Austria is the first race this year to be declared a heat hazard, amid a heatwave across Europe that is establishing record temperatures in many countries, including the UK.
The rule was first introduced last year, when the Singapore and US Grands Prix ran under the designation.
Some drivers prefer not to use the cooling kit because of discomfort, and because there have been issues with the coolant running out before a grand prix is finished, in which case the liquid ends up at car temperature, which is considerably higher than ambient.
Temperatures in the cockpit of an F1 car can be more than 40C, and drivers are wearing several layers of fireproof clothing in addition to a balaclava and helmet, so overheating is a serious concern.
