Forwarding WTC air monitoring scope for final review, Aug 2002

NYC 9/11 Public Portal Document

Environmental Protection Agency Pl. 763, Subpt. E, App. A sputtered or evaporated. A thin film of gold pling and analysis procedures. Because the Is evaporated on the specimen TEM grid to test Is sensitive, it may be Influenced by a obtain zone-axis ED patterns superimposed variety of factors. These include the supplies with a ring pattern from the polycrystalline used in the sampling operation, the perform­ gold film. ance of the sampling, the preparation of the 11. In practice, it is desirable to optimize grid from the Alter and the actual examina­ the thickness of the gold film so that only tion of this grid in the microscope. Each of one or two sharp rings are obtained on the these unit operations must produce a prod­ superimposed ED pattern. Thicker gold film uct of defined quality if the analytical result would normally give multiple gold rings, but it will tend to mask weaker diffraction spots is to be a reliable and meaningful test result. from the unknown fibrous particulates. Accordingly, a series of control checks and Since the unknown d-spacings of most inter­ reference standards Is performed along with est in asbestos analysis are those which Ue the sample analysis as Indicators that the closest to the transmitted beam, multiple materials used are adequate and the oper­ gold rings are unnecessary on zone-axis ED ations are within acceptable limits. In this patterns. An average camera constant using way. the quality of the data is defined and multiple gold rings can be determined. The the results are of known value. These checks camera constant is one-half the diameter, D, and tests also provide timely and specific of the rings times the Interplanar spacing, d, warning of any problems which might de­ of the ring being measured, velop within the sampling and analysis oper­ K, Quality Control/Quality Assurance ations. A description of these quality con- Procedures (Data Quality Indicators) trol/quallty assurance procedures is summa­ rized in the following Table III: Monitoring the environment for airborne asbestos requires the use of sensitive sam-

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