Document jBqO9M4356JND1X5Dkom1rE19

28 decreases to somewhat below the level of those unexposed otherwise. The percentages of abnormalities among those with other asbestos expo sure remain significantly different from those unexposed. If we consider the percentage of X-ray abnormalities a manifestation of a normal distribution with a variance reflected by the number of abnor mal X-rays, the respective standard deviations in the final column of Table 13 are calculated. While the percentage of abnormal X-rays in each of the job categories of Table 13 has a large uncertainty associ ated with it because of the limited number of individuals in a work activity (other than brake work), the pattern of observed percentages yields a remarkable consistency. The two groups with no identified asbestos exposure, non-garage controls and garage workers with no brake or body work have the lowest percentages of abnormalities, the various activities with probable asbestos exposure have the highest percent ages, and brake workers are intermediate. Individuals with other dust exposure appear to be unaffected by such materials. This is probably the result of the relatively short exposure times or the marginal expo sure circumstances. The other dusts included coal (23 men), silica (9 men), and other dusts (3 men). Five of the other dust exposures were for longer than ten years, (One of the five had an abnormal X-ray.) The average exposure of the other 30 was 3.2 years. In subsequent analysis these 35 individuals will be characterized by their garage (or non-garage) employment. One notable feature of Table 13 is the high percentage of abnormal X-rays among the 32 individuals who worked for some time in auto body repair. (See subsequent sections on auto body repair and undercoating work.) Smoking standardization of X-ray abnormalities Smoking has been identified as exacerbating the nou-malignant effects of asbestos. Death rates from asbestosis among 20+ cigarette/day smokers are 2.8 times greater than among nonsmokers (Hammond, Selikoff, and Seidman, 1979) and both parenchymal and pleural X-ray abnormalities have been reported as more common among current and ex-smokers than nonsmokers (Weiss, 1971; Rossiter and Harries, 1979; Weiss, Levin, and