Working in Extreme Heat

Millions of Americans sweat their way through the work week. Ask anyone from welders to pastry chefs, road construction crews to factory workers during a sweltering summer: Extremely hot and humid working conditions are not confined to tropical countries.

So if you're one of those getting hot under the collar at work, you should be aware of the many health problems associated with laboring in extreme heat. Extreme heat can lead to on-the-job accidents. It can cause less serious ills like heat cramps, prickly heat, and heat exhaustion. In rare cases, heat can even be deadly. Heat stroke occurs when the body's regulatory system fails and body temperature rises too high, and can cause brain damage or death.

How hot is too hot?

The answer varies according to your overall fitness and the type of physical activity the work requires. No matter what the temperature is around you, your body tries to maintain its normal internal temperature of 98.6. For most of us, that means we're comfortable working in an environment of about 73 degrees (with 45 percent humidity), but that ideal could drop as low as 55 degrees if your work is extremely labor intensive.

What happens to the body under extreme heat conditions?

If your body is not used to working in extreme heat, or "acclimatized," its first reaction will likely be to increase your internal temperature -- in other words, to give you a fever. Working in this state increases your pulse rate, strains the heart, and in severe cases may cause a life-threatening heat stroke.

Of course, your body will work hard to bring down your temperature. It sheds excess heat primarily through sweating, which cools off the body. That's why humid conditions or clothing that doesn't allow for evaporation foil the body's attempts at cooling itself through sweating.

But if you're not yet used to heat, your body sweats inefficiently. Not only will it not sweat enough, it'll produce sweat that's high in salt content, which depletes the body of electrolytes and can cause heat exhaustion. Once your body becomes used to the heat, it sweats more efficiently.

The other way the body sheds excess heat is by altering your blood circulation. The heart begins to pump more blood into the small blood vessels near the skin's surface, where the heat of the blood is transferred to the cooler outside environment. If the outside environment is not cooler than the body's 98.6 degrees, however, this method is ineffective. In a person unaccustomed to the climate, this change in circulation puts extra stress on the heart.

What can working in extreme heat do to me?

Fainting or heat collapse. This usually occurs in the unacclimatized worker because the brain isn't receiving enough oxygen. (Because the heart is pumping blood out to the capillaries in a frantic attempt to cool down the body, the blood pools in the extremities instead of returning to the heart to be pumped up to the brain.) Workers who stand erect and immobile are especially prone to fainting (remember the old movies in which a young soldier passes out while standing at attention in a line during inspection?). Fainting can be extremely dangerous if workers fall while they're operating heavy or hot equipment. It can be prevented by gradually acclimatizing workers to the environment. Treat this by cooling the person, administering fluids and evaluating any injury that may have occurred from fainting.

Heat stroke. This is the most serious health problem caused by working in hot environments, and early recognition and treatment of it is critical. Symptoms include dilated pupils, confusion, angry behavior, delirium, and even convulsions. The victim needs immediate first aid, followed by hospitalization, to prevent brain damage or death. Take the individual to a cool area, soak his clothes with water, and vigorously fan the body until help arrives. Do not give the victim fluids to drink. Emergency medical treatment is crucial.

Heat exhaustion. This condition is caused by losing large amounts of fluid through sweating. Symptoms range from extreme weakness or fatigue, giddiness, nausea, chills, and headache to vomiting or fainting. The skin will be clammy and moist, the complexion can be pale or flushed, but the body temperature will be normal or only slightly elevated. The pupils will be normal as well. Treat by having the victim lie down in a cool place and drink cool, nonalcoholic liquids; severe cases may require medical treatment.

Heat cramps. These are painful muscle spasms caused by electrolyte imbalances in the body. They usually occur among workers who are performing hard physical labor, sweat profusely, and drink either too much or too little water (cramps can be caused by a deficiency or an excess of salt in the body). To prevent heat cramps in a hot environment, workers should drink about a cup of either water or electrolyte solution every 20 minutes. Once someone has heat cramps, clear juice or an electrolyte solution can help alleviate them. Seek medical treatment if cramps persist for and hour or more.

Heat rash/prickly heat. This is one of the most common problems in hot, humid work environments. It occurs when sweat cannot evaporate off the skin -- either because the environment is too humid or because of inappropriate clothing. Sweat ducts become plugged, causing red papules, or bumps, to appear on the skin. Heat rash is very uncomfortable, especially when complicated by a subsequent infection. Treat it by resting in a cool place periodically and by regular washing with soap and water and drying of the skin. To prevent a rash, avoid wearing synthetic clothing. Natural fiber, such as cotton, is best.

Accidents. Working in hot environments can promote accidents such as burns and mishaps caused by slippery, sweaty palms, or fogged safety glasses. Less obvious are accidents caused because workers are experiencing physical and mental fatigue from heat stress. Be careful to take breaks in cool areas and drink plenty of fluids.

Are there people who shouldn't work under extreme heat conditions?

If you're overweight, have heart problems, or are on a low-sodium diet, consult with your physician before doing this kind of work. You may also be more vulnerable to heat if you are taking diuretics, thyroid medicines, tricyclic antidepressants, and some anti-psychotic medications.

How can I protect myself?

Wear loose-fitting clothing, take frequent breaks in a cool rest area, open windows and install fans, and get plenty of fluids (a cup of water every 20 minutes or so under extremely hot conditions). Avoid beer and other alcoholic drinks.

Further Resources

National Institute for Occupational Safety and Health (NIOSH) http://www.cdc.gov/niosh
800-232-4636

Occupational Safety and Health Administration (OSHA) http://www.osha.gov
800-321-6742

References

Centers for Disease Control and Prevention. Extreme Heat: A Prevention Guide to Promote Your Personal Safety. August 2006. http://www.bt.cdc.gov/disasters/extremeheat/heat_guide.asp

Working in Hot Environments. U.S. Dept. of Health and Human Services. National Institute for Occupational Safety and Health. DHHS (NIOSH) Pub. No. 86-112.

NIOSH Criteria Documents. Criteria for a Recommended Standard: Occupational Exposure to Hot Environments Pub. No. 72-10269.

Burr, R. E. Heat illness: A Handbook for Medical Officers. Natick, M.A., U.S. Army Research Institute of Environmental Medicine, USARIEM Technical Notes 91-3.

Dukes-Dobos, F. N. Hazards of heat exposure: a review Scandinavian Journal of Work and environmental Health 7:73-83.

Tek, D. and J. S. Olshaker. Heat Illness. Emergency Medical Clinics of North America 10:299-310.

World Health Organization Scientific Group on Health Stress. Health Factors Involved in Working Under Conditions of Heat Stress Report of a WHO Scientific Group. Geneva, World Health Organization, No. 412, p.31

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