U.S. Mine Safety and Health Administration pursues new regulations on sealed areas based on findings of its Sago Mine accident investigation
ARLINGTON, Va. - The U.S. Department of Labor's Mine Safety and Health Administration (MSHA) has determined that lightning was the likely ignition source for the explosion in an abandoned area of the Sago Mine on Jan. 2, 2006. The explosion produced forces far exceeding the strength of the alternative seals meant to keep the explosion from affecting miners in a working section of the mine. Beginning in 1992, seals constructed from alternative materials were permitted in underground coal mines provided they could withstand an overpressure of 20 pounds per square inch (psi).
"The 20-psi standard for underground seals that MSHA put in place in 1992 was inadequate to protect miners," said Richard E. Stickler, assistant secretary of labor for mine safety and health. "We already have increased the strength requirements for new alternative seals to 50 psi and are aggressively pursuing regulatory action to require mine operators to take additional steps to protect miners from the dangers of explosions in sealed areas. We at MSHA extend to the families our deepest condolences for their losses and thank them for their patience during our investigation."
As part of its investigation, MSHA contracted with Sandia National Laboratories to study if energy from a lightning strike could travel underground to help determine whether lightning caused the accident. Three lightning strikes were recorded about the time of the explosion. The bolts struck between one to five seconds before the effects of the explosion were registered by nearby seismographs. In their study, Sandia researchers found electromagnetic energy from lightning could travel through the strata above the sealed area of the Sago mine. Sandia also determined that this energy induced on an abandoned cable was sufficient to ignite the accumulated methane in the sealed area where the explosion occurred.
The forces from the explosion far exceeded the 20-psi seals that separated the abandoned area of the Sago Mine from the miners working in the active section. MSHA investigators determined that the force of the explosion exceeded 93 psi at the seals.
During its investigation into the accident, MSHA's team cited 149 violations of mandatory mine safety and health regulations. However, the investigation team found that none of these violations caused the accident or contributed to the deaths of 12 miners.
MSHA's investigation report of the Sago Mine accident is online at www.msha.gov.
