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Analytical Procedures—AHERA <br /> Transmission electron microscopy/energy dispersive X-ray spectrometry/selected area electron diffraction <br /> (TEM/EDX/SAED) was employed in the analysis of the samples, which were collected on 25 mm mixed <br /> cellulose ester air filters. A portion of each filter was collapsed with acetone and etched in a plasma asher. <br /> The etched filter was then coated with a thin layer of carbon in a carbon side down. The sample was then <br /> placed inside a condensation washer and treated with acetone to remove the filter matrix and expose any <br /> inert material. <br /> For each sample, enough grid openings on a 200 mesh TEM grid are analyzed to ensure an analytical <br /> sensitivity of at least 0.005 structures/cc. A minimum of four grid openings from two preparations are <br /> analyzed for each sample. The grid openings are searched for fibrous structures which, if present are <br /> analyzed by SAED and/or EDX (elemental analysis). The AHERA protocol requires SAED confirmation <br /> of enough chrysotile asbestos structures on each sample to cause the sample to exceed 70 structures/mm2 <br /> (usually 4 or 5 structures). Both SAED and EDX confirmation are required of enough amphibole structures <br /> on each sample to cause the sample to exceed 70 structures/mm2(usually 4 or 5 structures) per sample. <br /> Either SAED or EDX is required for the remaining asbestos structures of either type. The morphology of <br /> each structure is determined and the length and the diameter of any asbestos structures are recorded. <br /> Asbestos fibers, bundles, cluster and matrices were identified and recorded. The asbestos structures have <br /> been defined in AHERA as follows: <br /> Fiber: is a structure having a minimum length greater than or equal to 0.5 <br /> micron with an aspect ratio of 5:1 or greater with substantially parallel <br /> sides. <br /> Bundle: is a structure composed of three or more fibers in parallel arrangement, <br /> with each fiber closer than the diameter of one fiber. <br /> Cluster: is a structure with fibers in random arrangements such that all fibers are <br /> intermixed and no single fiber is isolated from the group. <br /> Matrix: is a fiber or fibers with one end free and the other end embedded or <br /> hidden by a particulate. The exposed fiber end must meet the fiber <br /> definition given above. <br /> If more than 50 asbestos structures are identified and confirmed on a sample, AHERA analysis may be <br /> terminated after completion of the grid opening, which contains the 50th structure. AHERA protocol <br /> requires the laboratory to reject any clearance sample which contains in excess of 2.5% total particulate <br /> loading or which appears to be unevenly loaded. <br /> The AHERA protocol includes specific sampling requirements, including minimum numbers of samples <br /> and minimum air volumes. Specifically, the 70 structures/mm2 clearance criteria is only allowed for sets <br /> five inside samples (collected in a group of 13 samples including: five outsides and three blanks) with <br /> volumes greater than 1200 liters (40 CFR Part 763, page 41894). Deviation from the AHERA sampling <br /> protocol may affect the validity of the analytical results. Analysis of samples collected by non-protocol <br /> methods are not accredited by NVLAP <br /> Equations Used for Calculations <br /> Area Analyzed,mm2=#GO counted x Average GO Area(mm) <br /> Concentration,s/cc=#Asbestos Structures x 1 x Eff.Filter Area(mm2) x 1L <br /> #GO Counted Volume(L) Average GO area(mm2) 1000cc <br /> Filter loading,s/mm2= #Asbestos structures <br /> Area Analyzed(mm2) <br /> GO=TEM grid opening <br /> File Shared on server T/Offforms sg/AHERA Procedures <br /> Revised 02/27/02 <br />