TY - JOUR
AU - Xu,, H
AB - Abstract Background Silicosis is caused by long-term exposure to silica dust. Crystal rhinestone workers can be exposed to high levels of silica dust and are at risk of silicosis. Aims To explore silicosis cases, silica dust exposure and control measures in a rhinestone factory in South China. Methods We extracted and analysed data on new silicosis cases reported to China’s occupational disease and occupational health information monitoring system between 2006 and 2012 from a rhinestone factory in South China. We measured the quartz content of bulk dust, static total and respirable dust samples. Results Ninety-eight silicosis cases were reported between 2006 and 2012. The mean duration of silica dust exposure was 9.2 years (range 3–16). Drilling and polishing workers accounted for 96 (98%) of cases. We collected 1479 static samples including 690 total dust and 789 respirable dust samples. Mean dust levels for drilling were 1.01 mg/m3 (range 0.20–3.80) for total dust and 0.51 mg/m3 (range 0.04–1.70) for respirable dust. Mean dust levels for polishing were 0.59 mg/m3 (range 0.20–2.10) for total dust and 0.28 mg/m3 (range 0.08–0.71) for respirable dust. Over a third [289/789 (37%)] of total dust samples and 129/690 (19%) respirable dust samples exceeded the national permissible exposure limit. Conclusion Exposure to silica dust, ineffective dust control measures and inefficient health surveillance may have contributed to the incidence of silicosis in the factory we studied. Identification of silica dust exposure and effective dust control measures would reduce the risk of silicosis in rhinestone workers. Crystal rhinestone manufacture, silica dust, silicosis Key learning points What is already known about this subject: Crystalline silica exposure occurs with sand, gravel, stones, ceramics and rhinestones. Silicosis is increasing in incidence in China despite being one of the oldest reported occupational diseases. Workers in rhinestone manufacturing are exposed to silica dust, but the health effects of this exposure have not been reported. What this study adds: This is the first study to report the incidence of silicosis in rhinestone manufacturing. Total and respirable silica dust levels in the factory studied exceeded China’s national permissible exposure levels. Drilling and polishing workers were at the highest risk of silicosis. What impact this may have on practice or policy: Effective local exhaust ventilation and other dust control measures, including respiratory protective equipment, are essential to minimize silica dust exposure in rhinestone manufacturing. Silica dust exposure should be investigated in other industries. Introduction Silicosis is the pneumoconiosis resulting from inhalation of crystalline silica dust [1]. It is one of the oldest occupational diseases, first reported in 1690 in miners [2]. Many industrial processes and activities such as construction work, mining, tunnelling, arts, crafts and sculpture, and jewellery involve exposure to respirable crystalline silica [3]. Silicosis is preventable, but in China, silicosis is a serious public health concern. The incidence of silicosis has increased since 2008, with >10 000 cases reported each year [4,5]. In jewellery industries, the activities of cutting, grinding, polishing and buffing expose workers to crystalline silica dust [6]. Silicosis has been reported in workers from jade and gemstone factories in Hong Kong and India [7,8]. First exposure to silica dust, job roles, duration of dust exposure and respirable silica dust exposure levels are key predictors of the risk of silicosis [9]. Artificial crystal stone, such as rhinestone, is used because of its lower cost than jade and gemstone. Crystal rhinestones are man-made imitation gemstones. The main raw material is quartz sand, and various activities expose workers to silica dust. Workers making crystal rhinestone from quartz can be exposed to high levels of silica dust unless exposure is adequately controlled. We noted that a few patients were reported with silicosis from a rhinestone factory in South China which was established in 1992. We investigated this cluster of cases by conducting a retrospective analysis of all silicosis cases and static silica dust measurements. This paper explores