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Applied Occupations I and Environmental Hygiene Volume 16(12): 1139-1146, 2001 Copyright 2001 Applied Industrial Hygiene 1047-322Xri)l $12.00 + .00 Characterization of Vehicular Brake Service Personnel Exposure to Airborne Asbestos and Particulate Francis W. Weir,1 Glenn Tolar,2 and LeAnne B. Meraz3 Francis W. Weir, PhD., Inc., Houston, Texas; 2Glen Tolar Co., Deer Park, Texas; 3Meraz & Associates, Friendswood, Texas Evaluation of fibers and total particulate generated dur ing the servicing of dram brakes on motor vehicles as well as during the resurfacing (arcing) of brake shoes was con ducted. Conditions for the studies were based on review of contemporary (~ 1950-1980) working practices in the In dustry. This work was conducted in two parts. Phase 1 es timated the release of asbestos fibers and total particulate during brake inspection and replacement of light-duty ve hicle rear drum brakes at an auto/track repair facility. Two distinct work practices were evaluated: One rear wheel from each vehicle was serviced using compressed air to remove dust while the second rear wheel was serviced without com pressed air. Area and personal monitoring of fiber levels demonstrated counts (without compressed air) that ranged from 0.05 to 0.2 t/cc. Fiber counts when using compressed air averaged from 0.05 to 0.9 t/cc. Results from real-time aerosol monitoring indicated elevated dust levels for about 15 minutes after blow out. With shop doors open, dust levels increased to 5.0 mg/m3 at blow out and returned to 0.08 mg/m3 within two minutes. When the shop doors were closed, the dust levels reached 13.5 mg/m3 at blow out and de creased to 1.68 mg/m3 within one minute and to background within 14 minutes. The Phase 2 series evaluated the release of fibers and other particulate from arc grinding. For oper ations conducted under conditions simulating a workplace, a mean of 0.19 See 0.16 was determined. Dust levels aver aged 0.25 mg/m3 0.05. Brake service monitoring in these tests demonstrates that asbestos fiber concentrations, con sidered on a time weighted average basis, should not exceed currently acceptable workplace standards whether or not the worker uses compressed air, nor during the arc grinding process when arcing is conducted in accord with the design of the equipment. Keywords Arcing, Asbestos. Automotive Brakes, Brake Repair, Brake Shoes, Friction Materials, Grinding, Particulate, Respirable Work activities associated with servicing and replacement of vehicular brake friction products have been of interest to health scientists for the past 2 or 3 decades based on a projected potential for asbestos fiber release. Publicly available studies, both published and unpublished,11-1 of the past 30 or so years demonstrate a concern that workers who conducted brake main tenance and repair during the interval when asbestos fibers were prevalent in these products may have been exposed to concen trations of asbestos fibers in excess of acceptable standards. It has been variably estimated that approximately 150,000*10) to 900,000-111 individuals have worked in this industry and have a potential for exposure to brake maintenance and repair work. There is a continuing consideration by some of these workers that they may be candidates for disease even though the epi demiological evidence supports that disease is unlikely/11-141 More often than not, the presence of visible dust in the air dur ing brake servicing tasks has served as an alert to individuals that there may have been anasbestos-related problem. In response to the continuing concerns, a series of investiga tions were conducted to evaluate both the presence of asbestos fibers available to the brake service worker as well as the total particulate generated during operation ofthe various procedures. The studies outlined in this report evaluate the levels of asbestos fiber and particulate during the servicing of drum brakes on light-duly motor vehicles as well as the resurfacing (arcing) of brake shoes to accommodate newly ground (turned) drums. This work was conducted in two pans. Phases 1 & 2. The purpose of the Phase 1 experiment was to estimate the release of as bestos fibers and total particulate during brake inspection and replacement of light-duty vehicle rear drum brakes. Until re cently, the brake mechanisms on many light-duty vehicles were 1139 HWBUI0011465 1140 F.W-WEIRETAL. drum-brake systems. This "closed" system permitted accumu lation'of abraded brake pad dust within the brake dram. During servicing of the brakes on such vehicles, the drum was removed so