When Plans Aren't Enough: Lessons from a Fatal Mud Rush

The most complex of all mining Geotechnical structures is the Sub-Level Cave (SLC). It’s designed to be an almost self-regulating system in which free-flowing broken rock, stable in-situ rock and induced subsidence adaptively interact and self-organise. As with all complex systems; it’s subject to continual change from the introduction of agents which can cause damage and disruption. In this article, an accumulation of water inside the SLC which infiltrated from outside sources caused a sudden and extreme release of rockfill, water and mud at an underground draw point, engulfing a Worker causing them fatal injuries.

In Findings, Comments and Recommendations of Coroner Simon Cooper following the holding of an inquest under the Coroners Act 1995 into the deaths of Craig Gleeson, Alistair Lucas and Michael Welsh - the tragic death of an experienced bogger operator in a mud rush incident at an underground Sub-Level Cave mine, despite comprehensive safety measures, offers critical lessons for the mining industry. Mud rushes, or inrushes of liquefied rockfill, were a known risk at this operation, particularly during high rainfall, and the mine had an extensive Mud Rush Management Plan and various administrative controls in place.

Existing controls included Trigger and Response Plans (TARPs), a Principal Mining Hazard Management Plan (PMHMP), risk zone categorisation, and regular supervisory inspections. Investigations confirmed that personnel were familiar with procedures, training was up-to-date, and controls were generally adhered to in the lead-up to the incident. Rainfall and water pumping, key indicators of mud rush risk, showed nothing unusual.

However, an important gap emerged: formal auditing of PMHMP compliance had not been implemented. While informal checks occurred, the judge recommended formalising these audits, aligning them with best practices like the 'New South Wales Code of Practice – Inundation and Inrush Hazard Management Guidelines'. This highlights that even with robust plans and trained personnel, a lack of formal, verifiable auditing can create critical blind spots, turning well-intended procedures into mere aspirations. In complex mining environments, consistent and documented oversight of risk management tools are paramount to preventing tragic outcomes.