The “Armstrong Limit” Is A Measurement Of The Maximum Amount Of What A Human Can Edure?
Answer: Altitude Without Protective Gear
If it’s been a few years since your high school physics course, then let’s do a quick refresh of the most fundamental concept required to appreciate what the Armstrong limit is. The boiling point of a liquid is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure surrounding the liquid. If you raise the atmospheric pressure, the temperature at which the liquid boils will rise. If you decrease the atmospheric pressure, the temperature at which the liquid boils will decrease. For example, water boils at 212 °F if you’re at sea level, but boils at only 203 °F if you’re one mile above sea level in, say, Denver, Colorado. Keep climbing up into the atmosphere and the temperature required to boil water drops. Climb high enough and the temperature required becomes that of the human body, and the very water on your tongue will boil with nothing more required than the heat of your tissue. That’s when you’ve reached the Armstrong limit.
Once you’re at that limit or higher, any exposed body fluids: the saliva in your mouth, the water that keeps the alveoli in your lungs wet, your tears, and so on, will boil away. Not only is this absolutely disconcerting, but you black out very quickly as the entire affair inhibits your very ability to breathe and absorb oxygen. If there is any silver lining to this, however, at least it’s that we’re using the term “boil” here in the purely scientific sense and not in the colloquial sense. The boiling you would feel on your tongue wouldn’t be scalding hot and damaging to your tissue, it would be more akin to having a mouthful of pop rocks candy wherein you could feel the water change states and the vapor pop and move off your tongue.
Now if all of this has you completely freaked out about the idea of being anywhere above sea level, let alone in an airplane, don’t worry. The Armstrong limit is only relevant to people who find themselves at elevations reserved for military flights. The Armstrong limit on Earth kicks in at approximately 59,000 feet above sea level, which is about twice the height that commercial flights fly at.
Finally, a bit of extra trivia to wrap up the whole treatment of the subject. The Armstrong limit is not named after Neil Armstrong, no matter how natural the association might be, but General Harry George Armstrong of the United States Air Force. General Armstrong was the first person to recognize the phenomenon.
Image courtesy of the USAF/Public Domain.