Laserfiche WebLink
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 [hen coated with a thin layer of carbon in a carbon side down. The sample was [hen <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 [o cause the sample to exceed 70 structures/mmZ <br />.(usually 4 or 5 structures). Both SAED and EDX confirmation are required of enough amphibole structures <br />on each sample [o cause the sample to exceed 70 structures/mmZ (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 [0 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 [hat 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 [he 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 50`" structure. AHERA protocol <br />requires the laboratory to reject any clearance sample which contains in excess of 25% 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/mmZ 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 Aualyzed, mmZ = # GO counted x Average GO Area (mm) <br />Concentratioq s/cc = # Asbestos Structures x 1 g Eff. Filter Area (mmZ) x 1 L <br /># GO Counted Volume (L) Average GO area (mm~) 1000cc <br />Filter loading, s/mm2 = # Asbestos s[mctures <br />Area Analyzed (mm~) <br />GO =TEM grid opening <br />File: $IIdreE m serer T/ORfortns.sg/AMERA RroceGUres <br />Revised: 11212]N2 <br />