Respirable Silica Concentrations Research Articles

The Evaluation of Worker Exposure to Airborne Silica Dust During Five OSHA Table I Construction Tasks.

Fifty-one (51) personal silica air samples were collected over 13 days on 19 construction employees while they performed five different construction tasks found in the Occupational Safety and Health Administration's (OSHA) respirable crystalline silica standard for construction, Table 1, which specifies engineering, work practice, and respiratory protection controls that employers can use in lieu of exposure monitoring to adhere to the standard. The average construction task time was 127 min (range: 18-240 min) with a mean respirable silica concentration of 85 μg m-3 (standard deviation [SD] = 176.2) for all 51 measured exposures. At least one OSHA-specified silica dust control measure was used during all 51 samples collected. The mean silica concentrations for the five tasks were: core drilling 11.2 μg m-3 (SD = 5.31 μg m-3), cutting with a walk-behind saw 126 μg m-3 (SD = 115 μg m-3), dowel drilling 99.9 μg m-3 (SD = 58.7 μg m-3), grinding 172 μg m-3 (SD = 145 μg m-3), and jackhammering 23.2 μg m-3 (SD = 5.19 μg m-3). Twenty four of 51 (47.1%) workers were exposed above the OSHA Action Level (AL) of 25 μg m-3 and 15 of 51 (29.4%) were exposed above the OSHA Permissible Exposure Limit (PEL) of 50 μg m-3 when exposures were extrapolated to an 8-h shift. When silica exposures were extrapolated to 4 h, 15 of 51 (29.4%) of workers sampled were exposed over the OSHA AL and 8 of 51 (15.7%) were exposed over the OSHA PEL. A total of 15 area airborne respirable crystalline silica samples were collected on days where the personal task-based silica samples were taken, with an average sampling time of 187 min. Of the 15 area respirable crystalline silica samples, only four were greater than the laboratory reporting limit of 5 μg m-3. The four area silica samples with reportable concentrations revealed background silica concentrations of 23 μg m-3, 5 μg m-3, 40 μg m-3, and 100 μg m-3. Odds ratios were used to analyze the apparent association between dichotomous background construction site exposures to respirable crystalline silica (detectable or not detectable), and personal exposure category (over or not over the OSHA AL and PEL) when exposure times were extrapolated to 8 h. The associations were strongly positive and significant between detectable background exposures and personal overexposures for workers conducting the five Table 1 tasks with engineering controls in place. The results of this study suggest that exposure to hazardous levels of respirable crystalline silica may be present even when OSHA-specified engineering controls are implemented. The current study findings also suggest that background construction site silica concentrations may potentially cause task-based overexposures, even when the OSHA Table 1 control methods have been put in place.

Reconstructing Historical Exposures to Respirable Dust and Respirable Silica in the Taconite Mining Industry for 1955-2010.

The goal of this study was to reconstruct the historical respirable silica (RS) and respirable dust (RD) exposures of workers in the Minnesota taconite industry from 1955 to 2010 as part of several epidemiological studies for assessing the association between exposure to components of taconite dusts and the development of respiratory diseases. A job-exposure matrix (JEM) was developed that uses 9127 RS and 19 391 RD occupational hygiene historical measurements. Historical RS and RD data were extracted from several sources and were grouped into seven mines and then into eight departments [Concentrating, Crushing, Janitor, Mining, Office/control room, Pelletizing, Shop (mobile), and Shop (stationary)]. Within each department, we applied a two-level random-intercept regression model which assumes that the natural log of Y (RD or RS concentration) changes over time at a constant rate. Among all predicted RD and RS values, we found that larger RD values were located in the following departments: Crushing, Concentrating, Pelletizing, and Shop (mobile). Larger RS values were located only in either Crushing or Shop (mobile). The annual rates of change for historical RD and RS exposures were between -3.3 and 3.2%. The silica percentage in the dust varied by mine/department with the highest value of 29.3% in Mine F (Crushing) and the lowest value of 2.1% in Mine B (Pelletizing). The predicted historical RD and RS arithmetic mean exposures ranged between <0.075 and 3.14 mg m-3, and between <0.005 and 0.36 mg m-3, respectively. The result of this study is a JEM by mine, department, and year for RD and RS for epidemiological studies.

