Document 6EZEOqVw6RN1mwxo00N7gNMd

FILE NAME Brakes BRK DATE 2009 DOC BRK193 DOCUMENT DESCRIPTION Journal Article - Airborne Asbestos Concentrations Associated with Heavy Equipment Brake Removal Ann Occup Hyg pp 1-19 'The Author 2009 Published by Oxford University Press on behalf of the British Occupational Hygiene Society do 10 mep056 Airborne Asbestos Concentrations Associated with Heavy Equipment Brake Removal A. K. MADL,,S. H. GAFFNEY,,J. L. BALZERand D. J. PAUSTENBACH,, ChemRisk Inc. 25 Jessie Street Suite Alamo CA 94507 USA 1800 San Francisco CA 94105 USA 2408 Horse Trail Court Received 6 January 2009 in final form 25 June 2009 containing brake linings were used in heavy construction equipments such as tractors backhoes and bulldozers prior to the 1980s While several published studies have evaluated exposures to mechanics during brake repair work most have focused on automobiles and light trucks not on heavy agricultural or construction vehicles The purpose of this study is to characterize the airborne concentration of asbestos to workers and bystanders from brake wear debris during brake removal from 12 backhoes and tractors manufactured be- tween 1960 and 1980. Asbestos content in brake lining average 20 chrysotile by polarized light microscopy and brake wear debris average 0.49 chrysotile by transmission electron microscopy TEM was also quantified Breathing zone samples on the lapel of mechanics n = 44 and area samples at bystander n = 34 remote n ==== 22 and ambient n = 12 locations were collected during 12 brake changes and analyzed using phase contrast microscopy PCM National Institute for Occupational Safety and Health NIOSH 7400 and TEM NIOSH 7402 In addition the fiber distribution by size and morphology were evaluated ac- cording to the International Organization for Standardization method for asbestos Applying the ratio of asbestos fibers fibers including asbestos as determined by TEM to the PCM results the average airborne chrysotile concentrations PCM equivalent were 0.024 cc for the mechanic and 0.009 cc for persons standing 1.2-3.1 m from the activity during the period of exposure 0.5 to h Considering the time involved in the activity and assuming three brake jobs per shift these results would convert to an average h weighted average of 0.009 cc for a mechanic and 0.006 cc for bystander The results indicate that ) the airborne concentrations for worker and bystander samples were significantly less than the current occupational exposure limit of 0.1 cc ii % of respirable fibers were 20 ...min length and iii 95 of chrysotile in the brake linings degraded in the friction process The industrial hygiene data presented here should be useful for conducting retrospective and current exposure assessments of individuals as well as hazard assessments of work activities that involve repair- ing and replacing containing brakes in heavy construction equipment Keywords asbestos brakes heavy equipment industrial hygiene a INTRODUCTION Once thought to be a miracle mineral asbestos gained widespread use beginning in the early 1900s and has been reportedly incorporated in some 3000 different products because of its low cost and desirable qualities such as heat and fire resistance wear and friction characteristics tensile strength heat electrical and sound insulation adsorption capacity and resistance to chemical and biological at- * Author to whom correspondence should be addressed Tel 1-415-896-2400 fax + 1-415-896-2444 mail amadl@chemrisk.com amadl@chemrisk.com tack Agency for Toxic Substances and Disease Registry ATSDR 2001 For these reasons asbestos specifically chrysotile was used for many deca- des by the automobile heavy equipment crane railroad and airline industries as a component of brakes Chrysotile's frictional characteristics such as good tensile strength durability flexibility and heat resistance provided the auto industry with a fric- tion material that could withstand extreme tempera- tures pressure and stress Skinner et al 1988 Paustenbach et al 2004 Maines 2005 These char- acteristics were particularly necessary for safety as automobiles throughout the 20th century became larger heavier and faster Harper 1998 1 of 19 2 of 19 A. K. Madl et al fi - Because of regulatory and societal concerns about the health effects caused by exposure asbestos use in the USA has precipitously declined since the 1970s ATSDR 2001 Maines 2005 dos Santos Antao et al 2009 Kelly and Matos 2009 Over the last 30 years significant attention has been paid to evaluating asbestos exposures and the potential risk of asbestos- related diseases among automobile garage mechanics Paustenbach et al 2004 Chrysotile asbestos was also used as a friction material in heavy construction equipment but potential asbestos exposures to mechanics repairing brakes on such equipment has been less well studied and understood Boelter et al 2007 Although the asbestos content in automobile brakes is generally between 30 and 50 Lynch 1968 Anderson et al 1973 Madl et al 2008 heat and pressure such as that exerted during vehicle braking can cause chrysotile asbestos to degrade to fibrous amorphous decomposition products as well as form other fibrous minerals such as forsterite and olivine Jacko et al 1973 Candela et 2007 The dehydration or retention of water in chrysotile decomposition products has been shown to influence the extent to which forsterite is formed .under heat and pressure Candela et al 2007 It has been suggested however that friction during mechanical braking disaggregates mineral bundles in the brake lining which liberates water and results primarily in amorphous fibrous magnesium silicate degradation products Candela et al 2007 Because the elemental ratios and ray diffraction XRD patterns of chrysotile and these degradation products are similar transmission electron microscopy TEM is often necessary to identify fibrous