NetDoc once bubbled...
and NAUI uses it as their max as well. 75fpm!!!
While there are no reasons given, I have heard that the onset of narcosis can be premature on a quick descent. I have no data or study to prove this, as I have only heard it from one doctor. Also the effects of inertia will be present, possibly driving you into the bottom if you try to slow at the last minute.
I can attest to the onset of narcosis with a rapid descent.
say on a 200 ft dive on air [i know, i know, don't start the air thing] at about 75 - 100 feet per minute narcosis hits my like a sledge hammer at 180 feet, [shallower is not a problem]
how ever a rapid descent does not bother my buddy at all.
now if we descend slow and steady i can stay quite a while with out having any obviouse symtoms of narcosis, however with my buddy the longer he stays at dapth the worse he gets.
the inertia thing could also be a factor if there is a bottom. i do some blue water diving, [dives where you are in the middle of the ocean and there is no bottom] this diving is for a specific reason and we descend fairly quickly - about 100 feet/ min. as timing is of the essence
in one perticular case i was to meet my buddy at 300 feet, he was on a rebreather, and went early to perform his task, i then descended down as the videoagrapher, my plan was to shoot to the bottom and start hitting the brakes when i saw his lights as i was videoing on the way down. well guess what, he was hanging out there with out his light on, just drifting along with the line, well i blew right by him. seeing him i hit the brakes and it took me about 50 feet to stop. if there had been a bottom i would have been planted deep in it. [wel not really, as i would have used a different plan]. now i mount a depth gauge onto the video housing for refference.
