Silicosis among foundry workers. Implication for the need to revise the OSHA standard

To evaluate the risk of pneumoconiosis among workers in a Midwestern automotive foundry, medical records and silica sand exposure data were analyzed for 1,072 current and retired employees with at least 5 years of employment as of June 1991. Approximately half of these employees had worked at the foundry for 20 or more years. Sixty workers were found to have radiographic evidence of pneumoconiosis. Twenty-eight workers had radiographs consistent with silicosis, of which 25 were consistent with simple silicosis and three with progressive massive fibrosis. The prevalence of radiographic changes consistent with silicosis increased with: number of years worked at the foundry (6% for 20-29 years and 12% for 30 or more years); cigarette smoking (12.2% among smokers with high silica exposure vs. 4.4% among never smokers with high silica exposure); work area within the foundry (cleaning room, core room, mold area, core knockout); and quantitative silica exposure (0.3-2.7% of workers at the current Occupational Safety and Health Administration (OSHA) standard and 4.9-9.9% of workers above the OSHA standard). In addition, the odds of developing radiographic changes consistent with silicosis were increased for African Americans (odds ratio = 2.14, 95% confidence interval 0.85-5.60) in comparison with whites. (The risk was similar when silica exposure was equal, but African-American workers on average had greater exposure to silica, despite having a similar duration of work as white workers.) Another eight workers had radiographic evidence of asbestosis, and 24 had pleural plaques. These asbestos-related changes were not associated with increasing exposure to silica but rather were associated with being in the maintenance department and performing repair work. After controlling for cigarette smoking, race, and exposure to silica at another job besides the foundry, the authors found a 1.45 increased risk of developing a radiograph consistent with silicosis after 20 years of work at the current OSHA standard, and a 2.10 increased risk after 40 years of work at the current OSHA standard. On the basis of these findings, the authors recommend maintaining silica air levels no higher than the exposure level of 0.05 mg/m3 recommended by the National Institute for Occupational Safety and Health.