44852 Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 

DEPARTMENT OF LABOR 

Mine Safety and Health Administration 

30 CFR Parts 56, 57, 60, 70, 71, 72, 75, 

and 90 

[Docket No. MSHA–2023–0001] 

RIN 1219–AB36 

Lowering Miners’ Exposure to 

Respirable Crystalline Silica and 

Improving Respiratory Protection 

AGENCY: Mine Safety and Health 

Administration (MSHA), Department of 

Labor. 

ACTION: Proposed rule; request for 

comments; notice of public hearings. 

SUMMARY: The Mine Safety and Health 

Administration (MSHA) proposes to 

amend its existing standards to better 

protect miners against occupational 

exposure to respirable crystalline silica, 

a carcinogenic hazard, and to improve 

respiratory protection for all airborne 

hazards. MSHA has preliminarily 

determined that under the Agency’s 

existing standards, miners at metal and 

nonmetal mines and coal mines face a 

risk of material impairment of health or 

functional capacity from exposure to 

respirable crystalline silica. MSHA 

proposes to set the permissible exposure 

limit of respirable crystalline silica at 50 

micrograms per cubic meter of air (mg/ 

m3) for a full shift exposure, calculated 

as an 8-hour time-weighted average, for 

all miners. MSHA’s proposal would also 

include other requirements to protect 

miner health, such as exposure 

sampling, corrective actions to be taken 

when miner exposure exceeds the 

permissible exposure limit, and medical 

surveillance for metal and nonmetal 

miners. Furthermore, the proposal 

would replace existing requirements for 

respiratory protection and incorporate 

by reference ASTM F3387–19 Standard 

Practice for Respiratory Protection. The 

proposed uniform approach to 

respirable crystalline silica occupational 

exposure and improved respiratory 

protection for all airborne hazards 

would significantly improve health 

protections for all miners and lower the 

risk of material impairment of health or 

functional capacity. 

DATES: Written comments. Written 

comments, including comments on the 

information collection requirements 

described in this preamble, must be 

received or postmarked by midnight 

Eastern Time on August 28, 2023. 

Public Hearings. MSHA will hold two 

public hearings on August 3, 2023 in 

Arlington, Virginia and August 21, 2023 

in Denver, Colorado. For more 

information on the public hearings, see 

SUPPLEMENTARY INFORMATION. 

ADDRESSES: All submissions must 

include RIN 1219–AB36 or Docket No. 

MSHA–2023–0001. You should not 

include personal or proprietary 

information that you do not wish to 

disclose publicly. If you mark parts of 

a comment as ‘‘business confidential’’ 

information, MSHA will not post those 

parts of the comment. Otherwise, MSHA 

will post all comments without change, 

including any personal information 

provided. MSHA cautions against 

submitting personal information. 

You may submit comments and 

informational materials, clearly 

identified by RIN 1219–AB36 or Docket 

Id. No. MSHA–2023–0001, by any of the 

following methods: 

Federal E-Rulemaking Portal: https:// 

www.regulations.gov. Follow the online 

instructions for submitting comments. 

Email: zzMSHA-comments@dol.gov. 

Include ‘‘RIN 1219–AB36’’ in the 

subject line of the message. 

Regular Mail: MSHA, Office of 

Standards, Regulations, and Variances, 

201 12th Street South, Suite 4E401, 

Arlington, Virginia 22202–5450. 

Hand Delivery or Courier: MSHA, 

Office of Standards, Regulations, and 

Variances, 201 12th Street South, Suite 

4E401, Arlington, Virginia, between 

9:00 a.m. and 5:00 p.m. Monday through 

Friday, except Federal holidays. Before 

visiting MSHA in person, call 202–693– 

9440 to make an appointment. Special 

health precautions may be required. 

Facsimile: 202–693–9441. Include 

‘‘RIN 1219–AB36’’ in the subject line of 

the message. 

Information Collection Requirements. 

Comments concerning the information 

collection requirements of this proposed 

rule must be clearly identified with 

‘‘RIN 1219–AB36’’ or ‘‘Docket No. 

MSHA–2023–0001,’’ and sent to MSHA 

by one of the methods previously 

explained. 

Docket. For access to the docket to 

read comments and background 

documents, go to https:// 

www.regulations.gov. The docket can 

also be reviewed in person at MSHA, 

Office of Standards, Regulations, and 

Variances, 201 12th Street South, 

Arlington, Virginia, between 9 a.m. and 

5 p.m. Monday through Friday, except 

Federal holidays. Before visiting MSHA 

in person, call 202–693–9440 to make 

an appointment. Special health 

precautions may be required. 

Email Notification. To subscribe to 

receive an email notification when 

MSHA publishes rulemaking documents 

in the Federal Register, go to https:// 

public.govdelivery.com/accounts/ 

USDOL/subscriber/new. 

FOR FURTHER INFORMATION CONTACT: S. 

Aromie Noe, Director, Office of 

Standards, Regulations, and Variances, 

MSHA, at: silicaquestions@dol.gov 

(email); 202–693–9440 (voice); or 202– 

693–9441 (facsimile). These are not tollfree numbers. 

SUPPLEMENTARY INFORMATION: 

MSHA will hold two public hearings 

to provide industry, labor, and other 

interested parties with an opportunity to 

present oral statements, written 

comments, and other information on the 

proposed rule. The public hearings will 

begin at 9 a.m. local time and end after 

the last presenter speaks on the 

following dates: 

Date Location Contact 

number 

August 3, 2023 ... Mine Safety and Health Administration, 201 12th Street South, Room 7W202, Arlington, VA 22202 ............. 202–693–9440 

August 21, 2023 Denver Federal Center, Building 25 Lecture Hall, West 6th Avenue and Kipling Street, Denver, CO 80225 .. 202–693–9440 

The public hearings will begin with 

an opening statement from MSHA, 

followed by an opportunity for members 

of the public to make oral presentations. 

Speakers and other attendees may 

present information to MSHA for 

inclusion in the rulemaking record. The 

hearings will be conducted in an 

informal manner. Formal rules of 

evidence or cross examination will not 

apply. 

A verbatim transcript of each of the 

proceedings will be prepared and made 

a part of the rulemaking record. Copies 

of the transcripts will be available to the 

public. MSHA will make the transcript 

of the hearings available at http://

www.regulations.gov and on MSHA’s 

website at https://arlweb.msha.gov/ 

currentcomments.asp. 

MSHA will accept post-hearing 

written comments and other appropriate 

information for the record from any 

interested party, including those not 

presenting oral statements, received by 


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Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 44853 

midnight (Eastern Time) on August 28, 

2023. 

Pre-registration is not required to 

attend the hearings. Interested parties 

may attend the hearings virtually or in 

person. Interested parties who intend to 

present testimony at the hearings are 

asked to register in advance on MSHA’s 

website (http://www.msha.gov). 

Speakers will be called in the order in 

which they signed up. Those who do 

not register in advance will have an 

opportunity to speak after all those who 

pre-registered have spoken. You may 

submit hearing testimony and 

documentary evidence, identified by 

docket number (MSHA–2023–0001), by 

any of the methods previously 

identified. Additional information on 

how to access the public hearings will 

be posted when available at https://

www.msha.gov/regulations/rulemaking. 

The preamble to the proposed 

standard follows this outline: 

I. Introduction 

II. Request for Comments 

III. Background 

IV. Existing Standards and Implementation 

V. Health Effects Summary 

VI. Preliminary Risk Analysis Summary 

VII. Section-by-Section Analysis 

VIII. Technological Feasibility 

IX. Summary of Preliminary Regulatory 

Impact Analysis and Regulatory 

Alternatives 

X. Initial Regulatory Flexibility Analysis 

XI. Paperwork Reduction Act 

XII. Other Regulatory Considerations 

XIII. References Cited in the Preamble 

XIV. Appendix 

Acronyms and Abbreviations 

COPD chronic obstructive pulmonary 

disease 

ESRD end-stage renal disease 

FEV forced expiratory volume 

FVC forced vital capacity 

L/min liter per minute 

mg milligram 

mg/m3 milligrams per cubic meter 

mL milliliter 

mg/m3 micrograms per cubic meter 

MNM metal and nonmetal 

NMRD nonmalignant respiratory disease 

PEL permissible exposure limit 

PMF progressive massive fibrosis 

RCMD respirable coal mine dust 

REL recommended exposure limit 

SiO2 silica 

TB tuberculosis 

TLV® Threshold Limit Value 

TWA time-weighted average 

I. Introduction 

With the passage of the Federal Mine 

Safety and Health Act of 1977 (Mine 

Act), Congress declared that ‘‘the first 

priority and concern of all in the coal 

or other mining industry must be the 

health and safety of its most precious 

resource—the miner[.]’’ 30 U.S.C. 

801(a). In furtherance of that clear 

guiding principle, this proposed rule 

promotes MSHA’s mission and statutory 

mandate to prevent death, illness, and 

injury from mining and promote safe 

and healthful workplaces for U.S. 

miners. This proposal provides the 

public with the opportunity to comment 

on the Agency’s proposed uniform and 

streamlined regulatory approach to 

lowering miners’ exposure to respirable 

crystalline silica and improving 

respiratory protection. 

Exposure to silica dust causes adverse 

health effects, including silicosis (acute 

silicosis, accelerated silicosis, simple 

chronic silicosis, and progressive 

massive fibrosis (PMF)), nonmalignant 

respiratory diseases (NMRD) (e.g., 

emphysema and chronic bronchitis), 

lung cancer, and renal diseases. Each of 

these effects is chronic, irreversible, and 

potentially disabling or fatal. Silica dust 

is generated in most mining activities, 

including cutting, sanding, drilling, 

crushing, grinding, sawing, scraping, 

jackhammering, excavating, and hauling 

materials that contain silica, and is 

found in all mines—underground and 

surface metal and nonmetal (MNM) and 

coal mines. In a mining context, silica 

exposures may occur in respirable dust 

together with exposures to other 

airborne contaminants and combustion 

biproducts. 

MSHA’s existing standards, 

established in the early 1970s, help 

protect miners from the most dangerous 

levels of exposure to respirable 

crystalline silica. However, since their 

promulgation, scientific understanding 

of respirable crystalline silica toxicity 

has advanced, and the National Institute 

for Occupational Safety and Health 

(NIOSH) has recommended a respirable 

crystalline silica exposure level of 50 

mg/m3 for workers. In 2016, the 

Occupational Safety and Health 

Administration (OSHA) established a 

permissible exposure limit (PEL) of 50 

mg/m3 in many industry sectors that it 

regulates. 

To provide miners with exposure 

limits consistent with workers in other 

industries and NIOSH’s 

recommendation, and to improve 

miners’ health, MSHA proposes to 

lower its existing exposure limits to 50 

mg/m3 for respirable crystalline silica in 

MNM and coal mines. MSHA 

considered exposure limits below 50 mg/ 

m3. However, MSHA believes, based on 

a review of the Agency’s available silica 

sample data, that an exposure limit of 

25 mg/m3 may not be achievable for all 

mines. The proposed PEL would be 

expressed as a full-shift exposure, 

calculated as an 8-hour time-weighted 

average (TWA). Importantly, a uniform 

proposed PEL for all mines would make 

compliance simpler—especially for coal 

mines by eliminating the existing 

respirable dust standard when quartz is 

present. 

To meet the requirements of the 

proposed PEL, mine operators would 

have to implement engineering controls, 

followed by administrative controls if 

supplementary protection is needed. 

Engineering controls, which are most 

effective, are designed to remove or 

reduce the hazard at the source and 

could include the installation of proper 

ventilation systems, use of water sprays 

or wetting agents to suppress airborne 

contaminants, installation of machinemounted dust collectors to capture 

respirable crystalline silica and other 

contaminants, and the installation of 

control booths or environmental cabs to 

enclose equipment operators. 

Administrative controls, which are often 

less effective than engineering controls, 

are designed to change the way miners 

work. One example would be ensuring 

that miners safely clean dust off their 

work clothes so that they are not 

exposed to respirable dust after their 

shift ends. 

MSHA’s proposed rule would further 

protect all miners by requiring exposure 

sampling and corrective actions when 

miners’ exposures exceed the proposed 

PEL, as well as periodic sampling when 

miners’ exposure levels meet or exceed 

the proposed action level. The proposed 

rule also includes medical surveillance 

requirements for MNM miners (medical 

surveillance requirements already exist 

for coal miners). Proposed medical 

examinations would include chest Xrays, spirometry, symptom assessment, 

and occupational history and would be 

provided at no cost to the miner. 

Finally, the proposed rule would 

incorporate by reference an updated 

respiratory protection standard, ASTM 

F3387–19, ‘‘Standard Practice for 

Respiratory Protection’’ (ASTM F3387– 

19), for respirable crystalline silica and 

all other regulated airborne 

contaminants. This voluntary consensus 

standard represents up-to-date 

advancements in respiratory protection 

technologies, practices, and techniques, 

including proper selection, use, and 

maintenance of respirators. The 

proposed incorporation of ASTM 

F3387–19 by reference would better 

protect all miners from airborne 

hazards. However, respiratory 

protection should only be relied upon as 

an exposure control measure in limited 

situations and on a temporary basis, and 

to supplement engineering controls, 

followed by administrative controls. 

Taken together, all elements of the 

proposed rule are technologically and 

economically feasible. MSHA’s 2014 


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44854 Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 

final rule, Lowering Miners’ Exposure to 

Respirable Coal Mine Dust, Including 

Continuous Personal Dust Monitors 

(Coal Dust Rule) improved health 

protections for coal miners by lowering 

exposure limits to respirable coal mine 

dust and establishing sampling 

requirements that included the use of a 

Continuous Personal Dust Monitor (79 

FR 24813, May 1, 2014). Coal mine 

operators have generally achieved 

compliance with the respirable dust 

standards primarily by implementing or 

adjusting existing engineering controls. 

Coal mine operators’ sampling data and 

MSHA’s compliance data show that 

operators have lowered coal miners’ 

exposures to respirable coal mine dust 

and to respirable crystalline silica. Data 

show that average exposures in coal 

mines are below the proposed PEL of 50 

mg/m3, and therefore, corrective 

measures would often not be needed. 

Similarly, for MNM miners, MSHA data 

also show that most exposures to 

respirable crystalline silica are below 

the proposed PEL. However, at MNM 

and coal mines where elevated 

exposures are found, operators will be 

able to reduce exposures to the 

proposed PEL through some 

combination of properly maintaining 

existing engineering controls, 

implementing new engineering controls, 

and requiring safe work practices. Mines 

and laboratories will be able to meet 

exposure monitoring requirements with 

existing validated and widely used 

sampling and analytical methods. The 

proposed revision to the respiratory 

protection standard is technologically 

feasible because MSHA’s existing 

respiratory protection requirements for 

selecting, fitting, using, and maintaining 

respiratory protection include similar 

requirements. 

MSHA’s Preliminary Risk Analysis 

(PRA) suggests that exposure consistent 

with a lower proposed PEL of 50 mg/m3

would deliver many health benefits to 

miners who currently experience 

exposures above the proposed PEL by 

reducing the likelihood of respirable 

crystalline silica-related diseases. For 

those miners working only under the 

proposed PEL, MSHA estimates that the 

proposed rule would result in a total of 

799 lifetime avoided deaths (63 in coal 

and 736 in MNM mines) and 2,809 

lifetime avoided morbidity cases (244 in 

coal and 2,566 in MNM mines) over a 

60-year period. MSHA expects full 

implementation and compliance to 

reduce lifetime mortality risk due 

specifically to silica exposures by 9.5 

percent and to reduce silicosis 

morbidity risk by 41.9 percent. The 

latter statistic is particularly important 

to coal miners given surveillance 

findings noted by the National 

Academies of Sciences, Engineering, 

and Medicine that severe 

pneumoconiosis where respirable 

crystalline silica is likely an important 

contributor is presenting in relatively 

young miners, sometimes in their late 

30’s and early 40’s. 

MSHA’s economic analysis estimates 

that the proposed respirable crystalline 

silica rule would cost an average of 

$56.1 million per year in 2021 dollars at 

an undiscounted rate, $57.6 million at a 

3 percent discount rate, and $59.9 

million at a 7 percent discount rate. 

Based on the results of the Preliminary 

Regulatory Impact Analysis (PRIA), 

MSHA estimates that the proposed 

rule’s benefits would exceed its costs, 

with or without discount rates. 

Monetized benefits are estimated from 

avoidance of 410 deaths related to 

NMRD, silicosis, ESRD, and lung cancer 

and 1,420 cases of silicosis associated 

with silica exposure over the first 60- 

year period after the promulgation of the 

final rule. The estimated annualized net 

benefit is approximately $212.8 million 

at an undiscounted rate, $118.2 million 

at a 3 percent discount rate, and $36.3 

million at a 7 percent discount rate. 

A rule is significant under Executive 

Order 12866 Section 3(f)(1), as amended 

by E.O. 14094, if it is likely to result in 

‘‘an annual effect on the economy of 

$200 million or more or . . . adversely 

affect in a material way the economy, a 

sector of the economy, productivity, 

competition, jobs, the environment, 

public health or safely, or State, local, 

or tribal governments or communities.’’ 

The Office of Management and Budget 

has determined that the proposed rule is 

significant within the meaning of E.O. 

12866 Section 3(f)(1). 

The proposed rule would strengthen 

MSHA’s existing regulatory framework. 

It would establish a uniform proposed 

PEL that provides all MNM and coal 

miners with the same exposure limits 

for respirable crystalline silica 

consistent with exposure limits that 

other U.S. workers currently receive in 

non-mining industries. It would update 

the existing respiratory protection 

standard to require mine operators to 

provide miners with NIOSH-approved 

respiratory equipment that has been 

fitted, selected, maintained, and used in 

accordance with recent consensus 

standards. The proposed rule would 

also include requirements for all MNM 

operators to provide medical 

surveillance in the form of a medical 

examination regime similar to what coal 

miners already receive. Cumulatively, 

the proposed provisions would lower 

miners’ risk of developing chronic, 

irreversible, disabling, and potentially 

fatal health conditions, consistent with 

MSHA’s mission and statutory mandate 

to prevent occupational diseases and 

protect U.S. miners from suffering 

material health impairments. 

II. Request for Comments 

MSHA requests comments on the 

proposed rule and all relevant issues, 

including the review and conclusions of 

the health effects discussion, 

preliminary risk analysis, feasibility 

analysis, preliminary regulatory impact 

analysis and regulatory alternatives, and 

preliminary regulatory flexibility 

analysis. While MSHA invites 

comments on any aspect of its proposed 

rule and related documents, the Agency 

particularly seeks information and data 

in response to questions posed in this 

section and any other aspect of this 

proposed rule. Instructions for 

submitting and viewing comments are 

provided under the DATES heading. 

MSHA will consider all timely 

comments and may change the 

proposed rule based on such comments. 

MSHA requests that commenters 

organize their comments, to the extent 

possible, around the following 

numbered questions. The Agency is 

interested in receiving responses to the 

listed questions and any information or 

data supporting the responses. 

Health Effects 

1. In the standalone, background 

document entitled ‘‘Health Effects of 

Respirable Crystalline Silica’’ and as 

summarized in Section V. Health Effects 

Summary of this preamble, MSHA has 

made a preliminary determination that 

miners’ exposure to respirable 

crystalline silica presents a risk of 

material health impairment due to the 

risk of developing silicosis, NMRD, lung 

cancer, and renal disease, based on its 

extensive review of the health effects 

literature. MSHA requests comments on 

this preliminary determination and its 

literature review, which draws heavily 

from the review conducted by OSHA for 

its 2016 rulemaking. Are there 

additional adverse health effects that 

should be included or more recent 

literature that offers a different 

perspective? MSHA requests that 

commenters submit information, data, 

or additional studies or their citations. 

Please be specific regarding the basis for 

any recommendation to include 

additional adverse health effects. 

Preliminary Risk Analysis 

2. In the standalone, background 

document entitled ‘‘Preliminary Risk 

Analysis’’ and as summarized in Section 

VI. Preliminary Risk Analysis Summary 


ddrumheller on DSK120RN23PROD with PROPOSALS2
Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 44855 

of this preamble, MSHA relied on risk 

models that OSHA used in support of its 

2016 respirable crystalline silica final 

rule. Does the context of the MSHA rule 

suggest that the model would benefit 

from changes? If so, please describe both 

the justification for those changes and 

the likely impact on the final risk 

estimates. Are there additional studies 

or sources of data that MSHA should 

consider? What is the rationale for 

recommending the use of these 

additional studies or data? 

3. MSHA’s risk analysis of lung 

cancer mortality uses the exposureresponse model from Miller and 

MacCalman (2010) instead of Steenland 

et al. (2001a), on which OSHA’s risk 

assessment of lung cancer mortality was 

based. MSHA uses Miller and 

MacCalman (2010) for several reasons. 

First, it covers coal mining-specific 

cohort large enough (with 45,000 

miners) to provide adequate statistical 

power to detect low levels of risk, and 

it covers an extended follow-up period 

(1959–2006). Second, the study 

provided data on cumulative exposure 

of cohort members and adjusted for or 

addressed confounders such as smoking 

and exposure to other carcinogens. 

Finally, it developed quantitative 

assessments of exposure-response 

relationships using appropriate 

statistical models or otherwise provided 

sufficient information that permitted 

MSHA to do so. The Agency is 

requesting comment on MSHA’s 

reliance on the Miller and MacCalman 

(2010) study in assessing lung cancer 

mortality. Please provide any other 

studies or information that MSHA 

should take into account in determining 

the risk of lung cancer mortality among 

miners. 

Technological Feasibility of the 

Proposed Rule 

4. As discussed in Section VIII. 

Technological Feasibility of this 

preamble, MSHA has preliminarily 

determined that it is technologically 

feasible for mine operators to conduct 

air sampling and analysis and to achieve 

the proposed PEL using commercially 

available samplers. MSHA has also 

determined that these technologically 

feasible samplers are widely available, 

and a number of commercial 

laboratories provide the service of 

analyzing dust containing respirable 

crystalline silica. In addition, MSHA 

has determined that technologically 

feasible engineering controls are readily 

available, can control crystalline silicacontaining dust particles at the source, 

provide reliable and consistent 

protection to all miners who would 

otherwise be exposed to respirable dust, 

and can be monitored. MSHA has also 

determined that administrative controls, 

used to supplement engineering 

controls, can further reduce and 

maintain exposures at or below the 

proposed PEL. Moreover, MSHA has 

preliminarily determined the proposed 

respiratory protection practices for 

respirator use are technologically 

feasible for mine operators to 

implement. MSHA requests comments 

on these preliminary conclusions. What 

methods have you used that proved 

effective in reducing miners’ exposure 

to respirable crystalline silica in mining 

operations? Please explain how those 

methods were effective in reducing 

miners’ exposures. To what extent do 

existing controls that reduce exposure to 

other airborne hazards (e.g., coal dust, 

diesel particulate matter) already reduce 

exposures to respirable crystalline silica 

below the proposed PEL? To what 

extent does the proposed rule including 

the PEL facilitate MSHA’s workplace 

health and safety goals? Please provide 

supporting information, such as 

quantitative data if available. 

5. MSHA has determined that the 

proposed medical surveillance 

requirements for MNM are 

technologically feasible. MSHA requests 

comments on this preliminary 

conclusion. Please provide supporting 

information, such as quantitative data if 

available. 

Preliminary Regulatory Impact Analysis 

and Regulatory Alternatives 

6. In the standalone background 

document entitled ‘‘Preliminary 

Regulatory Impact Analysis’’ and as 

summarized in Section IX. Summary of 

Preliminary Regulatory Impact Analysis 

and Regulatory Alternatives of this 

preamble, MSHA developed estimated 

costs of compliance with the proposed 

rule and estimated monetized benefits 

associated with averted cases of 

respirable crystalline silica-related 

diseases. MSHA requests comments on 

the methodologies, baseline, 

assumptions, and estimates presented in 

the Preliminary Regulatory Impact 

Analysis. Please provide any data or 

quantitative information that may be 

useful in evaluating the estimated costs 

and benefits associated with the 

proposed rule. 

7. MSHA considered two regulatory 

alternatives in developing the proposed 

rule discussed in Section IX. Summary 

of Preliminary Regulatory Impact 

Analysis and Regulatory Alternatives. In 

the regulatory alternatives presented, 

MSHA discussed alternatives to the 

proposed PEL, action level, sampling 

requirements, and semi-annual 

evaluations. MSHA requests comments 

on these and other regulatory 

alternatives and information on any 

other alternatives that the Agency 

should consider, including different 

average working-life spans and different 

average shift lengths. Please provide 

supporting information about how these 

alternatives could affect miners’ 

protection from respirable crystalline 

silica exposure and affect mine 

operators’ costs. 

Initial Regulatory Flexibility Analysis 

8. As summarized in Section X. Initial 

Regulatory Flexibility Analysis of this 

preamble, MSHA examined the impact 

of the proposed rule on small mines in 

accordance with the Regulatory 

Flexibility Act. MSHA estimated that 

small-entity controllers would be 

expected to incur, on average, 

additional regulatory costs equaling 

approximately 0.122 percent of their 

revenues (or $1,220 for every $1 million 

in revenues). MSHA is interested in 

how the proposed rule would affect 

small mines, including their ability to 

comply with the proposed 

requirements. Please provide 

information and data that supports your 

response. If you operate a small mine, 

please provide any projected impacts of 

the proposal on your mine, including 

the specific rationale supporting your 

projections. 

Scope and Effective Date 

9. MSHA is proposing a unified 

regulatory and enforcement framework 

for controlling miners’ exposures to 

respirable crystalline silica for the 

mining industry. MSHA requests 

comments on this unified regulatory 

and enforcement framework. MSHA 

requests the views and 

recommendations of stakeholders 

regarding the scope of proposed part 60, 

which would include all surface and 

underground MNM and coal mines. 

MSHA requests comments on whether 

separate standards should be developed 

for the MNM mining industry and the 

coal mining industry. Please provide 

supporting information. 

10. MSHA is proposing that the final 

rule would be effective 120 days after its 

publication in the Federal Register. 

This period is intended to provide mine 

operators time to evaluate existing 

engineering and administrative controls, 

update their respiratory protection 

programs, and prepare to comply with 

other provisions of the rule including 

recordkeeping requirements. Please 

provide your views on the proposed 

effective date. In your response, please 

include the rationale for your position. 


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44856 Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 

Definitions 

11. MSHA requests comments on the 

proposed action level. Stakeholders 

should provide specific information and 

data in support of or against a proposed 

action level. Stakeholders should 

include a discussion of how the use of 

a proposed action level would impact 

their mines, including the cost of 

monitoring respirable crystalline silica 

above the proposed action level, and 

other relevant information. Please 

provide supporting information. 

12. MSHA requests comments on the 

proposed definition for ‘‘objective data.’’ 

Is it appropriate to allow mine operators 

to use objective data instead of a second 

baseline sample? Please provide 

supporting information. 

Proposed Permissible Exposure Limit 

13. MSHA is proposing a PEL for 

respirable crystalline silica of 50 mg/m3

for a full-shift exposure, calculated as an 

8-hour TWA for MNM and coal miners. 

MSHA has made a preliminary 

determination that the proposed PEL 

would reduce miners’ risk of suffering 

material impairment of health or 

functional capacity over their working 

lives. MSHA seeks the views and 

recommendations of stakeholders on the 

proposed PEL. MSHA solicits comments 

on the approach of having a standalone 

PEL and whether to eliminate the 

reduced standard for total respirable 

dust when quartz is present at coal 

mines. Please provide evidence to 

support your response. 

14. MSHA is proposing a PEL of 50 

ug/m3 and an action level of 25 mg/m3

for respirable crystalline silica exposure. 

Which proposed requirements should 

be triggered by exposure at, above, or 

below the proposed action level? Please 

provide supporting information. 

Methods of Compliance 

15. MSHA requests comments on the 

proposed prohibition against rotation of 

miners as an administrative control. 

Please include a discussion of the 

potential effectiveness of this nonexposure approach and its impact on 

miners at specific mines. Please provide 

supporting information. 

16. MSHA requests comments on the 

proposed requirement that mine 

operators must install, use, and 

maintain feasible engineering and 

administrative controls to keep miners’ 

exposures to respirable crystalline silica 

below the proposed PEL. Please provide 

supporting information. 

Proposed Exposure Monitoring 

17. MSHA requests comments and 

information from stakeholders 

concerning the proposed approaches to 

monitoring exposures, and other 

approaches to accurately monitor miner 

exposure to respirable crystalline silica 

in MNM and coal mines. Please provide 

supporting information and data. 

18. MSHA proposes to require mine 

operators to collect a respirable 

crystalline silica sample for a miner’s 

regular full shift during typical mining 

activities. Many potential sources of 

respirable crystalline silica are present 

only when the mine is operating under 

typical conditions. MSHA requests 

comments on this requirement and 

whether to specify environmental 

conditions under which samples should 

be taken to ensure that samples 

accurately reflect actual levels of 

respirable crystalline silica exposure. In 

MSHA’s experience, for example, 

environmental conditions such as 

precipitation (e.g., rain or snow) or wind 

could affect the actual levels of 

respirable crystalline silica exposure at 

miners’ normal or regular workplaces 

throughout their typical workday. 

Please provide supporting information 

and data. 

19. MSHA recognizes that some 

mining facilities operate seasonally or 

intermittently and that cumulative 

exposures for miners at these facilities 

may be lower than that of miners 

working at year-round operations. 

MSHA requests comments on the 

exposure monitoring approach under 

proposed § 60.12, including the 

frequency of exposure monitoring 

necessary to safeguard the health of 

miners at seasonal or intermittent 

operations. Please provide supporting 

information and data. 

20. MSHA is proposing that each 

mine operator perform baseline 

sampling within 180 days after the rule 

becomes effective to assess the 

respirable crystalline silica exposure of 

each miner who is or may reasonably be 

expected to be exposed to respirable 

crystalline silica. MSHA requests 

comments on this proposed baseline 

sampling requirement. MSHA also 

requests comment on the ability of 

service providers used by mines such as 

industrial hygiene suppliers and 

consultants, and accredited laboratories 

that conduct respirable crystalline silica 

analysis, to meet the demand created by 

the baseline sampling requirements 

within the proposed timeline. Please 

include alternative approaches that 

might be equally protective of miners 

that should be implemented for 

assessing a miner’s initial exposure to 

respirable crystalline silica. 

21. MSHA is proposing a requirement 

that mine operators qualitatively 

evaluate every 6 months any changes in 

production, processes, engineering 

controls, personnel, administrative 

controls, or other factors, beginning 18 

months after the effective date. MSHA 

requests comments on the timing of the 

proposed semi-annual evaluation 

requirements, and in particular, whether 

miners would possibly be exposed 

unnecessarily to respirable crystalline 

silica levels above the PEL due to the 

gap between the effective date and the 

proposed requirements. Please provide 

supporting information. 

22. MSHA has determined that most 

occupations related to extraction and 

processing would meet the ‘‘reasonably 

be expected’’ threshold for baseline 

sampling. MSHA recognizes that some 

miners may work in areas or perform 

tasks where exposure is not reasonably 

expected, if at all. MSHA solicits 

comments on the assumption that most 

miners are exposed to at least some 

level of respirable crystalline silica, and 

on the proposed requirement that these 

miners should be subject to baseline 

sampling. Please provide supporting 

information. 

23. MSHA is proposing that mine 

operators would not be required to 

conduct periodic sampling if the 

baseline sampling result, together with 

another sampling result or objective 

data, as defined in proposed § 60.2, 

confirms miners’ exposures are below 

the proposed action level. MSHA seeks 

comments on this proposal. Please 

provide supporting information and 

data. 

24. MSHA is proposing that mine 

operators conduct periodic sampling 

within 3 months where the most recent 

sampling indicates miner exposures are 

at or above the proposed action level but 

at or below the proposed PEL and 

continue to sample within 3 months of 

the previous sampling until two 

consecutive samplings indicate that 

miner exposures are below the action 

level. MSHA solicits comments on the 

proposed frequency for periodic 

sampling, including whether the 

consecutive samples should be at least 

7 days apart. Please provide supporting 

information and data. 

25. MSHA is proposing that mine 

operators may discontinue periodic 

sampling when two consecutive 

samples indicate that miner exposures 

are below the proposed action level. 

MSHA requests comments on this 

proposal. Please provide supporting 

information and data. 

26. MSHA is proposing that mine 

operators conduct semi-annual 

evaluations to evaluate whether any 

changes in production, processes, 

engineering controls, personnel, 

administrative controls, or other factors 

may reasonably be expected to result in 


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new or increased respirable crystalline 

silica exposures. Please provide 

comments on this proposal, as well as 

alternative approaches that would be 

appropriate for evaluating any potential 

new or increased respirable crystalline 

silica exposures. Please provide 

supporting information and data. 

27. MSHA is proposing that miners’ 

exposures are measured using personal 

breathing-zone air samples for MNM 

operations and occupational 

environmental samples collected in 

accordance with §§ 70.201(c), 71.201(b), 

or 90.201(b) for coal operations. MSHA 

requests comments on this proposal. 

Please provide supporting information 

and data. 

28. MSHA is proposing the use of 

representative sampling. Where several 

miners perform the same task on the 

same shift and in the same work area, 

the mine operator may sample a 

representative fraction of miners to meet 

the proposed exposure monitoring 

requirements. MSHA seeks comments 

on the use of representative sampling. 

Please provide supporting information 

and data. 

29. MSHA is proposing that mine 

operators use laboratories accredited to 

ISO/IEC 17025 ‘‘General requirements 

for the competence of testing and 

calibration laboratories,’’ where the 

accreditation has been issued by a body 

that is compliant with ISO/IEC 17011 

‘‘Conformity assessment—requirements 

for accreditation bodies accrediting 

conformity assessment bodies.’’ MSHA 

solicits comments on this proposal. Are 

there additional requirements that 

should be incorporated into this 

proposal to ensure accurate sample 

analysis methods? Please provide 

supporting information and data. 

30. MSHA seeks comments on the 

proposal that mine operators ensure that 

laboratories evaluate all respirable 

crystalline silica samples using 

respirable crystalline silica analytical 

methods specified by MSHA, NIOSH, or 

OSHA. Are there additional 

requirements that should be 

incorporated into this proposal to 

ensure accurate sample analysis? Please 

provide supporting information and 

data. 

31. MSHA seeks comments and 

information on mine operator and 

stakeholder experience using NIOSH’s 

rapid field-based quartz monitoring 

(RQM) monitors for determining miners’ 

exposures to respirable crystalline 

silica. Please provide any information 

and data. 

Proposed Medical Surveillance for Metal 

and Nonmetal Miners 

32. MSHA is proposing to require 

medical surveillance for MNM miners. 

Medical surveillance is already required 

for coal miners under 30 CFR 72.100 

and has played an important role in 

tracking the burden of pneumoconiosis 

in coal miners but is not currently 

required for MNM miners. MSHA’s 

proposal would require MNM mine 

operators to provide each miner new to 

the mining industry with an initial 

medical examination and a follow-up 

examination no later than 3 years after 

the initial examination, at no cost to the 

miner. It would also require MNM mine 

operators to provide examinations for 

all miners at least every 5 years, which 

would be voluntary for miners. Is there 

an alternative strategy or schedule, such 

as voluntary initial or follow-up 

examinations, tying the medical 

surveillance requirement to miners 

reasonably expected to be exposed to 

any level of silica or to the action level 

that would be more appropriate for new 

MNM miners? Should the rule make 

each 5-year examination mandatory? 

Should the 5-year examination be 

mandatory for coal mine operators as 

well? Please provide data or cite 

references to support your position. 

33. MSHA’s proposed medical 

surveillance requirements for MNM 

miners do not include some 

requirements that are in MSHA’s 

existing medical surveillance 

requirements for coal mine operators in 

30 CFR 72.100. For example, § 72.100 

requires coal mine operators to use 

NIOSH-approved facilities for medical 

examinations. Should MNM operators 

be required to use NIOSH-approved 

facilities for medical examinations? Coal 

mine operators also are required to 

submit for approval to NIOSH a plan for 

providing miners with the examinations 

specified. This is because NIOSH 

administers medical surveillance for 

coal miners with requirements for coal 

operators, but not MNM operators, in 

NIOSH standards (42 CFR part 37). 

Should the plan requirements be 

extended to MNM operators? However, 

the proposed requirements also include 

some requirements for MNM operators 

that are not included for coal operators. 

For example, the proposed provisions 

require operators of MNM mines to 

provide MNM miners with periodic 

medical examinations performed by 

physicians or other licensed health care 

professionals (PLHCP) or specialists 

including a history and physical 

examination focused on the respiratory 

system, a chest X-ray, and a spirometry 

test. The proposed rule also requires a 

written medical opinion be provided by 

the PLHCP or specialist to the mine 

operator regarding the miner’s ability to 

wear a respirator. MSHA seeks comment 

on the differences between the medical 

surveillance requirements for MNM 

operators in this proposed rule and the 

existing medical surveillance 

requirements for coal mine operators in 

§ 72.100. MSHA also seeks comment on 

how best to collect health surveillance 

data from PLHCPs and specialists to 

track MNM miners’ health, for example 

how to know when pneumoconiosis 

cases occur. MSHA seeks comments on 

alternative approaches to scheduling 

periodic medical surveillance. MSHA 

proposes to require operators to keep 

medical surveillance information for the 

duration of a miner’s employment plus 

6 months. The Agency seeks comments 

on this proposed requirement and on 

any alternative recordkeeping schedules 

that would be appropriate. Please 

provide supporting information. 

34. MSHA’s proposed medical 

surveillance requirements for MNM 

miners would require operators of MNM 

mines to provide miners with periodic 

medical examinations performed by 

PLHCP or specialists, including a 

history and physical examination 

focused on the respiratory system, a 

chest X-ray, and a spirometry test. 

MSHA seeks comment on whether use 

of any new diagnostic technology (e.g., 

high-resolution computed tomography) 

for the purposes of medical surveillance 

should be used. 

35. MSHA’s proposed medical 

surveillance requirements would 

require that the MNM mine operator 

provide a mandatory follow-up 

examination to the miner no later than 

3 years after the miner’s initial medical 

examination. If a miner’s 3-year followup examination shows evidence of a 

respirable crystalline silica-related 

disease or decreased lung function, the 

operator would be required to provide 

the miner with another mandatory 

follow-up examination with a specialist 

within 2 years. For examinations that 

show evidence of disease or decreased 

lung function, MSHA seeks comment on 

how, and to whom, test results should 

be communicated. 

36. MSHA requests comments as to 

whether the proposed provisions should 

include a medical removal option for 

MNM miners who have developed 

evidence of silica-related disease that is 

equivalent to the transfer rights and 

exposure monitoring provided to coal 

miners in 30 CFR part 90 (part 90). 

Under part 90, any coal miner who has 

evidence of the development of 

pneumoconiosis based on a chest X-ray 

or other medical examinations has the 


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option to work in an area of the mine 

where the average concentration of 

respirable dust in the mine atmosphere 

during each shift to which that miner is 

exposed is continuously maintained at 

or below the applicable standard. Under 

part 90, coal miners are entitled to 

retention of pay rate, future actual wage 

increases, and future work assignment, 

shift and respirable dust protection. 

MSHA seeks comment on whether this 

medical removal option should be 

provided to MNM miners. What would 

be the economic impact of providing 

MNM miners a medical removal option? 

Please provide supporting information 

and data. 

Proposed Respiratory Protection 

Standard 

37. MSHA requests comments 

concerning the temporary, non-routine 

use of respirators and whether there are 

other instances or occupations in which 

the Agency should allow the use of 

respirators as a supplemental control. 

Please discuss any impacts on particular 

mines and mining conditions and the 

cost of air-purifying respirators, if 

applicable. MSHA also solicits 

comments on the proposed requirement 

that affected miners wear respiratory 

protection to maintain protection during 

temporary and non-routine use of 

respirators. Please provide supporting 

information. 

38. MSHA is proposing to incorporate 

by reference ASTM F3387–19, 

published in 2019. Whenever 

respiratory protective equipment is 

needed, mine operators would be 

required to follow practices for program 

administration, standard operating 

procedures, medical evaluations, 

respirator selection, training, fit testing, 

and maintenance, inspection, and 

storage in accordance with the 

requirements of ASTM F3387–19. 

Beyond these elements, MSHA is 

proposing to provide operators the 

flexibility to select the elements in 

ASTM F3387–19 that are applicable to 

their practices of respirator use at their 

mines. Should mine operators have the 

flexibility to choose the ASTM F3387– 

19 elements that are appropriate for 

their mine-specific hazards because the 

need for respirators may vary due to the 

variability of mining processes, 

activities, airborne hazards, and 

commodities mined? What, specifically, 

do you think should factor into the 

determination of what is applicable? 

MSHA seeks comments on its proposed 

approach and the impact it would have 

on mine operators and on miners’ life 

and health. 

39. ASTM F3387–19 identifies a 

variety of respiratory protection practice 

elements. MSHA proposes to require 

certain minimally acceptable program 

elements: program administration; 

standard operating procedures; medical 

evaluations; respirator selection; 

training; fit testing; and maintenance, 

inspection, and storage. Please comment 

on whether these are the appropriate 

elements to require, or if there are any 

other elements of ASTM F3387–19 that 

should be minimally included in any 

respiratory protection program. MSHA 

also welcomes comments on whether it 

would be appropriate to require the 

standard in its entirety. Please identify 

those elements that would ensure that 

approved respirators are selected, fitted, 

used, cleaned, and maintained so that 

the life and health of miners are 

safeguarded. MSHA also seeks data and 

information on the impact these changes 

would have on mine operators, 

especially smaller operators. What 

would be the economic impact if all or 

parts of ASTM F3387–19 were required 

respirator program elements? Please be 

specific with your response and provide 

details on respirator use at your mine to 

include information and data on mining 

processes and environmental 

conditions; level of exposures to 

airborne contaminants; frequency and 

duration of exposures; type and amount 

of work or physical labor, including 

frequency and duration; and medical 

evaluation on respirator use, if 

applicable. 

Recordkeeping Requirements 

40. MSHA is proposing to require 

recordkeeping for records of 

evaluations, records of samplings, 

records of corrective actions, and 

written determination records received 

from a PLHCP. The proposed rule’s 

recordkeeping requirements are 

discussed in the Section-by-Section 

Analysis section of this Preamble. 

MSHA seeks comment on the utility of 

these recordkeeping requirements as 

well as the costs of making and 

maintaining these records. Please 

provide supporting information. 

Training Requirements 

41. MSHA requests the views and 

recommendations of stakeholders 

regarding whether training requirements 

for miners should be included in 

proposed part 60. Please provide 

supporting information and data. 

Conforming Changes 

42. MSHA requests comments on the 

proposed conforming changes to remove 

the reduced coal dust standard from 30 

CFR and the potential impact on coal 

mines and miners and on whether to 

retain the reduced standard for part 90 

miners. Please provide supporting 

information. 

43. MSHA is not proposing to adopt 

a similar approach as the OSHA Table 

1 for the construction industry, where 

MSHA would prescribe specific 

exposure control methods for task-based 

work practices when working with 

materials containing respirable 

crystalline silica. See 29 CFR 

1926.1153(c)(1). MSHA requests 

comments on specific tasks and 

exposure control methods appropriate 

for a Table 1-approach for the mining 

industry that also would adequately 

protect miners from risk of exposure to 

respirable crystalline silica. Please 

provide specific rationale and 

supporting information, including data 

on how such an approach would be 

implemented. 

III. Background 

The purpose of this proposed rule is 

to reduce miners’ risk of developing 

occupational lung disease and other 

diseases caused by exposure to 

respirable crystalline silica and to better 

protect all miners from occupational 

exposure to airborne hazards. In 

promulgating mandatory standards 

dealing with toxic materials or harmful 

physical agents, MSHA is required 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 . . .’’ 30 U.S.C. 

811(a)(6)(A). 

A. Statutory Authority 

The statutory authority for this 

proposal is provided by the Mine Act 

under sections 101(a), 103(h), and 508. 

30 U.S.C. 811(a), 813(h), and 957. 

MSHA implements the provisions of the 

Mine Act to prevent death, illness, and 

injury from mining and promote safe 

and healthful workplaces for miners. 

The Mine Act requires the Secretary of 

Labor (Secretary) to develop and 

promulgate improved mandatory health 

or safety standards to prevent hazardous 

and unhealthy conditions and protect 

the health and safety of the nation’s 

miners. 30 U.S.C. 811(a). 

Congress passed the Mine Act to 

address these dangers, finding ‘‘an 

urgent need to provide more effective 

means and measures for improving the 

working conditions and practices in the 

Nation’s coal or other mines in order to 

prevent death and serious physical 

harm, and in order to prevent 

occupational diseases originating in 

such mines.’’ 30 U.S.C. 801(c). Congress 

concluded that ‘‘the existence of unsafe 

and unhealthful conditions and 

practices in the Nation’s coal or other 


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1Commodities such as sand, gravel, silica, and/ 

or stone for example are used in road building, 

concrete construction, manufacture of glass and 

ceramics, molds for metal castings in foundries, 

abrasive blasting operations, plastics, rubber, paint, 

soaps, scouring cleansers, filters, hydraulic 

fracturing, and various architectural applications. 

Some commodities naturally contain high levels of 

crystalline silica, such as high-quartz industrial and 

construction sands and granite dimension stone and 

gravel (both produced for the construction 

industry). 

mines is a serious impediment to the 

future growth of the coal or other 

mining industry and cannot be 

tolerated.’’ 30 U.S.C. 801(d). 

Accordingly, ‘‘the Mine Act evinces a 

clear bias in favor of miner health and 

safety.’’ Nat’l Mining Ass’n v. Sec’y, U.S. 

Dep’t of Lab., 812 F.3d 843, 866 (11th 

Cir. 2016). 

Section 101(a) of the Mine Act gives 

the Secretary the authority to develop, 

promulgate, and revise, as appropriate, 

mandatory health standards to address 

toxic materials or harmful physical 

agents. Under Section 101(a), standards 

must protect lives and prevent injuries 

in mines and be ‘‘improved’’ over any 

standard that it replaces or revises. 

Moreover, ‘‘the Mine Act does not 

contain the ‘significant risk’ threshold 

requirement . . . from the OSH Act.’’ 

Nat’l Mining Ass’n v. United Steel 

Workers, 985 F.3d 1309, 1319 (11th Cir. 

2021); see also Nat’l Min. Ass’n v. Mine 

Safety & Health Admin., 116 F.3d 520, 

527–28 (D.C. Cir. 1997) (contrasting the 

OSH Act at 29 U.S.C. 652 with the Mine 

Act at 30 U.S.C. 811(a) and noting that 

‘‘[a]rguably, this language does not 

mandate the same risk-finding 

requirement as OSHA’’ and holding that 

‘‘[a]t most, . . . . [MSHA] was required 

to identify a significant risk associated 

with having no oxygen standard at all’’ 

(emphasis in original)). 

The Secretary must set standards to 

assure, based on the best available 

evidence, that no miners will suffer 

material impairment of health or 

functional capacity from exposure to 

toxic materials or harmful physical 

agents over their working lives. 30 

U.S.C. 811(a)(6)(A). In developing 

standards that attain the ‘‘highest degree 

of health and safety protection for the 

miner,’’ the Mine Act requires that the 

Secretary consider the latest available 

scientific data in the field, the feasibility 

of the standards, and experience gained 

under the Mine Act and other health 

and safety laws. Id. However, MSHA’s 

‘‘duty to use the best evidence and to 

consider feasibility . . . cannot be 

wielded as counterweight to MSHA’s 

overarching role to protect the life and 

health of workers in the mining 

industry.’’ Nat’l Mining Ass’n, 812 F.3d 

at 866. Instead, ‘‘when MSHA itself 

weighs the evidence before it, it does so 

in light of its congressional mandate.’’ 

Id. 

Section 103(h) of the Mine Act gives 

the Secretary the authority to 

promulgate standards involving 

recordkeeping and reporting. 30 U.S.C. 

813(h). In general, section 103(h) 

requires that every mine operator 

establish and maintain records, make 

reports, and provide this information, if 

required by the Secretary. Id. Also, 

section 508 of the Mine Act gives the 

Secretary the authority to issue 

regulations to carry out any provision of 

the Mine Act. 30 U.S.C. 957. 

MSHA’s proposal to lower the 

exposure limits for respirable crystalline 

silica and adopt an integrated 

monitoring approach across all mining 

sectors and to update the existing 

respiratory protection requirements 

would fulfill Congress’ direction by 

preventing miners from suffering 

material impairment of health or 

functional capacity caused by exposure 

to respirable crystalline silica and other 

airborne contaminants. 

B. Respirable Crystalline Silica Hazard 

and Mining 

Silica is a common component of rock 

composed of silicon and oxygen 

(chemical formula SiO2), existing in 

amorphous and crystalline states. Silica 

in the crystalline state is the focus of 

this rulemaking. Respirable crystalline 

silica consists of small particles of 

crystalline silica that can be inhaled and 

reach the alveolar region of the lungs, 

where they can accumulate and cause 

disease. In crystalline silica, the silicon 

and oxygen atoms are arranged in a 

three-dimensional repeating pattern. 

The crystallization pattern varies 

depending on the circumstances of 

crystallization, resulting in a 

polymorphic state—several different 

structures with the same chemical 

composition. The most common form of 

crystalline silica found in nature is 

quartz, but cristobalite and tridymite 

may also be found in limited 

circumstances. Quartz accounts for the 

overwhelming majority of naturally 

occurring crystalline silica. In fact, 

quartz accounts for almost 12 percent of 

the earth’s crust by volume. All soils 

contain at least trace amounts of quartz 

and it is present in varying amounts in 

almost every type of mineral. Quartz is 

also abundant in most rock types, 

including granites, sandstones, and 

shale. Moreover, quartz is commonly 

found in limestone formations, although 

limestone itself does not contain quartz. 

Because of its abundance, crystalline 

silica in the form of quartz is present in 

nearly all mining operations. 

Cristobalite and tridymite are formed 

at very high temperatures and are 

associated with volcanic activity. 

Naturally occurring cristobalite and 

tridymite are rare, but they can be found 

in volcanic ash and in a relatively small 

number of rock types limited to specific 

geographic regions. Although rare, 

exposure to cristobalite occurs when 

volcanic deposits are mined. In 

addition, when other materials are 

mined, miners can potentially be 

exposed to cristobalite during certain 

processing steps (e.g., heating silicacontaining materials) and contact with 

refractory materials (e.g., replacing fire 

bricks in mine processing facility 

furnaces). Tridymite is rarely found in 

nature and miner exposure to tridymite 

is much more infrequent. 

Most mining activities generate silica 

dust because silica is often contained in 

the ore being mined or in the 

overburden (i.e., the soil and surface 

material surrounding the commodity 

being mined). Such activities include, 

but are not limited to, cutting, sanding, 

drilling, crushing, grinding, sawing, 

scraping, jackhammering, excavating, 

and hauling materials that contain 

silica. These activities can generate 

respirable crystalline silica and may 

therefore lead to miner exposure. 

Inhaled small particles of silica dust 

can be deposited throughout the lungs. 

A large number of crystalline silica 

particles can reach and remain in the 

deep lung (i.e., alveolar region), 

although some small particles are 

cleared from the lungs. Because 

respirable crystalline silica particles are 

not water-soluble and do not undergo 

metabolism into less toxic compounds, 

those particles remaining in the lungs 

for prolonged periods result in a variety 

of cellular responses that may lead to 

pulmonary disease. The respirable 

crystalline silica particles that are 

cleared from the lungs can be 

distributed to lymph nodes, blood, liver, 

spleen, and kidneys, potentially 

accumulating in those other organ 

systems and causing renal disease and 

other adverse health effects. 

In the U.S. in 2021, a total of 12,162 

mines produced a variety of 

commodities. As shown in Table III–1, 

of those 12,162 total mines, 11,231 

mines were MNM mines and 931 mines 

were coal mines. MNM mines can be 

broadly divided into five commodity 

groups: metal, nonmetal, stone, crushed 

limestone, and sand and gravel. These 

broad categories encompass 

approximately 98 different 

commodities.1 Table III–1 shows that a 

majority of MNM mines produce sand 

and gravel, while the largest number of 

MNM miners work at metal mines (not 


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including MNM contract workers (i.e., 

independent contractors and employees 

of independent contractors who are 

engaged in mining operations)). 

The 931 coal mines—underground 

and surface—produce bituminous, 

subbituminous, anthracite, and lignite 

coal. Coal mining activities generate 

mixed coal mine dust that contains 

respirable silicates such as kaolinite, 

oxides such as quartz, as well as other 

components (IARC, 1997). These 

activities include the general mining 

activities previously mentioned (e.g., 

cutting, sanding, drilling, crushing, and 

hauling materials), as well as roof bolter 

operations, continuous mining machine 

operations, longwall mining, and other 

activities. Table III–1 shows that there 

are more surface coal mines than 

underground coal mines, but more 

miners are working in underground coal 

mines than surface coal mines (not 

including coal contract workers). 

IV. Existing Standards and 

Implementation 

MSHA has maintained health 

standards to protect MNM and coal 

miners from excessive exposure to 

respirable crystalline silica for decades. 

MSHA’s existing standards, established 

in the early 1970s, limit miners’ 

exposures to respirable crystalline 

silica. These standards require mine 

operators to monitor occupational 

exposures to respirable crystalline silica 

and to use engineering controls as the 

primary means of suppressing, diluting, 

or diverting dust generated by mining 

activities. They also require mine 

operators to provide respiratory 

protection in limited situations and on 

a temporary basis. The existing 

standards for MNM and coal mines 

differ in some respects, including 

exposure limits and monitoring. This 

section describes MSHA’s existing 

standards for respirable crystalline silica 

and presents respirable crystalline silica 

sampling data to show how MNM and 

coal mine operators have complied with 

them in recent years. 

A. Existing Standards—Metal and 

Nonmetal Mines 

MSHA’s existing standards for 

exposure to airborne contaminants, 

including respirable crystalline silica, in 

MNM mines are found in 30 CFR part 

56, subpart D (Air Quality and Physical 

Agents), and 30 CFR part 57, subpart D 

(Air Quality, Radiation, Physical 

Agents, and Diesel Particulate Matter). 

These standards include PELs for 

airborne contaminants (§§ 56.5001 and 

57.5001), exposure monitoring 

(§§ 56.5002 and 57.5002), and control of 

exposure to airborne contaminants 

(§§ 56.5005 and 57.5005). 

Permissible Exposure Limits. The 

existing PELs for the three polymorphs 

of respirable crystalline silica are based 

on the TLVs® Threshold Limit Values 

for Chemical Substances in Workroom 

Air Adopted by the American 

Conference of Governmental Industrial 

Hygienists (ACGIH) for 1973, 

incorporated by reference in 30 CFR 

56.5001 and 57.5001 (ACGIH, 1974). 

The 1973 TLV® establishes limits for 

respirable dust containing 1 percent 

quartz or greater and is calculated in 

milligrams per cubic meter of air (mg/ 

m3) for each respirable dust sample. The 

TLV® for quartz is calculated by 

dividing the percent of respirable quartz 

plus 2, into the number 10. The TLV®

for cristobalite and the TLV® for 

tridymite, respectively, are calculated 

by multiplying the same mass formula 

by one-half using the percentages of 

either cristobalite or tridymite found in 

the sample. Thus, the resulting TLVs®

for respirable dust containing 1 percent 

respirable crystalline silica or greater are 

designed to limit exposures to less than 

0.1 mg/m3 or 100 mg/m3 for quartz, to 

less than 0.05 mg/m3 or 50 mg/m3 for 

cristobalite, and to less than 0.05 mg/m3

or 50 mg/m3 for tridymite. Throughout 

the remainder of this preamble, the 

concentrations of respirable dust and 

respirable crystalline silica are 

expressed in mg/m3. 


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2Quartz is defined in 30 CFR 70.2, 71.2, and 90.2 

as crystalline silicon dioxide (SiO2) not chemically 

combined with other substances and having a 

distinctive physical structure. Crystalline silicon 

dioxide is most commonly found in nature as 

quartz but sometimes occurs as cristobalite or, 

rarely, as tridymite. Quartz accounts for the 

overwhelming majority of naturally occurring 

crystalline silica and is present in varying amounts 

in almost every type of mineral. 

Exposure Monitoring. Under 30 CFR 

56.5002 and 57.5002, MNM mine 

operators must conduct respirable dust 

‘‘surveys . . . as frequently as necessary 

to determine the adequacy of control 

measures.’’ Mine operators can satisfy 

the survey requirement through various 

activities, such as respirable dust 

sampling and analysis, walk-through 

inspections, wipe sampling, examining 

dust control system and ventilation 

system maintenance, and reviewing 

information obtained from injury, 

illness, and accident reports. 

MSHA encourages MNM mine 

operators to conduct sampling for 

airborne contaminants to ensure a 

healthy and safe work environment for 

miners because sampling provides more 

accurate information about miners’ 

exposures to harmful airborne 

contaminants and the effectiveness of 

existing controls in reducing such 

exposures. When a mine operator’s 

respirable dust survey indicates that 

miners have been overexposed to any 

airborne contaminant, including 

respirable crystalline silica, the operator 

is expected to adjust its control 

measures (e.g., exhaust ventilation) to 

reduce or eliminate the identified 

hazard. After doing so, the mine 

operator is expected to conduct 

additional surveys to determine whether 

these efforts were successful. Resurveying should be done as frequently 

as necessary to ensure that the 

implemented control measures remain 

adequate. MSHA’s determination of 

whether a mine operator has surveyed 

frequently enough is based on several 

factors, including whether sampling 

results comply with the permissible 

exposure limit, whether there have been 

changes in the mining operation or 

process, and whether controls such as 

local exhaust ventilation systems need 

routine or special maintenance. 

Exposure Controls. MSHA’s existing 

standards for controlling a miner’s 

exposure to harmful airborne 

contaminants (§§ 56.5005 and 57.5005) 

require, if feasible, prevention of 

contamination, removal by exhaust 

ventilation, or dilution with 

uncontaminated air. The use of 

respiratory protective equipment is also 

allowed under specified circumstances 

such as when engineering controls are 

being developed or are not feasible. 

When respiratory protective equipment 

is used, the operator must have a 

respiratory protection program 

consistent with the requirements of 

American National Standards Practices 

for Respiratory Protection ANSI Z88.2– 

1969. 

Consistent with widely accepted 

industrial hygiene principles and 

NIOSH’s recommendations, MSHA 

requires the use of engineering controls, 

supplemented by administrative 

controls, in its enforcement for the 

control of occupational exposure to 

respirable crystalline silica and other 

airborne contaminants (NIOSH, 1974). 

Engineering controls designed to 

remove or reduce the hazard at the 

source are the most effective. Examples 

of engineering controls include the 

installation of proper ventilation 

systems, use of water sprays or wetting 

agents to suppress airborne 

contaminants, installation of machinemounted dust collectors to capture 

respirable crystalline silica and other 

contaminants, and the installation of 

control booths or environmental cabs to 

enclose equipment operators. 

Although considered a supplementary 

or secondary measure to engineering 

controls, mine operators may use 

administrative controls to further reduce 

miners’ exposures to respirable 

crystalline silica and other airborne 

contaminants. In applying 

administrative controls, mine operators 

can direct miners to perform certain 

activities in specific manners. For 

instance, as an administrative control, 

operators can specify adequate 

housekeeping procedures for miners to 

clean spills or handle contaminated 

clothing which could reduce 

occupational exposure to airborne 

contaminants, including respirable 

crystalline silica. 

In addition, respiratory protective 

equipment can be used in controlling 

miners’ exposures to airborne 

contaminants, including respirable 

crystalline silica, on a temporary basis 

or under non-routine, limited 

conditions. The use of respiratory 

protection is, however, considered to be 

a supplement, not an alternative to any 

engineering or administrative control, in 

reducing or eliminating a miner’s 

exposure to airborne contaminants 

including respirable crystalline silica. 

Under the existing standards in 

§§ 56.5005 and 57.5005, in 

circumstances where engineering 

controls are not yet developed or where 

it is necessary for miners to enter 

hazardous atmospheres to establish 

controls or to perform non-routine 

maintenance or investigation, a miner 

using appropriate respiratory protection 

‘‘may work for reasonable periods of 

time’’ in concentrations of airborne 

contaminants which exceed exposure 

limits. Respirators approved by NIOSH 

and suitable for their intended purpose 

must be provided by mine operators at 

no cost to the miner and must be used 

by miners to protect themselves against 

the health and safety hazards of airborne 

contaminants. Whenever respiratory 

protection is used, MNM mine operators 

are required to have a respirator 

program consistent with the 

requirements specified in ANSI Z88.2– 

1969. 

B. Existing Standards—Coal Mines 

Under existing standards, there is no 

separate standard for respirable 

crystalline silica for coal mines. 

MSHA’s existing standards for exposure 

to respirable quartz in coal mines, found 

in 30 CFR 70.101 and 71.101, establish 

a respirable dust standard when quartz 

is present for underground and surface 

coal mines, respectively. Under 30 CFR 

part 90 (Mandatory Health Standards— 

Coal Miners Who Have Evidence of the 

Development of Pneumoconiosis), 

§ 90.101 also sets the respirable dust 

standard when quartz is present for coal 

miners. Under these respirable dust 

standards, coal miners’ exposures to 

respirable quartz are indirectly 

regulated through reductions in the 

overall respirable dust standard. 

Under its existing respirable coal 

mine dust standards, MSHA defines 

quartz as crystalline silicon dioxide 

(SiO2), which includes not only quartz 

but also two other polymorphs, 

cristobalite and tridymite.2 Therefore, 

quartz and respirable crystalline silica 

are used interchangeably in the 

discussions of MSHA’s existing 

standards for controlling exposures to 

respirable crystalline silica in coal 

mines. 

Exposure Limits. The exposure limit 

for respirable crystalline silica during a 

coal miner’s shift is 100 mg/m3, reported 

as an equivalent concentration as 

measured by the Mining Research 

Establishment (MRE) instrument. This 

equivalent concentration of respirable 

crystalline silica must not be exceeded 

during the miner’s entire shift, 

regardless of duration. When the 

equivalent concentration of respirable 

quartz exceeds 100 mg/m3, under 

§§ 70.101, 71.101, and 90.101, MSHA 

imposes a reduced respirable dust 

standard designed to ensure that 

respirable quartz will not exceed 100 

mg/m3. The applicable dust standard, 

when the equivalent concentration of 

respirable crystalline silica exceeds 100 

mg/m3, is computed by dividing the 

percent of quartz into the number 10. 


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3A ‘‘Part 90 miner’’ is defined in 30 CFR 90.3 as 

a miner employed at a coal mine who shows 

evidence of having contracted pneumoconiosis 

based on a chest X-ray or based on other medical 

examinations, and who is afforded the option to 

work in an area of a mine where the average 

concentration of respirable dust in the mine 

atmosphere during each shift to which that miner 

is exposed is continuously maintained at or below 

the applicable standard. 

4This type of sampling equipment was developed 

to separate the airborne particles by size in a 

manner similar to the size-selective deposition and 

retention characteristics of the human respiratory 

system. It is important to note that size-selective 

sampling does not measure the deposition of 

respirable particles in the lung. Rather, it provides 

a measure of the particulate mass available for 

deposition to the deep lung during breathing (Raabe 

and Stuart, 1999). 

The result of this calculation becomes 

the exposure limit for respirable coal 

mine dust (RCMD), for the sections of 

the mine represented by the sample. 

Various sections within a mine may 

have different reduced RCMD exposure 

limits. Therefore, when a respirable dust 

sample collected by MSHA indicates 

that the average concentration of 

respirable quartz dust exceeds the 

exposure limit, the mine operator is 

required to comply with the applicable 

dust standard. By reducing the amount 

of respirable dust to which miners are 

exposed during their shifts, the miners’ 

exposures to respirable crystalline silica 

are reduced to a level at or below the 

exposure limit of 100 mg/m3. 

Exposure Monitoring. Under 

§§ 70.208, 70.209, 71.206, and 90.207, 

coal mine operators are required to 

sample for respirable dust on a quarterly 

basis for specified occupations and 

work areas. The occupations and work 

areas specified in the existing coal 

standards are the occupations and work 

areas at a coal mine that are expected to 

have the highest concentrations of 

respirable dust—typically in locations 

where respirable dust is generated. In 

addition, respirable dust sampling must 

be representative of respirable dust 

exposures during a normal production 

shift. Also, sampling must occur while 

miners are performing routine, day-today activities. Part 90 miners must be 

sampled for the air they breathe while 

performing their normal work duties, 

from the start of their work day to the 

end of their work day, in their normal 

work locations.3

Exposure Controls. Under §§ 70.208, 

70.209, 71.206, and 90.207, coal mine 

operators are required to use 

engineering or environmental controls 

as the primary means of complying with 

the respirable dust standards. Similar to 

the MNM standards, engineering and 

environmental controls include the use 

of dust collectors, water sprays, and 

ventilation controls. For many 

underground coal mines, providing 

adequate ventilation is the primary 

engineering control for respirable dust, 

ensuring that dust concentrations are 

continuously diluted with fresh air and 

exhausted away from miners. 

When a respirable dust sample 

exceeds the exposure limit of 100 mg/m3

for respirable quartz, the operator must 

reduce the average concentration of 

RCMD to a level designed to maintain 

the quartz level at or below 100 mg/m3. 

If operators exceed the reduced RCMD 

standard, they are required to take 

corrective action to reduce exposure and 

comply with the reduced standard. 

Corrective actions that lower respirable 

coal mine dust, thus lowering respirable 

quartz exposures, are selected after 

evaluating the cause or causes of the 

overexposure. Corrective actions can 

include increasing air flow, improving 

ventilation controls, repairing and 

maintaining existing dust suppression 

controls, adding water sprays or other 

controls, cleaning dust filters or 

collectors more frequently, or 

repositioning the miner away from the 

dust source. 

When taking corrective actions to 

reduce the exposure to respirable dust, 

coal mine operators must make 

approved respiratory equipment 

available to miners under §§ 70.208 and 

71.206. Whenever respiratory protection 

is used, § 72.700 requires coal mine 

operators to comply with requirements 

specified in ANSI Z88.2–1969. 

C. MSHA Inspection and Respirable 

Dust Sampling 

MSHA collects respirable dust 

samples at mines and analyzes them for 

respirable crystalline silica to determine 

whether the respirable crystalline silica 

exposure limits are met and whether 

exposure controls are adequate. This 

section describes the respirable dust 

samples collected at MNM and coal 

mines in recent years and presents the 

results of the sample data analyses. 

1. Respirable Dust Sample Collection 

This subsection offers a brief 

description of how MSHA samples for 

respirable crystalline silica under the 

existing standards. Upon their arrival at 

mines, MSHA inspectors determine 

which areas of the mine and which 

miners to select for respirable dust 

sampling. At MNM mines, the MSHA 

inspector often determines sampling 

locations based on sample results from 

previous inspections and on the 

inspector’s onsite observations of work 

practices and work areas. At coal mines, 

the MSHA inspector conducts sampling 

among the occupations or from the work 

areas that are specified for operator 

sampling under 30 CFR parts 70, 71, 

and 90. Generally speaking, MSHA 

inspectors collect respirable dust 

samples from the common occupations 

during typical and normal activities at 

the mine and from the positions that are 

commonly known to have the highest 

concentration of respirable dust. 

After identifying which miners and 

which areas at the mine will be sampled 

for respirable dust, MSHA inspectors 

place gravimetric samplers on the 

selected miners or at the selected 

locations. Gravimetric samplers consist 

of a portable air-sampling pump 

connected to a particle-size separator 

(i.e., cyclone) and collection medium 

(i.e., filter). MSHA inspectors use DorrOliver 10-mm nylon cyclones operated 

at a 1.7 liters per minute (L/min) flow 

rate for MNM mine sampling and at a 

2.0 L/min flow rate (reported as MREequivalent concentrations) for coal mine 

sampling.4 For the entire duration of the 

work shift, the gravimetric sampler 

captures air from the breathing zone of 

each selected miner or occupation and 

from each selected work area. 

MSHA inspectors use the full-shift 

sampling approach. When miners work 

longer than an 8-hour shift, which is 

common, those miners are sampled 

continuously throughout the extended 

work shifts. Full-shift sampling is used 

to minimize errors associated with 

fluctuations in airborne contaminant 

concentrations during the miners’ work 

shifts and to avoid any speculation 

about the miners’ exposures during 

unsampled periods of the work shift. 

Once sampling is completed, the 

inspectors send the cassettes containing 

the full-shift respirable dust samples to 

the MSHA Laboratory for analysis. 


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5The MSHA Laboratory has fulfilled the 

requirements of the AIHA Laboratory Accreditation 

Programs (AIHA–LAP), LLC accreditation to the 

ISO/IEC 17025:2017 international standard for 

industrial hygiene. 6The minimum mass gain criteria used by the 

MSHA Laboratory for the different samples are: 

• MNM mine respirable dust samples: greater 

than or equal to 0.100 mg; 

• Underground coal mine respirable dust 

samples: greater than or equal to 0.100 mg; and 

• Surface coal mine respirable dust samples: 

greater than or equal to 0.200 mg. 

Exception: For six surface occupations that have 

been deemed ‘‘high risk,’’ the laboratory uses a 

minimum mass gain criterion of greater than or 

equal to 0.100 mg. 

If cristobalite analysis is requested for MNM mine 

respirable dust samples, filters having a mass gain 

of 0.05 mg or more are analyzed. In the rare 

instance when tridymite analysis is requested, a 

qualitative analysis for the presence of the 

polymorph is conducted concurrently with the 

cristobalite analysis. 

7 Details on MSHA’s analytical procedures for 

respirable crystalline silica analysis can be found in 

‘‘MSHA P–2: X-Ray Diffraction Determination of 

Quartz and Cristobalite in Respirable Metal/ 

Nonmetal Mine Dust’’ and ‘‘MSHA P–7: 

Determination of Quartz in Respirable Coal Mine 

Dust by Fourier Transform Infrared Spectroscopy.’’ 

Department of Labor, Mine Safety and Health 

Administration, Pittsburgh Safety and Health 

Technology Center, X-Ray Diffraction 

Determination of Quartz and Cristobalite in 

Respirable Metal/Nonmetal Mine Dust. https://

arlweb.msha.gov/Techsupp/pshtcweb/MSHA

%20P2.pdf. Department of Labor, Mine Safety and 

Health Administration, Pittsburgh Safety and 

Health Technology Center, MSHA P–7: 

Determination of Quartz in Respirable Coal Mine 

Dust By Fourier Transform Infrared Spectroscopy. 

https://arlweb.msha.gov/Techsupp/pshtcweb/ 

MSHA%20P7.pdf. 

2. Respirable Dust Sample Analysis 

The MSHA Laboratory analyzes 

inspectors’ respirable dust samples, 

following its standard operating 

procedures (SOPs) summarized below.5

Any samples that are broken, torn, or 

visibly wet are voided and removed 

before analysis. Once weighing of the 

samples is completed, samples are again 

screened based on mass gain and 

examined for validity. All valid samples 

that meet the minimum mass gain 

criteria per the associated MSHA 

analytical method are then analyzed for 

respirable crystalline silica and for the 

compliance determination.6

The MSHA Laboratory uses two 

analytical methods to determine the 

concentration of quartz (and cristobalite 

and tridymite, if requested): X-ray 

diffraction (XRD) for respirable dust 

samples from MNM mines, and Fourier 

transform infrared spectroscopy (FTIR) 

for respirable coal mine dust samples.7

The XRD method uses X-rays to 

distinguish and measure the structure, 

composition, and physical properties of 

a sample. The FTIR method relies on the 

absorption of infrared light to determine 

the composition of a sample. The 

percentage of silica in the MNM mine 

dust sample is calculated using the mass 

of quartz or cristobalite determined from 

the XRD analysis and the measured 

mass of respirable dust. The percentage 

of silica is used to calculate MSHA’s 

PELs for quartz and cristobalite, in 

accordance with §§ 56.5001 and 

57.5001. Similarly, in the respirable coal 

mine dust sample, the percentage of 

quartz is calculated using the quartz 

mass determined from the FTIR analysis 

and the sample’s mass of dust. Current 

FTIR methods, however, cannot 

quantify quartz and cristobalite, and/or 

tridymite, in the same sample. For coal 

mines, the percentage of quartz is used 

to calculate the reduced dust standard 

when the quartz concentration exceeds 

100 mg/m3 (MRE). 

It is worth noting how MSHA 

calculates full-shift exposure to 

respirable crystalline silica (and other 

airborne contaminants). When a miner 

who works an 8-hour shift is sampled, 

the miner’s 8-hour TWA exposure is 

calculated as follows: 

However, for work shifts that last 

longer than 8 hours, a coal miner’s fullshift exposure is calculated differently 

than an MNM miner’s full-shift 

exposure. In accordance with § 70.2, the 

coal miner’s extended full-shift 

exposure has, since 2014, been 

calculated in the following way: 

For the MNM miner, MSHA 

calculates extended full-shift exposure 

according to the following formula: 

For respirable dust samples from 

MNM mines, 480 minutes is used in the 

denominator regardless of the actual 

sampling time. Contaminants collected 

over extended shifts (e.g., 600–720 

minutes) are calculated as if they had 

been collected over 480 minutes. MSHA 

has used this calculation approach (also 

known as ‘‘shift-weighted average’’) 

since the 1970s. 

Under the shift-weighted average 

approach, exposures for work schedules 

greater than 8 hours are proportionately 

adjusted to allow direct comparison 

with the 8-hour PEL. The ACGIH TLVs®

adopted by MSHA are based on 

exposure periods of no more than 8 

hours per day and 40 hours per week, 

with 16 hours of recovery time between 

shifts. 

D. Respirable Crystalline Silica 

Sampling Results—Metal and Nonmetal 

Mines 

This section presents the results of 

respirable dust samples that were 

collected by MSHA inspectors at MNM 

mines from 2005 to 2019. From January 

1, 2005, to December 31, 2019, a total 

of 104,354 valid samples were collected. 

Of this total, 57,769 samples that met 

the minimum mass gain criteria were 

analyzed for respirable crystalline silica. 


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8 If more than one polymorph is present the 

equation used to calculate the TLV® for respirable 

dust containing quartz is modified per Appendix C 

of the 1973 ACGIH TLV® Handbook, and the 

equation is modified as follows: 10/[(% quartz + 2) 

+ 2 (% cristobalite + 2)]. 

The vast majority of the 46,585 valid 

samples that were excluded from the 

analysis in this rulemaking did not meet 

the mass gain criteria described earlier 

and therefore the lab did not determine 

their silica concentration. Further 

information on the valid respirable dust 

samples that are excluded from the 

analysis in this rulemaking can be found 

in Appendix A of the preamble. 

The respirable crystalline silica 

concentration is calculated using the 

measured mass of each of the 

polymorphs and the air sampling 

volume. As discussed above, the 

existing PEL for quartz in MNM mines 

is approximately equivalent to 100 mg/ 

m3 for a full-shift exposure, calculated 

as an 8-hour TWA, while the existing 

PELs for cristobalite and tridymite, 

respectively, are approximately 

equivalent to 50 mg/m3 for a full-shift 

exposure, calculated as an 8-hour 

TWA.8

1. Annual Results of MNM Respirable 

Crystalline Silica Samples 

Table IV–1 below shows the variation 

between 2005 and 2019 in: (1) the 

numbers of MNM respirable dust 

samples analyzed for respirable 

crystalline silica; and (2) the number 

and percentage of samples that had 

concentrations of respirable crystalline 

silica greater than 100 mg/m3. Of the 

57,769 MNM respirable dust samples 

analyzed for respirable crystalline silica 

over the 15-year period, about 6 percent 

(3,539 samples) had respirable 

crystalline silica concentrations 

exceeding the existing PEL of 100 mg/ 

m3. The average annual rates of 

overexposure ranged from a maximum 

of approximately 10 percent in 2006 

(the second year) to a minimum of 

approximately 4 percent in 2019 (the 

last year of the time series). Compared 

with the rates in 2005–2008, 

overexposure rates were substantially 

lower in 2009–2017, with a further drop 

in 2018–19. 

BILLING CODE 4520–43–P 


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9For a full crosswalk of job codes included in 

each of these 11 Occupational Categories, please see 

Appendix C of the preamble. Also, note that the 

order of the presentation of the 11 Occupational 

Categories here follows the general sequence of 

mining activities: first development and 

production, then ore/mineral processing, then 

loading, hauling, and dumping, and finally all 

others. 

2. Analysis of MNM Respirable 

Crystalline Silica Samples by 

Commodity 

Because the MNM mining industry 

produces commodities that contain 

varying degrees of respirable crystalline 

silica, it is important to examine each 

commodity separately. MNM mines can 

be grouped by five commodities: metal, 

sand and gravel, stone, crushed 

limestone, and nonmetal (where 

nonmetal includes all other materials 

that are not metals, besides sand, gravel, 

stone, and limestone). This grouping is 

based on the mine operator-reported 

mining products and the North 

American Industry Classification 

System (NAICS) codes. (Appendix B of 

the preamble provides a list of the 

NAICS codes relevant for MNM mining 

and how each code is assigned to one 

of the five commodities.) 

Table IV–2 shows the distribution of 

the respirable dust samples analyzed for 

respirable crystalline silica by mine 

commodity. The percentage of samples 

with respirable crystalline silica 

concentrations greater than the existing 

exposure limit of 100 mg/m3 varies 

across the different commodities. It is 

highest for the metal, sand and gravel, 

and stone commodities (at 

approximately 11, 7, and 7 percent, 

respectively), and lowest for the 

nonmetal and crushed limestone 

commodities (at approximately 4 and 3 

percent, respectively). 

3. Analysis of MNM Respirable 

Crystalline Silica Samples by 

Occupation 

To examine how miners who perform 

different tasks differ in occupational 

exposure to respirable crystalline silica, 

MSHA grouped MNM mining jobs into 

11 occupational categories. These 

categories include jobs that are similar 

in terms of tasks performed, equipment 

used, and engineering or administrative 

controls used to control miners’ 

exposure. For example, backhoe 

operators, bulldozer operators, and 

tractor operators were grouped into 

‘‘operators of large powered haulage 

equipment,’’ whereas belt crew, belt 

cleaners, and belt vulcanizers were 

grouped into ‘‘conveyer operators.’’ The 

121 MNM job codes used by MSHA 

inspectors were grouped into the 

following occupational categories: 9

(1) Drillers (e.g., Diamond Drill 

Operator, Wagon Drill Operator, and 

Drill Helper), 

(2) Stone Cutting Operators (e.g., 

Jackhammer Operator, Cutting Machine 

Operator, and Cutting Machine Helper), 

(3) Kiln, Mill, and Concentrator 

Workers (e.g., Ball Mill Operator, 

Leaching Operator, and Pelletizer 

Operator), 

(4) Crushing Equipment and Plant 

Operators (e.g., Crusher Operator/ 

Worker, Scalper Screen Operator, and 

Dry Screen Plant Operator), 

(5) Packaging Equipment Operators 

(e.g., Bagging Operator and Packaging 

Operations Worker), 

(6) Conveyor Operators (e.g., Belt 

Cleaner, Belt Crew, and Belt 

Vulcanizer), 

(7) Truck Loading Station Tenders 

(e.g., Dump Operator and Truck Loader), 

(8) Operators of Large Powered 

Haulage Equipment (e.g., Tractor 

Operators, Bulldozer Operator, and 

Backhoe Operators), 

(9) Operators of Small Powered 

Haulage Equipment (e.g., Bobcat 

Operator, Scoop-Tram Operator, and 

Forklift Operator), 

(10) Mobile Workers (e.g., Laborers, 

Electricians, Mechanics, and 

Supervisors), and 

(11) Miners in Other Occupations 

(e.g., Welder, Dragline Operator, 

Ventilation Crew and Dredge/Barge 

Operator). 

