The committee’s statement of task calls for a comparison of the monitoring technologies and sampling protocols (including sampling frequency) currently used or required in the United States, and in similarly industrialized countries for the control of respirable coal mine dust (RCMD) exposure in underground coal mines (see Appendix A). In comparing monitoring technologies and sampling protocols, the committee described relevant regulatory requirements and identified apparent commonalities and dissimilarities among the different countries. Required medical surveillance programs for detection of diseases in coal miners are also included. The committee relied upon scientific literature, regulatory background documents, discussions with experts outside the committee (see Appendix C), and the expertise of its members.
The committee considered it beyond the scope of this study to assess the implementation of the requirements, rates of compliance with the regulations, and the extent to which the regulatory programs are successful in controlling RCMD exposures. Also, the committee did not attempt to compare associations between current monitoring and sampling approaches and disease prevalence data for individual countries. As discussed in Chapter 1, diseases related to RCMD exposures typically have a long latency (at least 10 years and often 20 to 30 years) and prevalence data are not reflective of current approaches for monitoring and controlling exposure. However, the potential for using compiled multinational exposure data and medical surveillance data for further assessments is considered in this chapter.
In 2015, about 8.8 billion tons (8 billion metric tons) of coal were mined in more than 50 countries and more than 50 percent of that production came from underground mining. The committee identified a set of countries that, based on its judgment, provides a reasonable representation of the range of monitoring and sampling approaches used in industrialized countries. The set of countries includes Australia, Germany, India, the People’s Republic of China, Poland, the Republic of South Africa, and the United States. Table 3-1 lists typical underground mining practices, mandated exposure limits, and required monitoring devices for several leading coal-producing countries.
In 2015, total U.S. coal production was approximately 897 million short tons (EIA, 2017) and underground coal mining accounted for about 34 percent (NMA, 2017). Two major methods of underground mining (the room-and-pillar method and the longwall method) are used in the United States (see Appendix F). In 1970, underground coal mining accounted for more than 60 percent of U.S. coal production, with longwall production being less than 5 percent of that production; in 2015, about 60 percent of underground production came from longwall mines. Underground mining in central Appalachian states, such as in Kentucky, Virginia, and West Virginia, included a large number of small-sized underground mines (fewer than 50 employees) that accounted for a small percent of the total production. (See Chapter 1 and Appendix E for discussions of trends in mining methods and employment that might affect disease risk.)
|Country||Total Production in 2015a||Underground Mining||Dust Exposure Limits and Required Monitoring Device|
|Rank||Thousand Short Tons||Est. Percent of Total Productiona||Typical Method|
|People’s Republic of China||1||4,376,984||90%||Longwall||Depending on a silica content ranging from 5% to 50%, exposure limits are between 6 and 1 mg/m3 for RCMD and between 20 and 2 mg/m3 for total coal mine dust, using a personal gravimetric sampler.|
|United States||2||896,941||34%||Room-and-pillar, longwall||RCMD exposure limit is 1.5 mg/m3, using a continuous personal dust monitor. Quartz exposure limit is 0.10 mg/m3, using a personal gravimetric sampler.|
|India||3||643,720||10%||Room-and-pillar, longwall||RCMD exposure limit is 2 mg/m3, when the silica content is less than 5%, using a monitoring device approved by the Indian government. When the silica concentration is 5% or more, the exposure limit is calculated as 10 divided by the percent silica content in the RCMD.|
|Australia||4||560,714||20%||Longwall||New South Wales: Exposure limits: 2.5 mg/m3 for RCMD with a quartz content less than 5%, 10 mg/m3 for the inhalable fraction (particles less than 100 µm in diameter), and 0.12 mg/m3 for quartz. Personal gravimetric sampling is used.|
|Queensland: Exposure limits: 3 mg/m3 for RCMD with a quartz content less than 5%, 10 mg/m3 for the inhalable fraction, and 0.10 mg/m3 for quartz. Personal gravimetric sampling is used.|
|Republic of South Africa||7||256,876||50%||Room-and-pillar, some longwall||Exposure limit is 2 mg/m3 for RCMD with a quartz content less than 5%. If the quartz content is greater than 5%, an exposure limit for quartz is 0.1 mg/m. Personal gravimetric sampling is used.|
|Germany||8||203,613||3%||Longwall||Using a dose-based approach, limiting cumulative exposure for a 2-year, 220-shift exposure would be an estimated dose accumulated from an average exposure of 4.0 mg/m3. Area gravimetric sampling is used.|
|Poland||9||149,147||53%||Longwall||Exposure limits: 1 mg/m3 for RCMD containing free crystalline silica from 2% to 50%, 4 mg/m3 for total dust. Personal gravimetric sampling is used.|
aEIA, 2017. International Energy Statistics. Online. Available at https://www.eia.gov/beta/international/rankings/#?cy=2015&pid=7 (accessed May 16, 2018).
