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.
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.
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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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.
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 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 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:
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:
Treatment. If a worker experiences heat exhaustion, employers should:
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:
Treatment. If a worker experiences heat stroke, employers should:
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.
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:
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:
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:
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:
In extremely hot conditions, the following thermally conditioned clothing might be used:
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