MINE SAFETY

Basis for Proposed 

Exposure Limit on 

Respirable Coal Mine 

Dust and Possible 

Approaches for 

Lowering Dust Levels

Report to Congressional Requesters

April 2014

GAO-14-345

United States Government Accountability Office
United States Government Accountability Office

Highlights of GAO-14-345, a report to 

congressional requesters

April 2014

MINE SAFETY

Basis for Proposed Exposure Limit on Respirable 

Coal Mine Dust and Possible Approaches for 

Lowering Dust Levels

Why GAO Did This Study

Underground coal miners face the 

threat of being overexposed to coal 

mine dust, which can cause CWP and 

other lung diseases, collectively 

referred to as black lung disease. In 

October 2010, MSHA—the federal 

agency responsible for setting and 

enforcing mine safety and health 

standards—proposed lowering the 

exposure limit for respirable coal mine 

dust to reduce miners’ risk of 

contracting black lung. In August 2012, 

GAO reported that the evidence MSHA 

used supported its conclusion that

lowering the exposure limit on coal 

mine dust would reduce miners’ risk of 

disease. However, some have 

questioned whether and how recent 

NIOSH trend data on CWP were used

in developing the proposed limit.

In May 2013, GAO was asked to 

provide additional information on

MSHA’s proposal. GAO examined (1)

the extent to which MSHA used recent 

CWP trend data as a basis for its 

proposed exposure limit, and (2) expert 

views on ways to lower the level of 

dust in coal mines, including their 

associated advantages,

disadvantages, and cost. GAO 

reviewed MSHA’s proposal and related 

documents; updated a previous GAO 

literature search; interviewed MSHA 

and NIOSH officials; and, with the help 

of the National Academies, convened a

group of experts knowledgeable about 

underground coal mining and methods 

for reducing coal mine dust. GAO is 

not making any recommendations in 

this report, and MSHA and NIOSH 

both generally concurred with the 

findings. 

What GAO Found

The Department of Labor’s Mine Safety and Health Administration (MSHA) 

appropriately did not use recent trend data on coal workers’ pneumoconiosis 

(CWP) as a basis for its proposal to lower the permissible exposure limit for 

respirable coal mine dust. These recent data from the Department of Health and 

Human Services’ National Institute for Occupational Safety and Health (NIOSH) 

are inappropriate for this purpose because they do not include the types of 

detailed information about individual miners needed to estimate the likelihood 

that miners would develop CWP at different exposure levels, such as historical 

dust exposures. MSHA primarily based its proposed new limit on two reports and

six epidemiologic studies, which each concluded that lowering the limit on 

exposure to coal mine dust would reduce miners’ risk of developing disease.

MSHA’s proposed coal mine dust limit was supported by these reports and 

studies because, unlike recent CWP trend data, they included information 

needed to conduct a reliable epidemiological analysis of disease risks associated 

with different levels of exposure to coal mine dust. 

Experts identified various approaches that could incrementally reduce overall

coal mine dust levels as well as individual miners’ exposure to dust. They said 

that air and water are the primary engineering controls used to reduce overall 

coal mine dust levels in the mine environment, which are used in various mining 

equipment, such as sprays. The experts also said that no one technology or 

approach would result in substantially lower dust levels, but instead could have a 

cumulative impact if used together. They also noted that all the approaches may 

not be effective in all types of mines, and that there are a number of cost drivers 

that would have to be considered, such as machine maintenance and training.

The experts also identified other approaches, such as personal protective 

equipment and administrative controls, which could reduce individual miners’ 

exposure to dust. Personal protective equipment includes respirators and air 

stream helmets; administrative controls include rotating workers and using

remote control devices. However, they noted that these approaches would not 

help mine operators comply with MSHA’s exposure limit because they would not 

reduce the overall level of coal mine dust in the mine environment. 

Miner Using Water Spray to Control Coal Dust

View GAO-14-345. For more information, 

contact Revae Moran at (202) 512-7215 or 

moranr@gao.gov
Page i GAO-14-345 Mine Safety

Letter 1

Background 3

MSHA Did Not Use Recent CWP Trend Data as a Basis for Its 

Proposed Exposure Limit on Coal Mine Dust, Which Was 

Appropriate 6

Experts Identified Various Approaches that Could Reduce Overall 

Coal Mine Dust Levels, as Well as Individual Miners’ Exposure 

to Dust 8

Agency Comments 12

Appendix I Objectives, Scope, and Methodology 15

Appendix II GAO Contacts and Staff Acknowledgments 17

Abbreviations

CWP coal workers’ pneumoconiosis 

DOL Department of Labor 

mg/m3 milligrams of dust per cubic meter of air 

Mine Act Federal Mine Safety and Health Act of 1977 

MSHA Mine Safety and Health Administration 

NIOSH Department of Health and Human Services’ National 

Institute for Occupational Safety and Health 

Contents

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Page 1 GAO-14-345 Mine Safety

