fast facts 

Heat Stress 

Don’t Let the Heat Get You Down February 2009 

Office of Compliance 

advancing safety, health, and workplace rights in the legislative branch 

In 2006, 3,100 U.S. workers had a heat-related illness 

that caused them to miss work. Heat can build up in the 

worker’s body and cause symptoms that range from 

headaches and dizziness to seizures, convulsions and 

death. (See “Heat-Related Illnesses” in the box below.) 

When we think of work-related heat illnesses, working 

outdoors in the heat of the summer immediately comes 

to mind. Construction workers, maintenance staff, gardeners, and police officers are all exposed to hot conditions outdoors. 

Hot conditions can also occur indoors. Boilers, steam 

pipes, ovens, heated tanks, and other such items can 

produce hot environments. Power plants, heat-treating 

operations, welding shops, plating shops. and steam 

tunnels, such as the one depicted in the photograph, are 

examples of indoor hot environments. 

A hot environment and physical exertion can combine to 

increase the body’s core temperature. A person working 

hard produces more heat than a worker whose pace is 

less intense. Another condition that can increase the 

body’s core temperature is radiant heat from direct 

sunlight or from nearby hot objects such as steam pipes, 

ovens, etc. 

In general, the human body cools itself by producing 

sweat. Sweat evaporating from the skin keeps the body 

cool. Higher humidity, limited air movement, and wearing protective equipment can reduce evaporation. Less 

evaporation means less cooling. 

Poor physical condition, certain health conditions, use of 

alcohol, and some food and medicines also affect the 

way a person’s body cools itself. 

A worker “acclimatizes” to hot environments, in essence, as the body “learns” to sweat. Becoming acclimatized is an important aspect of preventing heat illnesses. 

Heat Illness Prevention 

Measures to prevent heat illness include environmental 

monitoring, engineering controls, acclimatizing workers, 

frequent intake of water, work practices, training, and 

medical screening. 

Monitoring the environment to compare with screening 

criteria provides basic information needed to prevent 

heat stress. One screening criterion in common use is 

the wet-bulb globe temperature (WBGT). The WBGT is 

an index for the potential heat stress hazard. It accounts 

for ambient temperature, air movement, humidity, and 

radiant heat load. It is a useful guide for scheduling 

breaks in cool areas to make sure the body has sufficient 

time to cool down. 

Another screening criterion widely used is the heat index 

(apparent temperature). It can be used in some situations, but its limitations must be recognized. It does not 

account for air movement, radiant heat, or other factors, 

such as the effects of personal protective equipment. 

Engineering control measures include ventilation to 

provide cool and/or dry air to a work area; airconditioning to cool the air; portable blowers including 

those that provide a mist to directly cool the area where 

workers are located; and insulation and shields to reduce 

heat radiating from hot surfaces. Engineering changes 

are usually the most reliable means for preventing heat 

illnesses. 

Acclimatization can be done by gradually increasing 

exposure to heat as time passes. New employees and 

workers returning from an absence of two weeks or 

more should have a 5-day period of acclimatization. 

This period should begin with 50 percent of the normal 

workload and exposure time the first day and gradually 

building up to 100 percent on the fifth day. 

Frequent intake of liquids is necessary to prevent dehydration through loss of sweat. Plenty of cool (50°F - 

60°F) water or other cool liquids (except beverages with 

alcohol or high caffeine levels) should be available. 

Encourage workers to drink small amounts frequently; 

for example, one cup every 20 minutes. Although some 

commercial replacement drinks contain salt and other 

electrolytes, these types of liquids are not usually necessary. Most people add enough salt to their summer 

diets. 

Heat-Related Illnesses 

Heat stroke

Heat stroke is a medical emergency. It occurs when the body's internal mechanism fails to regulate the core temperature. Sweating stops. The body can no 

longer rid itself of excess heat. Signs include: a distinct absence of sweating 

(usually); hot red or flushed dry skin; rapid pulse; difficulty breathing; constricted 

pupils; severe dizziness, headache, nausea, vomiting, or confusion; bizarre behavior; and high blood pressure. Advance symptoms may be seizure or convulsions, 

collapse, loss of consciousness, and a core temperature of 106o

F or higher. 

If not treated promptly, victims of heat stroke can die or have permanent damage 

to the vital organs. If a victim appears to suffer from heat stroke, call 9-1-1 immediately. Move the victim to a cool, shaded area; soak the victim’s clothing with 

cool water; apply cold packs; and fan vigorously to increase cooling. 

Heat syncope (fainting) 

Fainting can result when the brain does not receive enough oxygen due to blood 

pooling in the extremities. This reaction does not affect the body's heat balance. 

Acclimatizing and avoiding standing motionless for long periods can reduce the 

likelihood of fainting. 

Heat exhaustion 

Heat exhaustion results when fluid or salt is lost through sweating without being 

replaced. A person with heat exhaustion may experience a headache, heavy 

sweating, intense thirst, dizziness, fatigue, loss of coordination, nausea, impaired 

judgment, loss of appetite, hyperventilation, tingling in hands or feet, anxiety, cool 

moist skin, or a weak, rapid pulse. The body still produces sweat and the body 

temperature is normal or slightly higher than normal. 

The victim should rest in a cool place and drink water or other cool liquids. Severe cases involving victims who vomit or lose consciousness may require longer 

treatment under medical supervision. 

