VTechWorks Repository :: Browsing by Author "Keles, Cigdem"

Browsing by Author "Keles, Cigdem"

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Application of a TGA Method to Estimate Coal, Carbonate, and Non-carbonate Mineral Fractions as a Proxy for the Major Sources of Respirable Coal Mine Dust
Jaramillo Taborda, Maria Lizeth (Virginia Tech, 2021-11-16)
Inhalation of respirable dust in coal mines is a serious occupational health hazard which can lead to the development of chronic and irreversible lung diseases, such as Coal Worker's Pneumoconiosis (CWP) and Progressive Massive fibrosis (PMF). After the passage of the Federal Coal Mine Health and Safety Act (CMHSA) in the late 1960's the prevalence of CWP among US coal miners decreased. However, since the late 1990's a resurgence of lung diseases has been reported, particularly in central Appalachia. On the other hand, dust monitoring data suggest that concentrations of respirable coal mine dust (RCMD) and crystalline silica have been on a downward trend. This contradiction has prompted keen interest in detailed characterization of RCMD to shed light on dust constituents-and their sources. Such information might help miners understand where and under what conditions specific sources contribute to RCMD, and how dust controls and monitoring could be enhanced to mitigate the exposure to respirable hazards. Respirable dust particles generated in coal mines are generally associated with three primary sources: the coal strata that is mined and generates mostly coal particles that could contribute for lung diseases, the rock strata that is cut along with the coal and generates most of the respirable silica and silicates, and the rock dust products that are the main source of carbonates which could produce respiratory irritations. Thermogravimetric Analysis (TGA) is one of many analytical tools that might be used for dust characterization. Its primary benefit is that it can be used to apportion the total sample mass into three mass fractions (i.e., coal, carbonates, non-carbonates) which should be roughly associated with the primary dust sources (i.e., coal strata, rock dust products, rock strata) in many coal mines. This thesis consists of two main chapters: Chapter 1, outlines the research motivation, recaps the efforts to establish a standard TGA method for RCMD, and shows results of the validation experiments that were performed in the current work to enable application of the TGA method to a large set of RCMD and laboratory-generated dust samples. In Chapter 2, 46 lab-generated samples from primary dust source materials collected in 15 coal mines, and 129 respirable dust samples from 23 US coal mines are analyzed using the TGA method validated in Chapter 1. Results for both sets of samples are presented and the mine samples are interpreted based on sampling location, mining method and region. Additionally, Chapter 3 summarizes recommendations for future work.
Applications of Thermal and Laser-Based Methods for Monitoring Airborne Particulates in Coal Mines
Phillips, Kent Thomas (Virginia Tech, 2017-09-22)
The purpose of this thesis is to examine applications of thermal and laser-based methods to monitor airborne particulates in underground coal mines. Specifically, coal and mixed mineral mine dust, as well as, diesel particulate matter (DPM). These particulates have historically, and continue to have, significant health impacts on underground miners. Chapters 1 and 2 of this thesis concentrate on using a novel method of thermogravimetric analysis (TGA) to characterize respirable coal and mixed mineral mine dust and presents the results of this method being applied to samples collected in Appalachia coal mines. Appalachia has been a geographic "hotspot" for the rise in occupational lung disease amongst underground coal miners, which began in 1990's after decades of steady decline. This has led researchers to propose there could be something unique about the respirable dust composition in Appalachia coal mines, which resulted in the surge of lung disease cases; however, the knowledge base regarding the actual composition of respirable coal mine dust is limited. The results of this thesis show that most of the mass fraction of respirable Appalachia coal mine dust is not coal, but rather carbonates and non-carbonate minerals (i.e. silica and silicates). These findings are significant as many researchers now suspect silica and silicates to be the true culprit in the occupational lung disease of coal miners. DPM presents an additional occupational health hazard to underground coal miners where diesel equipment is used and is difficult to monitor due to its complex nature. In underground metal/non-metal mines, airborne DPM is regulated and monitored using carbon surrogates. However, due to the potential interference from coal-sourced carbon, DPM in coal mines is monitored only by taking samples at the tailpipe of each piece of equipment. This thesis aims to investigate the potential for a laser-based instrument, the FLIR Airtec, to be used in underground coal mines. In particular, what effect the coal dust will have on the instrument, as it measures DPM by way of elemental carbon (EC). The results of this study show that while the Airtec will not over-estimate coal-sourced EC, there could be some sampling artifacts associated with its operation in coal mines, which may inhibit its effectiveness.
