State compliance guide, updated August 2026

Minnesota Heat Standard: Indoor WBGT Limits

Q: Does Minnesota have an outdoor heat rule?

No. Minnesota Rules 5205.0110 covers indoor work only. Outdoor heat exposure in Minnesota is enforced by MNOSHA under the general duty clause, and federal OSHA's Heat National Emphasis Program approach also shapes inspections.

Q: How is WBGT different from air temperature?

WBGT (wet bulb globe temperature) combines air temperature, humidity, radiant heat, and air movement into one number. A 90°F dry reading near a furnace line can be a much higher WBGT than 90°F in moving air. Minnesota's limits are WBGT values, so a plain thermometer cannot prove compliance.

Short answer: Minnesota Rules 5205.0110 sets hard indoor limits as a 2-hour average WBGT: 86°F for light work, 80°F for moderate work, 77°F for heavy work. Not guidance. Enforceable numbers, and they have been on the books for decades.

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At a glance

Minnesota's heat framework.

77–86°F

Hard WBGT limits

86°F WBGT light work, 80°F moderate, 77°F heavy, each a two-hour time-weighted average. Cross the line and the workroom is out of compliance. Limits assume acclimatized workers.

Indoor

Indoor rule

Covers indoor places of employment: foundries, non-AC warehouses, bakeries, laundries, plants. Outdoor work falls to MNOSHA's general duty enforcement.

WBGT

Not a thermometer

Compliance is measured in wet bulb globe temperature, which folds in humidity, radiant load, and airflow. A dry-bulb reading cannot prove you are inside the limit.

MNOSHA

State-plan enforcement

Minnesota runs its own OSHA program under the Department of Labor and Industry. Heat complaints in summer routinely trigger indoor WBGT measurement.

Source: Minnesota Rules 5205.0110, Minnesota Department of Labor and Industry.

What the rule actually requires

Minnesota, tier by tier.

Minnesota regulates the room, not the worker. The limits are WBGT ceilings by workload, and crossing one puts the workroom out of compliance.

86°F

Light work

Two-hour time-weighted average WBGT
Ventilation or engineering control below the ceiling

80°F

Moderate work

Walking or carrying puts you in this band
Airflow, shielding, or process change

77°F

Heavy work

Sustained lifting or hot-work tasks
The strictest ceiling in the country

Minnesota compliance: where do you stand?

0 of 8

WBGT measured, not air temperatureA dry-bulb thermometer cannot prove compliance.
Readings taken as a two-hour time-weighted averageSpot readings are not what the rule asks for.
Work intensity classified per areaLight, moderate, or heavy sets which ceiling applies.
Ventilation and engineering controls in placeThe rule limits the room, so the room is what you fix.
Acclimatization accounted forLimits assume fully clothed, acclimatized workers.
Water available on hot workroom floorsGood practice, and expected alongside controls.
Supervisors trained to recognise heat illnessIndoor heat illness looks the same as outdoor.
Written record of measurements and controlsWhat you show an MNOSHA inspector.

Where cooling vests fit

The rule limits the room. The vest protects the worker.

Ventilation upgrades to a foundry or a 1970s warehouse take capital budgets and months. A cooling vest does not lower the room's WBGT, and it does not excuse an over-limit workroom. What it does is hold the worker's microclimate down while engineering controls catch up, and keep crews functional through July peaks.

Program fitDocumented as a supplemental control alongside ventilation and work-rest schedules.
Radiant heatSolid-state cooling keeps working next to furnace and process heat where evaporative vests quit.
8–12 hrFull shift with one battery swap. No freezer logistics on a plant floor.
Indoor humidityNo evaporation needed, so performance holds in humid summer workrooms.
Low-profileSub-3 lbs, fits under smocks and over base layers.

FAQ

Minnesota heat standard: employer FAQ.

What is the Minnesota heat standard?

Minnesota Rules 5205.0110 sets enforceable indoor heat limits measured as a two-hour time-weighted average wet bulb globe temperature (WBGT): 86°F for light work, 80°F for moderate work, and 77°F for heavy work. It is one of the oldest enforceable heat rules in the United States. The limits assume fully clothed, acclimatized workers, so an unacclimatized crew is at risk well below them.

Does Minnesota's heat rule apply to warehouses and factories?

Yes. The rule applies to indoor places of employment, which includes non-air-conditioned warehouses, foundries, bakeries, laundries, and manufacturing floors. If the two-hour average WBGT exceeds the limit for the work intensity, the employer is out of compliance.

Does Minnesota have an outdoor heat rule?

No. The 5205.0110 limits cover indoor work only. Outdoor heat exposure in Minnesota is enforced under the general duty clause, with federal OSHA's Heat National Emphasis Program shaping how inspections run.

How is WBGT different from air temperature?

WBGT combines air temperature, humidity, radiant heat, and air movement into one number. A 90°F dry reading near a furnace line can be a much higher WBGT than 90°F in moving air. Minnesota's limits are WBGT values, so a plain thermometer cannot prove compliance. Our glossary covers WBGT in plain language.

Do cooling vests help with Minnesota heat compliance?

Cooling vests do not change the measured WBGT of a workroom, so they cannot substitute for ventilation or engineering controls. What they do is protect the worker inside the environment while controls catch up. See the cooling vest comparison for which technologies survive indoor radiant heat.

Minnesota Heat Standard: Indoor WBGT Limits

Minnesota's heat framework.

Minnesota, tier by tier.

Minnesota compliance: where do you stand?

The rule limits the room. The vest protects the worker.

Minnesota heat standard: employer FAQ.

Keep reading.

Federal OSHA Heat Standard

Maryland Heat Standard

Cooling Vest for Manufacturing

Keep crews under the limit in Minnesota.