The plaintiffs are not being denied participation to the process, just the interviews, MHSA contends. They will be entitled to copies of the witnesses' statements later and can use them as evidence in lawsuits.
The April 5 blast was the nation's worst coal mining disaster in 40 years. While federal regulators have identified highly explosive methane gas, coal dust or a combination of the two as the likely cause, the ignition source remains unknown.
MSHA's response also says the lawsuit makes "entirely unsupported assumptions'' about what investigators will explore during the private interviews and essentially asks the court to assume the investigation will be a failure.
MSHA also notes that if the demands of the UMW and the families were granted, Massey would likely want equal access. Allowing so many people to participate in the interviews raises the risk that witnesses will be less candid and that they could be subject to intimidation or retribution, the agency says.
"Subordinating MSHA's investigative powers to private interests would be disastrous to the investigative process and make a mockery of Congress' mandate to MSHA,'' it said.
No hearing dates have been set in the lawsuit.