Causes Of Heat Stress
There are many factors which can cause heat stress and heat-related illness, including:
Dehydration to keep healthy, our body temperature needs to stay around 37°C. The body cools itself by sweating, which normally accounts for 70 to 80 per cent of the bodys heat loss. If a person becomes dehydrated, they dont sweat as much and their body temperature keeps rising. Dehydration may happen after strenuous exercise , severe diarrhoea or vomiting, drinking too much alcohol, taking certain medications and not drinking enough water.
Lack of airflow working in hot, poorly ventilated or confined areas.
Sun exposure especially on hot days, between 11am and 3pm.
Hot and crowded conditions people attending large events in hot or crowded conditions may also experience heat stress that can result in illness.
Bushfires exposure to radiant heat from bushfires can cause rapid dehydration and heat-related illness. Bushfires usually occur when the temperature is high, which adds to the risk.
Some drugs, such as ecstasy and speed, also raise the bodys temperature, which can lead to heat stress.
Prevention Of Heat Stress: Workers
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Learn to recognize the symptoms of heat stress. Pace the work, taking adequate rest periods .
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Use adequate fans for ventilation and cooling, especially when wearing personal protective equipment .
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Wear light-colored, loose clothing .
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Keep shaded from direct heat where possible .
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Drink plenty of water: in hot environments the body requires more water.
Ways To Prevent A Heat
While knowing how to handle heat stress is vital in an emergency, the best strategy is to prevent heat stress altogether. Here are some helpful tips that you and your team should implement to avoid heat stress:
Check out our Heat Stress Resource Page for additional heat stress resources:
- Heat Index Chart
- Printable posters from OSHA and NIOSH you can hang in your office
- Ergodyne Toolbox Talks
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Help Workers Adjust To Hot Environments
The more time a worker has to acclimatize to a hot environment, the better their body handles the heat.
If workers have health problems or are not in good physical shape, they may need more time to adjust to hot environments.
For workers with no experience in hot conditions, there are two ways to help them tolerate the heat:
For workers withexperience in hot conditions, but who may have been ill or away from work for 9 or more days, the worker will need to gradually readjust to the heat.
You can find more information on heat acclimatization from The National Institute for Occupational Safety and Health: Heat Stress Recommendations.
Safety Tips For Working In Hot Weather

When the heat index rises, taking a few precautionary steps will help keep you and your crew safe on the job. Follow OSHA best practices for working in hot weather to prevent heat exhaustion, heat stroke and all other heat-related illnesses:
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Allow workers to take regular breaks in cooler areas with plenty of shade.
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Provide enough chilled water for each worker to have a drink as needed. OSHA requires employers to provide potable water from:
- Water fountains
- Covered containers with single-use drinking cups stored in a sanitary receptacle
- Single-use bottles
Bonus tip: If the jobsite is indoors and drinking fountains are installed, make sure to regularly maintain them to provide on-demand chilled water for workers.
Remember that working in direct sunlight can increase the heat index by 15° F, and the sun is at its brightest between 10:00 in the morning to 2:00 in the afternoon. If possible, schedule outside work early in the morning or later in the afternoon.
Bonus tip:The risk of sunburns is present when working in direct sunlight any time of day. While sunburn is not considered a heat-related illness, it should be taken seriously. Besides being uncomfortable or even painful, sunburns also increase the long-term risk of skin cancer. Promote the use of sunscreen by having it at the ready on every job.
With almost two decades of experience in the safety product industry, Frank uses his expert knowledge to empower trade professionals to stay safe on the job.
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Rest And Cool Down Breaks
Consider changes to your break practices to lower the risk of heat stress. Possible changes during heat-stressed conditions include:
- Encourage employees to take breaks and hydrate any time they feel necessary.
- Pace the job to allow more frequent breaks for fluid intake and sufficient recovery time.
- Take a break in a shaded area or an air conditioned building.
Managing Events Or Workplaces
If you are organising a large event or sports activity, managing workers in a hot environment or engaged in fire fighting:
- Develop and follow a heatstroke prevention plan.
- Dont rely on fans to cool people, unless there is adequate ventilation.
- Know the signs and symptoms of heatstroke and know how to respond.
- If drinks are confiscated from patrons at the entrances to large events , ensure there is plenty of free water available and easily accessible.
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Effective Ways To Prevent Heat Stress In The Workplace
Heat stress generally occurs when spending long periods of time outside/inside in excessive heat. Symptoms typically include physical exhaustion, cramping, rashes, and dehydration. In the most severe cases, heat stroke can result in confusion, irrational behavior, loss of consciousness and even death.
