WEBVTT - What is the heat index?

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<v Speaker 1>Welcome to brain Stuff from how stuff works dot com

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<v Speaker 1>where smart Happens. Hi. I'm Marshall Brain with today's question,

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<v Speaker 1>what is the heat index that the weather person talks

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<v Speaker 1>about during the summer. During an average day, your body

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<v Speaker 1>burns about two thousand calories. That means that during waking hours,

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<v Speaker 1>you're burning about two calories a minute as you sit

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<v Speaker 1>in a chair. These two calories don't sound like much,

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<v Speaker 1>but they raise your body temperature every minute. Your body

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<v Speaker 1>needs a way to dump that excess heat. If it doesn't,

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<v Speaker 1>then body temperature rises into the danger zone. Say you're

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<v Speaker 1>sitting in a chair outside with an outside temperature up

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<v Speaker 1>to about eighty degrees fahrenheit. It's easy to dump excess

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<v Speaker 1>heat simply through radiation. This is why air temperature feels

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<v Speaker 1>comfortable up to about eighty degrees fahrenheit. Above eighty degrees,

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<v Speaker 1>your body doesn't have enough surface area to get rid

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<v Speaker 1>of the heat fast enough, so your body turns to

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<v Speaker 1>your sweat ends to make evaporative cooling possible. Evaporative cooling

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<v Speaker 1>works great if the air is dry. In high humidity, however,

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<v Speaker 1>it doesn't work very well at all. The sweat can't

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<v Speaker 1>evaporate because the air is already saturated with humidity. In

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<v Speaker 1>high temperature, high humidity environments, your body can get into

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<v Speaker 1>a dangerous situation where it can't radiate or evaporate the

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<v Speaker 1>heat away. The heat index that you see on the

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<v Speaker 1>evening news is designed to make you aware of these

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<v Speaker 1>dangerous situations. The heat index takes the day's temperature and

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<v Speaker 1>the day's humidity into account and calculates what the temperature

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<v Speaker 1>would be if the air were at humidity. On this scale,

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<v Speaker 1>high humidity can make you excruciatingly hot because your body

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<v Speaker 1>has no way to eliminate excess heat. For example, a

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<v Speaker 1>hundred degrees fahrenheit with a hundred percent humidity is the

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<v Speaker 1>same as a hundred nine degrees fahrenheit humidity, nearly the

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<v Speaker 1>boiling point of water. That's way too hot for a

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<v Speaker 1>human being. Do you have any ideas or suggestions for

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<v Speaker 1>this podcast? If so, please send me an email at

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<v Speaker 1>podcast at how stuff works dot com. For more on

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<v Speaker 1>this and thousands of other topics, go to how stuff

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<v Speaker 1>works dot com.