US GP second F1 race in row to be 'heat hazard'

The United States Grand Prix is the second race in succession to be declared a "heat hazard" under Formula 1's rules.

Temperatures at the Circuit of the Americas in Austin, Texas, are forecast to be more than 31C during both the sprint race on Saturday and the grand prix on Sunday.

This triggers a heat index which governing body the FIA uses to define potentially dangerous conditions for drivers.

The temperatures are out of the ordinary for the US Grand Prix - Texas is going through a mid-October heatwave, external that is making conditions more akin to summer than autumn.

The 'heat hazard' designation - which is new this year - triggers a rule that gives drivers the option of wearing cooling vests in their cars.

For this season, the cooling vests are optional, and some drivers, such as four-time world champion Max Verstappen, do not like them because they consider them uncomfortable and flawed.

Mercedes driver George Russell did wear the vest when he won the Singapore Grand Prix in hot and humid conditions on 5 October.

If the driver chooses not to wear the vest, his car must carry 500 grams of ballast to compensate for the weight of the system so he does not gain a competitive advantage.

The system, which teams can make to their individual designs, typically features a liquid such as glycol pumped through a tank of dry ice and through the driver's fireproof top.

Issues with the system include the dry ice running out. This leads to liquid at car temperature, which is hotter than ambient temperature, being pumped through the system.