that the brake shoes could be inspected. Before inspection it was common to remove the accumulated dust using compressed air. If it was necessary to change the brakes, the old shoes were removed and discarded. A new set of brakes was then installed, adjustments were made, and the brake drum was replaced. A second series of experiments (Phase 2) evaluated the po tential for release of fibers and other particulate resulting from the arc grinding process. An arcing machine typical forthe inter val of greatest use was utilized to estimate the levels of airborne fibers and particulate in the operator breathing zone and imme diate work area during the arcing ofasbestos-containing brakes. Finally, an experiment was conducted to estimate the quan tity of asbestos-containing dust that remained on the operator's clothing after completing the arcing test sequences. The conditions developed forthe studies reportedherein were based on a review of the contemporary working circumstances in the industry during the time when drum brakes and arcing were prevalent in the interval centering on the 1960s. BACKGROUND During the operating life of an automotive drum-brake sys tem, the brake shoe wears away at a rate determined by the ap plication of the brakes. In turn, the portion of the metal drum in contact with the brake shoe also wears to some extent. Therefore when servicing the system, in addition to replacing the shoes, it was sometimes necessary to remove the imperfections (i.e. ridges) that develop as a result of such drum wear. The proce dure of smoothing the metal surface (referred to as "turning") resulted in a slightly increased diameter for the drum. Brake shoes for this altered drum would then be shaped (or arced) to match the arc of the enlarged diameter of the drum. The time required for turning one drum and taking measure ments was approximately 15 minutes/15* Arc grinding a pair of brake shoes required approximately one minute. On this basis, the most probable interval for arcing 4 pairs of brake shoes for one automobile would not exceed about 4-5 min/hr. Discussions with several operators of brake servicing/repair facilities in an urban area of a large U.S. city suggest that a fairly busy shop would turn a maximum of 16 drums per day, equal to 4 wheels on each of 4 vehicles or 2 wheels on 8 vehicles. METHODS Phase 1 To design an appropriate monitoring protocol for a "closed" drum brake system, typical brake repair and replacement pro cesses were observed through several cycles of operation. All details of an operation with opportunity for significant gener ation of dust were noted. Following this process, a monitoring program was designed to evaluate dust generated during the repair and replacement of brakes from the rear wheel of vehi cles in the facility. Phase 2 For purposes of the experiments described in Phase 2, it was assumed that a worker would conduct twice as many brakejobs in a day as would occur in a typical shop. If a worker did nothing but turn drums and arc grind the brake shoes, he could complete work era 8 vehicles within an 8-hour workday/15* An experienced, factory-trained person operated the arcing machine for all tests in this series. This person had been the owner-operator of an after-market automotive parts supply fa cility located in a suburb of a major U.S. city, during the interval when arc grinding was prevalent. His facility incorporated a fullservicedrum tuming/brake-shoe arcing shop on thepremises/15* FACILITY AND EQUIPMENT Phase 1 The site for this study was a public service organization auto/truck repair facility. The repair facility was situated in one end of a large warehouse structure. The vehicle repair section was an area approximately 16 m x 35 m with 7 m ceilings. Five 4-m-wide doors permitted vehicle access to the service bays of the garage. Air circulation was provided by way of the space heaters suspended from the ceiling or by opening the vehicle access doors. The facility maintained a fleet of approximately 100 vehicles, including passenger cars, trucks, and vans. Phase 2 The first test sequence of Phase 2 (identified as Run I) was conducted in a suburban garage setting, approximately 7.2 m wide x 12 m long x 2,4 m high- An arc grinding machine*16* was positioned on a 60 cm x 90 cm table approximately 75 cm from the floor. The machine was situated so that the oper ator would be working approximately 2 m from one sidewall of the room. Environmental conditions included no detectable net air flow and a temperature of 240C-25C during the study. All tests and procedures for the remainder of the Phase 2 ex periments were