“Innovative Rock-Dusting System to Assist with Respirable Dust Compliance”

Dear Coal Age:
In reference to the article “Innovative Rock-Dusting System to Assist with Respirable Dust Compliance” published in the October edition of Coal Age, I would like to clarify the appropriate use of wet rock dust, and specifically, foam rock dust, to treat an underground coal mine. While I acknowledge that foam rock dust could be an “innovative” tool to address the respirable dust rule, it is not an innovative method to mitigate an explosion in an underground coal mine. Furthermore, foam rock dust is not currently allowed by MSHA as the primary method of dusting a mine, as it must be used in combination with dry rock dust.

My concern is that the readers of Coal Age could misinterpret statements in the article as an opportunity to use foam-based rock dust to replace dry rock dusting, which would be incorrect. Despite all the test data generated on foam rock dust, it is still not recognized by the National Institute for Occupational Health (NIOSH) or the Mine Safety and Health Administration (MSHA) as an acceptable alternative to dry rock dusting.

While wet rock dusting has been around for decades, foam rock dust has been around for at least 11 years (see U.S. Patent # 6,726,894, Gay et al, dated 4/27/04). Foam rock dust as an alternative to dry rock dusting was revisited in 2010, as a result of the UBB disaster. DSI, in cooperation with MSHA, conducted application trials of foam rock dust in actual coal mines, and MSHA subsequently asked NIOSH to verify the efficacy of foam rock dust as a primary rock dusting method. Unfortunately, NIOSH refused to recommend foam rock dust prior to seeing test results from a controlled explosion in an underground mine. Due to the closing of NIOSH’s Lake Lynn experimental mine in 2013, such an underground test explosion, with foam rock dust replacing dry rock dust as the primary inerting agent, has not taken place.

The Final Rule in 30 CFR Part 75 states that the use of wet dusting technology (re: foam) has limitations, particularly forming a “coating” on mine surfaces on top of which new coal dust can accumulate. “This coating will not provide as effective inerting capability in the event of an explosion as dry rock dust1.”

Specifically related to the limitations of foam rock dusting, MSHA‟s program policy manual, updated July 2015\Release V-51 states “wet dusting, such as foam rock dust is limited to rib and roof surfaces in the face areas and shall not be used for redusting mine surfaces. In such applications, only limestone or marble dust which meets the specification contained in Section 75.2(d) shall be used. After the wet rock dust dries, additional dry rock dust shall be applied to all surfaces to meet applicable standards. Wet rock-dusting of ribs and roof does not eliminate the necessity for dry rock-dusting the floor2.”

I applaud DSI’s efforts to improve rock dusting technology. Recognizing its limitations, foam rock dust should continue to be another tool in a coal company’s toolbox to prevent underground disasters.

David Berg, market manager
Carmeuse Lime & Stone

1 30 CFR Part 75, RIN 1219-AB76, Maintenance of Incombustible Content of Rock Dust in Underground Coal Mines
AGENCY: Mine Safety and Health Administration, Labor. ACTION: Final rule.
2 MSHA Program Policy Manual, VOLUME V - COAL MINES, Subpart E, Combustible Materials and Rock Dusting
75.403 Maintenance of Incombustible Content of Rock Dust.