Newsgroups: sci.space.shuttle
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: What Atmosphere in Shuttle...in MIR??
Date: Fri, 8 Aug 1997 14:03:58 GMT

In article <33E90ECC.B90@greenms.com>,
Greg d. Moore <mooregr@greenms.com> wrote:
>> >       BTW, shouldn't a percentage of that be C02?
>> Only a very small one.  (And that too is an issue of debate.  Holding the
>> CO2 level down to what's normal on Earth's surface is quite difficult...
>
>	What is the Earth's surface normal % of CO2?

It's a bit variable, but the nominal number is 0.04%, about 0.3 torr.

The lithium-hydroxide systems used in short-duration systems like Apollo
and the usual shuttle hardware can hold it to about 1 torr.

Molecular-sieve systems -- used on Skylab, tested on the shuttle for
long-duration flights, and intended (last I heard) for the station -- have
the advantage of needing no consumables, but the disadvantage of being
unable to get the CO2 down much below 5 torr.

Anything above 7.6 torr (1%) is considered undesirable, and 15 torr (2%)
or more is considered an emergency (i.e., shuttle crews don oxygen masks).

Short-term exposures to 1% have no detectable effect, and 2% has detectable
but not serious effects.  Long-term exposures (weeks) show detectable
biochemical changes, considered indicative of mild stress, starting between
5 and 10 torr.
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu