I started watching F1 a long time ago and the first incident I remember seeing (on TV) was the accident involving Ronnie Peterson (my hero of the time) at Monza 1978.
The starter got it badly wrong and waved them off before the back of the grid had come to a halt. Consequently the pack funnelled up together, one thing led to another and Peterson’s car crashed and burst into flames.
Medical support was shockingly bad in those days and it was left to his fellow drivers, notably James Hunt, to pull him from the wreck, put the fire out and try to care for him for 20 minutes until medical help arrived. He was taken to hospital but died as a result of complications from his injuries.
1982 was a shocking year with two horrendous accidents… Giles Villeneuve in qualifying being thrown from his disintigrating car… and Paletti dying after ploughing into the back of Pironi’s stationary car at the start. I was at Uni at the time and wasn’t able to watch the races on TV so didn’t see those incidents but they are on Youtube and they are dreadful to watch.
Going back further, the most shocking incident of all that I read about and have watched on youtube was the incident involving Roger Williamson in 1973.
He crashed but was uninjured. However he was trapped in the car which burst into flames. His fellow driver Dave Purley stopped to help him and desperately tried to flag down other help, get marshalls to help, used the only (inadequate) fire extinguisher in the area to put the flames out, etc… meanwhile the race continued with only a yellow flag. Dave Purley got more and more distraught as he realized that his friend, uninjured but trapped, was burning to death.
It took 8 minutes for a fire truck to arrive and put the fire out, by which time Roger Williamson was dead. They threw a blanket over the car and the dead driver and the race carried on.
Dave Purley was awarded the George Medal for his bravery in trying to help his fellow driver.
If you watch that on youtube search for “Roger Williamson 1973″ but be prepared to be shocked by what you see.