BBC Learnings · Section 6

How much heat do you lose from your head

It's freezing cold outside today, Georgina. Make sure you wrap up warm.

Level: C1 · 107 sentences

Transcript

  1. It's freezing cold outside today, Georgina.
  2. Make sure you wrap up warm.
  3. I'll put my woolly hat on.
  4. When I was growing up, I was told that you lose half your body heat from your head.
  5. Oh no, don't believe that, Georgina.
  6. It's just a popular myth.
  7. You know, something...
  8. people think is true, which actually isn't.
  9. Like, bulls get angry when they see the colour red
  10. or goldfish only have a three-second memory.
  11. Oh, I thought red really did make bulls angry.
  12. But you're right, there is some disagreement over the age-old question,
  13. should I wear a hat when it's cold outside?
  14. In this programme,
  15. we'll be asking how much body heat we lose from our head
  16. and discovering that a simple answer isn't so easy to find.
  17. But first, it's time for my quiz question.
  18. And let's start by asking someone who knows all about surviving in the cold,
  19. the U.S. Army.
  20. According to the Cold Weather Survival chapter of the U.S. Army Field Guide,
  21. how much heat is lost in the cold through an uncovered head?
  22. Is it A. 30-35%? B. 40-45%? Or C. 50-55%?
  23. You might say it's just a popular myth, Rob,
  24. but I still think half your body heat is lost from the head, so I'll say c 50-55%.
  25. OK Georgina, we'll come back to that later.
  26. Anyway, whichever answer is correct,
  27. the US Army obviously thinks a large percentage of body heat
  28. escapes through the head,
  29. but that might not be the whole picture.
  30. Over the years,
  31. experiments to measure body temperature in the snowy wastelands of Canada
  32. and Alaska have given wildly different results,
  33. mostly because of variations in the methods used.
  34. For example, whether the volunteer's head was covered or not,
  35. and whether they were dry or submerged in water.
  36. So maybe the US Army's view is out of date.
  37. And here's some surprising information that Tim Harford,
  38. presenter of BBC World Service programme More or Less,
  39. found after a quick search on Google.
  40. The head accounts for about 7% of the body's surface area
  41. and the heat loss is fairly proportional to the amount of skin that's showing.
  42. A human body's surface area means the total area
  43. of skin on its outer surfaces.
  44. That's the head, chest or torso plus the arms and legs.
  45. According to this view, heat loss,
  46. meaning the total amount of heat transferred away from something through its surface,
  47. is proportional to body surface area.
  48. In that case, a 50% heat loss from the head,
  49. which only makes up 7% of the body's surface area,
  50. seems like an overestimation.
  51. In the 1950s,
  52. other military experiments were carried out in Canada on soldiers wearing Arctic warfare clothing,
  53. the kind of superwarm thermal clothes you might wear in sub-zero temperatures,
  54. but with nothing to cover their heads.
  55. Here's professor of physiology Mike Tipton
  56. taking up the story with BBC World Service programme More or Less.
  57. The question was how important is the head now
  58. to also provide some equipment for us,
  59. a hat or some form of insulation.
  60. And in that scenario, of course,
  61. when you've got insulation over much of the rest
  62. of the body preventing heat loss,
  63. then obviously the percentage of heat loss from the head is going to be high.
  64. And at minus four degrees Celsius,
  65. it amounted to about half of the resting heat
  66. production of the body.
  67. Here, the soldiers' bodies were protected with insulation
  68. thick material used to stop heat from escaping.
  69. Since their heads were exposed to the cold,
  70. around half of their body heat escaped that way
  71. when resting not moving or doing anything active.
  72. And so the idea that half your body heat
  73. is lost through the head slowly became a popular myth.
  74. But before you throw your woolly hats in the bin,
  75. there's another consideration to bear in mind
  76. one that concerns your core temperature.
  77. That's the internal temperature inside your body,
  78. including the blood, heart and other vital organs.
  79. When the head is allowed to get cold
  80. and the body is well insulated,
  81. the body's core temperature drops rapidly due to the circulation of blood.
  82. Wow! This question really is blowing hot and cold.
  83. Now I have no idea how much heat is actually lost from the head.
  84. Why don't you just tell me the answer, Rob?
  85. OK then. Well, in my quiz question,
  86. I asked how much heat the US Army Guide says
  87. is lost through the head.
  88. I guessed C 50 to 55 percent, or roughly one half.
  89. Was I right?
  90. Well, you were warm, Georgina, but not right.
  91. In fact, the Army Field Guide says B 40 to 45 percent.
  92. But as we've seen in this case,
  93. cold facts are hard to come by.
  94. Let's recap our vocabulary then,
  95. because we're still not sure if wearing a hat
  96. to keep warm is just a popular myth
  97. something people believe to be true,
  98. but which actually is not.
  99. It seems that heat loss the total heat transferred away from something
  100. is linked to the surface area
  101. or total area of the body's outer surfaces
  102. when exposed to the cold.
  103. But wearing insulation?
  104. Material used to stop heat from escaping may change
  105. the body's resting temperature its temperature when not moving and at rest.
  106. And also affect your core temperature your body's internal temperature,
  107. including the heart and blood.