WORKERS who are exposed to extreme heat or work in hot environments may be at risk of heat stress. Exposure to extreme heat can result in occupational illnesses and injuries. Heat can also increase the risk of injuries in workers as it may result in sweaty palms, fogged-up safety glasses, and dizziness. Burns may also occur as a result of accidental contact with hot surfaces or steam.
Workers at risk of heat stress include outdoor workers and workers in hot environments such as firefighters, bakery workers, farmers, construction workers, miners, boiler room workers, factory workers, and others. Workers at greater risk of heat stress include those who are 65 years of age or older, are overweight, have heart disease or high blood pressure, or take medications that may be affected by extreme heat.
Types of Heat Stress
1. Heat stroke
This is the most serious form of heat injury and is considered a medical emergency. Heat stroke results from prolonged exposure to high temperatures and usually in combination with dehydration, which leads to failure of the body’s temperature control system. The medical definition of heat stroke is a core body temperature greater than 105 degrees Fahrenheit (40.5oC), with complications involving the central nervous system that occur after exposure to high temperatures. Other common symptoms include nausea, throbbing headache, seizures, confusion, disorientation, and rapid, shallow breathing. Heat stroke can cause death or permanent disability if emergency treatment is not given. If a worker shows signs of possible heat stroke, get medical help immediately. Until medical help arrives, move the worker to a shady, cool area and remove as much clothing as possible. Wet the worker with cool water and circulate the air to speed cooling. Place cold wet cloths, wet towels or ice all over the body or soak the worker’s clothing with cold water.
2. Heat Exhaustion
This is the next most serious heat-related health problem. Heat exhaustion is the body’s response to an excessive loss of the water and salt, usually through excessive sweating. The signs and symptoms of heat exhaustion are headache, nausea, dizziness, weakness, irritability, confusion, thirst, heavy sweating and a body temperature greater than 100.4°F (38oC). Workers with heat exhaustion should be removed from the hot area and given liquids to drink. Cool the worker with cold compresses to the head, neck, and face or have the worker wash his or her head, face and neck with cold water. Encourage frequent sips of cool water.
3. Heat Syncope
Heat syncope is a fainting (syncope) episode or dizziness that usually occurs with prolonged standing or sudden rising from a sitting or lying position. Factors that may contribute to heat syncope include dehydration and lack of acclimatization. Symptoms of heat syncope include light-headedness, dizziness and fainting. Workers with heat syncope should sit or lie down in a cool place when they begin to feel symptoms. Slowly drink water, clear juice, or a sports beverage.
4. Heat Cramps
These are muscle pains usually caused by the loss of body salts and fluid during sweating. Workers with heat cramps should replace fluid loss by drinking water and/or carbohydrate-electrolyte replacement liquids (e.g., sports drinks) every 15 to 20 minutes.
5. Heat Rash
Heat rash the most common problem in hot work environments. It causes discomfort and itchiness. Heat rash is caused by sweating and looks like a red cluster of pimples or small blisters. Heat rash may appear on the neck, upper chest, groin, under the breasts and elbow creases. The best treatment for heat rash is to provide a cooler, less humid work environment. The rash area should be kept dry. Powder may be applied to increase comfort. Ointments and creams should not be used on a heat rash. Anything that makes the skin warm or moist may make the rash worse.
Prevention of heat stress in workers is important. Employers should provide training to workers so they understand what heat stress is, how it affects their health and safety, and how it can be prevented.
1. Designate a Person to Oversee the Heat Stress Program
Identify someone trained in the hazards, physiological responses to heat, and controls. This person can develop, implement and manage the program.
2. Hazard Identification
Hazard identification involves recognizing heat hazards and the risk of heat illness due to high temperature, humidity, sun and other thermal exposures, work demands, clothing or PPE and personal risk factors. Identification tools include a Wet Bulb Globe Thermometer (WBGT) which is a measure of heat stress in direct sunlight that takes into account temperature, humidity, wind speed, sun and cloud cover.
Ensure that cool drinking water is available and easily accessible. (Note: Certain beverages, such as caffeine and alcohol can lead to dehydration.) Encourage workers to drink a liter of water over one hour, which is about one cup every fifteen minutes. Provide or ensure that fully shaded or air-conditioned areas are available for resting and cooling down.
Acclimatization is a physical change that allows the body to build tolerance to working in the heat. It occurs by gradually increasing workloads and exposure and taking frequent breaks for water and rest in the shade. Full acclimatization may take up to 14 days or longer depending on factors relating to the individual, such as increased risk of heat illness due to certain medications or medical conditions, or the environment. New workers and those returning from a prolonged absence should begin with 20% of the workload on the first day, increasing incrementally by no more than 20% each subsequent day. During a rapid change leading to excessively hot weather or conditions such as a heat wave, even experienced workers should begin on the first day of work in excessive heat with 50% of the normal workload and time spent in the hot environment, 60% on the second day, 80% on day three, and 100% on the fourth day.
5. Modified Work Schedules
Altering work schedules may reduce workers’ exposure to heat:
Reschedule all non-essential outdoor work for days with a reduced heat index.
Schedule the more physically demanding work during the cooler times of day.
Schedule less physically demanding work during warmer times of the day.
Rotate workers and split shifts, and/or add extra workers.
Stop work if essential control methods are inadequate or unavailable when the risk of heat illness is very high. Keep in mind that very early starting times may result in increased fatigue. Also, early morning hours tend to have higher humidity levels.
Provide training in a language and manner workers understand, including information on health effects of heat, the symptoms of heat illness, how and when to respond to symptoms, and how to prevent heat illness.
7. Monitoring for Heat Illness Symptoms
Establish a system to monitor and report the signs and symptoms listed on the previous page to improve early detection and action. Using a buddy system will assist supervisors when watching for signs of heat illness.
8. Emergency Planning and Response
Have an emergency plan in place and communicate it to supervisors and workers, including:
What to do when someone is showing signs of heat illness.
How to contact emergency help.
How long it will take for emergency help to arrive and training workers on appropriate first-aid measures until help arrives.
9. Engineering Controls Specific to Indoor Workplaces
Indoor workplaces may be cooled by using air conditioning or increased ventilation, assuming that cooler air is available from the outside. Other methods to reduce indoor temperature include: providing reflective shields to redirect radiant heat, insulating hot surfaces, and decreasing water vapor pressure, e.g., by sealing steam leaks and keeping floors dry. The use of fans to increase the air speed over the worker will improve heat exchange between the skin surface and the air, unless the air temperature is higher than the skin temperature. However, increasing air speeds above 300 ft. per min. may actually have a warming effect. Industrial hygiene personnel can assess the degree of heat stress caused by the work environment and make recommendations for reducing heat exposure.