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As a physician, I must comment on the issue of CO and its "half-life."

As a practical matter, the affinity of CO for the hemoglobin molecule in red
blood cells is so high that the bond is generally considered irreversible in
the short term (210 times the strength of the oxygen bond). Oxygen binds in
the lungs and is then released in the periphery. CO binds in the lungs and
does not let go. It also leads to rubeosis (a reddish coloration of the
skin) which mimics the appearance of good oxygenation.

A CO concentration of 0.5mm Hg (658 ppm) allows CO to compete equally with
oxygen, and will result in 50% of the hemoglobin being bound to CO. The best
that you can achieve with normal breathing of oxygen in this circumstance is
to bring the oxygen level up to the normal level of oxygen in the veins
coming to the lungs! That's low! Further, carboxyhemoglobin interferes with
the release of oxygen from oxyhemoglobin, making the situation worse.

Generally, carboxyhemoglobin at levels less than 10% causes no symptoms.
(Smokers run around with CO Hgb levels of 3-7% all the time.) CO at 0.01%
will not raise CO Hgb above 10%. 0.05% CO with light activity (building?)
for 1 hour will yield 20% CO Hgb. This will tend to cause a light or
throbbing headache. Greater activity or longer exposure can raise CO Hgb to
30-50%. At this point symptoms include headache, visual disturbances,
nausea, vomiting, and fainting on exertion. Co Hgb over 50% can lead to
coma, convulsions, respiratory failure, and death.

On the ground it is tough to get in trouble. At altitude, the situation
changes. Because there is less oxygen, CO becomes a proportionally greater
problem as cabin pressure altitude increases.

The treatment for CO poisoning is 100% oxygen. At that level, the oxygen can
slowly replace the CO on the hemoglobin.

In your garage, if the alarm sounds, you are still safe, but it is time to
ventilate and get out. At altitude, go on oxygen ASAP at high flows and get
on the ground.

If at any time you are concerned that you may have a problem, a blood gas
analysis ($50-$100, and a needle stick) can measure CO Hgb directly. Don't
play with it.

Ted Noel MD

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