1 Head Death: Ah, Fireballs. Sit down.
2 Head Death: I hear you collected a second person killed by an insanely overpowered fireball. Kyros again?
3 Death of Insanely Overpowered Fireballs: No, sir. It was non-magical conflagration caused by a lovable rogue. It got into the coal cellar, where there was a lot of dust, and...
4 Head Death: Yes? And?
4 Death of Insanely Overpowered Fireballs: With all due respect, I'll give you one guess, sir.

Coal dust can be highly explosive when suspended in air.

Not only coal dust, but many other sorts of fine powder can be explosive in the right circumstances, including wheat, barley, and other grain dust, corn starch, sugar dust, flour, powdered plastics, and powdered metal. Heck, confetti will probably explode if you use too much of it at someone's wedding.

Especially if Kyros is a wedding guest.