I think Tesla has a problem.
There are only about 17,000 Tesla Model S on the roads right now, but there have been 3 fires due to damage to the battery. In two of these cases, it looks like the damage was mostly to the underbelly, and not due to a severe impact to the frame of the car.
In the third case, in Tennessee, the car apparently hit some debris, which caused a fire to start in the front area of the vehicle. If you look at the photos, which I scraped off of the web, there does not appear to be frame damage. In other words, the guy didn't hit another car, or a large stationary object. He hit something small, but it destroyed his Tesla.
By comparison, a gasoline vehicle can run over pretty severe piece of road debris without catching fire.
I wish I had statistics for vehicle fires, caused by driving (not arson, forest fires, etc.), in vehicles less than 2 years old. That would really put the probabilities in focus. I am not sure where to get such data, it is possible that IIHS has it.
In each of these cases, the vehicle is basically destroyed. Even if driver safety is not necessarily an issue, the cost to insure against a battery fire is going to drive up Tesla owner's insurance costs.
If these incidents continue to mount, Tesla is going to have to do several things to protect their business and consumer confidence. They will likely have to add additional shielding to the underside of the car, adding cost and weight, and possibly reducing range. They may also have to increase ride height.