From: gd@gehenna.sw.stratus.com (Greg Dawe)
Newsgroups: rec.scuba
Subject: Re: dangerous misconception (was Re: Human bodies explode...)
Date: 18 Nov 92 18:41:29 GMT
Organization: Stratus Computer, Software Engineering
NNTP-Posting-Host: gehenna.sw.stratus.com


In article <1e8ttiINN6s7@darkstar.UCSC.EDU> jdale@cats.ucsc.edu (Jonathan Dale) writes:
>
>I would question this whole tolerance concept.

It's healthy to question anything and everything to do with diving.  The
issue of tolerance/adaptation to nitrogen narcosis is totally based on
anecdotal evidence from within the diving community.  I had heard that a 
UHMS member had published something about this phenomenon, but a call to DAN 
turned up nothing (DAN did do a videographed study of narcosis with some 
volunteers from the military).

For the sake of clearer discussion let me clarify what I mean by "tolerance".
From my original posting:

"There are some divers who are able to function well at 200 FSW, and a rare 
 few, who can function well even deeper.  These divers have been diving deep 
 on air for years, and have developed some tolerance for the symptoms of 
 narcosis."                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ^^^^^^^^
In other words, we're not talking about eliminating narcosis.  How then, do 
we explain the fact that there are divers frequently, diving deeper than 
150 FSW, deeper than 200 FSW, and even deeper than 250 FSW on air?  These
divers are familiar, through progressive experience, with the symptoms of
narcosis, and their personal limitations.  With this familiarity comes a
"tolerance", or an understanding of what can be accomplished under a given
amount of narcosis.  If things feel like they're getting too "out of hand" 
the dive is aborted.

Other things are done in order to stack as many things as possible in favor
of the deep air diver.  Exertion is kept to a minimum, particularly during
the descent.  Class-A regulators are used in order to deliver the volume of
air necessary at depth and thereby minimize CO2 buildup, which contributes
to narcosis.  For safety, task loading is kept to a minimum because of the
dulled mental capacity and delayed responsiveness.  Deep training is done in
small increments, never in large leaps or bounds.  None of these things are
considered guarrantees: deep divers must understand and accept the inherent
risks.

Some quotable quotes:

"The more you dive deep, the more you get used to it." 
  -Gary Gentile, in "Gentile on Narcosis", AquaCorps DEEP issue, pg 51

"It is generally agreed by divers that frequent exposure to narcosis
 leads to adaptation."
"There is some evidence of adaptation that is specific to narcosis."
  -Barry Fowler PhD, in "A Performance Guide to Managing Narcosis",
                         AquaCorps DEEP issue, pg 50

>Based on what I've been taught and my personal experience, it seems that 
>nitrogen narcosis affects mainly judgement and creative thinking.  It tends 
>NOT to affect performance of routine acts.

I disagree - I don't think we can predict what higher mental processes will
be affected on a given dive.  I do agree that routine/repetitive tasks seem 
to be more easily performed than non-routine tasks as long as they aren't 
concurrent.  Perhaps this is the real basis for tolerance i.e relying on
routine, well-known, well-rehearsed, serial tasks, rather than on higher
functions such as memory or judgement.

As always, let me say that this is just a discussion.  I am not advocating
any particular form or practice of diving.  Narcosis is a very real and 
dangerous phenomenon, and a serious risk that must be carefully evaluated by 
divers.
-- 
Greg Dawe                        | Disclaimer: I don't speak for my employer,
Voice : (508)-490-6666           |             nor they for me...
e-mail: Greg_Dawe@vos.stratus.com|            
Newsgroups: rec.scuba