Many people are exposed to heat on the job, outdoors or in hot indoor environments. Operations involving high air temperatures, radiant heat sources, high humidity, direct physical contact with hot objects, or strenuous physical activities have a high potential for causing heat-related illness. Workplaces with these conditions may include iron and steel foundries, nonferrous foundries, brick-firing and ceramic plants, glass products facilities, rubber products factories, electrical utilities (particularly boiler rooms), bakeries, confectioneries, commercial kitchens, laundries, food canneries, chemical plants, mining sites, smelters, and steam tunnels.
Outdoor operations conducted in hot weather and direct sun, such as farm work, construction, oil and gas well operations, asbestos removal, landscaping, emergency response operations, and hazardous waste site activities, also increase the risk of heat-related illness in exposed workers. Every year, thousands of workers become sick from occupational heat exposure, and some even die. These illnesses and deaths are preventable.
Why is heat a hazard to workers?
When a person works in a hot environment, the body must get rid of excess heat to maintain a stable internal temperature. It does this mainly through circulating blood to the skin and through sweating. When the air temperature is close to or warmer than normal body temperature, cooling of the body becomes more difficult. Blood circulated to the skin cannot lose its heat. Sweating then becomes the main way the body cools off.
But sweating is effective only if the humidity level is low enough to allow evaporation, and if the fluids and salts that are lost are adequately replaced. If the body cannot get rid of excess heat, it will store it. When this happens, the body's core temperature rises and the heart rate increases. As the body continues to store heat, the person begins to lose concentration and has difficulty focusing on a task, may become irritable or sick, and often loses the desire to drink. The next stage is most often fainting and even death if the person is not cooled down. Excessive exposure to heat can cause a range of heat-related illnesses, from heat rash and heat cramps to heat exhaustion and heat stroke. Heat stroke can result in death and requires immediate medical attention. Exposure to heat can also increase the risk of injuries because of sweaty palms, fogged-up safety glasses, dizziness, and burns from hot surfaces or steam.
Who could be affected by heat?
Workers exposed to hot indoor environments or hot and humid conditions outdoors are at risk of heat-related illness, especially those doing heavy work tasks or using bulky or non-breathable protective clothing and equipment. Some workers might be at greater risk than others if they have not built up a tolerance to hot conditions, or if they have certain health conditions. The table below shows some environmental and job-specific factors that increase the risk of heat-related illness. Workers who are suddenly exposed to working in a hot environment face additional, but generally avoidable hazards to their safety and health. New workers and those returning from time away are especially vulnerable. That's why it is important to prepare for the heat: educate workers about the dangers of heat, and acclimatize workers by gradually increasing the workload or providing more frequent breaks to help new workers and those returning to a job after time away build up a tolerance for hot conditions.
How can heat-related illness be prevented?
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), shade, reflective shields to redirect radiant heat, insulation of hot surfaces (such as furnace walls), and elimination of steam leaks.
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.
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 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, or 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, and procedures to ensure that clear and precise directions to the work site will be provided to emergency medical services.
Most heat-related health problems can be prevented, or the risk of developing them can be reduced.