WorkSafe Victoria recently issued a safety alert about the risks associated with falling objects after a failed rock bolt section fell on to a working platform.
A mine ventilation shaft was under construction with ground support being installed top-down through the use of a two-level work platform, and ground support included split sets, resin rock bolts and mesh.
A 450-millimetre rock bolt section failed and fell approximately 80 metres on to the work platform below.
The failed section included a retaining plate and weighed approximately 2.7 kilograms, and the platform had no overhead protection and employees were working on the platform at the time of the failure.
Metallurgical testing of the rock bolt section confirmed there were no compositional or structural faults.
The alert said the likely mode of failure was ductile overloading, and a geotechnical investigation did not detect signs of ground movement, stress or abnormal ground conditions.
All remaining rock bolts sections within the shaft were tethered to the surrounding mesh to prevent any further incidents.
The alert recommended ways to control risks and in order to reduce the risk of falling objects, the alert said mine operators must:
identify all potential hazards during risk assessments and assess the adequacy of all considered control measures including types of ground support and its potential to fail
review and, if necessary, revise the need for and adequacy of overhead fall protection should employees be potentially exposed to falling objects. This includes working in shafts.
Mine operators should also include a broad range of expertise when developing risk assessment teams to ensure all aspects of risks are considered.