Respirable Crystalline Silica Concentrations Research Articles

Measurements of dust and respirable crystalline silica during indoor demolition and renovation.

Increased focus on renovating and maintaining the existing building stock is an integral part of the circular economy, however this might pose challenges to workers health. The aim of this study was to assess the renovation workers' exposure to inhalable dust, thoracic dust, respirable dust, and respirable crystalline silica (RCS). Personal aerosol samples were collected as full shift samples from 92 workers to a total of 407 samples. Fourteen locations around Oslo, Norway was visited for multiple days with repeated measurements of the same individual. Particulate matter from 3 aerosol fractions, respirable, thoracic, and inhalable, were analyzed gravimetrically, and the respirable fraction was analyzed for RCS by NIOSH 7500 method for X-ray diffraction (XRD)with low temperature plasma ashing sample preparation. The total measured concentrations of respirable dust (n = 192) had a geometric mean (GM) of 0.88mg/m3, RCS concentrations (n = 182) had a GM of 0.040mg/m3, thoracic dust (n = 131) had GM 2.4mg/m3, and inhalable dust (n = 84) had a GM of 8.5mg/m3. The maximum measured concentrations were 29mg/m3, 3.2mg/m3, 65mg/m3, and 163mg/m3, respectively. Workdays involving tasks such as mechanical demolition and clearing out demolished materials led to the highest exposure levels of both dust and RCS. However, other workers at the renovation sites were indirectly exposed to a considerable amount of RCS. This study revealed substantial exposure to both RCS and dust during renovation, and protective measures are warranted to reduce exposure levels in the industry.

Indoor/Outdoor particulate matter (respirable dust) and respirable crystalline silica source tracking in households located proximal to gold mine tailings in Johannesburg, South Africa

Introduction: This study aimed to investigate the concentration of Respirable Crystalline Silica (RCS) and respirable dust, Particulate matters (PM4) concentration in samples measured indoors and outdoors of the nine(9) selected households located proximal to gold mine tailings in Riverlea, Johannesburg. Materials and methods: Sampling locations were separated according to grids, based on distance from the tailings; A (<500 m from the dump), B (>500m<1 km) and C (1 km-3 km). Three households were selected from each grid zone to measure indoor and outdoor PM4 samples continuously over 24 h using GilAir constant sampling pumps. Samples were collected during dry and wet seasons, and respirable crystalline silica in PM4 samples were analysed by an X-ray diffraction method. Results: The mean indoor and outdoor PM4 mass concentrations ranged from 2.02±0.02 µg/m3 to 2.26±0.02 µg/m3, respectively. The dry season mean for PM4 mass concentrations were higher than the wet season PM4 mass concentrations in all zones. The pairwise comparison of PM4 mass concentration for dry and wet seasons revealed no statistically significant difference (p<0.05). The dry season means the indoor/outdoor ratio was greater than one across all zones, suggesting indoor activities as the primary source of PM. In both seasons, the mean indoor and outdoor RCS ranged from 0.02±0.01% to 0.06±0.03%. The mean indoor and outdoor 24 h RCS concentrations in both seasons were below the California Office of Environmental Health Hazard Assessment (OEHHA) defined 24 h ambient exposure threshold of 3 µg/m3. Conclusion: The study found that PM4 concentration was directly proportional to distance from the gold mine tailings. Using RCS as a signature chemical, we found a similar chemical composition in all samples collected in winter and dry season at varied distances. It is concluded that the gold mine tailings are the significant source of PM4 emissions. Therefore, further dust control measures needs to be implemented at the gold mine tailings.

New Afton Mine diesel and battery electric load-haul-dump vehicle field test: Heat and dust contribution study

ABSTRACT The New Afton Mine and CanmetMINING conducted a joint study to better understand the environmental and performance impacts of battery- and diesel-powered mobile equipment. The two main objectives were to: (1) determine if battery electric and diesel load-haul-dump vehicles (LHDs) could perform equivalent duties, and (2) gather environmental information for determining the ventilation airflow requirements for battery-powered vehicles. The study focused on the effects of the LHDs on heat and dust generation and energy consumption in a ramp and in a production level. For the production environment tested, respirable crystalline silica concentrations were the driver to assess the battery-powered LHD airflow volume. The potential to reduce this volume was identified in the controlled air streams and conditions tested. However, it depended on the scenario and the dust generation and suppression mechanisms. One scenario evaluated environmental conditions under a reduced airflow (50% less than the diesel LHD). For this mine site, area contaminants levels exceeded limits; therefore, the potential for savings was less than 50%. For the scenarios tested, the battery electric and diesel LHDs were able to move equivalent amounts of material in a similar time.