conducted within a shop/laboratory room ap proximately 8.5 m wide x 13 m long x 5 m high provided with positive flow ventilation. The experiments were confined to a dynamic flow exposure chamber similar in design to that of Hinners el al/17* The chamber was a 2.4 m x 2.4 in x 2.4 m cube, providing a volume of approximately 14 m3. The walls of the chamber were 10-mil polyethylene, held in place by an external wooden frame and sealed at all joints with a siliconebased caulking. Air was exhausted from the exposure chamber via a floor-to-ceiling slot manifold located in a comer of the chamber opposite the chamber entry. The manifold was, intum, connected to a pleated, extended-surface prefiller and a HEPA filterand then to an enclosed negativepressure blower system/18* HWBUI0011466 BRAKE SERVICE PERSONNEL EXPOSURE TO ASBESTOS 1141 Air flow through this system was maintained at a nominal 6400 L/min or 0.11 nrVsec. Air from the laboratory was supplied to the chamber through ports located in both the outer and inner doors of the air-lock entry system. Air pressure within the chamber was maintained at a nominal --2 mm H2O relative to the laboratoiy. The pat tern of air movement within die chamber was evaluated using a portable ihermoanemometer.^^ Air flow within the chamber was determined to be equal to or less than 1 m/sec at a height of 1.5 m above the floor at all points within the defined working area of the chamber (i.e. the 2 m x 2 m space located in the center of the chamber room). It was not possible to discern a consistent pattern of air flow direction from the air flow read ings. Temperature in the chamber was maintained at 26C 2C throughout the study. An arc grinding machine*16* equipped with a factory-provided dust collection bag system was positioned on a 60 cm x 90 cm table approximately 75 cm from the floor. The machine was situated so that the operator would be working in approximately the center of the chamber. For asbestos content verification, a bulk sample was collected from each of the 6 pairs of shoes used in this study. Sam ples were submitted to a certified independent laboratory.*20* The laboratory utilized a standard Polarized Light Microscopy (PLM) method for analysis of these samples,*21* indicating that chrysotile was the rally asbestifonn material present. Concen trations ranged from 50-65% chrysotile. STUDY DESIGN Phase 1 Three vehicles were monitored during the automotive brake inspection and replacement study, including: (a) a 1976 Chevro let van, (b) a 1977 Chevrolet 1/2-ton pickup truck, and (c) a 1981 Ford station wagon. During two of the replacement procedures, the doors to the facility were open with a 1 -2 m/sec breeze blow ing through the area. During the third replacement procedure, the doors to (he shop were closed. The gas heaters for the build ing were in operation, providing limited air circulation in the work area. Two distinct work practices were evaluated during this part of the monitoring program. One wheel from each vehicle had the brakes serviced with compressed air that was used to remove loose, accumulated dust before inspection. The brake from the other rear wheel of each vehicle was inspected and serviced without the use of compressed air. Phase 2 Four sequences of tests were conducted in this investiga tion. During the first experiment (Run 1), the operator arced the equivalent of one set of 8 shoes eight times to simulate the prob able maximum use of an arcing machine during a workday. The actual arcing process required about 4-5 minutes for each set of 8 shoes. The arcing machine was turned on immediately before grinding each set, then turned off again, as would be done in a workshop situation. This process permitted eight sequences of 8 shoes to be completed during a 40-rinhute interval. The second sequence (Run 2) was set up to reproduce the first sequence (Run 1) but was conducted within the chamber containment facility. The third sequence (Run 3) was set up to simulate one-halfof a day's work ofan arc-grinding operatorpri marily doing brake jobs. The operator, using 12 available brake shoes, arced each of these shoes twice to simulate brake servic ing, equivalent to 3 vehicles during a 3-hour period. He worked on one set of 8 shoes at the beginning of each hour. This closely simulates the frequency and pattern of arc grinding in a brake service shop.