Dust associated with mining operations is known to be a major cause of lung disease and other serious health problems. The impact of inhaled dust is cumulative, and can lead to a variety of medical conditions, including coal worker’s pneumoconiosis, silicosis, mixed dust pneumoconiosis, dust-related diffuse fibrosis, and progressive massive fibrosis. In response to this, the US introduced strict laws on the control of dust in coal mines in the 1970s, which resulted in a substantial decline in the number of cases of lung disease among mine workers. However, since the mid 1990s the number of miners with lung disease has risen again steadily, with many cases appearing in younger miners, who have worked their entire working lives in mines working with the new, tighter, regulations on dust control.
This re-appearance of mining-related lung diseases has been particularly prevalent in the Appalachian Region, and is thought to be linked to the practice of targeting thin coal seems, which involves cutting a larger amount of non-coal rock, primarily silica (i.e., quartz) and silicate minerals (cyclosilicates, phyllosilicates, tectosilicates, etc.), which are closely associated with lung disease (the body has no way to remove silica once it gets into the lungs, so that even tiny amounts of these minerals build up over time leading to severe health problems). A variety of other factors have also been suggested as possible caused of or contributers to this re-emergence, including duration and level of exposure, mine operation type, coal and rock-strata geological conditions, dust characteristics (i.e., size, shape, mineralogy, elemental content), dust mitigation techniques, mine size, coal rank, and advancements in cutting technologies.
The rising number of lung disease case appearing in coal miners has raised concerns with regulators and the scientific community, and in 2014 the Mine Safety and Health Administration brought in a number of new regulations, aimed at reducing exposure limits and improving measurement technology and sampling protocols. However, it is unclear if these measures actually tackle the roots of the problem, and the National Academies of Sciences, Engineering, and Medicine have called for research into a number of factors that are likely to be contributing to the problem.
In a paper published in the International Journal of Coal Science Technology on 13 October 2021, Younes Shekarian and Elham Rahimi of the Department of Mineral Engineering at the New Mexico Institute of Mining and Technology, and the Department of Information Systems at the University of Colorado Denver, Naser Shekarian of the John and Willie Leone Family Department of Energy and Mineral Engineering at Pennsylvania State University, Mohammad Rezaee, also of the Department of Information Systems at the University of Colorado Denver, and Pedram Roghanchi, also of the Department of Mineral Engineering at the New Mexico Institute of Mining and Technology, publish the results of a study which aimed to assess five separate hypotheses about the prevalence of coal worker’s pneumoconiosis in American mines, namely (1) that workers in underground mines are more likely to developing coal worker’s pneumoconiosis than those in other operations, (2) that geographical location is a contributing factor to the prevalence of coal worker’s pneumoconiosis, (3) that size of mine could influence the prevalence of coal worker’s pneumoconiosis among coal miners, (4) that coal rank contributes to the coal worker’s pneumoconiosis incidence rate, and (5) that coal seam thickness could influence the prevalence of coal worker’s pneumoconiosis among coal miners.
Shekarian et al. extracted data from Mine Safety and Health Administration accident/injury and employee/production records. This enabled them to determine the number of cases of coal worker’s pneumoconiosis at each mine, the type of mining caried out there, the number of workers at the mine, the coal production rate, the location of the mine, the coal seem thickness, and the rank of the coal. Each site where at least one instance of coal worker’s pneumoconiosis was recorded was classified as either underground, surface, or other (i.e. augur, milling and preparation plant, office, culm banks, independent shops and yards, surface at underground mine). A total of 21 396 operations were included in the study.
For the purpose of the study, the size of the mines was determined by their number of employees, with mines with less than 50 employees being classified as small, those with between 50 and 100 employees being classified as medium-sized, and those with more than 100 employees being classified as large. Seem width was classified as thin if it was less than 40 inches (101.6 cm) thick, medium if it was between 40 inches and 75 inches (190.5 cm) thick, and thick if it was greater than 75 inches thick. Coal rank was classified as either bituminous or anthracite.
Shekarian et al. found that 93% of the cases of coal worker’s pneumoconiosis recorded in workers at underground mines occurred in the Appalachian Region, with 4% occurring in the Interior Region and 3% in the Western Region. Furthermore, 80% of the mined where cases of coal worker’s pneumoconiosis were recorded were classified as small. At a county level, he highest number of coal worker’s pneumoconiosis cases recorded in underground miners occurred in Boone County, Wet Virginia, where there were 946 reported cases.
The situation at surface mines followed a similar pattern, with 86% of the cases of coal worker’s pneumoconiosis recorded at surface mines occurring in the Appalachian Region, 9% in the Interior Region, and 5% in the Western Region. This time 86% of the mines where ases of coal worker’s pneumoconiosis were recorded were classified as small. The highest number of coal worker’s pneumoconiosis recorded at surface mines in a single county was in Logan County, West Virginia, where there were 175 recorded cases.
