Semi tippers overturning while unloading

WorkSafe is issuing a reminder about the risks associated with unloading trucks, after two recent incidents involving semi tippers rolling over at mines.



The first incident involved a semi tipper rolling onto its side whilst unloading roadbase on a downward sloping roadway. Material that stuck within the trailer while it was being raised contributed to instability. The operator was restrained by a seat belt and was uninjured.

The second incident involved a B Double truck’s front trailer rolling on its side while unloading gypsum on flat ground. The material had consolidated as a result of being in the trailer for an extended period, causing it to stick in the trailer during unloading. The operator remained in the cab and was uninjured.

Semi-trailer with tipper trailer rolled on side.
Picture 1: Aerial view of semi-trailer with tipper trailer rolled on side.

Safety Issues

Hazards that may pose a risk to employee health and safety when unloading trucks at a mine or quarry include:

  • uneven, soft or unconsolidated ground
  • material consolidating within trailers 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."

- Source: Cement Concrete and Aggregates Australia

Unloading 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.

Ground view of semi-trailer with tipper trailer rolled on side.
Picture 2: Ground view of semi-trailer with tipper trailer rolled on side.

Recommended ways to control risks

To reduce the risk of trucks becoming unstable during unloading, employers (including mine and quarry operators) must:

  • identify all potential hazards before unloading
  • ensure appropriate safe systems of work are in place
  • ensure that systems of work are regularly monitored, reviewed and, if necessary, revised

Employers (including mine and quarry operators) should also:

  • include a broad range of expertise and personnel when conducting 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:

  • provide and maintain a working environment that is safe and without risks to health, so far as is reasonably practicable
  • 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, so far as is reasonably practicable

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

Further information