Rescuers are increasingly concerned that hypothermia may be threatening the survival of nine men who have been trapped in a flooded Pennsylvania coal mine for almost two days.

Temperatures in the mine are thought to be somewhere below 60 degrees Fahrenheit. Under dry conditions such temperatures would not present a serious risk of hypothermia. But the men may be wet or partly submerged by the water that rushed into the mine Wednesday when the miners unexpectedly breached an adjacent abandoned mine.

A severe decrease in the body's core temperature, hypothermia proceeds much more quickly when a person is exposed to water. People who are mostly submerged in 60-degree water can survive several hours. In water 50 degrees, they can typically survive a few hours.

Hypothermia begins to set in when core body temperature drops to around 95 degrees. The first signs of trouble are tight muscles and shivering, followed by a loss of coordination.

As body temperature keeps dropping, a person becomes confused and irrational. Sometimes, just before losing consciousness at a temperature of 87 degrees or so, people frantically remove their clothing under the mistaken impression that they are becoming overheated rather than freezing to death.

Death occurs when the body temperature drops below 80 degrees.

The proper treatment for hypothermia depends on severity. Mild cases can be alleviated by removing wet clothing and huddling against the hypothermic person to transfer body heat. More severe cases are treated with warm baths, the administration of heated oxygen and other methods.