Minnesota Requirements
Application & Scope
This section supplements OSHAcademy Course 645 Heat Injury and Illness Prevention: Employee and is designed to align the training with the Minnesota Department of Labor and Industry (DLI) administrative rules. For more in-depth review or questions about the standards please click on the link below:
- MAR 5205.0110 – Indoor Ventilation and Temperature In Places of Employment
Unlike many other state standards, Minnesota's rule applies only to indoor workplaces and establishes mandatory exposure limits for heat using the Wet Bulb Globe Temperature (WBGT) index rather than ambient air temperature or heat index.
It also establishes minimum air temperature requirements for cold conditions, making it one of the few state regulations addressing both heat and cold stress.
Who Must Comply
- Applies to all indoor workplaces in Minnesota
- Excludes outdoor worksites unless work is performed inside a structure (such as warehouses, maintenance shops, or manufacturing spaces)
- Does not apply where compliance with airflow or minimum temperature requirements is prohibited by process requirements (for example, certain refrigeration, foundry, or industrial oven operations)
Environmental Measurement and Limits
Minnesota's rule uses the Wet Bulb Globe Temperature (WBGT) to evaluate indoor heat exposure, which considers air temperature, humidity, radiant heat, and air movement. The regulation defines key components:
- Tnwb (Natural Wet-Bulb Temperature): Measures humidity and evaporative cooling.
- Tg (Globe Temperature): Captures radiant heat.
- WBGT = 0.7 Tnwb + 0.3 Tg
| Work Activity | Maximum WBGT (°F) |
|---|---|
| Heavy work (≥350 kcal/hr; e.g., shoveling, heavy lifting) |
|
| Moderate work (200–350 kcal/hr; e.g., walking, moderate lifting/pushing) |
|
| Light work (≤200 kcal/hr; e.g., sitting, light arm/hand work) |
|
Note: These WBGT limits are two-hour time-weighted averages and apply to fully clothed, acclimatized workers.
Controls and Airflow Requirements
Indoor places of employment must have air provided and distributed as required in this rule, unless prohibited by process requirements.
- Indoor workplaces must provide adequate airflow and circulation:
- 15 cubic feet of outdoor air per minute per person
- Air inlets must be arranged so employees are not subjected to air velocities >200 feet per minute unless specifically approved
Employee Training
Employees with exposure to indoor heat must receive training per Minnesota Rules Part 5206.0700, subparts 1 and 3 (Employee Right-to-Know Rule), covering:
- Health hazards associated with heat exposure
- Proper work practices, hydration, and personal protective measures
- Recognition and reporting of symptoms of heat illness
Employers must maintain records verifying completion of training as part of their general safety documentation.
Cold Stress Requirements
Minnesota uniquely includes minimum indoor air temperature requirements to protect workers from cold environments:
- Heavy work: Maintain at least 60°F, unless prohibited by process requirements.
- Light or moderate work: Maintain at least 65°F, unless prohibited by process requirements
Recirculated Air Restrictions
Air from exhaust systems handling substances listed under 29 CFR 1910, Subpart Z (toxic and hazardous materials) cannot be recirculated into the work environment without written permission from the Minnesota Department of Labor and Industry
Definitions
For clarity under Minnesota Rule 5205.0110:
- "Indoor" – Any space between a floor and a ceiling bound on all sides by walls (including doors, windows, or dividers).
- "Place of employment" – Any factory, plant, foundry, construction site, farm workplace, premises, vehicle or any other work environment where any employee is during the course of employment.
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9-Minnesota. Why does Minnesota's rule stand out compared to most other state standards?
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