Heat stress can affect many outdoor and indoor workers. To prevent heat-related illnesses (HRI) and injuries, employers should develop and use a comprehensive heat-related illness prevention program at the workplace.

In occupational settings, heat stress is the combination of the heat your body produces (metabolic heat), environmental factors (for example, temperature and humidity), and clothing and personal protective equipment (PPE). While many workers need to wear PPE for protection from workplace chemical, physical, and biological hazards, PPE can increase the risk for HRIs. PPE can often alter the rate and amount of heat exchange between the skin and air. For example, impermeable materials used for protection against chemical hazards can be very hot to wear, as they trap heat close to the skin and prevent sweat evaporation.

Below are some elements for addressing heat stress that need to be included in workplace HRI prevention programs.

Workers who are exposed to extreme heat or work in hot environments may be at risk of heat stress. Exposure to extreme heat can result in occupational illnesses and injuries. Heat stress can result in heat stroke, heat exhaustion, heat cramps, or heat rashes. Heat can also increase the risk of injuries in workers as it may result in sweaty palms, fogged-up safety glasses, and dizziness. Burns may also occur as a result of accidental contact with hot surfaces or steam.

Workers at risk of heat stress include outdoor workers and workers in hot environments such as firefighters, bakery workers, farmers, construction workers, miners, boiler room workers, factory workers, and others.

Workers at greater risk of heat stress include those who are 65 years of age or older, are overweight, have heart disease or high blood pressure, or take medications that may be affected by extreme heat.

Prevention of heat stress in workers is important. Employers should provide training to workers so they understand what heat stress is, how it affects their health and safety, and how it can be prevented.

Ultraviolet (UV) rays are a part of sunlight that is an invisible form of radiation. UV rays can penetrate and change the structure of skin cells. There are three types of UV rays: ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC). UVA is the most abundant source of solar radiation at the earth’s surface and penetrates beyond the top layer of human skin. Scientists believe that UVA radiation can cause damage to connective tissue and increase a person’s risk for developing skin cancer. UVB rays penetrate less deeply into skin, but can still cause some forms of skin cancer. Natural UVC rays do not pose a risk to workers because they are absorbed by the Earth’s atmosphere.

Sunlight exposure is highest during the summer and between 10:00 a.m. and 4:00 p.m. Working outdoors during these times increases the chances of getting sunburned. Snow and light-colored sand reflect UV light and increase the risk of sunburn. At work sites with these conditions, UV rays may reach workers’ exposed skin from both above and below. Workers are at risk of UV radiation even on cloudy days. Many drugs increase sensitivity to sunlight and the risk of getting sunburn. Some common ones include thiazides, diuretics, tetracycline, doxycycline, sulfa antibiotics, and nonsteroidal anti-inflammatory drugs, such as ibuprofen.

Exposure to excess heat at work could increase your chances of having a baby with a birth defect or other reproductive problems. Here, you can learn more about heat at work and what you can do to reduce your exposure for a healthier pregnancy.

What is excess heat exposure?

• If your job causes your body temperature to become higher than 39°C (102.2°F), you may suffer from heat exhaustion, heat stroke, or dehydration, which are not good for either you or your developing baby.
• If you are pregnant, you are more likely to get heat exhaustion or heat stroke sooner than a nonpregnant worker. This is because your body must work harder to cool down both your body and your unborn baby.
• If you are pregnant, you are also more likely to become dehydrated. This also means you won’t be able to cool yourself as well by sweating.

Why should I be concerned about excess heat exposure?

A mother’s circulation helps protect the developing baby, but in very hot work environments or specific work situations a pregnant woman’s core (internal body) temperature may rise. In some cases, this has been linked to birth defects and other reproductive problems.

Who is exposed to excess heat on the job?

Workers are most commonly exposed to excess heat in:

• Those who work outdoors
• Those working in buildings without climate control during hot weather
• Manufacturing workers, such as those employed in metal fabrication and glass or plastics manufacturing)
• Healthcare workers who perform diathermy therapy
• Cooks and dishwashers in commercial kitchens (e.g. restaurants)
• Fire Fighters

What is not known?

