Re: [PSUBS-MAILIST] Life Support Revisited

[Jonathan Wallace <jon@psubs.org>]

>The simple fact that there has NEVER (in recorded history) been a survivor of
>a "compartment fire" in which the PO2 was greater than 25%!

I'm not doubting the fire hazards involved with a higher than normal PO2.
I'm trying to understand the relationship between pressure in the vessel,
metabolizing O2, and adding O2 based upon a pressure standard.

Let me see if I can clarify what I'm looking for with another hypothetical
example.  If I close the hatch and note that I have an internal pressure of
30.00 (inches mercury) and a P02 of .2, I consider that my "dive atmosphere
standard".  If everything worked perfectly, when I came back to the surface
the internal pressure of my vessel would still be 30.00 and the PO2 would
still be .2 regardless of how many hours I had spent in the dive.

Now, I breathe and metabolize O2, and exhale C02.  The PO2 in the vessel
drops from .2 to .19999 and the CO2 finds it's way to the scrubber and is
collected causing the pressure in the vessel to drop to 29.999.  The very
sensitive barometric valve in this case, opens and allows in enough O2 to
bring the pressure in the vessel back up to 30.00.  Let's assume I hold my
breath for arguments sake so that I haven't altered the atmosphere any
further.

Is the PO2 now back at .2 or is it higher because I've bled pure oxygen 
into the cabin?  


Jon