Little Explosion in the Hyfire

I want to make this sweet and short, the better-half just told me that Friday night she heard a Explosion inside the coal stove,sounded like something hit the wall of the stoker from the inside. Well i have been thinking about this all heating season, i had my bulk coal dumped in my limestone driveway with plastic under it. Well scoupping and hand shoveling it up to put into the coal bin i may have grapped some limestone along with the coal. I do know that if you heat a piece of limestone with a torch it will pop,,,and to the better-half that would be a Explosion I've checked every thing out and every thing else looks ok,,,maybe with the warmer temps the chimney wasnt drafting like it should have been ( i have been keeping close watch on it since it warmed up, i'am always checking the draft with the guage ) and is it possible i had some gases build up and blow like a hand-fired stove ? I'am really leaning towards a piece of limestone theory, Like i mentioned earlier, i've thought about this all heating season ( trying to make sure there was no limestone in the coal ) My biggest worry was one would pop and brake out the glass window,,,, then what would happen ? Well i think i may have slacked some toward the end of the season,,,,,,,,,,

The limestone theory may be true. When we layed some limestone veneer from Ohio, when cut or broke it would smell like sulfer or petrolium. I don't know if stone itself would explode, but if there is moisture in the stone the moisture will make the stone expand and pop/crack.

Usually doesn't happen in a stoker, maybe you got a piece of limestone or a rock and it got hot enough to explode or pop. Usually you don;t get much if any volatiles in a stoker that would cause and explosion (you just see the blue ladies dancing and burning off), since you have an open flame all the time, unlike a hand fed when you load it up and you have to burn off the volatiles and if you smother the flame a bit, take a bit to get re-ignited.