• We don’t know what causes most birth defects and other reproductive problems. If you are exposed to excess heat on the job and have a baby with a birth defect or other reproductive problems, we often can’t tell if it was caused by heat exposure or if it was caused by something else.
• We don’t know what level of heat exposure is safe for every person. Follow guidelines and recommendations for your workplace to eliminate or reduce your excess heat exposure as much as possible.

What can I do to reduce or eliminate exposure?

• Take steps to prevent heat stress, like drinking plenty of fluids and taking breaks in the shade or an air-conditioned area. Avoid hot work environments which do not provide adequate cooling breaks.
• If you work in a hot environment, talk to your doctor or your workplace safety officer to find out how to reduce your risk of heat exhaustion.
• In healthcare, the heat from diathermy therapy is created with nonionizing radiation. If you are pregnant and administering diathermy therapy, you may need to consult with your workplace’s safety officer or contact us to find out if your work duties are safe for you.

Employers should reduce workplace heat stress by implementing engineering and work practice controls.

Engineering controls might include those that:

• Increase air velocity (if air temperature is below 95°F).
• Use reflective or heat-absorbing shielding or barriers.
• Reduce steam leaks, wet floors, or humidity.

Work practice controls include the following:

• Implement a buddy system and routinely check workers to ensure they make use of available water and shade, and they do not have symptoms of an HRI.
• Monitor the weather.
• Limit time in heat and/or increase rest time in a cool environment.
• Increase the number of workers per task.
• Require workers to conduct self-monitoring.
• Implement a heat alert program when a heat wave is likely.

Employers need to provide training before hot work begins, and tailor the training to cover worksite-specific conditions.

Workers and supervisors should be trained on:

• Recognition of the symptoms of HRIs.
• First aid.
• HRI risk factors.
• Importance of acclimatization.
• Importance of reporting HRI symptoms.

Additionally, supervisors should be trained on:

• How to implement appropriate acclimatization.
• Procedures for when a worker has symptoms of a HRI.
• How to monitor weather reports and respond to advisories (such as with the OSHA-NIOSH Heat Safety Tool App).
• How to monitor and encourage adequate fluid intake and rest breaks.

Workers become acclimatized to heat when they gradually work for longer periods in a hot environment. Benefits of acclimatization include less strain to the heart and vital organs, improved sweating (higher volume, earlier onset), and increased ability to perform physical tasks in the heat.

Employers must make certain that workers acclimatize by gradually increasing the time they work in hot conditions over 7-14 days.

New Workers Exposure Schedule

• Day 1 – Exposures to heat should be less than 20% of usual work duration.
• Increase a maximum of 20% per day after Day 1.

Experienced Workers Exposure Schedule (for those returning after an absence of 1 week or more)

• Day 1 – 50% of usual work duration; Day 2 – 60%; Day 3 – 80%; Day 4 – 100%

Employers should provide appropriate hydration.

• Water should be cool and near the work area.
• Individual drinking cups should be provided.
• Encourage workers to hydrate themselves.

Workers should drink an appropriate amount to stay hydrated.

• If in the heat <2 hours and involved in moderate work activities, then drink 1 cup (8 oz.) of water every 15–20 minutes.
• If experiencing prolonged sweating lasting several hours, then 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.

Employers should ensure and encourage rest and hydration breaks.

• Permit breaks when a worker feels discomfort.
• Assign new workers lighter work and longer, more frequent breaks.
• Shorten work and increase rest periods:
  • As temperature, humidity, and sunshine increase.
  • When there is no air
  • If protective clothing or PPE is worn.
  • For heavier work.

Can wearing personal protective equipment (PPE) increase the risk for heat-related illnesses?

Yes, wearing PPE and certain clothing ensembles can often increase your risk for heat-related illnesses.

PPE (e.g., waterproof aprons, surgical gowns, surgical caps, respirators, face shields, boots, and gloves):

• Is often necessary and required in order to reduce or eliminate exposure to external hazards (chemicals, physical hazards, and disease-causing organisms [e.g., viruses and bacteria]).
• Reduces the body’s normal way of getting rid of heat by sweating and other means.
• Holds excess heat and moisture inside, making the worker’s body even hotter.
• Increases the physical effort to perform duties while carrying the extra weight of the PPE and can lead to the worker getting hotter faster (e.g., working muscle increases body heat production).

