Cold kills. A rain-soaked hiker wearing cotton clothing loses body heat at about the same rate as someone immersed in water. Immersed in 40-degree water, that person has about 20 to 40 minutes before losing so much heat that he is probably beyond recovery. In 32-degree water he is in imminent danger of dying after 10 minutes exposure.

Failure to maintain a normal 98.6-degree body temperature is called hypothermia. It is the number one killer of outdoorsmen partly because many people cannot believe the 30- to 50-degree range in which it usually occurs is dangerous.

Hypothermia typically sets in when an outdoorsman is exposed to: a soaking rain on a spring or fall day, a shower on a mountain trail in summer, the piercing shock of icy water when a sailboat capsizes. The common denominators are temperatures below about 70 degrees and being wet. Lengthy exposure to winter temperatures can also result in hypothermia.

Most sportsmen anticipate severe weather in colder months and dress for it. But in warmer months, the need for insulation provided by appropriate clothing is not as obvious and many cases of hypothermia result when temperatures are well above freezing. Wet clothing has little insulating quality and wind causes evaporation, accelerating the loss of body heat.

The early symptoms of hypothermia are frequently ignored: numb fingers and toes; pale skin color; loss of dexterity; slurred speech; a general feeling of exhaustion; and finally, the key symptom, uncontrollable shivering.

At the point the victim begins to shiver, more debilitating symptoms progress rapidly: loss of memory; dizziness; incoherency; lightheadedness; difficulty making any movement; an overwhelming feeling of drowsiness. Near death the shivering stops and the victim may actually feel warm again.

When the body temperature falls to the critical range of 82 to 91 degrees, the heart, trying to pump more blood, may fibrillate and fail. Those who survive that critical temperature range show signs of reduced respiration and pulse.

The first line of defense against hypothermia is proper clothing: wool insulates better than cotton, down and synthetic fabrics, especially if wet. Loose layers of clothing are better than a single jacket or coat.

If you are outdoors and sense the onset of hypothermia symptoms, make camp and seek shelter immediately. Make a fire if possible, change into dry clothes and drink warm liquids. In advanced stages the victim should be stripped of clothing, kept awake at all costs, and put into a dry sleeping bag with another stripped person. Outdoorsmen have found that skin-to-skin contact is an effective treatment in wilderness conditions where shelter and heat aren't available.

Victims should be warmed as rapidly as possible. In severe cases artificial respiration and cardio-pulmonary resuscitation may be necessary. Remember that the victim is the worst judge of his own condition and may deny he needs help. Ignore protests and treat even mild symptoms immediately.