What Are Exposure Limits For Heat Stress
Exposure limits intended to minimize the risk of heat-related illnesses are set by provincial and territorial governments for most Canadian workplaces, and by Employment and Social Development Canada for workplaces under the federal jurisdiction. These agencies generally use the exposure guidelines recommended by the American Conference of Governmental Industrial Hygienists .
The ACGIH gives these limits in units of WBGT degrees Celsius . The WBGT unit takes into account environmental factors, such as air temperature, humidity and air movement, which contribute to perception of hotness by people. WBGT values are not the same as humidex values. In some workplace situations, solar load is also considered in determining the WBGT. More details about WBGT are available below.
The ACGIH publication “2016 TLVs® and BEIs®” provides recommended screening criteria for heat stress exposure for workers . This publication and the “Documentation of TLVs® and BEIs®” should be consulted for more detailed information on these screening criteria, categories of work demands, guidelines for limiting heat strain and heat strain management.
The ACGIH exposure limits are intended to protect most workers from heat-related illnesses. The limits are higher than they would have been if they had been developed to prevent discomfort. If you are wearing heavier clothing then the exposure limit should be lowered. ACGIH recommendations for such situations are suggested in Table 2.
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Preventive Measures Employees Can Take
Employees should take special precautions to avoid heat-related illness in unusually hot weather when working outdoors or in unconditioned indoor environments. People suffer heat-related illness when their bodies are unable to regulate internal body temperature. In hot weather, the body normally cools itself by sweating. Under some conditions, however, sweating isnt enough. Such conditions include high humidity, where air movement is limited, working in the direct sun, heavy physical exertion and poor physical condition. Some medical conditions and medications can also reduce the bodys ability to tolerate heat. Still, heat-related illness is preventable by following these guidelines when working outdoors in hot weather:
Signs and symptoms of heat-related illness include headache, dizziness, lightheadedness, fainting, weakness, malaise, mood change, mental confusion or irritability, nausea or vomiting, rapid pulse and excessive sweating or lack of sweating with hot dry skin. An employee experiencing any of these signs or symptoms should be taken to the UNC Hospitals Emergency Room as soon as possible. Contact the University Employee Occupational Health Clinic at 919-966-9119 if you have any questions.
Ways To Prevent Heat Exhaustion On The Worksite
Workers, especially those that work outside, are at a higher risk for heat illness and exhaustion during the summer months. Proper hydration, rest, and some other preventive measures will keep you safe while on the job. Check out our tips to keep safe while soaking up the sun:
The recommended daily intake of water is 13 cups for men and 9 cups for women. Increasing water breaks and allowing appropriate rest in shaded areas will increase an employees performance. Drinking water can also help balance body fluids and help prevent muscle fatigue.
Those who are new to working in the heat, or unadjusted to its effects, can be the most vulnerable to heat stress and should ease their way into working in the heat. This also applies to those who are returning to work after being off for week or more.
Workers should work as a team to be alert in the workplace. OSHA has revised their Heat Safety Tool app to allow workers to calculate the heat index level and determine what their heat illness risk levels are. The app provides workers with information on how to monitor themselves and their coworkers for heat illness symptoms.
Wearing a hat can help protect your scalp and neck from harsh UV rays and help provide relief from the sun. Light colored clothing will attract less heat from the sun and help keep your body temperature down.
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Heatstroke Can Cause Organ Damage Or Death
Heatstroke occurs when the core body temperature rises above 40.5 oC and the bodys internal systems start to shut down. Normally, sweating helps to maintain a healthy body temperature by increasing heat loss through evaporation. When a person becomes dehydrated, they do not sweat as much, their blood becomes concentrated and organ functioning is impaired.
Many organs in the body can suffer tissue damage and the body temperature must be reduced quickly. Most people will have profound central nervous system changes such as delirium, coma and seizures. As well as effects on the nervous system, there can be liver, kidney, muscle and heart damage.
What Are The Causes Of Heat Stress

There are various causes of heat stress which can be categorized into 3 sources:
- Environmental factors These are the high-temperature workplaces that can either be indoors or outdoors. Working in indoor areas such as bakeries, foundries, factories, and furnaces or in outdoor sites such as construction, road, mining, and agriculture can make the worker more susceptible to heat stress. Other environmental factors that can cause heat stress are places high with humidity such as kitchens and laundries.
- Metabolic heat This is the heat generated by a persons body during physical activity. Metabolic heat is ,in simple terms, internal heat. There are 3 ways the body can exchange heat with its surroundings, which are radiation, convection, and evaporation of sweat. Radiation is heat transfer from a source of heat, usually associated with the sun. Convection is the process wherein the body exchanges heat through the surrounding air. Lastly, the body cools itself through sweat evaporation. However, cooling through sweat is limited in areas with high humidity since the air cant easily accept more moisture.
