Tragic accident, from the unequipped Marshalls, to the drivers who didn't stop because they thought it was Purley who had safely exited the burning car and the firetruck that had to complete almost an entire lap. Misconceptions and a tragic lack of safety.
Another fatal F1 crash which is in the same sort of realm of tragicness is that of Tom Pryce:
Two marshalls were rushing across the track (unimaginable in these days) towards Zorzi's car which had broken down right after the brow of the hill in the track. At that time Pryce was driving right behind Stuck on the main straight, Stuck saw the marshalls and veered to the right but with his view obstructed by Stuck, Pryce did not see them and hit the second marshall at a speed of 270km/h.
The marshall was thrown into the air and landed yards in front of Zorzi and Bill. He died upon impact, his body being literally torn in half by Pryce's car.
The 20kg fire extinguisher the marshall had been carrying smashed into Pryce's head, before striking the Shadow's roll hoop. The force of the impact was such that the extinguisher was thrown up and over the adjacent grandstand. It came to ground in the car park to the rear of the stand, where it hit a parked car and jammed its door shut. The impact with the fire extinguisher had wrenched Pryce's helmet upward sharply, and he had been partially decapitated by the strap. Death was almost certainly instantaneous.