The Fort Worth Press - Formula One declares first official 'heat hazard' at Singapore GP

Race director Rui Marques issued a statement on Thursday afternoon notifying the teams of the regulation -- which means drivers will be able to wear cooling vests -- because ambient temperatures are expected to be 31 Celsius or higher.

"Having received a forecast from the official Weather Service predicting that the Heat Index will be greater than 31C at some time during the race... a Heat Hazard is declared," Marques said.

Singapore's bumpy Marina Bay Street Circuit is one of the most physically demanding F1 races, where extremes of heat, humidity and weather all play a part.

Drivers can shed up to three kilogrammes (more than six pounds) during the night race that often lasts the maximum two hours race limit.

The vests have coolant tubes connected to pumps and a heat exchanger, which some drivers in testing complained of making it very uncomfortable in an already cramped cockpit.

As a result, the governing body FIA said that wearing the vests will not be mandatory, but if drivers or teams opt out of using them their cars must still be fitted with the equipment to make the vests work.

Drivers not wearing the vests will have to carry an extra 0.5kg of ballast so they do not gain an advantage over those that do.

Every kilogramme of weight saved can equate to a tenth of a second off lap times, something that can be a big advantage.

The cooling vest system was developed after the 2023 Qatar Grand Prix, where several drivers needed medical attention after suffering in the heat.

George Russell trialled the cooling vest at this year's Bahrain Grand Prix and gave it the thumbs-up.

"Of course there's always room to improve," the Mercedes driver said. "I wanted to give it a whirl. So far, so good."

M.McCoy--TFWP