A “Toolbox” for Forensic Engineers

376 Forensic Materials Engineering: Case Studies
Figure 12.6 Beads of aluminum alloy in the heel of a boot, picked up by
walking on a floor close to metal casting operations.
working. He admitted that he did this from time to time but had no idea
where the barrels came from and said this job was usually done at night
because the furnace was in use by the other firms for car parts during normal
daytime hours.
His association with the beer barrel melting became clear after forensic
examination of metal particles found on the soles of the boots and on the
clothes he was wearing when arrested.
All the suspects’ clothes were brushed and a number of tiny particles of
metal were collected. In addition, there were numerous particles in the soles
of their boots, such as illustrated in Figure 12.6. Examination under the SEM
revealed that all were rounded particles characteristic of splashes and droplets
such as those emitted by molten metal running into open molds. Every one
of 20 samples taken from boots and clothing of all five men were found to
be aluminum alloy containing low percentages of magnesium and silicon.
This composition spread would include the alloy used for beer barrels, but
not the ones commonly used for automobile castings, which usually contain
greater amounts of silicon. Most significantly, no particle recovered from the
cable stripper’s clothing or boots was copper or lead but, even if there had
been any from this source, they would have taken the form of mechanical
slivers or clippings, not solidified droplets
The clothing exhibited numerous holes formed by hot particles landing
on them, particularly below the trouser knees. Figure 12.7A shows two holes
joined together in the side pocket of a nylon jacket worn by the cable stripper.
These had been formed by one, or possibly two, splashes of hot metal striking
the fabric and melting through the nylon. Figure 12.6B shows the lower leg
of corduroy trousers, where small hot particles had landed. These particles