1. An operator made a mistake and opened the wrong valve during a routine operation. 15000 liters of hydrochloric acid flooded the factory. As the flood started from the side with the emergency exits, it trapped the workers, 20 people died horribly.
2. At a chemical factory, the automated system that handles tank transfers was out of order. A worker was operating a manual override and attempted to open the wrong valve. A safety interlock prevented this. Violating procedure, the worker opened the safety interlock, causing 15000 liters of hydrochloric acid to flood the facility. As the main exit was blocked, workers scrambled towards an additional emergency exit hatch that had been installed, but couldn't open the door because a pallet of cement had been improperly stored next to it, blocking it. 20 people died horribly.
If you look at them in isolation, the first looks like just one mistake was made, while the second looks like one grossly negligent fuckup after another, making the second report look much worse. What you don't notice at first glance is that the first facility didn't have an automated system that reduced risk for most operations in the first place, didn't have the safety interlock on the valve, and didn't have the extra exit.
So, when you read an incident report, pay attention to this: If it doesn't look like multiple controls failed, often in embarrassing/bad/negligent/criminal ways, that's potentially worse, because the controls that should have existed didn't. "Human error took down production" is worse than "A human making a wrong decision overrode a safety system because they thought they knew better, and the presubmit that was supposed to catch the mistake had a typo". The latter is holes in the several layers of Swiss Cheese lining up, the former is only having one layer in the first place.