the epidemiology and exposure level of rhinestone workers with silicosis at a crystal rhinestone factory with a view to identifying measures to prevent silicosis. Methods We extracted data on silicosis cases from China’s national occupational disease and occupational health information monitoring system from 2006 to 2012, using the name of the factory. The national system is compulsory and was set up in 2006 by the Chinese Ministry of Health. All occupational diseases should be submitted after diagnosis by occupational physicians. We also examined occupational health documents from the factory to extract any cases identified before 2006. In China, a doctor making a diagnosis of occupational disease needs to record the worker’s history of exposure (including exposure duration, job title and exposed hazards), results of physical examination, exposure level of the workplace and other information. Moreover, the diagnosis of pneumoconiosis is defined by at least three occupational physicians and classified as stage Ⅰ, Ⅱ or Ⅲ according to the size, profusion and opacities on chest radiograph [10]. The silicosis cases we extracted were all diagnosed based on the diagnostic criteria of pneumoconiosis of China by three occupational physicians [10]. The factory began operating in 1992, and at the time of this investigation (2005–06), employed about 2448 workers. The main raw material is quartz sand with an annual amount of about 1080 tons. The raw materials, including quartz sand, are weighed and mixed according to formulae. The mixed materials are placed in a furnace and heated to about 1250°C. The material is melted and formed into gemstone blanks in prepared moulds. Gemstone blanks are screened flat through a drum, and placed in grinding rigs for drilling and polishing into different planes, which become semi-products. The semi-finished products are cleaned, dried, painted and delivered for inspection and package (Figure 1). The factory has a processes area comprising a batch house unit, furnace unit, screening unit, drilling workshop, polishing workshop, spray-painting unit, package unit and sewage treatment areas. The main products are semi-crystal rhinestones. Drilling and polishing are manual and labour-intensive activities, which employ 1792/1924 (93%) of the labour force of this factory. The factory improved silica dust control after the suspected silicosis cases were reported. Figure 1. Open in new tabDownload slide The crystal rhinestone manufacturing process of the factory. Figure 1. Open in new tabDownload slide The crystal rhinestone manufacturing process of the factory. After the suspected silicosis cases were found during occupational health examination from 2005 to 2006, we formed a study team to investigate the cases, including occupational hygienists and researchers with knowledge of the rhinestone production process. We performed our investigation in close cooperation with employees and employers based mainly on work tasks and dust prevention systems. We identified workplaces and activities with exposure to crystalline silica dust and designed a measurement strategy including different exposure activities (Table 1). We collected bulk samples from raw materials and fallout dust around the workplaces (Table 2). We performed stationary air sampling from the workers’ breathing zones during the normal working day. We included total dust and respirable dust. We selected numbers of monitoring samples from each of the exposure groups and workplaces, so that the results would represent similar exposure groups. We conducted repeated measurements three times as far as possible from three continuous working days. We performed sampling and analysis of the content of silica in dust, and total and respirable air samples, according to national methods for airborne dust measurement in the workplace (GB/T5748-1985) [11]. We collected 1483 air samples from seven process workshops. We collected two samples of quartz sand and 22 samples of bulk dust from five workshops. Except for raw materials, we collected bulk samples directly from fallout dust at the work sites, in an amount of about 0.2 g and determined the content using the pyrophosphoric acid method. We collected total and respirable dust from workers’ breathing zones using total and