1、Designation: D6058 96 (Reapproved 2011)Standard Practice forDetermining Concentration of Airborne Single-CrystalCeramic Whiskers in the Workplace Environment1This standard is issued under the fixed designation D6058; the number immediately following the designation indicates the year oforiginal adop
2、tion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is intended to assist individuals in thesampling and analy
3、sis of single-crystal ceramic whiskers(SCCW), such as silicon carbide and silicon nitride, in theworkplace environment. It describes sampling and analyticaltechniques used to assess the airborne concentration and sizedistribution of SCCW, which may occur in and around theworkplace where these materi
4、als are manufactured, processed,transported, or used.1.2 The protocols currently in use for asbestos and otherfibrous materials have been used as a guide in developingsampling and analytical procedures for characterizing fibersproduced from the manufacture and use of SCCW. Thesampling and analysis p
5、rotocols described here have beenwritten specifically for SCCW, however, they may be appro-priate for other man-made mineral fibers (MMMF).1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport t
6、o address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1356 Te
7、rminology Relating to Sampling and Analysis ofAtmospheresD6056 Test Method for Determining Concentration of Air-borne Single-Crystal Ceramic Whiskers in the WorkplaceEnvironment by Transmission Electron MicroscopyD6057 Test Method for Determining Concentration of Air-borne Single-Crystal Ceramic Whi
8、skers in the WorkplaceEnvironment by Phase Contrast MicroscopyD6059 Test Method for Determining Concentration of Air-borne Single-Crystal Ceramic Whiskers in the WorkplaceEnvironment by Scanning Electron Microscopy3. Terminology3.1 For definitions of terms used in this practice, refer toTerminology
9、D1356.3.2 Definitions:3.2.1 man-made mineral fiber, nany inorganic fibrousmaterial produced by chemical or physical processes.3.2.2 single-crystal ceramic whisker, na man-made min-eral fiber that has a single-crystal structure.3.2.2.1 DiscussionAlthough the terms fiber and whiskerare, for convenienc
10、e, used interchangeably in this practice,whisker is correctly applied only to single-crystal fiberswhereas a fiber may be single- or poly-crystalline or may benoncrystalline.4. Summary of Practice4.1 This practice is based on a three-tier approach to thequantitative assessment of airborne SCCW level
11、s. It includesdetailed procedures to analyze standard air sampling cassettesby phase contrast microscopy (PCM), scanning electron mi-croscopy (SEM), and transmission electron microscopy(TEM).4.2 The choice of a particular analytical method shall bebased on the visibility limitation of each instrumen
12、t and anunderstanding of the actual size distribution of the fibers beinganalyzed.4.3 In general, PCM is suitable for the analysis of fibers thatare greater than approximately 0.25 m in diameter. Dependingon the instrument and the sample preparation method used, theSEM may be capable of examining fi
13、bers as small as 0.10 min diameter. TEM has been shown to be suitable for the studyof even finer fibers. The high resolution of this instrumentmakes it well suited for the determination of the fraction of afiber population with diameters #0.10 to 0.25 m.4.4 In addition to an enhanced image resolutio
14、n, SEM andTEM have the further advantage of providing elementalcomposition information on a single fiber. Furthermore, TEMmay also be used to ascertain crystallographic data on the fiber.1This practice is under the jurisdiction of ASTM Committee D22 on Air Qualityand is the direct responsibility of
15、Subcommittee D22.04 on Workplace Air Quality.Current edition approved Oct. 1, 2011. Published October 2011. Originallyapproved in 1996. Last previous edition approved in 2006 as D6058 - 96 (2006).DOI: 10.1520/D6058-96R11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact
16、 ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.This additional informati
17、on is frequently helpful in the analysisof samples which contain numerous unknown fibers and, thus,SEM or TEM, or both, are preferred in such instances.5. Significance and Use5.1 The SCCW may be present in the workplace atmospherewhere these materials are manufactured, processed, trans-ported, or us
18、ed. The test methods discussed in this practice canbe used to provide guidance when monitoring airborne con-centrations of SCCW in these environments.5.2 Because of their visibility limitations, a significantfraction of the very small thin fibers that are present in somesamples may not be detected b
