BUCKHANNON — A 35-year-old U.S. government study indicates that federal rules for sealing worked-out areas of underground mines are far too weak to prevent explosions such as the one that killed 12 workers at the Sago Mine four months ago.The U.S. Mine Safety and Health Administration cited the study when it wrote its rules in 1992. But the 1971 federal Bureau of Mines report raises serious questions about the MSHA rules, meant to avoid sealed-area explosions such as the one investigators believe caused the Sago disaster.For example, the study notes that federal standards for sealing mines on government property — dating back to 1921 — required seals to be more than twice as strong as the current MSHA rule.In the Sago inquiry, state and federal investigators are focusing on a foam block wall that was used to seal off an area of the mine where International Coal Group struggled with repeated roof falls and water leaks.Federal law requires coal companies that abandon areas to take steps to ensure that these areas are “isolated from the active workings of the mine with explosion-proof seals or bulkheads.”In 1992, MSHA wrote rules to implement the “explosion-proof” criteria. Generally, MSHA required seals to be built with concrete. But it allowed alternate materials if those materials would withstand a blast with the force of 20 pounds per square inch, and cited the Bureau of Mines study as the source for that number.But the 1971 study indicates that there is more to it than that.For one thing, explosions can be much stronger than 20 pounds per square inch, the study said. Blasts are not expected to exert much more force than that 200 feet or more from the ignition point, the study said.But close to the blast point, “No one can foretell what forces would be exerted on a bulkhead in the event of an explosion,” the study said. “In the Bureau’s experimental mine, for example, propagating explosions have developed from 1 to 127 psi, and in a few trials pressure piling caused higher, unrecordable pressures and considerable damage.”The 1921 study also notes that the government set a 50-pounds-per-square-inch requirement on seals in mines located on federal lands. That regulation, the study said, “was based on the general opinion of men experienced in mine explosion investigations.”The study also notes that the United Kingdom determined that the 50 psi standard “gives a good margin of safety in practice” after studies of disasters there in 1933 and 1960.In Poland and Germany, the 1921 study said, the standard for seal construction is 72 pounds per square inch.Sago investigators and other mine safety experts say they are closely examining whether the MSHA rule was tough enough.“It’s the $50 question,” said Jurgen Brune, a researcher with the National Institute of Occupational Safety and Health, which took over mine safety work when the Bureau of Mines was eliminated. “Is explosion proof really 20 psi?”To contact staff writer Ken Ward Jr., use e-mail or call 348-1702.