In Formula One, safety standards have improved since the first World Championship Grand Prix at Silverstone in , where there was no medical back-up or safety measures in case of an accident. In the 1960s helmets and overalls became mandatory and the FIA assumed responsibility for safety at the circuits. Further steps were taken to improve the safety of the Formula One car in the 1970s: the cockpit opening was enlarged allowing the driver quicker escape in the event of an accident and outside mirrors became mandatory. In the 1980s the carbon fibre monocoque replaced aluminium, increasing protection upon impact. Following the death of Roland Ratzenberger and Ayrton Senna at Imola in , a number of measures were introduced in an attempt to slow the cars down, including a wooden undertray. In grooved tyres replaced racing slick tyres to reduce cornering speed. Safety measures continued to be introduced into the 21st century, with a number of circuits changing their configuration to improve driver safety.