jb (11/19/82)
This information was gathered from several publications prepared for glider pilots involved in high altitude soaring. Generally speaking, to maintain a reasonable level of arterial oxygen, supplemental breathing oxygen is required above 12,000 feet. At about 34k feet ambient pressure is down to about 1/4 atmosphere, and you must be breathing 100% oxygen. Above that altitude, pure oxygen is required at more than ambient pressure. Oxygen systems used above 30k feet effectively pressurize the lungs, reversing the normal ventilation cycle (exhaling takes a conscious effort, while inhaling is passive). Above about 50k feet, ~.11 atmosphere, a pressure suit or capsule is required to pressurize the entire body. Boiling of body fluids becomes a problem at about 63k feet, .06 atmosphere. It would seem to me that breathing pure oxygen at .1 atmosphere would be asking for trouble. However, a pressure in the neighborhood of .2 would be workable. Anybody have more information? By the way, the world record for altitude in soaring flight is 46,267 feet, set in 1961 in the U.S. At that altitude, a pilot has about 12 seconds of useful consciousness if the oxygen system fails. My personal high point in a glider is a little over 30k feet.
REM@MIT-MC@sri-unix (11/23/82)
From: Robert Elton Maas <REM at MIT-MC> Thanks for the fine info. That sounds like a good manual. One more question, does it say how long at zero pressure the human body can remain before boiling of body fluids causes damage to the body? (Like is it just a half second from vacuum to death, or could somebody "hold their breath" for 5 seconds while turning the pressure back on after an accidental depressurization?)