The FIA has issued a heat hazard warning ahead of the United States Grand Prix. This is only the second time in Formula 1 history that such a warning has been given, the first being earlier this year at the Singapore Grand Prix.

According to weather forecasts, temperatures at the Circuit of the Americas in Austin could rise to around 34°C during Saturday’s sprint race. This is above the 31°C limit set by the FIA for declaring a heat hazard. On Sunday, when the main race takes place, temperatures are expected to reach around 31°C.

Because of this, the FIA has reminded teams and drivers of the safety rules for hot weather. Drivers must either wear special cooling vests or have an extra 0.5 kg of weight added to their cars. The extra weight is meant to balance out the difference for those who choose not to use the vest.

At the Singapore Grand Prix, drivers had mixed opinions about the cooling vests. Ferrari’s Charles Leclerc said the vest helped for only about five laps, while Aston Martin’s Fernando Alonso found it useful for roughly the first hour of the race. Other drivers, such as Lewis Hamilton and Max Verstappen, were critical of the system and questioned whether it was really effective or comfortable.