The fatal April 5 explosion at the Upper Big Branch Mine started with a frictional ignition on the longwall face involving as little at 13 cubic feet of methane that would not normally be expected to cause such devastation, MSHA investigator believe from their analysis to date.
The ignition then "turned into a massive coal dust explosion," according to coal mine safety and health administrator Kevin Stricklin. Ordinarily, a combination of "air flow, rock dusting, water sprays and quality examinations" would prevent such a combination of circumstances, Stricklin said.
MSHA chief Joe Main, Solicitor of Labor Patricia Smith, and Stricklin all spoke during a media conference call this morning. The event followed an in-person briefing held Tuesday evening for families of the 29 victims. Officials cautioned that their findings were not yet entirely definitive and the investigation is continuing.
Investigators found cutter bits on the longwall shear seriously worn and a number of water sprays inoperable, both conditions that MSHA believes could contribute an ignition. The shear was cutting sandstone, which has sparking potential, at both the top and bottom of the coal, according to MSHA.
Reports called out from underground company examiners not long before the explosion indicated belt conveyors that needed to be rock dusted, officials said. The agency previously announced that some 80% of rock dust samples taken after the disaster were out of compliance with federal standards. Rock dusting is intended to inhibit suspended coal dust from propagating a coal mine explosion.
"At least two people" were in the neighborhood of the longwall shear, near the tailgate, at the time of the 70- to 90-second ignition, the federal officials stated. Those individuals are believed to have headed away from the ignition site and traveled about 400 to 600 feet, walking on the bases of the longwall shields toward the center portion of the longwall face, before the explosion overtook them. A total of six victims were found approximately mid-face by rescue teams.
At about the same time, a call may have been put in to the longwall headgate controls, where someone removed power from the longwall and at the same time disconnected the water sprays.
"We do not think [shutting off the water sprays] would be a good idea where an ignition is occurring," Stricklin commented in response to questioning, but he stated, this was probably "normal protocol."
No fire extinguishers were found in the area of the tailgate, Stricklin also stated in answer to a question from Mine Safety and Health News, nor are fire extinguishers required in that area. Other ignitions of similar magnitude in underground coal mines have been put out by miners wielding fire extinguishers and sometimes water hoses.
The agency hopes to produce further technical information on the cause of the explosion in about 60 to 90 days, "subject to review by any Department of Justice concerns," Main stated. In an unusual situation, MSHA is deferring to a request the U.S. Attorney for the Southern District of West Virginia to delay promised public hearings or release of interview transcripts on the grounds that these actions could interfere with an ongoing criminal investigation. The U.S. Attorney gave no specifics on how greater openness by MSHA would interfere, according to Smith. No termination date for the request was estimated.
MSHA has conducted 161 interviews and another 18 persons have declined to participate and taken the 5th Amendment, Main reported. "Ninety-nine percent" of the underground portion of the investigation was completed in December, he said.
Electrical equipment collected from near the origin of the explosion has been tested and found to have no defects that would have caused the explosion, according to the agency. Some 250 electrical items in all require testing. The agency needs to conduct further equipment testing, make some additional checks underground and conduct follow-up interviews, Main said.
Questions that remain to be fully addressed by investigators included the status of the ventilation system, including the possible effect of accumulated water Impeded by an official mine map that was out of date, Investigators reportedly were still trying to sort out whether locations of some stopping and regulators had been altered since initial construction.
Earlier in the shift the shear had been shut down to repair a problem but had resumed cutting before the explosion. Results of a preshift examination were called out to the surface from the longwall section about 20 minutes before the blast, officials said, and did not flag any shear problems.
A comment raised last night by one briefing attendee also had investigators seeking information about a possible later telephone call to the surface moments before the blast.
Investigators were able to download information from three hand-held gas detectors that showed high readings, but they now believe that these readings resulted from post-explosion combustible gases other than methane.
MSHA believes that immediately following the explosion, two persons donnned SCSRs and made their way to the longwall section where the blast initiated, Stricklin said. The agency is still working to determine their route of travel, but the two individuals have both taken the Fifth Amendment, Stricklin said. The individuals reportedly left several parts of used SCSRs behind them on their journey, but their activities are believed to have had no role in the explosion's cause.
MSHA has posted to its website a new PowerPoint presentation summarizing its investigative activities and findings to date.
A complete story of the press conference will be in Vol. 18, No. 2 issue of Mine Safety and Health News.