Several years ago one exploded (motorcycle battery) in my kitchen. It did quite a lot of damage. The expelled acid burnt holes in almost everything.
Luckily I was out ( I was single then) and the insurance picked up the cost.
I always now make sure the battery is in a safe well ventilated place and I take all of the caps out before I start to charge.
They are pretty dangerous things - mine exploded due to a fault in the charger.
