GAO-12-832R Coal Mine Dust Exposure 

United States Government Accountability Office

Washington, DC 20548 

August 17, 2012 

Congressional Committees 

Subject: MINE SAFETY: Reports and Key Studies Support the Scientific Conclusions 

Underlying the Proposed Exposure Limit for Respirable Coal Mine Dust 

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’ (HHS) 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 Department of Labor (Labor) has paid over $44 billion in benefits 

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

through the Black Lung Benefits Program. 

In October 2010, Labor’s Mine Safety and Health Administration (MSHA)—the federal 

agency responsible for setting and enforcing mine safety and health standards—proposed 

revising the existing standard for coal mine dust to lower the permissible exposure limit 

(PEL)2

 from 2.0 milligrams of dust per cubic meter of air (mg/m3) to 1.0 mg/m3.

3

 Several coal 

mining companies and others have questioned the evidence and analytical methods used to 

support the proposed PEL. In the Consolidated Appropriations Act, 2012, Congress required 

that GAO review and report on the data collection, sampling methods, and analyses MSHA 

used to support its proposal.4

 Although MSHA’s proposed rule includes other provisions, this 

review focuses on MSHA’s proposal to lower the PEL for coal mine dust from 2.0 mg/m3

 to 

1.0 mg/m3

. To respond to this requirement, we addressed the following question: What are 

 

1

In this report, we use the term coal mine dust to refer to respirable coal mine dust. Black lung is a term that 

includes CWP and other chronic respiratory or pulmonary impairments resulting from coal mine employment. 

2

In this report, the term PEL refers to the respirable coal mine dust standard. 

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 August 13, 2012, 

MSHA had not finalized this regulation. 

4

The Act provided that “[n]one of the funds made available by this Act may be used to implement or enforce 

[MSHA’s] proposed rule” until GAO “issues, at a minimum, an interim report...and...not later than 240 days after 

enactment of this Act, submits the report ...to the Committees on Appropriations of the House of Representatives 

and the Senate,” or until that deadline has passed. Pub. L. No. 112-74, div. F, tit. I, § 112, 125 Stat. 786, 1064 

(2011). 
Page 2 GAO-12-832R Coal Mine Dust Exposure 

the strengths and limitations of the data and analytical methods MSHA used to support its 

proposal to lower the PEL for coal mine dust? 

To conduct our work, we reviewed relevant federal laws and regulations, MSHA's proposed 

standard to lower the PEL for coal mine dust, the reports and key scientific studies cited in 

them that MSHA used to support its proposed standard, and the comments MSHA received 

on its proposal after it was published in the Federal Register. MSHA primarily relied on two 

reports and the studies cited in them to develop its proposed standard: NIOSH’s 1995 

Criteria for a Recommended Standard – Occupational Exposure to Respirable Coal Mine 

Dust (Criteria Document) and MSHA’s 2010 Quantitative Risk Assessment in Support of the 

Proposed Respirable Coal Mine Dust Rule (Quantitative Risk Assessment). MSHA also 

relied on the 1996 Report of the Secretary of Labor’s Advisory Committee (consisting of 

labor, industry and government representatives) on the Elimination of Pneumoconiosis 

Among Coal Mine Workers.5 Enclosure I lists and provides a detailed discussion of the 

reports and key scientific studies we reviewed. The focus of our work was primarily limited to 

determining whether the scientific studies MSHA used generally support its conclusion that 

lowering the exposure to coal mine dust would lower miners’ risk of disease over their 

working lives.6

 We assessed the adequacy of the data and measures employed, the 

reasonableness and rigor of the statistical techniques used to analyze them, and the validity 

of the conclusions drawn from the analyses. Our work was not designed to determine the 

optimal PEL for coal mine dust; analyze the costs and benefits of the proposed standard; or 

determine whether the proposed standard would meet MSHA’s legal requirements under the 

Federal Mine Safety and Health Act of 1977 (Mine Act) or other federal laws that govern the 

rulemaking process, such as the Administrative Procedure Act.7

In addition to reviewing the reports and key scientific studies cited in them that MSHA used 

to support its proposed standard, we conducted a literature search to identify other studies 

that examined the relationship between exposure to coal mine dust and its associated 

health effects. These included an April 2011 NIOSH report on a review of information since 

1995 on coal mine dust exposures and associated health outcomes. 

Finally, we interviewed MSHA and NIOSH officials and representatives from the mining 

industry and mine workers. We also reviewed related reports by GAO, Labor's Office of 

Inspector General, and others on the health effects of exposure to coal mine dust. We 

visited MSHA and NIOSH offices in Pittsburgh, Pennsylvania and Morgantown, West 

Virginia, which informed our understanding of the data and the analytical methods used to 

support MSHA’s proposal for lowering the PEL for coal mine dust. A further discussion of 

our scope and methodology is provided in Enclosure I. 

 

5

This report was included in our overall review of relevant materials, but we did not include it in our final analysis 

of the two reports and the key studies cited in them on which MSHA relied to develop its proposed standard 

because it did not contain new information or analyses of the relationship between coal mine dust exposure and 

its associated health effects.

6

For purposes of this proposed rule, MSHA defines a miner’s working life to be 45 years. 

7

Various federal statutes and executive orders require federal agencies to follow a number of procedural and 

analytic requirements when developing and issuing rules. For example, the Administrative Procedure Act 

generally requires agencies to publish proposed rules for public comment prior to issuing a final rule. 5 U.S.C. § 

553. In addition, section 101(a) of the Mine Act establishes certain procedural and analytic rulemaking 

requirements for MSHA standards. For example, before issuing a standard on toxic materials, MSHA must 

determine, based on research and other considerations, that the toxins pose a material impairment to miners’ 

health or functional capacity. 30 U.S.C. § 811(a)(6)(A). 
Page 3 GAO-12-832R Coal Mine Dust Exposure 

We conducted this performance audit from February 2012 through August 2012 in 

accordance with generally accepted government auditing standards. These 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. 

Results In Brief 

Our evaluation of the reports MSHA used to support its proposal and the key scientific 

studies on which the reports were based shows that they support the conclusion that 

lowering the PEL from 2.0 mg/m3

 to 1.0 mg/m3 would reduce miners’ risk of disease. The 

reports and key studies concluded that miners’ cumulative exposure to coal mine dust at the 

current PEL over their working lives places them at an increased risk of developing CWP, 

progressive massive fibrosis, and decreased lung function, among other adverse health 

outcomes. To mitigate the limitations and biases in the data, the researchers took 

reasonable steps, such as using multiple x-ray specialists to reduce the risk of misclassifying 

disease and making adjustments to coal mine dust samples where bias was suspected. In 

addition to addressing the limitations and biases in the data, researchers used appropriate 

analytical methods to conclude that lowering the existing PEL would decrease miners’ risk of 

developing black lung disease. For example, in addition to taking steps to precisely estimate 

a miner’s cumulative exposure, the researchers accounted for several factors in their 

analyses—such as the age of the miners, the carbon content of the coal (coal rank), and 

other factors known to be associated with the disease—to better estimate the effect of 

cumulative exposure to coal mine dust.8

 Further, the other studies we identified generally 

supported the conclusion that reducing the PEL would reduce miners’ risk of disease. 