Table IV–3 shows sample numbers 

and overexposure rates by MNM 

occupation. Operators of large powered 

haulage equipment accounted for the 

largest number of samples analyzed for 

silica (17,016 samples), whereas 

conveyor operators accounted for the 

fewest (215 samples). Table IV–3 also 

shows the number and percentage of the 

samples exceeding the existing 

respirable crystalline silica PEL of 100 

mg/m3. In every occupational category, 

some MNM miners were exposed to 

respirable crystalline silica levels above 

the existing PEL. In 9 out of the 11 

occupational categories, the percentage 

of samples exceeding the existing PEL is 

less than 10 percent, although two have 


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10Analysis of MSHA respirable dust samples 

from 2005 to 2010 showed that stone and rock saw 

operators had approximately 20 percent of the 

sampled exposures exceeding the PEL. Watts et al. 

(2012). 

higher rates, ranging up to more than 19 percent (in the case of stone cutting 

operators). 

4. Conclusion 

This analysis of MSHA inspector 

sampling data shows that MNM 

operators have generally met the 

existing standard. Of the 57,769 

respirable dust samples from MNM 

mines, approximately 6 percent 

exceeded the existing respirable 

crystalline silica PEL of 100 mg/m3, 

although there are several outliers with 

much higher overexposures. For 9 of the 

11 occupational categories, less than 10 

percent of the respirable dust samples 

had concentrations over the existing 

PEL of 100 mg/m3 for respirable 

crystalline silica. In addition, about 80 

percent of samples taken from stone 

cutting operators did not exceed the 

existing PEL, which historically has had 

high exposures to respirable dust and 

respirable crystalline silica; 10

nevertheless, this occupation continues 

to experience the highest overexposures 

relative to other MNM occupations. For 

the categories of drillers, miners in other 

occupations, and operators of large 

powered haulage equipment, 

approximately 5 percent or less of the 

respirable dust samples showed 

concentrations over the existing 

exposure limit. 

MSHA believes that improved 

technology, engineering controls, and 

better training contributed to the 

reductions in exposures for miners who 

work in occupations exposed to the 

highest levels of respirable crystalline 

silica. In summary, the analysis of 

MSHA inspector sampling data 

indicates that the controls that MNM 

mine operators are using, together with 

MSHA’s enforcement, have generally 

been effective in keeping miners’ 

exposure at or below the existing limit 

of 100 mg/m3. 

E. Respirable Crystalline Silica 

Sampling Results—Coal Mines 

To examine coal mine operators’ 

compliance with existing respirable 

crystalline silica standards, MSHA 

analyzed RCMD samples collected by 

MSHA inspectors from 2016 to 2021. 

(The data analyses for this rulemaking 

do not include any respirable dust 

samples collected by coal mine 

operators.) The analysis below is based 

on the samples collected by inspectors 

starting on August 1, 2016, when Phase 

III of MSHA’s 2014 Lowering Miners’ 

Exposure to Respirable Coal Mine Dust, 

Including Continuous Personal Dust 

Monitors (Coal Dust Rule) (79 FR 24813, 

May 1, 2014) went into effect. At that 

time, the exposure limits for RCMD 


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11Environmental samples were not included in 

the analysis to be consistent with the proposed 

sampling requirements to determine individual 

miner exposure. 12The conversion between ISO values and MRE 

values uses the NIOSH conversion factor of 0.857. 

In the 1995b Criteria Document, NIOSH presented 

an empirically derived conversion factor of 0.857 

for comparing current (MRE) and recommended 

(ISO) respirable dust sampling criteria using the 10 

mm Dorr-Oliver nylon cyclone operated at 2.0 and 

1.7 L/min, respectively (i.e., 1.5 mg/m3 BMRC–MRE 

= 1.29 mg/m3 ISO). 

13The coal samples for 2016 begin in August of 

that year and the coal samples for 2021 end in July 

of that year. 

were lowered from 2.0 mg/m3 to 1.5 mg/ 

m3 (MRE equivalent) at underground 

and surface coal mines, and from 1.0 

mg/m3 to 0.5 mg/m3 (MRE equivalent) 

for intake air at underground coal mines 

and for Part 90 miners. From August 1, 

2016, to July 31, 2021, MSHA inspectors 

collected a total of 113,607 valid RCMD 

samples. Of these valid samples, only 

those collected from the breathing zones 

of miners were used in the analysis for 

this rulemaking; no environmental dust 

samples were included.11 Of those 

samples, 63,127 samples that met the 

minimum mass gain criteria and had no 

other disqualifying issues were analyzed 

for respirable quartz and quartz 

concentrations were determined. The 

majority of the non-environmental valid 

samples excluded from this rulemaking 

analysis were excluded due to 

insufficient mass. Further information 

on the valid respirable dust samples that 

are not included in the rulemaking 

analysis can be found in Appendix A of 

the preamble. 

Of the 63,127 valid samples analyzed 

for respirable crystalline silica and used 

for this analysis, about 1 percent (777 

samples) were over the existing quartz 

exposure limit of 100 mg/m3 (MRE 

equivalent) for a full shift, calculated as 

a TWA.12 Overexposure rates (the 

percent of samples above the exposure 

limit, on average across all coal mining 

occupations) decreased by nearly a 

quarter between the first half and the 

second half of the 2016–2021 period. As 

in MNM mines, different miner 

occupations had different overexposure 

rates. Using broader groupings, surface 

mines experienced higher rates of 

overexposure than underground mines 

(2.4 percent versus 1.0 percent, 

respectively). 

1. Annual Results of Coal Respirable 

Crystalline Silica Samples 

In examining trends from one year to 

the next, the discussion below focuses 

on the samples collected in the 6 

calendar years from 2016 to 2021. The 

number of samples per year was stable 

from 2017 to 2019 before decreasing in 

2020.13 The overexposure rate 

decreased across the entire 2016 to 2021 

period, from 1.41 percent in 2016 to 

0.95 percent in 2021. As shown in Table 

IV–4, a review of the 6 calendar years 

reveals that the overexposure rate 

decreased by nearly a quarter from 

2016–2018 (1.38 percent) to 2019–2021 

(1.07 percent). 

2. Analysis of Coal Respirable 

Crystalline Silica Samples by Location 

Coal mining activities differ 

depending on the characteristics and 

locations of coal seams. When coal 

seams are several hundred feet below 

the surface, miners tunnel into the earth 

and use underground mining equipment 

to extract coal, whereas miners at 

surface coal mines remove topsoil and 

layers of rock to expose coal seams. Due 

to these differences, it is important to 

examine the respirable crystalline silica 

data by location to determine how 

underground and surface coal miners 

differ in occupational exposure to 

respirable crystalline silica. 

Table IV–5, which presents the 

overexposure rate by type of mine 

where respirable coal mine dust 

samples were collected, shows that 

samples from surface coal mines 

reflected higher rates of overexposure 

than samples from underground mines. 


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14For a full crosswalk of which job codes were 

included in each of these nine Occupational 

Categories, please see Appendix C of the preamble. 

Out of the 53,095 respirable coal mine 

dust samples from underground mines, 

1 percent (537 samples) were over the 

existing exposure limit. By contrast, 

there were 10,032 samples from surface 

coal mines, and approximately 2.4 

percent (240 samples) of those samples 

were over the existing exposure limit. 

3. Analysis of Coal Respirable 

Crystalline Silica Samples by 

Occupation 

To assess the exposure to respirable 

crystalline silica of miners in different 

occupations, MSHA has consolidated 

the 220 job codes for coal mines into 9 

occupational categories (using a similar 

process to the one it used for the MNM 

mines, but with different job codes and 

categories). For the coal mine 

occupational categories,14 a distinction 

is made between occupations based on 

whether the job tasks are being 

performed at the surface of a mine or 

underground. For example, bulldozer 

operators are assigned to the operators 

of large powered haulage equipment 

grouping and then sorted into separate 

occupational categories based on 

whether they are working at the surface 

of a mine or underground. 

Of the nine occupational categories 

used for coal miners, the five 

underground categories are: 

(1) Continuous Mining Machine 

Operators (e.g., Coal Drill Helper and 

Coal Drill Operator), 

(2) Longwall Workers (e.g., Headgate 

Operator and Jack Setter (Longwall)), 

(3) Roof Bolters (e.g., Roof Bolter and 

Roof Bolter Helper), 

(4) Operators of Large Powered 

Haulage Equipment (e.g., Shuttle Car 

Operator, Tractor Operator/Motorman, 

Scoop Car Operator), and 

(5) All Other Underground Miners 

(e.g., Electrician, Mechanic, Belt Cleaner 

and Laborer, etc.). 

The four surface occupational 

categories are: 

(1) Drillers (e.g., Coal Drill Operator, 

Coal Drill Helper, and Auger Operator), 

(2) Crusher Operators (e.g., Crusher 

Attendant, Washer Operator, and 

Scalper-Screen Operator), 

(3) Operators of Large Powered 

Haulage Equipment (e.g., Backhoe 

Operator, Forklift Operator, and 

Bulldozer Operator), and 

(4) Mobile Workers (e.g., Electrician, 

Mechanic, Blaster, Laborer, etc.). 

The most sampled occupational 

category was operators of large powered 

haulage equipment (underground), 

representing approximately 34 percent 

of the samples taken. The least sampled 

occupational category was crusher 

operators (surface), consisting of 1 

percent of the samples taken. Table IV– 

6 displays the number and percent of 

respirable coal mine dust samples with 

quartz greater than the existing exposure 

limit for each occupational category. 


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Looking at trends, every occupational 

category shows a decrease in 

overexposure rates over time. See Figure 

IV–1. Most of the nine categories had 

lower rates of overexposure in the 2019– 

2021 period than in the 2016–2018 

period. 


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15The drilling operation in the roof bolting 

process, especially in hard rock, generates excessive 

respirable coal and quartz dusts, which could 

expose the roof bolting operator to continued health 

risks (Jiang and Luo, 2021). 

BILLING CODE 4520–43–C 

In all occupational categories, coal 

miners were sometimes exposed to 

respirable crystalline silica levels above 

the existing exposure limit. But the 

sampling data showed that coal mine 

operators can generally comply with the 

existing exposure limit. For example, 

although mining tasks performed by the 

occupational category of roof bolters 

(underground) historically resulted in 

high levels of overexposure to quartz, 

the low levels of overexposure for that 

occupation in 2016–2021 (i.e., 1 

percent) suggest that roof bolters now 

benefit from the improved respirable 

dust standard, improved technology, 

and better training.15 Over the 2016– 

2021 period, coal miners in the 

occupational category drillers (surface) 

were the most frequently overexposed, 

with approximately 6 percent of 

samples over the existing quartz limit; 

they were followed by longwall workers 

(underground) (about 4 percent), 

operators of large powered haulage 

equipment (surface) (about 3 percent), 

and continuous mining machine 

operators (underground) (about 2 

percent). For all other occupational 

categories, the overexposure rate was 

less than 1 percent. 

4. Conclusion 

This analysis of MSHA inspector 

sampling data shows that coal mine 

operators can generally comply with the 

existing standards related to quartz. Of 

the 63,127 valid respirable dust samples 

from coal mines over the most recent 5- 

year period, 1.2 percent had respirable 

quartz over the existing exposure limit 

of 100 mg/m3 (MRE equivalent) for a 

full-shift exposure, calculated as a 

TWA. Seven of the nine occupational 

categories had overexposure rates of 2.5 

percent or less. Roof bolters 

(underground), which historically have 

had high exposures to respirable dust 

and respirable crystalline silica, had 

overexposure rates of 1 percent over this 

recent period. The data demonstrates 

that the controls that coal mine 

operators are using, together with 

MSHA’s enforcement, have generally 

been effective in keeping miners’ 

exposure to respirable crystalline silica 

at or below the existing exposure limit. 

V. Health Effects Summary 

This section summarizes the health 

effects from occupational exposure to 

respirable crystalline silica. MSHA’s full 

analysis is contained in the standalone 

document, entitled Effects of 

Occupational Exposure to Respirable 

Crystalline Silica on the Health of 

Miners (Health Effects document), 

which has been placed in the 

rulemaking docket for the MSHA silica 

rulemaking (RIN 1219–AB36, Docket ID 

no. MSHA–2023–0001) and is available 

on MSHA’s website. 

The purpose of the Agency’s scientific 

review is to present MSHA’s 

preliminary findings on the nature of 

the hazards presented by exposure to 

respirable crystalline silica and to 

present the basis for the Preliminary 


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Risk Analysis (PRA) to follow. (A PRA 

summary is presented in Section VI of 

this preamble and a standalone 

document entitled Preliminary Risk 

Analysis has been placed in the 

rulemaking docket for the MSHA silica 

rulemaking (RIN 1219–AB36, Docket ID 

no. MSHA–2023–0001) and is available 

on MSHA’s website.) MSHA reviewed a 

wide range of health research literature 

that included more than 600 studies 

exploring the relationship between 

respirable crystalline silica exposure 

and resultant health effects in miners 

and other workers across various 

industries. After discussing the toxicity 

of respirable crystalline silica, MSHA’s 

review of the literature covers the 

following topics: 

(1) Silicosis; 

(2) NMRD, excluding silicosis; 

(3) Lung cancer and cancer at other 

sites; 

(4) Renal disease; and 

(5) Autoimmune diseases. 

To develop this literature review, 

MSHA expanded upon OSHA’s (2013b) 

review of the health effects literature to 

support its final respirable crystalline 

silica rule (81 FR 16286, March 25, 

2016). MSHA also drew upon numerous 

studies conducted by NIOSH, the 

International Agency for Research on 

Cancer (IARC), the National Toxicology 

Program (NTP), and other researchers. 

These studies provided epidemiological 

data, morbidity (having a disease or a 

symptom of disease) and mortality 

(disease resulting in death) analyses, 

progression and pathology evaluations, 

death certificate and autopsy reviews, 

medical surveillance data, health hazard 

assessments, in vivo (animal) and in 

vitro toxicity data, and other 

toxicological reviews. These sources are 

cited throughout this summary and are 

listed in the References section of the 

Health Effects document. Additionally, 

these sources appear in the rulemaking 

docket. 

MSHA’s literature review is based on 

a weight-of-evidence approach, in 

which studies are evaluated for their 

overall quality. Causal inferences are 

drawn based on a determination of 

whether there is substantial evidence 

that exposure increases the risk of a 

particular adverse health effect. Factors 

MSHA considered in this weight-ofevidence analysis include: size of the 

cohort studied and power of the study 

to detect a sufficiently low level of 

disease risk, duration of follow-up of the 

study population, potential for study 

bias (such as selection bias or healthy 

worker effects), and adequacy of 

underlying exposure information for 

examining exposure-response 

relationships. Of the studies examined 

in the Health Effects document, studies 

were deemed suitable for inclusion in 

the PRA if there was adequate 

quantitative information on exposure 

and disease risks and the study was 

judged to be of sufficiently high quality 

according to the above criteria. 

The understanding of how respirable 

crystalline silica causes adverse health 

effects has evolved greatly in the more 

than 45 years since the Mine Act was 

passed in 1977. Based on its extensive 

review of health research literature, 

MSHA has preliminarily determined 

that occupational exposure to respirable 

crystalline silica causes silicosis (acute 

silicosis, accelerated silicosis, simple 

chronic silicosis, and PMF), NMRD 

(including COPD), and lung cancer, and 

it also causes end-stage renal disease 

(ESRD). In addition, MSHA believes that 

respirable crystalline silica exposure is 

causally related to the development of 

some autoimmune disorders through 

inflammation pathways. Each of these 

effects is exposure-dependent, chronic, 

irreversible, and potentially disabling or 

fatal. MSHA’s review of the literature 

indicates that under the existing 

standards found in 30 CFR parts 56, 57, 

70, 71, and 90, miners are still 

developing preventable diseases that are 

material impairments of health and 

functional capacity. Based on the 

assessment of health effects of respirable 

crystalline silica, MSHA preliminarily 

concludes that the proposed rule, which 

would lower the exposure limits in 

MNM and coal mining to 50 mg/m3 and 

establish an action level of 25 mg/m3 for 

a full-shift exposure, calculated as an 8- 

hour TWA, would reduce the risk of 

miners developing silicosis, NMRD, 

lung cancer, and renal disease. 

A. Toxicity of Respirable Crystalline 

Silica 

Respirable crystalline silica is 

released into the environment during 

mining or milling processes, thus 

creating an airborne hazard. The 

particles may be freshly generated or resuspended from surfaces on which it is 

deposited in mines or mills. Respirable 

crystalline silica particles may be 

irregularly shaped and variable in size. 

Inhaled respirable crystalline silica can 

be deposited throughout the lungs. 

Some pulmonary clearance of particles 

deposited in the deep lung (i.e., alveolar 

region) may occur, but a large number 

of particles can be retained and initiate 

or advance the disease process. The 

toxicity of these retained particles is 

amplified because the particles are not 

water-soluble and do not undergo 

metabolism into less toxic compounds. 

This is important biologically and 

physiologically, as insoluble dusts may 

remain in the lungs for prolonged 

periods, resulting in a variety of cellular 

responses that can lead to pulmonary 

disease (ATSDR, 2019). Respirable 

crystalline silica particles that are 

cleared from the lungs by the lymphatic 

system are distributed to the lymph 

nodes, blood, liver, spleen, and kidneys, 

potentially accumulating in these other 

organ systems and causing renal disease 

and other adverse health effects 

(ATSDR, 2019). 

Physical characteristics relevant to the 

toxicity of respirable crystalline silica 

primarily relate to its size and surface 

characteristics. Researchers believe that 

the size and surface characteristics play 

important roles in how respirable 

crystalline silica causes tissue damage. 

Any factor that influences or modifies 

these physical characteristics may alter 

the toxicity of respirable crystalline 

silica by affecting the mechanistic 

processes (OSHA, 2013b; ATSDR, 2019). 

Inflammation pathways affect disease 

development in various systems and 

tissues in the human body. For instance, 

it has been proposed that lung fibrosis 

caused by exposure to respirable 

crystalline silica results from a cycle of 

cell damage, oxidant generation, 

inflammation, scarring, and ultimately 

fibrosis. This has been reported by 

Nolan et al. (1981), Shi et al. (1989, 

1998), Lapp and Castranova (1993), 

Brown and Donaldson (1996), Parker 

and Banks (1998), Castranova and 

Vallyathan (2000), Castranova (2004), 

Fubini et al. (2004), Hu et al. (2017), 

Benmerzoug et al. (2018), and Yu et al. 

(2020). 

Respirable crystalline silica entering 

the lungs could cause damage by a 

variety of mechanisms, including direct 

damage to lung cells. In addition, 

activation or stimulation by respirable 

crystalline silica of alveolar 

macrophages (after phagocytosis) and/or 

alveolar epithelial cells may lead to: (1) 

release of cytotoxic enzymes, reactive 

oxygen species (ROS), reactive nitrogen 

species (RNS), inflammatory cytokines 

and chemokines, (2) eventual cell death 

with the release of respirable crystalline 

silica, and (3) recruitment and 

activation of polymorphonuclear 

leukocytes (PMNs) and additional 

alveolar macrophages. The elevated 

production of ROS/RNS would result in 

oxidative stress and lung injury that 

stimulates alveolar macrophages, 

ultimately resulting in fibroblast 

activation and pulmonary fibrosis. The 

prolonged recruitment of macrophages 

and PMN causes a persistent 

inflammation, regarded as a primary 

step in the development of silicosis. 

The strong immune response in the 

lung following exposure to respirable 


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crystalline silica may also be linked to 

a variety of extra-pulmonary adverse 

effects such as 

hypergammaglobulinemia, production 

of rheumatoid factor, anti-nuclear 

antibodies, and release of other immune 

complexes (Parks et al., 1999, Haustein 

and Anderegg, 1988; Green and 

Vallyathan, 1996). Respirable crystalline 

silica exposure has also been associated 

with nonmalignant renal disease 

through the initiation of immunological 

injury to the glomerulus of the kidney 

(Calvert et al., 1997). 

Proposed mechanisms involved in 

respirable crystalline silica-induced 

carcinogenesis have included: direct 

DNA damage, inhibition of the p53 

tumor suppressor gene, loss of cell cycle 

regulation; stimulation of growth 

factors, and production on oncogenes 

(Brown and Donaldson, 1996; 

Castranova, 2004; Fubini et al., 2004; 

Nolan et al., 1981; Shi et al., 1989, 

1998). 

B. Diseases 

1. Silicosis 

Silicosis is a progressive occupational 

disease that has long been identified as 

a cause of lung disease in miners. Based 

on its review of the literature, MSHA 

has preliminarily determined that 

exposure to respirable crystalline silica 

causes silicosis (acute silicosis, 

accelerated silicosis, simple chronic 

silicosis, and PMF) in MNM and coal 

miners, which is a significant cause of 

serious morbidity and early mortality in 

this occupational cohort (Mazurek and 

Attfield, 2008; Mazurek and Wood, 

2008a, 2008b; Mazurek et al., 2015, 

2018). 

When respirable crystalline silica 

particles accumulate in the lungs, they 

cause an inflammatory reaction, leading 

to lung damage and scarring. Silicosis 

can continue to develop even after silica 

exposure has ceased. It is not reversible, 

and there is only symptomatic 

treatment, including bronchodilators to 

maintain open airways, oxygen therapy, 

and lung transplants in the most severe 

cases (Cochrane et al., 1956; Ng et al., 

1987a; Lee et al., 2001; Mohebbi and 

Zubeyri, 2007; Kimura et al., 2010; 

Laney et al., 2017; Almberg et al., 2020; 

Hall et al., 2022). 

Respirable crystalline silica exposure 

in MNM miners can lead to all three 

forms of silicosis (acute, accelerated, 

and chronic). These forms differ in the 

rate of exposure, pathology (i.e., the 

structural and functional changes 

produced by the disease), and latency 

period from exposure to disease onset. 

Acute silicosis is an aggressive 

inflammatory process following intense 

exposure to respirable crystalline silica 

for ‘‘periods measured in months rather 

than years’’ (Cowie and Becklake, 2016). 

It causes alveolar proteinosis 

(accumulation of lipoproteins in the 

alveoli of the lungs). This restructuring 

of the lungs leads to symptoms such as 

coughing and difficult or labored 

breathing, and it often progresses to 

profound disability and death due to 

respiratory failure or infectious 

complications. In addition, symptoms 

often advance even after exposure has 

stopped, primarily due to the massive 

amount of protein debris and fluid that 

collects in the alveoli, which can 

suffocate the patient. The radiographic 

(X-ray) appearance and results of 

microscopic examination of acute 

silicosis are like those of idiopathic 

pulmonary alveolar proteinosis. 

Chronic silicosis is the most 

frequently observed form of silicosis in 

the United States today (Banks, 2005; 

OSHA, 2013b; Cowie and Becklake, 

2016). It is also the most common form 

of silicosis diagnosed in miners. 

Chronic silicosis is a fibrotic process 

that typically follows less intense 

respirable crystalline silica exposure of 

10 or more years (Becklake, 1994; 

Balaan and Banks, 1998; NIOSH, 2002b, 

Kambouchner and Bernaudin, 2015; 

Cowie and Becklake, 2016; Rosental, 

2017; ATSDR, 2019; Barnes et al., 2019; 

Hoy and Chambers, 2020). It is 

identified by the presence of the 

silicotic islet or nodule that is an agentspecific fibrotic lesion and is recognized 

by its pathology (Balaan and Banks, 

1998). Chronic silicosis develops slowly 

and creates rounded whorls of scar 

tissue that progressively destroy the 

normal structure and function of the 

lungs. In addition, the scar tissue 

opacities become visible by chest X-ray 

or computerized tomography (CT) only 

after the disease is well established and 

the lesions become large enough to 

view. As a result, surveys based on 

chest X-ray films usually underestimate 

the true prevalence of silicosis 

(Craighead and Vallathol, 1980; Hnizdo 

et al., 1993; Rosenman et al., 1997; 

Cohen and Velho, 2002). However, the 

lesions eventually advance and result in 

lung restriction, reduced lung volumes, 

decreased pulmonary compliance, and 

reduction in the gas exchange 

capabilities of the lungs (Balaan and 

Banks, 1998). As the disease progresses, 

affected miners may have a chronic 

cough, sputum production, shortness of 

breath, and reduced pulmonary 

function. 

Accelerated silicosis includes both 

inflammation and fibrosis and is 

associated with intense respirable 

crystalline silica exposure. Accelerated 

silicosis usually manifests over a period 

of 3 to 10 years (Cowie and Becklake, 

2016), but it can develop in as little as 

2 to 5 years if exposure is sufficiently 

intense (Davis, 1996). Accelerated 

silicosis may have features of both 

chronic and acute silicosis (i.e., alveolar 

proteinosis in addition to X-ray 

evidence of fibrosis). Although the 

symptoms are similar to those of 

chronic silicosis, the clinical and 

radiographic progression of accelerated 

silicosis evolves more rapidly, and often 

leads to PMF, severe respiratory 

impairment, and respiratory failure. 

Accelerated silicosis can progress with 

associated morbidity and mortality, 

even if exposure ceases. 

Among coal miners, silicosis is 

usually found in conjunction with 

simple coal worker’s pneumoconiosis 

(CWP) (Castranova and Vallyathan, 

2000) because of their exposures to 

RCMD that contains respirable 

crystalline silica. Coal miners also face 

an added risk of developing mixed-dust 

pneumoconiosis (MDP) (includes the 

presence of coal dust macules), mixeddust fibrosis (MDF), and/or silicotic 

nodules (Honma et al., 2004, see Figure 

2, Green 2019). The autopsy studies on 

coal miners that MSHA reviewed 

support a pathological relationship 

between mixed-RCMD or respirable 

crystalline silica exposures and PMF, 

silicosis, and CWP (Attfield et al., 1994; 

Cohen et al., 2016, 2019, 2022; Davis et 

al., 1979; Douglas et al., 1986; Fernie 

and Ruckley, 1987; Green et al., 1989, 

1998b; Ruckley et al., 1981, 1984; 

Vallyathan et al., 2011). Autopsy studies 

in British coal miners indicated that the 

more advanced the disease, the more 

mixed coal mine dust components were 

retained in the lung tissue (Ruckley et 

al., 1984; Douglas et al., 1986). Green et 

al. (1998b) determined that of 4,115 coal 

miners with pneumoconiosis autopsied 

as part of the National Coal Workers’ 

Autopsy Study (NCWAS), 39 percent 

had mixed dust nodules and 23 percent 

had silicotic nodules. 

PMF or ‘‘complicated silicosis’’ has 

been diagnosed in both coal and MNM 

miners exposed to dusts containing 

respirable crystalline silica. Recent 

literature on the pathophysiology of 

PMF supports the importance of 

crystalline silica as a cause of PMF in 

silica-exposed workers such as coal 

miners from the United States (Cohen et 

al., 2016, 2022), sandblasters (Abraham 

and Wiesenfeld, 1997; Hughes et al., 

1982), industrial sand workers (Vacek et 

al., 2019), hard rock miners (Verma et 

al., 1982, 2008), and gold miners 

(Carneiro et al., 2006a; Tse et al., 

2007b). 


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16The ‘‘Radiological Diagnostic Criteria of 

Pneumoconiosis and Principles for Management of 

Pneumoconiosis’’ (GB5906–86) (Chen et al., 2001; 

Yang et al., 2006). 

17On March 26, 1969, Charles C. Johnson, Jr., 

Administrator, Consumer Protection and 

Environmental Health Service, PHS, U.S. 

Department of Health, Education, and Welfare, 

testified before the General Subcommittee on Labor 

and presented remarks of the Surgeon General. 

They are referenced in the 91st Congress House of 

Representatives Report, 1st Session No. 91–563, 

Federal Coal Mine Health and Safety Act, October 

13, 1969 (https://arlweb.msha.gov/SOLICITOR/ 

COALACT/69hous.htm). 

a. Classifying Radiographic Findings of 

Silicosis 

Two classification methods used to 

characterize the radiographic findings of 

silicosis in chest X-rays are described in 

this literature review: the International 

Labour Office (ILO) Standardized 

System and the Chinese categorization 

system.16

To describe the presence and severity 

of pneumoconiosis from chest X-rays or 

digital radiographic images, the ILO 

developed a standardized system to 

classify the opacities identified (ILO, 

1980, 2002, 2011, 2022). The ILO system 

grades the size, shape, and profusion 

(frequency) of opacities in the lungs. 

The density of opacities is classified on 

a 4-point major category scale (category 

0, 1, 2, or 3), with each major category 

divided into three subcategories, giving 

a 12-point scale between 0/¥ and 3/+. 

Differences between ILO categories are 

subtle. For each subcategory, the top 

number indicates the major category 

that the profusion most closely 

resembles, and the bottom number 

indicates the major category that was 

given secondary consideration. For 

example, film readers may assign 

classifications such as 1/0, which means 

the reader classified it as category 1, but 

category 0 (normal) was also considered 

(ILO, 2022). Major category 0 indicates 

the absence of visible opacities and 

categories 1 to 3 reflect increasing 

profusion of opacities and a 

concomitant increase in severity of 

disease. 

MSHA’s analysis of silicosis studies 

uses NIOSH’s surveillance case 

definition to determine the presence of 

silicosis. NIOSH defines the presence of 

silicosis in terms of the ILO system and 

considers a small opacity profusion 

score of 1/0 or greater to indicate 

pneumoconiosis (NIOSH, 2014b). This 

definition originated from testimony 

before Congress regarding the 1969 Coal 

Act where the Public Health Service 

recommended that miners be removed 

from dusty environments as soon as 

they showed ‘‘minimal effects’’ of dust 

exposure on a chest X-ray (i.e., pinpoint, 

dispersed micro-nodular lesions).17

MSHA interprets ‘‘minimal effects’’ to 

mean an X-ray ILO profusion score of 

category 1/0 or greater. 

However, some studies in MSHA’s 

literature review use the Chinese 

categorization scheme, which includes 

four categories of silicosis: a suspected 

case (0+), stage I, stage II, or stage III. 

The four categories correspond to ILO 

profusion category 0/1, category 1, 

category 2, and category 3, respectively. 

A suspected case of silicosis (0+) in a 

dust-exposed worker refers to a dust 

response in the lung and its 

corresponding lymph nodes, or a scale 

and severity of small opacities that fall 

short of the level observed in a stage I 

case of silicosis (Chen et al., 2001; Yang 

et al., 2006). Under this scheme, a panel 

of three radiologists determines the 

presence and severity of radiographic 

changes consistent with 

pneumoconiosis. 

b. Progression and Associated 

Impairment 

Progression of silicosis is shown 

when there are changes or worsening of 

the opacities in the lungs, and 

sequential chest radiographs are 

classified higher by one or more 

subcategories (e.g., from 1/0 to 1/1) 

because of changes in the location, 

thickness, or extent of lung 

abnormalities and/or the presence of 

calcifications. The higher the category 

number, the more severe the disease. 

Due to the uncertainty in scoring films, 

some investigators count progression as 

advancing two or more subcategories, 

such as 1/0 to 1/2. 

MSHA reviewed studies referenced by 

OSHA (2013b) that examined the 

relationship between exposure and 

progression, as well as between X-ray 

findings and pulmonary function. 

Additionally, MSHA considered more 

recent literature (Dumavibhat et al., 

2013; Mohebbi and Zubeyri, 2007; Wade 

et al., 2011) not previously reviewed by 

OSHA (2013b). 

Overall, the studies indicate that 

progression is more likely with 

continued exposure, especially high 

average levels of exposure. Progression 

is also more likely for miners with 

higher ILO profusion classifications. As 

discussed previously, progression of 

disease may continue after miners are 

no longer exposed to respirable 

crystalline silica (Almberg et al., 2020; 

Cochrane et al., 1956; Hall et al., 2020b; 

Hurley et al., 1987; Kimura et al., 2010; 

Maclaren et al., 1985). In addition, 

although lung function impairment is 

highly correlated with chest X-ray films 

indicating silicosis, researchers 

cautioned that respirable crystalline 

silica exposure could impair lung 

function before it is detected by X-ray. 

Of the studies in which silicosis 

progression was documented in 

populations of workers, four included 

quantitative exposure data that were 

based on either existing exposure levels 

or historical measurements of respirable 

crystalline silica (Hessel et al., 1988 

study of gold miners; Miller and 

MacCalman, 2010 study of coal miners; 

Miller et al., 1998 study of coal miners; 

Ng et al., 1987a study of granite miners). 

In some studies, episodic exposures to 

high average concentrations were 

documented and considered in the 

analysis. These exposures were strong 

predictors of more rapid progression 

beyond that predicted by cumulative 

exposure alone. Otherwise, the variable 

most strongly associated in these studies 

with progression of silicosis was 

cumulative respirable crystalline silica 

exposure (i.e., the product of the 

concentration times duration of 

exposure, which is summed over time) 

(Hessel et al., 1988; Ng et al., 1987a; 

Miller and MacCalman, 2010; Miller et 

al., 1998). In the absence of 

concentration measurements, duration 

of employment in specific occupations 

known to involve exposure to high 

levels of respirable dust has been used 

as a surrogate for cumulative exposure 

to respirable crystalline silica. It has 

also been found to be associated with 

the progression of silicosis (Ogawa et 

al., 2003a). 

Miller et al. (1998) examined the 

impact of high quartz exposures on 

silicosis disease progression on 547 

British coal miners from 1990 to 1991 

and evaluated chest X-ray changes after 

the mines closed in 1981. The study 

reviewed chest X-rays taken during 

health surveys conducted between 1954 

and 1978 and data from extensive 

exposure monitoring conducted 

between 1964 and 1978. For some 

occupations, exposure was high because 

miners had to dig through a sandstone 

stratum to reach the coal. For example, 

quarterly mean respirable crystalline 

silica (quartz) concentrations ranged 

from 1,000 to 3,000 mg/m3 (1–3 mg/m3), 

and for a brief period, concentrations 

exceeded 10,000 mg/m3 (10 mg/m3) for 

one job. Some of these high exposures 

were associated with accelerated disease 

progression. 

Buchanan et al. (2003) reviewed the 

exposure history and chest X-ray 

progression of 371 retired miners and 

found that short-term exposures (i.e., ‘‘a 

few months’’) to high concentrations of 

respirable crystalline silica (e.g., >2,000 

mg/m3, >2 mg/m3) increased the silicosis 

risk by three-fold (compared to the risk 

of cumulative exposure alone) (see the 


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separate Preliminary Risk Analysis 

document). 

The risks of increased rate of 

progression, predicted by Buchanan et 

al. (2003) have been seen in coal miners 

(e.g., Cohen et al., 2016; Laney et al., 

2010, 2017; Miller et al., 1998), metal 

(Hessel et al., 1988; Hnizdo and SluisCremer, 1993; Nelson, 2013), and 

nonmetal miners such as silica plant 

and ground silica mill workers, 

whetstone cutters, and silica flour 

packers (Mohebbi and Zubeyri, 2007; 

NIOSH 2000a,b; Ogawa et al., 2003a). 

Accordingly, it is important to limit 

higher exposures to respirable 

crystalline silica in order to minimize 

the risk of rapid progressive 

pneumoconiosis (RPP) in miners. 

The results of many surveillance 

studies conducted by NIOSH as part of 

the Coal Workers’ Health Surveillance 

Program indicate that the pathology of 

pneumoconiosis in coal miners has 

changed over time, in part due to 

increased exposure to respirable 

crystalline silica. The studies of Cohen 

et al. (2016, 2022) indicate that a RPP 

develops due to increased exposure to 

respirable crystalline silica among 

contemporary coal miners as compared 

to historical coal miners. Through the 

examination of pathologic materials 

from 23 contemporary (born in or after 

1930) and 62 historical coal miners 

(born between 1910 and 1930) with 

severe pneumoconiosis, who were 

autopsied as part of NCWAS, Cohen et 

al. (2022) found a significantly higher 

proportion of silica-type PMF among 

contemporary miners (57 percent vs. 18 

percent, p <0.001). They also found that 

mineral dust alveolar proteinosis 

(MDAP) was more common in the 

current generation of miners and that 

the lung tissues of contemporary coal 

miners contained a significantly greater 

percentage and concentration of silica 

particles than those of past generations 

of miners. 

c. Occupation-Based Epidemiological 

Studies 

MSHA reviewed the occupation-based 

epidemiological literature (i.e., studies 

that examine health outcomes among 

workers and their potential association 

with conditions in the workplace). 

MSHA’s review included the 

occupation-based literature OSHA cited 

in developing its respirable crystalline 

silica standard (OSHA, 2013b). Overall, 

OSHA found substantial evidence 

suggesting that occupational exposure to 

respirable crystalline silica increases the 

risk of silicosis, and MSHA concurs 

with this conclusion. MSHA also 

reviewed additional occupation-based 

literature specific to respirable 

crystalline silica exposure in MNM and 

coal miners and preliminarily concludes 

that respirable crystalline silica 

exposure increases the risk of silicosis 

morbidity and early mortality. One 

study examined the acute and 

accelerated silicosis outbreak that 

occurred during and after construction 

of Hawk’s Nest Tunnel in West Virginia 

from 1930 to 1931. There, an estimated 

2,500 men worked in a tunnel drilling 

rock consisting of 90 percent silica or 

more. The study later estimated that at 

least 764 of the 2,500 workers (30.6 

percent) died from acute or accelerated 

silicosis (Cherniack, 1986). There was 

also high turnover among the tunnel 

workers, with an average length of 

employment underground of only about 

2 months. 

In a population of granite quarry 

workers (mean length of employment: 

23.4 years) exposed to an average 

respirable crystalline silica 

concentration of 480 mg/m3 (0.48 mg/ 

m3), 45 percent of those diagnosed with 

simple silicosis showed radiological 

progression of disease 2 to 10 years after 

diagnosis (Ng et al., 1987a). Among a 

population of gold miners, 92 percent 

showed progression after 14 years 

(Hessel et al., 1988). Chinese factory 

workers and miners who were 

categorized under the Chinese system of 

X-ray classification as ‘‘suspected’’ 

silicosis cases (analogous to ILO 0/1) 

had a progression rate to stage I 

(analogous to ILO major category 1) of 

48.7 percent, with an average interval of 

about 5.1 years (Yang et al., 2006). 

Strong evidence has shown that lung 

function deteriorates more rapidly in 

miners exposed to respirable crystalline 

silica, especially in those with silicosis 

(Hughes et al., 1982; Ng and Chan, 1992; 

Malmberg et al., 1993; Cowie, 1998). 

The rates of decline in lung function are 

greater where disease shows evidence of 

radiologic progression (Be ́gin et al., 

1987; Ng et al., 1987a; Ng and Chan, 

1992; Cowie, 1998). The average 

deterioration of lung function exceeds 

that in smokers (Hughes et al., 1982). 

Blackley et al. (2015) found 

progressive lung function impairment 

across the range of radiographic 

profusion of simple CWP in a cohort of 

8,230 coal miners that participated in 

the Enhanced Coal Workers’ Health 

Surveillance Program from 2005 to 

2013. There, 269 coal miners had 

category 1 or 2 simple CWP. This study 

also found that each increase in 

profusion score was associated with 

decreases in various lung function 

parameters: 1.5 percent (95 percent CI, 

1.0 percent–1.9 percent) in forced 

expiratory volume in one second (FEV1) 

percent predicted, 1.0 percent (95 

percent CI, 0.6 percent–1.3 percent) 

forced vital capacity (FVC) percent 

predicted, and 0.6 percent (95 percent 

CI, 0.4 percent–0.8 FEV1/FVC). 

Overall, MSHA preliminarily agrees 

with OSHA’s conclusion that 

substantial evidence suggests that 

occupational exposure to respirable 

crystalline silica increases the risk of 

silicosis. MSHA also preliminarily 

concludes that respirable crystalline 

silica exposure increases the risk of 

silicosis morbidity and early mortality 

among miners. 

d. Surveillance Data 

In addition to occupation-based 

epidemiological studies, MSHA 

reviewed surveillance studies, which 

provide and interpret data to facilitate 

the prevention and control of disease, 

and preliminarily finds that the 

prevalence of silicosis generally 

increases with duration of exposure 

(work tenure). However, the available 

statistics may underestimate silicosisrelated morbidity and mortality in 

miners. For example, the following have 

been reported: (1) misclassification of 

causes of death (e.g., as TB, chronic 

bronchitis, emphysema, or cor 

pulmonale); (2) errors in recording 

occupation on death certificates; and (3) 

misdiagnosis of disease (Windau et al., 

1991; Goodwin et al., 2003; Rosenman 

et al., 2003, Blackley et al., 2017). 

Furthermore, chest X-ray findings may 

lead to missed silicosis cases when 

fibrotic changes in the lung are not yet 

visible on chest X-rays. In other words, 

silicosis may be present but not yet 

detectable by chest X-ray, or may be 

more severe than indicated by the 

assigned profusion score (Craighead and 

Vallyathan, 1980; Hnizdo et al., 1993; 

Rosenman et al., 1997). 

e. Pulmonary Tuberculosis 

Finally, in addition to the relationship 

between silica exposure and silicosis, 

studies indicate a relationship between 

silica exposure, silicosis, and 

pulmonary TB. OSHA reviewed these 

and concluded that silica exposure and 

silicosis increase the risk of pulmonary 

TB (Cowie, 1994; Hnizdo and Murray, 

1998; teWaterNaude et al., 2006). MSHA 

agrees with this conclusion. 

Although early descriptions of dust 

diseases of the lung did not distinguish 

between TB and silicosis and most fatal 

cases described in the first half of the 

20th century were likely a combination 

of silicosis and TB (Castranova et al., 

1996), more recent findings have 

demonstrated that respirable crystalline 

silica exposure, even without silicosis, 

increases the risk of infectious (i.e., 

active) pulmonary TB (Sherson and 


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Lander, 1990; Cowie, 1994; Hnizdo and 

Murray, 1998; teWaterNaude et al., 

2006). These co-morbid conditions 

hasten the development of respiratory 

impairment and increased mortality risk 

even beyond the risk in unexposed 

persons with active TB (Banks, 2005). 

Ng and Chan (1991) hypothesized that 

silicosis and TB ‘‘act synergistically’’ 

(i.e., are more than additive) to increase 

fibrotic scar tissue (leading to massive 

fibrosis) or to enhance susceptibility to 

active mycobacterial infection. The 

authors found that lung fibrosis is 

common to both diseases, and that both 

diseases decrease the ability of alveolar 

macrophages to aid in the clearance of 

dust or infectious particles. 

These findings are also supported by 

new studies (Ndlovu et al., 2019; Oni 

and Ehrlich, 2015) published since 

OSHA’s review (2013b). Oni and 

Ehrlich (2015) reviewed a case of silicoTB in a former gold miner with ILO 

category 2/2 silicosis. Ndlovu et al. 

(2019) found that in a study sample of 

South African gold miners who had 

died from causes other than silicosis 

between 2005 and 2015, 33 percent of 

men (n = 254) and 43 percent of women 

(n = 29) at autopsy were found to have 

TB, whereas 7 percent of men (n = 54) 

and 3 percent of women (n = 4) were 

found to have pulmonary silicosis. 

Overall, MSHA agrees with OSHA’s 

conclusion that silica exposure 

increases the risk of pulmonary TB and 

that pulmonary TB is a complication of 

chronic silicosis. 

2. Nonmalignant Respiratory Disease 

(Excluding Silicosis) 

In addition to causing silicosis (acute 

silicosis, accelerated silicosis, simple 

chronic silicosis, and PMF), exposure to 

respirable crystalline silica causes other 

NMRD. NMRD includes emphysema 

and chronic bronchitis, which are both 

diagnoses within the category of COPD. 

Patients with COPD may have chronic 

bronchitis, emphysema, or both (ATS, 

2010a). 

Based on its review of the literature, 

MSHA preliminarily concludes that 

exposure to respirable crystalline silica 

increases the risk for mortality from 

NMRD. The following summarizes 

MSHA’s review of the literature. 

a. Emphysema 

Emphysema involves the destruction 

of lung architecture in the alveolar 

region, causing airway obstruction and 

impaired gas exchange. In its literature 

review, OSHA (2013b) concluded that 

exposure to respirable crystalline silica 

can increase the risk of emphysema, 

regardless of whether silicosis is 

present. OSHA also concluded that this 

is the case for smokers and that smoking 

amplifies the effects of respirable 

crystalline silica exposure, increasing 

the risk of emphysema. MSHA reviewed 

the studies cited by OSHA and agrees 

with its conclusion. The studies 

reviewed are summarized below. 

Becklake et al. (1987) determined that 

a miner who had worked in a high dust 

environment for 20 years had a greater 

chance of developing emphysema than 

a miner who had never worked in a high 

dust environment. In a retrospective 

cohort study, Hnizdo et al. (1991a) used 

autopsy lung specimens from 1,553 

white gold miners to investigate the 

types of emphysema caused by 

respirable crystalline silica and found 

that the occurrence of emphysema was 

related to both smoking and dust 

exposure. This study also found a 

significant association between 

emphysema (both panacinar and 

centriacinar emphysema types) and 

length of employment for miners 

working in high dust occupations. A 

separate study by Hnizdo et al. (1994) 

on life-long non-smoking South African 

gold miners found that the degree of 

emphysema was significantly associated 

with the degree of hilar gland nodules, 

which the authors suggested might serve 

as a surrogate for respirable crystalline 

silica exposure. While Hnizdo et al. 

(2000) conversely found that 

emphysema prevalence was decreased 

in relation to dust exposure, the authors 

suggested that selection bias was 

responsible for this finding. 

The findings of several cross-sectional 

and case-control studies discussed in 

the OSHA (2013b) Health Effects 

Literature were more mixed. For 

example, de Beer et al. (1992) found an 

increased risk for emphysema; however, 

the reported odds ratio (OR) was smaller 

than previously reported by Becklake et 

al. (1987). 

The OSHA (2013b) Health Effects 

Literature also recognized that several of 

the referenced studies (Becklake et al., 

1987 Hnizdo et al., 1994) found that 

emphysema might occur in respirable 

crystalline silica-exposed workers who 

did not have silicosis and suggested a 

causal relationship between respirable 

crystalline silica exposure and 

emphysema. Experimental (animal) 

studies found that emphysema occurred 

at lower respirable crystalline silica 

exposure concentrations than fibrosis in 

the airways or the appearance of early 

silicotic nodules (Wright et al., 1988). 

These findings tended to support 

human studies that respirable 

crystalline silica-induced emphysema 

can occur absent signs of silicosis. 

Green and Vallyathan (1996) reviewed 

several studies of emphysema in 

workers exposed to silica and found an 

association between cumulative dust 

exposure and death from emphysema. 

The IARC (1997) also reviewed several 

studies and concluded that exposure to 

respirable crystalline silica increases the 

risk of emphysema. Finally, NIOSH 

(2002b) concluded in its Hazard Review 

that occupational exposure to respirable 

crystalline silica is associated with 

emphysema. However, some 

epidemiological studies suggested that 

this effect might be less frequent or 

absent in non-smokers. 

Overall, MSHA agrees with OSHA 

that exposure to respirable crystalline 

silica causes emphysema even in the 

absence of silicosis. 

b. Chronic Bronchitis 

Chronic bronchitis is long-term 

inflammation of the bronchi, increasing 

the risk of lung infections. This 

condition develops slowly by small 

increments and ‘‘exists’’ when it reaches 

a certain stage (i.e., the presence of a 

productive cough sputum production 

for at least 3 months of the year for at 

least 2 consecutive years) (ATS, 2010b). 

OSHA considered many studies that 

examined the association between 

respirable crystalline silica exposure 

and chronic bronchitis, concluding the 

following: (1) exposure to respirable 

crystalline silica causes chronic 

bronchitis regardless of whether 

silicosis is present; (2) an exposureresponse relationship may exist; and (3) 

smokers may be at an increased risk of 

chronic bronchitis compared to nonsmokers. MSHA has reviewed the 

literature and agrees with OSHA’s 

conclusions. 

Miller et al. (1997) reported a 20 

percent increased risk of chronic 

bronchitis in a British mining cohort 

compared to the disease occurrence in 

the general population. Using British 

pneumoconiosis field research data, 

Hurley et al. (2002) calculated estimates 

of mixed-RCMD-related disease in 

British coal miners at exposure levels 

that were common in the late 1980s and 

related their lung function and 

development of chronic bronchitis with 

their cumulative dust exposure. The 

authors estimated that by the age of 58, 

5.8 percent of these men would report 

breathlessness for every 100 gram-hour/ 

m3 dust exposure. The authors also 

estimated the prevalence of chronic 

bronchitis at age 58 would be 4 percent 

per 100 gram-hour/m3 of dust exposure. 

These miners averaged over 35 years of 

tenure in mining and a cumulative 

respirable dust exposure of 132 gramhour/m3. 

Cowie and Mabena (1991) found that 

chronic bronchitis was present in 742 of 


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1,197 (62 percent) black South African 

gold miners, and Ng et al. (1992b) found 

a higher prevalence of respiratory 

symptoms, independent of smoking and 

age, in Singaporean granite quarry 

workers exposed to high levels of dust 

(rock drilling and crushing) compared to 

those exposed to low levels of dust 

(maintenance and transport workers). 

However, Irwig and Rocks (1978) 

compared symptoms of chronic 

bronchitis in silicotic and non-silicotic 

South African gold miners and did not 

find as clear a relationship as did the 

above studies, concluding that the 

symptoms were not statistically more 

prevalent in the silicotic miners, 

although prevalence was slightly higher. 

Sluis-Cremer et al. (1967) found that 

dust-exposed male smokers had a higher 

prevalence of chronic bronchitis than 

non-dust exposed smokers in a gold 

mining town in South Africa. Similarly, 

Wiles and Faure (1977) found that the 

prevalence of chronic bronchitis rose 

significantly with increasing dust 

concentration and cumulative dust 

exposure in South African gold miners 

of smokers, nonsmokers, and exsmokers. Rastogi et al. (1991) found that 

female grinders of agate stones in India 

had a significantly higher prevalence of 

acute bronchitis, but they had no 

increase in the prevalence of chronic 

bronchitis compared to controls 

matched by socioeconomic status, age, 

and smoking. However, the study noted 

that respirable crystalline silica 

exposure durations were very short, and 

control workers may also have been 

exposed to respirable crystalline silica. 

Studies examining the effect of years 

of mining on chronic bronchitis risk 

were mixed. Samet et al. (1984) found 

that prevalence of symptoms of chronic 

bronchitis was not associated with years 

of mining in a population of 

underground uranium miners, even 

after adjusting for smoking. However, 

Holman et al. (1987) studied gold 

miners in West Australia and found that 

the prevalence of chronic bronchitis, as 

indicated by ORs (controlled for age and 

smoking), was significantly increased in 

those that had worked in the mines for 

over 1 year, compared to lifetime nonminers. In addition, while other studies 

found no effect of years of mining on 

chronic bronchitis risk, those studies 

often qualified this result with possible 

confounding factors. For example, 

Kreiss et al. (1989) studied 281 hardrock (molybdenum) miners and 108 

non-miner residents of Leadville, 

Colorado. They did not find an 

association between the prevalence of 

chronic bronchitis and work in the 

mining industry (Kreiss et al., 1989); 

however, it is important to note that the 

mine had been temporarily closed for 5 

months when the study began, so 

miners were not exposed at the time of 

the study. 

The American Thoracic Society (ATS) 

(1997) published a review finding 

chronic bronchitis to be common among 

worker groups exposed to dusty 

environments contaminated with 

respirable crystalline silica. NIOSH 

(2002b) also published a review finding 

that occupational exposure to respirable 

crystalline silica has been associated 

with bronchitis; however, some 

epidemiological studies suggested this 

effect might be less frequent or absent in 

non-smokers. 

Finally, Hnizdo et al. (1990) found an 

independent exposure-response 

relationship between respirable 

crystalline silica exposure and impaired 

lung function. For miners with less 

severe impairment, the effects of 

smoking and dust together were 

additive. However, for miners with the 

most severe impairment, the effects of 

smoking and dust were synergistic (i.e., 

more than additive). 

Overall, MSHA agrees with OSHA’s 

conclusion that exposure to respirable 

crystalline silica causes chronic 

bronchitis regardless of whether 

silicosis is present and that an exposureresponse relationship may exist. 

c. Pulmonary Function Impairment 

Pulmonary function impairment, 

generally defined as reduction below 

the lower limit of normal predicted by 

reference equations (and in older 

literature as less than 80 percent 

predicted) of diffusion capacity for 

carbon monoxide (DLCOcSB), total lung 

capacity (TLC), FVC, or FEV1 is also a 

common condition of NMRD. Based on 

its review of the evidence in numerous 

longitudinal and cross-sectional studies 

and reviews, OSHA concluded that 

there is an exposure-response 

relationship between respirable 

crystalline silica and the development 

of impaired lung function. OSHA also 

concluded that the effect of tobacco 

smoking on this relationship may be 

additive or synergistic, and workers 

who were exposed to respirable 

crystalline silica but did not show signs 

of silicosis may also have pulmonary 

function impairment. MSHA has 

reviewed the studies cited by OSHA and 

agrees with their conclusions. 

OSHA reviewed several longitudinal 

studies regarding the relationship 

between respirable crystalline silica 

exposure and pulmonary function 

impairment. To evaluate whether 

exposure to silica affects pulmonary 

function in the absence of silicosis, the 

studies focused on workers who did not 

exhibit progressive silicosis. 

Among both active and retired 

Vermont granite workers exposed to an 

average quartz dust exposure level of 60 

mg/m3, researchers found no exposurerelated decreases in pulmonary function 

(Graham et al., 1981, 1994). However, 

Eisen et al. (1995) found significant 

pulmonary decrements among a subset 

of granite workers who left work and 

consequently did not voluntarily 

participate in the last of a series of 

annual pulmonary function tests 

(termed ‘‘dropouts’’). This group 

experienced steeper declines in lung 

function compared to the subset of 

workers who remained at work and 

participated in all tests (termed 

‘‘survivors’’), and these declines were 

significantly related to dust exposure. 

Exposure-related changes in lung 

function were also reported in a 12-year 

study of granite workers (Malmberg et 

al., 1993), in two 5-year studies of South 

African miners (Hnizdo, 1992; Cowie, 

1998), and in a study of foundry 

workers whose lung function was 

assessed between 1978 and 1992 

(Hertzberg et al., 2002). Similar 

reductions in FEV1 (indicating an 

airway obstruction) were linked to 

respirable crystalline silica exposure. 

Each of these studies reported their 

findings in terms of rates of decline in 

any of several pulmonary function 

measures (e.g., FEV1, FVC, FEV1/FVC). 

To put these declines in perspective, 

Eisen et al. (1995) reported that the rate 

of decline in FEV1 seen among the 

dropout subgroup of Vermont granite 

workers was 4 ml per 1,000 mg/m3-year 

(4 ml per mg/m3-year) of exposure to 

respirable granite dust. By comparison, 

FEV1 declines at a rate of 10 ml/year 

from smoking one pack of cigarettes 

daily. From their study of foundry 

workers, Hertzberg et al. (2002) reported 

a 1.1 ml/year decline in FEV1 and a 1.6 

ml/year decline in FVC for each 1,000 

mg/m3-year (1 mg/m3-year) of respirable 

crystalline silica exposure after 

controlling for ethnicity and smoking. 

From these rates of decline, they 

estimated that exposure to 100 mg/m3 of 

respirable crystalline silica for 40 years 

would result in a total loss of FEV1 and 

FVC that was less than, but still 

comparable to, smoking a pack of 

cigarettes daily for 40 years. Hertzberg et 

al. (2002) also estimated that exposure 

to the existing MSHA standard (100 mg/ 

m3) for 40 years would increase the risk 

of developing abnormal FEV1 or FVC by 

factors of 1.68 and 1.42, respectively. 

OSHA reviewed cross-sectional 

studies that described relationships 

between lung function loss and 

respirable crystalline silica exposure or 


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exposure measurement surrogates (e.g., 

tenure). The results of these studies 

were similar to those longitudinal 

studies already discussed. In several 

studies, respirable crystalline silica 

exposure was found to reduce lung 

function of: 

• White South African gold miners 

(Hnizdo et al., 1990), 

• Black South African gold miners 

(Cowie and Mabena, 1991; Irwig and 

Rocks, 1978), 

• Respirable crystalline silicaexposed workers in Quebec (Be ́gin et 

al., 1995), 

• Rock drilling and crushing workers 

in Singapore (Ng et al., 1992b), 

• Granite shed workers in Vermont 

(Theriault et al., 1974a, 1974b), 

• Aggregate quarry workers and coal 

miners in Spain (Montes et al., 2004a, 

2004b), 

• Concrete workers in the 

Netherlands (Meijer et al., 2001), 

• Chinese refractory brick 

manufacturing workers in an iron-steel 

plant (Wang et al., 1997), 

• Chinese gemstone workers (Ng et 

al., 1987b), 

• Hard-rock miners in Manitoba, 

Canada (Manfreda et al., 1982) and in 

Colorado (Kreiss et al., 1989), 

• Pottery workers in France 

(Neukirch et al., 1994), 

• Potato sorters in the Netherlands 

(Jorna et al., 1994), 

• Slate workers in Norway (Suhr et 

al., 2003), and 

• Men in a Norwegian community 

with years of occupational exposure to 

respirable crystalline silica (quartz) 

(Humerfelt et al., 1998). 

The OSHA (2013b) Health Effects 

Literature recognized that many of these 

studies found that pulmonary function 

impairment: (1) can occur in respirable 

crystalline silica-exposed workers 

without silicosis, (2) was still observable 

when controlling for silicosis in the 

analysis, and (3) was related to the 

magnitude and duration of respirable 

crystalline silica exposure, rather than 

to the presence or severity of silicosis. 

Many other studies in the OSHA 

(2013b) Health Effects Literature have 

also found a relationship between 

respirable crystalline silica exposure 

and lung function impairment, 

including IARC (1997), the ATS (1997), 

and Hnizdo and Vallyathan (2003). 

MSHA reviewed the studies and 

agrees with OSHA’s finding that there is 

an exposure-response relationship 

between respirable crystalline silica and 

the impairment of lung function. MSHA 

also agrees with OSHA’s finding that the 

effect of tobacco smoking on this 

relationship may be additive or 

synergistic, and that workers who were 

exposed to respirable crystalline silica, 

but did not show signs of silicosis, may 

also have pulmonary function 

impairment. 

3. Carcinogenic Effects 

a. Lung Cancer 

Lung cancer, an irreversible and 

usually fatal disease, is a type of cancer 

that forms in lung tissue. Agreeing with 

the conclusion of other government and 

public health organizations that 

respirable crystalline silica is a ‘‘known 

human carcinogen,’’ MSHA has 

preliminarily found that the scientific 

literature supports that respirable 

crystalline silica exposure significantly 

increases the risk of lung cancer 

mortality among miners. This 

determination is consistent with the 

conclusions of other government and 

public health organizations, including 

the IARC (1997b, 2012), the NTP (2000, 

2016), NIOSH (2002b), the ATS (1997), 

and the American Conference of 

Governmental Industrial Hygienists 

(ACGIH®, (2010)). The Agency’s 

determination is supported by 

epidemiological literature, 

encompassing more than 85 studies of 

occupational cohorts from more than a 

dozen industrial sectors including: 

granite/stone quarrying and processing 

(Carta et al., 2001; Attfield and Costello, 

2004; Costello et al., 1995; Gue ́nel et al., 

1989a,b), industrial sand (Sanderson et 

al., 2000; Hughes et al., 2001; McDonald 

et al., 2001, 2005; Rando et al., 2001; 

Steenland and Sanderson, 2001), MNM 

mining (Steenland and Brown, 1995a; 

deKlerk and Musk, 1998; Roscoe et al., 

1995; Hessel et al., 1986, 1990; Hnizdo 

and Sluis-Cremer, 1991; Reid and SluisCremer, 1996; Hnizdo et al., 1997; Chen 

et al., 1992; McLaughlin et al., 1992; 

Chen and Chen, 2002; Chen et al., 2006; 

Schubauer-Berigan et al., 2009; Hua et 

al., 1994; Meijers et al., 1991; 

Finkelstein 1998; Chen et al., 2012; Liu 

et al., 2017a; Wang et al., 2020a,b; Wang 

et al., 2021), coal mining (Meijers et al., 

1988; Miller et al., 2007; Miller and 

MacCalman, 2010; Miyazaki and Une, 

2001; Graber et al., 2014a,b; Tomaskova 

et al., 2012, 2017, 2020, 2022; Kurth et 

al., 2020), pottery (Winter et al., 1990; 

McLaughlin et al., 1992; McDonald et 

al., 1995), ceramic industries 

(Starzynski et al., 1996), diatomaceous 

earth (Checkoway et al., 1993, 1996, 

1997, 1999; Seixas et al., 1997; Rice et 

al., 2001), and refractory brick 

industries (cristobalite exposures) (Dong 

et al., 1995). 

The strongest evidence comes from 

the worldwide cohort and case-control 

studies reporting excess lung cancer 

mortality among workers exposed to 

respirable crystalline silica in various 

industrial sectors, confirmed by the 10- 

cohort pooled case-control analysis by 

Steenland et al. (2001a), the more recent 

pooled case-control analysis of seven 

European countries by Cassidy et al. 

(2007), and two national death 

certificate registry studies (Calvert et al., 

2003 in the United States; Pukkala et al., 

2005 in Finland). 

Recent studies examined lung cancer 

mortality among coal and non-coal 

miners (Meijers et al., 1988, 1991; 

Starzynski et al., 1996; Miyazaki and 

Une, 2001; Tomaskova et al., 2012, 

2017, 2020, 2022; Attfield and Kuempel, 

2008; Graber et al., 2014a, 2014b; Kurth 

et al., 2020; NIOSH, 2019a). These 

studies also discuss the associations 

between RCMD and respirable 

crystalline silica exposures with lung 

cancer in coal mining populations. 

Furthermore, these newer studies are 

consistent with the conclusion of 

OSHA’s final Quantitative Risk 

Assessment (QRA) (2016a) that 

respirable crystalline silica is a human 

carcinogen. MSHA preliminarily 

concludes that miners, both MNM and 

coal miners, are at risk of developing 

lung cancer due to their occupational 

exposure to respirable crystalline silica. 

In addition, based on its review of the 

literature, MSHA has preliminarily 

determined that radiographic silicosis is 

a marker for lung cancer risk. Reducing 

exposure to levels that lower the 

silicosis risk would reduce the lung 

cancer risk to exposed miners 

(Finkelstein, 1995, 2000; Brown, 2009). 

MSHA has also found that, based on the 

available epidemiological and animal 

data, respirable crystalline silica causes 

lung cancer (IARC, 2012; RTECS, 2016; 

ATSDR, 2019). Miners who inhale 

respirable crystalline silica over time are 

at increased risk of developing silicosis 

and lung cancer (Greaves, 2000; Erren et 

al., 2009; Tomaskova et al., 2017, 2020, 

2022). 

Toxicity studies provide additional 

evidence of the carcinogenic potential of 

respirable crystalline silica. Studies 

using DNA exposed directly to freshly 

fractured respirable crystalline silica 

demonstrate the direct effect respirable 

crystalline silica had on DNA breakage. 

Cell culture research has investigated 

the processes by which respirable 

crystalline silica disrupt normal gene 

expression and replication. Studies have 

demonstrated that chronic inflammatory 

and fibrotic processes resulting in 

oxidative and cellular damage may lead 

to neoplastic changes in the lung 

(Goldsmith, 1997). In addition, the 

biologically damaging physical 

characteristics of respirable crystalline 

silica and its direct and indirect 


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genotoxicity (Schins et al., 2002; Borm 

and Driscoll, 1996) support MSHA’s 

preliminary determination that 

respirable crystalline silica is an 

occupational carcinogen. 

b. Cancers of Other Sites 

In addition to lung cancer, OSHA 

reviewed studies examining the 

relationship between silica exposure 

and cancers at other sites. MSHA notes 

that OSHA reviewed these mortality 

studies (e.g., cancer of the larynx and 

the digestive system, including the 

stomach and esophagus) and found that 

studies suggesting a dose-response 

relationship were too limited in terms of 

size, study design, or potential for 

confounding variables to be conclusive. 

OSHA also pointed to the NIOSH 

(2002b) silica (respirable crystalline 

silica) hazard review, which concluded 

that no association has been established 

between respirable crystalline silica 

exposure and excess mortality from 

cancer at other sites. MSHA has 

reviewed these studies and agrees with 

OSHA’s conclusion. The following 

summarizes the studies reviewed with 

inconclusive findings. 

(1) Laryngeal Cancer 

Three lung cancer studies 

(Checkoway et al., 1997; Davis et al., 

1983; McDonald et al., 2001) included 

in OSHA’s health literature review 

suggest an association between 

respirable crystalline silica exposure 

and increased mortality from laryngeal 

cancer. However, a small number of 

cases were reported and researchers 

were unable to determine a statistically 

significant effect. Therefore, there is 

little evidence of an association based 

on these studies. 

(2) Gastric (Stomach) Cancer 

OSHA reviewed several studies in its 

2013b health literature review to assess 

a potential relationship between 

respirable crystalline silica exposures 

and stomach cancers. OSHA’s literature 

review noted observations made 

previously by Cocco et al. (1996) and in 

the NIOSH respirable crystalline silica 

hazard review (2002b), which found 

that most epidemiological studies of 

respirable crystalline silica and stomach 

cancer did not sufficiently adjust for the 

effects of confounding factors. In 

addition, some of these studies were not 

properly designed to assess a doseresponse relationship (e.g., Finkelstein 

and Verma, 2005; Moshammer and 

Neuberger, 2004; Selikoff, 1978; Stern et 

al., 2001) or did not demonstrate a 

statistically significant dose-response 

relationship (e.g., Calvert et al., 2003; 

Tsuda et al., 2001). For these reasons, 

MSHA determined these studies were 

inconclusive in the context of this 

rulemaking. 

(3) Esophageal Cancer 

OSHA considered several studies that 

examined the relationship between 

respirable crystalline silica exposures 

and esophageal cancer and found that 

the studies were limited in terms of size, 

study design, or potential for 

confounding variables. Three nested 

case-control studies of Chinese workers 

demonstrated a dose-response 

association between increased risk of 

esophageal cancer mortality and 

respirable crystalline silica exposure 

(Pan et al., 1999; Wernli et al., 2006; Yu 

et al., 2005). Other studies (Tsuda et al., 

2001; Xu et al., 1996a) also indicated 

elevated rates of esophageal cancer 

mortality with respirable crystalline 

silica exposure. However, OSHA noted 

that confounding factors due to other 

occupational exposures was possible. 

Additionally, two large national 

mortality studies in Finland and the 

United States did not show a positive 

association between respirable 

crystalline silica exposure and 

esophageal cancer mortality (Calvert et 

al., 2003; Weiderpass et al., 2003). 

MSHA agrees with OSHA’s conclusion 

that the literature does not support 

attributing increased esophageal cancer 

mortality to exposure to respirable 

crystalline silica. 

(4) Other Sites 

NIOSH (2002b) conducted a health 

literature review of the health effects 

potentially associated with respirable 

crystalline silica exposure, which 

identified only infrequent reports of 

statistically significant excesses of 

deaths for other cancers. Cancer studies 

have been reported in the following 

organs/systems: salivary gland, liver, 

bone, pancreas, skin, lymphopoietic or 

hematopoietic, brain, and bladder (see 

NIOSH, 2002b for full bibliographic 

references). However, the findings were 

not observed consistently among 

epidemiological studies, and NIOSH 

(2002b) concluded that no association 

has been established between these 

cancers and respirable crystalline silica 

exposure. OSHA concurred with NIOSH 

that these isolated reports of excess 

cancer mortality were insufficient to 

determine the role of respirable 

crystalline silica exposure. 

Overall, OSHA concluded that 

evidence of an association between 

silica exposure and cancer at sites other 

than the lungs is not sufficient. MSHA 

agrees with OSHA’s conclusion. 

4. Renal Disease 

Renal disease is characterized by the 

loss of kidney function, and in the case 

of ESRD, the need for a regular course 

of long-term dialysis or a kidney 

transplant. MSHA reviewed a wide 

variety of longitudinal and mortality 

epidemiological studies, including case 

series, case-control, and cohort studies, 

as well as case reports, and 

preliminarily concludes that respirable 

crystalline silica exposure increases the 

risk of morbidity and/or mortality 

related to ESRD. However, MSHA notes 

that the available literature on respirable 

crystalline silica exposures and renal 

disease in coal miners is less conclusive 

than the literature related to MNM 

miners. 

Epidemiological studies have found 

statistically significant associations 

between occupational exposure to 

respirable crystalline silica and chronic 

renal disease (e.g., Calvert et al., 1997), 

sub-clinical renal changes, including 

proteinuria and elevated serum 

creatinine (e.g., Ng et al., 1992a; Hotz et 

al., 1995; Rosenman et al., 2000), ESRD 

morbidity (e.g., Steenland et al., 1990), 

ESRD mortality (Steenland et al., 2001b, 

2002a), and Wegener’s granulomatosis 

(Nuyts et al., 1995) (severe injury to the 

glomeruli that, if untreated, rapidly 

leads to renal failure). The pooled 

analysis conducted by Steenland et al. 

(2002a) is particularly convincing 

because it involved a large number of 

workers from three combined cohorts 

and had well-documented, validated job 

exposure matrices. Steenland et al. 

(2002a) found a positive and monotonic 

exposure-response trend for both 

multiple-cause mortality and underlying 

cause data. MSHA has preliminarily 

determined that the underlying data 

from Steenland et al. (2002a) are 

sufficient to provide useful estimates of 

risk. 

Possible mechanisms suggested for 

respirable crystalline silica-induced 

renal disease include: (1) a direct toxic 

effect on the kidney, (2) a deposition in 

the kidney of immune complexes (e.g., 

Immunoglobulin A (IgA), an antibody 

blood protein) in the kidney following 

respirable crystalline silica-related 

pulmonary inflammation, and (3) an 

autoimmune mechanism (Gregorini et 

al., 1993; Calvert et al., 1997). Steenland 

et al. (2002a) demonstrated a positive 

exposure-response relationship between 

respirable crystalline silica exposure 

and ESRD mortality. 

Overall, MSHA preliminarily 

determines that respirable crystalline 

silica exposure in mining increases the 

risk of renal disease. 


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5. Autoimmune Disease 

Autoimmune diseases occur when the 

immune system mistakenly attacks 

healthy tissues within the body, causing 

inflammation, swelling, pain, and tissue 

damage. Examples include rheumatoid 

arthritis (RA), systemic lupus 

erythematosus (SLE), scleroderma, and 

systemic sclerosis (SSc). Based on its 

literature review, MSHA preliminarily 

concludes that there is a causal 

association between occupational 

exposure to respirable crystalline silica 

and the development of systemic 

autoimmune diseases in miners. 

However, no studies are available to 

date that can be used to model 

respirable crystalline silica-exposure 

risk in a formal quantitative risk 

analysis. 

Wallden et al. (2020) found that 

respirable crystalline silica exposure is 

correlated with an increased risk of 

developing ulcerative colitis, which 

increases with duration of exposure 

(work tenure) and the level of exposure. 

This effect was especially significant in 

men. Schmajuk et al. (2019) found that 

RA was significantly associated with 

coal mining and other non-coal 

occupations exposed to respirable 

crystalline silica. Finally, Vihlborg et al. 

(2017) found a significant increased risk 

of seropositive RA with high exposure 

(>0.048 mg/m3) to respirable crystalline 

silica dust when compared to 

individuals with no or lower exposure 

by examining detailed exposureresponse relationships across four 

different respirable crystalline silica 

dose groups (quartiles): <23 mg/m3, 24 to 

35 mg/m3, 36 to 47 mg/m3, and >48 mg/ 

m3. However, these researchers did not 

report the risk of sarcoidosis and 

seropositive RA in relation to respirable 

crystalline silica exposure using logistic 

regressions resulting in models that 

could be used in the risk assessment. In 

addition, the meta-analysis of 19 

published case-control and cohort 

studies on scleroderma by Rubio-Rivas 

et al. (2017) found statistically 

significant risks among individuals 

exposed to respirable crystalline silica, 

solvents, silicone, breast implants, 

epoxy resins, pesticides, and welding 

fumes, but did not provide detailed 

quantitative exposure information. 

C. Conclusion 

MSHA preliminarily concludes that 

occupational exposure to respirable 

crystalline silica causes silicosis (acute 

silicosis, accelerated silicosis, simple 

chronic silicosis, and PMF), NMRD 

(including COPD), lung cancer, and 

kidney disease. Each of these effects is 

exposure-dependent, chronic, 

irreversible, potentially disabling, and 

can be fatal. MSHA suspects that 

respirable crystalline silica exposure is 

also linked to the development of some 

autoimmune disorders through 

inflammation pathways. 

The scientific literature (including 

peer-reviewed medical, toxicological, 

public health, and other related 

disciplinary publications) is robust and 

compelling. It shows that miners 

exposed to the existing respirable 

crystalline silica limit of 100 mg/m3 still 

have an unacceptable amount of excess 

risk for developing and dying from 

diseases related to occupational 

respirable crystalline silica exposures 

and still suffer material impairments of 

health or functional capacity. 

VI. Preliminary Risk Analysis 

Summary 

MSHA’s preliminary risk analysis 

(PRA) quantifies risks associated with 

five specific health outcomes identified 

in the separate, standalone Health 

Effects document: silicosis morbidity 

and mortality, and mortality from 

NMRD, lung cancer, and ESRD. The 

standalone document, entitled 

Preliminary Risk Analysis (PRA 

document), has been placed into the 

rulemaking docket for the MSHA 

respirable crystalline silica rulemaking 

(RIN 1219–AB36, Docket ID no. MSHA– 

2023–0001) and is available on MSHA’s 

website. 

MSHA developed a PRA to support 

the risk determinations required to set 

an exposure limit for a toxic substance 

under the Mine Act. MSHA’s PRA 

quantifies the health risk to miners 

exposed to respirable crystalline silica 

under the existing exposure limits for 

MNM and coal miners, at the proposed 

PEL of 50 mg/m3, and at the proposed 

action level of 25 mg/m3. 

This analysis addresses three 

questions related to the proposed rule: 

(1) whether potential health effects 

associated with existing exposure 

conditions constitute material 

impairment to any miner’s health or 

functional capacity; 

(2) whether existing exposure 

conditions place miners at risk of 

incurring any material impairment if 

regularly exposed for the period of their 

working life; and 

(3) whether the proposed rule would 

reduce those risks. 

To answer these questions, MSHA 

relied on the large body of research on 

the health effects of respirable 

crystalline silica and several published, 

peer-reviewed, quantitative risk 

assessments that describe the risk of 

exposed workers to silicosis mortality 

and morbidity, NMRD mortality, lung 

cancer mortality, and ESRD mortality. 

These assessments are based on several 

studies of occupational cohorts in a 

variety of industrial sectors. The 

underlying studies are described in the 

Health Effects document and are 

summarized in Section V. Health Effects 

Summary of this preamble. 

This summary highlights the main 

findings from the PRA, briefly describes 

how they were derived, and directs 

readers interested in more detailed 

information to corresponding sections of 

the standalone PRA document. 

A. Summary of MSHA’s Preliminary 

Risk Analysis Process and Methods 

MSHA evaluated the literature and 

selected an exposure-response model for 

each of the five health endpoints— 

silicosis morbidity, silicosis mortality, 

NMRD mortality, lung cancer mortality, 

and ESRD mortality. The selected 

exposure-response models were used to 

estimate lifetime excess risks and 

lifetime excess cases among the current 

population of MNM and coal miners 

based on real exposure conditions, as 

indicated by the samples in the 

compliance sampling datasets. 

MSHA’s PRA is largely based on the 

methodology and findings from a peerreviewed January 2013 OSHA 

preliminary quantitative risk assessment 

(PQRA) and associated analysis of 

health effects in connection with 

OSHA’s promulgation of a rule setting 

PELs for workplace exposure to 

respirable crystalline silica. OSHA’s 

PQRA presented quantitative 

relationships between respirable 

crystalline silica exposure and multiple 

health endpoints. Following multiple 

legal challenges, the U.S. Court of 

Appeals for the D.C. Circuit rejected 

challenges to OSHA’s risk assessment 

methodology and its findings on 

different health risks. N. Am.’s Bldg. 

Trades Unions v. OSHA, 878 F.3d 271, 

283–89 (D.C. Cir. 2017). 

MSHA’s PRA presents detailed 

quantitative analyses of health risks 

over a range of exposure concentrations 

that have been observed in MNM and 

coal mines. MSHA applied exposureresponse models to estimate the 

respirable crystalline silica-related risk 

of material impairment of health or 

functional capacity of miners exposed to 

respirable crystalline silica at three 

levels—(1) the existing standards, (2) 

the proposed PEL, and (3) the proposed 

action level. As in past MSHA 

rulemakings, MSHA estimated and 

compared lifetime excess risks 

associated with exposures at the 

existing and proposed PEL (and at the 

proposed action level) over a miner’s 

full working life of 45 years. 


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18As discussed in the PRA, the existing PEL for 

coal is 100 mg/m3 MRE, measured as a full-shift 

time-weighted average (TWA). To calculate risks 

consistently for both coal and MNM miners, the 

PRA converts the MRE full-shift TWA 

concentrations experienced by coal miners to ISO 

8-hour TWA concentrations. (See Section 4 of the 

PRA document for a full explanation.) The equation 

used to convert MRE full-shift TWA concentrations 

into ISO 8-hour TWA concentrations is: 

ISO 8-hour TWA concentration = (MRE TWA) × 

(original sampling time)/(480 minutes) × 0.857 

Exposures at TWA 100 mg/m3 MRE and SWA 85.7 

mg/m3 ISO are only equivalent when the sampling 

duration is 480 minutes (eight hours). However, for 

the sake of simplicity and for comparison purposes, 

the risk analysis approximates exposures at the 

existing coal exposure limit of 100 MRE mg/m3 as 

85.7 mg/m3 ISO. Thus, ISO concentration values 

(measured as an 8-hour TWA) were used as the 

exposure metric when (a) calculating risk under the 

assumption of full compliance with the existing 

standards and (b) calculating risk under the 

assumption that no exposure exceeds the proposed 

PEL of 50 mg/m3. To simulate compliance among 

coal miners at the existing exposure limit, 

exposures were capped at 85.7 mg/m3 measured as 

an ISO 8-hour TWA. 

19Here, the ‘‘background’’ risk (or rate) refers to 

the risk of disease that the exposed person would 

have experienced in the absence of exposure to 

respirable crystalline silica. These background 

morbidity and mortality rates are measured using 

the disease-specific rates among the general 

population, which is not exposed to respirable 

crystalline silica. 

MSHA’s PRA is also based on a 

compilation of miner exposure data to 

respirable crystalline silica. For the 

MNM sector, MSHA evaluated 57,769 

valid respirable dust samples collected 

between January 2005 and December 

2019; and for the coal sector, MSHA 

evaluated 63,127 valid respirable dust 

samples collected between August 2016 

and July 2021. The compiled data set 

characterizes miners’ exposures to 

respirable crystalline silica in various 

locations (e.g., underground, surface), 

occupations (e.g., drillers, underground 

miners, equipment operators), and 

commodities (e.g., metal, nonmetal, 

stone, crushed limestone, sand and 

gravel, and coal). MSHA enforcement 

sampling indicates a wide range of 

exposure concentrations. These include 

exposures from below the proposed 

action level (25 mg/m3) to above the 

existing standards (100 mg/m3 in MNM 

standards, 100 mg/m3 MRE in coal 

standards, which is approximately 85.7 

mg/m3 ISO).18

The primary results of the PRA are the 

calculated number of deaths and 

illnesses avoided assuming full 

compliance after implementation of 

MSHA’s proposed rule. These 

calculations were performed for nonfatal silicosis illnesses (morbidity) and 

for deaths (mortality) due to silicosis, 

lung cancer, NMRD, and ESRD. For each 

health outcome, the reduced number of 

illnesses or deaths is calculated as the 

difference between (a) the number of 

illnesses and deaths currently occurring 

in the industry, assuming mines fully 

comply with the existing standards (100 

mg/m3 for MNM and 85.7 mg/m3 ISO for 

coal) and (b) the number of deaths and 

illnesses expected to occur following 

implementation of the proposed rule, 

which includes a proposed PEL of 50 

mg/m3 for a full shift exposure, 

calculated as an 8-hour TWA. 

