Getting to vital evidence in Pike River mine will cost $8m, mining experts say
Tuesday, 11 May 2021
An $8 million plan to get more evidence from the Pike River mine has been presented to the Government.
A group representing 23 families previously asked the Government to fully assess the risks and costs of recovering the main ventilation fan, considered a vital piece of evidence that may reveal the cause of the explosion that killed 29 men in 2010.
When the Government refused to spend any more money on the mine, the families asked a group of mining experts from around the world to develop a feasibility study for the project.
The Pike River Independent Technical Advisory Group, led by former chief mines inspector Tony Forster, presented the study to the Government on Tuesday.
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It said the recovery would cost $8m and take 12 weeks using standard mining techniques.
The Pike River Recovery Agency was tasked by the Government to complete a $50m re-entry of the mine’s access tunnel, or drift, which it achieved in February. It planned to hand the mine site over to the Department of Conservation in June.
Minister Responsible for Pike River Recovery Andrew Little previously said it would be a “technically phenomenal” task to go past the roof fall at the end of the 2.3-kilometre access tunnel because the area was “inherently unstable”.
The advisory group’s plan said the drift recovery team brought back new information that the roof fall was mainly coal rather than an extensive failure of the roof strata.
The furthest point the team reached was only a few metres from the junction to the main fan roadway.
It said having the main fan underground was unusual in coal mining and there were multiple reports of problems with the fan in the weeks leading up to the explosion.
The issues included serious technical commissioning problems, fan controllers overheating and non-certified, non-approved electrical cabinet doors being left wide open to keep components cool.
“If correct, this is manifestly unsafe and should have been remedied immediately or stopped, either voluntarily by the company, or challenged by the regulator using formal enforcement powers.”
It also said an independent technical report commissioned by the families in 2020, and provided to police, highlighted some unexpected findings, including electrical power loading at the moment of the explosion and a fault found to a feeder supplying the fan.
Police planned to put cameras down new boreholes down to examine the fan to aid the criminal investigation, which was reopened with the drift recovery. However, the experts said evidence from the fan could not be gathered remotely.
The group’s plan involved “conventional, well-proven mining techniques for excavating, supporting and stabilising the roof falls” by injecting a concrete-like foam into the void and supporting the roof with a new steel tunnel. It would be undertaken in fresh air using the agency’s existing ventilation system.
It said there was no evidence of increased ground instability as a result of the explosion or fire and geotechnical assessments showed “no known fatal flaws”.
In a statement, the Pike River Families Group said re-entry in this way would completely eliminate the risk of roof collapse, which was a serious risk associated with the police proposal.
“If the police borehole drilling creates a new roof collapse as it did at borehole 50, then their efforts will not uncover evidence, but will instead bury that vital evidence forever.”
The group said independent investigations by family experts also found problems with the power supply and sparking at multiple spots including the speed drive controlling the main fan motor.
It discovered a brass sealing ring had been removed from the fan, which allowed methane-enriched air to flow over electrical equipment, including the fan motor and associated control switches.
The remains of a non-explosion proof cabinet were photographed near the top of the ventilation shaft in 2010 but disappeared after being taken to the Pike River manager’s office, the group’s report said.
A section of the fan was recovered from the drift by the agency.
“The royal commission made many valid recommendations based on what they knew at the time but failed to identify the actual cause of the blast, so the international mining community is still none the wiser,” it said.
The families group said the recovery of the main fan site was “the most important forensic site within the mine workings”, asking the NZ Police, Government, and Pike River Recovery Agency to engage with the technical experts and committee to establish the way forward for its recovery.
Little said he had not seen the plan yet, but the Government’s position had not changed.
“The agency have advised me that proceeding beyond the roof fall would be technically difficult and would dramatically alter the risk profile of recovery operations … safety has always been a non-negotiable bottom line.
“There is no blank cheque,” he said.