Background 

CWP in the United States

The passage of the Federal Coal Mine Health and Safety Act of 1969 (Coal Act) 9

established the first comprehensive respirable dust standard for coal mines, setting the 

exposure limit at 2.0 mg/m3

.

10 Following the passage of the Coal Act, the prevalence of 

CWP among underground coal miners examined in NIOSH’s Coal Workers’ X-ray 

 

8

Coal rank is a classification of the amount of carbon in the coal. Coal is typically ranked as “high,” “medium” or 

“low,” where coal with a high rank has high carbon content. According to NIOSH, several factors are associated 

with a higher risk of developing CWP, including miners’ exposure to coal mine dust with high carbon content. 

 

9

Pub. L. No. 91-173, 83 Stat. 742. 

10The Coal Act set an interim standard of 3.0 mg/m3 that went into effect in 1970, 6 months after the date of 

enactment and continued until 1972, when the standard of 2.0 mg/m3

 then took effect. In 1977, the Mine Act 

was passed, which amended and renamed the Coal Act and established MSHA. Pub. L. No. 95-164, 91 Stat. 

1290 (1977). The Mine Act maintained the standard at 2.0 mg/m3, to be in effect until superseded by improved 

standards issued by MSHA. The Mine Act also authorized MSHA to issue improved standards, and prohibited it 

from issuing standards that would reduce the protection provided by existing standards. In 1980, via the 

rulemaking process, MSHA issued the current standard, keeping the PEL at 2.0 mg/m3

. 45 Fed. Reg. 23,990 

(Apr. 8, 1980), codified at 30 C.F.R. §§ 70.100, 71.100. 
Page 4 GAO-12-832R Coal Mine Dust Exposure 

Surveillance Program generally decreased about 80 percent from 1970 to 2009.11 But, 

according to NIOSH, despite this overall decrease, the observed prevalence of CWP has 

risen in recent years.12 NIOSH based this finding on data collected from its Coal Workers’ Xray Surveillance Program and, as a result, it may not be representative of the total 

population of coal miners since participation in the program is primarily voluntary.

In 2012, coal mine companies employed a total of 86,195 miners in 26 states.13 While 

miners across the country are at risk of developing CWP, CWP-related deaths are clustered 

in the Appalachian region, and, according to NIOSH, clusters of rapidly progressing CWP 

have been recently observed in Kentucky, Virginia, and West Virginia.14

Types of Lung Disease Resulting from Exposure to Coal Mine Dust 

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. 

Clinical diagnosis of CWP in an individual patient is generally based on the presence of 

typical chest radiological findings, history of working in coal mines, and exclusion of 

alternative diagnoses. Although CWP in its early stages may not be associated with 

impaired lung function or increased mortality, it can increase a miner’s risk of developing the 

advanced stage of the disease, known as progressive massive fibrosis, which can 

significantly decrease lung function and result in death. According to NIOSH, several factors 

are associated with a higher risk of developing CWP, including miners’ level of exposure to 

coal mine dust, coal rank, their length of employment in mining (especially years worked 

underground), their age, and their occupations in the mines.15

Role of MSHA 

MSHA is responsible for protecting miners by enforcing the provisions of the Mine Act, as 

amended by the Mine Improvement and New Emergency Response Act of 2006.16 Under 

these laws, 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 

 

11NIOSH’s Coal Workers’ X-ray Surveillance Program is a primarily voluntary medical monitoring and 

surveillance program. NIOSH reports prevalence data as averages of 5-year intervals. The overall decrease 

since 1970 reported here is based on the oldest and most recent intervals: 1970 to1974 and 2005 to 2009. 

 

12According to NIOSH, the prevalence of CWP appears to have stopped declining around the 1995 to 1999 

interval and has been on the rise since that time. 

13According to the Department of Energy’s Office of Oil, Gas, and Coal Supply Statistics, Wyoming mines the 

most coal, followed by West Virginia, Kentucky, and Pennsylvania. 

14Appalachia includes Alabama, Ohio, Kentucky, Pennsylvania, Tennessee, Virginia, and West Virginia. 

15Miners work in different occupations and locations within the mine and, as a result, are exposed to different 

levels of coal mine dust. 

 

16Pub. L. No. 109-236, 120 Stat. 493, codified as amended at 30 U.S.C. §§ 801-965. 
Page 5 GAO-12-832R Coal Mine Dust Exposure 

things. MSHA also conducts periodic mine inspections and, along with coal mine operators, 

periodically collects samples of coal mine dust to determine compliance with the PEL. 

According to MSHA, approximately 750,000 coal mine dust samples have been collected by 

inspectors and about 4.6 million dust samples have been collected by mine operators since 

1970.17 

MSHA inspectors and mine operators measure the concentration of coal mine dust over an 

entire production shift, or at a maximum, an 8-hour period, to determine compliance with the 

current dust standard. MSHA generally determines compliance with the PEL based on the 

average of coal mine dust concentration samples taken by the mine operator during five 

consecutive normal production shifts or five normal production shifts worked on consecutive 

days.18 Determinations of compliance are also based on an average of multiple 

measurements taken by an MSHA inspector. 

When MSHA sets standards for toxic materials 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.”19 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.20

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 

incurring any disability from...[an] occupation-related disease during or at the end of such 

period.”21

Role of NIOSH

NIOSH shares some responsibility with MSHA for improving mine safety and protecting 

miners’ health. It 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 PEL for coal 

mine dust. NIOSH recommends safety and health standards to MSHA and other regulatory 

agencies through its guidance documents (e.g., criteria documents), which provide the 

scientific basis for its recommended standards and a critical review of the scientific and 

technical information available on the prevalence of hazards, among other information. 

 

17These figures include only samples for underground mines. 

18See 30 C.F.R. §§ 70.201(b), 70.207, 70.208 (for underground coal mines). Similar sampling procedures apply 

to surface mines. 30 C.F.R. §§ 71.201(b), 71.208. 

1930 U.S.C. § 811(a)(6)(A). 

20See Nat’l Mining Ass’n v. Sec’y of Labor, 153 F.3d 1264, 1269 (11th Cir. 1998).

2130 U.S.C. § 841(b).
Page 6 GAO-12-832R Coal Mine Dust Exposure 

NIOSH also administers the Coal Workers’ X-ray Surveillance Program, a medical 

monitoring and surveillance program to detect and prevent lung disease.22 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, followed by voluntary periodic chest xrays 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. Miners’ chest x-rays are read and 

classified by at least two x-ray specialists who must meet certain qualifications.23

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 (NSCWP). Through 

the NSCWP, NIOSH analyzed epidemiological data for a sample of mines and miners 

across all major coalfields. The data included miners’ chest x-ray findings, lung function test 

results, and occupational and smoking histories, as well as available results of coal mine 

dust sampling.24 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. (CWP generally takes at least 10 

years from first exposure, and usually longer, to become clinically apparent). 

