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Apjjied Oorupatioiral and Environmental Hygiene Volume 16(12): U47-U49. ZOOt Copyrigto .2001 Applied Industrial Hygiene I047-322X/01 $12.00 + .00 Morphological Characteristics of Asbestos Fibers Released During Grinding and Drilling of Friction Products Francis W. Weir1 and LeAnne B. Meraz2 'Francis W. Weir, Ph.D., Inc., Houston, Texas; 2Meraz & Associates, Friendswood, Texas )J There has beea considerable interest during die past 30 years regarding the potential for exposure to asbestos fibers generated during asbestos-containing automobile and light-duty truck brake replacement and repair operations^ Less attention has been directed to asbestos fiber exposures resulting from servicing of brakes on heavy-duty trucks and other machinery. Potential for the generation of respirable fibers m a mult of using a rotary bench grinder and the drillingofasbestos-containing frictionpads was investigated toassess thecharacteristicsofthefibeisgeneratedfrom these procedures. Thedatafrom fhegrindingprocess revealed that this material was either min matrix or fibers bound to the resin matrix, fibers generated from the drilling procedure revealed morphology consistent with chrysolite asbestos. In each case, nonfibrous materials remained bound to the fibers released from these processes. Thesefibers had min deposits attached. This investigation offers evidence that drilling and grinding of brake pads generates fibers that, for the most part, remain bound to the underlyingmatrix, suggesting that grinding and drilling may not pose an Important source of exposure to respirable asbestos fibers. Keywords Asbestos, Automobile Brates. Brake Repair, Brake Shoes, Dptffne. Friction Materials, Grinding, Residue Occupational safety professionals and health scientists have shown considerable interest during the past 30 years regarding the potential for exposure to asbestos fibers generated during asbestos-containing brake replacement and repair operations. Epidemiologic studies of this industry, however, have not pro vided conclusive or convincing evidence to suggest that expo sure in these work activities will result in disease.**--4* Considerable attention has been directed to light-duty ve hicular servicing where the majority of the estimated 150,000 to 900,000 persons may have had some potential for elevated exposure,*5'12* With few exceptions*13* there has been little or no investigation of fiber release from friction product applica tions such as these on heavy-duty trucks and buses or heavy motorized machinery, as well as a wide variety of industrial brakes. Replacement and servicing of heavy-duty vehicular and in dustrial equipment brakes often required drilling of the friction pad to permit riveting or bolting to the shoe, band, or backing plate, hi addition, it was often customary to bevel the leading edge of these pads on the consideration that a beveled surface would produce a smoother interaction between the brake andthe opposing metal surface. An investigation was conducted to assess the potential for the generation of respirable fibers that may be produced as a result of (a) using a rotary bench grinder to bevel the leading edge of asbestos-containing friction pads, and (b) drilling asbestoscontaining frictionpads. Thepurpose of this investigation was to assess the morphological characteristics of the fibers generated during these procedures. METHODS Brake pads' that had previously been tested for asbestos content*14* were utilized for all tests. Thepad material contained 50% 10% chiysotile asbestos in a phenolic or cresylie.resin base along with a variety offriction surface modifiers.*15* AH procedures were conducted within a laboratory ventila tion hood operated at a face velocity ofapproximately0.S meters per second. Grinding procedures utilized a 16 cm x 2.5 cm alu minum oxide 60/80 grit abrasive grinding wheel attached to an unguarded-stationary bench grinder. The .grinder was operated ataspecdof 1,725 RPM and was located in the center and 15cm into the fume hood to ensure capture of all residue. Air samples were collected using 25 ram mixed cellulose ester filters located in the direct air stream approximately 25 cm from the surface of the hood table, and approximately 15 cm lateral to the grinding plume. Drilling procedures were conducted using a quarter-inch rotary drill fixed in a vertical position in the manner of a drill 1147 HWBUI0010210 1M8 F. W. WEIR AND L B. MERAZ press. A quarter-inch bit was used for all drilling tests and was operated at a speed of WO RPM. Numerous holes were drilled through each offourbrake pads. Samples ofthe residue resulting from the drilling of these pads were collected into glass sample vials. ANALYSES For the grinding procedure, samples from this process were analyzed using NIOSH 239 and scanning electron microscopy/ transmission election microscopy (SEM/TEM) procedures. Bulk material generated from (he drilling procedure was eval uated using SEM/TEM and energy dispersive X-ray analysis (EDX). All electron microscopy was submitted to an accredited and licensed testing laboratory for analysis.