"The focus has to be primarily on what happened at Pike River," Engineering, Printing and Manufacturing Union (EPMU) national secretary Andrew Little told NZPA.
Mr Little, who was to travel to Greymouth early today, said the inquiry could look at how Pike River's operations measured up to current industry standards, and whether those standards were adequate.
"There has been improvement in health and safety in mines -- (state-owned miner) Solid Energy has very much led the way in that regard," he said.
Privately-owned mines had never been as good as the state miner, he said, but Pike River Coal Ltd, the biggest private operator of an underground mine, had improved recently.
"In the past few months, they had stepped up their health and safety processes and management," Mr Little told NZPA.
But overall, the union was concerned about the number of fatalities and serious injury in NZ mines, where the environment was hazardous and consequences could be catastrophic.
The long history of mining disasters was why miners were given the right to elect their own safety representatives -- check inspectors -- who had special responsibilities in safety.
These check inspector roles were lost when the Health and Safety in Employment legislation was introduced in 1992, but some miners had lobbied strongly for the worker participation to be re-instated.
The EPMU supported the concept, because it was dedicated to safety, and was a good way to reduce accidents.
"They're in the mine, they're down there with every shift, they keep an eye on every aspect of health and safety.
"Given the hazardous nature of their job, every precaution that can be taken should be taken.
"Adding a check inspector to every shift just gives that extra degree of scrutiny and comfort -- we need to have them back".
Mr Little said not enough was known about the Pike River explosion to say whether check inspectors in the mine would have avoided the tragedy, but there had been enough evidence over the years to show an inspector was a worthwhile precaution.
Two years ago, the union called not only for worker participation in safety mechanisms for underground mining but also supported the concept of a safety case regime: operators would have to document their safety management systems and get approval from the department before they operated.
Pike River said at the time that check inspectors were "totally inappropriate and not required".
"Under such a regime there is a very high likelihood of abuse of such a position which will eventually ensure that health and safety will fail in that workplace."
It preferred a systems-based approach with plans required for an explosives inspection system, ventilation and gas management (unless the mine had a gas extraction system) electrical, mechanical and new equipment standards in an engineering management plan. Plans could also cover explosion suppression and fire fighting and gas monitoring.
