I don't know what I'm talking about!

Given that:

I'm of the impression that Rosalie is wrong, ie. CO2 is not "poisonous".
I also think that Dave is wrong.
I don't think that I would survive on a mixture of 80% CO2 and 20% O2. The
process of living is not unlike combustion in that the body converts "food"
using O2 to produce energy with a byproduct of CO2. The body needs to
eliminate that byproduct through the lungs. If the partial pressure of CO2
is high, then the transfer of CO2 "out" can't happen (efficiently) and
consequently the transfer of O2 "in" won't happen (enough). I have no idea
what the ratios of partial pressure are that would result in problems are
but suspect that they are finite.

Please refer to the first sentence.
BF


"Dave" wrote in message
...
On Sat, 12 Nov 2005 22:42:24 GMT, Rosalie B.
said:

Actually an excess of CO2 can be a problem, it's just a problem at a
higher concentration than CO is. The IDLH (immediately dangerous to
life and health) limit for CO2 is 40,000 ppm whereas CO has an IDLH
of 1200 ppm

CO2 is regarded as a simple asphixiant, just like an excess of
nitrogen or any other inert gas.

You're exhibiting the same confusion. The difference between CO2 and CO is
that CO2 may displace oxygen in the air, reducing the oxygen concentration
below the level required to sustain life. It is, as you say, an
asphixiant,
but is not a poison. I suspect that the assumption behind the figures you
quote is that the remaining gas other than the CO2 is air. Unless I'm
mistaken, you could live for an indefinite period breathing a mixture of
80%
CO2 and 20% O2, just as you could live for an indefinite period breathing
80% helium and 20% O2. CO2, being inert, doesn't combine with anything in
your blood's hemoglobin to block oxygen transport.

CO on the other hand, is a true poison in that even if there is enough
oxygen in the air to sustain life, the CO would prevent the blood from
transporting the oxygen from the lungs to the brain and other organs.

Matter of fact, O2 at high pressure and concentration is poisonous,
leading
to convulsions and ultimately death..

Most of the time what happens with O2 in excess of 23.5% is that there
is so much danger of fire (asphalt becomes combustible in pure
oxygen).

The context I'm familiar with is diving, where part of the decompression
process when you've been breathing helium oxygen mixture involves
switching
to pure O2 at the 60 ft. stop to reduce the partial pressure of the helium
and flush it out of your system. Can't switch at lower depths because of
the
risk of O2 poisoning at higher pressures.