This weekend’s Singapore Grand Prix was officially declared a Formula One “Heat Hazard” on Thursday, marking the first time this new rule—designed to help drivers stay cool—has been invoked.

Race director Rui Marques issued a statement on Thursday afternoon notifying the teams of the regulation. As a result, drivers will be permitted to wear cooling vests due to the high ambient temperatures expected during the event.
https://sports.inquirer.net/642805/f1-declares-first-official-heat-hazard-at-singapore-grand-prix