441 G St. N.W.

Washington, DC 20548

April 9, 2014

The Honorable Harold Rogers

Chairman

Committee on Appropriations

House of Representatives

The Honorable Jack Kingston

Chairman

Subcommittee on Labor, Health and Human

Services, Education and Related Agencies

Committee on Appropriations

House of Representatives

Coal mine dust is one of the most serious occupational hazards in the 

coal mining industry, and overexposure can cause coal workers’

pneumoconiosis (CWP) and a number of other lung diseases collectively 

referred to as black lung disease.1 CWP has been the underlying or 

contributing cause of death for more than 75,000 coal miners since 1968, 

according to the Department of Health and Human Services’ National 

Institute for Occupational Safety and Health (NIOSH), the federal agency 

responsible for conducting research on work-related diseases and injuries 

and recommending occupational safety and health standards. Since 

1970, the federal government has paid more than $45 billion in benefits to 

miners totally disabled by respiratory diseases (or to their survivors), 

including CWP, through the Black Lung Benefits Program.

In October 2010, the Department of Labor’s (DOL) Mine Safety and 

Health Administration (MSHA)—the federal agency responsible for setting 

and enforcing mine safety and health standards—proposed lowering the 

existing concentration limit2 for respirable coal mine dust from 2.0 

 1 In this report, we use the term coal mine dust to refer to respirable coal mine dust 

produced during the mining process in underground coal mines. Black lung disease is a 

term that includes CWP and other chronic respiratory or pulmonary impairments resulting 

from employment in coal mines.

2 In this report, we use the term exposure limit to refer to the concentration limit set by 

MSHA for respirable coal mine dust.
Page 2 GAO-14-345 Mine Safety

milligrams of dust per cubic meter of air (mg/m3) to 1.0 mg/m3.

3 In 

commenting on the proposed rule, representatives of the coal mining 

industry raised concerns about the feasibility and cost of reducing 

respirable coal mine dust concentrations to the proposed limit of 1.0 

mg/m3

, particularly at certain types of mines. The Consolidated 

Appropriations Act, 2012, required that GAO review and report on the 

data collection, sampling methods, and analyses MSHA used to support 

its proposal.4 Consistent with this requirement, in August 2012, we issued 

a report in which we assessed the strengths and limitations of the data 

and the analytical methods MSHA used to support its proposal to lower 

the exposure limit for coal mine dust.5 In that report, we concluded that 

the evidence MSHA used supported its conclusion that lowering the 

exposure limit as proposed would reduce miners’ risk of disease.

In May 2013, you requested that we conduct an additional analysis of the 

data MSHA used to support its proposal and provide information on 

existing technologies that could be used to reduce dust levels in coal 

mines. In this report, we address the following questions:

1. To what extent did MSHA use recent CWP trend data as a basis for 

its proposed exposure limit on coal mine dust?

2. What are experts’ views on ways to lower the level of dust in coal 

mines, including their associated advantages, disadvantages, and 

cost?

To determine the extent to which MSHA used recent CWP trend data as 

a basis for its proposed new limit for exposure to coal mine dust, we 

reviewed the proposed rule and related documents; reviewed our 

previous report and underlying analyses; and interviewed MSHA and 

NIOSH officials. We also updated our previous literature search to identify 

 3 Lowering Miners’ Exposure to Respirable Coal Mine Dust, Including Continuous 

Personal Dust Monitors, 75 Fed. Reg. 64,412 (Oct. 19, 2010) (to be codified at 30 C.F.R. 

pts. 70, 71, 72, 75, and 90). As of March 2014, MSHA had not finalized this regulation. 

Although MSHA’s proposed rule includes other provisions, the first objective of this report 

focuses on MSHA’s proposal to lower the limit for exposure to coal mine dust from 2.0 

mg/m3 to 1.0 mg/m3

.

4 Pub. L. No. 112-74, div. F, tit. I, § 112, 125 Stat. 786, 1064 (2011).

5 GAO, Mine Safety: Reports and Key Studies Support the Scientific Conclusions 

Underlying the Proposed Exposure Limit for Respirable Coal Mine Dust, GAO-12-832R

(Washington, D.C.: August 17, 2012). 
Page 3 GAO-14-345 Mine Safety

any additional recent studies on the prevalence of coal worker respiratory 

diseases and reviewed additional information on the strengths and 

limitations of CWP trend data. To gather experts’ views on the options 

that exist to lower the level of dust in coal mines and their associated 

advantages, disadvantages, and cost, we worked with the National 

Academies to convene a group of experts that included mine operators, 

equipment manufacturers, researchers, and other stakeholders.6 For 

more details on our scope and methodology, see appendix I. We 

conducted this performance audit from July 2013 to April 2014 in 

accordance with generally accepted government auditing standards. 

