Seen batteries bulging and burst but Neva witnessed the event. Have seen HUMVEE tires being aired up improperly and not in a cage and the aftermath of those booms tho.
When I was young, and was just getting rid of adolescent acne, I worked in a shop where we had performed work on a Camaro. (Ain't it funny how one can remember silly details germane to a BAD event?!)
When we went to start the car, post repairs, the battery was weak, and the starter struggled to even turn the engine over. So, I grabbed the roll around battery charger and set it up, and chose "Start/Boost" on the dial, and was under hood when the other mechanic got in the car and hit the key.
"BOOM" went the battery, spraying me down with battery acid. The burning was excruciating, and I got stripped down to my undies in the 25 or so feet to the bathroom (where we kept our uniforms).
In the bathroom, I was able to grab paper towels and take a sponge bathe, so to speak. My glasses had shielded my eyes, and I was EXTREMELY fortunate that my fast actions mitigated any serious scarring. I still have a few scars, but they ARE minor.
I don't know if I offended anyone for disrobing in the manner I had, but didn't care then and certainly do not now. I got a fresh uniform out of my locker and put it on and went back to work.
Years later, I had a second battery explode on an '84 Suburban with a Diesel. Fortunately, I was across the front of the vehicle from the one battery of the 2 and was unharmed.
I REALLY do respect the battery these days when I'm working on cars.
As a post script: I witnessed a car fire once when working in a full service gas station as a mechanic. One day, during my break, and during a slow moment, I was up in the glassed in office area chatting with the guys. Our attention was diverted when a car at the intersection in front of us caught fire. Th owner bailed out, we called 911, and here came the fire brigade post-haste.
When the fire truck arrived, a young firefighter got out with a pinch bar and commenced to pry the hood open (where the fire originated). An older Captain grabbed the young buck and pulled him away from the burning car, yelling at the young'un all the while.
As these 2 and other firefighters stood about 20 feet back, there came a very loud explosion from under that hood.... It was the battery. Then they pried the hood open and put out the fire.