What is Heat Stress?

What is Heat Stress?

Worker with Heat Stress

Heat stress is an illness that can be caused by exposure to extreme heat. It occurs when the body is unable to maintain a healthy temperature in response to a hot environment. Workers who are constantly exposed to high temperatures or an otherwise hot environment may be at risk for developing heat stress, as they typically have long shifts and may be either ill-equipped or inadequately trained by their employers to recognize this illness and take preventative measures.

Hot conditions present a definite threat to workers. High temperatures can be dangerous and even fatal at work, as they lead to injuries, illnesses, and death. In 2015, exposure to environmental heat led to 2,830 nonfatal occupational injuries and illnesses, as well as 37 work-related deaths. Of these deaths, 33 of them occurred during the months of June to September.

Are your employees at risk for heat-related illnesses?  

Our Heat Stress Calculator helps you determine heat stress levels for outdoor workers.

The Occupational Safety and Health Administration (OSHA) has published a map of U.S. heat-related fatalities for outdoor workers. This map shows the locations of these fatalities, and according to OSHA, there were 109 occupational fatalities that were heat-related from 2008 to 2014 alone. As time goes on and high temperature records continue to be broken, risk of heat stress is likely going to increase and precaution will become more important than ever.

Besides being a personal hazard, hot conditions may also put workers at risk for further injuries and can endanger their coworkers. For example, heat may result in sweaty palms, burns, fogged-up safety glasses, or dizziness. Measures should be taken to prevent or handle these factors so they do not interfere with a workers’ ability to perform safely and efficiently.

Who’s At Risk for Heat Stress?

Specific work environments may put workers especially at risk for heat stress. These environments are either outdoors or within a confined, heated space, and they include:
  • The outdoors (pools; landscaping; maintenance)
  • Bakeries
  • Firefighting and other emergency response
  • Farms
  • Construction sites
  • Exterior painting sites
  • Factories
  • Oil and gas well operations
  • Hazardous waste sites
  • Plants such as chemical or brick-firing plants
Hydrate to help heat stress

Individual factors may also put workers at risk of illness from heat. These include:

  • Workers who are 65 years or older
  • Those who have high blood pressure or heart disease and other underlying health conditions
  • Workers who are on medications that are potentially affected by extreme heat
  • Those who are overweight
  • Drug use
  • Cardiovascular fitness
  • Existing burns along the body that may interfere with sweat glands
  • Workers who have not performed in hot environments before
  • A low intake of liquids

There are technical methods of determining the risk of heat stress, such as determining the wet bulb globe temperature of the work environment. This measure considers radiant heat sources, air movement, and humidity on top of temperature. There are also occupational exposure limits (OELs) to consider as well. Certain operational and environmental variables can have an impact, such as:

  • Temperature of the work site itself
  • The environment’s relative humidity
  • Lack of training and awareness of heat stress
  • Workload/amount of muscular exertion required
  • Personal protective equipment (PPE) that prevents the body from sweating effectively, such as waterproof clothing

People who work in certain states may also be particularly at risk. For example, California, Kansas, and Texas tend to have the highest rates of work-related injuries and illnesses caused by environmental heat.

Symptoms of Heat Stress

Dizziness is a symptom of heat stress
It is highly recommended that employers use personal observations as well as technical measures to ensure that workers are safe. Certain indicators of heat stress can be observed, and it’s important to use professional judgement in order to assess the situation and quickly take action. An essential aspect to heat stress prevention training is recognizing the signs of heat stress, which include:
  • Fatigue
  • Sudden and severe headaches or nausea
  • An increase in incidents
  • A lack of alertness
  • Dizziness or fainting
  • Clammy, cold, or pale skin
  • Cramps or pains in the muscles
  • A weak or fast pulse
  • Excessive sweating

OSHA and the National Institute for Occupational Safety and Health (NIOSH) have worked together to provide a Heat Safety Tool App that not only provides real-time information on heat index information and weather conditions, but also acts a as a guide to identify symptoms of illnesses related to the heat.

