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My 2 cents on Carbon Monoxide (CO):  The problem with this odorless and
colorless gas is that it binds to hemoglobin in your blood better than O2,
and therefore decreases the ability of your blood cells to transport and
release regular O2 to the tissues--you don't need much of it to cause a
problem, and it is not easy to get rid of, once bound to the hemoglobin.
Getting on O2 mask once symptoms occur is only of marginal benefit, because
the extra O2 you are inhaling still can't catch a ride on your
hemoglobin--the mask's only 2 benefits are a) preventing inhalation of
further cabin CO and b) slightly raising the partial pressure of dissolved
O2 in the blood plasma (which in turn counts for only a few percent of the
O2 carried to your tissues).  Of interest, smokers routinely have 5-10% of
their hemoglobin already bound up by carbon monoxide, so they are starting
in a hole functionally.  Symptoms of labored breathing and headache occur at
levels of 20%, and impaired judgment at 30%.

  NASA maintains rigid criteria for max allowable concentrations in PPM in
the shuttle environment to preclude crew performance degradation, and they
are time-related as follows:  1hr exposure--max CO ppm=55; 24hr
exposure--max CO=20ppm.

Thus for our flights limited to a few hours, the transient noted levels of
41ppm noted by our test pilot should be OK;  more data on phase of flight
exposure, duration of exposure above 20ppm, measuring levels in a
pressurized IVP, etc, would be of interest.
Douglas W. Johnson, MD, FACR
Florida Radiation Oncology Group
(904) 202-7020 Voice
(904) 202-7029 Fax

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