durr, description of what happened is in the video description:
"The official report cited operator error, and rumor has it the operator was inexperienced and pulled the wrong lever and allowed the winch to go into free-fall. He tried to catch it on the drum brake but that overheated, exploded and caught fire as you can see.
The dragline boom was being lowered for maintenance, and as you can see the correct radius hadn't been chosen to let the drag line boom clear the M4600-based Transilift boom. The operator suffered minor injuries."
apparently some noob hit the wrong switch, causing the crane on the right (which was holding the crane on the left) to release all its cable. He then hit the emergency brake, which was totally overwhelmed and exploded. I think thats the brake drum getting launched into the air..?