I was with my friends diving last time, and a few non smokers friend really used up their air really fast compared to us.  Thus my friends made a new "theory"..smoking is good la actually la, cuz the tars block up ur lung and less oxygen goes in, while those non smokers have good lungs, so need more oxygen thats y finish air faster... ;D

Good topic. I have not met an instructor who is a non-smoker.
Difficult to come by these days.

 ;D ;D