Incident Investigation- Tower Crane Failures
Health and Safety Executive (HSE).
Each year we are asked by HSE to provide forensic support to
over 200 serious industrial accident investigations. Some of these
investigations arise from the failure of the many different types
of crane in use on industrial sites in the UK and, of these, the
collapse of tower cranes is probably the most catastrophic.
What We Did
The collapse of two tower cranes
in less than four months at sites in south London and Liverpool,
tragically took the lives of two workers and one member of the
public. The same company supplied both cranes, and HSE took the
precaution of prohibiting the use of cranes of this type until
their safety could be independently demonstrated.
HSL was called to the scene at an early stage in both
investigations. At one location, our mechanical engineers and
specialist photographers spent seven days on site, carrying out a
detailed examination of the collapsed structure and observing
recovery operations. The jib slewing rig and sections of the mast
were brought to HSL for further examination, a major logistical
exercise involving a fleet of seven lorries. Although the mechanism
of failure was quickly diagnosed, it became necessary to carry out
full-scale loading tests in order to validate the proposed failure
scenario. A crane test rig was therefore constructed on one of
HSL's outdoor test pads to replicate the upper part of the tower
crane assembly and a series of load tests were carried out. In
addition, a series of cyclic load tests were carried out in the
laboratory using a servo-hydraulic test machine.
At the other incident the HSL team was on site for nine days.
Here the recovery operation was hampered by high winds and the need
to free some of the evidence from concrete that had set after the
collapse. In this case the laboratory examination was less
protracted and, by eliminating a number of potential scenarios, the
failure was attributed to wind loading.
Understanding the cause of accidents is key to preventing their
recurrence. Both investigations led to a better understanding of
the behaviour of tower cranes under load and indicated the need for
additional research. In addition, the construction industry has
been reminded of the requirement for regular inspection of tower
cranes by a competent authority.
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