A comprehensive assessment of exposures to respirable dust and silica in the taconite mining industry

ABSTRACTThis study assessed the present-day levels (year 2010–2011) of exposure to respirable dust (RD) and respirable silica (RS) in taconite mines and evaluated how the mining process influences exposure concentrations. Personal samples (n = 679) were collected to assess exposure levels of workers to RD and RS at six mines in the Mesabi Iron Range of Minnesota. The RD and RS concentrations were measured using the National Institute for Occupational Safety and Health (NIOSH) 0600 and NIOSH 7500, respectively. Between-mine, between-SEG (similar exposure groups), within-SEG, and within-worker components of variability for RD and RS exposures were estimated using a two- or three-way nested random-effects ANOVA model. The majority of RD concentrations across all mines were below the Mine Safety and Health Administration (MSHA) Permissible Exposure Limit (PEL). The highest concentrations of RD were often observed in either the Pelletizing or Crushing departments, which are inherently dusty operations. With a few exceptions, the concentrations of RS in the crushing and concentrating processes were higher than those in the other mining processes, as well as higher than the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) for RS. The magnetic separation and flotation processes in the concentrating department reduced the levels of RS significantly, and lowered the percentage of quartz in RD in the pelletizing department. There was little variability among the six mines or between the two mineralogically distinct zones for either RD or RS exposures. The between-SEG variability for RS did not differ substantially across most of the mines and was a major component of exposure variance. The within-SEG (or between-worker) variance component was typically the smallest because in many instances one worker from a SEG within a mine was monitored multiple times. Some of these findings were affected by the degree of censoring in each SEG and mine, characteristics of the taconite rock, seasonal effects during sampling, or the tasks assigned to each job in that mine.

Silica exposure and disease in semi‐precious stone craftsmen, Minas Gerais, Brazil

Brazil is an exporter of precious stones and craftsmen often work in poor conditions. We assessed silica-related diseases among crystal craftsmen and the complexity of its control. Case-series including 118 subjects evaluated from 2006 to 2015, based on medical interviews, chest X-rays, spirometry, and respirable silica samples. Median age and length of exposure were 32 and 13 years, respectively. Silicosis, with 1/0 as a threshold, was diagnosed radiologically in 57 individuals (48.3%). Respirable silica concentrations were 0.9-29.3 times greater than the Brazilian occupational exposure limit. A Receiver Operating Characteristic (ROC) curve with the same diagnosis threshold showed best discrimination at a cut point of 12.5 years of exposure, corresponding to 4.85 mg-y/m3 of cumulative silica exposure. There was a significant decline in FEV1 across radiological and cumulative silica exposure categories. Eleven individuals (9.3%) had mycobacterial diseases at baseline or follow-up. Crystal craftsmen continue to suffer from silicosis, lung function impairment, comorbidity, and death due to silicosis. To date collective protection in some work sheds has not diminished silica levels. Long-term follow-up is needed to evaluate further improvements in preventive measures. Am. J. Ind. Med. 60:239-247, 2017. © 2017 Wiley Periodicals, Inc.

Trends in silicosis prevalence and the healthy worker effect among gold miners in South Africa: a prevalence study with follow up of employment status.

BackgroundGiven the intimate association between silicosis and tuberculosis, understanding the epidemiology of the South African gold mining industry silicosis epidemic is essential to current initiatives to control both silicosis and tuberculosis in this population, one of the most heavily affected globally. The study’s objectives were to compare the prevalence of silicosis among working black gold miners in South Africa during 2004–2009 to that of previous studies, including autopsy series, and to analyse the influence of silicosis and/or tuberculosis on exiting employment.MethodsRoutine chest radiographs from a cohort of gold miners were read for silicosis by an experienced reader (I), and a subset re-read by a B-trained reader (II). Two methods of presenting the readings were used. Additionally, with baseline status of silicosis and previous or active tuberculosis as predictors, survival analysis examined the probability of exiting the workforce for any reason during 2006–2011.ResultsReader I read 11 557 chest radiographs and reader II re-read 841. Overall, silicosis prevalence (ILO ≥1/0: 5.7 and 6.2 % depending on reader method) was similar to the age adjusted prevalence found in a large study in 1984 (5.0 %). When comparison was restricted to a single mine shaft previously studied in 2000, a decline in prevalence (ILO ≥1/1) was suggested for one of the reading methods (duration adjusted 20.5 % vs. 13.0 % in the current study). These findings are discordant with a long-term rising autopsy prevalence of silicosis over this period. Overall, relative to miners with neither disease, the adjusted hazard ratio for exiting employment during the follow-up period was 1.54 for baseline silicosis [95 % confidence interval (CI) 1.17, 2.04], 1.71 for tuberculosis (95 % CI 1.51, 1.94) and 1.53 for combined disease (95 % CI 1.20, 1.96).ConclusionsThis study found, a) there was no significant decline in overall silicosis prevalence among working black miners in the South African gold mining industry between 1984 and 2004–2009, and b) a possible decline at one mine shaft more recently. In the absence of evidence of declining respirable silica concentrations between the 1980s and 2000s, the trends found are plausibly due to a healthy worker survivor effect, which may be accelerating.Electronic supplementary materialThe online version of this article (doi:10.1186/s12889-015-2566-8) contains supplementary material, which is available to authorized users.

