Rapid FTIR analysis for respirable crystalline silica monitoring in coal mines using readily available sampling equipment

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Virginia Tech


In coal mines, workers can be exposed to respirable coal mine dust (RCMD) in conjunction with respirable crystalline silica (RCS). Overexposure can pose serious health risks, including development of coal workers' pneumoconiosis (CWP) (also known as "black lung"). CWP has the potential to progress to a more consequential form known as progressive massive fibrosis (PMF), for which a dramatic resurgence has been observed among US miners since the early 2000's. Recent rules promulgated by the Mine Safety and Health Administration (MSHA) have lowered the permissible exposure limit (PEL) of RCMD and RCS, but the nuances of dust monitoring are complicated. For RCMD, frequent monitoring is required using the continuous personal dust monitor (CPDM), which enables real time data—but the physical sample collected by the CPDM cannot currently be used for RCS analysis. For RCS monitoring, filter samples are still collected with the traditional coal mine dust personal sampling unit (CMDPSU)—but the standard RCS analysis must be done in a centralized lab and there is considerable lag time between sampling and data availability. To enable rapid RCS analysis of filter samples, NIOSH has developed a direct-on-filter (DOF) Fourier transform infrared (FTIR) spectroscopy method for use with CMDPSU filter samples. It can be performed in the field with a portable instrument. NIOSH has also developed a compatible software called the Field Analysis of Silica Tool (FAST), which simplifies processing of the FTIR spectral data to yield RCS mass results. While not allowed to demonstrate regulatory compliance with the RCS PEL, this method could be quite useful for routine non-regulatory monitoring (e.g., to support research or engineering studies). However, adoption of the method may hinge on a variety of factors such as costs, ease-of-use, and the usability and reliability of generated data. This thesis reports a field study designed to demonstrate how the DOF FTIR method (with FAST) might be used by mines with relatively low-cost, off-the-shelf sampling components for the CMDPSU. The field study also demonstrates how the percentage of RCS in RCMD (in addition to RCS mass) can be estimated by simply pairing a CPDM with the CMDPSU during sampling. Understanding RCS percentage may be important for a variety of research or engineering applications. While the DOF FTIR method can work well for CMDPSU samples, it is recognized that RCS analysis of CPDM samples would be ideal. However, the materials and construction of the filter assembly used by the CPDM is not conducive to DOF analysis. As part of an effort to develop a simple method for CPDM sample recovery, redeposition, and analysis by FTIR, the second study in this thesis focused on establishing the recovery procedure—and corrections to account for sample mass and RCS content attributed to any residue sourced from the CPDM filter assembly itself. Using blank CPDM filters and blank CPDM filters spiked with well characterized respirable dust, results show that the mass and RCS content of the CPDM residue may be quite small. Moreover, using field CPDM samples, results show that dust recovery can be quite high. Taken together, these are promising findings and suggest that a method for RCS analysis of CPDM samples is possible.



Respirable, Coal, RCMD, Quartz, Silica, RCS, direct-on-filter, DOF, FTIR, Monitoring, Sampling