Injuries and Illness

How Soon Can a Worker Return to Work After Heat Illness?

Protecting workers from the heat is a critical issue during the hot months of July and August—so critical that OSHA is ramping up its awareness and enforcement efforts around heat illness prevention this year. Ideally, employers are supposed to prevent workers from suffering heat illness in the first place, but what happens after a worker experiences a heat-related illness?

Most guidelines suggest that workers can easily relapse within a week after suffering heat illness, but new research indicates that their susceptibility may last far longer. “Heat intolerance” has been most closely studied in the armed forces because soldiers who collapse under conditions of high heat and heavy exertion and return to duty too soon tend to suffer secondary collapses.

Understanding and Assessing Heat Intolerance

Many factors can affect a worker’s underlying heat tolerance, including:

  • Air temperature and humidity,
  • Direct sun exposure,
  • Indoor radiant heat sources (ovens, hot manufacturing processes, etc.),
  • Limited air movement,
  • Physical exertion,
  • Not drinking enough fluids (dehydration),
  • Personal protective equipment (PPE) or clothing,
  • Certain medications,
  • Physical condition,
  • Lack of recent exposure (not acclimatized), and
  • Advanced age (65+).


Join us on Tuesday, July 14, for our in-depth webinar, Return-to-Work Programs: The Key to Minimizing Lost Workdays for Injured Employees


But once a worker has suffered a heat illness, the illness itself becomes a predisposing condition that can indicate an increased susceptibility to heat illness. Workers who have suffered heat illness should not return to work right away.

Whether and when a worker can return to working in the heat after suffering heat-related illness is affected by:

  • Preexisting susceptibility. Some people are naturally heat-intolerant, but this is not usually discovered until after they suffer a heat-related illness. These workers will remain intolerant to heat; acclimatization will not help them.
  • Recovery time. Some workers develop temporary intolerance to heat after suffering a heat-related illness. They may remain heat-intolerant for several months. A heat tolerance test, in which the individual walks on a treadmill in a climactic chamber while being closely monitored, can determine whether they can safely return to work.


Companies that have RTW programs can reduce workers’ compensation costs, including temporary disability, medical, rehabilitation, and retraining, and get employees back to their assigned positions more quickly. Click here to learn more!


One factor that doesn’t seem to affect a person’s heat tolerance following heat illness is the individual’s overall physical fitness. Overall fitness has no effect on whether a person becomes heat-intolerant after suffering a heat-related illness, so don’t use that as a return-to-duty criterion.

For more information on preventing heat-related illness for your workers, get acclimated to the resources you’ll find at Safety.BLR.com®.