A “Toolbox” for Forensic Engineers

Failure Due to Manufacturing Faults 159
This type of failure could, and should, have been avoided if a solid rivet
incorporating a shoulder or an external spacer had been used.
5.9 Scaffolding Guard Rail
This case does not strictly belong in this chapter but litigation was already
in progress to recover damages from a manufacturer on the grounds of
product liability, when a metallurgical investigation revealed that an allegedly
faulty casting was not responsible for a serious accident. The circumstances
were that an installation engineer fell from a scaffold tower and suffered
serious injury while installing an air conditioning unit in the roof space of
a shopping mall. He was working from a demountable scaffold. These are
structures that can be erected quickly by snapping together lengths of aluminum
alloy tubes and frames (Figure 5.21). The tubes have a C-shaped
hook at each end and are locked onto the frames by a spring loaded claw, so
all that has to be done to erect the scaffold is to press the hook over a crossing
tube so that the claw springs shut and holds the tube in position. To dismantle,
a trigger is lifted that opens the claw so that the tube may be lifted off.
The case pleaded was that the scaffold was defective in its material parts
and was inadequate in that it was “of insufficient strength and made of
unsound material,” despite the fact that such scaffolds were, and still are,
widely used. The specific allegation was that the end of a claw at one end of
the guard rail above the platform had broken off as the engineer leaned
against it, due to a manufacturing defect. As a consequence of this sudden
fracture the guard rail swung outward pulling the claw at the opposite end
Figure 5.21 Aluminum scaffolding showing mode of construction.