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.

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.

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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

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