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. It was not until the 1960s these were first introduced, as helmets and overalls became mandatory and the FIA assumed responsibility for safety at the circuits. Steps were taken to improve the safety of the Formula One car in the 1970s; the cockpit opening was enlarged allowing the driver to escape more quickly in the event of an accident and outside mirrors became mandatory. The 1980s saw further improvement in the structure of the Formula One car, with the monocoque being made out of carbon fibre instead of aluminium, increasing protection upon impact. Following the death of Ayrton Senna in , a number of measures were introduced in an attempt to slow the cars down, including bodywork aerodynamic limitations, a pit lane speed limit and temporary circuit modifications such as extra chicanes. Grooved tyres were introduced in instead of racing slick tyres to reduce cornering speed. Safety measures continued to be introduced into the 21st century, with a number of circuits having their configuration changed to improve driver safety.