Working in Hot Environment (Heat Stress)

Heat Stress

Heat stress occurs when the body’s means of controlling its internal temperature starts to fail. As well as air temperature, factors such as work rate, humidity and clothing worn while working may lead to heat stress. Heat Stress is very real and it can arise in many different situations. Forms of heat stress include heat rash, heat cramps, heat exhaustion, and heat stroke. Being able to recognize and prevent the signs and symptoms of heat stress and knowing how to treat them if they arise will be your first line of defense in making sure that heat related illness does not overtake you or your coworkers.

Certain behaviors also put people at greater risk: drinking alcohol, taking part in strenuous outdoor physical activities in hot weather, and taking medications that impair the body’s ability to regulate its temperature or that inhibit perspiration. Heat stress can be induced by high temperatures, heavy workloads, and clothing inappropriate for the heat and humidity.

The signs of heat stress are often overlooked by the victim. The individual may at first be confused or unable to concentrate, followed by more severe symptoms, such as fainting or collapsing. If heat stress symptoms occur, move the victim to a cool, shaded area, give him or her water and immediately contact a supervisor or another individual to provide assistance.

(High Temperature + High Humidity + Physical Work = Heat Stress)

Causes of Heat Stress and Heat related Illness

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 body’s heat loss. If a person becomes dehydrated, they don’t sweat as much and their body temperature keeps rising.
  • 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 (concerts, dance parties or sporting 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.

Recognition/ Identification

Heat Rash

Heat rash is skin irritation caused by sweat that does not evaporate from the skin. Heat rash is the most common problem in hot work environments. The symptoms of heat rash will look like clusters of red bumps on the skin and they will often appear on the neck, upper chest, and folds of skin. For first aid measures for these symptoms you should move the person into a cooler, less humid environment if possible. And it is going to best to keep the affected areas of the skin dry.

Heat Cramps

Heat cramps are caused by the loss of body salts and fluid during sweating. Low salt levels in muscles cause painful cramps. Tired muscles are usually the ones most affected by cramps. Cramps may occur during or after working hours. A person with heat cramps will most likely feel muscle spasms and pain. The areas affected will usually be somewhere in the abdomen, arms, or legs. The first aid measures for these symptoms will be to have the person rest in a shady, cool area. The person with heat related cramps should drink water or some other cool beverage. And the supervisor or manager should wait a few hours before allowing the worker with heat cramps to return to strenuous work. If the heat related cramps do not go away these first aid measures then the person should seek medical attention.

Dizziness and fainting

Heat-related dizziness and fainting results from reduced blood flow to the brain. Heat causes an increase in blood flow to the skin and pooling of blood in the legs, which can lead to a sudden drop in blood pressure. There can be a feeling of light-headedness before fainting occurs.

Heat Exhaustion

Heat exhaustion is the body’s response to loss of water and salt from heavy sweating. A person with heat exhaustion will most likely have the following symptoms: cool and moist skin, they will be sweating heavily, headache, nausea or vomiting, dizziness, light headedness, weakness, thirst, irritability and a fast heartbeat. The first aid measures for heat exhaustion are to have the person sit or lie down in a cool, shady area. Give them plenty of water or other cool beverages to drink. Cool the person with cold compresses or ice packs. Take them to the clinic or emergency room for medical evaluation or treatment if signs or symptoms worsen or do not improve within 60 minutes. The person should not return to work that day.

Heat Stroke

Heat stroke is the most serious form of heat-related illness and it happens when the body becomes unable to regulate its core temperature. Sweating stops and the body can no longer rid itself of excess heat. A person with heat stroke will show the following symptoms: confusion, fainting, seizures, excessive sweating or red, hot, dry skin and a very high body temperature. The best thing to do first is to call emergency. While you are waiting for the emergency services to arrive you should place the person in a shady, cool area. Loosen their clothing and remove outer clothing if possible. Fan air on the person and place cold packs in their armpit areas. Wet the person with cold water and apply ice packs, cool compresses or ice if it is available. Provide fluids, preferably water, as soon as possible. And stay with the person until help arrives.

Heat Stress Factors

There are three categories of factors that determine the degree to which an individual is at risk for heat stress:

  • Personal risk factors
  • Job factors
  • Environmental factors

Environmental factors are often the most commonly considered. After all, it’s harder to forget about the possibility of heat stroke when you’re spending the day working in the heat. But personal risk factors and job factors are often overlooked – and the results can be deadly.


Some medications can affect the body’s ability to tolerate (and effectively deal with) heat. Workers taking medication for the following conditions should be particularly vigilant:

  • Colds, allergies, and congestion
  • Blood pressure
  • Diarrhea
  • Psychosis
  • Depression
  • Dizziness or vertigo

Alcohol Use

Workers who have had alcohol in the past 24 hours are more susceptible to heat-related illnesses, as alcohol negatively impacts the body’s ability to regulate its temperature. Alcohol use can also contribute to dehydration, which can further spur on the development of heat stress.