structures of chrysotile at low bulk concentrations Using microscopy historical studies have shown that brake wear debris collected from an automobile dy- namometer or drum brakes contains on average be- tween 0.02 and 4.5 asbestos with the majority of wear debris samples containing % chrysotile Hickish and Knight 1970 Luxon 1970 Anderson et al 1973 Jacko et al 1973 Rohl et al 1977 Rowson 1978 Williams and Muhlbaier 1982 Cha et al 1983 Sheehy et al 1989 While these studies do not directly measure forsterite or other degradation products in brake wear debris the breakdown of chrysotile is inferred by comparing asbestos content in the lining to that in brake emissions or accu.mulated dust in the brake assembly Although it has been assumed that the forces that convert chrysotile in automotive brakes are at work during the use of heavy equipment e.g. dozers backhoes and graders little work has been conducted that confirms the degradation of chrysotile to forsterite or an amorphous form This matter is of particular interest since it is not well understood how the differ- ent speeds or weights of heavy construction equipment compared to passenger automobiles can influence the frictional mechanisms and thus by ex- tension the conversion to forsterite or other non- asbestos amorphous materials Understanding this matter will inform hygienists whether workers conducting brake repairs on heavy construction equipment during the period between the 1950s and the 1980s or in modern times were exposed to apprecia- ble concentrations of asbestos Only one published study has evaluated potential asbestos exposures to mechanics repairing heavy construction equipment brakes Boelter et al 2007 In this paper personal short 30 min and term h weighted average TWA samples for airborne asbestos were collected during repair activities involving the replacement of containing products i.e. engine gaskets brake and clutch linings in a dozer grader and two loaders Area samples were also analyzed to characterize potential exposures to a bystander nearby these activities The containing products removed from the construction equipment as well as brake wear debris were analyzed for asbestos content While this study filled an important data gap it did not address directly whether chrysotile asbestos was degraded to a similar extent as that observed with passenger automobiles and it only characterized a limited number of equipment representing a wide array of types and brake assembly configurations e.g. disc drum and band Complete enclosure of a brake system size of containing friction lining location and access configuration in relation to the mechanic's breathing zone as well as method of maintenance work are all likely to influence occupational exposures to airborne asbestos during brake repair activities With these factors in mind and without additional information it was uncertain how the information presented in the Boelter et al 2007 might compare to results from other types of heavy construction The handling and cleaning of contaminated work clothing worn in some occupational environments have been suggested as a possible source of paraoccupational or home chemical exposure Studies that have reported exposure through this possible secondary exposure pathway include industries where beryllium lead or even asbestos e.g. insulation workers exposures in the workplace were excessive For example Eisenbud et al 1949 found mean air concentrations of 500 gberyllium m` when the clothing of beryllium manufacturing workers was shaken out Piacitelli et al 1997 found elevated lead concentrations in the vehicles and homes of lead- exposed construction workers Some persons who live in the homes of workers exposed to free asbestos fibers developed asbestos disease Lieben and Pistawka 1967 Anderson et al 1976 1979 Li al 1978 Epler et al 1980 McDonald and McDonald 1980 Joubert et al 1991 Magnani et al 1993 Asbestos concentrations during heavy equipment brake removal 3 of 19 Generally workers in asbestos manufacturing mining and shipyard industries are exposed to very high air- borne concentrations of asbestos and come in direct contact with large amounts of bulk asbestos and in the majority of cases amphibole asbestos The takehome exposure of other household members called secondary exposure or occupational exposure is thought to occur as a result of bringing very dusty work clothing into the home which was usually contaminated due to daily contact with bulk or raw asbestos Although exposures associated with handling work clothes worn during brake repair work were expected to be extremely low it was felt that this issue deserved greater characterization as it has implications for both historical and current asbestos exposures of a group of individuals not previously studied Since a broader range of data would increase the confidence in the preliminary study we evaluated a number of vehicles for the purpose of understand- ing the extent of potential conversion of chrysotile asbestos in brake linings to forsterite and amorphous materials We also characterized worker and bystander exposures to airborne asbestos during brake removal in various types of heavy construction equipment and assessed the potential of home exposures from clothing worn during the brake removal activities In this study worker and environmental exposures were evaluated during the maintenance of 12 pieces of heavy construction equipment with similar brake assembly configurations Because of the relatively large number of pieces of equipment tested with similar brake assemblies the influence of the extent of equipment use e.g. hours of operation methods of brake removal used by different mechanics oily versus dry brake assemblies and type of equip- ment loader backhoe and tractor on the variability of the airborne asbestos measurements could be assessed In addition short samples