Simple calculations show that the Teslas are roughly 25x more likely to catch fire in a collision, but I suspect they are much less likely to catch fire for other reasons. So just don't hit anything.
What's the error rate on that? I don't think we've seen enough Teslas involved in major accidents to even begin to determine how likely they are to catch fire compared to other cars.
You don't need to know the accident rate--you just need to know the rates of fire from an accident per car-year driven. Tesla doesn't have a long history here, but they do have 10K cars on the road.