Faulty monitoring equipment is behind an oxygen reading that caused a delay in the re-entry of Pike River Mine, Minister for Pike River Re-entry Andrew Little says.
Plans to re-enter the sealed mine and take down the 30m seal were put on ice on Thursday after "unpredicted and unexplained" readings of oxygen were recorded.
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A reading of 3 percent oxygen was recorded on a monitor 2.3km up the tunnel inside the mine. The re-entry team cannot go inside the mine and resume work until they know what caused the reading.
Little told Newshub Nation more testing on the equipment is required to confirm it is faulty. The extra tests could take some time.
"The latest is that it looks almost certain that there is an issue about the monitoring equipment and it is faulty, there is more testing to do.
"What it now is that all of the monitoring equipment will now have to be tested, that will take some days possibly a couple of weeks."
New monitoring equipment has been brought in to test next to the old monitoring equipment, and both machines are giving different readings.
On top of this, Little said the machines underwent an integrity test which the old monitoring equipment failed.
"Different gases were deliberately put in front of those monitors and inaccurate readings were recorded by the old equipment, accurate readings were recorded by the new equipment."
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He said the operation won't be delayed by a matter of days or months - the actual timeframe is somewhere in the middle. But he's still very sure the mine is safe.
"I'm totally convinced it is [safer now] because of the work that's been done on it to fill it with nitrogen, to purge it of methane and to get it ready so that at the drift it will turn into breathable air, so that when the men go in they don't have to wear breathing apparatus.
"The mine is safer now than what it was at the time that it exploded and the months that followed."
Twenty-nine men were killed in a series of explosions inside the mine in November 2010. The previous National Government had said the mine was too dangerous to enter.
The current Labour Government disagreed and pledged during the 2017 election campaign to go back into the mine