A “Toolbox” for Forensic Engineers

Accidents in the Workplace 275
The sharp corner in the molding had initiated the crack and it represented
a possible design defect if it had failed and caused the accident. Sharp internal
corners are commonly present in many molded products, but are not necessarily
defects unless it can be shown that these features cause product failure
and hence accidents.
8.4.2 Ladder Stability
How was the ladder being used at the time of the accident? The key variables
are the angle of repose of the ladder and the coefficient of friction between
the feet and the ground. A visit to the site of the accident was essential, so
the witness statement could be checked, and any further evidence that could
clarify the circumstances could be examined directly. The visit showed visible
evidence of the intermittent contact between the tips of the ladder and the
wall below the window, and the traces of an impact with the small sill above
the patio doors. The trace contact marks corroborated the witness statement,
showing how the tips and hence the ladder structure itself had oscillated from
side to side as it slipped down the wall. No traces of marks from the feet on
the concrete slabs of the patio itself could be found. The angle of repose and
coefficient of friction of the feet remained unknown, however. A reconstruction
of events was essential to measure or calculate the data using the actual
ladder itself.
8.4.3 Reconstruction
Although the injured user attempted to guess the information requested
(especially the angle of repose and degree of extension of the ladder), it is
always best to measure independently. After traumatic injury, an individual
is more likely to forget such information, even if, in normal circumstances,
they could recall such details. The ladder had not been photographed in situ
just after the accident. There were no trace marks of the feet on the patio,
from which the extended length of the ladder could be inferred. However,
there were some key bits of information that seemed indisputable: the tips
of the ladder were resting on the sill, at about 16 ft (3.69 m) from the ground
(as measured directly during the site visit).
The events were reconstructed using the ladder fitted with new tips, and
started by assuming the ladder was fully closed since this fitted the known
facts. Another ladder owned by the investigator was placed by its side for the
purposes of comparison and safety during stability tests. The aims of the test
were as follows:
1. To estimate the static coefficient of friction of the feet