NIOSH responses to the National Academies of Sciences, Engineering, and Medicine recommendations on Monitoring and Sampling Approaches to Assess Underground Coal Mine Dust Exposures

General Response to Comments

A common theme throughout the National Academy recommendations is the need for industry, labor, academia, manufacturers, and government to work together on investigations, research, training, and solutions development to address issues related to respirable coal mine dust exposure (RCMD). The NIOSH Mining Program has a long history of successful partnerships that have led to significant impactful solutions to pressing health and safety issues. NIOSH, in collaboration with the Mine Safety and Health Administration (MSHA), plans to establish a multi stakeholder Respirable Coal Mine Dust Partnership in the near future to share information and solutions. Recognizing that NIOSH is currently fully committed to an existing portfolio of health and safety research and has limited resources, including staff, funding, and facilities, in order to immediately add topics addressed in this response document, NIOSH will use the proposed partnership engage with other research groups (private or academic). These interactions will serve as an important input into NIOSH’s research priorities and efforts to develop an ongoing program.

NIOSH also intends to fully utilize its external contracts and grants program to address topics as appropriate to augment its intramural capabilities. The National Academies’ report was specifically referenced in the Fiscal Year 2019 Broad Agency Announcement (BAA) solicitation notice, identifying Recommendations 1, 2, 7, and 9 as focus areas, although proposals related to any of the other recommendations were also encouraged.

Recommendation 1

The National Institute for Occupational Safety and Health (NIOSH) and organizations, such as the National Mining Association and the unions representing miners, should conduct a comprehensive investigation to identify key challenges that coal mine operators face in implementing an optimal, beyond-compliance approach to RCMD exposure monitoring and sampling for informing exposure control efforts. The organizations conducting the investigation also should recommend practical solutions for overcoming those challenges.

Response

NIOSH has long sought a “beyond compliance” approach to RCMD exposure control efforts. The first underground implementation of a near-real time RCMD monitor was designed to be mounted on a continuous mining machine to provide the operator in one of the highest exposure occupations with immediate exposure feedback [Cantrell et al. 1997]. This effort had limited success, primarily due to the difference between a fixed sample and the operator’s exposure [Kissell and Thimons 2001; Kissell and Sacks 2002]. However, it led to the development of the first generation of the continuous personal dust monitor (CPDM), integrated with the miner’s cap lamp, to empower the individual to make informed decisions regarding RCMD exposure [Volkwein et al. 2004]. The CPDM (as a second-generation stand-alone unit) did not become a viable commercial product until promulgation of the 2014 MSHA dust rule, which required all active underground coal mines in the U.S. to use it for compliance sampling beginning in 2016. A number of factors, including high unit cost, preclude widespread use of the CPDM outside of compliance. Other factors that make “beyond compliance” use challenging include technical (size, weight, maintainability, etc.), commercial (market size, limited development/manufacturing interest), and human (operator and miner acceptance), many of which are interrelated. NIOSH has actively engaged with our stakeholders to address these issues.

While technical and commercial challenges will be addressed more directly in later responses, the human challenges remain the key to building practical solutions. With the first-generation CPDM, NIOSH conducted interviews with active CPDM users at four coal mines on how they used the CPDM information, leading to the development of a conceptual model on how miners interpret and respond to personal dust monitor (PDM) information [Peters 2008]. After passage of the MSHA dust rule, an additional follow-up examination of behavior changes for coal miners using the CPDM at six mines was conducted [Haas and Helton 2017; Haas and Colinet 2018]. Miners reported using CPDM output to track their dust exposures and implemented changes to control technologies and/or operating practices in order to lower their dust exposures. More than 99 percent of the coal mine dust samples (operator and MSHA) are meeting the new 1.5 mg/m3 dust standard, with notable dust reductions observed for the Designated Occupations (DOs) and Other Designated Occupations (ODOs). This is an indication that the CPDM and the MSHA compliance requirements have already had a positive effect on lowering coal miners’ dust exposure, although more work remains to be done.