respirable dust cyclones. The volume of air drawn through the filter was 1–5 L/min. We calibrated the sampling pumps (DFC-3BT dust sampler and SFC-3BT dust sampler) before and after sampling. We included one field blank for each sampling location. We analysed the filter samples in accordance with GB/T5748-1985 and blank corrected the results. We calculated time-weighted averages (TWAs) according to the sampling duration and working hours. We also investigated the use of personal protective equipment and dust control ventilation. Table 1. Characteristics of silicosis cases Variables n (%) Age at first exposure, years, mean (SD) Duration of exposure, years, mean (SD) Age at diagnosis, years, mean (SD) Total 98 22.5 (3.76) 9.2 (2.85) 33.4 (4.39) Gender  Male 97 (99) – – –  Female 1 (1) – – – Stage  Stage I* 93 (95) 22.6 (3.79) 9.3 (2.83) 33.3 (4.46)  Stage II* 5 (5) 21.2 (3.27) 7.8 (3.02) 34.6 (2.61) Job activity  Drilling, n (%)* 88 (90) 22.3 (3.57) 9.2 (2.86) 33.2 (4.18)  Polishing, n (%)* 8 (8) 23.9 (5.01) 9.9 (3.09) 35.2 (6.63)  Miller, n (%) 1 (1) 22.0 10.3 33.0  Feeding, n (%) 1 (1) 28.0 7.7 36.0 Variables n (%) Age at first exposure, years, mean (SD) Duration of exposure, years, mean (SD) Age at diagnosis, years, mean (SD) Total 98 22.5 (3.76) 9.2 (2.85) 33.4 (4.39) Gender  Male 97 (99) – – –  Female 1 (1) – – – Stage  Stage I* 93 (95) 22.6 (3.79) 9.3 (2.83) 33.3 (4.46)  Stage II* 5 (5) 21.2 (3.27) 7.8 (3.02) 34.6 (2.61) Job activity  Drilling, n (%)* 88 (90) 22.3 (3.57) 9.2 (2.86) 33.2 (4.18)  Polishing, n (%)* 8 (8) 23.9 (5.01) 9.9 (3.09) 35.2 (6.63)  Miller, n (%) 1 (1) 22.0 10.3 33.0  Feeding, n (%) 1 (1) 28.0 7.7 36.0 *P > 0.05. Open in new tab Table 1. Characteristics of silicosis cases Variables n (%) Age at first exposure, years, mean (SD) Duration of exposure, years, mean (SD) Age at diagnosis, years, mean (SD) Total 98 22.5 (3.76) 9.2 (2.85) 33.4 (4.39) Gender  Male 97 (99) – – –  Female 1 (1) – – – Stage  Stage I* 93 (95) 22.6 (3.79) 9.3 (2.83) 33.3 (4.46)  Stage II* 5 (5) 21.2 (3.27) 7.8 (3.02) 34.6 (2.61) Job activity  Drilling, n (%)* 88 (90) 22.3 (3.57) 9.2 (2.86) 33.2 (4.18)  Polishing, n (%)* 8 (8) 23.9 (5.01) 9.9 (3.09) 35.2 (6.63)  Miller, n (%) 1 (1) 22.0 10.3 33.0  Feeding, n (%) 1 (1) 28.0 7.7 36.0 Variables n (%) Age at first exposure, years, mean (SD) Duration of exposure, years, mean (SD) Age at diagnosis, years, mean (SD) Total 98 22.5 (3.76) 9.2 (2.85) 33.4 (4.39) Gender  Male 97 (99) – – –  Female 1 (1) – – – Stage  Stage I* 93 (95) 22.6 (3.79) 9.3 (2.83) 33.3 (4.46)  Stage II* 5 (5) 21.2 (3.27) 7.8 (3.02) 34.6 (2.61) Job activity  Drilling, n (%)* 88 (90) 22.3 (3.57) 9.2 (2.86) 33.2 (4.18)  Polishing, n (%)* 8 (8) 23.9 (5.01) 9.9 (3.09) 35.2 (6.63)  Miller, n (%) 1 (1) 22.0 10.3 33.0  Feeding, n (%) 1 (1) 28.0 7.7 36.0 *P > 0.05. Open in new tab Table 2. Quartz content in raw material and bulk dust samples Location No. of samples (dust type) Min (%) Max (%) Batch house 2 (raw materials) 71 99.8 Batch house 4 (bulk dust) 17 48 Furnace workshop 3 (bulk dust) 10 47 Screening workshop 5 (bulk dust) 3 22 Drilling workshop 8 (bulk dust) 3 23 Polishing workshop 2 (bulk dust) 4 14 Location No. of samples (dust type) Min (%) Max (%) Batch house 2 (raw materials) 71 99.8 Batch house 4 (bulk dust) 17 48 Furnace workshop 3 (bulk dust) 10 47 Screening workshop 5 (bulk dust) 3 22 Drilling workshop 8 (bulk dust) 3 23 Polishing workshop 2 (bulk dust) 4 14 Open in new tab Table 2. Quartz content in raw material and bulk dust samples Location No. of samples (dust type) Min (%) Max (%) Batch house 2 (raw materials) 71 99.8 Batch house 4 (bulk dust) 17 48 Furnace workshop 3 (bulk dust) 10 47 Screening workshop 5 (bulk dust) 3 22 Drilling workshop 8 (bulk dust) 3 23 Polishing workshop 2 (bulk dust) 4 14 Location No. of samples (dust type) Min (%) Max (%) Batch house 2 (raw materials) 71 99.8 Batch house 4 (bulk dust) 17 48 Furnace workshop 3 (bulk dust) 10 47 Screening workshop 5 (bulk dust) 3 22 Drilling workshop 8 (bulk dust) 3 23 Polishing workshop 2 (bulk dust) 4 14 Open in new tab We conducted the study as a part of the compulsory renovation of ventilation assessment of the factory. Therefore, no preliminary ethical approval was sought. We performed statistical analysis using SASW Statistics 18.0 and SAS version 9.3. We determined