Construction workers toiling in the hot sun have a new guide setting out how long they can stay on the job without risking heatstroke.
The guide, drawn up by a research team from Polytechnic University, takes into account different factors including the nature of the job, the worker's fitness and habits, the weather and pollution.
For example, a 45-year-old rebar worker who smokes and drinks occasionally should labour for no longer than 70 minutes when the Observatory's very hot weather warning is in force and the air pollution index is at medium.
The research team found that a worker's heat tolerance time declines by about half an hour for every 10 years of their age. Tolerance time also drops by about five minutes for every one degree Celsius of temperature.
The study also calculated the optimal recovery time for workers to regain their strength before heading out again.
On average, a rebar worker would achieve about 78 per cent recovery after 15 minutes' rest. The longer the break, the better the recovery.