Families of the men who died last November when the Pike River mine exploded have been told there was almost no reliable certainty as to just when they could have been rescued.
The statement came from a Queensland mining expert who was making submissions to the Royal Commission inquiring into the tragedy, which left 29 men dead inside the West Coast coal mine.
There were hopes a rescue team could have entered the mine to save anyone who might have survived the first blast, which occurred on 19 November.
In the end a second, much larger, explosion on 24 November put an end to any hopes of survival.
Mine safety expert Darren Brady flew in from Queensland the day after the first blast and began analysing gas samples.
He told the inquiry in Greymouth on Thursday the presence of gas indicators of a coal fire, including ethylene and acetylene, meant that an ignition source could be present.
These, combined with methane concentrations likely to be in the mine, meant a secondary explosion was possible.
"On this basis the atmosphere could not be defined as safe for re-entry, which means that the opportunity to re-enter did not exist."
Mr Brady said mine disasters in Utah, West Virginia and Siberia showed just how widely differing second and subsequent explosions mine explosions could be.
He said attempts to enter a mine to save lives could easily cause more to be lost.
Families' representative differs
A spokesperson for families of victims, Bernie Monk, says he personally differed with Mr Brady.
Mr Monk says he still thinks it might have been possible to mount a rescue mission after the first explosion.
"Personally I reckon they should have gone in. They've got different regulations now than what some of the old fellows are telling me cos all the old miners say we should have gone in," he said.