statistical significance at P <0.05 and we used two-sided tests. We present the distribution of age at first exposure, duration of exposure and age at diagnosis [arithmetic means (AM) and standard deviation (SD)] by stage and job activities using independent t-tests. We also performed normality tests of total and respirable dust, which was lognormal distributed. We therefore describe the concentration of crystalline silica dust by AM, SD, minimum (Min), maximum (Max), geometric means (GM) and geometric standard deviation (GSD). Results We extracted 98 silicosis cases reported from 2006 to 2012 from a crystal rhinestone factory in Guangdong province, South China. One case was female. Ninety-three workers were diagnosed as stage Ⅰ and five workers as stage Ⅱ (Table 1). Four cases were diagnosed in 2006, 19 cases in 2007, 45 cases in 2008, 7 cases in 2009, 5 cases in 2010, 12 cases in 2011 and 6 cases in 2012 (Figure 2). Workers were removed from the factory when their silicosis was suspected. The first year of dust exposure ranged from 1992 to 2003. The mean age of first exposure to silica dust and the age of diagnosis were 22 and 33 years, respectively. The mean duration of exposure was 9.2 years (range 3–16) (Table 1). There were no significant differences between cases in stage Ⅰ and stage Ⅱ for age at first exposure and diagnosis, and duration of exposure (Table 1). Identified cases had four job titles. Eighty-eight (90%) were drilling workers and eight (8%) were polishing workers. There were no significant differences in the age of first exposure and diagnosis and duration of exposure between drilling and polishing workers (Table 1). Figure 2. Open in new tabDownload slide Number of reported silicosis cases by year, 2006–12. Figure 2. Open in new tabDownload slide Number of reported silicosis cases by year, 2006–12. Mixing at the batch house, feeding at the furnace unit, screening at the screening workshop, drilling at the drilling workshop and polishing at the polishing workshop were the main activities involving exposure to silica dust. All silica dust exposure activities were manual and labour intensive. About 1924 workers were exposed to silica dust (Table 3); 1624 (84%) being employed in drilling and 168 (9%) in polishing. Each work shift was 8 h plus 1½–2 h of overtime in the busy season. The factory provided disposable respiratory protective equipment (RPE) at the time of this investigation, and most of the workers wore it during field work and sampling days. Dust control measures and ventilation systems were implemented after 2005 (Table 3). Table 3. Description of RPE use and dust prevention measures in dust exposure workshops Name of workshops Description of tasks No. of workers exposed to dust Use of RPE Dust preventive ventilation and the main problems identified Batch house Weighing and mixing raw materials based on the formulae 8 Dust masks Four upper hoods were installed at the material mixing work site. The distance from the dust source to hood should be shorter and hoods should be enclosed. Furnace workshop Loading mixed materials into the furnace and inspecting the temperature 42 Dust masks Furnaces were isolated from the ventilation system. The operation of loading materials was manual. Screening workshop Placing the gemstone blanks through the drum, washing and drying 52 Dust masks Wet method was used for screen operation. Drilling workshop Putting the gemstone blanks into bonding machine to be burned with a flame and taking them out to grind; after grinding, performing the same process three more times 1624 Dust masks Wet method was used for all operations. Most of the grinding operation work sites were enclosed with upper hoods and three side curtains to capture dust, while some operation work sites were only enclosed with a curtain. The enclosed exhaust system could not completely enclose the dust source to prevent emission. Polishing workshop Putting the gemstone blanks through the polishing step 168 Dust masks Wet method was used for all operations. Enclosed exhaust systems were installed at the operation site. Sewage treatment Supervising the operation of sewage treatment equipment 15 Dust masks – Package workshop Performing the packing process 15 Dust masks – Name of workshops Description of tasks No. of