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 these are the direct casualties.
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 temperature and high humidity although some of
the worst have been catastrophically dry.
NOAA’s National Weather Service
Heat Index Program
Considering this tragic death toll,
the National Weather Service (NWS) 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 F, is an accurate measure of how hot it
really feels when relative humidity (RH) is added to the
actual air temperature.
To find the HI, look at the Heat Index
Chart below. As an example, if the air temperature is
95°F (found at the top of the table) and the RH is 55%
(found at the left side 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.
Heat Index/Heat Disorders:
Possible heat disorders for people in higher risk
groups.
Heat Index of 130° OR Higher:
HEATSTROKE/SUNSTROKE HIGHLY HIGHER LIKELY WITH CONTINUED
EXPOSURE,
Heat Index of 105°- 130°: SUNSTROKE,
HEAT CRAMPS OR HEAT EXHAUSTION LIKELY, AND HEATSTROKE
POSSIBLE WITH PROLONGED EXPOSURE AND/OR PHYSICAL
ACTIVITY.
Heat Index of 90°- 105°: SUNSTROKE,
HEAT CRAMPS AND HEAT EXHAUSTION POSSIBLE WITH PROLONGED
EXPOSURE AND/OR PHYSICAL ACTIVITY.
Heat Index of 80° - 90°: FATIGUE
POSSIBLE WITH PROLONGED EXPOSURE AND/OR PHYSICAL
ACTIVITY
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.
The “Heat Index vs. Heat Disorder”
table (next to the HI chart) relates ranges of HI with
specific disorders, particularly for people in higher
risk groups.
Summary of NWS’s Alert Procedures
The NWS will initiate alert procedures
when the HI is expected to exceed 105°- 1 10°F
(depending on local climate) for at least two
consecutive days. The procedures are:
-
Include HI values in zone and city
forecasts.
-
Issue Special Weather Statements
and/or Public Information Statements presenting a
detailed discussion of
-
Assist state/local health
officials in preparing Civil Emergency Messages in
severe heat waves. Meteorological information from
Special Weather Statements will be included as well
as more detailed medical information, advice, and
names and telephone numbers of health officials.
-
Release to the media and over
NOAA‘s own Weather Radio all of the above
information.
How Heat Affects the Body Human
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 over exercised for his 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 concentrations, 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
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 a 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
non-alcohol 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.
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
Know These Heat Disorder Symptoms
SUNBURN: Redness and pain. In
severe cases swelling of skin, blisters, fever,
headaches. First Aid: Ointments for mild cases if
blisters appear and do not break. If breaking occurs,
apply dry sterile dressing. Serious, extensive cases
should be seen by physician.
HEAT CRAMPS: Painful spasms
usually in muscles of legs and abdomen possible. Heavy
sweating. First Aid: 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. First Aid: 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 (106° F. or higher). Hot dry skin.
Rapid and strong pulse. Possible unconsciousness. First
Aid: HEAT STROKE IS A SEVERE MEDICAL EMERGENCY. SUMMON
EMERGENCY 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. Persons
on salt restrictive diets should consult a physician
before increasing their salt intake.
