7 Temperature homeostasis We are mammals; we are homeotherms. Biologically this means that our enzymes are designed to work best at about 37ø C (99ø F). If our body goes much above or below this temperature, the chemical reactions that keep us going simply don't work well. Body temperatures above 42ø (108ø F) are usually fatal or disabling. We can survive cold temperatures much better than warm ones, but rarely can function well below about 31ø (88ø F). Mountain soaring is a particular challenge because the flight may start in hot, dry conditions and proceed fairly quickly to cold, high altitudes near cloud base. If the cloud base is reached, the ambient temperature will be at the dewpoint, which may be 5ø C (41ø F) or less in dry desert conditions. The sweat that formed at low altitudes to save us from disabling hyperthermia becomes dangerous there, for its evaporation accelerates our body's cooling, and wet clothing conducts heat away. Little physical activity is possible in the cockpit that might generate extra warmth through muscle metabolism. Abnormal body temperatures slow thinking and impair judgment just as insidiously and just as surely as fatigue or hypoxia or dehydration; and of course all four factors may commonly combine during a single extended task. Concentrated attention to the basics and disciplined adherence to procedural flying can save you from serious or impulsive errors in judgment or technique at these times. The cardinal warning signal of impending hypothermia is shivering. Shivering begins at a body temperature of about 93ø F. or about 34ø C. If you begin shivering, it's time to descend to much warmer air, and to plan a landing. If you are shivering, count on half an hour to an hour to warm up even if you can quickly get into ambient temperatures above 85ø. The fastest cure for hypothermia is a nice bath at 100-110ø F, not available in any glider or at most glider ports. Temperature management in mountain soaring requires flexibility in managing clothing. Your greatest site of heat loss is your head, especially if balding. In hot conditions, ventilate your scalp and provide a breeze across it; in cold conditions cover it. The second greatest site of heat loss is the front side of your trunk, especially the area of your breastbone. A lightly insulated jacket that can be easily kept open in warm air on the ground and quickly closed at cool altitudes will provide maximum flexibility. Some pilots have a dark windbreaker which they don backwards in flight when it gets cold. Your hands and feet are relatively unimportant in managing your temperature except in extreme conditions, but can get distractingly painful. The chief meaning of cold hands or feet is as a signal that you will become hypothermic if you don't take action to conserve heat better. If you can't do that, land, or play at a warmer altitude. Clues you can use. If your hands or feet get cold, your body is struggling to stay warm. Get warmer somehow or go home. If you begin to shiver, abort the flight as soon as possible by getting into warm conditions. It will take you up to half an hour to warm up satisfactorily after you stop shivering even if you jump into a hot bath (This is the fastest, most effective treatment for hypothermia: it should be not warmer than 43ø C (110ø F).)