Those standards require that we plan and perform the audit to obtain 

sufficient, appropriate evidence to provide a reasonable basis for our 

findings and conclusions based on our audit objectives. We believe that 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives.

Inhaling excessive amounts of coal mine dust can cause CWP and other 

debilitating lung diseases, including chronic obstructive pulmonary 

disease, which encompasses chronic bronchitis and emphysema. 

According to NIOSH, it usually takes about 10 to 15 years of exposure to 

coal mine dust to develop CWP, although cases involving fewer years of 

exposure have been observed. Once contracted, CWP cannot be cured, 

making it critical to prevent the development of this disease by limiting 

miners’ exposure to coal mine dust.

MSHA is responsible for protecting miners by enforcing the provisions of 

the Federal Mine Safety and Health Act of 1977 (Mine Act), as amended.7

Under this law, MSHA has a number of responsibilities, including setting 

new safety and health standards and revising existing standards, 

approving training programs for mine workers, and developing regulations 

regarding training requirements for rescue teams, among other things. 

 6 The National Academies comprises the National Academy of Sciences, National 

Academy of Engineering, Institute of Medicine, and National Research Council. We 

worked with staff from the National Research Council to convene our group of experts.

7 See Pub. L. No. 95-164, 91 Stat. 1290 (codified as amended at 30 U.S.C. §§ 801-

965).The Federal Mine Safety and Health Amendments Act of 1977 amended and 

renamed the Federal Coal Mine Health and Safety Act of 1969 (Coal Act) and established 

MSHA. The Mine Improvement and New Emergency Response Act of 2006 recently 

amended the Mine Act. Pub. L. No. 109-236, 120 Stat. 493.

Background
Page 4 GAO-14-345 Mine Safety

MSHA also conducts periodic inspections of coal mines and, along with 

coal mine operators, periodically collects samples of coal mine dust to 

determine compliance with the exposure limit. MSHA set the current 

exposure limit for coal mine dust at 2.0 mg/m3.

8 This limit applies to the 

overall level of dust in the mine environment; specifically, it provides that 

each mine operator “shall continuously maintain the average 

concentration of respirable dust in the mine atmosphere during each shift 

to which each miner in the active workings of each mine is exposed” at or 

below that level.9 To measure the level of dust in the mine environment, 

MSHA requires that mine operators collect samples of dust in specific 

areas of the mine and for designated occupations. Designated 

occupations are those that have the greatest concentration of coal mine

dust, as determined through MSHA sampling.

10

When MSHA sets standards for toxic materials or harmful physical agents 

such as coal mine dust, the Mine Act requires the agency to set 

standards “which most adequately assure on the basis of the best 

available evidence that no miner will suffer material impairment of health 

or functional capacity even if such miner has regular exposure to the 

hazards...for the period of his working life.”

11 In developing a standard, 

the Mine Act also requires MSHA to consider, among other factors, the 

feasibility of the standard, and MSHA conducts analyses to determine 

whether a proposed standard is both economically and technologically 

feasible.12 Specific to coal mine dust, the Mine Act further specifies that 

one of its purposes is to “provide, to the greatest extent possible, that the 

working conditions in each underground coal mine are sufficiently free of 

respirable dust concentrations...to permit each miner the opportunity to 

work underground during the period of his entire adult working life without 

 8 The Coal Act set an interim exposure limit for coal mine dust of 3.0 mg/m3 that went into 

effect in 1970 and continued until 1972, when the standard of 2.0 mg/m3 then took effect. 

Pub. L. No. 91-173, § 202(b), 83 Stat. 742, 760-61 (1970). The 1977 Mine Act did not 

change the 2.0 mg/m3 exposure limit, which was to be in effect until superseded by 

improved standards issued by MSHA. In 1980, via the rulemaking process, MSHA issued 

the current standard, keeping the exposure limit at 2.0 mg/m3

. 45 Fed. Reg. 23,990, 

24,001 (Apr. 8, 1980) (codified at 30 C.F.R. § 70.100).

9 30 C.F.R. § 70.100(a).

10 30 C.F.R. §§ 70.2, 70.207, 70.208.

11 30 U.S.C. § 811(a)(6)(A).

12 See Nat’l Mining Ass’n v. Sec’y of Labor, 153 F.3d 1264, 1269 (11th Cir. 1998). 
Page 5 GAO-14-345 Mine Safety

incurring any disability from...[an] occupation-related disease during or at 

the end of such period.”

