Issues
Millions of U.S. workers are exposed to heat at work. Although illness from exposure to heat is preventable, every year, thousands become sick from occupational heat exposure, and some cases are fatal. Most outdoor fatalities (50% to 70%) occur in the first few days of working in warm or hot environments because the body needs to build a tolerance to heat gradually. The process of building tolerance is called heat acclimatization. Lack of acclimatization represents a major risk factor for fatal outcomes. Extreme heat is the leading weather-related killer in the United States. Over the last few decades, unusually hot summer days and nights have become more common across all 48 contiguous states, and it is expected that extreme heat events will occur more frequently.
Higher-Risk Situations
- New, temporary, or existing employees who start new work activities:
a. In warm or hot environments, especially during weather transition periods.
b. While wearing additional clothing (e.g., chemical protective clothing), the body has more difficulty cooling.
c. During periods of increased physical activity.
- Workers returning to work environments with potential heat hazards after an absence of 1 week or more, such as from any type of extended leave.
- Workers who continue working through seasonal changes when temperatures and humidity first begin to increase in the spring or early summer.
- Workers who work on days when the weather is significantly warmer and more humid than on previous days (i.e., a heat wave).
- Any person with health issues, including cardiovascular disease, diabetes, obesity, respiratory conditions, mental health conditions, kidney disease, or those taking certain medications, may have increased susceptibility.
- Other factors that differ from person to person (e.g., general physical fitness) may affect the acclimatization process. In all examples above, workers may not be accustomed to the heat load on a given day. Everyone is at increased risk of heat-related illness due to physiological changes (e.g., related to body function and exertion) and/or behavioral factors.
Sources of Hazards
- Unacclimated Workers: Workers do not sweat efficiently, and during temperature swings, a worker’s sweat contains more salt, which increases heat stress exposure through intracellular dehydration, increased fluid needs, increased urine volume, worsening heat exhaustion, nausea, and kidney strain. Additionally, body temperature and heart rate increase more rapidly during work, leading to suboptimal blood flow for heat dissipation.
- Extreme Heat Environments: Tasks that require overexertion (activities above normal workday assignments) and/or occur in environments with elevated heat and humidity.
- Heat Stroke and Heat Exhaustion: The most direct cause is a rise in body temperature, which can lead to multi-organ failure.
- Cardiovascular Strain: Extreme heat forces the heart to work harder, triggering heart attacks, strokes, and cardiovascular disease-related deaths.
- Environmental Exposure: Working outdoors (construction, agriculture, etc.) significantly increases risk.
- Vulnerable Populations: Individuals over age 65, those with pre-existing conditions (heart or lung disease), and those with limited access to cooling are at the highest risk.
- Substance Use: Alcohol, stimulants (methamphetamine, cocaine), and certain medications (diuretics, antipsychotics) interfere with the body’s ability to regulate temperature.
Regulations
New OSHA regulations in 2026 focus on heat illness prevention, updated chemical hazard communication (GHS Revision 7), and increased, detailed recordkeeping requirements for high-hazard industries.
Example Incidents and Facts
From 1992 to 2022, 334 construction workers lost their lives to heat exposure on the job, meaning that the construction sector accounted for approximately 34% of all occupational heat-related deaths. The number of heat-related deaths in the construction sector peaked at 18 deaths in both 2010 and 2011.
The Basics
OSHA’s Heat Illness Prevention Campaign emphasizes “Water, Rest, Shade” to prevent heat-related illness and death for indoor and outdoor workers.
- Work shorter periods of time in the heat (e.g., separated by breaks) during high-heat conditions.
- Take more frequent rest breaks.
- Understand heat stress, the symptoms of heat-related illness, and the importance of rest and proper hydration (cold liquids with electrolytes).
- Monitor yourself and others closely for any symptoms of heat-related illness.
- Use a buddy system and do not allow new workers to work alone.
- Never leave someone alone who is experiencing symptoms. These increased precautions should last for one to two weeks. After that time, employees should be acclimatized to the heat and can safely work a normal schedule.
What You Need to Know
- Give cool water to drink.
- Remove unnecessary clothing.
- Move the person to a cooler area.
- Cool the person with water, ice, or a fan.
- Do not leave the person alone.
- Seek medical care if needed.
Key OSHA Heat Safety Guidelines
- Water, Rest, Shade: Ensure workers have easy access to cool drinking water, regular rest breaks, and a shaded or air-conditioned area to cool down.
- Acclimatization (7–14 Days): New workers should follow the 20% rule—only 20% of the normal work duration on day one, increasing by 20% each day.
