The cause of the Grosvenor mine gas explosion has been the subject of much conjecture at the recent Board of Inquiry. The conduct and subsequent findings of the inquiry have now been delayed but there are some facts emerging into the incident which are now irrefutable.
An investigation conducted by the Australasian Mine Safety Journal can now reveal the concerning events surrounding the incident that left five miners seriously injured.
We have learned of the troubling goaf conditions at the mine that saw a range of goaf drainage holes being taken offline for cleaning of flame arrestors prior to the ill-fated event. These actions reportedly contributed to a range of exceedances in the tailgate roadways of the mine.
AMSJ has confirmed that the Queensland Department of Natural Resources and Mines received a range of methane exceedance notifications prior to the ill-fated event. Learning that since the commencement of the longwall block (LW104) at the Grosvenor mine, there were at least 14 reported exceedances of >2.5% methane at various parts of the mine. These exceedances, while varying in duration, were communicated to the Queensland Mines Inspectorate in accordance with regulatory requirements under Section 344 (2) of the Coal Mine Safety & Health Act by Anglo American.
We also discovered that on the 6th March 2020, Anglo American sort approval from the Queensland Mines Inspectorate to commence operations in the Longwall Block and commenced mining around the 9th March 2020. The challenges from exceedances in the block were well known with Anglo submitting a range of reports to the Queensland Mines Inspectorate. Anglo had also formed a Gas IMT in the early stages of mining of the block following gas exceedances.
Among the range of gas exceedance incidences, a Queensland inspector of mines issued a directive to cease mining in early April 2020 due to compliance issues with the methane monitoring system particularly in the tailgate of the goaf. After a range of actions by Anglo including the drilling an injecting of goaf holes, the mine was given the approval to recommence mining on or around the 17th April 2020.
But challenges in gas management lie ahead. Just four days after recommencement of mining activities the mine recorded more methane exceedances, some peaking over 3% methane. Once again, the Queensland Mines Inspectorate and now the CFMEU Industry Health & Safety Representative were notified and further investigations and corrective actions were initiated to mitigate effects of methane exceedances in the block.
Anglo was busy initiating a range of changes in the block including addressing some issues with strata management at the same time the Queensland Mines Inspectorate were informed via reports of gas incidents at the mine.
But in the days immediately before the ill-fated incident that saw miners seriously burned, Anglo formed another Gas IMT to investigate and correct gas issues in the tailgate. There was a history of ongoing stoppages around 1st of May after elevated methane in the tailgate area of the mine.
On the day of the incident, there was reportedly a range of strata challenges emerging including rocks falling off roof supports but there had also been challenges in getting the shearer underneath the roof support. Tips had to be raised to improve clearances for the shearer to pass. There were also problems emerging in the strata with two main structures present in the seam. Mining had continued following the intersection of the faults with at times “creating a full face of stone.”
Back on the 2nd May, there is also significant available evidence in the form of cavities forming above roof supports on the working face with a large cavity reportedly being formed at the tailgate end of the longwall. This cavity presented as a possible source for accumulation of methane and a potential point for the ignition which resulted in the tragic event.
AMSJ understands that the mine’s undermanager had also been present on the working face in the hour before the incident and had observed conditions including issues with cavity management.
At approximately 1457 on the day the explosion occurred, it appears, the roof supports moved. A sensor detects 4.31% methane and trips the power to the face.
The cause of the ignition still remains a matter of conjecture as does the source of the methane but AMSJ understands that there is a high probability that the cavity formed at the tailgate end of the face was a potential source for accumulation of gas and subsequently, aligns with the location of the miners during the explosion.
Investigators will examine a range of conditions associated with the ignition including rock on rock, frictional ignition, spontaneous combustion, electrical sources, static discharges, damaged cap lamps and potential use of contraband material in the mine.
Issues associated with Goaf drainage have also reportedly been investigated including a vertical well approximately 6 metres from the working face. The overall goaf was reportedly draining around >4000 litres a second of methane prior to the event.
Investigators have not ruled out the movement of a well liner as a potential source of ignition.
While the inquiry into the Grosvenor mine explosion continues, from AMSJ’s investigations there is ample evidence to support multiple parties, including Government, Unions and Anglo American knew and understood the conditions existing at LW104 Block.
Those conditions were clearly complicated and technical argument may remain a future feature of the Board of Inquiry. In fact, the source of ignition may never be identified given the limited window of access to the mine prior to sealing of the panel and the available evidence before the inquiry.
The Board of Inquiry will continue next year after it has been delayed due to technical evidence and the potential implications for a prosecution of Anglo American and its’ management associated with the explosion.
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