One driver got out of a running Formula 1 car, in a live session, and ran across the circuit to someone else's cockpit.
Blanchimont
Spa-Francorchamps is the fastest circuit on the calendar and Blanchimont is one of its fastest corners, taken flat or near enough. In 1992 the run-off there was not what it is now.
During practice for the Belgian Grand Prix, Erik Comas crashed his Ligier heavily at that corner. The car stopped on the track. He was unconscious, and his foot remained on the throttle, holding the engine at maximum revs in a broken car.
Why the engine mattered
An engine running at full load in a wrecked chassis, with fuel lines potentially compromised, is the most dangerous element of the whole scene. Anyone who has spent time in motorsport knows the first job is to switch it off.
Comas could not do it. He was unconscious.
What Senna did
Senna arrived next. He stopped his McLaren on the racing line, which is itself an extraordinary decision, because it made his own car a hazard and made him a pedestrian at a corner approached at close to two hundred miles an hour.
He ran to the Ligier, reached into the cockpit, and shut the engine down. He then supported Comas's head and kept the airway clear until the medical car arrived.
The marshals had not reached the car. Other cars were still circulating.
Afterwards
Comas was taken to hospital and recovered. He has spoken repeatedly over the following thirty years about what Senna did, and has said plainly that it saved his life.
Senna did not go back out that day. He gave the incident almost no oxygen at the time and did not use it afterwards.
In 1994 at Imola, Comas was released onto the circuit after Senna's accident, drove into the scene, and was in no state to continue the weekend.
Why it goes on a wall
Because Formula 1 is a sport with a very clear hierarchy of priorities, and on that afternoon a driver who was fighting for a world championship put his car, his session and his own body behind a competitor he had no particular relationship with.
He stopped the car on the racing line and ran.