NIOSH Plan

NIOSH has established partnerships for addressing mine worker health and safety challenges that solicit stakeholder input. Examples include the Refuge Alternatives and Rock Dust partnerships. NIOSH, in coordination with MSHA, plans to establish a Respirable Coal Mine Dust Partnership to examine current sampling practices and identify barriers to beyond-compliance sampling, among other issues, with the goal of developing potential solutions. Additionally, NIOSH plans a study on the 1% overexposures that occur while miners are wearing the CPDM to better understand the causes and possible preventions.

Recommendation 2

Conduct studies to evaluate the exposures of miners not wearing CPDMs to ensure that the approach of detecting and mitigating high-exposures for designated occupations reliably results in mitigating high exposures of all workers.

Response

Miners “not wearing CPDMs” at any particular time include those who are never required according to the regulations to wear them, and those who are required to wear them on a periodic basis but are not currently wearing one. The recent MSHA dust rule, as specified in 30 CFR § 70.208[1], requires sampling the Designated Occupations (DOs), which include the continuous miner and shearer operators for continuous mining and longwall sections, as well as the Other Designated Occupations (ODOs). The ODOs include roof bolter operators, face haulage personnel on blowing ventilation sections, and jacksetters. NIOSH has documented higher dust levels for these occupations during mining cycles, showing these ODO occupations have the potential for having higher dust exposures than the DOs during compliance sampling [Potts et al. 2011; Colinet et al. 2013].

Other occupations on the section such as mechanics, utility men, scoop operators, and face bosses move around in the face areas during production and may experience intermittent exposures to high dust levels during the shift because of their mobility around the production faces. Given their mobility, it may be difficult to correlate specific activities with high exposures, even if these individuals were to wear a CPDM or other continuous recording device, due to the intermittent exposure.

NIOSH Plan

Working with members of the planned Respirable Coal Mine Dust Partnership, NIOSH, in coordination with MSHA, will assess information gaps. NIOSH will use this discussion as an input into its research planning. Currently, NIOSH plans to conduct research to:

(1) verify that individuals identified as DO and ODO utilize the experience gained while wearing the CPDM to modify their exposure to RCMD even when not wearing the CPDM, (2) identify situations where increasing RCMD concentrations might occur that are a result of something outside of the miner’s immediate area/control and (3) conduct the exposure studies suggested under this recommendation to verify that the other mining occupations not included as DO or ODO are not exposed to respirable dust levels in excess of the applicable standard.

With regard to the non-DO/ODO employees, NIOSH has developed the Helmet-CAM for use in metal/nonmetal mining and processing operations to correlate exposure with activity [Cecala et al. 2013; Cecala et al. 2014]; that concept may have applicability. The Helmet-CAM concept has been successfully used in the metal/nonmetal industries to illustrate and train workers in utilizing better work habits to reduce their dust exposures; the technique merges real-time video files and data files from a continuous dust monitor by way of a NIOSH-developed software in order to identify dust generation associated with specific work tasks. While an MSHA-Approved version of the Helmet-CAM is not currently available for use in underground coal mines, intrinsically safe cameras used in the oil and gas industries might be used under an experimental permit. Following the same concept as the Hemet-CAM (video correlated to continuous monitoring), other methodologies, such as correlating the continuous mining machine power consumption, as a surrogate for video of the dust generation, with exposure as measured by the CPDM, might also be useful and more easily implemented.

[1] Code of Federal Regulations. See CFR in references. Dust standards are found in Subpart B, 70.100-101 and sampling procedures are outlined in Subpart C, 70.201 through 70.212.

Recommendation 3

NIOSH and MSHA should carry out a systematic examination of the content and implementation of training and education programs with respect to RCMD exposure. The examination should focus not simply on curricula, but also on the way adults learn. It should seek ways of implementing education and training programs in an effective and consistent manner across the coal mining industry. As a part of being effective, the programs should be relevant to all mine workers, not just the ones who wear CPDMs, as well as to operators and regulators. Programs should be assessed after they have been implemented for a few years to determine their overall effectiveness.

