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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STEVE INSKEEP, host:
It's MORNING EDITION, from NPR News. I'm Steve Inskeep.
RENEE MONTAGNE, host:
And I'm Renee Montagne.
Nine months after that deadly coal mine explosion in West Virginia, federal investigators have revealed their working theory about the cause. It directs blame toward a series of maintenance and equipment failures at the Upper Big Branch mine.
Last night, the Mine Safety and Health Administration briefed the families of the 29 coal miners who died. The briefing was closed to reporters but NPR's Howard Berkes spoke with several people who attended and joined us from Beckley, West Virginia.
Howard, good morning.
HOWARD BERKES: Good morning.
MONTAGNE: What did investigators say about this deadly accident how it started?
BERKES: Well, let me take you through this step by step. And remember, first, that this is a very gassy mine. Methane gas is common in this area and in this mine, and it seeped into the area where a massive long wall mining machine was cutting coal. The cutting tool, which is called a shearer, had several problems. Some of its carbide-tipped teeth were worn down to their steel nubbins, and when those teeth hit hard rocks, sandstone in the coal seam, they sent sparks flying.
Now problem number two, a water spraying system that's supposed to help control sparks wasn't working. Now investigators point out that the water sprayers also help control coal dust, which is explosive. The sparks ignited the methane in what is described as a small fireball. But without the sprayers to control or extinguish that ignition and with coal dust to fuel it, it exploded. Investigators reported excessive coal dust spread throughout the mine and that fed the blast, sending it coursing more than two miles underground.
MONTAGNE: It sounds like a lot of things went wrong in this Massey Energy mine. Did investigators explain that?
BERKES: You know, I talked to several people who were in the meeting, as you pointed out, and they all quote federal mine safety officials saying essentially the same thing, that this mine was non-compliant with federal safety laws in multiple ways and if the mine had been operating the way it was supposed to, this explosion would not have happened. One official pointed out that these small methane ignitions occur almost weekly around the country but without explosions.
Now, some people did ask about federal oversight were regulators doing enough? And the officials said regulators cited the mine repeatedly, they closed unsafe areas at times but Massey Energy would fix the problem so they could start cutting coal again and the violations would return.
MONTAGNE: And Howard, we're calling this a working theory. Does that mean that there is some uncertainty about what went wrong?
BERKES: I'm told that investigators were careful not to say that this is their final and firm conclusion. They're still working through evidence and it'll be 60 to 90 days, they said, before they'll have a final report. They also pointed out that there's a federal criminal investigation that's still underway. And by the way, the investigators themselves will talk publicly about their tentative findings in a news conference later this morning.
MONTAGNE: And any response so far from the owner of the Upper Big Branch mine, Massey Energy?
BERKES: Massey is set to conduct its own briefing for the families Friday morning in Charleston, West Virginia. And the company has had its own theory -based essentially on a natural and massive infusion of methane or natural gas that overwhelmed all the safety systems. Last night, one of the government's experts refuted that theory by presenting evidence he said contradicts it. We'll get Massey's response to that and the rest of the government's tentative conclusions I'm sure on Friday.
MONTAGNE: Howard, thanks very much.
BERKES: You're welcome, Renee.
MONTAGNE: NPR's Howard Berkes reporting from Beckley, West Virginia. Transcript provided by NPR, Copyright NPR.