Time to get prepared for the intense heat that a large group of workers will be exposed to during the next few months and prevent heat illness at work and on the job.
Outdoor and indoor heat exposure can be dangerous.
Millions of U.S. workers are exposed to heat in their workplaces. 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 the heat gradually over time. It’s our job as safety professionals to help prevent heat illness at work. The process of building tolerance is called heat acclimatization. Lack of acclimatization represents a major risk factor for fatal outcomes.
Occupational risk factors for heat illness include heavy physical activity, warm or hot environmental conditions, lack of acclimatization, and wearing clothing that holds in body heat.
Hazardous heat exposure can occur indoors or outdoors and can occur during any season if the conditions are right, not only during heat waves. The following is a list of some industries where workers have suffered heat-related illnesses.
Hazardous heat exposure for Indoors or Outdoors.
| Outdoors | Indoors |
| Agriculture | Bakeries, kitchens, and laundries (sources with indoor heat-generating appliances) |
| Construction – especially, road, roofing, and other outdoor work | Electrical utilities (particularly boiler rooms) |
| Construction – roofing work | Fire Service |
| Landscaping | Iron and steel mills and foundries |
| Mail and package delivery | Manufacturing with hot local heat sources, like furnaces (e.g., paper products or concrete) |
| Oil and gas well operations | Warehousing |
Steps to take to Prevent Heat Illness at Work
Controls Measures
Employers should reduce workplace heat stress by using engineering and administrative (work practice) controls. 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 (administrative control) recommendations include the following:
- Limit time in the heat and/or increase recovery time spent in a cool area.
- Reduce the metabolic (physical 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.
Training
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 in 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
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’ times 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 i n 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.
Hydration
Employers should provide the means for appropriate hydration of workers.
- Water should be portable, <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.
- Fluid intake should not exceed 6 cups per hour.
NIOSH Hydration Fact Sheet 2017-126.pdf
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 Schedules Fact Sheet 2017-127.pdf
Frequently Asked Questions: Preventing Heat Illness at Work
Heat illness is a range of conditions caused by the body overheating on the job, from heat rash and heat cramps to heat exhaustion and life-threatening heat stroke. Millions of U.S. workers are exposed to heat each year, and although heat illness is preventable, thousands become sick from occupational heat exposure and some cases are fatal.
Dangerous heat exposure can happen both outdoors and indoors, and it can occur in any season when conditions are right, not only during heat waves, which is why year-round awareness matters.
Early warning signs include heavy sweating, muscle cramps, headache, dizziness, nausea, weakness, and thirst. As heat exhaustion develops, workers may show cool and clammy skin, a fast pulse, and fainting. Heat stroke, the most severe stage, can bring hot and dry or heavily sweating skin, confusion, slurred speech, seizures, or loss of consciousness, and it is a medical emergency requiring an immediate call to emergency services.
Workers and supervisors should be trained to recognize these symptoms in themselves and coworkers and to report them right away, since most fatalities occur when early signs are missed.
Workers are most at risk during their first few days in a hot environment. Between 50% and 70% of outdoor heat fatalities occur in the first days on the job because the body needs time to gradually build tolerance to heat, a process called acclimatization.
Lack of acclimatization is a major risk factor for fatal outcomes, so new and returning workers need close supervision and a gradual ramp-up during their first two weeks.
The primary occupational risk factors are heavy physical activity, warm or hot environmental conditions, lack of acclimatization, and wearing clothing or personal protective equipment that holds in body heat.
Personal factors such as certain medications, alcohol use, and physical fitness levels also affect how well a worker tolerates heat, which is why training should address these influences.
Acclimatization is the set of beneficial physical adaptations, such as more efficient sweating, that occur when a worker is gradually exposed to a hot environment. Employers should build it over 7 to 14 days by increasing time in the heat step by step.
For new workers, allow no more than 20% of the usual workload in the heat on day one, then increase by no more than 20% each additional day. For experienced workers, a common schedule is 50% on day one, 60% on day two, 80% on day three, and 100% on day four. Workers who are less physically fit need more time, and acclimatization can be maintained through a few days away from heat, including breaks in air conditioning.
For moderate activity in the heat lasting less than two hours, workers should drink about 1 cup (8 ounces) of cool water every 15 to 20 minutes. Total fluid intake should not exceed 6 cups per hour. Water should be potable, kept cool (below 59°F / 15°C), and made accessible near the work area.
When sweating continues for several hours, workers should also use sports drinks with balanced electrolytes, and they should avoid alcohol and drinks high in caffeine or sugar.
Employers should use a combination of engineering controls and administrative (work practice) controls. Engineering controls change the workplace itself, for example increasing air velocity, adding reflective or heat-absorbing shielding, and reducing steam leaks, wet floors, or humidity.
Administrative controls change tasks and schedules: limiting time in the heat and increasing recovery time in a cool area, adding workers per task, using a buddy system, providing cool drinking water, running a heat alert program during forecast heat waves, and implementing an acclimatization plan.
Training for all workers should cover how to recognize the signs and symptoms of heat illness and give first aid, the causes and how to reduce risk (including drinking enough water and monitoring urine color and amount), proper use of heat-protective clothing and PPE, the effects of factors like medications and alcohol, the importance of acclimatization, and how to report symptoms and contact emergency services.
Supervisors need additional training on implementing acclimatization, responding to and monitoring workers with symptoms, watching weather reports and heat advisories, and encouraging adequate fluid intake and rest breaks. Training should be provided before hot work begins and tailored to worksite conditions.
Yes. Even though a dedicated federal heat standard is still in the rulemaking process and has not been finalized, employers are already required under OSHA’s General Duty Clause to protect workers from recognized hazards, including excessive heat. OSHA has also enforced heat protections through a National Emphasis Program and looks to NIOSH guidance on acclimatization, hydration, and rest.
Following recognized best practices now, including a written heat illness prevention plan with hydration, rest, acclimatization, and training, keeps workers safe and helps employers stay ahead of evolving regulations. ResponsAble can supply qualified safety professionals to build and oversee that plan on your site.