Learn how Ontario’s OHSA protects workers from heat stress. Discover causes, symptoms, and prevention strategies to keep workplaces safe and compliant.
Heat Stress in the Ontario Workplace
Heat stress occurs when the body cannot regulate its internal temperature, leading to serious health risks. This guide explains what causes heat stress, how Ontario’s Occupational Health and Safety Act (OHSA) applies, and what employers must do to protect workers through proper risk assessment, training, and environmental controls.
When the Heat Becomes a Hidden Hazard
The summer sun may feel energizing, but for many Ontario workers, it can also be deadly.
When physical exertion meets high temperatures, even a few minutes of overheating can trigger heat stress—a condition that overwhelms the body’s natural cooling system and leads to exhaustion, cramps, or even heat stroke.
Every year, Ontario sees preventable cases of heat-related illnesses, especially in construction, manufacturing, and outdoor maintenance sectors.
Under the Occupational Health and Safety Act (OHSA), employers have a legal duty to recognize heat stress as a workplace hazard and take every reasonable precaution to protect workers.
What Is Heat Stress?
Heat stress happens when the body absorbs more heat than it can release.
Normally, sweating and blood circulation regulate body temperature, but factors such as environmental heat, workload, and hydration can overwhelm this balance.
Common causes include:
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High temperatures: Working in hot environments without adequate ventilation.
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Strenuous activity: Performing heavy physical work increases internal heat production.
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Protective clothing: Wearing non-breathable or insulated PPE can trap heat.
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Dehydration: Insufficient water intake reduces the body’s cooling efficiency.
If untreated, heat stress can progress to heat exhaustion or heat stroke, both of which are medical emergencies.
Health Effects of Heat Stress
Understanding the stages of heat-related illness helps with early detection and intervention:
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Heat Cramps: Muscle spasms caused by fluid or electrolyte loss.
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Heat Exhaustion: Symptoms include heavy sweating, weakness, dizziness, nausea, and headache.
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Heat Stroke: A life-threatening emergency marked by confusion, rapid heartbeat, and body temperature above 40°C. Immediate medical attention is required.
Recognizing and responding to these early signs can save lives and prevent long-term injury.
Ontario’s Legal Framework on Heat Stress
Ontario does not have a single regulation solely for heat stress, but multiple legal and regulatory provisions ensure worker protection under various workplace conditions.
1. Occupational Health and Safety Act (OHSA)
The OHSA requires employers to take every precaution reasonable in the circumstances to protect workers. This includes implementing measures to minimize heat exposure and ensuring workers receive information and instruction on how to recognize and respond to symptoms.
2. Regulation 851 – Industrial Establishments
While this regulation does not specifically name “heat stress,” it includes provisions relevant to temperature control, ventilation, and access to drinking water. These are critical components of an effective heat stress prevention plan.
How Employers Can Prevent Heat Stress
Employers have both a moral and legal obligation to protect workers from heat-related hazards.
Practical steps include:
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Risk Assessment
Identify work areas where heat stress could occur, considering temperature, humidity, air movement, radiant heat, and workload intensity. -
Environmental Controls
Implement ventilation, cooling systems, and shading. Where possible, reschedule heavy labor to cooler parts of the day. -
Work Practice Adjustments
Introduce rest breaks, job rotation, and acclimatization schedules for new workers or those returning after time away. -
Hydration and Nutrition
Provide cool, potable water close to work areas. Encourage workers to drink small amounts frequently rather than waiting until thirsty. -
Training and Awareness
Train supervisors and workers to recognize early symptoms of heat stress, apply first aid measures, and know when to call for medical help. -
Monitoring and Supervision
Use buddy systems and environmental monitoring tools like Wet Bulb Globe Thermometers (WBGT) to track conditions. Adjust work as temperatures rise.
Worker Responsibilities
Workers also play a key role in preventing heat stress. They should:
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Stay hydrated before, during, and after work.
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Report symptoms such as dizziness or nausea immediately.
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Wear breathable clothing when possible.
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Follow employer safety instructions and attend training programs.
Early reporting helps prevent heat-related illnesses from becoming life-threatening emergencies.
Helpful Resources for Heat Stress Prevention
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Ministry of Labour, Immigration, Training and Skills Development (MLITSD):
Managing Heat Stress at Work -
Canadian Centre for Occupational Health and Safety (CCOHS):
Temperature and Humidity Limits -
Occupational Health Clinics for Ontario Workers (OHCOW):
Heat Stress Toolkit
These resources provide detailed guidance, assessment tools, and best practices for both employers and workers.
Stay Cool, Stay Compliant with Achieve Safety
Managing heat stress is not only about comfort; it is about compliance, prevention, and saving lives.
At Achieve Safety, we help Ontario employers create heat stress prevention programs that meet OHSA and MLITSD expectations.
Our Environmental Safety and Heat Stress Awareness Training teaches your team how to identify risks, implement cooling strategies, and respond effectively to emergencies.
👉 Book your Workplace Heat Stress Prevention Training with Achieve Safety and keep your workforce safe, hydrated, and compliant throughout Ontario’s warmest months.
FAQs – Heat Stress Ontario
Q1. What is heat stress in the workplace?
Heat stress occurs when the body cannot regulate its temperature due to high environmental heat, physical exertion, or dehydration. It can cause heat cramps, heat exhaustion, or even heat stroke, which is a medical emergency.
Q2. What are common causes of heat stress in Ontario workplaces?
Common causes include high temperatures, strenuous work, wearing heavy protective gear, inadequate ventilation, and insufficient hydration. These factors increase internal body heat and can overwhelm the body’s cooling system.
Q3. What symptoms should workers watch for?
Early symptoms include fatigue, dizziness, nausea, heavy sweating, and muscle cramps.
If untreated, symptoms can progress to confusion, rapid pulse, and high body temperature, which signal heat stroke and require immediate medical help.
Q4. What is an employer’s responsibility under the OHSA for heat stress?
Under the Occupational Health and Safety Act (OHSA), employers must take every precaution reasonable to protect workers, including preventing heat stress. They must provide ventilation, drinking water, training, and emergency procedures for working in hot environments.
Q5. What regulations cover heat stress in Ontario?
While there is no single regulation for heat stress, related safety requirements appear in:
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Regulation 851 for Industrial Establishments (ventilation and water access)
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Regulation 213/91 for Construction Projects (sanitation and first aid)
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Regulation 67/93 for Health Care and Residential Facilities (temperature and ventilation control)
Q6. How can employers prevent heat stress on the job?
Employers can:
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Schedule heavy tasks during cooler times of the day
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Provide shaded rest areas and cooling fans
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Encourage frequent water breaks
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Train workers on recognizing and reporting symptoms
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Monitor conditions using temperature and humidity sensors
Q7. What can workers do to protect themselves from heat stress?
Workers should stay hydrated, rest in cool areas, wear lightweight and breathable clothing, and report any signs of heat exhaustion immediately to a supervisor. They should also attend workplace heat stress training provided by their employer.
Q8. How can Achieve Safety help Ontario businesses manage heat stress risks?
Achieve Safety delivers Heat Stress Awareness and Environmental Safety Training designed for Ontario workplaces. Our experts help employers meet OHSA and MLITSD guidelines through practical education, on-site risk assessments, and policy implementation.
