Based on discussions in the previous chapters of this report, this chapter presents overall conclusions for trends in disease epidemiology and mining practices and the specific items listed in the committee’s statement of task (see Appendix A). The chapter also recommends research and development activities to address important information gaps regarding monitoring and sampling approaches for controlling mine workers’ exposure to respirable coal mine dust (RCMD).
Conclusion 1.1: The purpose of the Federal Coal Mine Health and Safety Act of 1969 was to protect the health and safety of the nation’s coal miners. The regulatory focus on controlling the RCMD mass concentration and silica-mass concentration has not changed over the past several decades. That approach has been associated with a substantial decline in rates of coal workers’ pneumoconiosis (CWP) from 1970 to 2000 across all coal mining regions in the United States. However, since around the year 2000, an increase in cases of rapidly progressive pneumoconiosis has been observed in various hot-spot geographic areas. (see Chapter 1)
Conclusion 1.2: Changes in mining practices and conditions (for example, increases in equipment size and horsepower and mining increasingly thinner coal seams) have resulted in an increased extraction of rock. Crystalline silica, silicates, and other RCMD components contributed by rock extraction likely play an important role in relationships between exposure and health outcomes. (see Chapter 1)
Conclusion 1.3: The requirements of the 2014 dust rule that went into effect on February 1, 2016, lowered the allowable airborne RCMD mass concentration in underground mines. However, most miners incurred much of their exposures when previous regulations were in effect. Given that the latency period of CWP disease onset is typically 10 or more years, sufficient time has not elapsed to assess the effect of the 2014 dust rule on disease incidence. It is important to note, that compliance with regulatory requirements by itself is not an adequate indicator of the rule’s effectiveness in protecting miners’ health. (see Chapter 1)
Conclusion 2.1: Continuous personal dust monitors (CPDMs) are being used to comply with the monitoring and sampling requirements of the 2014 dust rule. The ability to measure exposures in near real time by using CPDMs is an important technologic advancement compared to monitoring methods used previously. If a measurement collected over a full shift exceeds allowable limits, mine operators must take corrective actions immediately. In addition, miners wearing CPDMs receive information about their personal exposures and sometimes can modify their activities or locations within a mine in response to elevated readings. (see Chapters 1 and 4)
Conclusion 2.2: CPDMs worn by individual miners in designated occupations are used to determine whether mine operators maintain RCMD concentrations at or less than the allowable exposure concentration. However, only a small fraction of coal miners are required to use a CPDM during any given shift, and it is possible that those coal miners using the CPDMs are not representative of the dust exposure to other miners who are not using the CPDMs. When miners wearing CPDMs react to high monitor readings to reduce their personal dust exposure (for example, by altering their locations while carrying out their job duties), the required RCMD measurements might no longer be representative of the miners with the highest exposures. Whether demonstrations of compliance with allowable RCMD exposure concentration are being achieved only for those miners wearing the CPDM, or for all personnel in the work area, is unknown. (see Chapter 4)
Conclusion 2.3: Changes in mining technologies during the past several decades might have led to changes in typical particle-size distributions of RCMD. If so, there might have been a change in the relationship between CPDM measurements of RCMD mass concentrations and the health effects associated with particle type, size, concentration, and deposition, in the lung. (see Chapters 1 and 4)
Conclusion 3.1: The primary impetus for optimal sampling and monitoring strategies is the protection of worker health through reduction in disease risk. The strategies are conceived to enhance the reduction of health risks in recognition of practical constraints (such as costs, availability of technology, existing regulatory requirements, and program acceptance by various stakeholders). (see Chapter 5)
Conclusion 3.2: Optimal sampling and monitoring strategies manifest as programs that, in principle, exhibit these attributes:
- Aiding mine operators’ decision making related to reducing RCMD exposures in a maintainable manner with data that are representative of high-exposure episodes and cumulative exposures over the long-term for all workers throughout the mine, not only the ones wearing a monitoring instrument.
- Supporting the decision-making ability of individual mine workers to protect themselves through training in the use of CPDMs and education concerning important factors that affect exposure-response relationships.
