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Recent Coal Dust Particle Size Surveys and the Implications for Mine Explosions

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National Institute for Occupational Safety and Health (NIOSH) of the Centers for Disease Control and Prevention (CDC), Department of Health and Human Services (HHS).


Notice of draft publication available for public comment.


The National Institute for Occupational Safety and Health (NIOSH) of the Centers for Disease Control and Prevention (CDC) announces the following draft Publication available for public comment entitled “Recent Coal Dust Particle Size Surveys and the Implications for Mine Explosions.” The document and instructions for submitting comments can be found at​niosh/​review/​public/​174/​default.html.

Public Comment Period: Comment period from August 31, 2009 to September 30, 2009.


Written comments may be submitted to the NIOSH Docket Office, Robert A. Taft Laboratories, 4676 Columbia Parkway, MS-C34, Cincinnati, Ohio 45226. All material submitted to the NIOSH should reference docket number NIOSH-174 and must be submitted by September 30, 2009 to be considered by the Agency. All electronic comments should be formatted as Microsoft Word. In addition, comments may be sent via e-mail to or by facsimile to (513) 533-8285. A complete electronic docket containing all comments submitted will be available on the NIOSH Web page at​niosh/​docket, and comments will be available in writing by request. NIOSH includes all comments received without change in the electronic docket, including any personal information. All information received in response to this notice will be available for public examination and copying at the NIOSH Docket Office, Room 111, 4676 Columbia Parkway, Cincinnati, Ohio 45226, telephone (513) 533-8611.

Background: Spreading rock dust in bituminous coal mines is the primary means of reducing the explosion potential of coal dust that collects during the normal workings of an active coal mine. Accordingly, guidelines have been established by the Mine Safety and Health Administration (MSHA) about the relative proportion of rock dust that needs to be present in both intake and return airways. Specifically, current MSHA regulations require that intake airways contain at least 65% incombustible content and return airways contain at least 80%. The higher limit for return airways was set in large part because fine “float” coal dust (100% < 200 mesh or 75 μm) tends to collect in these airways. MSHA inspectors routinely monitor rock dust inerting efforts by collecting dust samples and measuring the percentage of total incombustible content (TIC). These regulations were based on two important findings: a survey of coal dust particle size that was performed in the 1920s and large-scale explosion tests conducted in the U.S. Bureau of Mines' Bruceton Experimental Mine (BEM) using dust particles of that size range to determine the amount of inerting material required to prevent explosion propagation.

Mining technology and practices have changed considerably since the 1920s when the original coal dust particle survey was performed. Also, it has been shown conclusively that as the average size of coal dust particles decreases, the explosion hazard increases. Given these factors, the National Institute for Occupational Safety and Health (NIOSH) and MSHA conducted a joint survey to determine the range of coal particle sizes found in dust samples collected from intake and return airways of U.S. coal mines. Results from this survey show that the coal dust found in mines today is much finer than in mines of the 1920s, presumably due to increased automation and a greater reliance on mining machinery.

In light of this recent comprehensive dust survey, NIOSH conducted additional large-scale explosion tests at the Lake Lynn Experimental Mine (LLEM) to determine the degree of rock dusting necessary to abate explosions using Pittsburgh seam coal dust blended as 38% < 200 mesh and referred to as medium-sized dust. Explosion tests indicate that medium-sized coal dust required 76.4% TIC to prevent explosion propagation. Even the coarse coal dust (20% < 200 mesh or 75 μm) representative of samples obtained from mines in the 1920s required approximately 68% TIC to be rendered inert, a level higher than the current regulation of 65% TIC. In return airways, the particle size survey revealed that the average dust particle size is roughly the same as float coal Start Printed Page 42318dust as defined in the Coal Mine Health and Safety Act of 1969.

Given the results of the recent coal dust particle size survey and large-scale explosion tests, NIOSH recommends a new standard of 80% TIC be required in the intake airways of bituminous coal mines. The survey results indicate that the current requirement of 80% TIC in return airways is still sufficient and appropriate. In addition, NIOSH agrees with and endorses an earlier recommendation that new rock dusting standards should be based on a worst-case scenario (using high volatile coals) with no relaxation for lower volatile coals.

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Dr. Jeff Kohler, NIOSH Associate Director for Mining and Construction, 626 Cochrans Mill Road, Pittsburgh, PA 15236, (412) 386-6544, E-mail

Reference: Web address for this publication:​niosh/​review/​public/​174/​pdfs/​RD-inertingOutToExtReview.pdf.

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Dated: August 14, 2009.

Christine M. Branche,

Acting Director, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention.

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[FR Doc. E9-20205 Filed 8-20-09; 8:45 am]