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

["Vikking" <vikking@mindspring.com>]

Sean, how about if we run some simulations,here on the forum to resume all
the good ideas about safety.

lets say a psubs of an average size, that we can all agree, average internal
volume etc.

lets say it suffers a midwater collision whith a submerge structure at 30
meters.
we can start whith a list of specifications so every member of psubs can
collaborate on his field of expertise

any takers?

Gabriel Feldman


----- Original Message -----
From: Sean T. Stevenson <ststev@uniserve.com>
To: Carsten Standfuß <MerlinSub@t-online.de>;
<personal_submersibles@psubs.org>
Sent: Tuesday, March 07, 2000 4:48 PM
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
>
>