13

NIOSH shares some responsibility with MSHA for improving mine safety 

and protecting miners’ health. For example, NIOSH conducts research on 

the causes of work-related diseases and injuries; researches, develops, 

and tests new technologies and equipment designed to improve mine 

safety; and recommends occupational safety and health standards, such 

as the exposure limit for coal mine dust. NIOSH also administers the Coal 

Workers’ X-ray Surveillance Program—a medical monitoring and 

surveillance program designed to detect and prevent lung disease.14 This 

program requires mine operators to provide up to three initial chest x-rays 

for coal miners within specified time frames after their employment 

begins. Miners then can opt to have periodic chest x-rays approximately 

every 5 years thereafter. NIOSH uses this program for disease 

surveillance, which includes tracking trends, setting prevention and 

intervention priorities, and assessing prevention and intervention efforts. 

In addition, to estimate the prevalence of lung disease among 

underground coal miners and to study the relationship between miners’

lung disease and their level of exposure to coal mine dust, NIOSH 

developed the National Study of Coal Workers’ Pneumoconiosis. In this 

study, NIOSH collected and analyzed epidemiological data—including 

findings from chest x-rays, results of lung function tests, and occupational 

and smoking histories—from a sample of coal miners across all major 

coalfields in the United States between 1969 and 1988. The data also 

allowed researchers to link to results of coal mine dust sampling over 

approximately the same period to estimate dust exposures for individual 

miners. According to NIOSH, epidemiological studies examining the 

relationship between coal mine dust and disease must contain a 

sufficiently large body of data over a time period that is adequate to 

derive reliable findings.

There are two primary types of underground coal mining in the United 

States: continuous mining and longwall mining. In continuous mining, a 

 13 30 U.S.C. § 841(b).

14 This program is part of NIOSH’s Coal Workers’ Health Surveillance Program, carried 

out pursuant to requirements of the Mine Act and NIOSH regulations. 30 U.S.C. § 843; 42 

C.F.R. §§ 37.1 - 37.80. Hereafter, we refer to data collected by this program as 

surveillance data. 
Page 6 GAO-14-345 Mine Safety

machine called a continuous miner cuts out rooms of coal from the coal 

bed leaving a series of pillars of coal to help support the mine roof. In 

addition to the pillars of coal, bolts are driven into the roof of the mine to 

help support the mine. The extracted coal from the continuous miner is 

loaded into shuttle cars for transport out of the mine. In longwall mining, a 

machine called a shearer moves back and forth across a wall of coal. 

After the coal is cut, a machine crushes it into small pieces and a 

conveyer belt removes it from the mine. While the shearer cuts the coal 

and the coal is extracted, the roof is held up temporarily with selfadvancing hydraulic supports. While both types of mining produce dust, 

certain pieces of machinery produce more coal mine dust than others. For 

example, in continuous mining, the continuous miner, roof bolting 

machines, and shuttle cars generate the most dust. Major sources of dust 

in longwall mining include the shearer and crusher.

Appropriately, MSHA did not use NIOSH’s surveillance data as the basis 

for its proposed new coal mine dust limit, although the data served to 

inform MSHA’s decision to take action. In the preamble to its proposed 

rule, MSHA cited an increase in the prevalence of CWP among 

underground coal miners based on NIOSH surveillance data, which may 

have led many to believe that these data were part of the basis for 

MSHA’s proposed change in the exposure limit. The surveillance data 

showed that the prevalence of CWP, which declined substantially 

between 1970 and the late 1990s, increased for several years in the early 

2000s before declining again between 2005 and 2009. According to 

MSHA and NIOSH officials, information about the increasing prevalence 

of CWP based on the surveillance data was mentioned in the preamble to 

the proposed rule to show that black lung disease still exists among 

active underground coal miners, thus helping to compel MSHA to take 

action to reduce miners’ exposure to dust, in accordance with its duties 

under the Mine Act. However, as we reported in August 2012, the data 

MSHA used to support its proposal were from two reports, which relied on 

six epidemiological studies, not the surveillance data.15 In addition, in a 

1996 notice in the Federal Register, well before the increase in the 

prevalence of CWP shown by the surveillance data, MSHA stated its 

 15 GAO, Mine Safety: Reports and Key Studies Support the Scientific Conclusions 

Underlying the Proposed Exposure Limit for Respirable Coal Mine Dust, GAO-12-832R

(Washington, D.C.: August 17, 2012). 

