Dust – related risks of radiological changes in coalminers over a 40-year working life: report on work commissioned by NIOSH

This study provides estimates, using data from the Pneumoconiosis Field Research (PFR) of the National Coal Board in Britain, of the prevalence of simple pneumoconiosis (CWSP) and of progressive massive fibrosis (PMF) in coalminers at various stages of a 40-year working life. It considers in particular the risks associated with work at dust concentrations of 2 rag nf3, and it explores the sensitivity of these estimates to variations in the proportion of men who transfer to work at concentrations of 1 mg nf3 once CWSP category 1 or more is diagnosed. Several simplifying assumptions were made, the most important being that men left the industry only after an attack of PMF, and that PMF is irreversible.Data from 52 264 intervals at risk were used to estimate the probabilities of radiological changes over five-year periods, for various combinations of age, dust exposure, and carbon content of the coal, using logistic regression methods. These estimates were applied in turn to the eight successive five-year periods which comprise a 40-year working life, to give estimates of the required long-term risks.Results suggest that for coal of carbon content 86.2%, typical of conditions in Britain, the 40-year risks of PMF incidence at 2 mg m-3 dust concentration are 1.19% for PMF, and 3.67% for simple pneumoconiosis category 2 or more (including PMF). Corresponding estimates for coal of 83% carbon, more typical of conditions in the USA, were 0.71% for PMF, and 2.49% for category 2 or 3 CWSP or PMF. The transfer to lower dust concentrations of men with simple pneumoconiosis had negligible effect on the estimated risks.The long-term risks of category 2 or more CWSP associated with work at high dust concentrations (say 6 to 7 mg nf3) were on average similar to estimates from previous PFR studies. However at lower dust levels, say 1 to 4 mg nf3, the risks estimated now were higher than those reported previously. On the other hand the new estimates of the long-term risks of PMF were lower than preliminary estimates reported last year.Results reinforce the conclusion from other recent studies of PMF, that the limitation of dust exposures for all miners is the only reliable way of limiting PMF. We think that the concentration-specific estimates of long-term PMF risks described are the most reliable indices of their kind available to date. They provide a sound basis for control strategies aimed directly at preventing PMF.