The Pike River Royal Commission is nearing the end of its third phase which is looking into the events leading up to the explosion which killed 29 men.
It resumes sitting in Greymouth on Wednesday for the first time this year and will look at the immediate cause of the first blast on 19 November, 2010.
The inquiry will hear from a Labour Department manager, Brett Murray, and David Reece, a consultant from Australia providing expert advice to the investigative team .
Issues to be discussed include the hazards, flammable gas and coal dust present in the mine immediately before the first explosion and the locations of the men in the mine at the time.
Evidence will also be heard on the likely ignition source for the explosion.