For the second successive race the FIA has declared this weekend's United States Grand Prix to be a heat hazard event.

"In accordance with Article 26.19 of the Sporting Regulations, having received a forecast from the Official Weather Service predicting that the Heat Index will be greater than 31.0 degrees C at some time during the Sprint or Race at this event, a Heat Hazard is declared," said race director Rui Marques.

The protocol was introduced following the 2023 Qatar Grand Prix when a number of drivers required medical treatment due to the heat and dehydration. Now, at designated events, cars must be fitted with a Driver Cooling System which includes pumps, a coolant reservoir and heat exchanger which feed coolant through a special vest that the drivers wear beneath their overalls.

While it was initially intended to be mandatory that the vest be worn, after drivers complained of being uncomfortable it was declared optional. However, those drivers who opt not to wear the vest must have 0.5kg of ballast added to their car in order to maintain the same overall minimum car weight as those that wear them. Whether the driver wear the vests or not, all cars must be fitted with the equipment that powers them.

While some drivers, most notably George Russell, have clearly taken to them, others are against the idea of them being made mandatory.

"I'm happy not to make it mandatory and the ones that don't want to use it have a disadvantage in the race," said Carlos Sainz, the Grand Prix Drivers' Association (GPDA) chairman, in Singapore. "For me it's as simple as that.

"I'm convinced it works and it helps," he added, "even though I've done ten Singapores without suffering physically and being able to finish. As soon as you study a bit of physiology you understand that there's a performance advantage.

"I think if it's not a huge safety issue they should leave it open. I agree with the guys that don't want to use it. If they don't want to because they feel really uncomfortable then don't use it."

"I don't think it should ever be forced on drivers," agreed Lewis Hamilton. "They keep saying it's a safety issue, but there's no driver that's ever died from overheating in the race, apart from obviously in flames back in the day. It's like, it's just getting silly. That should be our choice to have it."

"They will always throw it on safety," said Max Verstappen, "but then we can talk about a lot of stuff that can be improved on safety, including pit entries in certain places. I think that has a bit more priority than a vest in the car because I don't like it.

"I don't like the tubes that are on you, on your body, with the belts that go next to you," he admitted. "Then they can say it's just a bad design. I disagree. It just needs to be an option for the drivers to choose.

"Some like it, some don't, and that's fine. But it should be a personal preference," he insisted. "And I know this year we can, but probably next year they don't want to do that, and I feel that is not the right thing."