- Monitoring characteristics of RCMD particles that are directly related to the risk of occupational cardiopulmonary disease. Using appropriate tools and methods to collect samples that are representative of the dust to which mine workers are or may be exposed.
- Applying various monitoring technologies in engineering studies of RCMD exposure variability and exposure mitigation approaches.
- Integrating RCMD monitoring data with associated contextual information, such as sampling locations and frequencies, environmental and operational conditions during sampling and other periods, and general knowledge of the health risks associated with the RCMD exposure metrics being monitored.
- Involving a suitable and acceptable system of medical surveillance that provides regular, no-cost medical examinations for all miners to help assess the efficacy of exposure reduction efforts.
- Making integrated data readily available, accessible, and usable for timely decision making.
- Striving for continuous improvement in disease risk reduction, including periodic performance review and necessary modifications, and reaction to changes that remove or eliminate previous constraints. (see Chapter 5)
Conclusion 4.1: Measurements of airborne RCMD concentrations include respirable rock dust particles, by definition. However, it appears that complying with the rock-dusting requirements (30 Code of Federal Regulations [CFR] 75.2 and 30 CFR 75.402-403) has not been a large obstacle to demonstrating compliance with the 2014 dust rule. It is critical that efforts to comply with the rock-dusting requirements and RCMD requirements not compromise the effectiveness of either explosion mitigation or RCMD exposure reduction. (see Chapter 2)
Conclusion 5.1: Differences in exposure monitoring and sampling approaches among major coal-producing countries make it difficult to compare exposure measurements among different countries directly. Despite those differences, there are important commonalities, such as using gravimetric sampling devices to monitor mass concentrations of RCMD and silica. Those commonalities point to potential opportunities for harmonizing monitoring data collected in different countries, including RCMD and silica content. Additionally, a more complete understanding of international approaches to medical surveillance for coal mine dust diseases, including strengths and limitations, would lead to opportunities for improved understanding of the relationships between RCMD exposure and disease prevalence and ensuring that monitoring approaches are targeting the most important aspects of RCMD exposures. (see Chapter 3)
Conclusion 5.2: The various approaches to medical surveillance among coal-producing countries warrant an in-depth and appropriately critical analysis, which was beyond the scope of this report. Such an analysis would provide insight into the country-specific prevalence of RCMD-related diseases over time and would inform an understanding of the success of various strategies for monitoring and controlling exposures. (see Chapter 3)
The statement of task asked the committee to identify important research gaps regarding monitoring and sampling protocols for controlling miners’ RCMD exposures. The recommendations provided in this section include research and development activities to address the gaps identified by the committee. It is important to note, however, that the committee makes no recommendation concerning the requirements of the 2014 dust rule or the implementation of those requirements.
Challenges in Implementing Optimal Monitoring and Sampling Practices
Historically, the primary focus of RCMD sampling and monitoring efforts had been based on compliance with federal regulations. Additional sampling efforts were undertaken by coal mine operators to support improvements in mine ventilation and other dust controls, for instance to resolve noncompliance conditions. Over three decades, the compliance-driven approach led to a significant reduction in the rates of lung diseases associated with occupational exposure to RCMD among U.S. coal miners. However, it has not resulted in attainment of the ultimate goal of the Coal Mine Health and Safety Act of 1969, which is to eliminate such diseases. To continue progress toward reaching this goal, a fundamental shift is needed in the way that coal mine operators approach RCMD control, and thus sampling and monitoring.
Relative to the findings in this report, it is clear that an optimal sampling and monitoring strategy needs to support RCMD control efforts that go beyond compliance with regulations. This report offers a detailed discussion of various components that might comprise such a strategy, and
it identifies several possible challenges to implementation. It is important to note that the coal mine industry has faced similar challenges previously in the realm of beyond-compliance efforts. Most notably, the industry has worked for widespread adoption of a comprehensive safety management systems approach for pursuing the goal of zero accidents and injuries. As part of that approach, the industry recognized compliance as only a starting point in an effective process of safety risk management.
