Mining Contract: Temporal and Spatial Characterization of Respirable Coal Mine Dust (RCMD)

Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

In the coal mining industry, respirable coal mine dust (RCMD) is generated during mining operations. These airborne dust particles are comprised of a respirable fraction (<10 μm) that can be inhaled by miners and deposited in the distal airways and gas-exchange region of the lung. Overexposure to RCMD can cause serious health problems including coal workers’ pneumoconiosis (CWP), otherwise known as black lung disease. CWP is a lung disease that is nearly always fatal in its most severe form, progressive massive fibrosis (PMF), and is at minimum debilitating in its less severe forms. Exposure to an excessive amount of crystalline silica can cause silicosis, an equally debilitating and progressive disease that can occur alone or in conjunction with CWP.

The Federal Coal Mine Health and Safety Act of 1969 established the coal mine dust standard of 2.0 mg/m³ with the maximum allowable percentage of silica to be 5%. The Mine Safety and Health Administration (MSHA) set a lower respirable dust standard of 1.5 mg/m³ for underground coal mining operations. Compliance with this standard is monitored through periodic collections of gravimetric occupational dust samples. The RCMD generated in underground coal mines has many sources, including particles generated by the mined coal seam, rocks adjacent to the coal seam, rock dust products used to control explosions in mines, and any other particles associated with mining activities. Therefore, RCMD has many components, including coal particles, crystalline silica, silicate minerals, carbonates, and diesel particulate matter. Identifying the various sources' contributions of RCMD and establishing the relationship between RCMD metrics and CWP is critical to developing an optimal and beyond-compliance strategy to reduce exposure to RCMD for underground coal workers.

Over the last several decades, the compliance-driven approach has led to a significant reduction in incidences of lung diseases associated with occupational exposure to RCMD among U.S. coal mine workers. In 1968, the U. S. Bureau of Mines (USBM, the predecessor of the NIOSH Mining Program) conducted sampling at over 20 mines for selected occupations. The result showed that the average dust exposure levels were 5.63 mg/m³ for continuous miner operators and 3.39 mg/m³ for roof bolter operators. In 2009, after implementing the 2.0 mg/m³ dust standard for the past 40 years, the dust level was reduced significantly to 0.81 mg/m³ and 0.60 mg/m³ for continuous miner operators and roof bolter operators, respectively, marking a significant improvement in dust levels. Unfortunately, recent X-ray surveillance data between 2000-2006 shows an increase in CWP cases as compared to the data in previous years, and still nearly 8% of examined underground coal miners with 25 or more years of experience are diagnosed with CWP.

The National Academy of Sciences, Engineering, and Medicine committee specifies several objectives for the RCMD sampling and monitoring program including 1) tracking temporal and spatial trends in airborne RCMD concentrations that may be used for predictive analysis to lower the RCMD concentration or might be integrated in future smart mine systems; 2) correlating dust metrics with other operational parameters, such as production or operational variables, geologic or environmental conditions, and worker behaviors.

To address this research need, a collaborative team consisting of researchers at Michigan Technological University and University of Utah will gather information on temporal and spatial variations of RCMD within a mine using area (fixed-site) monitoring devices. The MSHA-approved gravimetric-based samplers will be installed at different locations within a mine on both short-term and long-term basis. To obtain the spatial and temporal variation of RCMD metrics, new characterization methods will be developed based on x-ray (micron and nano) computed tomography, field-flow fractionation, and/or micro x-ray fluorescence spectroscopy.