Formula One has activated heat hazard protocols for this weekend's Austrian Grand Prix, the first time the rules have been applied at a European event.
The regulations, introduced last year, apply when race day temperatures are forecast to be above 31C. Sunday's race is expected to reach 32C.
Under the rules, drivers must use cooling equipment or add extra weight to their cars to prevent competitive advantage. The vests pump cooling liquid through tubes connected to equipment inside the car.