17 Sep 97 23:56, Don Burke wrote to Jay Hanig:
 DB> oxygen of 3.75% at 18,000 feet.... more than enough.  The problem is
 DB> what happens at normal cruising altitudes for the average airliner:  I
 DB> know it'll be less, but I don't know how much less.
 DB> Maybe some of our airline buddies might favor us with with some
 DB> figures of altitude vs atmospheric pressure?
 DB> I can do that.  "Pocket Ref" by Thomas J Glover lists the following:
 DB>   FEET    PSIA
 DB>    820   14.26
 DB> It looks like pure oxygen is the only way at 35,000 or so.
 DB> Nitrox 50 wouldn't hack it above about 23,000.
Thanks very much.  I've archived this message for future discussions.  I 
intuitively knew the answer but didn't have the hard alt vs atm pressure 
figures to back me up.
The math necessary is fairly simple now.  We breath air at sealevel with a 
partial pressure of oxygen of 3 psi.  Take the atmospheric pressure of any 
altitude and multiply it by .2 to get the partial pressure of O2 at altitude.
That is based on air, which is 20% oxygen.
In the case of the 50/50 mix of nitrox, multiply atmospheric pressure (for 
whatever altitude interests you) by .5 to get the partial pressure.   Any 
figure that you derive that has a value of less than 2 isn't doing so well.
2 psi is the equivalent of breathing air at 10,000 feet.
Altitudes above 10,000 feet make me dizzy if I cough.
Jay
--- GoldED/386 2.50+
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