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

[Phil Nuytten <72020.572@compuserve.com>]

Hi, Pat:
        The choice of escape mix would depend on the proposed depth of
operations.  .I'd use air down to a depth that I was comfortable with . .
probably  350 feet or so  . .then ( for depths greater)  add the minumum
helium   consistent with maintaing an equivalent air depth of 350 and a
relative oxygen depth of about 90 feet. The idea is to use a gas that is
slower on the uptake than He . .the bottom exposure time will be short, but
the driving pressure is high . .so you want to both keep the inert gas at
the lowest tissue level possible and get the highest ratio of blood gas
pressure to ambient  pressure without  triggering bubble formation.  I pick
these numbers because they are real ones to me. I have breathed pure O2 at
ninety feet for 15 minutes on a number of occasions ( during O2 tolerence
tests/ decom table trials) and can tolerate deep air quite well ( during
the HeO2 surface bounce era it was critical to switch back to air as deep
as possible - to shorten bottom time on Heo2 and increase O2
percentage/pressure -  some guys handle it well, some do not. - A deep
swithch-back really rattles your cage!) More important than precise
designer gas mixtures  is the ability to flood fast and to have ballast air
and O2 plumbed in a manner that you can dump everything you've got  into
the cabin if you have to hit the road. All of this consistent with the
certifying agency requirement for O2 hull stops, - separation of O2 supply
containers to ensure that you cant accidentally dump a large HP cylinder of
O2 in to the cabin- etc.etc.
        Get out quick! - then streak to the light!  A good time to shoot
for ( from start of pressurization to start of ascent ) would be 3 minutes
or less. This means large flood valves or other flood means and lots of
blow-down gas. All of this is relative to depth. It's an easy matter to
figure out the best escape options for a 300 foot-rated sub compared to a
1000 feet. Past a thousand?? Hmmm . .Ascent rates: figure 200 to 300 feet
per minute for buoyant ascent. Please note usual disclaimer on the
foregoing:. These are my own opinions and I do not suggest that you use
them as a basis for your own decisions.
Phil Nuytten