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For four hours Tuesday night, investigators from the federal Mine Safety and Health Administration (MSHA) laid out their working theory about what happened April 5, just before a West Virginia coal mine exploded and 29 miners were killed.
They went through the explosion scenario step-by-step in an MSHA auditorium in Beckley, W.Va., filled with relatives of the victims, some weeping at times at the painful implications of the evidence.
This was the first family briefing in four months, and only family members and their attorneys were invited. Some participants spoke with NPR afterward on the condition that they not be named.
Much of what investigators discussed was revealed or leaked out earlier. But it hadn't been pieced together and backed by evidence, participants said. And it pointed to a tragedy that could have been prevented if the Upper Big Branch coal mine had complied with federal safety regulations.
MSHA investigators were careful to say that they have not reached final conclusions and noted that their final report is still 60 to 90 days away. They deferred to a federal criminal investigation that is still under way. And they reserved the right to adjust their scenario as they continued to analyze their findings. But they presented specialist after specialist who discussed detailed evidence.
One thing they did not do is pinpoint the source of the methane gas that they believe set off the chain of events that led to the nation's worst coal mine disaster in 40 years.
They noted that Upper Big Branch is a gassy mine with many possible sources of methane, and they said they're still working to pinpoint a specific source.
But they seemed confident, meeting participants say, in what the methane set in motion.
The gas seeped into the "tailgate" area of the longwall mining machine working a coal seam deep inside the mine. The longwall's cutting tool, called a shearer, was cutting into both coal and sandstone, and sparks were flying. The sparks were worse than usual, the investigators suggested, because some carbide-tipped teeth on the shearer were worn down to bare steel.
Those sparks would have been contained, cooled or extinguished by a system of water sprayers at the shearer, but they were not working properly, as NPR has reported. The sprayers also help control coal dust, which is an accelerant when it ignites. So, the investigators said, the combination of sparks, coal dust and methane, and no water, formed a volatile mix.
One of the government's experts told the families most of the mine was lined with excessive coal dust.
So, when methane hit the sparking shearer, a small ignition began. An MSHA official told the crowd that these small methane ignitions are common, occurring somewhere underground as much as once a week, but they rarely evolve into massive explosions.
But at Upper Big Branch, without working water sprayers, the investigators said, the small methane ignition persisted. Floating coal dust fueled it, and when it finally blew, the resulting blast was fed by coal dust spread throughout the mine, which explains an explosion that turned corners and killed along a 2-mile path.
Officials stopped short of blaming Massey Energy directly but said the mine was "noncompliant" in multiple ways. They suggested that the initial ignition would have burned out or been extinguished by the water sprays in 15 seconds had the shearer and its associated equipment and safety systems been maintained as required.
Massey Energy is scheduled to brief the families about its own investigation and conclusions in Charleston, W.Va., on Friday. In the past, the company has insisted that the blast was caused and fueled by an unpredictable and natural infusion of methane or natural gas from a crack in the mine floor.
But, an MSHA "flames and forces" expert told the crowd that blast residue and other evidence rule out Massey's theory completely, according to several participants in the meeting.
Some in the crowd suggested MSHA itself was negligent for allowing the mine to operate with deficiencies. But one federal official said the agency did what it could to cite Massey Energy for safety violations and shut down portions of the mine. As deficiencies were addressed, the official said, coal production resumed until new violations triggered additional citations and closures.
One participant said some family members were "reluctantly satisfied" with the presentation and the knowledge that a full and final explanation won't come until after the Justice Department concludes its criminal investigation.
Federal prosecutors have acknowledged the existence of that probe and a federal grand jury has taken testimony, but little else is known about the investigation's scope or duration.
MSHA plans to brief reporters on its investigation in a teleconference set for Wednesday morning.
West Virginia's mine safety agency is also assessing the evidence, as are the United Mine Workers of America and an independent investigative team led by former MSHA official Davitt McAteer, who has investigated other mine disasters.
Yet another probe by the Labor Department is scrutinizing the federal mine safety agency itself.
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