These were my thoughts, posted awhile back.
"I'm thinking that the explosion is caused by the occasional build-up of flammable gases released by the wood as it smolders but doesn't burn outright. The low heat and low oygen levels in the smoker don't normally allow them to burn with a flame. Mostly they go up the flue fast enough not to accumulate.
However, once in great awhile, the gas concentration builds up to a point where the proper ratio of gas to oxygen is just right and it goes off with a bang. Just like propane won't explode unless the correct mix of air and gas is reached: Too much or too little of either and no boom. I believe that's why our smokers don't pop too often. My AmeriQue hasn't blown once--maybe because it has two vents and smoke and gases moves through too fast.
May have to do with the type of wood. Not sure. Has anyone noticed which woods "bang" the most? Also, do new smokers belch more than older ones? Maybe the door seal gets better with time and gunk and won't let in enough air.
Wow! Way long answer. Anyone still reading?"