Course 602 - Heat and Cold Stress Safety

Safety guides and audits to make your job as a safety professional easier

Heat Stress and Safety


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 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. 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. Personal risk factors include medical conditions, lack of physical fitness, previous episodes of heat-related illness, alcohol consumption, drugs, and use of certain medication.

See the

Heat-Related Illness Symptoms and Signs
Heat stroke
  • Confusion
  • Slurred speech
  • Unconsciousness
  • Seizures
  • Heavy sweating or hot, dry skin
  • Very high body temperature
  • Rapid heart rate
Heat exhaustion
  • Fatigue
  • Irritability
  • Thirst
  • Nausea or vomiting
  • Dizziness or lightheadedness
  • Heavy sweating
  • Elevated body temperature or fast heart rate
Heat cramps
  • Muscle spasms or pain
  • Usually in legs, arms, or trunk
Heat syncope
  • Fainting
  • Dizziness
Heat rash
  • Clusters of red bumps on skin
  • Often appears on neck, upper chest, and skin folds
Rhabdomyolysis (muscle breakdown)
  • Muscle pain
  • Dark urine or reduced urine output
  • Weakness

Management should commit to preventing heat-related illness for all employees regardless of their heat tolerance levels. Measurement of heart rate, body weight, or body temperature can provide individualized data to aid decisions about heat controls.

OSHA Regulations

Under the General Duty Clause, Section 5(a)(1) of the Occupational Safety and Health Act of 1970, employers are required to provide their employees with a place of employment that "is free from recognized hazards that are causing or likely to cause death or serious harm to employees." This includes heat-related hazards that are likely to cause death or serious bodily harm.

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1. When do most outdoor workplace heat-related fatalities occur?

a. During the first few days of work
b. Within one month after being hired
c. During the first year of employment
d. When the temperature exceeds 50 degrees F

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The Dangers of Extreme Heat

sweaty worker
Sweating is necessary for the body to get rid of excess heat.

Workers, who are exposed to hot and humid conditions, including the outdoors, factories and hot kitchens, are at the most risk for heat illness. Workers doing heavy work or wearing bulky protective clothing and equipment are also at risk. Some workers also might be at a greater risk than others if they haven't built up a tolerance to hot conditions. This process usually takes about 5-7 days.

For the human body to maintain a constant internal temperature, the body must get rid of excess heat. This is achieved primarily through sweating. The evaporation of sweat cools the skin, releasing large amounts of heat from the body.

The human body has a normal core temperature between 97°F and 99°F, but on average, a normal body temperature is 98.6°F (37°C). To maintain this temperature without the help of warming or cooling devices, the surrounding environment needs to be at about 82°F (28°C). At higher temperatures, sweating may not be sufficient to cool the body.

In the range of 90° and 105°F (32° and 40°C), employees may experience heat cramps and exhaustion, and between 105° and 130°F (40° and 54°C), heat exhaustion is possible. Temperatures over 130°F (54°C) often lead to heatstroke. Employees should limit work in temperatures over 90°F.

2. How long does it take for workers to build up a tolerance to hot conditions?

a. A day or two
b. 5-7 days
c. Two weeks
d. 20 days or more

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Heat-Related Illnesses

Heat rash occurs in hot, humid environments.

Excessive exposure to hot environments can cause a variety of heat-related health problems. Body temperature can rise to dangerous levels if precautions are not taken immediately. Heat illnesses can range from heat rash and cramps to heat exhaustion and heat stroke.

Heat Rash

Heat rash often occurs in hot, humid environments where sweat doesn't evaporate from the skin. The sweat ducts become clogged and result in a rash. Heat rash can be very uncomfortable. Victims of heat rash will see clusters of red bumps on the skin. The rash usually appears on the neck, upper chest and folds of the skin. To prevent heat rash, employees should work in cooler and less humid environments, if possible. Also, make sure to keep the affected area dry.

Heat Cramps

Heat cramps may happen alone or with other heat-related illnesses. They are painful muscle spasms caused by dehydration while performing hard physical labor in a hot environment. The cramps are usually caused by too much salt in the body due to sweating, but can also be caused by too little salt. Tired muscles are also very susceptible to heat cramps.

