Silica exposure and silicosis among ontario hardrock miners: III. Analysis and risk estimates

Abstract

An epidemiological investigation was undertaken to determine the relationship between silicosis in hardrock miners in Ontario and cumulative exposure to silica (free crystalline silica-α quartz) dust. This report describes the analytic method and presents the risk estimates.

Silica exposure and silicosis among ontario hardrock miners: II. Exposure estimates

“…By using the "time task" breakdown of the "cohort work history" and by applying the converted gravimetric concentrations to each task, a lifetime cumulative dose of respirable silica for each miner in the cohort was calculated. The lifetime dose has been used in the derivation of the relationship between respirable silica concentration in mg/m 3 and the radiological silicosis described in the third part of our report [Muir et al, 1989b].…”

“…The basic methodology and cohort defi nitions are given in part I [Muir et al, 1989a] and the dose-response relationship in part III [Muir et al, 1989b]. …”

Prediction of silicosis and lung cancer in the Australian labor force exposed to silica.

“…In the modeling for the risk of silicosis, a five-year lagging of exposures was explicitly incorporated into the analysis (4). Thus the time between the deposition of silica in the lungs and the clinical appearance of silicosis was taken into account when the expected numbers of cases were computed.…”

Approaches for assessing the efficacy of occupational health and safety standards

“…For example, Figure 4 presents the results from an analysis of silicosis risk based on a study of Canadian hardrock miners [Muir et al, 1989;Muir, 19911. The silicosis cases and resulting risk estimates in this study were found to be influenced by the reader who reviewed the chest x-ray.…”

“…In addition to the surveillance program, the research program known as the National Study of Coal Workers' Pneumoconiosis (NSCWP) has provided the data used in the exposure-response studies of Seixas et al [ 19931 and Attfield and Seixas [1995]. Figure 5 demonstrates a rather dramatic decline in the prevalence of CWP for all tenure groups since the MSHA coal dust standard was enacted in [Muir et al, 1989;Muir, 19911. 1977. On the other hand, the most recent round of the CWXSP (1992)(1993)(1994)(1995) indicates that approximately 1 in 10 miners with greater than 25 years of mining experience suffers from CWP.…”