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A high heat index can end up becoming a killer

POSTED: August 3, 2014 12:44 a.m.

There’s a killer that probably takes more lives than warfare. In 2003, an estimated 50,000 people died during a devastating heat wave that affected most of Europe. Even in the U.S., where air conditioning is available on a much larger scale, the hot summer of 1980 resulted in 1,250 casualties, according to the National Weather Service (

Chicago lost 700 people during the deadliest event in its history when a heat wave struck the city in 1995.

This is the hottest time of the year, and besides watching the temperature, the “heat index” deserves close attention. It’s the temperature which the human body perceives.

The heat index can be considerably greater than the actual air temperature when humidity is high. That’s because the body has a built-in cooling system which works like the air conditioning systems found in the West: evaporation of fluids. When water evaporates, heat is absorbed in the process. Perspiration is intended to cool the skin in this way.

But large amounts of moisture in the air inhibit perspiration because the air is already close to saturation. Instead of feeling cooler, we get those wet spots on our clothing.

In Georgia, the nearby Gulf of Mexico provides ample moisture to drive the heat index up. At 86 degrees, a relative humidity of 85 percent makes it feel like 102 degrees. Dangerous conditions are reached when the heat index climbs beyond 124. During a heat wave, the thermometer might hit 100 degrees. At that point, it takes only 65 percent relative humidity to produce a sweltering heat index of 136.

The first danger sign is heat exhaustion. Heavy sweating, weakness and dizziness require removing the person to a cooler place and giving sips of water.

Heat stroke is more serious and can result in death. Confusion, rapid pulse and unconsciousness are warning signs requiring immediate medical attention. Many good Samaritans have noticed hikers and bikers at rest stops showing signs of heat exhaustion, and made sure that they got rest and fluids.

Leaving people in parked cars with the air conditioning running is risky. If the engine cuts out, the inside of a car can rapidly exceed 125 degrees. More than four dozen adults as well as children die in parked cars every year. An easy prevention method is to take grandpa and the kids along into the air conditioned shopping center.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at



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