Pressure suit

A pressure suit is an environmental suit worn when atmospheric pressure gets too low or too high to be survivable without. The minimum survivable pressure corresponds with an altitude of 15,000 meters above the surface of Earth, where the pressure dips to 102 millibars. Pressure suits must thus be worn by pilots who fly at high altitudes, unless the cabin of the airplane is pressurized. There's partial pressure suits and full pressure suits spacesuits are examples of the latter.

 Background 
The region from sea level to around 3,000 m (10,000 ft) is known as the physiological-efficient zone. Oxygen levels are usually high.

The physiological-deficient zone extends from 3,600 m (12,000 ft) to about 15,000 m (50,000 ft). There is an increased risk of problems such as hypoxia, trapped-gas dysbarism (where gas trapped in the body expands), and evolved-gas dysbarism (where dissolved gases such as nitrogen may form in the tissues, i.e., decompression sickness). Above approximately 4,267 m (14,000 ft), an oxygen-rich breathing mixture is required to approximate the oxygen available in the lower atmosphere, while above 12,000 m (40,000 ft), oxygen must be under positive pressure. Above 15,000 m (49,000 ft), respiration is not possible because the pressure at which the lungs excrete carbon dioxide (approximately 87 mmHg) exceeds outside air pressure. Above 19,000 m (62,000 ft), also known as the Armstrong limit, fluids in the throat and lungs will boil away. Generally, 100% oxygen is used to maintain an equivalent altitude of 3,000 m (10,000 ft).

Conversely, a hard diving suit protects against the extreme pressures deep below the surface of the ocean (below around 400 meters).

Category:Environmental suits