The ventilation shaft at the Pike River mine has been capped.
A helicopter operation at the mine today [Sunday 12 December] saw two 770-kilogram semi-circular steel plates fitted into place over the ventilation shaft, and secured with sandbags.
The operation was completed shortly after 2.00pm.
Police Superintendent Dave Cliff said weather conditions at the mine today had improved sufficiently to allow the capping to go ahead.
"This is good news for our ongoing operation. We're hopeful the cap will help to improve the effectiveness of the GAG engine, and stabilise conditions inside the mine."
Superintendent Cliff said gas levels would be closely monitored for several hours after the capping.
If results indicated a stable environment, the GAG engine will be shut down temporarily for maintenance, and more concrete will be added to the sealing of the portal.
Monitoring of oxygen levels will continue and the GAG will only be reactivated as required to reduce the levels.
"From that point it will be a case of maintaining a stable atmosphere inside the mine," said Superintendent Cliff. "With the cap in place the GAG may not need to run continuously, and we will only operate it as oxygen levels rise.
"Monitoring will continue over the coming week while we plan to introduce a nitrogen-generation unit. This will pump nitrogen into the mine to maintain an inert environment and reduce the temperature."
A Floxal nitrogen-generation unit is now on standby in Brisbane, and arrangements are being made to bring the unit to New Zealand later in the week.
Meanwhile, Police have reassured the families of the 29 men that although the current operation is being scaled back, they will continue to providing welfare support and coordination.
"We remain fully committed to supporting the families and working with other government agencies and local community groups to ensure the families' welfare needs and longer-term support are catered for," said Superintendent Cliff.
"Police will also retain a longer-term presence in Greymouth, with our investigation team leasing premises in the town for at least the next 12 months."
For more information:
Police media liaison team, Greymouth - 027 5015742