were col- lected and h TWA exposures were calculated for comparison to historical and current occupational exposure limits for asbestos The fiber size and morphology distributions were also measured to characterize the proportion of respirable airborne fibers free or associated with a matrix released during brake removal activities It is anticipated that this information will not only provide useful information regarding potential historical exposures experienced by mechanics conducting brake repair work on heavy construction equipment but will also provide a basis for correlating this information to the exposures and health experience of automobile mechanics METHODS Description of backhoe brake assemblies Table 1 provides a summary of the type of vehicles evaluated in the study as well as the years during td which the equipment was manufactured total hours of operation and the facility in which the brake repair work was performed Each of these vehicles contained a left and right dry drum and disc brake assembly Fig 1 each of which possessed an inner and outer drum lining and two band linings comprised friction material Equipment that potentially had containing linings was selected for the study based on the age of the equipment and repair maintenance records provided by the equipment owners A total of 12 pieces of equipment two tractors and 10 loader backhoes manufactured between 1960 and 1980 and operated between 943 and 6741 h were included in this study It should be noted that the hours of operation for each piece of equipment may not necessarily reflect the total number of hours on the brakes however measurements of lining thickness for each brake assembly showed significant brake wear It was not determined until after the testing through bulk sample analysis whether the equipment contained asbestos brake linings In fact all vehicles tested did have asbestos in the friction materials Description of test site and study conditions Brake repairs were performed at two heavy equipment service centers on six different days over a period of 17 months April 2005 to September 2006 5 days were spent at one center located in Stockton CA and the other day at a center in Big Rock IL Table 1 These service centers were selected because they were and continue to be active repair facilities for heavy construction equip- ment including tractors and backhoe loaders The weather conditions in Stockton were generally sunny and clear with temperatures ranging from 21 to 27 during the 5 days of testing The Big Rock testing took place during cloudy conditions with temperatures 15.6 All work was performed by two currently employed mechanics one in Stockton and one in Big Rock who had between 15 and 30 years of professional experience repairing heavy construction and agricultural equipment The mechanics performed the brake removal in the same manner they had reportedly used throughout their careers The service shop in Stockton CA was relatively large with four service bay doors and approximate dimensions of 30 m wide by 14.9 m deep with a ceiling height of 6.1 m Fig 2 The facility in Big Rock IL was less than half the size of the service center in Stockton CA with only one service bay door and approximate dimensions of 14.3 m wide by 11.9 m deep with a 6.1 ceiling Fig 3 All service bay and entry doors were closed while the brake removal was being conducted In addition both repair shops were not equipped with any active heating air conditioning or ventilation systems Prior to conducting the study permission from a medical institutional review board IRB was * 4 of 19 Table 1. Summary of equipment tested and bulk sample asbestos concentrations of brake linings and wear debris Equipment Date Equipment Hours Model Site type type Air exchange ACH Average thickness mm by assembly Brake linings XRD % weight chrysotile Left Right n n Average SD ND PLM % area chrysotile Range n 72 Average SD ND Brake wear debris TEM % weight chrysotile Range 12 72 Average SD ND Decomposition Range % Eq1 13 April 2005 580C 4360 Backhoe Stockton - 433 4.31 80 80 32 4 25-37 80 80 40 Eq2 14 September 580C 1232 Backhoe Stockton 0.6 4.46 4.26 80 80 19 3 15-22 80 80 26 2005 Eq3 Eq4 Eq5" 16 September 580 2005 16 September 430 2005 14November 580C 2005 1562 Tractor Big 0.6 Rock 943 Tractor Big 0.6 Rock . 6230 Backhoe Stockton 066 4.76 4.73 80 80 23 411 4.42 80 80 29 257 3.15 8 1 14 3 19-28 80 80 28 4 24-36 80 33 6 1-19 81 15 Eq6" 14 November 580C 3600 Backhoe Stockton 0.66 409 442 84 84 8 2005 9 1-25 85 8 Eq7 14November 580C 6741 Backhoe Stockton 0.66 3.41 4.36 80 80 17 3 14 22 80 19 2005 Eq8b 14 June 2006 580C 3264 Backhoe Stockton 1.55 4.04 4.13 80 80 27 7 18-39 80 17 Eq9b 14 June 2006 580CK 2744 Backhoe Stockton 155 4.43 4.56 62 62 15 12 1-29 60 15 Eq10 Eq11 Eq12 20 September 580C 2006 20 September 580B 2006 20 September 580C 2006 2743 Backhoe Stockton 1.28 4188 Backhoe Stockton 128 128 * 5320 Backhoe Stockton 128 128 462 376 82 82 20 13 1-36 82 82 25 7 ~ 4.46 4.36 80 80 19 4 12-25 80 16 4.31 2.18 85 85 1 0 1-2 84 84 1 Eq12 12 19 3.8 1-39 12 20 8 24-54 20 20 0.150 0.071 0.1-0.2 99.5 8 20-35 20 20 0.009 0.0010.001 0.008 0.009 100.0 5 20-35 20 20 0.075 = 0.021 0.06-0.09 99.7 10 15-40 20 . 