I once set fire to some cheap photographic paper in a darkroom, watching the resin coating crackle before extinguishing the flame and sticking the paper in the developer. The result was very strange, difficult to describe and I almost burned down the whole room trying to replicate the effects with absolutely no success. Something I do not recommend anyone trying. Seriously.
Anyway, on Tim Atherton's blog I read about Chris McCaw who allows the sun to burn his film and then prints the results, which I find very evocative.
Starting fires outdoors is much safer than in a room full of chemicals and paper. Trust me.