|
Overview :
Prolonged
exposure to severe cold can result in hypothermia and/or tissue necrosis. It is
important to keep the core body temperature from falling below 96.8 degrees
Fahrenheit, and to prevent cold injury to the extremities or exposed body
parts.
As the wind
speed increases, there is an additional cooling effect, decreasing the
effective temperature to the exposed individual. The effect increases until
wind speeds reach 40 miles per hour, after which there is little additional
effect. Tissue freezing will occur only at temperatures below 30.2 degrees
Fahrenheit, regardless of wind speed. The presence of wetting greatly increases
the risk for hypothermia and must be aggressively prevented.
Table of Effective Temperature
Experienced for a Given
Temperature in °F and Wind Speed in miles per
hour
|
Windmph
|
50 °F
|
40 °F
|
30 °F
|
20 °F
|
10 °F
|
0 °F
|
-10 °F
|
-20 °F
|
-30 °F
|
-40 °F
|
-50 °F
|
-60 °F
|
|
0
|
50
|
40
|
30
|
20
|
10
|
0
|
-10
|
-20
|
-30
|
-40
|
-50
|
-60
|
|
5
|
48
|
37
|
27
|
16
|
6
|
-5
|
-15
|
-26
|
-36
|
-47
|
-57
|
-68
|
|
10
|
40
|
28
|
16
|
4
|
-9
|
-24
|
-33
|
-46
|
-58
|
-70
|
-83
|
-95
|
|
15
|
36
|
22
|
9
|
-5
|
-18
|
-32
|
-45
|
-58
|
-72
|
-85
|
-99
|
-112
|
|
20
|
32
|
18
|
4
|
-10
|
-25
|
-39
|
-53
|
-67
|
-82
|
-96
|
-110
|
-121
|
|
25
|
30
|
16
|
0
|
-15
|
-29
|
-44
|
-59
|
-74
|
-88
|
-104
|
-118
|
-133
|
|
30
|
28
|
13
|
-2
|
-18
|
-33
|
-48
|
-63
|
-79
|
-94
|
-109
|
-125
|
-140
|
|
35
|
27
|
11
|
-4
|
-20
|
-35
|
-51
|
-67
|
-82
|
-98
|
-113
|
-129
|
-145
|
|
40+
|
26
|
10
|
-6
|
-21
|
-37
|
-53
|
-69
|
-85
|
-100
|
-116
|
-132
|
-148
|
Equation with Wind Speed Constant
effective
temperature in °F at a given wind speed in miles per hour =
= (a *
(temperature)) + b
|
wind
speed in mph
|
a
|
b
|
|
0
|
1
|
0
|
|
5
|
1.051049
|
-4.744755
|
|
10
|
1.2293706
|
-21.35315
|
|
15
|
1.3437063
|
-31.53147
|
|
20
|
1.4108392
|
-38.6958
|
|
25
|
1.4832168
|
-44.08392
|
|
30
|
1.5286713
|
-48.18998
|
|
35
|
1.5601399
|
-51.03263
|
|
40
|
1.5793706
|
-53.01981
|
Equation with External Temperature
Constant
wind speed < 10 miles per hour
effective
temperature for a given external temperature =
= (a * ((wind
speed in mph) ^2)) + (b * (wind speed in mph)) + c
|
external
temperature
|
a
|
b
|
c
|
|
-60 °F
|
-0.38
|
0.3
|
-60
|
|
-50 °F
|
-0.38
|
0.5
|
-50
|
|
-40 °F
|
-0.32
|
0.2
|
-40
|
|
-30 °F
|
-0.32
|
0.4
|
-30
|
|
-20 °F
|
-0.20
|
0.2
|
-20
|
|
-10 °F
|
-0.26
|
0.3
|
-10
|
|
0 °F
|
-0.28
|
0.4
|
0
|
|
10 °F
|
-0.22
|
0.3
|
10
|
|
20 °F
|
-0.16
|
0
|
20
|
|
30 °F
|
-0.16
|
0.2
|
30
|
|
40 °F
|
-0.12
|
0
|
40
|
|
50 °F
|
-0.12
|
0.2
|
50
|
Equation with External Temperature
Constant
wind speed >= 10 miles per hour
effective
temperature for a given external temperature =
= (a * ((wind
speed in mph) ^3)) + (b * ((wind speed in mph) ^2)) + (c * (wind speed in mph))
+ d
|
external
temperature
|
a
|
b
|
c
|
d
|
|
-60 °F
|
-0.000222
|
0.0642857
|
-4.501587
|
-56.64286
|
|
-50 °F
|
-0.000889
|
0.1152381
|
-5.525397
|
-38.57143
|
|
-40 °F
|
-0.000889
|
0.1095238
|
-5.011111
|
-18.14286
|
|
-30 °F
|
-0.001111
|
0.1314286
|
-5.772222
|
-24.28571
|
|
-20 °F
|
-0.000667
|
0.087619
|
-4.278571
|
-11.28571
|
|
-10 °F
|
-0.000889
|
0.1019048
|
-4.430159
|
1.8571429
|
|
0 °F
|
-0.000222
|
0.0414286
|
-2.573016
|
-2.142857
|
|
10 °F
|
-0.000667
|
0.0785714
|
-3.461905
|
18.428571
|
|
20 °F
|
-0.000444
|
0.0614286
|
-2.96746
|
27.785714
|
|
30 °F
|
-0.000667
|
0.0709524
|
-2.880952
|
38.428571
|
|
40 °F
|
-0.000444
|
0.0490476
|
-2.119841
|
44.571429
|
|
50 °F
|
-0.000222
|
0.0309524
|
-1.549206
|
52.714286
|
|
Effective Temperature
|
Interpretation
|
|
above–25°F
|
there is
little danger of freezing with short periods of exposure if skin dry
|
|
between -25
and -74 °F
|
this is a zone
of increasing danger, with exposed flesh freezing within 1 minute
|
|
below -74 °F
|
this is a zone
of great risk, with flesh freezing within 30 seconds of exposure
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