This past July, humidex readings climbed to 45 degrees Celsius across parts of southern Ontario and western Quebec. For most people, that meant adjusting summer plans. For millions of Canadian workers, the workday simply continued on construction sites, farms, loading docks, and inside factories, warehouses, and restaurant kitchens. New research reveals a hidden consequence of that heat: it makes ordinary workplace injuries more likely, even when the work itself has nothing to do with temperature.
Heat causes dehydration, fatigue, and impairs judgment, balance, and reaction time. Research on California workers shows that heat increases injuries seemingly unrelated to temperature, including falls and vehicle crashes. Official counts likely understate the problem, since heat is often a contributing factor rather than the injury named on the claim form.
A peer-reviewed study in the journal BMC Public Health offers one of the clearest pictures of this risk. Researchers linked 374,078 accepted workers' compensation claims in Quebec with daily temperatures from 2003 to 2010. They found that for every 1 degree Celsius increase in the daily maximum temperature, the workplace injury rate rose by about 0.2%. That sounds small, but it adds up across a heat wave and a large workforce. The increase occurred in both indoor and outdoor industries.
A recent nationwide U.S. study reached similar conclusions. Researchers mapped more than 845,000 injury reports to daily weather conditions. Compared to a heat index of 27 degrees Celsius, the odds of injury were 3% higher at 32 degrees Celsius, 10% higher at 38 degrees Celsius, and 20% higher at 43 degrees Celsius. The researchers estimated heat caused roughly 28,000 additional workplace injuries across the United States in 2023.
The good news is that rules can work. A study comparing California outdoor workers to those in neighboring states found that when the state began enforcing its heat protection standard in 2010, heat-related deaths among outdoor workers dropped by an estimated 33%. After rules were strengthened again in 2015, the estimated reduction rose to 51%.
Canada has no common minimum standard for protecting workers from extreme heat. Rules vary by province: British Columbia requires employers to assess heat exposure and create control plans, while other provinces and territories rely on broad employer duties with no specific heat legislation at all. Federally regulated workplaces have adopted new thermal-stress rules, but they will not take effect until February 2027.
The lesson from California is clear: effective protection requires clear triggers, practical controls, and enforcement. For Canadian workers facing another summer of rising temperatures, that message could not be more urgent.