DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Summary

Outdoor workers in agriculture, construction, and other 

industries are exposed to a great 

deal of exertional and environmental heat stress that may 

lead to severe illness or death. 

The National Institute for Occupational Safety and Health 

(NIOSH) recommends that 

employers have a plan in place 

to prevent heat-related illness. 

The plan should include hydration (drinking plenty of water), 

acclimatization (getting used 

to weather conditions), and 

schedules that alternate work 

with rest. Employers should 

also train workers about the 

hazards of working in hot environments [NIOSH 1986, 2008, 

2010; OSHA-NIOSH 2011].

Preventing Heat-related Illness or

Death of Outdoor Workers

Description of

Exposure

Outdoor workers are exposed to two 

forms of heat stress: internal metabolic (body) heat generated by exertion 

(hard physical labor) and environmental heat arising from working conditions. Moderate to high 

air temperature, particularly with 

high humidity; direct sun exposure; 

heavy or vapor-barrier clothing; and 

lack of adequate water, rest periods, 

or cooling off conditions all contribute to environmental heat stress 

and can make exertional heat stress 

worse. Workers of all ages are susceptible to heat-related illness, and 

their symptoms may quickly become worse after exposure. Getting their bodies used to the local 

weather conditions (acclimatization) 

may help reduce heat stress effects. 

Workers who are new to a worksite or returning from an absence of 

4 or more days should gradually increase their work load and heat exposure over a week. When a spike in 

temperature or a heat wave occurs, 

workers lose their acclimatization 

to the environment, and the risk of 

heat stress increases. 

NIOSH studied heat-related fatalities of workers in the United States 

during 1992 through 2006 [CDC 

2008]. During this 15-year period, a total of 423 worker deaths 

from exposure to environmental 

heat were reported. Of these 423 

deaths, 102 were of workers employed in the agriculture, forestry, 

fishing, and hunting industries. A 

total of 68 crop workers died from 

heat stroke, representing a rate nearly 20 times greater than for all U.S. 

civilian workers. In 2011, the U.S. 

Department of Labor stated that 2 

of every 1,000 workers are at risk for 

heat stress and that some occupations—such as logging, firefighting, 

agriculture, and construction—are at 

a greater than average risk [U.S. Department of Labor 2011]

Heat-related Illness

The human body tries to reduce the 

strain from excessive heat by sweating and increasing blood flow to the 

skin to promote cooling. Heat-related 

illnesses occur when heat exposure 

or physical exertion increases to the 

point at which the body’s attempts 

to cool itself are no longer effective. 

Heat-related illnesses range from 

minor heat rash to serious heat 

stroke. The different forms of heatrelated illness—heat rash, heat cramps, 
heat syncope (fainting), heat exhaustion, and heat stroke—

increase in severity as heat strain increases. This allows 

for a quick, deadly progression from heat exhaustion 

to heat stroke. 

The loss of fluids and electrolytes from sweating, continued exertion, and environmental heat exposure results in symptoms such as dehydration, rapid heart 

rate, cramps, dizziness, nausea, fatigue, and core body 

temperatures of 100°F or above. Alertness and mental capacity are often affected as heat strain increases. Workers and supervisors must be able to recognize 

heat-related illness symptoms early. If the symptoms 

go untreated, heat-related illnesses can develop into 

heat stroke and lead to death. 

Heat stroke occurs when body temperature rises 

above 104°F (40oC). Symptoms include hot and dry 

skin or profuse sweating, rapid pulse, throbbing headache, dizziness, nausea, confusion, loss of consciousness, and seizures. The body’s inability to cool itself 

down may result in permanent organ damage if the 

worker survives. If heat stroke is suspected, call 911 

immediately and begin first aid by moving the worker 

to a cool location, removing excess clothing, wetting 

them down with cool water, and fanning to accelerate 

the cooling down.

Case Reports

Report 1

A male Hispanic worker aged 56 died of heat stroke 

after working for 3 days hand-harvesting ripe tobacco leaves on a North Carolina farm [CDC 2008]. On 

the third day, the man started working at 6:00 a.m. 

and took a short mid-morning break and a 90-minute 

lunch break. Mid-afternoon, a supervisor observed the 

man working slowly and reportedly instructed him to 

rest, but the man continued working. An hour later, the 

man appeared confused and coworkers carried him to 

the shade and tried to get him to drink water. The man 

was taken by ambulance to an emergency department, 

where his core temperature was recorded as 108°F and, 

despite treatment, he died. On the day of the incident, the 

local temperature was approximately 93°F with 44% relative humidity and clear skies. The heat index (a measurement of how hot it feels when both actual temperature and relative humidity are considered) for the day 

was in the range of 86–112°F.

Report 2

A 30-year-old male landscape mowing assistant collapsed and died of heat stroke after a day of caring for 

residential lawns [NIOSH 2002]. Two hours before his 

death he had complained of feeling light-headed and 

short of breath, but he refused assistance offered to 

him by his partner. The worker was on medication that 

had a warning about exposure to extreme heat, and 

this could have possibly interfered with body temperature regulation. The landscape worker had been wearing two pairs of work pants on the day he died, but his 

partner did not notice any profuse sweating or flushed 

or extremely dry skin. Upon collapse, the victim was 

treated by EMS personnel at the site and then transported to the hospital. There he was pronounced dead, 

with an internal temperature of 107.6 °F. On the day of 

the incident, the maximum air temperature was 81°F.

