Families of the 29 men who died in the Pike River mine are disappointed by an eleventh-hour delay to tomorrow's re-entry operation but accept safety must come first.

Expert miners were due to enter the West Coast mine tomorrow morning in a long-awaited bid to try to recover the 29 men killed during the November 19, 2010 disaster.

The Pike River Recovery Agency (PRRA) has been working for months to purge methane and oxygen from the mine by pumping in nitrogen before they head underground tomorrow.

But yesterday, they got an "unknown reading of oxygen" from a borehole 2.3km into the mine's drift, where the roof collapsed in the 2010 explosions. The oxygen had the potential for a "spontaneous combustion event".

Advertisement

Pike River Recovery Minister Andrew Little made the shock announcement this afternoon.

"Yesterday, unexpected and unexplained readings were reported by the atmospheric monitoring systems in the Pike River mine, leading to re-entry operations being suspended," he said.

READ MORE:
Pike River re-entry: Everything you need to know
Faces of the 29 Pike victims

Tactical action response plans meant they had to immediately shut down operations and find out the cause of the oxygen leak before they can carry on.

The delay could last days, even weeks, but PRRA bosses say they will "definitely" still go into the mine.

Anna Osborne, chairwoman for the Pike River Family Reference Group and whose husband Milton died in the tragedy, said the families would be disappointed.

She is "slightly" disappointed too, but was glad that the agency was putting the health and safety of the men going back into the mine first.

It's not a showstopper, she said, and once the issues are investigated, "it will be back on".

Pike River Recovery Agency chief operating officer Dinghy Pattinson denied it was a tough call to delay the re-entry, because they have also stressed a safety first attitude.

"It was an easy decision to make," said Pattinson, who was due to lead a three-man team of miners back into the mine tomorrow.

If the oxygen was ignored, he said, then a "spontaneous combustion event" could have resulted – something different to an explosion.

Experts started breaching the concrete seal plugging the mine's entrance two days ago.

They discovered the elevated oxygen levels yesterday.

The cause could be as simple as a damaged tube in a borehole, Pattinson said, but they need to go through a process of elimination which will last "however long it takes".

"We've got the readings. We have an issue. We're going to sort through that issue," he said.

"At the moment, the mine is full of nitrogen, so nothing can happen. As it is now, the mine is stable."

Pike River Recovery Agency (PRRA) chief executive Dave Gawn said it was unhelpful to speculate on how long the operation would be delayed.

Osborne said Pike River "played Russian roulette with the men" and the PRRA won't be doing that, saying she is proud of all the work the agency has done.

"This is only a hiccup. They are working very hard to correct this," she said.

She is almost positive that the re-entry will go ahead soon but only when everyone is safe.

"That's what we want."

Osborne said the cost of the re-entry operation shouldn't come into it, as 29 men died in the mine "through no fault of their own - so what cost do you put on a life?"

It was not just about the Pike 29, she said, but about changing the working culture in New Zealand.

"This country owes our men and the rest of New Zealand a better and safer working environment," she said.

A service at the mine's entrance will still go ahead tomorrow, Gawn said, with Prime Minister Jacinda Ardern expected to attend along with several families, some travelling from overseas.

"The breaching operation has started, and we still have a way ahead. So absolutely, we're going to celebrate this," Gawn said.

Re-entry delayed

The re-entry into the mine's drift was scheduled for Friday, with Little, Prime Minister Jacinda Ardern, Deputy Prime Minister Winston Peters, Green Party co-leader James Shaw and National Party Pike River spokesman Mark Mitchell set to attend.

A sign on the Pike River Mine gate referencing the re-entry into the mine that has now been delayed. Photo / Kurt Bayer.
A sign on the Pike River Mine gate referencing the re-entry into the mine that has now been delayed. Photo / Kurt Bayer.

"Yesterday unexpected and unexplained readings were reported by the atmospheric monitoring systems in the Pike River mine, leading to re-entry operations being suspended," Little said.

The agency behind the re-entry into Pike River said they'd "definitely" still go into the mine but it is not clear when.

"If you can't explain it, you stop what you're doing until you can."

Little said the unpredictable nature of the operation was expected, and information about the events of the last 12 to 24 hours is now being looked at.

The elevated oxygen levels might be because the monitoring equipment is inaccurate. Another possibility is that it oxygen was coming through the strata.

Little said the delay "could be days, could be weeks", but a safety priority meant that further action could not take place until more is known about the elevated oxygen levels.

Minister Responsible for Pike River Re-entry Andrew Little says safety must come first and the re-entry has been delayed. Photo / Mark Mitchell
Minister Responsible for Pike River Re-entry Andrew Little says safety must come first and the re-entry has been delayed. Photo / Mark Mitchell

The elevated readings meant that the atmosphere in the drift has changed and the air is not breathable.

He said he was disappointed at the delay and for the families, but safety had to come first.

He said the families know the technical challenge of the project, and while the families were disappointed with the delay, they were also realistic.

"Safety must come first. No more lives can be put at risk," Little said.

Families had been readying themselves for an emotional moment when the 30m-seal at the mine's entrance was to be breached.

It has been more than eight years since the heartache from the loss of 29 men's lives, outrage over attempts to permanently seal the mine - which the families successfully fought - and frustration at the lack of accountability.

Twenty-nine white crosses with miner's helmets line the road to Pike River Mine commemorating the men who died there in 2010. Photo / Kurt Bayer.
Twenty-nine white crosses with miner's helmets line the road to Pike River Mine commemorating the men who died there in 2010. Photo / Kurt Bayer.

They've also wanted it to be treated as a crime scene, and any clues which may lead to a future prosecution, gathered and explored.

After the methane gas explosion, fears of further explosions prevented any search and rescue attempts.

Toxic gas levels and safety concerns meant the first attempt back into the mine – four days after the initial explosion – came with a New Zealand Defence Force robot sent underground. It broke down just 550m in after reaching water.

Four more robots would go in, with mixed results, including video footage on November 25, 2010 from 1600m into the mine, which showed extensive damage from the second blast and ended hope of recovering the 29 trapped miners.