Risks and cases were estimated under 

two scenarios: (a) a Baseline scenario 

where all exposures were capped at 100 

mg/m 3 for MNM miners and at 85.7 mg/ 

m 3 for coal miners, and (b) a proposed 

50 mg/m 3 scenario where all risks were 

capped at the proposed PEL of 50 mg/m 3

for both MNM and coal miners. The 

difference between the two scenarios 

yields the estimated reduction in 

lifetime excess risks and in lifetime 

excess cases due to the proposed PEL. 

To calculate risks, MSHA grouped 

MNM miners into the following 

exposure intervals: ≤25, >25 to ≤50, >50 

to ≤100, >100 to ≤250, >250 to ≤500, and 

>500 mg/m 3. MSHA grouped coal 

miners into the following exposure 

intervals: ≤25, >25 to ≤50, >50 to ≤85.7, 

>85.7 to ≤100, >100 to ≤250, >250 to 

≤500, and >500 mg/m 3. MSHA 

calculated the median of all exposure 

samples in each exposure interval and 

assumed the population of miners is 

distributed across the exposure intervals 

in proportion to the number of exposure 

samples from the compliance dataset in 

each interval. Then, miners were 

assumed to encounter constant exposure 

at the median value of their assigned 

exposure interval. MSHA adjusted the 

annual cumulative exposure by a fulltime equivalency (FTE) factor to account 

for the fact that miners may experience 

more or less than 2,000 hours of 

exposure per year. MSHA calculated the 

FTE adjustment factor as the weighted 

average of the production employee FTE 

ratio (0.99 for MNM and 1.14 for coal) 

and the contract miner FTE ratio (0.59 

for MNM and 0.64 for coal), where the 

weights are the number of miners 

(150,928 for MNM production 

employees, 60,275 for MNM contract 

miners, 51,573 for coal production 

employees, and 22,003 for coal contract 

miners). For example, the weighted 

average FTE ratio for MNM is (0.987 × 

150,928 + 0.591 × 60,275)/(150,928 + 

60,275) = 0.87 and is (1.139 × 51,573 + 

0.636 × 22,003)/(51,573 + 22,003) = 0.99 

for coal. 

MSHA calculated excess risk, which 

refers to the additional risk of disease 

and death attributable to exposure to 

respirable crystalline silica. For silicosis 

morbidity, MSHA used an exposureresponse model that directly yields the 

accumulated or lifetime excess risk of 

silicosis morbidity, assuming there is no 

background rate 19 of silicosis in an 

unexposed (i.e., non-miner) group. For 

the four mortality endpoints (silicosis 

mortality, lung cancer mortality, NMRD 

mortality, and ESRD mortality), MSHA 

used cohort life tables to calculate 

excess risks, assuming all miners begin 

working at age 21, retire at the end of 

age 65, and do not live past age 80. 

From the life tables, MSHA acquired the 

lifetime mortality risk by summing the 

miner cohort’s mortality risks in each 

year from age 21 through age 80. Life 

tables were also constructed for 

unexposed (i.e., non-miner) groups 

assumed to die from a given disease at 

typical rates for the U.S. male 

population. MSHA used 2018 data for 

all males in the U.S. (published by the 

National Center for Health Statistics, 

2020b) to estimate (a) the diseasespecific mortality rates among 

unexposed males and (b) the all-cause 

mortality rates among both groups 

(exposed miners and unexposed nonminers). 

For a given scenario (either Baseline 

or Proposed 50 mg/m3), MSHA 

constructed life tables in the manner 

described above, both for a miner cohort 

exposed to respirable crystalline silica 

and for an unexposed non-miner cohort. 

MSHA calculated excess risk of the 

disease as the difference between the 

two cohorts’ disease-specific mortality 

risk (due to silicosis, lung cancer, 

NMRD, or ESRD). MSHA determined 

the lifetime excess cases by multiplying 

the lifetime excess risk by the number 

of exposed miner FTEs (including both 

production employee FTEs and contract 

miner FTEs). Risks and cases were 

calculated separately for each exposure 

interval listed above. Then, the lifetime 

excess cases were aggregated across all 

exposure intervals. MSHA calculated 

the final lifetime excess risks per 1,000 

miners in the full population by 

dividing the total number of lifetime 

excess cases by the total number of 

miners in the population (exposed at 

any interval). Finally, to estimate the 

risk reductions and avoided cases of 

illness due to the proposed PEL, MSHA 

compared the lifetime excess risks and 

lifetime excess cases across the two 

scenarios (Baseline and Proposed 50 mg/ 

m3). 

B. Overview of Epidemiologic Studies 

MSHA reviewed extensive research 

on the health effects of respirable 

crystalline silica and several 

quantitative risk assessments published 

in the peer-reviewed scientific literature 


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regarding occupational exposure risks of 

illness and death from silicosis, NMRD, 

lung cancer, and ESRD. The Health 

Effects document describes the specific 

studies reviewed by MSHA. Of the 

many studies evaluated, MSHA believes 

that the 13 studies used by OSHA 

(2013b) to estimate risks provide 

reliable estimates of the disease risk 

posed by miners’ exposure to respirable 

crystalline silica. These studies are 

summarized in Table VI–1. 

BILLING CODE 4520–43–P 


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20FTEs were used to adjust the cumulative 

exposure over a year based on the average number 

of hours that miners work. 

Of these 13 studies, OSHA selected 

one per health endpoint for final 

modeling and estimation of lifetime 

excess risk and cases. Combining the 

five selected studies with the observed 

exposure data yields estimates of actual 

lifetime excess risks and lifetime excess 

cases among worker populations based 

on real exposure conditions. Table VI– 

2 presents the 13 studies from OSHA’s 

PQRA, which MSHA has also 

considered. MSHA evaluated the 

evidence of OSHA’s analysis of the 13 

studies and the accompanying risks 

associated with exposure at 25, 50, 100, 

250, and 500 mg/m3. Thorough 

evaluation has led MSHA to determine 

that the studies OSHA selected still 

provide the best available 

epidemiological models. However, 

MSHA utilized the Miller and 

MacCalman (2010) study to estimate 

risks. This study was published after 

OSHA completed much of its modeling 

for their 2013 PRA (OSHA, 2013b). The 

study was included in OSHA’s health 

effects assessment and its PQRA. The 

following lists the study used by MSHA 

for each health endpoint: 

Silicosis morbidity: Buchanan et al. 

(2003); 

Silicosis mortality: Mannetje et al. 

(2002b); 

NMRD mortality: Park et al. (2002); 

Lung cancer mortality: Miller and 

MacCalman (2010); and 

ESRD mortality: Steenland et al. 

(2002a). 

MSHA developed its risk estimates 

based on recent mortality data and using 

certain assumptions that differed from 

those used by OSHA, as explained in 

the standalone PRA document. 

Examples of these MSHA assumptions 

include a lifetime that ends at age 80, 

updated background mortality data and 

all-cause mortality, miner population 

sizes, and miner-specific full-time 

equivalents (FTEs).20

MSHA’s modeling has been done 

using life tables, in a manner consistent 

with OSHA’s PQRA. In general, the life 

table is a technique that allows 

estimation of excess risk of diseasespecific mortality while factoring in the 

probability of surviving to a particular 

age assuming no exposure to respirable 

crystalline silica. This analysis accounts 

for competing causes of death, 

background mortality rates of the 

disease, and the effect of the 

accumulation of risk due to elevated 

mortality rates in each year of a working 

life. For each cause of mortality, the 

selected study was used in the life table 

analysis to compute the increase in 

miners’ disease-specific mortality rates 

attributable to respirable crystalline 

silica exposure. 

MSHA uses cumulative exposure (i.e., 

cumulative dose) to characterize the 

total exposure over a 45-year working 

life. Cumulative exposure is defined as 

the product of exposure duration and 

exposure intensity (i.e., exposure level). 

Cumulative exposure is the predictor 

variable in the selected exposureresponse models. 


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BILLING CODE 4520–43–C 

For each health endpoint, MSHA 

generated two sets of risk estimates— 

one representing a scenario of full 

compliance with the existing standards 

(herein referred to as the ‘‘Baseline’’ 

scenario) and another representing a 

scenario wherein no samples exceed the 

proposed PEL (herein referred to as the 

‘‘Proposed 50 mg/m3’’ scenario). In the 

Baseline scenario, MNM miners in the 

>100–250, >250–500, and >500 mg/m3

groups were assigned exposure 

intensities of 100 mg/m3 ISO. Coal 

miners in the 85.7–100, >100–250, 

>250–500, and >500 mg/m3 groups were 

assigned exposure intensities of 85.7 mg/ 

m3 ISO, calculated as an 8-hour TWA. 

Exposure intensities were not changed 

for miners with lower exposure 

concentrations, because their exposures 

were considered compliant with the 

existing standards. A similar procedure 

was used for the Proposed 50 mg/m3

scenario, except that each miner group 

whose exposure exceeded the proposed 

PEL was assigned a new exposure of 50 

mg/m3 ISO (for both MNM and coal). 

This process—of creating an exposure 

profile based on actual exposure data 

and modifying it based on the existing 

standards or the proposed PEL— 

allowed MSHA to estimate real 

exposure conditions that miners would 

encounter under each scenario, thereby 

enabling estimates of the actual excess 

risks the current population of miners 

would experience under each scenario 

(Baseline and Proposed 50 mg/m3). 

For purposes of calculating risk in the 

PRA, both for MNM and coal miners, 

MSHA estimated excess risks by using 

the concentration collected over the full 

shift and calculating it as a full-shift, 8- 

hour TWA expressed in ISO standards. 

This metric of exposure intensity—the 

8-hour TWA concentration of respirable 

crystalline silica in ISO standards—was 

used consistently across all sets of 

estimates (both MNM and coal sectors, 

and both the Baseline and Proposed 50 

mg/m3 scenarios), thereby facilitating 

meaningful comparison. MSHA 

acknowledges that this metric does not 

correspond to the manner in which coal 

exposure concentrations are calculated 

for purposes of evaluating compliance 

under the existing standard. 

Nonetheless, MSHA believes that a fullshift, 8-hour TWA concentration 

accurately represents risks to miners 

and thus is the most appropriate 

cumulative exposure metric for 

computing risk given that FTEs were 

used to scale exposure durations 

relative to the assumption of 250 8-hour 

workdays per year. 

C. Summary of Studies Selected for 

Modeling 

1. Silicosis Morbidity 

Due to the long latency periods 

associated with chronic silicosis, 

OSHA’s respirable crystalline silica 

standard relied on the subset of studies 

that were able to contact and evaluate 

many workers through retirement. 

MSHA agrees that relying on studies 

that included retired workers comes 

closest to characterizing lifetime risk of 

silicosis morbidity. 

The health endpoint of interest in 

these studies was the appearance of 

opacities on chest radiographs 

indicative of pulmonary 

pneumoconiosis (a group of lung 

diseases caused by the lung’s reaction to 

inhaled dusts). The most reliable 

estimates of silicosis morbidity, as 

detected by chest X-rays, come from the 

studies that evaluated those X-rays over 

time, included radiographic evaluation 

of workers after they left employment, 

and derived cumulative or lifetime 

estimates of silicosis disease risk. 

To describe the presence and severity 

of pneumoconiosis, including silicosis, 

the International Labour Organization 

(ILO) developed a standardized system 

to classify lung opacities identified on 

chest radiographs (X-rays) (ILO, 1980, 

2002, 2011, 2022). The ILO system 


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grades the size, shape, and profusion of 

opacities. Although silicosis is defined 

and categorized based on chest X-ray, 

the X-ray is an imprecise tool for 

detecting pulmonary pneumoconiosis 

(Craighead and Vallyathan, 1980; 

Hnizdo et al., 1993; Rosenman et al., 

1997; Cohen and Velho, 2002). Hnizdo 

et al. (1993) recommended that an ILO 

category 0/1 (or greater) should be 

considered indicative of silicosis among 

workers exposed to high respirable 

crystalline silica concentrations. They 

noted that the sensitivity of the chest Xray as a screening test increases with 

disease severity and to maintain high 

specificity, category 1/0 (or 1/1) chest Xrays should be considered as a positive 

diagnosis of silicosis for miners who 

work in low dust occupations (Hnizdo 

et al., 1993). MSHA, consistent with 

NIOSH’s use of chest X-rays in their 

occupational respiratory disease 

surveillance program (NIOSH 2014b), 

agrees that a small opacity profusion 

score of 1/0 is consistent with chronic 

silicosis stage 1. Most of the studies 

reviewed by MSHA considered a 

finding consistent with an ILO category 

of 1/1 or greater to be a positive 

diagnosis of silicosis, although some 

also considered an X-ray classification 

of 1/0 or 0/1 to be positive. The low 

sensitivity of chest radiography to detect 

minimal silicosis suggests that risk 

estimates derived from radiographic 

evidence likely underestimate the true 

risk of this disease (Craighead and 

Vallyathan, 1980; Hnizdo et al., 1993; 

Rosenman et al., 1997; Cohen and 

Velho, 2002). 

OSHA summarized the Miller et al. 

(1995, 1998) and Buchanan et al. (2003) 

papers in their final respirable 

crystalline silica standard in 2016 

(OSHA 2016a, 81 FR 16286, 16316). 

These researchers reported on a 1991 

follow-up study of 547 survivors of a 

1,416-member cohort of Scottish coal 

workers from a single mine. These men 

had all worked in the mine during the 

period between early 1971 and mid1976, during which time they had 

experienced ‘‘unusually high 

concentrations of freshly cut quartz in 

mixed coal mine dust.’’ The 

population’s exposures to quartz dust 

had been measured in unique detail for 

a considerable proportion of the men’s 

working lives (OSHA 2013b, page 333). 

The 1,416 men had previous chest Xrays dating from before, during, or just 

after this high respirable crystalline 

silica exposure period. Of these 1,416 

men, 384 were identified as having died 

by 1990/1991. Of the 1,032 remaining 

men, 156 were untraced, and, of the 876 

who were traced and replied, 711 agreed 

to participate in the study. Of these, the 

total number of miners who were 

surveyed was 551. Four of these were 

omitted, two because of a lack of an 

available chest X-ray. The 547 surviving 

miners (age range: 29–85 years, average 

= 59 years) were interviewed and 

received their follow-up chest X-rays 

between November 1990 and April 

1991. The interviews consisted of 

questions on current and past smoking 

habits and occupational history since 

leaving the coal mine, which closed in 

1981. They were also asked about 

respiratory symptoms and were given a 

spirometry test (OSHA 2013b, pages 

333–334). 

Exposure characterization was based 

on extensive respirable dust sampling; 

samples were analyzed for quartz 

content by IR spectroscopy. Between 

1969 and 1977, two coal seams were 

mined. One had produced quarterly 

average concentrations of respirable 

crystalline silica much less than 1,000 

mg/m3 (only 10 percent exceeded 300 

mg/m3). The other more unusual seam 

(mined between 1971 and 1976) lay in 

sandstone strata and generated 

respirable crystalline silica levels such 

that quarterly average exposures 

exceeded 1,000 mg/m3 (10 percent of the 

quarterly measurements were over 

10,000 mg/m3). Thus, this cohort study 

allowed evaluation of the effects of both 

higher and lower respirable crystalline 

silica concentrations and exposure-rate 

effects on the development of silicosis 

(OSHA 2013b, page 334). 

Three physicians read each chest film 

taken during the current survey as well 

as films from the surveys conducted in 

1974 and 1978. Films from an earlier 

1970 survey were read only if no films 

were available from the subsequent two 

surveys. Silicosis cases were identified 

if the median classification of the three 

readers indicated an ILO category of 1/ 

1 or greater (Miller et al, 1995, page 24), 

plus a progression from the earlier 

reading. Of the 547 men, 203 (38 

percent) showed progression of at least 

1 ILO category from the 1970s’ surveys 

to the 1990–91 survey; in 128 of these 

(24 percent) there was progression of 2 

or more ILO categories. In the 1970s’ 

surveys, 504 men had normal chest Xrays; of these 120 (24 percent) acquired 

an abnormal X-ray consistent with ILO 

category 1/0 or greater at the follow-up. 

Of the 36 men whose X-rays were 

consistent with ILO category 1/0 or 

greater in the 1970s’ surveys, 27 (75 

percent) exhibited further progression at 

the 1990/1991 follow-up. Only one 

subject showed a regression from any 

earlier reading, and that was slight, from 

1/0 to 0/1. The earlier Miller et al. 

(1995) report presented results for cases 

classified as having X-ray films 

consistent with either 1/0+ and 2/1+ 

degree of profusion; the Miller et al. 

(1998) analysis and the Buchanan et al. 

(2003) re-analyses emphasized the 

results from cases having X-rays 

classified as 2/1+ (OSHA 2013b, page 

334). 

MSHA modeled the exposureresponse relationship by using 

cumulative exposure expressed as gram/ 

m3-hours, assuming 2,000 work hours 

per year and a 45-year working life (after 

adjusting for full-time equivalents, 

including production employees and 

contract workers). MSHA estimated risk 

at the existing standard assuming 

cumulative exposure to 100 mg/m3 ISO 

for MNM miners and 85.7 mg/m3 ISO 

(100 mg/m3 MRE) for coal miners. 

Respirable crystalline silica exposures 

were calculated by commodity, and 

median exposure values were used 

within a variety of exposure intervals. 

Risks were computed using a life table 

methodology which iteratively updated 

the survival, risk, and mortality rates 

each year based on the results of the 

preceding year. Covariates in the 

regression included smoking, age, 

amount of coal dust, and percent of 

quartz in the coal dust during various 

previous survey periods. 

Both Miller et al. papers (1995, 1998) 

presented the results of numerous 

regression models, and they compared 

the results of the partial regression 

coefficients using Z statistics of the 

coefficient divided by the standard 

error. Also presented were the residual 

deviances of the models and the 

residual degrees of freedom. In the 

introduction to the results section, 

Miller et al. (1995) stated that, ‘‘in none 

of the models fitted was there a 

significant effect of smoking habit 

(current, ex-smoker, and never smoker), 

nor was there any evidence of any 

difference between smoking groups in 

their relationship of response with age.’’ 

They therefore presented the results of 

the regression analyses without terms 

for smoking effects (i.e., without 

including smoking effects as a variable 

in the final regression analysis, because 

they found that smoking did not affect 

the modeling results). The logistic 

regression models developed by Miller 

et al. (1995) included terms for 

cumulative exposure and age. In their 

later publication, Miller et al. (1998) 

presented models similar to their 1995 

report, but without the age variable. 

Their logistic regression model A from 

Table 7 of their report (page 56) 

included only an intercept (¥4.32) and 

the respirable crystalline silica (quartz) 

cumulative exposure variable (0.416). 

They estimated that respirable 

crystalline silica exposure at an average 


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concentration of 100 mg/m3 for 15 years 

(2.6 gram/m3-hr assuming 1,750 hours 

worked per year) would result in an 

increased risk of silicosis (ILO > 2/1) of 

5 percent (OSHA 2013b, page 334). 

OSHA had a high degree of 

confidence in the estimates of silicosis 

morbidity risk from this Scotland coal 

mine study. This was mainly because of 

highly detailed and extensive exposure 

measurements, radiographic records, 

and detailed analyses of high exposurerate effects. However, in another paper, 

Soutar et al. (2004) noted that: ‘‘If the 

effects of silica vary according to the 

conditions of exposure, these risks are 

probably towards the high end of the 

risk spectrum, since the silica was 

freshly fractured from massive 

sandstone, and not derived from dirt 

bands where the quartz grains are aged 

and accompanied by clay minerals’’ 

(OSHA 2013b, page 336). MSHA has 

reviewed and agrees with OSHA’s 

conclusion. 

Buchanan et al. (2003) provided an 

analysis and risk estimates only for 

cases having X-ray films consistent with 

ILO category 2/1+ extent of profusion of 

opacities, after adjusting for the 

disproportionately severe effect of 

exposure to high respirable crystalline 

silica concentrations. Estimating the risk 

of 1/0+ profusions from the Buchanan et 

al. (2003) or the earlier Miller et al. 

(1995, 1998) publications can only be 

roughly approximated because of the 

summary information included. Table 4 

of Miller et al. (1998) (page 55) presents 

a cross-tabulation of radiograph 

progression, using the 12-point ILO 

scale, from the last baseline exam to the 

1990/1991 follow-up visit for the 547 

men at the Scottish coal mine. From this 

table, among miners having both early 

X-ray films and follow-up films, 44 men 

had progressed to 2/1+ by the last 

follow-up and an additional 105 men 

had experienced the onset of silicosis 

(i.e., X-ray films were classified as 1/0, 

1/1, or 1/2). Thus, by the time of the 

follow-up, there were three times more 

miners with silicosis consistent with 

ILO category 1 than there were miners 

with a category 2+ level of severity ((105 

+ 44)/44 = 3.38). This suggests that the 

Buchanan et al. (2003) model, which 

reflects the risk of progressing to ILO 

category 2+, underestimates the risk of 

acquiring radiological silicosis by about 

three-fold in this population (OSHA 

2013b, page 336). This type of analysis 

shows that the risk of developing 

silicosis estimated from the Buchanan et 

al. (2003) and Miller et al. (1998) studies 

is of the same magnitude as the risks 

reported by Hnizdo and Sluis-Cremer 

(1993b) (OSHA 2013b, page 338). 

MSHA estimated silicosis risk by 

using the Buchanan et al. (2003) model 

that predicted the lifetime probability of 

developing silicosis at the 2/1+ category 

based on cumulative respirable 

crystalline silica exposures. As 

discussed previously, MSHA applied 

the Buchanan et al. (2003) model, 

assuming that miners are exposed for 45 

years of working life extending from age 

21 through age 65, using a life table 

approach. Buchanan et al. provides an 

exposure-response model using 

cumulative exposure in mg/m3-hours as 

the predictor variable and lifetime risk 

of silicosis as the outcome variable. 

MSHA assumed 45 years of exposure, 

each such year having a duration of 

2,000 work hours, scaled by a weighted 

average FTE ratio that accounts for the 

average annual hours worked by 

production employees and contract 

miners. 

2. Accelerated Silicosis and Rapidly 

Progressive Pneumoconiosis (RPP) 

Study 

OSHA concluded in their risk 

assessment, and MSHA agrees, that 

there is little evidence of a dose-rate 

effect at respirable crystalline silica 

concentrations in the exposure range of 

25 mg/m3 to 500 mg/m3 (81 FR 16286, 

16396). OSHA noted that the risk 

estimates derived from the Buchanan et 

al. (2003) study were not appreciably 

different from those derived from the 

other studies of silicosis morbidity (see 

OSHA 2016a, 81 FR 16286, 16386; Table 

VI–1. Summary of Lifetime or 

Cumulative Risk Estimates for 

Crystalline Silica). However, OSHA also 

concluded that some uncertainty related 

to dose-rate effects exists at 

concentrations far higher than the 

exposure range of interest. OSHA stated 

that it is possible for such a dose-rate 

effect to impact the results if not 

properly addressed in study populations 

with high concentration exposures. 

OSHA used the model from the 

Buchanan et al. (2003) study in its 

silicosis morbidity risk assessment to 

account for possible dose-rate effects at 

high average concentrations (OSHA 

2016a, 81 FR 16286, 16396 OSHA 

2013b, pages 335–342). MSHA has 

reviewed and agrees with OSHA’s 

conclusions. 

NIOSH stated in its post-hearing brief 

to OSHA, that a ‘‘detailed examination 

of dose rate would require extensive and 

real time exposure history which does 

not exist for silica (or almost any other 

agent)’’ (81 FR 16285, 16375). Similarly, 

Dr. Kenneth Crump, a researcher from 

Louisiana Tech University Foundation 

who served on OSHA’s peer review 

panel for the Review of Health Effects 

Literature and Preliminary Quantitative 

Risk Assessment, wrote to OSHA that, 

‘‘[h]aving noted that there is evidence 

for a dose rate effect for silicosis, it may 

be difficult to account for it 

quantitatively. The data are likely to be 

limited by uncertainty in exposures at 

earlier times, which were likely to be 

higher’’ (OSHA 2016a, 81 FR 16286, 

16375). OSHA agreed with the 

conclusions of NIOSH and Dr. Crump. 

OSHA believed that it used the best 

available evidence to estimate risks of 

silicosis morbidity and sufficiently 

accounted for any dose rate effect at 

high silica average concentrations by 

using the Buchanan et al. (2003) study 

as part of their final Quantitative Risk 

Analysis (QRA) (OSHA 2016a, 81 FR 

16286, 16396). MSHA has reviewed and 

agrees with OSHA’s conclusions. 

MSHA is using the Buchanan et al. 

(2003) study to explain, in part, the 

observed cases of progressive lung 

disease in miners, known as RPP in coal 

miners (Laney and Attfield, 2010; Wade 

et al., 2010; Laney et al., 2012b; 2017; 

Blackley et al., 2016b, 2018b; Reynolds 

et al., 2018b; Halldin et al., 2019; 

Halldin et al., 2020; Almberg et al., 

2018a; Cohen et al., 2022) and 

accelerated silicosis in MNM miners 

(Dumavibhat et al., 2013; Hessel et al., 

1988; Mohebbi and Zubeyri 2007). The 

inclusion of this discussion in the risk 

analysis is to describe research that 

explains, in part, the progressive disease 

observed in shorter-tenured miners. 

MSHA believes that the risks estimated 

by the Buchanan et al. model can be 

applied to all mining populations that 

have similar respirable crystalline silica 

exposure exceedances. MSHA estimated 

the increase of silicosis risk in miners 

exposed to extreme respirable 

crystalline silica exposures for varying 

periods of time ranging from 0 hours to 

348 hours per year (i.e., 0.0 percent to 

20.0 percent of time at extreme 

exposures). This information is 

important because MSHA data indicate 

that many miners’ respirable crystalline 

silica exposure samples over the years 

have exceeded the existing exposure 

limit(s) of 100 mg/m3. MSHA data also 

indicate that a smaller number of MSHA 

samples showed respirable crystalline 

silica concentrations well above the 

existing MSHA standard of 100 mg/m3. 

Over the last 15 years of MNM 

compliance data, 188 samples (0.3 

percent) were over 500 mg/m3; the upper 

range of exposure was 4,289 mg/m3 ISO 

(see PRA Table 4 of the PRA document). 

Over the last 5 years of coal compliance 

data, eight samples (<0.1 percent) were 

over 500 mg/m3; the upper range of 


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exposure was 791.4 mg/m3 MRE (see 

PRA Table 7 of the PRA document). 

Analysis provided by Buchanan et al. 

(2003) provides strong evidence of an 

exposure-rate effect for silicosis in a 

British Pneumoconiosis Field Research 

(PFR) coal mining cohort exposed to 

high levels of respirable crystalline 

silica over short periods of time (OSHA 

2013b, page 335). Exposure was 

categorized as pre- and post-1964, the 

latter period being that of generally 

higher quartz concentrations used to 

estimate exposure-rate effects. For the 

purpose of this analysis, the results 

were presented for the 371 men (out of 

the original 547) who were between the 

ages of 50 and 74 at the time of the 

1990/1991 follow-up, ‘‘since they had 

experienced the widest range of quartz 

concentrations and showed the 

strongest exposure-response relations.’’ 

Thus, combined with their exposure 

history, which went back to pre-1954, 

many of these men had 30 to 40+ years 

of highly detailed occupational 

exposure histories available for analysis. 

Of these 371 miners, there were 35 men 

(9.4 percent) who had X-ray films 

consistent with ILO category 2/1+, with 

at least 29 of them having progressed 

from less severe silicosis since the 

previous follow-up during the 1970s 

(from Miller et al., 1998) (OSHA 2013b, 

page 335). 

The Buchanan et al. (2003) re-analysis 

presented logistic regression models in 

stages. In the final stage of modeling, 

using only the statistically significant 

post-1964 cumulative exposures, the 

authors separated these exposures into, 

‘‘two quartz concentration bands, 

defined by the cut-point 2.0 mg/m3.’’ 

This yielded the final simplified 

equation, adapted from Buchanan et al., 

2003, page 162: 

where p2 is the probability of profusion 

category 2/1 or higher (2/1+) at followup and E is the cumulative exposure. 

In this model, both the cumulative 

exposure concentration variables were 

‘‘highly statistically significant in the 

presence of the other’’ (Buchanan et al., 

2003, page 162). Since these variables 

were in the same units, mg/m3-hr, the 

authors noted that the coefficient for 

exposure concentrations >2,000 mg/m3

(≤2.0 mg/m3) was three times that for 

the concentrations <2,000 mg/m3 (<2.0 

mg/m3). They concluded that their latest 

analysis showed that ‘‘the risk of 

silicosis over a working lifetime can rise 

dramatically with exposure to such high 

concentrations over a timescale of 

merely a few months’’ (Buchanan et al., 

2003, page 163, OSHA 2013b, page 336). 

Buchanan et al. (2003) also used these 

models to estimate the risk of acquiring 

a chest X-ray classified as ILO category 

2/1+, 15 years after exposure ends, as a 

function of low <2,000 mg/m3 (<2.0 mg/ 

m3) and high >2,000 mg/m3 (≤2.0 mg/m3) 

quartz concentrations. OSHA chose to 

use this model to estimate the risk of 

radiological silicosis consistent with an 

ILO category 2/1+ chest X-ray for 

several exposure scenarios. They 

assumed 45 years of exposure, 2,000 

hours/year of exposure, and no 

exposure above a concentration of 2,000 

mg/m3 (2.0 mg/m3) (OSHA 2013b, page 

336). 

Buchanan et al. (2003) used these 

models to estimate the combined effect 

on the predicted risk of low quartz 

exposures (e.g., 100 mg/m3, equal to 0.1 

mg/m3) and short-term exposures to 

high quartz concentrations (e.g., 2,000 

mg/m3, equal to 2 mg/m3). Predicted 

risks were estimated for miners who 

progressed to silicosis level 2/1+ 15 

years after exposure ended. This 

analysis showed the increase in 

predicted risk with relatively short 

periods of quartz exceedance exposures, 

over 4, 8, and 12 months. Buchanan et 

al. predicted a risk of 2.5 percent for 15 

years quartz exposure to 100 mg/m3 (0.1 

mg/m3). This risk increased to 10.6 

percent with the addition of only 4 

months of exposure at the higher 

concentration. The risk increased 

further to 72 percent with 12 months at 

the higher exposure of 2,000 mg/m3 (2.0 

mg/m3). 

The results indicate miners exposed 

to exceedances above MSHA’s existing 

standard could develop progression of 

silicosis at an exaggerated rate. The 

results of Buchanan et al. also indicated 

that miners’ exposure to exceedances at 

MSHA’s proposed standard will also 

suffer increased risk of developing 

progressive disease, though at a reduced 

rate (see Buchanan et al. (2003), Table 

4, page 163). 

MSHA used a life table approach to 

estimate the lifetime excess silicosis 

morbidity from age 21 to age 80, 

assuming exposure from age 21 through 

age 65 (45 years of working life) and an 

additional 15 years of potential illness 

progress thereafter. MSHA used the 

Buchanan et al. (2003) model to 

estimate the effect of respirable 

crystalline silica exposure exceedances 

as seen in MSHA’s compliance data on 

miners’ silicosis risk at the existing and 

proposed standard. The model 

predicted the probability of developing 

silicosis at the 2/1+ category based on 

cumulative respirable crystalline silica 

exposures. Age-specific cumulative risk 

was estimated as 1/(1 + EXP(¥(¥4.83 + 

0.443 * cumulative exposure))). The 

model determined that even at 17.4 

hours on average per year at an 

exposure of 1,500 mg/m3 (1.50 mg/m3), 

miners’ risk of developing 2/1+ silicosis 

increased from a baseline of 24.8/1,000 

to 29.0/1,000 at the existing standard 

and 14/1,000 to 16.6/1,000 at the 

proposed standard. Of course, the more 

hours exposed to these levels of 

respirable crystalline silica resulted in 

even higher increased risk. It is 

important to note that NIOSH’s X-ray 

classification of the lowest case of 

pneumoconiosis is 1/0 profusion of 

small opacities (NIOSH 2008c, page A– 

2). Using a case definition of level 2/1+, 

the miners studied by Buchanan et al. 

(2003) would be more likely to show 

clinical signs of disease. MSHA 

emphasizes the importance of 

maintaining miner exposure to 

respirable crystalline silica at or below 

the proposed standard to minimize 

these health risks as much as possible. 

3. Silicosis and NMRD Mortality 

Silicosis mortality was ascertained in 

the studies included in the pooled 

analysis by Mannetje et al. (2002b). 

These studies included cohorts of U.S. 

diatomaceous earth workers 

(Checkoway et al., 1997), Finnish 

granite workers (Koskela et al., 1994), 

U.S. granite workers (Costello and 

Graham, 1988), U.S. industrial sand 

workers (Steenland and Sanderson, 

2001), U.S. gold miners (Steenland and 

Brown (1995a), and Australian gold 

miners (de Klerk et al., 1998). The 

researchers analyzed death certificates 

across all cohorts for cause of death. 

OSHA relied upon the published, peerreviewed, pooled analysis of six 

epidemiological studies first published 

by Mannetje et al. (2002b) and a 

sensitivity analysis of the data 

conducted by ToxaChemica, 

International, Inc. (2004). OSHA used 

the model described by Mannetje et al. 


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(2002b) and the rate ratios that were 

estimated from the ToxaChemica, 

International Inc. sensitivity analysis to 

estimate the risks of silicosis mortality. 

This process better controlled for age 

and exposure measurement uncertainty 

(OSHA 2013b, page 295). MSHA has 

reviewed and agrees with OSHA’s 

conclusions. These studies are 

summarized below, including detailed 

discussion and analysis of uncertainty 

in the studies and associated risk 

estimates. 

OSHA found that the estimates from 

Mannetje et al. (2002b) and 

ToxaChemica Inc. probably understated 

the actual risk because silicosis is 

underreported as a cause of death since 

there is no nationwide system for 

collecting silicosis morbidity case data 

(OSHA 2016a, 81 FR 16286, 16325). To 

help address this uncertainty, OSHA 

also included an exposure-response 

analysis of diatomaceous earth workers 

(Park et al., 2002). This analysis better 

recognized the totality of respirable 

crystalline silica-related respiratory 

disease than the datasets of Mannetje et 

al. (2002b) and ToxaChemica 

International Inc. (2004). Information 

from the Park et al. (2002) study 

(described in the next subsection) was 

used to quantify the relationship 

between cristobalite exposure and 

mortality caused by NMRD, which 

includes silicosis, pneumoconiosis, 

emphysema, and chronic bronchitis. 

The category of NMRD captures much of 

the silicosis misclassification that 

results in underestimation of the 

disease. NMRD also includes risks from 

other lung diseases associated with 

respirable crystalline silica exposures. 

OSHA found the risk estimates derived 

from Park et al. (2002) were important 

to include in their range of estimates of 

the risk of death from respirable 

crystalline silica-related respiratory 

diseases, including silicosis (OSHA 

2013b, pages 297–298). OSHA 

concluded that the ToxaChemica 

International Inc. (2004) re-analysis of 

Mannetje et al.’s (2002b) silicosis 

mortality data and Park et al.’s (2002) 

study of NMRD mortality provided a 

credible range of estimates of mortality 

risk from silicosis and NMRD across 

many workplaces. The upper end of this 

range, based on the Park et al. (2002) 

study, is less likely to underestimate 

risk because of underreporting of 

silicosis mortality. However, risk 

estimates from studies focusing on 

cohorts of workers from different 

industries cannot be directly compared 

(OSHA 2016a, 81 FR 16286, 16397). 

a. Silicosis Mortality: Mannetje et al. 

(2002b); ToxaChemica, International, 

Inc. (2004) 

Mannetje et al. (2002b) relied upon 

the epidemiological studies contained 

within the Steenland et al. (2001a) 

pooled analysis of lung cancer mortality 

that also included extensive data on 

silicosis. The six cohorts included: 

(1) U.S. diatomaceous earth workers 

(Checkoway et al., 1997), 

(2) Finnish granite workers (Koskela 

et al., 1994), 

(3) U.S. granite workers (Costello and 

Graham, 1988), 

(4) U.S. industrial sand workers 

(Steenland and Sanderson, 2001), 

(5) U.S. gold miners (Steenland and 

Brown, 1995b), and 

(6) Australian gold miners (de Klerk 

and Musk, 1998). 

These six cohorts contained 18,364 

workers and 170 silicosis deaths, where 

silicosis mortality was defined as death 

from silicosis (ICD–9 502, n = 150) or 

from unspecified pneumoconiosis (ICD– 

9 505, n = 20). Table VI–3 provides 

information on each cohort, including 

size, time period studied, overall 

number of deaths, and number of deaths 

identified as silicosis for the pooled 

analysis conducted by Mannetje et al. 

(2002b). The authors believed this 

definition to err on the side of caution 

in that some cases of death from 

silicosis in the cohorts may have been 

misclassified as other causes (e.g., 

tuberculosis or COPD without mention 

of pneumoconiosis). Four cohorts were 

not included in the silicosis mortality 

study. The three Chinese studies did not 

use the ICD to code cause of death. In 

the South African gold miner study, 

silicosis was not generally recognized as 

an underlying cause of death. Thus, it 

did not appear on death certificates 

(OSHA 2013b, page 292). 


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Mannetje et al. (2002a) described the 

exposure assessments developed for the 

pooled analysis. Exposure information 

from each of the 10 cohort studies 

varied and included dust measurements 

representing particle counts, mass of 

total dust, and respirable dust mass. 

Measurement methods also changed 

over time for each of the cohort studies. 

Generally, sampling was performed 

using impingers in earlier decades, and 

gravimetric techniques later. Exposure 

data based on analysis for respirable 

crystalline silica by XRD (the current 

method of choice) were available only 

from the study of U.S. industrial sand 

workers. To develop cumulative 

exposure estimates for all cohort 

members and to pool the cohort data, all 

exposure data were converted to units of 

mg/m3 (mg/m3) respirable crystalline 

silica. Cohort-specific conversion factors 

were generated based on the silica 

content of the dust to which workers 

were exposed. In some instances, results 

of side-by-side comparison sampling 

were available. Within each cohort, 

available job- or process-specific 

information on the silica composition or 

nature of the dust was used to 

reconstruct respirable crystalline silica 

exposures. Most of the studies did not 

have exposure measurements prior to 

the 1950s. Exposures occurring prior to 

that time were estimated either by 

assuming such exposures were the same 

as the earliest recorded for the cohort or 

by modeling that accounted for 

documented changes in dust control 

measures. 

To evaluate the reasonableness of the 

exposure assessment for the lung cancer 

pooled study, Mannetje et al. (2002a) 

investigated the relationship between 

silicosis mortality and cumulative 

exposure. They performed a nested 

case-control analysis for silicosis or 

unspecified pneumoconiosis using 

conditional logistic regression. Since 

exposure to respirable crystalline silica 

is the sole cause of silicosis, any finding 

for which cumulative exposure was 

unrelated to silicosis mortality risk 

would suggest that serious 

misclassification of the exposures 

assigned to cohort members occurred. 

Cases and controls were matched for 

race, sex, age (within 5 years), and 100 

controls were matched to each case. 

Each cohort was stratified into quartiles 

by cumulative exposure. Standardized 

rate ratios (SRRs) were calculated using 

the lowest-exposure quartile as the 

baseline. Odds ratios (ORs) were also 

calculated for the pooled data set 

overall, which was stratified into 

quintiles based on cumulative exposure. 

For the pooled data set, the relationship 

between the ORs for silicosis mortality 

and cumulative exposure, along with 

each of the 95 percent confidence 

intervals (95% CI), were as follows: 

(1) 4,450 mg/m3-years (4.45 mg/m3- 

years), OR=3.1 (95% CI: 2.5–4.0); 

(2) 9,080 mg/m3-years (9.08 mg/m3- 

years), OR=4.6 (95% CI: 3.6–5.9); 

(3) 16,260 mg/m3-years (16.26 mg/m3- 

years), OR=4.5 (95% CI: 3.5–5.8); and 

(4) 42,330 mg/m3-years (42.33 mg/m3- 

years), OR=4.8 (95% CI: 3.7–6.2). 

In addition, in seven of the cohorts, 

there was a statistically significant trend 

between silicosis mortality and 

cumulative exposure. For two of the 

cohorts (U.S. granite workers and U.S. 

gold miners), the trend test was not 

statistically significant (p=0.10). An 

analysis could not be performed on the 

South African gold miner cohort 

because silicosis was never coded as an 

underlying cause of death, apparently 

due to coding practices in that country. 

Based on this analysis, Mannetje et al. 

(2002a) concluded that the exposureresponse relationship for the pooled 

data set was ‘‘positive and reasonably 

monotonic.’’ That is, the response 

increased with increasing exposure. The 

results also indicated that the exposure 

assessments provided reasonable 

estimates of cumulative exposures. In 

addition, despite some large differences 

in the range of cumulative exposures 

between cohorts, a clear positive 

exposure-response trend was evident in 

seven of the cohorts (OSHA 2013b, page 

271). 

Furthermore, in their pooled analysis 

of silicosis mortality for six of the 

cohorts, Mannetje et al. (2002b) found a 

clear and consistently positive response 

with increasing decile of cumulative 

exposure, although there was an 

anomaly in the 9th decile. Overall, these 

data supported a monotonic exposureresponse relationship for silicosis. Thus, 

although some exposure 

misclassification almost certainly 

existed in the pooled data set, the 

authors concluded that exposure 

estimates did not appear to have been 

sufficiently misclassified to obscure an 

exposure-response relationship (OSHA 

2013b, page 271). 

As part of an uncertainty analysis 

conducted for OSHA, Drs. Steenland 

and Bartell (ToxaChemica International, 

Inc. 2004) examined the quality of the 

original data set and analysis to identify 

and correct any data entry, 

programming, or reporting errors 

(ToxaChemica International, Inc. 2004). 

This quality assurance process revealed 

a small number of errors in exposure 

calculations for the originally reported 

results. Primarily, these errors resulted 

from rounding of job class exposures 

when converting the original data file 

for use with a different statistical 

program. Although the corrections 

affected some of the exposure-response 

models for individual cohorts, 

ToxaChemica International, Inc. (2004) 

reported that models based on the 

pooled dataset were not impacted by the 

correction of these errors (OSHA 2013b, 

pages 271–272). 

Silicosis mortality was evaluated 

using standard life table analysis in 

Mannetje et al. (2002b). Poisson 

regression, using 10 categories of 

cumulative exposure and adjusting for 

age, calendar time, and cohort, was 

conducted to derive silicosis mortality 

rate ratios using the lowest exposure 

group of 0–100 mg/m3-years (0–0.1 mg/ 

m3-year) as the referent group. More 

detailed exploration of the exposureresponse relationship using a variety of 

exposure metrics, including cumulative 

exposure, duration of exposure, average 

exposure (calculated as cumulative 

exposure/duration), and the log 

transformations of these variables, was 

conducted via nested case-control 

analyses (conditional logistic 

regression). Each case was matched to 

100 controls selected from among those 

who had survived to at least the age of 

the case, with additional matching on 

cohort, race, sex, and date of birth 

within 5 years. The authors explored 

lags of 0, 5, 10, 15, and 20 years, noting 

that there is no a priori reason to apply 

an exposure lag, as silicosis can develop 

within a short period after exposure. 

However, a lag could potentially 

improve the model, as there is often a 

considerable delay in the development 

of silicosis following exposure. In 

addition to the parametric conditional 

logistic regression models, the authors 

performed some analyses using a cubicspline model, with knots at 5, 25, 50, 75, 

and 95 percent of the distribution of 

exposure. Models with cohort-exposure 

interaction terms were fit to assess 

heterogeneity between cohorts (OSHA 

2013b, page 294). 

The categorical analysis found a 

nearly monotonic increase in silicosis 

rates with cumulative exposure, from 

4.7 per 100,000 person-years in the 

lowest exposure category (0–990 mg/m3- 

years [0–0.99 mg/m3-years]) to 299 per 

100,000 person-years in the highest 

exposure category (>28,000 mg/m3-years 

[>28 mg/m3-years]). Nested case-control 

analyses showed a significant 

association between silicosis mortality 

and cumulative exposure, average 

exposure, and duration of exposure. The 

best-fitting conditional logistic 

regression model used log-transformed 

cumulative exposure with no exposure 

lag, with a model c2 of 73.2 versus c2


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values ranging from 19.9 to 30.9 for 

average exposure, duration of exposure, 

and untransformed cumulative exposure 

(1 degree of freedom). No significant 

heterogeneity was found between 

individual cohorts for the model based 

on log-cumulative exposure. The cubicspline model did not improve the model 

fit for the parametric logistic regression 

model using the log-cumulative 

exposure (OSHA 2013b, page 294). 

Mannetje et al. (2002b) developed 

estimates of silicosis mortality risk 

through age 65 for two levels of 

exposure (50 and 100 mg/m3 respirable 

crystalline silica), assuming a working 

life of occupational exposure from age 

20 to 65. Risk estimates were calculated 

based on the silicosis mortality rate 

ratios derived from the categorical 

analysis described above. The period of 

time over which workers’ exposures and 

risks were calculated (age 20 to 65) was 

divided into one-year intervals. The 

mortality rate used to calculate risk in 

any given interval was dependent on the 

worker’s cumulative exposure at that 

time. The equation used to calculate risk 

is as follows: 

Where timei is equal to one for every age 

i, and ratei is the age-, calendar time-, 

and cohort adjusted silicosis mortality 

rate associated with the level of 

cumulative exposure acquired at age i, 

as presented in Mannetje et al. (2002b, 

Table 2, page 725). The calculated 

absolute risks equal the excess risks 

since there is no background rate of 

silicosis in the exposed population. 

Mannetje et al. (2002b) estimated the 

lifetime risk of death from silicosis, 

assuming 45 years of exposure to 100 

mg/m3, to be 13 deaths per 1,000 

workers; at an exposure of 50 mg/m3, the 

estimated lifetime risk was 6 per 1,000. 

Confidence intervals (CIs) were not 

reported (OSHA 2013b, page 295). 

In summary, OSHA’s estimates of 

silicosis morbidity risks were based on 

studies of active and retired workers for 

which exposure histories could be 

constructed and chest X-ray films could 

be evaluated for signs of silicosis. There 

is evidence in the record that chest Xray films are relatively insensitive to 

detecting lung fibrosis (OSHA 2016a, 81 

FR 16286, 16397). MSHA agrees with 

OSHA’s estimate of silicosis morbidity 

risks. 

Hnizdo et al. (1993a) found chest Xray films to have low sensitivity for 

detecting lung fibrosis related to initial 

cases of silicosis, compared to 

pathological examination at autopsy. To 

address the low sensitivity of chest Xrays for detecting silicosis, Hnizdo et al. 

(1993a) recommended that radiographs 

consistent with an ILO category of 0/1 

or greater be considered indicative of 

silicosis among workers exposed to a 

high concentration of respirable 

crystalline silica-containing dust. In like 

manner, to maintain high specificity, 

chest X-rays classified as category 1/0 or 

1/1 should be considered as a positive 

diagnosis of silicosis in miners who 

work in low dust (0.2 mg/m3) 

occupations. The studies on which 

OSHA relied in its risk assessment 

typically used an ILO category of 1/0 or 

greater to identify cases of silicosis. 

According to Hnizdo et al. (1993), they 

were unlikely to have included many 

false positives (i.e., assumed diagnosis 

of silicosis in a miner without the 

disease), but may have included false 

negatives (i.e., failure to identify cases of 

silicosis). Thus, in OSHA’s risk 

assessment, the use of chest X-rays to 

ascertain silicosis cases in the morbidity 

studies may have underestimated risk 

given the X-rays’ low sensitivity to 

detect disease. MSHA agrees with 

OSHA’s assessment. 

To estimate the risk of silicosis 

mortality at the existing and proposed 

exposure limits, OSHA used the 

categorical model described by 

Mannetje et al. (2002b) but did not rely 

upon the Poisson regression in their 

study. Instead, OSHA used rate ratios 

estimated from a nested case-control 

design implemented as part of a 

sensitivity analysis (ToxaChemica, 

International, Inc. 2004). The casecontrol design was selected because it 

was expected to better control for age. 

In addition, the rate ratios derived from 

the case control study were derived 

from a Monte Carlo analysis to reflect 

exposure measurement uncertainty (See 

ToxaChemica, International, Inc. (2004), 

Table 7, page 40). The rate ratio for each 

interval of cumulative exposure was 

multiplied by the annual silicosis rate 

assumed to be associated with the 

lowest exposure interval, 4.7 per 

100,000 for exposures of 990 mg/m3- 

years (0.99 mg/m3-years), to estimate the 

silicosis rate for each interval of 

exposure. The lifetime silicosis 

mortality risk is the sum of the silicosis 

rate for each year of life through age 85 

and assuming exposure from age 20 to 

65. From this analysis, OSHA estimated 

the silicosis mortality risk for exposure 

to the then existing general industry 

exposure limit (100 mg/m3) and 

proposed exposure limit (50 mg/m3) to 

be 11 (95% CI 5–37) and 7 (95% CI 3– 

21) deaths per 1,000 workers, 

respectively. For exposure to 250mg/m3

(0.25 mg/m3) and 500 mg/m3 (0.5 mg/ 

m3), the range approximating the then 

existing construction/shipyard exposure 

limit, OSHA estimated the risk to range 

from 17 (95% CI 5–66) to 22 (95% CI 

6–85) deaths per 1,000 workers (OSHA 

2013b, page 294–295). 

In view of the foregoing discussion, 

MSHA agrees with OSHA’s analysis, 

and MSHA also selected the Mannetje et 

al. (2002b) study for estimating silicosis 

mortality risks and cases. MSHA used a 

life table analysis to estimate the 

lifetime excess silicosis mortality 

through age 80. To estimate the agespecific risk of silicosis mortality at the 

existing standards, the proposed PEL, 

and the proposed action level, MSHA 

used the same categorical model that 

OSHA used in their PQRA (as described 

above from Mannetje et al., 2002b; 

ToxaChemica International, Inc. 2004) 

to estimate lifetime risk following 

cumulative exposure of 45 years. MSHA 

used the 2018 all-cause mortality rates 

(NCHS, Underlying Cause of Death, 

2018 on CDC WONDER Online 

Database, released in 2020b) as all-cause 

mortality rates. As stated previously, the 

general (unexposed) population is 

assumed to have silicosis mortality rates 

equal to zero. 

b. NMRD Mortality: Park et al. (2002) 

In addition to causing silicosis, 

exposure to respirable crystalline silica 

causes increased risks of other NMRD. 

These include chronic obstructive 

pulmonary disease (COPD), which 

includes chronic bronchitis, 

emphysema, and combinations of the 

two and is a cause of chronic airways 

obstruction. COPD is characterized by 

airflow limitation that is usually 

progressive and not fully reversible. 

OSHA reviewed several studies of 

NMRD morbidity and used a study by 

Park et al. (2002) to assess NMRD risk. 

Checkoway et al. (1997) originally 

studied a California diatomaceous earth 


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cohort for which Park et al. (2002) then 

analyzed the effect of respirable 

crystalline silica exposures on the 

development of NMRD. The authors 

quantified the relationship between 

exposure to cristobalite and mortality 

from NMRD (OSHA 2013b, page 295). 

The California diatomaceous earth 

cohort consisted of 2,570 diatomaceous 

earth workers employed for 12 months 

or more from 1942 to 1994. As noted 

above, Park et al. (2002) was interested 

in the relationship between cristobalite 

exposure and mortality from chronic 

lung disease other than cancer (LDOC). 

LDOC included chronic diseases such as 

pneumoconiosis (which included 

silicosis), chronic bronchitis, and 

emphysema, but excluded pneumonia 

and other infectious diseases. The 

investigators selected LDOC as the 

health endpoint for three reasons. First, 

increased mortality from LDOC had 

been documented among respirable 

crystalline silica-exposed workers in 

several industry sectors, including gold 

mining, pottery, granite, and foundry 

industries. Second, the authors pointed 

to the likelihood that silicosis as a cause 

of death is often misclassified as 

emphysema or chronic bronchitis. 

Third, the number of deaths from the 

diatomaceous earth worker cohort that 

were attributed to silicosis was too 

small (10) for analysis. Industrial 

hygiene data for the cohort were 

available from the employer for total 

dust, respirable crystalline silica (mostly 

cristobalite), and asbestos. Smoking 

information was available for about 50 

percent of the cohort and for 22 of the 

67 LDOC deaths available for analysis, 

permitting Park et al. (2002) to partially 

adjust for smoking (OSHA 2013b, pages 

295–296). 

Park et al. (2002) used the exposure 

assessment previously reported by 

Seixas et al. (1997) and used by Rice et 

al. (2001) to estimate cumulative 

respirable crystalline silica exposures 

for each worker in the cohort based on 

detailed work history files. The average 

respirable crystalline silica 

concentration for the cohort was 290 mg/ 

m3 (0.29 mg/m3) over the period of 

employment (Seixas et al., 1997). The 

total respirable dust concentration in 

the diatomaceous earth plant was 3,550 

mg/m3 (3.55 mg/m3) before 1949 and 

declined by more than 10-fold after 

1973, to 290 mg/m3 (0.29 mg/m3) (Seixas 

et al., 1997). The concentration of 

respirable crystalline silica in the dust 

ranged from one to 25 percent and was 

dependent on the location within the 

worksite. It was lowest at the mine and 

greatest in the plant where the raw ore 

was calcined into final product. The 

average cumulative exposure values for 

total respirable dust and respirable 

crystalline silica were 7,310 mg/m3-year 

(7.31 mg/m3-year) and 2,160 mg/m3-year 

(2.16 mg/m3-year), respectively. The 

authors also estimated cumulative 

exposure to asbestos (OSHA 2013b, page 

296). 

Using Poisson regression models and 

Cox’s proportional hazards models, the 

authors fit the same series of relative 

rate exposure-response models that 

were evaluated by Rice et al. (2001) for 

lung cancer (i.e., log-linear, log-square 

root, log-quadratic, linear relative rate, a 

power function, and a shape function). 

In general form, the relative rate model 

was: 

Rate = exp(a0) × f(E), 

where exp(a0) is the background rate 

and E is the cumulative respirable 

crystalline silica exposure. Park et al. 

(2002) also employed an additive excess 

rate model of the form: 

Rate = exp(a0) + exp(aE). 

Relative or excess rates were modeled 

using internal controls and adjusting for 

age, calendar time, ethnicity, and time 

since first entry into the cohort. In 

addition, relative rate models were 

evaluated using age- and calendar timeadjusted external standardization to 

U.S. population mortality rates for 1940 

to 1994 (OSHA 2013b, page 296). 

There were no LDOC deaths recorded 

among workers having cumulative 

exposures above 32,000 mg/m3-years (32 

mg/m3-years), causing the response to 

level off or decline in the highest 

exposure range. The authors believed 

the most likely explanation for this 

observation (which was also observed in 

their analysis of silicosis morbidity in 

this cohort) was some form of survivor 

selection, possibly smokers or others 

with compromised respiratory function 

leaving work involving extremely high 

dust concentrations. These authors 

suggested several alternative 

explanations. First, there may have been 

a greater depletion of susceptible 

populations in high dust areas. Second, 

there may have been greater 

misclassification of exposures in the 

earlier years where exposure data were 

lacking (and when exposures were 

presumably the highest) (OSHA 2013b, 

pages 296–297). 

Therefore, Park et al. (2002) 

performed exposure-response analyses 

that restricted the dataset to 

observations where cumulative 

exposures were below 10,000 mg/m3- 

years (10 mg/m3-years). This is a level 

more than four times higher than that 

resulting from 45 years of exposure to 

the former OSHA PEL for cristobalite 

(which was 50 mg/m3 (0.05 mg/m3) 

when cristobalite was the only 

polymorph present). These investigators 

also conducted analyses using the full 

dataset (OSHA 2013b, page 297). 

Model fit was assessed by evaluating 

the decrease in deviance resulting from 

addition of the exposure term, and 

cubic-spline models were used to test 

for smooth departures from each of the 

model forms described. Park et al. 

(2002) found that both lagged and 

unlagged models fit well, but unlagged 

models provided a better fit. In addition, 

they believed that unlagged models 

were biologically plausible in that 

recent exposure could contribute to 

LDOC mortality. The Cox proportional 

hazards models yielded results that 

were similar to those from the Poisson 

analysis. Consequently, only the results 

from the Poisson analysis were reported. 

In general, the use of external 

adjustments for age and calendar time 

yielded considerably improved fit over 

models using internal adjustments. The 

additive excess rate model also proved 

to be clearly inferior compared to the 

relative rate models. With one 

exception, the use of cumulative 

exposure as the exposure metric 

consistently provided better fits to the 

data than did intensity of exposure (i.e., 

cumulative exposure divided by 

duration of exposure). As to the 

exception, when the highest-exposure 

cohort members were included in the 

analysis, the log-linear model produced 

a significantly improved fit with 

exposure intensity as the exposure 

metric, but a poor fit with cumulative 

exposure as the metric (OSHA 2013b, 

page 297). 

Among the models based on the 

restricted dataset (excluding 

observations with cumulative exposures 

greater than 10,000 mg/m3-years (10 mg/ 

m3-years)), the best-fitting model with a 

single exposure term was the linear 

relative rate model using external 

adjustment. Most of the other singleterm models using external adjustment 

fit almost as well. Of the models with 

more than one exposure term, the shape 

model provided no improvement in fit 

compared with the linear relative rate 

model. The log-quadratic model fit 

slightly better than the linear relative 

rate model, but Park et al. (2002) did not 

consider the gain in fit sufficient to 

justify an additional exposure term in 

the model (OSHA 2013b, page 297). 

Based on its superior fit to the cohort 

data, Park et al. (2002) selected the 

linear relative rate model with external 

adjustment and use of cumulative 

exposure as the basis for estimating 

LDOC mortality risks among exposed 

workers. Competing mortality was 

accounted for using U.S. death rates 

published by the National Center for 


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Health Statistics (1996). The authors 

estimated the lifetime excess risk for 

white men exposed to respirable 

crystalline silica (mainly cristobalite) for 

45 years at 50 mg/m3 (0.05 mg/m3) to be 

54 deaths per 1,000 workers (95% CI: 

17–150) using the restricted dataset, and 

50 deaths per 1,000 using the full 

dataset. For exposure to 100 mg/m3 (0.1 

mg/m3), they estimated 100 deaths per 

1,000 using the restricted dataset, and 

86 deaths per 1,000 using the full 

dataset. The CIs were not reported 

(OSHA 2013b, page 297). 

The estimates of Park et al. (2002) 

were about eight to nine times higher 

than those that were calculated for the 

pooled analysis of silicosis mortality 

(Mannetje et al., 2002b). Also, these 

estimates are not directly comparable to 

those from Mannetje et al. (2002b) 

because the mortality endpoint for the 

Park et al. (2002) analysis was death 

from all non-cancer lung diseases 

beyond silicosis (including 

pneumoconiosis, emphysema, and 

chronic bronchitis). In the pooled 

analysis by Mannetje et al. (2002b), only 

deaths coded as silicosis or other 

pneumoconiosis were included (OSHA 

2013b, pages 297–298). 

Less than 25 percent of the LDOC 

deaths in the Park et al. (2002) analysis 

were coded as silicosis or other 

pneumoconiosis (15 of 67). As noted by 

Park et al. (2002), it is likely that 

silicosis as a cause of death is often 

misclassified as emphysema or chronic 

bronchitis (although COPD is part of the 

spectrum of disease caused by 

respirable crystalline silica exposure 

and can occur in the absence of 

silicosis). Thus, the selection of deaths 

by Mannetje et al. (2002b) may have 

underestimated the true risk of silicosis 

mortality. The analysis by Park et al. 

(2002) would have more fairly captured 

the total respiratory mortality risk from 

all non-malignant causes, including 

silicosis and chronic obstructive 

pulmonary disease. Furthermore, Park 

et al. (2002) used untransformed 

cumulative exposure in a linear model 

compared to the log-transformed 

cumulative exposure metric used by 

Mannetje et al. (2002b). This would 

have caused the exposure-response 

relationship to flatten in the higher 

exposure ranges (OSHA 2013b, page 

298). 

It is also possible that some of the 

difference between Mannetje et al.’s 

(2002b) and Park et al.’s (2002) risk 

estimates reflected factors specific to the 

nature of exposure among diatomaceous 

earth workers (e.g., exposure to 

cristobalite vs. quartz). However, neither 

the cancer risk assessments nor 

assessments of silicosis morbidity 

supported the hypothesis that 

cristobalite is more hazardous than 

quartz (OSHA 2013b, page 298). 

Based on the available risk 

assessments for silicosis mortality, 

OSHA believed that the estimates from 

the pooled study by Mannetje et al.’s 

(2002b) represented those least likely to 

overestimate mortality risk. It was 

unlikely to have overstated silicosis 

mortality risks given that the estimates 

reflected only those deaths where 

silicosis was specifically identified on 

death certificates. Therefore, there was 

most likely an underestimate of the true 

silicosis mortality risk. In contrast, the 

risk estimates provided by Park et al. 

(2002) for the diatomaceous earth cohort 

would have captured some of this 

misclassification and included risks 

from other lung diseases (e.g., 

emphysema, chronic bronchitis) that 

have been associated with respirable 

crystalline silica exposure. Therefore, 

OSHA believed that the Park et al. 

(2002) study provided a better basis for 

estimating the respirable crystalline 

silica-related risk of NMRD mortality, 

including that from silicosis. Based on 

Park et al.’s (2002) linear relative rate 

model [RR = 1 + bx, where b = 0.5469 

(no standard error reported) and x = 

cumulative exposure], OSHA used a life 

table analysis to estimate the lifetime 

excess NMRD mortality through age 85. 

For this analysis, OSHA used all-cause 

and cause-specific background mortality 

rates for all males (National Center for 

Health Statistics, 2009). Background 

rates for NMRD mortality were based on 

rates for ICD–10 codes J40–J47 (chronic 

lower respiratory disease) and J60–J66 

(pneumoconiosis). OSHA believed that 

these corresponded closely to the ICD– 

9 disease classes (ICD 490–519) used by 

the original investigators. According to 

CDC (2001), background rates for 

chronic lower respiratory diseases were 

increased by less than five percent 

because of the reclassification to ICD– 

10. From the life table analysis, OSHA 

estimated that the excess NMRD risk 

due to respirable crystalline silica 

exposure at the former general industry 

PEL (100 mg/m3) and at OSHA’s final 

PEL (50 mg/m3) for 45 years are 83 and 

43 deaths per 1,000, respectively. For 

exposure at the former construction/ 

shipyard exposure limit, OSHA 

estimated that the excess NMRD risk 

ranged from 188 to 321 deaths per 1,000 

(OSHA 2013b, page 298). 

Following its own independent 

review, MSHA agrees with and has 

followed the rationale presented by 

OSHA in its selection of the Park et al. 

(2002) model to estimate NMRD 

mortality risk in miners. Coal miners 

were not included in the NMRD 

mortality analysis because the endpoint 

was included in the Quantitative Risk 

Assessment in Support of the Final 

Respirable Coal Mine Dust Rule (Dec. 

2013). 

MSHA used a life table analysis to 

estimate the lifetime excess NMRD 

mortality through age 80. MSHA used 

the Park et al. (2002) model to estimate 

age-specific NMRD mortality risk as 1 + 

0.5469 * cumulative exposure. MSHA 

used all-cause and cause-specific 

background mortality rates for all males 

for 2018 (National Center for Health 

Statistics, Underlying Cause of Death 

2018 on CDC WONDER Online 

Database, released in 2020b). 

Background rates for NMRD mortality 

were based on rates for ICD–10 codes 

J40–J47 (chronic lower respiratory 

disease) and J60–J66 (pneumoconiosis). 

4. Lung Cancer Mortality 

Since the publication of OSHA’s final 

rule in 2016, NIOSH has published two 

documents concerning occupational 

carcinogens, Chemical Carcinogen 

Policy (2017b) and Practices in 

Occupational Risk Assessment (2019a). 

NIOSH will no longer set recommended 

exposure levels for occupational 

carcinogens. Instead, NIOSH intends to 

develop risk management limits for 

carcinogens (RML-Cas) to acknowledge 

that, for most carcinogens, there is no 

known safe level of exposure. An RML– 

CA is a reasonable starting place for 

controlling exposures. An RML–CA 

limit is based on a daily maximum 8- 

hour TWA concentration of a 

carcinogen above which a worker 

should not be exposed (NIOSH 2017b, 

page vi). RML-Cas for occupational 

carcinogens are established at the 

estimated 95% lower confidence limit 

on the concentration (e.g., dose) 

corresponding to 1 in 10,000 (10¥4) 

lifetime excess risk (when analytically 

possible to measure) (NIOSH 2019a). 

NIOSH stated that in order to 

incrementally move toward a level of 

exposure to occupational chemical 

carcinogens that is closer to background, 

NIOSH will begin issuing 

recommendations for RML-Cas that 

would advise employers to take 

additional action to control chemical 

carcinogens when workplace exposures 

result in excess risks greater than 10¥4

(NIOSH 2017b, page vi). 

MSHA used the Miller et al. (2007) 

and Miller and MacCalman (2010) 

studies to estimate lung cancer mortality 

risk in miners. In British coal miners, 

excess lung cancer mortality was 

studied through the end of 2005 in a 

cohort of 17,800 miners (Miller et al., 

2007; Miller and MacCalman, 2010). By 

that time, the cohort had accumulated 


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516,431 person-years of observation (an 

average of 29 years per miner), with 

10,698 deaths from all causes. Overall 

lung cancer mortality was elevated 

(Standard Mortality Ratio (SMR) = 

115.7, 95% CI: 104.8–127.7), and a 

positive exposure-response relationship 

with respirable crystalline silica 

exposure was determined from Cox 

regression after adjusting for smoking 

history. Three strengths of this study 

were: 1) the detailed time-exposure 

measurements of quartz and total mine 

dust, 2) detailed individual work 

histories, and 3) individual smoking 

histories. For lung cancer, analyses 

based on Cox regression provided strong 

evidence that, for these coal miners, 

although quartz exposures were 

associated with increased lung cancer 

risk, simultaneous exposures to coal 

dust did not cause increased lung 

cancer risk (OSHA 2016a, 81 FR 16286, 

16308). 

Miller et al. (2007) and Miller and 

MacCalman (2010) conducted a followup study of cohort mortality, begun in 

1970. Their previous report on mortality 

presented a follow-up analysis on 

18,166 coal miners from 10 British coal 

mines followed through the end of 1992 

(Miller et al., 1997). The two reports 

from 2007 and 2010 analyzed the 

mortality experience of 17,800 of these 

miners (18,166 minus 346 men whose 

vital status could not be determined) 

and extended the analysis through the 

end of 2005. Causes of deaths that were 

of particular interest included 

pneumoconiosis, other NMRD, lung 

cancer, stomach cancer, and 

tuberculosis. The researchers noted that 

no additional exposure measurements 

were included in the updated analysis, 

since all the mines had closed by the 

mid-1980s. However, some of these men 

might have had additional exposure at 

other mines or facilities not reported in 

this study (OSHA 2013b, page 287). 

This cohort mortality study included 

analyses using both external and 

internal controls. The external controls 

used British administrative regional 

age-, time-, and cause-specific mortality 

rates from which to calculate SMRs. The 

internal controls from the mines used 

Cox proportional hazards regression 

methods, which considered each 

miner’s age, smoking status, and 

detailed dust and respirable crystalline 

silica (quartz) time-dependent exposure 

measurements. Cox regression analyses 

were done in stages, with the initial 

analyses used to establish what factors 

were required for baseline adjustment 

(OSHA 2013b, page 287). 

For the analysis using external 

mortality rates, the all-cause mortality 

SMR from 1959 through 2005 was 100.9 

(95% CI: 99.0–102.8), based on all 

10,698 deaths. However, these SMRs 

were not uniform over time. For the 

period from 1990–2005, the SMR was 

109.6 (95% CI:106.5–112.8), while the 

ratios for previous periods were less 

than 100. This pattern of increasing 

SMRs in the recent past was also seen 

for cause-specific deaths from chronic 

bronchitis, SMR = 330.0 (95% CI:268.1– 

406.2); tuberculosis, SMR = 193.4 (95% 

CI: 86.9–430.5); cardiovascular disease, 

SMR = 106.6 (95% CI: 102.0–111.5); all 

cancers, SMR = 107.1 (95% CI:101.3– 

113.2); and lung cancer, SMR = 115.7 

(95% CI: 104.8–127.7). The SMR for 

NMRD was 142.1 (95% CI: 132.9–152.0) 

in this recent period and remained 

highly statistically significant. In their 

previous analysis on mortality from 

lung cancer, reflecting follow-up 

through 1995, Miller et al. (1997) had 

not found any increase in the risk of 

lung cancer mortality (OSHA 2013b, 

page 287). 

OSHA reported that Miller and 

MacCalman (2010) used these analyses 

to estimate relative risks for a lifetime 

exposure of 5 gram-hours/m3 (ghm¥3) to 

quartz (OSHA 2013b, page 288). This is 

equivalent to approximately 55 mg/m3

(0.055 mg/m3) for 45 years, assuming 

2,000 hours per year of exposure and/ 

or 100 ghm¥3 total dust. The authors 

estimated relative risks (see Miller and 

MacCalman (2010), Table 4, page 9) for 

various causes of death including 

pneumoconiosis, COPD, ischemic heart 

disease, lung cancer, and stomach 

cancer. Their results were based on 

models with single exposures to dust or 

respirable crystalline silica (quartz) or 

simultaneous exposures to both, with 

and without 15-year lag periods. 

Generally, the risk estimates were 

slightly greater using a 15-year lag 

period. 

For the models using only quartz 

exposures with a 15-year lag, 

pneumoconiosis, RR = 1.21 (95% CI: 

1.12–1.31); COPD, RR = 1.11 (95% CI: 

1.05–1.16); and lung cancer, RR = 1.07 

(95% CI: 1.01–1.13) showed statistically 

significant increased risks. 

For lung cancer, analyses based on 

these Cox regression methods provided 

strong evidence that, for these coal 

miners, quartz exposures were 

associated with increased lung cancer 

risk, but simultaneous exposures to coal 

dust were not associated with increased 

lung cancer risk. The relative risk (RR) 

estimate for lung cancer deaths using 

coal dust with a 15-year lag in the single 

exposure model was 1.03 (95% CI: 0.96 

to 1.10). In the model using both quartz 

and coal mine dust exposures, the RR 

based on coal dust decreased to 0.91, 

while that for quartz exposure remained 

statistically significant, increasing to a 

RR = 1.14 (95% CI: 1.04 to 1.25). 

According to Miller and MacCalman 

(2010), other analyses have shown that 

exposure to radon or diesel fumes was 

not associated with an increased cancer 

risk among British coal miners (OSHA 

2013b, page 288). 

The RRs in the Miller and MacCalman 

(2010) report were used to estimate 

excess lung cancer risk for OSHA’s 

purposes. Life table analyses were done 

as in the other studies above. Based on 

the RR of 1.14 (95% CI: 1.04–1.25) for 

a cumulative exposure of 5 ghm10¥3, 

the regression slope was recalculated as 

b = 0.0524 per 1,000 mg-years (per mg/ 

m3-years) and used in the life table 

program. Similarly, the 95-percent CI on 

the slope was 0.0157–0.08926. From 

this study, the lifetime (to age 85) risk 

estimates for 45 years of exposure to 50 

mg/m3 (0.05 mg/m3) and 100 mg/m3

(0.100 mg/m3) respirable crystalline 

silica were 6 and 13 excess lung cancer 

deaths per 1,000 workers, respectively. 

These lung cancer risk estimates were 

less by about 2- to 4-fold than those 

estimated from the other cohort studies 

described above. 

However, three factors might explain 

these differences. First, these estimates 

were adjusted for individual smoking 

histories so any smoking-related lung 

cancer risk (or smoking–respirable 

crystalline silica interaction) that might 

possibly be attributed to respirable 

crystalline silica exposure in the other 

studies were not reflected in the risk 

estimates derived from the study of 

these coal miners. Second, these coal 

miners had significantly increased risks 

of death from other lung diseases, which 

may have decreased the lung cancersusceptible population. Of note, for 

example, were the higher increased 

SMRs for NMRD during the years 1959– 

2005 for this cohort (Miller and 

MacCalman, 2010, Table 2, Page 7). 

Third, the difference in risk seen in 

these coal miners may have been the 

result of differences in the toxicity of 

quartz present in the coal mines as 

compared to the work environments of 

the other cohorts. One Scottish mine 

(Miller et al., 1998) in this 10-mine 

study had been cited as having 

presented ‘‘unusually high exposures to 

[freshly fractured] quartz.’’ However, 

this was also described as an atypical 

exposure among miners working in the 

10 mines. Miller and MacCalman (2010) 

stated that increased quartz-related lung 

cancer risk in their cohort was not 

confined to that Scottish mine alone. 

They also stated, ‘‘The general nature of 

some quartz exposures in later years 

. . . may have been different from 

earlier periods when coal extraction was 


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largely manual . . .’’ (OSHA 2013b, 

page 288). 

All these factors in this mortality 

analysis for the British coal miner 

cohort could have combined to yield 

lower lung cancer risk estimates. 

However, OSHA believed that these coal 

miner-derived estimates were credible 

because of the quality of several study 

factors relating to both study design and 

conduct. In terms of design, the cohort 

was based on union rolls with very good 

participation rates and good reporting. 

The study group also included over 

17,000 miners, with an average of nearly 

30 years of follow-up, and about 60 

percent of the cohort had died. Just as 

important was the high quality and 

detail of the exposure measurements, 

both of total dust and quartz. However, 

one exposure factor that may have 

biased the estimates upward was the 

lack of exposure information available 

for the cohort after the mines closed in 

the mid-1980s. Since the death ratio for 

lung cancer was higher during the last 

study period, 1990–2005, this period 

contributed to the increased lung cancer 

risk. It is possible that any quartz 

exposure experienced by the cohort 

after the mines had closed could have 

accelerated either death or malignant 

tumor (lung cancer) growth. By not 

accounting for this exposure, if there 

were any, the risk estimates would have 

been biased upwards. Although the 15- 

year lag period for quartz exposure used 

in the analyses provided slightly higher 

risk estimates than use of no lag period, 

the better fit seen with the lag may have 

been artificial. This may have occurred 

since there appeared to have been no 

exposures during the recent period 

when risks were seen to have increased 

(OSHA 2013b, page 289). 

OSHA believed, as does MSHA, that 

this study of a large British coal mining 

cohort provided convincing evidence of 

the carcinogenicity of respirable 

crystalline silica. This large cohort 

study, with almost 30 years of followup, demonstrated a positive exposureresponse after adjusting for smoking 

histories. Additionally, the authors state 

that there was no evidence that 

exposure to potential confounders such 

as radon and diesel exhaust were 

associated with excess lung cancer risk 

(Miller and MacCalman (2010), page 

270). MSHA is relying on the British 

studies conducted by Miller et al. (2007) 

as well as Miller and MacCalman (2010) 

to estimate the lung cancer risk in all 

miners. 

MSHA found these two studies 

suitable for use in the quantitative 

characterization of health risks to 

exposed miners for several reasons. 

First, their study populations were of 

sufficient size to provide adequate 

statistical power to detect low levels of 

risk. Second, sufficient quantitative 

exposure data were available over a 

sufficient span of time to characterize 

cumulative respirable crystalline silica 

exposures of cohort members. Third, the 

studies either adjusted for or otherwise 

adequately addressed confounders such 

as smoking and exposure to other 

carcinogens. Finally, these investigators 

developed quantitative assessments of 

exposure-response relationships using 

appropriate statistical models or 

otherwise provided sufficient 

information that permits MSHA to do 

so. 

MSHA implemented the risk model in 

its life table analysis so that the use of 

background rates of lung cancer and 

assumptions regarding length of 

exposure and lifetime were consistent 

across models. Thus, MSHA was able to 

estimate lung cancer risks associated 

with exposure to specific levels of 

respirable crystalline silica of interest to 

the Agency. MSHA used the Miller et al. 

(2007) and Miller and MacCalman 

(2010) model to estimate age-specific 

cumulative lung cancer mortality risk as 

EXP(0.0524 * cumulative exposure), 

lagged 15 years. 

MSHA’s PRA uses risk estimates 

derived from 10 coal mines in the U.K. 

(Miller et al., 2007; Miller and 

MacCalman, 2010). These investigators 

developed regression analyses for timedependent estimates of individual 

exposures to respirable dust. Their 

analyses were based on the detailed 

individual exposure estimates of the 

PFR programme. To estimate mortality 

risk for lung cancer from the pooled 

cohort analysis, MSHA used the same 

life table approach as OSHA. However, 

for this life table analysis, MSHA used 

2018 mortality rates for U.S. males (i.e., 

all-cause and background lung cancer). 

The 2018 lung cancer death rates were 

based on the ICD–10 classification of 

diseases, C34.0, C34.2, C34.1, C34.3, 

C34.8, and C34.9. Lifetime risk 

estimates reflected excess risk through 

age 80. To estimate lung cancer risks, 

MSHA used the log-linear relative risk 

model, exp(0.0524 × cumulative 

exposure), lagged 15 years. The 

coefficient for this model was 0.0524 

(OSHA 2013b, page 290). 

5. ESRD Mortality 

Several epidemiological studies have 

found statistically significant 

associations between occupational 

exposure to respirable crystalline silica 

and renal disease, although others have 

failed to find a statistically significant 

association. These studies are discussed 

in the Health Effects document. Possible 

mechanisms suggested for respirable 

crystalline silica-induced renal disease 

included a direct toxic effect on the 

kidney, deposition of immune 

complexes (IgA) in the kidney following 

respirable crystalline silica-related 

pulmonary inflammation, and an 

autoimmune mechanism (Gregorini et 

al., 1993; Calvert et al., 1997; Parks et 

al., 1999; Steenland 2005b) (OSHA 

2016a, 81 FR 16286, 16310). 

MSHA, like OSHA, chose the 

Steenland et al. (2002a) study to include 

in the PRA. In a pooled cohort analysis, 

Steenland et al. (2002a) combined the 

industrial sand cohort from Steenland et 

al. (2001b), the gold mining cohort from 

Steenland and Brown (1995a), and the 

Vermont granite cohort studies by 

Costello and Graham (1988). All three 

were included in portions of OSHA’s 

PQRA for other health endpoints: under 

lung cancer mortality in Steenland et al. 

(2001a) and under silicosis mortality in 

the related work of Mannetje et al. 

(2002b). In all, the combined cohort 

consisted of 13,382 workers with 

exposure information available for 

12,783. The analysis demonstrated 

statistically significant exposureresponse trends for acute and chronic 

renal disease mortality with quartiles of 

cumulative respirable crystalline silica 

exposure (OSHA 2016a, 81 FR 16286, 

16310). 

The average duration of exposure, 

cumulative exposure, and concentration 

of respirable crystalline silica for the 

pooled cohort were 13.6 years, 1,200 mg/ 

m3-years (1.2 mg/m3-years), and 70 mg/ 

m3 (0.07 mg/m3), respectively. Renal 

disease risk was most prevalent among 

workers with cumulative exposures of 

500 mg/m3 or more (Steenland et al., 

2002a). SMRs (compared to the U.S. 

population) for renal disease (acute and 

chronic glomerulonephritis, nephrotic 

syndrome, acute and chronic renal 

failure, renal sclerosis, and nephritis/ 

nephropathy) were statistically 

significant and elevated based on 

multiple cause of death data (SMR 1.28, 

95% CI: 1.10–1.47, 194 deaths) and 

underlying cause of death data (SMR 

1.41, 95% CI: 1.05–1.85, 51 observed 

deaths) (OSHA 2013b, page 315). 

A nested case-control analysis was 

also performed which allowed for more 

detailed examination of exposureresponse. This analysis included 95 

percent of the cohort for which there 

were adequate work history and quartz 

exposure data. This analysis included 

50 cases for underlying cause mortality 

and 194 cases for multiple-cause 

mortality. Each case was matched by 

race, sex, and age within 5 years to 100 

controls from the cohort. Exposureresponse trends were examined in a 


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categorical analysis where renal disease 

mortality of the cohort divided by 

exposure quartile was compared to U.S. 

rates (OSHA 2013b, page 315). 

