US government agencies are likely significantly undercounting the number of workplace injuries caused by extreme heat, according to new research. Federal and state labor departments keep track of heat-related injuries, which include things like dehydration and heat strokes. But if a worker falls from a ladder because of heat-induced dizziness, it’s typically not categorized as a heat-related injury. New research published this week shows that when those injuries are taken into account, the actual toll of heat on US workers is orders of magnitude higher than official counts. In California, the state’s occupational safety division only counts about 60 heat-related injuries annually. But this paper estimates that, between 2001 and 2018, the number of heat-related injuries was actually hundreds of times higher: about 24,800 each year. “We expected heat would have impacts on other types of injuries, but the magnitude was surprising,” said A Patrick Behrer, who co-wrote the working paper with R Jisung Park and Nora Pankratz. The paper took advantage of a California law that requires all employers to have workers compensation insurance, which pays out to workers when they are injured at work. The researchers analyzed 11.6m claims in the state from 2001 to 2018 and combined that with local weather data to get a comprehensive understanding of how many injuries can be attributed to extreme heat. What they found was that, on days between 80F and 85F, a worker’s risk of injury increases by about 3.5% compared with a day in the 60s. On a day between 90F to 95F, the injury risk increases about 7%. “I see a lot of people get injured because they’re working in the sun and get fatigued,” said Guillermo Oseguera, a 49-year-old boilermaker who works in Los Angeles. “You get frustrated because you’re hot. But nobody is going to come and do the job for you.” The researchers also found that heat takes a larger toll on low-wage workers. Low-wage jobs tend to be more dangerous than high-wage work, so this disparity in workplace injuries could still show up on a 60F day. But as work days gets hotter, that disparity between the rich and the poor only increases. Using a worker’s home zip code as a way to measure income, the paper found that the injury risk for low-income workers increases at a much higher rate as the temperature rises. This is probably because low-income workers are more likely to work in occupations where they are exposed to heat, such as jobs that take place outdoors, Behrer said. Ultimately this means those who lived in the poorest 20% of zip codes suffered about 5.2 injuries per 100 taxpayers. Those who lived in the wealthiest 20% suffered about 2.2 injuries per 100 taxpayers. Notably, it’s not just outdoor workers who are more likely to be injured. This paper found that indoor workers, like those working in manufacturing, are also more likely to be injured in hot weather. That’s probably because many indoor workers are not in temperature controlled environments. Ryan Ruf was a bricklayer during the 2018 construction of the Chase Center in San Francisco – home of the Golden State Warriors basketball team. “Even though it wasn’t in the sun, it was mucky in there,” Ruf said. “You just try and drink a bottle of water an hour just to stay hydrated.” Ruf, who no longer works as a bricklayer, said when he started this work 20 years ago, he would start his days at 7am. But largely because of the heat, they are now starting several hours earlier. This finding is especially salient because Americans are projected to experience more and more hot days. The country could adapt – with more climate-controlled workplaces, a shift in working hours to avoid the hottest parts of the day and worker protection laws. But without adaptive responses, California workers can expect to see between 4% and 10.7% more injuries by 2050, according to an analysis Behrer did for the Guardian. There are no federal laws protecting workers from extreme heat, but some states have passed heat-related worker protection laws. In 2005, California lawmakers passed the Heat Illness Prevention Standard which requires employers to give outdoor workers access to cool water and shade, among other things. The researchers found that after the law was passed, worker injuries on days above 90F were reduced by about a third. In 2019, California congresswoman Judy Chu – who authored the California bill when she was a state assemblywoman – introduced a similar bill in Congress, but it has yet to see progress. Last week, Park, one of the researchers, testified in front of Congress about his research. While much of the interest was around the findings about the disparities in worker injuries, Park urged Congress to think about the issue of heat more holistically. “These are costs that are borne by society as a whole, as well,” he said. “The worker suffers in terms of pain and medical bills and lost wages. But employers suffer lost productivity, retraining costs, hiring costs. We all pay into insurance systems. It’s important to think of the issue of heat and climate risk in general as affecting all sectors.”