Pike's ventilation system 'unable to cope'
Pike River Disaster
Gas management and ventilation at the Pike River coalmine has been criticised by an expert mining panel investigating the November 2010 fatal blast.
Australian mine safety consultant David Reece today continued to give evidence at the royal commission of inquiry into the deaths of 29 men after an explosion ripped through the West Coast mine.
He was one of a panel of five experts, most from overseas, employed by the Labour Department to investigate what caused the explosion.
Reece said the mine's ventilation system was unable to cope with the amount of mining in such a gassy mine, so Pike River Coal should have cut back on mining.
Five areas underground were being mined by November 19, 2010, although most were not operating when the blast occurred.
He had never seen a mine with an underground ventilation fan like at Pike River, which was problematic and should not have been contemplated in a high-hazard area.
The fan was unreliable and struck problems when put into use on October 22 and was finally commissioned only nine days before the blast, he said.
''It is one of the fundamental pieces of equipment you must rely on.''
It was vulnerable to damage if an explosion occurred, which would stop ventilation.
Australian regulations used to specify fans could only be on the surface, Reece said.
''Even in a surface situation, it's still your primary means of controlling the atmosphere in the mine and giving people maximum opportunity for escape.''
If an underground fan stopped, it was difficult to reach and restart, particularly if the atmosphere was explosive, he said.
''You are starting to cut down your options as far as knowing what's going on down there and starting it up again.''
In his written submission, Reece said Pike's main ventilation system of one intake and one return was not uncommon in New Zealand coalmines ''but would not be considered acceptable for anything but initial development in an Australian context''.
Some of the mine's ventilation devices were ''substandard'' in controlling explosive gases, he said.
He harshly criticised the mine's gas monitoring system, highlighting variability and inaccuracy of data gained.
Some methane detectors were ''poisoned'' by high levels of the potentially explosive gas, stopping them from accurately measuring it, while other detectors were in poor condition, he said.
Mine management failed to recognise the seriousness of that failing, he said.
The methane drainage system was unable to properly remove gas coming out of the coal, including the 100-millimetre drainage pipe, which was too narrow.
That put further pressure on the mine's ventilation system, he said.
The panel found it unacceptable the mine's workers would have to climb up its 108-metre ventilation shaft to escape the mine.
Reece said the mine should have developed a better second egress.
In Australia, there was a strong push for mines to have three entries or exits, he said.
He agreed the location of the mine's fresh-air base should have been of concern to the regulator, which was the Labour Department.
Yesterday, he revealed the blast's most likely cause was a roof collapse in the hydro-mining goaf, a void left after coal was extracted, expelling a large volume of highly concentrated methane accumulated there.
The gas would then become diluted by air to within the explosive range before being ignited by an electric spark.
It was most likely a result of the electric supply being switched on to the water pumps, which happened shortly before the explosion.
''It was fairly significant to us and strongly coincidental that these pumps started very close to the same time.''
Analysis of the explosion showed it probably ignited deep in the mine, he said.
Temperatures of 1500 to 2000 degress Celsius were typical at the ignition point in a methane explosion.
However, he said blast survivors Daniel Rockhouse and Russell Smith, who were further out, did not experience great heat.
- © Fairfax NZ News