On certain passenger vehicles. If the engine fails to start and the driver holds the key in the "start" position for an extended period, high current flows through the ignition switch, and sometimes produces enough heat to melt internal switch parts.
Risk: If the switch is damaged, a fire could occur in the steering column, even with the engine off and the key removed. The fire could spread to the interior of the car, which could injure occupants or cause damage to adjoining structures.