8 05-25 22 22 0.450 0.354 0.2-0.7 0.050 = 0.000 005-0.05 12 0.05-30 2 2 0.050 0.000 0.05-0.05 2 15-20 2 1 0.825 1096 = 0.05-1.6 6 10-27 20 20 0.700 0.141 0.6-0.8 98.5 99.6 A. 99.4 Madl 95.1 et al 97.4 12 0.5-28 20 20 3.015 4.221 0.03 6 79.2 25 0.5-70 20 20 0.085 0021 0.07-0.1 99.6 6 6-25 20 0.035 0.021 0.02-0.05 99.8 1 0.5-3 40 40 0.435 0.422 004-0.8 65.2 6.1 0.05 7012 0.49 1.20 0.008-6 94.4 ND detectable Asbestos was not detected in both band and drum lining on right assembly No right drum lining was present detectable samples entered as half the limit of detection or sensitivity limit Asbestos concentrations during heavy equipment brake removal Drum Lining - Band Lining 5 of 19 Drum Lining Fig 1. Heavy equipment dry brake systems diagram my 81m Offices . Doot Sats Bay AhDor 1 Shey Bay Door 1 43m 43m x 4.9m 73 7,471 ,41 ** 3.7 3 2.43.7 2.43.7 2.43.7 2.43.7 4 ten FST Bay Door 2 3.7m x 4.3m Bay Door 3 3.7m x 4.3m Bay Door 4 * 3.7m x 4.3m Remote Area : , 2 $ 0.9m 5 Bystander M+ 3 0.9833 Bystander Mi $03 = 0099m m 0.9m = 0.9m Bystander <> 0.9m tm 4 0 am am 34.9m 8 Bystander 0.9m ** 0.9m Bystander M+ 09m = Bystander { a Remote 2 2 x" Area M , Ambient 0.38 Fig 2. Diagram of equipment repair facility Stockton CA and locations of area sampling stations requested and obtained Essex Institutional Review Board Inc. Lebanon NJ USA This IRB complies with the federal regulations of the National Institute of Health the Office of Human Research Protection 45 CFR 46 and the Food and Drug Administration 21 CFR 50 56 It is also accredited by the National Committee for Quality Assurance formerly The Partnership for Human Research Protection Description of exposure scenarios . Airborne asbestos concentrations were measured during brake removal and disassembly activities related to all 12 pieces of equipment Clothes handling tasks such as shaking and folding of coveralls worn during maintenance of 11 pieces of equipment were also studied Before any brake work was performed mechanics were fitted with new coveralls These coveralls were collected after the mechanic completed work on each piece of equipment and were later tested to evaluate the exposure of persons during the handling of these potentially contaminated work clothes Each coverall n == 11 was stored in separate plastic bags until the last day of testing when the clothes handling task was conducted 6 of 19 B. A. K. Madl et al Open threshold to adjacent roco 2mx 2mx 2.3m 1.5m Remo0.8mt0.e8m Asen 0.8m _ Sence Bay bes $ e www14.3M Area we Dose Be 27m , Ambient @ Ambient 3.385 Fig 3. Diagram of equipment repair facility Big Rock IL and locations of area sampling stations The simulated clothes handling task involved re- peatedly shaking folding and turning clothes inside out for 1 to 2 min for each pair of overalls by a volunteer to simulate the handling and laundering Although no fibers or debris were visible on the coveralls some particles were observed in the air during the clothes handling task TEM analysis of air samples was used to evaluate the proportion of asbestos versus asbestos airborne particles released during shaking The brake removal process was similar for all pieces of equipment with slight differences only in the work practices exhibited by each mechanic The mechanics worked on each piece of equipment one at a time To remove and disassemble the brakes the external brake housing was first removed from the tractor or loader backhoe using a manual or power wrench to loosen bolts that held the housing in place On four occasions Eq1 Eq9 Eq10 and Eq12 a blowtorch had to be applied to facilitate loosening of the external housing bolts Once the external housing was removed the entire brake assembly was removed from the vehicle At this point the mechanic at the Stockton facility would blow out the assembly and work area with compressed air and then repeat the entire process for the second brake housing Once both complete assemblies were removed he performed bench work which entailed disassembling the drum linings from both brake assemblies Using a slightly different order than the Stockton mechanic the mechanic in Big Rock IL completed the entire brake removal process on the first assembly before beginning the process on the second one More specifically once the brake assem- bly was removed from the external housing the brake assembly was moved to a workbench and the drum linings were removed from the face plates in preparation of shipment to a specialized shop for refacing After one complete brake assembly was disassembled and the linings removed the mechanic from Big Rock would repeat the same process for the second housing and then blow out both brake hous- ings at the end of the brake removal job . While performing the bench work the Stockton and Big Rock mechanics used different methods to remove the friction linings from the drum facings Specifically the Stockton mechanic used a hammer and punch to remove the rivets that attached the lin- ing to the drum face whereas the Big Rock mechanic used a power drill It is noteworthy that four of the 12 pieces of equipment tested contained at least one brake assembly that was saturated in oil that had leaked from an adjacent reservoir In these circumstances these assemblies were wiped clean before the linings were removed In general the Stockton mechanic took 30 min to remove and disassemble the linings from two brake housings from one piece of equipment whereas the Big Rock mechanic took 45 to 60 min to perform the same job Sampling and analytical methods All airborne samples for asbestos were collected in accordance with federally established criteria Airborne asbestos and other particulates were collected onto mixed cellulose ester membranes 25 mm 0.45 um pore size Zefon International St Petersburg Asbestos concentrations during heavy equipment brake removal 7 of 19 FL USA with either portable SKC Universal SKC- West Inc. Fullerton CA USA or volume Dawson 1300 sampling pumps Ashtead Technology. Rentals Hayward CA USA The sampling pumps were calibrated with a Bios DryCal DCLite primary flow calibrator Bios International Corporation Butler . NJ USA before and after each sampling event The temperature inside the garage was noted Springfield Precise Wind and Weather Instruments Fort Bragg CA USA during the collection of each air sample Asbestos sample collection equipment materials and procedures were consistent with National Institute for Occupational Safety and Health NIOSH Methods 7400 and 7402 Before any brake removal activities began background samples for airborne asbestos