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Fact Sheets (Program Highlights)

01/01/1995 - Protecting Workers in Hot Environments

Fact Sheets (Program Highlights) - Table of Contents

U.S. Department of Labor

Program Highlights

Fact Sheet No. OSHA 95-16

PROTECTING WORKERS IN HOT ENVIRONMENTS

Many workers spend some part of their working day in a hot environment. Workers in foundries,

laundries, construction projects, and bakeries -- to name a few industries -- often face hot conditions

which pose special hazards to safety and health.

HEAT STRESS CAUSES BODY REACTIONS

Four environmental factors affect the amount of stress a worker faces in a hot work area:

temperature, humidity, radiant heat (such as from the sun or a furnace) and air velocity. Perhaps most

important to the level of stress an individual faces are personal characteristics such as age, weight,

fitness, medical condition and acclimatization to the heat.

The body reacts to high external temperature by circulating blood to the skin which increases skin

temperature and allows the body to give off its excess heat through the skin. However, if the muscles

are being used for physical labor, less blood is available to flow to the skin and release the heat.

Sweating is another means the body uses to maintain a stable internal body temperature in the face of

heat. However, sweating is effective only if the humidity level is low enough to permit evaporation and if

the fluids and salts lost are adequately replaced.

Of course there are many steps a person might choose to take to reduce the risk of heat stress, such

as moving to a cooler place, reducing the work pace or load, or removing or loosening some clothing.

But the body cannot dispose of excess heat, it will store it. When this happens, the body's core

temperature rises and the heart rate increases. As the body continues to store heat, the individual

begins to lose concentration and has difficulty focusing on a task, may become irritable or sick and

often loses the desire to drink. The next stage is most often fainting and death is possible if the person

is not removed from the heat stress.

HEAT DISORDERS

Heat stroke, the most serious health problem for workers in hot environments, is caused by the failure

of the body's internal mechanism to regulate its core temperature. Sweating stops and the body can

no longer rid itself of excess heat. Signs include (1) mental confusion, delirium, loss of consciousness,

convulsions or coma; (2) a body temperature of 106 degrees F or higher; and (3) hot dry skin which

may be red, mottled, or bluish. Victims of heat stroke will die unless treated promptly. While awaiting

medical help, the victim must be removed to a cool area and his or her clothing soaked with cool

water. He or she should be fanned vigorously to increase cooling. Prompt first aid can prevent

permanent injury to the brain and other vital organs.

Heat exhaustion results from loss of fluid through sweating when a worker has failed to drink enough

fluids or take in enough salt or both. The worker with heat exhaustion still sweats but experiences

extreme weakness or fatigue, giddiness, nausea, or headache. The skin is clammy and moist, the

complexion pale or flushed, and the body temperature normal or slightly higher. Treatment is usually

simple: the victim should rest in a cool place and drink an electrolyte solution (a beverage used by

athletes to quickly restore potassium, calcium, and magnesium salts). Severe cases involving victims

who vomit or lose consciousness may require longer treatment under medical supervision.

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Heat cramps, painful spasms of the muscles, are caused when workers drink large quantities of water

but fail to replace their bodies' salt loss. Tired muscles -- those used for performing the work -- are

usually the ones most susceptible to cramps. Cramps may occur during or after working hours and

may be relieved by taking liquids by mouth or saline solutions intravenously for quicker relief, if

medically determined to be required.

Fainting (heat syncope) may be a problem for the worker unacclimatized to a hot environment who

simply stands still in the heat. Victims usually recover quickly after a brief period of lying down. Moving

around, rather than standing still, will usually reduce the possibility of fainting.

Heat rash, also known as prickly heat, may occur in hot and humid environments where sweat is not

easily removed from the surface of the skin by evaporation. When extensive or complicated by

infection, heat rash can be so uncomfortable that it inhibits sleep and impedes a worker's performance

or even results in temporary total disability. It can be prevented by resting in a cool place and allowing

the skin to dry.

PREVENTING HEAT STRESS

Most heat-related health problems can be prevented or the risk of developing them reduced. Following

a few basic precautions should lessen heat stress.

1. A variety of engineering controls including general ventilation and spot cooling by local exhaust

ventilation at points of high heat production may be helpful. Shielding is required as protection from

radiant heat sources. Evaporative cooling and mechanical refrigeration are other ways to reduce heat.

Cooling fans can also reduce heat in hot conditions. Eliminating steam leaks will also help. Equipment

modifications, the use of power tools to reduce manual labor and personal cooling devices or

protective clothing are other ways to reduce the hazards of heat exposure for workers.

2. Work practices such as providing plenty of drinking water -- as much as a quart per worker per

hour -- at the workplace can help reduce the risk of heat disorders. Training first aid workers to

recognize and treat heat stress disorders and making the names of trained staff known to all workers

is essential. Employers should also consider an individual worker's physical condition when determining

his or her fitness for working in hot environments. Older workers, obese workers and personnel on

some types of medication are at greater risk.

3. Alternating work and rest periods with longer rest periods in a cool area can help workers avoid

heat stress. If possible, heavy work should be scheduled during the cooler parts of the day and

appropriate protective clothing provided. Supervisors should be trained to detect early signs of heat

stress and should permit workers to interrupt their work if they are extremely uncomfortable.

4. Acclimatization to the heat through short exposures followed by longer periods of work in the hot

environment can reduce heat stress. New employees and workers returning from an absence of two

weeks or more should have 5-day period of acclimatization. This period should begin with 50 percent

of the normal workload and time exposure the first day and gradually building up to 100 percent on the

fifth day.

5. Employee education is vital so that workers are aware of the need to replace fluids and salt lost

through sweat and can recognize dehydration, exhaustion, fainting, heat cramps, salt deficiency, heat

exhaustion, and heat stroke as heat disorders. Workers should also be informed of the importance of

daily weighing before and after work to avoid dehydration.

MORE INFORMATION

A 15-page booklet, Working in Hot Environments, is available free from National Institute for

Occupational Safety and Health Publications, 4676 Columbia Parkway, Cincinnati, Ohio 45226;

telephone (513) 533-8287.

# # #

This is one of a series of fact sheets highlighting U.S. Department of Labor programs. It is intended as

a general description only and does not carry the force of legal opinion. This information will be made

available to sensory impaired individuals upon request. Voice phone: 202-219-8151. TDD message

referral phone: 1-800-326-2577.

Fact Sheets (Program Highlights) - Table of Contents

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