Concentrations of respirable crystalline silica and radon among tanzanite mining communities in Mererani, Tanzania.

Globally, the number of small-scale miners (SSM) is estimated to be more than 25 million, but it supports the livelihoods of around 100 million individuals. In Tanzania, the number of SSM has increased from an estimated 150,000 in 1987 to ~1.5 million in 2017. The miners are at a high risk of occupational-related health challenges. The study aimed to assess the concentrations of respirable crystalline silica (RCS) and radon among the tanzanite mining communities in Simanjiro District, Tanzania. We carried out a cross-sectional study involving the Mererani mines in Tanzania. These are underground mines comprised of informally employed miners, i.e. SSM. Concentrations of RCS and radon gas were measured in 44 study units, i.e. 22 mining pits and within 22 houses in the general community, e.g. shops in the peri-mining community. A total of 132 respirable personal dust exposure samples (PDS), 3 from each of the study units were taken, but only 66 PDS from the mining pits were analysed, as this was the main interest of this study. Radon concentration was measured by continuous monitoring throughout the working shift (and overnight for residences) using AlphaGuard monitor. The medians and comparison to the reference values, OSHA USA PEL and WHO/IARC references, were done for RCS and radon, respectively, using SPSS Ver. 27.0.0). The median time-weighted average (TWA) concentration of the RCS in the mining pits was 1.23 mg/m3. Of all 66 personal dust samples from the mining pits, 65 (98.5%) had concentrations of RCS above the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 0.05 mg/m3. Mining pits had a median radon concentration of 169.50 bq/m3, which is above the World Health Organization (WHO)/International Commission on Radiation Protection (ICRP) recommended reference of 100.00 bq/m3 but not above the upper reference of 300.00 bq/m3, while the community buildings had a median radon concentration of 88.00 bq/m3. Overall, 9 (20.5%) and 17 (38.6%) radon measurements were above 300.00 bq/m3 and between 100.00 and 300.00 bq/m3 references, respectively. Specifically, in the mining pits, 9 (40.9%) test results were above 300.00 bq/m3, while none of the test results in the community was above 300.00 bq/m3. The tanzanite SSM in Mererani we highly exposed to RCS, which increases the risk of pulmonary diseases, including silicosis, tuberculosis, and pulmonary malignancies. Immediate action by OSHA Tanzania should be enforcement of wearing respirators by all miners throughout the working hours. Health education programmes to the SSM must be strengthened and OSHA Tanzania should adopt the 0.05 mg/m3 PEL, and enforce other occupational health and safety measures, including regular use of dust suppression mechanisms (water spray and wet drilling) and monitoring of RCS exposures among SSM. Monitoring of radon exposure both in the mining pits and community buildings should be conducted, and mitigation measures should be implemented in areas that exceed the reference level of 100.00 bq/m3.

Determinants of respirable crystalline silica exposure in construction in western Canada.