were collected in three different locations in the service centers Per- sonal samples from workers lapels bystander area samples within 1.2-3.1 m of the work activities remote area samples at more distant locations 9-15 m from the work activities and ambient samples for airborne asbestos were collected during tractor brake or backhoe brake removal and disassembly Figures 2 and 3 illustrate the location of the bystander remote area and ambient airborne asbestos samples collected in relation to the work activities at both the Stockton and the Big Rock facilities Con- , secutive min samples were collected at an airflow rate ranging from 1 to 101 minflon the right and left lapel of the worker during the brake removal activi- , ties To characterize potential bystander exposures to asbestos air samples were collected at breathing zone height 1.5 m at three different locations 1.2 to 3.1 m from the vehicle Bystander samples were collected at an airflow rate of 5-111 min dur- ing brake removal activities on each vehicle 30-60 min Background samples of ambient air outside the shop 90-180 min and remote area inside the shop 30-60 min were also collected for airborne asbestos at an airflow rate of 10 minflduring the brake removal activities At least two field blanks were collected during each day of the above- described testing All airborne asbestos samples including personal area background and ambient samples were sent to an accredited laboratory EMS Laboratories Pasadena CA USA for asbestos analysis by phase contrast microscopy PCM NIOSH Method 7400 and TEM NIOSH Method 7402 NIOSH 1994a EMS Laboratories is an asbestos analysis laboratory accredited by the American Industrial Hygiene Asso- , ciation and the National Voluntary Laboratory Accreditation Program US Department of Commerce National Institute for Standards and Technology , Gaithersburg MD USA and utilizes analysts trained according to NIOSH 582 who adhere to the quality assurance and quality control requirements set forth by OSHA OSHA 1994 and the most cur- rent version of the NIOSH 7400 Method For the analysis of air samples by TEM selected area electron diffraction and dispersive ray were used to assess the fiber type via the diffraction pattern and elemental profile of the asbestos fibers respectively NIOSH 1994c Fibers were counted according to the NIOSH Methods 7400 and 7402 which define fibers as being > ...min length and 0.25 um in diameter and having at least a 3 aspect ratio NIOSH 1994a Air samples were also analyzed according to the International Organization for Standardization ISO method for characterization of fiber type size and morphology of fibers > ...min length ISO 1995 Fiber size and morphology analysis Because OSHA specifies PCM analysis with or without TEM analysis for evaluating occupational exposures to airborne asbestos most studies utilize NIOSH Method 7400. However PCM analysis under NIOSH Method 7400 does not differentiate asbestos fibers from other structurally similar asbestos fibers so OSHA has indicated that TEM analysis NIOSH Method 7402 can be used to quantify the ratio of asbestos fibers to total fibers OSHA 1994 While NIOSH Methods 7400 and 7402 are still used today to determine workplace compliance with the OSHA PEL for asbestos these methods are limited in their ability to account for fiber morphology e.g. presence of a resin that might influence the respirability or the health hazard of airborne fibers While not widely used the ISO Standard method allows for characterization of both fiber size and type as well as determination of the fiber size distribution of airborne asbestos and differentiation of free fibers from fibers associated with a respirable matrix ISO 1995 This method in addition to the NIOSH methods was used in this study because the data can then be employed in future doseresponse and risk assessment models while the NIOSH methods are most appropriate for comparing to the OSHA PEL OSHA 1994 Using the ISO methodology asbestos fibers were classified according to fiber size and morphology Asbestos fiber morphology was quantified by categorizing asbestos fibers that were > ...min length as free fibers free fiber bundles fiber clusters or matrix fibers including matrix fibers bundles and dispersed arrangements In those instances where asbestos fibers were associated with a cluster or matrix the di- mensions of the cluster or matrix structure as well as those of the individual fibers comprised within the cluster or matrix were recorded Asbestos fibers were characterized by their morphology and size to evaluate the proportion of airborne fibers that were potentially respirable While fibers up to 3.5 ...min diameter have been detected in the lungs of workers 8 of 19 A. K. Madl et al a and while fibers of this dimension may represent the very upper bound limit of respirability Gross et al 1971 Morgan and Holmes 1980 Timbrell 1989 1982 a number studies have shown that most fibers that are deposited in the pulmonary region of the lung are thinner than 0.7 ...mand almost all are thinner than 1 ...mHarris and Timbrell 1975 Sussman et al 1991a Strom and Yu 1994 Yu et al 1995 Respirable fibers free and bundles were therefore designated as those with diameters of /0. 