The Department of Labour inspector who visited the Pike River Mine had no experience in hydro mining, the mining method described today as a "prime suspect'' in the fatal November 19 explosion.
The Royal Commission of Inquiry into the disaster resumed this morning, five days out from the anniversary of the first explosion, as it starts to examine what happened underground at Pike River and in particular the role of the Department of Labour.
Last week, the department laid 25 charges against Pike River Coal Ltd (in receivership), former chief executive Peter Whittall and contractor Valley Longwall International.
Department of Labour inspector Michael Firmin's evidence today shows repeated requests for Pike River to install a refuge chamber underground.
It also shows that in 2007, Greymouth police reported that explosives were missing from the mine site.
The mine management could not confirm this.
Under questioning today, Mr Firmin said he did not do any formal auditing of the mine.
The limited time he had on site, often spent underground, meant less time for audits, for which he was not trained. It would also have required ventilation and geotechnical experts.
Mr Firmin said he had no personal experience in hydro mining.
He also inspected Solid Energy's Spring Creek underground mine, nearer to Greymouth, another hydro mining operation.
He was interviewed for two or three hours for the Gunningham and Neal report, which the department commissioned after the Pike River disaster and which largely exonerated the department. Only three of the 20 people interviewed were from Pike River Coal.
Earlier today in a media briefing, commission chairman Justice Graham Panckhurst said the area of the mine being hydraulically mined was a "prime suspect'' in determining what happened.
The hydro monitors were being turned back at the very moment of the first explosion.
The goaf - the void left when coal is extracted - was the scene of a "reasonably significant'' collapse there in October 2010, Justice Panckhurst said.
The commission was also interested in how the goaf was ventilated, and how potentially explosive methane gas was drawn out of the mine. If the goaf did collapse on November 19, the methane would have to have hit an ignition source to explode.
Commission lawyer Simon Mount said it was too early to say if hydro mining played a role in the disaster, but it warranted further investigation.
The commission had received between 65,000 and 70,000 documents, and the police and Department of Labour had spent 50,000 hours between them on their investigations.
Both parties were shortly expected to file a vast amount of information from those investigations with the commission.
The Department of Labour cases would not go before a jury, so there was no risk of prejudicing jurors, Mr Mount said.
The police investigation was ongoing.
Nine witnesses will be called over the coming fortnight.