MSHA Did Not Use 

Recent CWP Trend 

Data as a Basis for Its 

Proposed Exposure 

Limit on Coal Mine 

Dust, Which Was 

Appropriate
Page 7 GAO-14-345 Mine Safety

intent to respond to a 1995 NIOSH recommendation to lower the 

exposure limit for coal mine dust by developing a proposed rule.16

In our August 2012 report we noted that MSHA primarily relied on two 

reports to develop its proposed exposure limit: its 2010 Quantitative Risk 

Assessment in Support of the Proposed Respirable Coal Mine Dust Rule 

and NIOSH’s 1995 Criteria for a Recommended Standard—Occupational 

Exposure to Respirable Coal Mine Dust.17 These reports were based on 

six key epidemiologic studies that relied on data from NIOSH’s National 

Study of Coal Workers’ Pneumoconiosis.18 These epidemiological studies 

examined the disease risk associated with cumulative dust exposure,

while accounting for other relevant factors such as the age and smoking 

history of each miner. The studies found that cumulative exposure to coal 

mine dust over a working life at the current exposure limit was associated 

with adverse health outcomes, including CWP. Each of these studies 

concluded that lowering the exposure limit would reduce coal miners’ risk 

of developing disease. However, the studies also concluded that, even if 

coal mine dust concentrations were successfully reduced to the proposed 

exposure limit of 1.0 mg/m3

, miners would still be at some risk of 

developing disease.19

It would not have been appropriate for MSHA to use NIOSH’s 

surveillance data in developing its proposed exposure limit for coal mine 

 16 Response to National Institute for Occupational Safety and Health (NIOSH) Criteria 

Document, 61 Fed. Reg. 18,308 (Apr. 25, 1996).

17 MSHA also relied on the 1996 Report of the Secretary of Labor’s Advisory Committee 

on the Elimination of Pneumoconiosis Among Coal Mine Workers, but it contained no new 

information or analyses of the relationship between coal mine dust exposure and its 

associated health effects.

18 One study relied on an examination of autopsied miners’ lungs and data on work 

history, smoking, race, and age at death obtained from medical records and 

questionnaires completed by miners’ next of kin.

19 According to NIOSH, the goal of its recommendation to lower the exposure limit was to 

minimize, to the greatest extent possible, the health risks associated with a miner’s 

exposure to coal mine dust. In making this recommendation, NIOSH took into account an 

evaluation of data on health effects and the feasibility of collecting and analyzing dust 

samples. NIOSH also considered the technological feasibility of controlling exposures. 

Specifically, NIOSH determined that the recommended exposure limit of 1.0 mg/m3 would 

have clear beneficial health effects for all miners. At the time that NIOSH’s 1995 Criteria 

for a Recommended Standard was published, however, an exposure limit lower than 1.0 

mg/m3 was not considered to be technologically feasible. 
Page 8 GAO-14-345 Mine Safety

dust because of some important limitations of the data. For example, 

because the data do not include individual miners’ past exposures to coal 

mine dust, they cannot be used to estimate disease risk for individual 

miners. Based on principles of epidemiology and statistical modeling, 

measures of past exposures to coal mine dust are critical to assessing 

the relationship between miners’ cumulative coal mine dust exposure and 

their risk of developing CWP. Also, because there is no active selection of 

miners by researchers and participation in the surveillance program is 

voluntary, miners who choose to participate may differ in unknown ways 

from those who choose not to participate, which could result in an 

overestimation or underestimation of the prevalence of disease. This 

methodological limitation is known as participation bias, and there are 

many ways it could affect the prevalence of disease indicated by the 

surveillance data. For example, the prevalence of CWP could be 

underestimated because some miners may decline further x-ray 

screenings once CWP is detected.20 Alternatively, the prevalence of CWP 

could be overestimated because miners may be more likely to participate 

after years of dust exposure, when they believe they are at risk of 

developing CWP.

 20 NIOSH researchers explored the impact of some types of biases, including the 

possibility that miners would decline further x-ray screenings once CWP has been 

detected. They found that this and several other possible biases did not likely seriously 

undermine the use of the surveillance data for measuring prevalence of disease. See A. 

S. Laney and M. D. Attfield, “Examination of Potential Sources of Bias in the US Coal 

Workers’ Health Surveillance Program,” American Journal of Public Health, vol. 104, no. 1 

(2014).

Experts Identified 

Various Approaches 

that Could Reduce 

Overall Coal Mine 

Dust Levels, as Well 

as Individual Miners’

Exposure to Dust
Page 9 GAO-14-345 Mine Safety

Experts identified various engineering controls that could further reduce 

the overall level of coal mine dust, but they said reductions would likely be 

incremental.21 Since 1968, the mining industry has achieved significant 

reductions in the level of dust in underground coal mines. Average dust 

levels declined from about 7 mg/m3 in 1968 to below 2 mg/m3 in recent 

years. The experts also said that no one control would result in 

substantially lower dust levels, but that the cumulative impact of a number 

of approaches could further reduce dust levels. Currently, dust is 

controlled in the mine environment primarily through the use of air and 

water. In general, air is used to dilute the concentration of coal dust in the 

air, and to move coal dust away from workers. In addition, dust is 

removed from the air through the use of air filters and other devices that 

capture dust. Water sprays are used to reduce the amount of dust 

generated and to move dust away from workers.

