Which of these is NOT a common cause of vehicle fires?

2.21.1 – Causes of Fire
The following are some causes of vehicle fires:
After Accidents. Spilled fuel, improper use of flares.
Tires. Under-inflated tires and duals that touch.
Electrical System. Short circuits due to damaged insulation, loose connections.
Fuel. Driver smoking, improper fueling, loose fuel connections.
Cargo. Flammable cargo, improperly sealed or loaded cargo, poor ventilation.
[Commercial Driver’s License Manual]