Hurricanes Katrina & Rita: Fires?

After having been glued to the TV for the last few weeks watching news coverage about Hurricane Katrina, and now started to catch coverage on Rita's landfall, I've gotta wonder where all these fires are coming from. How is it that when people evacuate, things start burning? It's like the presence of a warm human body keeps the flames out. I'm sure there's a law of thermodynamics that can explain this.

Good luck with Round 2, Louisiana. Good luck with Round 1, Texas.