1、Designation: D6620 06 (Reapproved 2010)D6620 19Standard Practice forAsbestos Detection Limit Based on Counts1This standard is issued under the fixed designation D6620; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t 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 presents the procedure for determining the detection limit (DL)2 for measurements of fibers or structures3u
3、sing microscopy methods.1.2 This practice applies to samples of air that are analyzed either by phase contrast microscopy (PCM) or transmission electronmicroscopy (TEM), and samples of dust that are analyzed by TEM.1.3 The microscopy methods entail counting asbestos structures and reporting the resu
4、lts as structures per cubic centimeter ofair (str/cc) or fibers per cubic centimeter of air (f/cc) for air samples and structures per square centimeter of surface area (str/cm2)for dust samples.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are includ
5、ed in this standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regu
6、latory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organ
7、ization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:4D1356 Terminology Relating to Sampling and Analysis of AtmospheresD5755 Test Method for Microvacuum Sampling and Indirect Analysis of Dust by Transmission Electron Microscopy forAsbestos Structure Number S
8、urface LoadingD6281 Test Method for Airborne Asbestos Concentration in Ambient and Indoor Atmospheres as Determined by TransmissionElectron Microscopy Direct Transfer (TEM)D6480 Test Method for Wipe Sampling of Surfaces, Indirect Preparation, and Analysis for Asbestos Structure Number SurfaceLoading
9、 by Transmission Electron MicroscopyE456D7712 Terminology Relating to Quality and Statisticsfor Sampling and Analysis of Asbestos3. Terminology3.1 Definitions:3.1.1 For terms not defined in this practice, see Terminologies D1356 and D7712.3.2 Definitions of Terms Specific to This Standard:3.2.1 aver
10、age, nthe sum of a set of measurements (counts) divided by the number of measurements in the set.1 This practice is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct responsibility of Subcommittee D22.07 on Sampling and Analysis ofAsbestosSampling, Analysis, Management of
11、 Asbestos, and Other Microscopic Particles.Current edition approved Oct. 1, 2010Jan. 1, 2019. Published November 2010January 2019. Originally approved in 2000. Last previous edition approved 20062010 asD6620 06.D6620 06 (2010). DOI: 10.1520/D6620-06R10.10.1520/D6620-19.2 The DLalso is referred to in
12、 the scientific literature as Limitlimit of Detection (LOD), Method Detection Limitdetection (LOD), method detection limit (MDL), and othersimilar descriptive names.3 For purposes of general exposition, the term “structures” will be used in place of “fibers or structures.” In the examples in Section
13、 8, the specific term, “fiber” or“structure,” is used where appropriate. These terms are defined separately in Section 3.4 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer
14、 to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all chan
15、ges accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Un
16、ited States13.2.1.1 DiscussionThe average is distinguished from the mean. The average is calculated from data and serves as an estimate of the mean. The mean(also referred to as the population mean, expected value, or first moment) is a parameter of the underlying statistical distributionof counts.3
17、.2.2 background, na statistical distribution of structures introduced by (i) analyst counting errors and (ii) contamination onan unused filter or contamination as a consequence of the sample collection and sample preparation steps.3.2.2.1 DiscussionThis definition of background is specific to this p
18、ractice. The only counting errors considered in this definition of background areerrors that result in an over-count (that is, false positives). Analyst counting errors are errors such as, determining the length ofstructures or fibers and whether, based on length, they should be counted; counting ar
19、tifacts as fibers; determining the number ofstructures protruding from a matrix; and interpreting a cluster as one, two, or more structures that should be counted only as zeroor one structure. For purposes of developing the DL, assume that background contamination sources have been reduced to theirl
20、owest achievable levels.3.2.3 blank, na filter that has not been used to collect asbestos from thea target environment.population.3.2.3.1 DiscussionBlanks are used in this practice to determine the degree of asbestos contamination that is reflected in asbestos measurements.Contamination may be on th
21、e virgin filter or introduced in handling the filter in the field or when preparing it for inspection witha microscope. The data required to determine the degree of contamination consists, therefore, of measurements of field blanks thathave experienced the full preparation process.background levels
22、(also referred to as contamination) for asbestos measurementmethods. Blanks are analyzed by the same method employed to analyze filters used to collect particulate from the target population.3.2.4 count, nthe number of fibers or structures identified in a sample.3.2.5 decision value, na numerical va
23、lue used as a boundary in a statistical test to decide between the null hypothesis and thealternative hypothesis.3.2.5.1 DiscussionIn the present context, the decision value is a structure count that defines the boundary between “below detection” (the nullhypothesis) and “detection” (the alternative
24、 hypothesis). If a structure count were larger than the decision value, then one wouldconclude that detection has been achieved (that is, the sample is from a distribution other than the background distribution). If thecount were less than or equal to the decision value, the result would be reported
25、 as “below detection,” which means that the samplecannot be differentiated from a sample that would have been collected from the background distribution.3.2.5.2 DiscussionThe decision value is a threshold for measured values (or averages of measured values). If the measured value (or average) exceed
26、sthis threshold, one can conclude that asbestos has been detected in the sampled material. Measured values (or averages) below thedecision value may be reported but flagged to indicate that they fall below the decision value.Alternatively, they may be censored(that is, actual measured values not rep
27、orted) and simply reported as non-detects. Then users of the data will be able to specifyin advance whether values below the decision value are to be censored.3.2.6 detection limitthe mean of the statistical distribution of counts for a structure count population that is sufficiently largeso a measu
28、rement from a sample from this population would have a high probability (for example, 0.95 or larger) of exceedingthe decision value that determines detection.3.2.6.1 DiscussionThe detection limit (DL) is determined through the statistical hypothesis test described in 3.2.5.1. The DL is the value of
29、 aparameter, the true mean of a structure count population in the statistical hypothesis testing problem, that underlies the DLconcept.Specifically, it is the true statistical distribution of counts for a structure population, that is statistically larger than the mean of thealternative hypothesis t
30、hat ensures a sufficiently high power for the statistical test that determines detection.statistical distributionfor the background population of structures. The DL is the smallest of the means for which the power of the statistical test isD6620 192sufficiently large (for example, 0.95 or larger). T
31、he DL is not used to make decisions about individual measurements (for example,to decide whether they are detects or non-detects). The DL may be used to make decisions about methods, laboratories, ormeasurement systems. For example, to identify trace levels of asbestos a measurement method with a su
32、itably small DL wouldbe required.3.2.7 fiber, nany of various discrete entities with essentially parallel sides counted by a particular method that specifies length,width, and aspect ratio. (This definition of fiber, although adequate for purposes of this standard, Practice D6620, is not to beconfus
33、ed with the mineralogical term fiber.)3.2.7.1 DiscussionThe definitions of “fiber” and “structure” are similar because the measurement method employed specifies the shape, length, width,and aspect ratio.3.2.8 mean, nthe mean value of the number of structures in the population of air or dust sampled.
