Published in the August 2007 American Longwall Magazine

Kenneth Cashdollar of the National Institute for Occupational Safety and Health's Pittsburgh Research Laboratory teamed up with the Mine Safety and Health Administration's Terry Montgomery and John Going of the Fike Corporation for the project, which encompassed research on dust explosions based on samples taken after an accident. The details and results were presented at June's Longwall USA show in Pennsylvania.

They cited a rash of recent US explosions, including incidents in Utah, Alabama, West Virginia and Kentucky that totaled 32 fatalities and 12 injuries. "These events show that the mine explosion problem has not yet been solved," the trio said.

That was the impetus for the three to develop joint research on the topic, and to do so they secured research time at the NIOSH Lake Lynn Experimental Mine in southwestern Pennsylvania.

As part of the project, post-explosion dust samples were taken from areas on the mine's floor as well as at various areas of the face. When needed, such as when insufficient dust was available for collection from a single square, multiple squares or band samples were compiled.

The ignition point for the planned explosions at Lake Lynn was a methane-air zone, which was ignited using electric matches. The researchers said pure coal dust was also examined.

"In the tests involving pure fuel, all the dust was placed on roof shelves to enhance the dispersion. In the rock dust inerting tests, the coal dust and limestone rock dust mixture was placed half on roof rock dust and half on the floor," they noted.

At the same time, explosion research was also being conducted at other locations: in a one cubic meter chamber located at the Fike Corporation using a NIOSH-developed optical dust probe; at MSHA's laboratory in Mount Hope, West Virginia; and using the NIOSH PRL 20-L chamber.

The project did produce some results the researchers didn't expect at first: "The fact that large and very large amounts of coke were observed within the flame zones for the Lake Lynn tests with initial rock dust contents up to 65 percent, 77 percent and even 80 percent was initially somewhat surprising," they said, primarily because older research had noted the contrary (that no coke is formed when dust is more than 50% incombustible).

The group also experimented to confirm that coal dust has to be dispersed into a flame point in order for a notable amount of coke to be created. In another series of the study, various dust sizes were expended into explosions of methane gas that were then ignited by electric spark.

"In almost all the tests, large or very large amounts of coke were observed in dust samples collected after the tests," they said, adding the 30x20 mesh sieve left a large coke amount and only the 20x10 did not. "This shows that even very large coal particles up to 20 mesh become coked when they are in a flame, even though the size of coal is too large to propagate an explosion in the absence of methane."

Both groups of data from the various testing locations showed that post-explosion incombustibles were as prevalent as, if not more so than, typical readings.