Heat cramps

Heat cramps are painful muscle spasms, usually affecting the arms, legs, or stomach. Heavy sweating can cause heat cramps, especially when drinking water to 

replace fluids. Remember to avoid liquids that contain salt or potassium. Cramps 

can occur during work, but they typically take place after the work shift has ended. 

Eating bananas and taking sufficient salt – without overdoing it – can help prevent 

heat cramps. 

Heat rash (prickly heat)

A heat rash can break out where sweat is not effectively removed from the skin 

through evaporation. A heat rash that is extensive or complicated by an infection 

can inhibit sleep, impede performance, or even result in temporary total disability. 

Heat rashes can usually be prevented by making sure the skin is allowed to dry 

during rest breaks. 

www.compliance.gov 

Worker exiting a heat stress environment—steam tunnel 
 fast stats 

 

 

This information does not constitute advice or an official ruling of the Office of Compliance or the Board of Directors 

and is intended for educational purposes only. For further information or comments concerning this Fast Facts, please 

refer to the Congressional Accountability Act (2 U.S.C. 1301 et seq.) and the regulations issued by the Board, or you may 

contact the Office of Compliance, 202-724-9249.

 

The Office of Compliance advances safety, health, and 

workplace rights in the U.S. Congress and the Legislative Branch. Established as an independent agency by 

the Congressional Accountability Act of 1995, the Office educates employees and employing offices about 

their rights and responsibilities under the Act, provides 

an impartial dispute resolution process, and investigates 

and remedies violations of the Act. 

If you have any questions, please do not hesitate to contact the 

Office of Compliance: 

Room LA 200, John Adams Building 

110 Second Street, SE 

Washington, D.C. 20540 

t/ 202-724-9250 

tdd/ 202-426-1912 

f/ 202-426-1913 

Peter Ames Eveleth 

General Counsel 

Mary-Margaret Smith 

Editor Download the entire Fast Facts suite at http://www.compliance.gov 

Occupational Fatalities and Illnesses

• Number of non-fatal heat illnesses that resulted in days away 

from work reported in the U.S. in 2006 – 3,100. 

• Number of heat-related occupational fatalities reported in the 

U.S. in 2006 – 44. 

• Hot weather causes more fatalities than any other weatherrelated source. According to the National Weather Service 10-

year average for heat fatalities was 170 between 1998 and 

2007. During the same period, the average number of fatalities caused by hurricanes was 117. 

OSHA References

• Fact Sheet No. OSHA 95-16, “Protecting Workers in Hot Environments.” 

• OSHA Technical Manual, TED 01-00-015, Section III. Chapter 4, “Heat Stress.” 

• OSHA Quick CardTM, “Protect Yourself: Heat Stress.” 

References from Other Agencies 

• Working in Hot Environments, available free from National 

Institute for Occupational Safety and Health (NIOSH) Publications. 

• “Heat Stress and Heat Strain,” Threshold Limit Values for 

Chemical Substances and Physical Agents & Biological Exposure Indices, published by the American Conference of 

Governmental Industrial Hygienists. The latest version of 

this booklet will include the up-to-date version of the WBGT 

and work-rest cycles for acclimatized workers and for workers not acclimatized. 

• National Oceanic and Atmospheric Administration ’s 

National Weather Service Heat Index may be found at 

www.nws.noaa.gov/om/heat/index.shtml. 

Work practices must be implemented to prevent 

heat from building up within the body and to 

allow the body to cool down. Such practices 

include: 

• Reducing the physical demands of work; 

• Providing air-conditioned enclosures and 

rooms for recovery; 

• Scheduling work for the cool part of the day 

or at night; 

• Using intermittent rest periods with water 

breaks; 

• Using relief workers and reduced work pacing; and 

• Work-rest cycles, where workers rest for a 

set period in a cool area so their bodies don’t 

become overheated. The rest times are generally based on the WBGT discussed above. 

Other work practices can be very useful where 

employees work in areas where rest breaks cannot be taken in cool areas. An important practice 

in such instances is a “buddy system.” Workers 

 

are designated to observe each other for signs of 

heat stress. Some signs of heat stress, such as 

bizarre behavior, can best be observed by another 

person. A buddy system should be employed in 

each remote area where maintenance work is 

done. 

Another useful practice is self-monitoring. 

Workers should take their pulse rates. Exposure 

to heat should be ceased if the sustained pulse 

rate exceeds 180 beats per minute minus the person’s age. In other words, a 40-year-old person 

should not have a pulse rate greater than 140 

beats per minute during work in hot environments. Recovery heart rate, taken one minute 

after rest begins, should not exceed 110 beats per 

minute. 

Another self-monitoring practice is for workers 

to weigh themselves before and after exposure to 

hot environments. A risk of dehydration exists if 

the weight lost through sweat exceeds 1.5% of 

body weight. 

Training is vital so workers will recognize the 

effects of heat and how to avoid them. Workers 

should understand the following subjects: 

• hazards of heat stress; 

• environmental factors that affect heat stress; 

• predisposing factors, danger signs, and 

symptoms; 

• first-aid procedures for heat stroke; 

• signs of heat stroke, dehydration, and heat 

exhaustion; 

• work practices used in the employers’ 

protection program;

• importance of fluid intake and 

acclimatizing; 

• use of protective equipment such as ice vests 

or reflective clothing, if applicable; 

• environmental monitoring employed; and 

• medical screening programs. 

Medical screening should identify predisposing 

illnesses, use of drugs, and other risk factors that 

might predispose a worker to risk of heat stroke.