These are interesting to watch - just to try to figure out exactly the moment this was doomed to happen...

So the crane operator set the bucket on the pad and then a guy walks around fiddling with stuff - releasing safety latches?

Then, the crane operator tries to get the bucket handle off by moving the crane and hoping (?) the handle will drop off, which it doesn't - probably because one of the latches didn't unlatch, so he gives it some more sideways motion and splish splash, the foundry is taking a molten bath...

Wonder how many times he had done that goose the handle move before this one...