Forwarding WTC air monitoring scope for final review, Aug 2002

NYC 9/11 Public Portal Document

Environmental Protection Agency Pt. 763, Subpt. E. App. A known weight of a collapsed filter be estab­ be metric). A logbook must be maintained, lished and that the etching rate be cal­ and the dates of calibration and the values culated In terms of micrometers per second. obtained must be recorded. The frequency of The actual etching time used for the particu­ calibration depends on the past history of late asher and operating conditions will then the particular microscope. After any mainte­ be set such that a 1-2 gm {10 percent) layer nance of the microscope that involved ad­ of collapsed surface will be removed. justment of the power supplied to the lenses 111. Procedures as described In Unit III. or or the high-voltage system or the mechan­ other equivalent methods may be used to ical disassembly of the electron optical col­ prepare samples. umn apart from filament exchange, the mag­ nification must be recalibrated. Before the F. TEM Method TEM calibration Is performed, the analyst 1. An 80-120 kV TEM capable of performing must ensure that the cross grating replica is electron diffraction with a fluorescent screen placed at the same distance from the objec­ Inscribed with calibrated gradations Is re­ tive lens as the specimens are. For instru­ quired. If the TEM Is equipped with EDXA it ments that incorporate a eucentrlc tilting must either have a STEM attachment or be specimen stage, all specimens and the cross capable of producing a spot less than 250 nm grating replica must be placed at the In diameter at crossover. The microscope eucentrlc position, shall be calibrated routinely for magnifica­ 4. While not required on every microscope tion and camera constant. in the laboratory, the laboratory must have 2. Determination of Camera Constant and ED either one microscope equipped with energy Pattern Analysis. The camera length of the dispersive X-ray analysis or access to an TEM In ED operating mode must be cali­ equivalent system on a TEM In another lab­ brated before ED patterns on unknown sam­ oratory, ples are observed. This can be achieved by 5. Microscope settings: 80-120 kV, grid as­ using a carbon-coated grid on which a thin sessment 250-l,000X, then 15,000-20,000x film of gold has been sputtered or evapo­ screen magnification for analysis. rated. A thin film of gold Is evaporated on 6. Approximately one-half (0.5) of the pre­ the specimen TEM grid to obtain zone-axis determined sample area to be analyzed shall ED patterns superimposed with a ring pat­ be performed on one sample grid preparation tern from the polycrystalllne gold film. In and the remaining half on a second sample practice, It Is desirable to optimize the grid preparation. thickness of the gold film so that only one or 7. Individual grid openings with greater two sharp rings are obtained on the super- than 5 percent openings (holes) or covered Imposed ED pattern. Thicker gold film would with greater than 25 percent particulate normally give multiple gold rings, but it will matter or obviously having nonuniform load­ tend to mask weaker diffraction spots from ing must not be analyzed. the unknown fibrous particulate. Since the 8. Reject the grid If: unknown d-spaclngs of most interest in as­ a. Less than 50 percent of the grid openings bestos analysis are those which lie closest to covered by the replica are Intact. the transmitted beam, multiple gold rings b. The replica is doubled or folded. are unnecessary on zone-axis ED patterns. c. The replica Is too dark because of Incom­ An average camera constant using multiple plete dissolution of the filter. gold rings can be determined. The camera 9. Recording Rules. constant is one-half the diameter of the a. Any continuous grouping of particles in rings times the Interplanar spacing of the which an asbestos fiber with an aspect ratio ring being measured. greater than or equal to 5:1 and a length 3. Magnification Calibration. The magnifica­ greater than or equal to 0.5 gm Is detected tion calibration must be done at the fluores­ shall be recorded on the count sheet. These cent screen. The TEM must be calibrated at will be designated asbestos structures and the grid opening magnification (if used) and will be classified as fibers, bundles, clusters, also at the magnification used for fiber or matrices. Record as Individual fibers any counting. This is performed with a cross contiguous grouping having 0, 1, or 2 defin­ grating replica (e.g., one containing 2,160 able intersections. Groupings having more lines/mm). Define a field of view on the fluo­ than 2 Intersections are to be described as rescent screen either by markings or phys­ cluster or matrix. An Intersection Is a non­ ical boundaries. The field of view must be parallel touching or crossing of fibers, with metisurable or previously Inscribed with a the projection having an aspect ratio of 5:1 scale or concentric circles (all scales should or greater. See the following Figure 2:

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