If a worker experiences heat cramps, employers should have the worker:

  • rest in shady, cool area;
  • drink water or other cool beverages (not alcohol);
  • wait a few hours before returning to strenuous work; and
  • seek medical attention if cramps don't go away.

3. What is the cause of heat cramps?

a. Too much or little sugar
b. Too much or little salt
c. Too much or little magnesium
d. Too much or little water

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Heat-Related Illnesses (Continued)

Heat Exhaustion

Heat exhaustion is caused by a loss of large amounts of fluid.

Heat exhaustion is caused by the loss of large amounts of fluid. This can happen by sweating and sometimes with an extensive loss of salt. An employee suffering from heat exhaustion still sweats, but may also experience the following symptoms:

  • Cool, moist skin, heavy sweating
  • General weakness
  • Headache, dizziness, or irritability
  • Thirst, nausea or vomiting
  • Fast heart beat

Treatment. If a worker experiences heat exhaustion, employers should:

  • have the worker lie down or sit in a cool or shady area;
  • have the worker drink plenty of cool liquids, preferably a sports drink with carbohydrates and electrolytes;
  • spray water or apply cool, wet cloths to the worker's head and torso;
  • use a fan to speed evaporation and lower the body temperature; and
  • have the worker evaluated by medical staff if symptoms to not improve within an hour.

4. What causes heat exhaustion?

a. Too much water in the blood
b. Too much calcium in the body
c. A loss of a large amount of fluid
d. A loss of too much potassium in the muscles

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Heat-Related Illness (Continued)

Heat Stroke

Heat stroke is the most serious heat-related illness.

Heat stroke is the most serious heat-related illness. It occurs when the body's temperature-regulating system fails and sweating becomes an inadequate way of removing excess heat. Heat stroke requires immediate medical attention and can result in death. When heat stroke doesn't kill immediately, it can shut down major body organs causing acute heart, liver, kidney and muscle damage, nervous system problems, and blood disorders.

Signs an employee may be suffering from heat stroke are:

  • Confusion
  • Fainting
  • Seizures
  • Excessive sweating or red, hot, dry skin
  • Very high body temperature
  • Unconscious

Treatment. If a worker experiences heat stroke, employers should:

  • call for emergency help immediately;
  • lay the worker on their back unless the worker is unconscious;
  • remove any objects close by if the worker has a seizure;
  • provide cool water to drink if the worker is conscious; and
  • place ice packs under the armpits and in the groin area to cool the worker.

5. What is the most serious heat-related illness?

a. Heat cramps
b. Heat exhaustion
c. Heat stroke
d. Heat rash

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Real-Life Scenario #1

Safety Memo - Hot Enough For You?

A 44-year-old Hispanic migrant farm worker died after succumbing to heat stroke while working in a tobacco field on a farm in North Carolina. The victim arrived on the farm from Mexico on July 21st, 2006 and he was assigned to work in the tobacco fields, where he worked for the next week. On August 1st, 2006, it was hot and humid with a heat index (a measure of the combined effects of high temperatures and high humidity on the body) between 100 and 110. He had been working in a tobacco field when around 3 pm, he complained to the crew leader that he wasn't feeling well. The victim drank some water and was driven back to his housing and left alone to rest. A short time later, he was found unconscious on the steps of the house. Emergency medical service (EMS) personnel were immediately called and responded within five minutes. The victim was taken to the hospital where his core body temperature was recorded at 108 Fahrenheit and was pronounced dead. Heat stroke was listed as the death on the death certificate.

Real-Life Scenario #2

A 41-year-old male laborer died from heat stroke one day after being taken to the hospital. The laborer was working on an addition to a factory sawing boards to make concrete forms. He worked until 5:00 pm that day and was in the parking lot on his way to his car when he apparently collapsed. A worker on the second shift at the factory was taking scrap material outside to a dumpster when he found the victim on the ground. The company receptionist called EMS and the supervisor went to the parking lot to administer emergency care to the laborer until EMS arrived. When paramedics arrived, they recorded the laborer’s body temperature as 107 Fahrenheit. He was transported to a local hospital where he died the next day with an internal body temperature of 108 Fahrenheit.

