THIS DISCUSSION/EXAMPLE IS BY A RECREATIONAL DIVER FOR RECREATIONAL DIVING WITHIN RECREATIONAL LIMITS.
DO YOUR OWN CALCULATIONS USING YOUR OWN RMV VALUES AND YOUR OWN SAFETY ESTIMATES.
PLAN YOUR DIVE. DIVE YOUR PLAN.
What is "Minimum Reserve Gas"?
It is the minimum amount of gas you think you will need after a catestrophic event at the deapest part of the dive. Think of it as "the worst case, but realistic scenario". There are generally three ways to calculate the reserve gas and how you decide which one you use is by how much "Battlefield Math" or precision you require. There are endless arguments about which method to use, so just pick one...it's better than just winging it.- Simple to Calculate = Often called "CAT" = C.onsumption * A.verage Depth * T.ime
- More Realistic = Often called "Rock Bottom" = Consumption * Average Depth * (Time to 50% of depth + Time to surface from 50% of depth)
- More Precision = Do essentially 'Rock Bottom' but don't round or average anything and thus add no conservatism!
If we keep the basic information constant, you can see how different they all are simply based on how you prefer to calculate reserved gas.
Depth: 100 ft
RMV: 0.75 cuft/min per diver
Ascent Speed: no greater than 30ft/min with a preference for 10ft/min
Tank: Aluminum 80 filled to ~3,000 PSI
CAT = 41 cft of gas
Rock Bottom = 30 cft of gas
Rock Bottom /w Precision = 22 cft of gas
*Warning: Rock Bottom /w Precision has no conservatism...so your assumptions better be perfect and you're draining the tank to 0
Simple to Calculate - CAT
More Realistic - "Rock Bottom"
More Precision - No Rounding - No Conservatism