Characteristics of respirable dust in eight Appalachian coal mines: A dataset including particle size and mineralogy distributions, and metal and trace element mass concentrations
Sarver, Emily A.; Keles, Cigdem; Rezaee, Mohammad (Elsevier, 2019-08-01)
Respirable dust samples were collected in several key locations of eight underground coal mines in central and northern Appalachia. In total, there were 76 unique sampling events (i.e., specific location in a specific mine). Here, we present data from each event describing particle size and mineralogy class distributions across the ∼100–10,000nm size range, which were determined using SEM-EDX; and estimated mass concentrations of potentially bioaccessible and total acid-soluble metals and trace elements, which were determined using sequential digestions with digestate analysis by ICP-MS. Discussion of this dataset is included in a companion research article “Beyond conventional metrics: Comprehensive characterization of respirable coal mine dust” Sarver et al., 2019.
Characterization of Particulates from Australian Underground Coal Mines
LaBranche, Nikky; Keles, Cigdem; Sarver, Emily A.; Johnstone, Kelly; Cliff, David (MDPI, 2021-04-23)
The re-identification of coal workers’ pneumoconiosis in Queensland in 2015 has prompted improvements in exposure monitoring and health surveillance in Australia. The potential consequences of excessive exposure to respirable dust may depend upon the size, shape and mineralogical classes of the dust. Technology has now advanced to the point that the dust characteristics can be explored in detail. This research collected respirable dust samples from four operating underground coal mines in Australia for characterization analysis using scanning electron microscopy (SEM) with energy dispersive X-ray (EDX). The research found multiple mineralogical classes present with their own particle size distributions. The variation between mines appears to have had a larger effect on particle size distribution than the differences in mining processes within individual mines. This may be due to variations in the geologic conditions, seam variation or mining conditions.
Comparison of respirable coal mine dust constituents estimated using FTIR, TGA, and SEM-EDX
Pokhrel, Nishan; Agioutanti, el E.; Keles, Cigdem; Afrouz, Setareh; Sarver, Emily A. (Springer, 2022-02-24)
Since the mid-1990s, there has been a resurgence of severe lung disease among US coal miners. This has prompted efforts to better characterize and monitor respirable dust exposures—especially with respect to mineral constituents sourced from rock strata surrounding the coal, which is believed to play a central role in many cases of disease. Recently, a rapid analysis method for silica (quartz) mass has been developed using direct-on-filter Fourier transform infrared (FTIR) spectroscopy. It can concurrently provide an estimate of kaolinite, presumably a primary silicate mineral in many coal mines. Other methods, including thermogravimetric analysis (TGA) and scanning electron microscopy with energy-dispersive X-ray (SEM–EDX), can also be used to estimate respirable coal mine dust constituents. However, there have been few efforts to compare results across multiple methods. Here, FTIR, TGA, and SEM–EDX were used to analyze 93 sets of respirable dust samples collected in 16 underground coal mines across the USA.
A Computer-Controlled SEM-EDX Routine for Characterizing Respirable Coal Mine Dust
Johann-Essex, Victoria; Keles, Cigdem; Sarver, Emily A. (MDPI, 2017-01-23)
A recent resurgence in coal workers’ pneumoconiosis (or “black lung”) and concerns over other related respiratory illnesses have highlighted the need to elucidate characteristics of airborne particulates in occupational environments. A better understanding of particle size, aspect ratio, or chemical composition may offer new insights regarding causal factors of such illnesses. Scanning electron microscopy analysis using energy dispersive X-ray (SEM-EDX) can be used to estimate these particle characteristics. If conducted manually, such work can be very time intensive, limiting the number of particles that can be analyzed. Moreover, potential exists for user bias in interpretation of EDX spectra. A computer-controlled (CC) routine, on the other hand, can allow similar analysis at a much faster rate, increasing total particle counts and reproducibility of results. This paper describes a CCSEM-EDX routine specifically developed for analysis of respirable dust samples from coal mines. The routine is verified based on reliability of results obtained on samples of known materials, and reproducibility of results obtained on a set of 10 dust samples collected in the field. The characteristics of the field samples are also discussed with respect to mine occupational environments.
