Forwarding WTC air monitoring scope for final review, Aug 2002

NYC 9/11 Public Portal Document

Pt. 763, Subpt. E, App. A 40 CFR Ch. I (7-1-00 Edition) 1. Individual grid openings with greater loaded into the microscope and a particular than 5 percent openings (holes) or covered field is to be reliably identified. with greater than 25 percent particulate g. Scan the grid. matter or obviously having nonuniform load­ i. Select a field to start the examination. ing shall not be analyzed. ii. Choose the appropriate magnification il. Examine the grid at low magnification (15,000 to 20,000X screen magnification), (<1000X) to determine its suitability for de­ ill. Scan the grid as follows. tailed study at higher magnifications. (1) At the selected magnification, make a ill. Reject the grid if: series of parallel traverses across the field. (1) Less than 50 percent of the grid open­ On reaching the end of one traverse, move ings covered by the replica are intact. the Image one window and reverse the tra­ (2) It is doubled or folded. verse, (3) It is too dark because of Incomplete dis­ NOTE: A slight overlap should be used so as solution of the filter. not to miss any part of the grid opening iv. If the grid is rejected, load the next (field). sample grid. (2) Make parallel traverses until the entire V. If the grid is acceptable, continue on to grid opening (field) has been scanned. Step 6 if mapping Is to be used; otherwise h. Identify each structure for appearance proceed to Step 7. and size. f. Grid Map (Optional). 1. Appearance and size: Any continuous 1. Set the TEM to the low magnification grouping of particles in which an asbestos mode. fiber within aspect ratio greater than or 11. Use flat edge or finder grids for map­ equal to 5:1 and a length greater than or ping- equal to 0.5 gm is detected shall be recorded ill. Index the grid openings (fields) to be on the count sheet. These will be designated counted by marking the acceptable fields for asbestos structures and will be classified as one-half (0.5) of the area needed for analysis fibers, bundles, clusters, or matrices. Record on each of the two grids to be analyzed. as individual fibers any contiguous grouping These may be marked Just before examining having 0. 1. or 2 definable intersections. each grid opening (field), if desired. Groupings having more than 2 intersections iv. Draw in any details which will allow are to be described as cluster or matrix. See the grid to be properly oriented If it is re­ the following Figure 5:

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NYC-WTC_000139309