Document 2RdzqMZZmme23oN5dGB1VRdN7

1 such as you would find normally for phase contrast Page 2662 2 microscopy would be very low. 3 It would be .30 -- well, it would be around 4 four zeros, .00001 fibers per cc for ambient level. 5 For PEM structures in a building, one of the 6 EPA documents talks about .005 asbestos structures per 7 cc or structures per cc as being the ambient TEM 8 level. 9 Of course, they were looking at smaller 10 fibers. 11 Q This is the background level that may be in 12 the ambient air in an urban environment? 13 A That is correct. 14 Q How did the figures, or the results that you 15 found, compare with the permissible exposure level 16 that is in the regulations today? 17 A Well, the OSHA level was .01 fiber per cc. 18 That would be over an eight-hour time-weighted 19 average. 20 Q Can you describe for us what you mean by the 21 time-weighted average, and how it differs from what