Oxygen partial pressures and lifde support.
Can somebody bail me out here, I'm tying myself in knots.
(1) Air is 21% Oxygen
(2) Based upon ISA, the partial pressure of Oxygen at 10,000ft would be about 0.687668 x 0.21 = 0.145.
(3) So, 100% Oxygen at this partial pressure should give an equivalent level of human body performance – in this case at about 45,000ft from my standard atmosphere tables.
(4) However, I know that 25,000ft is generally quoted as the limit for breathing 100% unpressurised oxygen.
Why the difference? Is it just down to a reduced efficiency of the lungs at low pressures, or am I missing something?
G