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ICG Cleared In Sago Explosion, MSHA Reports
No wrongdoing by mine operator International Coal Group, Inc., contributed to the deaths of 12 miners in an explosion at Sago Mine in Buckhannon County, W.Va., mine 16 months ago, MSHA investigators have concluded. They reported yesterday that lightning most likely caused the January 2, 2006, blast, which originated in a sealed-off area.
But new safety standards may be needed to protect miners from future explosions due to lightning, according to one 104-page appendix to the MSHA report, prepared by Sandia National Laboratories, which described a novel ignition scenario as probably responsible for the explosion.
An electric cable attached to a pump that was left behind in the sealed area most likely responded like an antenna to the electromagnetic energy of a nearby lightning strike, through a phenomenon called “indirect coupling,” and produced an electric arc that triggered the explosion, the Sandia specialists reported. Previously, explosions due to lightning strikes have been attributed to direct conductors, such as a gas wells, transmitting electrical energy into sealed areas.
With further research, “. . . it is reasonable to expect that mitigation techniques and safety standards could be developed to secure coal mining systems from future lightning threats,” the Sandia scientists, Matthew B. Higgins and Marvin E. Morris, wrote.
The Sandia scientists acknowledged that two recorded cloud-to ground lightning strikes, the focus of much previous attention, were in fact too far from the sealed area for the vertical strokes to cause the assumed arcing on the pump cable. Their conclusion rested on “credible hypothetical scenarios”: either a horizontal branch of a lightning stroke, or an unrecorded lightning stroke closer to the sealed area, such as a ground-to-cloud strike not normally recorded by lightning detection networks. They virtually ruled out direct transmission of electricity from a lightning strike into the interior of the Sago mine through a combination of power lines and mine equipment, a scenario previously suggested.
MSHA admitted that “a roof fall cannot be definitively excluded as an ignition source” but called it “highly unlikely.”
MSHA investigators made three recommendation in a “root cause analysis” of the Sago accident: “Seals should be designed and installed to prevent an explosion from propagating to the opposite side. . . . The atmosphere in existing sealed areas should be monitored and maintained inert when the seals are not capable of resisting the forces of an explosion . . . Insulated cables and conductors should be removed from the area to be sealed prior to seal completion.”
“We . . . are aggressively pursuing regulatory action to require mine operators to take additional steps to protect miners from the dangers of explosions in sealed areas,” MSHA chief Richard E. Stickler said in a news release.
Among other findings, MSHA investigators implicitly defended allowing the use of Omega blocks to construct seals, based on NIOSH research conducted at the Lake Lynn experimental mine for the purposes of the investigation. Use of the light-weight composition blocks in place of conventional concrete block to construct seals had been widely criticized in the wake of both the Sago explosion and the Darby mine explosion four months later.
“The Omega block seal that was constructed in the same manner as the one which successfully passed explosion testing in 2001 [when the agency adopted a requirements of 20 psi for “alternative” seals] can successfully withstand static explosion pressures of at least 50 psi [the current requirement, administratively increased after Sago and Darby],” the investigators reported.
The investigators also reported that seals constructed similarly to those at Sago would withstand a pressure of 21 psi. “Although the . . . seals were not built in accordance with the approved ventilation plan requirements, the forces generated by the explosion would have completely destroyed the seals even if they had been in compliance with the plan,” they wrote.
MSHA said explosion forces hit the Sago seals with over 93 psi. “The 20-psi standard for underground seals that MSHA put in place in 1992 was inadequate to protect miners,” said Stickler. “We already have increased the strength requirements for new alternative seals to 50 psi. . . .”
Federal investigators also drew the conclusion that a more rapid emergency response to the Sago explosion would have been futile.
“. . . [H]ad agency officials and the mine rescue teams arrived earlier, the teams would not have been permitted underground any earlier than actually occurred due to the high levels of toxic gases and the possibility of another explosion,” they wrote. “Even if the mine rescue teams had been on site and entered the mine immediately . . . . they would have been withdrawn when they encountered the high carbon monoxide levels.”
The federal agency has been criticized for allowing reliance on contract mine rescue teams composed of individuals not employed at the mine. An initially confused response to the Sago explosion also received much criticism.
MSHA issued 149 citations and orders to ICG subsidiary Wolf Run Mining Co. during the investigation, but none of the alleged violations contributed to the causes, effects or severity of the accident, according to investigators.
An internal review into MSHA’s own activities at the Sago mine prior to the explosion remains pending.