He was killed in a 15-car pileup, after sustaining a fatal head injury after rolling his car and catching fire on the first lap of the 1958 Indianapolis 500.
Elisian spun in turn 3 of the first lap and collided with Rathmann's car, sending them both into the wall, and starting a 15-car pileup.
Although O'Connor was incinerated in the accident, medical officials said that he was probably killed instantly from a fractured skull.
Following the accident, race officials announced that they would change the starting procedure, abandoning the single-file trip down pit lane that was used in 1957 and 1958.
Also, for the 1959 Indy 500, metal roll bars welded to the frame behind the driver's head were mandated, and helmets were required to pass safety certification by Speedway medical officials.