Heat Index Table

Heat Index Readings and Associated Health Risks

The heat index (see chart below) is how hot the heat-humidity combination makes it feel. As relative humidity increases, the air seems warmer than it actually is because the body is less able to cool itself via evaporation of perspiration.

As the heat index rises, so do health risks. When the heat index is 90°-105°F, heat exhaustion is possible. When it is above 105°F, it is probable. Heatstroke is possible when the heat index is above 105°F, and very likely when it is 130°F and above. Physical activity and prolonged exposure to the heat increase the risks.

Heat Exhaustion occurs when the body is dehydrated.

  • Symptoms -- headache, nausea, dizziness, cool and clammy skin, pale face, cramps, weakness, profuse perspiration
  • First Aid -- move to a cooler spot, drink water with a small amount of salt added (one teaspoon per quart)
  • Without Intervention -- it can lead to collapse and heatstroke.

Heatstroke occurs when perspiration cannot occur and the body overheats.

  • Symptoms -- headache, nausea, face flushed, hot and dry skin, no perspiration, body temperature over 101°F, chills, rapid pulse
  • First Aid -- cool person immediately, move to shade or indoors, wrap in a cool, wet sheet, get medical assistance
  • Without Intervention -- it can lead to confusion, coma, and death.

The following chart shows the health risks as temperature and relative humidity rise.

The Heat Index
Air Temp
(° F)
Relative Humidity
40
45
50
55
60
65
70
75
80
85
90
95
100
110 °
136
143
152
 
 
105°
123
129
135
141
148
 
 
 
100°
111
115
119
124
129
135
141
147
 
 
 
95°
101
104
107
110
114
117
122
126
131
136
141
 
 
90°
92
94
96
98
100
103
106
109
112
115
119
127
132
85°
84
85
86
88
89
91
93
95
97
99
102
104
107
80°
80
80
81
81
82
82
83
84
84
85
86
86
87
Exposure to full sunshine can increase Heat Index values by up to 15° F.
Heat Index Category Possible heat disorders for people in high risk groups
130°F or higher Extreme Danger Heatstroke risk extremely high
105° - 129°F Danger Heat Exhaustion likely, Heatstroke possible
90° - 105°F Extreme Caution Heat Exhaustion possible
80° - 90 °F Caution Fatigue possible

Sources NSIS: Florida Wildlife: Newts. Your Florida Backyard. 2000, Marianne Cowley;
Meteorology for Scientists and Engineers, 2nd edition by Roland B. Stull

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Updated Monday, 22-Nov-2010 16:39:11 CST