The partial pressure of oxygen in the Apollo 1 capsule was about 16.7 PSI.

I had always assumed they just compensated with oxygen pressure to match atmospheric partial oxygen pressure, but I checked and indeed you’re right, but it was only that high an oxgen pressure for testing purposes on the ground. Once in flight, they would have dropped it to 5 PSI. It also makes sense as to why that Apollo 1 fire was so violent. Thanks for that learning opportunity ! :)

Partial pressure of the gases you breathe is what matters though, that’s why astronauts could breathe pure oxygen for days during the Mercury/Gemini/Apollo missions and be fine (as long as there’s no fire :/ ).

There are 850k people living in La Paz, Bolivia (elevation 3650m) with the equivalent of 13.2% sea level oxygen and they seem to be doing just fine. And granted, the natives of the region display some hemoglobin adaptation, but still… Even Aspen, Colorado sits at about 15% sea level oxygen and I’m pretty sure people don’t wear breathing gear while skiing there.

There are 850k people living in La Paz, Bolivia with the equivalent of 13.2% sea level oxygen and they seem to be doing just fine.

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