My dad once told me a similar story with water. He was a brand new apprentice pipefitter working on a Dow Chemical plant. They were bleeding water out of a system that had a 10" cap they had to remove to do their job. The guy he was working with walked away for a bit, and he saw the 0-25psi gauge drop to near zero and started unscrewing the cap. Next thing he knew, he was pinned to the wall on the opposite side of the room and couldn't breath, then the site foreman pulled him out of the stream of water. This was back in the days of "well, hope you learned your lesson" and work carried on.
Edit: Or another one of his stories along the lines of British Steel's: somebody in his highschool welding class dropped a compressed gas cylinder unloading it out of a truck, sheared the valve off and they watched it punch through a foundation wall of a house under construction in the field next door.