19、y PCM or SEM. Therefore,TEM is considered to be the reference technique for theanalysis of airborne SCCW. The TEM must be used todetermine both fiber count and morphology when samples arefrom previously uncharacterized workplaces or materials.5.3 Although TEM is the reference technique, PCM or SEMar
20、e considered to be the primary screening methods for theanalysis of airborne SCCW.5.4 Parallel TEM measurements shall be carried out, at leastinitially, to provide an index or relative measure of the fractionof total fibers that are seen by PCM or SEM. Only in instanceswhen this percentage has been
21、shown to be at a high andreproducible level may the lower resolution techniques (that is,PCM or SEM) be relied on exclusively.6. Evaluating Potential Methods6.1 The following three test methods address the determi-nation of SCCW concentrations in airborne samples. Each hasits own particular scope of
22、 application and varies from theother in the type of information provided. Thus, all are relevantin different situations, and the choice of which test method isused will depend on the primary objective of the monitoringprogram.6.1.1 Test Method D6057:6.1.1.1 Phase contrast microscopy is the analysis
23、 methodrequired by the Occupational Safety and HealthAdministration(OSHA) for the monitoring of airborne asbestos in the work-place. The asbestos permissible exposure limit and action levelare based on this technique. The test method which is discussedin this practice, although closely related to th
24、e asbestosmethod, differs in that the counting rules recommended forSCCW are those described in NIOSH 7400 B.3In contrast, forasbestos the A Counting Rules are typically followed. Underthe NIOSH 7400 A Counting Rules, fibers with aspect ratios$3:1 are counted. The B Rules count fibers with aspect ra
25、tios$5:1. The B Rules further place an upper limit on fiberdiameter of 3 m. The B Rules were selected to monitor SCCWbased on the nature of SCCWs which are not likely to splitlongitudinally as are asbestos fibers. While asbestos fibers oflow aspect ratio, are, in reality, bundles of finer fibrils wh
26、ichmay split longitudinally into high aspect ratio fibrils, theSCCW do not have this structure and thus would not beexpected to split into higher aspect ratio fibers.6.1.1.2 In practice, a portion of the membrane filter contain-ing the airborne particles is placed on a glass slide and renderedtransp
27、arent by exposure to acetone vapor. The slide is trans-ferred to a phase contrast microscope and examined at amagnification of approximately 4003. Fibers fitting the count-ing rules definition are counted if they lie within a measuredarea. The B Rules require that fiber ends be counted and thatthis
28、number then be divided by two to give the fiber count.From this fiber count, and knowing the volume of air sampled,it is possible to calculate the fiber concentration in the air thatwas sampled. This number is generally expressed in terms offibers per millilitre (f/mL) of air.6.1.1.3 The PCM method
29、only counts fibers that fit withinthe dimensional constraints of the counting rules. Thus, thelower limit of length to be counted will be 5 m and themaximum diameter counted will be 3 m. The lower limit ofdiameter is determined by the resolution and contrast (visibil-ity) of the microscope which is
30、approximately 0.25 m.6.1.1.4 The PCM method is also restricted to counting fibersof all types; the method does not identify or differentiatebetween different fiber types. In consequence, the PCM methodis applicable to measurement of those populations in whichSCCW is the only, or the prevalent, fiber
31、 type present. The testmethod is rapid, inexpensive and may be readily performedon-site. It is therefore a useful screening tool for monitoringworkplace environmental levels of fibers or potential workerexposure to fibers. However, one must bear in mind that thisapproach is inherently limited to the
32、 examination of fibersgreater than approximately 0.25 m in diameter, depending onthe difference between the refractive index of the immersionmedium and the fibers.6.1.2 Test Method D6059:6.1.2.1 The SEM may be used when a more definitiveestimate of airborne concentration of SCCW is required. Thetech
33、nique covers the size range covered by PCM and mayprovide information on thinner fibers down to approximately0.1 m in diameter. Unlike PCM, however, the technique iscapable of differentiating SCCW from other fibrous materialsbased on their elemental composition. Fiber counts are ob-tained, as for PC
34、M, by counting the number of fibers per unitarea on the filter, and, from this, calculating the fiber concen-tration per unit volume of air sampled.6.1.2.2 Sections cut from the membrane filter may bemounted on SEM support stubs, carbon coated, and examinedin the SEM. An alternative sample preparati
