NYC-WTC_000219925

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III. Nonmandatory Transmission Electron Microscopy Method

A, Definitions of Terms

1. Analytical sensitivity — Airborne asbestos concentration represented by each fiber counted under the electron microscope. It is determined by the air volume collected and the proportion of the filter examined. This method requires that the analytical sensitivity be no greater than 0.005 s <3>.

2. Asbestiform -- A specific type of mineral fibrosity in which the fibers and fibrils possess high tensile strength and flexibility.

3. Aspect ratio — A ratio of the length to the width of a particle. Minimum aspect ratio as defined by this method is equal to or greater than 5:1.

4. Bundle - A structure composed of three or more fibers in a parallel arrangement with each fiber closer than one fiber diameter.

5. Clean area -- A controlled environment which is maintained and monitored to assure a low probability of asbestos contamination to materials in that space. Clean areas used in this method have HEPA filtered air under positive pressure and are capable of sustained operation with an open laboratory blank which on subsequent analysis has an average of less than 18 structures/mm<2> in an area of 0.057 mm<2> (nominally 10 200 mesh grid openings) and a maximum of 53 structures/mm<2> for no more than one single preparation for that same area.

6. Cluster — A structure with fibers in a random arrangement such that all fibers are intermixed and no single fiber is isolated from the group. Groupings must have more than two intersections.

7. ED— Electron diffraction.

8. EDXA — Energy dispersive X-ray analysis.

9. Fiber - A structure greater than or equal to 0.5 pm in length with an aspect ratio (length to width) of 5:1 or greater and having substantially parallel sides.

10. Grid -- An open structure for mounting on the sample to aid in its examination in the TEM. The term is used here to denote a 200-mesh copper lattice approximately 3 mm in diameter.

11. Intersection — Nonparallel touching or crossing of fibers, with the projection having an aspect ratio of 5:1 or greater.

12. Laboratory sample coordinator — That person responsible for the conduct of sample handling and the certification of the testing procedures.

13. Eilter background level — The concentration of structures per square millimeter of filter that is considered indistinguishable from the concentration measured on blanks (filters through which no air has been drawn). For this method the filter background level is defined as 70 structures/mm<2>.

14. Matrix — Fiber or fibers with one end free and the other end embedded in or hidden by a particulate. The exposed fiber must meet the fiber definition.

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