Table 3.

Classification of the risk of heat illness according to heat index

Heat index		Risk of heat illness	Possible effects
°F	°C
<80	<26.7	No risk	No risk for developing heat illness
80 to 89	26.7 to 31.7	Caution	Fatigue possible with continued exposure and physical activity
90 to 104	32.2 to 40	Extreme caution	Sunstroke, heat cramps, and heat exhaustion possible
105 to 129	40.6 to 53.9	Danger	Sunstroke, heat cramps, and heat exhaustion likely, and heat stroke possible
>130	>54.4	Extreme danger	Heat stroke highly likely with prolonged exposure