According to the experts who participated in our panel, operators employ 

a number of technologies that use air to reduce the amount of coal mine 

dust in the mine atmosphere. For example, in continuous mining 

operations, air scrubbers can be an effective method of lowering dust 

concentrations. Scrubbers, which can be mounted on a continuous 

mining machine, run dust-laden air through a wet filter that collects dust, 

and remove a substantial amount of dust from the atmosphere. According 

to one expert, NIOSH is developing a stand-alone scrubber that can be 

placed at different locations in the mine to filter the air for workers in those 

areas, and preliminary tests have found it to be about 90 percent efficient 

at removing dust. NIOSH is also developing a device called a canopy air 

curtain, which filters air from the mine environment and provides this 

filtered air to miners who secure the roof (roof bolters) once coal is 

extracted by the continuous mining machine. Tests by NIOSH show that 

the canopy air curtain reduces the amount of dust that roof bolters are 

exposed to by about half. Mine operators also use enclosures, curtains, 

and vacuums to control where the dust goes to keep it away from 

workers’ breathing zones. Since mines also need to ensure that noxious 

gas levels remain low, operators use ventilation systems that constantly 

 21 To obtain the views of experts, with the assistance of the National Academies, we 

convened a panel of 16 experts, including academics; representatives of the coal industry 

and miners; and government officials, and asked them about approaches for reducing coal 

mine dust. For more details on the methodology we used to obtain the experts’ views, see 

appendix I.

Experts Identified Various 

Engineering Controls That 

Could Help Reduce 

Overall Coal Mine Dust 

Levels
Page 10 GAO-14-345 Mine Safety

replace contaminated air with fresh air, which also helps reduce the level 

of coal mine dust in the air.

The experts also described ways that operators use water to prevent dust 

from being generated in mining operations. For example, operators spray 

water on the surface of the coal and on the machines’ cutting surfaces as 

the coal is being cut to reduce the amount of dust generated. In some 

cases, operators also infuse water into the coal prior to cutting, but the 

experts reported limited success with that approach. Operators also use 

hygroscopic salts on mine floors to help maintain the moisture content of 

the mine floor, which in turn absorbs coal mine dust. The experts said 

that, with the increased productivity of mines in recent years, the water 

quantity and pressure for sprays may need to be increased. From 1978 to 

2007, the amount of coal produced per work hour has more than tripled. 

The experts cautioned, however, that using too much water could have 

adverse impacts, such as causing conveyor belts to slip, which would 

affect production.

The experts pointed to a number of factors that could limit mine operators’

use of engineering controls aimed at reducing coal mine dust in the mine 

environment. The experts said that fundamental differences between 

continuous mining and longwall mining operations render some 

technological approaches useful for one type of mining, but not both. For 

example, while scrubbers were cited as an effective tool for reducing dust 

in continuous mining operations, the experts cautioned that they may not 

be as effective for mines that require a lot of ventilation, such as longwall 

mines, because the amount of air flowing through the mine can 

overwhelm the scrubber. An expert noted that one way to reduce dust 

levels is to operate only one continuous mining machine at a time in a 

section of a mine instead of more than one. However, he estimated that 

this could significantly decrease the productivity of the mine and increase 

the cost of producing the coal. Another expert noted that controlling dust 

in a cost-effective manner requires some flexibility.

The experts did not quantify the cost of some of the technologies used in 

reducing dust levels because dust control is not the only purpose of some 

of the technologies, and future technologies have not been developed 

enough to fully determine their costs. However, they did identify primary 

cost drivers. For example, mines that contain high levels of gas must 

ventilate significant amounts of fresh air, which also helps lower coal mine 

dust levels. They also noted that while NIOSH has done some of the 

major research on dust control, overall, industry research on dust control 

technologies has declined. One expert made the point that research is 
Page 11 GAO-14-345 Mine Safety

directly proportional to the economic health of the coal industry. When the 

industry is contracting economically, manufacturers may not be willing to 

devote resources to research and development. While specific costs were 

difficult to assign, the primary drivers the experts identified for lowering 

dust levels were the cost of maintaining equipment; the cost of 

purchasing new or additional equipment, materials, and labor; and the 

cost of providing training.