*16* RESULTS Review ofthe data fromsamples collected during the grinding process revealed that the NIOSH 239 analytical procedure could not be utilized The particulate density on die filters was greater than the working range ofthe method. All samplescontained nu merous particulate as well as fibrous material. The overwhelm ing majority of the particulate appeared to be resin matrix. The majority of fibrous material was bound to resin matrix. . The SEM/TEM analyses of these samples revealed many fibers with a morphology consistent with cfatysotiie asbestos. Eneigy dispersive X-ray (EDX) analysis provided further con firmation. Representative examples of fibers identified from the grindingprocedurearepresented in scanning election microphotographs (Figures 1 and 2). SEM/TEM analyses offibers generated from the drilling pro cedure revealed many fibers with morphology consistent with FIGURE 2 Scanning election microjAiotograph of typical particulate matter observed from an air sample collected during the beveling of an asbestos-containing friction pad. chrysotile asbestos. ED2fc analysis provided further confirma tion. Representative examples of fibers identified during the dri lling procedure are presented in scanning electron micropho tographs (Figures 3 and 4). DISCUSSION Results of the SEM/TEM analyses demonstrate that fibrous material containing asbestos can be removed from the pad by either grinding or drilling procedures. In each case, however, it is evident that nonfibrous materials remained bound to the fibers that were released from these processes as observed in Figures 1-4. )) FIGURE I Scanning electron microphotograph of typical particulate matter observed from an air sample collected during the beveling of an asbestos-containing friction pad. FIGURE 3 Scanning electron microphotograph of a sample of brake residue obtained from drilling an asbestos-containing friction material pad. ) HWBUI0010211 ASBESTOS FIBERS RELEASED FROM FRICTION PRODUCTS 1149 FIGURE 4 Enlargement of scanning election microphotograph showing the central portion ofFigure 3. Figures 1-4 demonstrate that the majority of fibers collected os filters from the air stream have resin deposits attached. Such fibers would be expected to have aerodynamic characteristics considerably different from "clean" fibers of the same length and diameter. A resin-coated fiber would sot be expected to have much opportunity to gain entry into the respiratory system, or, ifinhaled, would more likely deposit higher in the respiratory tract where there is limited retention.*17- CONCLUSIONS The results of this investigation demonstrate that manipu lation of asbestos-containing friction products by drilling and grinding of brake pads generates residue containing fibers that, to a great extent, remain bound to the matrix of the underlying brake material- It appears that these procedures are insufficient to release aerodyttamically clean fibers from the friction ma terial matrix. These data offer support for a consideration that the processes of grinding and drilling do not pose an important source of exposure to respirable asbestos fibers. REFERENCES 1. Hansen, E.S.: Mortality of Auto Mechanics, a Ten-Year FollowUp. Scan 1 Work Environ Health 15:43-46 (1989). 2. Marcus, K.; Jarvholm, B.G.; Larssoa, S.; et al.: AsbestosAssociated Lung Effects in Car Mechanics. Scan J Work Environ Health 13:252-254 (1987). 3. Rushton, L.; Alderson, MR; Nagatajah, CJR.: Epidemiologic Survey of Maintenance Workers io London Transport Execu tive Bus Garages and Chiswick Works. Br I Ind Med 40:340345 (1983). 4. Wong, O.: Chrysotile Asbestos, Mesothelioma, and Garage Mechanics. Ami Ind Med 21:449-451 (1992), 5. Anderson. AJE.; Geatec RJL;McCuoe. R.C.; etaL: Asbestos Emis sions from Brake Dynamometer Tfests. Ford Scientific Research Staff, Automobile Engineering Meeting, Detroit, Ml (May 14-18, 1973). 6. Cheng, V.KX; O'Kelly, FJ.: Asbestos Exposure in the Motor Vehicle Repair and Servicing Industry io Hoag Kong. 1 SocOceup Med 36:104-106 (1986). 7. Hickish, D.E.; Knight, K.L.: Exposure to Asbestos During Brake Maintenance. Ann Occup Hyg 13:17-21 (1970). 8. Jacko, M.G.; DuCharme, R.T.; Somers, J.H.: Brake and Clutch Emissions Generated During Vehicle Operations. Society of Au tomotive Engineers, Detroit, MI (May 14-18, 1973). 9. Kauppineo, T.; Kothonen, K.: Exposure toAsbestos During Brake Maintenance of Automotive Vehicles by Different Methods. Am Ind Hyg Assoc J 48(51:499-504 (1987). 10. Park, N.W.; Lee, Y.H.: Characterization of Worker Exposure to Airborne Asbestos in Asbestos Industry. Korean tod Hyg Assoc J 10:144-153 (1991). 11. Robert, D.R.: NIOSH, Division of Surveillance, Hazard Eval uations, and Reid Studies, Industry-Wide Studies Branch, Cincinnati, OH: Industrial Hygiene Report, Asbestos at Reading Brake and Alignment Service, Reading, OH (March 1980). 12. Yeung, P.; Patience, K_; Apthorpe, L.; et al.: An Australian Study to Evaluate Worker Exposure to Chrysotile in the Auto motive Service Industry. Appl Occup Environ Hyg 14:448457 (1999). 13. Spencer, J.W.; Plisko, MX; Baker, XL: Asbestos Fiber Release from the Brake Pads of Overhead Industrial Cranes. Appl Occup Environ Hyg 14:397-402 (1999). 14. Weir, F.W.; Tolar, G.; Meraz, L.B.: Characterization of Vehicu lar Brake Service Personnel Exposure to Airborne Asbestos and Particulate Appl Occup Environ Hyg 16:1139-1146 (2001). 15. Nicholson, G.: Facts About Friction. Gedoran America Limited, Winchester; VA (1995). 16. The University of Texas Health Center at Tyler, Department of Cell Biology and Environmental Sciences, Tyler, TX. (Asbestos Analytical Laboratory later became ERI Consulting Engineers.) 17. Harris, RX. Jc; Timbrell, V.: The Influence of Fibre Shape io Lung Deposition--Mathematical Estimates. Inhaled Particles IV, pp. 75-89. Unwin Brothers Limited, The Gresham Press, Surrey, England (1977). 18. Medinsky, MA.; Asgharian, B.; Schlosser, PJM.: Toxicokinetics: Inhalation Exposure and Absorption of Toxicants. In: Compre hensive Toxicology, p. 73. J. Bond, Ed, Elsevier Science, Inc., New York (1997). 19. Timbrell, V.: The Inhalation of Fibres. In: Pneumoconiosis-- Proceedings of the International Conference, Johannesburg. South Africa, 1969, pp. 3-9. HA. Shapiro, Ed., Oxford Univer sity Ptess, Capetown, South Africa (1970). HWBUI0010212