I'm really not sure how it happened cuz the door was shut and the air was already mostly closed. What happened was this. Reload it full (nothing new) things were going as expected. I closed the primary almost all the way and the top was 550 with nice flames. Came back about 3 minutes later and the Hellfire was in my living room. I closed the primary completely then check the top temp with ir gun 700 and the fire did t reflect any signs of slowing down within a minute or so. I grabbed my handy dandy roll of aluminum tape and covered 90% of the 3" air inlet in the back. The fire went down but not out and continued at a lower temp about 600 for about 10-15min then I remove some of the tape and she stablized and finished the burn without incident. Boy did she smoke through a lot of wood quick. What should have been a nice 5 hour burn turned out to be 3. So now the tape stays real close by the stove for those "just in case" moments.