ISSUE DATE: 09/21/2010 

PROGRAM INFORMATION BULLETIN NO. P10-18 

FROM: KEVIN G. STRICKLIN

Administrator for 

Coal Mine Safety and Health 

SUBJECT: Accumulation of Combustible Materials and Rock Dust 

Scope

Operators of underground bituminous coal mines, miners’ representatives, Mine Safety and 

Health Administration (MSHA) enforcement personnel and other interested parties should have 

this information. 

Purpose

This Program Information Bulletin (PIB) provides important information regarding accumulation 

of combustible materials and rock dust requirements. 

Information

Under MSHA’s existing standards, it is the mine operator’s responsibility to regularly clean up 

and remove accumulations of coal dust, including float coal dust, loose coal, and other 

combustible materials. Also, mine operators must apply rock dust in areas of underground 

bituminous coal mines to inert coal and float coal dust, loose coal, and other combustible 

materials. As little as 0.005 inches (the thickness of a sheet of paper) of coal and float coal dust 

on top of rock dust is capable of propagating an explosion. Therefore, removal of coal dust, 

including float coal dust, loose coal, and other combustible materials, and the effective 

application of rock dust is essential to protect miners from the potential of a coal dust explosion; 

or if one occurs, to reduce its severity and prevent loss of life. Mine operators must comply with 

the Agency’s combustible materials and rock dusting standards under 30 C.F.R. Part 75, 

Subpart E. 

MSHA’s accumulation of combustible materials standard at 30 C.F.R. § 75.400 requires that 

coal dust, including float coal dust, loose coal and other combustible materials are cleaned up 

and not permitted to accumulate in active workings, or on diesel-powered equipment and electric 

equipment therein. In addition, 30 C.F.R. § 75.400-2 requires that mine operators establish and 

maintain a program for regular cleanup and removal of accumulations of coal and float coal 

dusts, loose coal, and other combustibles. Both standards are designed to prevent accumulations 

of combustible materials and reduce the danger of a mine fire or explosion. 
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MSHA’s rock dusting standard at 30 C.F.R. § 75.402 requires that all underground areas of a 

coal mine be rock dusted to within 40 feet of all working faces and that all crosscuts that are less 

than 40 feet from a working face be rock dusted. Exceptions to the rock dusting requirement 

include areas that are too wet or too high in incombustible content to propagate an explosion, 

areas that are inaccessible or unsafe to enter, or a finding by MSHA that an exception to rock 

dusting does not pose a hazard to miners. 

On September 23, 2010, MSHA published an emergency temporary standard (ETS) on 

Maintenance of Incombustible Content of Rock Dust. The ETS revises existing 30 C.F.R. § 

75.403 and is effective upon publication. Each mine operator must comply with the ETS by 

October 7, 2010, for newly mined areas, and November 22, 2010, for all other areas of the mine. 

The ETS is based on MSHA’s accident investigation reports of mine explosions in intake air 

courses that involved coal dust (Dubaniewicz 2009); the National Institute for Occupational 

Safety and Health’s (NIOSH) Report of Investigations 9679 (Cashdollar et al. 2010), 

“Recommendations for a New Rock Dusting Standard to Prevent Coal Dust Explosions in Intake 

Airways;” and MSHA’s experience and data. The ETS requires mine operators to increase the 

incombustible content of combined coal dust, rock dust, and other dust to at least 80 percent in 

all areas of underground bituminous coal mines. The ETS further requires that the incombustible 

content of such combined dust be raised 0.4 percent for each 0.1 percent of methane. The ETS 

strengthens the protection for miners in underground bituminous mines. 

Water tends to collect in active mining areas but, historically, information on mining disasters 

has shown that many wet areas of an active mine tend to dry out, particularly during winter 

months. The areas downwind of belt transfers, the returns of active sections, the tailgates of 

longwalls, and the bleeder entries often require continuous rock dusting with bulk dusters, trickle 

dusters or high-pressure rock dusting machines to maintain the required incombustible content 

levels and suppress float coal dust accumulations. Mine operators should use mechanical rock 

dusters on the working sections and in the return entries of these sections to maintain compliance 

with the ETS. Also, mine operators should use bulk dusters on a regular basis in other areas of 

the mine to assure compliance with the ETS and maintain the required incombustible content of 

total dust in all accessible areas. 

Background

According to MSHA's analyses of rock dust samples, sampling records, and enforcement data, 

underground bituminous coal mine operators are allowing combustible materials or coal dust to 

accumulate, are not applying rock dust in all required areas, and are not maintaining the required 

levels of rock dust applications in compliance with 30 C.F.R. §§ 75.400, 75.400-2, 75.402 and 

75.403. From January 1, 2008, to August 30, 2010, MSHA issued 25,824 citations and 779 

orders for violations of § 75.400; 529 citations and 24 orders for violations of § 75.402; and 

3,445 citations and 42 orders for violations of § 75.403. 
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Authority

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

C.F.R. §§ 75.400, 75.400-2, 75.402 and 75.403. 

Internet Availability

This PIB may be viewed on the Internet by accessing the MSHA home page 

(www.msha.gov) then choosing “Compliance Info” and “Program Information 

Bulletins.” 

Issuing Office and Contact Persons

Coal Mine Safety and Health, Division of Safety 

Erik Sherer, (202) 693-9523 

E-mail: sherer.hubert@dol.gov

Distribution

MSHA Program Policy Manual Holders 

Underground Coal Mine Operators 

Coal Special Interest Groups 

Miners’ Representatives