WASHINGTON — The West Virginia coal mine disaster last year that killed 29 miners was a preventable accident caused by a relatively small flare-up of methane gas that touched off a huge coal dust explosion, federal mine safety officials said Wednesday.
In a preliminary report, officials from the Mine Safety and Health Administration said their investigation found that Massey Energy, operator of the Upper Big Branch mine, had repeatedly violated federal rules governing ventilation and control of coal dust to reduce the risk of explosion.
The officials also said that the bits on a cutting tool known as a shearer, in use at the coal seam, were dull and produced sparks that could have ignited the methane gas. Water sprayers that should have doused the flame and controlled the explosive coal dust did not appear to be functioning properly, they said.
The mine safety officials cautioned that their findings, based on months of testing and hundreds of interviews, were tentative and that a more complete report would be ready in 60 to 90 days. They said that questions of negligence or culpability would be decided by a separate Department of Justice criminal investigation, which is continuing.
The Upper Big Branch mine explosion on April 5 was the deadliest coal mining accident in the United States in 40 years.
Shane Harvey, Massey Energy’s vice president and general counsel, said that the company had not been briefed on the interim federal findings provided to the news media on Wednesday and to the families of the dead and injured miners on Tuesday night. But he said that he had seen news accounts of the federal investigation and that the company disagreed with its major conclusions.
“Our findings are different than M.S.H.A.’s working theory, as we understand it,” Mr. Harvey said in an e-mailed statement. “We do not currently believe that there were issues with the bits or the sprays on the shearer that contributed to the explosion. We likewise do not believe that coal dust played a meaningful role in the explosion. We currently believe the mine was well rock dusted and that the mine exploded due to an infusion of high levels of natural gas.”
Mr. Harvey said that company officials would meet with families in the coming days to share their own conclusions about the accident. Federal investigators say they have found no evidence to support Massey’s theory that natural gas seeping into the mine had fueled the inferno.
Kevin G. Stricklin, the mine safety agency’s administrator for coal, said in a briefing for reporters on Wednesday that investigators had not yet pinpointed the source of ignition that led to the devastating explosion that tore through two miles of underground tunnels.
“We looked at 250 potential electrical sources and did not find any electrical ignition sources that could have created this explosion,” Mr. Stricklin said. He said that the most likely cause was sparks from the drilling machine hitting sandstone layers between coal seams, but that investigators had not ruled out sparks from a conveyor belt or a roof collapse.
Mr. Stricklin said that extensive testing had found that the multiple nozzles that were supposed to spray water to cool drill bits and control any sparks were not functioning properly. He said that small ignitions were not uncommon in other mines, but that they were generally controlled by ventilation, water sprayers and fire extinguishers.
He also noted that mine workers had reported significant buildups of coal dust on mining belts and machinery that had not been properly cleaned. He said that Massey had received hundreds of citations at the Upper Big Branch mine for noncompliance with coal dust control rules and other safety and health regulations.
Mr. Stricklin said that compliance with four critical mining practices was sufficient to prevent any underground explosion: adequate air flow, proper coal dust control, availability of water and regular quality-control inspections.
“We have always taken the position that all explosions are preventable,” Mr. Stricklin said, “and we stand by that today.”
After the findings were announced by mine safety officials on Wednesday, Representative George Miller, Democrat of California, released a statement calling on Congress to “close loopholes in federal mine safety law that contributed to the inability of M.S.H.A. to prevent the Upper Big Branch mine tragedy.”