Considerations for TGA of Respirable Coal Mine Dust Samples
Scaggs, Meredith; Sarver, Emily A.; Keles, Cigdem (2015)
Respirable dust in coal mining environments has long been a concern for occupational health. Over the past several decades, much effort has been devoted to reducing dust exposures in these environments, and rates of coal workers’ pneumoconiosis (CWP) have dropped significantly. However, in some regions, including parts of Central Appalachia it appears that incidence of CWP has recently been on the rise. This trend is yet unexplained, but a possible factor might be changes in specific dust characteristics, such as particle composition, size or shape. Prior work in our research group has developed a standardized methodology for analyzing coal mine dust particles on polycarbonate filter media using scanning electron microscopy with energy dispersive x-ray (SEM-EDX). While the method allows individual particles to be characterized, it is very time-intensive because the instrument user must interrogate each particle manually; this limits the number of particles that can practically be characterized per sample. Moreover, results may be somewhat user-dependent since classification of particle composition involves some interpretation of EDX spectra. Respirable dust in underground coal mines has long been associated with occupational Jung diseases, particularly coal workers' pneumoconiosis (CWP) and silicosis. Regular dust sampling is required for assessing occupational exposures , and compliance with federal regulations is determined! on the basis of total respirable dust concentration and crystalline silica content by mass. In light of continued incidence of CWP amongst coal miners, additional information is needed to determine what role specific dust characteristics might play in health outcomes . While particle-level analysis is ideal, current time requirements and costs make this simply unfeasible for large numbers of samples. However, opportunities do exist for gleaning additional information from bulk analysis (i.e., beyond total mass and silica content) using relatively quick and inexpensive methods. Thermogravimetric analysis (TGA) may be a particularly attractive option. It involves precise sample weight measurement in a temperature controlled environment, such that weight changes over specific temperature ranges can be correlated to cheruical changes of particular sample constituents. In principle, TGA offers the ability to determine the coal and total mineral mass fractions in respirable dust samples. Such analysis could conceivably be combined with standard methods currently used to measure total mass and silica content. Under some circumstances , TGA might also be extended to provide information on specific dust constituents of interest (such as calcite). In this paper, we consider the benefits and challenges of TGA of respirable coal mine dust samples, and provide preliminary results and observations from ongoing research on this topic.
Demonstration of Direct-on-filter FTIR to Estimate Silica, Kaolinite, and Calcite Mineral Fraction in Respirable Coal Mine Dust Samples
Pokhrel, Nishan (Virginia Tech, 2021-09-09)
Respirable coal mine dust (RCMD) has long been recognized as an occupational health hazard. In addition to coal, RCMD can contain minerals such as crystalline silica (i.e., most often present as quartz). There has been a resurgence of lung diseases among US coal miners since the late-1990s which has emphasized the need for better quartz monitoring, and better dust characterization in general. Quartz monitoring in coal mines has traditionally used infrared (IR) spectroscopy-based analytical methods such as the MSHA Method P7 that require significant sample preparation and must be performed in a centralized lab. There are generally thus days to weeks between dust sample collection and reporting of results, which can prevent the prompt mitigation efforts to better control dust and reduce exposures. Recently, a rapid analysis method for quartz has been developed by the US National Institute for Occupational Safety and Health (NIOSH) using direct-on-filter (DOF) Fourier Transform Infrared (FTIR) spectroscopy. The method has been demonstrated in a number of NIOSH-led studies using both laboratory and field samples, and the results show very good accuracy relative to the Method P7 reference. However, it has heretofore not been widely used by others or compared to results from other non-IR analytical methods. Moreover, while FTIR can allow the measurement of additional analytes, this has not yet been a focus of DOF FTIR for RCMD analysis. Analytes such as kaolinite and calcite could be of particular interest in the context of RCMD source apportionment. In this thesis, the DOF FTIR method is used to estimate silica, kaolinite, and calcite mineral fraction in RCMD samples collected in 16 coal mines, and in the laboratory using dust source materials from those same mines. The results are compared to results from other dust characterization methods such as mass-based thermogravimetric analysis (TGA) and particle-based scanning electron microscopy with energy dispersive X-ray (SEM-EDX). Results indicate the usefulness of the DOF FTIR method, and comparison suggests the presence of significant non-carbonate minerals other than silica and kaolinite in the coal mine dust. The results also show that SEM-EDX frequently indicates more mineral content (primarily other aluminosilicates), than that is predicted by either FTIR or the TGA. Additionally, by focusing mainly on calcite (generally sourced from limestone-based rock dust used in coal mines to prevent coal dust explosion), the second part of this study explores basic source apportionment by analyzing mine samples and samples of major dust source materials (such as run-of-mine coal, rock strata, and rock dust products). Results show that calcite can serve as a suitable proxy for rock dust in coal mine dust, and the results are consistent with expectations surrounding the contribution of dust from different mine locations and sample sources. Additionally, the DOF FTIR also showed good agreement with the TGA and SEM-EDX.