- Clothing Employees should avoid wearing extra layers of clothing and clothing that absorbs heat. Their clothing should be made up of materials that can reflect heat and are appropriate for their workplace and tasks.
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What Preventive Measures Can Be Taken
Increase the amount of fluids you drink, but avoid alcohol, caffeine, and overly sugary drinks if you are involved in heavy activity, experts recommend drinking 2-4 glasses of cool fluids each hour. Be sure there are cool places around and take frequent breaks in them. If you will be working in the sun, be sure to use a sunscreen rated at SPF15 or higher. You can also use a wide-brimmed hat to keep the sun off your head. Wear light, loose-fitting clothes.
Employers should make sure employees know the threats of working in hot conditions and have a system of breaks and rotation work. Cool areas, preferably an air conditioned one, should be made available for anyone who needs to escape the heat, and water around 50-60°F should be available in abundance. Workers wearing protective gear that includes tight-fitting clothes that do not breathe should be on a shorter rotation and have extra breaks to keep cool, as they are at higher risk.
For new workers or workers returning after two weeks or more out of the conditions, a graduated system should be used to get them acclimated to the heat. Start them off with only 50% of the load they would be expected to carry. Increase it gradually so at the end of a week they are performing the normal level of work.
How To Manage Heat Stress In The Workplace
Free resources: Download and share safety talk, presenter guide, hazard alert
Beat the Heat Safety Talk Presentation Beat the Heat Safety Talk Leader Guide Hazard Alert: Heat stress can be a killer Heat Stress Awareness Guide
Heat-related illnesses are cause for concern, and with summer almost here, its time for a refresher on the best ways to beat the heat at work. Keep in mind that severe heat-related illnesses like heat exhaustion can occur for several days after dehydration from exposure to high temperatures, according to the Canadian Centre for Occupational Health and Safety, whether you work outdoors as a tree planter, inside a mill, or toil year-round in toasty places like bakeries, foundries, or underground mines.
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Ten Hot Weather Safety Tips:
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What Is Heat Stress
Definition:
Heat stress is a condition caused by the bodys exposure to extreme temperatures.
Heat stress occurs when the body is no longer able to maintain a healthy body temperature in a hot environment. If the surrounding temperature is higher than your body’s temperature of 98.6ºF, your body will absorb heat instead of getting rid of it. This is where the problems begin.
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How Do I Calculate The Wbgt Index
The wet bulb globe temperature is calculated by using the following equations.
- For outdoors with direct sun exposure:
WBGT = 0.7 x Tempwet bulb + 0.2 x Tempglobe + 0.1 x Tempair
- For indoors or outdoors without direct sun exposure:
WBGT = 0.7 x Tempwet bulb + 0.3 x Tempglobe
where:
Tempwetbulb natural wet bulb temperature measured by using a thermometer whose bulb is covered with wet cotton cloth and is cooled by the natural air movement
Tempglobe temperature measured using a black globe thermometer
Tempair temperature measured using a conventional thermometer
All temperatures are to be expressed in °C.
Example
Workers employed in an outdoor workplace with direct exposure to the sun. Measurement of workplace conditions produced the following results.
Tempwetbulb = 24°C
How Iauditor Can Help To Protect Workers From Heat Stress
Employers can start their heat control programs by using digital tools and incorporating heat exposure checklists. The template can be used during toolbox talks, an essential tool most commonly used by the construction industry. All of these are possible with the leading health and safety app, iAuditor by SafetyCulture.
iAuditor features for heat control include:
- Alerts for Issues Immediately get notified when a problem arises.
- Corrective Action Workers can suggest corrective actions during an inspection.
- Data Insight Check if there are repetitive issues which can help pinpoint root causes.
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How To Avoid Heat Stress At Work
Heat stress occurs when our bodies heat up faster than they can cool down by sweating. Our bodies need to be between 36-38°. Its important to protect employees working in a hot environment because if you dont, this may lead to serious injuries and heat disorders.
The main causes of heat stress can be divided into three categories: the environment, the work, and the worker. In the environment, radiant heat from direct or indirect sunlight, air temperature hotter than that of the skin, and high humidity are some factors that need to be considered. The work means that the harder a person is working, the more heat their body produces. And for workers, the possible causes of heat stress are not getting enough water, lack of conditioning , poor health , and excess clothing or faulty personal protective equipment.
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When there is a rise in body temperature, the body sweats, losing salts and fluids in the process. This can lead to dehydration which makes the body less able to cool down on its own. Excessive sweating, dizziness, and nausea are three of the warning signs of heat stress that workers should be mindful of. If not treated early, heat disorders such as heat cramps, heat exhaustion, and heat stroke which can lead to cardiac arrest might occur and these have serious effects on the body.