Posted by Karl S. on January 30, 2003 at 12:58:35:
In Reply to: Re: A few questions about your article/ posted by tecdiver on January 29, 2003 at 12:00:22:
Techdiver's answer is perfect! Put another way, deep is relative.
For a new dive student just learning how to dive, the swimming pool is deep. Its funny-sad to watch them when they panic underwater, usually during their mask clearing drills, when they claw their way back to the surface of the pool, then cough and spit and snort to get the water out of their noses.
For a newly certified diver, 40 fsw is deep. And 60 fsw is "really deep." Can this diver safely ascend from depth back to the sufrace during an OOA or gear failure emergency? Who really knows?!
For an experienced freediver, diving on scuba, 100 fsw is probably not really deep. It all depends on the diver and his/her training and experience.
For an advanced diver with a pony bottle, deep is measured by the limits of his/her pony bottle for an ascent. A 13 or 20 cu ft pony bottle with air in it should suffice for an egression all the way from the 130 fsw recreational (arbitrary) limit.
Deeper than 130 fsw, you are now in the "technical diving" arena, and that requires stage bottles and tank switching protocols and training.
Europeans routinely dive to 150 fsw, some with and others without pony bottles. I have not yet seen any comparisons of European diving accidents with American diving accidents, so I cant say whether there is anything magically better about 130 fsw versus 150 fsw.
Any dive deeper than 40 fsw can have all the characteristics and problems of a much deeper dive, for a beginner. Although we usually say that 60 fsw is where deep begins. But deep is relative.
End of non-technical discussion.
On the technical side, deep also depends on the marine environment. For trimix decompression diving in California, the cold water makes any dive deeper than 250 fsw "really deep" because the deco hang times become so long that youre spending more than an hour underwater. For cold water, this is too long, therefore 250 fsw is "really deep."
And any dive deeper than 150 fsw for more than 20 mins also gives you a long, over one hour deco hang time.
In Mexico, where the water is warmer, 300 to 350 fsw is do-able with trimix and nitrox stages.
Any dive deeper than 350 fsw anywhere is probably best left to professional divers, and is too deep for recreational sportdivers.
I believe that covers it all.