Armstrong limit

Armstrong Limit is a measure of altitude above which atmospheric pressure is sufficiently low that water boils at the normal temperature of the human body. It is named after Harry George Armstrong, an American physician, who founded the field of aerospace medicine.

Overview

The Armstrong Limit is defined as the altitude at which the atmospheric pressure is down to 6.3 kPa (47 mm Hg), which is a level at which water boils at 37°C (98.6°F), the normal body temperature of humans. This limit is located at an altitude of about 18–19 km (11–12 miles) above sea level under average atmospheric conditions.

Implications

Above the Armstrong Limit, exposed body fluids such as saliva, tears, urine, and the water in lungs and tissues would boil away without a full-body pressure suit or a pressurized capsule. However, the skin and circulatory system can prevent this effect and keep the body under pressure, but this is not enough to keep the body safe for more than a few minutes.

Safety Measures

To survive above the Armstrong Limit, humans must wear a full pressure suit or be within a pressurized capsule. This is why astronauts wear pressure suits during certain phases of spaceflight, and why high-altitude pilots and balloonists use pressure suits or pressurized capsules.

See Also

• Aerospace Medicine
• Atmospheric Pressure
• Pressure Suit
• Space Medicine

References

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