An Australian mining consultant has told an inquiry into the Pike River Coal mine disaster the potential for sparking in the mine was great.
Twenty-nine men died after a series of explosions which began at the West Coast mine on 19 November 2010.
A Department of Labour witness told the Royal Commission in Greymouth last week a panel of experts believed a spark from an electrical system may have caused a build-up of methane gas to explode.
On Monday, Australian electrical expert Tony Reczek gave detailed evidence regarding the claim that distortions in the electricity current caused an arcing that triggered the explosions.
Mr Reczek says there was a 90-metre cable connecting the mine's main fan with the system that controlled the speed of the electrical current.
He says everywhere there was a joint in the cable was a potential source of sparking, which would have been enough to ignite any methane in the mine.
Mr Reczek also told the commission that in reading correspondence between mine authorities, there were anomalies with the fan, which was overheating and had varying speeds.
He says there seemed to be a degree of confusion as to what was causing the problems.
He also says there was inadequate testing of how safe it was to install a main ventilation fan as well as a power system underground.
He told the inquiry nowhere in the world has the main ventilation fan and power system been installed in an underground mine, and it should have been extensively safety tested.