Radiographic abnormalities in long-tenure vermont granite workers and the permissible exposure limit for crystalline silica

This study was undertaken to assess the prevalence of radiographic abnormal ities consistent with silicosis in a group of 600 retired granite workers w ho were receiving pensions. Files of regional clinics and hospitals were se arched for chest radiographs taken on these men, and 470 x-ray films suitab le for interpretation were located. After exclusions (women, and men who ha d worked in the granite industry elsewhere), 408 x-ray films were independe ntly read by three experienced readers using the 1980 International Labour Office scheme. Dust exposures were estimated for workers hired after 1940, when the dust-control standard of 10 million particles per cubic foot (mppc f) (equivalent to 0.1 mg/m(3)) was put in place and monitored by the Vermon t Division of Industrial Hygiene. Dust levels were initially high but were gradually reduced from 1940 to 1954, after which average quartz exposures s tabilized to a mean of approximately 0.05 to 0.06 mg/m(3); however, about 1 0% to 15% of samples after 1954 exceeded 0.1 mg/m(3). Of the 408 x-ray film s, 58 were taken on workers hired before dust controls were instituted in 1 940, and 25.9% showed abnormalities (a profusion score of 1/0 or greater). A total of 350 x-ray films were taken on workers hired in 1940 or after, an d the prevalence in this group was 5.7%. The radiographic changes in worker s hired after 1940 are likely due to excessive exposures during the first 1 5 years of dust control. We conclude that if the exposure standard of 0.1 m g/m(3) is rigorously observed in the workplace, radiographic, abnormalities caused by quartz dust in long-term workers will be rare.