Background
In Western Australia, personnel, including contractors, have been engaged to perform work associated with open pit wall stabilisation, wall control and geotechnical hazard remediation. Work involves personnel and specialist equipment working on or near pit walls (interim or final), using mechanical and rope access systems.
Activities include manual scaling using scaling bars or airbags, removal of geotechnical hazards by blasting techniques, installation of ground support and rockfall protection systems, ramp protection and reinstatement, erosion control, geotechnical instrumentation, mesh drapes and netting.
In March 2017, a fatal accident occurred at an open pit in Tasmania, involving four technicians working off ropes, manually scaling loose rocks from a pit wall in preparation for the construction of a catch fence. While they were standing on one of the berms, a large rockfall occurred directly above them, which struck one of the workers causing fatal injuries. The other three workers were able to abseil to the bench below.
In WA, four incidents involving near miss or injuries to persons working on walls have been reported since 2016. In all incidents, the consequences could have been far worse.
- In August 2016, six rope technicians were hand scaling a section of an open pit in readiness for meshing. A rock fell from above, striking one of the workers, resulting in injuries to his forehead, thigh and knee.
- In January 2018, two rope technicians were hydroscaling a section of a pit wall. The technicians stopped their task and began ascending the wall for a break when around 75 tonnes of rock fell from the wall. Two large rocks (approximately 2m x 2m x 1m) landed on the berm about 10 metres from where the technicians had been working.
- In November 2019, a section of the pit wall was being scaled using air bags in preparation for ground support. During the wall scaling, around 5000 tonnes of material was mobilised from the wall. Some material fell close to a crane that was operating on the pit floor near the designated exclusion zone.
- In January 2020, a rope technician was struck on the foot by a rock while scaling a pit wall with a scaling bar.
Summary of hazard
Hazards associated with working on walls include:
- wall failure above and below workers
- falling rocks
- falling from heights
- unknown condition of rock mass
- failure of rope or lifting equipment
- dropped objects
- incorrect use of equipment
- rotating parts (drilling rigs)
- manual handling
- exposure to heat, dust, and noise
- delays in emergency response/recovery.
Contributory factors
- Inadequate mine designs with poor control of excavation.
- Inadequate scaling standards and practices as part of the normal mining cycle.
- Inadequate ground support standards and practices as part of the normal mining cycle.
- Deterioration of the rock mass over time.
- Inadequate surface and groundwater management.
- Ineffective pit wall monitoring and interpretation of data.
- Working in close proximity to the pit wall.
- Workers in the line of fire of falling rocks either directly (part of the work team) or indirectly (ancillary activities).
- Inadequate geotechnical information and analysis, during planning and on an ongoing basis, to determine the hazards associated with the work being performed.
- Inadequate risk assessment and planning of proposed remedial works, including selection of proposed methodology and consideration of alternative options.
- Lack of, or inadequate, safe work procedures/work instructions.
- Inadequate training of rope technicians and other relevant personnel in geotechnical hazards and scaling.
- Ineffective determination of the size, location and extent of exclusion zones.
- Inadequate technical input and supervision of work teams at critical stages in the work plan and when changes occurred.
- Inadequate management of contractor work teams.
- Inadequate change management practices.