Was that a clip top drum that imploded? I'm amazed it built up that much of a vacuum, without sucking air through the top. I suppose maybe once it had started to vacuum, then it helped hold the lid on. Still, I'd have expected the drum rim or lid to distort a little, before it squashed it like that.
Nice page by the way.
When I made my now infamous soap batches,
I pumped 200L of hot (60°) mayo into an empty 205 clip top and put the lid on to stop meth fumes from escaping.
As it cooled it sucked the lid down and distorted the drum, I couldn't get the lid off even when leavering it with a crowbar,
I then put a small hole in the lid with a 6" nail and the lid lifted off with ease.
So yes the lids do seal very well, even bettor with a small amount of negative pressure.