For years I have heard that batteries could explode. The action of a
battery involves breaking water down into hydrogen and oxygen which is an explosive mix so of course an explosion is possible but I regarded it as a possibility that could happen but almost never does.
This is usually the case but when a battery is being charged more water is being broken down into hydrogen and oxygen and some of these gasses are vented through the vents of an older type vented battery to the outside. This can leave an accumulation of the combustible gasses around the outside of the battery and the vent hole can provide a connection to the gasses inside the battery.
My situation met all of the requirements for an explosion, but I wasn’t thinking about this. I had a charger on the battery and had disconnected it and was going to remove the battery. There was this accumulation of gasses outside the battery and I wasn’t thinking about that either.
I put my metal wrench on the nut on the positive terminal (Bad idea, as I have been told and have disregarded. The negative terminal should be disconnected first.) I pushed down on the tie wrench, and the end of the wrench touched a bare metal ground creating, what I though was, a tremendous electrical arc. The truth of the mater was that the sound I heard was a combination of an electrical arc and the explosion of the battery.
I looked down and saw that the top of the battery was blown off and I realized that everything, including me, was covered with battery acid. It was on my face and in my eyes and on the front of my coveralls.
I ran around to the back of the motor-home to the faucet and turned the hose on and squirted water on and in everything including my eyes. I got most of the acid washed off me and went to the front of the motor-home and washed the acid off everything there. I though that I had gotten water on my coveralls soon enough to save them; but in a short time, they began disintegrating. That acid is powerful stuff.
I had no permanent ill effects. My vision was slightly clouded at first but returned to normal soon.
Did I learn anything? You bet. Some of the things that you hear that can happen really do happen. Now I always disconnect the negative cable first and also follow the suggested procedure when connecting jumper cables.