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Re: [PSUBS-MAILIST] PSUB Fatalities...
There are several excellent reference books on this
matter ( I have the *bible* of dive physiology around
here somewhere - can't remember the exact blah title
"Dive Physiology 3rd edition" or something exciting
like that) and a trip to the local University Medial
Library yields much information.
I beleive what Sean was referring to the fact that
an O2 partial pressure over about 1.8 ATM for a short
time and 1.6 ATM for an extended duration (at least
these are the numbers I've known... research may show
differently now... it has a habit of doing so every
few years :-) ) are to be avoided.
At the surface, you are only inspiring *approx* .21
ATM of oxygen (partial pressures here - Normal surface
air is approx 21% O2) ... you head to 90m, talking
approximately 10 times the pressure, hence approx 10
times the ppo2 = 2.1ATM, which (if I'm not mistaken)
would be nicely under the convulsion curve for most
people. Although people with years of experience in
fouling up the blood gasses tend to behave a little
differently (in a lot of ways :-)) and have a habit of
producing a very high number of outlying points...
<soapbox>
It's my opinion (which is admittedly not worth much)
that anyone who is going to (potentially even) be
inspiring air from a compressed source be familiar
with basic dive physiology... a beginning SCUBA class
is a good start, and keeps you safe *within the
boundaries they set*. Psubbing lies far enough
outside these bounds (sinking boat/deepwater/etc) that
thoses rules do not even address all of the possible
pitfalls... i.e. one could be blissfully unaware of
fatal combinations of factors that "I didn't know
about". I implore everyone to spend 30-40 hours or
more reading (everything's not on the internet yet)
about such matters. Tech diving journals, Commercial
diving journals, anything. It's cold, dark and full
of old boots down there! Try not to stay!
</soapbox>
p.s. Please don't flame me. My asbestos underwear is
in the wash
Alex
--- Karl & Shirin Fuller <fullerk@voyager.co.nz>
wrote:
>
> ----- Original Message -----
> From: Sean T. Stevenson <ststev@uniserve.com>
> To: Carsten Standfuß <MerlinSub@t-online.de>;
> <personal_submersibles@psubs.org>
> Sent: 8 March 2000 10:48
> Subject: Re: [PSUBS-MAILIST] PSUB Fatalities...
>
>
> > On Tue, 07 Mar 2000 19:58:06 +0100, Carsten
> Standfuá wrote:
> >
> > >The bottom time for free escape without stopping
> is about 1 minute in
> > >90m deep...
> > >Its 2 minutes in 80 m deep,
> > >Its 2 minutes in 70 m deep,
> > >Its 3 minutes in 60 m deep,
> > >Its 4 minutes in 50 m deep,
> > >Its 7 minutes in 40 m deep,
> > >Its 17 minutes in 30 m deep,
> > >Its 45 minutes in 20 m deep,
> > >Its 653 minutes in 9 m deep,
> > >
> > >Carsten
> >
> > Sorry to have to call you on this, Carsten, but
> it's garbage. Where
> > are you getting these numbers from? You can not
> do a free ascent
> > without stopping while using an escape aid, and
> expect to be fine
> > because you are within the NDL of some arbitrary
> table. Most common
> > dive tables (PADI, NAUI, BSAC, TDI, IANTD, et al)
> utilize neo Haldanean
> > compartment based decompression models, the most
> common of these being
> > A.A. Buhlmann's ZHL-12 algorithm (Navy and DCIEM
> are experimentally
> > derived representations of the same thing). The
> Buhlman model assumes
> > a 33 foot per minute ascent rate (the equivalent
> of making a 20 second
> > stop every ten feet throughout the ascent). The
> tables distributed by
> > the dive training agencies are generously padded,
> but considering your
> > likely ascent rate during a psub escape (using
> liftbags etc.) the model
> > goes right out the window. Add to that the fact
> that, in the event of
> > flooding the psub, the trapped air inside
> (previously at 1 atm) is
> > compressed, and at 90 meters would have a partial
> pressure of 2.1 atm -
> > extremely dangerous in the water. To avoid any
> sort of oxygen toxicity
> > problem you would need to go on your escape gas
> from the start, which
> > contraindicates using a bailout cyclinder with as
> limited a volume as a
> > spare air.
> >
> > I don't know how long the procedure of flooding
> the sub, opening the
> > hatch and getting out would take, but I wouldn't
> bet my life on being
> > able to do it on a breath hold. Heliox 16 is the
> most logical choice
> > for a bailout gas, because it gives the deepest
> range that is
> > breathable all the way up, and eliminates the
> nitrogen to minimize the
> > severity of the bend. (When I say "bend" I mean
> it in the
> > physiological context. In some instances it may
> be entirely
> > sub-clinical.) This is a bit of a moot point.
> Regardless of
> > circumstances I would rather be bent and alive
> than the alternative...
> > Obviously, the less time at depth the better, but
> your numbers don't
> > really apply.
> >
> > When discussing these escape scenarios, I was
> thinking more along the
> > lines of a catastrophic loss of hull integrity,
> caused by a cracked
> > viewport or failed through-hull fitting. If I
> were merely disabled,
> > provided I wasn't going to sink to the crush
> depth, I would just sit
> > and wait for assistance until the life support ran
> out before bailing.
> >
> > -Sean
>
> Sean,
> You are quick to rubbish someone else's figures,
> where are your own to
> enlighten us all ?
>
> > Add to that the fact that, in the event of
> > flooding the psub, the trapped air inside
> (previously at 1 atm) is
> > compressed, and at 90 meters would have a partial
> pressure of 2.1 atm -
> > extremely dangerous in the water.
> Do I understand that you are saying, that at a depth
> of 90 meters, you have
> a pressure of 2.1 atmospheres ? At 1 atmosphere per
> 10 meters, I think you
> have made an error Sean.
>
> Karl.
>
>
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