Introduction Extreme heat has been associated with higher rates of mortality and morbidity. Excess heat may also influence the occurrence of work-related injuries, but this hypothesis has not been previously explored in detail. We analyse the relationship between high ambient temperatures and work-related injuries in Spain.

Methods Daily number of work-related injuries with at least 1 day of leave and daily maximum temperature were obtained for 50 provinces of Spain. We restricted the analysis to the warm period (May 1st–September 15th) of years 1994–2013. Poisson regression models were used to quantify in each province the association between daily injury claims and maximum temperature, adjusting for day of the week, month, year, holidays and year-specific splines of time with 3 degrees of freedom. We used a random-effects meta-analysis to obtain a national summary estimate. Analyses were stratified by sex, age, occupational class, duration of leave and economical sector.

Results The study included 5,636,300 work-related injuries (average of 2,042 per day). There was a positive and statistically significant association between daily maximum temperature and work-related injuries in 21 provinces. Overall, a 1°C increase in maximum temperature was associated with an increase in work-related injuries of 0.28% (95% confidence interval (CI): 0.24%, 0.32%). The highest associations were found among men (percentage change: 0.35%, 95% CI: 0.30%, 0.39%), workers younger than 24 years (0.38%, 95% CI: 0.31%, 0.44%), manual workers (0.30%, 95% CI: 0.26%, 0.34%), injuries with 4–15 days of leave (0.32%, 95% CI: 0.27%, 0.38%) and those workers performing activities in agriculture (0.75%, 95% CI: 0.61%, 0.89%), construction (0.44%, 95% CI: 0.38%, 0.51%) and extractive industries (0.40%, 95% CI: 0.16%, 0.64%).

Conclusions This study found a consistent increase in work-related injuries associated with high ambient temperatures. If casual, specific preventive interventions may reduce occupational injuries among the most vulnerable groups of workers.