HT30 V3.0 08/07

7

APPENDIX

The following is reprinted with permission of the National Oceanic and Atmospheric Administration.

A National Problem

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.

Considering this tragic death toll, the National Weather Service has stepped up its efforts to alert more

effectively the general public and appropriate authorities to the hazards of heat waves -- those prolonged

excessive heat/humidity episodes. Based on the latest research findings, the NWS has devised the "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

95°F (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 110°F. 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 15°F. Also, strong winds, particularly with very hot, dry

air, can be extremely hazardous. Note on the HI chart the shaded zone above 105°F. This corresponds

to a level of HI that may cause increasingly severe heat disorders with continued exposure and/or physical

activity.