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The Independent Online
JUST how hot can it get before the human body gives out?

Dr Ron Maughan, acclimatisation adviser for the British Olympic Association, spent last week working in the Mojave Desert in California in temperatures of 120F plus. "It was difficult to avoid serious dehydration you had to drink a lot but it was bearable," he says.

The body can withstand "enormous temperatures" if the atmosphere is very dry, humidity is low, and fluid intake is kept up, says Dr Maughan, a physiologist at Aberdeen University.

It can take up to three weeks to acclimatise properly to a hot environment. "As long as the body can keep its cool by sweating, and the sweat is evaporated off, and you are drinking lots of fluids, then you can cope for some time."

But problems for the human body start when both temperatures and humidity rise. In extreme conditions experienced in the American Mid-West last week, where temperatures hit 106F with 92 per cent humidity, almost 700 people died from heatstroke and heat exhaustion. The elderly and poor were most vulnerable. It is possible to lose between 2-3 per cent of body weight through dehydration before a thirst sets in. according to Dr Maughan. They would have become dehydrated, their blood pressure would have fallen and their hearts had to work harder to keep the decreased volume of blood flowing to vital organs. Urine output would have been reduced as the kidneys went into over-drive to retain water and salt.

At 102F, the first signs of heatstroke would have set in; the sweating process slows down, a severe headache develops, and the skin becomes red. At 103F, the body's internal thermostat breaks down, and confusion and delirium develop, progressing to convulsions.

When body temperature reaches 104F, sweating stops, the body overheats and the victims suffers hyperpyrexia or heatstroke, followed by a coma. Death can occur two to four hours after the first symptoms of heatstroke.