Demonstration of Optical Microscopy and Image Processing to Classify Respirable Coal Mine Dust Particles
Santa, Nestor (Virginia Tech, 2021)
Inhalation of respirable coal mine dust (RCMD) can lead to chronic lung diseases, including coal worker’s pneumoconiosis (CWP) and more severe forms such as progressive massive fibrosis. After the Federal Coal Mine Health and Safety Act was passed in 1969, limits on exposure to respirable dust were set, and the prevalence of CWP abruptly decreased. However, during the last two decades, a resurgence of the disease has been reported. Many authors have argued that the increasing numbers might be related to mining practices, including the extraction of thinner coal seams, characteristics of the mineral deposits, and more powerful cutting machines. Dust particles in coal mines are usually associated with three main sources: Coal particles are produced when the coal seam is being actively extracted. Silica and silicates are generated while cutting the rock strata surrounding the coal or during roof-bolting activities. Finally, rock dust application is the primary source of highly pure carbonates. Timely information about dust composition would allow the identification of potential dust sources and pursue efforts to control dust exposure efficiently. However, this information needs to be provided promptly since dust levels are dynamically changing through the shift. Currently, monitoring technologies such as the continuous personal dust monitor allow real-time measurements, but they are limited to total dust concentration and provide no information about dust composition. More recently, the National Institute for Occupational Safety and Health (NIOSH) has been developing an end-of-shift silica monitor. Still, technologies that offer information on dust composition in a semi-continuous manner are needed. In this work, a new monitoring concept is explored that has the potential to provide near real time data on RCMD constituents. The possible use of a portable optical microscopy (OM) combined with image processing techniques is explored as the basis for a novel RCDM monitoring device. The use of OM in different fields and the rapid development of automated image analysis reveals a clear opportunity that has not been yet exploited for mine dust monitoring applications. This thesis research consisted of two primary studies. The first was an analysis of lab-generated respirable dust samples containing the main mineralogical classes in RCMD (i.e., coal, silica, kaolinite as a proxy for silicate minerals, and a real rock dust product). Samples were imaged using a polarizing microscope and analyzed using an image processing routine to identify and classify particles based on optical characteristics. Specifically, birefringence of particles was exploited to separate coal particles form mineral particles. This is an exciting result since even such a basic fractionation of RCMD would be valuable to track changing conditions at the mine production face and enable rapid decision making. The second study was conducted to explore subclassification of the mineral fraction. A model was built to explore multiple particle features, including particle size, shape, color, texture, and optical properties. However, a simple stepwise method that uses birefringence for separating coal particles first and then classifying silica particles proved most effective. One particular challenge to the silica classification was determined to be the particle loading density. Future work to further enhance the output of the algorithm and next steps were depicted. This thesis research demonstrated that OM and image processing can be used to separate mineral and coal fractions. Subclassification of silica and other minerals using optical properties such as birefringence of particles alone was successful, but showed less accuracy. A robust sampling method that accounts for particle loading density and a more complex model with additional differentiating features might enhance the results. This approach should be considered as a potential candidate for the development of new RCMD monitoring technologies. This tool could enable better tracking of dust conditions and thus better decision-making regarding ventilation, dust controls, and operator position to reduce exposure hazards.
Demonstration of Optical Microscopy and Image Processing to Classify Respirable Coal Mine Dust Particles
Santa, Nestor; Keles, Cigdem; Saylor, J. R.; Sarver, Emily A. (MDPI, 2021-08-02)
Respirable coal mine dust represents a serious health hazard for miners. Monitoring methods are needed that enable fractionation of dust into its primary components, and that do so in real time. Near the production face, a simple capability to monitor the coal versus mineral dust fractions would be highly valuable for tracking changes in dust sources—and supporting timely responses in terms of dust controls or other interventions to reduce exposures. In this work, the premise of dust monitoring with polarized light microscopy was explored. Using images of coal and representative mineral particles (kaolinite, crystalline silica, and limestone rock dust), a model was built to exploit birefringence of the mineral particles and effectively separate them from the coal. The model showed >95% accuracy on a test dataset with known particles. For composite samples containing both coal and minerals, the model also showed a very good agreement with results from the scanning electron microscopy classification, which was used as a reference method. Results could further the concept of a “cell phone microscope” type monitor for semi-continuous measurements in coal mines.