Response

NIOSH has been focused on identifying interventions that successfully reduce RCMD dust exposures and promoting implementation within the mining industry. These interventions include control technologies, work practices, training approaches, and timely and accurate monitoring of the mine environment to empower workers to identify and correct conditions that lead to overexposures. NIOSH promotes stakeholder adoption of control interventions through collaborations, presentations, publications, and workshops—with emphasis to date given to workshops. NIOSH conducted eight regional workshops (2009–2010 and 2014–2015) in cooperation with MSHA and four workshops in response to direct requests from stakeholders to transfer information on successful control interventions to the mining industry and directly to the mine workers. The NIOSH Information Circular 9517 (Best Practices for Dust Control in Coal Mining) [Colinet et al. 2010] is a resource for mine operators and miners. Stakeholder-requested workshops have to date been the primary NIOSH training and education resource related to reducing RCMD exposures.

NIOSH/MSHA Plan

NIOSH plans to build on our prior work through engagement with stakeholders in a Respirable Coal Mine Dust Partnership as well as through research efforts in training and organizational-level interventions. NIOSH, in collaboration with MSHA, will develop outreach programs, using a variety of methodologies that will focus on how to communicate the hazards of dust exposure, effectively implement and maintain dust control measures, and identify when overexposures might be occurring. Outreach will also communicate the availability and importance of participating in medical monitoring (the NIOSH Coal Workers’ Health Surveillance Program, or CWHSP) and job transfer (30 CFR Part 90) programs to regulators, operators, and both new and existing miners. On-the-job training and consistent communication from the organization will address management of potential overexposures, including rapid implementation of dust control measures, worker positioning, and use of personal protection options (respirator and airstream helmet) until effective environmental dust control measures are in place. NIOSH anticipates that by identifying and improving gaps in organizational processes, managers can take on a more adaptive role in preparing and supporting workers during the introduction of new technologies, engineering controls, and work practices. This enhanced level of preparedness will serve not only to help operations maintain lower levels of RCMD exposure but also will help them to respond with more ease to other mining innovations such as varying types of automation. NIOSH, in collaboration with MSHA, will assess the effectiveness of the Institute and Agency educational outreach efforts using specific tailored approaches. Depending on the type of effort, these evaluations of effectiveness might include pre- and post-test examinations, surveys addressing what knowledge was acquired and how it affected behaviors, customer satisfaction surveys, and other forms of feedback from stakeholders. Educational research, based on stakeholder input, will be focused on improving knowledge uptake and behavior change in areas where educational effectiveness evaluations suggest the need for better approaches.

Recommendation 4

NIOSH, in collaboration with the Mine Safety and Health Administration (MSHA), should evaluate whether the current relationship between the particle-size distributions of RCMD samples and particles deposited in the lung that are associated with or implicated in the development of coal mine dust lung diseases (CMDLD) is similar to the relationship established decades ago, when the monitoring devices used for sampling were first adopted. In studying the particle-size distribution in modern-mining RCMD samples and their relationship to the particles deposited in the lung, it is important to consider associations with or implications in the development of CMDLD.

Response

NIOSH previously examined the size distributions of dust at various locations in coal mines [Potts et al. 1990] and later examined how size distributions measured in respirable coal dust samples affect crystalline silica analyses [Page 2003]. More recently, the Alpha Foundation has funded a $1.8 million, three-year grant research project led by Dr. Robert Cohen, clinical professor of environmental and occupational health sciences at the University of Illinois at the Chicago School of Public Health. NIOSH is a partner to this effort, which examines characteristics of dust particles depositing in the lungs of contemporary mine workers (e.g., size, composition) and compares them with characteristics of particles found in lung samples from the 1990s and earlier obtained as part of the National Coal Workers’ Autopsy Study conducted by NIOSH. In addition, Virginia Tech has been examining the mineral constituents in RCMD samples from various mining regions in the U.S. [Phillips et al. 2018]. Thus, research work is continuing in this area to better understand this size distribution-response relationship.

NIOSH/MSHA Plan

NIOSH investigators, in collaboration with MSHA, are building upon these efforts by developing projects to evaluate the toxicity of contemporary RCMD in animal models of pneumoconiosis. NIOSH has also conducted surveillance examining chest radiographic patterns in underground coal miners that implicated crystalline silica exposure as contributing to higher prevalence of pneumoconiosis in coal mining areas previously described as “hot spots” in the United States [Laney et al. 2010; NIOSH 2011]. This research is currently being updated through 2018 and will soon be submitted for publication. Results also indicate that increasing prevalence of CMDLD related to high respirable crystalline silica exposures is a result of cutting rock in these regions of the country [Pollock et al. 2010; Laney et al. 2010; NIOSH 2011]. Thus, research work is in progress to better understand the respiratory toxicity of contemporary RCMD.

