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

["Sean T. Stevenson" <ststev@uniserve.com>]

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