Guide

OSHA and heat: what the rules actually require

Is there an OSHA heat standard?

There is no federal numerical heat standard in force. OSHA enforces heat cases under the general duty clause, which requires employers to keep workplaces free of recognised hazards, and it has a specific heat rule at proposal stage. Several states run their own heat rules with real numbers, and those are enforceable where they apply.

What is enforceable today

Three layers, and conflating them is the source of most of the confusion:

The three kinds of "OSHA heat rule" people mean.
Layer	Status	Contains numbers?
General duty clause, §5(a)(1)	In force, enforceable, cited in heat cases	No
State plan heat rules	In force where the state has one	Yes, and they vary
Federal heat standard	Proposed, not in force	Yes, as proposed

The consequence: an employer asking "what am I legally required to do about heat" gets a different answer in Fresno than in Tulsa, and neither answer is a temperature.

What the general duty clause actually demands

It demands that a recognised hazard be addressed. In heat cases OSHA has treated the recognition question as settled — the science and the agency's own guidance are extensive — so the argument in practice is about whether the employer's controls were adequate.

What inspectors look for, in the pattern the agency's own materials describe:

A written heat illness prevention plan that exists before the hot weather, not after an incident.
Water, rest and shade actually available, not nominally available.
An acclimatisation process for new and returning workers. The acclimatisation plan builder implements the NIOSH schedule.
Training, so that workers and supervisors recognise the early signs.
Someone monitoring, because the person in trouble is usually the last to say so.

The proposed federal standard

The proposed rule takes the shape most state rules have: two trigger levels based on heat index, with progressively more required at the higher one — drinking water, break areas, acclimatisation protocols, monitoring, and a written plan.

Two things worth understanding about a proposal:

It is not law until it is final. A proposed rule creates no obligation, however widely it is reported.
The trigger being on heat index rather than WBGT is a deliberate simplification. Heat index needs two inputs anyone can get; WBGT needs an instrument. That trade-off is exactly why the heat index calculator and the WBGT estimator are separate pages here.

What to use in the meantime

The published tables. ACGIH's threshold limit values and NIOSH's recommended alert limits are what nearly every plan, including OSHA's own educational material, is built on — WBGT against workload, with separate limits for unacclimatised workers.

They are not regulations, and this site does not present them as such: work/rest schedules in heat sets out how to read them, and the calculator does the lookup.

For indoor questions — warehouses in particular, where there is real demand and real state-level rulemaking — indoor heat rules is the right page, and it starts by saying that an outdoor weather app cannot answer an indoor question.

Common questions

What temperature does OSHA say is too hot to work?

None. There is no federal temperature at which work must stop. That surprises people, but the enforceable duty is to assess and control a recognised hazard rather than to observe a threshold. The published numbers people cite — the NIOSH and ACGIH work/rest limits — are recommendations, not regulations.

What is the general duty clause?

Section 5(a)(1) of the Occupational Safety and Health Act. It requires each employer to furnish a place of employment free from recognised hazards likely to cause death or serious physical harm. Heat is a recognised hazard, so OSHA cites employers under it where there is no specific standard — and it has done so in heat fatality cases.

Do state rules differ from federal ones?

Substantially. States operating their own OSHA-approved plans can and do set specific heat requirements, including numerical triggers, mandatory shade, water and rest provisions, and acclimatisation plans. California, Washington, Oregon, Colorado, Minnesota and Maryland have all adopted heat rules of some kind. Check the rule for the state you are working in, not the federal position.

Does an employer have to provide shade and water?

Under several state rules, yes, with specific triggers and quantities. Federally it is not a line-item requirement, but failing to provide them where heat is a recognised hazard is exactly the kind of thing cited under the general duty clause. In practice every credible heat illness prevention plan includes water, rest, shade and acclimatisation.

How does this compare with other countries?

Japan is the clearest contrast: since 1 June 2025 workplace heat measures are legally required at WBGT 28°C or air temperature 31°C for work of more than one continuous hour or four hours a day, with criminal penalties available. The UK and Australia sit closer to the US position — a risk-assessment duty with no maximum temperature.

Sources

Published 30 July 2026