HEAT INDEX

Heat Index & Health Problems


HEAT KILLS

        Heat kills by taxing the human body beyond its abilities. In a normal year, about 175 Americans succumb to the demands of summer heat. Among the large continental family of natural hazards, only the cold of winter -- not lightning, hurricanes, tornadoes, floods, or earthquakes -- takes a greater toll. In the 40-year period from 1936 through 1975, nearly 20,000 people were killed in the United States by the effects of heat and solar radiation. In the disastrous heat wave of 1980, more than 1,250 people died.
        And those are the direct causalities. No one can know how many more deaths are advanced by heat wave weather -- how many diseased or aging hearts surrender, that under better conditions would have continued functioning.
        North American summers are hot; most summers see heat waves in one section or another of the United States. East of the Rockies, they tend to combine both high temperatures and high humidity although some of the worst have been catastrophically dry.

THE HEAT INDEX

        The NWS has devised a "Heat Index" (HI), (sometimes referred to as the "apparent temperature"). The HI, given in degrees Fahrenheit, is an accurate measure of how hot it really feels when the relative humidity (RH) is added to the actual air temperature.
        To find the Heat Index, look at the Heat Index Chart. As an example, if the air temperature is 95F (found on the left side of the table), and the relative humidity is 55% (found at the top of the table), the HI -- or how hot it really feels -- is 110F. This is at the intersection of the 95 row and the 55% column.
        Important: Since HI values were devised for shady, light wind conditions, exposure to full sunshine can increase HI values by up to 15F.  lso, strong winds, particularly with very hot, dry air, can be extremely hazardous.   


HEAT INDEX CHART 1
(Using Temperature and Relative Humidity)

RH
(%)
Temperature ( F)
90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105
90 119 123 128 132 137 141 146 152 157 163 168 174 180 186 193 199
85 115 119 123 127 132 136 141 145 150 155 161 166 172 178 184 190
80 112 115 119 123 127 131 135 140 144 149 154 159 164 169 175 180
75 109 112 115 119 122 126 130 134 138 143 147 152 156 161 166 171
70 106 109 112 115 118 122 125 129 133 137 141 145 149 154 158 163
65 103 106 108 111 114 117 121 124 127 131 135 139 143 147 151 155
60 100 103 105 108 111 114 116 120 123 126 129 133 136 140 144 148
55 98 100 103 105 107 110 113 115 118 121 124 127 131 134 137 141
50 96 98 100 102 104 107 109 112 114 117 119 122 125 128 131 135
45 94 96 98 100 102 104 106 108 110 113 115 118 120 123 126 129
40 92 94 96 97 99 101 103 105 107 109 111 113 116 118 121 123
35 91 92 94 95 97 98 100 102 104 106 107 109 112 114 116 118
30 89 90 92 93 95 96 98 99 101 102 104 106 108 110 112 114
Note: Exposure to full sunshine can increase HI values by up to 15 F

HEAT INDEX CHART 2
(Using Temperature and Dewpoint)

Dewpoint
( F)
Temperature ( F)
90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105
65 94 95 96 97 98 100 101 102 103 104 106 107 108 109 110 112
66 94 95 97 98 99 100 101 103 104 105 106 108 109 110 111 112
67 95 96 97 98 100 101 102 103 105 106 107 108 110 111 112 113
68 95 97 98 99 100 102 103 104 105 107 108 109 110 112 113 114
69 96 97 99 100 101 103 104 105 106 108 109 110 111 113 114 115
70 97 98 99 101 102 103 105 106 107 109 110 111 112 114 115 116
71 98 99 100 102 103 104 106 107 108 109 111 112 113 115 116 117
72 98 100 101 103 104 105 107 108 109 111 112 113 114 116 117 118
73 99 101 102 103 105 106 108 109 110 112 113 114 116 117 118 119
74 100 102 103 104 106 107 109 110 111 113 114 115 117 118 119 121
75 101 103 104 106 107 108 110 111 113 114 115 117 118 119 121 122
76 102 104 105 107 108 110 111 112 114 115 117 118 119 121 122 123
77 103 105 106 108 109 111 112 114 115 117 118 119 121 122 124 125
78 105 106 108 109 111 112 114 115 117 118 119 121 122 124 125 126
79 106 107 109 111 112 114 115 117 118 120 121 122 124 125 127 128
80 107 109 110 112 114 115 117 118 120 121 123 124 126 127 128 130
81 109 110 112 114 115 117 118 120 121 123 124 126 127 129 130 132
82 110 112 114 115 117 118 120 122 123 125 126 128 129 131 132 133
Note: Exposure to full sunshine can increase HI values by up to 15 F

