Document Z4Enn3rRp9O11RkdR2R5o7Vn8

1 that population. Page 3375 2 But Lanza felt that his data didn't allow 3 him to put a numerical value on dust control. That 4 was accomplished in 1938 when a U.S. Public Health 5 Service physician named Dreessen and his colleagues 6 studied workers in asbestos textile plants in North 7 Carolina. 8 They again basically duplicated the 9 Merewether and Lanza studies, measured the dust levels 10 at various jobs, examined the workers and found 11 disease. 12 What they did differently is that for each 13 worker knowing his job history over his working 14 career, they calculated according to the dust 15 measurements and how many years he worked in each job, 16 the average exposure over their working career. 17 And then when they plotted average exposure 18 versus incident of disease, what they found was that 19 all clear-cut cases of asbestosis were exposed to dust 20 levels greater than five million particles per cubic 21 foot of asbestos dust.