In this analysis, statistically 

significant exposure-response trends for 

SMRs were observed for multiple-cause 

(p < 0.000001) and underlying cause (p 

= 0.0007) mortality (Steenland et al., 

2002a; Table 1; Page 7). 

With the lowest exposure quartile 

group serving as a referent, the casecontrol analysis showed monotonic 

trends in mortality with increasing 

cumulative exposure. Conditional 

regression models using log-cumulative 

exposure fit the data better than 

cumulative exposure (with or without a 

15-year lag) or average exposure. Odds 

ratios by quartile of cumulative 

exposure were 1.00, 1.24, 1.77, and 2.86 

(p = 0.0002) for multiple cause analyses 

and 1.00, 1.99, 1.96, and 3.93 for 

underlying cause analyses (p = 0.03) 

(Steenland et al., 2002a; Table 2; Page 

7). For multiple-cause mortality, the 

exposure-response trend was 

statistically significant for cumulative 

exposure (p = 0.004) and log-cumulative 

exposure (p = 0.0002), whereas for 

underlying cause mortality, the trend 

was statistically significant only for logcumulative exposure (p = 0.03). The 

exposure-response trend was 

homogeneous across the three cohorts 

and interaction terms did not improve 

model fit (OSHA 2013b, pages 216, 315). 

Based on the exposure-response 

coefficient for the model with the log of 

cumulative exposure, Steenland (2005) 

estimated lifetime excess risks of death 

(age 75) over a working life (age 20 to 

65). At 100 mg/m3 (0.1 mg/m3) respirable 

crystalline silica, this risk was 5.1 

percent (95% CI 3.3–7.3) for ESRD 

based on 23 cases (Steenland et al., 

2001b). It was 1.8 percent (95% CI 0.8– 

9.7) for kidney disease mortality 

(underlying), based on 51 deaths 

(Steenland et al., 2002a) above a 

background risk of 0.3 percent (OSHA 

2013b, page 216). 

MSHA notes that these studies added 

to the evidence that renal disease is 

associated with respirable crystalline 

silica exposure. Statistically significant 

increases in odds ratios and SMRs were 

seen primarily for cumulative exposures 

of >500 mg/m3-years (0.5 mg/m3-years). 

Steenland (2005b) noted that this could 

have occurred from working for 5 years 

at an exposure level of 100 mg/m3 (0.1 

mg/m3) or 10 years at 50 mg/m3 (0.05 

mg/m3). 

OSHA had a large body of evidence, 

particularly from the three-cohort 

pooled analysis (Steenland et al., 

2002a), on which to conclude that 

respirable crystalline silica exposure 

increased the risk of renal disease 

mortality and morbidity. The pooled 

analysis by Steenland et al. (2002a) 

involved a large number of workers 

from three cohorts with welldocumented, validated job-exposure 

matrices. These investigators found a 

positive, monotonic increase in renal 

disease risk with increasing exposure 

for underlying and multiple cause data. 

Thus, the exposure and work history 

data were unlikely to have been 

seriously misclassified. However, there 

are considerably less data available for 

renal disease than there are for silicosis 

mortality and lung cancer mortality. 

Nevertheless, OSHA concluded that the 

underlying data were sufficient to 

provide useful estimates of risk and 

included the Steenland et al. (2002a) 

analysis in its PQRA (OSHA 2013b, 

pages 229, 316). 

To estimate renal disease mortality 

risk from the pooled cohort analysis, 

OSHA implemented the same life table 

approach as was done for the 

assessments on lung cancer and NMRD. 

However, for this life table analysis, 

OSHA used 1998 all-cause and 

background renal mortality rates for 

U.S. males, rather than the 2006 rates 

used for lung cancer and NMRD. The 

1998 rates were based on the ICD–9 

classification of diseases, which was the 

same as used by Steenland et al. (2002a) 

to ascertain the cause of death of 

workers in their study. However, U.S. 

cause-of-death data from 1999 to present 

are based on the ICD–10, in which there 

were considerable changes in the 

classification system for renal diseases. 

According to CDC (2001), the change in 

the classification from ICD–9 to ICD–10 

increased death rates for nephritis, 

nephritic syndrome, and nephrosis by 

23 percent, in large part due to 

reclassifying ESRD. The change from 

ICD–9 to ICD–10 did not materially 

affect background rates for those 

diseases grouped as lung cancer or 

NMRD. Consequently, OSHA conducted 

its analysis of excess renal disease 

mortality associated with respirable 

crystalline silica exposure using 

background mortality rates for 1998. As 

before, lifetime risk estimates reflected 

excess risk through age 85. To estimate 

renal mortality risks, OSHA used the 

log-linear model with log-cumulative 

exposure that provided the best fit to the 

pooled cohort data (Steenland et al., 

2002a). The coefficient for this model 

was 0.269 (SE = 0.120) (OSHA 2013b, 

page 316). Based on the life table 

analysis, OSHA estimated that exposure 

to the former general industry exposure 

limit of 100 mg/m3 and to the final 

exposure limit of 50 mg/m3 over a 

working life would result in a lifetime 

excess renal disease risk of 39 (95% CI: 

2–200) and 32 (95% CI: 1.7–147) deaths 

per 1,000, respectively. OSHA also 

estimated lifetime risks associated with 

the former construction and shipyard 

exposure limits of 250 and 500 mg/m3. 

These lifetime excess risks ranged from 

52 (95% CI 2.2–289) to 63 (95% CI 2.5– 

368) deaths per 1,000 workers (OSHA 

2013b, page 316). 

MSHA concludes that the evidence 

supporting causality regarding renal risk 

outweighs the evidence casting doubt 

on that conclusion. However, MSHA 

acknowledges the uncertainty 

associated with the divergent findings 

in the renal disease literature. To 

estimate renal disease mortality risk 

from the pooled cohort analysis, MSHA 

implemented the same life table 

approach as OSHA. However, MSHA’s 

life table analysis used 2018 all-cause 

and 1998 background renal mortality 

rates for U.S. males. The 1998 renal 

death rates were based on the ICD–9 

classification of diseases, 580–589. This 

is the same classification used by 

Steenland et al. (2002a) to ascertain the 

cause of death of workers in their study. 

Consequently, MSHA conducted its 

analysis of excess ESRD mortality 

associated with exposure to respirable 

crystalline silica using background 

mortality rates for 1998. The U.S. causeof-death data from 2018 were used as 

well. Lifetime risk estimates reflect 

excess risk through age 85. To estimate 

ESRD mortality risks, MSHA used the 

log-linear model with log-cumulative 

exposure that provided the best fit to the 

pooled cohort data (Steenland et al., 

2002a), as EXP(0.269 * ln (cumulative 

exposure)). The coefficient for this 

model was 0.269 (SE = 0.120) (OSHA 

2013b, page 316). 

6. Coal Workers’ Pneumoconiosis (CWP) 

Exposure to respirable coal mine dust 

causes lung diseases including CWP, 

emphysema, silicosis, and chronic 

bronchitis, known collectively as ‘‘black 

lung.’’ These diseases are debilitating, 

incurable, and can result in disability 

and premature death. There are no 

specific treatments to cure CWP or 

COPD. These chronic effects may 

progress even after miners are no longer 

exposed to coal dust. 

MSHA’s 2014 coal dust rule 

quantified benefits among coal miners 

related to reduced cases of CWP due to 

lower exposure limits for respirable coal 

mine dust. In this PRA, MSHA has not 

quantified the reduction in risk 

associated with CWP among coal 

miners. Nonetheless, MSHA believes 

that the proposed rule would reduce the 

excess risk of this disease. Many coal 


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miners work extended shifts, thus 

increasing their potential exposure to 

respirable crystalline silica. The result 

of calculating exposures based on a fullshift 8-hour TWA would be more 

protective. Thus, the proposed rule is 

expected to provide additional 

reductions in CWP risk beyond those 

ascribed in the 2014 coal dust rule. 

However, exposure-response 

relationships based on respirable 

crystalline silica exposure are not 

available for CWP, so the reductions in 

this disease due to reductions in silica 

exposure cannot be quantified. 

D. Overview of Results 

Table VI–4 summarizes the PRA’s 

main results: once it is fully effective 

(and all miners have been exposed only 

under the proposed PEL), the proposed 

rule is expected to result in at least 799 

avoided deaths and 2,809 avoided cases 

of silicosis morbidity among the 

working miner population. These 

numbers represent the lifetime health 

outcomes expected to occur after both 

45 years of employment under the 

proposed PEL (from 21 through 65 years 

of age) and 15 years of retirement (up to 

80 years of age). These estimates of the 

avoided lifetime excess mortality and 

morbidity represent the final 

calculations based on the 5 selected 

models and the observed exposure data. 

The first group of miners that would 

experience the avoided lifetime 

fatalities and illnesses shown in Table 

VI–4 is the population living 60 years 

after promulgation of the proposed rule. 

In other words, this group would only 

contain miners exposed under the 

proposed rule. To calculate benefits 

associated with the proposed 

rulemaking, the economic analysis 

monetizes avoided deaths and illnesses 

while accounting for the fact that, 

during the first 60 years following 

promulgation, miners would have fewer 

avoided lifetime fatalities and illnesses 

because they would be exposed under 

both the existing standards and the 

proposed PEL. 

Table VI–5 summarizes miners’ 

expected percentage reductions in 

lifetime excess risk of developing or 

dying from certain diseases due to their 

reduced respirable crystalline silica 

exposure expected to result from 

implementation of the proposed rule. 

The lifetime excess risk reflects the 

probability of developing or dying from 

diseases over a maximum lifetime of 45 

years of exposure during employment 

and 15 years of retirement. The excess 

risk reduction compares (a) miners’ 

excess health risks associated with 

respirable crystalline silica exposure at 

the limits included in MSHA’s existing 

standards to (b) miners’ excess health 

risks associated with exposure at this 

standard’s proposed PEL. MSHA 

expects full-scale implementation to 

reduce lifetime excess mortality risk by 

9.5 percent and to reduce lifetime 

excess silicosis morbidity risk by 41.9 

percent. Excess mortality risk includes 

the excess risk of death due to silicosis, 

NMRD, lung cancer, and ESRD. 


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21The FTE ratios used in these calculations are 

a weighted average of the FTE ratio for production 

employees and the FTE ratio for contract miners. 

BILLING CODE 4520–43–P 

Table VI–6 presents MSHA’s 

estimates of lifetime excess risk per 

1,000 miners at exposure levels equal to 

the existing standards, the proposed 

PEL, and the proposed action level. 

These estimates are adjusted for FTE 

ratios and thus utilize cumulative 

exposures that more closely reflect the 

average hours worked per year.21 For an 

MNM miner who is presently exposed 

at the existing PEL of 100 mg/m3 (and 

given the weighted average FTE ratio of 

0.87), implementing the proposed PEL 

would lower the miner’s lifetime excess 

risk of death by 58.8 percent for 

silicosis, 45.6 percent for NMRD (not 

including silicosis), 52.0 percent for 

lung cancer, and 19.9 percent for ESRD. 

The MNM miner’s risk of acquiring a 

non-fatal case of silicosis (would 

decrease by 80.4 percent). 

For a coal miner who is currently 

exposed at the existing exposure limit of 

85.7 mg/m3 (and given the weighted 

average FTE ratio of 0.99), 

implementing the proposed PEL would 

lower the miner’s lifetime excess risk of 

death by 42.3 percent for silicosis 

mortality, 40.2 percent for NMRD 

mortality (not including silicosis), 43.5 

percent for lung cancer mortality, and 

15.8 percent for ESRD mortality. The 

coal miner’s lifetime excess risk of 

acquiring non-fatal silicosis would 

decrease by 73.8 percent. While even 

greater reductions would be achieved at 

exposures equal to the proposed action 

level (25 mg/m3), some residual risks do 

remain at exposures of 25 mg/m3. 

Notably, at the proposed action level, 

ESRD risk is still 20.7 per 1,000 MNM 

miners and 21.6 per 1,000 coal miners. 

At the proposed action level, risk of 

non-fatal silicosis is 16.3 per 1,000 

MNM miners and 16.9 per 1,000 coal 

miners. 


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BILLING CODE 4520–43–C 

E. Healthy Worker Bias 

MSHA accounted for ‘‘healthy worker 

survivor bias’’ in estimating the risks for 

coal and MNM miners. The healthy 

worker survivor bias causes 

epidemiological studies to 

underestimate excess risks associated 

with occupational exposures. As with 

most worker populations, miners are 

composed of heterogeneous groups that 

possess varying levels of background 

health. Over the course of miners’ 

careers, illness tends to remove the most 

at-risk workers from the workforce 

prematurely, thus causing the highest 

cumulative exposures to be experienced 

by the healthiest workers who are most 

immune to risk. Failing to account for 

this imbalance of cumulative exposure 

across workers negatively biases risk 

estimates, thereby underestimating true 

risks in the population. Keil et al. (2018) 

analyzed a type of healthy worker bias 

referred to as the healthy worker 

survivor bias in the context of OSHA’s 

2016 life table estimates for risk 

associated with respirable crystalline 

silica exposure. After analyzing data 

from 65,999 workers pooled across 

multiple countries and industries, Keil 

et al. found that the ‘‘healthy worker 

survivor bias results in a 28% 

underestimate of risk for lung cancer 

and a 50% underestimate for other 

causes of death,’’ with risk being 

defined as ‘‘cumulative incidence of 

mortality [at age 80].’’ 

Given that MSHA has calculated risks 

using the same underlying 

epidemiological studies OSHA used in 

2016, the healthy worker survivor bias 

is likely impacting the estimates in 

Table VI–6 of lifetime excess risk and 

lifetime excess cases avoided. 

Accordingly, as part of a sensitivity 

analysis, MSHA re-estimated risks for 

MNM and coal miners to account for the 

healthy worker survivor bias. MSHA 

adjusted for this effect by increasing the 

risk estimates of lung cancer risk by 28 

percent and increasing the risk of each 

other disease by 50 percent. This 

produced larger estimates of lifetime 

excess risk reductions and lifetime 

excess cases avoided, which are 

presented in PRA Table 23 through PRA 

Table 26 of the PRA document. As these 

tables show, when adjusting for the 

healthy worker survivor bias, the 

proposed PEL would decrease lifetime 

silicosis morbidity risk by 20.8 cases per 

1,000 MNM miners (compared to the 

unadjusted estimate of 13.9 cases per 

1,000 MNM miners, see PRA Table 15 

of the PRA document) and 5.0 cases per 

1,000 coal miners (compared to 3.3 

cases per 1,000 coal miners, see PRA 

Table 16 of the PRA document). Still 

accounting for the healthy worker 

survivor bias, the proposed PEL would 

decrease total morbidity by 3,848 

lifetime cases among MNM miners 

(compared to 2,566 cases, see PRA Table 

17 of the PRA document) and by 366 


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22Often the threshold for analyzing Coal samples 

is ≥0.1 mg. There are, however, some exceptions 

based on Sample Type and Occupation Code. For 

samples with Sample Type 4 or 8, if the sample’s 

Occupation Code is not 307, 368, 382, 383, 384, or 

386, then the threshold is ≥0.2 mg. 

lifetime cases among coal miners 

(compared to 244 cases, see PRA Table 

18 of the PRA document). Among the 

current MNM and coal mining 

populations, implementation of the 

proposed PEL during their full lives 

would have prevented 1,091 deaths and 

94 deaths, respectively, over their 

lifetimes (compared to unadjusted 

estimates of 736 deaths and 63 deaths, 

respectively). 

MSHA believes adjusted estimates for 

the healthy worker survivor bias are 

more reliable than unadjusted estimates. 

However, given that the literature does 

not support specific scaling factors for 

each of the health endpoints analyzed, 

these adjustments for the healthy 

worker survivor bias have not been 

incorporated into the final lifetime 

excess risk estimates that served as the 

basis for monetizing benefits. Because 

the monetized benefits do not account 

for the healthy worker bias, MSHA 

believes the reductions in lifetime 

excess risks and lifetime excess cases, as 

well as the monetized benefits, likely 

underestimate the true reductions and 

benefits attributable to the proposed 

rule. 

F. Uncertainty Analysis 

MSHA conducted extensive 

uncertainty analyses to assess the 

impact on risk estimates of factors 

including treatment of data in excess of 

the proposed PEL, sampling error, and 

use of average rather than median point 

estimates for risk. The impact of 

excluding insufficient mass (weight) 

samples was also examined. 

1. Alternate Treatment of Exposure 

Samples in Excess of the Proposed 

Exposure Limit 

To estimate excess risks and excess 

cases under the proposed PEL, MSHA 

assumed that no exposures would 

exceed the proposed limit, which 

effectively reduced any exposures 

exceeding 50 mg/m3 to 50 mg/m3. 

However, if mines implement controls 

with the goal of reducing exposures to 

50 mg/m3 on every shift, then some 

exposure currently in excess of 50 mg/ 

m3 would likely decrease below the 

proposed PEL. For this reason, the 

estimation method of capping all 

exposure data at 50 mg/m3 represents a 

‘‘lowball’’ estimate of risk reductions 

due to the proposed PEL. In this section, 

MSHA presents estimates using an 

alternate ‘‘highball’’ method wherein 

exposures exceeding 50 mg/m3 are set 

equal to the median exposure value for 

the 25–50 mg/m3 exposure group. 

Because this highball method attributes 

larger reductions in exposure to the 

proposed PEL, it estimates higher 

lifetime excess risk reductions and more 

avoided lifetime excess cases. 

As with lifetime excess risks, the 

highball method also yields larger 

reductions in lifetime excess cases. 

Using the highball method, MNM 

miners are expected to experience 3,111 

fewer cases of non-fatal silicosis and 

coal miners are expected to experience 

344 fewer cases of non-fatal silicosis 

over their lifetimes. MNM miners would 

experience 1,137 fewer deaths and coal 

miners would experience 123 fewer 

deaths over their lifetimes. Compared to 

the lowball method—which estimates 

that the proposed PEL would prevent a 

total of 2,809 lifetime cases of non-fatal 

silicosis and 799 lifetime excess deaths 

(among both MNM and coal miners)— 

the highball method estimates totals of 

3,445 avoided lifetime cases of non-fatal 

silicosis and 1,260 avoided lifetime 

excess deaths. 

2. Sampling Error in Exposure Data 

To quantify the impact of sampling 

uncertainty on the risk estimates, 1,000 

bootstrap resamples of the original 

exposure data were generated (sampling 

with replacement). The resamples were 

stratified by commodity to preserve the 

relative sampling frequencies of coal, 

metal, non-metal, sand and gravel, 

crushed limestone, and stone 

observations in the original dataset. Risk 

calculations were repeated on each of 

the 1,000 bootstrap samples, thereby 

generating empirical distributions for all 

risk estimates. From these empirical 

distributions, 95 percent confidence 

intervals were calculated. These 

confidence intervals characterize the 

uncertainty in the risk estimates arising 

from sampling error in the exposure 

data. All lifetime excess risk estimates 

had narrow confidence intervals, 

indicating that the estimates of lifetime 

excess morbidity and mortality risks 

have a high degree of precision. 

In regard to use of average, rather than 

median, point estimates of risk, the 

estimates acquired from average 

exposures are similar to the estimates 

from median exposures, with 95 percent 

confidence intervals having similar 

widths. However, the 95 percent 

confidence intervals are not always 

overlapping, and average exposures 

tended to yield higher estimates of 

reduced morbidity and mortality. 

Among MNM miners, MSHA expects 

the proposed PEL to produce lifetime 

risk reductions of silicosis morbidity of 

2,546–2,777 using average exposures 

(see PRA Table 41 of the PRA 

document), compared to 2,453–2,683 

using median exposures (see PRA Table 

37 of the PRA document). Among coal 

miners, this reduction is expected to be 

246–279 using average exposures (see 

PRA Table 42 of the PRA document), 

compared to 229–265 using median 

exposures (see PRA Table 38 of the PRA 

document). The proposed PEL is 

estimated to reduce lifetime excess 

mortality by 735–791 MNM miner 

deaths and 65–73 coal miner deaths 

using average exposures (see PRA 

Tables 41 and 42 of the PRA document), 

compared to 708–764 MNM miner 

deaths and 60–69 coal miner deaths 

using median exposures (see PRA 

Tables 37 and 38 of the PRA document). 

3. Samples With Insufficient Mass 

The MNM exposure data gathered by 

enforcement from January 1, 2005, 

through December 31, 2019, contain 

samples that were analyzed using the P– 

2 method. As discussed, the P–2 method 

specifies that filters are only analyzed 

for quartz if they achieve a net mass 

gain of 0.100 mg or more. If cristobalite 

is requested, a mass gain of 0.050 mg or 

more is required for a filter to be 

analyzed (MSHA 2022a). During the 15- 

year sample period for MNM exposure 

data, 40,618 MNM samples were not 

analyzed because the filter failed to 

meet the P–2 minimum net mass 

(weight) gain requirements. 

Similarly, the coal exposure data 

gathered by enforcement from August 1, 

2016, through July 31, 2021, contains 

samples that were analyzed using the P– 

7 method. The P–7 method requires a 

minimum sample mass of 0.100 mg 22 of 

dust for the sample to be analyzed for 

quartz. During the five-year sample 

period for coal exposure data, 63,127 

coal samples were not analyzed because 

the P–7 method’s minimum mass 

requirement was not met. 

For samples that do not meet a 

minimum threshold for total respirable 

dust mass, the MSHA lab does not 

analyze these samples for respirable 

crystalline silica. These samples were 

excluded from the risk analysis because 

their concentrations of respirable 

crystalline silica are not known. 

Nonetheless, the unanalyzed samples all 

had very low total respirable dust mass, 

making it unlikely that many would 

have exceeded the existing standards or 

the proposed PEL. Excluding these 

unanalyzed samples from the exposure 

datasets thus may introduce bias, 

potentially causing the Agency to 

overestimate the proportion of highintensity exposure values. 


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As a sensitivity analysis, MSHA used 

imputation techniques to estimate the 

respirable crystalline silica mass for 

each sample based on the sample weight 

and the median percent silica content 

for each commodity and occupation. All 

the unanalyzed samples with imputed 

concentrations were estimated to be <25 

mg/m3, and thus including these 

unanalyzed samples in the analysis 

leads to lower estimates of estimated 

lifetime excess cases for both MNM and 

coal miners. 

When including the imputed values 

for the unanalyzed samples, the 

proposed PEL would result in 1,642 

fewer cases of non-fatal silicosis among 

MNM miners and 128 fewer cases 

among coal miners, over their lifetimes. 

The proposed PEL would also result in 

469 fewer deaths (due to all 4 diseases) 

among MNM miners and 34 fewer 

deaths among coal miners, over their 

lifetimes. This yields a total reduction of 

1,770 in lifetime excess morbidity and 

of 503 in lifetime excess mortality, 

respectively. While these estimates are 

lower than those presented in Table VI– 

4 (of 2,809 avoided lifetime cases of 

non-fatal silicosis and 799 avoided 

lifetime excess fatalities), MSHA 

nonetheless believes that—even 

including these unanalyzed samples— 

the proposed PEL would still reduce the 

risk of material impairment of health or 

functional capacity in miners exposed 

to respirable crystalline silica. 

Moreover, the possible positive bias that 

may arise when excluding these 

samples would be offset by other 

negative biases discussed herein (e.g., 

the healthy worker survivor bias and the 

assumption that full compliance with 

the proposed PEL would not produce 

any reductions in exposure below 50 mg/ 

m3). 

It should be noted that the imputation 

method has some limitations. For 

example, the method assumes that, if 

the insufficient mass samples had been 

analyzed, every sample would have 

possessed a percentage of quartz, by 

mass, equal to the median percentage 

for that sample’s associated commodity 

and occupation. (See Section 17.1 of the 

PRA document for a full discussion of 

the imputation method.) However, 

within a given occupation, this 

percentage varies substantially and is 

positively correlated with exposure 

concentration. Suppressing the variation 

in this percentage quartz, by mass, 

produces less variation in the resulting 

imputed concentrations. Consequently, 

the imputation method may 

underestimate the number of 

unanalyzed samples that would truly 

exceed 50 mg/m3. 

VII. Section-by-Section Analysis 

MSHA proposes to add a new part 60, 

titled Respirable Crystalline Silica, to 

title 30 CFR, chapter I, subchapter M— 

Uniform Mine Health Regulations. 

Proposed part 60, which would apply to 

all MNM and coal mines, contains 

health standards to protect all miners 

from adverse health risks caused by 

occupational exposure to respirable 

crystalline silica (as discussed in the 

standalone document entitled Effects of 

Occupational Exposure to Respirable 

Crystalline Silica on the Health of 

Miners and as summarized in Section V. 

Health Effects Summary of this 

preamble). This proposed part 

establishes a new PEL for respirable 

crystalline silica for all mines and 

includes other ancillary provisions to 

improve methods of compliance, 

exposure monitoring, corrective actions, 

respiratory protection, medical 

surveillance for MNM miners, and 

recordkeeping. In addition to the new 

part 60, MSHA proposes to incorporate 

by reference ASTM F3387–19, Standard 

Practice for Respiratory Protection, to 

replace its respiratory protection 

standards under 30 CFR parts 56, 57, 

and 72 to better protect all miners from 

airborne contaminants. This section-bysection analysis discusses each 

provision under the proposed part 60, 

the conforming amendments related to 

the proposed part, and the updated 

respiratory protection standard. 

A. Part 60—Respirable Crystalline Silica 

MSHA has preliminarily determined 

that occupational exposure to respirable 

crystalline silica causes adverse health 

effects, including silicosis (acute 

silicosis, accelerated silicosis, simple 

chronic silicosis, and PMF), NMRD (e.g., 

emphysema and chronic bronchitis), 

lung cancer, and renal diseases. MSHA 

has also preliminarily determined that 

under the existing standards, miners 

remain at risk of suffering material 

impairment of health or functional 

capacity from these adverse health 

effects. Each of these effects is exposuredependent, chronic, irreversible, and 

potentially disabling or fatal. MSHA has 

preliminarily concluded that lowering 

the PEL for respirable crystalline silica 

to 50 mg/m3 would substantially reduce 

the health risks to miners. 

MSHA proposes to replace its existing 

standards for respirable crystalline silica 

or respirable dust containing quartz 

with a single, uniform health standard 

for all miners. The proposed uniform 

standard would establish consistent, 

industry-wide requirements that 

directly address the adverse health 

effects of overexposure to respirable 

crystalline silica. This proposal would 

also facilitate mining-industry 

compliance and help MSHA and other 

stakeholders provide consistent 

compliance assistance. MSHA believes 

this unified regulatory framework for 

controlling miner exposure to respirable 

crystalline silica would improve 

protection for all miners and help the 

Agency fulfill its obligations under the 

Mine Act to prevent occupational 

diseases. 

Proposed part 60 includes: Scope and 

effective date; Definitions; Permissible 

exposure limit (PEL); Methods of 

compliance; Exposure monitoring; 

Corrective actions; Respiratory 

protection; Medical surveillance for 

metal and nonmetal miners; 

Recordkeeping requirements; and 

Severability. 

Detailed discussions of the proposed 

sections are followed by discussions on 

conforming amendments and 

discussions of the proposed update to 

the respiratory protection standard in 

parts 56, 57, and 72. 

1. Section 60.1—Scope; Effective Date 

This section provides that proposed 

part 60 would take effect 120 days after 

the final rule is published in the Federal 

Register. Mine operators would be 

required to comply with the 

requirements in this part starting on the 

proposed effective date. 

MSHA believes that the proposed 

120-day period gives operators the 

necessary time to plan and prepare for 

effective compliance with the new 

standards, while also ensuring that 

improved protections for miners from 

the hazards of respirable crystalline 

silica take effect as soon as practically 

possible. MSHA believes that it is 

important to reduce miner exposure to 

respirable crystalline silica promptly 

because every exposure at levels above 

the proposed PEL imposes adverse 

health risks on miners. However, for 

implementation to be successful, mine 

operators need enough time to 

understand the standard and to prepare 

for compliance (e.g., by purchasing 

gravimetric ISO-conforming samplers 

and/or selecting a commercial 

laboratory for respirable crystalline 

silica analysis, if necessary). MSHA 

believes that the proposed effective date 

of 120 days would provide enough time 

for mine operators to take necessary 

steps to achieve successful compliance. 

Under the existing standards, both 

MNM and coal operators have had many 

years of experience with monitoring and 

controlling airborne contaminants, 

including respirable crystalline silica, 

and this experience should facilitate 


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23The gas-exchange region of the human lung is 

the region where the exchange of carbon dioxide 

and oxygen occurs between the lung and blood and 

includes the alveoli and respiratory bronchioles. 

24The ISO 7708:1995 standard defines 

aerodynamic diameter as the ‘‘diameter of a sphere 

of density 1 g/cm3 with the same terminal velocity 

due to gravitational force in calm air as the particle, 

under the prevailing conditions of temperature, 

pressure, and relative humidity.’’ 

implementation of the proposed 

standard. 

2. Section 60.2—Definitions 

This section includes the proposed 

definitions of four terms: ‘‘action level,’’ 

‘‘objective data,’’ ‘‘respirable crystalline 

silica,’’ and ‘‘specialist.’’ 

The term ‘‘action level’’ would mean 

an airborne concentration of respirable 

silica of 25 micrograms per cubic meter 

of air (mg/m3) for a full-shift exposure, 

calculated as an 8-hour time-weighted 

average (TWA). The action level sets the 

level of respirable crystalline silica 

concentration at or above which 

operators would be subject to periodic 

sampling requirements, which are 

explained in proposed § 60.12. This 

proposed action level is intended to 

support operator compliance with the 

proposed PEL of 50 mg/m3 by initiating 

periodic sampling requirements. 

The proposed action level of 25 mg/ 

m3, one-half of the proposed PEL, is 

consistent with NIOSH research 

findings and other MSHA standards. 

According to NIOSH research, wherever 

exposure measurements are above onehalf the PEL, the employer cannot be 

reasonably confident that the employee 

is not exposed to levels above the PEL 

on days when no measurements are 

taken (NIOSH 1975). MSHA has 

experience with setting an action level 

equivalent to 50 percent of the PEL for 

occupational noise exposure (30 CFR 

62.101), applicable to MNM and coal 

mines, and an action level of 50 percent 

of the exhaust gas monitoring standards 

for underground coal mines (30 CFR 

70.1900). Based upon Agency 

experience, MSHA believes these action 

levels have allowed mine operators to 

be more proactive in providing 

necessary protection. 

The term ‘‘objective data’’ would 

mean information such as air 

monitoring data from industry-wide 

surveys or calculations based on the 

composition of a substance that 

indicates the level of miner exposure to 

respirable crystalline silica associated 

with a particular product or material or 

a specific process, task, or activity. Such 

data must reflect mining conditions 

closely resembling, or with a higher 

exposure potential than, the processes, 

types of material, control methods, work 

practices, and environmental conditions 

in the operator’s current operations. 

Some examples of information that 

would qualify as objective data under 

this definition include historical MSHA 

sampling data, NIOSH Health Hazard 

Evaluations and other published 

scientific reports, and industry-wide 

surveys compiled from mines with 

similar mining conditions, geological 

composition, work processes, miner 

tasks, and the same commodities. 

‘‘Respirable crystalline silica’’ would 

mean quartz, cristobalite, and/or 

tridymite contained in airborne particles 

that are determined to be respirable by 

a sampling device designed to meet the 

characteristics for respirable-particlesize-selective samplers that conform to 

the International Organization for 

Standardization (ISO) 7708:1995: Air 

Quality—Particle Size Fraction 

Definitions for Health-Related 

Sampling. These characteristics are 

described further below. 

First, the proposed definition would 

apply to airborne particles that contain 

collectively or individually, quartz, 

cristobalite, and/or tridymite, three 

polymorphs of respirable crystalline 

silica that may be encountered in 

mining and for which exposures are 

addressed in existing MSHA standards. 

Quartz is the most common polymorph 

and is present in varying amounts in 

almost every type of mineral, whereas 

naturally occurring cristobalite and 

tridymite are rare. 

Second, airborne particles determined 

to be respirable are those particles 

capable of entering the gas-exchange 

region (alveolar region) of the lungs. 

MSHA’s proposed definition would 

harmonize the Agency’s existing 

practice with current aerosol science 

and be consistent with the nationally 

and internationally accepted ISO 

definition of ‘‘respirable particulate 

mass’’ (i.e., the respirable mass fraction 

of total airborne particles that can be 

inhaled through the nose or mouth). ISO 

7708:1995 defines conventions for the 

‘‘inhalable,’’ ‘‘thoracic,’’ and 

‘‘respirable’’ fractions of total airborne 

particles. The inhalable fraction 

represents the fraction of total airborne 

particles capable of being inhaled 

through the nose or mouth. The thoracic 

fraction is the portion of the inhalable 

particles that pass the larynx and into 

the airways (trachea) and the bronchial 

region of the lungs. The respirable 

fraction is the portion of inhalable 

particles that can enter the gas-exchange 

region (alveolar region) of the lungs. The 

ISO 7708:1995 definition of ‘‘respirable 

particulate mass’’ corresponds to 

particulate matter (respirable dust) that 

is inhaled and capable of entering the 

gas-exchange region (alveolar region) of 

the lungs. MSHA considers this 

definition to be biologically relevant 

because exposures to airborne 

contaminants that are respirable can 

lead to material impairment of health or 

functional capacity.23

Third, respirable particles are those 

particles which can be collected by a 

sampling device designed to meet the 

characteristics for respirable-particlesize-selective samplers that conform to 

the ISO 7708:1995 standard. While 

‘‘respirable dust’’ generally refers to 

dust particles having an aerodynamic 

diameter of 10 micrometers (mm) or less, 

ISO 7708:1995 defines the term more 

precisely based on the respiratory 

system’s efficiency at collecting 

different types and sizes of particles. 

Collection efficiency is represented by 

particle collection efficiency curves 

based on the aerodynamic diameter of 

particles.24 The ISO 7708:1995 standard 

uses particle collection efficiency curves 

to approximate the fraction of respirable 

particles that can be deposited in the 

alveolar region of the human respiratory 

tract. A sampling device that conforms 

to the ISO 7708:1995 standard would 

ensure the collection of only respirable 

particles, including crystalline silica 

polymorphs. 

MSHA believes that the proposed 

definition of respirable crystalline silica 

has two main advantages. First, because 

the ISO 7708:1995 definition of 

respirable particulate mass represents 

an international consensus, adoption of 

the ISO 7708:1995 criterion would 

allow harmonization with standards 

used by other occupational health and 

safety organizations in the U.S. and 

internationally, including ACGIH, 

OSHA (29 CFR 1910.1053 and 29 CFR 

1926.1153), NIOSH (2003b, Manual of 

Analytical Methods), and the European 

Committee for Standardization (CEN) 

(ISO 7708:1995). Second, the proposed 

definition would eliminate 

inconsistencies in the existing standards 

for MNM and coal mines. Under the 

proposal, defining respirable crystalline 

silica to include quartz, cristobalite, 

and/or tridymite and establishing a PEL 

for exposure to respirable particles of 

any combination of these three 

polymorphs would provide consistency 

across the different mining sectors. 

Using samplers that conform to ISO 

7708:1995 would allow for uniform 

collection for these three polymorphs. 

The proposed streamlined approach 

would facilitate compliance and provide 

consistency in the development of best 

practices and would allow mine 

operators and MSHA to better promote 

the health and safety of all miners. 


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25NIOSH conducted a literature review of studies 

containing environmental data on the harmful 

effects of exposure to respirable crystalline silica. 

Based on these studies, and especially fifty years’ 

worth of studies on Vermont granite workers during 

which time dust controls improved, exposures fell, 

and silicosis diagnoses neared zero, NIOSH 

recommended an exposure limit of 50 mg/m3 for all 

industries. OSHA’s examination of health effects 

evidence and its risk assessment led to the 

conclusion that occupational exposure to respirable 

crystalline silica at the previous PELs, which were 

approximately equivalent to 100 mg/m3 for general 

industry and 250 mg/m3 for construction and 

maritime industries, resulted in a significant risk of 

material health impairment to exposed workers, 

and that compliance with the revised PEL would 

substantially reduce that risk. (81 FR at 16755). 

OSHA considered the level of risk remaining at the 

revised PEL to be significant but determined that a 

PEL of 50 mg/m3 is appropriate because it is the 

lowest level feasible. 

26For Part 90 miners, MSHA lowered the 

exposure to respirable coal mine dust during a coal 

miner’s shift to not exceed 0.5 mg/m3. 

27 Data on occupational mortality by industry and 

occupation can be accessed by visiting the CDC 

website at https://www.cdc.gov/niosh/topics/noms/ 

default.html. The NOMS database provides detailed 

mortality data for the 11-year period from 1999, 

2003 to 2004, and 2007 to 2014. https:// 

;wwwn.cdc.gov/niosh-noms/industry2.aspx; 

accessed November 7, 2022. 

‘‘Specialist’’ would mean an 

American Board-Certified Specialist in 

Pulmonary Disease or an American 

Board-Certified Specialist in 

Occupational Medicine. The proposed 

definition is applicable to proposed 

§ 60.15, which addresses medical 

surveillance for MNM miners. Under 

the proposed medical surveillance 

requirements, which will be discussed 

later, MNM mine operators would be 

required to provide miners with medical 

examinations performed by a specialist 

in pulmonary disease or occupational 

medicine or a PLHCP. 

3. Section 60.10—Permissible Exposure 

Limit (PEL) 

This section establishes a single, 

uniform PEL of 50 mg/m3 for respirable 

crystalline silica for all mines. Under 

this proposed provision, mine operators 

would be required to ensure that ‘‘no 

miner is exposed to an airborne 

concentration of respirable crystalline 

silica in excess of 50 mg/m3 for a fullshift exposure, calculated as an 8-hour 

TWA.’’ For coal mines, this proposal 

would establish a separate PEL for 

respirable crystalline silica. This 

proposed PEL would replace the 

Agency’s existing exposure limits for 

respirable crystalline silica or respirable 

quartz in 30 CFR parts 56, 57, 70, 71, 

and 90. 

The proposed PEL is consistent with 

NIOSH’s recommended exposure limit 

for workers and with the PEL for 

respirable crystalline silica covering 

U.S. workplaces regulated by OSHA. 

NIOSH recommended in 1974 that 

occupational exposure to crystalline 

silica be controlled so that ‘‘no worker 

is exposed to a TWA of silica [respirable 

crystalline silica] greater than 50 mg/m3

as determined by a full-shift sample for 

up to a 10-hour workday over a 40-hour 

workweek’’ (NIOSH 1974). In 2016, 

OSHA promulgated a rule establishing 

that for construction, general industry, 

and the maritime industry, workers’ 

exposures to respirable crystalline silica 

must not exceed 50 mg/m3, averaged 

over an 8-hour day (29 CFR 

1910.1053(c); 29 CFR 

1926.1153(d)(1)).25 MSHA’s 2014 rule 

on respirable coal mine dust established 

that the average concentration of 

respirable dust in the mine atmosphere 

during each shift to which each miner 

is exposed be at or below 1.5 mg/m3, 

calculated as a TWA, and that coal 

miners’ exposure to respirable 

crystalline silica be regulated through 

reductions in the overall respirable dust 

standard (30 CFR 70.100, 70.101, 

71.100, 71.101, 90.100, and 90.101).26

As discussed in the Health Effects 

Summary of this preamble, occupational 

exposure to respirable crystalline silica 

is detrimental to an individual’s health. 

Silicosis and other diseases caused by 

respirable crystalline silica exposure are 

irreversible, disabling, and potentially 

fatal. However, these diseases are 

exposure-dependent and are therefore 

preventable. The lower a miner’s 

exposure to respirable crystalline silica, 

the less likely that miner is to suffer 

from adverse health effects. 

As presented in the PRA, MSHA has 

preliminarily determined that: (1) under 

existing respirable crystalline silica or 

quartz standards, miners are exposed to 

respirable crystalline silica at 

concentrations that result in a risk of 

material impairment of health or 

functional capacity; and (2) that 

lowering the PEL to 50 mg/m3 would 

substantially reduce this risk. According 

to the CDC, between 1999 and 2014, 

miners died from silicosis, COPD, lung 

cancer, and NMRD at substantially 

higher rates than did members of the 

general population; for silicosis, the 

proportionate mortality ratio for miners 

was 21 times as high.27 Evidence in the 

standalone Health Effects document 

demonstrates that exposure to respirable 

crystalline silica at levels permitted 

under existing standards contributes to 

this excess mortality. 

In the case of coal mines, the 

proposed rule would establish a 

separate PEL for respirable crystalline 

silica. Under the existing standard, 

miners’ exposure to quartz is tied to 

exposure to respirable coal mine dust, 

making it more difficult to monitor coal 

miners’ exposure to respirable 

crystalline silica. The proposed separate 

standard would be more transparent and 

make compliance easier to track, 

allowing more effective control of 

respirable crystalline silica. 

The proposed PEL of 50 mg/m3 applies 

to a miner’s full-shift exposure, 

calculated as an 8-hour TWA. Under 

this proposal, a miner’s work shift 

exposure would be calculated as 

follows: 

Regardless of a miner’s actual working 

hours (full shift), 480 minutes would be 

used in the denominator. This means 

that the respirable crystalline silica 

collected over an extended period (e.g., 

a 12-hour shift) would be calculated (or 

normalized) as if it were collected over 

8 hours (480 minutes). For example, if 

a miner was sampled for 12 hours and 

55 mg of respirable crystalline silica was 

collected on the sample, the miner’s 

respirable crystalline silica 8-hour TWA 

exposure would be 67.4 mg/m3, 

calculated as follows: 


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28The pulmonary uptake and clearance of 

respirable crystalline silica are dependent upon 

many factors, including a miner’s breathing 

patterns, exposure duration, concentration (dose), 

particle size, and durability or bio-persistence of the 

particle. These factors will also affect the time to 

clear particles, even after exposure ceases. Of 

principal concern is the possibility that a 

continuous dust exposure over an extended period 

of time (or high dust level exposure during a short 

exposure period may excessively tax lung defense 

mechanisms (Industrial Minerals Association-North 

America and Mine Safety and Health 

Administration, 2008). 

The ACGIH (2022), while not specifically 

addressing silica, has stated, ‘‘numerous 

mathematical models to adjust for unusual work 

schedules have been described. In terms of 

toxicologic principles, their general objective is to 

identify a dose that ensures that the daily peak body 

burden or weekly peak body burden does not 

exceed that which occurs during a normal 8-hours/ 

day, 5-day/week shift.’’ There are associated 

concerns with the body burden from an ‘‘unusual 

work schedule’’ such as a 10- or a 12- hour shift. 

As Elias (2013) stated, ‘‘if the length of the workday 

is increased, there is more time for the chemical to 

accumulate, and less time for it to be eliminated. 

It is assumed that the time away from work will be 

contamination free. The aim is to keep the chemical 

concentrations in the target organs from exceeding 

the levels determined by the TLVs® (8-hour day, 5- 

day week) regardless of the shift length. Ideally, the 

concentration of material remaining in the body 

should be zero at the start of the next day’s work.’’ 

29Sampling hours of coal mine dust samples 

approximate the working hours of coal miners who 

were sampled. According to the coal mine dust 

samples for a 5-year period (August 2016–July 

2021), 90 percent of the samples by MSHA 

inspectors were from miners working 8 hours or 

longer and about 43 percent of the samples from 

miners working 10 hours or longer. The dust 

samples by coal mine operators show that over 98 

percent of them were from miners working 8 hours 

or longer and over 26 percent from the miners 

working 10 hours or longer. The coal mine dust 

samples are available at Mine Data Retrieval System 

| Mine Safety and Health Administration (MSHA). 

30Comment from Paul Schulte, NIOSH (Oct. 23, 

2019) to Docket No. MSHA 2016–0013. 

This proposed calculation method is 

the one that MSHA uses to calculate 

MNM miner exposures to respirable 

crystalline silica and other airborne 

contaminants; it differs from the 

existing method of calculating a coal 

miner’s exposure to respirable coal mine 

dust. For coal miners, the existing 

calculation method uses the entire 

duration of a miner’s work shift in both 

the denominator and numerator, 

resulting in the total mass of respirable 

coal mine dust collected over an entire 

work shift scaled by the sample’s air 

volume over the same period. 

MSHA’s proposal to apply the 

existing method of calculating MNM 

miner exposure to all miners has two 

main advantages. First, the proposal 

would improve protection for coal 

miners who work longer shifts. The goal 

of the proposed respirable crystalline 

silica PEL is to prevent miners from 

suffering a body burden high enough to 

cause adverse health effects. If a miner 

works longer than 8 hours, the miner’s 

body (lungs, in particular) may not have 

sufficient time to eliminate the 

respirable crystalline silica that enters 

the lungs or to reduce the body 

burden.28 Coal miners commonly work 

extended shifts, with many working 10- 

hour or longer shifts.29 In such cases, a 

coal miner’s recovery time would be 

reduced from 16 hours to 12 to 14 

hours. To account for this increased 

risk, the proposed calculation (like the 

current MNM calculation method) 

normalizes to an 8-hour TWA. The 

concept of adjusting occupational 

exposure limits for ‘‘extended shifts’’ 

has been addressed by researchers (Brief 

and Scala, 1986; Elias, 2013). 

Second, applying the proposed 

calculation method for all miners would 

be more straightforward and easier to 

understand for mine operators, miners, 

and other stakeholders. The current 

calculation method for coal miners 

requires first determining the percentage 

of quartz in the sample of collected 

respirable dust, then dividing the result 

into the number 10 to calculate an 

exposure limit for respirable dust. The 

proposed calculation method requires 

only measuring the total mass of 

respirable crystalline silica collected 

and dividing it by the air volume over 

480 minutes. 

This proposal would establish a lower 

PEL and apply it to all miners using a 

consistent method for calculating 

exposures. These changes would 

improve the health and safety of miners 

while making compliance more 

straightforward and transparent. The 8- 

hour TWA is the ‘‘gold standard’’ for 

exposure assessments, except in 

scenarios involving chemical substances 

that are predominantly fast-acting (i.e., 

those evoking acute effects). NIOSH has 

also supported the use of the TWA and 

discussed this term since the 

publication of the NIOSH Pocket Guide 

to Chemical Hazards (First Edition, 

1973) (the ‘‘White Book’’). 

4. Section 60.11—Methods of 

Compliance 

This proposed section would require 

mine operators to install, use, and 

maintain feasible engineering and 

administrative controls to keep each 

miner’s exposure to respirable 

crystalline silica at or below the 

proposed PEL. Mine operators would be 

required to use feasible engineering 

controls as the primary means of 

controlling respirable crystalline silica; 

administrative controls would be used, 

when necessary, as a supplementary 

control. However, under the proposal, 

rotation of miners—that is, assigning 

more than one miner to a high-exposure 

task or location, and rotating them to 

keep each miner’s exposure below the 

PEL—would be prohibited. Under the 

proposal, respiratory protection 

equipment could be used in specific and 

limited situations, as discussed in 

§ 60.14—Respiratory Protection, but the 

use of respiratory protection equipment 

would not be acceptable as a method of 

compliance. 

This proposed approach to controlling 

miners’ exposures is consistent with 

MSHA’s existing standards, NIOSH’s 

recommendations, and generally 

accepted industrial hygiene principles. 

The proposal is consistent with MSHA’s 

existing respirable dust standards, 

which require engineering controls as 

the primary means to protect miners. 

MSHA’s experience and data show that 

engineering controls provide improved, 

more consistent, and more reliable 

protection for miners than 

administrative controls or respirators. In 

its recommendations, NIOSH also 

stressed the importance of using 

engineering controls to control miners’ 

exposure to respirable crystalline silica. 

In 1995, NIOSH recommended that the 

dust standard state that ‘‘the mine 

operator shall use engineering controls 

and work practices [administrative 

controls] to keep worker exposures at or 

below the REL [recommended exposure 

limit]. . .’’ (NIOSH 1995a). In its public 

response to MSHA’s 2019 Request for 

Information for Respirable Silica 

(Quartz) (84 FR 45452, Aug. 29, 2019), 

NIOSH also supported the use of 

engineering controls as the primary 

means of protecting miners from 

exposure to respirable crystalline silica, 

stating that ‘‘[r]espirators should only be 

used when engineering control systems 

are not feasible. Engineering control 

systems, such as adequate ventilation or 

scrubbing of contaminants, are the 

preferred control methods for reducing 

worker exposures.’’ 30

As discussed in the technological 

feasibility and preliminary regulatory 

impact analysis sections of the 

preamble, MSHA has preliminarily 

determined that engineering and 

administrative controls are 

technologically and economically 

feasible, and the use of these controls 

would be sufficient to achieve 

compliance with the proposed PEL. 

After reviewing the effectiveness of 

various exposure reduction controls 

which are currently available and have 

been successfully adopted in various 

combinations in mines, MSHA has 

concluded that all mine operators can 

ensure miners’ exposures are below the 

proposed PEL through implementing 

some combination of enhanced 


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maintenance of existing engineering 

controls, new engineering controls, and 

improved administrative controls/work 

practices. 

a. Engineering Controls 

Proposed paragraph (a) would require 

mine operators to use feasible 

engineering controls as the primary 

means of controlling respirable 

crystalline silica; administrative 

controls would be used, when 

necessary, as a supplementary control. 

This proposed paragraph would 

require engineering controls to be used 

as the primary means of controlling 

respirable crystalline silica. Engineering 

controls can include ventilation systems 

(i.e., main, auxiliary, local exhaust), 

dust suppression devices (i.e., wet dust 

suppression and airborne capture), and 

enclosed cabs or control booths with 

filtered breathing air, as well as changes 

in materials handling, equipment used 

in a process, ventilation, and dust 

capture mechanisms. Engineering 

controls generally suppress (e.g., using 

water sprays, wetting agents, foams, 

water infusion), dilute (e.g., ventilation), 

divert (e.g., water sprays, passive 

barriers, ventilation), or capture dust 

(e.g., dust collectors) to minimize the 

exposure of miners working in the 

surrounding areas. The use of 

automated ore-processing equipment 

and use of video cameras for remote 

scanning and monitoring can also help 

to reduce or eliminate miners’ 

exposures to respirable crystalline 

silica. 

Engineering controls are the most 

effective means of controlling the 

amount of dust to which miners are 

exposed. They have the advantage of 

addressing dust at its source, thus 

ensuring that all miners in an area are 

adequately protected from overexposure 

to respirable crystalline silica. 

Engineering controls provide more 

consistent and more reliable protection 

to miners than other interventions 

because the controls are not dependent 

on an individual’s performance, 

supervision, or intervention to function 

as intended. In contrast to other controls 

and other interventions, engineering 

controls can also be continually 

evaluated and monitored relatively 

easily, allowing their effectiveness to be 

assessed regularly. 

b. Administrative Controls 

Under the proposed rule, mine 

operators would be permitted to 

supplement engineering controls with 

administrative controls as a means of 

controlling exposure to respirable 

crystalline silica. Administrative 

controls include practices that change 

the way tasks are performed to reduce 

a miner’s exposure. These practices 

would include housekeeping 

procedures; proper work positions of 

miners; cleaning of spills; and measures 

to prevent or minimize contamination of 

clothing to help decrease miners’ 

exposure to respirable crystalline silica. 

Administrative controls require 

significant effort by mine operators to 

ensure that miners understand and 

follow the controls. If not properly 

implemented, understood, or followed, 

or if persons responsible for 

administrative controls do not properly 

supervise their implementation, they 

would not be effective in controlling 

miners’ overexposure to respirable 

crystalline silica. Therefore, 

administrative controls would be 

permitted only as supplementary 

measures, with engineering controls 

required as the primary means of 

protection. 

Proposed paragraph (b) would 

prohibit mine operators from using 

rotation of miners—that is, assigning 

more than one miner to a high-exposure 

task or location, and rotating them to 

keep each miner’s exposure below the 

PEL—as an acceptable method of 

compliance. MSHA does not believe 

that rotation of miners is consistent with 

the Agency’s regulatory framework or its 

mandate under the Mine Act. Based on 

MSHA’s experience, rotation of miners 

may, if permitted, reduce the amount of 

time each miner is exposed to the 

hazard by rotating miners out of the task 

faster. However, it would increase the 

number of miners working in highexposure tasks or areas and would lead 

to increased material impairment of 

health or functional capacity for the 

additional miners. 

The concept of miner rotation, which 

may be an appropriate control to 

minimize musculoskeletal stress, is not 

acceptable for work involving 

carcinogens. Based on NIOSH’s 

publication entitled ‘‘Current 

Intelligence Bulletin 68: NIOSH 

Chemical Carcinogen Policy,’’ MSHA 

believes that the primary way to prevent 

occupational cancer is to reduce worker 

exposure to chemical carcinogens as 

much as possible through elimination or 

substitution at the source and through 

engineering controls (NIOSH 2017b). 

5. Section 60.12—Exposure Monitoring 

The proposed section addresses 

exposure monitoring, sampling method, 

and sample analysis methods. MSHA is 

proposing two types of exposure 

monitoring: quantitative, through 

sampling the air that miners breathe, 

and qualitative, through semi-annual 

evaluations of how changes in mining 

processes, production activities, and 

dust control systems affect exposures. 

For the quantitative monitoring, MSHA 

is proposing four types of sampling— 

baseline, periodic, corrective actions, 

and post-evaluation—together with 

methods for sampling and analyzing the 

samples. 

The proposed exposure monitoring 

requirements, which include sampling 

miners’ exposures, would facilitate 

operator compliance with the proposed 

PEL, harmonize MSHA’s approach to 

monitoring and evaluating respirable 

crystalline silica exposures in both 

MNM and coal mines, and lead to better 

protection of miners’ health. Monitoring 

miner exposures to airborne 

contaminants is an effective risk 

management tool. The sampling and 

evaluation requirements of proposed 

§ 60.12 are designed to ensure 

maximum protection for miners and 

prevent them from suffering material 

impairment of health or functional 

capacity, while providing operators 

flexibility to tailor their sampling 

program to the miners’ risk of exposure 

to respirable crystalline silica at their 

mines. 

The first type of exposure monitoring 

under the proposed rule is quantitative 

sampling for miners’ exposures to 

respirable crystalline silica. This 

sampling would help mine operators 

determine the extent and degree of 

exposures, identify sources of exposure 

and potential overexposure, maintain 

updated and accurate records of 

exposures, select the most appropriate 

control methods, and evaluate the 

effectiveness of those controls. The 

proposal would require operators to 

conduct sampling for a miner’s regular 

full shift during typical mining 

activities. The second type of exposure 

monitoring under the proposed rule 

would be qualitative evaluations, which 

would help operators identify changes 

in mining conditions and processes that 

affect the exposure risk to miners. 

a. Section 60.12(a)—Baseline Sampling 

The first action mine operators would 

take to assess miners’ exposures under 

the proposed rule would be to conduct 

baseline sampling. Baseline sampling 

would provide an initial measurement 

of respirable crystalline silica exposures 

that would be compared to the proposed 

action level and the proposed PEL to 

determine the effectiveness of existing 

controls and the need for additional 

controls. 

Proposed paragraph (a)(1) would 

require mine operators to perform 

baseline sampling to assess the fullshift, 8-hour TWA exposure of 

respirable crystalline silica for each 


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miner who is or may reasonably be 

expected to be exposed to respirable 

crystalline silica at any level. MSHA 

assumes that most mining occupations 

related to extraction and processing 

would meet the ‘‘reasonably be 

expected’’ threshold; however, MSHA 

recognizes that some miners may work 

in areas or perform tasks where 

exposures are not reasonably likely, and 

some miners may work in silica-free 

environments. Based on the Agency’s 

experience, both MNM and coal mine 

operators generally know from their 

existing sampling data and MSHA’s 

sampling data the occupations, work 

areas, and work activities where 

respirable crystalline silica exposures 

occur. The mine operator would be 

required to sample only those miners 

the operator knows or reasonably 

expects to be exposed to respirable 

crystalline silica. 

The proposed provisions would 

require that, within the first 180 days 

after the effective date of the final rule, 

the mine operator perform the baseline 

sampling. During this 180-day period, 

mine operators would acquire necessary 

sampling devices or sampling services, 

sample occupations or areas of known 

or reasonably expected exposures, 

identify appropriate laboratories, and 

arrange for analysis of samples. Given 

that the mining industry has experience 

with sampling programs for other 

airborne contaminants, as well as 

respirable crystalline silica, MSHA 

anticipates that the proposed 180 days 

would provide sufficient time for mine 

operators to comply with the proposed 

standard. 

Under this proposed standard, mine 

operators would need to accurately 

characterize the exposure of each miner 

who is or may reasonably be expected 

to be exposed to respirable crystalline 

silica. As discussed later in detail, mine 

operators would be permitted to use 

representative sampling whenever 

sampling is required. In some cases, 

however, operators may have to sample 

all miners to obtain an accurate 

assessment of exposures. 

This proposed requirement would 

ensure that mine operators have the 

quantitative information needed to 

evaluate miners’ exposure risks, 

determine the adequacy of existing 

engineering and administrative controls, 

and make necessary changes to ensure 

miners are not overexposed. In addition, 

the results of the baseline sampling 

would determine further operator 

obligations for periodic sampling. A 

baseline sample result at or above the 

proposed action level but at or below 

the proposed PEL, would require 

operators to conduct periodic sampling 

under proposed § 60.12(b). However, if 

the baseline sample indicated that 

exposures were below the proposed 

action level and operators can confirm 

those results, mine operators would not 

be required to conduct periodic 

sampling. The results can be confirmed 

in three ways: (1) sample data, collected 

by the operator or the Secretary in the 

12 months preceding the baseline 

sampling, that also shows exposures 

below the proposed action level; (2) 

objective data (as defined in the 

proposal) confirming that a miner’s 

exposure to respirable crystalline silica 

would remain below the proposed 

action level; or (3) another sample taken 

within 3 months showing exposure 

below the proposed action level. 

Proposed paragraph (a)(2) would 

allow mine operators to use objective 

data to confirm the baseline sample 

result. Under this proposal, objective 

data must demonstrate that respirable 

crystalline silica would not be released 

in airborne concentrations at or above 

the action level under any expected 

conditions. Objective data, as defined in 

proposed § 60.2, would include air 

monitoring data from industry-wide 

surveys that demonstrate miners’ 

exposure to respirable crystalline silica 

associated with a particular product or 

material or a specific process, task, or 

activity. Objective data must reflect 

mining conditions that closely resemble 

the processes, material, control 

methods, work practices, and 

environmental conditions in the mine 

operator’s current operations. The mine 

operator would have the burden of 

showing that the objective data 

characterizes miner exposures to 

respirable crystalline silica with 

sufficient accuracy. 

Also, proposed paragraph (a)(2) 

would permit mine operators to use 

sampling conducted by the Secretary or 

mine operator within the preceding 12 

months of baseline sampling to confirm 

miner exposures below the proposed 

action level. The proposed rule would 

require mine operator sampling that was 

conducted in accordance with sampling 

requirements in paragraph (f) and 

analyzed according to paragraph (g) of 

this section. Under proposed paragraph 

(a)(2), any subsequent sampling 

conducted by the operator or by the 

Secretary, collected within 3 months of 

the baseline sample, could also be used 

to confirm a baseline sample result. 

MSHA believes that before sampling 

is discontinued for miners previously 

determined to be exposed at or above 

the proposed action level, it is necessary 

to confirm any sample result that 

indicates miner exposures are below the 

proposed action level. When such a 

result is confirmed by a second 

measurement, an operator could 

reasonably expect exposures to remain 

below the action level if mining 

conditions and practices do not change. 

However, as discussed later, under 

proposed paragraph (d), if there is any 

change in conditions or practices that 

could be reasonably expected to result 

in exposures at or above the action 

level, sampling to assess these 

exposures would be required. 

b. Section 60.12(b)—Periodic Sampling 

Periodic sampling under the proposed 

rule would provide mine operators and 

miners with regular information about 

miners’ exposures. Changes in exposure 

levels can be caused by changes in the 

mine environment, inadequate 

engineering controls, or other changes 

in mining processes or procedures. 

Periodic sampling would inform mine 

operators about increases in exposures 

in a timely manner so they can prevent 

potential overexposures. In addition, 

periodic sampling alerts operators and 

miners of the continued need to protect 

against the hazards associated with 

exposure to respirable crystalline silica. 

If a mine operator installs new 

engineering controls and/or starts new 

administrative control practices, 

periodic sampling would show whether 

those controls are working properly to 

achieve the anticipated health results 

and would document their 

effectiveness. 

Proposed § 60.12(b) would require 

periodic sampling of miners’ exposures 

to respirable crystalline silica whenever 

the most recent sampling indicates that 

exposures are at or above the proposed 

action level but at or below the 

proposed PEL. Whether a mine operator 

would have to conduct periodic 

sampling under the proposal would 

depend on the results of the most recent 

sample, which could include a baseline 

sample, a corrective actions sample, or 

a post-evaluation sample, as well as 

samples taken by MSHA during its 

inspections. If operators are required to 

conduct periodic sampling, and 

periodic sampling results indicate that 

miner exposures are below the action 

level, a mine operator would be 

permitted to discontinue periodic 

sampling for those miners whose 

exposures are represented by these 

samples. If the most recent sample 

shows exposures at or above the action 

level but at or below the proposed PEL, 

periodic sampling every 3 months 

would continue until two consecutive 

sample analyses showed miners’ 

exposures below the action level. MSHA 

believes that two consecutive sample 

analyses showing exposures below the 


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action level would indicate a low 

probability that prevailing mining 

conditions would result in 

overexposures. 

MSHA believes that the proposed 

frequency for periodic sampling— 

repeating the sampling within 3 

months—is practical for mine operators 

and protective of the health and safety 

of miners. MSHA has preliminarily 

concluded that the health risks caused 

by respirable crystalline silica 

overexposure warrant more regular 

sampling when exposure levels 

approach the proposed PEL, because 

this periodic sampling would provide a 

higher level of confidence that miners 

would not be overexposed. Due to the 

unique conditions of mining 

environments, where conditions change 

quickly and exposures to respirable 

crystalline silica can vary frequently, 

MSHA is proposing a three-month 

periodic sampling schedule (NIOSH, 

2014e). This three-month schedule 

would provide a meaningful degree of 

confidence that mine operators would 

recognize quickly when exposures are 

increasing and approaching the 

proposed PEL and would respond by 

implementing additional controls to 

prevent overexposure. Periodic 

sampling data would also provide 

information that operators could use to 

select, implement, and maintain 

controls. MSHA has structured the 

proposal to balance the costs of periodic 

sampling requirements, including when 

sampling can be stopped, and the 

benefits of additional health protection 

for miners. Taking these factors into 

consideration, MSHA has preliminarily 

determined that the proposed frequency 

of periodic sampling is both 

economically and technologically 

feasible for mine operators. (See Section 

VIII. Technological Feasibility and 

Section IX. Summary of Preliminary 

Regulatory Impact Analysis.) 

As with the baseline sampling in 

proposed paragraph (a), in meeting the 

requirements of this paragraph, mine 

operators would be allowed to sample a 

representative fraction of at least two 

miners. The exposure result would be 

attributed to the remaining miners 

represented by this sample, as discussed 

in more detail below. When miners are 

not performing the same job under the 

same working conditions, a 

representative sample would not 

accurately characterize actual 

exposures, and individual samples 

would be necessary. 

c. Section 60.12(c)—Corrective Actions 

Sampling 

Under the proposed rule, MSHA 

would require mine operators to take 

corrective actions when any sampling 

shows exposures above the proposed 

PEL. After such corrective actions, 

proposed § 60.12(c) would require mine 

operators to conduct corrective actions 

sampling to determine whether the 

control measures taken under proposed 

§ 60.13 have reduced miner exposures 

to respirable crystalline silica to at or 

below the proposed PEL. If not, the 

mine operator would be required to take 

additional or new corrective actions 

until subsequent corrective actions 

sampling indicates miner exposures are 

at or below the proposed PEL. 

Once corrective actions sampling 

indicates that miner exposures have 

been lowered to levels at or below the 

proposed PEL, one of two scenarios 

could occur. First, if corrective actions 

sampling taken under proposed 

§ 60.12(c) indicate that miner exposures 

are at or below the proposed PEL, but 

at or above the proposed action level, 

the mine operator would be required to 

conduct periodic sampling as described 

in proposed § 60.12(b). The periodic 

sampling requirements would require 

mine operators to continue to conduct 

sampling every three months until two 

consecutive sampling results indicate 

miners’ exposures are below the action 

level. Second, if corrective actions 

sampling taken under proposed 

§ 60.12(c) indicate that miner exposures 

are below the proposed action level, the 

mine operator would be required to 

conduct a subsequent sample within 3 

months as described in proposed 

§ 60.12(b); if those results show miners’ 

exposures are below the action level, the 

mine operator could discontinue 

periodic sampling. 

Sampling after corrective actions 

would provide operators with specific 

information regarding the effectiveness 

of the corrective actions for the mine 

environment and provide additional 

data for use in making decisions about 

updating or improving controls. It 

would also provide mine operators with 

an updated profile of miners’ exposures 

against which future samples could be 

compared. 

d. Section 60.12(d) and (e)—SemiAnnual Evaluation and Post-Evaluation 

Sampling 

Historically, MSHA has recognized 

the importance of qualitatively 

evaluating changes in mining conditions 

and processes and assessing the effect of 

those changes on exposure risk. 

Operators have general experience with 

these types of evaluations. The 

proposed rule would require mine 

operators to qualitatively evaluate any 

changes in production, processes, 

engineering controls, personnel, 

administrative controls, or other factors 

including geological characteristics that 

might result in new or increased 

respirable crystalline silica exposures, 

beginning 18 months after the effective 

date and every 6 months thereafter. 

Such evaluations could identify changes 

in miners’ exposures to respirable 

crystalline silica. 

The proposed semi-annual evaluation, 

and post-evaluation sampling, as 

appropriate, would help confirm that 

the results of baseline and periodic 

sampling continue to accurately 

represent current exposure conditions. 

These proposed semi-annual evaluation 

and sampling requirements would also 

enable mine operators to take 

appropriate actions to protect exposed 

miners, such as implementing new or 

additional engineering controls, and 

would provide information to miners 

and their representatives, as necessary. 

An evaluation could identify a change 

in operation processes or control 

measures that might lead to increased 

exposures to respirable crystalline silica 

which need to be corrected. Under 

proposed paragraph (d)(1), the mine 

operator would be required to make a 

record of the evaluation, including the 

date of the evaluation. Under proposed 

paragraph (d)(2), the mine operator 

would be required to post the record on 

the mine bulletin board, and, if 

applicable, make the evaluation 

available electronically, for the next 31 

days. 

Once the evaluation is complete, a 

mine operator would be required to 

conduct post-evaluation sampling under 

proposed § 60.12(e) when the results of 

the evaluation show that miners may be 

exposed at or above the action level. 

Post-evaluation sampling would provide 

operators with information on whether 

existing controls are effective, whether 

additional control measures are needed, 

and whether respiratory protection is 

appropriate. When post-evaluation 

samples indicate that miner exposures 

are at or above the proposed action 

level, the mine operator would be 

required to conduct periodic sampling 

as described in proposed paragraph (b). 

Post-evaluation sampling, however, 

would not be required if the mine 

operator determines that mining 

conditions would not reasonably be 

expected to result in exposures at or 

above the action level. 

e. Section 60.12(f)—Sampling 

Requirements 

Knowledge of typical respirable dust 

exposure levels is critical to protect the 

health of miners. The proposed rule 

includes certain sampling requirements 

that would ensure mine operators’ 


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44908 Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 

31MSHA’s permissibility requirements are 

specified in 30 CFR parts 18 and 74. Part 18, 

Electric Motor-Driven Mine Equipment and 

Accessories, specifies the procedures and 

requirements for obtaining MSHA approval, 

certification, extension, or acceptance of electrical 

equipment intended for use in gassy mines. Part 74, 

Coal Mine Dust Sampling Devices, specifies the 

requirements for evaluation and testing for 

permissibility of coal mine dust sampling devices. 

32A cyclone is a centrifugal device used for 

extracting particulates from carrier gases (e.g., air). 

It consists of a conically shaped vessel. The 

particulate-containing gas is drawn tangentially into 

the base of the cone, takes a helical route toward 

the apex, where the gas turns sharply back along the 

axis, and is withdrawn axially through the base. 

The device is a classifier in which only dust with 

terminal velocity less than a given value can pass 

through the formed vortex and out with the gas. The 

particle cut-off diameter is calculable for given 

conditions. 

33An elutriator is a device that separates particles 

based on their size, shape, and density, using a 

stream of gas or liquid flowing in a direction 

usually opposite to the direction of sedimentation. 

The smaller or lighter particles rise to the top 

(overflow) because their terminal sedimentation 

velocities are lower than the velocity of the rising 

fluid. 

respirable crystalline silica monitoring 

is representative of miners’ actual 

exposures. 

(1) Typical Mining Activities and 

Sampling Device Placement 

Proposed paragraph (f)(1) would 

require mine operators to collect a 

respirable dust sample for the duration 

of a miner’s regular full shift and during 

typical mining activities. Many 

potential sources of respirable 

crystalline silica are present only when 

the mine is operating under typical 

conditions. If a sample is not taken 

during typical mining activities, the 

actual risk to the miner may not be 

known. This proposed requirement 

would ensure that respirable crystalline 

silica exposure data accurately reflect 

actual levels of respirable crystalline 

silica exposure at miners’ normal or 

regular workplaces throughout their 

typical workday, even if there are 

fluctuations in airborne contaminant 

concentrations during a work shift. As 

discussed in other sections of this 

preamble, the sample results from the 

full shift would be calculated as an 8- 

hour TWA concentration for 

comparison with the proposed action 

level and PEL and for compliance 

determinations. 

This proposed provision is consistent 

with existing standards and with 

generally accepted industrial hygiene 

principles, which recommend taking 

into consideration the entire duration of 

time a miner is exposed to an airborne 

contaminant, even if it exceeds 8 hours. 

Based on Agency data and experience, 

MSHA anticipates that operators would 

not have major challenges in meeting 

these sampling requirements. 

This proposal would continue 

existing procedures for sampling device 

placement during sampling. Under 

proposed § 60.12(f)(2)(i), for MNM 

miners the regular full-shift, 8-hour 

TWA exposure would be based on 

personal breathing-zone air samples. A 

breathing zone sample is an individual 

sample that characterizes a miner’s 

exposure to respirable crystalline silica 

during an entire work shift. More 

specifically, the sampler remains with 

the miner for the entire shift, regardless 

of the task or occupation performed. 

For coal miners, under proposed 

§ 60.12(f)(2)(ii), the regular full-shift, 8- 

hour TWA exposure would be based on 

an occupational environmental sample 

collected in compliance with existing 

standards found in §§ 70.201(c), 

71.201(b), and 90.201(b). Under the 

existing standards, the sampling device 

would be worn or carried ‘‘portal-toportal,’’ meaning from the time the 

miner enters the mine until the miner 

exits the mine. The sampling device 

would remain with the miner during the 

entire shift. For shifts that exceed 12 

hours, the operator would be required to 

switch the sampling pump prior to the 

13th-hour of operation. However, except 

in the case of Part 90 miners, if a miner 

who is being sampled changes positions 

or duties, the sampling device would 

remain with the position or duty chosen 

for sampling (rather than the miner). For 

Part 90 miners, the sampling device 

would be operated portal-to-portal and 

would remain operational with the 

miner throughout the Part 90 miner’s 

entire shift, which would include the 

time spent performing normal work 

duties and the time spent traveling to 

and from the assigned work location. 

(2) Representative Sampling 

Under the proposed rule, mine 

operators must accurately characterize 

miners’ exposure to respirable 

crystalline silica. In some cases, this 

would require sampling all exposed 

miners. In other cases, as proposed in 

paragraph (f)(3), sampling a 

‘‘representative’’ fraction of miners 

would be sufficient. Where several 

miners perform the same tasks on the 

same shift and in the same work area, 

the mine operator could sample a 

representative fraction of miners. Under 

this proposed rule, a representative 

fraction of miners would consist of two 

or more miners performing the same 

tasks on the same shift and in the same 

work area and who are expected to have 

the highest exposures of all the miners 

in an area. For example, sampling a 

representative fraction may involve 

monitoring the exposure of those miners 

who are closest to the dust source. The 

sampling results for these miners would 

then be attributed to the remaining 

miners in the group. When miners are 

not performing the same job under the 

same working conditions, a 

representative sample would not be 

sufficient to characterize actual 

exposures, and therefore individual 

samples would be necessary. 

MSHA has determined that requiring 

operators to sample at least two miners 

as representative, where they perform 

the same tasks on the same shift and in 

the same work area as the remaining 

miners, would be sufficient to ensure 

that exposures are accurately 

characterized and health protections are 

provided. This representative sampling 

provision of the proposal is similar to 

the approach that OSHA uses for both 

general industry (29 CFR 

1910.1053(d)(3)) and construction (29 

CFR 1926.1153(d)(2)) under the 

scheduled sampling options. 

(3) Sampling Devices 

Respirable dust sampling assesses the 

ambient air quality in mines and 

evaluates miners’ exposure to airborne 

contaminants. Respirable dust 

comprises particles small enough that, 

when inhaled, can reach the gas 

exchange region of the lung. 

Measurement of respirable dust 

exposure is based on the collection 

efficiency of the human respiratory 

system and the separation of airborne 

particles by size to assess their 

respirable fraction. Proposed paragraph 

(f)(4) would require mine operators to 

use sampling devices designed to meet 

the characteristics for respirableparticle-size-selective samplers that 

conform to the ISO 7708:1995, ‘‘Air 

Quality—Particle Size Fraction 

Definitions for Health-Related 

Sampling,’’ Edition 1, 1995–04 to 

determine compliance with the 

proposed respirable crystalline silica 

action level and PEL. MSHA proposes to 

incorporate by reference ISO 7708:1995, 

which is the international consensus 

standard that defines sampling 

conventions for particle size fractions 

used in assessing possible health effects 

of airborne particles in the workplace 

and ambient environment. Mine 

operators could use any type of 

sampling device they wish for respirable 

crystalline silica sampling, as long as it 

is designed to meet the characteristics 

for respirable-particle-size-selective 

samplers that conform to the ISO 

7708:1995 standard and, where 

appropriate, meets MSHA permissibility 

requirements.31

Sampling devices, such as cyclones 32

and elutriators,33 can separate the 


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Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 44909 

34National Institute for Occupational Safety and 

Health (NIOSH). Direct-on-filter analysis for 

respirable crystalline silica using a portable FTIR 

instrument. By Chubb LG, Cauda EG. Pittsburgh PA: 

U.S. Department of Health and Human Services, 

Centers for Disease Control and Prevention, 

National Institute for Occupational Safety and 

Health, DHHS (NIOSH) Publication No. 2022–108, 

IC 9533. https://doi.org/10.26616/NIOSHPUB

2022108. The document is intended for industrial 

hygienists and other health and safety mining 

professionals who are familiar with respirable 

crystalline silica exposure assessment techniques, 

but who are not necessarily trained in analytical 

techniques. It gives general instructions for setting 

up the field-based monitoring equipment and 

software. It also provides case studies and examples 

of different types of samplers that can be used for 

respirable crystalline silica monitoring. Guidance 

on the use, storage, and maintenance of portable IR 

instruments is also provided in the document. 

respirable fraction of airborne dust from 

the non-respirable fraction in a manner 

that simulates the size-selective 

characteristics of the human respiratory 

tract and that meets the ISO standard. 

These devices enable collection of dust 

samples that contain only particles 

small enough to penetrate deep into the 

lungs. Size-selective cyclone sampling 

devices are typically used in the U.S. 

mining industry. These samplers 

generally consist of a pump, a cyclone, 

and a membrane filter. The cyclone uses 

a rapid vortical flow of air inside a 

cylindrical or conical chamber to 

separate airborne particles according to 

their aerodynamic diameter (i.e., 

particle size). As air enters the cyclone, 

the larger particles are centrifugally 

separated and fall into a grit pot, while 

smaller particles pass into a sampling 

cassette where they are captured by a 

filter membrane that is later analyzed in 

a laboratory to determine the mass of 

the respirable dust collected. The pump 

creates and regulates the flow rate of 

incoming air. As the flow rate of air 

increases, a greater percentage of larger 

and higher-mass particles are removed 

from the airstream, and smaller particles 

are collected with greater efficiency. 

Adjustment of the flow rate changes the 

particle collection characteristics of the 

sampler and allows calibration to a 

specified respirable particle size 

sampling definition, such as the ISO 

criterion. 

MSHA and many mine operators use 

cyclone samplers. A cyclone sampler 

calibrated to operate at the 

manufacturer’s specified air flow rate 

that conforms to the ISO standard can 

be used to collect respirable crystalline 

silica samples under this proposed rule. 

MSHA reviewed OSHA’s feasibility 

analysis for its 2016 silica final rule and 

agrees with OSHA that there are 

commercially available cyclone 

samplers that conform to the ISO 

standard and allow for the accurate and 

precise measurement of respirable 

crystalline silica at concentrations 

below both the proposed action level 

and PEL (OSHA 2016a) Such cyclone 

samplers include the Dorr-Oliver 10-mm 

nylon cyclone used by MSHA and many 

mine operators, as well as the HigginsDewell, GK2.69, SIMPEDS, and SKC 

aluminum cyclone. Each of these 

cyclones has different operating 

specifications, including flow rates, and 

performance criteria, but all are 

compliant with the ISO criteria for 

respirable dust with an acceptable level 

of measurement bias. MSHA’s 

preliminary determination is that 

cyclone samplers, when used at the 

appropriate flow rates, can collect a 

sufficient mass of respirable crystalline 

silica to quantify atmospheric 

concentrations lower than the proposed 

action level and would meet MSHA’s 

crystalline silica sample analysis 

specifications for samples collected at 

MNM and coal mines. 

MNM mine operators who currently 

use a Dorr-Oliver 10 mm nylon cyclone 

could continue to use these samplers at 

a flow rate of 1.7 L/min, which 

conforms to the ISO standard, to comply 

with the proposed requirements. For 

coal mine operators, the gravimetric 

samplers previously used to sample 

RCMD (i.e., coal mine dust personal 

sampling units (CMDPSUs)) were 

operated at a 2.0 L/min flow rate. Those 

CMDPSUs could be adjusted to operate 

at a flow rate of 1.7 L/min to conform 

to the ISO standard. 

NIOSH’s rapid field-based quartz 

monitoring (RQM) approach is an 

emerging technology. It provides a fieldbased method for providing respirable 

crystalline silica exposure 

measurements at the end of a miner’s 

shift. With such an end-of-shift analysis, 

mine operators can identify 

overexposures and mitigate hazards 

more quickly. NIOSH Information 

Circular 9533, ‘‘Direct-on-filter Analysis 

for Respirable Crystalline Silica Using a 

Portable FTIR Instrument’’ provides 

detailed guidance on how to implement 

a field-based end-of-shift respirable 

crystalline silica monitoring program.34

The current RQM monitor, however, 

was designed as an engineering tool; it 

is not currently designed as a 

compliance tool with tamper-proof 

components and is susceptible to 

interferences which can affect its 

accuracy. This means that the integrity 

of the sample cannot be guaranteed, and 

therefore the monitor cannot be used as 

a compliance tool. MSHA continues to 

support NIOSH efforts to develop the 

RQM monitor for use in mines. 

f. Section 60.12 (g)—Methods of Sample 

Analysis. 

Proposed paragraph (g) specifies the 

methods to be used for analysis of 

respirable crystalline silica samples, 

including details regarding the specific 

analytical methods to be used and the 

qualifications of the laboratories where 

the samples are analyzed. Proposed 

paragraph (g)(1) would require mine 

operators to use laboratories that are 

accredited to the International 

Organization for Standardization (ISO) 

or International Electrotechnical 

Commission (IEC) (ISO/IEC) 17025, 

‘‘General requirements for the 

competence of testing and calibration 

laboratories’’ with respect to respirable 

crystalline silica analyses, where the 

accreditation has been issued by a body 

that is compliant with ISO/IEC 17011 

‘‘Conformity assessment—Requirements 

for accreditation bodies accrediting 

conformity assessment bodies.’’ 