Task-based respirable crystalline silica (RCS) exposure monitoring data was collected from construction work sites across 3 Canadian provinces: Alberta, British Columbia (BC), and Manitoba. In total 373 RCS samples were obtained from 70 worksites across 44 companies. Sampling was conducted between May 2015 and August 2020. The overall geometric mean (GM) RCS exposure was 0.045 mg/m3 (geometric standard deviation, GSD = 6.8). Alberta had the highest average exposure and the highest variability with GM of 0.060 mg/m3 (GSD = 9.3), the GM in BC was 0.044 (GSD = 4.3), and in Manitoba the GM was 0.033 (GSD = 7.0). A multivariable model was built using forward stepwise linear regression modeling. Province, task type, work environment (indoor vs. outdoor), construction material, sampling duration, and engineering control use were all statistically significant predictors of exposure level in partial F-tests (P < 0.05). Overall, the model explained 42% of the RCS concentration variability. Task type contributed most to the model's explanatory power. The task type with highest average exposure levels was demolition (GM 0.30 mg/m3, GSD 0.49). Breaking (GM 0.16 mg/m3, GSD 8.4) and grinding (GM 0.081 m/m3, GSD 7.4) also had high-exposure levels. Working outdoors was associated with exposure levels 39% lower than indoors. Exposure control measures such as local exhaust ventilation and wetting were also associated with lower exposure levels. Among construction materials, Cement, sand, and stone were associated with higher RCS exposure levels relative to the reference material, concrete. The results of this study indicate that workers in western Canada remain exposed to RCS at levels that exceed the health-based American Congress for Governmental Industrial Hygienists Threshold Limit Value of 0.025 mg/m3. Although there were some differences in exposure levels between the provinces, the determinants of exposure were similar in all 3. The overall GM RCS exposure was 0.045 mg/m3 (geometric standard deviation, GSD = 6.8). Alberta had the highest average exposure and the highest variability with GM of 0.060 mg/m3 (GSD = 9.3), the GM in BC was 0.044 (GSD = 4.3), and in Manitoba the GM was 0.033 (GSD = 7.0).

146 Meteorological Influence on Measurement Strategy and Estimated Respirable Dust and Respirable Crystalline Silica Exposure Levels Within the European Minerals Industry

Abstract The evidence of meteorological conditions on occupational exposure measurements is limited, despite is expected to be important determinants of long-term exposures. We describe meteorological conditions for measurement and non-measurement days and evaluate associations between temperature and total precipitation and respirable dust and respirable crystalline silica (RCS) concentrations of the European Industrial Minerals Association-Dust Monitoring Programme. Geo-matched RCS and dust measurements were evaluated against meteorological data (archived satellite observations and weather station measurements). Temperature(0C) and total precipitation (mm) for RCS measurement and non-measurement days were described. A linear regression model was used to investigate the association between dust and RCS concentration and meteorological conditions. Overall, 2,840 dust measurements (GM=0.20mg/m3; GSD=3.43mg/m3) and 2,658 quartz measurements (GM=0.01mg/m3; GSD=5.23mg/m3) were collected across 96 an 94 industrial mineral sites over 262 and 259 days in 2011. Mean temperature and precipitation for dust and RCS measurements were similar for measurement and non-measurement days (dust: 10.490C and 10.830C, 2.23mm and 2.12mm; RCS: 11.050C and 10.820C, 2.08mm and 2.12mm). For respirable dust concentrations a 6.4% decrease per 1°C was estimated for temperatures&amp;lt;200C (p&amp;lt;0.001) and an 8.2% increase for temperatures≥200C (p=0.002). For RCS a 2% decrease in was estimated for every 1mm increase in total precipitation (p=0.02). No difference in meteorological conditions were seen between measurements days and non-measurement days. Associations of these conditions with exposure concentrations with showed differences between agents despite being collected and measured on the same filter. Long-term changes in meteorological conditions might be an important factor when estimating long term exposures.

66 A New Raman Spectroscopy Approach for the Measurement of Respirable Crystalline Silica Aerosols Collected onto Filters: Practical Considerations and Advantages

Abstract It is estimated that 560,000 workers in the United Kingdom are potentially exposed to respirable crystalline silica (RCS), which can cause disabling diseases such as silicosis and cancer. The incidence of silicosis in exposed workers can occur at levels below current workplace exposure limits and sensitive analytical techniques are needed to measure low RCS concentrations. The analytical performance of a new Raman spectroscopy method was compared with current X-ray diffraction (XRD) methods. The study investigated limits of detection, measurement uncertainty and measured samples collected from inside respirators. In total, 119 respirable, thoracic, and samples from the Sioutas impactor (PM10 to PM2.5) were also collected from cutting and polishing of engineered and natural stones and analysed for RCS. The LOD for Raman of 0.26 µg is lower than those published for current XRD or infrared methods (5 to 10 µg). The coefficients of determination were between 0.97 and 0.94. The Raman response is as stable as XRD when measuring samples with different median particle sizes (from 0.5 to 7 µm). Raman measurements were significantly different at the 95 % confidence level for the respirable samples (slope = 1.11) but not for thoracic samples (slope = 1.03). Raman spectroscopy has an advantage when measuring quartz in the presence of some minerals that cause interferences with XRD such as zircon. Raman spectroscopy is a promising alternative to XRD for RCS measurements. It has a low LOD and few modifications of current protocols would be necessary to adopt a Raman analysis approach. 2022© Crown copyright

