Government investigators believe sparking water pumps are the most likely cause of the Pike River mine explosion which killed 29 men, but Peter Whittall's lawyer is suggesting miners' contraband may have ignited the deadly blast.
The third phase of the Royal Commission of Inquiry is looking at what caused the explosions that killed the men in November 2010. Their bodies are still in the West Coast mine.
In Greymouth on Wednesday, the inquiry was told a Department of Labour investigation found the most likely cause of the first explosion was a collapse in a "goaf", or roof cavity deep within the coal extraction area, which would have released methane gas.
The gas would have then ignited when water pumps in the mine were turned on in the above-ground control room, TVNZ reported.
The commissioners have stressed that the man who turned on the pumps, Daniel Duggan, who lost his brother Chris in the mine, did nothing wrong.
The Labour Department's Brett Murray said a report was sent to Pike River mine just 25 days before the explosion expressing concern about the stability of the roof after excavation work.
However, he said it was impossible to give a definitive answer on what caused the explosion, because nobody had access to the mine.
But Stacey Shortall, lawyer for Pike River and former chief executive Peter Whittall, suggested contraband such as matches and cigarettes, taken down by the miners, could have caused the explosion.
Pike River families spokesman Bernie Monk told media contraband was not an issue, and accused Ms Shortall of protecting her clients and putting the blame on the mine victims.
Next week the commission will hear from an Australian expert that a variable-speed drive used to control a water pump may have provided the spark.
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