Reports and Key Scientific Studies MSHA Used to Support Its Proposal Showed That 

Lowering the PEL Would Reduce Disease Risk

The two primary reports MSHA used to support its proposed standard—NIOSH’s Criteria 

Document and MSHA’s Quantitative Risk Assessment—and the six key scientific studies on 

which those reports were based each concluded that lowering the PEL from 2.0 mg/m3

 to 

1.0 mg/m3

 would reduce coal miners’ risk of developing disease.25 Furthermore, these 

studies concluded that cumulative exposure to coal mine dust over a working life at the 

current PEL is associated with adverse health outcomes. These outcomes include CWP, 

progressive massive fibrosis, emphysema, decreased lung function, and mortality. A 

statistical model used in both NIOSH’s Criteria Document and MSHA’s Quantitative Risk 

Assessment showed that reducing exposure to coal mine dust from 2.0 mg/m3

 to 1.0 mg/m3

over a miner’s working life would decrease the risk of developing CWP from 34 percent to 

12 percent for miners working in mines with high coal rank (high carbon content), and from 

17 percent to 6 percent for miners working in mines with medium- and low-rank coal (lower 

carbon content).26 Key scientific studies also showed that reducing miners’ cumulative 

exposure to coal mine dust over their working lives would decrease their risk of developing 

other respiratory diseases. For example, another model NIOSH used in its Criteria 

 

22This program is part of NIOSH’s Coal Workers’ Health Surveillance Program, carried out pursuant to 

requirements in the Mine Act and NIOSH regulations. 30 U.S.C. § 843; 42 C.F.R. §§ 37.1 - 37.80. 

23Through NIOSH’s B Reader program—a training and testing program that began in 1974—a pool of qualified 

readers is established, using initial and periodic examinations to verify the competence of physician-readers in 

assessing and classifying pneumoconiosis. 

24NIOSH’s NSCWP was conducted in four rounds of medical surveys. This NSCWP differs from NIOSH’s Coal 

Workers’ X-ray Surveillance Program in that the NSCWP achieved higher participation rates and collected more 

detailed medical information for each miner than the Coal Workers X-ray Surveillance Program. 

25See Enclosure I for additional information on these reports and studies. 

26These estimates are for a hypothetical population of 65-year-old miners who have been exposed to coal mine 

dust over a 45-year working life. 
Page 7 GAO-12-832R Coal Mine Dust Exposure 

Document showed that the same reduction in exposure to coal mine dust would reduce the 

risk of a miner developing a dust-caused reduction in lung function by roughly half, and this 

would be the case for miners across different regions of the United States. However, the 

studies also concluded that, even if coal mine dust concentrations were successfully 

reduced to the proposed PEL of 1.0 mg/m3

, miners would still be at some risk of developing 

disease.27

Reasonable Steps Were Taken to Mitigate the Limitations and Biases in the Data MSHA 

Relied on to Estimate the Health Effects of Exposure to Coal Mine Dust 

Researchers who prepared the reports and key scientific studies on which they were based 

took reasonable steps to mitigate the limitations and biases in the data MSHA relied on to 

support its proposal to lower the PEL. These steps included: 

 Using a sufficiently large number of coal mine dust samples. An accurate 

examination of the association between exposure to coal mine dust and disease 

depends, in part, on the reliability of the coal mine dust samples. Precisely 

measuring coal mine dust is difficult, partly because of the large degree of variation 

in the levels of coal mine dust in a particular area. However, the reports and the key 

scientific studies on which they were based relied on a sufficiently large number of 

coal mine dust samples, which helped mitigate the effect of random variation 

between individual samples and ensure more accurate measurements of coal mine 

dust overall.28

 Adjusting coal mine dust samples where bias was suspected. To improve the 

accuracy of coal mine dust samples, researchers developed specific procedures to 

adjust the samples where bias was suspected. For example, according to MSHA, 

coal mine dust samples collected by mine operators have historically been 

systematically lower than coal mine dust samples collected by MSHA inspectors at 

the same mines. Because of this downward bias, according to NIOSH, samples 

taken by operators likely underestimated miners’ exposure to coal mine dust. To 

address this bias, researchers of some of the key scientific studies systematically 

adjusted coal mine dust samples upward to complete their analyses. 

 

 Addressing potential limitations where there were lower participation rates. 

Researchers also addressed potential limitations in the data resulting from lower 

participation rates of miners in medical examinations. Although participation of coal 

miners in some rounds of the medical examinations was lower than in other rounds, 

researchers conducted additional analyses to check whether those who participated 

were systematically different from those who did not participate, which could bias the 

 

27According to NIOSH, the goal of its recommendation to lower the PEL is 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 health effects data as well as the feasibility of collecting and analyzing 

dust samples. NIOSH also considered the technological feasibility of controlling exposures. Specifically, NIOSH 

determined that the recommended PEL of 1.0 mg/m3

 would have clear beneficial health effects for all miners. At 

the time the Criteria Document was published, however, a PEL lower than 1.0 mg/m3

 was not considered to be 

technologically feasible. According to NIOSH, if improvements in the technological feasibility of dust controls 

become available in the future, the agency would consider recommending a lower PEL. 

28To develop the statistical model of CWP used by NIOSH in its Criteria Document and by MSHA in its 

Quantitative Risk Assessment, researchers drew on 293,292 coal mine dust samples in order to estimate a 

personal cumulative coal mine dust exposure for each of 3,194 miners.
Page 8 GAO-12-832R Coal Mine Dust Exposure 

data. For example, chest x-rays used to identify and classify the presence of CWP 

were obtained from medical surveys from NIOSH’s NSCWP, which was conducted in 

multiple rounds over roughly two decades.29 The participation rates for these four 

rounds of surveys ranged from as low as 52 percent to as high as 90 percent.30 Low 

participation in the medical surveys could have introduced bias into the analysis if the 

characteristics of the miners who did not participate—such as their age, the number 

of years they had worked in the mines, or other factors associated with the 

development of disease—differed substantially from those who did participate in the 

surveys. To mitigate this possible bias, researchers conducted additional analyses of 

the NSCWP data and found that those who participated in these surveys were 

similar to those who did not participate in terms of age, years working in underground 

mines, and presence of CWP in a prior round of the NSCWP.31 These analyses lend 

greater confidence to the conclusion that lower participation rates did not influence 

the results of the studies. 

