New research out of George Washington University and Harvard has confirmed what many in the field have known for years: hot days are dangerous for workers. But the numbers behind it are even more serious than expected.

The study reviewed workplace injury data from OSHA’s Injury Tracking Application. It focused on businesses with 100 or more employees in high-hazard industries and linked injury records to detailed weather reports for the exact day and location of each incident. 

The result? Nearly 28,000 injuries in 2023 were directly tied to extreme heat. And that’s likely a low estimate.

According to David Michaels, one of the study’s senior authors and a professor of environmental and occupational health at George Washington University, heat-related injuries are rarely reported as such. 

“A strong OSHA standard will not only prevent heat illness and death,” he said, “but will also prevent thousands of work injuries every year.”

It Starts Sooner Than You Think

One of the most important findings was how early heat becomes a problem. 

The study found that injury risk starts climbing when the heat index hits 85°F, and it rises sharply past 90°F. And this goes beyond crews working outdoors. Researchers found heat-linked injuries across every industry sector, including indoor work. 

That means crews inside warehouses, mechanical rooms, or job trailers with limited airflow face real risk when the heat kicks in.

States With Standards See Lower Risk

The study also noted that workers in states with workplace heat regulations had a lower risk of injury on hot days. That includes standards for shade, water, breaks, and training. These basic protections can make a big difference when crews are pushing through long hours in high heat.

Currently, OSHA has proposed a national rule to require employers to protect workers from extreme heat, but it hasn’t gone into effect yet. This new research supports that move, showing how heat can lead to lost wages, long-term health problems, and even fatalities if left unaddressed.

What It Means for the Field

Contractors and field leaders have dealt with heat risk for decades. But this study puts hard data behind the day-to-day reality. 

The dangers aren’t just limited to obvious heat illness. The research shows that even moderate heat raises the chance of slips, falls, tool mishandling, fatigue, and other mistakes that lead to serious injury.

Barrak Alahmad, the study’s lead author and director of the occupational health and climate change program at Harvard, explained it this way: “Even moderate hot conditions can subtly increase the risk of workplace injuries. That was consistent across almost all industries we examined.”

Bottom Line

As temperatures rise, so does the risk to crews. This research confirms that extreme heat has a direct and measurable impact on safety, and that common-sense protections work. With 28,000 injuries linked to heat in just one year, the case for smarter planning, better training, and jobsite policies that protect workers is clear.

Stay alert and watch the heat index. If you’re running crews in high temps, have a plan in place that includes water, breaks, shade, and heat safety training. Make sure your team knows those steps aren’t optional and that nobody catches heat for taking a break when they need it.