Welcome to brain Stuff from how stuff works dot com where smart Happens. Hi. I'm Marshall Brain with today's question, what is the heat index that the weather person talks about during the summer. During an average day, your body burns about two thousand calories. That means that during waking hours, you're burning about two calories a minute as you sit in a chair. These two calories don't sound like much, but they raise your body temperature every minute. Your body
needs a way to dump that excess heat. If it doesn't, then body temperature rises into the danger zone. Say you're sitting in a chair outside with an outside temperature up to about eighty degrees fahrenheit. It's easy to dump excess heat simply through radiation. This is why air temperature feels comfortable up to about eighty degrees fahrenheit. Above eighty degrees, your body doesn't have enough surface area to get rid of the heat fast enough, so your body turns to
your sweat ends to make evaporative cooling possible. Evaporative cooling works great if the air is dry. In high humidity, however, it doesn't work very well at all. The sweat can't evaporate because the air is already saturated with humidity. In high temperature, high humidity environments, your body can get into a dangerous situation where it can't radiate or evaporate the heat away. The heat index that you see on the evening news is designed to make you aware of these
dangerous situations. The heat index takes the day's temperature and the day's humidity into account and calculates what the temperature would be if the air were at humidity. On this scale, high humidity can make you excruciatingly hot because your body has no way to eliminate excess heat. For example, a hundred degrees fahrenheit with a hundred percent humidity is the same as a hundred nine degrees fahrenheit humidity, nearly the boiling point of water. That's way too hot for a
human being. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com.