*'5* In addition, at the end of each arc-grinding ses sion, the operator moved out of the exposure chamber, through the air lock and into other parts of the testing laboratory, as he would in a traditional brake servicing facility. The fourth sequence (Run 4} was designed to duplicate the third sequence described above. OPERATOR CLOTHING STUDY In addition to the four sequences of testing presented above, the operator's one-piece suit was carefully removed and then evaluated for the presence of fibers potentially generated during his arcing work. For this part of the investigation, a nonrigjd freeform dy namic flow chamber with a volume of approximately 150 liters was constructed from 2-mil polyethylene to allow agitation of the clothing while extracting an air sample from the chamber. Filtered air from an oil-free pump was introduced into one end of the chamber containing the clothing at a rate of 2.5 L/min. After the chamber was inflated to approximately 100 L, a pump drawing Z5 L/min of air was started at the opposite end of the chamber. Thus the chamber was maintained at a constant vol ume of about 100 L throughout the study. Air from the exhaust was drawn through the sampling apparatus using an airsampling pump.2* The experiment was operated for a period of30 minutes dur ing which the clothing within the chamber was agitated for each alternating 5-minute interval^ then allowed to sit at rest for the next 5 minutes. This schedule ofagitation and rest continued for the duration of the experiment. ENVIRONMENTAL MONITORING Phase 1 Monitoring for Phase 1 consisted of collecting airborne par ticulate at five sampling stations located at breathing zone height (1.3 m above the floor), spaced in a semi-circular pattern on a radius of 1.2 m from the center of the wheel being repaired, and a personal sampling pump placed on the worker to directly monitor his breathing zone. See Figure 1 for details of sampling locations. All monitoring was conducted at a nominal rate of HWBUI0011467 1142 F.W.WHRETAL. JUJTOHOBIIX BRAKE IEST1IIS LAYOUT During Runs 2, 3, and 4, the environment of the exposure chamber was evaluated for several analytes, including total fibers, respirable fibers, total dust, and respirable dust. To under stand the placement of sampling apparatus within the chamber, consider that the operator stood at the 12 o'clock position fac ing the wall Personal sampling pumps,23 set at a nominal flow rate of 2.5 L/min, combined with cyclone technology43 for res pirable fraction capture (using a 4 micron cut point), were used to estimate the airborne concentration of respirable fibers and respirable particulate in the breathing zone of the operator (at the 12 o'clock position). Additional personal sampling pumps were set up on stands to provide general area monitoring at the FIGURE 1 Phase 1 study showing sampling locations. breathing zone level (located at the 2 o'clock and 10 o'clockpo sitions approximately 46 cm from the operator). Total airborne fiberconcentrations and total particulate samples were collected in these same locations using personal sampling pumps set at a 1.5 to 2.0 L/min. The sampling period at all locations was for ap flow rate of 2.0 L/min. Fiber samples were also collected at the proximately 15 minutes starting with removal of the first wheel 6 o'clock location (immediately behind the arcing machine near nut through inspection, removal, and installation of new brake the side of the chamber), both at 35 cm from the floor (this posi shoes and replacement of the brake drum. tion was about 40 cm from the exhaust dust collection bag) and A total of 36 samples were collected during this series. Five at breathing zone height (approximately 13 m from the floor). stationary samples and one personal sample were collected for Samples were collected for the duration ofeach run. each rear wheel ofevery vehicle. A real-time aerosol monitor33 All sample pumps were calibrated using a bubble meter prior was used to evaluate the particulate levels in the area around' to, and again after completion of, the experiments to ensure flow the automobile brake replacement operation. The intake for this rates were consistent throughout the tests. Actual flow rates were instrument was located approximately 75 cm from the brake be provided to the analytical laboratory for sample analysis. ing serviced at a height of approximately 13 m. Background For the Operator Clothing Study, air was drawn at the rate levels were collected at the beginning of the work shift. Mon of 23 L/min for airborne fiber determination. The sample was itoring was conducted during the brake replacement procedure collected for the duration of the experiment. and continued until the monitor indicated a return to background level. The sensitivity of the instrument was set and calibrated at 0-20 mg/m3 for particulate with a mass medium diameter less than 10 