Earlier this month, a Tesla parked in a Toronto garage caught fire. This does not seem to be charger related, as the Model S was not plugged in to a charger at the time. While Tesla fires have been in the news lately, this one was unique in that there was no collision involved.
Tesla said it has definitively determined that the Toronto fire did not originate in the battery, the charging system, the adapter or the electrical receptacle, noting that these components were untouched by the fire.
The battery is the underside of the car, somewhere between 5 to 10 cm thick. Placing the battery pack under the body will allow you (some time in the future) to drive to a battery swap station, and in 5 to 10 minutes, the entire battery pack for another one with a full charge.
Petty much all of the Tesla fires are either the result of a puncture to the battery pack (large, metal road debris or various types of collisions) or related to the charger. The fires burned in a controlled manner and put out by untrained firemen not prepped to combat a lithium fire in a vehicle. Most of the charging issues have not been fire related, but rather dead batteries after a night of charging, or vampire charging of unreasonable magnitudes (leading to bigger than expected electric bills). The charging issues have been address so far with software updates, and in a few cases new hardware.
When it comes to construction, the body and the side panels are all aluminum, joined by rivets, spot welding, MIG welding, and ridiculous amounts of adhesive. These things are build like aluminum tanks. I don't recall seeing any significant amount of composites on the body.