Long-term exposure to silica dust and risk of total and cause-specific mortality in Chinese workers: a cohort study.

Human exposure to silica dust is very common in both working and living environments. However, the potential long-term health effects have not been well established across different exposure situations. We studied 74,040 workers who worked at 29 metal mines and pottery factories in China for 1 y or more between January 1, 1960, and December 31, 1974, with follow-up until December 31, 2003 (median follow-up of 33 y). We estimated the cumulative silica dust exposure (CDE) for each worker by linking work history to a job-exposure matrix. We calculated standardized mortality ratios for underlying causes of death based on Chinese national mortality rates. Hazard ratios (HRs) for selected causes of death associated with CDE were estimated using the Cox proportional hazards model. The population attributable risks were estimated based on the prevalence of workers with silica dust exposure and HRs. The number of deaths attributable to silica dust exposure among Chinese workers was then calculated using the population attributable risk and the national mortality rate. We observed 19,516 deaths during 2,306,428 person-years of follow-up. Mortality from all causes was higher among workers exposed to silica dust than among non-exposed workers (993 versus 551 per 100,000 person-years). We observed significant positive exposure-response relationships between CDE (measured in milligrams/cubic meter-years, i.e., the sum of silica dust concentrations multiplied by the years of silica exposure) and mortality from all causes (HR 1.026, 95% confidence interval 1.023-1.029), respiratory diseases (1.069, 1.064-1.074), respiratory tuberculosis (1.065, 1.059-1.071), and cardiovascular disease (1.031, 1.025-1.036). Significantly elevated standardized mortality ratios were observed for all causes (1.06, 95% confidence interval 1.01-1.11), ischemic heart disease (1.65, 1.35-1.99), and pneumoconiosis (11.01, 7.67-14.95) among workers exposed to respirable silica concentrations equal to or lower than 0.1 mg/m(3). After adjustment for potential confounders, including smoking, silica dust exposure accounted for 15.2% of all deaths in this study. We estimated that 4.2% of deaths (231,104 cases) among Chinese workers were attributable to silica dust exposure. The limitations of this study included a lack of data on dietary patterns and leisure time physical activity, possible underestimation of silica dust exposure for individuals who worked at the mines/factories before 1950, and a small number of deaths (4.3%) where the cause of death was based on oral reports from relatives. Long-term silica dust exposure was associated with substantially increased mortality among Chinese workers. The increased risk was observed not only for deaths due to respiratory diseases and lung cancer, but also for deaths due to cardiovascular disease. Please see later in the article for the Editors' Summary.

Reconstruction of Silica Exposure at a Foundry for Evaluation of Exposure–Response

The reconstruction of working lifetime exposures to silica at a large foundry was described. Through the use of interviews with long-term employees, a history of the facility was developed for the years 1960–90, areas of similar work activities were identified and work locations for those with various job titles were documented over time. Two thousand and seventy historical industrial hygiene measurements of exposure collected during these three decades were linked to work area and an estimate of average respirable silica concentration was calculated for each area, by year. Overall, exposures declined between 1960 and 1990; however, substantial differences in exposure were estimated across work areas. Exposure at a specific job was calculated from the estimates of work-area respirable silica concentration, weighted by the amount of time persons with that job were in the area. These job-related exposure estimates were used to calculate three exposure metrics for persons employed in the foundry: cumulative, working lifetime average and highest daily exposure.

Exposure to respirable crystalline silica in eastern North Carolina farm workers.

Occupational exposure to crystalline silica has been linked to silicosis, some forms of cancer, and certain autoimmune diseases. Little information exists on exposure levels of respirable silica in the agricultural industry. This study assessed respirable silica exposure of farm workers in eastern North Carolina. Sandy soils in this region have been shown to contain high levels of respirable silica. Personal breathing zone samples (n = 37) were collected from 27 workers at seven farms during various agricultural activities. The highest respirable silica concentrations were measured during sweet potato transplanting (3.91 +/- 2.07 mg/m3). Respirable silica exposure was observed to be associated with agricultural activity, soil moisture, relative humidity, and wind speed. Most of the variation in exposure (79%) was explained by agricultural activity and soil moisture. The observed percentage of silica levels (mean 34.7%) were almost twice as high as was reported in studies of California agriculture. This may be due to the loamy sand and sandy loam soil types in the regions in this study. In agriculture, respirable silica exposure is highly variable, but the potential for exposures above the threshold limit value of 0.05 mg/m3 exists during particular agricultural activities.