The current exposure limit for RCMD in underground mines is 1.5 mg/m3; the limit for quartz is 100 µg/m.3 Additional information, including a description of early regulatory efforts, is provided in Chapter 1 and Appendix G.
Monitoring Technology and Sampling Protocols
The exposure monitoring and sampling program for regulatory compliance involves coal mine operators and Mine Safety and Health Administration (MSHA) inspectors, using approved personal devices to obtain required dust measurements. After nearly two decades of research and development, the use of a continuous personal dust monitor (CPDM) is now required. The CPDM is a sampler and gravimetric analysis instrument that is worn by a miner and provides a display of a cumulative-mass concentration of RCMD (see Chapter 4). Mine operators are required to use the CPDM to monitor personal dust exposures of miners in designated occupations (DOs) that are considered to be exposed to the highest RCMD concentrations, miners in other designated occupations (ODOs) that are frequently exposed to high RCMD concentrations, and miners who have medical findings of pneumoconiosis and who opt to transfer to a less dusty job in the mine (Part 90 miners).
Use of the CPDM is optional for meeting sampling requirements for designated areas (DAs), such as the point where coal is loaded onto a conveyor belt, and designated work positions (DWPs) at the surface of an underground mine that are exposed to the highest RCMD concentrations.
The operator must collect respirable dust samples for the full shift that a miner works. The sampling frequency for DOs and ODOs is 15 shifts per quarter. The DO and ODO cannot be sampled concurrently. DAs and Part 90 miners must be sampled during five shifts per quarter. For each DWP, one valid sample must be obtained every quarter. Data from the CPDM sampling for regulatory compliance must be transmitted within 24 hours to MSHA.
In addition to the monitoring carried out by operators, MSHA uses a personal gravimetric sampler to measure RCMD concentrations and the concentration of quartz in the mine atmosphere. Samples are collected onto filters that are mailed to a laboratory for quartz analysis using an infrared spectroscopy method referred to as the MSHA P-7 method (MSHA, 2013).
As indicated in Chapter 1, the National Institute for Occupational Safety and Health (NIOSH) Coal Workers’ Health Surveillance Program requires that mandatory chest radiograph examinations be provided by a NIOSH-approved facility for each miner at the beginning of their coal mine employment and within 3 years after the initial examination. Voluntary medical examinations must be provided at least every 5 years. The program also includes a medical and occupational history questionnaire along with spirometry testing via a mobile examination unit that travels to the mine site (Antao and Pinheiro, 2016).
In 2015, Australia was the fourth largest coal producer in the world at about 561 million short tons (EIA, 2017). Nearly 80 percent of its production comes from surface mining (Mishra et al., 2013; Minerals Council of Australia, 2018). Longwall mining accounts for nearly 90 percent of the underground coal production. Australian underground coal mines tend to be large, operate on thick seams, and mostly incorporate modern longwall methods.
Underground coal mining is regulated on a state-by-state basis in Australia. The states of New South Wales (NSW) and Queensland (QLD) are the major producers of coal in the country and are the focus of this discussion.
For RCMD with a quartz content less than 5 percent, NSW’s exposure limit is 2.5 mg/m3 and QLD’s exposure limit is 3.0 mg/m3. Both states have an exposure limit of 10 mg/m3 for the inhalable fraction (particles less than 100 µm in diameter). NSW and QLD have an exposure limit of 0.10 mg/m3 for respirable crystalline silica (NSW, 2006, 2007; Coal Services, 2016; QLD, 2017a).
All exposure limits for NSW and QLD mentioned above are for time-weighted measurements averaged over an 8-hour shift. Exposure standards may require adjustments when work shifts are longer or the workweek exceeds 5 days, to account for the greater exposure and decreased recovery time between shifts (Ren, 2017). In 2017, a parliamentary committee in QLD recommended that the exposure limit be lowered to1.5 mg/m3 for RCMD and 0.05 mg/m3 for respirable crystalline silica (QLD, 2017a).
