An epidemiological survey of respiratory morbidity among granite quarry workers in Singapore: radiological abnormalities

Abstract

This report presents baseline findings from the first of a series of epidemiological studies to evaluate inter alia the effects of control measures introduced in 1972-79 to reduce dust exposure in all quarries in Singapore. The prevalence of radiological abnormalities among 219 currently employed quarry workers were estimated according to a number of parameters of dust exposure. Large-sized chest x-ray films were read, independently and in random order, by a panel of three experienced readers, who were "blinded" to the personal particulars and exposure of the subjects, using standard chest x-ray films to record opacities according to the International Standard Classification of Radiographs of Pneumoconioses. Silicosis as defined by radiological small opacities (both rounded and irregular) of profusion 1/1 or greater as read by at least two readers were noted in 11 subjects. The prevalence of silicosis was 12.5% in highly exposed drilling and crushing workers, and 0.8% in maintenance and transportation workers with low level exposure to granite dust. Among those who were first exposed to granite dust after 1979, no cases of silicosis were noted in any quarry worker. It is concluded that reduction in dust exposure since 1979 has so far been successful in producing nil or negligible risks of silicosis among active quarry workers over ten years, but further follow-up studies are needed.