To me it looks obvious where the fire originated. Look at the white at the bottom of the door around the area that Ron L points out in the pic. I agree with you Ron. Having cooked on FEC's for seceral years now, I understand these cookers. Also, having two of these burned up on me. I do agree that the drip pan is in a location that would have caused the pooling of renderred fat and allowed it to leak down to the ignition source and cause the burn.
But, also having said that, I have seen the pot overfill itself with pellets and then take fire, only to burn up the inside. This is what happened to mine both times. I had just put two butts in my FEC100(which was new). The butts were 36*F internal. I set the temp of the pit to 224*F at 12:30am. I went to bed only to be woke up from the smell of a burning gasket on the cooker at 2:00. The butts were charcoal. Someone explain that on. 1 1/2 hours to take two butts from 36* to crisp black charcoal? How about that circuit board having a issue maybe?