11 Raman Spectroscopy to Monitor Short-Term and Transient RCS Aerosol Exposure

Abstract Exposure to respirable crystalline silica (RCS) at concentrations at or below the OSHA permissible exposure limit (PEL) of 50 µg/m3 are challenging to monitor with the current industry standard methods X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). In particular, the assessment of short-term or transient exposure to RCS concentration calls for more sensitive analytical methods that are able to quantify RCS from low dust amounts within the desired uncertainty limits. Here, we present results from a verification study of a Raman spectroscopy-based Identifier system including dedicated respirable air samplers (badges) for the collection of airborne RCS. The air sampling badges concentrate the analyte onto dedicated 1 mm2 collection membranes suitable for direct-on-filter (DOF) Raman analysis. The sampling efficiency of the badges was assessed experimentally and shown to closely adapt the respirable sampling convention according to ISO 7708, with a low sampler bias of &amp;lt; 10%. Using a fully automated Raman-based bench-top reader, the limit of detection (LOD) and limit of quantification (LOQ) were determined empirically with 0.1 and 0.3 µg, respectively. The limits are approx. an order of magnitude lower than for the current industry standards and enable the relevant monitoring of short-term or transient exposure of workers to RCS, as they typically occur in construction or mining environments. The optimized workflow of the Identifier system makes it an attractive alternative to the industry standards XRD and FTIR, with the opportunity to monitor exposure down to the action level.

Exposure to Particulate Matter and Respirable Crystalline Silica in Tunnel Construction Workers Using Tunnel Boring Machines.

This study aimed to assess the exposure to a selection of aerosols and gases in the work environment for workers performing tunnel construction using tunnel boring machines (TBMs), to identify determinants of exposure based on the information available and to calculate robust estimates of exposure using a statistical model. The focus was particulate matter (PM) and respirable crystalline silica (RCS). In addition, concentrations of nitrogen dioxide (NO2), elemental carbon (EC), and oil mist were assessed. Personal sampling was conducted from February 2017 to February 2019. PM in the thoracic and the respirable aerosol fractions was collected, and RCS was determined in the respirable aerosol fraction. Context information was collected on questionnaires. Because the workers could participate in the sampling more than once and multiple measurements were performed on the same date a mixed model was used in the analysis. Concentrations of PM and RCS are presented as estimated and measured geometric means (GMest and GMmea) and estimated arithmetic mean (AMest) in addition to the median. Measured concentrations of NO2, EC, and oil mist are presented as geometric means. A total of 290 and 289 personal samples of PM in the thoracic and respirable aerosol fractions were available for analysis, respectively. Work title/work location, type of work (production, maintenance, or a combination of the two), and date of sampling were identified as determinants of exposure. Workers in the front of the TBMs had the highest exposure to PM and RCS. The GMest of RCS exposure varied from 35 to 413 μg m-3 depending on the work title. The geometric standard deviations for measured RCS concentrations by work title ranged from 1.6 to 3.5. A total of 16 samples of NO2 and EC and 12 samples of oil mist were collected. Maximum values of NO2 and EC were 54 µg m-3 and 23 µg m-3, respectively. The maximum measured value of oil mist was 0.08 mg m-3. All TBM workers were exposed to PM and RCS. Exposure to RCS may be substantial, and workers in front of the TBM were exposed to the highest concentrations of both PM and RCS. A day-to-day variation was found, probably caused by differences in drilling activities. Preventive measures are warranted to keep the exposure to PM and consequently the exposure to RCS as low as possible to protect the health of workers in tunnel construction.