35、on procedure isdescribed which involves collapsing the filter membrane byexposure to dimethyl formamide/acetic acid/water solution,then lightly etching it in a low-temperature asher prior tocoating it with carbon or gold/palladium, or both. This alter-native procedure gives less background interfere
36、nce from thefilter structure, which may improve fiber visibility in the SEM.The prepared sample is examined in the SEM first at amagnification of approximately 1003 to ensure that the filter isevenly loaded. Counting of the fibers is done at an accuratelycalibrated magnification of approximately 200
37、03, using count-ing rules similar to the NIOSH B Rules for PCM. Because the3Baron, P., “Fibers, Method 7400 Issue 2-8-15-94,” NIOSH Manual of Analyti-cal Methods, 4th ed., P. M. Eller, ed., U.S. Department of Health and HumanServices, DHHS (NIOSH) Publication No. 93-113, Cincinnati, OH 45226.D6058 9
38、6 (2011)2SEM enables discrimination between SCCW and other fibers,it is possible to provide a more specific count of the variousfiber types present.6.1.3 Test Method D6056:6.1.3.1 TEM, because of the increased resolution and posi-tive identification capabilities, provides the most definitiveanalysis
39、 of the airborne concentration of SCCW. Because ofthe high resolution of the TEM, there is no practical lower limitto the fiber diameter that may be observed. In addition, thetechnique permits identification of SCCW, based on a combi-nation of elemental composition and crystal structure. Fibercounts
40、 are obtained by counting the number of fibers per unitarea on the filter and, from this, calculating the fiber concen-tration per unit volume of air sampled. Because of the positiveidentification capabilities of the TEM, the counts may bevalidly expressed as fibers of SCCW per millilitre of air.6.1
41、.3.2 Sections cut from the membrane filter are preparedand mounted on TEM support grids. The fibers are identified,sized, and counted at a magnification in the range from 8000 to120003 in the TEM, using criteria described in the protocol.Provision is also made in the protocol for a supplementary low
42、magnification count in the range from 800 to 12003. By usingspecific counting criteria, this approach provides a result thatmay be correlated with any previously obtained PCM data.7. Recommended Guidelines for Analysis of Single-Crystal Ceramic Whiskers7.1 Analyze SCCW samples for the presence and c
43、oncen-tration of fibers using PCM or SEM techniques and NIOSH7400 B Counting Rules (fibers 5 m in length, less than 3 min width with an aspect ratio $5:1).7.2 Analyze a statistically representative subset of SCCWsamples for the presence and concentration of fine-diameterfibers (diameters #0.25 m) us
44、ing TEM techniques (fibers0.5 m in length, less than 3 m in width with an aspect ratio$5:1).7.3 Based on the results obtained in 7.1 and 7.2, a determi-nation can be made on which analytical technique(s) is (are)appropriate to document airborne fiber concentrations in agiven workplace environment. F
45、or example, if the results of aTEM survey of all processes in use in a particular facility showthat fine-diameter fibers are never present in the atmosphere,analysis by PCM or SEM on a routine basis would beappropriate. In situations such as these, TEM must be per-formed on a subset of at least 5 %
46、of the samples on acontinuing basis to confirm that the distribution of fibers in theworkplace environment has not changed with time.7.4 In situations where fine-diameter fibers are detected byTEM, then TEM analysis shall be performed in addition to thePCM or SEM analysis until such time that suffic
47、ient data havebeen acquired that a determination can be made regardingindexing of the PCM and SEM counts. With this scenario,PCM or SEM data are correlated with the TEM results. If thedata are consistent, the fine-diameter fiber concentration can beestimated based on results obtained from PCM or SEM
48、analysis. While this approach will be more cost-effective froman analytical perspective, the fine-diameter fiber results will be,at best, estimates. Therefore, if this approach is adopted, TEMshall be performed on a subset of, at least, 10 % of the sampleson a continuing basis to confirm that the in
49、dexing proceduresused are a reasonable estimate of the actual conditions.7.5 Maintain a control chart of the TEM fraction of fine-diameter fibers. Use the data from 7.2 to determine the initialcontrol limits as outlined in the Manual on Presentation ofData and Control Chart Analysis.4If the fraction of fine-diameter fibers falls outside the control limits, then TEM shallbe performed routinely on a subset of, at least, 25 % of thesamples collected on a continuing basis.7.6 For situations where a manufacturing change is made, anew TEM survey shall be conducted to establ
