A finding from a Department of Labour investigation into the Pike River mine disaster that an electrical fault caused the explosion has been challenged at the Royal Commission examining the disaster.
The contents of the investigation have been revealed as the hearings focus on the immediate cause of the first explosion which killed 29 men.
But the findings have been challenged by the lawyer for the mine's former chief executive, Peter Whittall.
In Stacey Shortall's cross examination of Brett Murray of the Labour Department, he admitted the explosion could also have been caused by a worker in the mine using a cigarette lighter.