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Heat Bulletin


Periods of extremely hot weather — heat waves — can cause serious health problems for everyone. In fact, among weather-related events, heat waves are a leading cause of death. Illinois experienced this first-hand in July 1995, when extreme heat contributed to the deaths of more than 700 people in the Chicago area. Here are some commonly asked questions about hot weather and heat-related illnesses and how to safely cope with these conditions.

What is the heat index?

The heat index (HI) measures what hot weather "feels like." It is determined by the air temperature and the relative humidity. Figure 1 shows how temperature and humidity combine to produce apparent, or "feels like," temperatures.

The National Weather Service issues a heat advisory when the heat index is expected to reach 105·F during any 24-hour period and the minimum HI during that period remains 75·F or higher. A heat warning is issued when the heat index is expected to reach or exceed 115·F on at least two consecutive days and the minimum heat index during the period remains 80·F or higher.

These guidelines may be locally adjusted, however, for large metropolitan areas. In Chicago, a heat warning is to be issued when one of the three following conditions exists or is expected imminently:

  • three consecutive days with the heat index between 100·F and 105·F and either 85 percent or more sunshine on two of the three days or a minimum HI of 75·F on each of the three days;

  • two consecutive days with a heat index of 105·F to 110·F; or

  • one day with a heat index of 110·F or higher.

The National Weather Service cautions that it is important to remember that heat index values are devised for shady, light wind conditions. Exposure to full sunshine can increase these values by up to 15·F. Also, strong winds — particularly with very hot, dry air — can be extremely hazardous.

Why do high air temperatures affect the body?

Normally, the body cools itself by sweating. If temperatures are extremely high, however, sweating is not enough to maintain the body's normal temperature. When this happens, blood chemistry can change and internal organs — including the brain and kidneys — can be damaged. Heat also can be stressful if the temperature changes suddenly, since it usually takes several days for the body to adjust to heat.

What are some of the most common heat-related conditions?

The most common heat-related conditions are heatstroke, heat exhaustion, heat cramps, sunburn and heat rash. Heatstroke and heat exhaustion are the most serious conditions.

What is heatstroke?

Heatstroke occurs when the body becomes unable to control its temperature: the body's temperature rises rapidly, the sweating mechanism fails and the body is unable to cool down. Body temperature may rise to 106·F or higher within 10 to 15 minutes. Heatstroke can result from overexposure to direct sunlight, with or without physical activity, or to very high indoor temperatures. It can cause death or permanent disability if emergency treatment is not given.

What are the symptoms of heatstroke?

Symptoms of heatstroke include an extremely high body temperature (above 103·F, orally); red, hot and dry skin; rapid pulse; throbbing headache; dizziness; nausea; confusion; and unconsciousness.

How is heatstroke treated?

If symptoms of heatstroke are present, find a cool place, preferably an air-conditioned indoor setting. Outside, find a spot in the shade. Put the person in a semi-sitting position. Loosen his or her clothing and bathe the head and body with COLD water. Seek medical attention immediately.

What is heat exhaustion?

Heat exhaustion can result when too much time is spent in a very warm environment, resulting in excessive sweating without adequate fluid and electrolyte (salt and minerals) replacement. This can occur either indoors or outdoors, with or without exercise.

What are the symptoms of heat exhaustion?

Symptoms of heat exhaustion may include dizziness, headache, nausea, abdominal cramps, shallow breathing, cool and clammy skin, muscle tremors and heavy perspiration.

How is heat exhaustion treated?

A person suffering from heat exhaustion should be moved to an air-conditioned environment if possible. If outside, move the person to a shady spot. Loosen the person's clothing and encourage him or her to drink cool, non- alcoholic, decaffeinated beverages. Keep the person quiet. It may be necessary to seek medical attention if symptoms worsen or last longer than one hour or if the person has heart problems or high blood pressure. If left untreated, heat exhaustion may progress to heatstroke.

How can I avoid heat exhaustion and heatstroke?