New employees and those who are returning from time away from the heat should do so slowly to allow the body to get used to the temperature. Workers already acclimatized may be more prone to heat stress when there is a sudden change in temperature at the worksite, such as heat waves or when there is mining in the area.

Proximity to Hot Equipment

Workers doing tasks with, or in close proximity to, engines and other heat-generating equipment are at increased risk for heat illnesses. The equipment produces heat that raises the temperature in the work area, and it doesn’t take long before workers’ own temperatures start rising.

Clothing and PPE

Some PPE is heavy and lacks the ability to breathe, making it easy for the body to overheat. Workers should pay special attention to the coated and non-woven materials often used in protective garments, which prevent the evaporation of sweat. In general, the heavier the clothing, the longer it takes for evaporation to effectively cool the skin.

Fluid Loss

While this factor varies heavily from person to person, workers who lose more than 1.5 percent of their body weight in a single day from sweating are at greater risk of heat stress. This can be remedied by ensuring adequate fluid intake to balance the fluid loss.

Work Schedule

Doing strenuous work during the hottest parts of the day puts workers at severe risk for developing heat-related illness. When possible, modify work schedules so that strenuous work is done early in the morning and later in the afternoon, instead of mid-day. This will help prevent exposure to extreme heat.


Most heat-related health problems can be prevented, or the risk of developing them can be reduced. Recognizing the hazard before it arises is the key to preventing a heat related illness. Good engineering controls and work practices will help you avoid these issues before they arise. Wearing the right personal protective equipment and educating the workforce on heat stress matters will help in creating a safer work environment for all.

Engineering Controls

The best way to prevent heat-related illness is to make the work environment cooler. This is possible in an indoor environment but not always possible in outdoor operations. A variety of engineering controls can reduce workers’ exposure to heat:

  • Air conditioning (such as air-conditioned mobile equipment cabs and air conditioning in break rooms).
  • Increased general ventilation.
  • Cooling fans.
  • Local exhaust ventilation at points.
  • Reflective shields to redirect radiant heat.
  • Insulation of hot surfaces (such as furnace walls).
  • Elimination of steam leaks.

Work Practices

Employers should have an emergency plan in place that specifies what to do if a worker has signs of heat-related illness, and ensures that medical services are available if needed.

  • Employers should take steps that help workers become acclimatized (gradually build up exposure to heat), especially workers who are new to working in the heat or have been away from work for a week or more. Gradually increase workloads and allow more frequent breaks during the first week of work.
  • Workers must have adequate potable (safe for drinking) water close to the work area, and should drink small amounts frequently.
  • Rather than being exposed to heat for extended periods of time, workers should, wherever possible, be permitted to distribute the workload evenly over the day and incorporate work/rest cycles.
  • If possible, physical demands should be reduced during hot weather, or heavier work scheduled for cooler times of the day.
  • Rotating job functions among workers can help minimize overexertion and heat exposure.
  • Workers should watch out for each other for symptoms of heat-related illness and administer appropriate first aid to anyone who is developing a heat-related illness.
  • In some situations, employers may need to conduct physiological monitoring of workers

Personal Protective Equipment

Workers should be aware that use of certain personal protective equipment (e.g. certain types of respirators and impermeable clothing) can increase the risk of heat-related illness. In some situations, special cooling devices can protect workers in hot environments:

In some workplaces, insulated gloves, insulated suits, reflective clothing, or infrared reflecting face shields may be needed. Thermally conditioned clothing might be used for extremely hot conditions; for example:

  • A garment with a self-contained air conditioner in a backpack.
  • A garment with a compressed air source that feeds cool air through a vortex tube.
  • A plastic jacket whose pockets can be filled with dry ice or containers of ice.


Workers and supervisors should be trained about the hazards of heat exposure and their prevention. Topics should include:

  • Risk factors for heat-related illness.
  • Different types of heat-related illness, including how to recognize common signs and symptoms.
  • Heat-related illness prevention procedures.
  • Importance of drinking small quantities of water often.
  • Importance of acclimatization, how it is developed, and how your worksite procedures address it.
  • Importance of immediately reporting signs or symptoms of heat-related illness to the supervisor.
  • Procedures for responding to possible heat-related illness.
  • Procedures to follow when contacting emergency medical services.
  • Procedures to ensure that clear and precise directions to the work site will be provided to emergency medical services.


The impact on human function and health in work situations is a ‘neglected’ effect of global climate change. The potential health risks and worker productivity reductions due to climate change are substantial. The lack of attention until recently may well be due to the fact that this is mostly a problem in low and middle-income tropical countries where climate change impacts during this century will be prominent and air conditioning is not widely available, while in high-income countries air conditioning is already very common in workplaces.

The increasing heat exposure due to local climate changes is likely to create occupational health risks and to have a significant impact on the productivity of many workers, unless effective preventive measures (‘adaptation’) reducing the occupational heat stress are implemented. This may be practically and economically possible for indoor environments, but it is much more difficult for outdoor environments. Eventually, this will hamper economic and social development in affected countries unless appropriate preventive measures are taken in the planning processes for workplaces and urban development.

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