Handling Heat Stress

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Handling Heat Stress

Linda Gail Johnson, RN, BSN, MPH, COHN-S

As we move into June, days heat up and the risk for heat stress among workers begins to rise. Occupational exposure to heat can result in injuries, disease, reduced productivity, and death. To address this hazard, the National Institute for Occupational Safety and Health (NIOSH) has evaluated the scientific data on heat stress and hot environments and has updated the Criteria for a Recommended Standard: Occupational Exposure to Hot Environments. This revi­sion includes additional information about the physiological changes that result from heat stress; updated information from relevant studies, such as those on caffeine use; evidence to redefine heat stroke and associated symptoms; and updated information on physiological monitoring and per­sonal protective equipment and clothing that can be used to control heat stress.

Workers who are exposed to extreme heat or work in hot environments indoors or outdoors, or even those engaged in strenuous physical activities may be at risk for heat stress. Exposure to extreme heat can result in occupational illnesses caused by heat stress, including heat stroke, heat exhaustion, heat syncope, heat cramps, heat rashes, or death. Heat can also increase workers’ risk of injuries, as it may result in sweaty palms, fogged-up safety glasses, dizziness, and may reduce brain function responsible for reasoning ability, creating additional hazards. Other heat injuries, such as burns, may occur as a result of contact with hot surfaces, steam, or fire. Those at risk of heat stress include outdoor workers and workers in hot environments, such as fire fighters, bakery workers, farmers, construction workers, miners (particularly surface miners), boiler room workers, and fac­tory workers.

In 2011, NIOSH published with the Occupational Safety and Health Administration (OSHA) a co-branded info sheet on heat illness. Through this combined effort, many recommendations were updated, including those on water consumption. In addition, factors that increase risk and symp­toms of heat-related illnesses were more thoroughly defined. In 2013, NIOSH published “Preventing Heat-related Illness or Death of Outdoor Workers”, since outdoor workers are exposed to a great deal of exertional and environmental heat stress.

Chapters on basic knowledge of heat balance and heat exchange largely remain unchanged, although clothing insulation factors have been updated to reflect current International Organization for Standardization (ISO) recommendations. Additional information on the biological effects of heat has become available in recent studies, specifically increasing the understanding of the central ner­vous system, circulatory regulation, the sweating mechanism, water and electrolyte balance, and dietary factors.

Heat stress can be reduced by modifying metabolic heat production or heat exchange by convection, radiation, or evaporation. In a controlled environment, these last three can be modified through engineering controls, including increasing ventilation, bringing in cooler outside air, reducing the hot temperature of a radiant heat source, shielding the worker, and using air conditioning equip­ment. Heat stress can also be administratively controlled through limiting the exposure time or temperature (e.g., work/rest schedules), reducing metabolic heat load, and enhancing heat toler­ance (e.g., acclimatization). Although most healthy workers will be able to acclimatize over a period of time, some workers may be heat intolerant. Heat intolerance may be related to many factors; however, a heat tolerance test can be used to evaluate an individual’s tolerance.  Additional preventive strategies against heat stress include establishing a heat alert program and providing auxiliary body cooling and protective clothing (e.g., water-cooled garments, air-cooled garments, cooling vests, and wetted over-garments).

Employers should establish a medical monitoring program to prevent adverse outcomes and for early identification of signs that may be related to heat-related illness. This program should include preplacement and periodic medical evaluations, as well as a plan for monitoring workers on the job.

Health and safety training is important for employers to provide to workers and their supervi­sors before they begin working in a hot environment. This training should include information about recognizing symptoms of heat-related illness; proper hydration (e.g., drinking 1 cup [8 oz.] of water or other fluids every 15–20 minutes); care and use of heat-protective clothing and equip­ment; effects of various factors (e.g., drugs, alcohol, obesity, etc.) on heat tolerance; and importance of acclimatization, reporting symptoms, and giving or receiving appropriate first aid. Supervisors also should be provided with appropriate training about how to monitor weather reports and weather advisories.

The NIOSH Recommended Alert Limits (RALs) and Recommended Exposure Limits (RELs) were evaluated. It was determined that the current RALs for unacclimatized workers and RELs for accli­matized workers are still protective for most workers. No new data were identified to use as the basis for updated RALs and RELs.

Although research has produced substantial new information since the previous revision of this document, the need for additional research continues. Two newer areas of research that will likely continue to grow are the effects of climate change on workers and how heat stress affects the toxic response to chemicals.

Below is a brief summary of the serious manifestations of heat stress:

Heat stroke, the most serious heat-related illness, is life-threating and requires immediate first aid. It occurs when the body becomes unable to control its temperature: the body's temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. When heat stroke occurs, the body temperature can rise to 106°F or higher within 10 to 15 minutes. Heat stroke is a 9-1-1 emergency and can result in death or permanent disability if emergency treatment is not given.  Cooling the employee quickly is imperative. Move to the coolest area possible and apply ice water by immersion in a tub, with ice compresses or by continuous and thorough cold water hosing with a garden hose until advanced medical care arrives.

Heat exhaustion, the precursor to heat stroke, is the body's response to an excessive loss of the water and salt, usually through excessive sweating. Symptoms of heat exhaustion include:  heavy sweating, weakness, muscle cramps, headache, nausea, dizziness, irritability and thirst.  Immediate first aid includes removing excess clothing, moving to a cooler location, cooling the worker with cold compresses and providing fluids.  Medical evaluation is needed even when the worker seems improved.

Heat Syncope is the collapse and/or loss of consciousness during heat exposure without an increase in body temperature or cessation of sweating. Treat as if fainting and once alert, provide 8 oz. of water and if possible a carbohydrate-electrolyte replacement liquid (e.g., sports drinks) every 15 to 20 minutes.

Heat cramps usually affect workers who sweat a lot during strenuous activity. Sweating depletes the body's salt and fluid levels, resulting in painful cramps, usually in the abdomen, arms or legs. Heat cramps may also be a symptom of heat exhaustion. Treatment includes 8 oz. of water and if possible a carbohydrate-electrolyte replacement liquid (e.g., sports drinks) every 15 to 20 minutes.  Medical evaluation is needed if the cramps continue for longer than 1 hour.

Heat rash is a skin irritation caused by excessive sweating during hot, humid weather. It appears as a cluster of pimples or small blisters, usually on the neck, upper chest, elbow creases and groin. Keeping affected areas dry and cool is the preferred treatment, using powder, rather than ointments and creams.

Primary Resource for this article: Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments - Revised Criteria 2016Brenda Jacklitsch, MS; W. Jon Williams, PhD;Kristin Musolin, DO, MS; Aitor Coca, PhD; Jung-Hyun         DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Institute for Occupational Safety and Health


For additional information and training support on Heat Stress contact Blue Ridge Safety Association.