The most expensive misconception in workplace heat safety is that because OSHA has no specific heat standard, heat is not regulated and employers are not exposed.
OSHA enforces heat hazards under the General Duty Clause, Section 5(a)(1) of the Occupational Safety and Health Act, which requires every employer to furnish a workplace free from recognized hazards likely to cause death or serious physical harm. Heat is a recognized hazard with well-published control measures, which is precisely the situation the clause exists for. OSHA has issued citations and penalties on that basis and has run a National Emphasis Program on heat since 2022.
What the General Duty Clause requires in practice
To cite under 5(a)(1), OSHA must show four things. Reading them backwards tells you what a defensible program looks like.
- A hazard existed in the workplace. Heat qualifies whenever conditions can cause heat illness.
- The hazard was recognized, by the employer, the industry, or common knowledge. NIOSH criteria, ACGIH limits and OSHA's own campaign all establish recognition.
- The hazard was causing or likely to cause death or serious physical harm. Heat stroke qualifies.
- A feasible means of abatement existed. Water, rest, shade, acclimatization and scheduling are cheap and well documented, which is why this element is rarely in dispute.
That last element is the one that decides cases. The controls are known, published and inexpensive, so an employer who did not apply them has little to argue with.
The proposed federal heat standard
OSHA has been developing a federal Heat Injury and Illness Prevention standard covering both outdoor and indoor work. The proposed rule is built around initial and high heat trigger points, with required water, rest breaks, shade or cooling, acclimatization for new and returning workers, training, and a written plan.
Rulemaking is slow and the final rule is not in force. Two practical consequences: today you are governed by the General Duty Clause plus any state standard, and a program built now to the proposed rule's structure will satisfy both and need little change later.
The proposed rule references WBGT as a monitoring option alongside heat index, which is a reasonable signal about where enforcement expectations are heading.
Indoor heat: what the rules actually say
This is the most searched and most misunderstood corner of the topic, so to be precise: OSHA has no regulation setting a maximum indoor working temperature. There is no legal number at which an employer must send people home.
What exists is a recommendation. In a standard interpretation letter OSHA has suggested a comfort range of roughly 68 to 76°F with humidity between about 20 and 60 percent. That is guidance about office comfort, not an enforceable limit, and it does not apply meaningfully to warehouses, kitchens, foundries or laundries.
Indoor heat hazards are still enforceable under the General Duty Clause, and the proposed federal standard covers indoor work explicitly. Warehouses without conditioning, commercial kitchens and manufacturing near hot processes are the usual cases, and WBGT measured in indoor mode, with no solar term, is the appropriate measure for them.
State standards that go further
Several states operate OSHA-approved plans with enforceable heat rules that apply regardless of the federal timeline. If you work across state lines, build to the strictest one rather than maintaining several programs.
| State | Scope | Typical requirements |
|---|---|---|
| California | Outdoor, with indoor rules added | Shade and water at trigger temperatures, cool-down rests, acclimatization, written plan, training |
| Washington | Outdoor | Water, shade, mandatory cool-down periods at higher temperatures, training |
| Oregon | Outdoor and indoor | Shade, water, rest schedules, acclimatization, emergency planning |
| Colorado | Agricultural work | Water, shade, rest periods and training for agricultural workers |
| Minnesota | Indoor | Indoor ventilation and heat limits tied to workload |
| Maryland | Outdoor and indoor | Heat stress plan, acclimatization, water, rest and shade |
Check your own state's current rule directly. Several have been adopted or amended recently, and a program written to an older version may no longer comply.
A compliant program
Measurement, trigger levels, water, shade, acclimatization, training, emergency response and records.
What an inspector asks for
Citations rarely turn on whether a plan existed. They turn on whether it operated, and that is a documentation question.
- The written heat illness prevention plan, and when it was last revised.
- Environmental readings with date, time, location and who took them.
- Training records: who, on what, when, and in what language they understood.
- Acclimatization schedules for new and returning workers, which is where most fatalities occur.
- Records of any heat-related incident, including near misses and workers sent home.
- Evidence that water and shade were actually provided at the work area, not at the gate.
Warning signs of heat illness
Heat stress shows up before it becomes an emergency. Anyone on site should speak up immediately on any of these:
When in doubt, cool first and call for help. Collapse or confusion in the heat should be treated as possible exertional heat stroke: begin cold-water immersion immediately and call 911. Cooling comes before transport.
The measurement half of compliance
A plan needs numbers behind it. The app gives WBGT in OSHA mode for any site, with hourly and 14-day forecasts so heavy work can be scheduled into the cooler hours rather than stopped in the afternoon.
- OSHA mode with occupational thresholds
- Any jobsite or city
- Forecasts for shift planning
- A consistent number to record across crews
WBGT is estimated from weather data with the peer-reviewed Liljegren model. Where a policy requires on-site measurement, use the app for planning and as a cross-check alongside your instrument.
Sources
- Occupational Safety and Health Administration. Heat — Standards. U.S. Department of Labor.
- Occupational Safety and Health Administration. OSHA Technical Manual, Section III Chapter 4: Heat Stress.
- National Institute for Occupational Safety and Health. Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments. DHHS (NIOSH) Publication No. 2016-106, February 2016.
Common questions
Does OSHA have a heat standard?
Not a specific federal standard in force. OSHA enforces heat hazards under the General Duty Clause, Section 5(a)(1), and has been developing a dedicated Heat Injury and Illness Prevention standard. Several states have their own enforceable heat rules.
What temperature is OSHA's legal limit for working?
There is no legal maximum working temperature, indoors or outdoors. OSHA regulates the hazard rather than a temperature, through the General Duty Clause. The ACGIH threshold limit values, written in WBGT, are the technical reference used to judge whether conditions were adequately controlled.
What are OSHA's indoor temperature regulations?
There is no enforceable indoor temperature regulation. OSHA has recommended a comfort range of roughly 68 to 76°F with 20 to 60 percent humidity in an interpretation letter, but that is guidance, not a rule. Indoor heat hazards remain enforceable under the General Duty Clause.
Can OSHA cite an employer for heat with no heat standard?
Yes, and it does. Citations are issued under the General Duty Clause where a recognized hazard existed, was likely to cause serious harm, and a feasible means of abatement was available. Water, rest, shade and acclimatization are all well-documented feasible controls.
Which states have their own heat regulations?
California, Washington, Oregon, Colorado, Minnesota and Maryland among others, with varying scope across outdoor and indoor work. They apply regardless of federal rulemaking, so check your own state's current requirement directly.
What does an employer have to document?
A written heat illness prevention plan, environmental readings with time and location, training records, acclimatization schedules for new and returning workers, and any heat-related incidents. An unrecorded reading cannot demonstrate that a program operated.
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