Every summer, Ontario workers in construction, landscaping, agriculture, and other outdoor industries face serious risk from heat stress and heat stroke. Under the Occupational Health and Safety Act, employers have a general duty to take every reasonable precaution to protect worker health — and that includes extreme heat. While Ontario does not yet have a standalone heat regulation with specific temperature thresholds, employers who fail to protect workers from heat-related illness can face Ministry of Labour orders, fines, and liability. A proactive heat stress program is not just good practice — it's a legal obligation.
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Develop a written heat stress prevention program before hot weather arrives — don't wait for an incident
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Provide workers with cool, clean drinking water nearby — at least 250ml every 20 minutes in extreme heat
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Allow workers to acclimatize gradually — new or returning workers need 7–14 days to adjust to heat
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Schedule heavy outdoor work during cooler parts of the day and build in rest breaks in shaded areas
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Train supervisors to recognize early signs of heat exhaustion: dizziness, heavy sweating, weakness, nausea
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Monitor the Humidex — when it reaches 35 or above, additional controls and rest periods are strongly recommended
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