Most people probably understand by now how dangerous it can be for workers to labor in high heat: heat stroke can kill, and heat related disease — even if it doesn’t kill you — can lead to kidney disease and other chronic health conditions.
But few people know that the hazards of heat go beyond just the common heat-related illnesses that we already know about. A recent study out of Harvard University and George Washington University, “A Nationwide Analysis of Heat and Workplace Injuries,” published October 6 in the journal Environmental Health, shows that high heat contributes to at least 27,953 excess workplace injuries each year — — slips, trips, and falls, as well as cuts and other traumatic injuries.
The study was led by former OSHA Assistant Secretary David Michaels, currently a professor at the Milken Institute School of Public Health at George Washington University. According to Michaels, “It’s very clear that heat causes more than simply heat illness and unfortunately heat fatalities. But it also causes thousands of injuries every year. When you’re working in heat, you can much more easily make mistakes.”
Heat related worker injuries were tied to exposure to extreme heat and were seen across almost all industry sectors, including indoor jobs.
Why does high heat cause more work-related injuries?
Studies have shown that elevated temperatures can impair hand-eye coordination, cause postural instability, lead to muscular fatigue, and reduce physical reaction times. Cognitive effects of heat include reduced attention memory, information processing, and overall judgment. Put together, physiological and cognitive impairments increase the risk of workplace injuries few of which are officially classified as “heat” injuries.
Many other studies have reached similar conclusions, and the fact that high heat causes more injuries (as well as illnesses) isn’t a new discovery. The preamble to the Biden Heat proposal notes that:
In 1972, NIOSH identified occupational heat exposure as contributing to workplace injuries, and discussed how accidents and injuries were outcomes that could be prevented by a heat stress standard (NIOSH, 1972). Specifically, NIOSH highlighted how reduced physical and psychological performance, fatigue, accuracy of response, psychomotor performance, sweaty palms, and impaired vision may result in a workplace heat-related injury.
But this study was much larger than other studies — looking at 845,000 injury cases in 48 states. In order to estimate the number and fraction of overall injuries that could be attributable to heat exposure, the study geocoded each injury and matching them with high-resolution weather data for the specific injury date. The authors used OSHA’s recently established Injury Reporting Application which was the result of a 2023 OSHA rule that required large establishments in certain high-hazard industries to electronically submit detailed records of every work-related injury and illness through the agency’s Injury Tracking Application (ITA).
This study also was able to look at whether states that have heat standards similar to OSHA’s proposal resulted in fewer heat-related injuries. (Spoiler alert: they did.)
Undercounting
Both heat-related injuries and illnesses are undercounted, but undercounting is even more problematic for heat-related injuries than for heat-related illnesses. Heat related illnesses are significantly undercounted because heat-related illnesses and heat stroke deaths can be mis-diagnosed as heart attacks or strokes. Other heat-related illnesses have symptoms like fatigue, nausea, dizziness, and vomiting are similar to flu and are unlikely to be identified by the employer (or even the worker) as heat related or work related.
But while heat stroke and heat exhaustion are becoming increasingly well recognized, heat-related injuries are rarely reported as resulting from high heat. In fact, the authors characterize heat-related injuries as the “hidden toll,” because most heat-driven injuries are not recorded as “heat injuries” even though heat contributed to their occurrence.
The authors call these heat-related injuries the “hidden toll,” because most heat-driven injuries are not recorded as “heat injuries” even though heat contributed to their occurrence
Even the 28,000 heat-related injuries identified in this study are likely undercounted. The baseline to which the injury numbers are compared is the self-reported Bureau of Labor Statistics (BLS) injury data which have been shown — by BLS’s own studies — to be underreported by as much as 20% to 70%.
Injuries were also missed because the OSHA injury data only includes larger employers, and only 42% of U.S. employment in 2023 was in large establishments with more than 100 employees. This undercounting is even more pronounced in construction where 90% of construction companies employ fewer than 100 workers.
In addition, public employees were excluded. Their injury records are inconsistent because public employees are not covered by OSHA — even its General Duty Clause — in 23 states. Motor vehicle crashes were also not included, even though heat could be a factor in vehicle accidents, especially in unairconditioned vehicles.
