Rising temperatures continue to increase the risk of heat-related illness in Ontario workplaces, particularly in environments where physical exertion, protective clothing, or outdoor work are involved. Heat stress does not only affect worker health; it can also impact productivity, decision-making, and incident risk.
Many employers are unsure when a heat stress assessment is required or how to determine whether existing controls are sufficient. This guide outlines when a heat stress assessment should be considered and how a proactive approach can support worker safety and regulatory compliance.
Understanding Heat Stress in the Workplace
Heat stress occurs when the body cannot adequately cool itself. This risk increases with:
- High air temperatures
- Physical workload
- Humidity
- Limited air movement
- Use of personal protective equipment
- Direct sun exposure
Early symptoms can include fatigue, dizziness, headache, and reduced concentration. Without proper controls, heat stress can escalate to heat exhaustion or heat stroke.
When Employers Should Consider a Heat Stress Assessment
- High or Rising Workplace Temperatures
If workers are exposed to elevated temperatures during warmer months or in heat-generating environments, an assessment can help determine whether existing controls are adequate.
- Physically Demanding Work
Tasks involving sustained physical effort, manual handling, or repetitive movement increase metabolic heat production and elevate risk.
- Use of Protective Clothing or PPE
Respirators, chemical suits, or layered protective clothing can limit the body’s ability to cool itself and should be factored into risk evaluations.
- Outdoor or Seasonal Work
Construction, landscaping, municipal maintenance, and utility work often involve prolonged outdoor exposure during peak summer conditions.
- Worker Symptoms or Productivity Issues
Reports of fatigue, heat-related symptoms, increased errors, or near misses may indicate heat stress concerns.
- Regulatory and Due Diligence Considerations
While Ontario does not have a standalone heat stress regulation, employers are expected to assess and control heat-related hazards under the general duty clause of the Occupational Health and Safety Act, where employers must take all reasonable precautions to protect workers from workplace hazards. A documented assessment supports due diligence.
What a Heat Stress Assessment Typically Reviews
A heat stress assessment may include:
- Measurement of environmental conditions (temperature, humidity, air movement)
- Evaluation of workload and work-rest cycles. This may include interviews with workers.
- Review of clothing and PPE impacts
- Assessment of existing controls and policies
- Recommendations for engineering, administrative, and work practice controls
How THEM Supports Heat Stress Management
THEM supports employers by conducting heat stress assessments, providing training, and developing practical prevention plans tailored to specific tasks and environments.
Taking action early in the season allows organizations to implement controls before temperatures peak.