Monitoring Technology and Sampling Protocols
The monitoring and sampling procedures used in each state adhere to the Australian standards for sampling and gravimetric determination of respirable dust in workplace atmospheres and inhalable dust (Australian Standard, 2009). Those standards are very similar to the ones specified by the International Organization of Standardization (ISO, 1995).
Specific requirements for underground coal mines in NSW are based on Order 42 of the Coal Industry Act of 2001 (NSW, 2011) and the Work Health and Safety (Mines) Act 2013 (NSW, 2014). In general, production shifts are monitored at a frequency of 6-12 months depending on the crew’s location, tasks undertaken, and exposure-related health risk. Typically, samples are collected from the breathing zones of at least five persons on the crew during the shift being monitored. The approved sampling method adopted by the coal industry in NSW is personal gravimetric sampling, using a battery-operated pump and cyclone (Ren, 2017). All monitoring is conducted by NSW Coal Services, which is a collaborative organization with independent monitoring authority that includes participants from industry, NSW government, unions, and mine workers. All results of required dust samples are sent to the mine operator where samples were taken and to other organizations, including the relevant NSW government agency, the union representing the miners, and an expert advisory committee. All government-required dust sampling results from across the industry are maintained in a single database (NSW, 2017).
QLD monitoring and sampling requirements are based on the Coal Mining Safety and Health Act of 1999 and Recognized Standard 14 (QLD, 2016). The Safety in Mines Testing and Research Station, which was established by the QLD government (QLD, 2017b), and other commercial organizations conduct and provide coal mine dust monitoring functions at a cost to the mines. Mine operators are required to review their safety and health management system and report monitoring results on a regular basis. In cases of an exceedance of the exposure limit, operators must check within 2 weeks for the success of revised dust control measures (QLD, 2017a). Operators are required to keep monitoring records for at least 30 years.
QLD monitoring involves the use of similar exposure groups (SEGs). SEGs are established by the site’s senior executive and are based on mining operations (such as longwall operations), development operations, or maintenance activities. The number of mandatory initial samples for each SEG (minimum of eight) that are collected to obtain a baseline depends upon the number of workers employed within the SEG and the type of sampling performed (QLD, 2016). The statistical basis for that approach is the NIOSH Occupational Exposure Sampling Strategy Manual
(NIOSH, 1977). The number and frequency of periodic sampling after the baseline has been established is based on the ratio of the initial measurement results to the exposure limit. Depending on the ratio, the required sampling frequency is monthly (ratio greater than 0.75), quarterly (ratio between 0.5 and 0.75), annually (ratio less than 0.5 and greater than 0.1), or none (ratio less than 0.1). One sample is collected for every 10 miners in the SEG.
In addition to the requirements for the number and frequency of periodic sampling, a minimum of 8 to 10 samples must be taken quarterly for SEGs involved in longwall production and development production (QLD, 2016).
In general, personal sampling is used for compliance purposes, and area sampling (static sampling) is used for engineering dust control purposes. (Personal sampling provides a concentration measurement of airborne dust to which an individual is exposed; area sampling provides a concentration that reflects the general dust concentration at a fixed location in the workplace.)
In NSW, a preemployment medical examination is mandatory for coal miners. In addition, miners must undergo a medical examination every 3 years. Additional chest radiography is required every 6 years for miners considered to be at high risk from dust exposure (Ren, 2017).
In QLD, coal workers’ pneumoconiosis (CWP) screening is done according to the Coal Workers’ Health Scheme (Queensland-based scheme), established by the Coal Mining Safety and Health Regulation 2001. Preemployment health assessments are mandatory for potential mine workers and are required to be provided periodically by the employer’s Nominated Medical Adviser. At a minimum, medical surveillance must be conducted at least once every 5 years. In addition, coal miners can request medical examinations at the expense of the employer at the time of their retirement (QLD, 2017a,b).
Several years after concluding that the problem of RCMD-related lung disease had been eliminated in Australia, in-depth investigations showed that cases of CWP were occurring in active and retired coal miners but had not been identified by the Coal Worker’s Health Scheme (QLD Parliament, 2017c). A number of recommendations were made:
- Identification and surveillance of coal mine dust respiratory disease should be explicit;
- Designated high-dust-exposure jobs should be linked to clearly stated frequency of health assessments and chest radiographs for workers in these areas;
- Medical staff performing the health assessments should be trained to perform high-quality spirometry and chest x-ray B readings;
- Electronic data collection, aggregate analysis, and reporting should be implemented; and
- Plans for communication of medical surveillance results with individual miners and medical referral, as needed, should be developed (QLD Parliament, 2017c).
