A story from my grandpa, an EN3 on the USS Laffey DD-724, paraphrased by me... --- You see, ships like the USS Laffey were powered by steam. High-pressure steam ran through the ship. When something needed to be fixed, you turned the steam off and tagged the line so no-one turned it back on, then you fixed the part you needed to, then you took off the tag and turned the line back on. Well, one day, someone went to service something (note from me: he never said what it was the guyy was fixing) and followed standard protocol: well, almost. He turned off the line and FORGOT to put the tag on. Unsurprisingly, someone else who walked by that panel noticed that a line was off with no tag. They turned it back on. They could hear the poor guy's scream halfway across the ship. They had to send him home, but luckily, his injuries weren't fatal. --- My grandpa (not the subject of this story) died of cancer in June of this year. (2016 if you're reading this in the future)