What pressure to end a dive? A debate!

[The Kraken]

Ok I believe you, but why? Is the 80 cu ft a measurement of how much air you have at a given pressure? If so what is it??

A good deduction ! ! !

Exactly!!! The volume is expressed in the capacity of the tank at its normal service pressure.

the K

 

[MikeFerrara]

So therefore if you have 80 cu ft at a lower pressure the tank would have to be bigger right???

Boyle is our friend when trying to figure these things out. If we take a fixed amount of gas and compress it, the pressure goes up. The more we compress it, the less space it takes up and the higher the pressure.

 

[kidspot]

ya' know ... as I was re-reading some of this thread it dawned on me that I can't recall ever being told "be back on the boat with 500psi" ... I have heard what psi to begin an ascent however. Usually it's "begin your ascent at 500psi" when the dive is under 50fsw and 800psi on dives up to 100fsw. Might not be the same concept as rock bottom, but at least it makes more "doable" for infrequent divers. Of course on these same dives the DM is also constantly checking everyone's remaining air and "sending them up" when they hit ascent pressure...

There have also been times I've seen where an ascent begun at 700psi (about 50fsw) left a diver with only 100psi back on the boat... good reminder that every diver needs to know how to calculate these things for themselves and their air consumption.