it was too easy, do not stretch the pole like that!
the stoves have almost always been in depression, the smoke extractor being all at the exit.
The explosion occurs either at startup or after flame extinction and maintenance of fresh pellets. The embers and / or the spark plug make the wood smoke, the fireplace fills with smoke and the appearance of the flame all these unburned gases burn up at once. Techniques to reduce the risk: 2 candles, ceramic candles, fireplaces powered from the bottom. The idea at startup is either to start more brutally, or there is less pellets above the candle. During operation, only the fireplaces powered by the bottom are completely safe. Others go back a little power mini to prevent the flame is lost.
In a wood-burning appliance, light the fire and close the air before it is well gone and the chimney draws well; the hearth is filled with smoke; give a little more air can be enough to reignite a flame and boom
The tank fire is usually due to a lack of combustion air due to lack of maintenance. The pellets burn too slowly, accumulate until the filling tube is filled. In general, the stove ends up mistaking itself and makes a stop cycle. an ember rolls up the tube, lowers the screw, and lights the tank. There must be a hundred cases a year in France.
This problem does not exist with watertight appliances, there is quickly no more oxygen and the embers are extinguished before reaching the bottom of the screw. Well-designed bottom feeding also eliminates this risk.