OT Spacecraft atmosphere (was Re: Magnetic Memory making a comeback?)

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Wed Jun 11 21:06:00 2003

--- Brian Chase <vaxzilla_at_jarai.org> wrote:
> On Wed, 11 Jun 2003, TeoZ wrote:
>
> > Never heard of the lower pressure before. I thaught humans breath
> > because of the buildup of co2.

That, and to intake O2.

> > So lowering the pressure and just using oxygen wouldnt help much
> > would it?

On the contrary... (see below)

> > Besides 100% oxygen makes things
> > that are normally low combustible highly combustible.

That is certainly true.
 
> Take a cubic meter of air at STP. Remove all the non-essential gasses,
> leaving only the oxygen behind. You'll end up with same amount of
> oxygen necessary to support human life, but the overall pressure will
> be lower owing to the lack of those useless gasses.
>
> Well, that's my educated guess at least.

That's it. It's due to the partial pressure gas law... our respiratory
systems depend on there being O2 at around 0.20 atmospheres. It doesn't
really matter (within limits) what "inert" gasses are mixed with it.
It's not about total pressure - it's only the partial pressures of the
individual consituents that matter for the a variety of physical processes
to work, including respiration. CO2 is used as a regulator as well as
being a waste gas - we detect CO2 buildup in our lungs and regulate
the breathing rate to keep it down below, IIRC, 1%-2%.

Heliox is great for diving because it's a mix of O2 plus He2 to about
one Atm... solves the pressure problem at depth plus the problem of
N2 at depth being bad for you. Other gasses would work, too, but
AFAIK, He2 is used for cost as well as inertness (by-product of the
natural gas industry, IIRC). As an aside, there's a heliox tank
that visitors can suck on at the local science museum. All the
fun of a Donald-Duck-voice without the unpleasant side-effects of
pure Helium! (asphyxiation, embolism, etc.)

Humans can survive in a 100% oxygen atmosphere at ~20-25% of pressure
at sea-level, but there are other, non-biological consequences, mainly
severely increased risk of fire.

-ethan
Received on Wed Jun 11 2003 - 21:06:00 BST