 Limiting the risk of misclassifying disease. To further improve the reliability of the 

medical data used in the key scientific studies, some researchers took steps to limit 

the risk of misclassifying disease by using x-ray data that were read and classified by 

multiple x-ray specialists using a standardized process. MSHA largely relied on two 

key scientific studies to examine the relationship between exposure to coal mine dust 

and CWP. In one of these studies, researchers used x-ray data classified by one 

specialist, and in the other study, researchers used x-ray data independently 

classified by three specialists. Using x-ray data classified by multiple independent 

specialists limits the possible error that can be introduced when relying on 

classifications by one specialist. Although one of the two studies used only one x-ray 

specialist to classify disease, the findings of that specialist were similar to those in 

the study that used three x-ray specialists to classify disease.32 In addition, these 

three x-ray specialists used the same standardized classification system for 

determining the presence and severity of CWP, consistent with standard practices 

for epidemiological research.33 Furthermore, since classifications of disease have 

been known to vary among multiple x-ray specialists interpreting the same x-ray, 

researchers mitigated this concern by using selected specialists who were known, 

 

29Medical surveys from the NSCWP included a chest x-ray, test of lung function, and a questionnaire on current 

symptoms, demographics, smoking and work history. Examinations in Round 1 were conducted from 1969 to 

1971, Round 2 from 1972 to 1975, Round 3 from 1977 to 1981, and Round 4 from 1985 to 1988. 

30Participation rates of eligible participants were 90, 75, 52, and 70 percent for Rounds 1 though 4, respectively. 

 

31In Round 4 of the NSCWP—which was the basis for one of the key exposure-response models relating dust 

exposure and risk of CWP—miners who participated in the study and those who did not were very similar with 

regard to age. Non-participants, however, had worked underground for a slightly longer period of time. Despite 

this, the non-participants had a slightly lower prevalence of CWP in an earlier round of the study. None of the key 

scientific studies we reviewed included data collected from Round 3—the Round with the lowest participation 

rate (52 percent). 

32The study that used only one x-ray specialist originally included classifications from three specialists who 

classified disease, but the classifications of two of them were excluded because one specialist did not apply the 

correct system of classification and the other specialist’s readings were found to show unusually high levels of 

disease. 

33These x-ray specialists used the International Labour Organization classification system, an internationallyaccepted means for assessing the severity and types of abnormality arising from inhalation of mineral dusts. A 

summary classification of CWP was used for each participant by taking the median category of disease when 

three x-ray readings were available. The three specialists classified similar overall prevalences of CWP (7 

percent, 7 percent, and 9 percent, respectively). 
Page 9 GAO-12-832R Coal Mine Dust Exposure 

based on historical data, to assign CWP classifications at rates close to the median 

of multiple readers. 

The statistical models in the key scientific studies generally included samples of coal mine 

dust collected from 1968 to 1987, and the researchers used these data to estimate the 

relationship between exposure to coal mine dust and risk of disease. We find it reasonable 

that NIOSH and MSHA used these models to estimate risk of disease due to exposure to 

coal mine dust in present mining conditions. It is possible, however, that changes in the 

composition of coal mine dust or characteristics of the coal mine workforce since 1987 have 

altered the relationship between exposure to coal mine dust and risk of disease. For 

example, the research we reviewed showed that the quartz (silica) component of coal mine 

dust, which is known to increase the risk of disease, may have increased in certain states in 

the years since key scientific studies were conducted.34 It follows that the health risks of a 

given level of exposure to coal mine dust may be even greater today than estimated in the 

models. Therefore, we concluded that an increase in silica levels would not undermine the 

proposal to lower the exposure limit, and that it was reasonable to rely on the coal mine dust 

samples used in the key scientific studies to estimate disease risk in support of the 

proposal.35

Appropriate Analytical Methods Were Used in the Key Scientific Studies MSHA Relied on to 

Develop its Proposed Standard

The researchers for the reports and six key scientific studies that supported MSHA’s 

proposed standard used appropriate analytical methods to conclude that lowering miners’ 

exposure to coal mine dust over their working lives reduces their risk of developing black 

lung disease. For example, they accounted for known factors associated with black lung 

disease and precisely estimated miners’ cumulative exposure to coal mine dust. Previous 

research established that the development of black lung disease is affected by certain 

factors other than cumulative exposure to coal mine dust, such as coal rank and a miner’s 

age. By taking these factors into account, the researchers were able to better isolate the 

effect of cumulative exposure to coal mine dust and provide greater confidence in their 

assessment of the relationship between exposure to coal mine dust and the development of 

disease. For example, one key scientific study that examined the association between lung 

function and exposure to coal mine dust accounted for each miner’s age, height, cigarette 

smoking, ethnicity, mining status (current or ex-miner), and years worked in non-mining yet 

dusty occupations. In all of the key scientific studies, coal mine dust was found to be a 

statistically significant predictor of health risk, even when taking other known factors into 

 

34Some mining involves cutting and extracting rock containing silica overlying or underlying the coal seam. 

Inhaling silica can cause silicosis, a form of pneumoconiosis. Currently, when the respirable coal mine dust 

contains more than 5 percent quartz (silica), the PEL is determined based on a formula that reduces the PEL 

commensurate with the proportion of the dust that is silica. 30 C.F.R. §§ 70.101, 71.101. NIOSH has 

recommended a separate PEL for silica of 0.05 mg/m3 and MSHA is planning to establish a separate standard for 

silica. 

35Other factors that may have changed since 1987 and could affect the relationship between exposure to coal 

mine dust and disease risk include the prevalence of smoking among coal miners and the age composition of the 

mining workforce. Although smoking has its own health effects, it does not appear to alter the risk of CWP due to 

exposure to coal mine dust, according to researchers. We did not identify any other research on how age affects 

the relationship between exposure to coal mine dust and disease. 
Page 10 GAO-12-832R Coal Mine Dust Exposure 

account.36 Furthermore, some key scientific studies tested several different combinations of 

factors that may contribute to disease to further assess the effect of each factor and better 

determine the relationship between exposure to coal mine dust and development of 

disease.37 While many known factors were taken into account, none of the key scientific 

studies accounted for exposure to silica dust because, according to NIOSH, reliable 

information on silica exposure was not available at the time these studies were conducted. 

 

In addition to accounting for known factors associated with disease to better isolate the 

effect of exposure to coal mine dust on health outcomes, researchers took steps to increase 

the precision of a miner’s estimated cumulative exposure to help ensure greater reliability in 

their predictions of health outcomes. The key scientific studies estimated each miner’s 

cumulative exposure to coal mine dust from the beginning of his or her employment as a 

miner to the time of his or her medical examination. Estimating the cumulative exposure to 

coal mine dust over many years is important because, according to NIOSH, black lung 

disease generally develops slowly over time. Steps were taken to collect coal mine dust 

measurements in specific mines and include specific occupations for each year of the study 

so that precise estimates of a coal miner’s exposure could be calculated based on the 

miner’s actual occupation and tenure in that occupation.38 Some key scientific studies 

included miners who began mining prior to the establishment of the first PEL in 1970 and 

MSHA’s systematic sampling of coal mine dust concentrations.39 For these miners, the 

researchers took reasonable steps to estimate miners’ exposure to coal mine dust in years 

prior to 1970, despite having limited data for those years. Furthermore, to ensure that the 

conclusions did not depend on the exact method used to estimate coal mine dust exposure 

prior to 1970, the researchers used various alternatives to estimate a miner’s exposure to 

coal mine dust. Using these alternative methods, the researchers found similar results, 

lending greater confidence in the accuracy of the estimates of disease risk. 