Investigation of respirable coal mine dust (RCMD) and respirable crystalline silica (RCS) in the U.S. underground and surface coal mines

Dust is an inherent byproduct of mining activities that raises notable health and safety concerns. Cumulative inhalation of respirable coal mine dust (RCMD) and respirable crystalline silica (RCS) can lead to obstructive lung diseases. Despite considerable efforts to reduce dust exposure by decreasing the permissible exposure limits (PEL) and improving the monitoring techniques, the rate of mine workers with respiratory diseases is still high. The root causes of the high prevalence of respiratory diseases remain unknown. This study aimed to investigate contributing factors in RCMD and RCS dust concentrations in both surface and underground mines. To this end, a data management approach is performed on MSHA’s database between 1989 and 2018 using SQL data management. In this process, all data were grouped by mine ID, and then, categories of interests were defined to conduct statistical analysis using the generalized estimating equation (GEE) model. The total number of 12,537 and 9050 observations for respirable dust concentration are included, respectively, in the U.S. underground and surface mines. Several variables were defined in four categories of interest including mine type, geographic location, mine size, and coal seam height. Hypotheses were developed for each category based on the research model and were tested using multiple linear regression analysis. The results of the analysis indicate higher RCMD concentration in underground compared to RCS concentration which is found to be relatively higher in surface coal mines. In addition, RCMD concentration is seen to be higher in the Interior region while RCS is higher in the Appalachia region. Moreover, mines of small sizes show lower RCMD and higher RCS concentrations. Finally, thin-seam coal has greater RCMD and RCS concentrations compared to thicker seams in both underground and surface mines. In the end, it is demonstrated that RCMD and RCS concentrations in both surface and underground mines have decreased. Therefore, further research is needed to investigate the efficacy of the current mass-concentration-based monitoring system.

Benefits and limitations of field-based monitoring approaches for respirable dust and crystalline silica applied in a sandstone quarry

With the advent of new sensing technologies and robust field-deployable analyzers, monitoring approaches can now generate valuable hazard information directly in the workplace. This is the case for monitoring respirable dust and respirable crystalline silica concentration levels. Estimating the quartz amount of a respirable dust sample by nondestructive analysis can be carried out using portable Fourier transform infrared spectroscopy (FTIR) units. Real-time respirable dust monitors, combined with small video cameras, allow advanced assessments using the Helmet-CAM methodology. These two field-based monitoring approaches, developed by the National Institute for Occupational Safety and Health (NIOSH), have been trialed in a sandstone quarry. Twenty-six Helmet-CAM sessions were conducted, and forty-one dust samples were collected around the quarry and analyzed on-site during two events. The generated data generated were used to characterize concentration levels for the monitored areas and workers, to identify good practices, and to illustrate activities that could be improved with additional engineered control technologies. Laboratory analysis of the collected samples complemented the field finding and provided an assessment of the performance of the field-based techniques. Only a fraction of the real-time respirable dust monitoring sessions data could be corrected with laboratory analysis. The average correction factor ratio was 5.0. Nevertheless, Helmet-CAM results provided valuable information for each session. The field-based quartz monitoring approach overestimated the concentration by a factor of 1.8, but it successfully assessed the quartz concentration trends in the quarry. The data collected could be used for the determination of a quarry calibration factor for future events. The quartz content in the dust was found to vary from 14% to 100%, and this indicates the need for multiple techniques in the characterization of respirable dust and quartz concentration and exposure. Overall, this study reports the importance of the adoption of field-based monitoring techniques when combined with a proper understanding and knowledge of the capabilities and limitations of each technique.

Excess iron promotes emergence of foamy macrophages that overexpress ferritin in the lungs of silicosis patients.

Background and objectiveInhalation of high concentrations of respirable crystalline silica (RCS) can lead to silicosis. RCS contains varying levels of iron, which can cause oxidative stress and stimulate ferritin production. This study evaluated iron‐related and inflammatory markers in control and silicosis patients.MethodsA cohort of stone benchtop industry workers (n = 18) were radiologically classified by disease severity into simple or complicated silicosis. Peripheral blood and bronchoalveolar lavage (BAL) were collected to measure iron, ferritin, C‐reactive protein, serum amyloid A and serum silicon levels. Ferritin subunit expression in BAL and transbronchial biopsies was analysed by reverse transcription quantitative PCR. Lipid accumulation in BAL macrophages was assessed by Oil Red O staining.ResultsSerum iron levels were significantly elevated in patients with silicosis, with a strong positive association with serum ferritin levels. In contrast, markers of systemic inflammation were not increased in silicosis patients. Serum silicon levels were significantly elevated in complicated disease. BAL macrophages from silicosis patients were morphologically consistent with lipid‐laden foamy macrophages. Ferritin light chain (FTL) mRNA expression in BAL macrophages was also significantly elevated in simple silicosis patients and correlated with systemic ferritin.ConclusionOur findings suggest that elevated iron levels during the early phases of silicosis increase FTL expression in BAL macrophages, which drives elevated BAL and serum ferritin levels. Excess iron and ferritin were also associated with the emergence of a foamy BAL macrophage phenotype. Ferritin may represent an early disease marker for silicosis, where increased levels are independent of inflammation and may contribute to fibrotic lung remodelling.

