I guess you could design trams or electric trains that cannot catch fire. Without fuel and batteries you do not need to have that much flammable things on board.
Plastic trim, seat and seat covers, liners, floors are all flammable, insulation on wiring, lots of stuff. An all-stainless steel interior would be very amusing, though.
While true, what causes the fires? That’s important. Non-electric vehicle fires are most often caused by external causes, not something inherent in the design or during normal operation.
Cooling system breaks down. Gas drips onto hot exhaust.