During lunch and tea breaks, we usually gather underneath the old tree if the weather permits. We not only swap stories, but also actively indulge in engineering topics in an effort to educate Japie.
The other day, Hennie started our topic of the hour by mentioning the number of times he has seen batteries explode. When a battery is fully charged but still connected to the charger, any further input of current causes the water to dissociate into oxygen and hydrogen. This is a wonderfully explosive mixture and, if the crocodile clips of the charger are removed without switching off the charger, an explosion is very likely.
I capped that by saying that I once saw the oil vapour inside a tappet cover explode when one of the plug leads touched the metal cover. The tappet covers bulged and bits of cork gasket flew in all directions.
August mentioned that big marine diesels usually have special panels at the side of the crankcase. These are designed to pop out if the crankcase vapour explodes. This usually happens when a bearing overheats.