Dear Tom,
Jet aircraft are always pressurized so we are more comfortable. How high can we actually go and still be able to breathe without artificial help?
— Stan Jankowski
Dear Stan,
A specific “safe height” does not exist, because it depends on your physical condition and the duration of your high-altitude visit, but there are limits on how high we can go. Breathing becomes more difficult with increasing altitude.
The density of air decreases as we go higher, and the amount of oxygen also decreases (although its proportion in the mix of gases stays constant). It is the lack of oxygen that actually limits the “safe breathing height.”
An elevation of about 20,000 feet above sea level is the maximum altitude at which sufficient oxygen exists in the air to sustain us long-term. By comparison, the summit of the Earth’s highest mountain, Mt. Everest, sits at 29,029 feet, commercial jet aircraft routinely cruise at 35,000 to 40,000 feet and thunderstorms build to 40,000 to 60,000 feet.
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