microns. For those circumstances where accumulated dust was sot removed using compressed air, bulk samples were collected by brushing the material with a camel hair brush into a 25 ml screw top vial for subsequent evaluation of content. ANALYSIS Phase 1 Samples collected during Phase 1 were analyzed using Phase Contrast Microscopy (PCM) (NIOSH 239) by a qualified microscopist. Two filters from the procedure not using compressed air and 3 fitters from the procedure using compressed air were ana Phase 2 During Run 1, sampling pumps, set at a nominal flow rate of 2.0 L/min, were used to estimate the airborne concentration of lyzed using Scanning Electron Microscopy/Transmission Electron Microscopy (SEM/TEM) and Energy Dispersive X-ray analysis (EDX). AlTefectron microscopy was submitted to an accredited and licensed testing laboratory for analysis.3 chiysotile fibers in the breathing zone of the operator (located at Accumulated dust that was collected in bulk from the drum the 12 o'clock position). Additional personal sampling pumps where air was not used was analyzed using the SEM/TEM were set up cm stands to provide general area monitoring at the process. breathing zone level (located at the 3 o'clock and 9 o'clock positions approximately 1.25 m to either side of the machine). These sampling pumps operated for the 40-minute duration of Phase 2 the experiment. Two additional area pumps, set to draw 15 L/min Samples collected during the Phase 2 tests were submitted through the filters, were placed approximately 35 cm from the to an accredited and licensed testing laboratory for analysis.03 center ofthe dust collection system toestimate any breakthrough The analytical laboratory utilized NIOSH Method #7400 (PCM) of fibers from the collection bag. One of these area pumps was to evaluate all area and personal total and respirable airborne on for the duration of the experiment. The second of these area fiber samples. NIOSH Methods #0500 and #0S)0 were used to pumps was utilized for sampling only during each arcing period determine total and respirable dust concentrations. Bulk, samples (3-5 minutes for each interval). from the brake pads were analyzed by PLM. HWBUI0011468 BRAKE SERVICE PERSONNEL EXPOSURE TO ASBESTOS 1143 RESULTS Phase 1 In the three brake replacement operations where compressed air was not used, considerable particulate matter accumulated on the sample filters; however, there was no excessive airborne dust identifiable to the observers of the process. Fiber counts of these 16 filters (NIOSH 239) ranged from 0.05 to 0.2 f/cc of air. The two filters analyzed using SEM/TEM methodology de monstrated either particulate not characteristic of the federally defined fiber or a few matrix-bound fibers as exhibited in Figure 2. For the brake repair and replacement process in which com pressed air was utilized to remove accumulated dust, a total of 18 samples were analyzed. Fifteen of the filters were analyzed using NIOSH 239 procedures. Fiber counts for these 15 samples averaged from 0.05 to 0.9 f/cc of air. Three filters from this series were analyzed using the SEM/TEM procedures. The majority of structures present on the filters were less than 3 micrometers in length. Most of these structures bad material adhered to them. A rare longer fiber found in these samples is presented in Figure 3, demonstrating an example of matrix material adhering to the fiber. Accumulated dust that was collected in bulk from the drum where air was not used to clean the area was analyzed using the SEM/TEM process. An overwhelming majority of the sam ple was nonfibious material, as depicted in Figure 4. Results from real-time aerosol monitoring indicated elevated dust lev els (above background) following the blow out process. When air was used, with automotive shop doors open, dust levels in creased to 5.0 mg/m3 at blow out and returned to 0.08 mg/m3 within two minutes (0.06 mg/m3 = background). When the shop doors were closed, the dust levels reached 13.5 mg/m3 at blow out and decreased to 1.68 mg/m3 in less than one minute and FIGURE 3 Scanning Election Microphotograph depicting rare long fiber with adhered matrix. reached background levels (0.07 mg/m3) within 14 mimdes. When air was not used, there was a small but detectable in crease (to 0.09 mg/m3) in shop particulate for a minute or so following removal of the drum, after winch dust levels returned to background. Phase 2 Analyses of the air samples, both personal and area, were conducted using PCM. The personal sample level of the opera tor was 0.40 f/cc. The Time Weighted Average (TWA) for this sample is 0.03 f/cc. The TWA for all