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Heat Stress – Recommendations

This page has basic recommendations that apply to different workplaces. If heat stress is a hazard at your workplace, consult a safety and health professional. Review the full recommendations in the NIOSH Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments.

Control of Heat Stress

Employers should reduce workplace heat stress by using engineering and administrative (work practice) controls. An engineering control could be a change to the design of the workplace that reduces exposure to heat. Administrative controls are changes to tasks or schedules to reduce heat stress.

Engineering controls might include those that:

  • Increase air velocity.
  • Use reflective or heat-absorbing shielding or barriers.
  • Reduce steam leaks, wet floors, or humidity.

Work practice recommendations include the following:

  • Limit time in the heat and/or increase recovery time spent in a cool area.
  • Reduce the metabolic (physically difficult) demands of the job.
  • Use tools intended to minimize manual strain.
  • Increase the number of workers per task.
  • Train supervisors and workers about heat stress.
  • Use a buddy system where workers observe each other for signs of heat-related illnesses.
  • Require workers to conduct self-monitoring and create a work group (i.e., workers, a qualified healthcare provider, and a safety manager) to make decisions on self-monitoring options and standard operating procedures.
  • Provide adequate amounts of cool, potable water near the work area and encourage workers to drink often.
  • Use a heat alert program whenever the weather service forecasts a heat wave.
  • Institute a heat acclimatization plan and encourage increased physical fitness.


Train workers before hot outdoor work begins. Tailor the training to worksite conditions.

Employers should provide a heat stress training program for all workers and supervisors about the following:

  • Recognition of the signs and symptoms of heat-related illnesses and administra­tion of first aid.
  • Causes of heat-related illnesses and steps to reduce the risk. These include drinking enough water and monitoring the color and amount of urine output.
  • Proper care and use of heat-protective clothing and equipment and the added heat load caused by exertion, clothing, and per­sonal protective equipment.
  • Effects of other factors (drugs, alcohol, obesity, etc.) on tolerance to occupational heat stress.
  • The importance of acclimatization.
  • The importance of immediately reporting any symptoms or signs of heat-related illness in themselves or in coworkers to the supervisor.
  • Procedures for responding to symptoms of possible heat-related illness and for contacting emergency medical ser­vices.

Supervisors should also be trained on the following:

  • Implementing appropriate acclimatization.
  • What procedures to follow when a worker has symptoms of heat-related illness, including emergency response procedures.
  • Monitoring weather reports.
  • Responding to hot weather advisories.
  • Monitoring and encouraging adequate fluid intake and rest breaks.


Acclimatization is the result of beneficial physiological adaptations (e.g., increased sweating efficiency, etc.) that occur after gradual increased exposure to a hot environment. Employers should ensure that workers are acclimatized before they work in a hot environment.

  • Gradually increase workers’ time in hot conditions over 7 to 14 days.
  • For new workers, the schedule should be:
    • No more than 20% of the usual duration of work in the heat on day 1.
    • No more than 20% increase on each additional day.
  • For workers with previous experience, the schedule should be:
    • No more than 50% of the usual duration of work in the heat on day 1
    • No more than 60% of the usual duration of work in the heat on day 2
    • No more than 80% of the usual duration of work in the heat on day 3
    • No more than 100% of the usual duration of work in the heat on day 4.
  • Closely supervise new employees for the first 14 days or until they are fully acclimatized.
  • Workers who are not physically fit need more time to fully acclimatize.
  • Acclimatization can be maintained for a few days of non-heat exposure.
  • Taking breaks in air conditioning will not affect acclimatization.

NIOSH Acclimatization Fact Sheet


Employers should provide the means for appropriate hydration of workers.

  • Water should be potable, <15°C (59°F), and made accessible near the work area.
  • Estimate how much water will be needed and decide who will get and check on water supplies.
  • Provide individual drinking cups for each worker.
  • Encourage workers to hydrate themselves.

Workers should drink an appropriate amount to stay hydrated.

  • For moderate activities in the heat that last less than 2 hours, drink 1 cup (8 oz.) of water every 15–20 minutes.
  • If sweating lasts for several hours, drink sports drinks containing balanced electrolytes.
  • Avoid alcohol and drinks with high caffeine or sugar.
  • Generally, fluid intake should not exceed 6 cups per hour.

NIOSH Hydration Fact Sheet

Rest Breaks

Employers should ensure and encourage workers to take appropriate rest breaks to cool down and hydrate.

  • Permit rest and water breaks when a worker feels heat discomfort.
  • Modify work/rest periods to give the body a chance to get rid of excess heat.
  • Assign new and unacclimatized workers lighter work and longer, more frequent rest periods.
  • Shorten work periods and increase rest periods:
    • As temperature, humidity, and sunshine increase.
    • When there is no air movement.
    • If protective clothing or equipment is worn.
    • For heavier work.

NIOSH Work/Rest Schedules Fact Sheet