After ruling out other possible ignition sources such as electrical systems, smoking, equipment malfunction and roof falls, MSHA investigators contracted Sandia National Laboratories to study if lightning – three lightning strikes were recorded around the time of the explosion – could be the likely culprit.
In their study, Sandia researchers found that electromagnetic energy from lightning could travel underground, just through the strata above the sealed area of the Sago Mine. According to the researchers, lightning traveled laterally about a mile underground and then created a spark on a pump cable left behind when a section of the mine had been sealed weeks earlier.
“The electromagnetic energy could induce a voltage onto the pump cable [that] generates an arc near the explosive methane mixture in the sealed area,” the 198-page report states. “ ... Measurements and analyses indicate that the pump cable is the most likely receiver of electromagnetic energy in the sealed area.”
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.
Explosion Exceeded 93 psi at the Seals
The explosion produced forces that far exceeded the federal standard for blast resistance by mine seals, which were meant to keep the explosion from affecting miners in a working section of the mine.
Since 1992, seals were meant to withstand an overpressure of 20 pounds per square inch (psi). However, since the Sago incident, that level has been increased, according to MSHA Administrator Richard Stickler.
“The 20-psi standard for underground seals that MSHA put in place in 1992 was inadequate to protect miners,” Stickler said. “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.”
The explosion at Sago exceeded 93 psi at the seals, according to the report.
Report Could Spawn Emergency Regulations
As a result of the report, MSHA is proposing new emergency regulations that would require mine operators to remove insulated cables from abandoned areas before they are sealed, build stronger seals and monitor methane levels.
In addition, MSHA said it has cited the International Coal Group (ICG) for 149 violations of mandatory safety and health regulations, one of which was failing to test the self-contained self-rescuers and keep adequate records on them. One unit was out of date, according to MSHA.
However, the investigation team found that none of the violations caused the accident or contributed to the death of the 12 miners. In the example of not properly testing the breathing devices, the report said that even in the best circumstances, the men would have exhausted their oxygen before they were rescued.
After the report was released, ICG President and CEO Ben Hatfield said the report “seems to be consistent with the findings of three earlier investigations of the Sago accident.”
“In three separate investigations, a diverse group of mining, electrical, combustion and structural experts has now reached many of the same technical conclusions about the cause of the accident,” Hatfield said. “We hope this report provides some of the answers that the families of the accident victims need and deserve.”
“Those Miners Still Did Not Have to Die”
Others are finding it hard to buy into the lightning strike theory. Back in March, the United Mine Workers of America (UMWA) had submitted its own report stating that the cause of the explosion was from “frictional activity from the mine roof, roof support or support material” inside the sealed area.
UMWA President Cecil Roberts stated that the conclusions drawn from the MSHA report are “a far-fetched theory.”
“We do not believe MSHA or anyone else has conclusively or satisfactorily demonstrated how a charge from a lightning strike over 2 miles away entered the sealed area of the mine without a conduit from the surface,” Roberts said.
Rep. George Miller, D-Calif., chairman of the House Education and Labor Committee, asserted that although the cause of the explosion was important in the investigation, it still doesn't solve the issue of mine safety.
“Regardless of whether the explosion’s ignition source was lightning or friction in the roof of the mine, the fact remains that, after the explosion, those miners still did not have to die,” Miller said. “We know what steps should be taken to prevent such a tragedy from happening again, and Congress will work to make sure that MSHA and the industry take those actions.”
MSHA's fatal accident report can be accessed on its Web site.