Exposure to respirable coal mine dust varies greatly with the type of mining being carried out. Workers at underground mines are at much greater risk of coal worker’s pneumoconiosis due to the limitations of artificial ventilation systems and the confined spaces in which they are working, which typically means they are exposed to much higher levels of respirable coal mine dust. This was reflected in Shekarian et al.'s study, where 76% of cases of coal worker’s pneumoconiosis reported occurred in underground mineworkers, with 11% of cases reported in workers at surface mines and 13% in workers in other mine operations, mainly mills or preparation plants. Examination of the data chronologically confirmed the drop in the number of cases following the introduction of new tighter regulations in the 1970s, with a sunsequent rise in the number of cases from the 1990s onwards.
Geography is known to be a major factor when assessing exposure to respirable coal mine dust, as clusters of mines in different areas are targeting rocks with different geology, that produce different amounts and types of dust. The mines of Central Appalachia, for example, are known to produce more dust sources from non-coal rock strata than mines elsewhere in the US. Correspondingly, previous studies have shown that mineworkers in the eastern region of Appalachian coal field, which includes West Virginia and Pennsylvania, suffer higher rates of coal worker’s pneumoconiosis than miners in other parts of America.
Shekarian et al. found that, between 1986 and 2018, 106 counties in 16 states reported cases of coal worker’s pneumoconiosis, with the highest number of cases being reported in West Virginia, Kentucky, Virginia, and Pennsylvania. There are thought to be a number of contributing factors behind this, including a higher proportion of silica in respirable coal mine dust, caused by the mines in this region targeting thin coal seems in host rocks with high quarz contents, the smaller size of mining operations here, and a culture of working longer shifts in these mines, resulting in a higher daily exposure to dust.
Previous studies have found that mine size is a significant predictor of health issues in mineworkers in the US, with workers at smaller mines having higher rates of coal worker’s pneumoconiosis and abnormal lung functions, and that this is particularly true in Kentucky, Virginia, and West Virginia. It has been suggested that this is because smaller mining operations have fewer resources to invest in health and safety measures, and that concentrations of respirable coal mine dust will tend to be higher in smaller mines.
Shekarian et al. found that most mines in the US, both surface and above ground, are small in size (i.e. have less than 50 employees), but that most miners work at large mines (i.e. mines with more than 100 employees). Simply split by size category, a greater number of cases of coal worker’s pneumoconiosis occurred in miners working at large mines, but that individual miners were more likely to contract coal worker’s pneumoconiosis at smaller mines.
Coal seam thickness is considered to be another contributing factor for a high instance of coal worker’s pneumoconiosis, and varies from region to region depending on the local geology. The average coal seam thickness in the Central Appalachian Region is lower than in other regions in the US, and mines in this region which target thin coal seams are known to have a high instance of coal worker’s pneumoconiosis.
Shekarian et al. found that only 11% of US mines targeted thick coal seams, with medium seems being the type most often targeted by underground mines (44%) and thin seams the type most often targeted by surface mines (50%). Furthermore, more underground mines targeting medium coal seams reported cases of coal worker’s pneumoconiosis than underground mines targeting either thick or thin seams, while more overground mines targeting thick seams recorded cases than mines targeting medium or thin mines, but in both cases the greatest number of cases were reported at mines targeting thin seams.
A connection between coal rank (the carbon content of coal, with anthracitic coals having a higher carbon content and therefore yielding more energy than bituminous or sub-bituminous coals) and the occurrence of coal worker’s pneumoconiosis. It has been suggested that the incidence of coal worker’s pneumoconiosis is higher among miners working with bituminous coals than those working with anthracitic coals, even where the levels of respirable coal mine dust remain the same. In the Appalachian Region bituminous coals typically have a high quartz content, which may account for this, although it has been suggested that the surface charge of coal dust particles may be different in mines working anthracitic and bituminous coals.
Examination of the available data by Shekarian et al. revealed that the vast majority (95%) of US coal mines target bituminous coals, with only 9 underground and 59 surface mines targeting anthracites in 2018. Around 95% of cases of coal worker’s pneumoconiosis occurred in mines targeting bituminous coals.
The re-appearance of coal worker’s pneumoconiosis among mineworkers in the US in the 1990s caused alarm among many medical workers and scientists studying the field. A number of studies have looked at different factors which might have led to this resurgence, but until Shekarian et al.'s work, no single study had attempted to look at all the possible causes together. Shekarian et al. collated 33 years of mine safety statistics collected by the Mine Safety and Health Administration. Their findings suggest that mine operation, geographic location, mine size, coal seam thickness, and coal rank all contribute to the health risks for underground mineworkers, while at surface mines the picture is less clear, with mine size, geographic location, coal rank, and seam height playing a role, but the correlation between instances and these factors being somewhat more complicated.
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