Accredited laboratories are held to 

internationally recognized laboratory 

standards and must participate in 

quarterly proficiency testing for all 

analyses within the scope of the 

accreditation. 

The ISO/IEC 17025 standard is a 

consensus standard developed by the 

International Organization for 

Standardization and the International 

Electrotechnical Commission (ISO/IEC) 

and approved by ASTM International 

(formerly the American Society for 

Testing and Materials). This standard 

establishes criteria by which 

laboratories can demonstrate 

proficiency in conducting laboratory 

analysis through the implementation of 

quality control measures. To 

demonstrate competence, laboratories 

must implement a quality control 

program that evaluates analytical 

uncertainty and provides estimates of 

sampling and analytical error when 

reporting samples. The ISO/IEC 17011 

standard establishes criteria for 

organizations that accredit laboratories 

under the ISO/IEC 17025 standard. For 

example, the American Industrial 

Hygiene Association (AIHA) accredits 

laboratories for proficiency in the 

analysis of respirable crystalline silica 

using criteria based on the ISO 17025 

and other criteria appropriate for the 

scope of the accreditation. 

Many MNM mine operators currently 

use third-party laboratories to perform 

respirable crystalline silica sample 

analyses, and under the proposed 

standard, MSHA anticipates that they 

would continue to use third-party 

laboratories. 

For most coal mine operators, using a 

third-party accredited laboratory to 


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analyze respirable crystalline silica 

samples would be a new requirement 

because respirable coal mine dust 

samples are currently analyzed only by 

MSHA. Under the proposed standard, 

all mine operators would have to use 

third-party laboratories accredited to 

ISO/IEC 17025 to have respirable dust 

samples analyzed for respirable 

crystalline silica. By requiring all mines 

to use third-party laboratories, proposed 

paragraph (g)(1) would ensure that 

sample analysis requirements and 

MSHA enforcement efforts are 

consistent across all mines. 

Proposed paragraph (g)(2) would 

require mine operators to ensure that 

laboratories evaluate all samples using 

analytical methods for respirable 

crystalline silica that are specified by 

MSHA, NIOSH, or OSHA. These are 

validated methods currently being cited 

by third party accredited labs for 

measuring respirable crystalline silica in 

mine dust matrices. MSHA and NIOSH 

have specific FTIR methods for 

analyzing quartz in coal mine dust. The 

NIOSH 7603 method is based on the 

MSHA P–7 method which was 

collaboratively tested and specifically 

addresses the interference from 

kaolinite clay. All three methods, 

MSHA P–2, NIOSH 7500, and OSHA 

ID–142 for analyzing respirable 

crystalline silica using X-ray diffraction 

(XRD) have similar procedures for 

measuring respirable crystalline silica 

and are capable of distinguishing 

between the three silica polymorphs. 

Additional steps such as acid treatment 

can be taken to remove respirable 

crystalline silica interferences from 

other minerals that can be found in 

mine dust sample matrices. Consistent 

with MSHA’s current practices for the 

analysis of respirable crystalline silica 

samples, analytical techniques used for 

samples from MNM mines and coal 

mines would generally be different due 

to potential sources of interference and 

cost considerations. Under the proposed 

rule, as discussed below, MSHA expects 

that samples collected in MNM mines 

would continue to be analyzed by X-ray 

diffraction (XRD) and samples collected 

for coal mines would continue to be 

analyzed by Fourier transform infrared 

spectroscopy (FTIR). 

Coal mine samples are currently 

analyzed using the FTIR method 

because it is cheaper, faster, and better 

suited for the coal mining sector, where 

samples contain little or no minerals 

that could interfere or confound 

respirable crystalline silica analysis 

results. Current FTIR methods, however, 

cannot quantify quartz if either of the 

other two forms of crystalline silica 

(cristobalite and tridymite) are present 

in the sample. Unlike coal dust samples, 

MNM samples may have a variety of 

minerals present, which could cause 

interference with respirable crystalline 

silica measurements if FTIR were used. 

Thus, MNM samples are currently 

analyzed by XRD because the XRD 

method can distinguish and isolate 

respirable crystalline silica for 

measurement, thereby avoiding 

interference or confounding of 

respirable crystalline silica analysis 

results. The XRD method could be used 

for both MNM and coal samples but 

using the XRD method is more time 

consuming and more costly, with no 

additional benefit for coal mine sample 

analysis. For this reason, MSHA does 

not expect the use of XRD on samples 

from coal mines. 

For MNM samples, the methods used 

for respirable crystalline silica sample 

analysis using XRD include MSHA P–2, 

NIOSH 7500, and OSHA ID–142. For 

coal samples, the methods used for 

respirable crystalline silica sample 

analysis using FTIR include MSHA P– 

7, NIOSH 7602, and NIOSH 7603. 

(OSHA does not currently have an 

established FTIR method for analysis of 

respirable crystalline silica.) 

g. Section 60.12 (h)—Sampling Records 

Proposed paragraph (h) would 

establish requirements for sampling 

records, including what mine operators 

would be required to do after receiving 

the analytical reports from laboratories. 

For each sample taken, this proposed 

paragraph would require mine operators 

to create a record that includes the 

sample date, the sampled occupations, 

and the reported concentrations of both 

respirable dust and respirable 

crystalline silica. After making such a 

record, the mine operator would be 

required to post the record, together 

with the laboratory report, on the mine 

bulletin board and, if applicable, make 

the record and the laboratory report 

available electronically, for the next 31 

days upon receipt. 

When electronic means are available, 

mine operators would be required to use 

those electronics means such as 

electronic bulletin boards or 

newsletters, in addition to physically 

posting the sampling record and 

laboratory report on the mine bulletin 

board. MSHA believes that most mines 

have the ability to display this 

information electronically. For any 

mines where electronic means are not 

available, mine operators would only be 

required to physically post the sampling 

record and laboratory report on the 

mine bulletin board. Also, as required in 

proposed § 60.16(b), the sampling 

records created under this section may 

be requested at any time by, and must 

promptly be made available to, miners, 

authorized representatives of miners, or 

an authorized representative of the 

Secretary. 

MSHA believes that the posted 

information including sampling results 

and methodology and other relevant 

information would inform miners of the 

sampled exposures and would 

encourage them to have heightened 

awareness of potential health hazards 

that could impact not only them but 

other miners. It would also provide 

them with knowledge to take proactive 

actions to protect themselves and fellow 

miners through better and safer work 

practices and more active participation 

in health and safety programs. This is 

consistent with the Mine Act which 

states that mine operators, with the 

assistance of miners, have the 

responsibility to prevent the existence 

of unsafe and unhealthful conditions 

and practices in mines. 30 U.S.C. 801(e). 

Making miners aware that respirable 

crystalline silica exposures below the 

PEL may still pose a health risk could 

encourage them to take steps to manage 

their health risks. 

6. Section 60.13—Corrective Actions 

This proposed section includes 

several actions a mine operator would 

be required to take to protect miners’ 

health and safety when any sampling 

result indicates that a miner’s exposure 

to respirable crystalline silica exceeds 

the proposed PEL. Proposed paragraph 

(a)(1) would require the mine operator 

to make NIOSH-approved respirators 

available to affected miners before the 

start of the next work shift. Proposed 

paragraph (a)(2) would require mine 

operators to ensure that affected miners 

wear respirators for the full shift or 

during the period of overexposure to 

protect miners until miner exposures 

are at or below the PEL. 

Proposed paragraph (a)(3) would 

require operators to take immediate 

corrective actions to lower the 

concentration of respirable crystalline 

silica to levels at or below the PEL. 

Some examples of corrective actions 

include increasing air ventilation and/or 

water flow rates, adding more water 

sprays, and improving maintenance of 

the existing engineering controls. 

Once corrective actions have been 

taken, proposed paragraph (a)(4)(i) 

would require the operator to conduct 

sampling in accordance with § 60.12(c) 

to determine if the corrective actions 

have been successful in lowering 

exposures to at or below the PEL. If 

sampling indicates that the corrective 

actions did not reduce miner exposures 

to at or below the PEL, proposed 


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Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 44911 

paragraph (a)(4)(ii) would require the 

operator to implement additional or 

new corrective actions until sampling 

indicates miner exposures are at or 

below the PEL. 

Proposed § 60.13(b) would require the 

mine operator to make a record of 

corrective actions required under 

proposed paragraph (a) of this section 

and the dates of those actions. These 

records would help the operator and 

MSHA identify whether existing 

controls are effective, or whether 

maintenance or additional control 

measures are needed. 

7. Section 60.14—Respiratory Protection 

This proposed provision addresses 

the use of respiratory protection 

equipment. As noted earlier, the use of 

respiratory protection equipment, 

including powered air-purifying 

respirators (PAPRs), would not be 

permitted as a control to achieve 

compliance with the proposed PEL 

because engineering controls are more 

effective than respirators in protecting 

miners. However, temporary nonroutine use of respirators would be 

allowed under limited circumstances. 

Proposed paragraph (a) would require 

the mine operator to provide respirators 

to miners as a temporary measure in 

accordance with proposed paragraph (c) 

of this section, when miners are 

working in concentrations of respirable 

crystalline silica above the PEL under 

specific, limited circumstances. 

Proposed paragraph (a)(1) would require 

the temporary use of respirators when 

miners’ exposures exceed the proposed 

PEL during the development and 

implementation of engineering controls. 

Proposed paragraph (a)(2) would 

require the use of respirators for 

temporary, nonroutine work to prevent 

miners’ exposures at levels above the 

proposed PEL. Examples include when 

a miner is mixing cement to build a 

stopping to separate a main intake from 

return airways or is engaged in an 

unplanned entry into an atmosphere 

with excessive respirable crystalline 

silica concentrations to perform a repair 

or investigation that must occur before 

feasible engineering or administrative 

controls can be implemented. 

The proposal is consistent with 

NIOSH’s recommendation in the 1995 

Criteria Document (NIOSH 1995a) and 

is similar to the existing standards for 

MNM and coal mines. NIOSH (1995a) 

recommended the use of respirators as 

an interim measure when engineering 

controls and work practices are not 

effective in maintaining worker 

exposures for respirable crystalline 

silica at or below the proposed PEL. 

MSHA’s existing MNM standards in 

parts 56 and 57 permit mine operators 

to allow miners to work for reasonable 

periods of time protected by appropriate 

respiratory protection in locations 

where concentrations of contaminants 

(including respirable crystalline silica) 

exceed permissible levels and where 

feasible engineering control measures 

have not been developed or where 

necessary by the nature of the work 

involved (e.g., occasional entry into 

hazardous atmospheres to perform 

maintenance or investigation). MSHA’s 

existing standards for respirable coal 

mine dust require the mine operator to 

make respiratory protection equipment 

available while the operator evaluates 

and implements engineering control 

measures when a valid sample meets or 

exceeds the applicable standard during 

operator exposure monitoring. (30 CFR 

70.208(e)(1); 30 CFR 71.206(h)(1); 30 

CFR 72.700–72.701; 30 CFR 

90.207(c)(1)). 

Proposed paragraph (b) addresses 

situations where miners are not able to 

wear a respirator while working. 

Proposed paragraph (b) would require 

the mine operator, upon written 

notification by a PLHCP, to transfer an 

affected miner who is unable to wear a 

respirator to work in another area of the 

same mine, or to another occupation at 

the same mine, where respiratory 

protection is not required. 

The operator must ensure that the 

occupation and the area of the mine to 

which the miner is temporarily 

transferred do not expose the miner to 

respirable crystalline silica above the 

proposed PEL. Proposed paragraph 

(b)(1) would require the mine operator 

to continue to compensate the affected 

miner at no less than the regular rate of 

pay in the occupation held by that 

miner immediately prior to the transfer. 

Under proposed paragraph (b)(2), the 

miner may be transferred back to the 

initial work area or occupation when 

the temporary, non-routine use of 

respirators is no longer required. 

MSHA believes that this proposed 

provision is consistent with the 

mandate in the Mine Act to provide the 

maximum health protection for miners. 

Also, any effect on miners by this 

provision should be temporary since the 

concentration of respirable crystalline 

silica to which the miner would be 

exposed must be controlled through 

feasible engineering and administrative 

controls on a long-term basis. 

Proposed paragraph (c) includes the 

respiratory protection requirements that 

an operator must address when 

providing respirators to miners. 

Proposed paragraph (c)(1), like the 

existing standards in parts 56, 57, and 

72, would require mine operators to 

provide respiratory protection 

equipment approved by NIOSH under 

42 CFR part 84. Whenever respirators 

are used by miners, proposed paragraph 

(c)(1) would require the mine operator 

to provide miners with NIOSHapproved atmosphere-supplying 

respirators or air-purifying respirators. 

Atmosphere-supplying respirators 

provide clean breathing air from a 

separate source (e.g., a self-contained air 

tank), whereas air-purifying respirators 

use filters, cartridges, or canisters to 

remove contaminants from the air. 

In mines, commonly used types of airpurifying respirators include 

elastomeric respirators, filtering 

facepiece respirators (FFRs), and PAPRs. 

Elastomeric respirators, such as halffacepiece or full-facepiece tight-fitting 

respirators, are made of synthetic or 

natural rubber material and can be 

cleaned, disinfected, stored, and 

repeatedly re-used. FFRs (i.e., dust 

masks), designed to cover areas of the 

wearer’s face from the bridge of the nose 

to the chin, are disposable respirators 

composed of a weave of electrostatically 

charged synthetic filter fibers and an 

elastic head strap. PAPRs utilize a 

blower to move ambient air through an 

air-purifying filter that removes 

particulates and delivers clean air to the 

wearer. When air-purifying respirators 

(elastomeric respirators, FFRs, and 

PAPRs) are used, under proposed 

paragraph (c)(1), the mine operator 

would be required to select only highefficiency NIOSH-certified particulate 

protection (i.e., 100 series or HE filters) 

for respirable crystalline silica 

protection. A 100 series and high 

efficiency filter means that the filter 

must demonstrate a minimum efficiency 

level of 99.97 percent (i.e., the filter is 

at least 99.97 percent efficient in 

removing particles of 0.3 mm 

aerodynamic mass median diameter). 

Under proposed paragraphs (c)(1)(i) 

through (c)(1)(ii), air-purifying 

respirators would be required to be 

equipped with one of the following 

three particulate protection types: (1) 

particulate protection defined as a 100 

series under 42 CFR part 84; or (2) 

particulate protection defined as High 

Efficiency ‘‘HE’’ under 42 CFR part 84. 

MSHA believes that air-purifying 

respirators with the highest efficiency 

NIOSH classifications for particulate 

protection are most suitable in 

protecting miners from occupational 

exposure to a carcinogen such as 

respirable crystalline silica. 

Proposed paragraph (c)(2) would 

require mine operators to follow the 

provisions, as applicable, of ASTM 

F3387–19, ‘‘Standard Practice for 


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Respiratory Protection,’’ when 

respiratory protection equipment is 

needed. Under the proposal, MSHA 

would require that the respiratory 

program would be in writing and would 

include the following minimally 

acceptable program elements: program 

administration; standard operating 

procedures; medical evaluations; 

respirator selection; training; fit testing; 

and maintenance, inspection, and 

storage. Beyond the minimally 

acceptable program elements, mine 

operators would be allowed to comply 

with the provisions of the 2019 ASTM 

standard that they deem applicable. The 

need for temporary non-routine use of 

respirators may vary, given the 

variability of mining processes, 

activities, and commodities that are 

mined. MSHA believes that flexibility 

afforded to mine operators under this 

paragraph may lead mine operators to 

focus more appropriately on those 

provisions that are relevant to their 

mine-specific situations, allowing them 

to comply more efficiently and 

effectively. 

ASTM F3387–19 is a voluntary 

consensus standard published by ASTM 

International and was approved in 2019. 

MSHA proposes to incorporate by 

reference this consensus standard for 

two reasons. 

First, adopting this voluntary 

consensus standard is consistent with 

OMB Circular A–119, which encourages 

Federal agencies to ‘‘minimize reliance 

on government-unique standards where 

an existing standard would meet the 

Federal government’s objective.’’ ASTM 

F3387–19 comprehensively addresses 

all aspects of establishing, 

implementing, and evaluating 

respiratory protection programs, and 

describes respiratory protection program 

elements which include: program 

administration; standard operating 

procedures; medical evaluation; 

respirator selection; training; fit testing; 

and respirator maintenance, inspection, 

and storage. 

Second, ASTM F3387–19 reflects 

current respirator technology and an upto-date understanding of effective 

respiratory protection. For example, 

ASTM F3387–19 provides detailed 

information on respirator selection that 

are based on NIOSH’s long-standing 

experience of testing and approving 

respirators for occupational use and 

OSHA’s research and rulemaking on 

respiratory protection. 

More detailed discussion on ASTM 

F3387–19 is provided later in C. 

Updating MSHA Respiratory Protection 

Standards: Proposed Incorporation of 

ASTM F3387–19 by Reference. 

8. Section 60.15—Medical Surveillance 

for Metal and Nonmetal Miners 

This proposed provision would 

require MNM mine operators to provide 

mandatory medical examinations to 

miners who begin in the mining 

industry after the effective date of the 

rule and offer voluntary periodic 

examinations to all other miners. These 

medical examinations would be 

provided by a PLHCP or specialist. The 

proposed requirements in this section 

are consistent with the Mine Act’s 

mandate to provide maximum health 

protection for miners and provide MNM 

miners with information needed for 

early detection of respirable crystalline 

silica-related disease, resulting in 

prevention of disabling disease. 

The proposed requirements for MNM 

mine operators are also generally 

consistent with existing medical 

surveillance requirements for coal mine 

operators under 30 CFR 72.100 although 

the requirements differ in some 

respects. For example, the proposed 

provision specifies that medical 

examinations must be provided by a 

PLHCP or specialist, while the existing 

medical surveillance requirements for 

coal miners in § 72.100 coordinate with 

the surveillance system managed by 

NIOSH’s Coal Workers’ Health 

Surveillance Program (CWHSP) which 

works with coal mine operators under 

NIOSH regulations to provide medical 

surveillance. Proposed paragraph 

60.15(a) would require that each MNM 

mine operator make medical 

examinations available to each MNM 

miner, at no cost to the miner, 

regardless of whether miners are 

reasonably expected to be exposed to 

any level of respirable crystalline silica. 

This proposed requirement is consistent 

with section 101(a)(7) of the Mine Act. 

Proposed paragraph 60.15(a) would 

also require medical examinations to be 

performed by a PLHCP or specialist. A 

PLHCP is an individual whose legally 

permitted scope of practice (i.e., license, 

registration, or certification) allows that 

individual to independently provide or 

be delegated the responsibility to 

provide some or all of the required 

health services (i.e., chest X-rays, 

spirometry, symptom assessment, and 

occupational history). A specialist, as 

defined in proposed § 60.2, refers to an 

American Board-certified specialist in 

pulmonary disease or occupational 

medicine. The Agency believes it is 

appropriate to allow not only a 

physician, but also any State-licensed 

health care professional, to perform the 

required medical examinations. This 

would provide operators with the 

flexibility needed to use professionals 

with necessary medical skills and 

minimize cost and compliance burdens. 

Proposed paragraph (a)(1) requires 

periodic examinations to be offered to 

all MNM miners at the frequencies 

specified in this section. Proposed 

paragraph (a)(2) specifies the types of 

medical examinations and is consistent 

with the existing requirements for coal 

mine operators under existing § 72.100. 

Proposed paragraphs (a)(2)(i) and (ii) 

would require MNM operators to 

provide each miner with a medical 

examination that includes a review of 

the miner’s medical and work history 

and a physical examination. The 

medical and work history would cover 

a miner’s present and past work 

exposures, illnesses, and any symptoms 

indicating respirable crystalline silicarelated diseases and compromised lung 

function. The medical and work history 

should focus not only on any history of 

tuberculosis, smoking, or exposure to 

respirable crystalline silica, but also on 

any diagnoses and symptoms of 

respiratory system dysfunction, 

including shortness of breath, coughing, 

or wheezing. The physical examination 

under (a)(2)(ii) would be focused on the 

respiratory tract. For the reasons stated 

above, these proposed requirements 

differ from the existing requirements for 

coal miners. The existing medical 

surveillance requirements for coal 

miners in 42 CFR 37 specify 

standardized data collection elements 

for occupational histories and 

respiratory symptom assessment while 

proposed paragraphs (a)(2)(i) and (ii) 

specify a respiratory-focused history 

and physical examination by a clinician. 

Under proposed paragraph (a)(2)(iii), 

MSHA would require all medical 

examinations to include a chest X-ray. 

The required chest X-ray is a posterior/ 

anterior view no less than 14 x 17 

inches and no more than 16 x 17 inches 

at full inspiration, recorded on either 

film or digital radiography systems. The 

chest X-ray must be classified by a 

NIOSH-certified B Reader, in 

accordance with the Guidelines for the 

Use of the International Labour Office 

(ILO) International Classification of 

Radiographs of Pneumoconioses. The 

ILO recently made additional standard 

digital radiographic images available 

and has published guidelines on the 

classification of digital radiographic 

images (ILO 2022). This is a standard 

practice in pneumoconiosis surveillance 

programs and can potentially detect 

other respirable crystalline silica-related 

conditions, including lung cancer 

(Industrial Minerals Association-North 

America and Mine Safety and Health 

Administration, 2008). The test would 

provide data that can be used to assess 


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for progression of silicosis and for other 

respirable crystalline silica-related 

conditions in MNM miners. 

MSHA preliminarily concludes that 

the number of B readers in the U.S. is 

adequate to classify chest X-rays 

conducted as part of the respirable 

crystalline silica rule (OSHA 2016a, 81 

FR 16286, 16821). As discussed in 

OSHA’s 2016 final silica rule, the 

number of B Readers is driven by 

supply and demand created by a free 

market, and many physicians choose to 

become B readers based on demands for 

such services (OSHA 2016a, 81 FR 

16286, 16822). NIOSH is also able to 

train enough B readers to handle any 

potential increase in demand, providing 

several pathways for physicians to 

become B readers, such as free selfstudy materials by mail or download 

and free B reader examinations (OSHA 

2016a, 81 FR 16286, 16822). In addition, 

courses and examinations for 

certification are periodically offered for 

a fee through the American College of 

Radiology (OSHA 2016a, 81 FR 16286, 

16822). Even if B readers are scarce in 

certain geographical locations, digital Xrays can be easily transmitted 

electronically to B readers located 

anywhere in the U.S. (OSHA 2016a, 81 

FR 16286, 16822). 

Under proposed paragraph (a)(2)(iv), 

MSHA would require that pulmonary 

function testing (including spirometry) 

be part of every medical examination. 

The pulmonary function test must be 

administered by a spirometry technician 

with a current certificate from a NIOSHapproved Spirometry Training 

Sponsorship. The purpose of spirometry 

is to measure baseline lung function 

followed by periodic tests to detect early 

impairment patterns, such as 

obstruction of air flow and restriction 

caused by underlying respiratory 

disease. This measurement can provide 

critical information for the primary, 

secondary, and tertiary prevention of 

workplace-related lung diseases, 

including respirable crystalline silicarelated diseases. The use of spirometry 

is consistent with recommendations of 

the Dust Advisory Committee (U.S. 

DOL, 1996) and the NIOSH Criteria 

Document (1974). Indeed, NIOSH 

(2014a) notes that properly conducted 

spirometry should be part of a 

comprehensive workplace respiratory 

health program. Spirometry and chest 

X-rays are complementary examinations 

for detecting adverse health effects from 

respirable crystalline silica exposures. 

In order to maintain a certificate from 

a NIOSH-approved course, technicians 

must complete an initial training and 

then refresher training every five years 

(OSHA 2016a, 81 FR 16286, 16825). As 

discussed in OSHA’s 2016 silica final 

rule, course sponsors are located 

throughout the U.S. and some sponsors 

will travel to a requested site to teach a 

course (OSHA 2016a, 81 FR 16286, 

16825). One NIOSH-approved sponsor 

offers instructor-led live virtual initial 

training. Several live virtual and webbased refresher training options are also 

available. Because the required training 

is not too frequent and course sponsors 

appear to be widely available 

throughout the U.S., MSHA 

preliminarily concludes that the 

requirement that technicians maintain a 

certificate from a NIOSH-approved 

course will not impose substantial 

burdens on providers of spirometry 

testing. 

MSHA believes that the proposed 

medical examinations consisting of a 

medical and work history, a physical 

examination, a chest X-ray, and a 

spirometry test would help medical 

professionals identify early symptoms of 

respirable crystalline silica-related 

diseases, assist MNM miners in 

protecting their health, and lower the 

risk that MNM miners become 

materially impaired due to occupational 

exposure to respirable crystalline silica. 

Under proposed paragraph (b), MSHA 

would require MNM mine operators to 

provide every miner employed at MNM 

mines with the opportunity to have 

periodic medical examinations. Miner 

participation would be voluntary, as in 

the case of the examination requirement 

for coal miners in 30 CFR 72.100(b). 

Starting on the proposed effective date, 

mine operators must provide the 

opportunity for an examination to MNM 

miners no later than 5 years after the 

date of their last medical surveillance 

examination, and in addition, during a 

6-month period that begins no less than 

3.5 years and not more than 4.5 years 

from the end of the last 6-month period 

for medical examinations. Periodic 

examinations would allow for 

comparisons with a miner’s prior 

examination results, help detect 

respirable crystalline silica-related 

disease including silicosis, and address 

further progression of existing 

respiratory disease. If a miner has a 

positive chest X-ray (ILO category of 1/ 

0+), it is important to intervene as 

promptly as possible for maximum 

health protection. In addition, an 

interval of 5 years or less between each 

miner’s periodic examinations can 

ensure detection of declines in a miner’s 

lung function due to potential 

occupational exposure. MSHA believes 

that the proposed schedule, which is 

consistent with the periodic 

examination for coal miners required 

under § 72.100(b), would provide MNM 

mine operators with flexibility in 

offering examinations to miners. 

Proposed paragraph (c) would require 

MNM mine operators to provide a 

mandatory initial medical examination 

for each MNM miner who is new to the 

mining industry. Consequently, if a 

miner had previous mining experience 

(such as working in a coal mine) and 

subsequently came to work in an MNM 

mine, MSHA would not require that the 

MNM mine operator provide the miner 

with an initial examination after the 

miner begins employment. Mandatory 

initial examinations would be 

conducted when miners are first hired 

in the mining industry and would 

provide an individual baseline of each 

miner’s health status. This initial 

examination would assist in the early 

detection of respirable crystalline silicarelated illnesses and conditions that 

may make the miner more susceptible to 

the toxic effects of respirable crystalline 

silica. The individual baseline would 

also be valuable in assessing any future 

health changes in each miner. Overall, 

the initial examination results would 

enable miners to respond appropriately 

to information about their health status. 

Proposed paragraph (c)(1) would 

require that the mandatory initial 

medical examination occur no later than 

30 days after a miner new to the 

industry begins employment. Proposed 

paragraphs (c)(2) and (3) would require 

MNM mine operators to provide 

mandatory follow-up examinations to 

new miners who were eligible for an 

initial mandatory medical examination 

under proposed paragraph (c). MSHA 

believes follow-up examinations are 

important for assessments of any 

changes in a new miner’s health status 

and for future diagnoses. 

Under proposed paragraph (c)(2), 

MSHA would require that the mine 

operator provide a mandatory follow-up 

examination to the miner no later than 

3 years after the miner’s initial medical 

examination. Under proposed paragraph 

(c)(3), if a miner’s 3-year follow-up 

examination shows evidence of a 

respirable crystalline silica-related 

disease or decreased lung function, the 

operator would be required to provide 

the miner with another mandatory 

follow-up examination with a specialist, 

as defined in proposed § 60.2, within 2 

years. This proposed requirement is 

intended to ensure that any miner 

whose follow-up medical examination 

shows evidence of silicosis or evidence 

of decreased lung function, as 

determined by the PLHCP or specialist, 

is seen by a professional with expertise 

in respiratory disease. This would 

ensure that miners would benefit from 

not only expert medical judgment but 


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also counseling regarding work 

practices and personal habits that could 

affect the miners’ health. For the reasons 

stated above, this proposed requirement 

differs from the existing requirements 

for coal miners, which provides for 

follow up surveillance testing but does 

not include interaction with a PLHCP or 

specialist. 

Proposed paragraph (d) would require 

that the results of any medical 

examination performed under this 

section be kept confidential and 

provided only to the miner. The miner 

is also entitled to request that the 

medical examination results be 

provided to the miner’s designated 

physician. Based on MSHA’s experience 

with coal miners’ medical surveillance, 

the Agency believes that confidentiality 

regarding medical conditions is 

essential and that it encourages miners 

to take advantage of the opportunity to 

detect early adverse health effects due to 

respirable crystalline silica. See 79 FR 

24813, at 24928, May 1, 2014. 

Under proposed paragraph (e), MNM 

mine operators would be required to 

obtain a written medical opinion from a 

PLHCP or specialist within 30 days of 

the medical examination that includes 

only the date of a miner’s medical 

examination, a statement that the 

examination has met the requirements 

of this section, and any recommended 

limitations on the miner’s use of 

respirators. This would allow the mine 

operator to verify the examination has 

occurred and would provide the mine 

operator with information on miners’ 

ability to use respirators. Proposed 

paragraph (f) would require the mine 

operator to maintain a record of the 

written medical opinions obtained from 

the PLHCP or specialist under proposed 

paragraph (e). 

9. Section 60.16—Recordkeeping 

Requirements. 

Section 60.16 lists all the proposed 

recordkeeping requirements under this 

proposed part. To ensure that mine 

operators track actual or potential 

exposures, risks, and controls and keep 

miners, miners’ representatives, and 

other stakeholders informed about them, 

the proposed part 60 establishes five 

recordkeeping requirements. Discussion 

of these requirements follow and are 

summarized in table 1 to paragraph (a) 

in § 60.16 of the rule text. 

First, this section would require that, 

once mine operators complete the 

sampling or semi-annual evaluations 

required under proposed § 60.12, the 

operators retain the associated exposure 

monitoring records for at least 2 years. 

Examples of exposure monitoring 

records include the date of sampling or 

evaluation, names and occupations of 

miners who were sampled, description 

of sampling or evaluation method, and 

laboratory reports of sampling analysis. 

The 2-year period would give mine 

operators sufficient exposure 

monitoring data to evaluate the 

effectiveness of their engineering and 

administrative controls over different 

mining and weather conditions. 

Second, mine operators would also be 

required to retain records of corrective 

actions made under proposed § 60.13(b) 

for at least 2 years from the date when 

each corrective action was taken. This 

proposed requirement is similar to the 

recordkeeping requirements related to 

other corrective-action requirements 

under parts 56 and 57 (for MNM mines) 

and parts 70, 71, and 90 (for coal 

mines). 

Third, this proposed section would 

require mine operators to maintain any 

written determination records that they 

receive from a PLHCP or specialist. 

When a PLHCP or specialist certifies in 

writing that a miner cannot wear a 

respirator, including a PAPR, that miner 

must be temporarily transferred to a 

different work area or task where 

respiratory protection is not required (or 

needed). In such cases, mine operators 

would be required to retain the written 

determinations by a PLHCP or specialist 

for the duration of the miner’s 

employment plus 6 months. 

Fourth, under this section, MNM 

mine operators would be required to 

maintain written medical opinion 

records that they obtain from a PLHCP 

or specialist who conducts medical 

examinations of their miners under 

proposed § 60.15. This proposed 

recordkeeping requirement would apply 

only to MNM mine operators. Under 

proposed § 60.15, after the examination 

has taken place, the MNM mine 

operator would receive from the PLHCP 

or specialist a written medical opinion 

that contains the date of the medical 

examination, a statement that the 

examination has met the requirements 

under this proposed rule, and any 

recommended limitations on the 

miner’s use of respirators. Upon receipt, 

the mine operator would retain the 

medical opinion for the duration of the 

miner’s employment plus 6 months. 

Proposed paragraph (b) would ensure 

that all the listed records would be 

made available promptly upon request 

to miners, authorized representatives of 

miner(s), and authorized representatives 

of the Secretary of Labor. 

10. Section 60.17—Severability 

The severability clause under 

proposed § 60.17 serves two purposes. 

First, it expresses MSHA’s intent that if 

any section or provision of the Lowering 

Miners’ Exposure to Respirable 

Crystalline Silica and Improving 

Respiratory Protection rule—including 

its conforming amendments in sections 

of 30 CFR parts 56, 57, 70, 71, 72, 75, 

and 90 that address respirable 

crystalline silica or respiratory 

protection—is held invalid or 

unenforceable or is stayed or enjoined 

by any court of competent jurisdiction, 

the remaining sections or provisions 

should remain effective and operative. 

Second, the severability clause 

expresses MSHA’s judgment, based on 

its technical and scientific expertise, 

that each individual section and 

provision of the rule can remain 

effective and operative if some sections 

or provisions are invalidated, stayed, or 

enjoined. Accordingly, MSHA’s 

inclusion of this severability clause 

addresses the twin concerns of Federal 

courts when determining the propriety 

of severability: identifying agency intent 

and clarifying that any severance will 

not undercut the structure or function of 

the rule more broadly. Am. Fuel & 

Petrochem. Mfrrs. v. Env’t Prot. Agency, 

3 F.4th 373, 384 (D.C. Cir. 2021) 

(‘‘Severability ‘depends on the issuing 

agency’s intent,’ and severance ‘is 

improper if there is substantial doubt 

that the agency would have adopted the 

severed portion on its own’ ’’) (quoting 

North Carolina v. FERC, 730 F.2d 790, 

796 (D.C. Cir. 1984) and New Jersey v. 

Env’t Prot. Agency, 517 F.3d 574, 584 

(D.C. Cir. 2008)). 

Under the principle of severability, a 

reviewing court will generally presume 

that an offending provision of a 

regulation is severable from the 

remainder of the regulation, so long as 

that outcome appears consistent with 

the issuing agency’s intent, and the 

remainder of the regulation can function 

independently without the offending 

provision. See K Mart Corp. v. Cartier, 

Inc., 486 U.S. 281, 294 (1988) 

(invalidating and severing subsection of 

a regulation where it would not impair 

the function of the statute as a whole 

and there was no indication the 

regulation would not have been passed 

but for inclusion of the invalidated 

subsection). Consequently, in the event 

that a court of competent jurisdiction 

stays, enjoins, or invalidates any 

provision, section, or application of this 

rule, the remainder of the rule should be 

allowed to take effect. 

B. Conforming Amendments 

The proposed rule would require 

conforming amendments in 30 CFR 

parts 56, 57, 70, 71, 72, 75, and 90 based 

on the proposed new part 60. 


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35Office of Inspector General Audit 05–21–001– 

06–001, MSHA Needs to Improve Efforts to Protect 

Coal Miners from Respirable Crystalline Silica 

(Nov. 12, 2020). The Inspector General 

recommended that MSHA: 

1. Adopt a lower legal exposure limit for silica 

in coal mines based on recent scientific evidence. 

2. Establish a separate standard for silica that 

allows MSHA to issue a citation and monetary 

penalty when violations of its silica exposure limit 

occur. 

3. Enhance its sampling program to increase the 

frequency of inspector samples where needed (e.g., 

by implementing a risk-based approach). 

1. Part 56—Safety and Health 

Standards—Surface Metal and 

Nonmetal Mines 

a. Section 56.5001—Exposure Limits for 

Airborne Contaminants 

For respirable crystalline silica, 

proposed part 60 would establish 

exposure limits and other related 

requirements for all mines. Existing 

paragraph (a) of § 56.5001 governs 

exposure limits for airborne 

contaminants, except asbestos, for 

surface MNM mines. MSHA is 

proposing to amend paragraph (a) of 

§ 56.5001 to add respirable crystalline 

silica as an exception. The amended 

paragraph (a) of § 56.5001 would govern 

exposure limits for airborne 

contaminants other than respirable 

crystalline silica and asbestos for 

surface MNM mines. 

2. Part 57—Safety and Health 

Standards—Underground Metal and 

Nonmetal Mines 

a. Section 57.5001—Exposure Limits for 

Airborne Contaminants 

Existing paragraph (a) of § 57.5001 

governs exposure limits for airborne 

contaminants, except asbestos, for 

underground MNM mines. Similar to 

the proposed changes discussed above 

for § 56.5001, MSHA is proposing to 

amend paragraph (a) of § 57.5001 to add 

respirable crystalline silica as an 

exception. The amended paragraph (a) 

of § 57.5001 would govern exposure 

limits for airborne contaminants other 

than respirable crystalline silica and 

asbestos for underground MNM mines. 

3. Part 70—Mandatory Health 

Standards—Underground Coal Mines 

a. Section 70.2—Definitions. 

MSHA proposes to remove the Quartz 

definition in § 70.2. With the adoption 

of an independent respirable crystalline 

silica standard in proposed part 60, the 

Agency is proposing to remove RCMD 

when quartz is present in § 70.101 and 

the term quartz would no longer appear 

in part 70. 

b. Section 70.101—Respirable Dust 

Standard When Quartz Is Present 

MSHA is proposing to remove the 

entire section and reserve the section 

number. The RCMD when quartz is 

present in § 70.101 would no longer be 

needed because MSHA is proposing an 

independent respirable crystalline silica 

standard in proposed part 60. 

MSHA’s proposed independent 

standard for respirable crystalline silica 

would result in miners’ exposure to 

respirable crystalline silica no longer 

being controlled indirectly by reducing 

respirable dust. NIOSH, the Secretary of 

Labor’s Advisory Committee on the 

Elimination of Pneumoconiosis Among 

Coal Mine Workers (Dust Advisory 

Committee), and the Department of 

Labor’s Inspector General 35 have each 

recommended the adoption of an 

independent standard for respirable 

quartz exposure in coal mines. NIOSH 

evaluated the effectiveness of the 

existing standard and found the 

approach of controlling miners’ 

exposures to respirable crystalline silica 

indirectly through the control of 

respirable dust did not protect miners 

from excessive exposure to respirable 

quartz in all cases (Joy GJ 2012). The 

study concluded that a separate 

respirable quartz standard, as described 

by the 1995 NIOSH Criteria Document, 

could reduce miners’ risk of 

overexposures to respirable quartz and, 

by extension, their risk of developing 

silicosis. The adoption of a separate 

standard would hold operators 

accountable, at risk of a citation and 

monetary penalty, when overexposures 

of the respirable crystalline silica PEL 

occur and enhance its sampling program 

to increase the frequency of operator 

sampling. 

c. Section 70.205—Approved Sampling 

Devices; Operation; Air Flowrate 

MSHA is proposing to amend 

paragraph (c) of § 70.205 to remove the 

reference to the reduced RCMD 

standard. References to the RCMD 

exposure limit specified in § 70.100 

would replace references to the 

applicable standard. The rest of the 

section would remain unchanged. 

d. Section 70.206—Bimonthly 

Sampling; Mechanized Mining Units 

MSHA is proposing to amend subpart 

C, Sampling Procedures, by removing 

§ 70.206 and reserving the section 

number. Section 70.206 included 

requirements for bimonthly sampling of 

mechanized mining units which were in 

effect until January 31, 2016, and are no 

longer needed. 

e. Section 70.207—Bimonthly Sampling; 

Designated Areas 

MSHA is proposing to amend subpart 

C, Sampling Procedures, by removing 

§ 70.207 and reserving the section 

number. Section 70.207 included 

requirements for bimonthly sampling of 

designated areas that were in effect until 

January 31, 2016, and are no longer 

needed. 

f. Section 70.208—Quarterly Sampling; 

Mechanized Mining Units 

MSHA is proposing to amend § 70.208 

to remove references to a reduced 

RCMD standard. Paragraph (c) in 

§ 70.208 would be removed and the 

paragraph designation reserved. 

References to the respirable dust 

standard specified in § 70.100 would 

replace references to the applicable 

standard throughout the section. 

A new table 1 to § 70.208 would be 

added. The table contains the Excessive 

Concentration Values (ECV) for the 

section based on a single sample, 3 

samples, or the average of 5 or 15 fullshift coal mine dust personal sampler 

unit (CMDPSU) or continuous personal 

dust monitor (CPDM) concentration 

measurements. This table contains the 

remaining ECV after the removal of the 

reduced standard in § 70.101. It was 

generated from data contained in 

existing Tables 70–1 and 70–2 to 

subpart C of part 70. Conforming 

changes are made to paragraphs (e) and 

(f)(1) and (2) to update the name of the 

table to table 1 to § 70.208. 

g. Section 70.209—Quarterly Sampling; 

Designated Areas 

Similar to the proposed changes 

discussed above for § 70.208, MSHA is 

proposing to amend § 70.209 to remove 

references to a reduced RCMD standard. 

Paragraph (b) in § 70.209 would be 

removed and the paragraph designation 

reserved. References to the RCMD 

exposure limit specified in § 70.100 

would replace references to the 

applicable standard. 

A new table 1 to § 70.209 would be 

added. The table contains the ECVs for 

the section based on a single sample, 2 

or more samples, or the average of 5 or 

15 full-shift CMDPSU/CPDM 

concentration measurements. This table 

contains the remaining ECV after the 

removal of the reduced RCMD standard 

in § 70.101. It was generated from data 

contained in existing Tables 70–1 and 

70–2 to subpart C of part 70. 

Conforming changes are made to 

paragraphs (c) and (d)(1) and (2) to 

update the name of the table to table 1 

to § 70.209. 


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h. Subpart C—Table 70–1 and Table 70– 

2 

MSHA is proposing to amend subpart 

C, Sampling Procedures, by removing 

Table 70–1 Excessive Concentration 

Values (ECV) Based on Single, Full-Shift 

CMDPSU/CPDM Concentration 

Measurements and Table 70–2 Excessive 

Concentration Values (ECV) Based on 

the Average of 5 or 15 Full-Shift 

CMDPSU/CPDM Concentration 

Measurements because § 70.101 would 

be removed. These tables would be 

replaced with new tables added to 

§§ 70.208 and 70.209. 

4. Part 71—Mandatory Health 

Standards—Surface Coal Mines and 

Surface Work Areas of Underground 

Coal Mines 

a. Section 71.2—Definitions 

As discussed in the analysis of 

conforming amendments for § 70.2, 

MSHA also proposes to remove the 

Quartz definition in § 71.2 because the 

Agency is proposing to remove the 

respirable dust standard when quartz is 

present in § 71.101. The term quartz 

would no longer appear in part 71. 

b. Section 71.101—Respirable Dust 

Standard When Quartz Is Present 

MSHA is proposing to remove the 

entire section of § 71.101 and reserve 

the section number. Similar to the 

proposed conforming amendments for 

§ 70.101, the respirable coal mine dust 

standard when quartz is present in 

§ 71.101 would no longer be needed 

because MSHA is proposing an 

independent respirable crystalline silica 

standard in part 60. 

MSHA’s proposal to adopt an 

independent standard for respirable 

crystalline silica would replace the 

existing method of indirectly controlling 

miners’ exposure to silica by reducing 

respirable coal dust. As stated 

previously, NIOSH evaluated the 

effectiveness of the existing standard 

and found the existing approach of 

controlling miners’ exposures to 

respirable crystalline silica indirectly 

through the control of respirable dust 

did not protect miners from excessive 

exposure to respirable crystalline silica 

in all cases. The study concluded that 

a separate respirable crystalline silica 

standard, as described by the 1995 

NIOSH Criteria Document, could reduce 

miners’ risk of overexposures to 

respirable crystalline silica and, by 

extension, their risk of developing 

silicosis. The adoption of a separate 

standard would allow MSHA to issue a 

citation and monetary penalty when 

overexposures of the respirable 

crystalline silica PEL occur and enhance 

its sampling program to increase the 

frequency of inspector sampling. 

c. Section 71.205—Approved Sampling 

Devices; Operation; Air Flowrate 

MSHA is proposing to amend 

paragraph (c) of § 71.205 to remove the 

reference to the reduced RCMD 

standard. References to the respirable 

dust standard specified in § 71.100 

would replace the reference to the 

applicable standard. The rest of the 

section would remain unchanged. 

d. Section 71.206—Quarterly Sampling; 

Designated Work Positions 

Similar to the analysis of conforming 

amendments for §§ 70.208 and 70.209, 

MSHA is proposing to amend § 71.206 

to remove references to the reduced 

RCMD standard. Paragraph (b) in 

§ 71.206 would be removed and the 

paragraph designation reserved. Other 

conforming changes for § 71.206 would 

remove references to the applicable 

standard and replace them, where 

needed, with references to the respirable 

dust standard specified in § 71.100 

throughout the section. 

MSHA is also proposing to amend 

paragraph (l) by removing Table 71–1 

Excessive Concentration Values (ECV) 

Based on Single, Full-Shift CMDPSU/ 

CPDM Concentration Measurements and 

Table 71–2 Excessive Concentration 

Values (ECV) Based on the Average of 

5 Full-Shift CMDPSU/CPDM 

Concentration Measurements since 

reference to a reduced RCMD standard 

in § 71.101 would be removed. They 

would be replaced with a new table 

added to § 71.206. 

Existing paragraph (m) would be 

modified by removing the language, ‘‘in 

effect at the time the sample is taken, or 

a concentration of respirable dust 

exceeding 50 percent of the standard 

established in accordance with 

§ 71.101,’’ because the reduced standard 

in § 71.101 would be removed, as 

discussed above, which removes the 

reference to the reduced standard and 

replaces it with a reference to the 

respirable dust standard specified in 

§ 71.100. 

A new table 1 to § 71.206 would be 

added. This table contains the ECV for 

the section based on a single sample, 

two or more samples, or the average of 

five full-shift CMDPSU/CPDM 

concentration measurements. This table 

contains the remaining ECV after the 

removal of the reduced standard in 

§ 71.101. It was generated from data 

contained in existing Tables 71–1 and 

71–2 to subpart C of part 71. 

Conforming changes are made to 

paragraphs (h) and (i)(1) and (2) to 

update the name of the table to table 1 

to § 71.206. 

e. Section 71.300—Respirable Dust 

Control Plan; Filing Requirements 

MSHA is proposing to amend § 71.300 

to remove references to the reduced 

RCMD standard. The respirable dust 

standard specified in § 71.100 would 

replace references to the applicable 

standard. The rest of the section would 

remain unchanged. 

f. Section 71.301—Respirable Dust 

Control Plan; Approval by District 

Manager and Posting 

MSHA is proposing to amend § 71.301 

to remove references to the reduced 

RCMD standard. The respirable dust 

standard specified in § 71.100 would 

replace references to the applicable 

standard. The rest of the section would 

remain unchanged. 

5. Part 72—Health Standards for Coal 

Mines 

a. Section 72.800—Single, Full-Shift 

Measurement of Respirable Coal Mine 

Dust 

MSHA is proposing to amend § 72.800 

in subpart E, Miscellaneous, and remove 

references to the reduced RCMD 

standard. The proposed section would 

also replace references to Tables 70–1, 

71–1, and 90–1 with references to tables 

in §§ 70.208, 70.209, 71.206, and 90.207. 

6. Part 75—Mandatory Safety 

Standards—Underground Coal Mines 

a. Section 75.350(b)(3)(i) and (ii)—Belt 

Air Course Ventilation 

MSHA is proposing to update 

§ 75.350 by revising paragraph (b)(3)(i) 

and removing paragraphs (b)(3)(i)(A) 

and (B) and (b)(3)(ii). 

Paragraph (b)(3)(i)(A) would be 

removed because its provision has not 

been in effect since August 1, 2016. 

Paragraph (b)(3)(i)(B) would be removed 

because the proposed revised language 

in paragraph (b)(3)(i) would be 

simplified by stating that ‘‘[t]he average 

concentration of respirable dust in the 

belt air course, when used as a section 

intake air course, shall be maintained at 

or below 0.5 mg/m3.’’ This would 

ensure that miners would be protected 

from coal dust overexposures, including 

respirable crystalline silica 

overexposures, by maintaining the 

RCMD PEL in the belt air course at 50 

mg/m3. Therefore, paragraph (b)(3)(i)(B) 

which sets the PEL for belt course air at 

0.5 mg/m3 would be redundant. 

Existing paragraph (b)(3)(ii) would be 

removed since it refers to a reduced 

RCMD standard under § 70.101 that 

would also be removed. Existing 


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paragraph (b)(3)(iii) would be 

redesignated to (b)(3)(ii). 

7. Part 90—Mandatory Health 

Standards—Coal Miners Who Have 

Evidence of the Development of 

Pneumoconiosis 

a. Section 90.2—Definitions 

Similar to the proposed changes for 

§§ 70.2 and 71.2, MSHA proposes to 

remove the Quartz definition in § 90.2 

because the Agency proposes to remove 

the respirable dust standard when 

quartz is present in § 90.101. The term 

quartz would no longer appear in part 

90. 

In addition, MSHA is revising the 

definition of Part 90 miner to remove 

references to the reduced RCMD 

standard. The respirable dust standard 

specified in § 90.100 would replace the 

reference to the applicable standard. 

The definition of Part 90 miner would 

also be updated to define Part 90 miners 

as miners who have exercised the 

option to work in an area of a mine 

where the average concentration of 

respirable dust in the mine atmosphere 

during each shift to which that miner is 

exposed is continuously maintained at 

or below the respirable dust standard 

specified in § 90.100. 

b. Section 90.3—Part 90 Option; Notice 

of Eligibility; Exercise of Option 

MSHA is proposing to revise 

paragraph (a) in § 90.3 to require that 

miners diagnosed with pneumoconiosis 

must be afforded the option to work in 

an area of a mine where the average 

concentration of respirable dust is 

continuously maintained below the 

respirable dust standard specified in 

§ 90.100 rather than at or below the 

applicable standard. The rest of the 

section would remain unchanged. 

c. Section 90.101—Respirable Dust 

Standard When Quartz Is Present 

MSHA is proposing to remove the 

entire section and reserve the section 

number. The respirable coal mine dust 

standard when quartz is present in 

§ 90.101 would no longer be needed 

because MSHA is proposing an 

independent respirable crystalline silica 

standard in proposed part 60. 

MSHA’s proposal to adopt an 

independent standard for respirable 

crystalline silica would replace the 

existing method of indirectly controlling 

miners’ exposure to respirable 

crystalline silica by reducing respirable 

coal dust. As stated previously, NIOSH 

evaluated the effectiveness of the 

existing standard and found the existing 

approach of controlling miners’ 

exposures to respirable crystalline silica 

indirectly through the control of 

respirable dust did not protect miners 

from excessive exposure to respirable 

quartz in all cases. The study concluded 

that a separate respirable quartz 

standard, as described by the 1995 

NIOSH Criteria Document, could reduce 

miners’ risk of overexposures to 

respirable quartz and, by extension, 

their risk of developing silicosis. 

d. Section 90.102—Transfer; Notice 

MSHA is proposing to amend § 90.102 

to remove references to the reduced 

RCMD standard. The respirable dust 

standard specified in § 90.100 would 

replace references to the applicable 

standard. The rest of the section would 

remain unchanged. 

e. Section 90.104—Waiver of Rights; ReExercise of Option 

MSHA is proposing to amend § 90.104 

to remove references to the reduced 

RCMD standard. The respirable dust 

standard specified in § 90.100 would 

replace references to the applicable 

standard. The rest of the section would 

remain unchanged. 

f. Section 90.205—Approved Sampling 

Devices; Operation; Air Flowrate 

MSHA is proposing to amend § 90.205 

to remove the reference to the reduced 

RCMD standard. The respirable dust 

standard specified in § 90.100 would 

replace the reference to the applicable 

standard. The rest of the section would 

remain unchanged. 

g. Section 90.206—Exercise of Option or 

Transfer Sampling 

MSHA is proposing to amend § 90.206 

to remove references to the reduced 

RCMD standard. The respirable dust 

standard specified in § 90.100 would 

replace references to the applicable 

standard. The rest of the section would 

remain unchanged. 

h. Section 90.207—Quarterly Sampling 

Similar to the analysis of conforming 

amendments for §§ 70.208, 70.209, and 

71.206, MSHA is proposing to amend 

§ 90.207 to remove references to the 

reduced RCMD standard. Paragraph (b) 

in § 90.207 would be removed and the 

paragraph designation reserved. The 

respirable dust standard specified in 

§ 90.100 would replace references to the 

applicable standard. The rest of the 

section would remain unchanged. 

MSHA is proposing to amend 

paragraph (g) by removing the Table 90– 

1 Excessive Concentration Values (ECV) 

Based on Single, Full-Shift CMDPSU/ 

CPDM Concentration Measurements and 

Table 90–2 Excessive Concentration 

Values (ECV) Based on the Average of 

5 Full-Shift CMDPSU/CPDM 

Concentration Measurements because 

§ 90.101 would be removed. 

A new table 1 to § 90.207 would be 

added to replace the tables removed in 

paragraph (g). The table contains the 

ECV for the section based on a single 

sample, two or more samples, or the 

average of 5 full-shift CMDPSU/CPDM 

concentration measurements. This table 

contains the remaining ECV after the 

removal of the reduced standard in 

§ 90.101. It was generated from data 

contained in existing Tables 90–1 and 

90–2 to subpart C of part 90. 

Conforming changes are made to 

paragraphs (c) and (d)(1) and (2) to 

update the name of the table to table 1 

to § 90.207. 

i. Section 90.300—Respirable Dust 

Control Plan; Filing Requirements 

MSHA is proposing to amend § 90.300 

to remove references to the reduced 

RCMD standard. The respirable dust 

standard specified in § 90.100 would 

replace references to the applicable 

standard. The rest of the section would 

remain unchanged. 

j. Section 90.301—Respirable Dust 

Control Plan; Approval by District 

Manager; Copy to Part 90 Miner 

MSHA is proposing to amend § 90.301 

to remove references to the reduced 

RCMD standard. The respirable dust 

standard specified in § 90.100 would 

replace references to the applicable 

standard. The rest of the section would 

remain unchanged. 

C. Updating MSHA Respiratory 

Protection Standards: Proposed 

Incorporation of ASTM F3387–19 by 

Reference 

MSHA is proposing to update the 

Agency’s existing respiratory protection 

standard to help safeguard the life and 

health of all miners exposed to 

respirable airborne hazards at MNM and 

coal mines. The proposed rule would 

incorporate by reference ASTM F3387– 

19, ‘‘Standard Practice for Respiratory 

Protection’’ (ASTM F3387–19), as 

applicable, in existing §§ 56.5005, 

57.5005, and 72.710, as well as in 

proposed § 60.14(c)(2). The ASTM 

F3387–19 standard includes provisions 

for selection, fitting, use, and care of 

respirators used to remove airborne 

contaminants from the air using filters, 

cartridges, or canisters, as well as 

respirators that protect in oxygendeficient or immediately dangerous to 

life or health (IDLH) atmospheres. 

ASTM F3387–19 is based on the most 

recent consensus standards recognized 

by experts in government and 

professional associations on the 

selection, use, and maintenance for 


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respiratory equipment. The ASTM 

Standard would replace American 

National Standards Institute’s ANSI 

Z88.2–1969, ‘‘Practices for Respiratory 

Protection’’ (ANSI Z88.2–1969), which 

is incorporated in the existing 

standards. 

Incorporating this voluntary 

consensus standard complies with the 

Federal mandate—as set forth in the 

National Technology Transfer and 

Advancement Act of 1995 and OMB 

Circular A119—that agencies use 

voluntary consensus standards in their 

regulatory activities unless doing so 

would be legally impermissible or 

impractical. This standard proposed for 

incorporation would also improve 

clarity because it is a consensus 

standard developed by stakeholders. 

Under existing standards, whenever 

respiratory protective equipment is 

used, mine operators are required to 

have a respiratory protection program 

that is consistent with the provisions of 

ANSI Z88.2–1969. At the time of its 

publication, ANSI Z88.2–1969 reflected 

a consensus of accepted practices for 

respiratory protection. 

Respirator technology and knowledge 

on respiratory protection have since 

advanced and as a result, changes in 

respiratory protection standards have 

occurred. For example, in 2006, OSHA 

revised its respiratory protection 

standard to add definitions and 

requirements for Assigned Protection 

Factors (APF) and Maximum Use 

Concentrations (MUCs) (71 FR 50121, 

50122, Aug. 24, 2006). In addition to 

this rulemaking, OSHA updated 

Appendix A to § 1910.134: Fit Testing 

Procedures (69 FR 46986, 46993, Aug. 4, 

2004). 

After withdrawing the 1992 version of 

Z–88.2 in 2002, ANSI published the 

American National Standard, ANSI/ 

AIHA Z88.10–2010, ‘‘Respirator Fit 

Testing Methods,’’ approved in 2010. 

These rules and standards addressed the 

topics of APFs and fit testing. APFs 

provide employers with critical 

information to use when selecting 

respirators for employees exposed to 

atmospheric contaminants found in 

industry. Finally, in 2015, ANSI 

published ANSI/ASSE Z88.2–2015, 

‘‘Practices for Respiratory Protection,’’ 

which referenced OSHA regulations. 

These updates included requirements 

for classification of considerations for 

selection and use of respirators, 

establishment of cartridge/canister 

change schedules, use of fit factor value 

for respirator fit testing, calculation of 

effective protection factors, and 

compliance with compressed air dew 

requirements, compressed breathing air 

equipment, and systems and 

designation of positive pressure 

respirators. In July 2017, ANSI/ASSE 

transferred the responsibilities for 

developing respiratory consensus 

standards to ASTM International. 

ASTM F3387–19 is based on the most 

recent consensus standards recognized 

by experts in government and 

professional associations on the 

selection, use, and maintenance for 

respiratory protection equipment. The 

standard contains detailed guidance and 

provisions on respirator selection that 

are based on NIOSH’s long-standing 

experience of testing and approving 

respirators for occupational use and 

OSHA’s research and rulemaking on 

respiratory protection. ASTM F3387–19 

also addresses all aspects of 

establishing, implementing, and 

evaluating respiratory protection 

programs and establishes minimum 

acceptable respiratory protection 

program elements in the areas of 

program administration, standard 

operating procedures, medical 

evaluation, respirator selection, training, 

fit testing, respirator maintenance, 

inspection, and storage. ASTM F3387– 

19 comprehensively covers numerous 

aspects of respiratory protection and 

provides the most up-to-date provisions 

for current respirator technology and 

effective respiratory protection. 

Therefore, MSHA believes that ASTM 

F3387–19 would provide mine 

operators with information and 

guidance on the proper selection, use, 

and maintenance of respirators, which 

would protect the health and safety of 

miners. 

Under this proposed rule, MSHA 

would require that operators establish a 

respiratory protection program in 

writing, that includes minimally 

acceptable program elements: program 

administration; standard operating 

procedures; medical evaluations; 

respirator selection; training; fit testing; 

and maintenance, inspection, and 

storage. 

Beyond the minimally acceptable 

program elements, MSHA proposes to 

provide mine operators with flexibility 

to select the provisions in ASTM 

F3387–19 that are applicable to the 

conditions of their mines and respirator 

use by their miners. In MSHA’s 

experience, the need for and actual use 

of respirators varies among mines for 

different reasons, including the type of 

commodity mined or processed and the 

mining method and controls used. At 

some mines, miners may not use or may 

only rarely use respirators. At other 

mines, miners may use respirators more 

frequently. Recognizing these 

differences, MSHA would allow mine 

operators to comply with the provisions 

in ASTM F3387–19 that they deem are 

relevant and appropriate for their 

mining operations and conditions. 

MSHA has observed that many 

operators, in particular larger mine 

operators, have already implemented in 

their respiratory programs many OSHA 

requirements, which are substantially 

similar to many requirements in ASTM 

F3387–19. Indeed, ASTM F3387–19 

refers to OSHA’s regulations on 

respiratory protection programs, APFs 

and MUCs, and fit testing. MSHA 

believes that the mining industry is 

already familiar with many provisions 

in ASTM F3387–19. MSHA anticipates 

that for many large mine operators, few 

changes to their respiratory protection 

program may be warranted, whereas 

small mines, or mines that use 

respirators intermittently, may need to 

revise their respiratory practices in 

accordance with the requirements, as 

applicable, in ASTM F3387–19. 

1. Respiratory Program Elements 

Under the proposed rule, MSHA 

would require that the respiratory 

protection program be in writing and 

that it include the following minimally 

acceptable program elements: program 

administration; standard operating 

procedures; medical evaluations; 

respirator selection; training; fit testing; 

and maintenance, inspection, and 

storage. 

a. Program Administration 

ASTM F3387–19 specifies several 

practices related to respiratory 

protection program administration, 

including the qualifications and 

responsibilities of a program 

administrator. For example, ASTM 

F3387–19 provides that responsibility 

and authority for the respirator program 

be assigned to a single qualified person 

with sufficient knowledge of respiratory 

protection. Qualifications could be 

gained through training or experience; 

however, the qualifications of a program 

administrator must be commensurate 

with the respiratory hazards present at 

a worksite. 

This individual should have access to 

and direct communication with the site 

manager about matters impacting 

worker safety and health. ASTM F3387– 

19 notes a preference that the 

administrator be in the company’s 

industrial hygiene, environmental, 

health physics, or safety engineering 

department; however, a third-party 

entity meeting the provisions may also 

provide this service. ASTM F3387–19 

outlines the respiratory program 

administrator’s responsibilities, 

specifying that they should include: 

measuring, estimating, or reviewing 


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information on the concentration of 

airborne contaminants; ensuring that 

medical evaluations, training, and fit 

testing are performed; selecting the 

appropriate type or class of respirator 

that will provide adequate protection for 

each contaminant; maintaining records; 

evaluating the respirator program’s 

effectiveness; and revising the program, 

as necessary. 

b. Standard Operating Procedures (SOP) 

SOPs are written policies and 

procedures available for all wearers of 

respirators to read and are established 

by the employer. ASTM F3387–19 states 

that written SOPs for respirator 

programs are necessary when respirators 

are used routinely or sporadically. 

Written SOPs should cover hazard 

assessment; respirator selection; 

medical evaluation; training; fit testing; 

issuance, maintenance, inspection, and 

storage of respirators; schedule of airpurifying elements; hazard reevaluation; employer policies; and 

program evaluation and audit. ASTM 

F3387–19 also provides that wearers of 

respirators be provided with copies of 

the SOP and that written SOPs include 

special consideration for respirators 

used for emergency situations. The 

procedures are reviewed in conjunction 

with the annual respirator program 

audit and are revised by the program 

administrator, as necessary. 

c. Medical Evaluation 

Medical evaluations determine 

whether an employee has any medical 

conditions that would preclude the use 

of respirators, limitation on use, or other 

restrictions. ASTM F3387–19 provides 

that a program administrator advise the 

PLHCP of the following conditions to 

aid in determining the need for a 

medical evaluation: type and weight of 

the respirator to be used; duration and 

frequency of respirator use (including 

use for rescue and escape); typical work 

activities; environmental conditions 

(e.g., temperature); hazards for which 

the respirator will be worn, including 

potential exposure to reduced-oxygen 

environments; and additional protective 

clothing and equipment to be worn. 

ASTM F3387–19 also incorporates ANSI 

Z88.6 Respiratory Protection— 

Respirator Use—Physical Qualifications 

for Personnel. 

d. Respirator Selection 

Proper respirator selection is an 

important component of an effective 

respiratory protection program. ASTM 

F3387–19 provides that proper 

respirator selection consider the 

following: the nature of the hazard, 

worker activity and workplace factors, 

respirator use duration, respirator 

limitations, and use of approved 

respirators. ASTM F3387–19 states that 

respirator selection for both routine and 

emergency use include hazard 

assessment, selection of respirator type 

or class that can offer adequate 

protection, and maintenance of written 

records of hazard assessment and 

respirator selection. 

ASTM F3387–19 provides specific 

steps to establish the nature of 

inhalation hazards, including 

determining the following: the types of 

contaminants present in the workplace; 

the physical state and chemical 

properties of all airborne contaminants; 

the likely airborne concentration of the 

contaminants (by measurement or by 

estimation); potential for an oxygendeficient environment; an occupational 

exposure limit for each contaminant; 

existence of an IDLH atmosphere; and 

compliance with applicable health 

standards for the contaminants. 

ASTM F3387–19 includes other 

information to support the respirator 

selection process, including information 

on operational characteristics, 

capabilities, and performance 

limitations of various types of 

respirators. These limitations must be 

considered during the selection process. 

ASTM F3387–19 also describes types of 

respirators and consideration for their 

use, including service life, worker 

mobility, compatibility with other 

protective equipment, durability, 

comfort factors, compatibility with the 

environment, and compatibility with job 

and workforce performance. Finally, 

ASTM F3387–19 provides other 

essential information regarding 

respirator selection such as oxygen 

deficiency, ambient noise, and need for 

communication. 

e. Training 

Employee training is essential for 

correct respirator use. ASTM F3387–19 

provides that all users be trained in 

their area of responsibility by a qualified 

person to ensure the proper use of 

respirators. A respirator trainer must be 

knowledgeable in the application and 

use of the respirators and must 

understand the site’s work practices, 

respirator program, and applicable 

regulations. Employees who receive 

training include the workplace 

supervisor, the person issuing and 

maintaining respirators, respirator 

wearers, and emergency teams. To 

ensure the proper and safe use of a 

respirator, ASTM F3387–19 also 

provides that the minimum training for 

each respirator wearer includes: the 

need for respiratory protection; the 

nature, extent, and effects of respiratory 

hazards in the workplace; reasons for 

particular respirator selections; reasons 

for engineering controls not being 

applied or reasons why they are not 

adequate; types of efforts made to 

reduce or eliminate the need for 

respirators; operation, capabilities, and 

limitations of the respirators selected; 

instructions for inspecting, donning, 

and doffing the respirator; the 

importance of proper respirator fit and 

use; and maintenance and storage of 

respirators. The standard provides for 

each respirator wearer to receive initial 

and annual training. Workplace 

supervisors and persons issuing 

respirators are retrained as determined 

by the program administrator. Training 

records for each respirator wearer are 

maintained and include the date, type of 

training received, performance results 

(as appropriate), and instructor’s name. 

f. Respirator Fit Testing 

A serious hazard may occur if a 

respirator, even though properly 

selected, is not properly fitted. For 

example, if a proper face seal is not 

achieved, the respirator would provide 

a lower level of protection than it is 

designed to provide because the 

respirator could allow contaminants to 

leak into the breathing area. Proper fit 

testing verifies that the selected make, 

model, and size of a respirator 

adequately fits and ensures that the 

expected level of protection is provided. 

ASTM F3387–19 includes provisions for 

qualitative and quantitative fit testing to 

determine the ability of a respirator 

wearer to obtain a satisfactory fit with 

a tight-fitting respirator and 

incorporates ANSI/AIHA Z88.10, 

Respirator Fit Testing Methods, for 

guidance on how to conduct fit testing 

of tight-fitting respirators and 

appropriate methods to be used. ASTM 

F3387–19 also provides information on 

conducting quantitative and qualitative 

fits test to determine how well a tightfitting respirator fits a wearer. This 

includes information on the application 

of fit factors and assigned protection 

factors, and how these factors are used 

to ensure that a wearer is receiving the 

necessary protection. ASTM F3387–19 

provides for each respirator wearer to be 

fit tested before being assigned a 

respirator (currently at least once every 

12 months or repeated when a wearer 

expresses concern about respirator fit or 

comfort or has a condition that may 

interfere with the face piece seal). 

g. Maintenance, Inspection, and Storage 

Proper maintenance and storage of 

respirators are important in a respiratory 

protection program. ASTM F3387–19 

includes specific provisions for 


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decontaminating, cleaning, and 

sanitizing respirators, inspecting 

respirators, replacing, and repairing 

parts, and storing and disposing of 

respirators. For example, the 

decontamination provisions state that 

respirators are decontaminated after 

each use and cleaned and sanitized 

regularly per manufacturer instructions. 

Following cleaning and disinfection, 

reassembled respirators are inspected to 

verify proper working condition. ASTM 

F3387–19 states that employers consult 

manufacturer instructions to determine 

component expiration dates or end-ofservice life, inspect the rubber or other 

elastomeric components of respirators 

for signs of deterioration that would 

affect respirator performance, and repair 

or replace respirators failing inspection. 

ASTM F3387–19 also provides that 

respirators are stored according to 

manufacturer recommendations and in a 

manner that will protect against hazards 

(i.e., physical, biological, chemical, 

vibration, shock, temperature extremes, 

moisture, etc.). It also provides that 

respirators are stored to prevent 

distortion of rubber or other parts. 

2. Section-by-Section Analysis of 

Incorporation by Reference—ASTM 

F3387–19 

a. Part 56—Safety and Health 

Standards—Surface Metal and 

Nonmetal Mines—Section 56.5005— 

Control of Exposure to Airborne 

Contaminants 

Existing § 56.5005 provides that 

whenever respiratory protective 

equipment is used, a program for 

selection, maintenance, training, fitting, 

supervision, cleaning, and use shall 

meet the requirements of paragraph (b). 

Paragraph (b) requires that mine 

operators implement a respirator 

program consistent with the 

requirements of ANSI Z88.2–1969. 

MSHA is proposing to revise paragraph 

(b) to remove the incorporation by 

reference to ANSI Z88.2–1969 and 

incorporate by reference ASTM F3387– 

19. 

MSHA is proposing to revise 

paragraph (b) to state that approved 

respirators must be selected, fitted, 

cleaned, used, and maintained in 

accordance with the requirements of 

ASTM F3387–19 ‘‘as applicable.’’ Under 

the proposal, MSHA would require that 

the respiratory program be in writing 

and that it include the following 

minimally acceptable program elements: 

program administration; standard 

operating procedures; medical 

evaluations; respirator selection; 

training; fit testing; and maintenance, 

inspection, and storage. 

Also, MSHA is proposing to change 

paragraph (c) to require the presence of 

at least one other person with backup 

equipment and rescue capability when 

respiratory protection is used in 

atmospheres that are IDLH. This change 

is needed to conform to language in the 

proposed incorporation by reference of 

ASTM F3387–19, which defines IDLH 

as ‘‘any atmosphere that poses an 

immediate hazard to life or immediate 

irreversible debilitating effects on 

health’’ (ASTM International 2019). 

b. Part 57—Safety and Health 

Standards—Underground Metal and 

Nonmetal Mines—Section 57.5005— 

Control of Exposure to Airborne 

Contaminants 

Existing § 57.5005 provides that 

whenever respiratory protective 

equipment is used, a program for 

selection, maintenance, training, fitting, 

supervision, cleaning, and use shall 

meet the requirements of paragraph (b). 

Paragraph (b) requires that mine 

operators implement a respirator 

program consistent with the 

requirements of ANSI Z88.2–1969. 

MSHA is proposing to revise paragraph 

(b) to remove the incorporation by 

reference to ANSI Z88.2–1969 and 

incorporate by reference ASTM F3387– 

19. 

MSHA is proposing to revise 

paragraph (b) to state that approved 

respirators must be selected, fitted, 

cleaned, used, and maintained in 

accordance with the requirements of 

ASTM F3387–19 ‘‘as applicable.’’ Under 

the proposal, MSHA would require that 

the respiratory program be in writing 

and that it include the following 

minimally acceptable program elements: 

program administration; standard 

operating procedures; medical 

evaluations; respirator selection; 

training; fit testing; and maintenance, 

inspection, and storage. 

Also, MSHA is proposing to change 

paragraph (c) to require the presence of 

at least one other person with backup 

equipment and rescue capability when 

respiratory protection is used in 

atmospheres that are IDLH. This change 

is needed to conform to language in the 

proposed incorporation by reference of 

ASTM F3387–19, which defines the 

term IDLH as ‘‘any atmosphere that 

poses an immediate hazard to life or 

immediate irreversible debilitating 

effects on health’’ (ASTM International 

2019). 

c. Part 72—Health Standards for Coal 

Mines—Section 72.710—Selection, Fit, 

Use, and Maintenance of Approved 

Respirators 

Existing § 72.710 requires approved 

respirators be selected, fitted, used, and 

maintained in accordance with the 

provisions of ANSI Z88.2–1969, which 

was incorporated by reference into coal 

standards in 1995 (60 FR 30398, June 8, 

1995). MSHA is proposing to revise 

§ 72.710 by removing the requirement in 

the first sentence that coal mine 

operators must ensure that the 

maximum amount of respiratory 

protection is made available to miners 

when respirators are used. MSHA 

believes that the use of approved 

respirators and the proposed 

incorporation by reference of ASTM 

F3387–19 would ensure that coal 

miners’ health is protected. Under the 

proposal, MSHA would require that the 

respiratory program be in writing and 

that it include the following minimally 

acceptable program elements: program 

administration; standard operating 

procedures; medical evaluations; 

respirator selection; training; fit testing; 

and maintenance, inspection, and 

storage. 

VIII. Technological Feasibility 

This technological feasibility analysis 

considers whether currently available 

technologies, used alone or in 

combination with each other, can be 

used by operators to comply with the 

proposed standard. 

MSHA is required to set standards to 

assure, based on the best available 

evidence, that no miner will suffer 

material impairment of health or 

functional capacity from exposure to 

toxic materials or harmful physical 

agents over his working life. 30 U.S.C. 

811(a)(6)(A). The Mine Act also 

instructs MSHA to set health standards 

to attain ‘‘the highest degree of health 

and safety protection for the miner’’ 

while considering ‘‘the latest available 

scientific data in the field, the feasibility 

of the standards, and experience gained 

under this and other health and safety 

laws.’’ 30 U.S.C. 811(a)(6)(A). But the 

health and safety of the miner is always 

the paramount consideration: ‘‘[T]he 

Mine Act evinces a clear bias in favor 

of miner health and safety,’’ and ‘‘[t]he 

duty to use the best evidence and to 

consider feasibility are appropriately 

viewed through this lens and cannot be 

wielded as counterweight to MSHA’s 

overarching role to protect the life and 

health of workers in the mining 

industry.’’ Nat’l Min. Ass’n v. Sec’y, 

U.S. Dep’t of Lab., 812 F.3d 843, 866 

(11th Cir. 2016); 30 U.S.C. 801(a). 


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36Other similar XRD methods include NIOSH– 

7500 and OSHA ID–142. XRD methods are able to 

distinguish between the different polymorphs— 

quartz, cristobalite and tridymite. Other IR methods 

include NIOSH 7602 and 7603. IR methods are 

efficient, but they are more prone to interferences 

and should only be used for samples with a wellcharacterized matrix (e.g., coal dust). 

The D.C. Circuit clarified the 

Agency’s obligation to demonstrate the 

technological feasibility of reducing 

occupational exposure to a hazardous 

substance. MSHA ‘‘must only 

demonstrate a ‘reasonable possibility’ 

that a ‘typical firm’ can meet the 

permissible exposure limits in ‘most of 

its operations.’’ Kennecott Greens Creek 

Min. Co. v. Mine Safety & Health 

Admin., 476 F.3d 946, 958 (D.C. Cir. 

2007) (quoting American Iron & Steel 

Inst. v. OSHA, 939 F.2d 975, 980 (D.C. 

Cir. 1991)). 

This section presents technological 

feasibility findings that guided MSHA’s 

selection of the proposed PEL. MSHA’s 

technological feasibility findings are 

organized into two main sections 

covering: (1) the technological 

feasibility of proposed part 60; and (2) 

the technological feasibility of the 

proposed revision to existing respiratory 

protection standards. Based on the 

analyses presented in the two sections, 

MSHA preliminarily concludes that the 

Agency’s proposal is technologically 

feasible. MSHA’s feasibility 

determinations in this rulemaking are 

supported by its findings that the 

majority of the industry is already using 

technology that would be sufficient to 

comply with the proposed rule. 

First, MSHA has preliminarily 

determined that proposed part 60 is 

technologically feasible. Many mine 

operators already maintain respirable 

crystalline silica exposures at or below 

the proposed PEL of 50 mg/m3, and at 

mines where there are elevated 

exposures, operators would be able to 

reduce exposures to at or below the 

proposed PEL by properly maintaining 

existing engineering controls and/or by 

implementing new engineering and 

administrative controls that are 

currently available. In addition, mines 

would be able to satisfy the exposure 

monitoring requirements of proposed 

part 60 with existing, validated, and 

widely used sampling technologies and 

analytical methods. 

Second, the analysis shows that the 

proposed update to MSHA’s respiratory 

protection requirements is also 

technologically feasible. The mining 

industry’s existing respiratory 

protection practices for selecting, fitting, 

using, and maintaining respiratory 

protection include program elements 

that are similar to those of ASTM 

F3387–19, ‘‘Standard Practice for 

Respiratory Protection’’ (ASTM F3387– 

19), which MSHA is proposing to 

incorporate by reference. 

A. Technological Feasibility of 

Sampling and Analytical Methods 

1. Sampling Methods 

MSHA’s proposed rule would require 

mine operators in both MNM and coal 

mines to conduct sampling for 

respirable crystalline silica using 

respirable particle size-selective 

samplers that conform to the 

‘‘International Organization for 

Standardization (ISO) 7708:1995: Air 

Quality—Particle Size Fraction 

Definitions for Health-Related 

Sampling’’ standard. The ISO 

convention defines respirable 

particulates as having a 4 micrometer 

(mm) aerodynamic diameter median cutpoint (i.e., 4 mm-sized particles are 

collected with 50 percent efficiency), 

which approximates the size 

distribution of particles that when 

inhaled can reach the alveolar region of 

the lungs. For this reason, the ISO 

convention is widely considered 

biologically relevant for respirable 

particulates and provides appropriate 

criteria for equipment used to sample 

respirable crystalline silica. MSHA’s 

current sampling method for MNM 

mines meets the ISO criteria by using a 

10 mm Dorr-Oliver cyclone and a 

sampling pump operated at a flow rate 

of 1.7 liter per minute (L/min), and 

MNM mine operators also already use 

this type of sampler for MNM sampling 

under existing standards. MSHA’s 

current sampling method for RCMD, 

including respirable crystalline silica, 

uses a 10 mm Dorr-Oliver cyclone but 

operated at 2.0 L/min to approximate 

the British Mining Research 

Establishment (MRE) sampling criteria, 

and thus does not meet the ISO criteria. 

Although, the existing sampling pumps 

can be adjusted to operate at a flow rate 

of 1.7 L/min flow rate to meet the ISO 

criteria. To comply with this proposed 

requirement, coal mine operators that 

currently use coal mine dust personal 

sampler units (CMDPSU) would need to 

adjust their samplers to the flow rate 

specified by the manufacturer for 

complying with the ISO. 

There are a variety of size-selective 

samplers on the market that meet the 

ISO respirable-particle-size selection 

criteria. Examples include Dorr-Oliver 

cyclone currently used by MSHA and 

OSHA, operated at 1.7 L/min; SKC 

aluminum cyclone (2.5 L/min); HD 

cyclone (2.2 L/min); SKC GS–3 multiinlet cyclone (2.75 L/min); and BGI GK 

2.69 (4.2 L/min). Each cyclone has 

different operating specifications and 

performance criteria, but they all are 

compliant with the ISO criteria for 

respirable dust with an acceptable level 

of measurement bias. Manufacturers of 

size-selective samplers specify the flow 

rates that are necessary to conform to 

the particle size collection criteria of the 

ISO standard. Samplers used in both 

MNM and coal mines can be used to 

perform the proposed sampling, and 

because other commercially available 

(already on the market) samplers 

conform to the ISO standard, MSHA 

preliminarily finds that sampling in 

accordance with the ISO standard is 

technologically feasible. 

2. Analytical Methods and Feasibility of 

Measuring Below the Proposed PEL and 

Action Level 

After a respirable dust sample is 

collected and submitted to a laboratory, 

it must be analyzed to quantify the mass 

of respirable crystalline silica present. 

The laboratory method must be 

sensitive enough to detect and quantify 

respirable crystalline silica at levels 

below the applicable concentration. The 

analytical limit of detection (LOD) and/ 

or limit of quantification (LOQ), 

together with the sample volume, 

determine the airborne concentration 

LOD and/or LOQ for a given air sample. 

