There is no maximum working temperature, and there never was

Every July the same claim goes round an office WhatsApp group. Thirty degrees and you can go home. Sometimes it is 27, sometimes it is 35, and the number changes depending on who is retelling it.

There is no such rule. There never has been one, and the Health and Safety Executive says so in as many words: there is no law for maximum working temperature, or for when it is too hot to work, because every workplace is different.

That is worth knowing before you go looking for a threshold that does not exist. It is also not the end of the answer, because a duty without a number is still a duty.

What the law actually says

The relevant provision is regulation 7 of the Workplace (Health, Safety and Welfare) Regulations 1992. It is four lines long and the first is the one that matters:

During working hours, the temperature in all workplaces inside buildings shall be reasonable.

That is the whole standard. No figure, no ceiling, no trigger. What counts as reasonable in a bakery is not what counts as reasonable in a call centre, and the regulation is written that way deliberately.

The part almost nobody quotes is the third paragraph, which requires a sufficient number of thermometers so that people at work can determine the temperature in the building. It is the only concrete obligation in the regulation, and it is the easiest thing in this entire piece to ask for.

You cannot argue about whether a room is reasonable if nobody in it knows what the temperature is.

The minimums that do exist

The asymmetry surprises people. There is no maximum, but the guidance on the cold end is specific.

Those minimums are guidance rather than hard law, but they are the numbers an inspector would reach for, and they are the reason a cold office is an easier complaint to make than a hot one.

How often this actually matters

The honest position is that Britain has spent most of its working history not needing a maximum, because the weather did not produce one often enough to argue about.

That has changed, and this site holds the daily record to show by how much. Across the 25 towns with a complete series back to 1950, the average number of days a year above 25 degrees has risen from about 1 in the 1960s to about 8 in the last decade. Days above 28 have gone from a fraction of one to about 2.

The national average hides most of the story, because this is not evenly spread.

London now gets more than a fortnight of them a year, and 6 or 7 days above 28. Glasgow gets two days above 25 and effectively none above 28. A single national threshold would be wrong in one of those cities whichever number it was set at, which is the strongest argument for the law working the way it does.

The counter argument is that a duty nobody can measure themselves against is easy to ignore, and the thermometer requirement exists precisely because somebody in 1992 saw that coming.

What to ask for instead of a number

Since there is no threshold to invoke, the useful move is to treat heat as a hazard like any other, which is what the duty already requires.

• A thermometer, in the room. Regulation 7(3) is the clearest thing you can point at, it costs a few pounds, and it converts an argument about feelings into an argument about a reading.
• Heat in the risk assessment. An employer already has to assess risks to health. On a 30 degree day in a top floor office with sealed windows, heat is one, and writing it down is what forces the next question.
• Adjustments, in order of how cheap they are. Relaxed dress code, cold drinking water, more frequent breaks, moving physical work to the morning, shifting hours, then shading and ventilation, then cooling.
• Attention to who is affected first. Pregnancy, age, medication and some conditions all change how somebody copes with the same room. A rule set by the average person in the office is set wrong.

The order matters because each step up costs more, and the first four are usually available on the day rather than after a procurement cycle.

The thing the myth gets right

The 30 degree rule is wrong on the law and roughly right on the instinct. People are less productive, less careful and more prone to mistakes in a room that is too hot, and in some jobs that is a safety problem rather than a comfort one.

What the myth does is send people looking for a right that does not exist, which usually ends with them concluding that nothing can be done. Something can. It just starts with a thermometer rather than a threshold.

Nothing here is legal advice, and the regulations quoted apply to Great Britain. Northern Ireland has its own equivalent, and if your situation is serious enough to need an answer you can rely on, it is serious enough to take to a union representative or a solicitor.