Document je7e6jX3X4b9vqnLv8yw58xp

22690 Federal Register / Vol. 51, No. 119 / Friday, June 20, 1986 / Rules and Regulations the ALA's CV estimate for intersample method reflects a truer estimate of the variability necessarily reflects a random random variability of the method error that is intrinsic to the P&CAM 239 because of the greater degree of or NIOSH 7400 methods, finding instead consistency in laboratory practices and that nonrandom error, caused by training between the different Johns- inadequate sampling times, low fiber Manville laboratories that generated the counts, etc. accounts for what the A1A sampling data. NIOSH's estimate of the terms intersample variability. OSHA overall precision of the phase contrast thus rejects the argument that method of asbestos analysis are similar intersample variability may be a more to the estimates reported by Ogden (Ex. significant source of sampling and 84-446), who also studied analytical analytical error than intra- or results from laboratories that implement interlaboratory errors. similar training and laboratory Summary of Evidence on Sampling and Analytical Variability practices. OSHA believes that, by promulgating requirements for specific - monitoring procedures and quality In the preceding discussion, OSHA control measures, it is possible to limit reviewed the rulemaking evidence sources of sampling and analytical error describing the sources and extent of to those that are random. Therefore, sampling and analytical error associated OSHA finds that NIOSH's estimates for with measuring airborne asbestos- the overall precision of Ihe P&CAM 239 concentrations using the NIOSH method, and consequently for .the P&CAM 239 or NIOSH 7400 methods. NIOSH 7400 and OSHA Reference The major sources of sampling and methods, are Ihe most reliable estimates analytical variability described by-the in the record of the random sampling ALA (Ex. 328) include intralaboratory and analytical variability of these variability, interlaboratory variability, methods. As long as samples are and intersample variability. Together, obtained with a fiber density of 80-100 AIA estimated that these sources of fibers per 100 fields counted. OSHA variability result in an overall CV for the believes that the standard analytical NIOSH P&CAM method ranging from error (SAE) of the ORM will be between 0.45 to.0.65 (Ex, 326. p. A-23). Based on 18.9 and 21.3 percent, with an upper this estimate for total CV, the AIA estimate of 24.7 percent, based on the argued that analysis of Dr. Ogden. This SAE OSHA must recognize that this unique variability limits the degree to which the asbestos PEL can be reduced, calls for more than usual enforcement flexibility, and. at the coincides With the SAE of 25 percent currently used by OSHA for evaluating compliance samples of airborne asbestos. Therefore, OSHA will retain same time, assures that workplaces in the SAE for asbestos at 25 percent. The compliance with a PEL will keep average exposures much lower than the PEL.'(Ex. 328, p.A-1) Agency also finds that use of the ORM will not require employers to reduce their employees' exposures to levels The AIA further argued that, given the high variability of the NIOSH P&CAM 239 and NIOSH 7400 methods, substantially below the PEL of 0.2 f/cc to ensure that they are in compliance with the new PEL. promulgation of a 0.2 f/cc PEL would not leave an adequate margin between the PEL and the "practical limit of detection" (Ex. 328, p. 11-18), and that employers would thus not be able to reliably determine whelher their employees' exposures are in excess of the PEL, Reliable Limit of Detection NIOSH has reported that Ihe 7400 method for asbestos sampling and analysis has a reliable limit of detection of 0.02 f/cc. based on collecting a 1,920liter sample (i,e,, collecting an 8-hour sample using a flow rale of 41pm) and OSHA rejects these arguments for two obtaining the minimum acceptable fiber reasons. First, OSHA does not agree density of 60 fibers per .100 fields. Using with the AIA's estimate of the overall the formulas for calculating limits of precision of the NIOSH P&CAM 239 detection (Exs. 84-444, 84-478), OSHA method. As discussed in the section has determined that the reliable limit of above, the data relied upon by the AIA do not predominantly reflect random detection for the ORM is 0.03 f/cc/, based on obtaining a fiber density of 80 sources of sampling and analytical error; fibers/100 fields from a 1,200-liter instead, they reflect nonrandom error sample (2.5 Ipm over 8 hours); the limit caused by the use of different of detection for the ORM is thus well monitoring methods and quality control below the 0.1 f/cc action level included programs by laboratories participating in the revised standards for general in the study. On the other hand, the - industry and construction. . . study: by Busch et al. (Ex. 84-62) of the The AIA argued that, because of the precision of the NIOSH P&CAM 239 problem of nuisance dust obscuring asbestos fibers on a filter, the practical limit of detection for the NIOSH 7400 method is much higher . . . The practical limit of reliable detection incorporates important practical factors that prevent the theoretical detection limit from being achieved such as reasonable sampling times, reasonable pumping rates and filter loading with nuisance dust. Problems with nuisance dust loading will vary from one atmosphere to another and may seriously limit the range of the method. . . . A number of measurement methods in Ihe record have suggested that practical limits of reliable detection fall in the range of 0.1 f/cc to 0.5 f/cc. In fact. P&CAM 239 establishes 0.1 f/cc. as its lower bound even though exposure levels ivell below this may be obtained using the method. NIOSH's new Method 7400 does claim a tower value. 0.02 f/cc, but made clear that this is only a theoretical limit of detection by stutiug that it applies only in the absence of excessive nuisance dust loading. NIOSH has not explained why it chose to depart in Method 7400 from the practical limit of reliable detection employed in- P&CAM 239. Considering the total absence in the record of any published testing results on Method 7400, there has never been any . demonstration that it is practical to achieve the cluimod value in manufacturing workplaces (Ex. 128, pp. A-24 through A-27). Dr. Chatfield also expressed this view al the hearing, stating that Ihe higher flow rates permitted by the NIOSH 7400 method ". . . will result in (the) capture of even larger pieces of nuisance dust than are collected currently using P&CAM 239 adding further lo ihe filter obstruction problem" (Tr7/6, p. 64). In his testimony, Dr. Taylor stated that NIOSH intended the higher flow rates permitted by the 7400 method io be used for taking clearance samples and not for the routine monitoring of airborne asbestos levels in workplaces (Tr. 6/21, p. 181). OSHA agrees that the higher flow rates permitted by the 7400 method may contribute to filter overload' or interference by other particles, and has therefore limited the ORM's flow rate to 2.5 Ipm. Although OSHA believes that limiting flow rate will, in the great majority of cases, eliminate the filter overload problem, the ORM does permit the use of a 37-mm diameter filter in specific instances where filter overloading may be a problem. However, since the use of the 37-mm diameter filler doubles Ihe limit of detection that can be achieved with the smaller filler, the larger filter may only be used if employers provide a written . justification for its.use. OSHA believes, based on testimony presented by Drs. Ogden and Taylor to the effect that nuisance dust overload is a rare GLEASON-000938