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Investigators from the Mine Safety and Health Administration today briefed reporters on what they believe caused the Upper Big Branch mine explosion that killed 29 in West Virginia last April.
Methane gas, they said again, started it all, although they could not identify the specific source of the methane. As we've reported before, Upper Big Branch is an especially gassy mine and methane seeps in from the coal seam, the mined out area behind it and cracks in the mine floor.
Using video and slides to illustrate their findings, they also noted that small methane fires or ignitions are not uncommon in coal mines and typically do not cause massive explosions.
This video from the National Institutes of Occupational Safety and Health provides a primer on how methane ignitions start and how they're typically controlled or quenched by properly operating safety systems:
But at Upper Big Branch, maintenance and equipment failures allowed the methane ignition to persist.
Take the longwall mining machine itself, a behemoth more than three football fields long: Its cutting tool, a monstrous drum with carbide-tipped teeth, was so poorly maintained that some of the teeth were worn to steel nubbins, as this photo shows:
That led to excessive sparking, investigators said, as the cutting tool, which is called a shearer, cut into a sandstone layer in the coal. Normally, water sprayers shower the shearer and the area in front of the coal seam. The spray controls coal dust and sparks but the water sprayers weren't fully functional on April 5.
Investigators tested the water sprayers on the shearer just before Christmas and this video shows the results:
With such little water, a lot of sparks and methane, an ignition developed and it persisted. The failure of the water sprayers left coal dust in the air. And as this mine map shows, investigators found excessive coal dust throughout the area affected by the blast:
Coal dust, investigators believe, provided the fuel that turned this small methane ignition into a fiery concussive force that traveled more than two miles underground and took 29 lives along the way.
"We still stand by our point that all mine explosions are preventable," concluded Kevin Stricklin, MSHA's mine safety chief.
The maintenance and equipment failures "should have been caught [by Massey Energy] during normal operations," said Joe Main, assistant labor secretary for mine safety and health, rejecting the notion that MSHA's inspection process may have failed.
In a statement, Massey Energy Vice President and General Counsel Shane Harvey repeated the company's theory that a massive and natural infusion of methane or natural gas was the sole cause of the explosion.
"We do not currently believe that there were issues with the bits or the sprays on the shearer that contributed to the explosion," Harvey said. "We likewise do not believe that coal dust played a meaningful role in the explosion."
MSHA's briefing included a series of slides that purportedly refute Massey's theory about the blast.
(Click here to see more of the reporting that Howard Berkes and other NPR journalists have been doing about Mine Safety In America — including their reports about the April 5 disaster at Massey Energy's Upper Big Branch coal mine in West Virginia, where 29 miners died.)