The experts identified options that could reduce individual miners’

exposure to respirable coal mine dust, specifically, personal protective 

equipment and administrative controls. However, they noted that these 

options would not help mines reduce the overall level of coal mine dust in 

the mine environment, and therefore would not help mine operators 

comply with MSHA’s exposure limit. Personal protective equipment 

includes items such as respirators and air stream helmets. Respirators 

filter the air that an individual miner breathes and air stream helmets 

actively filter and push air across a miner’s face. While respirators and air 

stream helmets could reduce the amount of coal dust to which individual 

miners are exposed, the experts noted that miners have concerns that 

these devices limit communication between miners and thus could raise 

safety issues.22 The experts also said that personal dust monitors could 

be used to reduce individual miners’ exposure to dust because they 

provide workers with real time data on dust levels in the area of the mine 

in which they are working. This information allows workers to adjust their 

position in the mine to reduce their exposure to coal mine dust. Although 

personal dust monitors have no effect on dust levels in the mine, the 

experts noted that they may provide data that could be used by mine 

operators to identify problem areas in the mines and to change work 

practices to reduce miners’ exposure to coal mine dust. One of the 

experts told us personal dust monitors cost about $13,000 to $18,000 per 

unit, which could be a significant expense if all miners were outfitted with 

them.

The experts also noted that administrative controls could limit miners’

exposure to coal mine dust, although they do not control the overall level 

 22The Mine Act requires that approved respiratory equipment be made available to 

anyone exposed to concentrations of coal mine dust in excess of the permissible 

exposure limit; however, the use of respirators “shall not be substituted for environmental 

control measures in the active workings” of the mine. 30 U.S.C. § 842(h).

Experts Noted Options 

That Could Reduce 

Individual Miners’

Exposure to Dust
Page 12 GAO-14-345 Mine Safety

of dust in the mine. These controls include rotating workers more 

frequently from positions that are exposed to higher levels of dust, cutting 

the coal using a remote control device, and changing the sequence by 

which coal is cut. Experts said that rotating workers to other positions 

could help reduce their exposure to dust, but this could also require 

changes to the current collective bargaining agreement at unionized 

mines because the jobs that involve highest exposure to dust may also 

pay more. This approach may also increase costs for mine operators 

because, for example, the collective bargaining agreement might require 

them to continue to pay workers a higher rate of pay when they rotate to a 

lower paying position. The experts also said that some mines use remote 

control devices to keep miners farther away from the source of dust. 

Controlling the mining machine from a greater distance than is currently 

done may require high resolution imaging equipment. One expert said 

that this is especially true for mining operations where geologic conditions 

change frequently, requiring miners to make judgments about where to 

move the machinery. According to the experts, another way to limit 

exposure to individual miners in continuous mining is by modifying the 

sequence in which coal is mined. The experts explained that this 

approach reduces the number of miners who are downwind from the dust 

generated by the continuous mining machine. However, this type of 

change could result in decreased productivity in the mine.

We provided a draft of this report to the Secretaries of Labor and Health 

and Human Services for review and comment. Both agencies generally 

concurred with the findings of the report, but provided no formal written 

comments. The agencies did, however, provide technical comments, 

which we incorporated as appropriate. 

We are sending copies of this report to the appropriate congressional 

committees and the Secretaries of Labor and Health and Human 

Services. In addition, the report is available at no charge on the GAO 

website at http://www.gao.gov. If you or your staff have any questions 

about this report, please contact me at (202) 512-7215 or 

Agency Comments
Page 13 GAO-14-345 Mine Safety

moranr@gao.gov. Contact points for our Offices of Congressional 

Relations and Public Affairs may be found on the last page of this report. 

GAO staff who made key contributions to this report are listed in appendix 

II.

Revae Moran

Director, Education, Workforce,

and Income Security Issues
Page 14 GAO-14-345 Mine Safety

List of Requesters

The Honorable Harold Rogers

Chairman

Committee on Appropriations

House of Representatives

The Honorable Jack Kingston

Chairman

Subcommittee on Labor, Health and Human

Services, Education and Related Agencies

Committee on Appropriations

House of Representatives
Appendix I: Objectives, Scope, and 

Methodology

Page 15 GAO-14-345 Mine Safety

The objectives of our review were to: (1) determine the extent to which 

the Mine Safety and Health Administration (MSHA) used recent coal 

workers’ pneumoconiosis (CWP) trend data as a basis for its proposed 

exposure limit on coal mine dust, and (2) obtain experts’ views on ways to 

lower the level of dust in coal mines, including their associated 

advantages, disadvantages, and cost.

