Heat stroke in the work environment

Zachary J. Schlader, PhD, FACSM

With increases in temperatures worldwide, of the experience of hot weather and the length of the hot weather season is increasing throughout the globe. The impacts of these hotter temperatures will be first encountered in the workplace, with workers regularly exposed to hot environments taking the burden of the adverse health effects. With increased heat exposure there is a heightened risk of developing heat illness, with nearly everyone at exposed being at risk. In fact, according to the United States Centers for Disease Control and Prevention there is an average of 702 deaths and 67,512 emergency department visits from heat-related causes every year The term heat illness describes a series of disorders ranging from relatively mild to life threatening. 

Mild heat illnesses include heat syncope (fainting) and heat exhaustion, which can be treated with rest and removal from the hot environment. Heat stroke is the most severe heat illness. Heat stroke causes bodily dysfunction and can be deadly. There are two forms of heat stroke, classic heat stroke and exertional heat stroke. Both classic and exertional heat stroke are caused by extreme elevations in internal body temperature. Classic heat stroke occurs during resting exposures to extreme heat and more frequently affects the very young, older adults, and/or those with underlying illness. 

By contrast, exertional heat stroke more often occurs in healthy adults, such as workers engaging in intense manual labor. In the workplace, exertional heat stroke is caused by the inability to get rid of enough body heat to offset the heat load caused by manual labor and heat exposure. As a result, while exertional heat stroke is more likely to occur during heat exposure it can also occur in cooler conditions.

Heat stroke is diagnosed through clinical signs and symptoms. In general, heat stroke is the likely diagnosis when internal body temperature exceeds 40.5°C (105°F) and nervous system alterations are observed (including confusion, coma, disorientation), amongst others (Box 1). With early diagnosis and rapid cooling, the outlook for heat stroke victims is very good, with nearly 100% survival. The standard for cooling is ice water immersion, but other body cooling modalities may be successfully employed if ice water immersion is not possible. For example, cold showers, forearm cold water immersion, amongst others, may be used, but these are not as effective as ice water immersion. The risk of hospitalization, prolonged illness, and even death is increased when heat stroke diagnosis and treatment are delayed. Therefore, it is important to be prepared in the workplace to prevent, diagnose, and provide rapid cooling to potential heat stroke victims.

Workers and supervisors should be educated on the risk factors for heat stroke (Box 2). For example, one of the easiest risk factors to modify in the workplace is maintaining good hydration practices by regularly drinking water or an electrolyte beverage, particularly if work is longer than two hours. This is because dehydration can cause greater increases in internal body temperature. Additionally, worker training involving understanding the signs, symptoms and treatment of heat stroke is important, particularly if emergency services can be delayed. Collectively, heat stroke in the workplace is preventable and if it does occur survivorship is nearly 100% with rapid diagnosis and aggressive body cooling. 

Box 1: Signs and symptoms of heat stroke

- Internal body temperature (≥40.5°C (105°F); can be difficult to accurately measure in workplace settings).
- Central nervous system dysfunction (confusion, altered mental status, slurred speech, collapse, seizures, loss of consciousness)
- Headache
- Nausea, vomiting, diarrhea
- High heart rate and breathing rate

Box 2: Workplace-relevant risk factors for heat stroke:

- High intensity manual labor in a hot and/or humid environment.
- Dehydration.
- Prior viral illness.
- History of heat stroke.
- Poor physical fitness.
- Lack of heat acclimatization.
- Obesity.
- Underlying chronic disease (cardiovascular disease, diabetes, etc.).