A Strong Workplace Heat Standard is Needed
If you had listened to the testimony of business associations at the recent OSHA heat hearings or read some of their comments, you may remember that they didn’t really want any heat standard. But if the heat is on and OSHA felt compelled to issue something, then they preferred a “performance” standard (with no real requirements) — similar to Nevada’s — as opposed to a “specification” standard that tells employers what they have to do, depending on how hot it is. They also wanted separate (or no) standards for construction, general industry, agriculture, indoor and outdoor workers.
We now know with much more certainty the value of strong standards. It’s clear that strong heat standards protect workers. One recent study of the impact of California’s outdoor heat standard by the Workers Compensation Research Institute found that the standard had reduced heat-related injuries by 15-17 percent in construction, 24-27 percent in agriculture and by 19-25 percent in transportation, and that the beneficial effect was strongest at higher temperatures. Another study found that the CalOSHA heat standard had reduced overall heat-related deaths by as much as 43%.
But this is the first study to compare heat injuries in states with heat standards to states without heat standards. The study looked at several states that have standards (like California, Washington and Oregon) and found that employees in states with workplace heat exposure regulations have a lower risk of injury on hot days than workers in states with no heat standards.
The study looked at several states that have standards (like California, Washington and Oregon) and found that employees in states with workplace heat exposure regulations have a lower risk of injury on hot days than states with no heat regulations.
The study also showed that higher temperatures were more dangerous than lower temperatures. The hotter it gets, the more likely workers are to suffer injuries. The study found that work injury risks begin to rise when the heat index reaches around 85°F and increase sharply after 90°F. And on a 105°F and 110°F days the odds were about 15% and 20% higher compared to an 80 °F day, respectively.
That all seems kind of obvious, but if you listened to the OSHA heat hearings last summer, or read any of the written comments submitted to OSHA, you are aware of the controversy over “heat thresholds” — at what temperature (or “heat index,” which factors in humidity) should certain requirements kick in? The proposed OSHA standard, for example had an 80°F lower heat index threshold and a 90°F high heat threshold. Industry witnesses argued that we don’t need mandatory heat thresholds; employers should just be allowed to figure out for themselves at what temperatures certain measures might be good to implement.
So What Does This Mean?
The authors concluded that the risk of work-related injuries are getting is getting worse, workers must be made aware of these hazards and that they need strong standards to protect them.
The findings demonstrate that hot temperatures are not just a health concern for heat illness or heat stroke, but also a significant risk factor for a wide array of workplace injuries. These injuries are typically not labeled as “heat-related,” reflecting a subtle yet pervasive impact of heat on worker vigilance, coordination, and judgment. Occupational safety training and education requirements should explicitly warn about the role of heat in such injuries. Heat safety measures by employers (acclimatization, rest, water, shade, written heat plans, etc.) will be critical for safeguarding worker health, and reducing the ‘hidden’ economic costs of heat-related injuries. As climate change intensifies and extreme heat events become more frequent and pervasive, adopting and enforcing comprehensive heat safety regulations will become increasingly important. Our study provides a quantitative baseline for these efforts and highlights the need for continued surveillance of injuries and research to monitor the effectiveness of heat interventions that best protect the workforce.
And those conclusions are not just rhetoric or wishful thinking — they are based on data and science.
“The numbers on this one are a little bit eye-opening,” said Juanita Constible, a senior advocate for environmental health at the Natural Resources Defense Council, who described this study as the first national look at the impact of heat on workplace injury….Constible added that worker injuries hurt employers’ pocketbooks in the form of workers’ compensation claims. People know it intuitively when they’re out mowing their lawn for a few hours and they get really hot and miserable, right?” said Constible. “It impairs our judgment, makes our hands slippery, affects our posture.”
This study confirms that if we are serious about protecting workers against high heat, and if we are serious about basing an OSHA standard on science and not politics, then OSHA needs to issue a standard that is as strong as the Biden standard with specific heat thresholds and requirements for water, shade, rest, acclimatization, emergency response procedures and training for employers and workers.
But is OSHA serious? Given the hostility of the Trump administration, Congressional Republicans and the business community to issuing any new OSHA standards (except those that weaken worker protections), it is likely that if we see a heat standard in the next three years, it will be significantly weaker than the strong Biden administration proposal.
But if I were a betting man, I’d wager that we won’t see any standard: OSHA just doesn’t have the staff to go back to the drawing board and start over again to create a standard that is not based on the science — especially when they’ve been ordered devote scarce resources to prioritize deregulatory actions, not initiatives that actually improve worker safety and protect American workers.