A “Toolbox” for Forensic Engineers

Component Failure in Road Traffic Accidents 339
Figure 10.16 Bulb from motorcycle headlight showing fragment of glass adhering
to filament.
Figure 10.17 Bulb from rear headlight of car.
part of this filament must have been heated above this temperature in the
middle of the coil by radiation from the main beam filament but the junction
at which it connected to the support post where the fracture occurred had
been below the ductile/brittle transition temperature.
The above evidence thus establishes conclusively that the motorcyclist
had been riding on main beam when the collision occurred.
Figure 10.17 shows the bulb from the rear headlight of the car, found
not to be working when the lights were tested after the accident. This is
photographed against a black background in order to show up the yellowish/white
tungsten tri-oxide coating toward the ends, but there is also dark
blue di-oxide over the center left-hand side. This evidence shows that the
filament had been incandescent when the glass envelope was cracked and air
entered, but the filament cooled rapidly and did not break until its temperature
had fallen below 340∞C. Inertia force from the collision had caused the