What is the heat index?

Your body has efficient ways to release excess heat, but high temperatures and high humidity create a sticky situation. Find out how the heat index keeps you abreast of dangerous heat situations in this HowStuffWorks podcast.

Learn more about your ad-choices at https://www.iheartpodcastnetwork.com

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:00):
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

(00:23):
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

(00:44):
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,

(01:08):
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

(01:29):
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

(01:52):
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

(02:12):
podcast at how stuff works dot com. For more on
this and thousands of other topics, go to how stuff
works dot com.