MSHA proposes a PEL for respirable 

crystalline silica of 50 mg/m3 as a full 

shift, 8-hour TWA for both MNM and 

coal mines. Several analytical methods 

are available for measuring respirable 

crystalline silica at levels well below the 

proposed PEL of 50 mg/m3 and action 

level of 25 mg/m3. 

MSHA uses two main analytical 

methods (1) P–2: X-Ray Diffraction 

Determination Of Quartz And 

Cristobalite In Respirable Metal/ 

Nonmetal Mine Dust (analysis by X-ray 

diffraction, XRD) for MNM mines and 

(2) P–7: Determination Of Quartz In 

Respirable Coal Mine Dust By Fourier 

Transform Infrared Spectroscopy 

(analysis by infrared spectroscopy, FTIR 

or IR) for coal mines.36 The MSHA P– 

2 and P–7 methods, reliably analyze 

compliance samples collected by MSHA 

inspectors, including 15 years of MNM 

compliance samples and 5 years of coal 

industry compliance samples MSHA 

used for the exposure profile portion of 

this technological feasibility analysis. 

These methods are capable of measuring 

respirable crystalline silica exposures at 

levels below the proposed PEL and 

action level. 

For an analytical method to have 

acceptable sensitivity for determining 


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37The small capacity laboratory has a maximum 

respirable crystalline silica sample analysis 

capacity of 300 samples per month (280 additional 

samples per month above the current number of 

samples analyzed), a level which the laboratory 

could sustain for two months. 

38The medium capacity laboratory has a 

maximum respirable crystalline silica sample 

analysis capacity of 2,025 samples per month. Surge 

from the mining industry is considered to replace, 

rather than be in addition to the current number of 

samples analyzed. 

39The large capacity laboratory has a maximum 

respirable crystalline silica sample analysis 

capacity of 4,500 samples per month (3,700 

additional samples per month above the current 

number of samples analyzed). 

exposures at the proposed PEL of 50 mg/ 

m3 and action level of 25 mg/m3, the 

LOQ must be at or below the amount of 

analyte (e.g., quartz) that would be 

collected in an air sample where the 

concentration of analyte is equivalent to 

the proposed PEL or action level. To 

determine the minimum airborne 

concentration that can be quantified, the 

LOQ mass is divided by the sample air 

volume, which is determined by the 

sampling flow rate and duration. Table 

VIII–1 presents minimum quantifiable 

quartz concentrations, for various 

cyclones and established analytical 

methods. 

Based on this discussion, MSHA 

preliminarily finds that current 

analytical methods are sufficiently 

sensitive to meet the proposed PEL and 

action level. 

3. Laboratory Capacity 

MSHA’s proposed standard would 

require that mines conduct baseline 

sampling, periodic sampling, corrective 

actions sampling, and post-evaluation 

sampling with analyses conducted by 

laboratories that meet ISO 17025, 

General Requirements for the 

Competence of Testing and Calibration 

Laboratories (ISO 17025). The majority 

of U.S. industrial hygiene laboratories 

that perform respirable crystalline silica 

analysis are accredited to ISO 17025 by 

the American Industrial Hygiene 

Association (AIHA) Laboratory 

Accreditation Program (LAP). The AIHA 

LAP lists 23 accredited commercial 

laboratories nationwide that, as of April 

2022, perform respirable crystalline 

silica analysis using an MSHA, NIOSH 

or OSHA method. 

MSHA interviewed a sample of three 

laboratories (one small-capacity 

laboratory,37 one medium-capacity 

laboratory,38 and one large-capacity 

laboratory) 39 to estimate their sampleprocessing capacity. Insights from these 

interviews suggest that laboratories have 

the ability to provide surge capacity as 

the proposed rule is phased in. 

Collectively, these three laboratories 

could process approximately 33,240 

samples by XRD (suitable for MNM 

mines) and 1,752 samples by FTIR or IR 

(suitable for coal mines) within a 6- 

month period. Extrapolating this across 

all laboratories that can analyze 

respirable crystalline silica samples, 

MSHA estimates that 232,680 samples 

for MNM mines and 12,250 samples for 

coal mines could be processed in the 

phase-in 6-month period. Over the first 

12 months after the standard goes into 

effect, analysis would be available for 

465,360 samples for MNM mines and 

24,500 samples for coal mines. 

Based on exposure profiles for the 

MNM and coal mining industries and 

MSHA’s experience and knowledge of 

the mining industry, MSHA estimates 

that within this first 12-month period, 

mines would seek analysis for a total of 

172,907 respirable crystalline silica 

samples (including 58,126 samples for 

MNM mines and 12,373 samples for 

coal mines associated with the 6-month 

baseline sampling period). In the 

subsequent 12-month period, mines 

would require analysis for 102,409 

samples (includes process/control 

measure evaluation samples and 

periodic samples associated with the 


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40MSHA anticipates that in the initial six-month 

baseline period mine operators will collect 70,498 

baseline samples, of which 12,373 will be coal mine 

samples. In the 12 months beginning after the initial 

baseline period, mines will collect 88,281 samples 

for miners who are exposed at or above the 

proposed action level (25 mg/m3), but at or below 

the proposed PEL, plus 14,128 samples to evaluate 

corrective action and process change (i.e., processes 

which must be analyzed to determine whether 

newly implemented dust control measures are 

successful and processes newly identified during 

periodic walk-through evaluations), for a total of 

102,409 samples per year (including 25,152 coal 

mine samples). Estimates are as of December 2022. 

41Where several miners perform similar activities 

on the same shift, only a representative fraction of 

miners (minimum of two miners) would need to be 

sampled, including those expected to have the 

highest exposures. 

42 489,860 total annual laboratory analyses 

divided by 172,907 mine samples to be analyzed, 

equals 2.83 percent surplus sample analyses. 

489,860 total analyses¥70,498 baseline analyses = 

a surplus of 419,362 analyses available for the 

102,409 periodic, corrective actions, and process 

change sampling. 

43These respirable crystalline silica exposure 

data consist of 15 years of MNM mine samples 

(January 1, 2005, through December 31, 2019) and 

five years of coal mine samples (August 1, 2016, 

through July 31, 2021). These MSHA compliance 

samples represent the conditions identified by 

MSHA inspectors as having the greatest potential 

for respirable crystalline silica exposure during the 

periodic inspection when sampling occurred. While 

MSHA’s laboratory also analyzes mine operators’ 

respirable coal mine dust samples containing 

respirable crystalline silica, those samples are not 

included in the data used for this analysis. 

44Together, these two recent reports provide 

more than 500 pages of detailed descriptions, 

discussion, and illustrations of dust control 

technologies currently used in mines. 

45MSHA also analyzes RCMD samples collected 

by mine operators, including those containing 

respirable crystalline silica, in addition to the 

compliance samples collected by MSHA inspectors 

(mentioned in the first bullet of this series). 

46Project personnel reviewed 104,365 samples 

collected and analyzed by MSHA for respirable 

crystalline silica, plus another 103,745 samples 

collected but not analyzed due to insufficient 

respirable dust collected in the sample. They 

examined over 200 published reports, proceedings, 

case studies, analytical methods, and journal 

articles, in addition to inspecting more than 200 

web page, product brochures, user manuals, 

service/maintenance manuals and descriptive 

literature for dust control products, mining 

equipment, and related services. 

proposed action level), a number that 

will decline over years 1 through 6 as 

the mine operators reduce some miner 

exposures below the proposed action 

level.40 Comparing these figures with 

the surge capacity estimates previously 

noted above, MSHA believes that there 

would be sufficient processing capacity 

to meet the sampling analysis schedule 

envisioned in the proposed rule. 

a. Baseline Sampling 

MSHA’s proposal would require 

baseline sampling for each miner who is 

or may reasonably be expected to be 

exposed to respirable crystalline silica 

within 180 days (6 months) of the 

standard’s effective date.41 This would 

require an initial increase in analytical 

laboratory capacity of approximately 

70,498 sample analyses over 6 months. 

MSHA expects that with months of lead 

time during the proposed rule and final 

rule stages of the rulemaking, 

laboratories would anticipate the initial 

baseline period increase in demand and 

would respond by increasing their 

analytical capacity. For example, 

laboratories could acquire additional 

instrumentation, train additional 

analysts, or add a second or third 

operating shift. This is particularly 

likely given that demand would be 

based on a regulatory requirement and 

during the rulemaking process MSHA 

would conduct outreach to make all 

relevant stakeholders aware of the rule’s 

provisions. MSHA is specifically 

soliciting comments on the 

technological feasibility of laboratory 

capability to conduct baseline sampling. 

At this point in the rulemaking, MSHA 

believes that the proposed rule is 

technologically feasible for laboratories 

to conduct baseline sampling analyses. 

b. Periodic, Corrective Actions, and 

Post-Evaluation Sampling 

Under proposed § 60.12 (b)–(e), three 

conditions would require mine 

operators to conduct additional 

sampling after the initial 6-month 

baseline period. First, when the most 

recent sampling indicates that miner 

exposures are at or above the proposed 

action level (25 mg/m3) but at or below 

the proposed PEL (50 mg/m3), the mine 

operator would be required to sample 

within 3 months of that sampling and 

continue to sample within 3 months of 

the previous sampling until two 

consecutive samplings indicate that 

miner exposures are below the action 

level. Second, where the most recent 

sampling indicates that miner exposures 

are above the PEL, the mine operator 

would be required to sample after 

corrective actions are taken to reduce 

overexposures, until sampling results 

indicate miner exposures are at or below 

the PEL. Third, if the mine operator 

determines, as a result of the semiannual evaluation, that miners may be 

exposed to respirable crystalline silica 

at or above the action level, the mine 

operator would be required to perform 

sampling to assess the full-shift, 8-hour 

TWA exposure of respirable crystalline 

silica for each miner who is or may 

reasonably be expected to be at or above 

the action level. 

MSHA estimates that the total number 

of analyses (489,860) that laboratories 

will be able to perform per year is more 

than 2.5 times the total estimated 

number of samples for which mines will 

seek analyses in the first year (172,907). 

Based on the estimated surplus analyses 

available beyond baseline sampling 

(419,362), MSHA preliminarily finds 

that periodic, corrective actions, and 

post-evaluation sampling would also be 

technologically feasible both in the first 

year and in subsequent years.42

B. Technological Feasibility of the 

Proposed PEL 

1. Methodology 

The technological feasibility analysis 

for the proposed PEL relies primarily on 

information from three key sources: 

• MSHA’s Standardized Information 

System (MSIS) respirable crystalline 

silica exposure data, which includes 

57,769 MNM and 63,127 coal mine 

compliance samples collected by MSHA 

inspectors; these samples were of 

sufficient mass to be analyzed for 

respirable crystalline silica by MSHA’s 

analytical laboratory.43

• The National Institute for 

Occupational Safety and Health 

(NIOSH) series on reducing respirable 

dust in mines, including: ‘‘Dust Control 

Handbook for Industrial Minerals 

Mining and Processing, Second Edition’’ 

(NIOSH, 2019b) and ‘‘Best Practices for 

Dust Control in Coal Mining, Second 

Edition’’ (NIOSH, 2021a).44 With 

cooperation from the MNM and coal 

mining industries, NIOSH has 

extensively researched and documented 

engineering and administrative controls 

for respirable crystalline silica in mines. 

• MSHA’s knowledge of the mining 

industry. MSHA has over four decades 

of experience inspecting surface mines 

at least twice per year and underground 

mines at least four times per year and 

in assisting mine operators and miners 

with technological issues, including 

control of respirable dust (including 

respirable crystalline silica) exposure. 

MSHA offers informational programs, 

training, publications, onsite 

evaluations, and investigations that 

document conditions in mines and help 

mines operate in a safe and healthy 

manner.45

MSHA also consulted other published 

reports, scientific journal articles, and 

information from equipment 

manufacturers and mining industry 

suppliers.46

2. The Technological Feasibility 

Analysis Process 

a. Mining Commodity Categories and 

Activity Groups 

As described in the Preliminary 

Regulatory Impact Analysis (PRIA), 

MSHA categorized mine types into six 

MNM ‘‘commodity categories’’ (using 


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47MSHA removed duplicate samples, samples 

missing critical information, and those identified as 

invalid by the mine inspector, for example because 

of a ‘‘fault’’ (failure) of the air sampling pump 

during the sampling period. 

48MSHA MSIS respirable crystalline silica data 

for the MNM industry, January 1, 2005, through 

December 31, 2019 (version 20220812); MSHA 

MSIS respirable crystalline silica data for the Coal 

Industry, August 1, 2016, through July 31, 2021 

(version 20220617). All samples were collected by 

mine inspectors and were of sufficient mass to be 

analyzed for respirable crystalline silica by MSHA’s 

laboratory. 

49MSHA selected these ranges based on the 

proposed PELs under consideration, then multiples 

of 100 mg/m3 to show how data are distributed in 

the higher ranges. Table VIII–5 also presents 

additional exposure ranges corresponding to the 

85.7 mg/m3 concentration for coal samples. 

the method of Watts et al., 2012) based 

on similarities in exposure 

characteristics. MNM mine categories 

include metal, nonmetal, stone, crushed 

limestone, and sand and gravel. All coal 

mines are categorized together as one 

commodity category. 

Within each commodity, MSHA 

further separated mining operations into 

the four activity groups widely used by 

the industry: (1) development and 

production miners (drillers, stone 

cutters); (2) ore/mineral processing 

miners (crushing/screening equipment 

operators and kiln, mill, and 

concentrator workers in mine facilities); 

(3) miners engaged in load/haul/dump 

activities (conveyor, loader, and large 

haulage vehicle operators, such as dump 

truck drivers); and (4) miners in all 

other occupations (mobile and utility 

workers, such as surveyors, mechanics, 

cleanup crews, laborers, and operators 

of compact tractors and utility trucks). 

Before determining the feasibility of 

reducing miners’ exposure to respirable 

crystalline silica, MSHA gathered and 

analyzed information to understand 

current miner exposures by creating an 

‘‘exposure profile,’’ identified the 

existing (i.e., baseline) conditions and 

the exposure levels associated with 

those conditions, and determined 

whether mines would need additional 

control methods, and if so, whether 

those methods were available. 

b. Exposure Profiles 

MSHA classified all valid respirable 

crystalline silica samples in the 

Agency’s MSIS data,47 grouping the data 

by commodity category, followed by 

activity group.48 MSHA created an 

exposure profile to better examine the 

sample data for each commodity 

category. These profiles include basic 

summary statistics, such as sample 

count, mean, median, and maximum 

values, presented as ISO 8-hour TWA 

values. They also show the sample 

distribution within the following 

exposure ranges: ≤25 mg/m3, >25 mg/m3

to ≤50 mg/m3, >50 mg/m3 to ≤100 mg/m3

(equivalent to 85.7 mg/m3 in coal mines 

for a sample calculated as an 8-hour 

TWA), >100 mg/m3 to ≤250 mg/m3, >250 

mg/m3 to ≤500 mg/m3, and >500 mg/m3.49

In Table VIII–2, the respirable 

crystalline silica exposure data for 

MNM miners are summarized by 

commodity and for the MNM industry 

as a whole, while Table VIII–3 presents 

the exposure profile as the percentage of 

samples in each exposure range. 

Overall, approximately 82 percent of the 

57,769 MNM compliance samples were 

at or below the proposed PEL (50 mg/ 

m3). The exposure profile shows 

variability between the commodity 

categories: approximately 73 percent of 

metal miner exposures at or below the 

proposed PEL (50 mg/m3) (the lowest 

among all MNM mines), compared with 

approximately 90 percent of the crushed 

limestone miner exposures (the highest 

among all MNM mines). 

Table VIII–4 and Table VIII–5 present 

the corresponding respirable crystalline 

silica exposure information for coal 

miners by location (underground or 

surface). Overall, approximately 93 

percent of the 63,127 samples obtained 

by MSHA inspectors for coal miners 

were at or below the proposed PEL (50 

mg/m3). There was little variation 

between samples for underground 

miners and surface miners (with 

approximately 93 and 92 percent of the 

samples at or below 50 mg/m3, 

respectively). Exposure values from the 

coal industry are expressed as ISO 8- 

hour TWAs, compatible with the 

proposed PEL. 

BILLING CODE 4520–43–P 


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c. Existing Dust Controls in Mines 

(Baseline Conditions) 

MNM and coal mines are controlling 

dust containing respirable crystalline 

silica in various ways. As shown in 

Tables VIII–2 through VIII–5, respirable 

crystalline silica exposures exceeded 

the proposed PEL of 50 mg/m3 in about 

18 percent of all MNM samples 

collected. Of all coal samples, exposure 

levels exceeded the proposed PEL in 

about seven percent of the samples. 

Overall, metal mines and sand and 

gravel mines had higher exposure levels 

than other commodity mines. 

Despite the extensive dust control 

methods available, dust control 

measures have been implemented in 

some commodity categories to a greater 

degree than in others. This is partly 

because some commodity categories 

tend to have larger mines. MSHA has 

found that the larger the amount 

(tonnage) of material a mine moves 

(including overburden and other waste 

rock), the faster the mine tends to 

operate its equipment (i.e., closer to the 

equipment capacity), creating more air 

turbulence and therefore generating 

more respirable crystalline silica. The 

amount of material moved also 

influences the number of miners 

employed at a mine, and therefore, the 

number of miners can be indirectly 

correlated to the amount of dust 

generated. MSHA has observed that in 

large mines, dusty conditions typically 

prompt more control efforts, usually in 

the form of added engineering controls. 

MSHA has also found that metal 

mines, which are typically large 

operations with higher numbers of 

miners, tend to have available 

engineering controls for dust 

management. On the other hand, sand 

and gravel mines, which generally 

employ fewer miners and handle 

modest amounts of material, have very 

limited, if any, dust control measures. 

This is because most of the mined 

material is a commodity that only 

requires washing and screening into 

various sizes of product stockpiles, 

generating little waste material. 

Nonmetal, stone, and crushed limestone 

mines occupy the middle range in terms 

of employment, existing engineering 

controls, and maintenance practices. 

Over the years, staff from multiple 

MSHA program areas have worked 

alongside miners and mine operators to 

improve safety and health by inspecting, 

evaluating, and researching mine 

conditions, equipment, and operations. 

These key programs, each of which has 

an onsite presence, include (but are not 

limited to) Mine Safety and Health 

Enforcement; Directorate of Educational 

Policy and Development which includes 

the National Mine Health and Safety 

Academy and the Educational Field and 

Small Mine Services; and the 

Directorate of Technical Support, which 

is comprised of the Approval and 

Certification Center and the Pittsburgh 

Safety and Health Technology Center 

(including its Health Field Division, 

National Air and Dust Laboratory, 

Ventilation Division, and other 

specialized divisions). Table VIII–6 

reflects the collective observations of 

these MSHA programs, presented in 

terms of existing dust control (baseline 

conditions) and the classes of additional 

control measures that would provide 

those mines with the greatest benefit to 

reduce exposures below the proposed 

PEL and action level. 

Table VIII–6 shows MSHA’s 

assessment of existing dust controls in 

mines (baseline conditions) and 

additional controls needed to meet the 

proposed PEL for each commodity 

category, including the need for 

frequent scheduled maintenance. By 

conducting frequent scheduled 

maintenance, mine operators can reduce 

the concentration of respirable 

crystalline silica. Table VIII–6 shows 

that metal mines have adopted 

extensive dust controls, while sand and 

gravel mines tend to have minimal 

engineering controls, if any. 


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50Control measures that reduce respirable 

crystalline silica can also reduce exposures to other 

hazardous particulates, such as RCMD, metals, 

asbestos, and diesel exhaust. Operator enclosures 

and process enclosures also reduce hazardous 

levels of noise by creating a barrier between the 

operator and the noise source. 

BILLING CODE 4520–43–C 

Based on MSHA’s experience, NIOSH 

research, and effective respirable dust 

controls currently available and in use 

in the mining industry, MSHA 

preliminarily finds that the baseline 

conditions include various 

combinations of existing engineering 

controls selected and installed by 

individual mines to address respirable 

crystalline silica generated during 

mining operations. 

d. Respirable Crystalline Silica 

Exposure Controls Available to Mines 

Under the proposal, the mine operator 

must install, use, and maintain feasible 

engineering controls, supplemented by 

administrative controls, when 

necessary, to keep each miner’s 

exposure at or below the proposed PEL. 

Engineering controls reduce or prevent 

miners’ exposure to hazards.50

Administrative controls establish work 

practices that reduce the duration, 

frequency, or intensity of miners’ 

exposures (although rotation of miners 

would be prohibited under the proposed 

rule). 

MSHA data and experience show that 

mine operators already have numerous 

engineering and administrative control 

options to control miners’ exposures to 

respirable crystalline silica. These 

control options are widely recognized 

and used throughout the mining 

industry. NIOSH has extensively 

researched and documented engineering 

and administrative controls for 

respirable crystalline silica in mines. As 

noted previously, NIOSH has published 

a series on reducing respirable dust in 

mines (NIOSH, 2019b; NIOSH, 2021a). 

(1) Engineering controls 

Examples of existing engineering 

controls used at mines and 

commercially available engineering 

controls that MSHA considered include: 

• Wetting or water sprays that 

prevent, capture, or redirect dust; 

• Ventilation systems that capture 

dust at its source and transport it to a 

dust collection device (e.g., filter or bag 

house), dilute dust already in the air, or 

‘‘scrub’’ (cleanse) dust from the air in 

the work area; 

• Process enclosures that restrict dust 

from migrating outside of the enclosed 

area, sometimes used with an attached 

ventilation system to improve 

effectiveness (e.g., crushing equipment 

and associated dump hopper enclosure, 

with curtains and mechanical 

ventilation to keep dust inside); 

• Operator enclosures, such as mobile 

equipment cabs or control booths, 

which provide an environment with 

clean air for an equipment operator to 

work safely; 

• Protective features on mining 

process equipment to help prevent 

process failures and associated dust 

releases (e.g., skirtboards on conveyors, 

which protect the conveyor system from 

damage and prevent material on the 

conveyor from falling off, which 

generates airborne dust); 

• Preventive maintenance conducted 

on engineering controls and mining 

equipment that can influence dust 

levels at a mine, to keep them 

functioning optimally; and 

• Instrumentation and other 

equipment to assist mine operators and 

miners in evaluating engineering control 


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51These instruments include dust monitors; 

water, air, and differential air pressure gauges; pitot 

tubes and air velocity meters; and video camera 

(NIOSH recommends software that pairs video with 

a dust monitor to track conditions that could lead 

to elevated exposures if not corrected). These 

instruments are discussed in NIOSH’s best practices 

guides and dust control handbooks. 

52Proposed paragraph 60.11(b) prohibits the use 

of rotation of miners as an administrative control 

used for compliance with this part. 

53NIOSH believes this study, like many of its 

other mining studies on operator enclosures and 

surface drill dust controls, is relevant to both MNM 

mining and coal mining. NIOSH reports on this 

study, conducted at an underground limestone 

mine, in detail in both its Dust control handbook 

for industrial minerals mining and processing 

(second edition) (2019b) and its best practices for 

dust control in coal mining (second edition) 

(2021a). 

54Acronyms: High efficiency particulate air 

(HEPA). Minimum efficiency reporting value 

(MERV). 

effectiveness and recognizing control 

failures or other conditions that need 

corrective action.51

(2) Administrative controls 

Administrative controls include 

practices that change the way tasks are 

performed to reduce a miner’s exposure. 

Administrative controls can be very 

effective and can even prevent exposure 

entirely. MSHA has preliminarily 

determined that various administrative 

controls are readily available to provide 

supplementary support to engineering 

controls. Examples of administrative 

controls would include housekeeping 

procedures; proper work positions of 

miners; walking around the outside of a 

dusty process area rather than walking 

through it; cleaning of spills; and 

measures to prevent or minimize 

contamination of clothing to help 

decrease miners’ exposure to respirable 

crystalline silica. However, these 

control methods depend on human 

behavior and intervention and are less 

reliable than properly designed, 

installed, and maintained engineering 

controls. Therefore, administrative 

controls would be permitted only as 

supplementary measures, with 

engineering controls required as the 

primary means of protection. 

Nevertheless, administrative controls 

play an important role in reducing 

miners’ exposure to respirable 

crystalline silica.52

(3) Combinations of Controls 

Various control options can also be 

used in combinations. NIOSH has 

documented in detail most control 

methods and has confirmed that they 

are currently used in mines, both 

individually and in combination with 

each other (2019b, 2021a). 

e. Maintenance 

MSHA preliminarily finds that a 

strong and feasible preventive 

maintenance program plays an 

important role in achieving consistently 

lower respirable crystalline silica 

exposure levels. MSHA has observed 

that when engineering controls are 

installed and maintained in working 

condition, respirable dust exposures 

tend to be below the existing exposure 

limits. When engineering controls are 

not maintained, dust control efficiency 

declines and exposure levels rise. When 

engineering controls fail due to a lack of 

proper maintenance, a marked rise in 

exposures can occur, resulting in 

noncompliance with MSHA’s existing 

exposure limits. Some examples of the 

impact that proper maintenance can 

have on respirable dust levels include: 

• Water spray maintenance: An 

experiment using water spray bars that 

could be turned on or off showed that 

dust reduction was less effective each 

time additional spray nozzles were 

deactivated. A 10 percent decrease 

occurred when three of 21 sprays were 

shut off, but a 50 percent decrease 

occurred when 12 out of the 21 sprays 

were shut off. Decreased total water 

spray volume and gaps in the spray 

pattern (due to deactivated nozzles) 

were both partially responsible for the 

decreased dust control (Seaman et al., 

2020). 

• Water added to drill bailing air: 

When introduced into the drill hole 

(with the bailing air through a hollow 

drill bit), water mixes with and 

moistens the drill dust ejected from the 

hole and can reduce respirable dust by 

more than 90% (NIOSH 2021a, 2019b). 

NIOSH reports that this same control 

measure, and others, are similarly 

effective for MNM and surface coal 

mine drills preparing the blasting holes 

used to expose the material below 

(whether ore or coal). 

• Ventilation system maintenance: 

The amount of air cleaned by an air 

scrubber is decreased by up to one-third 

(33 percent) after one continuous 

mining machine cut. Cleaning the 

scrubber screens restores scrubber 

efficacy, but this maintenance must be 

performed after every cut. Spare 

scrubber screens make frequent cleaning 

practical without slowing production 

(NIOSH, 2021a). 

• Operator enclosure maintenance: 

Tests with mining equipment showed 

that maintenance activities including 

repairing weather stripping and 

replacing clogged and missing cab 

ventilation system filters (intake, 

recirculation, final filters) increased 

miner protection, by up to 95 percent 

(NIOSH 2019b, 2021a). 

• Filter selection during maintenance: 

Airflow is as important as filtration and 

pressurization in operator enclosures; 

during maintenance, filter selection can 

influence all three factors. Performing 

serial end-shift testing of enclosed cabs 

(on a face drill and a roof/rock bolter) 

at an underground crushed limestone 

mine, NIOSH compared installed HEPA 

filters and an alternative (MERV 16 

filters). The latter provided an equal 

level of filtration and better overall 

miner protection by allowing greater 

airflow and cab pressurization. As an 

added advantage, NIOSH showed that 

these filters cost less and required lessfrequent replacement, reducing 

maintenance expenses in this mining 

environment (Cecala et al., 2016; NIOSH 

2021a, 2019b).53 54

• Proper design and installation— 

foundation for effective maintenance: A 

new replacement equipment operator 

enclosure (control booth) installed 

adjacent to the primary crusher at a 

granite stone quarry initially provided 

50 to 96 percent respirable dust 

reduction, even with inadequate 

pressurization. The protection it offered 

miners tripled after the booth’s second 

pressurization/filtration unit was 

activated (Organiscak et al., 2016). 

MSHA has observed that when 

engineering controls are properly 

maintained, exposure levels decrease or 

stay low. Metal mines, which typically 

have substantial controls already 

installed, primarily need reliable 

preventive maintenance programs to 

achieve the proposed PEL. It is also 

important to repair equipment damage 

that contributes to dust exposure (for 

example, damage to conveyor 

skirtboards that protect the conveyor 

system from damage and prevent 

spillage which generates airborne dust). 

Maintenance and repair programs must 

ensure that dust control equipment is 

functioning properly. 

3. Feasibility Determination of Control 

Technologies 

MSHA is proposing a PEL of 50 mg/ 

m3 for MNM and coal mines. As NIOSH 

has documented, the mining industry 

has a wide range of options for 

controlling dust exposure that are 

already in various configurations in 

mines (2019b; 2021a). NIOSH has 

carefully evaluated most of the dust 

controls used in the mining industry 

and found that many of the controls 

may be used in combinations with other 

control options. NIOSH has documented 

protective factors and exposure 

reductions of 30 to 90 percent or higher 

for many engineering and 

administrative controls. 


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55Calculating the exposure for the shift: 8-hour 

TWA = [(10 mg/m3 × 6 hours) + (100 mg/m3 × 2 

hours)]/8 hours = 33 mg/m3. 

56Calculating the exposure with both the wellmaintained operator enclosure (6 hours) and dust 

suppression hopper, assuming only the minimum 

documented respirable dust concentration 

reduction (39 percent): [(10 mg/m3 × 6 hours) + (100 

mg/m3 × (1–0.39) × 2 hours)]/8 hours = 23 mg/m3. 

57The 8-hour TWA exposure level of the helper, 

including the 30-minute period of elevated 

exposure, is calculated as: [(35 mg/m3 × 7.5 hours) 

+ (35 mg/m3 × 20 × 0.5 hours)]/8 hours = 77 mg/m3. 

Drill bits designed for use with water may need to 

be replaced sooner if used dry. 

MSHA also preliminarily finds that 

maintaining (including adjusting) or 

repairing existing controls would help 

achieve exposures at or below 50 mg/m3. 

For example, NIOSH found that 

performing maintenance on an operator 

enclosure can restore enclosure 

pressurization and reduce the respirable 

dust exposure of a miner by 90 to 98.9 

percent (e.g., by maintaining weather 

stripping, reseating or replacing leaking 

or clogged filters, and upgrading 

filtration) (NIOSH, 2019b). When an 

equipment operator remains inside a 

well-maintained enclosure for a portion 

of a shift (for example 75 percent of an 

8-hour shift), the cab can reduce the 

exposure of the operator proportionally, 

to a level of 50 mg/m3 (or lower). This 

point is demonstrated by the following 

example involving a bulk loading 

equipment operator in a poorly 

maintained booth, exposed to respirable 

crystalline silica near the existing 

exposure limit (in the MNM sectors, 100 

mg/m3, as ISO 8-hour TWA value; in the 

Coal sector, 85.7 mg/m3 ISO, calculated 

as an 8-hour TWA). During the 25 

percent of their shift (two hours of an 

eight-hour shift) that the operator was 

working in the poorly maintained 

enclosure, their exposure would 

continue to be 100 mg/m3, while for the 

other six hours (operating mobile 

equipment with a fully refurbished 

protective cab), the exposure level 

would be 90 percent lower, or 10 mg/m3, 

resulting in an 8-hour TWA exposure of 

33 mg/m3 for that miner’s shift.55 Greater 

exposure reductions could also be 

achieved by repairing or replacing the 

poorly maintained enclosure, or 

modifying the miner’s schedule so that 

the miner works seven hours, rather 

than six, inside of the well-maintained 

enclosure. 

Other engineering controls (e.g., 

process enclosure, water dust 

suppression, dust suppression hopper, 

ventilation systems) could reduce dust 

concentrations in the area surrounding 

the poorly maintained enclosure, which 

would reduce the exposure of the 

operator inside. For example, if the 

poorly maintained enclosure was an 

open-air control booth (windows do not 

close) at a truck loading station, adding 

a dust suppression hopper (which 

reduces respirable dust exposure by 39 

to 88 percent during bulk loading) 

(NIOSH, 2019b), would lead to lower 

exposure during the two hours the 

miner was inside the open-air booth. 

The calculated respirable crystalline 

silica 8-hour TWA exposure of that 

miner could be reduced from 33 mg/m3

(with improved operator enclosure 

alone) to 23 mg/m3 (improved operator 

enclosure plus dust suppression 

hopper).56 As an added benefit, any 

helper or utility worker in the truck 

loading area would also experience 

reduced exposure. 

Similarly, considering an example for 

a coal miner helper who spends 90 

minutes (1.5 hours) per 8-hour shift 

assisting a drilling rig operator (in a 

protective operator’s cab) drilling blast 

holes. The combination of controls used 

to control drilling dust (including water 

added to the bailing air, which can 

reduce airborne respirable dust 

emissions by up to 96 percent) usually 

maintain the helper’s respirable 

crystalline silica exposure in the range 

of 35 mg/m3 (ISO) as an 8-hour TWA. If, 

however, the drill’s on-board water tank 

runs dry due to poor maintenance, the 

respirable crystalline silica 

concentration near the drill will rise by 

95 percent, meaning that the 

concentration is 20 times greater than 

the usual level (NIOSH 2021a). If the 

drill operator idles the drill and calls for 

water resupply, the helper will not 

experience an elevated exposure. If 

instead the drill is operated dry for 

another 30 minutes until water resupply 

arrives, the helper will experience a 

respirable crystalline silica exposure of 

77 mg/m3 (ISO) as an 8-hour TWA. If dry 

drilling continued for 1.5 hours, the 

helper would have an exposure of 160 

mg/m3 ISO as an 8-hour TWA.57 After 

water is delivered, drill respirable dust 

emissions will return to their normal 

level once water is again introduced 

into the drill bailing air. 

Based on these examples and the 

wide range of effective exposure control 

options available to the mining 

industry, MSHA preliminarily finds that 

control technologies capable of reducing 

miners’ respirable crystalline silica 

exposures are available, proven, 

effective, and transferable between 

mining commodities; however, they 

must be well-designed and consistently 

used and maintained. 

a. Feasibility Findings for the Proposed 

PEL 

Based on the exposure profiles in 

Table VIII–2 and Table VIII–3 for MNM 

mines, and in Table VIII–4 and VIII–5 

for coal mines, and the examples in the 

previous section that demonstrate the 

beneficial effect of combined controls, 

MSHA preliminarily finds that the 

proposed PEL of 50 mg/m3 is 

technologically feasible for all mines. 

Table VIII–7 summarizes the 

technological feasibility of control 

technologies available to the mining 

industry, by commodity. MSHA 

preliminarily finds that control 

technologies are technologically feasible 

for all six commodities and their 

respective activity groups. Under 

baseline conditions, mines in each 

commodity category have already 

achieved respirable crystalline silica 

exposures at or below 50 mg/m3 for most 

of the miners represented by MSHA’s 

57,769 samples for MNM miners and 

63,127 samples for coal miners. 

BILLING CODE 4520–43–P 


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BILLING CODE 4520–43–C 

b. Feasibility Findings for the Proposed 

Action Level 

MSHA believes that mine operators 

can achieve exposure levels at or below 

the proposed action level of 25 mg/m3, 

for most miners by implementing 

additional engineering controls and 

more flexible and innovative 

administrative controls, in addition to 

the existing control methods already 

discussed in this technological 

feasibility analysis. MSHA notes that 

the exposure profiles in Table VIII–2 

and Table VIII–3 for MNM mines, and 

Table VIII–4 and VIII–5 for coal mines 

indicate that mine operators have 

already achieved the proposed action 

level for at least half of the miners who 

MSHA has sampled in each commodity 

category. However, to do so reliably for 

all miners, operators would need to 

upgrade equipment and facility designs, 

particularly in mines with higher 

respirable crystalline silica 

concentrations, that may be due to an 

elevated silica content in materials. 

One control option would be 

increased automation, such as 

expanding the use of existing 

autonomous or remote-controlled 

drilling rigs, roof bolters, stone cutting 

equipment, and packaging/bagging 

equipment. This type of automation can 

reduce exposures by increasing the 

distance between the equipment 

operator and the dust source. Other 

options include completely enclosing 

most processes and ventilating the 

enclosures with dust extraction 

equipment or controlling the speed of 

mining equipment (e.g., longwall 

shearers, conveyors, dump truck 

emptying) and process equipment (e.g., 

crushers, mills) to reduce turbulence 

that increases dust concentrations in air. 

Additionally, where compatible with 

the material, exposure levels can be 

reduced by increased wetting to 

constantly maintain the material, 

equipment, and mine facility surfaces 

damp through added water sprays and 

frequent housekeeping (i.e., hosing 

down surfaces as often as necessary). In 

addition, vacuuming will minimize the 

amount of dust that becomes airborne 

and prevent dust that does settle on a 

surface from being resuspended in air. 

Mines that only occasionally work 

with higher-silica-content materials may 

not be equipped with the controls 

required to achieve the proposed action 

level of 25 mg/m3, or they may not 

currently have procedures to ensure 

miners are protected when they do work 

with these materials. Examples of these 

activities include cutting roof or floor 

rock with a continuous mining machine 

in underground coal mines; packaging 

operations that involve materials from 

an unfamiliar supplier, including 

another mine; and rebuilding or 

repairing kilns. To address these 

activities, under the proposed rule, 

mine operators would have to add 

engineering controls to address any 

foreseeable respirable crystalline silica 

overexposures. Examples of additional 

controls include pre-testing batches of 

new raw materials; improving hazard 

communication when batches of 

incoming raw materials contain higher 

concentrations of crystalline silica, and 


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58Class 100 particulate respirators (currently the 

most widely used respirator filter specification in 

the U.S.) are available from numerous sources 

including respirator manufacturers, online safety 

supply companies, mine equipment suppliers, and 

local retail hardware stores. 

59The NIOSH list of approved models does not 

guarantee that each model is currently 

manufactured. However, the list does not include 

obsolete models, and the more popular models are 

widely available, including in bulk quantities. 

augmenting enclosure and ventilation 

(e.g., adding ventilation to all crushing 

and screening equipment, increasing 

mine facility ventilation to 30 air 

changes per hour, and fully enclosing 

and ventilating all conveyor transfer 

locations). NIOSH (2019b, 2021a) 

describes all of the dust control methods 

described in this section, which are 

already used in mines, although to a less 

rigorous extent than would be necessary 

to reliably achieve exposure levels of 25 

mg/m3 or lower for all miners. 

MSHA preliminarily finds that the 

proposed action level of 25 mg/m3 is 

technologically feasible for most mines. 

This finding is based on the exposure 

profiles, presented in Table VIII–2 and 

Table VIII–3 for MNM mines, and Table 

VIII–4 and VIII–5 for coal mines, which 

shows that within each commodity 

category, the exposure levels are at or 

below 25 mg/m3 for at least half of the 

miners sampled. MSHA’s finding is also 

based on the extensive control options 

documented by NIOSH, which can be 

used in combinations to achieve 

additional control of respirable 

crystalline silica. Although most mines 

would need to adopt and rigorously 

implement a number of the control 

options mentioned in this section, the 

technology exists to achieve this level 

and is already in use in mines. 

C. Technological Feasibility of 

Respiratory Protection (Within Proposed 

Part 60) 

Under the proposed rule, respiratory 

protection would only be allowed for 

temporary, non-routine use. MSHA has 

preliminarily determined that it is 

technologically feasible to limit 

respirator use to temporary, non-routine 

activities based on the Agency’s 

knowledge of and experience with the 

mining industry, evidence presented by 

NIOSH (2019b, 2020a), and Tables VIII– 

2 through VIII–5 (exposure profiles for 

MNM and coal mines). These tables 

indicate that the proposed PEL (50 mg/ 

m3) has already been achieved for 

approximately 82 percent of the MNM 

miners and approximately 93 percent of 

the coal miners sampled by MSHA. 

Proposed § 60.14(b) requires that any 

miner unable to wear a respirator must 

receive a temporary job transfer to an 

area or to an occupation at the same 

mine where respiratory protection is not 

required. The proposed paragraph 

would also require that an affected 

miner continue to receive compensation 

at no less than the regular rate of pay in 

the occupation held by that miner 

immediately prior to the transfer. MNM 

mine operations have complied with the 

job transfer provisions under the 

existing standard in § 57.5060(d)(7) that 

states miners unable to wear a respirator 

must be transferred to work in an 

existing position in an area of the mine 

where respiratory protection is not 

required. Proposed § 60.14(b) is similar 

to these existing requirements. MSHA 

anticipates that mine operators would 

have a similar experience implementing 

the job transfer provisions of proposed 

§ 60.14(b). Therefore, MSHA 

preliminarily finds that the proposed 

requirement in § 60.14(b) is 

technologically feasible. 

For miners who would need to wear 

respiratory protection on a temporary 

and non-routine basis, proposed 

§ 60.14(c)(1) would require the mine 

operator to provide NIOSH-approved 

atmosphere-supplying respirators or 

NIOSH-approved air-purifying 

respirators equipped with highefficiency particulate filters in one of 

the following NIOSH classifications 

under 42 CFR part 84: 100 series or High 

Efficiency (HE). As previously 

discussed, MSHA preliminarily finds 

that particulate respirators meeting 

these criteria would offer the best 

filtration efficiency (99.97 percent) and 

protection for miners exposed to 

respirable crystalline silica and are 

widely available and used by most 

industries. This finding is based on the 

suitability of the three particulate 

classifications for respirable size 

particle filtration and the broad 

commercial availability of these NIOSHapproved particulate respirators.58

NIOSH publishes a list of approved 

respirator models along with 

manufacturer/supplier information. In 

November 2022, the NIOSH-approved 

list contained 221 records on 

atmosphere-supplying respirator 

models, 160 records on elastomeric 

respirators with P–100 classification, 

and 23 records on filtering facepiece 

respirators with P–100 classification 

(NIOSH, 2022 list P–100 elastomeric, P– 

100 filtering facepiece, and atmospheresupplying respirator models).59 Based 

on this information, MSHA 

preliminarily finds that proposed 

§ 60.14(c)(1) is technologically feasible. 

Proposed § 60.14(c)(2) would 

incorporate the ASTM F3387–19 

‘‘Standard Practice for Respiratory 

Protection’’ to ensure that the most 

current and protective respiratory 

protection practices would be 

implemented by operators who 

temporarily use respiratory protection to 

control miners’ exposures to respirable 

crystalline silica. The Agency is also 

incorporating this respiratory protection 

consensus standard under §§ 56.5005, 

57.5005, and 72.710. This proposed 

update is also addressed in the next 

section (see Technological feasibility of 

updated respiratory protection 

standards). Based on the information 

contained in that section, MSHA 

preliminarily finds that the proposed 

§ 60.14(c)(2) is technologically feasible. 

Based on information contained in 

this section, MSHA preliminarily finds 

that proposed § 60.14 is technologically 

feasible. 

D. Technological Feasibility of Updated 

Respiratory Protection Standards 

(Amendments to 30 CFR Parts 56, 57, 

and 72) 

1. Incorporation by Reference 

Respirators are commonly used by 

miners as a means of protection against 

a multitude of respiratory hazards, 

including particulates, gases, and 

vapors. Respirators are needed in 

immediately life-threatening (i.e., IDLH) 

situations as well as operations where 

engineering controls and administrative 

controls do not provide sufficient 

protection against respiratory hazards. 

Where respirators are used, they must 

seal and isolate the miner’s respiratory 

system from the contaminated 

environment. The risk that a miner will 

experience an adverse health effect from 

a contaminant when relying on 

respiratory protection is a function of 

the toxicity or hazardous nature of the 

air contaminants present, the 

concentrations of the contaminants in 

the air, the duration of exposure, and 

the degree of protection provided by the 

respirator. When respirators fail to 

provide the proper protection, there is 

an increased risk of adverse health 

effects. Therefore, it is critical that 

respirators perform as they are designed. 

Accordingly, MSHA is proposing to 

incorporate by reference ASTM F3387– 

19 under 30 CFR 56.5005, 30 CFR 

57.5005, and 30 CFR 72.710. With this 

action, the Agency intends to assist 

mine operators in developing effective 

respiratory protection practices and 

programs that meet current industry 

standards. This proposed revision 

would better protect miners who 

temporarily wear respiratory protection. 

The American National Standards 

Practices for Respiratory Protection 

ANSI Z88.2–1969 is currently 

incorporated by reference in 30 CFR 

56.5005, 30 CFR 57.5005, and 30 CFR 


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60ASTM 3387–19 is the revised version of ANSI/ 

ASSE Z88.2–2015. In 2017, the Z88 respirator 

standards were transferred from ANSI/ASSE to 

ASTM International (source: F3387–19, Appendix 

XI). 

72.710.60 Since MSHA issued these 

standards, respirator technology and 

knowledge on respirator protection have 

advanced and as a result, changes in 

respiratory protection standard practices 

have occurred. ASTM F3387–19 is 

based on the most recent consensus 

standard and provides more 

comprehensive and detailed guidance. 

MSHA believes that most mines that use 

respiratory protection are already 

following current respiratory protection 

practices and standards such as ANSI/ 

ASSE Z88.2—2015 ‘‘Practices for 

Respiratory Protection’’ standard, its 

similar ASTM replacement (the F3387– 

19 standard), or OSHA 29 CFR 

1910.134—Respiratory protection. 

ASTM F3387–19 standard practices are 

substantially similar to the standard 

practices included in ANSI/ASSE 

Z88.2–2015 or OSHA’s respiratory 

standards. 

2. Availability of Respirators 

The updated respiratory protection 

standard reflects current practice at 

many mines that currently use 

respiratory protection and does not 

require the use of new technology. 

Thus, MSHA preliminarily finds that 

the proposed update is technologically 

feasible for affected mines of all sizes. 

3. Respiratory Protection Practices 

By incorporating the updated 

respiratory protection consensus 

standard (ASTM F3387–19), MSHA 

intends that mine operators would 

develop effective respiratory protection 

practices that meet the updated 

consensus standard and that would 

better protect miners from respirable 

hazards not yet controlled by other 

methods. 

MSHA presumes that most mines 

with respiratory protection programs, 

and particularly those MNM mines that 

have operations under both MSHA and 

OSHA jurisdiction, are already 

following either the ANSI/ASSE 

Z88.2—2015 standard, the ASTM 

F3387–19 standard, or OSHA 1910.134. 

The respiratory protection program 

elements under ASTM F3387–19 are 

largely similar to those in the existing 

standard. 

MSHA expects that some operators 

may need to adjust their current 

respiratory protection practices and 

standard operating procedures to reflect 

ASTM F3387–19 standard practices. 

Examples of adjustments include 

formalizing fit testing and respirator 

training annually; updating the training 

qualifications of respirator trainers, 

managers, supervisors, and others 

responsible for the respiratory 

protection program; reviewing the 

information exchanged with the 

physician or other licensed health care 

professional (PLHCP); and formalizing 

internal and external respiratory 

protection program reviews or audits. 

Overall, MSHA preliminarily finds 

that the proposed amendments to 

existing parts 56, 57, and 72 are 

technologically feasible because the 

requirements of ASTM F3378–19 are 

already implemented at some mines. 

E. Technological Feasibility of Medical 

Surveillance (Within Proposed Part 60) 

Under the proposed rule, mine 

operators would be required to provide 

periodic medical examinations for each 

MNM miner, at no cost to the miner. 

The proposed medical surveillance 

standards would extend to MNM miners 

similar protections available to coal 

miners under 30 CFR 72.100. The 

requirements in proposed § 60.15 are 

consistent with the Mine Act’s mandate 

to provide maximum health protection 

for miners. 

Under the proposed standards, MNM 

miners new to the mining industry 

would receive an initial examination, 

within 30 days. If they are not new to 

mining, they are categorized as 

belonging to a group of workers who are 

eligible for an examination every 5 

years. Workers who are new to mining, 

after they have their initial examination, 

would be provided another follow-up 

examination within 3 years. If the 3-year 

follow-up examination indicates any 

medical concerns associated with chest 

X-ray findings or decreased lung 

function, these miners are eligible to 

have another follow-up exam in 2 years. 

After this additional 2-year follow-up 

exam, or if the 3-year follow-up 

examination indicates no medical 

concerns associated with chest X-ray 

findings or decreased lung function, 

these miners will enter the category of 

miners eligible for periodic 5-year 

exams. 

MSHA is proposing that medical 

examinations would be performed by a 

PLHCP or specialist. A medical 

examination would include a review of 

the miner’s medical and work history 

and physical examination. The medical 

and work history would cover a miner’s 

present and past work exposures, 

illnesses, and any symptoms indicating 

respirable crystalline silica-related 

diseases and compromised lung 

function. The medical examination 

would include a chest X-ray. The 

required chest X-ray would be required 

to be classified by a NIOSH-certified B 

Reader, in accordance with the 

Guidelines for the Use of the 

International Labour Office (ILO) 

International Classification of 

Radiographs of Pneumoconioses. The 

ILO recently made additional standard 

digital radiographic images available 

and has published guidelines on the 

classification of digital radiographic 

images (ILO 2022). These guidelines 

provide standard practices for detecting 

changes of pneumoconiosis, including 

silicosis, in chest X-rays. The proposed 

rule would also require spirometry test 

be part of the medical examination. 

MSHA has preliminarily determined 

that it is technologically feasible for 

MNM mine operators to provide 

periodic examinations. The procedures 

required for initial and periodic medical 

examination are commonly conducted 

in the general population (i.e., medical 

history, physical examination, chest Xray, spirometry test) by a wide range of 

practitioners with varying medical 

backgrounds. Because the proposed 

medical examinations consist of 

procedures conducted in the general 

population and because MSHA would 

be giving MNM mine operators 

maximum flexibility in selecting a 

PLHCP who would be able to offer these 

services, MSHA anticipates that 

operators would not experience 

difficulty in finding PLHCPs who are 

licensed to provide these services. 

In addition, in the case of classifying 

chest X-rays, MSHA has preliminarily 

determined that the availability of 

digital X-ray technology allows for 

electronic submission to remotely 

located B Readers for interpretation; 

therefore, MSHA anticipates that the 

limited number of B Readers in certain 

geographic locations would not be an 

obstacle for MNM operators. Overall, 

MSHA preliminarily finds that the 

proposed medical surveillance 

provisions are technologically feasible. 

F. Conclusions 

Based on MSHA’s technological 

feasibility analysis, MSHA has 

determined that all elements of the 

proposed rule on Lowering Miners’ 

Exposure to Respirable Crystalline 

Silica and Improving Respiratory 

Protection are technologically feasible. 

IX. Summary of Preliminary Regulatory 

Impact Analysis and Regulatory 

Alternatives 

A. Introduction 

Executive Orders (E.O.s) 12866 and 

13563 direct agencies to assess all costs 

and benefits of available regulatory 

alternatives and, if regulation is 


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61Miner employment is based on the information 

submitted quarterly through the MSHA Form 7000– 

2, excluding Subunit 99—Office (professional and 

clerical employees at the mine or plant working in 

an office); https://www.msha.gov/sites/default/files/ 

Support_Resources/Forms/7000-2_0.pdf. 

necessary, to select regulatory 

approaches that maximize net benefits 

(including potential economic, 

environmental, public health and safety 

effects, distributive impacts, and 

equity). E.O. 13563 emphasizes the 

importance of quantifying both costs 

and benefits, of reducing costs, of 

harmonizing rules, and of promoting 

flexibility. E.O.s 12866 and 13563 

require that regulatory agencies assess 

both the costs and benefits of 

regulations. 

A regulatory action is considered 

‘‘significant’’ if it is likely to ‘‘have an 

annual effect on the economy of $200 

million or more . . .’’ under E.O. 12866 

Section 3(f)(1), as amended by E.O. 

14094. The proposed rule ‘‘Lowering 

Miners’ Exposure to Respirable 

Crystalline Silica and Improving 

Respiratory Protection’’ is a significant 

rule. To comply with E.O.s 12866 and 

13563, MSHA has prepared a 

standalone PRIA for this proposed rule. 

A summary of the PRIA is presented 

below. The standalone PRIA contains 

detailed supporting data and 

explanation for the summary materials 

presented here, including the mining 

industry, costs and benefits, and 

economic feasibility. The standalone 

PRIA can be accessed electronically at 

http://www.msha.gov and has been 

placed in the rulemaking docket at 

www.regulations.gov, docket number 

MSHA–2023–0001. MSHA requests 

comments on all estimates of costs and 

benefits presented in this PRIA and on 

the data, assumptions, and 

methodologies the Agency used to 

develop the cost and benefit estimates. 

B. Miners and Mining Industry 

The proposed rule would affect mine 

operators and miners. This section 

provides information on the structure of 

the Metal/Nonmetal (MNM) and coal 

mining industries, including the 

revenue, number, employment by 

commodity and size; economic 

characteristics of MNM and coal mines; 

and the respirable crystalline silica 

exposure profiles for miners across 

different occupations in the MNM and 

coal industry. The data come from the 

U.S. Department of the Interior (DOI), 

U.S. Geological Survey (USGS); U.S. 

Department of Labor (DOL), Mine Safety 

and Health Administration (MSHA), 

Educational Policy and Development 

and Program Evaluation and 

Information Resources; the Statistics of 

US Businesses (SUSB); and the Energy 

Information Administration (EIA). 

1. Structure of the Mining Industry 

The mining industry can be divided 

into two major sectors based on 

commodity: (1) Metal/Nonmetal mines 

(hereafter referred to as MNM mines) 

and (2) coal mines with further 

distinction made regarding type of 

operation (e.g., underground coal mines 

or surface coal mines). The MNM 

mining sector is made up of metal mines 

(copper, iron ore, gold, silver, etc.) and 

nonmetal mines. Nonmetal mines can 

be categorized into four commodity 

groups: (1) nonmetal (mineral) materials 

such as clays, potash, soda ash, salt, 

talc, and pyrophyllite; (2) sand and 

gravel, including industrial sand; (3) 

stone including granite, limestone, 

dolomite, sandstone, slate, and marble; 

and (4) crushed limestone. 

MSHA categorizes mines by size 

based on employment. For purposes of 

this industry profile, MSHA has 

categorized mines into the following 

four groups for analytical purposes 61— 

mines that employ: (1) 1–20 miners 

(Emp ≤20); (2) 21 to 100 miners (20< 

Emp ≤100); (3) 101 to 500 miners (100< 

Emp ≤500); and (4) 501 or more miners 

(500< Emp). 

MSHA tracks mine characteristics and 

maintains a database containing the 

number of mines by commodity and 

size, number of employees, and 

employee hours worked. MSHA also 

collects data on the number of mining 

contractors, their employees, and 

employee hours. While contractors are 

issued a unique MSHA contractor 

identification number, they may work at 

any mine. 

Table IX–1 presents an overview of 

the mining industry, including the 

number of MNM and coal mines, their 

employment, excluding contractors, and 

revenues by commodity and size. All 

data are current in reference to the year 

2019. In 2019, the MNM mining sector 

of 11,525 mines employed 169,070 

individuals, of which 150,928 were 

miners and 18,142 were office workers. 

There were 1,106 coal mines that 

reported production and that employed 

52,966 individuals, of which 51,573 

were miners and 1,393 were office 

workers. 

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BILLING CODE 4520–43–C 

a. Metal Mining 

There are 24 groups of metal 

commodities mined in the U.S. Metal 

mines, which represent about 2.4 

percent (280 out of 11,525) of all MNM 

mines and employ roughly 24.5 percent 

of all MNM miners. Of these 280 mines, 

157 employ 20 or fewer miners and 22 

employ greater than 500 miners. 

Additionally, the 2019 MSHA data 

show that there are a total of 13,792 

contract miners in the metal mining 

industry. 

b. Non-Metal (Mineral) Mining 

Thirty-five non-metal commodities 

are mined in the U.S., not including 

stone, and sand and gravel. Non-metal 

mines represent about 7.8 percent of all 

MNM mines and employ roughly 15 

percent of all MNM miners. The 

majority of non-metal mines (71.9 

percent) employ fewer than 20 miners 

and less than 1 percent employ more 

than 500 employees. In 2019, there were 

11,346 contract miners in the non-metal 

mining industry. 

c. Stone Mining 

The stone mining subsector includes 

eight different stone commodities. 

Seven of the eight are further classified 

as either dimension stone or crushed 

and broken stone. Stone mines make up 

20.9 percent of all MNM mines and 

employ 23.4 percent of all MNM miners. 

The majority of these mines (83.1 

percent) employ less than 20 miners. In 

2019, there were 18,559 contract miners 

in the stone mining industry. 


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62Source: MSHA MSIS Data (reported on MSHA 

Form 7000–2). 

d. Crushed Limestone 

Crushed limestone mines make up 

16.2 percent of all MNM mines and 

employ about the same percentage (16.0 

percent) of all MNM miners. Of the 

1,862 crushed limestone mines, 83.5 

percent employ fewer than 20 miners, 

and there are no crushed limestone 

mines that employ over 500 miners. In 

2019, there were 9,605 contract miners 

in the crushed limestone mining 

industry. 

e. Sand and Gravel Mining 

Sand and gravel mines account for 

52.7 percent of all MNM mines and 

employ 21.1 percent of all MNM miners. 

Nearly all (96.7 percent) of these mines 

employ fewer than 20 employees. In 

2019, MSHA data show that there were 

7,512 contract miners in the sand and 

gravel mining industry. 

f. Coal 

In the coal sector, 707 mines (63.9 

percent) employed fewer than 20 

miners. Overall, coal mine employment 

in 2019 was 52,966, of which 51,573 

were miners and the remaining 1,393 

were office workers. Additionally, there 

were a total of 22,003 contract miners in 

the coal mining industry in 2019. 

2. Economic Characteristics of the 

Metal/Non-Metal Mining Industry 

The value of all MNM mining output 

in 2019 was estimated at $83.8 billion 

(U.S. Department of Interior, 2019). 

Metal mines, which include iron, gold, 

copper, silver, nickel, lead, zinc, 

uranium, radium, and vanadium mines, 

contributed $26.9 billion. In the USGS 

Mineral Commodity Summaries, 

nonmetals, stone, sand and gravel, and 

crushed limestone are combined in to 

one commodity group called industrial 

minerals. MSHA estimated the 

production value of each individual 

commodity by applying the proportion 

of revenues represented by each among 

all commodities in the SUSB and 

applying that proportion to the 2019 

production value for all industrial 

minerals reported by USGS. This 

approach yielded the following 

estimates: metal production was valued 

at $26.9 billion, non-metal production at 

$22.3 billion, stone mining at $12.85 

billion, sand and gravel at $9.0 billion, 

and crushed limestone at $12.7 billion. 

Production in the U.S. coal sector 

amounted to 706.1 million tons in 

2019.62 To estimate coal revenues in 

2019, MSHA combined production 

estimates with prices per ton. Mine 

production data was taken from MSHA 

quarterly data and the coal price per ton 

was taken from the 2019 EIA Annual 

Coal Report. As shown in Table IX–1, 

total coal revenues in 2019 equaled 

$25.6 billion. 

The U.S. coal mining sector produces 

three major types of coal: bituminous, 

lignite, and anthracite. According to 

MSHA data, bituminous operations 

account for approximately 92.1 percent 

of total coal production in short tons, 

and 91.9 percent of all coal miners. 

Lignite operations account for roughly 

7.5 percent of total coal production and 

6.2 percent of coal miners. Anthracite 

operations account for 0.4 percent of 

coal production and 1.9 percent of coal 

miners. 

C. Cost-Benefit Analysis 

The PRIA is based on MSHA’s 

Preliminary Risk Analysis and the 

Technological Feasibility analysis. The 

PRIA presents estimated benefits and 

costs of the proposed rule for 

informational purposes only. Under the 

Mine Act, MSHA is not required to use 

estimated net benefits as the basis for its 

decision. MSHA requests comments on 

the methodologies, baseline, 

assumptions, and estimates presented in 

the PRIA and also asks for any data or 

quantitative information that may be 

useful in evaluating the estimated costs 

and benefits associated with the 

proposed rule. The PRIA assesses the 

costs and benefits in the MNM and coal 

industries of reducing miners’ 

exposures to silica to 50 mg/m3 for a full 

shift, calculated as an 8-hour time 

weighted average (TWA) and of 

complying with the standard’s ancillary 

requirements. The PRIA also assesses 

the costs and benefits from requiring 

medical surveillance of MNM miners. It 

also assesses the costs and benefits from 

revising the existing respiratory 

protection standards. MSHA is 

proposing to incorporate by reference 

ASTM F3387–19, ‘‘Standard Practice for 

Respiratory Protection’’ (ASTM F3387– 

19). ASTM F3387–19 would replace the 

1969 American National Standards 

Institute (ANSI) ‘‘Practices for 

Respiratory Protection.’’ 

MSHA estimates the proposed rule 

would have an annualized cost of $57.6 

million in 2021 dollars at a real 

discount rate of 3 percent. Of this cost, 

over 55 percent is attributable to 

exposure monitoring; 30 percent to 

medical surveillance; 10 percent to 

engineering, improved maintenance and 

repair, and administrative controls; 2.4 

percent related to the selection, use, and 

maintenance of approved respirators in 

accordance with ASTM F3387–19, 

respiratory protection practices; and 1.8 

percent to additional respiratory 

protection (e.g., when miners need 

temporary respiratory protection from 

exposure at the proposed PEL when it 

would not have been necessary at the 

existing PEL). MSHA further estimates 

that the MNM sector will incur $52.7 

million (91 percent), and the coal sector 

will incur $4.9 million (9 percent) in 

annualized compliance costs (see Table 

IX–2). 

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63This modeling strategy implicitly assumes that 

the ten-year cost annualization repeats five more 

times to cover the same 60-year analytic period as 

the benefits model. Thus, one-time costs incurred 

in the first year implicitly repeat in years 11, 21, 

31, 41 and 51. This may introduce a tendency 

toward overestimation of compliance costs. 

In its analysis, MSHA annualizes all 

costs using 3 percent and 7 percent 

discount rates as recommended by 

OMB. MSHA bases the annualization 

periods for expenditures on equipment 

life cycles and primarily uses a 10-year 

annualization period for one-time costs 

and 20-year for medical surveillance. 

However, MSHA annualizes the benefits 

of the proposed rule over a 60-year 

period to reflect the time needed for 

benefits to reach the steady-state values 

projected in MSHA’s PRA. Therefore, 

MSHA’s complete analysis of this rule 

is 60 years (which corresponds to 45 

years of working life and 15 years of 

retirement for the current miner 

population). MSHA holds the 

employment and production constant 

over this period for purposes of the 

analysis.63

For both MNM and coal mines, the 

estimated costs to comply with the 

proposed PEL (50 mg/m3), assumes that 

all mines are compliant with the 

existing PEL of 100 mg/m3 for MNM 

mines (for a full shift, calculated as an 

8-hour TWA) and 85.7 mg/m3 for coal 

mines (for a full shift, calculated as an 

8-hour TWA). 

MSHA estimates that: 

D The proposed respirable crystalline 

silica rule will result in a total of 799 

lifetime avoided deaths (63 in coal and 

736 in MNM mines) and 2,809 lifetime 

avoided morbidity cases (244 in coal 

and 2,566 in MNM mines) once it is 

fully effective (i.e., beginning 60 years 

post rule promulgation through year 120 

such that all miners, working and 

retired, have been exposed only under 

the proposed PEL) (see Table IX–3). 

D Over the first 60 years, annual cases 

avoided will increase gradually to the 

steady-state values (i.e., long-run peryear averages). Upon reaching the 

steady-state values, annual cases 

avoided will be constant from year 60 

onward because all miner cohorts will 

have identical lifetime risks. From Table 

IX–4, in the first 60 years, the proposed 

rule would result in a total of 410 

avoided deaths (377 in MNM and 33 in 

Coal) and 1,420 avoided morbidity cases 

(1,298 in MNM and 122 in Coal), which 

are the benefits MSHA monetized in its 

benefits analysis. 

D The total benefits of the proposed 

respirable crystalline silica rule from 

these avoided deaths and morbidity 

cases are $175.7 million per year in 

2021 dollars. 

—The majority (60.7 percent) of these 

benefits ($108.0 million) are 

attributable to avoided mortality due 

to non-malignant respiratory disease 

(NMRD) ($52.8 million), silicosis 

($28.1 million), and end-stage renal 

disease (ESRD) ($19.9 million), and 

lung cancer ($7.2 million). 

—Benefits from avoided morbidity due 

to silicosis are $53.2 million per year: 

$48.7 million for MNM mines and 

$4.6 million for coal mines (see Table 

IX–5). 

—Benefits from avoided morbidity that 

precedes fatal cases associated with 

NMRD, silicosis, renal disease, and 

lung cancer, are $14.5 million: $13.3 

million for MNM mines and $1.2 

million for coal mines (see Table IX– 

5). 


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64MSHA recognizes that it is impossible to 

predict economic factors over such a long period. 

Given known information and forecast limitations, 

MSHA believes this is a reasonable assumption. 

65The following references document miner 

exposures that could be simultaneously below the 

PEL for RCMD but exceed the PEL for silica: 

Rahimi, E., Shekarian, Y., Shekarian, N. et al. 

Investigation of respirable coal mine dust (RCMD) 

and respirable crystalline silica (RCS) in the U.S. 

underground and surface coal mines. Sci Rep 13, 

1767 (2023). https://doi.org/10.1038/s41598-022- 

24745-x. 

Doney BC, Blackley D, Hale JM, Halldin C, Kurth 

L, Syamlal G, Laney AS. Respirable coal mine dust 

in underground mines, United States, 1982–2017. 

Am J Ind Med. 2019 Jun;62(6):478–485. doi: 

10.1002/ajim.22974. Epub 2019 Apr 29. PMID: 

31033017; PMCID: PMC6800046. 

Doney BC, Blackley D, Hale JM, Halldin C, Kurth 

L, Syamlal G, Laney AS. Respirable coal mine dust 

at surface mines, United States, 1982–2017. Am J 

Ind Med. 2020 Mar;63(3):232–239. doi: 10.1002/ 

ajim.23074. Epub 2019 Dec 9. PMID: 31820465; 

PMCID: PMC7814307. 

MSHA acknowledges that its benefit 

estimates are influenced by the 

underlying assumptions and that the 

long-time frame of this analysis (first 60 

years) is a source of uncertainty. The 

main assumptions underlying these 

estimates of avoided mortality and 

morbidity include the following: 

D Employment and production are 

held constant over the 60 years—the 

analysis period of the proposed rule.64

D Any miners currently exposed 

above the existing PELs are exposed to 

levels of respirable crystalline silica at 

existing standards (100 mg/m3 for a fullshift exposure, calculated as an 8-hour 

TWA at MNM mines and 85.7 mg/m3 for 

a full-shift exposure, calculated as an 8- 

hour TWA at coal mines). 

D The proposed rule will result in 

miners being exposed at or below the 

proposed PEL (50 mg/m3). 

D Miners have identical employment 

and hence exposure tenures (45 years). 

The assumptions inherent in developing 

the exposure-response functions for the 

modeled health outcomes are reasonable 

throughout the exposure ranges relevant 

to this benefits analysis. In the final 

rule, the agency plans to augment the 

Regulatory Impact Analysis, for 

informational purposes, so as to 

incorporate different durations of 

working life based on exposure 

information, while continuing to also 

present calculations based on a 45-year 

working life assumption. 

In addition to the above quantified 

health benefits of the lower PEL, MSHA 

projects that there would be additional 

benefits from requiring approved 

respirators be selected, used, and 

maintained in accordance with the 

requirements, as applicable, of ASTM 

F3387–19. The ASTM standard reflects 

developments in respiratory protection 

since MSHA issued its existing 

standards. These developments include 

OSHA’s research and rulemaking on 

respiratory protection. Under the 

proposed rule, MSHA would require 

operators’ respiratory protection plans 

to include minimally acceptable 

respiratory program elements: program 

administration; standard operating 

procedures (SOPs); medical evaluation; 

respirator selection; training; fit testing; 

and maintenance, inspection, and 

storage. Given the uncertainty about the 

current state of operator respiratory 

protection practices, MSHA did not 

quantify the benefits that would be 

realized by requiring approved 

respirators to be selected, used, and 

maintained in accordance with ASTM 

F3387–19. 

MSHA believes the proposed rule 

would lower exposures to respirable 

crystalline silica and respirable coal 

mine dust. The available exposureresponse models do not account for 

separate health effects from exposure to 

mixed dust that contains both respirable 

crystalline silica and coal mine dust. 

However, MSHA anticipates that there 

would be additional unquantified 

benefits provided by the proposed 

rule—reduced adverse health outcomes 

attributable to respirable coal mine dust 

exposure, such as CWP.65 The proposed 

rule does quantify the benefits of 

avoided deaths and illnesses from 

reducing coal miners’ exposures to 

respirable crystalline silica. Among coal 

miners, MSHA estimates 35 lifetime 

avoided deaths and illnesses from 

NMRD (see Table IX–3). 

Finally, MSHA also expects that the 

proposed rule’s medical surveillance 

provisions would reduce mortality and 

morbidity from respirable crystalline 

silica exposure among MNM miners. 

The initial mandatory examination that 

assesses a new miner’s baseline 

pulmonary status, coupled with 

periodic examinations, would assist in 

the early detection of respirable 

crystalline silica related illnesses. Early 

detection of illness often leads to early 

intervention and treatment, which may 

slow disease progression and/or 


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improve health outcomes. However, as 

noted, MSHA lacks data to quantify 

these additional benefits. 

The net benefits of the proposed rule 

are the differences between the 

estimated benefits and costs. Table IX– 

6 shows estimated net benefits using 

alternative discount rates of 0, 3, and 7 

percent for benefits and costs. As is 

observed from the table, the choice of 

discount rate has a significant effect on 

annualized costs, benefits, and hence 

net benefits. While the net benefits of 

the proposed respirable crystalline silica 

rule vary considerably depending on the 

choice of discount rate used to 

annualize costs and benefits, total 

benefits exceed total costs under each 

discount rate considered. MSHA’s 

estimate of the net annualized benefits 

of the proposed rule, using a uniform 

discount rate for both costs and benefits 

of 3 percent, is $118.2 million a year 

with the largest share ($108.8 million; 

92.0 percent) attributable to the MNM 

sector. 

D. Economic Feasibility 

To establish economic feasibility, 

MSHA uses a revenue screening test— 

whether the yearly costs of a rule are 

less than 1 percent of revenues, or are 

negative (i.e., provide net cost 

savings)—to presumptively establish 

that compliance with the regulation is 

economically feasible for the mining 

industry. The resulting ratio of 

annualized compliance costs to 

revenues from the screener analysis 

should be interpreted with care. If 

annualized compliance costs comprise 

less than 1 percent of revenue, the 

Department of Labor presumes that the 

affected entities can incur the 

compliance costs without significant 

economic impacts. 

For the MNM and coal mining sectors, 

MSHA estimates the projected impacts 

of the rule by calculating the average 

annualized compliance costs for each 

sector as a percentage of total revenues. 

To be consistent with costs that are 

calculated in 2021 dollars, MSHA first 

inflated mine revenues expressed in 

2019 to their 2021 equivalent using the 

GDP Implicit Price Deflator. Due to 

inflation, the nominal value of a dollar 

in 2021 is estimated to be about 5.4 

percent higher than in 2019. 


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Table IX–8 presents the projected 

impacts of the proposed rule. The table 

compares aggregate annualized 

compliance costs for MNM and coal 

sectors at a 0 percent, 3 percent, and 7 

percent real discount rate to total annual 

revenues. At a 3 percent real discount 

rate, total aggregate annualized 

compliance costs are projected to be 

$57.6 million (including both 30 CFR 

part 60 and 2019 ASTM Upgrade Costs), 

while aggregate revenues are estimated 

to be $115.3 billion in 2021 dollars. 

Thus, the mining industry is expected to 

incur compliance costs that comprise 

0.05 percent of total revenues. 

For the MNM sector, MSHA estimates 

that the annualized costs of the 

proposed rule (including ASTM update 

costs) would be $52.7 million at 3 

percent discount rate, which is 

approximately 0.06 percent of total 

annual revenue of $88.3 billion ($52.7 

million/$88.3 billion) for MNM mine 

operators. For the coal sector, MSHA 

estimates that the annualized cost of the 

proposed rule would also be $4.9 

million at 3 percent, which is 

approximately 0.02 percent of total 

annual revenue of $27.0 billion ($4.9 

million/$27.0 billion) for coal mine 

operators. 

The ratios of screening analysis are 

well below the 1.0 percent threshold, 

and therefore, MSHA has concluded 

that the requirements of the proposed 

rule are economically feasible, and no 

sector of the industry will likely incur 

significant costs. 

E. Regulatory Alternatives 

The proposed rule presents a 

comprehensive approach for lowering 

miners’ exposure to respirable 

crystalline silica. The proposal includes 

the following regulatory provisions: 

lowering miners’ respirable crystalline 

silica exposure to a PEL of 50 mg/m3 for 

a full-shift exposure, calculated as an 8- 

hour TWA; initial baseline sampling for 

miners who are reasonably expected to 

be exposed to respirable crystalline 

silica; periodic sampling for miners who 

are at or above the proposed action level 

of 25 mg/m3 but at or below the 

proposed PEL of 50 mg/m3; and semiannual evaluation of changing mining 

processes that would reasonably be 

expected to result in new or increased 

exposures. 

In developing the proposed rule, 

MSHA considered two regulatory 

alternatives. Both alternatives include 

less stringent monitoring provisions 

than the proposed monitoring 

provisions. One of the alternatives also 

combines less stringent monitoring with 

a more stringent PEL. MSHA discusses 

the regulatory options in the sections 

below, from least expensive to most 

expensive. Both alternatives would 

retain the respiratory protection updates 

and medical surveillance from the 

proposed rule. 

1. Regulatory Alternative #1: Changes in 

Sampling and Evaluation Requirements 

Under this alternative, the proposed 

PEL would remain unchanged at 50 mg/ 

m3 and the proposed action level would 

remain unchanged at 25 mg/m3. Further, 

mine operators would conduct: (1) 

baseline sampling for miners who may 

be exposed to respirable crystalline 

silica at or above the proposed action 

level of 25 mg/m3, (2) periodic sampling 

twice per year for miners who are at or 

above the proposed action level of 25 

mg/m3 but at or below the proposed PEL 

of 50 mg/m3, and (3) annual evaluation 

of changing mining processes or 

conditions that would reasonably be 


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expected to result in new or increased 

exposures. 

Mine operators would be required to 

undertake sampling under this 

regulatory alternative and would thus 

incur compliance costs. However, 

monitoring requirements under this 

alternative are less stringent than the 

requirements under the proposed rule 

because the number of miners to be 

sampled for baseline sampling would be 

smaller than in the proposed rule and 

the frequency of periodic sampling and 

evaluations of changing mining 

processes or conditions are set at half 

the frequency of the proposed 

monitoring requirements. Therefore, the 

cost of compliance will be lower under 

this alternative. MSHA estimates that 

annualized monitoring costs will total 

$17.3 million for this alternative (at a 3 

percent discount rate), compared to 

$32.0 million for the proposed 

monitoring requirements, resulting in an 

estimated $14.7 million in lower costs 

per year (Table IX–9). 

Although this alternative does not 

eliminate exposure monitoring, the 

requirements are minimal relative to the 

monitoring requirements under the 

proposed rule. However, MSHA 

believes it is necessary for mine 

operators to establish a solid baseline 

for any miner who is reasonably 

expected to be exposed to respirable 

crystalline silica. In addition, quarterly 

monitoring helps mine operators 

correlate mine conditions to miner 

exposure levels and see exposure trends 

more rapidly than would result from 

semi-annual or annual sampling. This 

would enable mine operators to take 

measures necessary to ensure continued 

compliance with the PEL. Further, more 

frequent monitoring would enable mine 

operators to ensure the adequacy of 

controls at their mines and better 

protect miners’ health. These benefits 

cannot be quantified, but they are 

nevertheless material benefits that 

increase the likelihood of compliance. 

MSHA also believes that requiring 

more frequent periodic sampling would 

provide mine operators with greater 

confidence that they are in compliance 

with the proposed rule. Because of the 

variable nature of miner exposures to 

airborne concentrations of respirable 

crystalline silica, maintaining exposures 

below the proposed action level 

provides mine operators with 

reasonable assurance that miners would 

not be exposed to respirable crystalline 

silica at levels above the PEL on days 

when sampling is not conducted. MSHA 

believes that the benefits of the 

proposed sampling requirements justify 

the additional costs relative to 

Regulatory Alternative 1. 

2. Regulatory Alternative #2: Changes in 

Sampling and Evaluation Requirements 

and the Proposed PEL 

Under this regulatory alternative, the 

proposed PEL would be set at 25 mg/m3; 

mine operators would install whatever 

controls are necessary to meet this PEL; 

and no action level would be proposed. 

Further, mine operators: (1) would not 

be required to conduct baseline 

sampling or periodic sampling; (2) 

would conduct semi-annual evaluations 

of changing conditions; and (3) would 

sample as frequently as necessary to 

determine the adequacy of controls. 

Mine operators would not be required 

to undertake baseline or periodic 

sampling. However, mine operators 

would be required to perform semiannual evaluations of changing mining 

processes or conditions. Further, mine 

operators would be required to perform 

post-evaluation sampling when the 

operators determine as a result of the 

semi-annual evaluation that miners may 

be exposed to respirable crystalline 

silica at or above proposed PEL at 25 mg/ 

m3. When estimating the cost of the 

proposed monitoring requirements, 

MSHA assumes that the number of 

samples for corrective action and semiannual evaluation are relatively small 

(2.5 percent of miners) because samples 

from sampling to determine the 

adequacy of controls and from MSHA 

can both be used to meet the 

requirements. Since this alternative 


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66About 8,053 of mines active in 2019 either did 

not have a sample > 25 mg/m3 or did not have a 

sample in the last 5 years. 

does not require periodic sampling, 

MSHA increases samples after each 

evaluation to 10 percent of miners to 

ensure the monitoring requirements can 

be met. 

This alternative also sets the proposed 

PEL at 25 mg/m3. In addition to the 

estimated cost of compliance with a PEL 

of 50 mg/m3, mine operators would 

incur additional engineering control 

costs to meet a PEL of 25 mg/m3. To 

estimate these additional engineering 

control costs, MSHA largely uses the 

same methodology as for mines affected 

at the proposed PEL of 50 mg/m3. 

a. Number of Mines Affected Under 

Regulatory Alternative 2 

MSHA first estimated the number of 

mines expected to incur the cost of 

implementing engineering controls to 

reach the more stringent PEL. After 

excluding mines that are affected at the 

proposed PEL of 50 mg/m3 (to avoid 

double-counting), MSHA finds that 

3,477 mines (2,991 MNM mines and 486 

coal mines) operating in 2019 had at 

least one sample at or above 25 mg/m3

but below 50 mg/m3.66

To this number, MSHA adds the 1,226 

affected mines expected to incur costs to 

reach the proposed PEL of 50 mg/m3. 

Based on its experience and knowledge, 

MSHA does not expect the mines that 

installed engineering controls to meet 

the PEL of 50 mg/m3 will also be able to 

comply with a PEL of 25 mg/m3. For 

example, to comply with the proposed 

PEL of 50 mg/m3, a mine might need to 

add the engineering controls necessary 

to achieve an additional 10 air changes 

per hour over that achieved by existing 

controls, which are costed in the 

following section. However, such a 

mine facility would then need to add an 

additional 10 air changes per hour to 

meet the more stringent PEL of 25 mg/ 

m3, which is not costed in the following 

section. Thus, MSHA expects that the 

1,226 affected mines will incur 

additional costs to meet the PEL of 25 

mg/m3 specified under this alternative. 

MSHA estimates a total of 4,703 

mines will incur costs to purchase, 

install, and operate engineering controls 

to meet the PEL of 25 mg/m3 under this 

alternative. MNM mines account for 

4,087 (87 percent) and coal mines 616 

(13 percent). Further, of the estimated 

4,087 MNM mines and 616 coal mines, 

1,096 MNM mines (27 percent) and 130 

coal mines (21 percent) are also 

estimated to incur compliance costs to 

reach the proposed PEL of 50 mg/m3. 

b. Estimated Engineering Control Costs 

Under Regulatory Alternative 2 

MSHA identified potential 

engineering controls that would enable 

mines with respirable crystalline silica 

dust exposures at or above 25 mg/m3 but 

below 50 mg/m3 categories to meet the 

PEL of 25 mg/m3 under consideration for 

this alternative. While MSHA assumes 

that mine operators will base such 

decisions on site-specific conditions 

such as mine layout and existing 

infrastructure, MSHA cannot make 

further assumptions about the specific 

controls that might be adopted and 

instead assumes the expected value of 

purchased technologies should equal 

the simple average of the technologies 

listed in each control category. 

