"Ultimately, the complete re-entry to 'pit bottom in stone' would be conditional on the integrity of the drift rock tunnel.
"That could only become apparent by systematic inspection and geotechnical assessment during staged entry."
Forster said he would be honoured to take part in or lead the drift recovery: "I would never ask anyone to do what I would not be prepared to do myself".
Sonya Rockhouse, whose son Ben died in the 2010 explosion, said the e-mail showed that re-entry was possible and the permanent sealing must be stopped.
"The Government needs to work with us to put a re-entry plan in place so that we can recover any remains that are down there and find any evidence of what caused this disaster."
West Coast-Tasman MP Damien O'Connor, who tabled Forster's e-mail in Parliament, said an independent perspective was required as the Government was "making excuses and hiding behind Solid Energy".
"The letter ... explains the facts and provides no justification for sealing off the mine," Mr O'Connor said.
Smith told Parliament the seal would be 600mm thick and made of Stopcrete. There was an additional wall 30m further away at the portal. That was then in-filled with softer material.
Justifying the decision not to look at the drift, he said the mine was 98% methane, and had within it over 100,000 cubic metres of explosive gas.
Secondly, the experts advised that there were still likely to be residual heat sources capable of triggering an explosion if oxygen was ever present.
Thirdly, the 2010 explosions in the mine would have fractured the strata in the mine, and there was a high risk of further rockfalls.
Finally, there was just one means of egress.
"If there is any lesson to learn from Pike, it is that politicians should not be making decisions on safety," Smith said.
- Greymouth Star