BM>The reasoning behind the 100 foot depth limit deals with nitrogen 
arcosis.
BM>NASDS is founded on stressing the highest safety standards for the Sport
BM>and that is why they have shallower depth limits (which coincedentally
BM>the Caymans and other areas are moving towards) and shorter bottom times
BM>than any other agency that I know about.
BM>Regarding the depth limit, the incidence of nitrogen narcosis shallower 
than
BM>100 foot is significantly smaller than that below 100 feet.  I can't cite
BM>numbers, but if the majority of divers never experience narcosis above 100
BM>feet, then they are themselves safer, and one less problem they will 
probabl
BM>never encounter.
BM>I know people will argue differently, but NASDS is founded on Sport Safety 
f
BM>Recreational diving, not for commercial or technical diving.
I think P.A.D.I. used 135ft when I took classes.
Have been to 153 ft and don't think I was affected, and some of the guys
I dive with should have o2 poisoning but no ill effects.
Not sure what research says, but I think that if you are going to do
deep dives then you need to work your way into it. And ascent rates
definately need to be monitored.
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