TEMPERATURE STRESS

physiological stress induced by excessive heat or cold that can impair functioning and cause injury or death. Exposure to intense heat increases body temperature and pulse rate. If body temperature is sufficiently high, sweating may cease, the skin may become dry, and deeper and faster breathing may follow. Headaches, nausea, disorientation, fainting, and unconsciousness also may occur. The initial symptom of cold stress is pain in exposed areas. Continued exposure may lead to numbness, mental confusion, lethargy, and irregular heartbeat. Temperature stress is a particular problem in aerospace medicine, and elaborate precautions must be taken to protect fliers and astronauts from it. Between 30,000 and 40,000 feet (9,000 and 12,000 m), the cruising altitude of most jet aircraft, air temperature ranges from -40 F to -70 F (-40 C to -57 C). Modern aircraft have sealed cabins and heaters to protect pilots and passengers from wind blast and cold air. Protective clothing and electrically heated flight suits are used when exposure to the open air is possible. Above 100,000 feet (30,000 m), the sun's radiant heat can be intense. Supersonic aircraft, which sometimes fly at such altitudes, also must withstand frictional heat caused by high speed. Such vehicles are made of heat-resistant materials and have air-conditioned cabins or cockpits. Fliers also wear reflective outerwear and ventilated or porous clothing to promote circulation of air in order to permit perspiration. Spacecraft and space suits utilize special insulation, air-conditioning, and heating units to maintain a balance between the excessive heat and cold encountered in the vacuum of space. Excessive heat arises from solar radiation, human metabolism, operation of on-board equipment, and (while passing through Earth's atmosphere) atmospheric friction. Extreme cold arises when an astronaut or a spacecraft remains in the shadow of another object long enough for internal heat to radiate into space. See also hypothermia; heatstroke.