7 ...mThe deposition of fibers contained within clusters or matrices was assumed to be based on the dimensions of the overall cluster or matrix structure Depending on the size and shape of these structures the fiber cluster or matrix may act aerodynamically more like a particle than as a fiber Nonetheless respirability of fiber clusters or matrices was evaluated in two ways as a respirable fiber of diameter 0.7 um or a respirable particle with diameter 10 ...m In addition fibers 20 ...min length were considered in the size distribution analysis There is a basis of data to suggest that asbestos fibers of this length or greater pose the greatest risk whereas those < m do not Stanton et al conducted a series of animal ex- posure experiments with asbestos and asbestos fibers and ultimately concluded that fibers /8...m in length have little or no mesotheliogenic potential Stanton 1973 Stanton et al 1977 1981 Berman et al 1995 evaluated data from 13 rat inhalation bioassays in which the animals were exposed to nine different types of asbestos dusts and concluded in this analysis that structures contributing to lung tu- mor risk appeared to be long 5...mand thin 0.4 ...mfibers Berman et al 1995 Berman further noted that potency appeared to increase with increas- ing length with structures longer than 40 ...mbeing 500 times more potent than those between 5 and 40 ...min length These researchers suggested that structures < ...min length did not contribute to lung tumor risk Modeling results reported by Miller et al 1999 indicated that the concentration of fibers longer than 20 ...mand thinner than 1 ...min diameter is most influential in determining the tumorigenic potential of fibers Miller et al 1999 In addition the US Environmental Protection Agency US EPA contracted the preparation of a technical sup- port document for a protocol to assess asbestos- related risk Berman and Crump 2003 Based on the modeling results presented in the technical sup- port document the authors concluded that the best estimate of risk for both lung cancer and mesotheli- oma for fibers between 5 and 10 ...min length is hundredth of the risk assigned to fibers longer than 10 ...mFurther the best estimate of the potency of fibers shorter than 5 ...mwas zero for mesothelioma and lung cancer The authors also ex- plained that results from their review of the supporting literature suggest that the optimum cutoff for increased potency occurs at a length that is closer to 20 ...mthan 10 m Collection and analysis ofbulk asbestos samples For each piece of equipment filings of the brake material from each assembly two drum linings and two band linings and samples of brake wear debris one from each assembly were collected for bulk sample asbestos analysis Both types of bulk material . were analyzed by EMS Laboratories using polarized light microscopy PLM according to NIOSH Method 9002 NIOSH 1994b and XRD according to NIOSH Method 9000 NIOSH 1994d Because the asbestos concentration in brake wear debris was anticipated to be below the detection limit for PLM or XRD % a modified approach based on the US EPA methods for detecting asbestos in bulk samples and drinking water was utilized Chatfield and Dillon 1983 Perkins and Harvey 1993 More specifically this approach involved ashing the sample to remove organic material using muffle furnace suspending the ashed sample in water filtering an aliquot of the water suspension transferring the filtered sample onto a TEM grid and characterizing dimensions of fibers according to those measured under NIOSH 7400/7402 Air exchange measurements using tracer gas Sulfur hexafluoride SF was used as a tracer gas to estimate the air exchange rate within the service centers Briefly measurements of the gas were taken according to American Society for Testing and Materials ASTM Method E741-00 ASTM 2001 and air exchange measurements using this method were collected during each day of testing A steady state concentration of 1 p.p.m. for SF6 Aldrich St Louis MO was targeted as the initial room concentration for the tracer gas analysis Tedlar bags Fisher Scientific Hampton NH USA filled with SF6 were then released in the garage with all doors closed Fans on either end of the garage were used to facilitate the gas dispersion After steady state was reached fans were turned off and SF6 measure- ments were taken in 30 intervals with a MIRAN SapphIRe Analyzer Electron Corporation Waltham MA USA Ashtead Technology Rentals for 1 h The air exchange in the garage was calculated using the concentration decay optional regression test method by plotting the natural logarithm of SF6 concentration over time ASTM 2001 Data and statistical analysis For the purposes of statistical analyses results below the analytical sensitivity limit were imputed using a value equal to half the sensitivity limit Analytical sensitivity limits were estimated based_ on the presumption that one fiber could be counted Asbestos concentrations during heavy equipment brake removal 9 of 19 within 100 microscopic fields and divided by the volume of air sampled PCM measurements were adjusted for asbestos fiber content according to the method outlined in NIOSH Method 7402 which specifies multiplying the ratio of asbestos fibers to total fibers observed in the TEM analysis by the PCM fiber concentration NIOSH 1994c The ratios of asbestos to total fibers asbestos and asbestos fibers were based on TEM fiber counts for the same filters from which the PCM fiber counts were obtained The PCM measurements adjusted by the ratio of asbestos versus total fibers are referred to as equivalent PCME airborne asbestos con- centrations In circumstances where PCM measure- ments were above the sensitivity limit but asbestos fibers were not detectable by TEM a PCME asbestos concentration was not calculated Descriptive statistics were performed on PCM TEM and PCME measurements of airborne fiber concentrations collected during the removal of asbescontaining brake assemblies from tractors and loader backhoes and also during the clothes handling activities Results were analyzed by sample location worker bystander remote area and background by testing location Stockton and Big Rock and by assembly oiliness when applicable Eight TWA asbestos exposures during brake removal were also calculated based on the PCME measurements, for both the worker and the bystander based on the assumption that three brake jobs could be conducted in a single workday and the remaining time the worker would be exposed to background concentrations For