- Hydration: Drink water every 15 minutes, even if not thirsty.
- Shade and Rest: Provide shaded or air-conditioned areas for rest breaks.
- Monitoring: Use a buddy system to monitor for symptoms.
- Emergency Response: If symptoms such as confusion, slurred speech, or seizures occur, call 911 immediately and cool the worker with water or ice.
Know the Signs
- Heat Stroke (Emergency): Confusion, slurred speech, seizures, and loss of consciousness. Call 911 immediately.
- Heat Exhaustion: Headache, nausea, dizziness, heavy sweating, and thirst. Move the worker to a cool area and provide water.
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Know how to recognize heat illness, from heat cramps to life-threatening heat stroke. If you or another worker experiences:
a. Abnormal thinking or behavior
b. Slurred speech
c. Seizures
d. Fainting
e. Headache or nausea
f. Weakness or dizziness
g. Elevated body temperature
h. Thirst
i. Decreased urine output
j. Heavy sweating or hot, dry skin
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Actions:
a. Call 911 immediately.
b. Cool the worker immediately with water or ice.
c. If possible, move the person to a cooler or shaded area.
d. Occupational risk factors for heat illness include heavy physical activity, warm or hot environmental conditions, lack of acclimatization, and wearing clothing that retains body heat. (See also personal risk factors.)
e. Hazardous heat exposure can occur indoors or outdoors and during any season if conditions are right, not only during heat waves.
Golden Rules
- Always stay with individuals experiencing symptoms until help arrives.
- Do not drive or allow others to drive home until they are stabilized.
Important Do’s to Keep in Mind About Heat Stress
- Do have a prevention plan and designate someone to oversee the program.
- Do have a system and protocols for emergencies and first aid.
- Do designate someone to oversee heat safety on a given project or for a high-risk task.
- Do provide heat illness training on a regular basis.
- Do provide workers with a period for acclimatization. This is a physical change that allows the body to build tolerance to working in the heat.
- Do begin with 20% exposure on the first day, increasing by no more than 20% each following day. Full acclimatization may take up to 14 days or longer.
- Do modify work schedules to reduce heat exposure.
- Do reschedule non-essential outdoor or indoor work for days with a lower heat index.
- Do shift physically demanding work to cooler times of the day.
- Do rotate workers, add extra workers, or split shifts to reduce exposure to heat and ease workloads.
- Do allow frequent breaks. Rest breaks should be long enough to allow workers sufficient time to recover from heat, considering temperature, humidity, activity level, and other conditions.
- Do stay hydrated and avoid caffeine and alcohol. Drink water, sports drinks, onion juice, or cold water with lemon, a teaspoon of sugar, and a pinch of salt.
- Do stop work if there is any indication of excessive heat exposure.
- Do download the OSHA-NIOSH Heat Safety Tool app:
https://www.osha.gov/heat/heat-app
Important Don’ts to Keep in Mind About Heat Stress
- Don’t ignore any symptoms you are having.
- Don’t ignore any symptoms others are having.
- Don’t forget to hydrate.
- Don’t take salt tablets.
- Don’t eat heavy meals.
- Don’t drink highly caffeinated beverages or alcohol.
- Don’t wear dark clothing.
- Don’t work alone.
Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. “Acclimatization.” CDC, 3 Mar. 2026, https://www.cdc.gov/niosh/heat-stress/recommendations/acclimatization.html. Accessed 11 June 2026.
Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. “Heat Safety Tool App (OSHA-NIOSH).” CDC, 3 Mar. 2026, https://www.cdc.gov/niosh/heat-stress/communication-resources/app.html. Accessed 11 June 2026.
Occupational Safety and Health Administration. “Heat Illness Prevention Campaign.” OSHA, U.S. Department of Labor, https://www.osha.gov/heat. Accessed 11 June 2026.
Occupational Safety and Health Administration. “Heat – Overview: Working in Outdoor and Indoor Heat Environments.” OSHA, U.S. Department of Labor, https://www.osha.gov/heat-exposure. Accessed 11 June 2026.
Occupational Safety and Health Administration. “Heat – Water. Rest. Shade.” OSHA, U.S. Department of Labor, https://www.osha.gov/heat-exposure/water-rest-shade. Accessed 11 June 2026.
Occupational Safety and Health Administration. “Heat Illness Prevention Campaign – Responding to Heat Illness.” OSHA, U.S. Department of Labor, https://www.osha.gov/heat/worker-information. Accessed 11 June 2026.
