I feel like it's been covered pretty well that there are some mechanics for fire starting, but no rules to handle starting a wildfire or the way it spreads. It becomes a story process more than a mechanical process at that point.

But I'm replying to this thread anyway because I think that it's a really compelling story process that sets up a lot of immediate tension as well as long-term story repercussion and I wish people would post requests for RAW guidance on interesting things like this more often.