Germany was the eighth largest coal producer in the world in 2015, having produced more than 203 million tons of coal (lignite, bituminous, and anthracite) in that year (EIA, 2017). About 3 percent of that total was from underground production, which constitutes all of the bituminous and anthracite coal still mined in Germany (Yearbook of the European Energy and Raw Materials Industry, 2017). Due to unfavorable economic conditions, underground mining of bituminous and anthracite coal will terminate in Germany by the end of 2018.
In the past, underground coal mining has been carried out in three different regions: Saar district, Ruhr district, and northwest Germany. Those mines have employed several thousands of miners (Falk et al, 2016). All of Germany’s underground coal mining is done by the longwall method. Nearly all mines operate at depths greater than 2,600 ft (800 m). With very few exceptions, the seams have been comparably thin.
The German Federal Hazardous Substances Ordinance (BAuA, 2017) and the Health Protection Mining Ordinance (BMJV, 2017) provide a basis for regulating miners’ exposures to hazardous substances in underground coal mines in Germany. RCMD (often referred to in Germany as fibrogenic mine dust) is the regulatory focus for disease prevention of in coal miners. The RCMD component of greatest concern is respirable crystalline silica, whose amount in the dust depends on the mine, the coal seam being mined, and the work location within the mine. That regulatory focus on RCMD is based on several decades of research on the health protection of coal miners (North Rhine Westphalia Ministry of Economy, 1991) which resulted in these conclusions, among others:
- Crystalline silica in RCMD is responsible for the development of pneumoconiosis in coal miners.
- The crystalline silica in RCMD displays varying toxicity. For example, RCMD in anthracite mines was found to be much more toxic than the RCMD from mining of bituminous coal mines.
- The cumulative dose of RCMD in miners’ lungs is a more important consideration than the short-term exposure concentration regarding the development of pneumoconiosis. However, all actions taken to lower the RCMD concentration in underground mines will lower the accumulated dose as well.
- It is very important to conduct frequent medical surveillance of miners with respect to lung diseases and take appropriate actions in response to the results.
In general, little focus has been placed on individual measurements of dust exposure. Instead, emphasis is placed on the classification of workplace exposure types, personal registration of cumulative exposures for individual workers, and relocating miners to different work areas depending on their individual cumulative dust exposures. Based on the above-mentioned conclusions, the airborne concentration of crystalline silica in coal mines in Germany is not determined separately from RCMD. Only RCMD concentrations are monitored, and sampling is conducted gravimetrically to obtain an average exposure over an 8-hour shift for all workers in the specific work area.
The mass concentration measurements are weighted with factors to take into account the variability of crystalline silica attributable to specific mining environment, which was sampled (see below). The monitored concentration is used to calculate the average RCMD exposure of all workers in a specific work area. The number of shifts that each miner works in that work area is recorded in a miner’s personal exposure file and exposures are accumulated over a 2-year period. Depending on the estimated individual risk, relocation of a miner to a workplace with lower RCMD exposures might be required or done voluntarily. That approach involves the classification of all workplaces into four dust burden classes, ranging from zero to three, with dust burden class “zero” being the least dusty one and nobody being allowed to work above the highest dust concentration of dust burden class “three.”
There are no regulations for short-term exposure, and the values classifying the dust burden classes cannot be directly compared to an exposure limit concentration. However, the limiting cumulative exposure for a miner that would result in a mandatory relocation is based on working at an average concentration of 4 mg/m3 for 220 shifts per year and for 2 years (i.e., 440 shifts) (Morfeld et al., 2002).
Monitoring Technology and Sampling Protocols
The above-mentioned health-protection mining ordinance does not specify the use of a particular monitoring technology or sampling protocol, but it requires that coal mine operators estab-
lish them. In addition, it requires that persons performing the monitoring and data processing have special qualifications and training. Monitoring and sampling follow a specific protocol, which has been developed by RAG (the major coal mining company) and the mining inspection institution of the State of North Rhine Westphalia (RAG DSK, 2006).