What steps can be taken to protect workers wearing PPE from heat-related illness?

Wearing certain types of PPE can increase core body temperature (i.e., internal temperature) more quickly than wearing other types of PPE in the same environment.

• Basic recommendations that can be applied to many different workplaces can be found on the Heat Stress Recommendations.
• If heat stress is a hazard at your workplace, consult with a safety and health professional, and review the full recommendations provided in the NIOSH Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments.
• Additionally, if PPE is a concern, consider the following when developing work/rest cycles:
  • Type of PPE.
  • Length of time an individual can wear the PPE.
  • Individual worker’s actual work rate, fitness level, hydration level, and acclimatization.
  • Environmental conditions, such as level of heat and humidity, radiant heat from sun if outdoors, and wind speed if outdoors or using a fan indoors.

Are there types of PPE that can be worn to protect against heat exposures?

Yes, wearable PPE that protects against heat exposures are called auxiliary cooling systems or personal cooling systems (e.g., water-cooled garments, air-cooled garments, cooling vests, and wetted overgarments) and can range in simplicity, cost, and maintenance.

Exceeding Recommended Occupational Exposure Limits

In situations, where heat stress levels exceed the NIOSH recommended occupational exposure limit (RAL or REL), some form of heat-protective clothing or equipment should be provided.

During Rest Breaks

Wearable personal cooling systems could also be used during a rest period where the worker is not actively engaged in work. Core body temperature decreases rela­tively slowly, and simply stopping hard work will not result in an immediate decrease. Therefore, increasing the rate of heat removal from the body would reduce the risk for heat-related illness. Using wearable personal cooling systems could reduce the time required to lower core body temperature.

For example, during rest breaks:

• Remove PPE and clothing ensembles.
• While rehydrating, apply active (e.g., cold packs; cool, wet towels; wearable personal cooling system) or passive cooling (e.g., physical rest, move to a cool environment [e.g., air-conditioned room, or shaded area) methods.

This reduces body core temperature and allows for a more rapid “rehabilitation” during the rest break.

Limitations

Wearable personal cooling systems have limitations within a work setting, such as:

• Ice vests are cheap, but their tem­perature cannot be controlled and they often do not stay cool long enough to be practical.
• If the cooling system is too cold, this will result in reduced heat transfer from the body to the environ­ment.
• Water-cooled garments require that the worker be tethered to a system that circulates the cool water, which limits the person’s range of operation.
• Many of the wearable personal cooling systems are too heavy or too cumbersome to be practical in a work environment.

Every year, thousands of workers suffer from symptoms of heat-related illnesses, and some will die from heat stroke. To help workers stay safe while on the job outdoors this summer, the National Institute for Occupational Safety and Health (NIOSH) offers several resources for employers and workers to help tackle working in extreme heat and hot environments.

Working outside can produce heat stress, resulting in heat stroke, heat exhaustion, heat cramps, or heat rashes. Heat can also increase the risk of injuries in workers as it may result in sweaty palms, fogged-up safety glasses, and dizziness.

Who is at risk?

Workers exposed to hot and humid conditions, including construction workers, landscapers, farmers, and others who spend time outdoors are at risk for a heat-related illness. Additionally, workers who are new to the job or not fully acclimatized, 65 years of age or older, are overweight, have heart disease or high blood pressure, or take certain medications are at greater risk for a heat-related illness.

How to stay safe when working in heat

Some examples of NIOSH recommendations that can be applied in many different outdoor workplaces include:

• Limit time in the heat and/or increase recovery time in a cool environment.
• Increase the number of workers per task.
• Train supervisors and workers about heat stress, including symptoms of heat-related illness, first aid, and risk factors.
• Use a buddy system where workers observe each other for signs of heat intolerance.
• Provide adequate amounts of cool, potable water near the work area and encourage workers to drink frequently.
• Use a heat alert program (additional written guidelines) whenever the weather service forecasts that a heat wave is likely to occur.
• Develop a plan to get employees acclimatized to hot work conditions and to increase physical fitness.