internal body temperature due to prolonged exposure to
cold air or immersion in cold water.
Frostbite may cause only localized tissue death; but
hypothermia, if not reversed, will kill people. When the
normal internal body temperature falls below 98.6°F,
shivering begins. As internal body temperature
approaches 95°F, the body will usually be in
uncontrolled, violent-shivering spasms. Lower
temperatures cause loss of mental processes, a cessation
of shivering, muscle rigidity, unconsciousness, and
then death as the body cools below 80°F.
Wind Chill Equivalent Temperature
The wind chill equivalent temperature (also called
the wind chill index, the wind chill factor, or just plain
wind chill), is the temperature required under no-wind
conditions that will equal the cooling effect of the air
(the actual air temperature) and the wind on an average
size, nude person in the shade. Moisture content of the
air, visible moisture on the skin or clothing, presence of
sunshine, clothing, and physical activity are not
considered.
Wind chill equivalent temperature is found by use
of the wind chill nomogram (fig. 1-39). The vertical
lines on the nomogram indicate air temperature, in
degrees Fahrenheit; the horizontal lines indicate wind
speed, in knots; and the curved lines indicate wind chill
equivalent temperature. From the intersection of the air
temperature line and the wind speed line, follow the
curved line downward to the left to read the wind chill.
The dashed lines on the nomogram illustrate an
example of a wind chill determination with an air
temperature of 20°F and a wind speed of 29 knots: the
resultant wind chill is -10°F. Interpolate between the
lines as necessary. Other tables are used to determine
wind chill, but unfortunately, most require wind speed
in miles per hour rather than the standard measurement
of knots used by the Navy and Marine Corps.
Weather observers should avoid making any
recommendations for when and how long people may
work outdoors during cold weather.
Frostbite and
hypothermia depend on the clothing people wear, their
level of activity, and the length of time exposed to the
cold.
Seawater Immersion Survivability
When a person is immersed in water, the major
factor on the length of time the person can survive is the
seawater temperature. Some other factors are the sea
condition (height and length of the waves), the person’s
ability to swim, the person’s physical condition, and the
person’s clothing.
When immersed in water, the human body loses
heat to the water by conduction. If a person is immersed
long enough, internal body temperature falls and
unconsciousness or death occurs (fig. l-40). The
survivability assumes that the sea condition is not a
factor, and that the person is an average swimmer, in
average physical condition, with no special clothing.
Figure 1-39.—Wind Chill Equivalent Temperature nomogram.
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