Document Xz6RN20L604M0eMXERxdGywKG

Page 2620 1 You end up preparing the filter so that it 2 is transparent to the electron beam, and the electron 3 microscope is a much larger instrument, probably about 4 the size of the table there. And then the electron 5 beam comes down through the sample and it appears on 6 the screen at the bottom. And just to give you an 7 idea, a human hair magnified 20,000 times would be 8 about six feet wide. So we are looking at individual 9 fibers that are much smaller, thinner than that. 10 So with the electron microscope you can see 11 all of the asbestos fibers that are in the air, all of 12 the different sizes. So you can come up with a really 13 good number of how many fibers are present there. 14 And the Environmental Protection Agency in 15 their clearance of schools, uses the electron 16 microscope as the test for final clearance, whereas 17 the OSHA or occupational groups use the light 18 microscope currently for doing monitoring. 19 They acknowledge that there are a lot of 20 smaller ones there, but they will count the large ones 21 to give some idea of what the total amount is.