1. A safety manager at a West Virginia coal mine reported that
his operation had been fined $9,000 by MSHA after the
mine’s rock dust was found to contain only 78% of incom-
bustible particles, slightly under MSHA’s 80% standard.
MSHA’s latest crackdown is a response to the agency’s find-
ings related to the Upper Big Branch (UBB) mine explosion,
where rock dust samples indicated there was an insufficient
amount of rock dusting and insufficient amounts of incom-
bustible materials in the sampled rock dust. As a result, the
agency has begun to issue more rock dust related citations.
Following an October 27 bulletin, MSHA began inform-
ing coal operators it would begin enforcing regulations
around rock dust samples and content. According to a
Program Information Bulletin (PIB) from MSHA, 47% of
various rock dust samples taken from underground coal
mines did not meet particle size standards. Noncompliant
dust was found at 51% of the mines sampled. Rock dust is
used by underground coal mines to dilute the atmospheric
content of highly combustible coal particles with inert rock
such as pulverized limestone, shale, adobe, dolomite, anhy-
drite or some other inert material.
MSHA now believes the UBB mine explosion was propa-
gated by inadequate rock dusting.
“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,” the PIB
bulletin states. “It should be noted that the Low
Temperature Ashing procedure used by MSHA to deter-
mine the incombustible content of coal dust samples is
insensitive to both oversized and caked particles.” This
means that even though a mine operator may achieve the
necessary 80% or greater incombustible content, the “mix-
ture may not prevent a coal dust explosion from propagat-
ing.” MSHA is recommending coal mine operators test their
supplies of rock dust upon receipt and ask for documenta-
tion of quality testing from the manufacturer.
MSHA’s new “final” rule replaces the Mine Safety and
Health Administration’s Emergency Temporary Standard
(ETS) pursuant to section 101(b) of the Federal Mine Safety
and Health Act of 1977. Under the new rule, mine operators
must maintain the incombustible content of combined coal
dust, rock dust and other dust to at least 80% in under-
ground areas of bituminous coal mines. The final rule fur-
ther requires that the incombustible content of such
combined dust be increased 0.4% for each 0.1% of methane
present in the mine. As is well known, accumulations of
coal dust can ignite, resulting in an explosion, or after an
explosion, they can intensify flame propagation, increasing
the severity of explosions. The latter seems to be part of the
underpinning explanation for the severity of the UBB dis-
taster. The final rule, like the ETS, should reduce both the
potential for a coal mine explosion and the severity of
explosions should they occur.
What is Rock Dust and How Do I Know?
Rock dust is pulverized stone used to mix with coal dust
and render accumulations of it inert. MSHA defines “rock
dust” under 30 CFR 75.2 as “pulverized limestone,
dolomite, gypsum, anhydrite, shale, adobe or other inert
material, preferably light colored, 100% of which will pass
through a 20-mesh sieve and 70% or more of which will
pass through a 200-mesh sieve; 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% combustible
matter or more than a total of 4% free and combined silica
(SiO2), or, where the Secretary finds that such silica concen-
trations are not available, which does not contain more
than 5% of free and combined silica.”
Where rock dust is required to be applied, according to
MSHA standards, “it shall be distributed upon the top, floor
rock dust
Are New Rock Dust Standards
Crushing You?
42 www.coalage.com January 2012
MSHA’s new regulations once again challenge the status quo
BY LEE BUCHSBAUM, ASSOCIATE EDITOR & PHOTOGRAPHER
MSHA is recommending coal
mine operators test their supplies of
rock dust upon receipt and ask for
documentation of quality testing
from the manufacturer.
“ “

2. and sides of all underground areas of a coal mine and main-
tained in such quantities that the incombustible content of
the combined coal dust, rock dust and other dust shall be
not less than 80%. Where methane is present in any venti-
lating current, the per centum of incombustible content of
such combined dust shall be increased 0.4 per centum for
each 0.1 per centum of methane present.
Rock dust also acts as a heat sink to absorb and mini-
mize explosions. The active ingredient of the rock dust
sucks the heat out of the fire—that is the primary mecha-
nism for rock dust. The fact that rock dust is heavier than
coal dust forces the float coal to fall to the floor. The rock
dust will then drag the coal dust out of the air to the ground.
On June 21, 2011, under section 101(b) of the Mine Act,
MSHA published their final rule revising the existing stan-
dard at 30 CFR 75.403, “Maintenance of incombustible con-
tent of rock dust” applicable to underground areas of
bituminous coal mines.
To clarify MSHA’s enforcement under the ETS, the agency,
prior to the final rule, issued PIB No. P10-18, “Accumulation
of Combustible Materials and Rock Dust,” on September 21,
2010 (September 2010 PIB). The PIB emphasized that under-
ground coal mine operators had not been rock dusting in all
required areas and were not maintaining the required levels
of rock dust applications in compliance with the previous
MSHA standard of no less than 65 per centum in intake air-
courses, and no less than 80 per centum in return aircourses
under 30 CFR 75.403.Sh.
On October 14, 2010, MSHA issued Procedure Instruction
Letter No. 10-V-16, “Accumulation of Combustible Materials
and Rock Dust” (October 2010 PIL). The October 2010 PIL pro-
vided instruction for MSHA enforcement personnel regarding
accumulation of combustible materials and rock dust. In the
2010 PIL, MSHA emphasized each mine operator’s responsibil-
ity to comply with the ETS by October 7, 2010, for newly mined
areas; and November 22, 2010, for all other areas of the mine.
MSHA provided instruction to agency personnel for enforcing
the ETS and for taking spot rock dust samples at applicable
mines.
