I was just about to mention this, I actually had a bag catch on fire in the microwave once. Its the dust that is in the popcorn that actually catches on fire. If this occurs, what ever you do dont open the door, this just gives the fire oxygen to burn. I had to replace the top inside of my microwave. It could have been a whole lot worse so now I just stick to the bags you buy with popcorn in them for popping.