While the analytical methods researchers used in the six key scientific studies supported the 

conclusion that lowering coal mine dust exposure would reduce the risk of disease for 

miners over their working lives, the actual estimates of disease risk for miners at the end of 

their working lives may lack precision. The Mine Act requires MSHA to set standards to 

protect miners even if they are exposed to hazards for their full working lives. Therefore, 

predicting the risk of disease at the end of a miner’s career (for example, miners age 65 with 

45 years of employment) is important when considering a new PEL. However, in most of the 

key scientific studies, few miners actually had 45 or more years work experience in a mine, 

and few were 65 or older. Because the key scientific studies predicted disease risk at the 

end of a miner’s career, the estimated levels of risk may not be as precise as if there had 

been more data on miners at the end of their careers. This limitation, however, does not 

 

36Specifically, coefficients for coal mine dust exposure were statistically significant in all of the key models used 

by MSHA and NIOSH. A coefficient is considered statistically significant if the probability of observing a value as 

large as it is, due to chance alone, is less than a specified probability—often 5 percent. In this case, statistical 

significance means that the observed association between coal mine dust exposure and disease risk, after 

accounting for other factors such as age and coal rank, is unlikely to be due to chance alone. 

37The model fit, or how well the model’s predictions of disease prevalence matched observed prevalence, was 

generally good for the key scientific studies. For example, NIOSH evaluated how well model predictions matched 

actual observations and found that the model-predicted prevalence of early stages of CWP fit the observed 

prevalence closely within the range of cumulative dust exposure corresponding to the current and proposed PEL. 

38Information on a miners’ work history, including the dates of starting and stopping work in each occupation in 

each mine, was obtained from interviews of each participant of the NSCWP. 

39Prior to 1970, coal mine dust concentrations often exceeded the current PEL of 2.0 mg/m3

, according to 

NIOSH. There is evidence indicating that dust concentrations were as high as 6.0 mg/m3

 for certain occupations 

within mines prior to 1970. 
Page 11 GAO-12-832R Coal Mine Dust Exposure 

undermine the studies’ overall conclusion that a reduction in exposure to coal mine dust is 

associated with a reduction in the risk of disease. 

In addition to our evaluation of the reports MSHA used to support its proposal and the key 

scientific studies on which the reports were based, we identified and reviewed several other 

scientific studies that examined the association between exposure to coal mine dust and 

respiratory disease. See Enclosure I for additional information on these other studies. These 

other studies generally supported the conclusion that lowering miners’ exposure to coal 

mine dust would reduce their risk of developing CWP and other dust-induced respiratory 

diseases. We also found no evidence of other findings or other methodological approaches 

that would call into question the underlying conclusions in the key scientific studies on which 

MSHA based its proposal. 

Agency Comments and Our Evaluation 

We provided a draft of this report to Labor and HHS to obtain their comments. In its written 

comments, which are reproduced in enclosure II, Labor agreed with our findings. HHS also 

agreed with our findings, but did not provide formal written comments. Labor and HHS both 

provided 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. Should you or your staff have 

questions concerning this report, please contact me at (202) 512-7215 or moranr@gao.gov. 

Contact points for our Offices of Congressional Relations and Public Affairs may be found 

on the last page of this report. Key contributors to this report are listed in enclosure III. 

Revae Moran 

Director 

Education, Workforce, and Income Security Issues 

Enclosures - 3 
Page 12 GAO-12-832R Coal Mine Dust Exposure 

List of Committees 

The Honorable Tom Harkin 

Chairman 

The Honorable Richard C. Shelby 

Ranking Member 

Subcommittee on Labor, Health and Human 

 Services, Education, and Related Agencies 

Committee on Appropriations 

United States Senate 

The Honorable Denny Rehberg 

Chairman 

The Honorable Rosa L. DeLauro 

Ranking Member 

Subcommittee on Labor, Health and Human 

 Services, Education, and Related Agencies 

Committee on Appropriations 

House of Representatives 
Page 13 GAO-12-832R Coal Mine Dust Exposure 

Enclosure I: Scope and Methodology 

In the Consolidated Appropriations Act, 2012, Congress required that GAO review and 

report on the data collection, sampling methods, and analyses the Department of Labor’s 

(Labor) Mine Safety and Health Administration (MSHA) used to support its recent proposal 

to lower the permissible exposure limit (PEL) for respirable coal mine dust40 from 2.0 

milligrams of dust per cubic meter of air (mg/m3

) to 1.0 mg/m3.

41 Although MSHA’s proposal 

includes other provisions,42 our review focused on MSHA’s proposal to lower the PEL. To 

respond to this requirement, we answered the following question: What are the strengths 

and limitations of the data and analytical methods MSHA used to support its proposal to 

lower the permissible exposure limit for coal mine dust? 

To conduct our work, we reviewed relevant federal laws and regulations, MSHA’s proposed 

standard for exposure to coal mine dust, the comments MSHA received in response to the 

proposed rule, and the reports and the key scientific studies MSHA used to support its 

proposed standard. We also reviewed additional scientific studies as well as related reports 

by GAO, Labor's Office of Inspector General, and others on the health effects of exposure to 

coal mine dust. We interviewed officials with MSHA and the Department of Health and 

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

representatives from the mining industry and mine workers. We also conducted site visits to 

MSHA and NIOSH offices in Pittsburgh, Pennsylvania and Morgantown, West Virginia, 

which informed our understanding of the data and analytical methods used to support 

MSHA’s proposal to lower the PEL for coal mine dust. 

We conducted this performance audit from February 2012 through August 2012 in 

accordance with generally accepted government auditing standards. These 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. 

Analysis of Reports Used by MSHA and the Key Scientific Studies on Which They Were 

Based

To determine the strengths and limitations of the data and analytical methods MSHA used to 

support its proposal to lower the PEL for coal mine dust, we identified and reviewed the 

reports and key scientific studies cited in them that MSHA relied on to support its proposed 

standard. MSHA primarily relied on two reports and the studies cited in them to develop its 

proposed standard: NIOSH’s 1995 Criteria for a Recommended Standard – Occupational 

Exposure to Respirable Coal Mine Dust (Criteria Document) and MSHA’s 2010 Quantitative 

Risk Assessment in Support of the Proposed Respirable Coal Mine Dust Rule (Quantitative 

 

40In this report, we use the term coal mine dust to refer to respirable coal mine dust. 

41Pub. L. No. 112-74, div. F, tit. I, § 112, 125 Stat. 786, 1064 (2011). MSHA’s proposed rule was published in 

October 2010. 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 

August 13, 2012, MSHA had not finalized this regulation. 

