How Pike River could be made safe for the recovery of miners' bodies

A miner's Headlamp still shines in the Pike River mine after the first blast in this image taken by an Army robot. Photo / Supplied

After the devastating news that there was no survivors following a second explosion at the Pike River mine yesterday, the thoughts of families and mine staff are of recovering the bodies of the 29 men.

"We want our boys back, and we want them out," said Pike River CEO Peter Whittall.

"We want the miners out of the mines and into the loving arms of the families," Grey District Mayor Tony Kokshoorn told the Herald.

Authorities are now taking the appropriate measures to ensure a recovery can happen as quickly as possible.

Last night the gas composition in the mine was still too volatile for a recovery team to enter.

But EPMU National Secretary Andrew Little told Radio New Zealand mine staff would look at "gagging the mine" a process which involves blasting carbon dioxide into the mine to douse any burning.

'Gagging'

An Australian mine expert from the University of Queensland, David Cliff, said the process was essential to ensure another explosion did not occur.

"If there's no controls initiated and we don't know the ignition source, it's quite possible there will be subsequent explosions, he said.

Superintendent Gary Knowles said Pike River officials were currently considering how to best stabalise the gas composition in the mine.

Mr Cliff explained that the process of "gagging" often involved a piece of equipment very similar to a "jet engine from a Soviet-era plane".

The engine burned fuel and produced an exhaust gas comprising of nitrogen and carbon dioxide, he said.

"They blast this gas into the mine and displace the air. This removes any oxygen from the mine," Mr Cliff said.

As combustion cannot occur without the presence of oxygen, Mr Cliff said the process removed the risk of another blast.

But he said methane levels would still remain very high in the tunnels as it was emitted by the mine itself.

Explanation of the second explosion.

The second explosion at the Pike River mine which sealed the fate of the 29 trapped men had been an ever-looming threat, says Mr Cliff

He said that because rescue staff were unsure of what caused the initial explosion, they had no way of knowing where the ignition source was located and if it was still burning.

"[The second explosion] depended on the methane build up and its proximity to the ignition source," he said.

However Mr Cliff said it was unlikely the second blast was sparked deep into the mine because the methane levels would have been too high and the oxygen content far too low.

"The second explosion means the ignition source was somewhere near the ventilation shaft," he said.

Even though there were five days between the two blasts, the gap between them could have easily been closer.

"Because we don't know the location of the ignition source the [second] explosion could have happened much earlier," he said.

Commenting on the first blast, Mr Cliff said there was still "a glimmer of hope" after it occurred, because the air would have been breathable.

However, he said that Pike River authorities have known there were no survivors yesterday afternoon from the "physical pressure wave" coming out of the mine entrance following the explosion.

"They could tell it was much more dangerous, much larger and the probability of surviving goes down each time [there is an explosion]," he said.