PERTH (miningweekly.com) – The New Zealand government has approved NZ$7.2-million for search teams to re-enter and explore the main tunnel of the Pike River coal mine, where 29 people died after explosions in 2010.

Energy and Resources Minister Simon Bridges said this week that the government’s approval for re-entry into the main tunnel leading up to the rock fall area was based on a risk assessment done by the Solid Energy board.

“Our criteria are that any re-entry into the tunnel, up to the rock fall, must be safe, technically feasible and financially credible. Safety is paramount and the high hazard unit of the Ministry of Business, Innovation and Employment has reviewed the plan and is comfortable with it,” said Bridges.

He added that the re-entry would be a highly complex and technical operation, and would be carefully conducted over stages, with risk assessment undertaken at each stage.

“Ensuring the safety of workers is an absolute bottom line for the government and Solid Energy,” the Minister said.

The first stage of re-entry would see workers plug the top of the 100-m-deep ventilation shaft to ensure full control of the mine atmosphere. Construction of an effective plug would require the replacement of up to 700 m of concrete and other material.

The Stage 2 work would see new boreholes being drilled into the top of the main tunnel, after which a camera would be inserted to check where a second plug would be placed.

Expanding foam would be pumped into the tunnel through a borehole from surface, which would then form a plug at around 2.3 km into the mine, and 40 m on the portal side of the rock fall, which would prevent entry into the main mine workings.

Inert nitrogen would be pumped into the area between the plug and the rock fall, preventing fresh air from reaching the inner mine and removing the risk of re-igniting any fires in the mine.

The main tunnel would then be ventilated.

Once the tunnel is ventilated, trained mines rescue personnel would enter and explore the tunnel.

Bridges noted that work would likely start in October this year, and would be subject to continuous review as it progressed.

The Pike River mine was closed following the explosion that claimed the lives of 29 workers. An independent report has subsequently revealed that all participants in the mine, including the Department of Labour and the Ministry of Economic Development, had contributed to the tragedy.