Background
Since January 2018, more than 180 interactions with windrows (or bunds) have been reported on Western Australian mine sites. These involved vehicles breaching windrows, with incidents resulting in injuries to workers and one fatality.
Windrows are a safety device to prevent workers in vehicles, and those working in the areas below, from being exposed to more severe hazards when a vehicle has a loss of control. Regulation 13.7(5) of the Mines Safety and Inspection Regulations states that "the manager of a mine must ensure that an adequate windrow or bund of material is provided on the outer edge of roadways in the open pit and on the outer edge of any roadway on the surface adjacent to a bank or steep slope".
Mines inspectors have identified more than 150 defects and issued notices related to the inadequacy of bunds or windrows. An analysis of serious injuries and fatalities in the last two years shows that:
- in 80% of cases, the windrow was not adequate for the vehicle impact
- in 60% of cases, the vehicle was not travelling parallel to the windrow, impacting the windrow perpendicular to, or up to an angle of 45 degrees.
Summary of hazard
Inadequate windrows expose workers to additional and greater hazards on a mine site than the original vehicle loss of control. These include:
- falls from height as a vehicle breaches the windrow and descends the adjacent steep slope
- impact with obstacles protected by inadequate windrows
- vehicles entering water filled pits or tailings dams
- vehicles cartwheeling or unintended rollovers
- workers beyond or below the windrow/incident being exposed to falling objects and/or the vehicle.
Emergency workers involved in the retrieval of injured workers and damaged equipment are exposed to increased risks as they work on unstable vehicles and slopes.
Contributory factors
- Not engaging competent person(s) to design the windrow and roads.
- Inadequate design of critical windrows for T intersections, downhill ramps and sharp corners.
- Failure to assess alternatives to windrows such as vertical face forms and other barriers. Inadequate analysis of the geotechnical parameters for material used in building windrows.
- Road layouts that allow excessive speed impacts with the windrow and near perpendicular impacts.
- Inadequate specification and supervision of windrow construction.
- Narrowing by undercutting or pushing up the windrow during road maintenance or bench preparation activities.
- Maintenance activities or erosion resulting in loss of effective windrow profile, shape and height.