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Heat rules in Manitoba: Workplace Safety and Health Regulation section 4.12

What Manitoba's regulation says about heat and cold at work, which ACGIH values it points to, and the screening values and acclimatization schedule in the Workers Compensation Board's Thermal Stress Guide of December 2025.

Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.

This page reports what the official source says. It is not legal advice: ask the office named here. It restates sections 4.12 and 4.13 of the Workplace Safety and Health Regulation (Manitoba Regulation 217/2006), as the Manitoba government's consolidation showed them on October 9, 2026, with the Workers Compensation Board's hot weather page and its Thermal Stress Guide of December 2025 (the Board's SAFE Work Manitoba division, written with the provincial Workplace Safety and Health department). The comparison of every place is on the heat rules overview.

The regulation

Section 4.12, headed "Thermal stress", says that when a workplace or work process exposes a worker to conditions that may create a risk to safety or health because of heat or cold, the employer must implement safe work procedures and control measures so that two things hold. First, the threshold limit values for thermal stress that the American Conference of Governmental Industrial Hygienists (ACGIH) set out in its 2019 publication are followed. Second, the worker is given information, instruction and training in the symptoms of thermal stress and the precautions to avoid injury from it. A note beside the text shows the ACGIH reference was introduced by Manitoba Regulation 128/2019. Section 4.13 separately says that, subject to 4.12, an employer in an indoor workplace must keep air temperature, radiant temperature, humidity and air movement appropriate to the nature of the work.

What the Board's guide adds

The guide states that the Act and regulations do not specify a maximum temperature above which work must stop. It says the combination of work and conditions is measured and judged against the ACGIH screening criteria, commonly with a wet bulb globe temperature (WBGT) instrument, and that WBGT is calculated differently with and without direct sun. It lists Table 1 of screening values, in degrees Celsius WBGT, for a worker doing a cycle of work and recovery.

Share of the cycle spent workingAcclimatized worker: light, moderate, heavy, very heavyUnacclimatized worker: light, moderate, heavy, very heavy
75% to 100%31.0, 28.0, no value, no value28.0, 25.0, no value, no value
50% to 75%31.0, 29.0, 27.5, no value28.5, 26.0, 24.0, no value
25% to 50%32.0, 30.0, 27.5, 28.029.5, 27.0, 25.5, 24.5
0% to 25%32.5, 31.5, 30.5, 30.030.0, 29.0, 28.0, 27.0

The guide says the values assume healthy workers in one layer of customary work clothing, and gives clothing additions to the measured WBGT: 0 for a long-sleeve shirt and pants, 3 degrees for double-layer woven clothing, 11 degrees for limited-use vapor-barrier coveralls, and 1 degree more for a hood covering head and neck. Its worked example is for indoor construction, not tree work.

Acclimatization and the Board's hot weather page

The guide says acclimatization may take five to seven days for a healthy worker, with work in the heat for at least two hours a day. The Board's hot weather page repeats that section 4.12 requires safe work procedures based on the ACGIH values and training, and says employers should create hot weather procedures with the safety and health committee, the worker representative or the workers themselves.

Sources