Recommendation 5

Develop a real-time crystalline silica monitor. As an interim measure, NIOSH should continue its efforts to develop an end-of-shift silica monitor.

Response

NIOSH included the development of a mass-based, real-time dust monitor to detect RCS as a focus area for the 2017 Broad Agency Announcement—solicitation BAA 2017-N-180452. No proposals were submitted in response to this solicitation, so NIOSH negotiated with the University of Illinois at Chicago to modify an existing contract to include respirable crystalline silica. Contract Number 200-2016-91153, “Miniaturized Wearable Personal Dust Exposure Monitor for Respirable and Alveolar Dust in Underground Coal Mines,” was modified on 08/02/2017 to include crystalline silica speciation. This contract was to provide a prototype miniature dust monitor that included crystalline silica speciation, however the technical issues associated with crystalline silica measurement, magnified by the miniaturization, could not be overcome. This contract has now been limited to respirable coal dust measurement.

NIOSH included a “next-generation” miniaturized personal dust monitor, a respirable crystalline silica monitor, or a combination of the two as focus areas in a 2018 Broad Agency Announcement—solicitation BAA 2018-N-67627. Six concept papers addressing these topics were received in response to this solicitation. Full proposals were requested from three firms; two proposals specified dust measurement only, with one proposal aimed at crystalline silica measurement.

NIOSH Plan

In September 2018, NIOSH awarded a contract to Thermo Fisher Scientific, a research and manufacturing organization, to develop a stand-alone, near real time, compliance grade crystalline silica dust monitor. Recent research [Wei et al. 2017] has successfully utilized commercially available quantum cascade laser (QCL) technology to quantify crystalline silica deposited on a gravimetric filter. However, the current QCL technology was developed for a benchtop application. The contract awardee plans to use the QCL as the basis for its sampling instrument while striving for reduced power consumption (battery operation), compact size, and resistance to vibration and ambient temperature variation.

NIOSH is continuing the development of a field-based respirable crystalline silica monitoring approach, as an engineering tool, that will allow for direct-on-filter end-of-shift assessment of the exposure of miners at mines that elect to do non-regulatory gravimetric sampling for crystalline silica. The approach uses portable, commercially available, Fourier transform infrared spectrometers (FTIR) [Cauda et al. 2016a; Cauda et al. 2016b; Cauda et al. 2017] to analyze dust samples collected on gravimetric filters. To facilitate field implementation, NIOSH established a Cooperative Research and Development Agreement (CRADA) with Zefon International for the development of a sampling cassette that minimizes filter handling and allows for simplified insertion into the FTIR analyzer. This cassette became commercially available in August 2018. In addition, NIOSH developed a software package that transforms the raw data from the FTIR units into crystalline silica exposure information. This software was released in October 2018; although the software was released in beta form, it is available for immediate operator use.

Recommendation 6

NIOSH should continue to facilitate the development of a less costly and less ergonomically stressful real-time RCMD monitoring device that would facilitate the use of the personal monitors for engineering studies and other purposes in addition to compliance monitoring. As part of that effort, NIOSH should incorporate appropriate filter media that is compatible with an end-of-shift analyzer for respirable crystalline.

Response

As noted in the response to Recommendation 5, work had been initiated in 2016 under Contract Number 200-2016-91153, “Miniaturized Wearable Personal Dust Exposure Monitor for Respirable and Alveolar Dust in Underground Coal Mines” with the University of Illinois at Chicago (UIC); this unit is intended to be a miniaturized wearable respirable dust exposure monitor for underground coal mines. While the contract was modified on 08/02/17 to include respirable crystalline silica speciation and was scheduled for completion on 08/30/2019, NIOSH now anticipates that research-grade pre-commercialization prototypes without crystalline silica measurement will be developed. The unit is intended to be a mass-based respirable coal dust monitoring unit that is more economical, smaller, lighter, and in an improved ergonomic form factor compared to the existing available unit. Depending on the viability of the prototype, NIOSH will determine to fund further work to move this concept forward.