Generally, sampling is carried out by means of an area approach that involves the use of the pressurized-air-driven MPG II (Dahmann et al., 2001) working with a BMRC-type (Johannesburg) pre-separator (horizontal elutriator). The sampling is performed at specific sites within a longwall operation or other workplaces. RCMD samples are collected onto glass fiber filters by trained personnel of the mining company for subsequent analysis. Inspectors may perform additional measurements at irregular intervals. Under very special circumstances, for example, in case of encountering a geological anomaly in the seam, the general procedure might be replaced with a specific set of measures only during the time in which mining is performed at the site of the anomaly. In these cases, every miner at that site is required to wear a personal respirable sampler (a French CIP 10 device; Stacey et al., 2014) and personal dust protection masks. Also, in these cases the analytical determination has to be done externally by an accredited laboratory.
After the dust RCMD concentration has been determined, the result is multiplied by a factor depending on the actual workplace. (As mentioned previously, the factor is intended to take into account the variability of crystalline silica in RCMD.) Currently only two factors are applied: 1.0 (for example, mining low-volatility coal) or 0.7 (for example, mining medium-volatility coal).
Optical, tyndalometric (light-scattering) measurements have been used regularly to identify episodes of high concentrations for informing decisions concerning engineering dust controls. An empirical formula is applied to those measurements to develop an average exposure concentration with a safety margin for an entire shift. That approach may be used only for the lower RCMD concentration classes.
Frequency of the measurements is directly related to the results of earlier measurements. For example, in the highest dust-burden class (greater than 6 mg/m3), sampling has to be repeated within 7 days. On the other hand, in the lowest class (less than 2 mg/m3), measurements have to be repeated every 6 months.
All data are stored and processed by the mining company. The inspectors may see the data at any time. The personal dust exposure data of an individual employee may be reviewed by that employee at any time. The workers’ union has the right to see the data at any time. In addition, union representatives are present at nearly all stages of mining company decision making, up to and possibly including the senior management level.
The nature and frequency of medical surveillance is regulated in the Health Protection Mining Ordinance (BMJV, 2017). Mine operators may employ people only for whom no medical concern has been raised about working in the intended workplaces (BMJV, 2017). The miner is medically examined before employment begins and at regular intervals during employment. The frequency of examinations depends upon the individual worker’s situation. The most common frequency is every 2 years. The physician issues a written report to the worker and the employer, without details on the individual diagnosis. The operator must offer the worker a less dangerous occupation, if concern was raised. The miner’s employment is precarious only if the operator proves that it does not have a suitable alternate work assignment. In cases of serious medical impairment, the social security system (BG RCI) would pay a pension. In addition, the miners have the right to be examined after they have left the mining operation (either as pensioners or in a different job). The mining company is required to pay for all examinations.
Germany requires accident insurance (BG RCI, 2017) to provide for compensation, prevention, and rehabilitation of occupational diseases. BG RCI will compensate every case of coal miners’ pneumoconiosis (depending on the degree according to the latest ILO classification scheme).
Although the system of regular mandatory medical surveillance for coal miners will not be changed for German underground mining of bituminous and anthracite coal (scheduled to end in 2018), in all other workplaces the requirement has been abolished. Miners who are not underground coal miners will still have the right to see a doctor but may individually decide not to be examined. If they agree to be examined, any positive results do not need to be forwarded to their employer. The worker can continue to work under conditions where high dust exposures might occur.
In 2015, India was ranked third in the world in coal production at about 644 million short tons (EIA, 2017). In the past four decades, the coal production growth in India has largely been in the surface mining sector, and underground mining accounts for about 10 percent of the current coal production (Jha, 2011; Mishra et al., 2013). Mechanized longwall mining accounts for less than 10 percent of the underground production. Room-and-pillar mining, using either a mechanized or semimechanized system, employs a comparatively larger workforce relative to the longwall mining method, which accounts for the low productivity of the Indian mines (Mishra et al., 2013).
The Indian Directorate General of Mine Safety (DGMS) established an RCMD exposure limit of 2 mg/m3 for an 8-hour time-weighted average, when the silica concentration in the dust is less than 5 percent. When the silica concentration is 5 percent or higher, the exposure limit is calculated as 10 divided by the percent silica content in the RCMD (Gazette of India: Extraordinary, 2017). In 2010, DGMS advised that the crystalline silica concentration in underground mines in India be kept at less than 0.1 mg/m3 (DGMS, 2010).
