At 34, Senna was hardly a newcomer to Grand Prix-racing. But from the start, events at Imola during the San Marino Grand Prix were to shake him deeply. On Friday, Rubens Barrichello, Senna's protege, was involved in a serious accident and withdrew from the race. On the following day, Roland Ratzenberger, who had only recently achieved his ambition to become a Formula One driver, was killed during the qualifying round as his Simtek vehicle crashed into the Villeneuve corner at around 300km/h. Senna was reported to have been carrying an Austrian flag in his car the next day.

Two laps after the start of the race on 1 May, Senna, who was driving the Williams FW16 had a lead over Michael Schumacher. Suddenly, he was seen to swerve to the right at the Tamburello corner, which had been the site of previous accidents for Gerhard Berger and Nelson Piquet. Despite managing to slow the vehicle enormous impact of hitting concrete at great speed, Senna fell into a coma, and was to die later that evening.

The accident was attributed by the Williams team to Senna's decision to swerve to avoid debris, but the Italian police thought otherwise, accusing Frank Williams and a team of racing officials of manslaughter. An investigation had suggested that Senna's car was based on an inappropriate design and implementation when it was modified to make it lighter, using a smaller steering column than was appropriate.

The trial rested on whether the steering column broke before or after the collision, and whether the debris on the track amounted to negligence on the part of racing officials. The Williams team asserted that the steering column broke after, and not before, the accident, and it was difficult for the magistrate to demonstrate that the debris was the cause of the accident. The untimely death of a sporting legend brought international scrutiny to Formula One: however, the charges were eventually dropped in 1997. It is worth bearing in mind that if the Williams team had been found guilty, it would in all likelihood have meant an end to F1 racing it Italy.

While the accident haunted F1 drivers and enthusiasts for many years, the events that took place in 1994 instigated a new era for the manufacture of the Formula 1 vehicles, with cars being thoroughly crash tested, and featuring a 'tub' combination of cockpit and safety cell, to protect drivers, so that impact is absorbed rather than deflected. The latest developments in Formula One vehicle design mean that drivers can now endure phenomenal impact with minimal injuries. However, it remains by nature a dangerous sport.

The site of the San Marino track was later modified to reduce speed at the Tamburello corner. Drivers including Senna, just before his death, and Schumacher instigated a Grand Prix drivers' association, to ensure greater protection for F1 drivers. In his native Brazil, Ayrton Senna is revered alongside the nation's football heroes, both for his exploits as a driver and a philanthropist, who donated substantial amounts of money to children's charities. BBC commentator Murray Walker described May 1 1994 as "the blackest day for Grand Prix racing".