42For example, the proposed rule also contained provisions that would change dust sampling procedures— 

including requirements for the use of continuous personal dust monitors—and expand medical surveillance.
Page 14 GAO-12-832R Coal Mine Dust Exposure 

Risk Assessment). Table 1 lists the reports and the key scientific studies. We selected 

these reports because they were used by MSHA to develop or support the proposed rule.43

In addition, we reviewed MSHA’s policies and procedures for its coal mine dust sampling 

program and NIOSH’s processes for administering the Coal Workers’ X-ray Surveillance 

Program.44 The focus of our work was limited to determining whether the scientific studies 

MSHA used generally supported its conclusion that lowering the PEL from 2.0 mg/m3

 to 1.0 

mg/m3

 would lower the risk of disease over a miner’s working life.45 We assessed the 

adequacy of the data and measures employed, the reasonableness and rigor of the 

statistical techniques used to analyze them, and the validity of the conclusions drawn from 

the analyses. Our work was not designed to determine the optimal limit for coal mine dust 

exposure; assess the cost-benefit analysis MSHA conducted in support of its proposed 

standard; or determine whether MSHA’s proposed rule complied with any legal 

requirements imposed by the Federal Mine Safety and Health Act of 1977 (Mine Act), the 

Administrative Procedure Act, or other applicable federal laws or executive orders that 

govern the rulemaking process.46 

Through interviews with NIOSH officials, we identified four key scientific studies in its Criteria 

Document that served as the primary basis for its recommendation to lower the PEL from 

2.0 mg/m3

 to 1.0 mg/m3. During our review of the Criteria Document, we identified and 

reviewed an additional five studies that contained important details necessary for evaluating 

NIOSH’s report.47 In addition, through an interview with the principal author of the 

Quantitative Risk Assessment and MSHA officials, we identified three key scientific studies 

used in that report to quantify the relationship between coal mine dust exposure and disease 

risk. Two GAO specialists with expertise in social science methods, statistics, or 

 

43These reports are referenced in the proposed rule, 75 Fed. Reg. 64,412, 64,414, 64,469 (Oct. 19, 2010). We 

also confirmed with MSHA officials that the agency used these reports to develop and support its proposal to 

lower the PEL. 

44The Coal Workers’ X-ray Surveillance Program is a component of NIOSH’s Coal Workers’ Health Surveillance 

Program, a medical monitoring and surveillance program carried out pursuant to requirements in the Mine Act 

and NIOSH regulations. 30 U.S.C. § 843, 42 C.F.R. §§ 37.1-37.80. 

 

45For purposes of this proposed rule, MSHA defines a miner’s working life to be 45 years. 

46Various federal statutes and executive orders require federal agencies to follow a number of procedural and 

analytic requirements when developing and issuing rules. For example, the Administrative Procedure Act 

generally requires agencies to publish proposed rules for public comment prior to issuing a final rule. 5 U.S.C. § 

553. In addition, section 101(a) of the Mine Act establishes certain procedural and analytic rulemaking 

requirements for MSHA standards. For example, before issuing a standard on toxic materials, MSHA must 

determine, based on research and other considerations, that the toxins pose a material impairment to miners’ 

health or functional capacity. 30 U.S.C. § 811(a)(6)(A). 

47The five additional studies reviewed contained more detailed information on the derivation of dust exposure 

estimates, the cohort of miners examined, the sampling design, and the overall analysis methods. The five 

studies include (1) Attfield, M. D., & Morring, K. “The derivation of estimated dust exposures for U.S. coal miners 

working before 1970,” American Industrial Hygiene Association, vol. 53, no. 4 (1992); (2) Seixas, N. S., Moulton, 

L. H., Robins, T. G., Rice, C. H., Attfield, M. D., & Zellers, E. T. “Estimation of cumulative exposures for the 

National Study of Coal Workers’ Pneumoconiosis,” Applied Occupational and Environmental Hygiene, vol.6, 

no.12 (1991); (3) Seixas, N. S., Robins, T.G., Attfield, M. D., & Moulton, L. H. “Exposure-response relationships 

for coal mine dust and obstructive lung disease following enactment of the Federal Coal Mine Health and Safety 

Act of 1969,” American Journal of Industrial Medicine, vol. 21, no. 5 (1992); (4) Morgan, W. K. C., Burgess, D. B., 

Jacobson, G., O'Brien, R. J., & Pendergrass, E. P., Reger, R. B., & Shoub, E. P. “The prevalence of coal 

workers' pneumoconiosis in US coal miners,” Archives of Environmental Health, vol. 27, no.4 (1973); and (5) 

Kuempel, E. D., Smith, R. J., Attfield, M. D., & Stayner, L. T. “Risks of occupational respiratory diseases among 

U.S. coal miners,” Applied Occupational and Environmental Hygiene, vol. 12, no.12 (1997).
Page 15 GAO-12-832R Coal Mine Dust Exposure 

epidemiology and public health examined each study to assess the adequacy of the 

samples and measures employed, the reasonableness and rigor of the statistical techniques 

used to analyze them, and the validity of the conclusions drawn from the analyses. For 

selected studies, we contacted the researchers directly as necessary for clarification or 

additional information. 
Page 16 GAO-12-832R Coal Mine Dust Exposure 

Table 1: Reports and Key Scientific Studies MSHA Used to Support Its Proposed 

Standard 

Report Key Studies Cited in the Report Description of Study 

NIOSH’s 1995 Criteria 

for a Recommended 

Standard: Occupational 

Exposure to Respirable 

Coal Mine Dust 

Attfield, M.D. and K. Morring, “An 

Investigation into the Relationship Between 

Coal Workers’ Pneumoconiosis and Dust 

Exposure in U.S. Coal Miners” (1992) 

Provides an estimate of the 

relationship between the cumulative 

coal mine dust miners are exposed to 

over their working lives and disease 

prevalence in U.S. coal miners. 

 Attfield, M.D. and N.S. Seixas, “Prevalence 

of Pneumoconiosis and its Relationship to 

Dust Exposure in a Cohort of U.S. 

Bituminous Coal Miners and Ex-Miners” 

(1995) 

Provides an estimate of the 

relationship between the cumulative 

coal mine dust miners are exposed to 

over their working lives and disease 

prevalence among current and former 

miners. 

Attfield M.D. and T.K. Hodous, “Pulmonary 

Function of U.S. Coal Miners Related to 

Dust Exposure Estimates” (1992) 

Provides an estimate of the effects of 

coal mine dust exposure on lung 

function in U.S. coal miners. 

Seixas N.S., T.G. Robins, M.D. Attfield, 

L.H. Moulton, “Longitudinal and Cross 

Sectional Analyses of Exposure to Coal 

Mine Dust and Pulmonary Function in New 

Miners” (1993) 

Provides an estimate of the effects of 

coal mine dust exposure on lung 

function in U.S. coal miners. 

MSHA’s 2010 

Quantitative Risk 

Assessment 

Attfield, M.D. and N.S. Seixas, “Prevalence 

of Pneumoconiosis and its Relationship to 

Dust Exposure in a Cohort of U.S. 

Bituminous Coal Miners and Ex-Miners” 

(1995)a

Provides an estimate of the 

relationship between the cumulative 

coal mine dust miners are exposed to 

over their working lives and disease 

prevalence among current and former 

miners. 

Kuempel et al., “Emphysema and 

Pulmonary Impairment in Coal Miners: 

Quantitative Relationship with Dust 

Exposure and Cigarette Smoking” (2009) 

Provides predictions of the 

relationship between the cumulative 

coal mine dust miners are exposed to 

and their risk of developing 

emphysema. 