As also noted in the response to Recommendation 5, NIOSH included a “next-generation” miniaturized personal dust monitor in one of the focus areas in our 2018 Broad Agency Announcement—solicitation BAA 2018-N-67627. Two full proposals were requested pertaining to dust measurement only.

NIOSH Plan

In September 2018, NIOSH awarded a contract to Thermo Fisher Scientific to develop the next generation of the current CPDM. As stated by Thermo, “Since the TEOM [tapered element oscillating microbalance] is a direct mass measurement device that has already been proven to provide accurate in-mine measurement results, this solution will allow a quicker time to commercialization for a next generation instrument than new approaches that have not been proven in the underground coal mine environment.” The next-generation unit would be of a reduced size, weight, and noise level. Additional goals with the next-generation sampler would be to make further improvements regarding temperature control and instrument run time, and to address any additional industry concerns with the current CPDM.

NIOSH also awarded a contract in September 2018 to Biomarine, Inc., a research/manufacturing organization, for the development of a different type of sensor for use in the miniaturization and cost reduction of an underground continuous personal dust monitor. The contractor anticipates that a commercial unit would be smaller, lighter, and quieter than the existing CPDM. However, with the use of a piezoelectric film for determining dust mass, a successful prototype instrument would need to undergo extensive testing similar to the original CPDM to demonstrate compliance-grade accuracy in mining environments before it can be approved as a sampling device according to 30 CFR part 74.

NIOSH has included the design of a real-time RCMD monitoring device that would facilitate the use of the personal monitors for non-compliance engineering studies and other purposes in its BAA solicitation for FY2019.

Recommendation 7

Explore the broader use of area monitoring devices for gathering trend information on RCMD concentrations and particle characteristics in underground mines.

Response

The U.S. Bureau of Mines (USBM) had a long history of developing continuous recording mine instruments for area monitoring in underground coal mines [Lilienfeld 1974; Lilienfeld et al. 1983; Quackenbos and Tiani 1982]. Research has shown that there is a lack of correlation between area monitoring and the mining machine operators’ exposures due to environmental dust gradients present in coal mines [Kissell and Sacks 2002]. USBM and NIOSH have successfully used area sampling methods for conducting engineering control studies of respirable dust sources in underground coal mines and examining the size characteristics and quartz content of the dust [Potts et al. 1990; Organiscak et al. 1990; Page 2003; Kissell 2003; Colinet et al. 2010]. However, most of this dust sampling has been gravimetrically based because of sampler permissibility in coal mines—i.e., sampling has been limited to Coal Mine Dust Personal Sampler Units (CMDPSUs), PDMs, and Marple 298 personal impactors. Permissible light-scattering instruments were also used to examine shorter-term mining activities in conjunction with CMDPSUs to achieve a more accurate calibration of the light-scattering instruments’ instantaneous outputs, which are affected by such factors as size distributions and dust refractive index [Williams and Timko 1984; Listak et al. 2007].

Given the inaccuracy of area sampling for measuring the exposure of mining machine operators in coal mines and consistent with other recommendations [U.S. Department of Labor 1996], a personal dust monitor (Thermo Fisher Scientific PDM Model 3600) was developed to provide an end-of-shift respirable dust exposure measurement to the miner based on mass [Kissell and Sacks 2002; Volkwein et al. 2006]. The modified version of this sampler, the PDM Model 3700, has been approved for compliance dust sampling under MSHA’s new dust rule. Although more sophisticated laser particle counting and aerodynamic sizing instruments are commercially available for examining dust sizes and concentrations, none are permissible for underground coal mine use. Pursuing MSHA permissibility approval for underground coal mine use may not be attractive to manufacturers given the small market sector.

NIOSH Plan

As noted in responses to Recommendations 5 and 6, NIOSH is pursuing the development of lower-cost dust monitors that could facilitate area monitoring by mining companies. Given that past research has shown a lack of correlation between area monitoring and individual exposures due to environmental dust gradients present in coal mines, NIOSH feels that the primary approach is to focus on worker exposure rather than area monitoring. However, the use of area sampling technology to gather data on particle size distributions rather than exposures will also be assessed.

