Armstrong limit
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The Armstrong limit, also called Armstrong's line, is a measure of altitude above which atmospheric pressure is sufficiently low that water boils at the normal temperature of the human body. Exposure
The Armstrong limit is above most of Earth's atmosphere.
If the cockpit lost pressure while the aircraft was above the Armstrong limit, even a positive pressure oxygen mask (shown) could not protect the pilot.
A pressure suit developed for high altitude, 1937 (worn by Mario Pezzi)
Kármán line
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The Kármán line is a conventional definition of the edge of space; it is widely but not universally accepted. The international record-keeping body FAI defines the Kármán line at an altitude of 100 ki
Armstrong limit
…Effect of spaceflight on the human body – Medical issues associated with spaceflight Kármán line – Conventional definition of the edge of space Ebullism – Formation of vapour bubbles in bodily fluids due to reduced environmental pressure…
Earth's atmosphere photographed from the International Space Station. The orange and green line of airglow is at roughly the altitude of the Kármán line.
Atmospheric gases scatter the blue wavelengths, thus giving the Earth a blue arc. As the altitude increases the atmosphere decreases such that by several criteria it ceases to exist. Optically the atmospheric halo here gradually fades into the blackness of space.