Respirable Dust and Respirable Silica Concentrations from Construction Activities

Measurements of respirable dust (RD) and respirable crystalline silica (RCS) concentrations are reported for a range of activities, materials and workplaces in the construction industry. Some activities leading to high dust exposures are identified, such as work in confined spaces, the use of hand-held Stihl^TM saws and angle grinders without suppression or extraction, and dry sweeping and removal of rubble. RD and RCS concentrations are related to conditions on site including such factors as the softness, friability and silica content of the material; the weather conditions (dampness) and whether indoors or out; the proximity of the source of the dust to the worker’s breathing zone, and the use of water suppression or extraction and general ventilation.

Respirable Dust and Respirable Silica Concentrations from Construction Activities

Measurements of respirable dust (RD) and respirable crystalline silica (RCS) concentrations are reported for a range of activities, materials and workplaces in the con struction industry. Some activities leading to high dust exposures are identified, such as work in confined spaces, the use of hand-held Stihl™ saws and angle grinders without suppression or extraction, and dry sweeping and removal of rubble. RD and RCS concentra tions are related to conditions on site including such fac tors as the softness, friability and silica content of the material; the weather conditions (dampness) and wheth er indoors or out; the proximity of the source of the dust to the worker's breathing zone, and the use of water sup pression or extraction and general ventilation.

Radiographic Evidence of Silicosis in Relation to Silica Exposure

Abstract Although the risk of silicosis has long been recognized as a consequence of exposure to crystalline silica, there are only limited data available for quantitatively estimating risk in relation to modern concentrations. Reports on three large groups of workers (Vermont granite workers, South African gold miners, and Ontario hardrock miners) form the basis for estimating silicosis risk; two other smaller studies, of British gypsum miners and North Carolina dusty trades workers, provide additional but less quantitative information. For 40 years of exposure to a respirable silica concentration of 0.1 mg/m3, the estimated cumulative risk of radiographic evidence of silicosis is approximately 1 to 3 percent based on the Ontario miners (depending on whether diagnosis requires a positive reading by a majority of five readers or by only one reader) and is 60 percent based on South African miners. Findings from Vermont granite workers and North Carolina dusty trades workers are more consistent with the low...

Abrasive Blasting with Quartz Sand: Factors Affecting the Potential for Incidential Exposure to Respirable Silica

In this study fixed sampling arrays using personal respirable samplers and high volume samplers were positioned in potential down-plume positions for 10 different sandblasting worksites in a large Gulf Coast steel fabrication yard during the month of July 1991. Results revealed that in general, downwind respirable silica concentrations varied as distance raised to the −1.17 power from the source. Turbulent “free jet” mixing theory with normal work patterns for sandblasting were used to explain measured respirable concentrations in and close to the blast zone. The geometry of the worksite and the position of the workers will affect concentrations observed by orders of magnitude, in some cases leading to exposure conditions inadequately protected by the “CE” supplied-air respirators.

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The efficiency of vacuum cleaners of both wet and dry types has been assessed in terms of the quality of the air returned to the atmosphere. Tests were carried out in the laboratory and on-site at potteries, using apparatus designed to contain the air issuing from the cleaner, so that it could be analysed with a real-time dust sampling instrument. Examination of the dust collected by a dry vacuum cleaner during on-site tests, or the slurry collected by a wet cleaner, enables test material to be specified for use in laboratory measurements of efficiency. Dry cleaners have the potential of achieving higher efficiency than wet cleaners, provided that good filters are used. Wet cleaners achieve a higher standard of floor cleaning than dry cleaners, but the quality of air that they return is not, in general, as good, since the filtration system that they employ is simple. A large fraction of the cleaners tested returned dust to the atmosphere at a concentration equivalent to a respirable silica concentration of approximately 0.1 mgm−3.

Silica content of dusts from five texas cottonseed oil mills

AbstractTotal dust samples, collected with high‐volume samplers, were ashed and then analyzed for aluminum, silicon and silica (SiO2). Ash and aluminum contents agreed with earlier reported data, but the silicon content was lower. The amounts of silica ranged from 2–7% in dusts from the cleaning rooms to 0.01–0.05% in dusts from the baling rooms. Agreement with silica contents determined by infrared (IR) spectrometry was good. IR spectra indicated silica particle diameters were in the range of 6–8 µm in the cleaning rooms and 10 µm or more in the delintering and baling rooms. Threshold limit values (TLV) calculated on the basis of total silica in the high‐volume samples suggest silica values above the limit in 4 of the cleaning rooms, and possibly one at the delintering rooms. Calculation of respirable silica concentrations and TLV for respirable silica was precluded by the sampling method.