Respirable Dust and Respirable Crystalline Silica Concentration in Workers of Copper Mine, Mongolia

Introduction: Prosperity in the mining industry in Mongolia has led to an increase in the number of mining workers, resulting in an increase in occupational exposures and the prevalence of occupational diseases and disabilities. The aim of this study was to assess the personal exposure of workers to respirable dust (RD) and respirable crystalline silica (RCS). Method: A cross-sectional study was conducted at the Erdenet Copper Ore Mining and included 581 personal samples of RD and 324 samples of RCS, collected in 2018-2020. Results: The study results revealed that the geometric mean (GM) of RD was 0.35 mg/m3 (95% CI 0.32 - 0.39). The RD concentration in 5.9% (n = 34) of all the samples exceeded the permissible exposure level (PEL) (3 mg/mg3). The GM of RCS was 0.012 mg/m3 (95% CI 0.010 - 0.016). In total, 12.0% (n = 39) of all RCS sample concentrations exceeded the PEL (0.1 mg/m3). Conclusion: Steel smelters, blasters, welders, and maintenance laborers were exposed to RD, while crushers, operators, drilling machinists, and maintenance laborers were exposed to RCS. Therefore, regular monitoring of the work environment, risk-based health examinations for dust-exposed workers, efficient support for dust mitigation, reduction measures at the source, and engineering controls are needed.

Multicomponent Measurement of Respirable Quartz, Kaolinite and Coal Dust using Fourier Transform Infrared Spectroscopy (FTIR): A Comparison Between Partial Least Squares and Principal Component Regressions.

Exposure to respirable crystalline silica (RCS) is potentially hazardous to the health of thousands of workers in Great Britain. Both X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy can be used to measure RCS to assess exposures. The current method outlined in the Health and Safety Executive's (HSE) Methods for the Determination of Hazardous Substances (MDHS) guidance series is 'MDHS 101 Crystalline silica in respirable airborne dust - Direct-on-filter analyses by infrared spectroscopy or x-ray'. This describes a procedure for the determination of time-weighted average concentrations of RCS either as quartz or cristobalite in airborne dust. FTIR is more commonly employed because it is less expensive, potentially portable and relatively easy to use. However, the FTIR analysis of RCS is affected by spectral interference from silicates. Chemometric techniques, known as Partial Least Squares Regression (PLSR) and Principal Component Regression (PCR), are two computational processes that have the capability to remove spectral interference from FTIR spectra and correlate spectral features with constituent concentrations. These two common chemometric processes were tested on artificial mixtures of quartz and kaolinite in coal dust using the same commercially available software package. Calibration, validation and prediction samples were prepared by collecting aerosols of these dusts onto polyvinylchloride (PVC) filters using a Safety in Mines Personal Dust Sampler (SIMPEDS) respirable cyclone. PCR and PLSR analyses were compared when processing the same spectra. Good correlations between the target values, measured using XRD, were obtained for both the PCR and PLSR models e.g. 0.98-0.99 (quartz), 0.98-0.98 (kaolinite) and 0.96-0.97 (coal). The level of agreement between PCR and PLSR was within the 95% confidence value for each analyte. Slight differences observed between predicted PCR and PLSR values were due to the number of optimal principal components applied to each chemometric process. The presence of kaolinite in these samples caused an 18% overestimation of quartz, for the FTIR, when following MDHS 101 without a chemometric method. Chemometric methods are a useful approach to obtain interference-free results for the measurement of RCS from some workplace environments and to provide a multicomponent analysis to better characterise exposures of workers.

