Armstrong limit

Armstrong Limit

The Armstrong limit, also known as Armstrong's line, is the altitude above which atmospheric pressure is sufficiently low that water boils at the normal temperature of the human body, approximately 37 °C (98.6 °F). This limit is named after Harry George Armstrong, who was a pioneering figure in aviation medicine.

Atmospheric Pressure and Boiling Point

Comparison of International Standard Atmosphere for space diving

At sea level, the atmospheric pressure is about 101.3 kPa (14.7 psi), which is sufficient to keep water in a liquid state at body temperature. However, as altitude increases, atmospheric pressure decreases. At the Armstrong limit, which is approximately 18,900 meters (62,000 feet) above sea level, the pressure drops to about 6.3 kPa (0.91 psi). At this pressure, the boiling point of water matches the normal body temperature.

Implications for Human Physiology

Above the Armstrong limit, humans cannot survive without a pressurized environment. If exposed to such low pressures, the moisture in the lungs and other body tissues would begin to boil, leading to a condition known as ebullism. This is a serious medical emergency that can result in rapid loss of consciousness and death if not addressed immediately.

F-16 pilot closeup

To prevent ebullism and other altitude-related health issues, pilots and astronauts use pressurized suits or cabins. These environments maintain a pressure similar to that at lower altitudes, allowing the body to function normally.

Historical Context and Research

The concept of the Armstrong limit was first identified in the 1940s by Harry George Armstrong, who was studying the effects of high-altitude flight on human physiology. His research laid the groundwork for modern aviation and space medicine.

Caproni Ca.161 pilot

Applications in Aviation and Space Exploration

The Armstrong limit is a critical consideration in the design of high-altitude aircraft and spacecraft. For example, pilots of high-altitude reconnaissance aircraft, such as the Lockheed U-2, must wear pressure suits to protect against the low-pressure environment.

High-altitude balloon during ATLAS0 mission

In space exploration, the Armstrong limit is surpassed by the vacuum of space, where pressure is effectively zero. Spacecraft and space suits are designed to provide a pressurized environment to ensure the safety and survival of astronauts.

Related Pages

• Aviation medicine
• Space medicine
• Ebullism
• Pressure suit
• High-altitude flight