Recommendation 1: The National Institute for Occupational Safety and Health (NIOSH) and other 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. (see Chapter 5)
Consideration of All Miners’ Exposures
RCMD Exposures of Mine Workers Not Wearing CPDMs
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. (see Chapters 4 and 5)
Consistency and Effectiveness of Worker Training and Education Programs Across the Coal Industry Regarding RCMD Exposures
Training in the use of CPDMs and education concerning important factors that affect exposure-response relationships can enhance workers’ ability to take precautions that reduce RCMD exposures. It is important to ensure that training and education programs are implemented in a consistent manner across the coal mining industry.
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. (see Chapters 4 and 5)
Particle Size Distribution Represented by Cyclone Sampler Data
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. (see Chapter 4)
Real-Time Monitoring of Crystalline Silica
The health hazards posed by crystalline silica exposure warrant greater focus on developing improved sampling and monitoring techniques.
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. (see Chapter 5)
Disincentives for Mine Operators’ Use of Personal Monitoring Devices for Engineering Studies
Although CPDMs have the potential to be used by operators for engineering studies of exposure mitigation approaches, the predominant use is for determining regulatory compliance by providing end-of-shift readings. Disincentives for nonregulatory applications include the size and cost of the device, and requirements to notify MSHA in advance of using the CPDM for purposes other than determining compliance.
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. (see Chapters 4 and 5)
RCMD Spatial and Temporal Information
Area monitoring, which involves the use of measurement devices at fixed locations in underground mines, is critical for understanding environmental and operational factors that influence the concentration and particle characteristics of RCMD.
RCMD Exposure and Disease Rates
Association of Changes in Mining Technology and Activities with the Occurrence of Disease Hot Spots
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 had been co-located with disease hot spots. The evaluation should identify important focus areas for optimal sampling and monitoring strategies in the future. (see Chapters 1 and 5)
Key Characteristics of RCMD Particles to Be Monitored by Future Exposure Studies
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 consider making provisions for tracking temporal trends in the future. Further research and development are needed to improve analytic methods for evaluating source contributions of RCMD. (see Chapter 5)
Efficacy of Exposure Reduction Efforts in Reducing Disease Risks
No specific medical treatment is effective in reversing coal mine dust lung diseases or in controlling disease progression. Consequently, efforts to minimize RCMD exposure along with medical surveillance for early disease detection and removal from exposure are the mainstays in protecting a miner’s health.
Since around the year 2000, an increase in cases of rapidly progressive pneumoconiosis observed in various hot-spot geographic areas points to a need for an in-depth evaluation to identify key risk factors, some of which might be more strongly associated with certain RCMD components rather than RCMD mass concentration.
Medical surveillance of miners that includes comprehensive occupational histories containing details of mining processes and exposures (for example, chronology of specific mine employment, duration of work at the coal face, job titles and duties, and use of respiratory protection) is an important tool for understanding disease trends and risk factors and assessing the efficacy of exposure monitoring and reduction efforts.
Disincentives for Participation in Voluntary Medical Surveillance
The lack of worker participation in medical surveillance impairs the effectiveness of that tool for assessing the efficacy of exposure reduction efforts.
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. (see Chapters 1 and 5)
Opportunities for Using Data from Coal-Producing Countries for Epidemiologic Research
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. (see Chapter 3)
Research Capacity and Resources
Reliable information on RCMD exposures in underground coal mines is crucial for predicting, reducing, and preventing miners’ disease risks. As the committee has identified a number of important information needs, NIOSH and other organizations clearly will need sufficient capacity and resources to carry out the recommended activities. The committee also recognizes that some of the recommendations may be difficult to undertake, and that sufficient resources may not be available to undertake them all in the near term. For example, an experimental mine, such as the
former Lake Lynn facility, is currently not available to conduct full-scale underground mine testing. (see Chapter 2)
In addition, implementing the committee’s recommendations will require a commitment by all parties to collaborate. A case in point would be the conduct of field testing in working mines to assess RCMD concentration variability caused by different sources within the mines.
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.