workers exposed to dust Use of RPE Dust preventive ventilation and the main problems identified Batch house Weighing and mixing raw materials based on the formulae 8 Dust masks Four upper hoods were installed at the material mixing work site. The distance from the dust source to hood should be shorter and hoods should be enclosed. Furnace workshop Loading mixed materials into the furnace and inspecting the temperature 42 Dust masks Furnaces were isolated from the ventilation system. The operation of loading materials was manual. Screening workshop Placing the gemstone blanks through the drum, washing and drying 52 Dust masks Wet method was used for screen operation. Drilling workshop Putting the gemstone blanks into bonding machine to be burned with a flame and taking them out to grind; after grinding, performing the same process three more times 1624 Dust masks Wet method was used for all operations. Most of the grinding operation work sites were enclosed with upper hoods and three side curtains to capture dust, while some operation work sites were only enclosed with a curtain. The enclosed exhaust system could not completely enclose the dust source to prevent emission. Polishing workshop Putting the gemstone blanks through the polishing step 168 Dust masks Wet method was used for all operations. Enclosed exhaust systems were installed at the operation site. Sewage treatment Supervising the operation of sewage treatment equipment 15 Dust masks – Package workshop Performing the packing process 15 Dust masks – Open in new tab Table 3. Description of RPE use and dust prevention measures in dust exposure workshops Name of workshops Description of tasks No. of workers exposed to dust Use of RPE Dust preventive ventilation and the main problems identified Batch house Weighing and mixing raw materials based on the formulae 8 Dust masks Four upper hoods were installed at the material mixing work site. The distance from the dust source to hood should be shorter and hoods should be enclosed. Furnace workshop Loading mixed materials into the furnace and inspecting the temperature 42 Dust masks Furnaces were isolated from the ventilation system. The operation of loading materials was manual. Screening workshop Placing the gemstone blanks through the drum, washing and drying 52 Dust masks Wet method was used for screen operation. Drilling workshop Putting the gemstone blanks into bonding machine to be burned with a flame and taking them out to grind; after grinding, performing the same process three more times 1624 Dust masks Wet method was used for all operations. Most of the grinding operation work sites were enclosed with upper hoods and three side curtains to capture dust, while some operation work sites were only enclosed with a curtain. The enclosed exhaust system could not completely enclose the dust source to prevent emission. Polishing workshop Putting the gemstone blanks through the polishing step 168 Dust masks Wet method was used for all operations. Enclosed exhaust systems were installed at the operation site. Sewage treatment Supervising the operation of sewage treatment equipment 15 Dust masks – Package workshop Performing the packing process 15 Dust masks – Name of workshops Description of tasks No. of workers exposed to dust Use of RPE Dust preventive ventilation and the main problems identified Batch house Weighing and mixing raw materials based on the formulae 8 Dust masks Four upper hoods were installed at the material mixing work site. The distance from the dust source to hood should be shorter and hoods should be enclosed. Furnace workshop Loading mixed materials into the furnace and inspecting the temperature 42 Dust masks Furnaces were isolated from the ventilation system. The operation of loading materials was manual. Screening workshop Placing the gemstone blanks through the drum, washing and drying 52 Dust masks Wet method was used for screen operation. Drilling workshop Putting the gemstone blanks into bonding machine to be burned with a flame and taking them out to grind; after grinding, performing the same process three more times 1624 Dust masks Wet method was used for all operations. Most of the grinding operation work sites were enclosed with upper hoods and three side curtains to capture dust, while some operation