EFFECTIVE DATE: 10/14/2010 EXPIRATION DATE: 03/31/2012 

PROCEDURE INSTRUCTION LETTER NO. I10-V-16 

FROM: KEVIN G. STRICKLIN 

 Administrator for 

 Coal Mine Safety and Health 

SUBJECT: Accumulation of Combustible Materials and Rock Dust 

Scope

This Procedure Instruction Letter (PIL) applies to Coal Mine Safety and Health 

(CMS&H) enforcement personnel. 

Purpose

This PIL provides instruction for enforcement personnel on accumulation of 

combustible materials and rock dust. An Emergency Temporary Standard (ETS) for 

Maintenance of Incombustible Content of Rock Dust was published on September 23, 

2010. The ETS was 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. This PIL provides instruction for enforcement personnel for 

implementing this ETS and taking spot rock dust samples. 

Procedure Instructions

District personnel should review the mine operator’s program and the enforcement 

history for regular cleanup and removal of accumulations of coal and float coal dust, 

loose coal, and other combustibles. 

Section 75.400, regarding accumulation of combustible materials, requires that coal 

dust, including float coal dust deposited on rock-dusted surfaces, loose coal, and other 

combustible materials must be cleaned up and not permitted to accumulate in active 

areas of underground coal mines, or on diesel-powered and electric equipment therein. 

Section 75.400 is applicable to all underground coal mines, including anthracite coal 

mines. 

Section 75.400-2, regarding the cleanup program, requires mine operators to establish 

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

float coal dusts, loose coal, and other combustibles. 
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Section 75.402, regarding rock dusting, requires mine operators to apply rock dust in 

sufficient quantities to all areas of an underground coal mine to within 40 feet of 

working faces, unless underground areas are too wet or too high in incombustible 

content to propagate an explosion or the areas are inaccessible or unsafe to enter. This 

would include all crosscuts that are less than 40 feet from a working face. 

Section 75.403, regarding maintenance of incombustible content of rock dust, as revised 

by the ETS, requires bituminous mine operators to apply and maintain rock dust so the 

total incombustible content (TIC) of combined coal dust, rock dust, and other dust will 

be maintained at 80 percent in all accessible areas of a coal mine. Where methane is 

present in an aircourse, the TIC must be increased by 0.4 percent for each 0.1 percent of 

methane. 

If mine operators allow coal, float coal dust, and other combustible materials to 

accumulate in active workings and on equipment in the mine, or if the TIC of the 

combined coal dust, rock dust, and other dust in any area of the mine does not meet the 

quantities required by the ETS, inspectors should take appropriate enforcement action. 

Selective Spot Sampling

During regular inspections, MSHA inspectors should continue to sample the 

incombustible content as required by MSHA’s existing sampling policy and procedures 

for collecting rock dust samples, including sampling to within 50 feet of the tailpiece. In 

addition, inspectors should take selective spot samples in areas that were rock dusted 

prior to September 23, 2010, to determine whether the mine operator is maintaining the 

80 percent TIC requirements of the ETS. Inspectors should also conduct selective spot 

sampling in immediate return entries, especially longwall tailgate entries, and areas 

containing seals. Inspectors should begin spot sampling near the active faces and in 

areas that contain ignition sources, such as conveyor belt drives and conveyor belt 

entries because these areas pose the greatest potential for methane and coal dust 

explosions. Inspectors need to identify the spot samples in the same manner as samples 

collected under the existing sampling policy and use the same mailing procedures. 

When a violation of 30 C.F.R. §§ 75.400, 75.402, or 75.403 is found, abatement should be 

set at the shortest reasonable time after careful evaluation of conditions on a mine-bymine basis, including whether the mine liberates large volumes of methane gas or has a 

history of methane ignitions. If an operator fails to totally abate within the specified 

time, a Section 104 (b) Order of Withdrawal should be issued. 

If a mine operator has repeat violations of §§ 75.400, 75.402 or 75.403, inspection 

personnel should discuss the adequacy of the cleanup program with the mine operator 

and consider requiring the use of more effective methods for controlling and 

maintaining the incombustible content of the combined coal dust, rock dust, and other 

dust along with elevated enforcement actions. Inspection personnel should also 
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consider changes to the cleanup program which would require the use of bulk dusters, 

trickle dusters or high-pressure rock dusting machines to continuously rock dust the 

areas downwind of belt transfers, the returns of active sections, the tailgates of 

longwalls and the bleeder entries. 

Background

MSHA’s analyses of rock dust samples, sampling records, and enforcement data, 

indicate that some underground coal mine operators are allowing combustible 

materials or coal dust to accumulate and are not applying rock dust in all required 

areas. Also, some operators are not maintaining the required levels of rock dust 

application under 30 C.F.R. §§ 75.400, 75.400-2, 75.402, and 75.403.

Authority

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

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

Internet Availability

This PIL may be viewed on the Internet by accessing MSHA's home page at 

(www.msha.gov), choosing "Compliance Info" and "Procedure Instruction Letters." 

Issuing Office and Contact Person

Coal Mine Safety and Health, Safety Division 

Michael G. Kalich, (202) 693-9714 

E-mail: kalich.michael@dol.gov

Distribution

MSHA Program Policy Manual Holders