Heat Illness Risks Extend Beyond the Hottest Days

New and returning workers can face heightened heat illness risks before they acclimatize

• By Stasia DeMarco
• Sep 22, 2026

Heat illness prevention often focuses on the hottest days of summer, but some of the workers at greatest risk may be those who have spent the least amount of time working in the heat.

New employees and workers returning from vacation, illness or extended absences may not have developed — or may have lost — the physiological adaptations that help the body tolerate hot conditions.

“The highest-risk moment is often the first week on the job or the first days back from time off, before the body has adapted,” said Bill Shoemaker, senior risk control specialist at Travelers.

OSHA says more than 70% of heat-related worker deaths occur during a worker’s first week, underscoring the importance of gradually acclimatizing employees to hot conditions.

Heat Isn't Just an Outdoor Hazard

Workers performing strenuous physical tasks, working in direct sunlight or wearing bulky or non-breathable protective equipment can face elevated heat risks. But employers shouldn't view heat exposure solely as an outdoor summer hazard.

Foundries, commercial kitchens, bakeries, glass production facilities and manufacturing operations can expose employees to significant heat indoors.

Temperature alone also doesn't determine risk. Humidity can reduce the body's ability to cool through sweat, while radiant heat from equipment, surfaces and sunlight can increase a worker's overall heat burden.

“The most important thing that employers can do is to ensure proper planning and awareness, as heat illness is largely preventable,” Shoemaker said.

Plan Before Temperatures Climb

Shoemaker recommends employers establish a written heat stress prevention plan rather than deciding how to respond during a heat wave.

New and returning employees should be gradually acclimatized over several days. Employers should also make cool drinking water readily available, schedule more frequent breaks in shaded or air-conditioned locations and consider rotating employees through hotter jobs.

As conditions worsen, employers can schedule strenuous work during cooler periods, reduce workloads and use engineering controls such as ventilation, air conditioning, heat shields and reflective barriers.

Employers should also monitor more than the air temperature. Heat index, humidity, radiant heat, workload and clothing can all affect workers' heat exposure.

Recognize the Warning Signs

Even with preventive measures, workers and supervisors need to recognize heat illness and respond quickly.

Heat exhaustion can cause dizziness, weakness, headaches, nausea, heavy sweating and other symptoms. Heat stroke is a medical emergency that can involve confusion, loss of consciousness, high body temperature, seizures and other serious symptoms.

One challenge is that affected workers may not recognize their own condition.

“Impaired judgment is also an early symptom, so a worker may not recognize their own condition,” Shoemaker said. “That is why a buddy system matters, along with extra attention to new and returning employees during their first days in the heat.”

Workers showing signs of heat exhaustion should be moved to a cooler location and actively cooled. If heat stroke is suspected, employers should call 911 immediately and begin cooling the worker while awaiting emergency assistance.

For Shoemaker, heat prevention works best when it becomes part of routine workplace safety rather than a response reserved for extreme weather.

“Heat safety also works best when built into everyday safety culture, not something that surfaces only when temperatures climb,” he said.

That means preparing before temperatures rise, routinely monitoring conditions and paying particular attention to workers who haven't yet adapted to the heat.