Sep 7, 2023
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Heat waves have been increasing in frequency and duration as a result of climate change.

The health impacts of extreme heat are widespread and will impact workers across sectors. Outdoor workers, such as delivery drivers, farmworkers (many of whom are migrant workers), gardeners and landscapers, and construction workers will be particularly impacted. Indoor workplaces such as smelters, manufacturing plants, and kitchens can also generate too much heat for workers to safely complete their work duties during heat waves.

Historically gendered professions, such as teaching and nursing, will also be impacted. Studies have found that students are less likely to access education and learning when heat-exposed and teachers are less likely or to be able to provide quality education when heat-exposed. Climate change will make existing health inequities worse and will significantly increase the burden on Canada’s healthcare system and the work required of nurses, personal support workers, and other health care providers.

Workers with disabilities and older workers are disproportionately impacted by heat stress, as well as workers who are pregnant or have pre-existing conditions. Socioeconomic status also impacts a person’s ability to access adequate housing, air-conditioning, and other resources during extreme heat events. The Ontario Human Rights Commission (“OHRC”) found that “access to cooling during extreme heat waves is a human rights issue” and notes that “as temperatures rise due to climate change, extreme heat waves have and will continue to disproportionately impact groups protected under the Code.”


Heat stress is a human rights and health and safety issue that employers must take seriously. There are some existing mechanisms that can protect workers from extreme heat and provide them with recourse if they become ill or injured at work as a result of heat.

The Workplace Safety Insurance Board (“WSIB”) has approved benefits to workers who became ill or injured at work as a result of extreme heat in the workplace. For example, in Workplace Safety and Insurance Appeals Tribunal (“WSIAT”) Decision No. 757/17 (2017), a crane operator was entitled to initial benefits for heat exhaustion, dehydration, and migraines after working in a crane for 20-30 minutes without air conditioning. The temperature was around 30C outside and it was thought to be warmer inside the crane.

Another example is WSIAT Decision No. 298/16 (2016) where a high school teacher was injured when she fainted at work. The classroom was very hot and there was no air conditioning. The WSIAT found that it was more likely than not that the heat contributed to the worker’s fainting.

There is no maximum workplace temperature set out in the Ontario legislation. However, employers have an obligation under s. 25(2)(h) of the Occupational Health and Safety Act, R.S.O. 1990 (“OHSA”) to “take every precaution reasonable in the circumstances for the protection of a worker.” The Government of Ontario released a resource on “managing heat stress at work” which provides guidance on what might be a reasonable precaution in response to heat stress. It includes various workplace design changes and administrative and work practices controls that can be implemented to reduce heat, and recommends that employers develop and implement a hot weather or heat stress control plan.

The Ministry of Labour (MOL) recently proposed heat stress regulations under the OHSA. The regulations would require the following, among other things:

  • Employers must “take all measures reasonably necessary in the circumstances to protect workers from exposure to hazardous thermal conditions that may result in a heat-related illness or a worker’s core body temperature exceeding 38C”
  • Engineering controls must be used to maintain a worker’s heat exposure within the heat stress exposure limits, under certain circumstances
  • Additional measures and procedures must be developed in consultation with the Joint Health and Safety Committee (“JHSC”)
  • Employers must provide cool, potable drinking water close to work areas
  • Employers must advise workers working outdoors of heat warnings and the importance of staying hydrated and taking breaks, as well as the rest periods available to them

Regulations must create clear workplace standards to be effective. Employers must also consider the disproportionate impact of heat on different workers and adapt their approach to protecting workers impacted by heat stress in line with their overarching obligations under s. 25(2)(h) of the OHSA and their duty to accommodate workers.

It is important to note that the MOL proposal follows calls from worker-led organizations, such as Justice for Migrant Workers (J4MW), for stronger occupational health and safety protections regarding heat stress. In the midst of the July 2023 heat wave, J4MW demanded emergency protections for farm workers who work in sweltering temperatures in fields and greenhouses. The called for protections are broader than the MOL proposal and include implementing paid breaks for agricultural workers, providing sufficient shelter and drinking water for workers, shutting down farms and paying workers in extreme crisis events, and incorporating race and gender analysis into occupational health and safety and employment standards.


Workers are encouraged to speak with their union representative, worker representative, JHSC, or supervisor in a non-unionized workplace, about their concerns with regards to heat in the workplace, as well as to seek potential accommodations for workers with pre-existing health conditions or other risk factors. Workers and union representatives are reminded that under s. 43(3) of the OHSA, workers have the right to refuse unsafe work.

We continue to monitor developments in this area.

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