Document VG0qQ8oXD0E0Rj8Zz2xd4VOw8

Federal Register /Vol. 51, No. 119 / Friday, June 20, 1986 / Rules and Regulations 22685 estimates of airborne asbestos concentrations than the use'of other counting rules because fibers that appear to be attached to non-fibrous particles.arenot counted in the AtA method (Tr. 6/20, p. 13). OSHA believes timits of reliable detection to justify the targe increase in analytical expenses that would result if an electron microscopy.method were adopted. The primary advantages of electron microscopy methods are better visualization of very thin asbestos fibers and more precise fiber identification capabilities. Neither of a SO-mm-long cowl extension. The Chatfield method does not require the use of a cowl. The NIOSH 7400 method requires that the flow rate be greater than 0-5 liters per. minute (1pm). The AIA. Chatfield, and ISO methods require a 11pm flow rate. The NIOSH 7400 method requires a that much of the testimony and evidence these advantages are necessary for routine minimum filter loading of lOO fibers/mm2 The describing interlaboratory error (that is. workplace analysis. Moreover, at the present AIA, (SO, end Chatfield methods require a differences in analytical results time, standard electron microscopy analytical minimum filter loading of 50 fibers/mm2. obtained by different laboratories methods have not been sufficiently tested The NIOSH 7400. AIA. ISO and Chatfield analyzing the same sample) reflects the use of different analytical procedures by these laboratories. OSHA also believes that mandating a specific monitoring procedure will ensure a greater degree of consistency in monitoring results under workplace conditions-for either precision or comparability to historical PCM measurements. (Ex. 328) Similarly, the Duilding and Construction Trades Department (BCTD) or the AFI^CIO stated: methuds all require the use of-acetonetriacetin clearing solution for the preparation of samples for analysis, and a WaltonDeckctt graticule to provide the counting area on the microscope. The NIOSH 7400. AIA. ISO, and Chatfield methods all require the use of a among different employers who use different laboratories. Furthermore, by using the same sampling and analytical procedure as that adopted by OSHA's Salt Lake City laboratory, employers will have greater confidence that their monitoring results will parallel those that would be obtained from OSIIA's compliance monitoring. Selection of a Standardized Monitoring Method Electron microscopy has the advantage of counting all the fibers present, including the thin ones that cannot be seen under current optical microscopy. However, due to the additional cost and time in preparation, the BCTD is recommending It only as the method to be used in categorizing products or processes und for clearance samples to declassify regulated areas when greater accuracy is needed. (Ex. 330)' Dr. Eric Chatfield of the Department of Applied Physics, Ontario Research phase shift test slide to calibrate the microscope. The NIOSH 7400 method permits the use of the same counting rules (designated as the "A" rules) as the NIOSH P&CAM 239. The AIA, ISO, and Chatfied .methods permit the use of the "A" rules except that fibers with a diameter of greater than 3 microns or fibers that appear to he attached to particles with a diameter of greater than 3 microns are not counted. The NIOSH 7400. AIA. ISO. and Chatfield methods at) permit the use of the "11" counting rules as an alternative. OSHA reviewed a number of asbestos sampling and analytical methods described during these rulemaking proceedings (Exs. 84-62, 84-230. 84-238. 84-444,84-446, 86-002). As noted by OSHA in the April proposal, phase contrast microscopy has been widely adopted and used internationally as an accepted and reliable indicator of asbestos concentrations. The major disadvantage^ this method is its inability to distinguish among different types of asbestos and.among Foundation, stated that "in view of the number and frequency of nieaseremcnts required (in the field) there is currently no fully developed alternative [to phase contrast microscopy] which could be immediately Implemented" (Ex. 84-319). These similar comments reaffirm OSHA's view, as expressed in the April proposal, that requirements in the revised standard for asbestos sampling and analysis must be based on the use of phase contrast microscopy, which has proven to be adequate for most Several commenters agreed that the NIOSH 7400 and similar methods represent vast improvements over the currently used NIOSH P&CAM 239 (Exs. 117-A, 123-A, 328. 330: Tr. 8/20. p. 10: Tr. 0/21, p. 186; Tr. 7/8. p. 69). For example, the AIA stated that it has . . . looked favorably in the past on a number of modifications to the existingNIOSH analytical method. P and CAM 238. that will increase standardization and quality control. . . These improvements include the specification of a standardized graticule, a. asbestiform fibers and other types of situations in the past. reduction in the sample filter size, the fibrous particles. Although electron The sampling and analytical method required use of a test slide to maintain microscopic analysis of asbestos samples can distinguish among different fiber types, OSHA noted in the proposal used by most laboratories in the United States has been the N10SH P&CAM 239. This method requires the use of a 37-mrrt appropriate resolution und a change to the acetone-triacetin slide mounting method (Ex. 328). that because of. the costs involved and . diameter filter, phthalate-oxalate Dr. Chatfield testified at the hearing the length of time required for analysis. ", . . it is not practical or necessary to clearing solution. Porton graticule, and the set "A" counting rules. that.the NIOSH Method 7400 is an improvement over the existing NIOSH . . . require electron microscopic In February 1984. NIOSH issued a method in its provisions for analysis'instead of phase contrast light revision of the P&CAM 239 method (Ex. microscopy" (49 FR.14126). In addition. 84-444), incorporating a nuntber of standardization of counts between counters and laboratories. Its adoption OSHA noted that standard counting analytical changes that were being used. of the acetone-triacetin fixing technique methods-for the electron microscope have brily.recently been developed and one in need of improvement, while those for phase microscopy, are widely known and used. ! Rulemaking participants Were in agreement that OSHA should rely for routine monitoring of asbestos on a sampling and analytical method that utilizes phase contrast microscopy (Exs. 123A. 253, 328. 330; Tr. 7/5, p. 121). For example, the AIA slated: for other methods worldwide; NIOSH (Ex.-117D) presented a concise comparison of the new method, called the NIOSH 7400 method, with other sampling and analytical methods,: including the AIA-recommended method. Chatfield's method, and the method recommended by the International. Standards Organization (ISO). Their findings were as follows: The NIOSH 7400. AIA. ISO. and Chulfield methods require the use of a 25 follows the international trend in that direction (Tr. 7/81 p. 69). As.part of the. submittal from Organization Resources Counselors, Inc., Graham W. Gibbs. Ph.D., also agreed that the modification of P&CAM 239 is appropriate: The reduction in the filter [size) to 25 mm Idiamcter] to improve the uniformity of the dust deposit is probably a sound move..... The use of acetone to collapse the filler results in a much (more thinly) mounted sample than The record does not dempnslrnte any mm-diameter filter. with previous methods, which in turn helps to significant advantages in.terms of The NIOSH 7400, AIA. and ISO methods reduce the error if the observer fails to focus reproducibility of results or lowered practical require the use of a 3-piece. filter cassette and properly through the sample. . . . GLEASON-000933