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Excessive Heat
map of current heat index values
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.  

Too Much Heat 
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.  

Cities Pose Special Hazards 
The stagnant atmospheric conditions of the heat wave trap pollutants in urban areas and add the stresses of severe pollution to the already dangerous stresses of hot weather, creating a health problem of undiscovered dimensions. A map of heat-related deaths in St. Louis during 1966, for example, shows a heavier concentration in the crowded alleys and towers of the inner city, where air quality would also be poor during a heat wave.  

The high inner-city death rates also can be read as poor access to air-conditioned rooms.  While air-conditioning may be a luxury in normal times, it can be a lifesaver during heat wave conditions.  

The cost of cool air moves steadily higher, adding what appears to be a cruel economic side to heat wave fatalities. Indications from the 1978 Texas heat wave suggest that some elderly people on fixed incomes, many of them in buildings that could not be ventilated without air conditioning, found the cost too high, turned off their units, and ultimately succumbed to the stresses of heat.  

Know These Heat Disorder Symptoms 

Symptoms First Aid
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.
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.
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.
(or sunstroke)
High body temperature (106°F, 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 
Elderly persons, small children, chronic invalids, those on certain medications or drugs (especially tranquilizers and anticholinergics), and persons with weight and alcohol problems are particularly susceptible to heat reactions, especially during heat waves in areas where moderate climate usually prevails.  

Heat Wave Safety Tips 

Slow down.  Strenuous activities should be reduced, eliminated, or rescheduled to the coolest time of the day.  Individuals at risk should stay in the coolest available place, not necessarily indoors.  

Dress for summer.   Lightweight, light-colored clothing reflects heat and sunlight, and helps your body maintain normal temperatures.  

Put less fuel on your inner fires. Foods (like proteins) that increase metabolic heat production also increase water loss.  

Drink plenty of water or other nonalcoholic fluids.  Your body needs water to keep cool. Drink plenty of fluids even if you don't feel thirsty. Persons who (1) have epilepsy or heart, kidney, or liver disease, (2) are on fluid restrictive diets, or (3) have a problem with fluid retention should consult a physician before increasing their consumption of fluids.  

Do not drink alcoholic beverages.  

Do not take salt tablets unless specified by a physician.  Persons on salt restrictive diets should consult a physician before increasing their salt intake.  

Spend more time in air-conditioned places. Air conditioning in homes and other buildings markedly reduces danger from the heat. If you cannot afford an air conditioner, spending some time each day (during hot weather) in an air conditioned environment affords some protection.  

Don't get too much sun.  Sunburn makes the job of heat dissipation that much more difficult.  

Produced as a cooperative effort of NOAA's National Weather Service, the Federal Emergency Management Agency, and the American Red Cross 

Related information about Heat Waves

The information presented here is taken from products produced by the U.S. National Weather Service and other national and international agencies. The U.S. National Weather Service does not present this as official information.