Back about 40 years ago when I was a couple years in the mechanic field working at Kmart Auto I had the hood open on a late 70`s Ford truck. When I went to start it the battery blew up and soaked everything under hood and the mechanic next to me. Lucky it was on his back and not his face. The whole battery top was gone and the cables still hooked to the standing plates.
Similar tale. Back when I was managing the NAPA store in Savage, MN, we had a P/T, evening parts delivery driver (high school kid) who desperately wanted to work his way onto the counter. Good kid. Energetic, enthusiastic, and always wanted to learn. (Kind of ashamed to admit I can't remember his name right now, but we called him "Opie", as his father was a cop.) Anyway, one evening someone carried-in a dead battery for warranty, and NAPA's policy was (and may still be) that all dead batteries had to be charged before they could be tested.
We had a small workbench right behind the rear wall (the one behind the counter) where we did alternator and starter testing, and the battery charger was mounted on the wall there as well.
Somehow Opie got involved with this customer, and he carried the battery back behind the wall, set it on the bench, and hooked it up to the charger....but with reversed polarity. Opie leaned over, threw the switch on the charger....and you can imagine what happened next.
Since he was leaning way from the battery, Opie wasn't hurt, thankfully, as the battery blew "upwards". But it did scare the hell out of him!
And we had quite a mess to clean-up back there.