Drill will probe mine damage

The entrance to the Pike River Coal mine. Photo / Simon Baker

A 15cm-wide hole, which will be drilled 150m through rock, is expected to reveal the scale of the West Coast mining explosion.

Rescuers were yesterday using trucks and helicopters to move a drill rig from one part of the Pike River Mine to a mountain-top area where they will drill the bore hole.

The complicated effort is expected to provide the first picture of the damage and, hopefully, reveal where the miners may be trapped.

But the drilling carries risks and could cause more rock falls, collapses and explosions.

The hole will be used to test the mine's methane and carbon dioxide levels before police give the go-ahead for rescuers to go in.

A camera will also show any debris that may have fallen during Friday's explosion.

Rescuers must take extra care and time with the drilling, encasing the hole to prevent it from falling in, which would further complicate an already difficult situation.

Mining expert David Feickert, a mine safety adviser to the Chinese Government, said the tricky rescue effort would be a delicate operation and rescuers risked further explosions.

"As the drill gets close to the roof of the tunnel, they'll have to be very careful because they don't want to set off a gas explosion by doing that.

"They will take it easy."

Mr Feickert said the new hole would be used to get air samples of methane and carbon dioxide levels.

Methane gas was explosive only in certain mixtures of air and measuring the levels would show the risk rescuers faced by entering the mine.

Mr Feickert said the carbon monoxide levels would give rescuers an idea of whether there was any fire or heat inside the mine which could provide a source for another explosion.

The level for methane to become explosive was usually between 2 and 17 per cent of the air content, depending on the country. At higher levels it was no longer explosive but could asphyxiate miners exposed to it.

"To have a gas explosion, you have to have methane in the explosive range in the air and you need to have a source of ignition.

"There has to be something that sets off the explosion," he said.

"It could be an electrical spark, it could be a spark of metal hitting rock, it could be some heating in the coal - in some mines you get spontaneous combustion with coal.

"That has been a problem in some New Zealand mines."