A thermometer may end your shift

Under a model site agreement of the kind now circulating among regional construction employers and unions, the end of an outdoor shift would no longer be fixed at half past four. It would be fixed at a wet-bulb reading, taken by a sensor on a mast near the site gate, and the shift would end whenever that reading crossed the threshold: at eleven in the morning, at three in the afternoon, or not at all.

The figure in question is not a temperature in the ordinary sense. Wet-bulb temperature folds heat and humidity into the single number that decides whether sweating still works, which is why a moderate afternoon in a wet climate can be more dangerous than a ferocious one in a dry country. The draft would put that number on a display at the gate, refreshed every ten minutes, beside the notice board that has advertised the same first aid course since spring.

“We would not be sending anyone home because of the weather,” a spokesperson for the employers' side would say. “We would be sending them home because of a measurement. On a building site the weather is a matter of opinion. The measurement is not, and that is the entire reason for proposing one.”

The dispute the draft would generate is not about the number. Everyone consulted would accept that the number is real and that working past it is dangerous. The dispute would be about the four hours after it: whether they are paid, partly paid, made up on a Saturday, or treated as the private misfortune of someone who chose a trade that happens outdoors. The draft leaves that clause blank and marks it to be agreed nationally, which is where such clauses go to be quiet.

Sensor placement would become, within a single season, a genuine industrial relations question. A mast in the shade behind the site office reads lower than a mast on the roof deck where the work actually is. Foremen would learn this. So would inspectors. A trade that has spent a century arguing about where the tape measure starts would find the argument immediately familiar.

For the person on the scaffold the change would be smaller and stranger than either side expects. The forecast would stop mattering; only the display at the gate would. A worker would learn to read their own afternoon off a two-digit number the way an earlier generation read it off the sky, and would acquire the habit one submission describes as checking the wall the way you check a clock, every twenty minutes from eleven onwards.

Nothing has been signed, and model texts on building sites are famous for being adopted three years after everyone stopped reading them. But the sensor is cheap, the threshold is calculable, and the first summer with the number on the wall would be the last summer in which the argument was about whether it was hot.