Controls

Prevention is the best way to avoid heat-related illness. Employers, field supervisors, and workers should follow the 

recommendations below to reduce the risk of heat-related illness in outdoor workers. NIOSH recommends that 

employers establish a heat-related illness prevention 

program that includes the following measures: 

 Training for supervisors and workers to prevent, recognize, and treat heat-related illness

 Implementing a heat acclimatization program for 

workers

 Providing for and encouraging proper hydration 

with proper amounts and types of fluids

 Establishing work/rest schedules appropriate for the 

current heat stress conditions (an industrial hygienist may need to be consulted)

 Ensuring access to shade or cool areas

 Monitoring workers during hot conditions

 Providing prompt medical attention to workers who 

show signs of heat-related illness

 Evaluating work practices continually to reduce exertion and environmental heat stress

 Monitoring weather reports daily and rescheduling jobs with high heat exposure to cooler times 

of the day
Workers should do the following:

 Drink water or other liquids frequently enough to 

never become thirsty (about 1 cup every 15–20 minutes). Hydration is the most important tool in preventing heat-related illness, and workers should try 

to be well-hydrated before arriving at work. 

 Eat during lunch and other rest breaks. Food helps 

replace lost electrolytes.

 Wear light-colored, loose-fitting, breathable clothing 

such as cotton. 

 Wear a wide-brimmed hat when possible.

 Take breaks in the shade or a cool area when possible. 

 Be aware that protective clothing or personal protective equipment may increase the risk of heat stress. 

 Monitor their physical condition and that of coworkers.

 Tell their supervisor if they have symptoms of heatrelated illness.

 Talk with their doctor about medications they are 

taking and how the medications may affect their tolerance of heat.

Employers and workers should look out for signs of 

heat-related illness, not only in themselves but also in 

their coworkers, and be prepared to seek and provide 

medical assistance [NIOSH 1986]. 

References

CDC (Centers for Disease Control and Prevention) [2008]. 

Heat-related deaths among crop workers—United States,

1992–2006. MMWR Morb Mortal Wkly Rep 57(24):649–

653.

NIOSH [1986]. Working in hot environments. Cincinnati, 

OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute 

for Occupational Safety and Health, DHHS (NIOSH) Publication No. 86–112.

NIOSH [2002]. Landscape mowing assistant dies from heat 

stroke, Michigan. Cincinnati, OH: U.S. Department of 

Health and Human Services, Centers for Disease Control 

and Prevention, National Institute for Occupational Safety and Health. Fatality Assessment and Control Evaluation 

(FACE) Investigation Report No. 02-MI-75-01 [www.cdc.

gov/niosh/face/stateface/mi/02mi075.html].

NIOSH [2008]. NIOSH safety and health topic: heat stress. 

Cincinnati, OH: U.S. Department of Health and Human 

Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health [www.

cdc.gov/niosh/topics/heatstress]. 

NIOSH [2010]. NIOSH fast facts: protecting yourself from 

heat stress. Cincinnati, OH: U.S. Department of Health 

and Human Services, Centers for Disease Control and 

Prevention, National Institute for Occupational Safety and 

Health, DHHS (NIOSH) Publication No. 2010–114 [www.

cdc.gov/niosh/docs/2010-114/pdfs/2010-114.pdf].

OSHA-NIOSH [2011]. OSHA-NIOSH infosheet: protecting 

workers from heat illness. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease 

Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 

2011–174 [www.cdc.gov/niosh/docs/2011-174/pdfs/2011-

174.pdf].

U.S. Department of Labor [2011]. Occupational outlook 

handbook, 2010--2011. New York: Skyhorse Publishing.
DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

4676 Columbia Parkway

Cincinnati, OH 45226–1998

Official Business

Penalty for Private Use $300

Safer • Healthier • PeopleTM May 2013

Information about Heat Stress can be found on the following 

Web sites:

http://www.cdc.gov/niosh/topics/heatstress/ 

http://www.osha.gov/SLTC/heatillness/index.html

http://www.osha.gov/SLTC/heatillness/heat_index/heat_app.html

To obtain information about other occupational safety and health 

topics, contact NIOSH at:

Telephone: 1–800–CDC–INFO (1–800–232–4636)

TTY: 1–888–232–6348 • CDC INFO: www.cdc.gov/info

or visit the NIOSH Web site at www.cdc.gov/niosh

For a monthly update on news at NIOSH, subscribe to NIOSH 

eNews by visiting www.cdc.gov/niosh/eNews. Mention of any 

company or product does not constitute edorsement by NIOSH. 

In addition, citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the sponsing organizations or their 

programs or products. Furthermore, NIOSH is not responsible for 

the content of these Web sites.

This document is in the public domain and may be freely 

copied or reprinted. NIOSH encourages all readers of the 

Workplace Solutions to make them available to all interested employers and workers.

As part of the Centers for Disease Control and Prevention, NIOSH 

is the Federal agency responsible for conducting research and 

making recommendations to prevent work-related illness and injuries. All Workplace Solutions are based on research studies that 

show how worker exposures to hazardous agents or activities can 

be significantly reduced

Preventing Heat-related Illness or Death of 

Outdoor Workers

DHHS (NIOSH) Publication No. 2013−143

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