example 90 min of brake removal activities representing work on three pieces of equipment at a concentration of 0.024 cc and a min exposure to background at a concentration of 0.005 cc would result in an h TWA of 0.009 cc Air concentration data were determined to be lognormally distributed based on probability Oneway analysis of variance and pairwise comparisons based on the Tukey's test for each group were conducted for natural transformed air concentration data of worker bystander and remote area samples sample test of the transformed worker data was conducted with respect to dry versus oily brake assemblies based on unequal variances Power calculations of the above comparisons were estimated to be 100 A Pearson and Spearman non- . parametric analysis was performed to evaluate whether airborne chrysotile concentrations for the worker untransformed and natural log transformed . were influenced or correlated with the asbestos con- tent in the brake lining or brake wear debris and whether the asbestos content in the brake wear debris was influenced by the extent of wear e.g. lining thickness or the original asbestos content in the brake lining RESULTS All equipment contained at least one brake assembly with containing linings The thickness of the brake linings ranged from completely worn to the metal support to 5.94 mm and their asbestos content is presented in Table 1. In summary the asbestos content of the brake lining averaged 19 chrysotile by weight range 1-39 as measured by XRD and 20 chrysotile by area range 0.5 70 as measured by PLM Table 2 Table 1 also presents the asbestos content measured in the break wear debris The average asbestos content found in these samples was 0.49 of chrysotile asbestos range 0.008-6 All heavy equipment showed brake wear debris with % chrysotile asbestos with the exception of Equipment 9 which had brake debris in one assembly containing % asbestos It should be noted that this assembly was also missing both drum linings These results indicate that nearly all average of 94.4 range 58-100 the chrysotile in the brake linings degraded or was converted to an amorphous material Specifically for 10 of the 12 pieces of equipment over 95 of the chrysotile in the brake linings was degraded to fibrous particles in the brake wear debris Interestingly there were no correlations found between the asbestos con- tent in the brake lining and brake wear debris suggesting that the asbestos content in the brake lining does not influence the amount of asbestos remaining in the brake wear debris after degradation processes Air sampling results are reported in Tables 2 and 3 Table 2 presents the short 30 min and brake removal airborne asbestos concentrations measured by PCM TEM and PCME for the worker bystander remote and background locations by facility The average airborne chrysotile concentrations as measured by PCM TEM and PCME were 0.053 0.087 and 0.024 cc respectively for the Stockton mechanic and 0.558 0.012 and 0.010 cc measured by PCM TEM and PCME respectively for the Big Rock mechanic Table 2 The overall worker average airborne asbestos concentrations by analytical method are presented and compared to the OSHA min asbestos excursion limit in Fig 4. No corre- lations were found between concentrations of air- borne asbestos for the worker PCME 30 min and the asbestos content in the brake lining or wear debris this lack of correlation is likely attributed to the low asbestos concentrations in the air samples and in the brake wear debris The results of the clothes handling activity are also presented in Table 2. The average airborne asbestos concentrations measured on the volunteer handling the clothes were 0.231 0.011 and 0.036 cc when measured by PCM TEM and PCME respectively Likewise at the bystander location average asbestos concentrations of 0.093 0.012 and 0.010 cc were 4 Table 2. Summary of air sampling results brake removal and clothes handling by PCM TEM and PCME 30 min by worker bystander remote and background as well as location 10 of Sample location Equipment Asbestos fiber concentrations cc 19 PCM TEM PCMEd n n Avg GM SD ND NR Range n n Avg GM SD ND NR Range n Avg SD Range Worker Brake and bench work Stockton Big Rock Clothes handling Eq 30 30 0 0.056 0.038 0.059 0.013 0.123 3 1 0 0.009 0.009 0.004 = 0.005-0.013 2 0.038 0.055 0.013-0.101 Eq2 30 30 0 0.156 0.120 0.103 0.037 0.220 30 30 1 0.055 0.053 0.021 0.40-.070.040-0.070 2 0.036 0.018 0.023-0.048 Eq5 4 I 0.038 0.027 0.027 0.007-0.059 40 40 2 0.300 0.300 = 0.000 0.300 0.300 2 0.044 0.005 0.040-0.048 Eq6 40 0 0.024 0.024 0.004 0.021-0.029 41 41 1 0.048 0.040 0.029 0.015-0.070 2 0.009 0.008 0.012-0.016 Eq7 4 0 0.016 0.015 0.007 0.011--0.026 4 1 0 0.015 0.011 0.011 0.003-0.030 3 0.003 0.003 0.001-0.008 Eq8 40 0 0.075 0.071 0.028 0.042-0.103 4 0 0 0.225 0.200 0.126 0.100-0.400 4 0.042 0.034 0.035-0.090 Eq9 0 0 0.058 0.057 0.011 0.046 0.071 4 0 | 0 0.048 0.039 0.036 =:0.020-0.100 0.020-0.100 4 0.033 0.012 0.018-0.043 Eq10 4 0 0.029 0.027 0.015 0.021-0.052 4 1 0 0.031 0.022 0.023 0.004-0.060 3 0.009 0.008 0.004 Eq11 Eq12 A. 4 0 0.028 0.026 0.013 0.017-0.046 40 40 0 0.125 0.089 0.120 0.030-0.300 4 0.018 0.014 0.006-0.038 4 0 0 0.050 0.047 0.023 0.036 0.084 4 1 0 0.011 0.009 0.007 0.003-0.020 3 0.003 0.002 0.003-0.006 Eq2 10 Eq12 0.053 0.045 0.029 0.007 0.22010 0.087 0.077 0.038 0.003 0.400 10 0.024 0.016 0.001 0.090 Madl et Eq3 4 0 0.256 0.230 0.130 0.110 0.425 4400 4400 4400 0.003 0.003 0.001 0.002 0.004 _- = al Eq4 0 0 0.419 0.354 0.236 0.131 0.622 4 0 3 0.020 0.020 - 0.020 1 0.010 0.010 Eq4 2 0.338 0.292 0.183 0.110 0.622 2 0.012 0.011 0.001 0.002 0.004 1 0.010 - 0.010 400 400 0.231 0.199 0.125 0.080 0.360 22 22 0 0.011 0.007 0.010 0.002-0.020 2 0.036 0.0 0.032 0.039 Bystander Brake and bench work . Stockton Eq1 Eq2 Eq5 Eq6 Eq7 Eq8 Eq9 Eq10 Eq11 0- 30 0 30 30 1 30 30 0 30 30 0 30 30 0 30 0 30 30 0 30 0 _ 0- 0.029 0.029 