Fluctuating gas levels have delayed an attempt this weekend to use expanding foam to seal cracks around a secondary shaft at the Pike River Coal mine and speed up the efforts to make the mine safe.
Preparations were continuing at the West Coast site this afternoon, but sealing the slimline shaft had not started yet, police spokeswoman Barbara Dunn said.
"It's just complicated by the environment basically.
"There have been gas levels coming through at levels where we've had to move people from the hill, so they haven't had a straight run at setting up," she said.
Temperatures and methane gas levels inside the mine continue to fluctuate, hindering attempts to get into the West Coast mine and recover the bodies of 29 men killed in a series of explosions since November 19.
The latest effort was needed to help stabilise the mine, where temperatures had varied by more than 100degC and difficult terrain was complicating the recovery.
Foam that expands to 35 times its original volume and hardens within about five minutes was planned to create a seal around the slimline shaft, a bore hole near the ventilation shaft. That would allow the GAG and Floxal machines - which are pumping water and nitrogen into the mine - to operate more efficiently.
The expanding Rocsil Foam had been used in coal mines in Europe and Australia.
The GAG and Floxal teams have continued working throughout the Christmas period.