During the last decade, the practice of opening public school in eary August has led to environmental stresses on students and teachers due to extremes of heat and humidity. In the South and Southwest, it is not unusual to have 15 to 20 days of 90°F(32.2°C) and relative humidity of 60% and higher during August. This puts a strain on teachers' and students' adaptability.

In surveying eight southern states, J. W. Trieschmann (unpublished data, 1983) found that the availability of air conditioning in public schools ranged from 15% in some states to 30% in others. The smaller, poorer, usually rural school districts had the least access to cooling equipment. Thus, a large school population is at the mercy of the elements. This is especially significant because the majority of this population has been acclimatized to air-conditioned homes and stores, and extremes of heat discomfort are not well tolerated.

Heat stress is defined as the overall effect of excessive heat on the human body. The important factors contributing to heat stress are air temperature, humidity, air movement, radiant heat, atmospheric pressure, physiologic factors (handicap or chronic disease), physical activity,1 and time exposure. Under normal conditions, temperature and humidity are the most important elements influencing comfort. The American Society of Heating, Refrigeration, Air Conditioning Engineers (ASHRAE) has published an index for determining heat stress based on human physiology, clothing, and standard room conditions.2 This index, called the "ET" or effective temperature (in Fahrenheit), is a measure of what hot weather feels like to the average person at different temperatures and humidities.

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