Development and Implementation of an Automated SEM-EDX Routine for Characterizing Respirable Coal Mine Dust
Johann, Victoria Anne (Virginia Tech, 2016-11-02)
This thesis describes the development and use of a computer-automated microscopy routine for characterization of respirable dust particles from coal mines. Respirable dust in underground coal mining environments has long been known to pose an occupational health hazard for miners. Typically following years of exposure, coal workers' pneumoconiosis (CWP) and silicosis are the most common disease diagnoses. Although dramatic reductions in CWP and silicosis cases were achieved across the US between about 1970-1999 through a combination of regulatory dust exposure limits, improved ventilation and dust abatement practices, a resurgence in disease incidence has been noted more recently – particularly in parts of Appalachia. To shed light on this alarming trend and allow for better understanding of the role of respirable dust in development of disease, more must be learned about the specific characteristics of dust particles and occupational exposures. This work first sought to develop an automated routine for the characterization of respirable dust using scanning electron microscopy with energy dispersive x-ray (SEM-EDX). SEM-EDX is a powerful tool that allows determination of the size, shape, and chemistry of individual particles, but manual operation of the instrument is very time consuming and has the potential to introduce user bias. The automated method developed here provides for much more efficient analysis – with a data capture rate that is typically 25 times faster than that of the manual method on which it was based – and also eliminates bias between users. Moreover, due to its efficiency and broader coverage of a dust sample, it allows for characterization of a larger and more representative number of particles per sample. The routine was verified using respirable dust samples generated from known materials commonly observed in underground coal mines in the central Appalachian region, as well as field samples collected in this region. This effort demonstrated that particles between about 1-9μm were accurately classified with respect to defined chemical categories, and suggested that analysis of 500 particles across a large area of a sample filter generally provides representative results. The automated SEM-EDX routine was then used to characterize a total of 210 respirable dust samples collected in eight Appalachian coal mines. The mines were located in three distinct regions (i.e., northern, mid-central and south-central Appalachia), which differed in terms of primary mining method, coal seam thickness and mining height, and coal and/or rock mineralogy. Results were analyzed to determine whether number distributions of particle size, aspect ratio, and chemistry classification vary between and within distinct mine regions, and by general sampling location categories (i.e., intake, feeder, production, return). Key findings include: 1) Northern Appalachian mines have relatively higher fractions of coal, carbonate, and heavy mineral particles than the two central Appalachian regions, whereas central Appalachian mines have higher fractions of quartz and alumino-silicate particles. 2) Central Appalachian mines tended to have more mine-to-mine variations in size, shape, and chemistry distributions than northern Appalachian mines. 3) With respect to particle size, samples collected in locations in the production and return categories have the highest percentages of very small particles (i.e., 0.94-2.0μm), followed by the feeder and then the intake locations. 4) With respect to particle shape, samples collected in locations in the production and return categories have higher fractions of particles with moderate (i.e., length is 1.5 to 3x width) to relatively high aspect ratios (i.e., length is greater than 3x width) compared to feeder and intake samples. 5) Samples with relatively high fractions of alumino-silicates have higher fractions of particles with moderate aspect ratios than samples with low alumino-silicate fractions. 6) Samples with relatively high fractions of quartz particles have higher fractions of particles with moderate aspect ratios and higher percentages of very small particles than samples with no identified quartz particles. 7) Samples with high fractions of carbonates have higher percentages of particles with relatively low aspect ratios (i.e., length and width are similar) than samples with no identified carbonate particles.
Direct-on-Filter FTIR Spectroscopy to Estimate Calcite as A Proxy for Limestone ‘Rock Dust’ in Respirable Coal Mine Dust Samples
Pokhrel, Nishan; Keles, Cigdem; Jaramillo, Lizeth; Agioutanti, Eleftheria; Sarver, Emily A. (MDPI, 2021-08-25)
Application of fine, inert ‘rock dust’ (RD) to the surfaces in underground coal mines is a common method for mitigating coal dust explosion hazards. However, due to its size, RD has the potential to contribute to the respirable coal mine dust (RCMD) concentration. Though the RD component of RCMD does not appear to pose the sort of health hazards associated with other components such as crystalline silica, understanding its relative abundance may be quite helpful for evaluating and controlling primary dust sources. Given that RD products are frequently comprised of high-purity limestone (i.e., primarily calcite mineral), calcite may serve as a suitable proxy for measuring RD. To estimate the mass percentage of calcite in RCMD samples, this study demonstrates the successful application of direct-on-filter (DOF) Fourier-transform infrared (FTIR) spectroscopy. Incidentally, DOF FTIR has been the focus of recent efforts to enable rapid measurement of crystalline silica in RCMD. Concurrent measurement of other constituents such as calcite is thus a logical next step, which can allow a broader interpretation of dust composition and source contributions.
Effects of Dust Controls and Dust Sources on Respirable Coal Mine Dust Characteristics
Animah, Festus Ayinimi (Virginia Tech, 2024-10-14)
Respirable coal mine dust (RCMD) continues to pose serious health hazards to workers. Over the past few decades, new regulations, monitoring technologies, and improved dust controls have emerged, and all are based on the presumption that limiting RCMD on the basis of mass will effectively mitigate the exposure hazards. Given the latency of exposure outcomes, it will be some time before the full impact of these strategies can be evaluated. In the meantime, there is increasing awareness that RCMD particle characteristics, in addition to mass, might be important. This dissertation comprises four separate studies which explore the effects of primary RCMD sources and/or engineering controls on particle size and constituents. To enable a direct comparison of dust generation from primary dust sources, a field study was conducted to investigate the dust generation and particle characteristics between coal and the rock strata. Results indicated that finer and more dust was generated when mining predominantly into the rock strata versus the coal strata, while the operation of a flooded bed scrubber and an increase in water sprays pressure and volume generally suppressed dust. Prior government research, conducted within the Mining Research Division of the National Institute of Occupational Safety and Health (NIOSH) evaluated the dust mass concentrations removal efficiency of different dust controls (i.e., a dry and wet scrubber, canopy air curtain, and a wet versus dry dust collection boxes). In the second and third studies, preserved samples from these prior NIOSH dust control studies were re-analyzed and evaluated to understand their effects on dust characteristics. Results indicated that the efficiency of dust controls was particle size dependent, as these controls mostly showed no appreciable effects on dust constituents. Generally, the cleaning of dust from a novel wet dust collection box versus a traditional dry dust box led to a reduction in operator exposure to hazardous dust. In the final study, a laboratory prototype flooded bed scrubber was evaluated to understand its efficiency on dust between different particle size bins (i.e., by particle count) ranging from 0.3-10 µm. From the results, removal efficiencies were generally low – and sometimes negative, for dust particles mostly in each of the size bins less than 2 µm. The results presented here highlight the need to holistically evaluate dust controls to understand their efficiency on dust of different particle sizes and constituents, so that informed decisions can be made on the best controls to adopt in mine operations.
