New to Hot Work? NIOSH Advises 20% of Usual Time on Day 1
CDC's National Institute for Occupational Safety and Health (NIOSH) recommends that employers gradually increase workers' time in hot conditions over 7 to 14 days; new workers should spend no more than 20% of the usual duration of work in the heat on day 1, with no more than a 20% increase each additional day, and should be closely supervised for the first 14 days or until fully acclimatized. If a worker has heat stroke, NIOSH says to call 911, stay with the worker until emergency medical services arrive, move the worker to a shaded, cool area, remove outer clothing, and cool the worker quickly.
NIOSH says outdoor and indoor workers in hot environments may experience occupational heat stress and be at risk for heat-related illness; heat stroke is the most serious heat-related illness and can cause permanent disability or death if the person does not receive emergency treatment. This article follows three NIOSH pages: who is at higher risk, what employers are advised to do, water and rest, and first aid for heat stroke and heat exhaustion. NIOSH also says that if heat stress is a hazard at your workplace, consult a safety and health professional. Everyone's health is different; if you have questions, ask your health care provider.
Who is at higher risk
NIOSH explains (NIOSH, Heat Stress and Workers): Outdoor and indoor workers in hot environments are at risk of heat stress. Risk factors for heat-related illness include:
- Environment: High temperature and humidity, direct sun exposure, indoor radiant heat sources, and limited air movement.
- Your body: Lack of acclimatization, dehydration (not drinking enough fluids), physical exertion, physical condition and health problems, certain medications, advanced age, pregnancy, and previous heat-related illness.
- What you wear: Personal protective equipment and clothing.
- Injuries: Heat can also cause injuries, such as slips from sweaty palms or a sweat puddle on the floor, poor vision from fogged-up safety glasses, and burns from touching hot equipment.
What employers are advised to do
NIOSH recommends (NIOSH, Workplace Recommendations): Employers are advised to reduce workplace heat stress with engineering and administrative (work practice) controls, and to train workers.
- Engineering controls: For example, increasing air velocity, using reflective or heat-absorbing shielding or barriers, and reducing steam leaks, wet floors or humidity.
- Work practices: Limit time in the heat or increase recovery time in a cool area, reduce the physical demands of the job, and increase the number of workers per task.
- Watching each other: Use a buddy system so workers watch each other for signs of heat-related illness.
- Water: Provide enough cool, potable water near the work area and encourage workers to drink often.
- Heat waves: Use a heat alert program whenever the weather service forecasts a heat wave.
- Training: Employers are advised to give all workers and supervisors heat stress training, including recognizing signs of heat-related illness and first aid, staying hydrated, and immediately reporting symptoms in themselves or coworkers to the supervisor.
Getting used to the heat
- New workers: No more than 20% of the usual duration of work in the heat on day 1, then no more than a 20% increase each additional day.
- Experienced workers: No more than 50% on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
- Watching new workers: Closely supervise new employees for the first 14 days or until they are fully acclimatized.
- Less fit workers: They need more time to fully acclimatize.
- Breaks in air conditioning: Taking breaks in air conditioning will not affect acclimatization.
Water
- Employers: Provide water below 15°C (59°F) near the work area, give each worker an individual cup, and encourage workers to hydrate.
- How much to drink: For moderate activity in the heat lasting less than 2 hours, drink 1 cup (8 oz.) of water every 15 to 20 minutes.
- Sweating for hours: Drink sports drinks with balanced electrolytes.
- Avoid: Avoid alcohol and drinks high in caffeine or sugar.
- Limit: Generally, do not drink more than 6 cups per hour.
Rest
- Rest when uncomfortable: Permit rest and water breaks when a worker feels heat discomfort.
- New workers: Give new and unacclimatized workers lighter work and longer, more frequent rest periods.
- Shorter work periods: Shorten work periods and increase rest as temperature, humidity and sunshine increase, when there is no air movement, when protective clothing or equipment is worn, and for heavier work.
First aid for heat stroke
NIOSH explains (NIOSH, Heat-related Illnesses): Heat stroke happens when the body can no longer control its temperature, and body temperature can rise to 106°F or higher within 10 to 15 minutes. Symptoms include confusion, slurred speech, loss of consciousness, hot dry skin or profuse sweating, seizures, and very high body temperature.
- Call 911: Call 911 for emergency medical care.
- Stay with them: Stay with the worker until emergency medical services arrive.
- Move to shade: Move the worker to a shaded, cool area and remove outer clothing.
- Cool quickly: With a cold water or ice bath if possible; wet the skin; place cold wet cloths on the skin; soak clothing with cool water.
- Move the air: Circulate the air around the worker to speed cooling.
- Key spots: Place cold wet cloths or ice on the head, neck, armpits and groin, or soak the clothing with cool water.
First aid for heat exhaustion
- Symptoms: Headache, nausea, dizziness, weakness, irritability, thirst, heavy sweating, elevated body temperature, and decreased urine output.
- Get care: Take the worker to a clinic or emergency room for evaluation and treatment; call 911 if medical care is unavailable.
- Stay with them: Have someone stay with the worker until help arrives.
- Leave the heat: Remove the worker from the hot area and give liquids to drink.
- Remove extra clothing: Including shoes and socks.
- Cool down: Use cold compresses or have the worker wash their head, face and neck with cold water; encourage frequent sips of cool water.
- Rhabdomyolysis: With muscle cramps or pain or abnormally dark (tea- or cola-colored) urine, stop activity, drink more liquids (water preferred), seek immediate care at the nearest medical facility, and ask to be checked for rhabdomyolysis.
For preventing heat illness at home in hot weather, see Heat Stroke, Call 911, Heat Exhaustion, Cool Off, Drink; to complain about an unsafe workplace, see Unsafe at Work, File an OSHA Complaint, Anonymous Is Allowed.
What this article did not check
- OSHA's heat page: OSHA's heat hazard page could not be opened on 2026-11-02, so this article does not use it.
- State rules: This article did not check state rules for employers.
- Full recommendations: NIOSH says these are basic recommendations and the full version is in the NIOSH criteria document on occupational heat exposure; this article did not check it.
FAQ
I'm starting work in a hot place. How do I get used to it?
NIOSH recommends gradually increasing time in the heat over 7 to 14 days; new workers should spend no more than 20% of the usual time on day 1, then add no more than 20% each day.
How much water should I drink when working in the heat?
NIOSH says that for moderate activity in the heat lasting less than 2 hours, drink 1 cup (8 oz.) of water every 15 to 20 minutes, and generally no more than 6 cups per hour.
What if a coworker seems to have heat stroke?
NIOSH says to call 911 for emergency medical care, stay with your coworker until emergency medical services arrive, move them to a shaded, cool area, remove outer clothing, and cool them quickly with cold water, wet cloths or ice.
Will resting in air conditioning affect acclimatization?
No. NIOSH says taking breaks in air conditioning will not affect acclimatization.
Sources and date checked
All checked on 2026-11-02.
- CDC NIOSH, Heat Stress and Workers (page dated 2026-03-03):https://www.cdc.gov/niosh/heat-stress/about/index.html
- CDC NIOSH, Workplace Recommendations (page dated 2026-07-16):https://www.cdc.gov/niosh/heat-stress/recommendations/index.html
- CDC NIOSH, Heat-related Illnesses (page dated 2026-03-03):https://www.cdc.gov/niosh/heat-stress/about/illnesses.html