Blood does not actually boil at a specific altitude, but rather the ambient pressure surrounding a human body becomes so low that water within the body starts to boil at normal body temperature. This occurs at an altitude of approximately 60,000 to 62,000 feet (18,288 to 18,898 meters).
Understanding the Boiling Point
The boiling point of a liquid is the temperature at which its vapor pressure equals the surrounding atmospheric pressure. As altitude increases, atmospheric pressure decreases. This means that at higher altitudes, water will boil at lower temperatures. The boiling point of water at sea level (1 atmosphere of pressure) is 100°C (212°F). At the altitudes we're discussing, the atmospheric pressure is so low that water within the body, typically around 37°C (98.6°F), begins to boil.
Armstrong Limit
This altitude range is known as the Armstrong Limit or Armstrong Line, named after US Air Force General Harry G. Armstrong. It's the altitude at which atmospheric pressure is so low that human body fluids start to boil at body temperature, leading to rapid death in an unpressurized environment.
| Feature | Description |
|---|---|
| Armstrong Limit | 60,000 to 62,000 feet (18,288 to 18,898 meters) |
| Effect | Water within the body boils at body temperature. |
| Cause | Dramatically reduced atmospheric pressure |
| Consequence | Rapid loss of consciousness and death without a pressurized environment. |
Practical Implications
- Space Travel: Astronauts use pressurized suits and spacecraft to prevent this phenomenon.
- High-Altitude Flying: Pilots and passengers in commercial aircraft rely on pressurized cabins.
- Mountaineering: While climbers don't reach altitudes where blood boils, they must still consider the effects of low air pressure and oxygen levels.
It's important to remember that the human body cannot survive in an unpressurized environment at or above the Armstrong Limit due to the physics of boiling point changes with pressure. The water within your body would vaporize if exposed to this atmospheric pressure, causing rapid death.