Effects of dust controls on respirable coal mine dust composition and particle sizes: case studies on auxiliary scrubbers and canopy air curtain
Animah, Festus; Keles, Cigdem; Reed, W. R.; Sarver, Emily A. (2024-04-20)
Control of dust in underground coal mines is critical for mitigating both safety and health hazards. For decades, the National Institute of Occupational Safety and Health (NIOSH) has led research to evaluate the effectiveness of various dust control technologies in coal mines. Recent studies have included the evaluation of auxiliary scrubbers to reduce respirable dust downstream of active mining and the use of canopy air curtains (CACs) to reduce respirable dust in key operator positions. While detailed dust characterization was not a focus of such studies, this is a growing area of interest. Using preserved filter samples from three previous NIOSH studies, the current work aims to explore the effect of two different scrubbers (one wet and one dry) and a roof bolter CAC on respirable dust composition and particle size distribution. For this, the preserved filter samples were analyzed by thermogravimetric analysis and/or scanning electron microscopy with energy dispersive X-ray. Results indicate that dust composition was not appreciably affected by either scrubber or the CAC. However, the wet scrubber and CAC appeared to decrease the overall particle size distribution. Such an effect of the dry scrubber was not consistently observed, but this is probably related to the particular sampling location downstream of the scrubber which allowed for significant mixing of the scrubber exhaust and other return air. Aside from the insights gained with respect to the three specific dust control case studies revisited here, this work demonstrates the value of preserved dust samples for follow-up investigation more broadly.
Exploration of Respirable Dust Particles Sourced From Rock Strata in an Underground Coal Mine
Gonzalez Jaramillo, Jonathan (Virginia Tech, 2021-11-12)
Enactment of regulatory standards for respirable coal mine dust (RCMD) concentration and crystalline silica content, and advancements in mine ventilation and dust controls led to a steady decline of occupational lung disease among US coal miners between the early 1970s and the mid-1990s. Since that time, there has been an alarming resurgence of disease especially in central Appalachia—with little hard data to pinpoint the causative factors in the mine environment. This situation has emphasized the knowledge gap surrounding specific dust characteristics and their sources. Key observations from many disease cases have suggested that dust constituents sourced from the rock strata in the mine (i.e., the rock layers that surround the target coal seam) may be particularly important; and this fits with the general tendency to extract thinner coal seams, and thus more rock, in many central Appalachian mines. To explore the characteristics of rock-strata sourced dust and its possible influence on the overall RCMD, this thesis reports two primary research efforts: Chapter 1 encompasses a case study conducted in an underground coal mine in West Virginia. (This chapter was previously published in the proceedings of the 18th North American Mine Ventilation Symposium, and is being reproduced with permission of the licensor through.) Following precedent from other studies, respirable dust samples were collected from key locations including in the intake airway, downwind an operating roof bolter, and adjacent to the feeder breaker. Additionally, three locations downwind the production face were simultaneously sampled during four individual continuous miner cuts—which was a unique feature of the current study. Dust was analyzed using previously established methods, including scanning electron microscopy with energy dispersive X-ray (SEM-EDX) to determine particle size and mineralogy distributions. Where comparable, results were generally consistent with those from other central Appalachian mines. However, the unique production sampling scheme offered new insights regarding the shift in particle characteristics as dust moves downwind from the generation point. Changes in size and mineralogy suggested that rock-strata sourced particles, especially aluminosilicates, might interfere with the SEM-EDX classification of other particles, especially coal. To explore the issue of aluminosilicate interference with coal classification, and the possible reasons, Chapter 2 covers two main lines of study. First, existing RCMD samples and SEM-EDX metadata were re-examined. Results suggested that particle loading effects could be at least partly responsible for the appearance of inordinately high aluminosilicate abundance (and conversely low coal) in some samples (i.e., the mineral particles might deposit on the sample filter in close proximity to the coal). Additionally, the presence of coal-mineral microagglomerates (MAGs) was demonstrated. The second line of study in Chapter 2 was therefore to explore whether MAG formation could be due to the RCMD generation process or environmental conditions—rather than merely an artifact of the sampling procedure—and the dispersibility of MAGs, which may have important implications with respect to dust exposure and biological response. Laboratory-generated samples collected passively demonstrated that coal-mineral MAGs can indeed occur without influence from typical RCMD sampling equipment. MAGs were significantly dispersed by sonication in deionized water, though gentle swirling did not yield consistent results. Moreover, in a surfactant solution that mimics natural lung fluid, MAGs were also dispersed. Compared to deionized water, the surfactant may promote more dispersion of coal particles in particular.
