Re: [PSUBS-MAILIST] Epilepsy (was: A question for you Scuba guys)

[John Brownlee <jonnie@cobweb.scarymonsters.net>]

	Well, I just started reading for my enriched air class down in
Mey-hi-co, and I would feel it necessary to put two things on the table to
think about when considering worst-case bail-outs on 1atm subs:

	1. Under high enough pressures (>1.6bar) oxygen is toxic to your
central nervous system in a big way, and this toxicity can occur in rapid
and frightening ways. The most common and dangerous symptom is akin to
grand mal seizures, something that on a plain old regulator is
disasterous. A K-350 at max operating depth is in the hunt for O2
toxicity when free-flooded for a bail-out, though short exposure times
work in your favor. O2 toxicity is more of an issue for bail-outs than any
narcosis, IMHO.

	2. All things considered, drowning sucks. It's important when
running scenarios against scuba tables for gas use, etc. to remember the
difference between the pressure exposure profiles used to calculate them
vs. going from 1atm to many atms in a hurry. Better bent/O2 poisoned than
dead.

	Knowing a little thing about O2 CNS toxicity and the potentially
rapid onset in some people, I think I'd probably want my bail-out to be a
full face mask. That way if you're deep (i.e on the bottom 250 feet down
after an uncontrolled dive) and you have trouble getting out you don't
have to worry about a long exposure to potentially poisonous O2
concentrations and drowning, at least you still breathe. People with
epilepsy in their history are supposedly more succeptable to this
poisoning, though there isn't a lot of evidence for obvious reasons.
	Another thought: depending on your bail-out gear are you
positively buoyant? -HOW- positively buoyant are you, do you need
floatation? You'd think the answers were yes and plenty, respectively but
it pays to check in contingency planning.
	A little knowledge is a dangerous thing, and I haven't actually
done the wet part of the class yet. Just thought this was interesting
considering I started reading the nitrox book tonight and saw this on the
list. If your boat is actually going to be operated below 120fsw you
should at least think about it. You might also consider some basic nitrox
scuba if you're already carrying a PADI C-card, it's not expensive to do
the basic training and you learn a lot about gas toxicity at depth. At
least I have.

						Onwards!

							John

John Brownlee
Chief Systems Administrator
Scary Monsters Network
jonnie at scarymonsters dot net