st5 - scuba diving, snorkeling & land tours in sabah · divers need sufficient gas to carry out...
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ST5.1 08/02
Breathing Gas Planning & Systems
BSAC Sports Diver Training
Breathing Gas Planning &
Systems
ST5.2 08/02
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
Breathing Gas Planning &
Systems
ST5.3 08/02
Sufficient Gas for the Dive
Rule of Thirds
1/3
1/3
1/3 ! One Third Gas supply for
second half of dive or return including surfacing
! One Third Gas supply for reserve
! One Third Gas supply for descent, to half way or turn around point.
How much gas is required for the Dive? What size cylinder is needed?
Breathing Gas Planning &
Systems
ST5.4 08/02
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.)
Breathing Gas Planning &
Systems
ST5.5 08/02
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 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
Breathing Gas Planning &
Systems
ST5.6 08/02
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
Breathing Gas Planning &
Systems
ST5.7 08/02
Gas Calculation Example
Dive Plan 25m for 20mins.
! 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
10L cylinder at 220bar 12L cylinder at 220bar
= 2200 litres = 2640 litres
Breathing Gas Planning &
Systems
ST5.8 08/02
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
Breathing Gas Planning &
Systems
ST5.9 08/02
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!
Breathing Gas Planning &
Systems
ST5.10 08/02
AS Configurations
No one configuration of AS suitable for all circumstances
Configuration must be appropriate to diving conditions Types of Configuration ! Advantages ! Disadvantages ! Practicalities
Breathing Gas Planning &
Systems
ST5.11 08/02
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)
Breathing Gas Planning &
Systems
ST5.12 08/02
‘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
Breathing Gas Planning &
Systems
ST5.13 08/02
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
Breathing Gas Planning &
Systems
ST5.14 08/02
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
Breathing Gas Planning &
Systems
ST5.15 08/02
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
Breathing Gas Planning &
Systems
ST5.16 08/02
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
Breathing Gas Planning &
Systems
ST5.17 08/02
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
Breathing Gas Planning &
Systems
ST5.18 08/02
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
Breathing Gas Planning &
Systems
ST5.19 08/02
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!
Breathing Gas Planning &
Systems
ST5.20 08/02
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
Breathing Gas Planning &
Systems
ST5.21 08/02
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