Summer is here, and so is the heat. For Ontario employers, that means heat stress should be back on their radars. With temperatures rising every year, heat stress is no longer a seasonal inconvenience, it’s a serious workplace hazard.
While Ontario employers don’t face specific heat-stress legislation, the Occupational Health and Safety Act (OHSA), imposes a clear general duty: take every reasonable precaution to protect workers.
What is Heat Stress?
Heat stress occurs when the body can’t shed excess heat fast enough, forcing the heart to work harder and risking consequences from cramps and exhaustion to life-threatening heat stroke. Early warning signs such as heavy sweating, muscle cramps, and excessive thirst can quickly escalate to dizziness, nausea, confusion or fainting. Since affected workers often can’t recognize their own symptoms, supervisors play a critical role in catching problems early.
Heat stress isn’t exclusive to outdoor work either; confined spaces, equipment that throws off heat, and physically demanding tasks can all put workers at risk, regardless of where the job takes place.
What Ontario Law Says
While Ontario’s Occupational Health and Safety Act, has no specific heat stress rules or maximum workplace temperature limits, that doesn’t mean employers are off the hook.
Under the OHSA, both employers and supervisors must take every reasonable precaution to protect workers. The Ministry of Labour has been clear as well: employers are expected to proactively identify and address heat hazards; doing nothing during extreme heat can still mean breaking the law.
Employers are also required to:
- Ensure workers receive the training, guidance and oversight they need to stay safe on the job;
- Keep workers informed about hazards they may be exposed to at work, including heat;
- Support and active Joint Health and Safety Committee (JHSC) or Health and Safety Representative, with a real role in spotting and addressing workplace hazards; and
- Meet applicable industry standards and follow recognized best practices for heat safety.
Practical Steps Employers Can Take
- Build a written heat stress Plan. Document where workers face the greatest exposure. Your plan should cover how temperatures and humidity will be monitored, when action is triggered, modified schedules during heat alerts, and emergency response procedures.
- Control the environment. Use fans when temperatures are below 35°C (above that fans recirculate hot air). Install air conditioning or exhaust systems where possible, shield heat generating equipment and provide shaded or cool rest areas.
- Adjust when and how work gets done. Schedule demanding tasks for cooler parts of the day, increase rest breaks during heat alerts, and reduce individual workloads by slowing the pace or adding workers.
- Hydrate and train. Keep cool water accessible near work areas. Train supervisors to spot early heat illness symptoms and train workers to know the risks and look out for each other.
- Know your vulnerable workers. Age, fitness, certain medications and underlying health conditions can all increase heat sensitivity. Encourage workers to flag relevant health factors, and consider accommodation obligations under the Ontario Human Rights Code.
Key Takeaway
Ontario may not have a specific heat stress law, but employers who take heat seriously are doing right by their workers. The tools and steps are straightforward; the biggest difference is choosing to act and building a safer, stronger workplace in the process.
Heat safety is just one of the broader employer obligations under the OHSA. If you have questions or want to make sure your workplace is covered, contact Greenwood Law.