34、3.2.8.1 DiscussionThe mean in this definition is intended to be the population mean, mean (equivalently expected value, or first momentmoment)of a statistical distribution. It is a theoretical parameter of the distribution that may be estimated by forming an average ofmeasurements (refer to Terminol
35、ogy measurements. E456 for definition of population).3.2.9 power, nthe probability that a count exceeds the decision value for a sample that was obtained from a population otherthan the background population.given that the count is from a distribution whose mean exceeds the background mean by a spec
36、ifiedamount.3.2.9.1 DiscussionPower is the probability of selecting, based on a statistical test, the alternative hypothesis when it is true. In the present context,this means the probability of making the correct decision to report a structure concentration for a sample that was collected froma pop
37、ulation other than the background population. The power of the statistical test equals 1 minus the type II error rate.3.2.10 replicate, na second measurement is a replicate of the initial measurement if the second measurement is obtained froman identical sample and under identical conditions as the
38、initial measurement.3.2.10.1 Discussion“Identical,” as applied to sample, can mean“ samemean “same subsample preparation,” “separate preparation of a distinctsubsample,” or a distinct sample obtained from the same population as the initial sample. For this practice, “identical” meansdistinct sample
39、obtained from the same population as the initial sample.3.2.11 sample, nthe segment of the filter that is inspected, and thereby, embodies the air or dust that was collected and thesubset of structures that were captured on the portion of the filter subjected to microscopic inspection total particul
40、ate collectedon a filter or dust collected on a wipe from a population of structures; also, the portion a filter or wipe that is analyzed bymicroscopy (also, see Terminology D1356).3.2.12 sensitivity, nthe structure concentration corresponding to a count of one structure in the sample.3.2.13 statist
41、ical distribution, nthe set of probabilities of structure count outcomes (0, 1, 2, 3, ).3.2.14 structure, nany of various discrete entities counted by a particular method that specifies shape, length, width, andaspect ratio.3.2.15 type I error, nchoosing, based on a statistical test, the alternative
42、 hypothesis over the to reject the null hypothesis whenthe null hypothesis is, in fact, true; a false positive outcome of a statistical test.3.2.15.1 DiscussionAWhen testing a material that truly has zero or background levels of asbestos, a type I error would occur if the count for a sampleexceeded
43、the decision value, but the sample was, in fact, obtained from the background population. The analyst erroneously occurswhen a measured value falls above the decision value. The analyst, based on the data, would be led by the statistical test to reporta structure concentration (that is, choose the a
44、lternative hypothesis of the statistical test), where the result should be reported as“below the detection limit” (that is, the null hypothesis of the statistical test is true).detection.”D6620 1933.2.16 type II error, nchoosing, based on a statistical test, failing to reject the null hypothesis ove
45、r the alternative hypothesiswhen the alternative hypothesis when it is, in fact, true;false; a false negative outcome of a statistical test.3.2.16.1 DiscussionAtype II error would occur if the count for a sample does not exceed the decision value, but the sample was, in fact, obtained froma populati
46、on other than the background population. The analyst would erroneously analyst, based on the data, would be led by thestatistical test to report a “below the detection limit” result (that is, choose the null hypothesis of the statistical test), detection”result where the result should be reported as
47、 a structure concentration (that is, the alternative hypothesis of the statistical test istrue).concentration.3.2.17 type I error rate, nthe probability of a type I error (also referred to as the significance level, -level, or p-value of thestatistical test).3.2.18 type II error rate, nthe probabili
48、ty of a type II error (also referred to as the -level of the statistical test).3.2.19 lambda, the Greek letter used to represent the population mean of a Poisson distribution.3.2.20 0the population mean of the Poisson distribution of background counts.3.2.20.1 Discussion0 is the population mean of t
49、he Poisson distribution under the null hypothesis in the statistical hypothesis testing problem thatdefines the DL.3.2.21 1the population mean of the Poisson distribution under the alternative hypothesis in the statistical hypothesis testingproblem that defines the DL (DL = 1).3.2.22 x0decision value for determining detection. If the count in a measurement is not greater than x0, the measurement isreported as “below detection.”3.2.23 XPoisson distributed random variable used to denote the number of structures (fibers) counted in a sa
