1
00:00:00,560 --> 00:00:03,600
Speaker 1: Welcome to brain Stuff from how stuff works dot com

2
00:00:03,600 --> 00:00:08,039
Speaker 1: where smart Happens. Hi. I'm Marshall Brain with today's question,

3
00:00:08,600 --> 00:00:11,600
Speaker 1: what is the heat index that the weather person talks

4
00:00:11,600 --> 00:00:15,600
Speaker 1: about during the summer. During an average day, your body

5
00:00:15,680 --> 00:00:20,239
Speaker 1: burns about two thousand calories. That means that during waking hours,

6
00:00:20,280 --> 00:00:23,120
Speaker 1: you're burning about two calories a minute as you sit

7
00:00:23,160 --> 00:00:26,639
Speaker 1: in a chair. These two calories don't sound like much,

8
00:00:26,880 --> 00:00:30,560
Speaker 1: but they raise your body temperature every minute. Your body

9
00:00:30,600 --> 00:00:33,600
Speaker 1: needs a way to dump that excess heat. If it doesn't,

10
00:00:33,640 --> 00:00:37,440
Speaker 1: then body temperature rises into the danger zone. Say you're

11
00:00:37,479 --> 00:00:41,199
Speaker 1: sitting in a chair outside with an outside temperature up

12
00:00:41,200 --> 00:00:44,559
Speaker 1: to about eighty degrees fahrenheit. It's easy to dump excess

13
00:00:44,600 --> 00:00:49,080
Speaker 1: heat simply through radiation. This is why air temperature feels

14
00:00:49,159 --> 00:00:53,320
Speaker 1: comfortable up to about eighty degrees fahrenheit. Above eighty degrees,

15
00:00:53,400 --> 00:00:56,240
Speaker 1: your body doesn't have enough surface area to get rid

16
00:00:56,280 --> 00:00:59,080
Speaker 1: of the heat fast enough, so your body turns to

17
00:00:59,160 --> 00:01:04,080
Speaker 1: your sweat ends to make evaporative cooling possible. Evaporative cooling

18
00:01:04,200 --> 00:01:08,319
Speaker 1: works great if the air is dry. In high humidity, however,

19
00:01:08,440 --> 00:01:11,560
Speaker 1: it doesn't work very well at all. The sweat can't

20
00:01:11,600 --> 00:01:15,920
Speaker 1: evaporate because the air is already saturated with humidity. In

21
00:01:16,120 --> 00:01:20,160
Speaker 1: high temperature, high humidity environments, your body can get into

22
00:01:20,200 --> 00:01:23,840
Speaker 1: a dangerous situation where it can't radiate or evaporate the

23
00:01:23,840 --> 00:01:26,680
Speaker 1: heat away. The heat index that you see on the

24
00:01:26,680 --> 00:01:29,440
Speaker 1: evening news is designed to make you aware of these

25
00:01:29,520 --> 00:01:34,280
Speaker 1: dangerous situations. The heat index takes the day's temperature and

26
00:01:34,520 --> 00:01:38,480
Speaker 1: the day's humidity into account and calculates what the temperature

27
00:01:38,520 --> 00:01:43,640
Speaker 1: would be if the air were at humidity. On this scale,

28
00:01:43,880 --> 00:01:48,600
Speaker 1: high humidity can make you excruciatingly hot because your body

29
00:01:48,720 --> 00:01:52,480
Speaker 1: has no way to eliminate excess heat. For example, a

30
00:01:52,560 --> 00:01:56,040
Speaker 1: hundred degrees fahrenheit with a hundred percent humidity is the

31
00:01:56,160 --> 00:02:02,600
Speaker 1: same as a hundred nine degrees fahrenheit humidity, nearly the

32
00:02:02,680 --> 00:02:05,680
Speaker 1: boiling point of water. That's way too hot for a

33
00:02:05,760 --> 00:02:09,720
Speaker 1: human being. Do you have any ideas or suggestions for

34
00:02:09,760 --> 00:02:12,760
Speaker 1: this podcast? If so, please send me an email at

35
00:02:12,840 --> 00:02:15,880
Speaker 1: podcast at how stuff works dot com. For more on

36
00:02:16,000 --> 00:02:18,360
Speaker 1: this and thousands of other topics, go to how stuff

37
00:02:18,360 --> 00:02:21,520
Speaker 1: works dot com.