After adding a bed of wood chips and a few logs, opening the air to max my stove experienced a 'blow back' where by it seemed to 'explode' in the firebox, smoke and some ash came out, but was otherwise apparently OK. I immediately opened the door a crack and allowed ventilation that way until the fire was underway. I have been careful subsequently to ensure the air intake is not 'suffocated' by wood chips (which I otherwise find an excellent fuel and excellent use of smaller tree limbs). What exactly caused the problem, and how can I avoid it in future?