Five physicians' radiological assessments of coalworkers' simple pneumoconiosis (CWP) in 2600 coalminers at 10 British collieries have been studied in relation to the individuals' estimated lifetime (mean 33 years) exposure to respirable coalmine dust. Estimates of exposure were based on 20 years of observations at each colliery. Radiographic classifications were clearly associated with the measures of dust exposure. Important unexplained differences between some of the collieries were disclosed. Among men with similar cumulative dust exposures those with longer exposure time had higher prevalence of CWP. In general there was no evidence that the quartz concentrations experienced (average 5 % of mixed dust) affected the probability of developing coalworkers' simple pneumoconiosis. Some men reacted unfavourably (two or more steps of change on the 12-point radiological scale) over a 10-year period to coalmine dust with a relatively high quartz content.Earlier reports from the National Coal Board's Pneumoconiosis Field Research have described an association between exposure to respirable coalmine dust and incidence of coalworkers' simple pneumoconiosis (CWP).1-5 The effect of quartz has also been studied.6 These were interim investigations, based on a 10-year period of observations of coalface workers at 20 British collieries. Results from a longer-term study at 10 collieries are presented in this paper, which has two main objectives. The first is to report new dust-related estimates of long-term incidence risks of pneumoconiosis among working miners. The second is to present further information on how the chances of developing CWP are influenced by the quartz content of the coalmine dust to which men are exposed. SubjectsSince 1953 medical surveys of the Pneumoconiosis Field Research have been carried out at roughly five-year intervals at selected collieries from all the major British coalfields. Ten collieries were surveyed at least five times. They cover a wide range of environmental and geological conditions. All currently employed miners were asked to take part on each occasion. This report considers primarily the 2600 men who attended the first, third, and fifth surveys at the 10 collieries, and for whom complete and reliable data were available. Men no longer in the industry were not studied: 8394 men, examined at these collieries at the first surveys, were alive and under 65 years old 20 years later. The 2600 long-term working miners studied form 31 % of that group. Some results are reported for a further 1730 men who attended the third and fifth surveys, but not the first, at these same collieries. Methods RADIOLOGICAL DATAEach of five physicians experienced in the radiology of pneumoconiosis classified the fifth survey fullsized (posteroanterior) chest radiographs of the men separately, independently, and in random order according to the ILO U/C International Classification of Radiographs of the Pneumoconioses,7 using 1968 standard films. Additionally, the readers classified all 4330 pairs of the third a...

The respiratory health of workers exposed to polyvinylchloride (PVC) dust has been investigated in 818 men sampled from the work force of a factory manufacturing PVC. In a crosssectional survey, the lung function and prevalences of respiratory symptoms and chest radiographic abnormalities were compared with estimates of individual PVC dust exposures based o, detailed occupational histories and current measurements of respirable PVC dust. Complaints of slight exertional dyspnoea were associated with PVC dust exposure, though age and smoking effects were much stronger. The forced expired volume in one second (FEV,) and forced vital capacity (FVC) were inversely related to dust exposure after age, height, and smoking effects had been taken into account. This effect was seen principally in cigarette smokers, and there was suggestive evidence that PVC dust exposure and cigarette smoking interacted in the reduction of FEV, and FVC. Gas transfer factor was not related to dust exposure. The chest radiographs were read according to the ILO U/C classification by three experienced readers. One reader recorded a low prevalence of small rounded opacities, and these were not related to age or dust exposure. Another reader recorded a higher prevalence of small rounded opacities category 0/1 or more, and these were related to age but not to dust exposure. The third reader recorded the highest prevalence of small rounded opacities (though none greater than category 1/1), and these were independently related both to age and to PVC dust exposure, indicating an effect of PVC dust on the appearances of the chest radiograph. These appearances were so slight that only the higher sensitivity of this reader in the interpretation of profusion of small rounded opacities on the ILO U/C scale enabled detection of this effect of PVC dust. In conclusion, exposure to PVC dust is associated with some deterioration of lung function, slight abnormalities of the chest radiograph, and complaints of slight dyspnoea. The mean decline in FEVy associated with the average dust exposure experienced in the study was small, though some of the men with higher dust exposures may have suffered clinically important 1h)ss of lung function as a result of their occupation.

A preliminary epidemiological study has been carried out to investigate a report that some men working in a factory manufacturing polyvinylchloride (PVC) had abnormally low values of the single breath diffusing capacity for carbon monoxide (TLCO). All monoxide (TLCO). All 265 present and past employees of the PVC factory were studied, together with 219 men from the workforce of a nearby foundry. Each man's TLCO was measured and a smoking history and detailed occupational history obtained. The distribution of standardised TLCO results from all persons examined was symmetrical and did not indicate an unexpectedly high proportion of men with having allowed for age, height, weight, and smoking habit, TLCO was associated with a history of working in the PVC factory before 1975 (when levels of vinylchloride monomers (VCM) were much higher than subsequently), and slightly associated with working in jobs where exposure to VCM was likely to have been highest. The men with low TLCO also tended to have smoked more heavily than controls. The relative importance of occupational factors and smoking in relation to low TLCO is not clear, but the results give some support to the hypothesis that work in the PVC factory before 1975 entailed exposure to a substance that caused impairment of lung function in a small number of men.

Under controlled conditions 16 people (eight non-medical) inexperienced in the radiology of occupational lung diseases repeatedly classified 300 selected chest radiographs using the 1971 ILO U/C International Classification of Radiographs of Pneumoconioses. Eight experienced medical readers had previously classified 220 of the selected radiographs for profusion of small rounded opacities. Variability among readers was greater in the experimental panels than among the experienced readers. But

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