WASHINGTON -- Federal mine safety researchers in Western Pennsylvania first identified the problem in the 1980s, delved into it in the 1990s and warned about its consequences over the past few years: Standards for preventing coal dust explosions are outdated and insufficient.
Yet the Mine Safety and Health Administration did not act on proposed recommendations on how to combat floating coal dust, a powerful explosive fuel. Now as a result of the April 5 explosion at the Upper Big Branch mine in West Virginia that killed 29 miners and likely was caused, at least in part, by coal dust, regulation of the tiny and potentially deadly particles is certain to be re-examined.
"MSHA has been aware of this issue with coal dust and rock dust for some time now," MSHA spokeswoman Amy Louviere wrote in an e-mail. "It has been working its way through the pipeline, along with a number of other mine safety issues, and will continue to be on MSHA's radar screen."
President Barack Obama will deliver the eulogy today for the miners at a memorial service in Beckley, W.Va., and the president has pledged an expansive investigation into the causes of the blast. West Virginia Gov. Joe Manchin has appointed an independent team led by former MSHA official J. Davitt McAteer, and the U.S. House and Senate are mounting their own inquiries.
Federal and state regulators will look at a variety of areas in the aftermath of Upper Big Branch. On Wednesday, the West Virginia Board of Coal Mine Health and Safety proposed requiring underground mines to install barometers and regularly check methane gas monitors.
But improper coal dust cleanup is by far the most common type of citation MSHA issues to underground coal mines: Since 2007, 30,486 such citations have been issued -- or about 12 percent of the total.
Dust comes naturally from mining coal, and it can be a particularly dangerous accelerant to an explosion when floating in the air surrounded by oxygen. A spark to a small amount of methane -- another naturally occurring result of the mining process -- can be multiplied many times over if it catches onto airborne coal dust.
Researchers in the early 1900s found a simple way to render coal dust inert: ground up limestone. Long-standing federal law mandates rock dust be applied around mine entryways to keep the coal dust grounded, with a concentration of at least 65 percent rock dust in that mixture.
But new mining practices have brought machinery that grinds coal into smaller dust particles. Those smaller particles can more easily become suspended in the air and thus require more rock dust to keep the coal dust grounded.
"According to past full-scale dust explosion test results, the current rock dusting practices used in today's mines to inert a coal dust explosion may not be adequate," Marcia Harris and three of her colleagues at the National Institute for Occupational Safety and Health wrote in a 2009 report.
The research forming the basis of the current rock dust-coal dust regulations was conducted in the 1920s. NIOSH now recommends that instead of 65 percent rock dust, the concentration should be more like 80 percent.
The research has been cultivated for decades, said Jeffrey Kohler, who directs the agency's Office of Mine Safety and Health Research in South Park, though it was not certified and peer-reviewed until recent years. Even then, MSHA did not act to update its regulations to reflect those findings.
"In the past two to three years, it has been of concern to them, and I think they have been addressing a number of considerable safety and health issues in rule making, and I think this was on their list of things to do," Dr. Kohler said.
The Government Accountability Office also raised the coal dust problem in a 2003 report, chiding MSHA for inconsistent enforcement of its existing regulations.
"Several district officials in two of the districts we visited told us that the lack of specific criteria for floating coal dust makes it difficult to determine what is an allowable level," GAO wrote in the expansive report on MSHA and mine safety.
"According to some of the inspectors we interviewed, this has led, in some cases, to inconsistencies in inspectors' interpretations of the procedures -- some inspectors have cited violations for levels of floating coal dust that have not brought citations from other inspectors."
Then-MSHA head David Lauriski responded in a letter, saying: "The presence of float coal dust is a condition that must be evaluated on a case-by-case basis. There is no 'shopping list' or clear-cut formula to indicate when and to what degree the presence of float coal dust poses a distinct hazard to miners."
Coal dust has been cited as a factor in at least six major deadly explosions in the United States since 1970, according to a review of federal documents and news media reports. Dr. Kohler said preliminary information from Upper Big Branch suggests coal dust played a bigger role in the blast than any disaster in decades.
Such a major coal dust explosion -- if confirmed -- would prompt NIOSH to take a closer look at preventing and mitigating such explosions, Dr. Kohler said.
For example, in the NIOSH test mine in the Lake Lynn Laboratory, 50 miles from Pittsburgh in Fayette County, researchers have looked into whether suspending bags of rock dust in the air throughout a mine could slow down an explosion.
"I believe that we certainly will look at perhaps ways of quenching explosions," Dr. Kohler said. "Perhaps we'll give that a higher priority now than we would have six months ago."
The Associated Press contributed. Daniel Malloy: email@example.com or 202-445-9980. Follow him on Twitter at PG_in_DC.