>[!abstract] >The Armstrong limit or 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 to pressure below this limit results in a rapid loss of consciousness, followed by a series of changes to cardiovascular and neurological functions, and eventually death, unless pressure is restored within 60–90 seconds. > >At or above the Armstrong limit, exposed body fluids such as saliva, tears, urine, and the liquids wetting the alveoli within the lungs—but not vascular blood (blood within the circulatory system)—will boil away if the subject does not wear a full-body pressure suit. > >On Earth, the limit is around 18–19 km (11–12 mi; 59,000–62,000 ft) above sea level, above which atmospheric air pressure drops below 0.0618 atm. The U.S. Standard Atmospheric model sets the Armstrong limit at an altitude of 63,000 feet (19,202 m). > >The term is named after United States Air Force General Harry George Armstrong, who was the first to recognize this phenomenon. (Wikipedia, 2025). >[!related] >- **North** (upstream): — >- **West** (similar): [[Time of useful consciousness]] >- **East** (different): — >- **South** (downstream): —