Halting a cycle of multiple-fatality coal-mining disasters in this country will be difficult, given the inherent dangers of such mining, University of Otago geologist Dr Mike Palin says.
The US-born Dr Palin worked in gold and copper mines in the United States and overseas early in his career, joining Otago University's geology department in 2002.
In 2008, the Department of Labour produced a report on "improving health and safety hazard management in the underground mining industry" after two miners died in separate underground coal-mining accidents in 2006.
Although prepared earlier, this report casts light on the Pike River Coal disaster.
The report notes that, since it started in the mid-1800s, underground coal mining in this country had been marked by "major incidents".
Between 1850 and 1998, there had been 204 fatalities in such incidents (19% of 1096 total mining fatalities).
Over the past 50 years, there had been fewer deaths per multiple-fatality incident, suggesting "major improvements to safety practices".
On average, such events, involving three or more deaths, occurred every 13 years.
The report cited a series of such events: Westhaven, 1958, four deaths; Strongman, 1967, 19 deaths; Boatmans, 1985, 4; Mt Davy, 1998, 3.
The last of these multiple deaths was 12 years ago.
Most of the incidents involved "explosions caused by ignited mine gases", the report noted.
Dr Palin said New Zealand was viewed internationally as one of the world's safest coal mining nations, and its industry went to great lengths to achieve high safety standards.
Nevertheless, even when full precautions were taken, there were inherent risks in underground coal mining. This was partly because of the presence of natural gases such as methane which could form an explosive combination with air, particularly at about 10% methane.
The presence in some mines of "very fine particulate [coal] dust", when mixed with air, also added to the risk of explosion, if there was a source of ignition.
Various forms of mining technology, including ventilation, and knowledge about safety-related issues had improved over the years, but coalmining had also become more technically challenging.
Easily accessible deposits had already been mined, so operators had to go to much greater lengths to find coal.
In the case of Pike River Coal, the mine was reached via a 2.3km-long tunnel bored under Paparoa National Park.
Conservation and other restrictions meant roads could not be built to the mine's main ventilation shaft, with equipment flown in by helicopter.
"It's a technically challenging, rugged environment."