Recommendation 8

Conduct a systematic evaluation of changes in mining technology and activities to determine the extent to which those changes have caused increased extraction of rock and the extent to which past rock extraction has been co-located with disease hot spots. The evaluation should identify important focus areas for optimal sampling and monitoring strategies in the future.

Response

In 2005, NIOSH published information indicating that a greater prevalence of rapidly progressive CWP was clustered in central Appalachia [Antao et al. 2005]. As a follow-up, NIOSH examined MSHA data on some of the mines with dust compliance issues in the central Appalachia “hot spot” areas and additionally conducted field studies within a limited number of these mines to examine their operating conditions, dust controls, and dust/ crystalline silica levels generated [Pollock et al. 2010]. Mines cutting 20%-30% of roof rock and having difficulty maintaining compliance with reduced dust standards were not adequately applying proper dust control practices. Other mines using proper dust control practices were able to comply with stricter quartz standards when cutting significant amounts of rock. In the previous decade, improved coal preparation plant efficiencies, higher coal prices, and larger-horsepower mining machines provided the impetus to economically mine high percentages of rock in these thinner coal seams.

These findings are consistent with feedback from evaluations of case clusters of Appalachian miners with severe pneumoconiosis in Kentucky [Blackley et al. 2016] and Virginia [Reynolds et al. 2018]. Cutting rock (including slope development to coal seams using continuous mining machines), working downwind of dust-generating equipment (i.e., operation of a roof bolting machine in potentially dusty air), non-adherence to mine ventilation plans (including dust controls), and improper sampling of respirable coal mine dust exposures were identified as hazardous situations that may have contributed to the development of severe respiratory disease in these miners.

Another issue examined by NIOSH was the administration of MSHA’s dust regulations in effect since 1969 to address elevated quartz levels. This regulation required the determination of a reduced dust standard (10/% quartz) when the percentage of quartz in the sample exceeded 5%. With a permissible exposure limit of 2.0 mg/m3, this regulation was designed to effectively limit worker exposures below 100 µg/m3 quartz. A NIOSH study showed that the reduced dust standard determinations due to elevated quartz were not always providing the protection as intended [Joy 2012]. Mines that must comply with a reduced respirable dust standard and still exceed 100 ug/m3 quartz are subject to having the dust standard further reduced. In addition, determining quartz percentages from lower mass filters increases the propagation of errors into the quartz percentage determination [Page 2003].

NIOSH Plan

Examination of current mining activities regarding rock extraction during coal mining is warranted and will be included in NIOSH’s future respirable coal mine dust research proposals. Stakeholder partnerships, as described in Recommendation 1, will be an important input. The work by Joy referenced above covered the years through 2008 and will be extended to include current data to see if trends have changed over time.

Recommendation 9

NIOSH should conduct or facilitate a comprehensive assessment of RCMD particle characteristics, including their variability, to help target future exposure studies, because different particle characteristics (for example, composition and surface area) can pose different health hazards. In addition, the assessment should characterize and quantify important source contributions to airborne RCMD, including rock dusting and extraction of rock strata adjacent to the mined coal seam. To the extent possible, NIOSH should assess how RCMD characteristics have changed over time and make provisions for tracking temporal trends in the future. Further research and development are needed to improve analytic methods for evaluating source contributions of RCMD.

