Dave wrote:
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

The figures I quoted came from NIOSH, and the ppm (parts per million)
are in air. NIOSH's Immediately Dangerous to Life and Health mean
just that -- 40,000 ppm would kill you even though that would be only
..04% if I've got my decimals correct. You could still have enough
oxygen (20%) in air to sustain life even with that amount of carbon
dioxide in the air, but you would have symptoms including headache,
dizziness, restlessness, paresthesia; dyspnea (breathing difficulty);
sweating, malaise (vague feeling of discomfort); increased heart rate,
cardiac output, blood pressure; coma; asphyxia; convulsions; or
frostbite (if it was liquid, or dry ice)

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.

No you couldn't live for any period of time with that amount of CO2 in
the air like you could with helium which is really an inert gas. It
is a simple asphyxiant but you don't have to have 81% of it in the air
to die from it. It screws up your brain's notice to the body to
breathe. Any gas that displaces oxygen down below about 19% will
asphyxiate you whether it is poisonous or not. For instance Freon or
an excess of nitrogen will both do it.

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.

Yes you can be poisoned by CO even in the presence of plenty of O2.
Of course it is also true that any burning or other oxidation produces
CO2, but when there's insufficient O2 to form CO2, the CO will be
formed instead. Other poisonous gases are chlorine, and of course
cyanide.

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.

OK - I was thinking of industrial uses of pure oxygen. Big tanks of
pure oxygen like they have in hospitals or places where they do a lot
of oxyacetylene welding can cause fire problems.

grandma Rosalie