Prime Minister John Key says Solid Energy "did everything they possibly could" to recover the bodies of 29 miners at Pike River.
He said Government had accepted the company's decision to abandon recovery efforts, which was revealed to the victims' families last night.
Government Ministers also confirmed that the mine would be converted into conservation land and preserved as a memorial.
In a press conference in Greymouth this morning, Mr Key said Solid Energy went through "an exceptionally rigorous process" before deciding against re-entering the mine.
"In the course of their work they did everything they possibly could to see whether it was possible to go up the drift."
Families made a number of requests to the Government following the decision not to re-enter the mine.
Mr Key said the Government had agreed to most of these requests.
Acting Conservation Minister Nick Smith would begin work on transferring the land into the conservation estate.
A memorial site would be created at the mine and access would be guaranteed for friends and relatives of those affected.
The families asked for a legal opinion about whether further criminal prosecutions could take place.
Mr Key said officials would revisit this, but it would be "immensely challenging" because an extensive amount of work had already been done on criminal prosecutions.
But he confirmed it could be possible that civil proceedings could be taken against a variety of parties. Government would ask Crown Law to investigate this possibility.
If Crown Law found civil proceedings could be brought against culpable parties, Government would fund the proceedings.
Mr Key ruled out a request by the families to introduce corporate manslaughter charges in New Zealand, though he said more advice had been sought on this issue.
He praised the families for their advocacy.
"This has been a tragedy that has been incredibly draining and they've had to live with it every single day."
He said if there were any positives to take away from the disaster, it was the changes to workplace safety laws which were implemented in response to it.
Solid Energy confirmed today it will not re-enter the Pike River Mine because the company has deemed the risks to life remain too high.
Board Chair Pip Dunphy made the announcement this morning after a meeting with Mr Key in Greymouth.
"We know this decision will be very disappointing to the family members and friends of the men who died in the mine," Ms Dunphy said. "However any further loss of life in this mine is unacceptable and any possibility of other families having to go through what the Pike families have suffered is not something our board can support."
Families of the 29 miners lost in the explosions, which began on November 19, 2010, had predicted the decision and asked supporters to protest outside the meeting this morning.
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Ms Dunphy said following the Solid Energy board reaching its decision about the drift project, the board has decided to surrender the Pike River Mining Permit.
She said the next steps are a matter for discussion with the Government.
Ms Dunphy said Solid Energy had been tasked with developing a re-entry plan that was technically feasible, financially credible and safe.
"In doing so, we have undertaken a rigorous risk assessment process supported by input from independent technical advisors. Safety has been our primary focus throughout. Despite our best endeavours we have been unable to reach a level of confidence that any re-entry plan can adequately protect the lives of those who would undertake the work.
"Our analysis shows that, despite every effort to control or eliminate risks to life, there remain a number of potentially fatal risk factors."
Solid Energy said these included:
- Risks associated with deterioration in the conditions inside the mine. For example it is impossible to rule out some degree of significant fire-related damage to parts of the roof and the associated potential for collapse.
- Risks associated with managing and maintaining gas and ventilation in an environment compromised by difficult terrain, unpredictable weather and unreliable services and infrastructure including electricity supply.
- Risks associated with the sheer complexity of implementing 600+ risk control activities, where failure of one or more controls due to human error or events outside of our control could have fatal consequences.
- Entrapment, for example as a result of roof fall or vehicle fire.
Ms Dunphy said these were all foreseeable risks, which escalate as the distance from the portal increases because of the distance to safety. "Ultimately, we need to be able to rescue people if they became trapped. That would require us to be able to communicate to determine where along the 2.3km drift the entrapment occurred and be able to sustain life whilst drilling a rescue shaft.
"In recent successful rescues the location of trapped personnel was accurately known. They had to wait while a small diameter hole was bored to enable life to be sustained and then a large diameter bore hole was drilled, through which rescue was achieved. In this instance, there is no guarantee we would be able to do any of these things. The terrain alone is too steep and makes it impossible to site a drill rig of the size needed to facilitate recovery," she said.
The father of one of the Pike River victims said he expected it would be some time before the next steps in the saga were worked out.
Laurie Drew's son Zen was killed in the tragedy.
He said he had accepted the reality of the situation. Everyone was prepared for it and now the reality check had come.
He said it would be tough, especially when it came to reunions.
Anna Osborne's husband Milton was killed in the disaster. She said they were being punished for others' mistakes.
Earlier, there were calls of 'shame' as the Prime Minister arrived in Greymouth for a face to face meeting with Pike River families.
The families were called to the meeting by mine owner Solid Energy to discuss the possibility of re-entering the mine, nearly four years since the explosion which killed 29 men.
Ashen-faced family members entered the meeting armed with pictures of their loved ones with yellow ribbons pinned to their clothes.
Bernie Monk brought with him a box of files ready to argue against the expected claims from Solid Energy that a re-entry operation isn't feasible.
A small group of protestors also gathered outside the meeting, playing music and holding signs demanding re-entry to Pike River.
- additional reporting Newstalk ZB