Attfield, M.D. and E.D. Kuempel, “Mortality 

Among U.S. Underground Coal Miners: A 

23-Year Follow-Up” (2008) 

Examines the contributing and 

underlying causes of death in U.S. 

coal miners. 

Source: GAO review of reports. 

a

Attfield, M.D., and N.S. Seixas (1995) is a key study that was used in both the NIOSH Criteria Document and the MSHA 

Quantitative Risk Assessment. 

NIOSH’s Criteria Document included a review of all available information through 1995 and 

estimated the adverse health effects associated with exposure to coal mine dust over a 

miner’s working life to provide the scientific basis for NIOSH’s recommendation for a 

reduced PEL. In this report, NIOSH concluded that epidemiological studies demonstrated 

that miners have an elevated risk of developing black lung disease, which includes coal 

workers pneumoconiosis (CWP) and other respiratory or pulmonary impairments, when they 

are exposed over their working lives to coal mine dust at the current PEL of 2.0 mg/m3

. This 

conclusion represents a change in the understanding of disease risk since the time the 2.0 

mg/m3

 PEL was initially established. 48 Further, based on its evaluation of health effects 

data, the feasibility of collecting and analyzing coal mine dust samples, and technological 

 

48According to NIOSH, the current PEL of 2.0 mg/m3

 for coal mine dust exposure was based primarily on 

estimates of earlier studies of coal miners in the United Kingdom, where the probability of disease progression 

was thought to be zero for miners’ exposure to coal mine dust at an average concentration of 2.0 mg/m3

 over a 

35-year working life.
Page 17 GAO-12-832R Coal Mine Dust Exposure 

feasibility of controlling exposures, NIOSH recommended that the PEL be reduced to 1.0 

mg/m3

 as a time-weighted average concentration for up to 10 hours per day during a 40-

hour work week. NIOSH concluded, however, that even at an exposure level of 1.0 

mg/m3

—the lowest PEL NIOSH considered feasible—miners exposed at this concentration 

over a working life still have a risk of developing black lung disease. 

In response to NIOSH’s Criteria Document in support of its recommendation to lower the 

PEL, MSHA completed a Quantitative Risk Assessment in September 2010 to determine 

whether current conditions involving exposure to coal mine dust place miners at risk for 

developing black lung and whether the proposed rule will substantially reduce those risks. 

The report addressed three questions related to MSHA’s proposed rule: whether (1) the 

potential health effects associated with current exposure levels constitute material 

impairments to a miner’s health or functional capacity; (2) current conditions place miners at 

a significant risk of incurring any of these material impairments; and (3) the proposed rule 

will substantially reduce those risks.49 MSHA’s report concluded that the current exposure 

level of 2.0 mg/m3

 placed miners at a significant risk of incurring each of the material 

impairments considered and that the proposed rule would substantially reduce the risks of 

CWP, severe emphysema, and mortality attributable to coal mine dust exposure.50

We also reviewed NIOSH’s April 2011 report, Coal Mine Dust Exposures and Associated 

Health Outcomes: A Review of Information Published Since 1995.

51 This report provides a 

summary of information on exposure to coal mine dust and its associated health effects 

since 1995. NIOSH’s intent was to determine whether its recommendations in 1995 to lower 

the PEL to 1.0 mg/m3

 remained valid in light of new findings. We reviewed the sections of 

the report most relevant to respiratory disease outcomes. We also reviewed two studies that 

were referred to in this report that were especially relevant to our research objective, as they 

contained additional information about the relationship between exposure to coal mine dust 

and risk of disease in British coal miners.52

Additional Scientific Studies Reviewed

We also conducted a search for studies that explored the relationship between exposure to 

coal mine dust and respiratory disease. This search drew on several sources: 

 an extensive literature search for such studies; 

 

49The Mine Act establishes the criteria for MSHA’s Quantitative Risk Assessment, 30 U.S.C. § 811(a)(6)(A). 

According to MSHA, these three questions are based on court interpretations of similar statutory language in the 

Occupational Safety and Health Act of 1970.

50We did not assess whether MSHA met applicable statutory requirements in issuing this proposed rule. 

Specifically, we did not evaluate whether the risk posed by coal mine dust at current conditions constitutes a 

“material impairment” to a miner’s health, whether the current conditions create a “significant risk” of impairment, 

or whether the proposed rule will “substantially reduce” those risks, as those terms are used in the statute and 

related court decisions. 30 U.S.C. § 811(a)(6)(A); see, for example, Indus. Union Dep’t, AFL-CIO v. Am. 

Petroleum Inst., 448 U.S. 607, 639 (1980). 

 

51This report had not been issued at the time MSHA published its proposed rule in October 2010. Our review of 

studies in this report was limited to those published before October 2010.

 

52These studies included Hurley J.F., and W.M. Maclaren, “Dust-related risks of radiological changes in 

coalminers over a 40-year working life: Report on work commissioned by NIOSH,” Institute of Occupational 

Medicine. (1987) and Soutar C.A., J.F. Hurley, B.G. Miller, H.A. Cowie, D. Buchanan, “Dust concentrations and 

respiratory risks in coalminers: key risk estimates from the British pneumoconiosis field research.” Occupational 

and Environmental Medicine. 61 (2004).
Page 18 GAO-12-832R Coal Mine Dust Exposure 

 a review of materials submitted to MSHA in response to its proposed rule during the 

public comment period; and, 

 interviews with MSHA and NIOSH officials, mining company representatives, and 

representatives of mine workers. 

The initial search netted hundreds of research studies. We applied the following criteria in 

order to limit our review to include only studies with the potential to shed new light on the 

scientific support for the proposal to lower the PEL: 

(1) studies not cited in the two reports MSHA used to develop its proposed rule, or any of 

the key scientific studies on which they were based;53

(2) studies published in the last 50 years and before October 19, 2010, the publication date 

of MSHA’s proposed rule; and, 

(3) studies containing original analysis (as opposed to those that used or relied on research 

already conducted). 

This effort yielded 10 research studies that met our criteria (see table 2). 

 

53In addition to MSHA’s proposed rule published in 2010, we reviewed two prior proposed rules related to coal 

mine dust published on July 7, 2000, and March 6, 2003, to further identify any additional epidemiological studies 

examining the relationship between exposure to coal mine dust and respiratory disease. 65 Fed. Reg. 42,122 

(July 7, 2000), 68 Fed. Reg. 10,784 (March 6, 2003).
Page 19 GAO-12-832R Coal Mine Dust Exposure 

Table 2. Additional Studies That Met Our Criteria 

Source: GAO review of additional studies. 

Each of these studies was then reviewed by a GAO specialist with expertise in social 

science methods, statistics, or epidemiology and public health. Each specialist made an 

initial determination of whether the study's results were inconsistent with, or revealed 

limitations in the work used to support the proposal to lower the PEL. If a study met this 

criterion, then an additional GAO specialist conducted a further review to assess the 

adequacy of the samples and measures employed, the reasonableness and rigor of the 

statistical techniques used to analyze them, and the validity of the conclusions drawn from 

the analyses.