All underground areas of a coal mine, except those areas in
which the dust is too wet or too high in incombustible content
to propagate an explosion, shall be rock dusted to within 40 ft of
all working faces, unless such areas are inaccessible or unsafe to
enter or unless the Secretary or his authorized representative
permits an exception upon his finding that such exception will
not pose a hazard to the miners. All crosscuts that are less than
40 ft from a working face shall also be rock dusted.
The September 2010 PIB provided guidance to operators
on existing § 75.402 and ETS § 75.403. It suggested that they
use bulk dusters, trickle dusters or high-pressure rock dust-
ing machines to blow the rock dust into inaccessible areas
to maintain the 80% TIC in remote areas.
rock dust continued
January 2012 www.coalage.com 43

3. MSHA thoroughly believes that as little as 0.005 inch
(the thickness of a sheet of paper) of coal and float coal dust
on top of rock dusted surfaces is capable of propagating an
explosion. Therefore, removal of coal dust, including float
coal dust, loose coal, other combustible materials, and the
application and re-application, where necessary, of rock
dust are essential to effectively protect miners from the
potential of a coal dust explosion; or if one occurs, to reduce
its severity and prevent loss of life.
Application of rock dust by hand is not prohibited under
the final rule, as long as the 80% incombustible content of
the combined coal dust, rock dust and other dust is main-
tained. Based on MSHA experience, mine operators are
capable of maintaining the requirements of the final rule
through application of rock dust by hand.
To ensure that coal mines are using rock dust that is with-
in MSHA specifications, the agency started conducting blind
testing of various rock dusts. It found that a large majority of
them were not meeting the proper spec on sizing. The agen-
cy’s recent PIB states that each mine needs to ensure that not
only is the rock dust being used making the spec, but that
there is documentation that it does and will continue to do
so. According to one company representative, the new stan-
dard hasn’t resulted in an increase of in the usage of rock
dust, but in making sure there are more checks and balances.
“MSHA is asking producers of rock dust to provide evidence
that we are providing what we say we are providing,” said the
representative. Though to date MSHA has not issued any
rules on how to test the rock dust, suppliers are beginning to
provide a certificate of regulatory compliance.
Anecdotally, MSHA field inspectors are doing a much
more thorough job testing rock dust. “More than in the
past, these inspectors are being very vigilant in terms of
making sure that you have enough rock dust,” said another
insider. Inspectors are taking grab samples or doing on-
sight sieve analysis. So far, for someone to get fined, it has
to be pretty bad. And if they are down 20% from what they
needed, then they have a problem,” he said.
Is There a Shortage of Rock Dust Available?
Historically, limestone has always been a stable, low cost
product. Following the UBB disaster, several major suppli-
ers have put in new capacity and installed larger equipment
to ensure that as rock dust production increases, quality
remains steady and reliable as well. “There is plenty of
capacity to cover the increase demand for rock dust. No
one is being shorted materials today. Every coal mine that
needs it, gets it. There are no shortages where people can’t
get rock dust today,” said David Berg, market manager,
industrial milled limestone, Carmeuse Lime & Stone. While
statistics and figures are hard to come by, Berg estimates
that North America’s underground coal mines use about
1.5 million tons of rock dust per year. “Looking over pro-
duction statistics, I estimate that for every 250 tons of coal
produced you need 1 ton of rock dust,” Berg said.
Following the UBB disaster, Berg said there was a brief
bump in demand of rock dust. That has since abated.
Today, the most important issue for rock dust providers is
to sell rock dust that meets MSHA’s standards. One of the
problems with the rock dust sector is that, up until this lat-
est MSHA ruling, any aggregate quarry or ready-mix con-
crete plant could legally supply rock dust. “But as MSHA
ratchets up field inspections, these mom and pop quarries
will have to meet the MSHA rock dust spec. So if someone is
using a small quarry a mile from the mine, unless that plant
can produce to the new standards, then they’ll have to start
buying from a larger, compliant rock dust producer,” said
Berg. Some of these smaller producers have been selling
their “quarry fines” as rock dust. This product might not
meet the new rock dust spec, however.
Though many quarries supply rock dust, several coal
producers also mine or quarry rock dust for internal use as
well. These vertically integrated companies will most likely
weather this storm with little incident. More challenged,
however, will be the third party brokers who sell rock dust
as well. Many of these outfits are a combination of trucking
companies, coal brokers and distributors that also sell or
distribute rock dust. Some will buy existing rock dust and
put a different label on it. However, if they adulterate the
rock dust, they could find themselves in MSHA’s cross-
hairs, especially if that dust is found to be problematic.
In fact, to ensure quality, some rock dust producers like
Carmeuse are developing certificates to further underscore
a strict adherence to quality. “When these new rules came
out, most of our customers didn’t push the panic button—
they just needed documentation from us that says what
they purchased meets the spec. We will guarantee that our
product meets legal specifications as it leaves our facility.
However, if we sell it to a third party, then we have no qual-
ity control. But for anything we ship directly from our facili-
ties, we’ll prove that our materials meet the spec. That
should be the end of the discussion. Now it’s up to the coal
producer to make sure they are living up to their ends, that
they are using enough, that it doesn’t cake, and that they
stay within engineering best practices and standards.
Keeping the mine safe is our number one priority. We want
to make sure that our product and all rock dust being used
gives coal operators the assurance that rock dust is part of
the solution to safety, not the problem,” said Berg.
rock dust continued
44 www.coalage.com January 2012
MSHA has not issued any rules
on how to test the rock dust; suppliers
are beginning to provide a certificate
of regulatory compliance.
“ “