Laserfiche WebLink
ASBESTOS and OTHER FIBERS by PCM:METHOD 7400,Issue 2,dated 15 August 1994-Page 8 of 15 <br /> C= <br /> EAC <br /> VX103 <br /> NOTE: Periodically check and adjust the value of A,if necessary. <br /> 22. Report intralaboratory and interlaboratory relative standard deviations(from Step 11)with each set <br /> of results. <br /> NOTE: Precision depends on the total number of fibers counted [1,16].Relative standard deviation <br /> is documented in references[1,15-17]for fiber counts up to 100 fibers in 100 graticule fields. <br /> Comparability of interlaboratory results is discussed below.As a first approximation,use <br /> 213%above and 49%below the count as the upper and lower confidence limits for fiber <br /> counts greater than 20(Figure 1). <br /> EVALUATION OF METHOD: <br /> Method Revisions: <br /> This method is a revision of P&CAM 239[10].A summary of the revisions is as follows: <br /> 1. Sampling: <br /> The change from a 37-mm to a 25-mm filter improves sensitivity for similar air volumes.The change <br /> in flow rates allows for 2-m3 full-shift samples to be taken,providing that the filter is not overloaded <br /> with non-fibrous particulates.The collection efficiency of the sampler is not a function of flow rate in <br /> the range 0.5 to 16 L/min [10]. <br /> 2. Sample preparation technique: <br /> The acetone vapor-triacetin preparation technique is a faster,more permanent mounting technique <br /> than the dimethyl phthalate/diethyl oxalate method of P&CAM 239[2,4,10].The aluminum"hot <br /> block"technique minimizes the amount of acetone needed to prepare each sample. <br /> 3. Measurement: <br /> a. The Walton-Beckett graticule standardizes the area observed [14,18,191. <br /> b. The HSE/NPL test slide standardizes microscope optics for sensitivity to fiber diameter[4,141. <br /> c. Because of past inaccuracies associated with low fiber counts,the minimum recommended <br /> loading has been increased to 100 fibers/mm2 filter area (a total of 78.5 fibers counted in 100 <br /> fields,each with field area=0.00785 mm2.)Lower levels generally result in an overestimate <br /> of the fiber count when compared to results in the recommended analytical range[20].The <br /> recommended loadings should yield intracounterSr in the range of 0.10 to 0.17[21-23]. <br /> Interlaboratory Comparability: <br /> An international collaborative study involved 16 laboratories using prepared slides from the asbestos <br /> cement,milling,mining,textile,and friction material industries [9].The relative standard deviations(S,) <br /> varied with sample type and laboratory.The ranges were: <br /> Rules Intralaboratory Sr Interlaboratory Sr Overall S, <br /> AIA(NIOSH A Rules)* 0.12 to 0.40 0.27 to 0.85 0.46 <br /> Modified CRS(NIOSH B Rules)t 0.11 to 0.29 0.20 to 0.35 0.25 <br /> *Under AIA rules,only fibers having a diameter less than 3 pm are counted and fibers attached to particles <br /> larger than 3 pm are not counted.NIOSH A Rules are otherwise similar to the AIA rules. <br /> 'See Appendix C. <br /> A NIOSH study conducted using field samples of asbestos gave intralaboratory Sr in the range 0.17 to <br /> 0.25 and an interlaboratory S,of 0.45 [21].This agrees well with other recent studies [9,14,161. <br /> NIOSH Manual of Analytical Methods(NMAM),Fourth Edition <br />