To prevent similar incidents from occurring, investigators made the following recommendations:

  • Employers should train supervisors and employees to recognize symptoms of heat exhaustion/stroke when working in high heat index and/or humid conditions.
  • To avoid dehydration and heat stress/stroke, employees should be given frequent breaks and be provided water and other hydrating drinks when working in humid and hot conditions.
  • Work hours should be adjusted to accommodate environmental work conditions such as high heat index and/or high humidity.

6. To avoid heat-related illness, work hours should be adjusted to accommodate environmental work conditions such as _____.

a. the duration of a job or task
b. high heat index and/or high humidity
c. maximum performance exposure limits
d. turnover of atmospheric conditions

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Preventing Heat Illnesses Using Controls

Air-conditioned heavy equipment
Heavy equipment with air-conditioned cab.

Engineering Controls

Engineering controls can eliminate or reduce exposure to heat-related hazards by properly designing tools, equipment, machinery, and the facility. The best engineering controls to prevent heat-related illness is to make the work environment cooler and to reduce manual workload with mechanization. A variety of engineering controls can reduce workers' exposure to heat:

  • Air conditioning (such as air-conditioned crane or construction equipment cabs, air conditioning in break rooms)
  • Increased general ventilation
  • Cooling fans
  • Local exhaust ventilation at points of high heat production or moisture (such as exhaust hoods in laundry rooms)
  • Reflective shields to redirect radiant heat
  • Insulation of hot surfaces (such as furnace walls)
  • Elimination of steam leaks
  • Cooled seats or benches for rest breaks
  • Use of mechanical equipment to reduce manual work (such as conveyors and forklifts).
  • Misting fans that produce a spray of fine water droplets

7. Reflective shields, local exhaust ventilation, and cooling fans are examples of _____.

a. administrative controls
b. safety controls
c. engineering controls
d. equipment controls

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Administrative Controls - Work Practices


Some worksites cannot be cooled by engineering controls. At those locations, employers should use administrative controls to modify work practices when heat stress is too high to work safely. Consider the following activity modifications:

  • Modify work schedules and activities for workers who are new to warm environments.
  • Schedule shorter shifts for newly hired workers and unacclimatized existing workers. Gradually increase shift length over the first 1-2 weeks.
  • Require mandatory rest breaks in a cooler environment (such as a shady location or an air conditioned building). The duration of the rest breaks should increase as heat stress rises.
  • Consider scheduling work at a cooler time of day, such as early morning or late afternoon.
  • Reduce physical demands as much as possible by planning the work to minimize manual effort (such as delivering material to the point of use so that manual handling is minimized).
  • Rotate job functions among workers to help minimize exertion and heat exposure.
  • Ensure that workers drink an adequate amount of water or electrolyte-containing fluids. Avoid drinking hot beverages during lunch and afternoon breaks.
  • Employers should have an emergency plan that specifies what to do if a worker has signs of heat-related illness, and ensures that medical services are available if needed.
  • Workers should watch out for each other for symptoms of heat-related illness prepared to administer appropriate first aid to anyone who is developing a heat-related illness.
  • Administer appropriate first aid to any worker who is developing a heat-related illness.
  • In some situations, employers may need to conduct physiological monitoring of workers.
  • Implement a buddy system for new workers and in heat stress environments.

8. Modified work schedules, rest breaks, and job rotation are examples of _____.

a. regulatory controls
b. work practice controls
c. engineering controls
d. administrative controls

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Personal Protective Equipment

Drinking Water
Wear clothing that helps to cool the body.

In most cases, heat stress should be reduced by engineering or administrative controls. However, in some limited situations, special cooling devices can protect workers in hot environments:

  • Insulated suits
  • Reflective clothing
  • Infrared reflecting face shields
  • Cooling neck wraps

In extremely hot conditions, the following thermally conditioned clothing might be used:

  • Vest that receives cooled air from a vortex tube connected to an external compressed air source.
  • Jackets or vests with reusable ice packs or phase change cooling packs in the pockets.
  • Workers should be aware that use of certain personal protective equipment (e.g., certain types of respirators, impermeable clothing, and head coverings) can increase the risk of heat-related illness.

9. In addition to engineering and administrative controls, which of the following could be effective in reducing heat-related stress?

a. job rotation
b. special cooling devices
c. physiological monitoring
d. reflective shields

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Remembering Tim: A life lost to heat illness at work.

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