c. The windchill chart can predict frostbite only to exposed flesh. Any clothing or
material which stops or reduces the wind will give some protection to the covered area.
Wet clothing or boots, however, do not have much insulating value and will result in
heat loss nearly equal to that of exposed flesh.
d. To use the windchill chart, locate the actual or estimated wind speed in the
left hand column and the temperature of the air in degrees Fahrenheit across the top of
the chart. Draw a line into the chart from each figure; the temperature with the windchill
figured in is the point in the chart where those two lines cross (intersect).
(1)
Example.
Air temperature
-10 F
calm
Wind speed
Equivalent temperature
-10 F
No wind is making the air colder; therefore, the temperature of the air which touches
exposed flesh is -10 F. According to the windchill chart, the danger of frostbite to a
properly clothed person is slight.
(2)
Example
.
Air temperature
-10 F
10 mph
Wind speed
Equivalent temperature
-33 F
Note that if the wind speed increases to only ten miles per hour or if the individual is
riding in an open vehicle which is being driven only ten miles per hour, the rate of heat
loss to exposed flesh increases as if the temperature was -33F with no wind. This lies
within the zone of increasing danger from frostbite, indicating that the person must
protect himself against exposure. Looking at the chart, you should note the bottom
line--trench foot and immersion foot may occur at any point on this chart.
MD0587
5-19
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