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Coal Inspectorate | Bulletin | No.212 V 1 | 04 April 2023

Overburden drill rollover – Investigation summary

What happened?

During a night shift on 14 September 2021, two Coal Mine Workers (CMWs) (maintainers) arrived at an overburden drill rig to inspect and repair a reported oil leak. In preparation for the repair, the machine was washed and jacked to near full height with the mast raised. The two maintainers were standing on the deck of the machine and the operator was in the cab when the drill began to slowly topple, coming to rest on the drill cab side, and making contact with an adjacent light vehicle (refer Figures 1 & 2).

The operator and one maintainer exited the drill safely. The other maintainer was trapped between the deck handrail and the light vehicle parked beside the drill. An emergency was initiated, and the Emergency Response Team (ERT) assisted with the safe recovery of the trapped maintainer.

How did it happen?

Events leading up to the incident

Prior events

Key issues

The investigation identified that the toppling of the drill while on levelling jacks was caused when the maximum lateral stable angle of the drill was exceeded. Contributing factors were:

The investigation identified that the cab side hydraulic levelling jack cylinder piston and rod seals were severely worn, failed to carry the load and were unlikely to support the drill. Testing of the cylinder showed the hydraulic system operating pressure and cylinder relief pressures were well below what is required according to the operating manual.

Survey data coupled with the jack extension measurements taken after the incident, indicate that the drill was outside safe working limit design parameters for roll/tilting.

Stability alarms installed at the time of the previous incident did not alert the operator when the drill was positioned outside the equipment design parameters, when supported on levelling jacks.

Drill training requirements did not include information related to the safe operation of jacks including risks associated with imbalance between jacks.

The maintainers intended to inspect and be underneath the drill whilst it was raised and only supported by the hydraulic levelling jacks.


All Site Senior Executives should:

  1. Review and update as required, site processes and standards for the introduction of equipment to:
  2. Update site standards, related documentation and training requirements, and communicate this to all affected CMWs.
  3. Ensure CMWs are aware of the risks associated with working under suspended loads unless appropriate jack stands are in place.
  4. Implement and monitor systems which validate that CMWs are following the requirements of the documents held in the Safety and Health Management System to maintain an acceptable level of risk.

OEMs and third-party suppliers:

Authorised by Shaun Dobson - Chief Inspector – Coal

Contact: Anthony Logan, Senior Inspector of Mines , 0477 373 213

Issued by Resources Safety & Health Queensland

Safety: This information is issued to promote safety through experience. It is not to be taken as a statement of law and must not be construed to waive or modify any legal obligation.
Placement: Place this announcement on noticeboards and ensure all relevant people in your organisation receive a copy, understand the content, findings and recommendations as applicable to their operation. SSEs should validate that recommendations have been implemented.

All information on this page (Overburden drill rollover – Investigation summary - is correct as of time of printing (31 May 2023 9:07 pm).