Assessment of silica dust exposure profile in relation to prevalence of silicosis among Indian sandstone mine workers: Need for review of standards

Background In Indian mines, the prescribed exposure limit (PEL) for free silica dust is 0.15 mg/m(3) which is much higher than those of OSHA and the ACGIH. Because of the reporting of high numbers of silicosis cases among Indian sandstone mine workers, the present study was designed to assess the dust exposure profile of the workers and to substantiate correlation of silica exposure with radiographic findings of silicosis. Methods A cross-sectional study of 1012 workers actively engaged in sandstone mining was conducted. Chest x-rays were evaluated by the ILO Classification for the detection of pneumoconiosis. Representative 26 personal dust samples were collected using a personal dust sampler and free silica content estimated. Results Radiographs compatible with silicosis were seen in 12.3% of workers, of which about 90% were ILO category 1 & 2. Prevalence of abnormal profusion increased from 2.9% to 13.1% to 22% as work exposure increased from <10 to 11 to 20 to >20 years, respectively. In dust samples, the mean silica concentration was 0.12 mg/m(3) with 70% samples below the prescribed standard of 0.15 mg/m(3). Conclusion The study indicates that silica exposure below the prescribed limit in India is likely to be harmful. The PEL for crystalline silica in India of 0.15 mg/m(3) is not adequately protective. Hence, there is an urgent need to reduce exposure to silica in these workplaces to prevent silicosis and to review the present standards as the government of India remains committed to the elimination of silicosis by 2030.