U.S. Department of Labor Mine Safety and Health Administration 

11 00 Wilson Boulevard 

Arlington, Virginia 22209-3939 

ISSUE DATE: OCT 2 7 2011 

PROGRAM INFORMATION BULLETIN NO. P11-50 

FROM: 

Administrator 

KEVIN G. STRICKLIN 

for :d~U.Ar:IV Coal Mine Safety and alth 

LINDA F. ZEILER~?<. J/c. ~_.t,.,__,__ /,?..._ 

Director of Technical Supp6'rt ~~& 

SUBJECT: Rock Dust Composition, 30 C.F.R. § 75.2 

Scope 

This Program Information Bulletin (PI B) applies to operators of underground bituminous 

coal mines, miners' representatives, Mine Safety and Health Administration (MSHA) 

enforcement personnel, and other interested parties including rock dust manufacturers. 

Purpose 

The purpose of this PIB is to alert coal mine operators and rock dust manufacturers of a 

possible problem with rock dust meeting the definition in 30 C.F.R. § 75.2 regarding 

particle size and tendency to form a cake. 

Information 

MSHA's existing definition of "Rock dust" at 30 C.F.R. § 75.2 states: 

Pulverized limestone, dolomite, gypsum, anhydrite, shale, adobe, or other 

inert material, preferably light colored, 100 percent of which will pass 

through a sieve having 20 meshes per linear inch and 70 percent or more 

of which will pass through a sieve having 200 meshes per linear inch; the 

particles of which when wetted and dried will not cohere to form a cake 

which will not be dispersed into separate particles by a light blast of air; 

and which does not contain more than 5 percent combustible matter or 

more than a total of 4 percent free and combined silica (Si02), or, where 

the Secretary finds that such silica concentrations are not available, which 

does not contain more than 5 percent of free and combined silica. 

You can now file your MSHA forms online at www.MSHA.gov. It's easy, it's fast, and it saves you money! 
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Underground coal mining methods produce fugitive coal dust which is deposited 

throughout the underground mine. Application of rock dust is one of the means of 

preventing propagation of coal dust explosions. Sufficient application of rock dust 

throughout a mine is required by MSHA to achieve an inert dust mixture. The National 

Institute for Occupational Safety and Health (NIOSH) recently released updated 

recommendations (RI 9679) for maintaining a minimum of 80 percent incombustible 

content of dusts in all areas of underground coal mines through the addition of inert 

pulverized rock dust. MSHA adopted these recommendations in June 2011, in its 

standard addressing "Maintenance of Incombustible Content of Rock Dust in 

Underground Coal Mines," 30 C.F.R. § 75.403. Rock dust must meet the definition of 

30 C.F.R. § 75.2. 

In October 2011, NIOSH issued a Hazard ID which states, in part, that: "In September 

2011, the NIOSH Office of Mine Safety and Health Research investigation of rock dust 

revealed two significant concerns with the supply of rock dust to US mines: 

1. Insufficient particles <200 mesh (75 um): In a population of 393 rock dust 

samples which were collected by MSHA personnel from 278 underground coal 

mines, 47% were found to contain less than the minimum specification of 70% 

passing through a 200-mesh (75 IJm) sieve. Noncompliant rock dust was found 

at 51% of the mines sampled. 

2. Tendency to form a cake: Examinations of the tendency of the rock dust 

samples to cake when wetted and subsequently dried revealed that all ten of the 

examined samples formed cakes and were not easily dispersed with the 

subjective requirement of a light blast of air. The rock dust samples NIOSH 

analyzed contained very fine (<1 0-1-Jm) particles. Fine particles enhance the 

caking potential of rock dust when wetted." 

These two issues indicate a possible lack of product quality control during the 

manufacturing process of rock dust that is intended for use by mine operators. 

It should be noted that the Low Temperature Ashing procedure used by MSHA to 

determine the incombustible content of coal dust samples is insensitive to both 

oversized and caked particles. Therefore, the mine operator may be applying sufficient 

rock dust to achieve an 80 percent or greater incombustible content, as confirmed by a 

Low Temperature Ashing Test, but if the rock dust purchased by the operator does not 

conform to 30 C.F.R. § 75.2, the mixture may not prevent a coal dust explosion from 

propagating. 

Action 

The NIOSH Hazard ID contains two recommendations that MSHA believes are 

important for mine operators, miners' representatives, and manufacturers to know. 

NIOSH recommends that operators: 
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1. Test their supply of rock dust upon receipt to assure that it meets the 

requirements of the 30 C.F.R. § 75.2. Rock dust that does not meet the 

requirements must not be used in the mine. 

2. Obtain documented assurance, based on testing from the rock dust 

manufacturer, that rock dust intended for use in underground coal mines 

meets the requirements of 30 C.F.R. § 75.2. 

MSHA inspectors will check whether operators are following these recommendations, 

and have manufacturers' documentation, to assure compliance with 30 C.F.R. § 75.2. 

MSHA will continue to work with NIOSH to examine the issues associated with the use 

of rock dust for explosion prevention. 

Background 

The application of rock dust in underground mines is one of the safety measures that 

helps prevent, limit, and mitigate fires and explosion in underground coal mines. 

Other safety measures include the use of proper ventilation, water sprays, methane 

monitoring, use of permissible equipment, and cleanup and removal of accumulations of 

coal and float coal dust, loose coal, and other combustibles. 

Authority 

The Federal Mine Safety and Health Act of 1977, 30 U.S.C. § 801 et seq.; 

30 C.F.R. § 75.2 

Issuing Offices and Contact Persons 

Coal Mine Safety and Health, Division of Safety 

Michael G. Kalich, 202-693-9714 

E-mail: kalich.michael@dol.gov 

Technical Support 

Mark Wesolowski, 412-386-6893 

E-mail: wesolowski .mark@dol.gov 

Internet Availability 

This PIB may be viewed on the internet by accessing MSHA's home page at 

http://msha.gov and then choosing "Compliance Info and Program Information 

Bulletins." 

Distribution 

Coal Mine Safety and Health All Volume Program Policy Manual Holders 

Underground Mine Operators 

All Independent Contractors 

Special Interest Groups 

Equipment Manufacturers 

Miners' Representatives