Response

NIOSH has a long history of identifying chemical and physical characteristics of RCMD that determine their toxicity. In 1997, NIOSH published a report evaluating aluminosilicate clay surface coating of particles with high crystalline silica content from 12 coal mine dust samples using multiple-voltage scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) [Harrison et al. 1997]. Significantly lower frequencies of these particles in anthracite dusts showed evidence of aluminosilicate surface occlusion than was observed in bituminous dusts. Subsequently, NIOSH performed a similar evaluation of dusts collected in conjunction with an epidemiological evaluation of silicosis risk in Chinese tin and tungsten miners and pottery workers [Harrison et al. 2005]. Lower frequencies of aluminosilicate surface occlusion were found in silica particles within tungsten and tin mine dusts relative to pottery dusts. It was speculated that greater surface occlusion of silica particles from pottery dusts was responsible for lower risk per unit of cumulative respirable crystalline silica exposure and that this phenomenon delayed onset of disease in pottery workers relative to tungsten and tin miners. It was also speculated that earlier findings on coal mine dusts might account for greater risks of progressive massive fibrosis associated with high-rank coal mine dust. The proposed mechanism was that aluminosilicate clay coating of crystalline silica particles altered biological interactions, causing them to behave more like clay particles than crystalline silica particles. The authors also raised the question of whether such coatings would have long-term durability after deposition of coated particles in the lung [Harrison et al. 2005]. NIOSH has also characterized limestone and marble rock dusts used in explosion suppression in underground coal mines and found that quartz content in the respirable size aerosolized fraction was enhanced relative to the bulk material [Soo et al. 2016].

NIOSH Plan

Current investigations of the physical and chemical characteristics of RCMD underway by NIOSH include scanning electron microscopy coupled with energy-dispersive x-ray spectrometry (SEM-EDX). SEM-EDX characterizes the shape and elemental composition of individual particles. This approach is particularly useful in that it reveals the variations in these parameters, not just an average over a large number of particles. This method is also used to determine if quartz particles are occluded.

Thermogravimetric analysis (TGA) techniques are also being used currently by NIOSH to examine coal, carbonate, and non-carbonate mineral mass fractions on coal mine dust filters [Phillips et al. 2018; Barone et al. 2016]. Automation of these techniques is being pursued to help develop coal mine dust data bases in assessing particle size and mineral content relationships.

These current investigations should assist in evaluating temporal changes going forward. In addition, NIOSH has a large number of gravimetric filter samples in storage dating from 2001 (although the majority are from the current decade). These filters are currently being inventoried and further analysis is planned to give insight into historical data.

In addition, as previously noted, NIOSH is collaborating with investigators funded by the Alpha Foundation to examine characteristics of the size and composition of dust particles depositing in the lungs of contemporary mine workers (e.g., dimensional characteristics, mineral composition, crystalline habit). Furthermore, these particle characteristics will be compared to those of particles deposited in lungs of coal miners obtained at autopsy in past decades. The results of this study will provide important clues about RCMD characteristics associated with the risk of respiratory disease and how those characteristics have changed over time.

The pairing of chemical and physical characterization of RCMD particles with ongoing epidemiological data will enhance NIOSH’s ability to identify and ameliorate the fundamental causes of CWP and other dust-induced occupational diseases.

Recommendation 10

Link medical surveillance programs directly with exposure monitoring programs and integrate health-related data on active and retired mine workers. 

Response

One of the most challenging barriers to this recommendation is that lifetime exposures of individual coal miners cannot be quantified given that compliance samples are environmental samples for certain mining occupations. Not all occupations are required to be sampled. In addition, quantitative differences between exposures measured for compliance purposes and exposures measured for research purposes can be sufficiently great so as to bias or even obscure exposure-response relationships in epidemiological studies [Seixas et al. 1990]. Other challenges include the relatively low frequency of required quartz sample analysis and unquantified full-shift exposures before the 2014 dust rule (8-hr versus full-shift sampling).

NIOSH Plan

Scientifically reliable assessment of true exposures requires a rigorous approach that might be feasible for a defined research study, but will not be feasible or sustainable over time in routine work settings. For this reason, at the population level, it is best to use surveillance as a means to assess whether prevention efforts are working and to better target prevention efforts. In order to link actual contemporary exposures with health effects, it would be best to carry out a rigorous, well-designed, and carefully executed epidemiological investigation. However, it would be very costly to carry out such a study and it is unclear that the results would provide benefits commensurate with the cost. This topic will be included as part of our Partnership agenda for further discussion.

Recommendation 11

Elucidate factors that act as disincentives for participation in the voluntary portions of the NIOSH medical surveillance programs and in the MSHA Part 90 Program, with the goal of addressing those disincentives and improving participation rates.

