Summary: The Resources Regulator has been made aware of an incident that occurred in Western Australia recently on an elevated work platform (EWP).
The telescopic boom “uncontrollably retracted under its own weight approximately 8 metres and stopped on its hard limit”. The unplanned movement occurred due to the failure of two wire rope cables that controlled the boom during the retraction function. An investigation found that the retraction cable mechanism was not maintained to the manufacturer’s specifications, the ropes were not captive in the pulley sheaves and it was evident that one cable had been severed for some time.
The retraction cables are inside the telescopic boom section and cannot be inspected visually without disassembly. The detection of rope failure relies on a broken cable indicator system (proximity sensor) to detect excessive movement of the rope as well as a schedule of maintenance and inspections to ensure correct alignment, adjustment and function.
Recommendations to industry: The circumstances of this failure demonstrates the importance of completing maintenance and inspections as specified by the manufacturer. Mines using EWPs must ensure that all maintenance and inspection procedures are completed including those applicable to the concealed rope and sheave mechanisms that control boom retraction.