Compilation and Evaluation of Ambient Respirable Crystalline Silica Air Quality Data near Sand Quarries and Processing Facilities

Ambient respirable crystalline silica air quality is of concern to many communities near mineral processing facilities and to regulatory agencies serving these communities. Accurate air quality data are needed to compare measured respirable crystalline silica concentrations at the fencelines of mineral processing facilities with the published health effect guideline published by the California Office of Health Hazard Assessment (OEHHA). This article is a compilation and evaluation of air quality studies around a diverse set of nineteen sand producing facilities. The respirable crystalline silica air quality data compiled by Air Control Techniques, P.C. and most of the data compiled by other researchers cited in this article have been measured using EPA Reference Method samplers adjusted for respirable crystalline silica sampling and NIOSH Method 7500 X-ray diffraction analyses. The authors conclude that (1) the ambient concentrations in the diverse set of mineral processing facilities were consistently lower than the 3.0 microgram per cubic meter chronic reference exposure level (REL) adopted by OEHHA, (2) upwind-to-downwind fenceline concentration differences were small, and (3) the fenceline t concentrations were often at background concentration levels. The authors recommend additional sampling studies to better characterize background concentrations of ambient respirable crystalline silica.

Measurement of respirable crystalline silica concentration by X-ray diffraction: Evaluation of metrological performances

Worker exposure to Respirable Crystalline Silica (RCS) is related with increased risk for lung cancer, so it is important to correctly assess it, through measurements of RCS. There are several methods for the uncertainty evaluation of the concentration of RCS measured by X-ray diffraction, however, none involves the calculation of the sensitivity coefficients of the mathematical measurement model. Hence, the aim of this research work is to propose an improved method, in which the sensitivity coefficients are calculated as partial derivatives of the model. The method was applied to four measurements campaigns in a factory, and the results seem to be comparable with those published in literature. It arose that for low concentrations the major contribution of uncertainty is due to the X-ray diffraction calibration line. This may mean that the minimum number of six calibration test filters, as suggested by the standards, is not sufficient, especially for low concentrations.

Occupational exposure to respirable crystalline silica in municipal household waste collection and road cleaning workers

Despite the increase in the number of cases among South Korean sanitation workers, lung cancer as a result of exposure to occupational carcinogen has not been sufficiently investigated. This study aimed to identify exposure levels of sanitation workers to respirable crystalline silica (RCS) for various tasks and factors that affect individual RCS exposure. Exposure to RCS was assessed for 90 sanitation workers from seven companies. The obtained geometric mean value of the RCS was 2.6 µg m–3, which is a similar level to recommendations set by California’s Office of Environmental Health Hazard Assessment's Recommended Exposure Limit. Meanwhile, coal briquette ash (CBA) collectors exhibited the highest RCS concentration (24 µg m–3), followed by road cleaning workers who used a blower, municipal household waste collectors, sweepers, and drivers (p < 0.05). Additionally, when the ANOVA was conducted, statistically significant differences were observed in RCS concentrations among various factors such as job task, season, employment type and city scale. Our study confirmed that sanitation workers who work outdoors could be exposed to RCS. Due to the possibility of exposure to high RCS concentrations, special attention should be paid to the collection of used CBA and road cleaning involving the use of a blower.

Estimating Historical Exposure to Respirable Crystalline Silica in the Mining Industry in Ontario, Canada Using a Newly Developed Exposure Database.