HEAT INDEX  CALCULATOR

HEAT INDEX  CONVERSIONS SPREADSHEET


HEAT RELATED MEDICAL CONSEQUENCES

HEAT INDEX HEAT DISORDERS
80 - 90F Fatigue possible with prolonged exposure and/or physical activity.
90 - 105F Sunstroke, heat cramps and heat exhaustion possible with prolonged exposure and/or physical activity.
105 - 130F Sunstroke, heat cramps or heat exhaustion likely, and heatstroke possible with prolonged exposure and/or physical activity.
130F or higher Heatstroke/sunstroke highly likely with continued exposure.


HOW HEAT AFFECTS THE BODY

        Human bodies dissipate heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and -- as the last extremity is reached -- by panting, when blood is heated above 98.6 degrees. The heart begins to pump more blood, blood vessels dilate to accommodate the increased flow, and the bundles of tiny capillaries threading through the upper layers of skin are put into operation. The body's blood is circulated closer to the skin's surface, and excess heat drains off into the cooler atmosphere. At the same time, water diffuses through the skin as perspiration. The skin handles about 90 percent of the body's heat dissipating function.
        Sweating, by itself, does nothing to cool the body, unless the water is removed by evaporation -- and high relative humidity retards evaporation. The evaporation process itself works this way: the heat energy required to evaporate the sweat is extracted from the body, thereby cooling it. Under conditions of high temperature (above 90 degrees) and high relative humidity, the body is doing everything it can to maintain 98.6 degrees inside. The heart is pumping a torrent of blood through dilated circulatory vessels; the sweat glands are pouring liquid -- including essential dissolved chemicals, like sodium and chloride -- onto the surface of the skin.
        Heat disorders generally have to do with a reduction or collapse of the body's ability to shed heat by circulatory changes and sweating, or a chemical (salt) imbalance caused by too much sweating. When heat gain exceeds the level the body can remove, or when the body cannot compensate for fluids and salt lost through perspiration, the temperature of the body's inner core begins to rise and heat-related illness may develop.
        Ranging in severity, heat disorders share one common feature: the individual has overexposed or overexercised for his/her age and physical condition in the existing thermal environment.
        Sunburn, with its ultraviolet radiation burns, can significantly retard the skin's ability to shed excess heat.
        Studies indicate that, other things being equal, the severity of heat disorders tend to increase with age -- heat cramps in a 17-year-old may be heat exhaustion in someone 40, and heat stroke in a person over 60.
    Acclimatization has to do with adjusting sweat-salt concentration, among other things. The idea is to lose enough water to regulate body
temperature, with the least possible chemical disturbance.

HEAT DISORDER SYMPTOMS

CONDITION SYMPTOM TREATMENT
Sunburn Redness and pain. In severe cases, swelling of skin, blisters, fever, headaches Ointment for mild cases if blisters appear. If breaking occurs, apply dry sterile dressing. Serious, extensive cases should be
seen by a physician.
Heat 
Cramps
Painful spasms usually in muscles of legs and abdomen possible. Heavy sweating. Firm pressure on cramping muscles, or gentle massage to relieve spasm. Give sips of water. If nausea occurs, discontinue use.
Heat 
Exhaustion
Heavy sweating, weakness, skin cold, pale and clammy.  Pulse thready. Normal temperature possible. Fainting and vomiting. Get victim out of sun. Lay down and loosen clothing. Apply cool wet cloths. Fan or move victim to air conditioned room. Sips of water. If nausea occurs, discontinue use. If vomiting continues, seek immediate medical attention.
Heat 
Stroke 
(or sunstroke)
High body temperature (106F, or higher). Hot dry skin. Rapid and strong pulse. Possible unconsciousness.  Heat stroke is a severe medical emergency. Summon medical assistance or get the victim to a hospital immediately. Delay can be fatal.  Move the victim to a cooler environment. Reduce body temperature with cold bath or sponging. Use extreme caution.  Remove clothing, use fans and air conditioners. If temperature rises again, repeat process. Do not give fluids.


PREVENTING HEAT-RELATED ILLNESS


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