Exploring the Effect of Particle Loading Density on Respirable Dust Classification by SEM-EDX
Sweeney, Daniel; Keles, Cigdem; Sarver, Emily (MDPI, 2024-07-20)
Exposure to respirable coal mine dust (RCMD) still poses health risks to miners. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) is a powerful tool for RCMD characterization because it provides particle-level data, including elemental ratios (via the EDX signals) that can enable classification by inferred mineralogy. However, if the particle loading density (PLD) is high on the analyzed substrate (filter sample), interference between neighboring particles could cause misclassification. To investigate this possibility, a two-part study was conducted. First, the effect of PLD on RCMD classification was isolated by comparing dust particles recovered from the same parent filters under both low- and high-PLD conditions, and a set of modified classification criteria were established to correct for high PLD. Second, the modified criteria were applied to RCMD particles on pairs of filters, with each pair having one filter that was analyzed directly (frequently high PLD) and another filter from which particles were recovered and redeposited prior to analysis (frequently lower PLD). It was expected that application of the modified criteria would improve the agreement between mineralogy distributions for paired filters; however, relatively little change was observed for most pairs. These results suggest that factors other than PLD, including particle agglomeration, can have a substantial effect on the particle EDX data collected during direct-on-filter analysis.
An Improved Thermogravimetric Analysis Method for Respirable Coal Mine Dust and Comparison to Results by SEM-EDX
Agioutanti, Eleftheria (Virginia Tech, 2019-07-24)
It has long been known that chronic exposures to high concentrations of respirable coal mine dust can lead to the development of lung diseases such as Coal Worker's Pneumoconiosis, commonly referred to as "black lung", and silicosis. Since the mid-1990s, an alarming resurgence of diseases has been documented in central Appalachia, where underground mining often necessitates significant extraction of rock strata along with the thin seams of coal. These circumstances have prompted concern over if or how changing dust composition might be a factor in contemporary disease prevalence. Until now, the total mass concentration and quartz mass fraction of respirable dust have been regulated and monitored in US coal mines. Unfortunately, however, these two metrics alone do not paint a full picture of dust composition. Earlier work in the author's research group established a preliminary thermogravimetric analysis (TGA) method for coal mine dust. The method is intended to allow estimation of three key mass fractions of the dust from separate sources: coal from the coal strata being mined; non-carbonate minerals from the rock strata being mined or drilled; and carbonates that are primarly sourced from application of rock dust products to the mine floor or ribs. However, accuracy of the preliminary method was substantially limited by poor dust recovery from the fibrous filter media used for sample collection. This thesis includes two studies: The first study aims to establish an improved TGA method. It uses smooth polycarbonate (PC) filters for dust sampling and a modified thermal ramping routine. The method is verified using laboratory-generated respirable dust samples. In the second study, the improved TGA method is used to analyze 75 respirable mine dust samples, collected in 15 US mines. Replicate samples are also analyzed by scanning electron microscopy using energy dispersive X-ray (SEM-EDX). TGA and SEM-EDX results are compared to gain insights regarding the analytical methods and general trends in dust composition within and between mines.
