Some of the combustion experiences I've had with the FF are similar to those of
@Marctraider. I experienced combustion only seconds into the first draw of a cold unit, so it was not an issue of overheating.
I frequently use my FF in front of a mirror in a dark bathroom, so I can see the glow pretty well. One combustion event I experienced lit up the room pretty well as the flame flared in the bowl.
The other day, while using the FF in the dark in front of the mirror, I saw a small "spark" in the heating chamber, as if something had come in contact with the coil and was quickly incinerated. Fortunately I did not experience combustion, but it seemed to me that if the "spark" had made it's way through one of the holes in the metal plate and into the bowl it could have ignited the material in the bowl.
FWIW, I have not experienced combustion since I started using the seven hole screen "disc" that others in this thread recommended (sorry I can't remember what they're called, but they're in this thread somewhere
). It may just be luck though...