Response

Participation in the NIOSH Coal Workers’ Health Surveillance Program (CWHSP) during 2000–2016 was 40.1%. Miners working in central Appalachian states were less likely to participate in radiographic surveillance compared to miners working in other states (21.6% vs. 66.8%), suggesting that region-specific factors acting as disincentives may be playing a role [Reynolds et al. 2017]. In order to identify ways to improve participation in these programs, NIOSH requested information on barriers to participating in health screening offered by the CWHSP from coal miners, miner advocates, unions, industry stakeholders, and other interested parties through a Request for Information (RFI) posted to the Federal Register; eight comments were received in response to this notice. Responses received suggest that miners’ concerns about confidentiality and the impact of their health status on employability in coal mining are important disincentives to participation in surveillance. In addition, some miners feel that they would have to keep working even if they were found to have a disease due to lack of other employment options with comparable pay and benefits.

Participation in the CWHSP determines eligibility for the Part 90 transfer program. A recent NIOSH report [Reynolds et al. 2017] found that 14.4% of eligible miners exercised their Part 90 option, which was generally consistent with historical evaluations of Part 90 participation [Hoffman 1986; Spieler 1989]. Miners working in central Appalachian states were less likely to exercise their Part 90 option compared to miners working in other states (13.1% vs. 17.4%), suggesting that region-specific disincentives may exist. Regardless, national participation in Part 90 remains low irrespective of region. Formal assessments of eligible but non-participating miners regarding their lack of Part 90 program participation have not been conducted for approximately 30 years. However, as previously noted, NIOSH has received feedback from some miners that they would keep working even if found to have a disease due to lack of other desirable employment options.

NIOSH Plan

NIOSH will continue outreach efforts, providing surveillance services directly by NIOSH mobile medical units as a potential way to overcome miners’ concerns about the privacy of health information obtained by medical clinics contracted through their employers. NIOSH will also continue public health communications efforts to raise awareness of respiratory disease caused by coal mine dust and the importance of primary and secondary prevention. In addition, NIOSH will conduct research to further elucidate factors that act as disincentives for participation in voluntary screening (CWHSP) and job transfer (Part 90) programs offered to U.S. coal miners, with the ultimate goal of improving participation rates.

Recommendation 12

Conduct a comprehensive assessment of the requirements for exposure monitoring, including RCMD and silica mass content, and medical surveillance as well as the implementation of those requirements in major coal-producing countries. The assessment should identify opportunities for data harmonization and the use of that data for improving exposure monitoring approaches and conducting epidemiologic research.

Response

The diversity of sampling instrumentation, permissible exposure limits, sampling procedures, and medical surveillance between major coal-producing countries provides challenges to effective data harmonization and epidemiologic studies. While some studies are available [Joy et al. 2012; Han et al. 2018], an initial assessment suggests that the scientific literature provides limited information on legal requirements and methods for exposure monitoring and medical surveillance in other coal-producing countries.

NIOSH Plan

Data sharing and input directly from international partners would be required to initiate a research effort into exposure monitoring and medical surveillance requirements and practices in other countries. NIOSH plans to reach out to international partners to gather information that might be useful to improving miner’s respiratory health in the U.S.

Recommendation 13

NIOSH, MSHA, and other organizations should set priorities for addressing the committee’s recommendations and develop a strategy for addressing them. Federal agencies should provide the capability for research to be conducted in an experimental underground mine. Federal, academic, and coal mine industry researchers should seek opportunities for conducting collaborative research and development activities.

Response

The NIOSH Mining Program periodically reviews research efforts and results with the Mining Safety and Health Research Advisory Committee (MSHRAC). This committee provides input that helps guide future research efforts of NIOSH. Recommendations from the NAS report will be discussed at the next MSHRAC meeting for input from the committee. NIOSH is currently pursuing the acquisition of property that would be used for the development of an experimental underground mine.

NIOSH Plan

Developing a Respirable Coal Mine Dust Partnership (as discussed under Recommendation 1) will create a space to share information and solutions for RCMD exposure monitoring and control. NIOSH is funding research to make technical improvements to the CPDM to make it smaller, lighter, and quieter, in addition to researching alternative mass-based instruments. NIOSH is also working to improve technology for rapid determination of respirable crystalline silica (quartz) exposures. NIOSH will continue to assess barriers to participation in health surveillance and work to improve participation.

References

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