Where more precise information is 

unavailable, MSHA assumes operating 

and maintenance (O&M) costs to be 35 

percent of initial capital expenditure 

and installation cost, when appropriate, 

will be equal to the initial capital 

expenditure (Table IX–10). MSHA also 

assumes the larger capital expenditure 

controls will have a 30-year service life. 

MSHA welcomes public comment 

concerning the engineering controls 

selected for this analysis and the 

assumptions used to estimate 

installation and O&M costs for these 

controls. 

However, the difficulty of meeting a 

PEL of 25 mg/m3 is such that MSHA’s 

experience suggests a single control 

from Table IX–10 will not be sufficient. 

For example, respirable crystalline silica 

dust exposure at such a stringent limit 


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as 25 mg/m3 is likely to occur at more 

than one area of the mine; in addition 

to increasing ventilation to a crusher/ 

grinder, enclosing and ventilating the 

conveyor belt mine would be necessary 

to reduce concentrations below the 

limit. Similarly, increasing facility 

ventilation from 20 to 30 air changes per 

hour may not be adequate to meet the 

limit; 40 air changes per hour might be 

necessary. Therefore, MSHA assumes 

mine operators will purchase and install 

at least two of the engineering controls 

listed in Table IX–10. This may be a 

conservative assumption. 

Table IX–11 presents the average 

annualized engineering control costs per 

mine and total annualized engineering 

control costs by mine sector. Because 

the service life of nearly all components 

is expected to be 30 years, the costs of 

all engineering controls are annualized 

over 30 years. At a 3 percent real 

discount rate, the average annualized 

engineering control costs are about 

$94,300 per mine, resulting in an 

additional cost of $443.6 million if the 

PEL is set at 25 mg/m3 instead of 50 mg/ 

m3. 

Table IX–12 summarizes the 

estimated annualized cost of this 

alternative under consideration. At a 3 

percent real discount rate, exposure 

monitoring costs less than the proposed 

rule; however, this lower cost is more 

than offset by the increased control 

costs necessitated by the requirement 

that mines maintain respirable 

crystalline silica exposure levels below 

25 mg/m3. At an estimated annualized 

cost of $491.2 million, this alternative 

would cost nearly eight times more than 

the proposed requirements. 


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This alternative requires exposure 

monitoring that is more stringent than 

Regulatory Alternative 1, but less 

stringent than the proposed 

requirements. In addition, Regulatory 

Alternative 2 increases miner protection 

by proposing to set the PEL at 25 mg/m3, 

resulting in measurable avoided 

mortality and other health benefits. 

Table IX–13 presents the avoided 

morbidity and mortality cases over the 

60-year regulatory analysis time horizon 

under this alternative. Under this 

alternative, the avoided 60-year 

mortality is expected to be 981, which 

is 2.4 times higher than the expected 

avoided mortality of 410 under a 

proposed PEL of 50 mg/m3. The avoided 

60-year morbidity under the regulatory 

alternative of 25 mg/m3 is expected to be 

1,948, which is 1.4 times higher than 

the expected avoided 60-year morbidity 

of 1,420 under the proposed PEL of 50 

mg/m3. 

Table IX–14 presents the benefits 

associated with this avoided morbidity 

and mortality. The expected total 

benefits, discounted at 3 percent, are 

$365.5 million, which is twice the 

expected total benefits of $175.7 million 

under the proposed PEL of 50 mg/m3. 

Under this regulatory alternative, these 

benefits are made up of $258.0 million 

due to avoided mortality, $34.5 million 

due to morbidity preceding mortality, 

and $73.0 million due to morbidity not 

preceding mortality. However, when 

compared to the annualized costs, the 

net benefits of this alternative are 

negative at both a 3 percent and 7 

percent real discount rate. 


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BILLING CODE 4520–43–C 

MSHA solicits further comment on 

the extent to which these or other 

regulatory alternatives (including 

different ways of calculating respirable 

crystalline silica concentration) may 

change the effects of the proposed rule. 

X. Initial Regulatory Flexibility 

Analysis 

The Regulatory Flexibility Act (RFA) 

of 1980, as amended by the Small 

Business Regulatory Enforcement 

Fairness Act (SBREFA) of 1996, requires 

preparation of an Initial Regulatory 

Flexibility Analysis (IRFA) for any rule 

that by law must be proposed for public 

comment, unless the agency certifies 

that the rule, if promulgated, will not 

have a significant economic impact on 

a substantial number of small entities. 5 

U.S.C. 601- 612. Because MSHA’s 

proposed rule on respirable crystalline 

silica, including the incorporation of 

ASTM F3387–19 by reference, would 

regulate the mining industry, the 

proposed rule falls within the purview 

of the RFA. MSHA has evaluated the 

impact of the proposed rule on small 

entities in this IRFA. MSHA’s analysis 

is presented in the following. 

Description of the Reasons Why MSHA 

is Considering Regulatory Action 

Based on its review of the health 

effects literature, MSHA has 

preliminarily determined that 

occupational exposure to respirable 

crystalline silica causes silicosis and 

other diseases. Based on its preliminary 

risk analysis, MSHA has also 

determined that under its existing 

standards, miners face a risk of material 

impairment of health or functional 

capacity from exposures to respirable 

crystalline silica. 

Based on these preliminary 

determinations, MSHA proposes to 

amend its existing standards to better 

protect miners against occupational 

exposure to respirable crystalline silica, 

a carcinogen, and to improve respiratory 

protection for all airborne contaminants. 

The proposed rule would establish for 

mines of all sizes, a PEL of 50 mg/m3 for 

a full shift, calculated as an 8-hour 

TWA, for all miners, and an action level 

of 25 mg/m3 for a full-shift exposure, 

calculated as 8-hour TWA. MSHA’s 

proposal would also include other 

requirements to protect miner health, 

such as periodic exposure sampling and 

corrective actions to be taken when 

miners’ exposures exceed the PEL. 

MSHA also proposes to replace existing 

requirements for respiratory protection 

and to incorporate by reference the 

ASTM F3387–19 Standard Practice for 

Respiratory Protection. MSHA believes 

that the proposed changes would 

significantly improve health protections 

for all miners over the course of their 

working lives. 

Objectives of, and Legal Basis for, the 

Proposed Rule 

The proposed rule would fulfill 

MSHA’s statutory obligation to 

‘‘promulgate improved mandatory 

health . . . standards to protect’’ 

miners’ health under the Mine Act, as 

amended. 30 U.S.C. 801(g). The Mine 

Act requires the Secretary of Labor 

(Secretary) to develop and promulgate 

improved mandatory health or safety 

standards to prevent hazardous and 

unhealthy conditions and protect the 

health and safety of the nation’s miners. 

30 U.S.C. 811(a). The Secretary must set 

standards to assure, based on the best 

available evidence, that no miners will 

suffer material impairment of health or 

functional capacity from exposure to 

toxic materials or harmful physical 

agents over their working lives. 30 

U.S.C. 811(a)(6)(A). Section 103(h) of 

the Mine Act gives the Secretary the 

authority to promulgate standards 

involving recordkeeping and reporting. 

30 U.S.C. 813(h). Additionally, section 

508 of the Mine Act gives the Secretary 

the authority to issue regulations to 

carry out any provision of the Mine Act. 

30 U.S.C. 957. 


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67The NAICS classifications used in this analysis 

are drawn from a recent version of the NAICS 

(though, for reasons described below, not the latest 

version, which was published in January 2022). 

SBA established definitions of small entities for 

each of the categories in the earlier version, which 

were effective in August 2019. This version of 

NAICS categories was needed for this analysis, in 

order for MSHA to cross-tabulate (or crosswalk) its 

data on mines and controllers with Bureau of 

Census data on revenues by NAICS codes, where 

these Census data were organized by the same 

NAICS codes that were in the earlier version. No 

comparable revenue data, at this writing, had yet 

been revised to the most recent NAICS categories, 

which prevented MSHA from using those 

categories. MSHA identified 25 NAICS categories 

(in the previous system) that accounted for all 

mining activities. 

68The number of controllers and mines examined 

in this regulatory flexibility analysis are those 

specifically known to operate in 2021. The year 

2021 is the most current year for which complete 

information were available. Such information about 

controllers as parent companies might include, for 

example, knowledge of whether the parent 

company is a large, multinational corporation, 

which has bearing on this regulatory flexibility 

analysis. Because the benefit-cost analysis 

performed on the proposed rule did not need this 

kind of detailed information about controllers, it 

was able to have a broader scope to include data 

from other years besides 2021, which it did. As a 

result, the benefit cost analysis included a larger 

number of mines (and affected mines) and 

controllers. The key factor for this regulatory 

flexibility analysis is the estimated ratio of the 

regulatory cost per revenue for controllers, as 

reflected by the most current data. The estimation 

of this ratio is robustly addressed in MSHA’s 

analysis of the 5,879 controllers in 2021 (which is 

not impacted by the exclusion of other years in this 

analyis). 

Description and Estimate of the Number 

of Small Entities to Which the Proposed 

Rule Would Apply 

The proposed rule would affect MNM 

and coal mining operations. To 

determine the number of small entities 

subject to the proposed rule, MSHA 

reviewed the North American Industrial 

Classification System (NAICS), the 

standard used by Federal statistical 

agencies in classifying business 

establishments, as well as information 

from the Office of Advocacy of the 

Small Business Administration (SBA). 

MSHA used its data from the MSHA 

Standardized Information System 

(MSIS) to identify the responsible party 

for each mine. MSHA then combined 

that information with the size 

classification information. 

First, MSHA determined that mining 

operations that fall into 25 NAICS-based 

industry classifications may be subject 

to the proposed rule. These industry 

categories and their accompanying sixdigit NAICS codes are shown in Table 

X–1.67

Second, MSHA matched the NAICS 

classifications with SBA small-entity 

size standards (based on number of 

employees) to determine the number of 

small entities within each of the 

respective NAICS codes. See Table X–1. 

Third, MSHA counted the number of 

small-entity controllers in each NAICS 

code, after determining that a 

‘‘controller’’ who owns and controls a 

mine as the appropriate unit of this 

IRFA analysis (based on SBA guidance) 

(Small Business Administration 2017). 

A controller is a parent company 

owning or controlling one or more 

mines. A controller can also be a firm, 

whereas a mine can be an 

establishment. Table X–1 shows the 

count of all controllers and a count of 

small-entity controllers in each NAICS 

code. Some ‘‘unique controllers’’ are 

included in more than one NAICS code 

because they own or control multiple 

mines, each producing a different 

commodity. For this analysis, however, 

MSHA single-counted these unique 

controllers; for example, a controller 

who owns three mines in three different 

NAICS codes was only counted once. 

Based on this methodology, MSHA 

estimated that in 2021, there were a 

total of 5,879 controllers, 5,007 of which 

were small-entity controllers. Many 

controllers owned one or two mines, 

while some controllers owned hundreds 

of mines nationwide (or worldwide). 

The 5,007 small-entity controllers 

owned a total of 8,240 mines out of 

11,791 mines in operation in 2021.68

BILLING CODE 4520–43–P 


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BILLING CODE 4520–43–C 


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69U.S. Census Bureau, ‘‘Statistics of U.S. 

Businesses,’’ released May 2021. https://

www.census.gov/data/tables/2017/econ/susb/2017- 

susb-annual.html. Data in the report were in 

reference to the year 2017, which MSHA adjusted 

to 2021 dollars. Data on revenues are presented in 

the report under the equivalent term ‘‘receipts.’’ 

MSHA converted the 2017 revenues to 2021 dollars 

using the GDP Implicit Price Deflator published by 

the Bureau of Economic Analysis October 26, 2022, 

Table 1.1.9 Implicit Price Deflators for Gross 

Domestic Product, Series A191RD. https://

apps.bea.gov/histdata/fileStructDisplay.cfm?HMI=7

&DY=2022&DQ=Q3&DV=Advance

&dNRD=October-28-2022. The index was 107.749 

for 2017 and 118.895 for 2021, creating an 

adjustment factor (from 2017 to 2021 dollars) of 

118.895/107.749 or 1.103. 

70 In a small number of cases (in terms of NAICS 

codes and size categories) the SUSB data were 

incomplete. In these cases, MSHA imputed 

revenue/employee ratios based on closely related 

data for comparable NAICS-size categories. MSHA 

then used these imputed revenue/employee ratios 

to estimate the revenues of some small-entity 

controllers, by the methodology just described. 

Description of the Projected Reporting, 

Recordkeeping, and Other Compliance 

Requirements for Small Entities 

As explained earlier, the proposed 

rule would establish a PEL of 50 mg/m3

and an action level of 25 mg/m3 for a 

full-shift exposure, calculated as 8-hour 

TWA. The proposed rule would also 

include other requirements. Examples 

include baseline, periodic, and 

corrective action sampling, semi-annual 

evaluations, medical surveillance, 

respiratory protection, and 

recordkeeping. 

With regard to the paperwork burden 

on small entities, MSHA’s proposed rule 

would create new information 

collection requests for the mining 

industry. As described in greater detail 

in Section XI below, these requirements 

include the collection of information 

involving: (1) exposure monitoring— 

samplings and semi-annual evaluations, 

(2) corrective actions taken, (3) miners 

unable to wear respirators, and (4) 

medical surveillance for MNM miners. 

Table XI–2 displays an annual estimate 

of information collection burden for the 

whole mining industry. Compliance 

costs on small entities that include 

recordkeeping costs are discussed 

below. 

Estimation of the Compliance Costs and 

Relative Burden to Small Entities 

MSHA estimated the average annual 

regulatory cost per small-entity 

controller (based on a 3 percent 

discount rate), as well as the average 

annual revenue per small-entity 

controller. MSHA estimated, for each 

controller, the additional annual cost of 

the proposed regulation as a proportion 

of that controller’s annual revenue. The 

average of these proportions (weighting 

controllers equally) was 0.122 percent, 

below a 3 percent threshold used for 

significant impact. That is, for every $1 

million in revenue earned by a 

controller, the average regulatory cost 

was estimated to be $1,220. 

Total Compliance Cost. MSHA 

estimated that the proposed rule would 

have an average cost of $60.23 million 

per year in 2021 dollars at a real 

discount rate of 3 percent. The 

estimated costs for the proposed rule 

would represent the additional costs 

necessary for mine operators to achieve 

full compliance with the proposed rule. 

Compliance Costs by Small-Entity 

Controllers. Because mines (as well as 

controllers) vary in the scale of their 

operations, MSHA first estimated 

additional regulatory costs on a perminer basis. MSHA anticipated that the 

additional regulatory costs per miner 

would vary across the six major 

commodity categories: coal, metal, 

nonmetal, stone, crushed limestone, and 

sand and gravel. MSHA analyzed 

employment data linked with controller 

data. By combining this information 

with compliance cost information, 

MSHA derived estimates of the 

regulatory costs for small-entity 

controllers. MSHA then estimated the 

regulatory cost for each of the 5,007 

small-entity controllers identified in 

2021. See the average annual regulatory 

cost per controller in Table X–2. 

Revenues by Small-Entity Controllers. 

MSHA estimated revenues for each 

small-entity controller. The Agency 

estimated revenues per employee, by 

mine, and by controller, using data 

published by the U.S. Bureau of Census 

in their report, ‘‘Statistics of U.S. 

Businesses’’ (SUSB).69 The SUSB data 

provided revenue estimates for 

enterprises in each NAICS code and for 

each ‘‘size category’’ (based on number 

of employees) within each NAICS code. 

The enterprise data considered 

controllers that had operations in more 

than one NAICS code. MSHA summed 

the estimated revenue for the 

establishments within the same NAICS 

code to create multiple enterprises with 

different NAICS codes and compare 

constructed enterprises with the SUSB 

data to estimate the revenue for each of 

these size-category-specific enterprises. 

This methodology was relevant for the 

‘‘largest’’ of small-entity controllers, 

which controlled more than one mine, 

sometimes operating in different NAICS 

categories. Most small-entity controllers 

operated only one mine, meaning that 

no summation was required because 

only the number of employees in a 

single mine needed to be counted. 

MSHA estimated revenues for each 

small-entity controller. Some smallentity controllers had mines belonging 

to different NAICS codes. This factor 

precluded MSHA from being able to 

precisely categorize small-entity 

controllers by NAICS code. MSHA 

estimated each small-entity controller’s 

revenues.70

Some of the small-entity controllers 

may also have operations in non-mining 

industries. If so, total revenues, 

including those from non-mining 

operations, would be higher than 

estimated here, and the ratios of 

regulatory costs to revenues shown in 

the summary table may be 

overestimated. 

MSHA developed estimates of the 

number of miners for each small-entity 

controller, and for each NAICS category 

within each controller’s activities. 

MSHA then combined these data with 

SUSB data on revenues by NAICS 

category and size category to generate 

estimated revenues for each small-entity 

controller. See the estimated average 

annual revenue per controller in Table 

X–2. 

Ratio of Compliance Cost to Revenue. 

From the two sets of estimates described 

above—costs and revenues—for each 

small-entity controller, MSHA generated 

estimates of the ratios of regulatory cost 

to revenue, for each controller. Table X– 

2 shows the number of controllers, 

average annual regulatory costs, average 

annual revenue, and average cost as a 

percent of revenue. 


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Relevant Federal Rules Which May 

Duplicate, Overlap, or Conflict With the 

Proposed Rule 

There are no Federal rules that may 

duplicate, overlap, or conflict with the 

proposed rule. 

Significant Alternatives and Their 

Impact on Small Entities 

MSHA considered two alternatives in 

the proposed rule. Under Alternative 1, 

the proposed PEL would remain 

unchanged at 50 mg/m3 and the 

proposed action level would remain 

unchanged at 25 mg/m3. Further, mine 

operators would conduct: (1) baseline 

sampling for miners who may be 

exposed to respirable crystalline silica 

at or above the proposed action level of 

25 mg/m3, (2) periodic sampling twice 

per year, and (3) annual evaluation of 

changing mining processes or 

conditions that would reasonably be 

expected to result in new or increased 

exposures. Under Alternative 2, the 

proposed PEL would be set at 25 mg/m3; 

mine operators would install whatever 

controls are necessary to meet this PEL; 

and no action level would be proposed. 

Further, mine operators would: (1) not 

be required to conduct baseline 

sampling or periodic sampling, (2) 

conduct semi-annual evaluations of 

changing conditions, and (3) sample as 

frequently as necessary to determine the 

adequacy of controls. Additional detail 

on the two regulatory alternatives 

MSHA considered can be found in IX. 

Summary of Preliminary Regulatory 

Impact Analysis and Regulatory 

Alternatives and in the standalone PRIA 

document. 

MSHA believes the proposed rule 

would provide improved health 

protections for miners and would be 

achievable for all mines. In developing 

the proposed rule, MSHA has included 

flexibilities for operators in the 

implementation of updated respiratory 

protection standard, which would 

reduce the burden on small entities. 

MSHA has made the following 

determinations regarding the two 

alternatives considered: 

• Alternative 1, ‘‘Changes in 

Sampling and Evaluation 

Requirements,’’ would reduce overall 

costs to the mining industry by 26.2 

percent, for costs calculated at both a 3 

percent and 7 percent discount rate. 

These reduced costs would be 

proportionally experienced by small 

entities. The average costs as a percent 

of revenues for small entities would 

then be reduced (relative to the 

proposed rule) from 0.12 percent to 0.09 

percent. 

• Alternative 2, ‘‘Changes in 

Sampling and Evaluation Requirements 

and the Proposed PEL,’’ would increase 

overall costs to the mining industry by 

701.9 percent, for costs calculated at a 

3 percent discount rate, and by 930.2 

percent for costs calculated at a 7 

percent discount rate. The average costs 

as a percent of revenues for small 

entities would then rise (relative to the 

proposed rule) from 0.12 percent to 0.98 

percent, based on a 3 percent discount 

rate, and from 0.12 percent to 1.259 

percent based on a 7 percent discount 

rate. 

MSHA is seeking comments or 

additional information from 

stakeholders on whether there are 

alternatives the Agency should consider 

that would accomplish the objectives of 

this rulemaking while reducing the 

impact on small entities. 

Conclusion 

MSHA estimated that small-entity 

controllers would be expected to incur, 

on average, additional regulatory costs 

equaling approximately 0.122 percent of 

their revenues (or $1,220 for every $1 

million in revenues). 

As required under the RFA, MSHA is 

complying with its obligation to consult 

with the SBA’s Chief Counsel for 

Advocacy on this proposed rule and on 

this initial regulatory flexibility 

analysis. Consistent with Agency’s 

practice, notes of any meetings with the 

Chief Counsel for Advocacy’s office on 

this proposed rule, or any written 

communications, will be placed in the 

rulemaking record. 

XI. Paperwork Reduction Act 

The Paperwork Reduction Act of 1995 

(44 U.S.C. 3501–3521) provides for the 

Federal Government’s collection, use, 


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and dissemination of information. The 

goals of the Paperwork Reduction Act 

include minimizing paperwork and 

reporting burdens and ensuring the 

maximum possible utility from the 

information that is collected under 5 

CFR part 1320. The Paperwork 

Reduction Act requires Federal agencies 

to obtain approval from the Office of 

Management and Budget (OMB) before 

requesting or requiring ‘‘a collection of 

information’’ from the public. 

As part of the Paperwork Reduction 

Act process, agencies are generally 

required to provide a notice in the 

Federal Register concerning each 

proposed collection of information to 

solicit, among other things, comment on 

the necessity of the information 

collection and its estimated burden, as 

required in 44 U.S.C. 3506(c)(2)(A). To 

comply with this requirement, MSHA is 

publishing a notice of proposed 

collection of information in the 

proposed rule titled, Lowering Miners’ 

Exposure to Respirable Crystalline 

Silica and Improving Respiratory 

Protection. 

This rulemaking would require the 

creation of a new information collection 

as well as modification to the burdens 

for existing collections. As required by 

the Paperwork Reduction Act, the 

Department has submitted information 

collections, including a new 

information collection and revisions of 

two existing collections, to OMB for 

review to reflect new burdens and 

changes to existing burdens. 

I. New Information Collection Under 

Proposed Part 60, Respirable 

Crystalline Silica 

Under proposed part 60 entitled 

‘‘Respirable Crystalline Silica,’’ some 

new burdens would apply to all mine 

operators, and other burdens would 

apply to only some mine operators. 

Below, the new information collection 

burden that would be created by 

proposed part 60 is discussed. 

Proposed § 60.16 lists all the 

recordkeeping requirements related to 

proposed part 60. Each of the 

requirements are discussed below: 

Proposed § 60.12 would require mine 

operators to make a record for each 

sampling and each evaluation 

conducted pursuant to this section. The 

sampling record would consist of the 

sample date, the occupations sampled, 

and the concentrations of respirable 

crystalline silica and respirable dust. 

The mine operator would also retain 

laboratory reports on sampling results. 

The semi-annual evaluation record 

would include the date of the evaluation 

and a record of the mine operator’s 

evaluation of any changes in mining 

operations that may reasonably be 

expected to result in new or increased 

respirable crystalline silica exposures. 

In addition, the mine operator would be 

required to post the sampling and 

evaluation records and the laboratory 

report on the mine bulletin board and, 

if applicable, by electronic means, for 

the next 31 days, upon receipt. All 

records would be retained for at least 2 

years from the date of each sampling or 

evaluation. 

Proposed § 60.13 would require mine 

operators to make a record of corrective 

actions and the dates of the corrective 

actions. The corrective action records 

would be retained for at least 2 years 

from the date of each corrective action. 

Proposed § 60.14 would require mine 

operators to retain a record of the 

written determination by a PLHCP that 

a miner who may be required to use a 

respirator is unable to wear a respirator. 

The written determination record would 

be retained for the duration of a miner’s 

employment plus 6 months. 

Proposed § 60.15 would require MNM 

mine operators to obtain a written 

medical opinion from the PLHCP or 

specialist within 30 days of a miner’s 

medical examination. The written 

medical opinion would contain the date 

of the medical examination, a statement 

that the examination has met the 

requirements of this proposed section, 

and any recommended limitations on 

the miner’s use of respirators. The 

written medical opinion record would 

be retained for the duration of a miner’s 

employment plus 6 months. 

II. Changes to Existing Information 

Collections 

This proposed rulemaking would 

result in non-substantive changes to 

existing information collection 

packages. One change under OMB 

Control Number 1219–0011 is to occur 

after 1219–0NEW, Respirable 

Crystalline Silica Standard, is approved 

by OMB. The other change is the 

discontinuance of the existing 

information collection package under 

OMB Control Number 1219–0048 which 

is also to occur after OMB approval of 

1219–0NEW, Respirable Crystalline 

Silica Standard. 

OMB Control Number 1219–0011, 

Respirable Coal Mine Dust Sampling, 

involves records for quarterly sampling 

of respirable dust in coal mines. The 

supporting statement references quartz 

and a reduced standard for respirable 

dust when quartz is present; however, 

there is no specific recordkeeping 

requirement that is associated with 

those references. Due to changes in the 

proposed rule, MSHA would make a 

non-substantive change to the 

supporting statement by removing such 

references. However, there would be no 

changes in paperwork burden and costs 

in this information collection. 

OMB Control Number 1219–0048, 

Respirator Program Records, involves 

recordkeeping requirements under 30 

CFR parts 56 and 57 for MNM mines 

when respiratory protection is used. 

MSHA is proposing to update the 

existing respiratory protection standard 

and permit mine operators to select the 

requirements of the standard that are 

applicable to their mines. This proposed 

change would eliminate the paperwork 

burden associated with respiratory 

protection resulting in the request to 

discontinue the existing information 

collection. 

A. Solicitation of Comments 

Pursuant to the Paperwork Reduction 

Act, MSHA has prepared and submitted 

an information collection request (ICR) 

to OMB for the collection of information 

requirements identified in this proposed 

rule for OMB’s review in accordance 

with 44 U.S.C. 3507(d). MSHA is 

soliciting comments concerning the 

proposed information collection related 

to respirable crystalline silica. MSHA is 

particularly interested in comments 

that: 

• Evaluate whether the proposed 

collection of information is necessary 

for the proper performance of the 

functions of the agency, including 

whether the information will have 

practical utility; 

• Evaluate the accuracy of the 

agency’s estimate of the burden of the 

proposed collection of information, 

including the validity of the 

methodology and assumptions used; 

• Suggest methods to enhance the 

quality, utility, and clarity of the 

information to be collected; and 

• Minimize the burden of the 

collection of information on those who 

are to respond, including through the 

use of appropriate automated, 

electronic, mechanical, or other 

technological collection techniques or 

other forms of information technology 

(e.g., permitting electronic submission 

of responses). 

B. Proposed Information Collection 

Requirements 

I. Type of Review: New Collection. 

OMB Control Number: 1219–0NEW. 

1. Title: Respirable Crystalline Silica 

Standard. 

2. Description of the ICR: The 

proposed rule on respirable crystalline 

silica contains collection of information 

requirements that would assist miners 

and mine operators in identifying 

exposures to respirable crystalline silica 


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in order to track actual and potential 

occupational exposure and action taken 

to control such exposure. 

There are provisions of this proposed 

rule that would take effect at different 

times after the implementation of this 

proposed rule, and there are provisions 

that would have different burden hours, 

burden costs, and responses each year. 

Therefore, MSHA shows the estimates 

of burden hours, burden costs, and 

responses in three separate years. 

3. Summary of the Collection of 

Information: Highlighted below are the 

key assumptions, by provision, used in 

the burden estimates in Table XI–1: 

Proposed § 60.12—Exposure Monitoring 

ICR. Proposed § 60.12 would require 

mine operators to make a record for 

each baseline sampling, corrective 

action sampling, periodic sampling, 

semi-annual evaluation, and postevaluation sampling, as previously 

described. 

Number of respondents. For proposed 

§ 60.12, the respondents would consist 

of all active mines because operators of 

active mines are assumed to perform 

baseline sampling and conduct semiannual evaluations. 

MSHA counts the number of active 

mines in 2019, defining an active mine 

as one that had at least 520 employment 

hours (equivalent to 1 person working 

full time for a quarter) in at least one 

quarter of 2019. Using this definition, 

MSHA estimates that a total of 12,631 

mines (11,525 MNM mines and 1,106 

coal mines) would generate sampling 

and evaluation records. 

Annual number of responses. The 

estimated average annual number of 

responses would be 142,408, including 

24,439 for baseline sampling, 9,237 for 

sampling after corrective actions, 64,116 

for periodic sampling, 42,103 for semiannual evaluation recording and 

posting, and 2,513 for post-evaluation 

sampling. 

MSHA assumes that all the active 

mines (12,631 mines) would conduct 

baseline sampling once in the first year. 

In succeeding years, about 253 new 

mines would conduct baseline sampling 

with an average of 5.6 samples per 

mine. The estimated number of periodic 

samplings is calculated based on the 

following factors: the number of miners 

with sampling results at or above the 

proposed action level (25 mg/m3) but at 

or below the PEL (50 mg/m3), the percent 

of miners needed for representative 

samples, and the number of quarters 

mines would be in operation. In year 1, 

MSHA expects the sampling to begin in 

the second half of the year, thereby 

decreasing the number of samples by 

half. As a result, MSHA estimates that 

an annual average of 64,116 periodic 

samples would be conducted in the first 

three years. Furthermore, MSHA 

assumes that all 12,631 mines would 

record semi-annual evaluation results 

twice a year—except in year 1, when it 

would be done once—and then post 

those results on a mine bulletin board, 

or if applicable, by electronic means. 

MSHA estimates mines would conduct 

sampling as a result of their semi-annual 

evaluations and an average of four 

miners would be sampled, resulting in 

an annual average of 2,513 samples. 

MSHA estimates that about 22 percent 

of active mines (2,771 mines in total) 

would have at least one miner 

overexposed to respirable crystalline 

silica. MSHA further estimates that the 

2,771 mines that would then conduct 

corrective action sampling for about 

four areas per mine. In year 1, they 

would sample in half as many areas. 

Estimated annual burden. The 

estimated average annual burden would 

be 31,392 hours, including 6,110 hours 

for baseline sampling, 2,309 for 

corrective action sampling, 16,029 hours 

for periodic sampling, 6,316 hours for 

semi-annual evaluation recording and 

posting, and 628 hours for postevaluation sampling. MSHA estimates 

that it would take 15 minutes to record 

the sampling results, 15 minutes to 

record the results of a semi-annual 

evaluation, and 3 minutes to post each 

of the evaluation results on the mine 

bulletin board, and, if applicable, by 

electronic means. 

Proposed § 60.13—Corrective Actions 

ICR. Proposed § 60.13 would require 

mine operators to make a record of 

corrective actions, as previously 

described. 

Number of respondents. For proposed 

§ 60.13, only those mines with at least 

one miner exposure above the proposed 

PEL are assumed to carry out the 

proposed requirement. MSHA estimates 

that about 22 percent of active mines 

(2,771 mines in total) would have at 

least one miner overexposed to 

respirable crystalline silica. 

Annual number of responses. The 

estimated average annual number of 

responses would be 14,922, including 

9,237 for corrective action records, and 

5,685 for miner respirator records. 

MSHA estimates that the 2,771 mines 

that will be required to conduct and 

record corrective actions will do so for 

about four mine areas, except in year 1, 

when it would be done in half as many 

mine areas. MSHA further estimates this 

will affect 6,822 miners per year— 

except in year 1, when half as many 

miners would be affected—with each 

miner requiring a record of the miner 

being given access to a respirator until 

the corrective action is taken. 

Estimated annual burden. The 

estimated average annual burden would 

be 1,054 hours, including 769.7 for 

corrective action records and 284.3 for 

miner respirator records. MSHA 

estimates that it takes five minutes to 

record a corrective action and the date. 

On average, it takes three minutes to 

note a miner’s access to a respirator. 

Proposed § 60.14—Respiratory 

Protection 

ICR. Proposed § 60.14 would require 

mine operators to retain a record of the 

determination by a PLHCP that a miner 

who may be required to use a respirator 

is unable to wear a respirator, as 

previously described. 

Number of respondents. For proposed 

§ 60.14, MSHA assumes that 33 percent 

of mine operators would have their 

miners use respiratory protection as a 

temporary measure and keep records of 

their miners’ ability to wear respirators. 

The number of respondents would be, 

on average, 603 mines per year, with 

each mine assumed to have at least 

some miners wearing respirators. 

Annual number of responses. The 

estimated annual number of responses 

would be 1,205, with an average of two 

miners for each of the 603 mines. 

Estimated annual burden. The 

estimated annual burden would be 603 

hours. MSHA assumes it takes 30 

minutes to record this information for 

about two miners for each of the 603 

mines. 

Proposed § 60.15—Medical Surveillance 

for Mental and Nonmetal Miners 

ICR. Proposed § 60.15 would require 

MNM mine operators to obtain a written 

medical opinion from a PLHCP or 

specialist regarding any recommended 

limitations on a miner’s use of 

respirators, as previously described. 

Number of respondents. MSHA 

assumes that 75 percent of eligible 

MNM miners (current MNM miners), 

including contract workers, would make 

use of the opportunity to receive a 

voluntary medical exam that is paid by 

their mine operator. As a result, an 

average of 25,175 current miners are 

estimated to receive voluntary medical 

exams per year. This estimate represents 

the upper range of the participation rate 

of voluntary medical exams by miners. 

MSHA is using the upper end of the 

range to avoid underestimating 

compliance costs. 

MSHA further estimates that 8,392 

miners in a given year, including 

contract workers, would be new miners 

and contractors who would undergo 

mandatory medical examinations. 


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MSHA estimated that the turnover of 

MNM miners would be 8,392 miners per 

year (1/22 of the estimated total of 

184,615 MNM workers with an average 

number of 22 years on the job before 

leaving the mining industry). The 

estimated total respondents per year 

therefore would be 33,567 (= 8,392 + 

25,175). 

Annual number of responses. The 

estimated annual number of responses 

would be 33,567, including 8,392 new 

miners and 25,175 current miners. 

Estimated annual burden. The 

estimated annual burden would be 

8,392 hours, including 2,098 hours for 

new MNM miners and 6,294 hours for 

current miners. MSHA estimates it takes 

15 minutes to record the medical 

examination results for each of the 

33,567 miners. 

Total Recordkeeping and 

Documentation Burden for Proposed 

Part 60 

As shown in Table XI–1, the total 

number of respondents is 46,198: 12,631 

mines plus 33,567 miners; the estimated 

annual number of responses would be 

192,102; and the estimated annual 

burden would be 41,440 hours. These 

estimates are based on the conservative 

assumption that 75 percent of eligible 

current miners would take part in 

medical surveillance, which could 

overestimate the recordkeeping cost and 

burden. The following estimates of 

information collection burden are 

summarized in Table XI–2. 

1. Affected Public: Businesses or ForProfit. 

2. Estimated Number of Respondents: 

47,456 respondents in the first year; 

46,198 respondents in the second year; 

and 44,939 respondents in the third 

year. 

3. Frequency: On Occasion. 

4. Estimated Number of Responses: 

192,990 responses in the first year; 

197,021 responses in the second year; 

and 186,294 responses in the third year. 

5. Estimated Number of Burden 

Hours: 44,678 hours in the first year; 

41,162 hours in the second year; and 

38,480 hours in the third year. 

6. Estimated Hour Burden Costs: 

$2,843,901 in the first year; $2,558,724 

in the second year; and $2,377,996 in 

the third year. 

7. Estimated Capital Costs to 

Respondents: $25,262 in each of the 

three years. 

Most of the reduction in the number 

of responses and burden hours from the 

first year to the second year is a result 

of baseline sampling being carried out 

in all current mines in the first year 


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while only being carried out in new 

mines starting from the second year. 

For a detailed summary of the burden 

hours and related costs by provision, see 

the Preliminary Regulatory Impact 

Analysis (PRIA) accompanying the 

proposed rule. The PRIA includes the 

estimated costs and assumptions for the 

paperwork requirements related to this 

proposed rule. 

C. Changes to Existing Information 

Collection Requirements 

I. Type of review: Non-substantive 

change to currently approved 

information collection. 

OMB Control Number: 1219–0011. 

1. Title: Respirable Coal Mine Dust 

Sampling. 

2. Description of the ICR: 

Background 

In October 2022, MSHA received 

OMB approval for the reauthorization of 

the Respirable Coal Mine Dust Sampling 

under OMB Control Number 1219–0011. 

This information collection request 

outlines the legal authority, procedures, 

burden, and costs associated with 

recordkeeping and reporting 

requirements for coal mine operators. 

MSHA’s standards require that coal 

mine operators sample respirable coal 

mine dust quarterly and make records of 

such samples. 

Summary of Changes 

This non-substantive change request 

is to revise the supporting statement for 

this information collection request due 

to the proposed PEL for respirable 

crystalline silica for all miners in this 

proposed rule. These proposed revisions 

would remove any reference in the 

information collection request to quartz 

or the reduction of the respirable dust 

standard due to the presence of quartz. 

This change does not modify the 

authority, affected mine operators, or 

paperwork burden. 

3. Summary of the Collection of 

Information: 

Changes in Burden 

The calculated burden including 

respondents and responses remain the 

same. 

Affected Public: Businesses or ForProfit. 

Estimated Number of Respondents: 

676 (0 from this rulemaking). 

Frequency: On occasion. 

Estimated Number of Responses: 

995,102 (0 from this rulemaking). 

Estimated Number of Burden Hours: 

58,259 (0 from this rulemaking). 

Estimated Hour Burden Costs: 

$3,271,611 ($0 from this rulemaking). 

Estimated Capital Costs to 

Respondents: $29,835 ($0 from this 

rulemaking). 

II. Type of Review: Discontinued 

information collection request. 

OMB Control Number: 1219–0048. 

1. Title: Respirator Program Records. 

2. Description of the ICR: 

Background 

Title 30 CFR parts 56 and 57 

incorporate by reference requirements of 

ANSI Z88.2–1969, ‘‘Practices for 

Respiratory Protection.’’ Under this 

standard, certain records are required to 

be kept in connection with respirators. 

The proposed rule would incorporate by 

reference ASTM F3387–19, ‘‘Standard 

Practice for Respiratory Protection,’’ in 

30 CFR parts 56 and 57 to replace the 

Agency’s existing respiratory protection 

standard. The proposal would require 

mine operators’ respiratory protection 

plans to include certain minimally 

acceptable program elements, but 

beyond that, would permit mine 

operators to select the requirements of 

ASTM F3387–19 that are applicable to 

their mines. 

Summary of Changes 

The proposed rule would remove the 

paperwork burden associated with 

respiratory protection in the information 

collection request. 

3. Summary of the Collection of 

Information: 

Changes in Burden 

MSHA has submitted a request to 

discontinue OMB Control Number 

1219–0048, eliminating all paperwork 

burden associated with the information 

collection request. It would discontinue 

upon the effective date of the final rule. 

Affected Public: Businesses or ForProfit. 

Estimated Number of Respondents: 0 

(¥350 from this rulemaking). 

Frequency: On occasion. 

Estimated Number of Responses: 0 

(¥630 from this rulemaking). 

Estimated Number of Burden Hours: 0 

(¥3,588 from this rulemaking). 

Estimated Hour Burden Costs: $0 

(¥$284,084 from this rulemaking). 

Estimated Capital Costs to 

Respondents: $0 (¥$140,000 from this 

rulemaking). 

D. Submitting Comments 

The information collection package 

for this proposal has been submitted to 

OMB for review under 44 U.S.C. 3506(c) 

of the Paperwork Reduction Act of 1995, 

as amended. Comments on the 

information collection requirements 

should be sent to MSHA by one of the 

methods previously explained in the 

DATES section of this preamble. 

The information collection request 

will be available on http://

www.regulations.gov. MSHA cautions 

the commenter against providing any 

information in the submission that 

should not be publicly disclosed. Full 

comments, including personal 

information provided, will be made 

available on www.regulations.gov and 

www.reginfo.gov. 

The public may also examine publicly 

available documents at the Mine Safety 

and Health Administration, 201 12th 

South, Suite 4E401, Arlington, VA 

22202–5450. Sign in at the receptionist’s 

desk on the 4th floor via the East 

elevator. Before visiting MSHA in 

person, call 202–693–9440 to make an 

appointment and determine if any 

special health precautions are required 

in keeping with the Department of 

Labor’s COVID–19 policy. 

Questions about the information 

collection requirements may be directed 

to the contact person listed in the FOR

FURTHER INFORMATION CONTACT section of 

this preamble. 

E. Docket and Inquiries 

Those wishing to download 

comments and other materials relating 

to paperwork determinations should use 

the procedures described in this 

preamble. One may also obtain a copy 

of this ICR by going to http://

www.reginfo.gov/public/do/PRAMain, 

clicking on ‘‘Currently under Review— 

Open for Public Comments’’ and 

scrolling down to ‘‘Department of 

Labor.’’ 

A Federal agency cannot conduct or 

sponsor a collection of information 

unless it is approved by OMB under the 

Paperwork Reduction Act and displays 

a currently valid OMB control number. 

The public is not required to respond to 

a collection of information unless the 

collection of information displays a 

currently valid OMB control number. 

XII. Other Regulatory Considerations 

A. National Environmental Policy Act 

The National Environmental Policy 

Act (NEPA) of 1969 (42 U.S.C. 4321 et 

seq.), requires each Federal agency to 

consider the environmental effects of 

final actions and to prepare an 

Environmental Impact Statement on 

major actions significantly affecting the 

quality of the environment. MSHA has 

reviewed the proposed standard in 

accordance with NEPA requirements, 

the regulations of the Council on 

Environmental Quality (40 CFR part 

1500), and the Department of Labor’s 

NEPA procedures (29 CFR part 11). As 

a result of this review, MSHA has 

determined that this proposed rule will 


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not have a significant environmental 

impact. Accordingly, MSHA has not 

conducted an environmental assessment 

nor provided an environmental impact 

statement. 

B. The Unfunded Mandates Reform Act 

of 1995 

MSHA has reviewed the proposed 

rule under the Unfunded Mandates 

Reform Act of 1995 (2 U.S.C. 1501 et 

seq.). The Unfunded Mandates Reform 

Act requires Federal agencies to assess 

the effects of their discretionary 

regulatory actions. In particular, the Act 

addresses actions that may result in the 

expenditure by State, local, and Tribal 

governments, in the aggregate, or by the 

private sector, of $100 million or more 

(adjusted annually for inflation) in any 

1 year (5 U.S.C. 1532(a)). MSHA has 

determined that this proposed rule does 

not result in such an expenditure. 

Accordingly, the Unfunded Mandates 

Reform Act requires no further Agency 

action or analysis. 

C. The Treasury and General 

Government Appropriations Act of 

1999: Assessment of Federal 

Regulations and Policies on Families 

Section 654 of the Treasury and 

General Government Appropriations 

Act of 1999 (5 U.S.C. 601 note) requires 

agencies to assess the impact of Agency 

action on family well-being. MSHA has 

determined that the proposed rule will 

have no effect on family stability or 

safety, marital commitment, parental 

rights and authority, or income or 

poverty of families and children, as 

defined in the Act. The proposed rule 

impacts the mine industry and does not 

impose requirements on states or 

families. Accordingly, MSHA certifies 

that this proposed rule will not impact 

family well-being, as defined in the Act. 

D. Executive Order 12630: Government 

Actions and Interference With 

Constitutionally Protected Property 

Rights 

Section 5 of E.O. 12630 requires 

Federal agencies to ‘‘identify the takings 

implications of proposed regulatory 

actions . . .’’ MSHA has determined 

that the proposed rule does not 

implement a taking of private property 

or otherwise have takings implications. 

Accordingly, E.O. 12630 requires no 

further Agency action or analysis. 

E. Executive Order 12988: Civil Justice 

Reform 

The proposed rule was written to 

provide a clear legal standard for 

affected conduct and was carefully 

reviewed to eliminate drafting errors 

and ambiguities so as to minimize 

litigation and avoid undue burden on 

the Federal court system. Accordingly, 

the proposed rule meets the applicable 

standards provided in section 3 of E.O. 

12988, Civil Justice Reform. 

F. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

E.O. 13045 requires Federal agencies 

submitting covered regulatory actions to 

OMB’s Office of Information and 

Regulatory Affairs (OIRA) for review, 

pursuant to E.O. 12866, to provide OIRA 

with (1) an evaluation of the 

environmental health or safety effects 

that the planned regulation may have on 

children, and (2) an explanation of why 

the planned regulation is preferable to 

other potentially effective and 

reasonably feasible alternatives 

considered by the agency. In E.O. 13045, 

‘‘covered regulatory action’’ is defined 

as rules that may (1) be significant 

under Executive Order 12866 Section 

3(f)(1) (i.e., a rulemaking that has an 

annual effect on the economy of $200 

million or more or would adversely 

affect in a material way the economy, a 

sector of the economy, productivity, 

competition, jobs, the environment, 

public health or safety, or State, local or 

Tribal governments or communities), 

and (2) concern an environmental 

health risk or safety risk that an agency 

has reason to believe may 

disproportionately affect children. 

Environmental health risks and safety 

risks refer to risks to health or to safety 

that are attributable to products or 

substances that the child is likely to 

come in to contact with or ingest 

through air, food, water, soil, or product 

use or exposure. 

MSHA has determined that, in 

accordance with E.O. 13045, while the 

proposed rule is considered significant 

under E.O. 12866 Section 3(f)(1), it does 

not concern an environmental health or 

safety risk that may have a 

disproportionate impact on children. 

MSHA’s proposed rule would lower the 

occupational exposure limit to 

respirable crystalline silica for all 

miners, take other actions to protect 

miners from adverse health risks 

associated with exposure to respirable 

crystalline silica, and require updated 

respiratory standards to better protect 

miners from all airborne hazards. 

MSHA is aware of studies which have 

characterized and assessed the risks 

posed by ‘‘take-home’’ exposure 

pathways for hazardous dust particles. 

However, the proposed rule’s primary 

reliance on engineering and 

administrative controls to protect 

miners from respirable crystalline silica 

exposures helps minimize risks 

associated with ‘‘take-home’’ exposures 

by reducing or eliminating silica that is 

in the mine atmosphere or the miner’s 

personal breathing zone. The risks of 

take-home exposures are further 

minimized by MSHA’s existing 

standards, operators’ policies and 

procedures, and operators’ use of 

clothing cleaning systems. 

MSHA’s existing standards limit 

miners’ exposures to respirable 

crystalline silica. MSHA also requires 

coal mine operators to provide miners 

bathing facilities and change rooms. 

Miners have access to these facilities to 

shower and change their work clothes at 

the end of each shift. In addition, some 

mine operators provide miners with 

clean company clothing for each shift, 

have policies and procedures for 

cleaning or disposing of contaminated 

clothing, and provide a boot wash for 

miners to clean work boots during and 

after each shift. Moreover, some 

operators use clothing cleaning systems 

that can remove dust from a miner’s 

clothing. Many of these systems include 

NIOSH-designed dust removal booths 

that use compressed air to remove dust, 

which is then vacuumed through a filter 

to remove airborne contaminants. 

Overall, the Agency’s standards, mine 

operators’ policies and procedures, and 

other safety practices including the use 

of clothing cleaning systems help to 

reduce or eliminate the amount of takehome exposure, therefore protecting 

other persons in a miner’s household or 

persons who come in to contact with the 

miner outside of the mine site. 

MSHA identified one epidemiological 

study (Onyije et al., 2022) that suggests 

a possible association between paternal 

exposure to respirable crystalline silica 

and childhood leukemia. However, this 

study does not provide dose-response 

data which would be needed to 

establish the dose of respirable 

crystalline silica which results in a noadverse-effect-level (NOAEL) for 

childhood leukemia. This potential 

association has not been independently 

confirmed by another study. MSHA 

invites comment on the identification of 

any other scientific or academic study 

or information that evaluates the 

potential association between paternal 

exposure to respirable crystalline silica 

and childhood leukemia during the 

NPRM’s public comment period. 

MSHA also invites comment on the 

identification of any scientific or 

academic study or information that 

evaluates the potential risks to female 

workers who are exposed to respirable 

crystalline silica during pregnancy. 

MSHA has no evidence that the 

environmental health or safety risks 

posed by respirable crystalline silica, 


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71National data on workers by race were not 

available for the year 2008; comparable data for 

2012 are provided for comparison under the 

assumption that there would not be major 

differences in distributions between these two 

years. 

72Although 2 percent may appear to be a small 

number for identifying a mining community, one 

might consider that if the average household with 

one parent working as a miner has five members in 

total, then approximately 10 percent of households 

in the area would be directly associated with 

mining. While 10 percent may also appear small, 

this refers to the county. There are likely particular 

areas that have a heavier concentration of mining 

households. 

73This is a simple average rather than a weighted 

average by population. 

including ‘‘take-home’’ exposure to 

respirable crystalline silica, 

disproportionately affect children. 

Therefore, MSHA preliminarily 

concludes no further analysis or action 

is needed, in accordance with E.O. 

13045. 

G. Executive Order 13132: Federalism 

MSHA has determined that the 

proposed rule does not have ‘‘federalism 

implications’’ because it will not ‘‘have 

substantial direct effects on the States, 

on the relationship between the national 

government and the States, or on the 

distribution of power and 

responsibilities among the various 

levels of government.’’ Accordingly, 

under E.O. 13132, no further Agency 

action or analysis is required. 

H. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

MSHA has determined the proposed 

rule does not have ‘‘tribal implications’’ 

because it will not ‘‘have substantial 

direct effects on one or more Indian 

tribes, on the relationship between the 

Federal Government and Indian tribes, 

or on the distribution of power and 

responsibilities between the Federal 

Government and Indian tribes.’’ 

Accordingly, under E.O. 13175, no 

further Agency action or analysis is 

required. 

I. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use 

E.O. 13211 requires agencies to 

publish a Statement of Energy Effects for 

‘‘significant energy actions,’’ which are 

agency actions that are ‘‘likely to have 

a significant adverse effect on the 

supply, distribution, or use of energy’’ 

including a ‘‘shortfall in supply, price 

increases, and increased use of foreign 

supplies.’’ MSHA has reviewed the 

proposal for its impact on the supply, 

distribution, and use of energy because 

it applies to the mining industry. The 

proposed rule would result in 

annualized compliance costs of $4.85 

million using a 3 percent real discount 

rate and $4.97 million using a 7 percent 

real discount rate for the coal mine 

industry relative to annual revenue of 

$27.03 billion. The proposal would also 

result in annualized compliance costs of 

$54.23 million using a 3 percent real 

discount rate and $55.72 million using 

a 7 percent real discount rate for the 

metal/nonmetal mine industry relative 

to annual revenue of $88.32 billion. 

Because it is not ‘‘likely to have a 

significant adverse effect on the supply, 

distribution, or use of energy’’ including 

a ‘‘shortfall in supply, price increases, 

and increased use of foreign supplies,’’ 

it is not a ‘‘significant energy action.’’ 

Accordingly, E.O. 13211 requires no 

further agency action or analysis. 

J. Executive Order 13272: Proper 

Consideration of Small Entities in 

Agency Rulemaking 

MSHA has thoroughly reviewed the 

proposed rule to assess and take 

appropriate account of its potential 

impact on small businesses, small 

governmental jurisdictions, and small 

organizations. MSHA’s analysis is 

presented in Section X. Initial 

Regulatory Flexibility Analysis. 

K. Executive Order 13985: Advancing 

Racial Equity and Support for 

Underserved Communities Through the 

Federal Government 

E.O. 13985 provides ‘‘that the Federal 

Government should pursue a 

comprehensive approach to advancing 

equity for all, including people of color 

and others who have been historically 

underserved, marginalized, and 

adversely affected by persistent poverty 

and inequality.’’ E.O. 13985 defines 

‘‘equity’’ as ‘‘consistent and systematic 

fair, just, and impartial treatment of all 

individuals, including individuals who 

belong to underserved communities that 

have been denied such treatment, such 

as Black, Latino, and Indigenous and 

Native American persons, Asian 

Americans and Pacific Islanders and 

other persons of color; members of 

religious minorities; lesbian, gay, 

bisexual, transgender, and queer 

(LGBTQ+) persons; persons with 

disabilities; persons who live in rural 

areas; and persons otherwise adversely 

affected by persistent poverty or 

inequality.’’ To assess the impact of the 

proposed rule on equity, MSHA 

considered two factors: (1) the racial/ 

ethnic distribution in mining in NAICS 

212 (which does not include oil and gas 

extraction) compared to the racial/ 

ethnic distribution of the U.S. workforce 

(Table XII–1), and (2) the extent to 

which mining may be concentrated 

within general mining communities 

(Table XII–2). 

In 2008, NIOSH conducted a survey of 

mines, which entailed sending a survey 

packet to 2,321 mining operations to 

collect a wide range of information, 

including demographic information on 

miners. NIOSH’s 2012 report, entitled 

‘‘National Survey of the Mining 

Population: Part I: Employees’’ reported 

the findings of this survey (NIOSH 

2012a). Race and ethnicity information 

about U.S. mine workers is presented in 

Table XII–1. Of all mine workers, 

including miners as well as 

administrative employees at mines, 93.4 

percent of mine workers were white, 

compared to 80.6 percent of all U.S 

workers.71 There were larger 

percentages of American Indian or 

Alaska Native and Native Hawaiian or 

Other Pacific Islander people in the 

mining industry compared to all U.S. 

workers, while there were smaller 

percentages of Asian, Black or African 

American, and Hispanic/Latino people 

in the mining industry compared to all 

U.S. workers. 

Table XII–2 shows that there are 22 

mining communities, defined as 

counties where at least 2 percent of the 

population is working in the mining 

industry.72 Although the total 

population in this table represents only 

0.15 percent of the U.S. population, it 

represents 12.0 percent of all mine 

workers. The average per capita income 

in these communities in 2020, 

$47,977,73 was lower than the U.S. 

average, $59,510, representing 80.6 

percent of the U.S. average. However, 

each county’s average per capita income 

varies substantially, ranging from 56.4 

percent of the U.S. average to 146.8 

percent. 

The proposed rule would lower 

exposure to respirable crystalline silica 

and improve respiratory protection for 

all mine workers. MSHA determined 

that the proposed rule is consistent with 

the goals of E.O. 13985 and would 

support the advancement of equity for 

all workers at mines, including those 

who are historically underserved and 

marginalized. 

BILLING CODE 4520–43–P 


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74The read-only version of ASTM F3387–19 

available for public review during the comment 

period can be accessed using the following link— 

https://tinyurl.com/mwk97hjn. 

BILLING CODE 4520–43–C 

L. Availability of Materials To Be 

Incorporated by Reference 

The Office of the Federal Register 

(OFR) has regulations concerning 

incorporation by reference. 5 U.S.C. 

552(a); 1 CFR part 51. These regulations 

require that information that is 

incorporated by reference in a rule be 

‘‘reasonably available’’ to the public. 

They also require discussion in the 

preamble to the rule of the ways in 

which materials it proposes to 

incorporate by reference are reasonably 

available to interested parties or how it 

worked to make those materials 

reasonably available to interested 

parties. Additionally, the preamble to 

the rule must summarize the material. 1 

CFR 51.5(b). 

In accordance with the OFR’s 

requirements, MSHA provides in the 

following: (a) summaries of the 

materials to be incorporated by 

reference and (b) information on the 

public availability of the materials and 

on how interested parties can access the 

materials during the comment period 

and upon finalization of the rule. 

ASTM F3387–19, ‘‘Standard Practice 

for Respiratory Protection’’ (ASTM 

F3387–19) ASTM F3387–19 is a 

voluntary consensus standard that 

represents up-to-date advancements in 

respiratory protection technologies, 

practices, and techniques. The standard 

includes provisions for selection, fitting, 

use, and care of respirators designed to 

remove airborne contaminants from the 

air using filters, cartridges, or canisters, 

as well as respirators that protect miners 

in oxygen-deficient or immediately 

dangerous to life or health atmospheres. 

These provisions are based on NIOSH’s 

long-standing experience of testing and 

approving respirators for occupational 

use and OSHA’s research and 

rulemaking on respiratory protection. 

The proposed rule would incorporate by 

reference ASTM F3387–19 in existing 

§§ 56.5005, 57.5005, and 72.710 and in 

proposed § 60.14(c)(2) to better protect 

all miners from airborne hazards. MSHA 

believes that incorporating by reference 

ASTM F3387–19 would provide mine 

operators with up-to-date requirements 

for respirator technology, reflecting an 

improved understanding of effective 

respiratory protection and therefore 

better protecting the health and safety of 

miners. For further details on MSHA’s 

proposed update to the Agency’s 

existing respiratory protection standard, 

please see section VII.C of this 

preamble, Updating MSHA Respiratory 

Protection Standards by Incorporating 

by Reference ASTM F3387–19. 

A paper copy or printable version of 

ASTM F3387–19 may be purchased by 

mine operators or any member of the 

public at any time from ASTM 

International, 100 Barr Harbor Drive, PO 

Box C700, West Conshohocken, PA 

19428–2959; https://www.astm.org/. 

ASTM International makes read-only 

versions of its standards that have been 

referenced or incorporated into Federal 

regulation or laws available free of 

charge at its online Reading Room, 

https://www.astm.org/products-services/ 

reading-room.html. During the comment 

period, a read-only version of ASTM 

F3387–19 will be made available free of 

charge.74

In addition, during the comment 

period and upon finalization of this 

rule, ASTM F3387–19 will be available 

for review free of charge at MSHA 

headquarters at 201 12th Street South, 

Arlington, VA 22202–5450 (202–693– 

9440). 

ISO 7708:1995: Air Quality—Particle 

Size Fraction Definitions for HealthRelated Sampling. 

ISO 7708:1995 is an international 

consensus standard that defines 

sampling conventions for particle size 

fractions used in assessing possible 

health effects of airborne particles in the 

workplace and ambient environment. It 

defines conventions for the inhalable, 

thoracic, and respirable fractions. The 

proposed rule would incorporate by 

reference ISO 7708:1995 in proposed 

§ 60.12(f)(4) to ensure consistent 

sampling collection by mine operators 

through the utilization of samplers 

conforming to ISO 7708:1995. 

A paper copy or printable version of 

ISO 7708:1995 may be purchased by 

mine operators or any member of the 

public at any time from ISO, CP 56, CH– 

1211 Geneva 20, Switzerland; phone: + 

41 22 749 01 11; fax: + 41 22 733 34 30; 

website: www.iso.org/. ISO makes readonly versions of its standards that have 

been incorporated by reference in the 

CFR available free of charge at its online 

Incorporation by Reference Portal, 

http://ibr.ansi.org/Default.aspx. 

In addition, during the comment 

period and upon finalization of this 

rule, ISO 7708:1995 will be available for 

review free of charge at MSHA 

headquarters at 201 12th Street South, 

Arlington, VA 22202–5450, (202–693– 

9440). 

TLV’s Threshold Limit Values for 

Chemical Substances in Workroom Air 

Adopted by ACGIH for 1973. 

This material is referenced in the 

amendatory text of this document but 

has already been approved for appendix 

A. No changes are proposed. 

XIII. References Cited in the Preamble 

Abraham, J.L. and Wiesenfeld, S.L. 1997. 

Two cases of fatal PMF in an ongoing 

epidemic of accelerated silicosis in 

oilfield sandblasters: Lung pathology and 

mineralogy. Annals of Occupational. 

Hygiene, Vol. 41, Supplement 1, pp. 

440–447, 1997. 

Agency for Toxic Substances and Disease 

Registry (ATSDR). 2019. Toxicological 

profile for silica. U.S. Department of 

Health and Human Services, Centers for 

Disease Control and Prevention, Division 

of Toxicology and Human Health 

Sciences, Atlanta, GA. 

Almberg, K.S., Friedman, L.S., Rose, C.S., Go, 

L.H.T., Cohen, R.A. 2020. Progression of 

coal workers’ pneumoconiosis absent 

further exposure. Occupational and 

Environmental Medicine. 77:748–751. 

Almberg, K.S., Halldin, C.N., Blackley, D.J., 

Laney, A.S., Storey, E., Rose, C.S., Go, 

L.H.T. and Cohen, R.A. 2018a. 

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black lung benefits, 1970–2016. Annals 

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Industrial Hygienists (ACGIH). 2010: 

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cristobalite. Documentation of TLV 

Recommendation. Cincinnati, Ohio. 

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substances in workroom air adopted by 

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American Society of Testing and Materials 

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D., Romieu, I., Silverman, E.K., and 

Balmes, J.R. American Journal of 

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Le Bert, M., Lambers, C., Geleff, S., Roth, 

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Calvert, G., Rice, F. L., Boiano, J. M., Sheehy, 

J. W., Sanderson, W. T.. 2003. 

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various diseases: an analysis using death 

certificates from 27 states of the United 

States. Occupational and Environmental 

Medicine. 60:122–129. 

Calvert, G.M., Steenland, K., and Palu, S. 

1997. End-stage renal disease among 

silica-exposed gold miners: A new 

method for assessing incidence among 

epidemiologic cohorts. Journal of the 

American Medical Association. 

277:1219–1223. 

Carneiro, A.P., Barreto, S.M., Siqueira, A.L., 

Cavariani, F., and Forastiere, F. 2006a. 

Continued exposure to silica after 

diagnosis of silicosis in Brazilian gold 

miners. American Journal of Industrial 

Medicine. 49:811–818. 

Carta, P., Aru, G., and Manca, P. 2001. 

Mortality from lung cancer among 

silicotic patients in Sardinia: An update 

study with 10 more years of follow up. 

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Medicine. 58:786–793. 

Cassidy, A., Mannetje, A., Van Tongeren, M., 

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75Only valid (non-void) MNM respirable dust 

samples were included in the LIMS dataset. Voided 

samples include any samples with a documented 

reason which occurred during the sampling and/or 

the MSHA’s laboratory analysis for invalidating the 

results. 

76For example, contaminant code 523 indicates 

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XIV. Appendix 

Appendix A 

Description of MSHA Respirable Crystalline 

Silica Samples 

This document describes the respirable 

crystalline silica samples used in this 

rulemaking. The Mine Safety and Health 

Administration (MSHA) collected these 

samples from metal/nonmetal (MNM) and 

coal mines and analyzed the data to support 

this rulemaking. Technical details are 

discussed in the following attachments. 

MNM Respirable Dust Sample Dataset, 

2005–2019 

From January 1, 2005, to December 31, 

2019, 104,354 valid MNM respirable dust 

samples were entered into the MSHA 

Technical Support Laboratory Information 

Management System (LIMS) database.75 The 

dataset includes MNM mine respirable dust 

personal exposure samples collected by 

MSHA inspectors. A total of 57,824 samples 

contained a respirable dust mass of 0.100 mg 

or greater (referred as ‘‘sufficient-mass dust 

samples’’), while a total of 46,530 samples 

contained a respirable dust mass of less than 

0.100 mg (referred as ‘‘insufficient-mass dust 

samples’’). 

Respirable dust samples collected by 

MSHA inspectors are assigned a three-digit 

‘‘contaminant code’’ based on the 

contaminant in the sample. MSHA’s 

contaminant codes group contaminants based 

on their health effects 76 and are assigned by 

the MSHA Laboratory based on sample type 

and analysis results. The codes link 

information, such as contaminant 

description, permissible exposure limit 

(PEL), and the units of measure for each 

contaminant sampled. 

The MNM respirable crystalline silica 

dataset includes five contaminant codes. 

MNM Respirable Dust Sample Contaminant 

Codes 

• Contaminant code 521—MNM respirable 

dust samples that were not analyzed for 

respirable crystalline silica. 

• Contaminant code 523—MNM respirable 

dust samples containing 1 percent or more 

quartz. 

• Contaminant code 525—MNM respirable 

dust samples containing cristobalite. 

• Contaminant code 121—MNM respirable 

dust samples containing less than 1 percent 

quartz where the commodity is listed as a 

‘‘nuisance particulate’’ in Appendix E of the 

TLVs® Threshold Limit Values for Chemical 

Substances in Workroom Air Adopted by 

ACGIH for 1973 (reproduced in Table A–1). 

• Contaminant code 131—MNM respirable 

dust samples containing less than 1 percent 

quartz where the commodity is not listed as 

a ‘‘nuisance particulate’’ in Appendix E of 

the 1973 ACGIH TLV® Handbook. 

BILLING CODE 4520–43–P 

MNM Respirable Dust Samples With a Mass 

of at Least 0.100 milligram (mg) (SufficientMass Dust Samples) 

The 57,824 samples that contained at least 

0.100 mg of respirable dust were analyzed to 

quantify their respirable crystalline silica 

content—mostly respirable quartz but also 

respirable cristobalite. The respirable 

crystalline silica concentrations were entered 

into the MSHA Standardized Information 

System (MSIS) database (internal facing) and 

Mine Data Retrieval System (MDRS) database 

(public facing). Those MNM respirable dust 

samples with a mass of at least 0.100 mg are 

analyzed and contained in MSIS. MSIS and 

MDRS differ from LIMS in that some of the 

fields associated with a sample can be 

modified or corrected by the inspector. These 

correctable fields include Mine ID, Location 

Code, and Job Code. Inspectors cannot access 

or modify the fields in the LIMS database. 


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77There were 55 samples removed: 7 samples had 

no detected mass gain (denoted as ‘‘0 mg’’); 

1 sample was a partial shift that was not originally 

marked correctly; 1 sample was removed at the 

request of the district; 44 samples had flow rates 

outside the acceptable range of 1.616–1.785 L/min; 

and 2 samples were duplicates of samples that were 

already in the dataset. This resulted in the final 

sample size of 57,769 = 57,824¥(7 + 1 + 1 + 44 

+ 2). 

78There were 167 samples removed: 75 samples 

had a cassette mass less than ¥0.03 mg (based on 

instrument tolerances, samples that report a cassette 

mass between ¥0.03 mg and 0 mg were treated as 

having a mass of 0 mg, samples with masses below 

that threshold of ¥0.03 mg were excluded); 52 

samples had Mine IDs that did not report 

employment for any year from 2005–2019; 31 

samples had flow rates outside the acceptable range 

of 1.615–1.785 L/min; six samples had sampling 

times of less than 30 minutes; and three samples 

had invalid Job Codes. This resulted in the final 

sample size of 46,363 = 46,530¥(75 + 52 + 31 + 

6 + 3). 

79Only valid (non-void) coal respirable dust 

samples were included in the LIMS dataset. Voided 

samples include any samples with a documented 

reason which occurred during the sampling and/or 

the MSHA’s Laboratory analysis for invalidating the 

results. 

From the database, 55 samples 77 were 

removed because they were erroneous, had 

an incorrect flow rate, had insufficient 

sampling time, or were duplicated. This 

resulted in a final dataset of 57,769 MNM 

samples that contained a mass of at least 

0.100 mg of respirable dust. Datasets 

containing the analyzed samples that MSHA 

removed and retained can be found in the 

rulemaking docket MSHA–2023–0001. 

MNM Respirable Dust Samples With a Mass 

of Less Than 0.100 mg (Insufficient-Mass 

Samples) 

The LIMS database also included 46,530 

MNM respirable dust samples that contained 

less than 0.100 mg of respirable dust. These 

samples did not meet the minimum dust 

mass criterion of 0.100 mg and were not 

analyzed for respirable crystalline silica by 

MSHA’s Laboratory. 

From these 46,530 samples, 167 samples 78

were removed because they were erroneous, 

had an incorrect flow rate, or had insufficient 

sampling time. This resulted in 46,363 

remaining MNM samples containing less 

than 0.100 mg of respirable dust. These 

samples were assigned to contaminant code 

521, indicating that the samples were not 

analyzed for quartz. Datasets containing the 

unanalyzed samples that MSHA removed 

and retained can be found in the rulemaking 

docket MSHA–2023–0001. 

All MNM Respirable Dust Samples 

After removing the 222 samples mentioned 

above (55 sufficient-mass and 167 

insufficient-mass), the dataset consisted of 

104,132 MNM respirable dust samples: 

57,769 sufficient-mass samples and 46,363 

insufficient-mass samples. A breakdown of 

the MNM respirable dust samples is included 

in Table A–2. 

BILLING CODE 4520–43–C 

Coal Respirable Dust Sample Dataset, 2016– 

2021 

From August 1, 2016, to July 31, 2021, 

113,607 valid respirable dust samples from 

coal mines were collected by MSHA 

inspectors and entered in the LIMS 

database.79 For coal mines, the analysis is 

based on samples collected by inspectors 

beginning on August 1, 2016, when Phase III 

of MSHA’s 2014 respirable coal mine dust 

(RCMD) standard went into effect. Samples 

taken prior to implementation of the RCMD 

standard would not be representative of 

current respirable crystalline silica exposure 

levels in coal mines. 

Of these samples collected by MSHA 

inspectors, 67,963 samples were analyzed for 

respirable crystalline silica; 45,644 samples 


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80As mentioned in the section concerning 

samples for MNM mines, MSIS and MDRS differ 

from LIMS in that some data fields can be modified 

or corrected by the inspector. These correctable 

fields include Mine ID, Location Code, and Job 

Code. 

81There were 4,836 samples removed: 4,199 

samples were environmental and not personal 

samples (see Sample Type explanation for more 

detail); 631 samples had been voided after they had 

been entered into MSIS; and 6 had invalid Job 

Codes. This resulted in the final sample size of 

63,127 = 67,963¥(4,199 + 631 + 6). 

82 In addition to the criteria listed above, samples 

from Shop Welders (code 319) are not analyzed for 

respirable crystalline silica as they are instead 

analyzed for welding fumes. 

83There were 13,243 samples removed: 6 samples 

had typographical errors; 14 samples had a cassette 

mass less than ¥0.03 mg (based on instrument 

tolerances, samples that report a cassette mass 

between ¥0.03 mg and 0 mg were treated as having 

a mass of 0 mg); 92 samples had invalid Job Codes; 

12,724 were environmental samples; 44 samples 

had an occupation code of 000 despite having a 

personal sample ‘Sample Type’; 271 samples had 

controls that were voided; and 92 came from Job 

Code 319—Welder (see Footnote 82). This resulted 

in the final sample size of 32,401 = 50,545¥(6 + 

14 + 92 + 12,724 + 44 + 271 + 92). 

84This dataset did not include any other coal 

mine respirable dust sample types collected by 

MSHA inspectors—i.e., sample types 3 (designated 

area samples), types 6 (Non-face occupations) and 

7 (Intake air), samples taken on the surface mine 

shop welder (n=319), and all voided samples. 

Voided samples are any samples that have a 

documented reason which occurred during the 

sampling and/or laboratory analysis for invalidating 

the results. 

were not. Respirable dust samples from coal 

mines contain the records of the sample type, 

and the occupation of the miner sampled. A 

coal sample’s type is based on the location 

within the mine as well as the occupation of 

the miner sampled. Below is a list of coal 

sample types and descriptions, as well as the 

mass of respirable dust required for that type 

of sample to be analyzed for respirable 

crystalline silica. 

• Type 1—Designated occupation (DO). 

The occupation on a mechanized mining unit 

(MMU) that has been determined by results 

of respirable dust samples to have the 

greatest respirable dust concentration. 

Designated occupation samples must contain 

at least 0.100 mg of respirable dust to be 

analyzed for respirable crystalline silica. 

• Type 2—Other designated occupation 

(ODO). Occupations other than the DO on an 

MMU that are also designated for sampling, 

required by 30 CFR part 70. These samples 

must contain at least 0.100 mg of respirable 

dust to be analyzed for respirable crystalline 

silica. 

• Type 3—Designated area (DA). 

Designated area samples are from specific 

locations in the mine identified by the 

operator in the mine ventilation plan under 

30 CFR 75.371(t), where samples will be 

collected to measure respirable dust 

generation sources in the active workings. 

These samples must contain at least 0.100 mg 

of respirable dust to be analyzed for 

respirable crystalline silica. 

• Type 4—Designated work position 

(DWP). A designated work position in a 

surface coal mine or surface work area of an 

underground coal mine designated for 

sampling to measure respirable dust 

generation sources in the active workings. 

Designated work position samples must 

contain at least 0.200 mg of respirable dust 

to be analyzed for respirable crystalline 

silica. There are exceptions for certain 

occupations: bulldozer operator (MSIS 

general occupation code 368), high wall drill 

operator (code 384), high wall drill helper 

(code 383), blaster/shotfirer (code 307), 

refuse/backfill truck driver (code 386), or 

high lift operator/front end loader (code 382). 

Samples from these occupations must have at 

least 0.100 mg of respirable dust to be 

analyzed for respirable crystalline silica. 

• Type 5—Part 90 miner. A Part 90 miner 

is employed at a coal mine and has exercised 

the option under the old section 203(b) 

program (36 FR 20601, Oct. 27, 1971) or 

under 30 CFR 90.3 to work in an area of a 

mine where the average concentration of 

respirable dust in the mine atmosphere 

during each shift to which a miner is exposed 

is continuously maintained at or below the 

applicable standard and has not waived these 

rights. A sample from a Part 90 miner must 

contain at least 0.100 mg of respirable dust 

to be analyzed for respirable crystalline 

silica. 

• Type 6—Non-designated area (NDA). 

Non-designated area samples are taken from 

locations in the mine that are not identified 

by the operator in the mine ventilation plan 

under 30 CFR 75.371(t) as areas where 

samples will be collected to measure 

respirable dust generation sources in the 

active workings. These samples are not 

analyzed for respirable crystalline silica. 

• Type 7—Intake air samples are taken 

from air that has not yet ventilated the last 

working place on any split of any working 

section or any worked-out area, whether 

pillared or non-pillared, as per 30 CFR 

75.301. These samples are not analyzed for 

respirable crystalline silica. 

• Type 8—Non-designated work position 

(NDWP). A work position in a surface coal 

mine or a surface work area of an 

underground coal mine that is sampled 

during a regular health inspection to measure 

respirable dust generation sources in the 

active workings but has not been designated 

for mandatory sampling. For the analysis of 

respirable crystalline silica, these samples 

must have at least 0.200 mg of respirable 

dust. There are exceptions for certain 

occupations: bulldozer operator (MSIS 

general occupation code 368), high wall drill 

operator (code 384), high wall drill helper 

(code 383), blaster/shotfirer (code 307), 

refuse/backfill truck driver (code 386), or 

high lift operator/front end loader (code 382). 

Samples taken from these occupations must 

contain at least 0.100 mg respirable dust to 

be analyzed for respirable crystalline silica. 

Coal Respirable Dust Samples Analyzed for 

Respirable Crystalline Silica 

There were 67,963 samples from coal 

mines collected by MSHA inspectors from 

underground and surface coal mining 

operations that were analyzed for respirable 

crystalline silica. These results were entered 

first into LIMS, and then into MSIS and 

MDRS. Results from MSIS were used as they 

may be updated by the inspectors at later 

dates.80 From those 67,963 samples, 4,836 

samples were removed as they were 

environmental samples, voided in MSIS, or 

had other errors.81 This resulted in a dataset 

of 63,127 samples from coal mines that were 

analyzed for respirable crystalline silica. 

Datasets containing the analyzed samples 

that MSHA removed and retained can be 

found in the rulemaking docket MSHA– 

2023–0001. 

Coal Respirable Dust Samples Not Analyzed 

for Respirable Crystalline Silica 

Similar to MNM respirable dust samples, 

the LIMS database includes 45,644 coal 

samples that did not meet the criteria for 

analysis and were thus not analyzed for 

respirable crystalline silica content.82 After 

removing 13,243 83 samples that were 

environmental samples, erroneous, or had 

voided controls, there were 32,401 samples 

that were not analyzed for respirable 

crystalline silica. Datasets containing the 

unanalyzed samples that MSHA removed 

and retained can be found in the rulemaking 

docket MSHA–2023–0001. 

All Coal Respirable Dust Samples 

In total, 18,079 respirable dust samples 

from coal mines were removed from the 

original datasets: 4,836 samples that were 

analyzed for respirable crystalline silica and 

13,243 samples that were not. This created a 

final dataset of 95,528 samples: 63,127 

analyzed samples and 32,401 samples that 

were not analyzed.84 A breakdown of 

respirable dust samples from coal mines is 

included in Table A–3. 

BILLING CODE 4520–43–P 


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85See Attachment 2. Technical Background about 

Measuring Respirable Crystalline Silica, for more 

information. 

86See Attachment 2. Technical Background about 

Measuring Respirable Crystalline Silica, for more 

information. 

Attachment 1. MNM Samples Analyzed for 

Cristobalite 

Cristobalite is one of the three polymorphs 

of respirable crystalline silica analyzed by 

MSHA’s Laboratory upon request that is 

included in this proposed rule. At the request 

of the inspector, MNM 85 respirable dust 

samples that contain at least 0.050 mg of 

respirable dust are analyzed for cristobalite. 

Of the 57,769 retained MNM samples that 

contained at least 0.050 mg of respirable 

dust, 0.6 percent (or 359 samples) were 

analyzed for cristobalite. Coal respirable dust 

samples are not analyzed for cristobalite.86

While the samples that were analyzed for 

cristobalite were assigned to all four 

contaminant codes seen in this dataset, the 

majority were assigned contaminant code 

523. 


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87Of the 369 samples that were analyzed for 

cristobalite, 334 had a value for cristobalite mass 

that was less than the limit of detection (LOD) for 

cristobalite, 10 mg. As such these samples were 

assigned a value of 5 mg of cristobalite, one half the 

LOD. See Attachment 2. Technical Background 

about Measuring Respirable Crystalline Silica, for 

more information. 

88One sample had a cristobalite concentration of 

53 mg/m3. It was sampled in July of 2011 at Mine 

ID 4405407 and cassette number 610892. The 

commodity being mined was Stone: Crushed, 

Broken Quartzite. The occupation of the miner 

being sampled was Miners in Other Occupations: 

Job Code 513—Building and Maintenance. 

The distribution of the 359 samples by 

cristobalite mass can be seen in Table A1– 

3.87

The mass of each sample was then used to 

calculate a cristobalite concentration by 

dividing the mass of cristobalite by the 

volume of air sampled (0.816 m3). The 

calculated concentrations ranged from 6 mg/ 

m3 to 53 mg/m3.88


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BILLING CODE 4520–43–C 

Attachment 2. Technical Background About 

Measuring Respirable Crystalline Silica 

In the proposed rule, respirable crystalline 

silica refers to three polymorphs: quartz, 

cristobalite, and tridymite. MSHA’s 

Laboratory uses two methods to analyze 

respirable crystalline silica content in mine 

respirable dust samples. The first method, Xray diffraction (XRD), separately analyzes 

quartz, cristobalite, and tridymite contents in 

respirable dust samples that mine inspectors 

obtain at MNM mine sites (MSHA Method P– 

2, 2018a). The second method, Fourier 

transform infrared spectroscopy (FTIR), is 

used to analyze quartz in respirable dust 

samples obtained at coal mines (MSHA 

Method P–7, 2018b and 2020). Although the 

XRD method can be expanded from MNM to 

coal dust samples, MSHA chooses to use the 

FTIR method for coal dust samples because 

it is a faster and less expensive method. 

However, the current MSHA P–7 FTIR 

method cannot quantify quartz if cristobalite 

and/or tridymite are present in the sample. 

The method also corrects the quartz result for 

the presence of kaolinite, an interfering 

mineral for quartz analysis in coal dust. 

Limits of Detection and Limits of 

Quantification for Silica Sample Data 

The Limits of Detection (LOD) and Limits 

of Quantification (LOQ) are the two terms 

used to describe the method capability. The 

LOD refers to the smallest amount of the 

target analyte (respirable crystalline silica) 

that can be detected in the sample and 

distinguished from zero with an acceptable 

confidence level that the analyte is actually 

present. It can also be described as the 

instrument signal that is needed to report 

with a specified confidence that the analyte 

is present. The LOQ refers to the smallest 

amount of the target analyte that can be 

repeatedly and accurately quantified in the 

sample with a specified precision. The LOQ 

is higher than the LOD. The values of the 

LOD and LOQ are specific to MSHA’s 

Laboratory as well as the instrumentation 

and analytical method used to perform the 

analysis. These values do not change from 

one batch to another when samples are 

analyzed on the same equipment using the 

same method. However, their levels may 

change over time due to updated analytical 

methods and technological advances. The 

values of the LOD and LOQ for the methods 

(XRD and FTIR) used in analyzing respirable 

crystalline silica samples are explained in 

MSHA documents for MNM samples and 

coal samples (MSHA Method P–2, 2018a; 

MSHA Method P–7, 2018b and 2020). MSHA 

periodically updates these values to reflect 

progress in its analytical methods. The values 

of LOD and LOQ were last updated in 2022 

for MNM samples and in 2020 for coal 

samples. 

