Breathing rate x absolute pressure x dive time (mins)25 l/min x bar (20m) x mins = litresThis represents two thirds (750 litres = 1/3)Reserve third (750 litres) needs to be added = litresTotal Air required = litres10L Cylinder will be suitable for this dive
6Calculating Reserve Gas Dive to 20m for 20 minsBreathing rate x absolute pressure x dive time25 l/min x 3 bar (20m) x 20 mins = litresThis represents gas for dive (Two Thirds)Add reserve third x 1.5 = litres TotalReserve judged against type of diving undertaken
7Gas Calculation Example Dive Plan25m for 20mins.= 2200 litres= 2640 litres10L cylinder at 220bar12L cylinder at 220barBreathing rate x absolute pressure x dive time25 l/min x 3.5 (25m) bar x 20mins = 1750 litresOne third reserve (875 litres) = litresTotal required = 2625 litresORReserve = 1750 litres x 1.5 = 2625 litres12L Cylinder needed for this dive
8Emergency Gas Planning Gas Consumption - a Function of:DepthTime to ascend (and ‘settle’ time)Any decompression stops requiredStress under waterEnd of dive to first stop/check depthOut of gas - sharing single systemAccelerated breathing rates > 25l/min
9Alternative Supply - AS Why have an AS?Gas supply loss - life threateningUrgent need to re-establish air supplyAlternative supply carried by diverAlternative supply carried by buddySharing techniques stressful and have poor record of successAll divers should carry an AS!
10AS ConfigurationsNo one configuration of AS suitable for all circumstancesConfiguration must be appropriate to diving conditionsTypes of ConfigurationAdvantagesDisadvantagesPracticalities
11BC Demand Valve Advantage Disadvantages Minimises number of hoses No protection against first stage failureCannot be used by buddyRestricts diver’s head movementDivers must remain very close togetherBoth divers consume gas from the same cylinder (1st stage)
12‘Octopus’ demand valve Should be visible & easily accessibleAdvantagesEasy access for buddyDiver retains own regulatorLong hoseBuddy use easierCan also be used by wearerDisadvantagesNo protection against first stage failureBoth divers breathing from same cylinderBoth divers breathing from the same 1st stage1st stage performance not assured
13Two Independent Regulators Pillar valve with two independent outletsAdvantagesAll the advantages of an ‘octopus’Can protect against some primary first stage failuresDisadvantagesNo protection against massive leak or free-flowBoth divers breathing gas from the same cylinder
14Pony Cylinder & Regulator ComprisesAdditional cylinder, usually of 3 litre capacityDedicated second regulatorAdvantagesTrue emergency back-up to diver’s own gas supplyAdditional gas capacityFairly lightDisadvantageCapacity inadequate for deeper dives involving decompression stops
15Twin Cylinders with Independent Regulators AdvantagesSame as pony cylinderGreater gas capacityBalanced trim underwaterConsiderationsMonitoring two suppliesRegulator switchingDisadvantagesRegulator failure loses access to gas in that cylinderRequires extra buoyancy
16Twin Cylinders with Isolation Manifold Isolation valve closes connection between cylindersAdvantagesNo need for regulator switchingMonitoring one supplyConsiderationsIsolator must be accessible to wearerDisadvantagesAdditional ‘O’ ringsRequires extra buoyancy
17AS is a Back-up SystemGas consumption must be planned with any kit configurationGas back up/reserve should :Always be kept for emergency use (Emergency Gas Consumption)Not used to extend dive durationBe adequate for dive depth or conditionsBe adequate for self and buddy at worst point in the dive
18Maintenance Equipment is your lifeline Ensure All equipment is washed in fresh water after useTo remove dirtPrevent build up of salt crystalsEquipment is regularly serviced by competent technicianEquipment treated with respect
19Updating 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 systemOverall weight of equipmentCheck buoyancy changesShallow water check out diveSkillsPractice - Practice - Practice!
20Summary Gas Planning Alternative Supply New Equipment Adequate size of cylinder for diveCalculating reservesAlternative SupplyAll divers should carry an ASHave suitable equipment configuration for planned diveMaintenance and careNew EquipmentUpdating or new - implicationsBecome familiar in safe, confined conditionsPractice - Practice - Practice