Read the ruleCHARLESTON, W.Va. -- Citing a "grave danger" to the nation's coal miners, the Obama administration said Tuesday that mine operators must take additional steps to control the buildup of highly explosive coal dust underground.The U.S. Mine Safety and Health Administration issued an emergency rule that will force operators to apply more crushed stone to the walls, floors and other surfaces in underground coal mines.Experts from the National Institute for Occupational Safety and Health urged a toughening of federal "rock dusting" standards in reports published in 2006 and 2009. But MSHA officials did not act until another NIOSH report was published this May, a month after 29 miners died in an explosion at Massey Energy's Upper Big Branch Mine in Raleigh County."It's something that's long overdue," said Dennis O'Dell, safety and health director for the United Mine Workers union. "We support it, absolutely."Coal dust is highly explosive, and can turn what might be minor ignitions of methane gas in underground mines into massive blasts that take many more lives. Federal and state investigators and independent experts believe that's exactly what happened on April 5, when a huge explosion ripped through the Upper Big Branch Mine, causing the worst U.S. coal-mining disaster in 40 years.Mine safety experts have known for decades how to prevent coal dust explosions: Apply large amounts of "rock dust," usually powdered limestone, to wall and floor surfaces underground. Even if there is an explosion, the rock dust mixes with coal dust and helps prevent it from fueling a larger blast.Under the 1969 federal Coal Mine Health and Safety act, coal companies must apply enough rock dust so that "incombustible content" of mine dust in clean-air intake tunnels makes up at least 65 percent of all dust measured. In "return air" sources, rock dusting must be adequate to make the incombustible content 80 percent of all dust measured.But that 41-year-old law is based on coal-dust surveys of U.S. mines conducted in the 1920s. More recent NIOSH studies, conducted after a series of disasters in 2006, found that more modern and highly mechanized mining practices produce significantly finer coal dust that requires more rock dust to control.Under the change announced Tuesday by MSHA, the incombustible content of dust in all areas of underground mines would have to be at least 80 percent. Higher incombustible percentages would be required where methane is present."Coal dust can cause explosions, and explosions kill miners," said Labor Secretary Hilda Solis. "Compliance with the new standard will strengthen the protection for miners by minimizing the potential for such an explosion and, ultimately, will save lives."MSHA issued its new rule as an "Emergency Temporary Standard," allowed under federal law only when the agency determines that miners are at "grave danger." MSHA can temporarily avoid public comment and hearings, but must begin that process now and issue a final rule within nine months. Congress gave MSHA authority for such emergency rules in 1977, and the agency has taken that rulemaking route only four times since."Explosions caused by coal dust are particularly violent and deadly," said MSHA Secretary Joe Main. "We know that it will take mine operators a little bit of time to bring their mines into compliance with the new standard, but coal dust explosions are serious, and we expect mine operators to act quickly to reduce the threat to those mining coal underground."Officials from the National Mining Association did not immediately respond to a request for comment Tuesday.In its rulemaking announcement, MSHA said that the change would cost the nation's 415 underground coal mines a total of $22 million a year for additional rock dust and for employee time applying that rock dust. The agency noted that six coal dust explosions killed 46 miners over the last 26 years, or an average of two miners per year."MSHA acknowledges that the requirements in this ETS probably would not have prevented all of the deaths from the six explosions, and estimates that the ETS would have prevented approximately one to one and a half deaths per year," MSHA said in a Federal Register notice.Reach Ken Ward Jr. at firstname.lastname@example.org or 304-348-1702.