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The wind chill calculation is only valid for temperatures less than 40 °F and wind speeds greater than
0 mph, according to the National Weather Service.
Figure 26
5.12.4
Heat Index
Heat Index is an index that combines air temperature and relative humidity, as an attempt to
determine the human-perceived equivalent temperature.
Figure 27
The heat index calculation is only valid for temperatures greater than 80 °F and less than 120 °F, and
humidity greater than 40%, according to the National Weather Service.
Level
Heat Index
Range (°F)
Notes
Caution
80-90
Fatigue is possible with prolonged exposure and activity.
Continuing activity could result in heat cramps.
Extreme Caution 90-105
Heat cramps and heat exhaustion are possible. Continuing
activity could result in heat stroke.
Danger
105-130
Heat cramps and heat exhaustion are likely; heat stroke is
probable with continued activity.
Extreme Danger
Over 130
Heat stroke is imminent.
Figure 28