Singapore (AFP) - This weekend’s Singapore Grand Prix was on Thursday declared an official Formula One “Heat Hazard” – the first time a new rule to help drivers stay cool has been invoked.

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.

George Russell trialled the cooling vest, which is worn under the driver’s fireproof suit, at this year’s Bahrain Grand Prix.

“Not everybody finds the top comfortable, but I think some find it more comfortable than others, and of course over time you’ll be able to adjust it to your own preferences,” Russell told reporters in Singapore.

“But the concept is good, and when you’re racing in 90 percent humidity and the cockpits are getting on for 60C, it’s a bit of a sauna inside the car, so I think we all welcome it.”

Ferrari’s Lewis Hamilton said: “I’ve never used it, but I’ll try it.”

- ‘It’s a trade-off’ -

The vests have coolant tubes connected to pumps and a heat exchanger, which some drivers find 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.

Williams driver Carlos Sainz welcomed the decision, saying he didn’t mind heat, if there was no humidity, but the combination of the two in tropical Singapore was a big problem.

“In Hungary where it gets really hot but it’s not humid it’s not too bad,” Sainz told BBC Sport.

“But when it’s 28C, 30C degrees plus humid that is when it gets to Singapore levels and it’s tough.”

Aston Martin veteran Fernando Alonso said: “The system works. The shirt itself, the material is a little bit thicker with all the system on it so it is less comfortable.

“It is a trade-off,” added the Spaniard. “It is less comfy when you drive it but it is a little bit cooler.”