A “Toolbox” for Forensic Engineers

Accidents in the Workplace 267
Figure 8.6 One of several chipped teeth on dummy shaft.
hard brittle case broken by an oblique impact. As the outer corners of these
gear teeth were extremely hard (>900 HV), under relatively light blows the
exposed corners would be likely to emit tiny, sharp edged particles at high
speed.
Such a small flying particle would not have caused a penetrating eye
injury if eye protection had been worn. The injured man had been issued
safety glasses but he claimed the glasses did not stay in position when he was
working beneath a vehicle and spots of oil and greasy finger marks smeared
the glass and made it difficult to see what he was doing. There was a foreseeable
risk of eye injury given the tools he was using and the way he had to
work with his face so close to the object he was striking. However, no amount
of legal argument about whether or not the risk of injury was reasonably
foreseeable could ever compensate for the loss of his eye, although damages
awarded would be substantially reduced on the grounds of contributory
negligence.
The sad fact is there would have been nothing wrong with using the old
shaft as the dummy and the injury need never have occurred if the casehardened
gear teeth had first been softened by tempering.
8.3.2 Lath Axe
A self-employed building contractor was reslating a roof, using a tool called
a lath axe, illustrated in Figure 8.7. This has an axe head at one end and a
square-faced hammer head with serrations on the striking face at the other.
Since purchasing the tool several weeks before his accident the contractor
had noticed the outside of the hammer head had chipped in places, but he
had continued to use it, because it “was one of the best tools he had ever