Monitoring Technology and Sampling Protocols
The Indian government requires coal mine dust sampling at least every month, using a monitoring device approved by DGMS. Examples of approved devices include the Mine Research Establishment, 113A Gravimetric Dust Sampler, and personal samplers (AFC 123), Cassella, London (Mukherjee at al., 2005). Sampling requirements are provided in Box 3-1. In addition, mine managers are required to prepare and implement a monitoring and sampling scheme that specifies the following:
- Location, frequency, timing, duration, and pattern of sampling;
- Instruments and accessories to be used for sampling;
- Laboratory at which the RCMD content of samples and quartz content are to be determined;
- Format in which the results of measurements of dust concentration and other particulars are to be recorded;
- Organization for dust monitoring and for the examination and maintenance of dust prevention and suppression measures and dust respirators; and
- Manner of making all persons concerned with the implementation of the dust control measures fully conversant with the nature of work to be performed by each in that behalf (Gazette of India: Extraordinary, 2017, see pp. 238-239).
DGMS recommended in 2010 that medical examinations of coal miners be conducted annually and that the results be correlated with RCMD exposure profiles of the mine or the process within the mine. Among other additional recommendations, DGMD indicated that, if a person is diagnosed with pneumoconiosis or silicosis: “the details regarding the [miner’s] work profile, degree of disability, medical history and expenses, compensation and the status of health and rehabilitation measures taken by the company, etc. should be sent to this Directorate immediately” (DGMS, 2010, p. 5).
People’s Republic of China
China is currently the world’s largest coal producer. In 2015, the country’s coal production was nearly 4.4 billion short tons (EIA, 2017). The vast Chinese coal industry comprises a wide diversity of mine sizes, mining methods, technology, and number of employees per mine. Nearly 90 percent of the Chinese coal production is from underground mines. Chu et al. (2016) reported that the average mine depth in 2010 was about 2,300 ft (700 m). The Chinese coal mining industry is undergoing rapid changes, including a dramatic reduction in the number of mines, an increase in mine sizes, and an increased application of mechanized longwall mining and associated safety practices (Peng, 2010).
Chinese regulations for airborne dust control in mines cover RCMD and total dust, and the exposure limits are related to the amount of silica content in the dust. The Safety Regulations in Coal Mines requires an exposure limit between 2 and 20 mg/m3 for total coal mine dust, and be-
tween 1 and 6 mg/m3 for RCMD, depending on the silica content, which can range from 5 to 50 percent (Yinlin et al., 2016).
Monitoring Technology and Sampling Protocols
National standard methods specify the use of a gravimetric personal sampler for coal mine dust and the pyrophosphate method for the determination of free silica content (Shen et al., 2013).
In 2002, a national law went into effect for the prevention and control of occupational diseases (National People’s Congress, 2016). It requires employers to make arrangements and pay for preemployment, in-service, and job-leaving occupational health exams of workers and to inform the workers of the results (see Article 35 of the law). Employers are required to keep medical files that indicate a worker’s professional history, history of exposure to occupational disease hazards, the results of occupational health checkups, diagnosis and treatment of occupational diseases, and other information related to the worker’s health (see Article 36 of the law). A national network of occupational disease information allows for Internet reporting to the Institute of Occupational Health and Poisoning Control. The reporting includes real-time data on the number of cases of pneumoconiosis and prevalence trends (Antao et al., 2015).
Approximately 149 million short tons of coal were produced in Poland in 2015 (EIA, 2017). Of that amount, about 53 percent was produced from underground mines. The average working depth of the mines is almost 2,000 ft, with more than 90 percent of coal produced by longwall systems. Coal is expected to play a major role in Polish energy production for many years to come (Euracoal, 2018).
Exposure limits for coal mine dust containing crystalline silica from 2 to 50 percent are 4 mg/m3 for the total fraction and 1 mg/m3 for RCMD. Annual measurements are required using a personal gravimetric method (Lebecki et al., 2016). Medical surveillance examinations are carried out based on agreements with individual employers at facilities that mainly offer services to the general population (Grzesik and Sokal, 2003).
Republic of South Africa
The Republic of South Africa’s (RSA’s) coal production of about 257 million short tons in 2015 ranked seventh in the world (EIA, 2017). The production is distributed nearly evenly between underground and surface mining methods (Eberhard, 2011; Universal Coal PLC, 2018). The bulk of the production is from 5 companies and from about 11 mines. The room-and-pillar mining method, using continuous miner machines, is the dominant extraction method. Longwall mining accounts for about 10 percent of the underground production. Frequent geologic intrusions into coal seams, such as dykes and clay veins, present mining difficulties.