work sites were only enclosed with a curtain. The enclosed exhaust system could not completely enclose the dust source to prevent emission. Polishing workshop Putting the gemstone blanks through the polishing step 168 Dust masks Wet method was used for all operations. Enclosed exhaust systems were installed at the operation site. Sewage treatment Supervising the operation of sewage treatment equipment 15 Dust masks – Package workshop Performing the packing process 15 Dust masks – Open in new tab Routine measurement of dust levels were not conducted before 2005. In 2005, workers exposed to dust were examined including chest radiography and pulmonary function tests, and some suspected silicosis cases were identified. Before 2005, few workers exposed to dust in the factory were examined. For the bulk dust from fallout dust, the content of quartz in mixed raw material from the batch house ranged from 71 to 99.8%. Quartz content from the furnace was lower, and drilling and polishing were the lowest (Table 2). Table 4 shows that 1479 (99.7%) samples (1479/1483) were TWAs; 690 (47%) of these were respirable dust samples and 789 (53%) were total dust samples (Table 4). We collected 464 (59%) of the total dust samples and 454 (66%) of the respirable dust samples from drilling activity. The highest levels for total dust and respirable dust were 15 and 2.67 mg/m3, respectively, which we collected from screening activities. For drilling activity, the mean levels were 1.01 mg/m3 (range 0.20–3.80 mg/m3) for total dust and 0.51 mg/m3 (range 0.04–1.70 mg/m3) for respirable dust (Table 4). For polishing activity, the mean levels were 0.59 mg/m3 (range 0.10–2.10 mg/m3) for total dust and 0.28 mg/m3 (range 0.08–0.71 mg/m3) for respirable dust (Table 4). The GM concentrations for total and respirable dust of drilling activity were 0.82 and 0.41 mg/m3, respectively, which were higher than the levels for other activities. In total, 289/789 (37%) total dust samples exceeded China’s national permissible exposure limit (PEL) for total silica dust, of 1 mg/m3 and 129/690 (19%) respirable dust samples exceeded the PEL (0.7 mg/m3 [10]) for respirable silica dust. For drilling activity, 211/456 (45%) of total dust and 114/456 (25%) of respirable dust exceeded the PEL (Table 4). Table 4. Sampling data of total dust and respiratory dust Location Dust type Test type n Mean, mg/m3 SD Min, mg/m3 Max, mg/m3 GM, mg/m3 GSD % >PEL Batch house Total dust TWA 36 1.19 1.22 0.10 5.00 0.72 0.12 33 Respiratory dust TWA 24 0.23 0.16 0.08 0.73 0.19 0.02 4 Furnace workshop Total dust TWA 161 0.95 0.92 0.10 6.30 0.66 0.04 30 Respiratory dust TWA 89 0.31 0.25 0.08 1.16 0.23 0.02 10 Screening workshop Total dust TWA 44 1.28 2.64 0.20 15.00 0.65 0.09 18 Respiratory dust TWA 36 0.36 0.43 0.08 2.67 0.26 0.03 6 Drilling workshop Total dust TWA 464 1.01 0.63 0.20 3.80 0.82 0.03 45 Respiratory dust TWA 456 0.51 0.30 0.04 1.70 0.41 0.01 25 Polishing workshop Total dust TWA 55 0.59 0.36 0.20 2.10 0.50 0.04 9 Respiratory dust TWA 55 0.28 0.15 0.08 0.71 0.24 0.02 2 Sewage treatment Total dust TWA 6 0.95 0.48 0.20 1.60 0.80 0.24 50 Respiratory dust TWA 6 0.47 0.32 0.11 0.93 0.37 0.12 33 Package workshop Total dust TWA 23 0.43 0.23 0.20 1.20 0.39 0.04 4 Respiratory dust TWA 24 0.20 0.11 0.07 0.44 0.18 0.02 0 Total Total dust TWA 789 0.98 0.94 0.10 15.00 0.73 0.02 37 Respiratory dust TWA 690 0.44 0.30 0.04 2.67 0.34 0.01 19 Location Dust type Test type n Mean, mg/m3 SD Min, mg/m3 Max, mg/m3 GM, mg/m3 GSD % >PEL Batch house Total dust TWA 36 1.19 1.22 0.10 5.00 0.72 0.12 33 Respiratory dust TWA 24 0.23 0.16 0.08 0.73 0.19 0.02 4 Furnace workshop Total dust TWA 161 0.95 0.92 0.10 6.30 0.66 0.04 30 Respiratory dust TWA 89 0.31 0.25 0.08 1.16 0.23 0.02 10 Screening workshop Total dust TWA 44 1.28 2.64 0.20 15.00 0.65 0.09 18 Respiratory dust TWA 36 0.36 0.43 0.08 2.67 0.26 0.03 6 Drilling workshop Total dust TWA 464 1.01 0.63 0.20 3.80 0.82 0.03 45 Respiratory dust TWA 456 0.51 0.30 0.04 1.70 0.41 0.01 25 Polishing workshop Total dust TWA 55 0.59 0.36 0.20 2.10 0.50 0.04 9 Respiratory dust TWA 55 0.28 0.15 0.08 0.71 0.24 0.02 2 Sewage treatment Total dust TWA 6 0.95 0.48 0.20 1.60 0.80 0.24 50 Respiratory dust TWA 6 0.47 0.32 0.11 0.93 0.37 0.12 33 Package workshop Total dust TWA 23 0.43 0.23 0.20 1.20 