Pike River recovery operation fraught with danger - chief executive

The operation to recover Pike River mine is no simple undertaking, according to the head of its recovery agency.

Pike River Recovery Agency Chief Executive Dave Gawn says the mountainous terrain, confined space, rock falls and unknown conditions will make re-entry a challenging job

"There's an understanding of what conditions are like, but there's no understanding as to what contributed to the explosions," he said at a select committee on Wednesday morning.

"Just after the explosion, there were cameras put down boreholes, so we know some areas are flooded for example, while others are relatively clear."

But, pictures and videos are only a small slice of the difficulties.

"It's different being able to look at a photo or a video, versus actually exploring it."

The re-entry will not be without risk.

"There's a lake of about 65 litres of methane, so we have an explosive atmosphere that we are managing by filling the mine with nitrogen" said Mr Gawn.

"There is also a risk of spontaneous combustion. We know it was on fire previously, so we manage that by pressurising the mine, and plugging it with nitrogen."

The mine is currently being pumped full of nitrogen, with the methane being vented out of boreholes into the atmosphere.

Rock fall is also a concern, as cameras have shown parts of the mine have collapsed.

"We're confident that it's relatively stable, but every stage that is recovered will include a geo-strata inspection, and ensuring in the he first instance that it's safe."

He says the process will be driven by events and conditions. No one will progress through to the next step of exploration until the conditions are safe.

Despite the risks, Mr Gawn says he is confident they are prepared.

"I am confident we have minimised the risk to the smallest amount we can - you can't undertake a mining operation without an element of risk but in terms of contingency plans and training, we have done the most we can."

If the operation for re-entry goes smoothly, Mr Gawn estimates crews will reach the site of the explosion at the beginning of September.

He hopes the operation will bring answers to the families of the men who lost their lives in the tragedy, and provide some closure.

"This is a chapter of New Zealand history that's not closed," said Mr Gawn 

"Families can never move on from losing a loved one and from circumstances that haven't been answered."