Tesla's fire issues have been a little worrisome, but in all cases, they aren't really defects with the vehicle.
- first one was road debris - in most cars this would at the very least cause severe damage and the fires were slow burning (vehicle alerted owner to problem, gave them limited power to leave freeway for about 30 seconds)
- second was crashing into a tree at 60+mph - occupants survived with minimal injuries and fire occurred after a long time - most likely electrical arcing in 12V system like in ordinary car
- third one was also road debris, car drove for 5 minutes with no problems and took another 5 minutes before fire occurred indicating it was attempting to manage the battery problem until it decided it could not do so
- fourth one was due to poorly torqued screws on charging socket where the plug connected due to electrician error, nothing to do with car
24,000 cars shipped, 4 fires, and two arguably not related to vehicle defects, that's about right for the average car.
I think it's probably wrong to assign a probability to EV fire and compare to ICE. Fires are probably, in the long run, going to occur at about the same rate. But when a petrol car has a fire, it can be engulfed in flames within 30 seconds, especially after an accident with fuel leak compared to battery puncture/connector arcing, an EV will generally burn a lot slower.