Hi Emie1,
The guest left a wooden chopping board on the hob and left the hob turned on a low heat. Over the next 36 hours it presumably heated up and eventually ignited. Airbnb's limited communications so far have simply tried to wash their hands and said we are not even eligible for the Host Guarantee because the fire occurred after the booking period! I find that quite outrageous!!! Also also just plain wrong according to their own T's and C's. But we'll see what happens there.
I called the guest on the morning when we found the fire and of course they were shocked to hear what they had caused but they haven't responded to any communications since. As @Mike-And-Jane0 have said get your own insurance. Now that I've read through Airbnb's Host Guarantee's pages of T's and C's that are so full of exclusions and limits that it is unlikely to be of much use unless in very specific cases and you have to document everything. Also there is no appeals process if Airbnb make a decision to suit themselves (a least the insurance industry is regulated) and the process can take 3 months. I don't think anyone should be relying on the Host Guarantee. For a large amount of damage like we have you need professional loss assessors to itemise the damage, basically the entire contents of the house in our case, damaged walls, ceiling, floors, furniture, electrics, plumbing, cleaning costs, restoration costs etc etc etc. Trying to do this through Airbnb would be impossible and take forever...