Heat is an underrated danger, with an average of 175 Americans losing their lives annually from heat-related causes.According to the Centers for Disease Control and Prevention, from 1979-2003 excessive heat exposure caused 8,015 deaths in the United States. During this period, more people died from extreme heat than from hurricanes, lightning, tornadoes, and floods combined.
Heat kills by taxing the human body beyond its ability to cool itself. Cooling is primarily accomplished by the evaporation of perspiration. How efficiently this process functions is directly related to the amount of water vapor in the air. High moisture content reduces the evaporative cooling rate of perspiration, making it difficult for the body to maintain a steady and safe internal temperature. One way to measure the combined effect of temperature and moisture on the human body is the heat index.
In 1979, R. G. Steadman constructed an apparent temperature table using temperature, relative humidity, and other factors, based on a number of published research papers over a 54-year span. The National Weather Service (NWS) developed a heat index equation based on Steadman’s work as guidance for heat-related advisories or warnings. Heat advisories or warnings are issued to the public when values approach dangerous levels.
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