Mobile plant rollovers in quarries

WorkSafe is issuing a reminder about the risks associated with mobile plant operating over uneven ground after multiple recent incidents involving rollovers at quarries.



In recent months' WorkSafe have been notified of a number of incidents involving mobile plant rollovers at quarries. The rollovers reported involved a bulldozer, drill rig, water cart and trucks. The truck rollovers occurred during tipping activities.

Fortunately, in all cases the plant operators did not suffer any injuries. Whilst the incidents have occurred across multiple sites and operators, a common causal factor identified has been the operation of plant over uneven, inclined or unstable running surfaces.

Safety issues

Hazards that may pose a risk to employee health and safety when operating mobile plant at a mine or quarry include:

  • uneven, soft or unconsolidated ground
  • material consolidation within trailers prior to unloading due to retention times and/or physical property change
  • slippery or low traction surfaces
  • overhead powerlines or structures
  • faulty or misused braking systems
  • nearby mobile or fixed plant

'Unloading' in this safety alert refers to the process of discharging the entire load of material from a tipper truck. The process of unloading starts as soon as the body rises from the chassis and continues until the body lowers to a stable position.

Unloading trucks on a downward slope, with the cabin at the downhill end, increases the potential for material to remain within a trailer whilst raising the plant's centre of gravity. It is important to recognise that this may significantly reduce overall stability.

During unloading, material may consolidate within trailers. If plant is positioned on uneven ground, this consolidated material may cause the plant to become unbalanced and rollover.

Controlling risks

To reduce the risks associated with mobile plant becoming unstable during unloading, employers (including mine and quarry operators) must:

  • identify all potential hazards before mobile plant operation
  • ensure tipping locations are level and adequately compacted to support the plant
  • ensure appropriate safe systems of work are in place
  • ensure that systems of work are regularly monitored, reviewed and, if necessary, revised

Other recommended ways to control risks

  • Include a broad range of expertise and personnel when conducting a risk assessment to ensure all aspects of risk are considered.
  • Ensure that tipping areas are level and stable.
  • Ensure that the density and flowability of material being unloaded is known and understood.
  • Ensure that material in trailers is monitored while unloading to check whether it is sticking in the trailer.

Legal duties

Under the Occupational Health and Safety Act 2004, employers must so far as is reasonably practicable:

  • provide and maintain a working environment that is safe and without risks to health
  • provide such information, instruction, training or supervision to employees of the employer as is necessary to enable those persons to perform their work in a way that is safe and without risks to health
  • ensure that persons other than employees are not exposed to risks to their health or safety arising from the conduct of the undertaking of the employer

Under the Occupational Health and Safety Regulations 2017, employers must eliminate, or if not reasonably practicable, reduce the risk of powered mobile plant overturning.

In addition, mine operators must also:

  • identify all mining hazards at the mine and assess associated risks, so far as is reasonably practicable
  • implement controls that eliminate risks associated with mining hazards or, if not reasonably practicable to do so, reduce the risks so far as is reasonably practicable
  • review, and if necessary revise, the identification and assessment of risks associated with mining hazards, and the risk control measures implemented.