Background
There have been several bridge and gantry crane incidents reported to the department involving loading of a crane beyond its rated capacity. In two recent incidents, a crusher bowl (still partially attached to the supporting structure) was being lifted by a semi-gantry crane to allow the bowl to be rotated out of its support using hydraulic powered equipment.
In the first incident, there was a catastrophic failure of the hoisting rope.
In the second incident, the load limiting system (i.e. weight overload protection system) did not stop hoisting when the rated capacity of the crane was exceeded. The load display unit indicated that the hoisting load had reached around 140% of the rated capacity before the emergency stop was manually activated by the crane operator.
Summary of hazard
Operating any crane beyond its rated capacity has the potential to cause a catastrophic failure of the crane, its support structure or both due to associated loss of control of the load.
When control of the load is lost, workers on or near the crane may be exposed to harm.
Contributory factors
Work practices
- Inadequate assessment of the mass to be lifted prior to attempting the lift.
- Inability to determine the mass due to the load not being free for hoisting.
Design and construction
- Failure to disseminate adequate information on the load limiting system by designers, manufacturers, importers or suppliers of the crane.
- Inadequate design, construction and installation of the crane allowing load limiting systems to operate at environmental conditions above the manufacturer’s recommended ratings (e.g. high operating temperatures).
- Inadequate fail-to-safe design and construction of the load limiting system (e.g. malfunction of load limiting device and associated electronic components could result in a loss of load control).
- Ineffective load display and warning devices when the load approaches or exceeds the rated capacity of the crane.
Commissioning and maintenance
- No calibration or incorrect calibration of load cells, load limiting and load display devices.
- Failure to perform functional testing of the load limiting device and its controls.
- Inadequate logging of service history data for preventative maintenance.