RSA’s Department of Minerals and Energy requires that RCMD concentrations not exceed 2 mg/m3, measured as a time-weighted 8-hour-shift average. The respirable fraction is defined according to ISO/CEN standards (CEN, 1993; ISO, 1995). The crystalline silica content of RCMD should be less than 5 percent by mass. If the content is greater than 5 percent, an exposure limit is invoked for crystalline silica of 0.1 mg/m3, time-weighted average (RSA DOL,
1995). The regulations require the formation of homogenous exposure groups (HEGs) for uniform sampling areas, which are defined as having common intake and return air. HEGs are further subdivided into “activity areas,” for example, conventional mining and development.
Monitoring Technology and Sampling Protocols
Personal sampling for gravimetrical analysis is performed according to NIOSH 0600 (Higgins-Dewell cyclones and polyvinyl chloride[PVC] filters; NIOSH, 1998) or the similar United Kingdom Methods for the Determination of Hazardous Substances 14-4, using Institute of Occupational Medicine (IOM) samplers, cyclones, and 25-mm PVC filters (HSE, 2014). There is recent evidence that the Higgins-Dewell cyclones applied in South Africa do not conform to respirable size-selective specifications (Belle, 2018). Sampling within an HEG is performed during an entire full shift on a random selection of either five workers or 5 percent of the workers in the group (whichever is greater). When the actual shift time deviates from 480 minutes, a time-weighting correction factor is applied to the individual measurement results (Brouwer, 2017). The HEG results are grouped into three exposure categories and assigned a minimum sampling frequency of quarterly, semiannually, or annually.
The mine operators are responsible for obtaining coal mine dust measurements, but they often delegate those activities to approved subcontractors (RSA DOL, 2012). The results have to be reported regularly to the Department of Mineral Resources, that is, the federal government. The frequency of reporting is aligned to the sampling requirements (exposure groups).
Also, the sampling results are supposed to be communicated back during monthly meetings to the individual miner who wore the sampling instruments. Later, sampling results are disseminated to the general public by the Mine Health & Safety Inspectorate.
According to Brouwer (2017), the construction of HEGs using job titles sometimes appears to be arbitrary, there seems to be no statistical evaluation of current or historical exposure data, and real-time direct-reading monitoring techniques play no role in the required sampling.
The miners fill out routine health questionnaires every year. They also receive annual physical examinations (Brouwer, 2017). In certain cases, medical examinations can be given semiannually or quarterly, depending on the miner’s health status. In addition, there is a preemployment examination to assess a miner’s health status. Upon leaving employment, an exit medical examination is performed and copies of the results are given to the employee and the employer. Employers are required to keep these records for 40 years. If safety or health concerns are raised by employer or employee, a special examination can be conducted on an ad hoc basis. The mining companies are informed about the numbers of miners with a certain occupational problem rather than provided with names of people with those conditions (confidentiality issues).
The occupational medical practitioner (OMP, physician) informs the employer of a possible risk associated with a particular exposure and also the OMP will recommend what steps should be taken ranging from preventing or limiting further exposure to removing an employee from a dangerous environment.
The occurrence of diseases caused by coal mine dust exposures has been recognized as an important occupational health problem by major coal-producing countries, and strategies for monitoring and controlling miners’ exposures to reduce disease prevalence have been implemented in those countries. In general, RCMD has been clearly defined and sampled according to well-documented methods since the early 1990s.
The countries considered by the committee tend to establish exposure limits that are focused on controlling mass concentrations of RCMD and silica in the air of underground mines. As discussed in Chapter 1, the U.S. exposure limit for RCMD was lowered to 2 mg/m3 in 1972, and that allowable limit was reduced further whenever the respirable crystalline silica content of the RCMD was greater than 5 percent. The intended effect was to keep the silica concentration at less than 0.1 mg/m3. In 1995, NIOSH recommended that RCMD exposures be limited to 1 mg/m3 and silica exposures not exceed 0.05 mg/m3. The U.S. exposure limit for RCMD was lowered to 1.5 mg/m3 in 2016 and the limit for silica was not changed. In most cases, other countries considered by the committee have RCMD exposure limits either equal to or greater than 2 mg/m3 and a silica exposure limit equal to or greater than 0.1 mg/m3. Several states in Australia also have set exposure limits for the inhalable size fraction of coal mine dust particles.
