The Chief Coroner has ruled 29 Pike River Coal workers died during or immediately after the first explosion at the West Coast mine.
An inquest was held at Greymouth on Thursday. The bodies of the workers remain in the mine following the blasts, which began on 19 November last year.
Chief Coroner Judge Neil MacLean said the clear cause of death, which may have varied between individuals, was due to a substantial explosion, combined with a lack of oxygen and exposure to methane and carbon monoxide.
A medical expert giving evidence via police told the inquest the men would have died within minutes of the first explosion.
Robin Griffiths, director of occupational and aviation medicine at Otago University said that, in his opinion, the men would have fallen unconscious immediately after the first explosion and remained that way until they died three to five minutes later.
Based on gas levels at a sampling point, Dr Griffiths said the workers would have been inhaling just 1.1% oxygen. Death occurs when oxygen is at or below 8%.
In evidence presented by the officer in charge of the operation, Superintendent Gary Knowles, Dr Griffiths also said the methane and other asphyxiating gases in the atmosphere amounted to 98% and carbon monoxide 1.2%.
Dr Griffiths said that putting on self-contained rescue equipment would not have improved the men's survival chances.
In opening comments, Judge MacLean said the inquest was not the place to discuss the police's handling of the disaster and was limited to determining who died, the cause and time of their deaths, and - to a lesser extent - where they died.
Judge MacLean says any other evidence could prejudice the Royal Commission, to be held later this year, and any investigation by the Department of Labour.
A spokesperson for the families, Bernie Monk, was emotional when speaking after the inquest, but said it was a relief for the families that their loved-ones did not suffer.
The inquest has been adjourned indefinitely, but could be re-opened after the Royal Commission if the Coroner deems it necessary.
