CHARLESTON, W.Va. -- Nine years ago last Thursday, a series of explosions rocked the Jim Walter Resources No. 5 Mine in Brookwood, Ala. Thirteen coal miners died.Federal investigators blamed the disaster in part on Jim Walter Resources' failure to apply enough "rock dust" to control explosive coal dust that can build up underground. The company appealed, and a federal judge ruled that the U.S. Mine Safety and Health Administration's dust samples -- gathered after the explosion -- didn't accurately reflect conditions at the time of the blast.Now, Massey Energy Co. is raising similar arguments about dust samples. MSHA believes the samples show the coal giant did not do enough to control the buildup of explosive coal dust at its Upper Big Branch Mine, where 29 workers died in a massive blast on April 5.MSHA might have avoided such legal battles had the agency long ago forced coal-mine operators to install special meters that would allow real-time monitoring of coal-dust conditions in underground mines across the country.Over the years, experts from the National Institute for Occupational Safety and Health and the now-defunct Bureau of Mines repeatedly urged the mining industry to deploy such equipment.In one report in 1989, the Bureau of Mines said dust meters were among "the most promising methods" for helping to prevent deadly coal-dust explosions."The Bureau of Mines has developed an optical rock-dust meter that can be used underground to give a direct and rapid read-out of the rock-dust content of mine dust samples, thus eliminating the need for laborious and time-consuming laboratory analysis of rock-dust content," said the report, presented to the International Conference of Safety in Mines Research Institutes."The in-situ measurement allows for immediate corrective action and has high potential for improving mine explosion safety," the report said. "The Bureau device is in the process of being commercialized."So far, the United States still does not require rock-dust testing meters. Legislation pending in Congress would force operators to start using them, but block MSHA from basing enforcement actions on the test results for two years or more while the devices undergo further study.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 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 walls, floors and other surfaces underground. Even if there is an explosion, the rock dust mixes with coal 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 the "incombustible content" of mine dust in clean-air intake tunnels makes up at least 65 percent of all dust measured. In "return air" and other tunnels, rock dusting must be adequate to make the incombustible content 80 percent of all dust measured.Along with improved mine ventilation practices and explosion-proof electrical equipment, the use of rock dust underground has made massive coal-dust explosions far less frequent, but between 1976 and 2001, inadequate rock-dusting was blamed at least in part on six explosions that killed 46 U.S. coal miners, records show.Last week, MSHA issued an emergency rule to require mine operators to use enough rock dust to make the incombustible content in clean-air intake tunnels also measure 80 percent of all dust measured.In doing so, MSHA chief Joe Main cited a May 2010 report in which NIOSH recommended that change. Main didn't mention that NIOSH also had made similar recommendations in separate reports issued in 2006 and 2009.In that May 2010 report, NIOSH researchers noted that questions about the adequacy of the 65 percent incombustible-content requirement were raised as far back as the 1929 Bureau of Mines report on which the requirement originally was based.Mine safety experts and researchers who study mine explosions have been arguing for many years that the very tiny coal-dust particles created by advanced mining techniques -- especially those using longwall machines -- require more rock dust and called for a tougher rock-dusting standard.Michael Sapko, a now-retired NIOSH researcher, outlined similar questions about the rock-dusting standards in a 1989 report."There is little data regarding the rate of float dust deposition in mechanized mines, but there is no doubt that it correlates with production rates," Sapko said. "With the increased utilization of longwall mining methods it represents a problem of growing concern."Regardless of the standard, the problem of taking rock-dusting samples and getting timely results remains. Dust samples from around the country are analyzed at one MSHA lab in Mount Hope, and the work can take two weeks or more.At Upper Big Branch, for example, MSHA inspectors took rock-dusting samples during a visit to the mine on March 13 of this year, but at least in part because of the time involved in analysis, MSHA did not get around to citing the mine for inadequate rock-dusting until April 13 -- after the deadly explosion."Why in the world are we sending samples away for weeks' time in this day and age?" said longtime mine safety chief Davitt McAteer, who headed MSHA during the Clinton administration. "It hampers enforcement and it hampers the prevention cycle."In a 2006 report, Sapko and fellow NIOSH researcher Harry Verakis outlined how the agency's "Coal Dust Explosibility Meter," or CDEM, could speed such enforcement actions."The CDEM's in situ explosibility measurement can help mine operators reduce the danger of operating under hazardous conditions of explosible dusts and help provide a better balance between the applied rock dust and generated coal dust," Sapko and Veraki wrote."Relative to compliance, an inspector could focus specifically on deficient or borderline samples for subsequent laboratory analysis," they wrote. "Most importantly, the CDEM shows promise as a useful tool for mine operators and safety inspectors for the in situ determination of the explosible nature of coal and rock dust deposits and thereby would enable immediate corrective action."Coming Monday: Could buckets of water hung from mine roofs prevent coal-dust disasters?Reach Ken Ward Jr. at firstname.lastname@example.org or 304-348-1702.