Scenario

Is it ever legally too hot to work?

Is there a legal maximum working temperature?

Not in the UK, Australia or the United States. All three impose a duty to assess and control heat risk rather than a temperature at which work stops. Japan is the counter-example: since June 2025 it requires specific measures at WBGT 28°C or air temperature 31°C for work over one continuous hour or four hours a day.

The answer nobody writes plainly

There is no maximum working temperature in the United Kingdom, in Australia, or in the United States.

That is not an oversight, and it is not the same as "there are no rules". All three place a duty on the employer to identify the risk and control it. What none of them does is give you a number to point at.

Four jurisdictions. Verify the current text before relying on any of it.
Where	Maximum temperature	What is required instead
United Kingdom	None	A "reasonable" indoor temperature, plus the general duty to assess and control risk. HSE declines to set an upper figure.
Australia	None in the WHS laws	Eliminate or minimise risk so far as is reasonably practicable. Some awards and agreements add contractual triggers.
United States	None federally	General duty clause; several state plans add real numbers; a federal heat rule is at proposal stage.
Japan	Effectively yes, as a trigger	Measures required at WBGT 28°C or air 31°C for work over one continuous hour or four hours daily.

What "assess and control" means in practice

It is vaguer than a number and, done properly, more demanding. A defensible position looks like this:

You know the conditions, which means a measurement or a defensible estimate, at the work location rather than at the airport.
You know the workload, because every published limit has a workload axis. Work/rest schedules sets out the categories.
You have controls in place — water, rest, shade, rotation, timing — and they exist before the hot day.
You handle acclimatisation, because new and returning workers are the documented risk group.
Someone is monitoring. People do not self-report heat strain reliably.

If a regulator asks, "there is no legal maximum" is not the answer. "Here is our assessment, here are the controls, here is what triggered them" is.

Where the frustration comes from

The question is usually asked by someone who is already too hot, and the honest answer is unsatisfying: the law does not have a line, so the argument is about adequacy rather than about a threshold. That is genuinely harder to win than pointing at a thermometer.

Two things that help make the case concretely:

Use the published limits. ACGIH and NIOSH work/rest tables are the numbers that safety professionals, including OSHA's own educational material, actually cite. The calculator turns them into minutes.
Get the conditions on the record — where you work, at the hot part of the day, with the workload noted. A measured WBGT is best; an estimate is a start, and a start is more than most disputes begin with.

Indoors is a different question

Warehouses, kitchens and plant rooms come up constantly, and the outdoor framing above does not cover them well — nor can an outdoor weather app answer them. Indoor heat rules has that version, including California's indoor standard, which is one of the few places where a specific indoor trigger exists.

Common questions

Can I legally refuse to work because it is too hot?

Not simply because of a temperature, in any of these three jurisdictions. There are separate protections for refusing work that presents a serious and imminent danger — the shape and name of that right differs by country and by state — and heat can reach that level, but it is judged on the actual risk rather than on a thermometer reading. Raise it with the employer and, if needed, the regulator or union first.

What does the UK actually require?

The Workplace (Health, Safety and Welfare) Regulations require a "reasonable" temperature indoors, and the general risk-assessment duty covers heat. The Health and Safety Executive publishes a minimum guideline for cold work but explicitly declines to set a maximum, on the grounds that comfort depends on humidity, air movement, radiant heat, clothing and workload.

What about Australia?

The model Work Health and Safety laws impose a duty to eliminate or minimise risks so far as is reasonably practicable, and Safe Work Australia publishes heat guidance — but no maximum temperature. Some awards and enterprise agreements do contain temperature-based provisions, which is a contractual matter rather than a statutory one, and in construction those clauses are often the practical trigger.

Why won't regulators just set a number?

Because a single air temperature does not determine heat strain. The same 30°C is trivial for a seated office worker and dangerous for someone in a vapour-barrier suit doing heavy work in direct sun. A number strict enough for the second case would shut down the first; one lenient enough for the first would not protect the second.

Which country does have a number?

Japan. Since 1 June 2025 its workplace heat rules require specific measures where WBGT reaches 28°C or air temperature reaches 31°C, for work exceeding one continuous hour or four hours in a day, with criminal penalties available under the underlying act. It is the clearest statutory example anywhere.

Sources

Published 30 July 2026