From: mayne@phi.cs.fsu.edu (William Mayne)
Subject: Re: dangerous misconception (was Re: Human bodies explode...)
Reply-To: mayne@cs.fsu.edu
Organization: Florida State University Computer Science Department
Date: Mon, 16 Nov 92 14:59:52 GMT

In article <1992Nov16.074547.5322@nntp.uoregon.edu> davidw@cie.uoregon.edu (David Weingarten) writes:
>
>Nitrogen Narcosis can occur at depths as shallow as 70-80'.
>SYMPTOMS occur generally at depths around 120'-140'.  That is,
>beyond 100' and you can have truly hazardous effects.  This is,
>of course, dependant on your personal susceptability.

True. I have on a couple of occassions experienced a subtle but
definite nitrogen buzz at 65 feet. I admit that it was so subtle
I probably wouldn't have recognized what was if I hadn't been
experienced with narcosis on much deeper dives. Most of the time
I don't feel anything that shallow.

Individual susceptability does vary, but most people with experience
can tolerate the effects quite well to 130 feet and deeper.
Susceptability of the same individual is quite variable from one
day or even one dive to the next, too. If you are diving deep it
is very important to know what to look out for and to concentrate
on knowing how are you doing so you can abort the dive or get to
shallower water if you need to. Pausing to check how you are
tolerating narcosis (as well as other checks) on the way down is
also a good idea.

>At 300', OXYGEN TOXICITY occurs.  This an ENTIRELY DIFFERENT
>problem and is MUCH more hazardous.  Oxygen Toxicity happens
>suddenly and as subtly as a sledgehammer to your head.  It
>causes violent convulsions and unconsciousness, and, as a result,
>death.  This is not something that we are individually susceptible
>to; it's pretty uniformally deadly, at about 298'.
>
>Anybody diving to 200' and deeper is going to be SERIOUSLY narc'ed.
>Whether they feel panicky, euphoric or start hallucinating varies
>from person to person.  But at 300', getting narc'ed is the LEAST
>of your worries. 

While on the subject of dangerous misconceptions, oxygen toxicity
doesn't kick in suddenly at 298', nor does it usually strike without
any warning. One widely accepted standard is that anything over
1.6 ATA of O_2, which is 218 fsw on air, is risky, particularly
if exposure exceeds 45 minutes. Even more conservative rules are
prudent. Note that I said it doesn't *usually* strike without
warning, not that you can count on getting any warning. But since
it can happen at much less that 300' and there may be some warning
symptoms it is wise to know the symptoms so if you are pushing the
limits, or start to have problems within the usual limits (which is
possible), you can abort the dive. Don't ignore or fail to recognize
symptoms in the belief that there is never any warning.

>p.s. Please be sure about such things before posting them.
>300' for N2 narcosis is a hazardous misconception.  And, as 
>much as people should always check things they read on the
>net, many people don't.

Heed thy own advice. Besides, although I don't practice or advocate
it people do dive to 300 feet breathing air. On a quick bounce dive
the odds of not having an O_2 seizure are actually pretty good.
(That is like saying the 5/6 chance of surviving Russian roulette
are good - not that a sensible person will take the unnecessary risk.)
Narcosis is still a big factor since it may lead to going even deeper,
not coming right back up to safer depths, or other bizarre (sp?) or
fatal behavior. It compounds all other dangers, including O_2.

Bill Mayne
Newsgroups: rec.scuba