There are also different severities of heat stress. For example, the illness may lead to heat rashes, heat cramps, heat exhaustion, or heat stroke. The most serious severity is heat stroke, which is a real medical emergency and may be fatal, as in this case the body becomes completely unable to regulate its temperature. During a heat stroke, a worker’s body temperature will be 103ºF or higher, and they may be confused or lose consciousness.   

What to Do When A Worker Suffers from Heat Stress

When it has been determined that a worker is ill due to the heat, remain calm and get help immediately. If there is not a supervisor nearby or the supervisor determines it’s a serious situation, call 911. If possible, move the worker into the shade or a cooler area, remove any outer clothing, and have someone stay with them until help arrives. As soon as possible, provide cool water to the worker to drink, apply ice, and attempt to fan or mist them. If the worker is confused or unable to stay alert/conscious these are indications they may be suffering from a heat stroke. In this case, call 911 immediately and apply ice as soon as possible.

An important aspect of assessing heat illness is creating a buddy system for workers. Implementing this system brings attention to occupational risks, and ensures that action is taken as quickly as possible. Workers should be familiar with the symptoms of heat illnesses and heat stroke in particular in order to monitor the situation. Or, a responsible person may be designated to monitor conditions and protect workers. A complete heat illness prevention program will prevent injuries and fatalities.

Methods of Prevention

summer work schedule
It’s important to take action and prevent heat stress in workers. Prevention begins with high quality training. Employers should provide education through safety courses and other resources so workers understand what heat stress is and its causes, the different severities and types, and how it impacts their health and safety. OSHA also provides a Heat Stress Quick Card which describes potential symptoms and actions to take.

Both employers and employees may undertake daily tasks to protect against heat stress and other heat-related illnesses.

There are daily tasks that may be undertaken by both employers and employees to protect against heat related illness. These include:

  • Finding or providing shade and using other means of blocking out direct sunlight and other sources of heat
  • Providing and drinking water every 15 minutes (it is recommended to get at least one pint per hour); avoid beverages that contain alcohol or caffeine, since these can cause dehydration
  • Modify work schedules to begin and end earlier, avoiding the most intense times of the day
  • Arranging frequent breaks that include provided water and are in air-conditioned or shaded areas
  • Providing and wearing light and/or loose clothing that provides cooling
  • Gradually increase the workload for workers who have been away from work or not been exposed to hot conditions previously so they can adapt; OSHA recommends to begin with 20% of their regular workload for the first day and slowly increase by 20% each following day

There are many heat stress safety products available that can help prevent heat illnesses and aid in worker protection. These include water bottles, towels, sweatbands, and cooling vests to mitigate heat stress and keep heat-related injuries and illnesses at bay.


Additional Heat Stress facts:

  • Heat stress is the effect of heat load on a worker’s body from exposure to a combination of factors such as the environment, metabolic heat, and clothing. Heat stress causes the body to lose the ability to control heat and can lead to heat exhaustion and heat stroke. Source: https://safetyculture.com/topics/heat-stress/
  • Heat stress can result in heat stroke, heat exhaustion, heat cramps, heat syncope, heat rash, or rhabdomyolysis. These conditions vary in severity and symptoms, but all require immediate medical attention. Source: https://www.cdc.gov/niosh/topics/heatstress/heatrelillness.html
  • 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. 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. Source: https://ehs.research.uiowa.edu/occupational/heat-stress
  • 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. Source: https://www.mayoclinic.org/diseases-conditions/heat-exhaustion/symptoms-causes/syc-20373250
  • 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. Source: https://www.osha.gov/heat-exposure
  • Some of the prevention measures for heat stress include: acclimatization, rest breaks, fluid intake, shade, ventilation, cooling fans, personal protective equipment, and heat stress monitoring. Source: https://safetyculture.com/topics/heat-stress/
  • Heat stress is one of the most frequently cited OSHA standards, with over 4,000 violations issued in fiscal year 2020. The most common violations include failure to maintain a written program, failure to provide training, and failure to monitor the heat index. Source: https://www.cdc.gov/niosh/topics/heatstress/heatrelillness.html
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