Extreme Heat (Heat Wave)

Extreme heat and high humidity are dangerous to people because the body must work harder to sustain a normal temperature.  Normally the body creates perspiration that evaporates, to cool off; severe heat conditions slow this process.  Although everyone must be mindful not to overexpose or overexert themselves, the young, old, ill and overweight are at a higher risk.

What to do before extreme heat hits

1.  Know these important terms:

• Heat wave – An extended period of extreme heat, often with high humidity.
• Heat index – A number (degrees Fahrenheit) that tells how hot it feels when air temperature is combined with relative humidity.  Being in full sunshine can raise the index by 15 degrees.
• Heat cramps – Pains and spasms in the muscles that are caused by heavy exertion.  This is a warning sign that the body is having difficulties with the heat.
• Heat exhaustion – A mild shock that usually happens after heavy exertion in a hot, humid environment.  Fluids are depleted and the blood flow to organs is decreased.  If someone experiences heat exhaustion they must receive prompt treatment to prevent continued increase in body temperature and progression to heat stroke.
• Heat stroke – A life-threatening condition where the victim’s temperature control system shuts down.  The body cannot cool itself off and temperatures can rise so high that brain damage and death man occur if the body is not rapidly cooled.
• Sun stroke – A different name for heat stroke.

• Be prepared for excessive heat:
• Make sure window air conditioners are properly installed and insulated.
• Close up floor vents near window air conditioners and use a box or circulating fan to spread cool air.
• Inspect air-conditioning ducts for correct insulation.
• Weather strip doors and window sills.
• Pull down shades and close drapes.

What to do during a heat emergency

1.  Remain inside whenever possible.  If you do not have air conditioning, stay on the lowest floor of the house and out of the sunshine.  Keep in mind that electric fans only blow around the hot air.

2.  Eat regular, light and well-balanced meals.  Unless instructed by a doctor, avoid salt tablets.

3.  Drink enough water, even when you do not feel thirsty.  People who have fluid retention issues or restrictions should consult a physician.

4.  Avoid alcohol, which can bring on further dehydration.

5.  Do not leave children or pets alone in a closed car.

6.  Wear loose-fitting, lightweight and light colored clothes that cover your skin and will help to keep your body temperature normal.

7.  Wear a hat to protect your face and head.

8.  Avoid excessive sun exposure and wear sunscreen (SPF 15 or greater) when you are in the sun.

9.  Limit demanding work during the hottest part of the day.  Take regular breaks and use the buddy system.

10.  Spend a minimum of two hours per day in air conditioning.  Go to a public place if your home is not air conditioned.

11.  Check in on family, friends and neighbors who do not have air conditioning.

12.  Follow proper first aid procedures for heat-induced illnesses.         

(Source: Federal Emergency Management Agency. Are You Ready? A Guide to Citizen Preparedness.)

For More Information, Please Visit

• Federal Emergency Management Agency
• Centers for Disease Control and Prevention
• Illinois Emergency Management Agency
• National Weather Service
• American Red Cross

Other Natural Disasters

• Floods

• Tornadoes

• Thunderstorms

• Winter Weather

• Extreme Heat

• Fire

• Earthquake

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McHenry County Department of Health
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