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) 9. Signature of laboratory official to indi­ calculation. On most microscopes, however. cate that the laboratory met specifications the magnification is substantially constant of the AHERA method. only within the central 8-10 cm diameter re­ 10, Report form must contain official lab­ gion of the fluorescent screen. oratory identification (e.g.. letterhead). Iv. Calculate the true magnification (M) on 11. Type of asbestos. the fluorescent screen: M=XG/Y J. Calibration Methodology where: Note: Appropriate implementation of the X=total distance (mm) between the des­ method requires a person knowledgeable in ignated grating lines: electron diffraction and mineral identifica­ G=callbration constant of the grating replica tion by ED and EDXA. Those inexperienced (llnes/mm): laboratories wishing to develop capabilities Y=number of grating replica spaces counted may acquire necessary knowledge through along X. analysis of appropriate standards and by fol­ c. Calibration of the EDXA System. Ini­ lowing detail^ methods as described in Ref­ tially. the EDXA system must be calibrated erences 8 and 10 of Unit III.L. by using two reference elements to calibrate 1. Equipment Calibration. In this method, the energy scale of the Instrument. When calibration is required for the air-sampling this has been completed in accordance with equipment and the transmission electron mi­ the manufacturer’s instructions, calibration croscope (TEM). in terms of the different types of asbestos a. TEM Magnification. The magnification at can proceed. The EDXA detectors vary In the fluorescent screen of the TEM must be both solid angle of detection and In window calibrated at the grid opening magnification (ff used) and also at the magnification used thickness. Therefore, at a particular accel­ for fiber counting. This is performed with a erating voltage in use on the TEM. the count cross grating replica. A logbook must be rate obtained from specific dimensions of maintained, and the dates of calibration de­ fiber will vary both in absolute X-ray count pend on the past history of the particular rate and in the relative X-ray peak heights microscope: no frequency is specified. After for different elements. Only a few minerals any maintenance of the microscope that in­ are relevant for asbestos abatement work. volved adjustment of the power supplied to and in this procedure the calibration is spec­ the lenses or the high-voltage system or the ified in terms of a “fingerprint” technique. mechanical disassembly of the electron opti­ The EDXA spectra must be recorded from In­ cal column apart from filament exchange, dividual fibers of the relevant minerals, and the magnification must be recalibrated. Be­ identifications are made on the basis of fore the TEM calibration Is performed, the semiquantitatlve comparisons with these analyst must ensure that the cross grating reference spectra. replica is placed at the same distance from d. Calibration of Grid Openings. the objective lens as the specimens are. For 1. Measure 20 grid openings on each of 20 instruments that incorporate an eucentrlc random 200-mesh copper grids by placing a tilting specimen stage, all speclments and grid on a glass slide and examining It under the cross grating replica must be placed at the PCM. Use a calibrated graticule to meas­ the eucentrlc position. ure the average field diameter and use this b. Determination of the TEM magnifica­ number to calculate the field area for an av­ tion on the fluorescent screen. erage grid opening. Grids are to be randomly 1. Define a field of view on the fluorescent selected from batches up to 1.000. screen either by markings or physical bound­ Note: A grid opening is considered as one aries. The field of view must be measurable field. or previously Inscribed with a scale or con­ 11. The mean grid opening area must be centric circles (all scales should be metric). measured for the type of specimen grids in 11. Insert a diffraction grating replica (for use. This can be accomplished on the TEM at example a grating containing 2.160 llnes/mm) a properly calibrated low magnification or into the specimen holder and place into the on an optical microscope at a magnification microscope. Orient the replica so that the of approximately 400X by using an eyepiece grating lines fall perpendicular to the scale fitted with a scale that has been calibrated on the TEM fluorescent screen. Ensure that against a stage micrometer. Optical micros­ the goniometer stage tilt Is 0 degrees. copy utilizing manual or automated proce­ ill. Adjust microscope magnification to dures may be used providing instrument cali­ lO.OOOX or 20.000X. Measure the distance bration can be verified. (mm) between two widely separated lines on e. Determination of Camera Constant and the grating replica. Note the number of ED Pattern Analysis. spaces between the lines. Take care to meas­ 1. The camera length of the TEM in ED op­ ure between the same relative positions on erating mode must be calibrated before ED the lines (e.g.. between left edges of lines). patterns on unknown samples are observed. Note: The more spaces Included in the This can be achieved by using a carbon-coat­ measurement, the more accurate the final ed grid on which a thin film of gold has been

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