We based our findings primarily on the results of the models used in the key scientific 

studies, which are based on data for U.S. miners only. While our methodology included a 

review of other studies, we found only one different type of model employed by others that 

attempted to estimate disease risk based on dust exposure.54 This model used data on 

British coal miners only. We did not evaluate whether the predicted estimates of disease risk 

in the key scientific studies of U.S. coal miners would be similar if they were generated from 

the models presented in other studies. The key scientific studies were used to determine the 

predicted risk of disease due to exposure to coal mine dust, according to NIOSH, because 

they are more relevant to mining conditions in the United States. The results from other 

studies generally showed lower risk of CWP and progressive massive fibrosis compared 

 

54This model was included in Hurley J.F., and W.M. Maclaren, “Dust-related risks of radiological changes in 

coalminers over a 40-year working life: Report on work commissioned by NIOSH,” Institute of Occupational 

Medicine. (1987).

(1) Leigh, J., Todorovic, M., & Driscoll, T., “Histological Changes in Hilar Lymph Glands in Relation to Coal 

Workers’ Progressive Massive Fibrosis and Lung Coal and Quartz Contents,” The Annals of Occupational 

Hygiene, Vol.41, (1997) 

(2) Wang, X.R. and D. Christiani, “Respiratory Symptoms and Functional Status in Workers Exposed to Silica, 

Asbestos, and Coal Mine Dusts,” Journal of Occupational and Environmental Medicine, Vol.42, No.11, (2000) 

(3) Noble, R.B., Bailer, A.J., & Park, R., “Model-Averaged Benchmark Concentration Estimates for Continuous 

Response Data Arising from Epidemiological Studies,” Risk Analysis, Vol.29, No.4, (2009) 

(4) Liu, H., Tang, Z., Yang, Y., Weng, D., Sun, G., Duan, Z., & Chen, J., “Identification and Classification of High 

Risk Groups for Coal Workers’ Pneumoconiosis Using an Artificial Neural Network Based on Occupational 

Histories: A retrospective Cohort Study,” BMC Public Health, Vol.9, No.366, (2009) 

(5) Liu, H., Tang, Z., Weng, D., Yang, Y., Tian, L., Duan, Z., & Chen, J., “Prevalence Characteristics and 

Prediction of Coal Workers’ Pneumoconiosis in the Tiefa Colliery in China,” Industrial Health, Vol.47, (2009) 

(6) Ashford, J.R., Fay, J.W.J., & Smith, C.S., “The Correlation of Dust Exposure with Progression of Radiological 

Pneumoconiosis in British Coal Miners,” American Industrial Hygiene Association Journal, Vol.26, No.4, (1965) 

(7) Mamuya, S. HD., Bratveit, M., Mashalla, Y., & Moen, B., “High Prevalence of respiratory Symptoms Among 

Workers in the Development Section of a Manually Operated Coal Mine in a Developing Country: A Cross 

Sectional Study,” BMC Public Health, Vol.7, No.17, (2007) 

(8) Atlin, R., Savranlar, A., Kart, L., Mahmutyazicioglu, K., Ozdemir, H., Akdag, B., & Gundogdu, S., “Presence 

and HRCT Quantification of Bronchiectasis in Coal Workers,” European Journal of Radiology, Vol,52, (2004) 

(9) Morefeld, P., Ambrosy, J., Bengtsson, U., Bicker, H., Kalkowsky, B., Kosters, A., Lenaerts, H., Ruther, M., 

Vautrin, H.J., & Piekarski, C., “The Risk of Developing Coal Workers’ Pneumoconiosis in German Coal Mining 

Under Modern Mining Conditions,” The Annals of Occupational Hygiene, Vol.46, (2002) 

(10) Attfield, M.D., Kuempel, E., & Wagner, G., “Exposure Response for Coal Workers’ Pneumoconiosis in 

Underground Coal Miners: A Discussion of Issues and Findings,” The Annals of Occupational Hygiene, Vol.41, 

(1997) 
Page 20 GAO-12-832R Coal Mine Dust Exposure 

with the predicted risk of disease in the key scientific studies. These differences in predicted 

risk, however, may be due to a number of factors, including differences in the models and 

the underlying assumptions used. While these differences may exist, they do not indicate 

that the relationship between coal mine dust exposure and disease risk is different in 

different countries. For example, all of the studies we reviewed indicate that a reduction in 

exposure to coal dust is associated with a reduction in risk of developing disease. 

Interviews with MSHA, NIOSH, and Other Groups

To further inform our review of the evidence used to develop the proposed rule, we 

interviewed MSHA and NIOSH officials as well as representatives from the mining industry 

and mine workers. At MSHA, we spoke with officials in the Office of Standards, Regulations, 

and Variances, the Safety and Health Technology Center, and its District 2 field office in 

Prosperity, Pennsylvania. At NIOSH, we spoke with officials in its Office of Mine Safety and 

Health Research in Pittsburgh, Pennsylvania; its Division of Respiratory Disease Studies in 

Morgantown, West Virginia; its Education and Information Division in Cincinnati, Ohio; and 

its Office of the Director in Washington, D.C. We also spoke with several representatives 

from the mining industry and mine workers, including officials from the National Mining 

Association, the Bituminous Coal Operators’ Association, the United Mine Workers of 

America, Murray Energy, Alliance Coal Company, and Consol Energy. 

Site Visits

To obtain information on the research on improved dust control technologies and sampling 

methods used to measure the level of coal mine dust to which miners are exposed, we 

visited NIOSH’s Office of Mine Safety and Health Research in Pittsburgh, Pennsylvania. To 

obtain information about epidemiological studies used to support NIOSH’s recommendation 

to lower the existing PEL for coal mine dust, we also visited NIOSH’s Division of Respiratory 

Disease Studies, in Morgantown, West Virginia. Officials from NIOSH’s Education and 

Information Division, in Cincinnati, Ohio, and NIOSH’s Office of the Director, in Washington, 

D.C. also participated in these discussions. In addition, we visited MSHA’s Safety and 

Health Technology Center at the Bruceton Laboratory in Pittsburgh, Pennsylvania to obtain 

information on how samples containing coal mine dust, including silica, are processed and 

analyzed. To observe the conditions under which underground coal miners work, we also 

visited the Bailey Coal Mine in Wind Ridge, Pennsylvania. 
Page 21 GAO-12-832R Coal Mine Dust Exposure 

Enclosure II: Comments from the Department of Labor 
Page 22 GAO-12-832R Coal Mine Dust Exposure 

Enclosure III: GAO Contact and Staff Acknowledgments 

GAO Contact 

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

Staff Acknowledgments 

In addition to the individual named above, Mary Crenshaw, Assistant Director, and Claudine 

Pauselli, Analyst in Charge, managed all aspects of this assignment and Russell Burnett, 

Sarah Cornetto, Kathleen van Gelder, Brian Schwartz, Sushil Sharma, Shana Wallace, and 

Monique Williams made significant contributions to this report. 

(131148)
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