Speaker 1: Welcome to brain Stuff from how stuff works dot com
Speaker 1: where smart Happens. Hi. I'm Marshall Brain with today's question,
Speaker 1: what is the heat index that the weather person talks
Speaker 1: about during the summer. During an average day, your body
Speaker 1: burns about two thousand calories. That means that during waking hours,
Speaker 1: you're burning about two calories a minute as you sit
Speaker 1: in a chair. These two calories don't sound like much,
Speaker 1: but they raise your body temperature every minute. Your body
Speaker 1: needs a way to dump that excess heat. If it doesn't,
Speaker 1: then body temperature rises into the danger zone. Say you're
Speaker 1: sitting in a chair outside with an outside temperature up
Speaker 1: to about eighty degrees fahrenheit. It's easy to dump excess
Speaker 1: heat simply through radiation. This is why air temperature feels
Speaker 1: comfortable up to about eighty degrees fahrenheit. Above eighty degrees,
Speaker 1: your body doesn't have enough surface area to get rid
Speaker 1: of the heat fast enough, so your body turns to
Speaker 1: your sweat ends to make evaporative cooling possible. Evaporative cooling
Speaker 1: works great if the air is dry. In high humidity, however,
Speaker 1: it doesn't work very well at all. The sweat can't
Speaker 1: evaporate because the air is already saturated with humidity. In
Speaker 1: high temperature, high humidity environments, your body can get into
Speaker 1: a dangerous situation where it can't radiate or evaporate the
Speaker 1: heat away. The heat index that you see on the
Speaker 1: evening news is designed to make you aware of these
Speaker 1: dangerous situations. The heat index takes the day's temperature and
Speaker 1: the day's humidity into account and calculates what the temperature
Speaker 1: would be if the air were at humidity. On this scale,
Speaker 1: high humidity can make you excruciatingly hot because your body
Speaker 1: has no way to eliminate excess heat. For example, a
Speaker 1: hundred degrees fahrenheit with a hundred percent humidity is the
Speaker 1: same as a hundred nine degrees fahrenheit humidity, nearly the
Speaker 1: boiling point of water. That's way too hot for a
Speaker 1: human being. Do you have any ideas or suggestions for
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Speaker 1: works dot com.