Effect of further dust exposure among men with early and more advanced signs of simple pneumoconiosis. Final report on CEC Contract 6244-00/8/107

Statistical analyses have been made to quantify risks of simple pneumoconiosis progression for coalminers with early or more advanced signs of the disease. Three overlapping sets of data from the British Pneumoconiosis Field Research have been studied. The first consists of radiological and dust exposure data for 4 122 coalface workers who had attended at three quinquennial medical surveys at 20 collieries. Radiological changes over 10 years were assessed by eight doctors each classifying all 4 122 film-pairs in terms of the International Labour Office’s (ILO) 12-point scale of simple pneumoconiosis. The second data set refers to more than 13 000 miners from 2k collieries who were also surveyed three times. The classifications of corresponding triplets of serial radiographs were on the short (four-point) ILO classification only, and were made by various doctors at different times. The third set of results were from a sample of men from 10 collieries who had attended at four consecutive surveys over a 15-year period. The sets of four radiographs for all men had each been classified separately, independently, and during the same year by each of six physicians.Individual miners’ exposures to respirable dust during the research periods were calculated from results of dust sampling in occupational groups and records of the numbers of shifts worked in the occupational groups. All the exposure data used for the analyses are expressed in gravimetric units.The results from the 4 122 face workers were first expressed as ten-year incidence rates of the earliest radiological changes (category 0/1 or more) at the 20 collieries. These statistics correlated significantly with the averages of all coalface dust concentrations during the ten years at the collieries. The , incidence rates were compared with estimates of corresponding probabilities of further radiological change (one or more steps of progression on the 12-point scale) for men with category 0/1 initially and for those with category 1/0. At k mg/m3 these probabilities were 29.2 and 40.6 percent respectively, as compared with a 6.4 percent probability of movement from category 0/0 at the same average concentration over 10 years. Analyses of the men’s individual exposures and responses showed a similar pattern of relative risk with increasing initial category for 10-year exposures to k mg/m3 or more. It is estimated that for men with radiological signs less than category 2/1, the probability of progressing to category 2/1 or higher during 10 years’ exposure to 4mg/m3 respirable dust is about three times higher than the probability that men with no pneumoconiosis (category 0/0) develop category 2/1 or more during 35 years’ exposure to 4 mg/m3.Analysis of radiological classifications on the four-point scale for more than 13 000 men showed that among those with category 0 initially the development of pneumoconiosis during 10 years depends on exposure both before and after the start of the interval. No similar relationships were detected for miners with category 1 initially, but they had an approximately five to six-fold greater chance of developing category 2 or more during 10 years compared with the average results from those with category 0.Further prior and subsequent exposure-specific comparisons were made between men with category 0 and others with category 1. They confirmed that in general men with category 1 initially were more likely to develop category 2 over both five and over 10 year intervals. Attempts were made to quantify the relative risks, using more refined radiological data from men whose exposures had been measured for 15 years. These efforts were not successful: only 81 of 151 men with category 0/1 initially showed further radiological changes during the 15 years. An exposure-response relationship was detectable only in the group with category 0/0.There is evidence that some coal miners are more susceptible to the effects of dust exposure than others. The mathematical model which was used to make long-term predictions of pneumoconiosis risks took no specific account of this factor or of exposure prior to the start of the study period. Nevertheless, it is shown that in practice, the method of extrapolation used gave reasonable predictions from data involving less than 10 years’ prior exposure.It is concluded that dust standards designed to restrict long-term pneumoconiosis risks for new entrants to the industry should be supplemented by appropriate measures for the protection of miners with pneumoconiosis.