The values of LODs and LOQs for 

respirable crystalline silica in samples from 

MSHA inspectors depend on several factors, 

including the analytical method used (XRD 

or FTIR) and the silica polymorph analyzed 

(quartz, cristobalite, or tridymite), as 

presented in Table A2–1. 

For a sample with respirable crystalline 

silica content less than the method LOD, the 

maximum concentration is calculated as the 

respirable crystalline silica mass equivalent 

to LOD divided by the volume of air 

sampled. For example, if no quartz is 

detected by XRD analysis for an MNM 

sample, the method LOD is 5 mg. If that 

sample is collected at 1.7 L/min air flow rate 

for 480 minutes (i.e., 8 hours), the air sample 

volume would be 816 L (= 1.7 L/min * 480 

minutes), or 0.816 m3. The calculated 

maximum concentration associated with a 

sample having respirable crystalline silica 

mass below the method LOD would be 6 mg/ 

m3 (= 5 mg/0.816 m3). The ‘‘half maximum 

concentration’’ is the midpoint between 0 

and the calculated maximum respirable 

crystalline silica concentration, which is 3 

mg/m3 (= 1⁄2 * 6 mg/m3) in this example. 

BILLING CODE 4520–43–P 


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89 In its Final Regulatory Economic Analysis 

(FREA) for its 2016 silica rule, OSHA observed: 

‘‘. . . that XRD analysis of quartz from samples 

prepared from reference materials can achieve 

LODs and LOQs between 5 and 10 mg was not 

disputed in the [rulemaking] record.’’ (OSHA, 

2016). 

The air volume is treated differently for 

MNM and coal samples under the existing 

standards. In the case of MNM samples, 8- 

hour equivalent time weighted averages 

(TWAs) are calculated using 480 minutes (8 

hours) and a flow rate of 1.7 L/min, even if 

samples are collected for a longer duration. 

In contrast, coal TWAs are calculated using 

the full duration of the shift and a flow rate 

of 2.0 L/min and converted to an MRE 

equivalent concentration under existing 

standards. 

Assumptions for Analyzed Samples 

Samples from MNM mines that contain at 

least 0.100 mg of dust mass are analyzed for 

the presence of quartz and/or cristobalite. For 

samples from coal mines, the minimum 

amount of respirable dust in a sample to be 

analyzed for respirable crystalline silica is 

determined by sample type and the 

occupation of the miner sampled. For Sample 

Types 1, 2, and 5, the sample must contain 

at least 0.100 mg of respirable dust. For 

Sample Types 4 and 8, the sample must 

contain at least 0.200 mg of respirable dust 

unless it comes from one of the following 

occupations: bulldozer operator (MSIS 

general occupation code 368), high wall drill 

operator (code 384), high wall drill helper 

(code 383), blaster/shotfirer (code 307), 

refuse/backfill truck driver (code 386), and 

high lift operator/front end loader (code 382). 

Samples taken from these occupations must 

contain at least 0.100 mg respirable dust to 

be analyzed for respirable crystalline silica. 

Samples from Shop Welders (code 319) are 

never analyzed for quartz, as they instead are 

sent for welding fume analysis. 

MSHA makes separate assumptions based 

on the mass of respirable crystalline silica for 

a sample, whether it is above or below the 

method LOD. For all samples reporting a 

mass of respirable crystalline silica greater or 

equal to the method LOD, MSHA used the 

reported values to calculate the respirable 

crystalline silica concentration for the 

sample. For samples with values below the 

method LOD, including samples reported as 

containing 0 mg of silica, MSHA used 1⁄2 of 

the LOD to calculate the respirable 

crystalline silica concentration of the sample. 

MSHA understands that its assumptions 

regarding samples with respirable crystalline 

silica mass below the method LOD will have 

a minimal impact on the assessment.89


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The reported value of respirable crystalline 

silica mass from an MNM or coal sample can 

fall under one of the four groups: (1) at or 

above the method LOQ, (2) at or above the 

method LOD but below the LOQ, (3) greater 

than 0 mg but less than the method LOD, or 

(4) equal to 0 mg. MSHA treats these samples 

differently based on their respirable 

crystalline silica mass. 

Quartz Mass at or Above the Method LOQ 

For MNM and coal samples reporting 

quartz mass at or above the method LOQs, 

MSHA uses the values reported by the 

MSHA’s Laboratory. 

Quartz Mass Between Method LOD and LOQ 

For MNM and coal samples reporting 

quartz mass at or above the method LOD but 

below the LOQ, MSHA uses the values 

reported by the MSHA’s Laboratory. 

Quartz Mass Between the Method LOD and 

0 μg 

A review of respirable crystalline silica 

samples in LIMS reveals that some samples 

had a respirable crystalline silica mass below 

the LOD of the analytical methods but greater 

than 0 mg. Values in this range (i.e., below the 

method LOD but greater than 0 mg) cannot 

reliably indicate the presence of respirable 

crystalline silica. The mass of silica in these 

is too small to reliably detect, but the 

concentration of silica could be up to the 

calculated maximum concentration based on 

the method LOD. For example, consider a 

sample from an MNM mine that was 

analyzed for quartz and had a reported quartz 

mass of 4 mg. This falls below the LOD of 5 

mg but above 0 mg, and as such the sample 

could actually contain anywhere from 0 mg of 

quartz up to the LOD value of 5 mg of quartz. 

In these cases, MSHA used 1⁄2 the LOD 

value to calculate respirable crystalline silica 

concentration. MSHA explored other options 

to treat these samples such as treating the 

reported silica mass as 0 mg/m3 (lower 

bound) as well as assuming the sample silica 

mass is just below the LOD and assigning 

each sample a value of the method LOD 

(upper bound). The use of the 1⁄2 LOD value 

is considered a reasonable assumption since 

using either the lower bound of 0 mg/m3 or 

the upper bound of the associated method’s 

LOD could under or overestimate exposures, 

respectively. The assumption is not expected 

to impact the assessment of silica 

concentration because any sample results 

with respirable crystalline silica mass below 

the method LODs (between 3–10 mg/m3) 

would also have been well below the lowest 

exposure profile range (<25 mg/m3). 

Quartz Mass of 0 μg 

A portion of the MNM and coal samples 

below the LOD are listed as having respirable 

crystalline silica (specifically quartz) mass 

levels of 0 mg. For these samples, instead of 

treating the mass of silica in the sample as 

a true zero, MSHA replaced the value with 

1⁄2 the LOD of the associated method. 

Although the respirable crystalline silica 

mass of these samples is less than the LOD, 

it is likely that the sample still contains a 

small amount of respirable crystalline silica. 

Hence, MSHA assumes a value of 1⁄2 LOD in 

its calculation of respirable crystalline silica 

concentration for these samples. This 

assumption is considered to be reasonable 

because using the lower bound of 0 mg/m3 for 

these samples could underestimate the 

respirable crystalline silica concentration 

while using the upper bound of method 

LODs could overestimate the respirable 

crystalline silica concentration. 

Table A2–3 presents an example for quartz, 

one of the respirable crystalline silica 

polymorphs. This table shows the LOD of 

quartz mass and the possible range of quartz 

concentrations for samples reporting a quartz 

mass of 0 mg. These adjusted concentrations 

are expected to have a limited impact of the 

assessment of respirable crystalline silica 

concentration, as supported by MSHA’s 

sensitivity analyses. 


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Cristobalite Measurement 

Respirable dust samples from MNM mines 

are rarely analyzed for cristobalite by MSHA, 

and respirable coal dust samples are not 

analyzed for the presence of cristobalite. 

MNM samples are analyzed for the presence 

of cristobalite only when requested by MSHA 

inspectors because the geological or work 

conditions indicate this specific polymorph 

may be present. The LIMS database includes 

samples for which cristobalite was analyzed, 

either with or without quartz analysis. MSHA 

uses similar assumptions for cristobalite and 

quartz. 

The cristobalite LOD for these samples is 

10 mg. The MSHA Laboratory-reported values 

are used for analyzed dust samples with 

cristobalite mass values equal to or above the 

method LODs. Samples that were analyzed 

for cristobalite and had a cristobalite mass 

value below the method LOD were assigned 

values of 1⁄2 LOD, or 5 mg. For example, 267 

samples, or 74.4 percent of the 359 samples 

that were analyzed for cristobalite, reported 

a value of 0 mg of cristobalite; these were 

assigned a value of 5 mg. 

When a sample is analyzed for two 

polymorphs (i.e., both quartz and 

cristobalite), detectable quartz and 

cristobalite are summed to generate the total 

respirable crystalline silica. If only one of 

these polymorphs is detected, the sample 

concentration is based on the detected 

polymorph. If the concentrations of both 

polymorphs (quartz and cristobalite) are 

reported as 0 mg/m3, 1⁄2 mass LOD is assumed 

in calculating the concentrations and the 

resulting concentrations are summed. 

Unanalyzed Samples 

There are also samples whose dust mass 

fell below their associated mass threshold, 

and as such, they were not analyzed for the 

presence of quartz and/or cristobalite. The 

respirable dust mass for a sample was 

considered to be 0 mg when the net mass gain 

of dust was 0 mg or less. 

References 

MSHA. 2018. P–2: X-Ray Diffraction 

Determination of Quartz and Cristobalite 

in Respirable Metal/Nonmetal Mine 

Dust. 

MSHA. 2018a. P–7: Infrared Determination of 

Quartz in Respirable Coal Mine Dust. 

MSHA. 2020. P–7: Determination of Quartz 

in Respirable Coal Mine Dust by Fourier 

Transform Infrared Spectroscopy. 

OSHA, 2016. Final Regulatory Economic 

Analysis (FEA) for OSHA’s Final Rule on 

Respirable Crystalline Silica, Chapter 

IV.3.2.3—Sensitivity of Sampling and 

Analytical Methods. 

Appendix B 

Mining Commodity Groups 

For this rulemaking analysis, the mining 

industries are grouped into six 

commodities—Coal, Metal, Nonmetal, Stone, 

Crushed Limestone, and Sand and Gravel. 

The table below shows the six commodity 

groupings based on the Standard Industrial 

Classification (SIC) codes and the North 

American Industry Classification System 

(NAICS) codes. The SIC system is a 

predecessor of NAICS using industry titles to 

standardize industry classification. The 

NAICS is widely used by Federal statistical 

agencies, including the Small Business 

Administration (SBA), for classifying 

business establishments for the purpose of 

collecting, analyzing, and publishing 

statistical data related to the U.S. business 

economy. 


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90For coal mines, the analysis is based on 

samples collected by inspectors beginning on 

August 1, 2016, when Phase III of MSHA’s 2014 

RCMD standard went into effect. Samples taken 

prior to implementation of the RCMD standard 

would not be representative of current respirable 

crystalline silica exposure levels in coal mines. 

91The job codes have been referred to as both job 

codes and occupation codes by MSHA. For 

example, in the Mine Data Retrieval System, they 

are called job codes; in other materials, including 

MSHA’s Inspection Application System (IAS), they 

are called occupational codes. For the purposes of 

this document, the term job code has been used to 

clearly differentiate the job codes from the 

occupational categories. 

Appendix C 

Occupational Categories for Respirable 

Crystalline Silica Sample Collection 

This Appendix explains how MSHA 

categorized MNM and coal samples in 

constructing respirable crystalline silica 

exposure profile tables for the current 

rulemaking. MSHA has developed respirable 

crystalline silica exposure profile tables 

using its inspectors’ sampling data and 

results. One set of exposure profile tables 

displays the analysis of 15 years of respirable 

crystalline silica sampling data from MNM 

mines (Attachment 1), and the other set 

displays the analysis of 5 years of respirable 

crystalline silica samples collected at coal 

mines (Attachment 2).90 In the MNM tables, 

the respirable crystalline silica concentration 

information is broken out by 5 commodities 

(e.g., ‘‘Metal,’’ ‘‘Crushed Limestone,’’ etc.) 

and then by 11 occupational categories (e.g., 

‘‘Drillers,’’ ‘‘Stone Cutting Operators,’’ etc.). 

The data for coal mining is disaggregated by 

2 locations (‘‘Underground’’ and ‘‘Surface’’) 

and then by 9 occupational categories (e.g., 

‘‘Crusher Operators,’’ ‘‘Continuous Mining 

Machine Operators,’’ etc.). 

Job Codes and Respirable Dust Sampling 

MSHA inspectors use job codes to label 

samples of respirable dust when they 

conduct health inspections.91 Following the 

sampling strategy outlined in the most recent 


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92 IAS also contains 272 coal job codes that are 

used to fill out a Mine Accident, Injury and Illness 

Report (MSHA Form 7000–1). These codes were not 

included in the respirable crystalline silica 

exposure profile tables and are not discussed 

further in this document. 

MSHA Health Inspection Procedures 

Handbook (December 2020; PH20–V–4), the 

inspectors determine potential airborne 

hazards to which miners may be exposed, 

including respirable dust, and then take 

samples from the appropriate miners or 

working areas at a mine. Using gravimetric 

samplers, the inspectors collect respirable 

dust samples at MNM and coal mines. When 

submitting the collected samples to MSHA’s 

Laboratory for analysis, the inspectors label 

their samples with the three-digit job code 

that best describes the duties that each miner 

was performing during the sampling period. 

The three-digit job codes are taken from 

MSHA’s Inspection Application System 

(IAS), which includes 220 job codes for coal 

mines and 121 job codes for MNM mines. 

Attachments 3 and 4 include the IAS job 

codes for coal and MNM operations, 

respectively. 

Coal Job Codes: The coal job codes have 

generally been consistent over time, with 

new codes added when needed. For example, 

IAS has the same job code for the duties of 

a coal ‘‘supervisor/foreman’’ as two 

predecessor documents—the ‘‘Job Code 

Pocket Cards’’ for coal mining, used by 

MSHA’s predecessor, the Mining 

Enforcement and Safety Administration 

(MESA) (see Attachment 5), and a Fall 1983 

Mine Safety and Health publication. An 

example is presented below in Table C–1. In 

the three-digit coal job code, the first digit 

generally identifies where the work is taking 

place in the mine: 0 (Underground Section 

Workers—Face); 1 (General Underground— 

Non-Face); 2 (Underground Transportation— 

Non-Face); 3 (Surface); 4 (Supervisory and 

Staff); 5 (MSHA—State); and 6 (Shaft and 

Slope Sinking). The coal codes starting with 

6 were added in 2020 to better delineate the 

samples for miners conducting shaft and 

slope sinking activities. 

MNM Job Codes: Many of the 121 MNM job 

codes are similar to the coal job codes, as 

noted in Attachment 4. One major difference 

is that unlike the coal job codes, MNM job 

codes are not based on the location of the 

work/job. The first digit of the three-digit 

MNM job code does not indicate whether a 

job is located at an underground or surface 

area of the mine. For example, a ‘‘MNM 

Diamond Drill Operator’’ (Job Code 034) 

could be working on the surface or 

underground, whereas a ‘‘Coal Drill 

Operator’’ would have a different job code 

based on the miner’s location within a mine 

(Job Code 034—underground at the face; Job 

Code 334—at the surface). 

Occupational Categories for the Respirable 

Crystalline Silica Rulemaking 

Some of the original work to group the 

MNM job codes into occupational categories 

was completed in 2010 in support of earlier 

rulemaking efforts. The MNM occupational 

categories were developed first and were 

later updated with additional sampling data 

as it became available. The coal occupational 

categories were developed several years later 

and were generally modeled after the MNM 

tables; however, coal occupational categories 

are first divided based on surface and 

underground locations because occupational 

activities at different locations of a mine can 

have differing impacts on coal miners’ 

exposures to respirable crystalline silica. In 

2020, MSHA’s Laboratory used 9 coal and 14 

MNM occupational categories for its 

respirable crystalline silica data analyses. 

For the respirable crystalline silica 

exposure profile tables in the proposed 

respirable crystalline silica rule, MSHA made 

no change to the 9 coal occupational 

categories, but condensed the 14 MNM 

occupational categories to 11. These 

occupational categories are meant to 

reasonably group multiple job codes with 

similar occupational activities/tasks and 

engineering controls. The grouping of job 

codes into occupational categories purposely 

focused on the occupational activities/tasks 

and exposure risk of the miner performing a 

particular job rather than the type of mining 

equipment utilized by the miner. The 

creation of occupational categories based on 

the types of equipment utilized by miners 

would have failed to accurately characterize 

the risk of individual miners. 

Coal Occupational Categories 

There are 220 job codes for coal miners in 

IAS.92 Overall, 209 job codes are included in 

the 9 occupational categories. Some job codes 

were excluded, primarily because sampling 

data were not available for those job codes. 

The codes that have been excluded are: 

• Job code 0 ‘‘Area,’’ because area samples 

are not specific to any one occupation. 

• Job code 398 ‘‘Groundman,’’ because 

there were no sample data for this code in 

the respirable crystalline silica sampling 

dataset. 

• Job codes 590 ‘‘Education Specialist,’’ 

591 ‘‘Mineral Industrial Safety Officer,’’ 592 

‘‘Mine Safety Instructor,’’ and 594 ‘‘Training 

Specialist,’’ because there were no coal 

respirable crystalline silica (quartz) data for 

these codes for the timeframe selected. 

• Job codes 602 ‘‘Electrician,’’ 604 

‘‘Mechanic,’’ 609 ‘‘Supply Person,’’ 632 

‘‘Ventilation Worker,’’ and 635 ‘‘Continuous 

Miner Operator Helper,’’ because there were 

no sample data for these codes in the 

respirable crystalline silica sampling dataset. 

The remaining 209 coal job codes are first 

divided by the job location—underground or 

surface—because potential respirable 

crystalline silica exposures at coal mines can 

vary depending on where a miner works at 

a given mine. (Three job codes are used in 


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both underground and surface locations: job 

codes 402 ‘‘Master Electrician,’’ 404 ‘‘Master 

Mechanic,’’ and 497 ‘‘Clerk/Timekeeper.’’) 

The underground and surface job codes are 

further grouped on the basis of the types of 

tasks and typical engineering controls. For 

example, as shown in Figure 1, the 

underground ‘‘Continuous Mining Machine 

Operators’’ occupational category includes 14 

different occupations that involve drilling 

activities—occupations such as ‘‘Coal Drill 

Helper,’’ ‘‘Coal Drill Operator,’’ and ‘‘Rock 

Driller.’’ The underground ‘‘Operators of 

Large Powered Haulage Equipment’’ 

occupational category has 12 similar 

occupations including ‘‘Loading Machine 

Operator,’’ ‘‘Shuttle Car Operator,’’ and 

‘‘Motorman.’’ 

There are five categories of underground 

occupations and four categories of surface 

occupations. 

The five underground occupational 

categories include: 

(1) Continuous Mining Machine Operators 

(e.g., Coal Drill Helper and Coal Drill 

Operator); 

(2) Operators of Large Powered Haulage 

Equipment (e.g., Shuttle Car, Tractor, Scoop 

Car); 

(3) Longwall Workers (e.g., Headgate 

Operator and Jack Setter (Longwall)); 

(4) Roof Bolters (e.g., Roof Bolter and Roof 

Bolter Helper); and 

(5) Underground Miners (e.g., Electrician, 

Mechanic, Belt Man/Conveyor Man, and 

Laborer, etc.). 

The four surface occupational categories 

include: 

(1) Drillers (e.g., Coal Drill Operator, Coal 

Drill Helper, and Auger Operator); 

(2) Operators of Large Powered Haulage 

Equipment (e.g., Backhoe, Forklift, and 

Shuttle Car); 

(3) Crusher Operators (e.g., Crusher 

Attendant, Washer Operator, and ScalperScreen Operator); and 

(4) Mobile Workers (e.g., Electrician, 

Mechanic, Blaster, Cleanup Man, Mine 

Foreman, etc.). 

Attachments 1 and 3 provide the full lists 

of occupational categories and coal job codes. 

MNM Occupational Categories 

From the 121 MNM job codes in IAS, 120 

job codes are included in the occupational 

categories and 1 job code is excluded. The 

code that has been excluded is: 

• Job code 413 ‘‘Janitor,’’ because there 

were no sample data for this code in the 

respirable crystalline silica sampling dataset. 

Of the 120 job codes included, 1 job code 

was listed in both the ‘‘Crushing Equipment 

and Plant Operators’’ occupational category 

and the ‘‘Kiln, Mill and Concentrator 

Workers’’ category. The code that was used 

twice is: 

• Job Code 388 ‘‘Screen/Scalper 

Operators,’’ because MNM job codes do not 

indicate the location where the work is 

taking place and this work can be conducted 

either in a plant or on the surface of the 

mine. 

The final 121 MNM job codes (with job 

code 388 included twice) were first grouped 

into 14 occupational categories based on the 

types of tasks and typical engineering 

controls used. For example, as seen in Figure 

2, the ‘‘Drillers’’ occupational category 

includes the 20 different occupations that 

involve drilling activities, such as ‘‘Diamond 

Drill Operator,’’ ‘‘Drill Operator Churn,’’ and 

‘‘Continuous Miner Operator.’’ ‘‘Belt 

Cleaner,’’ ‘‘Belt Crew,’’ and ‘‘Belt Vulcanizer’’ 

are included in the occupational category, 

‘‘Conveyor Operators.’’ Similar tasks were 

grouped together because the work activities 

and respirable crystalline silica exposures 

were anticipated to be comparable. 


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93Crushed Limestone and Sand and Gravel were 

considered separately because these commodities 

make up a large percentage of inspection samples. 

Watts et al. (2012). Respirable crystalline silica 

[Quartz] Concentration Trends in Metal and 

Nonmetal Mining, J Occ Environ Hyg 9:12, 720– 

732. 

The 14 occupational categories were: 

(1) Bagging Machines; 

(2) Stone Saws; 

(3) Stone Trimmers, Splitters; 

(4) Truck Loading Stations; 

(5) Mobile Workers (e.g., Laborers, 

Electricians, Mechanics, and Supervisors); 

(6) Conveyors; 

(7) Crushers; 

(8) Dry Screening Plants; 

(9) Kilns/Dryers, Rotary Mills, Ball Mills, 

and Flotation/Concentrators; 

(10) Large Powered Haulage Equipment 

(e.g., Trucks, FELs, Bulldozers, and Scalers); 

(11) Small Powered Haulage Equipment 

(e.g., Bobcats and Forklifts); 

(12) Jackhammers; 

(13) Drills; and 

(14) Other Occupations. 

After additional consideration, it was 

determined that the original 14 categories 

could be further condensed into the final 11 

categories since some of the occupational 

categories contained job codes where the 

types of tasks and engineering and 

administrative controls were similar enough 

to be combined. 

The final 11 occupational categories 

include: 

(1) Drillers (e.g., Diamond Drill Operator, 

Wagon Drill Operator, and Drill Helper); 

(2) Stone Cutting Operators (e.g., 

Jackhammer Operator, Cutting Machine 

Operator, and Cutting Machine Helper); 

(3) Operators of Large Powered Haulage 

Equipment (e.g., Trucks, Bulldozers, and 

Scalers); 

(4) Conveyor Operators (e.g., Belt Cleaner, 

Belt Crew, and Belt Vulcanizer); 

(5) Crushing Equipment and Plant 

Operators (Crusher Operator/Worker, Scalper 

Screen Operator, and Dry Screen Plant 

Operator); 

(6) Kiln, Mill, and Concentrator Workers 

(e.g., Ball Mill Operator, Leaching Operator, 

and Pelletizer Operator); 

(7) Operators of Small Powered Haulage 

Equipment (e.g., Bobcats, Shuttle Car, and 

Forklifts); 

(8) Packaging Equipment Operators (e.g., 

Bagging Operator and Packaging Operations 

Worker); 

(9) Truck Loading Station Tenders (e.g., 

Dump Operator and Truck Loader); 

(10) Mobile Workers (Laborers, 

Electricians, Mechanics, and Supervisors, 

etc.); and 

(11) Miners in Other Occupations (Welder, 

Dragline Operator, Shotcrete/Gunite Man, 

and Dredge/Barge Operator, etc.). 

The sampling data for each of the 11 

occupational categories were then 

summarized by commodity group (‘‘Metal,’’ 

‘‘Nonmetal,’’ ‘‘Stone,’’ ‘‘Crushed Limestone,’’ 

and ‘‘Sand and Gravel’’) based on the 

material being extracted.93 The available 

sampling data were then collated for each 

occupation and commodity and summarized 

by concentration ranges in the exposure 

profile tables for MNM mines. 

Attachment 1: Tables for MNM 


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Attachment 2: Tables for Coal 


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Attachment 3: Coal Job Codes 

The complete list of job codes that are 

found in IAS, as of March 11, 2022, are 

included below, with Table C3–1 listing job 

codes for coal miners. For coal, the first digit 

of the job code identifies where the work is 

taking place. For example, codes starting 

with 0 represent jobs that occur at the 

underground face of the mine. Job codes that 

start with 6 were added in 2020. 

0—Underground Section Workers (Face) 

1—General Underground (Non-Face) 

2—Underground Transportation (Non-Face) 

3—Surface 

4—Supervisory and Staff 

5—MSHA—State 

6—Shaft and Slope Sinking 


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Attachment 4: MNM Job Codes 

The complete list of job codes that are 

found in IAS, as of March 11, 2022, are 

included below with Table C4–1 outlining 

job codes for MNM miners. 


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Attachment 5. Examples of Job Code Pocket 

Cards 

Inspectors previously received pocketsized job code cards for use in filling out 

forms with the correct job code. Now, a dropdown menu in IAS is used to select the 

codes. Table C5–1 contains Underground 

Coal Mining Occupation Codes from Coal Job 

Code Cards used by MESA between 1973 and 

1977. Table C5–2 contains Surface 

Occupation Codes from Coal Job Codes used 

by MESA between 1973 and 1977. 


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MNM Job Code Cards (1997) 

Table C5–3 includes MNM Job Codes from 

a MNM Job Code Card printed in 1997 by the 

GPO and which referenced a 1981 MSHA 

form (MSHA Form 4000–50, Sept. 1981). 


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BILLING CODE 4520–43–C 

List of Subjects 

30 CFR Part 56 

Chemicals, Electric power, 

Explosives, Fire prevention, Hazardous 

substances, Incorporation by reference, 

Metal and nonmetal mining, Mine safety 

and health, Noise control, Reporting and 

recordkeeping requirements, Surface 

mining. 

30 CFR Part 57 

Chemicals, Electric power, 

Explosives, Fire prevention, Gases, 

Hazardous substances, Incorporation by 

reference, Metal and nonmetal mining, 

Mine safety and health, Noise control, 

Radiation protection, Reporting and 

recordkeeping requirements, 

Underground mining. 

30 CFR Part 60 

Coal, Incorporation by reference, 

Metal and nonmetal mining, Medical 

surveillance, Mine safety and health, 

Respirable crystalline silica, Reporting 

and recordkeeping requirements, 

Surface mining, Underground mining. 

30 CFR Part 70 

Coal, Mine safety and health, 

Reporting and recordkeeping 

requirements, Respirable dust, 

Underground coal mines. 

30 CFR Part 71 

Coal, Mine safety and health, 

Reporting and recordkeeping 

requirements, Surface coal mines, 

Underground coal mines. 

30 CFR Part 72 

Coal, Health standards, Incorporation 

by reference, Mine safety and health, 

Training, Underground mining. 

30 CFR Part 75 

Coal, Mine safety and health, 

Reporting and recordkeeping 

requirements, Underground coal mines, 

Ventilation. 


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30 CFR Part 90 

Coal, Mine safety and health, 

Reporting and recordkeeping 

requirements, Respirable dust. 

Christopher J. Williamson, 

Assistant Secretary of Labor for Mine Safety 

and Health. 

For the reasons discussed in the 

preamble, the Mine Safety and Health 

Administration is proposing to amend 

30 CFR subchapters K, M, and O as 

follows: 

Subchapter K-Metal and Nonmetal 

Mine Safety and Health 

PART 56—SAFETY AND HEALTH 

STANDARDS—SURFACE METAL AND 

NONMETAL MINES 

■ 1. The authority citation for part 56 

continues to read as follows: 

Authority: 30 U.S.C. 811. 

Subpart D—Air Quality and Physical 

Agents 

■ 2. Amend § 56.5001 by revising 

paragraph (a) to read as follows: 

§ 56.5001 Exposure limits for airborne 

contaminants. 

* * * * * 

(a) Except as provided in paragraph 

(b) of this section and in part 60 of this 

chapter, the exposure to airborne 

contaminants shall not exceed, on the 

basis of a time weighted average, the 

threshold limit values adopted by the 

American Conference of Governmental 

Industrial Hygienists, as set forth and 

explained in the 1973 edition of the 

Conference’s publication, entitled 

‘‘TLV’s Threshold Limit Values for 

Chemical Substances in Workroom Air 

Adopted by ACGIH for 1973,’’ pages 1 

through 54. This publication is 

incorporated by reference into this 

section with the approval of the Director 

of the Federal Register under 5 U.S.C. 

552(a) and 1 CFR part 51. This material 

is available for inspection at the Mine 

Safety and Health Administration 

(MSHA) and at the National Archives 

and Records Administration (NARA). 

Contact MSHA at: MSHA’s Office of 

Standards, Regulations, and Variances, 

201 12th Street South, Arlington, VA 

22202–5450; 202–693–9440; or at any 

MSHA Metal and Nonmetal Mine Safety 

and Health District Office. For 

information on the availability of this 

material at NARA, visit 

www.archives.gov/federal-register/cfr/ 

ibr-locations.html or email 

fr.inspection@nara.gov. The material 

may be obtained from American 

Conference of Governmental Industrial 

Hygienists, 1330 Kemper Meadow 

Drive, Attn: Customer Service, 

Cincinnati, OH 45240; www.acgih.org. 

* * * * * 

■ 3. Amend § 56.5005 by revising the 

introductory text and paragraphs (b) and 

(c) to read as follows: 

§ 56.5005 Control of exposure to airborne 

contaminants. 

Control of employee exposure to 

harmful airborne contaminants shall be, 

insofar as feasible, by prevention of 

contamination, removal by exhaust 

ventilation, or by dilution with 

uncontaminated air. However, where 

accepted engineering control measures 

have not been developed or when 

necessary by the nature of work 

involved (for example, while 

establishing controls or occasional entry 

into hazardous atmospheres to perform 

maintenance or investigation), 

employees may work for reasonable 

periods of time in concentrations of 

airborne contaminants exceeding 

permissible levels if they are protected 

by appropriate respiratory protective 

equipment. Whenever respiratory 

protective equipment is used, its 

selection, fitting, maintenance, cleaning, 

training, supervision, and use shall meet 

the following minimum requirements: 

* * * * * 

(b) Approved respirators shall be 

selected, fitted, cleaned, used, and 

maintained in accordance with the 

requirements, as applicable, of ASTM 

F3387–19. ASTM F3387–19, Standard 

Practice for Respiratory Protection 

approved August 1, 2019, is 

incorporated by reference into this 

section with the approval of the Director 

of the Federal Register under 5 U.S.C. 

552(a) and 1 CFR part 51. This material 

is available for inspection at the Mine 

Safety and Health Administration 

(MSHA) and at the National Archives 

and Records Administration (NARA). 

Contact MSHA at: MSHA’s Office of 

Standards, Regulations, and Variances, 

201 12th Street South, Arlington, VA 

22202–5450; 202–693–9440; or any 

Mine Safety and Health Enforcement 

District Office. For information on the 

availability of this material at NARA, 

visit www.archives.gov/federal-register/ 

cfr/ibr-locations.html or email 

fr.inspection@nara.gov. The material 

may be obtained from ASTM 

International, 100 Barr Harbor Drive, 

P.O. Box C700, West Conshohocken, PA 

19428–2959; www.astm.org/. 

(c) When respiratory protection is 

used in atmospheres immediately 

dangerous to life or health (IDLH), the 

presence of at least one other person 

with backup equipment and rescue 

capability shall be required in the event 

of failure of the respiratory equipment. 

PART 57—SAFETY AND HEALTH 

STANDARDS—UNDERGROUND 

METAL AND NONMETAL MINES 

■ 4. The authority citation for part 57 

continues to read as follows: 

Authority: 30 U.S.C. 811. 

Subpart D—Air Quality, Radiation, 

Physical Agents, and Diesel Particulate 

Matter 

■ 5. Amend § 57.5001 by revising 

paragraph (a) to read as follows: 

§ 57.5001 Exposure limits for airborne 

contaminants. 

* * * * * 

(a) Except as provided in paragraph 

(b) of this section and in part 60 of this 

chapter, the exposure to airborne 

contaminants shall not exceed, on the 

basis of a time weighted average, the 

threshold limit values adopted by the 

American Conference of Governmental 

Industrial Hygienists, as set forth and 

explained in the 1973 edition of the 

Conference’s publication, entitled 

‘‘TLV’s Threshold Limit Values for 

Chemical Substances in Workroom Air 

Adopted by ACGIH for 1973,’’ pages 1 

through 54. Excursions above the listed 

thresholds shall not be of a greater 

magnitude than is characterized as 

permissible by the Conference. This 

publication is incorporated by reference 

into this section with the approval of 

the Director of the Federal Register 

under 5 U.S.C. 552(a) and 1 CFR part 51. 

This material is available for inspection 

at the Mine Safety and Health 

Administration (MSHA) and at the 

National Archives and Records 

Administration (NARA). Contact MSHA 

at: MSHA’s Office of Standards, 

Regulations, and Variances, 201 12th 

Street South, Arlington, VA 22202– 

5450; 202–693–9440; or any MSHA 

Metal and Nonmetal Mine Safety and 

Health District Office. For information 

on the availability of this material at 

NARA, visit www.archives.gov/federalregister/cfr/ibr-locations.html or email 

fr.inspection@nara.gov. The material 

may be obtained from American 

Conference of Governmental Industrial 

Hygienists by writing to 1330 Kemper 

Meadow Drive, Attn: Customer Service, 

Cincinnati, OH 45240; www.acgih.org. 

* * * * * 

■ 6. Amend § 57.5005 by revising the 

introductory text and paragraphs (b) and 

(c) to read as follows: 

§ 57.5005 Control of exposure to airborne 

contaminants. 

Control of employee exposure to 

harmful airborne contaminants shall be, 

insofar as feasible, by prevention of 

contamination, removal by exhaust 


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ventilation, or by dilution with 

uncontaminated air. However, where 

accepted engineering control measures 

have not been developed or when 

necessary by the nature of work 

involved (for example, while 

establishing controls or occasional entry 

into hazardous atmospheres to perform 

maintenance or investigation), 

employees may work for reasonable 

periods of time in concentrations of 

airborne contaminants exceeding 

permissible levels if they are protected 

by appropriate respiratory protective 

equipment. Whenever respiratory 

protective equipment is used, its 

selection, fitting, maintenance, cleaning, 

training, supervision, and use shall meet 

the following minimum requirements: 

* * * * * 

(b) Approved respirators shall be 

selected, fitted, cleaned, used, and 

maintained in accordance with the 

requirements, as applicable, of ASTM 

F3387–19. ASTM F3387–19, Standard 

Practice for Respiratory Protection 

approved August 1, 2019, is 

incorporated by reference into this 

section with the approval of the Director 

of the Federal Register under 5 U.S.C. 

552(a) and 1 CFR part 51. This material 

is available for inspection at the Mine 

Safety and Health Administration 

(MSHA) and at the National Archives 

and Records Administration (NARA). 

Contact MSHA at: MSHA’s Office of 

Standards, Regulations, and Variances, 

201 12th Street South, Arlington, VA 

22202–5450; 202–693–9440; or any 

Mine Safety and Health Enforcement 

District Office. For information on the 

availability of this material at NARA, 

visit www.archives.gov/federal-register/ 

cfr/ibr-locations.html or email 

fr.inspection@nara.gov. The material 

may be obtained from ASTM 

International, 100 Barr Harbor Drive, 

P.O. Box C700, West Conshohocken, PA 

19428–2959; www.astm.org/. 

(c) When respiratory protection is 

used in atmospheres immediately 

dangerous to life or health (IDLH), the 

presence of at least one other person 

with backup equipment and rescue 

capability shall be required in the event 

of failure of the respiratory equipment. 

Subchapter M-Uniform Mine Health 

Regulations 

■ 7. Add part 60 to subchapter M to read 

as follows: 

PART 60–RESPIRABLE CRYSTALLINE 

SILICA 

Sec. 

60.1 Scope; effective date. 

60.2 Definitions. 

60.10 Permissible exposure limit (PEL). 

60.11 Methods of compliance. 

60.12 Exposure monitoring. 

60.13 Corrective actions. 

60.14 Respiratory protection. 

60.15 Medical surveillance for metal and 

nonmetal miners. 

60.16 Recordkeeping requirements. 

60.17 Severability. 

Authority: 30 U.S.C. 811, 813(h) and 957. 

§ 60.1 Scope; effective date. 

This part sets forth mandatory health 

standards for each surface and 

underground metal, nonmetal, and coal 

mine subject to the Federal Mine Safety 

and Health Act of 1977, as amended. 

Requirements regarding medical 

surveillance for metal and nonmetal 

miners are also included. The 

provisions of this part are effective [date 

120 days after publication of the final 

rule]. 

§ 60.2 Definitions. 

The following definitions apply in 

this part: 

Action level means an airborne 

concentration of respirable crystalline 

silica of 25 micrograms per cubic meter 

of air (mg/m3) for a full-shift exposure, 

calculated as an 8-hour time-weighted 

average (TWA). 

Objective data means information, 

such as air monitoring data from 

industry-wide surveys or calculations 

based on the composition of a 

substance, demonstrating miner 

exposure to respirable crystalline silica 

associated with a particular product or 

material or a specific process, task, or 

activity. The data must reflect mining 

conditions closely resembling or with a 

higher exposure potential than the 

processes, types of material, control 

methods, work practices, and 

environmental conditions in the 

operator’s current operations. 

Respirable crystalline silica means 

quartz, cristobalite, and/or tridymite 

contained in airborne particles that are 

determined to be respirable by a 

sampling device designed to meet the 

characteristics for respirable-particlesize-selective samplers that conform to 

the International Organization for 

Standardization (ISO) 7708:1995: Air 

Quality—Particle Size Fraction 

Definitions for Health-Related 

Sampling. 

Specialist means an American BoardCertified Specialist in Pulmonary 

Disease or an American Board-Certified 

Specialist in Occupational Medicine. 

§ 60.10 Permissible exposure limit (PEL). 

The mine operator shall ensure that 

no miner is exposed to an airborne 

concentration of respirable crystalline 

silica in excess of 50 mg/m3 for a fullshift exposure, calculated as an 8-hour 

TWA. 

§ 60.11 Methods of compliance. 

(a) The mine operator shall install, 

use, and maintain feasible engineering 

controls, supplemented by 

administrative controls when necessary, 

to keep each miner’s exposure at or 

below the PEL, except as specified in 

§ 60.14. 

(b) Rotation of miners shall not be 

considered an acceptable administrative 

control used for compliance with this 

part. 

§ 60.12 Exposure monitoring. 

(a) Baseline sampling. (1) The mine 

operator shall perform baseline 

sampling within the first 180 days after 

[date 120 days after publication of the 

final rule] to assess the full shift, 8-hour 

TWA exposure of respirable crystalline 

silica for each miner who is or may 

reasonably be expected to be exposed to 

respirable crystalline silica. 

(2) The mine operator is not required 

to conduct periodic sampling under 

paragraph (b) of this section if the 

baseline sampling indicates that miner 

exposures are below the action level and 

if the conditions in either paragraph 

(a)(2)(i) or (ii) of this section are met: 

(i) One of the following sources from 

within the preceding 12 months of 

baseline sampling indicates that miner 

exposures are below the action level: 

(A) Sampling conducted by the 

Secretary; or 

(B) Mine operator sampling 

conducted in accordance with 

paragraphs (f) and (g) of this section; or 

(C) Objective data. 

(ii) Subsequent sampling that is 

conducted within 3 months after the 

baseline sampling indicates that miner 

exposures are below the action level. 

(b) Periodic sampling. Where the most 

recent sampling indicates that miner 

exposures are at or above the action 

level but at or below the PEL, the mine 

operator shall sample within 3 months 

of that sampling and continue to sample 

within 3 months of the previous 

sampling until two consecutive 

samplings indicate that miner exposures 

are below the action level. 

(c) Corrective actions sampling. 

Where the most recent sampling 

indicates that miner exposures are 

above the PEL, the mine operator shall 

sample after corrective actions taken 

pursuant to § 60.13 until the sampling 

indicates that miner exposures are at or 

below the PEL. 

(d) Semi-annual evaluation. At least 

every 6 months after [date one year after 

the effective date of the final rule], mine 

operators shall evaluate any changes in 


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production, processes, engineering or 

administrative controls, or other factors 

that may reasonably be expected to 

result in new or increased respirable 

crystalline silica exposures. Once the 

evaluation is completed, the mine 

operator shall: 

(1) Make a record of the evaluation 

and the date of the evaluation; and 

(2) Post the record on the mine 

bulletin board and, if applicable, by 

electronic means, for the next 31 days. 

(e) Post-evaluation sampling. If the 

mine operator determines as a result of 

the semi-annual evaluation under 

paragraph (d) of this section that miners 

may be exposed to respirable crystalline 

silica at or above the action level, the 

mine operator shall perform sampling to 

assess the full shift, 8-hour TWA 

exposure of respirable crystalline silica 

for each miner who is or may reasonably 

be expected to be at or above the action 

level. 

(f) Sampling requirements. (1) 

Sampling shall be performed for the 

duration of a miner’s regular full shift 

and during typical mining activities. 

(2) The full-shift, 8-hour TWA 

exposure for such miners shall be 

measured based on: 

(i) Personal breathing-zone air 

samples for metal and nonmetal 

operations; or 

(ii) Occupational environmental 

samples collected in accordance with 

§ 70.201(c) or (b) or § 90.201(b) of this 

chapter for coal operations. 

(3) Where several miners perform the 

same tasks on the same shift and in the 

same work area, the mine operator may 

sample a representative fraction (at least 

two) of these miners to meet the 

requirements in paragraphs (a) through 

(e) of this section. In sampling a 

representative fraction of miners, the 

mine operator shall select the miners 

who are expected to have the highest 

exposure to respirable crystalline silica. 

(4) The mine operator shall use 

respirable-particle-size-selective 

samplers that conform to ISO 7708:1995 

to determine compliance with the PEL. 

ISO 7708:1995, Air Quality—Particle 

Size Fraction Definitions for HealthRelated Sampling, Edition 1, 1995–04, is 

incorporated by reference into this 

section with the approval of the Director 

of the Federal Register under 5 U.S.C. 

552(a) and 1 CFR part 51. This material 

is available for inspection at the Mine 

Safety and Health Administration 

(MSHA) and at the National Archives 

and Records Administration (NARA). 

Contact MSHA at: MSHA’s Office of 

Standards, Regulations, and Variances, 

201 12th Street South, Arlington, VA 

22202–5450; 202–693–9440; or any 

Mine Safety and Health Enforcement 

District Office. For information on the 

availability of this material at NARA, 

visit www.archives.gov/federal-register/ 

cfr/ibr-locations.html or email 

fr.inspection@nara.gov. The material 

may be obtained from the International 

Organization for Standardization (ISO), 

CP 56, CH–1211 Geneva 20, 

Switzerland; phone: + 41 22 749 01 11; 

fax: + 41 22 733 34 30; website: 

www.iso.org. 

(g) Methods of sample analysis. (1) 

The mine operator shall use a laboratory 

that is accredited to ISO/IEC 17025 

‘‘General requirements for the 

competence of testing and calibration 

laboratories’’ with respect to respirable 

crystalline silica analyses, where the 

accreditation has been issued by a body 

that is compliant with ISO/IEC 17011 

‘‘Conformity assessment—Requirements 

for accreditation bodies accrediting 

conformity assessment bodies.’’ 

(2) The mine operator shall ensure 

that the laboratory evaluates all samples 

using respirable crystalline silica 

analytical methods specified by MSHA, 

the National Institute for Occupational 

Safety and Health (NIOSH), or the 

Occupational Safety and Health 

Administration (OSHA). 

(h) Sampling records. For each sample 

taken pursuant to paragraphs (a) 

through (e) of this section, the mine 

operator shall make a record of the 

sample date, the occupations sampled, 

and the concentrations of respirable 

crystalline silica and respirable dust, 

and post the record and the laboratory 

report on the mine bulletin board and, 

if applicable, by electronic means, for 

the next 31 days, upon receipt. 

§ 60.13 Corrective actions. 

(a) If any sampling indicates that a 

miner’s exposure exceeds the PEL, the 

mine operator shall: 

(1) Make approved respirators 

available to affected miners before the 

start of the next work shift in 

accordance with § 60.14; 

(2) Ensure that affected miners wear 

respirators properly for the full shift or 

during the period of overexposure until 

miner exposures are at or below the 

PEL; and 

(3) Immediately take corrective 

actions to lower the concentration of 

respirable crystalline silica to at or 

below the PEL. 

(4) Once corrective actions have been 

taken, the mine operator shall: 

(i) Conduct sampling pursuant to 

§ 60.12(c); and 

(ii) Take additional or new corrective 

actions until sampling indicates miner 

exposures are at or below the PEL. 

(b) The mine operator shall make a 

record of corrective actions and the 

dates of the corrective actions under 

paragraph (a) of this section. 

§ 60.14 Respiratory protection. 

(a) Temporary non-routine use of 

respirators. The mine operator shall use 

respiratory protection as a temporary 

measure in accordance with paragraph 

(c) of this section. Miners must use 

respirators when working in 

concentrations of respirable crystalline 

silica above the PEL while: 

(1) Engineering control measures are 

being developed and implemented; or 

(2) It is necessary by the nature of 

work involved. 

(b) Miners unable to wear respirators. 

Upon written determination by a 

physician or other licensed health care 

professional (PLHCP) that an affected 

miner is unable to wear a respirator, the 

miner shall be temporarily transferred 

either to work in a separate area of the 

same mine or to an occupation at the 

same mine where respiratory protection 

is not required. 

(1) The affected miner shall continue 

to receive compensation at no less than 

the regular rate of pay in the occupation 

held by that miner immediately prior to 

the transfer. 

(2) The affected miner may be 

transferred back to the miner’s initial 

work area or occupation when 

temporary non-routine use of respirators 

under paragraph (a) of this section is no 

longer required. 

(c) Respiratory protection 

requirements. (1) Affected miners shall 

be provided with a NIOSH-approved 

atmosphere-supplying respirator or 

NIOSH-approved air-purifying 

respirator equipped with the following: 

(i) Particulate protection classified as 

100 series under 42 CFR part 84; or 

(ii) Particulate protection classified as 

High Efficiency ‘‘HE’’ under 42 CFR part 

84. 

(2) Approved respirators shall be 

selected, fitted, used, and maintained in 

accordance with the requirements, as 

applicable, of ASTM F3387–19. ASTM 

F3387–19, Standard Practice for 

Respiratory Protection approved August 

1, 2019, is incorporated by reference 

into this section with the approval of 

the Director of the Federal Register 

under 5 U.S.C. 552(a) and 1 CFR part 51. 

This material is available for inspection 

at the Mine Safety and Health 

Administration (MSHA) and at the 

National Archives and Records 

Administration (NARA). Contact MSHA 

at: MSHA’s Office of Standards, 

Regulations, and Variances, 201 12th 

Street South, Arlington, VA 22202– 

5450; 202–693–9440; or any Mine Safety 

and Health Enforcement District Office. 

For information on the availability of 


ddrumheller on DSK120RN23PROD with PROPOSALS2
45014 Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 

this material at NARA, visit 

www.archives.gov/federal-register/cfr/ 

ibr-locations.html or email 

fr.inspection@nara.gov. The material 

may be obtained from ASTM 

International, 100 Barr Harbor Drive, PO 

Box C700, West Conshohocken, PA 

19428–2959; www.astm.org/. 

§ 60.15 Medical surveillance for metal and 

nonmetal miners. 

(a) Medical surveillance. Each 

operator of a metal and nonmetal mine 

shall provide to each miner periodic 

medical examinations performed by a 

physician or other licensed health care 

professional (PLHCP) or specialist, as 

defined in § 60.2, at no cost to the 

miner. 

(1) Medical examinations shall be 

provided at frequencies specified in this 

section. 

(2) Medical examinations shall 

include: 

(i) A medical and work history, with 

emphasis on: past and present exposure 

to respirable crystalline silica, dust, and 

other agents affecting the respiratory 

system; any history of respiratory 

system dysfunction, including 

diagnoses and symptoms of respiratory 

disease (e.g., shortness of breath, cough, 

wheezing); history of tuberculosis; and 

smoking status and history; 

(ii) A physical examination with 

special emphasis on the respiratory 

system; 

(iii) A chest X-ray (a single 

posteroanterior radiographic projection 

or radiograph of the chest at full 

inspiration recorded on either film (no 

less than 14 x 17 inches and no more 

than 16 x 17 inches) or digital 

radiography systems), classified 

according to the International Labour 

Office (ILO) International Classification 

of Radiographs of Pneumoconioses by a 

NIOSH-certified B Reader; and 

(iv) A pulmonary function test to 

include forced vital capacity (FVC) and 

forced expiratory volume in one second 

(FEV1) and FEV1/FVC ratio, 

administered by a spirometry technician 

with a current certificate from a NIOSHapproved Spirometry Program Sponsor. 

(b) Voluntary medical examinations. 

Each mine operator shall provide the 

opportunity to have the medical 

examinations specified in paragraph (a) 

of this section at least every 5 years to 

all miners employed at the mine. The 

medical examinations shall be available 

during a 6-month period that begins no 

less than 3.5 years and not more than 

4.5 years from the end of the last 6- 

month period. 

(c) Mandatory medical examinations. 

For each miner who begins work in the 

mining industry for the first time, the 

mine operator shall provide medical 

examinations specified in paragraph (a) 

of this section as follows: 

(1) An initial medical examination no 

later than 30 days after beginning 

employment; 

(2) A follow-up medical examination 

no later than 3 years after the initial 

examination in paragraph (c)(1) of this 

section; and 

(3) A follow-up medical examination 

conducted by a specialist no later than 

2 years after the examinations in 

paragraph (c)(2) of this section if the 

chest X-ray shows evidence of 

pneumoconiosis or the spirometry 

examination indicates evidence of 

decreased lung function. 

(d) Medical examinations results. The 

results of medical examinations or tests 

made pursuant to this section shall be 

provided only to the miner, and at the 

request of the miner, to the miner’s 

designated physician. 

(e) Written medical opinion. The mine 

operator shall obtain a written medical 

opinion from the PLHCP or specialist 

within 30 days of the medical 

examination. The written opinion shall 

contain only the following: 

(1) The date of the medical 

examination; 

(2) A statement that the examination 

has met the requirements of this section; 

and 

(3) Any recommended limitations on 

the miner’s use of respirators. 

(f) Written medical opinion records. 

The mine operator shall maintain a 

record of the written medical opinions 

received from the PLHCP or specialist 

under paragraph (e) of this section. 

§ 60.16 Recordkeeping requirements. 

(a) Table 1 to this paragraph (a) lists 

the records the mine operator shall 

retain and their retention period. 

(1) Evaluation records made under 

§ 60.12(d) shall be retained for at least 

2 years from the date of each evaluation. 

(2) Sampling records made under 

§ 60.12(h) shall be retained for at least 

2 years from the sample date. 

(3) Corrective action records made 

under § 60.13(b) shall be retained for at 

least 2 years from the date of each 

corrective action. These records must be 

stored with the records of related 

sampling under § 60.12(h). 

(4) Written determination records 

received from a PLHCP under § 60.14(b) 

shall be retained for the duration of the 

miner’s employment plus 6 months. 

(5) Written medical opinion records 

received from a PLHCP or specialist 

under § 60.15(f) shall be retained for the 

duration of the miner’s employment 

plus 6 months. 

TABLE 1 TO PARAGRAPH (a)—RECORDKEEPING REQUIREMENTS

Record Section references Retention period 

1. Evaluation records .................................................. § 60.12(d) ....................................... At least 2 years from date of each evaluation. 

2. Sampling records .................................................... § 60.12(h) ....................................... At least 2 years from sample date. 

3. Corrective action records ........................................ § 60.13(b) ....................................... At least 2 years from date of each corrective action. 

4. Written determination records received from a 

PLHCP.

§ 60.14(b) ....................................... Duration of miner’s employment plus 6 months. 

5. Written medical opinion records received from a 

PLHCP or specialist.

§ 60.15(f) ........................................ Duration of miner’s employment plus 6 months. 

(b) Upon request from an authorized 

representative of the Secretary, from an 

authorized representative of miners, or 

from miners, mine operators shall 

promptly provide access to any record 

listed in this section. 

§ 60.17 Severability. 

Each section of this part, as well as 

sections in 30 CFR parts 56, 57, 70, 71, 

72, 75, and 90 that address respirable 

crystalline silica or respiratory 

protection, is separate and severable 

from the other sections and provisions. 

If any provision of this subpart is held 

to be invalid or unenforceable by its 

terms, or as applied to any person, 

entity, or circumstance, or is stayed or 

enjoined, that provision shall be 

construed so as to continue to give the 

maximum effect to the provision 

permitted by law, unless such holding 

shall be one of utter invalidity or 

unenforceability, in which event the 

provision shall be severable from these 


ddrumheller on DSK120RN23PROD with PROPOSALS2
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sections and shall not affect the 

remainder thereof. 

Subchapter O—Coal Mine Safety and 

Health 

PART 70—MANDATORY HEALTH 

STANDARDS—UNDERGROUND COAL 

MINES 

■ 8. The authority citation for part 70 

continues to read as follows: 

Authority: 30 U.S.C. 811, 813(h), 957. 

Subpart A—General 

§ 70.2 [Amended] 

■ 9. Amend § 70.2 by removing the 

definition of ‘‘Quartz’’. 

Subpart B—Dust Standards 

§ 70.101 [Removed and Reserved] 

■ 10. Remove and reserve § 70.101. 

Subpart C—Sampling Procedures 

■ 11. Amend § 70.205 by revising 

paragraph (c) to read as follows: 

§ 70.205 Approved sampling devices; 

operation; air flowrate. 

* * * * * 

(c) If using a CPDM, the person 

certified in sampling shall monitor the 

dust concentrations and the sampling 

status conditions being reported by the 

sampling device at mid-shift or more 

frequently as specified in the approved 

mine ventilation plan to assure: The 

sampling device is in the proper 

location and operating properly; and the 

work environment of the occupation or 

DA being sampled remains in 

compliance with the standard at the end 

of the shift. This monitoring is not 

required if the sampling device is being 

operated in an anthracite coal mine 

using the full box, open breast, or slant 

breast mining method. 

§ 70.206 [Removed and Reserved] 

■ 12. Remove and reserve § 70.206. 

§ 70.207 [Removed and Reserved] 

■ 13. Remove and reserve § 70.207. 

■ 14. Amend § 70.208 by: 

■ a. Removing and reserving paragraph 

(c); 

■ b. Revising paragraphs (d), (e) 

introductory text, (e)(2), (f), (g), (h) 

introductory text, (h)(2), (i) introductory 

text, and (i)(1); and 

■ c. Adding table 1. 

The revisions and addition read as 

follows: 

§ 70.208 Quarterly sampling; mechanized 

mining units. 

* * * * * 

(d) If a normal production shift is not 

achieved, the DO or ODO sample for 

that shift may be voided by MSHA. 

However, any sample, regardless of 

production, that exceeds the standard 

by at least 0.1 mg/m3 shall be used in 

the determination of the equivalent 

concentration for that occupation. 

(e) When a valid representative 

sample taken in accordance with this 

section meets or exceeds the ECV in 

table 1 to this section that corresponds 

to the particular sampling device used, 

the operator shall: 

* * * * * 

(2) Immediately take corrective action 

to lower the concentration of respirable 

dust to at or below the respirable dust 

standard; and 

* * * * * 

(f) Noncompliance with the standard 

is demonstrated during the sampling 

period when: 

(1) Three or more valid representative 

samples meet or exceed the ECV in table 

1 to this section that corresponds to the 

particular sampling device used; or 

(2) The average for all valid 

representative samples meets or exceeds 

the ECV in table 1 to this section that 

corresponds to the particular sampling 

device used. 

(g)(1) Unless otherwise directed by 

the District Manager, upon issuance of 

a citation for a violation of the standard 

involving a DO in an MMU, paragraph 

(a)(1) of this section shall not apply to 

the DO in that MMU until the violation 

is abated and the citation is terminated 

in accordance with paragraphs (h) and 

(i) of this section. 

(2) Unless otherwise directed by the 

District Manager, upon issuance of a 

citation for a violation of the standard 

involving a type of ODO in an MMU, 

paragraph (a)(2) of this section shall not 

apply to that ODO type in that MMU 

until the violation is abated and the 

citation is terminated in accordance 

with paragraphs (h) and (i) of this 

section. 

(h) Upon issuance of a citation for 

violation of the standard, the operator 

shall take the following actions 

sequentially: 

* * * * * 

(2) Immediately take corrective action 

to lower the concentration of respirable 

coal mine dust to at or below the 

standard; and 

* * * * * 

(i) A citation for a violation of the 

standard shall be terminated by MSHA 

when: 

(1) Each of the five valid 

representative samples is at or below the 

standard; and 

* * * * * 

TABLE 1 TO § 70.208—EXCESSIVE CONCENTRATION VALUES (ECV) BASED ON A SINGLE SAMPLE, THREE SAMPLES, OR

THE AVERAGE OF FIVE OR FIFTEEN FULL-SHIFT CMDPSU/CPDM CONCENTRATION MEASUREMENTS

Section Samples 

ECV (mg/m3) 

CMDPSU CPDM 

70.208 (e) ........................................ 70.100(a)—Single sample ......................................................................... 1.79 1.70 

70.100(b)—Single sample ......................................................................... 0.74 0.57 

70.208(f)(1) ...................................... 70.100(a)—3 or more samples ................................................................. 1.79 1.70 

70.100(b)—3 or more samples ................................................................. 0.74 0.57 

70.208(f)(2) ...................................... 70.100(a)—5 sample average ................................................................... 1.63 1.59 

70.100(b)—5 sample average ................................................................... 0.61 0.53 

70.208(f)(2) ...................................... 70.100(a)—15 sample average ................................................................. 1.58 1.56 

70.100(b)—15 sample average ................................................................. 0.57 0.52 

70.208(i)(1) ...................................... 70.100(a)—Each of 5 samples ................................................................. 1.79 1.70 

70.100(b)—Each of 5 samples ................................................................. 0.74 0.57 

■ 15. Amend § 70.209 by: 

■ a. Removing and reserving paragraph 

(b); 

■ b. Revising paragraphs (c) 

introductory text, (c)(2), (d), (e), (f) 

introductory text, (f)(2), (g) introductory 

text, and (g)(1); and 

■ c. Adding table 1. 

The revisions and addition read as 

follows: 


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45016 Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 

§ 70.209 Quarterly sampling; designated 

areas. 

* * * * * 

(c) When a valid representative 

sample taken in accordance with this 

section meets or exceeds the ECV in 

table 1 to this section that corresponds 

to the particular sampling device used, 

the operator shall: 

* * * * * 

(2) Immediately take corrective action 

to lower the concentration of respirable 

dust to at or below the respirable dust 

standard; and 

* * * * * 

(d) Noncompliance with the standard 

is demonstrated during the sampling 

period when: 

(1) Two or more valid representative 

samples meet or exceed the ECV in table 

1 to this section that corresponds to the 

particular sampling device used; or 

(2) The average for all valid 

representative samples meets or exceeds 

the ECV in table 1 to this section that 

corresponds to the particular sampling 

device used. 

(e) Unless otherwise directed by the 

District Manager, upon issuance of a 

citation for a violation of the standard, 

paragraph (a) of this section shall not 

apply to that DA until the violation is 

abated and the citation is terminated in 

accordance with paragraphs (f) and (g) 

of this section. 

(f) Upon issuance of a citation for a 

violation of the standard, the operator 

shall take the following actions 

sequentially: 

* * * * * 

(2) Immediately take corrective action 

to lower the concentration of respirable 

coal mine dust to at or below the 

standard; and 

* * * * * 

(g) A citation for a violation of the 

standard shall be terminated by MSHA 

when: 

(1) Each of the five valid 

representative samples is at or below the 

standard; and 

* * * * * 

TABLE 1 TO § 70.209—EXCESSIVE CONCENTRATION VALUES (ECV) BASED ON A SINGLE SAMPLE, TWO SAMPLES, OR THE

AVERAGE OF FIVE OR FIFTEEN FULL-SHIFT CMDPSU/CPDM CONCENTRATION MEASUREMENTS

Section Samples 

ECV (mg/m3) 

CMDPSU CPDM 

70.209 (c) ......................................... 70.100(a)—Single sample ......................................................................... 1.79 1.70 

70.100(b)—Single sample ......................................................................... 0.74 0.57 

70.209(d)(1) ..................................... 70.100(a)—2 or more samples ................................................................. 1.79 1.70 

70.100(b)—2 or more samples ................................................................. 0.74 0.57 

70.209(d)(2) ..................................... 70.100(a)—5 sample average ................................................................... 1.63 1.59 

70.100(b)—5 sample average ................................................................... 0.61 0.53 

70.209(d)(2) ..................................... 70.100(a)—15 sample average ................................................................. 1.58 1.56 

70.100(b)—15 sample average ................................................................. 0.57 0.52 

70.209(g)(1) ..................................... 70.100(a)—Each of 5 samples ................................................................. 1.79 1.70 

70.100(b)—Each of 5 samples ................................................................. 0.74 0.57 

Table 70—1 to Subpart C of Part 70 

[Removed] 

■ 16. Remove table 70–1 to subpart C of 

part 70. 

Table 70—2 to Subpart C of Part 70 

[Removed] 

■ 17. Remove table 70–2 to subpart C of 

part 70. 

PART 71—MANDATORY HEALTH 

STANDARDS—SURFACE COAL MINES 

AND SURFACE WORK AREAS OF 

UNDERGROUND COAL MINES 

■ 18. The authority citation for part 71 

continues to read as follows: 

Authority: 30 U.S.C. 811, 813(h), 957. 

Subpart A—General 

§ 71.2 [Amended] 

■ 19. Amend § 71.2 by removing the 

definition of ‘‘Quartz’’. 

Subpart B—Dust Standards 

§ 71.101 [Removed and Reserved] 

■ 20. Remove and reserve § 71.101. 

Subpart C—Sampling Procedures 

■ 21. Amend § 71.205 by revising 

paragraph (c) to read as follows: 

§ 71.205 Approved sampling devices; 

operation; air flowrate. 

* * * * * 

(c) If using a CPDM, the person 

certified in sampling shall monitor the 

dust concentrations and the sampling 

status conditions being reported by the 

sampling device at mid-shift or more 

frequently as specified in the approved 

respirable dust control plan, if 

applicable, to assure: The sampling 

device is in the proper location and 

operating properly; and the work 

environment of the occupation being 

sampled remains in compliance with 

the standard at the end of the shift. 

■ 22. Amend § 71.206 by: 

■ a. Removing and reserving paragraph 

(b); 

■ b. Revising paragraphs (e), (g), (h) 

introductory text, (h)(2), (i), (j), (k) 

introductory text, (k)(2), and (l); 

■ c. Removing tables 71–1 and 71–2; 

■ d. Revising paragraphs (m) and (n); 

and 

■ e. Adding table 1. 

The revisions and addition read as 

follows: 

§ 71.206 Quarterly sampling; designated 

work positions. 

* * * * * 

(e) Each DWP sample shall be taken 

on a normal work shift. If a normal work 

shift is not achieved, the respirable dust 

sample shall be transmitted to MSHA 

with a notation by the person certified 

in sampling on the back of the dust data 

card stating that the sample was not 

taken on a normal work shift. When a 

normal work shift is not achieved, the 

sample for that shift may be voided by 

MSHA. However, any sample, 

regardless of whether a normal work 

shift was achieved, that exceeds the 

standard by at least 0.1 mg/m3 shall be 

used in the determination of the 

equivalent concentration for that 

occupation. 

* * * * * 

(g) Upon notification from MSHA that 

any valid representative sample taken 

from a DWP to meet the requirements of 

paragraph (a) of this section exceeds the 

standard, the operator shall, within 15 

calendar days of notification, sample 

that DWP each normal work shift until 

five valid representative samples are 


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Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 45017 

taken. The operator shall begin 

sampling on the first normal work shift 

following receipt of notification. 

(h) When a valid representative 

sample taken in accordance with this 

section meets or exceeds the excessive 

concentration value (ECV) in table 1 to 

this section that corresponds to the 

particular sampling device used, the 

mine operator shall: 

* * * * * 

(2) Immediately take corrective action 

to lower the concentration of respirable 

coal mine dust to at or below the 

standard; and 

* * * * * 

(i) Noncompliance with the standard 

is demonstrated during the sampling 

period when: 

(1) Two or more valid representative 

samples meet or exceed the ECV in table 

1 to this section that corresponds to the 

particular sampling device used; or 

(2) The average for all valid 

representative samples meets or exceeds 

the ECV in table 1 to this section that 

corresponds to the particular sampling 

device used. 

(j) Unless otherwise directed by the 

District Manager, upon issuance of a 

citation for a violation of the standard, 

paragraph (a) of this section shall not 

apply to that DWP until the violation is 

abated and the citation is terminated in 

accordance with paragraphs (k) and (l) 

of this section. 

(k) Upon issuance of a citation for 

violation of the standard, the operator 

shall take the following actions 

sequentially: 

* * * * * 

(2) Immediately take corrective action 

to lower the concentration of respirable 

coal mine dust to at or below the 

standard; and 

* * * * * 

(l) A citation for violation of the 

standard shall be terminated by MSHA 

when the equivalent concentration of 

each of the five valid representative 

samples is at or below the standard. 

(m) The District Manager may 

designate for sampling under this 

section additional work positions at a 

surface coal mine and at a surface work 

area of an underground coal mine where 

a concentration of respirable dust 

exceeding 50 percent of the standard 

has been measured by one or more 

MSHA valid representative samples. 

(n) The District Manager may 

withdraw from sampling any DWP 

designated for sampling under 

paragraph (m) of this section upon 

finding that the operator is able to 

maintain continuing compliance with 

the standard. This finding shall be based 

on the results of MSHA and operator 

valid representative samples taken 

during at least a 12-month period. 

TABLE 1 TO § 71.206—EXCESSIVE CONCENTRATION VALUES (ECV) BASED ON A SINGLE SAMPLE, TWO SAMPLES, OR THE

AVERAGE OF FIVE FULL-SHIFT CMDPSU/CPDM CONCENTRATION MEASUREMENTS

Section Samples 

ECV (mg/m3) 

CMDPSU CPDM 

71.206(h) ...................................................................... Single sample ............................................................... 1.79 1.70 

71.206(i)(1) ................................................................... 2 or more samples ....................................................... 1.79 1.70 

71.206(i)(2) ................................................................... 5 sample average ......................................................... 1.63 1.59 

71.206(l) ........................................................................ Each of 5 samples ........................................................ 1.79 1.70 

Subpart D—Respirable Dust Control 

Plans 

■ 23. Amend § 71.300 by revising 

paragraph (a) introductory text to read 

as follows: 

§ 71.300 Respirable dust control plan; 

filing requirements. 

(a) Within 15 calendar days after the 

termination date of a citation for 

violation of the standard, the operator 

shall submit to the District Manager for 

approval a written respirable dust 

control plan applicable to the DWP 

identified in the citation. The respirable 

dust control plan and revisions thereof 

shall be suitable to the conditions and 

the mining system of the coal mine and 

shall be adequate to continuously 

maintain respirable dust to at or below 

the standard at the DWP identified in 

the citation. 

* * * * * 

■ 24. Amend § 71.301 by revising 

paragraph (a)(1) to read as follows: 

§ 71.301 Respirable dust control plan; 

approval by District Manager and posting. 

(a) * * * 

(1) The respirable dust control 

measures would be likely to maintain 

concentrations of respirable coal mine 

dust at or below the standard; and 

* * * * * 

PART 72—HEALTH STANDARDS FOR 

COAL MINES 

■ 25. The authority citation for part 72 

continues to read as follows: 

Authority: 30 U.S.C. 811, 813(h), 957. 

Subpart E—Miscellaneous 

■ 26. Revise § 72.710 to read as follows: 

§ 72.710 Selection, fit, use, and 

maintenance of approved respirators. 

Approved respirators shall be 

selected, fitted, used, and maintained in 

accordance with the provisions of a 

respiratory protection program 

consistent with the requirements, as 

applicable, of ASTM F3387–19. ASTM 

F3387–19, Standard Practice for 

Respiratory Protection approved August 

1, 2019, is incorporated by reference 

into this section with the approval of 

the Director of the Federal Register 

under 5 U.S.C. 552(a) and 1 CFR part 51. 

This material is available for inspection 

at the Mine Safety and Health 

Administration (MSHA) and at the 

National Archives and Records 

Administration (NARA). Contact MSHA 

at: MSHA’s Office of Standards, 

Regulations, and Variances, 201 12th 

Street South, Arlington, VA 22202– 

5450; 202–693–9440; or any Mine Safety 

and Health Enforcement District Office. 

For information on the availability of 

this material at NARA, visit 

www.archives.gov/federal-register/cfr/ 

ibr-locations.html or email 

fr.inspection@nara.gov. The material 

may be obtained from ASTM 

International, 100 Barr Harbor Drive, 

P.O. Box C700, West Conshohocken, PA 

19428–2959; www.astm.org/. 

■ 27. Revise § 72.800 to read as follows: 

§ 72.800 Single, full-shift measurement of 

respirable coal mine dust. 

The Secretary will use a single, fullshift measurement of respirable coal 

mine dust to determine the average 

concentration on a shift since that 

measurement accurately represents 

atmospheric conditions to which a 

miner is exposed during such shift. 

Noncompliance with the respirable dust 

standard, in accordance with this 

subchapter, is demonstrated when a 

single, full-shift measurement taken by 


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45018 Federal Register / Vol. 88, No. 133 / Thursday, July 13, 2023 / Proposed Rules 

MSHA meets or exceeds the applicable 

ECV in table 1 to § 70.208, table 1 to 

§ 70.209, table 1 to § 71.206, or table 1 

to § 90.207 of this chapter that 

corresponds to the particular sampling 

device used. Upon issuance of a citation 

for a violation of the standard, and for 

MSHA to terminate the citation, the 

mine operator shall take the specified 

actions in this subchapter. 

PART 75—MANDATORY SAFETY 

STANDARDS—UNDERGROUND COAL 

MINES 

■ 28. The authority citation for part 75 

continues to read as follows: 

Authority: 30 U.S.C. 811, 813(h), 957. 

Subpart D—Ventilation 

■ 29. Amend § 75.350 by: 

■ a. Revising paragraph (b)(3)(i); 

■ b. Removing paragraph (b)(3)(ii); and 

■ c. Redesignating (b)(3)(iii) as (b)(3)(ii). 

The revision reads as follows: 

§ 75.350 Belt air course ventilation. 

* * * * * 

(b) * * * 

(3) * * * 

(i) The average concentration of 

respirable dust in the belt air course, 

when used as a section intake air 

course, shall be maintained at or below 

0.5 milligrams per cubic meter of air 

(mg/m3). 

* * * * * 

PART 90—MANDATORY HEALTH 

STANDARDS—COAL MINERS WHO 

HAVE EVIDENCE OF THE 

DEVELOPMENT OF 

PNEUMOCONIOSIS 

■ 30. The authority citation for part 90 

continues to read as follows: 

Authority: 30 U.S.C. 811, 813(h), 957. 

Subpart A—General 

■ 31. Amend § 90.2 by revising the 

definition of ‘‘Part 90 miner’’ and 

removing the definition of ‘‘Quartz’’. 

The revision reads as follows: 

§ 90.2 Definitions. 

* * * * * 

Part 90 miner. A miner employed at 

a coal mine who has exercised the 

option under the old section 203(b) 

program (36 FR 20601 preview citation 

details, October 27, 1971), or under 

§ 90.3 to work in an area of a mine 

where the average concentration of 

respirable dust in the mine atmosphere 

during each shift to which that miner is 

exposed is continuously maintained at 

or below the standard, and who has not 

waived these rights. 

* * * * * 

■ 32. Amend § 90.3 by revising 

paragraph (a) to read as follows: 

§ 90.3 Part 90 option; notice of eligibility; 

exercise of option. 

(a) Any miner employed at a coal 

mine who, in the judgment of the 

Secretary of HHS, has evidence of the 

development of pneumoconiosis based 

on a chest X-ray, read and classified in 

the manner prescribed by the Secretary 

of HHS, or based on other medical 

examinations shall be afforded the 

option to work in an area of a mine 

where the average concentration of 

respirable dust in the mine atmosphere 

during each shift to which that miner is 

exposed is continuously maintained at 

or below the standard. Each of these 

miners shall be notified in writing of 

eligibility to exercise the option. 

* * * * * 

Subpart B—Dust Standards, Rights of 

Part 90 Miners 

§ 90.101 [Removed and Reserved] 

■ 33. Remove and reserve § 90.101. 

■ 34. Amend § 90.102 by revising 

paragraph (a) to read as follows: 

§ 90.102 Transfer; notice. 

(a) Whenever a Part 90 miner is 

transferred in order to meet the 

standard, the operator shall transfer the 

miner to an existing position at the same 

coal mine on the same shift or shift 

rotation on which the miner was 

employed immediately before the 

transfer. The operator may transfer a 

Part 90 miner to a different coal mine, 

a newly created position or a position 

on a different shift or shift rotation if the 

miner agrees in writing to the transfer. 

The requirements of this paragraph do 

not apply when the respirable dust 

concentration in a Part 90 miner’s work 

position complies with the standard but 

circumstances, such as reductions in 

workforce or changes in operational 

status, require a change in the miner’s 

job or shift assignment. 

* * * * * 

■ 35. Amend § 90.104 by revising 

paragraph (a)(2) to read as follows: 

§ 90.104 Waiver of rights; re-exercise of 

option. 

(a) * * * 

(2) Applying for and accepting a 

position in an area of a mine which the 

miner knows has an average respirable 

dust concentration exceeding the 

standard; or 

* * * * * 

Subpart C—Sampling Procedures 

■ 36. Amend § 90.205 by revising 

paragraph (c) to read as follows: 

§ 90.205 Approved sampling devices; 

operation; air flowrate. 

* * * * * 

(c) If using a CPDM, the person 

certified in sampling shall monitor the 

dust concentrations and the sampling 

status conditions being reported by the 

sampling device at mid-shift or more 

frequently as specified in the approved 

respirable dust control plan, if 

applicable, to assure: The sampling 

device is in the proper location and 

operating properly; and the work 

environment of the Part 90 miner being 

sampled remains in compliance with 

the standard at the end of the shift. This 

monitoring is not required if the 

sampling device is being operated in an 

anthracite coal mine using the full box, 

open breast, or slant breast mining 

method. 

■ 37. Amend § 90.206 by revising 

paragraphs (b) and (c) to read as follows: 

§ 90.206 Exercise of option or transfer 

sampling. 

* * * * * 

(b) Noncompliance with the standard 

shall be determined in accordance with 

§ 90.207(d). 

(c) Upon issuance of a citation for a 

violation of the standard, the operator 

shall comply with § 90.207(f). 

■ 38. Amend § 90.207 by: 

■ a. Removing and reserving paragraph 

(b); 

■ b. Revising paragraphs (c) 

introductory text, (c)(2), (d), (e), (f) 

introductory text, (f)(2) introductory 

text, (f)(2)(ii), and (g); 

■ c. Removing tables 90–1 and 90–2; 

and 

■ d. Adding table 1. 

The revisions and addition read as 

follows: 

§ 90.207 Quarterly sampling. 

* * * * * 

(c) When a valid representative 

sample taken in accordance with this 

section meets or exceeds the ECV in 

table 1 to this section corresponding to 

the particular sampling device used, the 

mine operator shall: 

* * * * * 

(2) Immediately take corrective action 

to lower the concentration of respirable 

coal mine dust to below the standard; 

and 

* * * * * 

(d) Noncompliance with the standard 

is demonstrated during the sampling 

period when: 

(1) Two or more valid representative 

samples meet or exceed the ECV in table 

1 to this section that corresponds to the 

particular sampling device used; or 

(2) The average for all valid 

representative samples meets or exceeds 


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the ECV in table 1 to this section that 

corresponds to the particular sampling 

device used. 

(e) Unless otherwise directed by the 

District Manager, upon issuance of a 

citation for a violation of the standard, 

paragraph (a) of this section shall not 

apply to that Part 90 miner until the 

violation is abated and the citation is 

terminated in accordance with 

paragraphs (f) and (g) of this section. 

(f) Upon issuance of a citation for a 

violation of the standard, the operator 

shall take the following actions 

sequentially: 

* * * * * 

(2) Immediately take corrective action 

to lower the concentration of respirable 

dust to below the standard. If the 

corrective action involves: 

* * * * * 

(ii) Transferring the Part 90 miner to 

another work position at the mine to 

meet the standard, the operator shall 

comply with § 90.102 and then sample 

the affected miner in accordance with 

§ 90.206(a). 

* * * * * 

(g) A citation for a violation of the 

standard shall be terminated by MSHA 

when the equivalent concentration of 

each of the five valid representative 

samples is below the standard. 

TABLE 1 TO § 90.207—EXCESSIVE CONCENTRATION VALUES (ECV) BASED ON A SINGLE SAMPLE, TWO SAMPLES, OR THE

AVERAGE OF FIVE FULL-SHIFT CMDPSU/CPDM CONCENTRATION MEASUREMENTS

Section Samples 

ECV (mg/m3) 

CMDPSU CPDM 

90.207(c) ....................................................................... Single sample ............................................................... 0.74 0.57 

90.207(d)(1) .................................................................. 2 or more samples ....................................................... 0.74 0.57 

90.207(d)(2) .................................................................. 5 sample average ......................................................... 0.61 0.53 

90.207(g) ...................................................................... Each of 5 samples ........................................................ 0.74 0.57 

Subpart D—Respirable Dust Control 

Plans 

■ 39. Amend § 90.300 by revising 

paragraphs (a) and (b)(3) to read as 

follows: 

§ 90.300 Respirable dust control plan; 

filing requirements. 

(a) If an operator abates a violation of 

the standard by reducing the respirable 

dust level in the position of the Part 90 

miner, the operator shall submit to the 

District Manager for approval a written 

respirable dust control plan for the Part 

90 miner in the position identified in 

the citation within 15 calendar days 

after the citation is terminated. The 

respirable dust control plan and 

revisions thereof shall be suitable to the 

conditions and the mining system of the 

coal mine and shall be adequate to 

continuously maintain respirable dust 

below the standard for that Part 90 

miner. 

(b) * * * 

(3) A detailed description of how each 

of the respirable dust control measures 

used to continuously maintain 

concentrations of respirable coal mine 

dust below the standard; and 

* * * * * 

■ 40. Amend § 90.301 by revising 

paragraphs (a)(1) and (b) to read as 

follows: 

§ 90.301 Respirable dust control plan; 

approval by District Manager; copy to part 

90 miner. 

(a) * * * 

(1) The respirable dust control 

measures would be likely to maintain 

concentrations of respirable coal mine 

dust below the standard; and 

* * * * * 

(b) MSHA may take respirable dust 

samples to determine whether the 

respirable dust control measures in the 

operator’s plan effectively maintain 

concentrations of respirable coal mine 

dust below the standard. 

* * * * * 

[FR Doc. 2023–14199 Filed 7–6–23; 11:15 am] 

BILLING CODE 4520–43–P 


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