On Wed, 10 Mar 2004 11:46:52 -0500, "Leslie Swartz"
wrote:

You live off off something called the "partial pressure of oxygen" in the
medium you are breathing. As altitude increases, the partial pressure of
oxygen in air decreases. Therefore, you must "enrich" the breathing medium
with more oxygen in order to achieve the *same* partial pressure of oxygen
that exists at lower altitudes.

Two solutions: 1) increase the relative percentage of oxygen inht e
medium, or 2) pressurize hte medium. 1) is much less expensive than 2).

Steve Swartz

(The partial pressure of oxygen is what gets the O2 across your lung tissue
into your bloodstream. As total pressure decreases, the partial pressure of
oxygen decreases. Eventually, as ambient pressure goes down, you would need
to breathe pure *pressurized* [3.2 psi IIRC] oxygen in order to make up the
deficit.)

"Arquebus257WeaMag" wrote in message
om...
Im just wondering why pure oxygen is used for high altitude flying
instead of regular air. I thought prolonged exposures to breathing
pure oxygen can be harmfull as you can become oxygen dependant.

Same basic idea of the PPO2 is why SCUBA divers going down need to cut
the oxy levels of their breathing gas down to avoid PPO2 levels above
1.4 ATA... so you can find divers using as low as 5% oxy in a deep
dive Trimix (Oxy, Nitrogen, and Helium) bottom gas