Re-entry risks high, ‘but can be managed’

The risk of people becoming trapped and killed re-entering the Pike River mine drift is potentially high, but can be managed, experts say.

About 24 people have been involved in a two-week risk assessment of the re-entry concept plan, including representatives from the Pike River families, NZ police, WorkSafe, the Department of Conservation and Mines Rescue. A two-hour session was open to the public and media at the Mines Rescue Training Centre near Greymouth yesterday.

Three people attended the session, including Pike River survivor Russell Smith, who said the risk assessment process was detailed and thorough.

The coalition Government set up the Pike River Recovery Agency to recover the mine drift eight years after the explosion that killed 29 men on November, 19, 2010.

The public session included discussion of the risks associated with the driving of a new small tunnel. A new tunnel would provide a second means of escape to those reentering the mine drift.

The high risks identified included people slipping or falling over steep uneven terrain, unplanned movement of machinery and entrapment by roof fall or portal obstructed by slope instability.

The experts also discussed how to minimise damage to forensic evidence once the tunnellers broke through to the drift.

Geotechnical expert Stu MacGregor said the risk of entrapment could be managed by regular stability and geotech inspections and using the right people and equipment for the job under competent supervision. He said the correct design and location of the tunnel would ensure its stability.

‘‘When you look at Pike reports it’s shocking in terms of what they were doing . . . The quality of installation was woeful. Substandard installation will cause collapse,’’ he said.

MacGregor said the concept plan included five possible tunnel locations, two of which traversed a faultline. All the options included steep terrain and needed Department of Conservation approval.

He said if an earthquake happened during re-entry and a worker became trapped in the tunnel, they would die before they could be rescued due to the remote location and nitrogen and methane leaking into the tunnel.

Agency chief operations officer Dinghy Pattinson said the agency had identified all the tasks required to safely re-enter and recover the drift. The 14 key tasks included drilling boreholes, purging the drift of methane, breaching the 30m and 170m seals and forensically examining the drift.

The expert panel would assess the risks in three re-entry options: A small tunnel to provide a second means of escape; single entry; and single entry with a large diameter borehole escape.

The agency’s concept plan was approved by Minister Responsible for Pike River Re-entry Andrew Little. Once the risk assessment is completed, it will go to a detailed plan which will be ultimately signed off by Little.

‘‘When you look at Pike reports it’s shocking in terms of what they were doing . . . The quality of installation was woeful.’’ Geotechnical expert Stu MacGregor