samples was calculated us ing OSHA's time weighted average calculation/26-273 The sta tionary breathing zone sample levels were 0.14 and 0.45 f/cc (TWAs = 0.01 and 0.04 f/cc, respectively). The area samples FIGURE 2 Scanning Electron Microphotograph depicting brake dust and a chrysotile fiber with attached matrix. FIGURE 4 Scanning Electron Microphotograph ofresidue from brake drum demonstrating nonfiber particulate. HWBUI0011469 1144 F.W.WHRETAL collected approximately 35 cm fromthe collection bag had levels that ranged from <0.08-1.47 f/cc. The TWA for the highest area sample level is 0.02 f/cc. In addition, the operator's sample was analyzed by TEM and yielded a result of 0.86 stiuctures/cc (TWA = 0.07 structurcs/cc). A few bundles and matrices were longer than 5 microns. Review of the data from Runs 2-4 supports that there was little difference between the respirable and total fiber concentra tions in each of these runs. Therefore, all fiber data points from each run were combined and utilized to determine a mean and Standard Deviation (SD), as well as a TWA.Fbr purposes of es tablishing a mean and SD, data reported as "less than" numbers were assumed to be one-half the actual numeric value. The mean fiber concentration for Run 2 was 0.46 flee, with an SD of 0.17. The eight-hour TWA for fibers in Run 2 was 0.05 f/cc. All fiber data points from Runs 3 and 4 were combined to produce a mean of 0.19 flee and an SD of 0.17. Utilizing Runs 3 and 4 to most reliably reflect the potential airborne asbestos exposure to the operator during a workday, the 8-hour TWA for fiber concentration was 0.05 flee. , Total and respirable dust concentrations, similar to the air borne fiber results reported above, were not significantly differ ent Therefore, these data were combined to produce a mean, SD, and eight-hour TWA. As before, values reported as "less than" numbers were divided by 2 for data analysis. Run 2 produced a dust concentration mean of 0.58 mg/m3, with an SD of0.09. The 8-hourTWA for Run 2 was 0.05 mg/m3. Data from Runs 3 and 4 were combined, resulting in a dust concentration mean of 0.21 mg/m3, with an SD of 0.08. The combined 8-hour TWA for Runs 3 and 4 was 0.16 mg/m3. Clothing Study In the experiment to determine the quantify of fibers that remained on the operator's clothing, the airborne fiber concen tration generated from the agitation of the operator's coveralls was 0.72 See during the 30 minutes oftesting. Background con centration in the laboratory was determined to be <0.065 f/cc. The analystreported the presence ofa variety offiber types in the sample; however, only small portions of these were considered to be asbesdfbrm. The asbestifbnn fibers present in this sample were determined to be chrysotile. DISCUSSION The vehicular brake service monitoring described in this in vestigation (Phase 1 Tests) support that service workers are not exposed to quantities of asbestos fibers in excess of acceptable standards based on TWA of fiber concentrations in the environ ment Eight-hour TWA levels are well below current regulatory requirements for the workplace. This is tree whether or not the worker used compressed air to remove accumulated road and brake dust. These data are in accord with the results of various investigators in the U.S. as well as in other locations/4-7.!) Hatch*4* repotted on airborne asbestos concentrations released during the cleaning of brake drums using compressed air jets, with results ranging from 2.1-8.2 f/cc with a 10-minute aver age of 0.8 f/cc. Likewise, Paik and Lee*7* reported on a vari ety of activities, including grinding, assembling, brushing, and cleaning with compressed air, which resulted in airborne as bestos concentrations ranging from 0.01-7.28 f/cc. Sheehy of NIOSH*10* reported a range of <0.003-0.166 f/cc during brake repair operations. Even those rare fibers that escape destruction during brake application apparently do not represent an important source of exposure (see Figure 3). Figure 4 is a photomicrograph of the residue from a drum showing considerable nonfiber particulate similar to that reported by Lynch in 1968.*11* There were very few fibers in this residue, with most of the fiber-like structures observed less than 3 microns in length. The fibers depicted in Figures 2 and 3 show what appears to be phenolic resin residue deposited along their length. The presence of residue on such a fiber is reasonable based on the consideration that the phenolic resin that forms the basic structure of a brake shoe pad must bond tightly to each fiber in the matrix. If this were not so, the pad could not bold together during the many cycles of hearing and coding required during the life of the pad.