Point of no return on air, what is it?

[islandah]

yeah, I think the original question may have been a bit confusing. I wanted to get a feel for your own personal limit given your own experience, for instance, "if I was given an 80 with a full tank of air I would not go below xxx feet because beyond this I feel I would not be able to get back alive".

Well, I can give you 2 specific opinions from personal experience of 2 very different divers. 1st diver is a young brash fit guy in his mid twenties, diving before "tech" was established. He was diving a lot, fit, experienced for his age, comfortable in his gear. Diving with an older brother who liked to push limits. They bounced the Skycliffe wreck off Boynton Beach and hit 190' for a couple minutes on AL 80's. Not sure of the air consumption, but I know they had enough for safety stop and weren't sucking fumes.

2nd diver is a 43 year old far more experienced and educated diver, up on newer technologies and physiology, and a little more self-confident in thinking for himself. He would probably not venture much past 120-130' without a damn good reason for all the previously mentioned reasons.

You've probably figured out that both divers are the same person.

 

[crispix]

OP's original question is begging for a reply about Rock Bottom.

"Rock Bottom" is a way of calculating the minimum pressure needed at a certain depth in order to get you and a buddy to the surface safely and with a margin of error. There's a nice web site that summarizes it that appears to be offline right now, but I found it in the google cache:

Rock Bottom and Gas Management for Recreational Divers