Working in the heat poses a risk of heat stress when there is high humidity, high temperatures, direct sun or heat with little air movement. A worker’s physical condition and the level of physical exertion are also important factors when reviewing the risks involved.
The human body functions best within a narrow internal temperature range of 36 to 38 degrees. In hot environments, blood moves toward the skin surface and perspiration increases to help cool the body. When heat loss or gain becomes more than the body can balance, internal systems will begin to fail, leading to illness.
Section 4.12 of Manitoba’s Workplace Safety and Health Regulation (WSH Regulation) notes that when a worker is exposed to heat, it may create a risk to the worker’s safety or health. The employer must implement safe work procedures and control measures to reduce the risk of heat stress. The employer must also provide the worker with information, instruction and training in the symptoms of thermal stress and provide precautions toavoid injury.
When assessing workers’ exposure to the heat, the threshold limit values for thermal stress must be followed as outlined by the American Conference of Governmental Industrial Hygienists. See legislation references for more information.
Part 4.12 of the WSH Regulation notes that the employer must provide workers with information, instruction and training on heat stress. This would include:
It is recommended that your workplace develop a thermal stress management program. It will help mitigate the risk of your workplace being exposed to heat stress.
Always monitor the weather and workers, and ensure workers have access to protective measures such as:
Occupations with a high risk of heat stress include those involved with outdoor work, physical labour or working in poorly ventilated indoor environments. Examples include construction, agriculture, fire fighters, kitchens, factories, warehousing, manufacturing and retail.
When assessing workers’ exposure to the heat and their risk of experiencing heat stress, it is important to consider:
Symptoms of heat stress range and can include nausea, muscle cramps, dizziness, headache, fatigue, rapid heart rate and heavy perspiration. In severe cases, heat stress can lead to heat exhaustion or heat stroke, which may present with symptoms like confusion, irrational behaviour or loss of consciousness.
Manitoba’s Workplace Safety and Health Act andRegulation MR217/2006
Guide for Thermal Stress
American Conference of Governmental Industrial Hygienists (ACGIH) – 2025 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices
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The Workers Compensation Board of Manitoba serves workers and employers through a no-fault insurance system integral to the Manitoba economy. Funded collectively by employers, the WCB promotes safe and healthy workplaces, facilitates recovery and return to work, delivers compassionate and supportive compensation services to workers and employers, and ensures responsible stewardship of Manitoba's workers' compensation system.
