The Fire Service advised that a rescue attempt at the Pike River Mine should not go ahead - just three minutes before the second and more devastating explosion.
Fire Service national manager of special operations James Stuart-Black was involved at Pike River until the second Christchurch earthquake, when he led the urban search and rescue effort.
He told the Royal Commission of Inquiry in Greymouth today that although firemen at the mine thought most of the 29 men were dead, the police - who have been criticised for giving the families false hope - had an obligation to consider that people might be alive.
Mr Stuart-Black said that five days after the first blast, he was told there was a "sudden move'' for Mines Rescue to stage an entry. He later learned that was not, in fact, correct.
On that Wednesday, he told police nothing had changed operationally to justify the change of approach.
There was still a lack of reliable gas information, and at 2.34pm he advised that the Fire Service did not believe the mine was safe to enter.
The second explosion occurred at 2.37pm.
Had the atmosphere been right there could "possibly'' have been a rescue or recovery that first night, November 19, but the gas levels were not right, he said.
Firemen at the site, along with Mines Rescue, believed very early on that they were dealing with mass fatalities.
He said the police - also criticised during the commission of inquiry for filling all three main rescue roles - had a moral responsibility to consider all possibilities, including the possibility of survivors.
"Being in a position where you have to make ultimate decisions is extremely lonely. What was apparent very early on this was big, with a national and international dimension a role such as this required the influence of a big organisation (police).''
However, Mr Stuart-Black flagged to the police controller the need to consider "how far down the line you go before you make a decision''.
He was part of an expert panel in Wellington convened by the police five days after the blast to advise on the recovery effort.
Some people have already told the inquiry the best experts were actually at the mine site but they were not heard.
Mr Stuart-Black said the Wellington experts were not there to "pick apart'' the on-site experts but to flag omissions. Decisions were turned around "extremely quickly''.
However, one night the panel refused to sign off a risk assessment as it was "clear further work'' needed to be done.
Fire Service national commander Mike Hall, in a written brief today, said he issued an order to keep his men out of the mine.
Coal mines were particularly dangerous after a blast, and it would have been "reckless'' to send men down without full information on what was happening with gas levels.
The commission opened this morning with Justice Graham Panckhurst recording sympathies for the loss of four Welsh miners last week, when their mine pit was flooded.
"The agony of the search and rescue effort to follow ... and now we are learning something of the impact upon a small ...mining community. It is a pattern which is all too familiar.''
The Pike River families said they also stood squarely with the Welsh families.
"We know the shock and loss in this dangerous industry and the grief and the questions they will have,'' they said in a statement.
The inquiry continues.