0.39 0.04 4 Respiratory dust TWA 24 0.20 0.11 0.07 0.44 0.18 0.02 0 Total Total dust TWA 789 0.98 0.94 0.10 15.00 0.73 0.02 37 Respiratory dust TWA 690 0.44 0.30 0.04 2.67 0.34 0.01 19 TWA occupational exposure limit for total dust in China (quartz content from 10 to 50%) is 1.0 mg/m3, and exposure limit of respirable dust (quartz content from 10 to 50%) is 0.7 mg/m3. Open in new tab Table 4. Sampling data of total dust and respiratory dust Location Dust type Test type n Mean, mg/m3 SD Min, mg/m3 Max, mg/m3 GM, mg/m3 GSD % >PEL Batch house Total dust TWA 36 1.19 1.22 0.10 5.00 0.72 0.12 33 Respiratory dust TWA 24 0.23 0.16 0.08 0.73 0.19 0.02 4 Furnace workshop Total dust TWA 161 0.95 0.92 0.10 6.30 0.66 0.04 30 Respiratory dust TWA 89 0.31 0.25 0.08 1.16 0.23 0.02 10 Screening workshop Total dust TWA 44 1.28 2.64 0.20 15.00 0.65 0.09 18 Respiratory dust TWA 36 0.36 0.43 0.08 2.67 0.26 0.03 6 Drilling workshop Total dust TWA 464 1.01 0.63 0.20 3.80 0.82 0.03 45 Respiratory dust TWA 456 0.51 0.30 0.04 1.70 0.41 0.01 25 Polishing workshop Total dust TWA 55 0.59 0.36 0.20 2.10 0.50 0.04 9 Respiratory dust TWA 55 0.28 0.15 0.08 0.71 0.24 0.02 2 Sewage treatment Total dust TWA 6 0.95 0.48 0.20 1.60 0.80 0.24 50 Respiratory dust TWA 6 0.47 0.32 0.11 0.93 0.37 0.12 33 Package workshop Total dust TWA 23 0.43 0.23 0.20 1.20 0.39 0.04 4 Respiratory dust TWA 24 0.20 0.11 0.07 0.44 0.18 0.02 0 Total Total dust TWA 789 0.98 0.94 0.10 15.00 0.73 0.02 37 Respiratory dust TWA 690 0.44 0.30 0.04 2.67 0.34 0.01 19 Location Dust type Test type n Mean, mg/m3 SD Min, mg/m3 Max, mg/m3 GM, mg/m3 GSD % >PEL Batch house Total dust TWA 36 1.19 1.22 0.10 5.00 0.72 0.12 33 Respiratory dust TWA 24 0.23 0.16 0.08 0.73 0.19 0.02 4 Furnace workshop Total dust TWA 161 0.95 0.92 0.10 6.30 0.66 0.04 30 Respiratory dust TWA 89 0.31 0.25 0.08 1.16 0.23 0.02 10 Screening workshop Total dust TWA 44 1.28 2.64 0.20 15.00 0.65 0.09 18 Respiratory dust TWA 36 0.36 0.43 0.08 2.67 0.26 0.03 6 Drilling workshop Total dust TWA 464 1.01 0.63 0.20 3.80 0.82 0.03 45 Respiratory dust TWA 456 0.51 0.30 0.04 1.70 0.41 0.01 25 Polishing workshop Total dust TWA 55 0.59 0.36 0.20 2.10 0.50 0.04 9 Respiratory dust TWA 55 0.28 0.15 0.08 0.71 0.24 0.02 2 Sewage treatment Total dust TWA 6 0.95 0.48 0.20 1.60 0.80 0.24 50 Respiratory dust TWA 6 0.47 0.32 0.11 0.93 0.37 0.12 33 Package workshop Total dust TWA 23 0.43 0.23 0.20 1.20 0.39 0.04 4 Respiratory dust TWA 24 0.20 0.11 0.07 0.44 0.18 0.02 0 Total Total dust TWA 789 0.98 0.94 0.10 15.00 0.73 0.02 37 Respiratory dust TWA 690 0.44 0.30 0.04 2.67 0.34 0.01 19 TWA occupational exposure limit for total dust in China (quartz content from 10 to 50%) is 1.0 mg/m3, and exposure limit of respirable dust (quartz content from 10 to 50%) is 0.7 mg/m3. Open in new tab Discussion In our study, 88/98 (90%) reported silicosis cases were in drilling workers and 8/98 (8%) were in polishing workers. Although the factory implemented control measures to reduce silica dust levels in 2005, 289/789 (37%) total dust samples and 129/690 (19%) respirable dust samples exceeded China’s PEL of 1.0 and 0.7 mg/m3. To our knowledge, this is the first study to report silicosis in crystal rhinestone manufacturing. We conducted comprehensive sampling, including bulk dust from quartz sand and fallout dust, total air dust and respirable dust with repeated measurements, to explore possible exposure levels of the silicosis cases. We made full-shift measurements to avoid underestimating exposure. Although our aim was to assess exposure levels for the silicosis cases, we conducted air sampling after the factory implemented control measures to improve dust control. We measured total and respirable dust levels from 1924 air samples, but these did not represent the crystalline dust exposure level for the 98 silicosis cases. Thus, we could not calculate cumulative exposure levels for each case nor the dose–response relationship between the level of respirable silica dust exposure or duration of exposure and the occurrence of silicosis. Also, we did not conduct personal exposure monitoring for technical reasons in 2005. In our study, the duration of dust exposure (AM 9.2 years) was shorter than for 1058 silicosis cases from Hubei province, China [12]. Many epidemiological studies have reported