3.0 Heat Stress Index Scale
The Heat Index is a valuable measure of the affect of humidity on how "hot it
feels". Since our bodies primary cooling mechanism is through perspiration and the
cooling effect of evaporation from our skin; as the humidity increases, there is less
evaporation and we feel hotter.
At a certain point, high Heat Index values become a health issue and a serious one
for people who are working or exercising in it. The color LCD scale reflects the Heat
Stress Index values and relates to the health affects outlined below:
IN RANGE
Condition
Temperature
Level
Cold
Below 9.4°C/49°F
Cool
10°C to 20°C
50°F to 69°F
Comfort
21°C to 26°C
70°F to 79°F
Caution
Extreme
Caution
Danger
Extreme
Danger
Heat Index /
Humidex Value
27°C to 31°C
80°F to 89°F
32°C to 40°C
90°F to 104°F
41°C to 53°C
105°F to 129°F
54°C/130°F or
higher
OUT OF RANGE
Physical Response
• Fatigue possible with
prolonged exposure and
physical activity
• Sunstroke, muscle cramps
and heat exhaustion are
possible with prolonged
exposure and physical
activity
• Sunstroke, muscle cramps
and heat exhaustion are likely
• Heat stroke possible with
prolonged exposure and
physical activity
• Heat stroke and
sunstroke likely