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The new 93 page working paper – Temperature, Workplace Safety, and Labor Market Inequality – by researchers from the University of California, Los Angeles and Stanford University documents, for the first time, the growing safety risks of excessive heat for U.S. workers in occupations not just where the work is mostly outside but also indoors.

The researchers examined 11,146,912 confidential records of workplace injuries in California from the Department of Workers’ Compensation (DWC) over the period 2001 to 2018 combined with zip code level information on daily temperature from the same period. The data also included the medically determined cause (e.g. fall), type (e.g. strain), and body parts affected (e.g. knee) by the incident, as well as some limited demographic information including age and gender for each claim.

They found that hotter temperature significantly increases the likelihood of injury on the job. A day with high temperatures between 85 and 90 leads to a 5 to 7 percent increase in same-day injury risk, relative to a day in the 60’s. A day above 100 leads to a 10 to 15 percent increase. Causal identification relies on the premise that idiosyncratic variation in daily temperature within a given zip code-month is plausibly exogenous, and that the resulting effect on injuries is not driven by potential endogenous changes in labor inputs.

Higher temperatures also increase injuries in some industries where work typically occurs indoors. In manufacturing, for instance, a day with highs above 95 increases injury risk by approximately 7 percent relative to a day in the low 60’s. In wholesale, the effect is nearly 10 percent. They also found that claims for many injuries not typically considered heat-related rise on hotter days. These include injuries caused by falling from heights, being struck by a moving vehicle, or mishandling dangerous machinery. The increase in injuries affects a wide range of body parts, suggesting that the mechanisms may not be limited to heat-illnesses such as heat stroke or heat syncope.

The risks are “substantially larger for men versus women; for younger versus older workers; and for workers at the lower end of the income distribution.

“These are previously undocumented facts with possibly significant policy implications, given the nearly exclusive attention to date on outdoor workers and heat illnesses: i.e. incidents that are medically coded as due to heat exposure.”

The researcher estimated that hotter temperature has caused approximately 360,000 additional injuries in California over the period 2001-2018, or roughly 20,000 per year relative to a hypothetical benchmark in which all workers experience only optimal temperatures.

“For perspective, this is roughly eleven times the number of workplace concussions, and at least nineteen times the annual number of workplace injuries the worker compensation microdata records as caused by extreme temperature.”

They estimate the socioeconomic costs of these injuries are on the order of $525 million to $875 million per year, given the costs of healthcare, lost wages and productivity, and other knock-on costs such as work disruptions and potential permanent disability.

However researchers also found evidence of significant adaptation potential, as they noted that the effect of temperature on injuries falls significantly during the study period.  For instance, the effect of a day above 90 falls by roughly a third between 2000 and 2018, and the effect of days above 100 is statistically indistinguishable from zero after 2005.  The temporal profile of heat’s effects on injuries coincides with the introduction of what was at the time the nation’s first heat safety mandate, the California Heat Illness Prevention Standard (Q3 2005), which applied only to outdoor workplaces.

“While we remain agnostic to the source of the decline in heat-related injuries, our findings are consistent more broadly with the possibility of adaptation using existing technologies.”

A new AB 1643 – California Heat Study: Advisory Committee is set to use this data as part of a roadmap to tackle hot workplace issues. The group of state agency staffers and scholars will examine persistent problems with underreported heat-related illness and injuries, as well as gaps in data collection and the financial toll on workers and businesses when temperatures rise and production falls.