Evidence at the Pike River Royal Commission on Wednesday suggested workers could have ignited the methane that caused the explosion at the mine.
The Commission is looking at the immediate cause of the explosion.
Lawyer for former chief executive, Peter Whittal, said the methane could have been ignited by contraband such as cigarette lighters, carried into the mine by the workers.
However, a spokesperson for some families of the dead miners, Bernie Monk, said it was wrong for the lawyer to try to shift the blame.
The hearing has been discussing the Department of Labour investigation into the disaster, which found that higher levels of methane combined with electrical arcing caused the explosion.
The department's Brett Murray told the hearing Pike River Coal failed to address issues with the width of the mined-out section in the tunnel, despite the report warning of the danger of collapse and sudden release of methane.
The results of the investigation have been revealed for the first time on Wednesday at the Royal Commission hearing into the disaster that killed 29 men on 19 November, 2010.
Under cross-examination, the head of the investigation, Mr Murray, said the findings are not definitive because of lack of access to the mine and are instead based on a balance of probabilities.
The Royal Commission's report will be now delayed until 28 September.
Attorney-General Chris Finlayson says the Commissioners asked last year for the extension because the hearing was taking longer than expected to get through the evidence.