*4* A fiberwith resin deposits along its length will have different aerodynamic characteristics (Le. a larger aerodynamic diameter) compared with an otherwise clean fiber of similar size. Such a fiber would be expected to either not gain entry into the respi ratory system or have a greater opportunity to deposit higher in the system where there is limited retention.*28-30* Independent from the fiber level results, the real-time gravi metric analysis ofthe dust in the area ofthe brake service worker offers strong support for a contention that dust, and presumably any residual asbestos fibers, does not remain in the breathing zone of the worker for an extended interval. In the first and second runs of the Phase 2 investigation, the work activities of the operator were constrained to reproduce the arc grinding process of an 8-hour day into approximately 40 minutes. This work was conducted in rooms with essen tially no detectable air movement (i.e. <2 m/sec). In the normal shop circumstance, arc grinding is conducted for up to possibly S min/hr. This intermittent use of the arc-grinding machine gives the environment an opportunity to dissipate any fibers that may be generated. Therefore, the conditions of the present experi ment should be considered as a worst-case scenario. In the third and fourth runs of Phase 2, the activities most closely simulate the normal functioning of a busy brake ser vice/arcing machine operator throughout a workday. The as sumption of this present study design was that twice as many drum and brake jobs could be accomplished in an 8-hour day as is typical for a normal shop; therefore, the conditions of the present series ofexperiments should also be considered a worstcase scenario. The Permissible Exposure Limit (PEL) as promulgated by OSHA (July 1,1999) for asbestos is a TWA of 0.1 f/cc, with an j HWBUI0011470 BRAKE SERVICE PERSONNEL EXPOSURE TO ASBESTOS 1145 excursion limit of 1.0 f/cc for a monitoring period of 30 min utes.131 3 Results of the investigation reported herein suggest that even in a busy shop, a workerwould be expected to have been ex posed to concentrations of fibers at a concentration considerably less than the PEL for asbestos. In regard to nuisance dust, OSHA's PEL for total dust is 15 mg/m3 with a respirable fraction concentration of 5 mg/m3. Total and respirable dust concentrations in the Phase 2 portion of our study were less than 10% of OSHA's current acceptable limits.*263 Occasionally, questions are raisedregarding "take-home" ex posures due to fibers generated in a worker's environment. The concern is that fibers attach to the worker's clothing and are car riedhome, thus exposing the various members ofthe household. In particular, there is concern regarding those individuals han dling the clothing to remove excess dustpriorto laundering. The results support little reason to conclude that the persons handling such clothing might beexposed tochrysotile fiberconcentrations above the acceptable standards. The majority of fibers found in this study were not asbestiform, but other types of benign fibers such as cotton, etc. CONCLUSIONS Phase 1 The results of this investigation clearly support a contention, in agreement with the epidemiological literature, that during the years where asbestos-containing brakes were utilized, brake service workers were not exposed to levels of asbestos fibers in excess of currently acceptable workplace concentrations. Phase 2 Essentially, the analyses of the environment of such work support that a small quantity of chrysotile is released into the air during the process of arc grinding. However, when this equip ment is utilized in a manner consistent with the manufacturer's design, there is little or no basis to conclude that excessive asbestos concentrations will be generated. In summary, based on the data provided in this study, it is rea sonable to opine that the process ofarc grinding brake shoes un der conditions consistent with those described herein would not expose the operators, or those working nearby, toconcentrations of chrysotile fibers in excess of currently acceptable standards. ACKNOWLEDGMENTS The work reported in this document was supported in pan by a grant from Hemessy Industries, Inc. Technical and research assistance and analytical services for Phase 1 were provided by Kathryn Williams Cavender, CSP. REFERENCES 3. Anderson, A.E.; Gcaler, R.L.; McCune, R.C.; Sprys, J.W.: As bestos Emissions from Brake Dynamometer Tests. Ford Scien tific Research Staff, Automobile Engineering Meeting, Detroit, Ml (May 14-18, 1973). 