Austrian rookie Roland Ratzenberger and Brazilian three-time world champion Ayrton Senna lost their lives in separate accidents during the event.

Senna was given a state funeral in his home town of São Paulo, Brazil, where around 500,000 people (some numbers say 2 million) lined the streets to watch the coffin pass.

[6][7] The top three cars of Michael Schumacher, Nicola Larini and Mika Häkkinen were investigated and their teams were asked to surrender their systems' source code to the company.

[8] On Friday, 29 April, during the first practice session,[10] Rubens Barrichello, who was driving for Jordan at the time, hit a kerb at the Variante Bassa corner at 225 km/h (140 mph), launching him into the air.

[11] He hit the top of the tyre barrier, and was knocked unconscious by an impact measured at 95 g.[12] Barrichello's car rolled several times after landing before coming to rest upside down.

Barrichello's tongue blocked his airway during the crash and emergency work done by FIA doctor Sid Watkins saved his life.

[14][15] Ten years after the incident, Damon Hill, who drove for the Williams-Renault team at the time, described the feeling after the crash: "We all brushed ourselves off and carried on qualifying, reassured that our cars were tough as tanks and we could be shaken but not hurt.

"[16] Despite a spin,[17] Senna was the fastest driver at the end of Friday's session with a time of 1:21.548, almost five-tenths of a second faster than Schumacher and Berger.

[19] Eighteen minutes into the final qualifying session, Austrian driver Roland Ratzenberger failed to negotiate the Villeneuve curva in his Simtek; he subsequently hit the opposing concrete retaining barrier wall almost head-on and was critically injured.

Ratzenberger, in his first season as a Formula One driver, had run over a kerb at the Acque Minerali chicane on his previous lap, the impact of which is believed to have damaged his front wing.

[20][21] There were no tyre barriers or any other impact absorbing installations in place at the Villeneuve curva, and the Simtek hit the bare concrete wall with a resulting g-force measured to be 500 g, the highest ever registered in F1.

After initially being taken by ambulance to the on-circuit medical centre, Ratzenberger was airlifted to the anaesthesia and resuscitation unit of Maggiore Hospital at 14:07 local time, the second driver to be admitted there during the weekend.

He was found to have suffered three separate fatal injuries due to the enormity of the impact: a basilar skull fracture, blunt trauma from the front-left tyre penetrating the survival cell and a ruptured aorta.

With Barrichello injured, Pacific's Paul Belmondo, the only driver to miss the cut, was promoted to the final position as the alternate by rule.

The association subsequently pressed for improvements to car and circuit safety in the wake of Imola and other serious crashes during the 1994 season; for 2003, the FIA mandated the use of the HANS device, designed to prevent the type of injury suffered by Ratzenberger.

[35] No stoppage of the race was declared as a result of the accident between Lehto and Lamy,[34] but the safety car driven by Max Angelelli was deployed, with all the remaining competitors holding position behind it while travelling at a reduced speed.

When a race is stopped under a red flag, cars must slow down and make their way back to the pit lane or starting grid unless notified of a restart.

[12] The pictures shown on the world feed, supplied by host broadcaster RAI, of Senna being treated were considered by the BBC, the corporation responsible for broadcasting the San Marino Grand Prix live to viewers in the United Kingdom, to be too upsetting for general viewing at the time (around 13:20 BST), and the BBC abandoned RAI's feed to focus on their own camera in the pit lane.

Referring to the number of times the incident was replayed on the world feed, Ferrari team principal Jean Todt stated that "even if you didn't want to watch it, you could barely fail to".

[12] Senna was lifted from the wrecked Williams, and after approximately fifteen minutes of on-site medical attention, was airlifted directly to Maggiore Hospital, becoming the third and final driver to be admitted there during the weekend.

[35] On the second formation lap, Heinz-Harald Frentzen stalled the engine fitted to his Sauber whilst attempting to leave the grid and was forced to start from the pit lane.

Christian Fittipaldi, battling for fifth position with Ukyo Katayama's Tyrrell and Damon Hill's Williams, would eventually retire his Footwork due to an hardening brake pedal that saw him become beached in the gravel on lap 55.

[50] Two hours and 20 minutes after Schumacher crossed the finish line, at 18:40 local time, Dr. Maria Teresa Fiandri announced that Senna had died.

The circuit was heavily modified following the race, including a change at Tamburello—also the scene of major accidents for Gerhard Berger (1989) and Nelson Piquet (1987)—from a high speed corner to a much slower chicane.

The front two grid slots at the Monaco Grand Prix that year, which were painted with Brazilian and Austrian flags, were left clear in memory of the two drivers who had lost their lives, while both Williams and Simtek entered only one car each.

[62] On 28 May, during the second qualifying session for the Spanish Grand Prix, Ratzenberger's replacement Andrea Montermini crashed heavily and broke his ankles.

Mercedes contacted HANS Performance Products, owned by sportscar racer Jim Downing and his brother-in-law, Michigan State University College of Engineering professor Robert Hubbard, with a view to adapting their device for Formula One.

Initial tests proved successful, and at the 2000 San Marino Grand Prix the final report was released which concluded that the HANS should be recommended for use.

Senna was the last driver for twenty years to die in a Formula One accident, until the death of Jules Bianchi in 2015 from injuries sustained at the 2014 Japanese Grand Prix.

Even being found responsible for Senna's accident, Patrick Head was not arrested, as the verdict was delivered past the Italian statute of limitation for manslaughter.