- The monitoring device that is commonly identified in the regulations for RCMD measurement is a gravimetric personal sampler, which contains a battery-powered pump, a cyclone for selecting the respirable fraction from the total airborne dust, and a filter assembly for collecting the selected fraction. Some countries, such as RSA and Australia, are considering the use of CPDM-type instruments for personal sampling, as is now required in the United States. Differences in one or more of the factors discussed below make it difficult to compare exposure measurements among different countries directly.
- While almost all regulations require determination of the crystalline silica concentration in RCMD, most do not advocate a specific analytic method for determining the concentration. The U.S. regulations prescribe the use of the P-7 method (an infrared spectroscopy method) for RCMD samples collected on a filter; laboratories and contractors in other countries use infrared (IR) and x-ray diffraction methods. It is important to note that the results of these techniques are dependent on the size distribution of the RCMD sample, and calibration and other test procedures.
- Sampling requirements mainly target an individual miner or group of miners during a shift in the mine, occupations that have a potential for high exposures, and areas of mines where miners are likely to come into contact with elevated dust concentrations. A significantly different approach has been taken in Germany, where regulations have focused on monitoring the cumulative exposure of miners, using area sampling of RCMD to characterize the personal exposure of each miner in the respective area. There is variability among countries regarding required sampling frequencies, number of samples, and the organizations responsible for conducting the monitoring.
- Most regulations call for mandatory medical surveillance of miners just prior to employment and either mandatory or voluntary surveillance at periodic intervals after that. However, it is not apparent how medical surveillance findings are used to revise procedures for monitoring and controlling RCMD exposures.
- Requirements for exposure monitoring and medical surveillance have developed over many years in different coal-mining countries. Some of the dissimilarities in those requirements are likely due to differences in social, legal, and administrative structures. Examples include the strong federal influence on the compensation system for occupational diseases in Germany and the decentralized administration of requirements in Australia at the state level, rather than at the national level. In addition, some countries have experienced changes within their regulatory structures over the years, which likely have resulted in changes in exposure monitoring requirements.
- Various geologic factors, including the depth and thickness of a coal seam and the nature of rock strata surrounding the seam, influence the kind of coal mining conducted in a particular country. Those factors can contribute to differences in the amount of underground mining conducted relative to surface mining, the choice of mining methods, the
extent of mechanization, and the amount of surrounding rock strata that is removed, which in turn can influence RCMD particle characteristics (for example, composition) and the kinds of exposures experienced by miners.
- The commonalities among multinational exposure monitoring approaches suggest potential opportunities for using compliance data for scientific investigations of linkages between miners’ exposure monitoring data and medical surveillance results collected from across a broad range of underground mining conditions in different countries. That could help improve the understanding of exposure-response relationships, RCMD aspects of greatest relevance to disease risk, and approaches for monitoring and controlling exposures.
- A comprehensive assessment is needed to determine the potential for using compliance data from major coal-producing countries for conducting epidemiologic research and improving exposure monitoring approaches. Considerations in conducting the assessment include detailed descriptions of
- Procedures and systems that mines have used to demonstrate regulatory compliance, processes for inspecting the mines, and how historical sampling and analysis methods compare with currently accepted practices.
- Extent to which data on miners’ long-term cumulative exposures had been collected, and whether there are indicators of how the use of those data for exposure controls had influenced the prevalence, and possibly the severity, of coal-mine-dust-related diseases.
- Feasibility of accounting for differences in monitoring and sampling practices by applying correction factors, algorithms, or other appropriate techniques of retrospective exposure assessment (for example, see Naidoo et al., 2006, and Dahmann et al., 2008).
- Potential for the introduction of bias into epidemiologic studies of coal miners from the use of regulatory compliance data (for example, see Pearce and Douwes, 2008; Dahmann, 2016).
- Extent to which standardized approaches are used for medical diagnoses in multiple countries. For example, widespread use of the International Labour Office B reader program for categorizing radiographic abnormalities for pneumoconiosis (International Labour Office, 2011) as well as use of standards recommended by the American Thoracic Society/European Respiratory Society (Culver at al., 2017) for characterizing miners’ lung function would facilitate international comparisons and strengthen efforts to prevent coal-mine-dust-related diseases.
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