Tragic 60 seconds: Mine blast findings released
Investigators have been unable to determine what sparked a central Queensland coal mine blast on May 6 that nearly killed five workers.
Mining giant Anglo American's internal investigators have pieced together a tragic minute in the underground Grosvenor coal mine that followed an unusually large release of methane gas.
Staff were briefed earlier on Wednesday on the findings but the mine remains closed as the company continues to review the safety of its operations.
Three of the injured miners have been released from hospital in the past fortnight, leaving one man in the Royal Brisbane and Women's Hospital in a stable condition.
Miner Turi Wiki was discharged about two weeks after the blast.
Investigators found that in the hours before the blast there had not been any non-compliant methane releases near the longwall face.
But at 2.57pm, as workers were shifting chocks, or hydraulics, a "significant over pressure event occurred", staff were told in a presentation.
"Around 13 seconds later a light flash was observed using the camera on the shearer towards the tailgate end of the face, and a second over pressure event occurred," according to investigators.
The source and point of ignition have not been identified despite nearby electrical equipment and potential spark sources being tested.
The initial gas release did not trip detectors, which would have automatically shut off power to the area, before the ignition, according to investigators.
Anglo American metallurgical coal CEO Tyler Mitchelson said it was "unacceptable" that five miners had been seriously injured and the company was providing them ongoing support.
He also committed to ensure that all "relevant leanings" from the internal investigation and a separate probe by the Queensland Mines Inspectorate would be incorporated across the business.
The company, which is Queensland's largest underground coal miner, has been reviewing its methane management controls and assessing new technology to improve safety.
"As a first step, we are beginning a pilot study at our Moranbah north mine to assess the use of pressure sensors to remove power from the longwall face as an additional control if a significant over pressure event occurs," Mr Mitchelson said.
He said the company had invested $230 million on gas drainage and management works at the Grosvenor mine since 2016.
"Despite this investment and extensive controls in place to prevent an underground ignition of methane we need to further improve our controls to respond to the specific combination of factors of an unusual and large over pressure event in the vicinity of the longwall with a potential ignition source," he said.
Originally published as Tragic 60 seconds: Mine blast findings released