2. Cheng, VJC.1.; O'Kelly, FJ_- Asbestos Exposure in the Motor Vehicle Repair and Servicing Industry'SHong Kong. J Soc Occup Med 36:104-106 (1986). 3. Core, LJB.; NATLSCO (National Loss Control Service Corpo ration): Industrial Hygiene Report for AMMCO Tools. North Chicago, IL (October 2,1986). 4. Hatch, D.: Possible Alternatives to Asbestos As a frictionMaterial, Arm Occup Hyg 13:25-29 (1970). 5. Hickish, D.E.; Knight, KX.: Exposure to Asbestos During Brake Maintenance. Ann Occup Hyg 13:17-21 (1970). 6. 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). 7. Paik, N.W.; Lee, YU.: Characterization of Worker Exposure to Airborne Asbestos in Asbestos Industry. Korean Ind Hyg Assoc J 1(2): 144-153 (1991). 8. Roberts, D.R.; NIOSH: Industrial Hygiene Report Asbestos at Allied Brake Shop, Cincinnati, OH (June 30,1980). 9. Rohl, AJN.; Langer, A-M.; Klimentidis, R.; et ale Asbestos Content of Dust Encountered in Brake Maintenance and Repair. Ptroc Roy Soc Med 70:32-37 (1977). 10. Sbeehy, I.W.; Cooper, T.C.; O'Brien, DM.: Control of Asbestos Exposure During Brake Drum Service. Appl Ind Hyg 4(12):313- 319 (1989). 11. Roberts, D.R.; NIOSH: Industrial Hygiene Section, Industry-Wide Studies Brandt, Division of Surveillance, Hazard Evaluations and Field Studies, Cincinnati, OH: Industrial Hygiene Survey Report of the New York City Sanitation, Traffic, and Police Brake Servicing Facilities. Queens, NY (May 12,1980). 12. Hansen, E.S.: Mortality of Auto Mechanics, a Ten-Year Follow- Up. Scan J Work Environ Health 15:43-46 (1989). 13. Rushton, L.; Aldersoo, M.R.; Nagarajah, C.R.: Epidemiologic Survey of Maintenance Worksrs in London Transport Execu tive Bus Garages and Chiswick Works. Br J Ind Med 40:340- 345 (1983). 14. Wong, O.: Chrysotile Asbestos, Mesothelioma, and Garage Mechanics. Am J fad Med 21:449-451 (1992). 15. Personal Communication with Glenn Tolar, Glenn Tolar Co., 4650 Center Street, Dew Park, TX 77536. 16. AMMCO Model 2000 Safe-Arc Brake Shoe Grinder, Manufac tured by AMMCO Took, Inc., 2100 Commonwealth Avenue, North Chicago, IL. ----- 17. Hinners, R.G.; Burkart, J.KL; Punte, CJL.: Animal Inhalation Ex posure Chambers. Arch Environ Health 16:194 (1968). 18. Ace Air OeanertTreatmenl One Man Portable Unit, Model 73-20OG, Grainger Industrial Supply, 8200 Pinemont Drive, Houston, TX 77040. 19. Alnor Thermoanemometer, Model 9850, Alnor Instrument Com pany, 7555 No. Linder Avenue, Skokie, DL 60077; Purchased from Grainger Industrial Supply, 8200 Pinemont Drive, Houston, TX 77040. 20. ERI Consulting Engineers, Inc., 2024 Republic Drive, T)r!er, TX 75701; NIST/NVLAP Bulk Asbestos Analysis Lab Accreditation Code No. 1232; Texas Asbestos Laboratory License No. 30-0007. 21. EPA: Improved Method for the Determination of Asbestos in Bulk Building Materials. EPA/600/R-93/116. (1993) Percentage of asbestos was determined by visual estimation. HWBUI0011471 1146 E W. WEIRETAL. 22. SKC Airchek Sampler, Model #224-PCSR4, SKC Gulf Coast Inc., 9827 Whithorn Drive, Houston, TX 77095; GilAir-5, Model #GILGA5RC, rented from Response Rentals, 1208 North Post Oak Rd, Ste. 100, Houston, TX 77055. 23- GCA Environmental Instruments, RAM-1 Aerosol Monitor. 24. SKC Respirable Dust Aluminum Cyclones, Model Numbers 225-01-01 (for 25 mm cassette respirable asbestos sam ples) and 225-01-02 {for 37 mm respirable dust sam ples); SKC Gulf Coast Inc, 9827 Whithorn Drive, Houston, TX 77095. 25. The University of Texas Health Center at lyier. Department of Cell Biology and Environmental Sciences, P.O. Box 2003, Tyler, TX 75710 (Asbestos Analytical Laboratory later becameERI Con sulting Engineers, Reference 42). 26. Code of Federal Regulations, 29 CFR 1910.1000, Subpart Z, Section 1910.1000 Air Contaminants (July 1,1999). 27. National Safety Council: Fundamentals of Industrial Hygiene, pp. 477-483.4th Edition. B.A. Plog, Ed. National Safety Council, Itasca, EL (1996). 28. Harris, R.L., Jr.; Timbrel!, V.: TbeTSfiueoce of Fibre Shape in Lung Deposition--Mathematical Estimates. Inhaled Particles IV, pp. 75-89. Unwin Brothers Limited, The Gresham Press, Surrey, England (1977). 29. Medinsky, M.A.; Asgharian. B.; Schlosser, EM.: Toxicokinetics: Inhalation Exposure and Absorption of Toxicants. In: Compre hensive Toxicology, pg. 73. J. Bond, Ed. Elsevier Science, Inc., New York (1997). 30. Timbrelh V: The Inhalation of Fibres. In: Pneumoconiosis-- Proceedings of the International Conference, Johannesburg, South Africa, 1969, pp. 3-9. H.A. Shapiro, Ed. Oxford Univer sity Press, Capetown, South Africa (1970). 31. Code ofFederal Regulations, 29 CFR 1910.1001, Asbestos (1999). HWBUI0011472