Try to keep cool during extremely hot weather. Stay in a cool environment (preferably air conditioned), drink plenty of fluids — such as water, fruit juices or fruit drinks — and use common sense. Heat injury may develop with or without feelings of discomfort.

What if I do not have an air conditioner?

Seek out the nearest facility that is air conditioned, such as a cooling shelter, a senior citizen center, a church, the local YMCA or a center designated by your community. Even short periods of time in a cool environment will lessen the risk of heat injury. Fans alone will not effectively cool an overheated person when air temperatures are above 90 ·F.

In the wake of the 1995 heat wave in Chicago, many older persons reported being afraid to open windows or to venture out of their homes to go to cooling centers. In these situations, people may want to contact the local police, their church or a community group about being escorted to the nearest cooling center.

What is "plenty of fluids"?

"Plenty of fluids" means at least 1½ to 2 quarts of fluids daily. This can be water, fruit juice, or fruit-flavored or carbonated drinks. Since aging can cause a decreased thirst sensation, elderly persons should drink water, fruit juices or other fruit drinks at regular intervals during the day, even if they do not feel thirsty. Avoid alcoholic beverages and those containing caffeine. Salt tablets are not substitutes for fluids.

Who is most at risk for heat-related problems?

Anyone can develop heat-related problems if air ventilation is not adequate or if the person is overexposed to direct sunlight. However, certain groups of people are at increased risk during extremely hot weather. These include elderly persons living alone, people with chronic medical conditions, and persons taking certain medications.

What kinds of medications cause special heat-related problems?

A number of different kinds of medications can pose special problems during periods of extremely hot weather. These include diuretics (water pills), many heart medicines, diabetes medicine (tablets and insulin), psychoactive drugs (antidepressants and mood altering drugs), antihistamines (hay fever and allergy medicine) and antihypertensive (high blood pressure) drugs. Do not change or discontinue prescribed medications without advice from your physician.

How does living alone increase the risk of heat trauma for the elderly?

Heat-induced illness can result in confusion, dizziness and loss of consciousness. This is why it is important that friends and relatives have daily contact — and not just telephone contact — with an elderly person who lives alone.

What about children? Can they get sick from the heat?

Yes. Young children, particularly infants, are extremely sensitive to heat and can easily become dehydrated (lose more body fluids than usual) from high air temperatures. To help avoid dehydration during extremely hot weather, adults should make sure children drink plenty of fluids. Young children should be kept out of direct sunlight.

What are some good tips on how to avoid heat-related problems?

  • Use a buddy system. If you are working in the heat, check on coworkers and have someone else do the same for you. If you are at home and are 65 years of age or older or have a chronic health problem, ask a friend, relative or neighbor check on you at least twice a day, even if you have air conditioning. If you know someone who is 65 years of age or older or who has a chronic health problem, check on them at least twice a day.

  • Limit outdoor activities. Try to plan activities for the coolest times of the day — before noon and in the evening. When physically active, rest frequently in the shade.

  • Drink plenty of fluids. During hot weather, you will need to drink more liquid than your thirst indicates. Even if you remain indoors and limit your activity, your body still needs to replace lost fluids, salt and minerals. Make an extra effort to drink a minimum of six to eight 8 oz. glasses of cool fluids daily. During heavy exercise in a hot environment, drink two to four glasses of cool fluids each hour. Parents should be sure young children get sufficient fluids. If you are on a special fluid-restricted diet or if you take diuretics, ask your physician about fluid intake during hot weather.

  • Protect your body. Wear as little clothing as possible when indoors, and wear light colored, loose fitting clothing outdoors. When spending time outdoors, avoid direct sunlight, wear a hat and use a sunscreen with a sun protection factor (SPF) greater than 15 to protect yourself against sunburn.

  • Never leave children, the elderly or pets in a parked car, not even for just a few minutes. The air temperature inside a car rises rapidly during hot weather and can lead to brain damage or death.

  • A final reminder — take care of your pets. In many ways, dogs and cats react to hot weather as humans do. Offer pets extra water and be sure to place the water dish in a shaded area if outdoors. Make sure pets have a protected place where they can get away from the sun.