It's remembered as the race that claimed the life of one of the greatest racing drivers of all time, but Ayrton Senna's fatal crash at the 1994 San Marino Grand Prix was only one of five major accidents which took place over the darkest weekend in the modern Formula One era.

The teams came to Imola¹ for the third race of a season which had started controversially with the introduction of several new rules, such as the reintroduction of refuelling during pit stops and the prohibition of computerised driver aids such as traction control². However this had left the teams with a feeling that safety was being compromised in exchange for greater spectacle. Senna himself had predicted serious accidents in the season ahead. Sadly he was about to be proved right.

First Qualifying Session - Friday 29th April

The tone of the weekend was set in the first qualifying session when Rubens Barrichello, in his second year in F1 with the Jordan team, lost control of his car at the Variante Bassa chicane. The car took off over the kerb and flew sideways over the tyre barrier³, bounced off the wire fencing behind the barrier, overturned and came to rest upside down. The medical team arrived at the scene of the accident within a minute and the session was halted while the unconscious Barrichello was attended to by the side of the track. He was taken to hospital but discharged later in the day, having remarkably suffered nothing more serious than a broken nose, concussion and a cut lip.

At any normal race meeting this would have been the talking point of the weekend. Sadly it was to become a comparitively minor incident.

Second Qualifying Session - Saturday 30th April

Saturday started positively, with Rubens Barrichello returning to the circuit, albeit only as a spectator. The second qualifying session began and was progressing reasonably uneventfully until the Austrian driver Roland Ratzenberger crashed at the Villeneuve Corner⁴. This was clearly even more serious than the previous day's accident; whereas Barrichello's momentum had been slowed by the wire fencing, Ratzenberger's car smashed into a concrete wall at 180 mph and most of the left hand side of the vehicle was simply torn off. Again the session was stopped and the medical team was quickly on the scene. After being given treatment on the track Ratzenberger was taken to the circuit's medical centre and subsequently airlifted to hospital, but he had suffered multiple injuries in the crash from which he did not recover. His death was announced shortly afterwards.

This was a major shock to everyone involved in Formula One. Fatalities had not been uncommon in the sport's early days, but by now it was twelve years since a driver had died during a Grand Prix weekend⁵ and this had generated a sense of security, a feeling that these things just didn't happen anymore. The shock was compounded by the fact that Ratzenberger had only competed in one Formula One race, having been recruited by the tiny Simtek team at the beginning of the season. Ratzenberger failed to qualify for the first race of the season in Brazil, but competed in the Pacific Grand Prix two weeks later in Japan, finishing eleventh. The former Formula 3 and Formula 3000 driver never got the chance to show his potential in Formula One.

However, despite the shock, the show had to go on and the race went ahead as planned the following day.

The Race - Sunday 1st May

The bleak mood which had settled on the paddock on Saturday afternoon had lifted slightly by Sunday morning, as the teams busied themselves getting ready for the race.

The disjointed qualifying sessions had left Ayrton Senna in pole position with his new rival, the young upstart Michael Schumacher right behind him. Senna had started the previous two races on pole but failed to finish either; Schumacher had won both and left Senna with something to prove.

As the race started, fifth place driver JJ Lehto's engine stalled. The drivers directly behind managed to avoid his stationary Benetton but the Lotus driver Pedro Lamy, starting from 22nd position and still accelerating, ran into the back of it. Neither driver was hurt but the impact sent one of Lamy's wheels bouncing over a fence and into the crowd, injuring several spectators.

The seemingly jinxed race continued behind the safety car as the debris was cleared from the track. When the safety car went in on lap six, race leader Senna was just managing to hold off Schumacher but as they arrived at the Tamburello corner Senna's Williams failed to turn and hit the wall.

Yet again the red flags came out and the medical team rushed to the injured driver, who was quickly taken to hospital, although it is now widely speculated that Senna was already dead, having suffered massive head injuries from a piece of the car's suspension which pierced his helmet. With hindsight, it may seem strange that everyone didn't just pack up and go home at this point. However, with the extent of Senna's injuries not yet fully apparent, the remaining drivers returned to their grid positions and the race was restarted.

Astonishingly there was yet another serious accident towards the end of the race when a wheel detached itself from Michele Alboreto's Minardi and bounced down the pit lane, injuring mechanics in the Ferrari and Lotus garages.

In the end, Michael Schumacher won the race for the Benetton team, with Nicola Larini second for Ferrari and Mika Hakkinen third in the McLaren. The drivers were not in celebratory mood, however, and a couple of hours after the end of the race it was announced that Senna had succumbed to his injuries. The world's greatest racing driver, who had visited his compatriot Rubens Barrichello in hospital two days before and mourned his colleague Roland Ratzenberger only the previous day, had now lost his own life in the same manner.

The aftermath

Williams team boss Sir Frank Williams, director of engineering Patrick Head and chief designer Adrian Newey all faced charges of culpable homicide in a series of lengthy legal processes which dragged on for over a decade after the accident. The Williams team attempted to prove that Senna's accident could have been caused by a number of factors, such as an uneven track surface and the loss of heat in the car's tyres after five slow laps behind the safety car. After a series of hearings and appeals the court's eventual decision, announced in 2005, was that the crash was caused by a broken steering column, although nobody was found to be at fault and all three Williams employees were acquitted.

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¹ San Marino itself is too small to host a Grand Prix so the race is traditionally held at Imola in northern Italy.
² An electronic system which limits wheel spin and makes cornering easier.
³ A protective barrier made of old tyres, designed to absorb and dissipate the energy from impacts such as this one.
⁴ Named after the late F1 driver Gilles Villeneuve, father of 1997 World Champion Jacques.
⁵ The last fatality before Ratzenberger was Riccardo Paletti in the 1982 Canadian Grand Prix.