a dose–response relationship between the level of respirable silica dust exposure or duration of the exposure period and the occurrence of silicosis [9,13,14]. However, mean duration of silica dust exposure varies in silicosis cases. One study found mean dust exposure duration of 16 years (range 5–33) in jade workers [7]. The mean duration of silica dust exposure in a South African study was also 16 years (range 3–34) [15]. Several studies report mean dust exposure durations from 21.8 to 27 years in gold and tin mining industries [16–18]. In our study, mean silica exposure duration was 9.2 years (range 3–16). Progression and latency of silicosis are not only associated with duration of exposure but also with the content of crystal quartz and exposure levels. In our study, the quartz content in the raw material of sand was 99.8%. The quartz content of drilling dust was 22%. In China, the PEL of silica dust varies according to quartz content. When the quartz content is ≥10% but ≤50%, the PELs of total dust and respirable dust are 1.0 and 0.7 mg/m3. We found that the total and respirable silica dust levels in the factory we studied were several orders of magnitude higher than China’s PEL, and much higher than the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) of 0.025 mg/m3. Silica dust exposure might have been much higher than we report in this study. Effective local exhaust ventilation plays an important role in dust control in rhinestone manufacturing. After the factory implemented dust control measures in 2005, no new silicosis cases were reported with a first exposure after 2005. The reduction in silica dust levels and the use of RPE from 2005 probably helped to protect workers. The main control methods to reduce the risk of dust are elimination, substitution, wet methods and enclosures [19]. In our study, wet methods were used at the screening unit, drilling and polishing workshop to allow particles to become wet before dispersing into the air. Wet cleaning of floors and work surfaces were also used after each work shift. Although local exhaust ventilation systems were installed at mixing, furnace, drilling and polishing work sites, dust levels could not be reduced to meet the national PEL. The hood is an important part of the local exhaust ventilation system. Silica dust is heavier than air so hoods should be positioned below and to the side of the dust source. However, in the factory we studied, hoods were located above the dust source. Also, the distance between hoods and dust source was too far to capture dust transmission. Hoods should be located as close as possible to the dust source without blocking workers’ movement. Capture velocity at the hood should exceed the capture velocity at the mixing or drilling work site. When the factory was built, ventilation systems were not installed. Local exhaust ventilation systems in crystal rhinestone factories should be designed consistent with the building of production flow. Silicosis is one of the oldest occupational diseases worldwide [3]. However, workers in some new industries are still at risk of crystalline silica dust exposure without effective ventilation and personal protective equipment. The occurrence of silicosis in crystal rhinestone-manufacturing workers due to exposure to crystalline silica dust highlights the need to ensure preventive measures to minimize silica dust exposure and the risk of silicosis. Funding This work was supported by the National Natural Science Foundation of China (81602804), Guangdong Medical Research Foundation (B2016017) and Guangdong Provincial Key Laboratory of Occupational Disease Prevention and Treatment (2017B030314152). Competing interests None declared. References 1. World Health Organization ; Wagner GR. Screening and Surveillance of Workers Exposed to Mineral Dust . http://www.who.int/occupational_health/publications/oehmineraldust.pdf ( 24 December 2017 , date last accessed). 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TI - Silicosis in rhinestone-manufacturing workers in South China
JF - Occupational Medicine
DO - 10.1093/occmed/kqz107
DA - 2019-12-07
UR - https://www.deepdyve.com/lp/oxford-university-press/silicosis-in-rhinestone-manufacturing-workers-in-south-china-GZnrihaML4
SP - 475
VL - 69
IS - 7
DP - DeepDyve
ER -