To use the recently developed Ontario Mining Exposure Database (OMED) to describe historical silica exposure in the Ontario metal mining industry and identify predictors of historical silica exposure. Personal respirable crystalline silica (RCS) data for metal mines were extracted from OMED and included both individual and summary measures, where multiple exposure measurements (n > 1) were aggregated and entered as a single exposure value (n = 1). Data were stratified by sample location (underground/surface) for analysis. Monte Carlo simulation was used to simulate individual measures from the summary measures. A fixed effects multiple linear regression model was used to assess the effects of commodity (ore mined), sample year, source of exposure data, and occupational group on RCS concentration. Parameter estimates (β), standard errors, and 95% upper and lower confidence intervals were reported. The OMED contained 12 995 silica measurements. After limiting to RCS measurements in metal mines, and measures with sufficient information for analysis, 2883 RCS measurements collected from 1974 to 1991 remained, including 2816 individual and 67 summary measurements. In total, 321 individual RCS measurements were simulated from the 67 summary measures. The analysis database contained 2771 (12% simulated) underground measurements and 366 surface measurements (0% simulated). In the underground group, an overall geometric mean (GM) of 0.05 [geometric standard deviation (GSD) 3.09] mg m-3 was estimated with a 6% annual decrease over time. In this group, the commodity with the highest average RCS level was zinc mines (GM = 0.07 mg m-3) and the lowest was iron mines (GM = 0.01 mg m-3). In the surface group, an overall GM of 0.05 (GSD 3.70) mg m-3 was estimated with an 8% decreased over time. In this group, the commodity with the highest average RCS level was gold mines (GM = 0.07 mg m-3) and the lowest was zinc mines (GM = 0.03 mg m-3). In both groups, company collected data had lower estimated RCS compared with regulator collected data. Historical RCS levels decreased over time. Mean measurements exceeded the American Conference of Governmental Industrial Hygienists current health-based threshold limit value (0.025 mg m-3). The main predictors of exposure were commodity, source of exposure data, and sample year. However, low R2 and high GSD values suggest additional predictors of RCS exposures in Ontario's metal mines exist that were unavailable in OMED.

Estimation of the number of workers exposed to respirable crystalline silica by industry: Analysis of OSHA compliance data (1979-2015).

Respirable crystalline silica (RCS) can potentially cause silicosis, lung cancer, and renal failure. The current study estimates the percentages of workers potentially overexposed to concentrations of RCS dust and silicosis proportional mortality rates (PMRs) by industry. Occupational Safety and Health Administration compliance inspection sampling data for RCS collected during 1979 to 2015 were used to estimate percentages of workers exposed. The results were used in combination with US Census Bureau estimates to produce industry specific worker population estimates for 2014. Estimates of the numbers and percentages of workers exposed to RCS concentrations at least 1, 2, 5, and 10 times the National Institute for Occupational Safety and Health recommended exposure limit (REL) were calculated by industry using the 2002 North American Industry Classification System. Silicosis PMRs by industry were estimated using National Center for Health Statistics multiple cause of death data. RCS concentrations/workers exposed were highest in the poured concrete foundation and structure contractors; commercial and institutional building construction; and masonry contractors. Approximately 100 000 workers were exposed above the RCS REL, and most (79%) worked in the construction industry. Tile and terrazzo contractors (12%); brick, stone, and related construction merchant wholesalers (10%); masonry contractors (6%) and poured concrete foundation and structure contractors (6%) were the highest percentages of workers potentially overexposed. PMRs were highest for the structural clay product manufacturing and the foundries industries. Percentages of workers exposed to RCS varied by industry and in some industries workers are exposed over 10 times the REL. Exposures can be reduced below the REL by implementing the hierarchy of controls.

Occupational Exposures in an Equestrian Centre to Respirable Dust and Respirable Crystalline Silica.

Sand-based products are regularly used as footing material on indoor equestrian arenas, creating a potential occupational exposure risk for respirable crystalline silica (RCS) for equestrian workers training and exercising horses in these environments. The objective of this study was to evaluate an equestrian worker’s personal RCS and respirable dust (RD) exposure. Sixteen personal full-shift RD measurements were collected from an equestrian worker and analysed for RD, quartz and cristobalite. Geometric mean exposures of 0.12 mg m−3 and 0.02 mg m−3 were calculated for RD and RCS concentrations, respectively. RCS exposures of between 0.01 to 0.09 mg m−3 were measured on days when the indoor arena surface was not watered, compared to lower exposures (<LOD-0.03 mg m−3) on days when the indoor arena was watered (p < 0.01); however, manual watering is time intensive and less likely to be implemented in practice. This small-scale study provides new data on RCS and RD exposures among equestrian workers. RCS exposures are within the range considered to be associated with increased risk for lung cancer. The use of dust control solutions such as water suppression should be promoted for equestrian work in horse riding arenas. Equestrian workers need to receive occupational health training on the health risks associated with RCS exposure.