The Pike River Mine explosion was probably caused by a rockfall that sent explosive gases rushing through the mine, just as the water pumps were turned back on, causing electrical equipment to spark.
The Royal Commission of Inquiry resumed in Greymouth this morning, where it finally delivered some answers about the deadly November 2010 explosion that left 29 men dead in the underground West Coast mine.
Justice Graham Panckhurst told media before the start of today's hearing the preferred theory was a large collapse in the ''goaf'', the void left by mining, which would have sent methane rushing through the mine.
About the same time, the surface control room operator Daniel Duggan had turned on the water pumps back into the mine after a period of maintenance, although not to the hydro monitor coal-cutting machine.
This in turn re-powered the underground electrical system.
The Department of Labour's experts believe the combination of that caused the variable speed drive, which had components throughout the mine and moderated the supply of current, to spark. Problems with variable speed drives have been reported in Australia.
There was possibly arcing.
"Nothing Daniel did was wrong,'' commissioner David Henry said.
Analysis of the actual blast suggested it was largely methane-based.
No one has been fully underground since the explosion, and the commissioners stressed this morning that their idea of what happened was based on the most likely probabilities. The Department of Labour had reached these findings largely using its investigation report, with a panel of five experts.
Department of Labour general manager national services and support Brett Murray, a lead investigator, is due to give evidence this morning, followed by other key experts.
Mine staff are due to give evidence next week.
Mr Duggan's brother Chris, also a coalminer, died in the explosion.
- Laura Mills, Greymouth Star
