Re: [PSUBS-MAILIST] PSUB Fatalities...

["Karl & Shirin Fuller" <fullerk@voyager.co.nz>]

Alex,
Good explanation !
Karl.

>
>   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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