A mine ventilation shaft was under construction with ground support being installed top-down through the use of a two level work platform. 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.
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 likely mode of failure was ductile overloading. 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.
Note: The images above display the rock bolt section and its original position in the ventilation shaft.
Recommended ways to control risks
To reduce the risk of falling objects, 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.
Under the Occupational Health and Safety Regulations 2017 (OHS Regulations), mine operators must:
- so far as is reasonably practicable identify all mining hazards at the mine and assess associated risks with all mining hazards
- so far is reasonably practicable, eliminate any risks associated with mining hazards, and if it is not reasonably practicable to eliminate all risks associated with mining hazards at the mine, the operator must reduce the risk so far as is reasonably practicable
- establish and implement a safety management system for the mine, which provides a comprehensive and integrated management system for all identified risks
- review and, if necessary, revise the safety management system at least once every three years, as well as before a mine modification is made or after an incident involving a mining hazard occurs.