Gym accidents...oh boy, have I seen plenty over some 5 decades of training! One of the scariest incidents was when I was into back BB quarter and half squats in my middle teens. I finished up with my sets and walked off and left the loaded bar, some 700-800 lbs., on what was then called an "iron staircase" support rack.
Right next to this loaded bar on the rack was a vertical leg press machine and some older business man was in the process of doing a set of leg presses on it. His body and head were resting on a pad just below, and to the right, of the racked loaded bar. Well, some guy goes to the other/left side of the bar and, you guessed it, starts pulling plates just off of that end of the bar!
Well...there was this rumble and then BOOM as the bar flipped over, slammed into the floor, tore a chunk out of the leg press machines' pad, missing the man's body/head by about 6 inches (!), bending the bar, and spewing plates all over the place! Of course, the guy, using the leg press machine at the time, was catatonic!
Besides getting justly royally chewed out by the gym's owner, I had to pay for replacement of the leg press machine's pad and buy a new Olympic bar...quite a chunk of change for a 16 yr. old!
Anyway, thank God no one was hurt and i wasn't kicked out of the gym. After that tragic dumb incident, I've always "broken down" my bars when I've finished using them!