To address our first objective, we reviewed MSHA’s Notice of Proposed 

Rulemaking,1 including the proposed exposure limit and related 

documents, updated the literature search from our prior report, and 

interviewed officials from MSHA and the National Institute for 

Occupational Safety and Health (NIOSH) to identify recent data on the 

prevalence of coal worker respiratory diseases. Two GAO research 

methodologists and one public health specialist reviewed information 

gathered about CWP trend data, to assess its strengths and limitations, 

and reviewed a recent study by NIOSH researchers on the usefulness of 

these data for estimating disease prevalence. We also reviewed our prior 

report and the analyses that supported it, and interviewed MSHA and 

NIOSH officials to determine what role, if any, recent CWP trend data had 

in developing the proposal to lower the exposure limit. We examined 

whether these data would have been appropriate for MSHA to use in 

developing its proposed exposure limit using principles of social science 

research and epidemiology.

For our second objective, we worked with the National Academies to 

convene a group of experts to obtain their views on these issues.2 To 

prepare for our discussions with experts, we reviewed NIOSH and other 

studies on the ability of currently available and alternative technologies to 

control coal mine dust. We also reviewed the technological and economic 

feasibility assessments MSHA used to develop its proposed exposure 

limit. The group included experts from all of the major stakeholder groups: 

NIOSH researchers, academics, other technical experts, individuals from 

 1 Lowering Miners’ Exposure to Respirable Coal Mine Dust, Including Continuous 

Personal Dust Monitors, 75 Fed. Reg. 64,412 (Oct. 19, 2010) (to be codified at 30 C.F.R. 

pts. 70, 71, 72, 75, and 90).

2 The National Academies have extensive experience identifying experts and convening 

panels and maintain a membership of the nation’s top scientists, engineers, and other 

professionals. The National Academies comprises the National Academy of Sciences, 

National Academy of Engineering, Institute of Medicine, and National Research Council. 

We worked with staff from the National Research Council to convene our group of experts.

Appendix I: Objectives, Scope, and 

Methodology
Appendix I: Objectives, Scope, and 

Methodology

Page 16 GAO-14-345 Mine Safety

companies that manufacture mining equipment, and individuals who 

represent coal mine operators and workers. In identifying the experts, the 

National Academies compiled a preliminary list of 53 experts who 

represented 17 universities, 7 coal companies or coal associations, 5 

equipment manufacturers, 1 mine workers’ association, and 2 

government agencies. The nominees were grouped by sector and field of 

expertise, and were vetted by 10 individuals working in the public, private, 

and academic sectors who have expertise in coal mining or a related 

field. Feedback from these individuals, along with biographical information 

about the experts, was used to prioritize the experts within each sector 

and field of expertise. Using this information, we invited 17 experts to 

participate in a 1-day panel discussion, although 1 person subsequently 

cancelled. The resulting 16 experts included 3 representatives of mine 

operators, 1 representative of underground coal miners, 3 representatives 

of equipment manufacturers, 6 academics, and 3 representatives of 

federal government agencies.3

To ensure that there were no unforseen biases or conflicts of interest, 

each panelist reported to the National Academies his or her investments, 

sources of earned income, organizational positions, relationships, and 

other circumstances that could affect, or could be viewed to affect, his or 

her view on the topic of methods for reducing the level of respirable dust 

in underground coal mines. We asked the experts to discuss the 

technological and other options available for lowering the level of dust in 

coal mines below the existing permissible exposure limit and the costs, 

advantages, and disadvantages of these technologies. We did not ask the 

experts about the proposed new limit. In addition to the 16 panelists, we 

allowed 5 observers to sit in on the panel discussion. The observers 

included representatives of mining equipment manufacturers, coal mine 

operators, and one government agency.

We conducted this performance audit from July 2013 to April 2014 in 

accordance with generally accepted government auditing standards. 

Those standards require that we plan and perform the audit to obtain 

sufficient, appropriate evidence to provide a reasonable basis for our 

findings and conclusions based on our audit objectives. We believe that 

the evidence obtained provides a reasonable basis for our findings and 

conclusions based on our audit objectives.

 3 One representative was a retired agency official.
Appendix II: GAO Contacts and Staff 

Acknowledgments

Page 17 GAO-14-345 Mine Safety

Revae Moran, (202) 512-7215 or moranr@gao.gov.

In addition to the contact listed above, individuals making key 

contributions to this report were Mary Crenshaw (Assistant Director), 

Nabajyoti Barkakati, Russell Burnett, Sarah Cornetto, Andrea Dawson, 

Timothy Guinane, Kristy Kennedy, Kathy Leslie, Sheila McCoy, Sara 

Pelton, Tim Persons, Martin Scire, Sushil Sharma, Walter Vance, 

Kathleen van Gelder, and Shana Wallace.

Appendix II: GAO Contacts and Staff 

Acknowledgments

Contact

Staff 

Acknowledgments

(131260)
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