Heat Illness: Would Your Workers Recognize Exertional Heatstroke?


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 document was last updated in 1986, and in recent years, including during the Deepwater Horizon oil spill response of 2010, questions were raised regarding the need for revision to reflect recent research and findings.

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.

The most significant change to the NIOSH document is a change in the definition of “heatstroke.” At one time, the accepted definition of “heatstroke” included confusion, unconsciousness, and/or convulsions, accompanied by a lack of sweating. In fact, workers were warned that if they stopped sweating, heatstroke was imminent. 

Unfortunately, this type of heatstroke, now called “Classic Heatstroke”, isn’t the type that most commonly strikes workers.

NIOSH has recognized that another type of heatstroke, known as “external heatstroke”, is more common in workers – and profuse sweating is one of its symptoms. So, workers who have been taught that sweating is a positive sign, are actually at increased risk. Because exertional heatstroke is more likely to occur in workers than classic heatstroke, NIOSH recommends that all workers exposed to hot working conditions be retrained to recognize exertional heatstroke.