Investigating the Effects of Particle Loading and Agglomeration on Respirable Coal Mine Dust Particle Classification by SEM-EDX
Sweeney, Daniel Joseph (Virginia Tech, 2024-06-03)
Respirable coal mine dust (RCMD) still poses serious occupational health hazards to coal miners and can lead to incurable lung diseases such as coal workers' pneumoconiosis (CWP, also referred to as "black lung"). Further, CWP can develop into a more severe form known as progressive massive fibrosis (PMF). There has been a resurgence of PMF since the late 1990s. Coal miners are also exposed to crystalline silica, which can lead to a lung disease known as silicosis. While coal mining related disease is on the rise, the historic dust monitoring data does not indicate such a striking resurgence. As a result, there has been an increased interest in research surrounding RCMD to understand exposure as well as prevent health effects. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) is a powerful tool that can analyze RCMD on a particle-level. The images produced by the SEM can size and characterize morphology of micron and submicron-sized particles. In addition, the EDX can determine elemental content, which can be used to infer mineralogy. However, particle classification can be impacted by interferences due to particle loading density (PLD) and agglomeration. PLD refers to the number of particles per unit area of substrate, while agglomeration describes clustered or overlapping particles. This thesis includes two studies aimed at exploring the effects of both PLD and agglomeration on SEM-EDX analysis. Study 1 includes an investigation into the effect of PLD on RCMD classification by SEM-EDX analysis. Dust recovered from the sample parent filters under low and high PLD conditions were used to isolate the effect of PLD. The comparison between the low and high PLD filters was then used to establish modified classification criteria to correct for high PLD. When the modified criteria were then applied to RCMD particles analyzed direct-on-filter, minimal change was observed in the apparent mineralogy distributions for most samples. These results suggest that particle agglomeration may have substantial effects on the particle classification of respirable dust analyzed direct-on-filter. Study 2 includes an investigation into the effect of particle agglomeration on RCMD by SEM-EDX analysis. Automated and manual SEM-EDX analysis was performed on paired filters collected from a parent filter. The manual analysis targeted respirable silica containing agglomerates. Each pair consisted of a filter analyzed directly and a filter that underwent a recovery process to deposit dust particles onto a new filter. The mineralogy distributions from the automated analysis suggest that agglomeration affects sizing and particle classification. Based on the manual analysis, there was an apparent increase in independent silica and a decrease in respirable silica-containing agglomerates after the recovery process. A limited collection of passive samples revealed more agglomerates than on the filters that were collected using a pump and size-selector cyclone. The work in this thesis is relevant to the research efforts aimed at the resurgence of coal mining related lung diseases, as the use of SEM-EDX can characterize RCMD by geographic region, geology, and location within a mine. Future work in this area of study might look at methods to estimate PLD in the field, other dust recovery methods, and a comparison of sampling methods.
On the occurrence and persistence of coal-mineral microagglomerates in respirable coal mine dust
Gonzalez, Jonathan; Keles, Cigdem; Sarver, Emily A. (Springer, 2022-02-10)
A previous effort to characterize respirable coal mine dust in 16 US mines turned up a curious finding: particle-based analysis using scanning electron microscopy (SEM) tended to overpredict the abundance of dust sourced from rock strata, and underpredict the abundance of coal, when compared to mass-based thermogravimetric analysis (TGA). One possible explanation is the occurrence of coal-mineral microagglomerates (MAGs). Coal particles covered with fine mineral dust could be mostly coal by mass but classified as minerals by SEM due to their surface elemental content. In the current study, a subset of the previously analyzed mine dust samples was re-examined, and SEM images and elemental mapping showed that MAGs are indeed present. Furthermore, dust samples were created and sampled passively in the laboratory, demonstrating that MAG formation can occur due to dust generation processes and the sampling environment, rather than as a mere artifact of respirable dust sampling procedures. Finally, experiments were conducted to evaluate dispersibility of MAGs in liquid suspensions, which might shed some light on their possible fate upon inhalation. Results indicated that sonication in deionized water was effective for MAG dispersion, and a solution that mimics natural lung surfactant also appeared to enhance dispersibility. An understanding of MAG occurrence might be important in terms of exposure assessment.
Particle size and mineralogy distributions in respirable dust samples from 25 US underground coal mines
Sarver, Emily A.; Keles, Cigdem; Ghaychi Afrouz, Setareh (Elsevier, 2021-11-01)
Detailed characterization of respirable coal mine dust is critical to understanding occupational health outcomes, as well as improving exposure monitoring and dust controls in mines. However, data on characteristics such as particle size and mineralogy are still scarce, and there are virtually no datasets available that allow direct comparisons across many mines. Following up on a previous effort to characterize dust from eight underground mines in the Appalachian region of the United States, the current study expands the dataset to cover a total of 25 mines across the country. A total of 171 respirable dust samples were collected in standard locations of each mine and analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Results demonstrate that significant differences in particle size and mineralogy distributions exist both within and between mines based on sampling location, mine region and/or mining method–and characteristics can be indicative of dust sources. In locations nearby to production or roof bolting, the respirable dust was clearly sourced from the mine strata. Interestingly, in the production location rock-strata sourced dust appeared to be inordinately abundant relative to the actual coal and rock strata heights being mined during sampling. With respect to particle size, diesel particulates and coal dust were generally found to be finer than mineral dust; and mineral dust likely sourced from the rock strata in the mine was finer than that associated with rock dusting products. On average, when considering all particles analyzed between 100 and 10,000 nm, results indicate that about 75% are in the submicron range, however these particles are estimated to account for only about 6% of the mass.

Browsing by Author "Keles, Cigdem"

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