0.006 0.024 0.035 31 31 0 0.007 0.007 0.002 0.006 0.008 30 30 3 0.014 0.012 0.010 0.007 0.025 3 3 0 0.009 0.009 0.002 0.007 0.010 3 3 0 0.021 0.019 0.012 0.008-0.032 31 31 0 0.013 0.013 0.004 0.009 0.016 32 32 0 0.012 0.010 0.008 0.007-0.021 3 3 0 0.019 0.015 0.015 0.007 0.036 3 1 0 a 0.007 0.005 0.005 7 od 0.002 0.010 2 0.006 - 0001 0.008-0.009 _ _ _ _- 0.002 0.002 0.001 0.002-0.003 - = _ 0.002 0.001 0.001 01-0.02 0001-0.002 0.010 0.008 0.009 0.004-0.020 _ 2 0.017 _- 0.008 0.008-0.0323 0.003 0.003 0.001 0.002-0.004 1 0.008 0.000 0.008 0.003 0.002 0.001 0.002 0.004 - = 0.011 0.008 0.009 0.003-0.020 2 0.005 0.005 0.006-0.010 Table 2. Continued Sample location Equipment Asbestos fiber concentrations cc PCM n n Avg ND NR GM _ SD Range TEM n n Avg GM SD ND NR Range PCME" n Avg SD Range Big Rock Clothes handling Eq 20 20 0 0.004 0.003 0.005 0.001-0.008 22 22 0 0.004 0.003 0.001 0.002-0.003 _ = - = Eq1 9 0.014 0.013 0.007 0.001 0.036 9 0.005 0.004 0.003 0.001-0.020 4 0.009 0.004 0.006-0.023 Eq12 Eq3 500 500 0.015 0.014 0.007 0.007 0.026 5 5 0 0.003 0.002 0.001 0.002-0.004 - = Asbetos Eq4 30 30 0 0.055 0.054 0.005 0.049 0.059 32 32 0 0.002 0.001 0.001 0.001-0.002 1 0.0024 0.002 Eq4 2 0.035 0.034 0.006 0.007 0.059 2 0.002 0.002 0.001 0.001 0.004 1 0.002 - 0.002 200 200 200 0.093 0.080 0.066 0.046 0.140 200 200 200 0.012 0.008 0.012 0.003-0.020 2 0.010 0.011 0.003-0.018 Remote area conetrais Brake and bench work Stockton Eq1 0 _a aa 0 __ ae _ Eq2 20 0 0.004 0.004 0.001 0.004 0.005 22 22 0 0.002 0.002 0.000 0.002 0.002 - = - during Eq5 Eq6 + 2. 0 0 0.005 0.004 0.002 0.003 0.006 2 1 0 0.002 0.002 0.000 0.002-0.002 1 0.001 0.000 0.001 20 0 0.004 0.004 0.000 0.004 0.004 22 22 .0 0.002 0.002 0.000 0.002 - - - . 20 20 0 0.005 0.005 0.002 0.003 0.007 22 22 0 0.001 0.001 0.000 0.001 EEqq78 heavy 20 20 0 0.009 0.009 0.003 0.007 0.011 22 22 0 0.002 0.002 0.000 0.002 _ = _ - - = Eq9 equipment Eq10 Eq11 brake Eq 20 20 0 0.006 0.006 0.000 0.006 0.006 2 1 0 0.002 0.002 0.001 0.002 0.003 1 0.0016 0.000 0.002 20 20 0 0.005 0.004 0.004 0.002 0.007 22 22 0 0.002 0.002 0.000 0.002 - - = - = 2 0 0 0.008 0.008 0.002 0.007 0.010 22 22 0 0.002 0.002 0.000 0.002 - = 20 20 0 0.008 0.008 0.000 0.008 22 0 0.002 0.002 0.000 0.002 - - - Eq2 10 0.006 0.006 0.002 0.002 0.01110 0.002 0.002 0.000 0.001-0.003 2 0.001 0.000 0.001-0.002 removal Big Rock Eq12 Eq3 200 200 200 0.010 0.010 0.001 0.010 0.011 2 2 0 0.001 0.001 0.000 0.001 - , a Eq4 200 200 200 0.035 0.035 0.002 0.033 0.036 22 22 0 0.001 0.001 0.000 0.001 - = - Eq4 22 0.022 0.022 0.001 0.010 0.036 2 0.001 0.001 0.000 0.001 0.001 _-_ - Clothes handling 20 0 0.040 0.037 0.021 0.025 0.055 22 22 0 0.001 0.001 0.000 0.001-0.002 o. - - Background Brake and bench work Stockton Eql 0 __ _ _ 0 _ _ _ oo = of E42 2 0 0 0.023 0.023 0.006 0.019 0027 210 210 210 0.003 0.002 0.002 0001-0.004 1 0.005 0.000 0.005 19 12 of Table 2. Continued 19 Sample location Equipment Asbestos fiber concentrations cc PCM n n Avg GM SD ND NR Range TEM n n Avg GM SD ND NR Range PCMEd n Avg SD Range : . Big Rock Ambient Eq5 30 30 0 0.010 0.007 0.008 0.003 0.019 32 32 1 0.001 0.001 0.000 0.001 - - Eq6 30 30 0 0.007 0.006 0.002 0.004 0.008 3 3 0 0.002 0.002 0.001 0.002 0.003 - = Eq7 30 0 0.008 0.005 0.008 0.002 0.017 33 33 0 0.002 0.002 0.001 0.002-0.003 = - = Eq8 30 30 0 0.006 0.005 0.002 0.003-0.007 3 3 0 0.002 0.002 0.000 0.002 - - = Eq9 30 30 0 0.008 0.008 0.001 0.007 0.009 3 3 0 0.001 0.001 0.000 0.001-0.002 - = Eq10 30 30 0 0.007 0.006 0.005 0.002 0.012 3 3 0 0.002 0.002 0.000 0.015 - = - = Eq11 30 30 0 0.007 0.006 0.001 0.006-0.007 33 33 0 0.002 0.002 0.000 0.002 - = - = Eq12 30 30 0 0.008 0.008 0.001 0.006-0.009 33 33 0 0.002 0.002 0.000 0.002 _ oo - - = Eq2 10 0.009 0.008 0.004 0.002 0.02710 0.002 0.002 0.000 0.001 0.004 1 0.005 - 0.005 Eq12 . Ld Eq3 A. 20 20 0 0.008 0.008 0.000 0.008 . 22 0 0.002 0.002 0.000 0.002 - Eq4 2 0 0 0.021 0.021 0.019 0.007-0.035 22 22 0 0.002 0.002 0.000 0.002 - _ = Madl Eq4 2 0.015 0.015 0.010 0.007 0.035 2 0.002 0.002 0.000 0.002 _- _ et al Brake and bench work Stockton . Big Rock Eq1 0 _ 0 oe _ _ - = - = Eq2 10 0 0.001 0.001 _ 0.001 11 0 0.0004 0.0004 0.0004 - = - = Eq5 30 0 0.002 0.002 0.002 0.001 0.005 33 33 0 0.0004 0.0004 0.0001 0.0004-0.0005 Eq8 30 30 0 0.002 0.002 0.002 0.001-0.004 3 1 0 0.001 0.001 0.0001 0.0005-0.0007 2.0.004 2.0.0004 0.0000 0.0004 Eq10 30 30 0 0.003 0.003 0.001 0.003 0.004 310 310 310 0.001 0.001 0.0001 0.0008 0.0010 2 0.0002 0.0000 0.0001-0.0002 Eql 4 Eq12 0.002 0.002 0.001 0.001 0.005 4 0.001 0.001 0.000 0.0004 0.0010 2 0.0003 - 0.0001 0.0004 . Eq3 0 0 0.001 0.001 0.001 I 0 0.0003 0.0003 0.0003 - _- Eq4 100 100 0.001 0.001 0.001 1 0 0.0005 0.0005 0.0005 - _- Eq4 I 0.001 0.001 0.001 I 0.0004 0.0004 0.0003 0.0005 _ PCMadj PCM concentration multiplied by the ratio of asbestos fibers to total fibers measured by TEM n number of samples NR number of samples not readable ND number of samples in which asbestos was not detected Avg average SD standard deviation -- not applicable Based on samples in which asbestos fibers were detected by TEM Asbestos concentrations during heavy equipment brake removal 13 of 19 Table 3. Summary of fiber size and morphology of airborne asbestos fibers collected on the worker during brake removal Fiber structure n Total Percent fibers % classified as fiber or particle with dimensions of classification fibers % Respirable fiber . Respirable particle 0.7 ...mwidth < ...mwidth 10 ...mwidth 5 ...m length % 20 ...m length % > ...m length % 20 ...m length % 5 ...m length % 20 ...m length % Total fibers 261 Free bundle 95 ww 18 2 35 2 _ Fiber clusters 8 ww 2 2 i 2w Matrix disperse 158 61 0 .0 7 0 2w 9 1.2 1.0 cn ne ee ae ner ee ee a cc 0.8 + Concentration Concentration 0.6 - Concentration i Concentration : Concentration H Concentration i Concentration 0.4 + OSHA 30 Minute Excursion Limit ee new Maximum > " Mirumu # Average . 0.0 4 + t $ PCM TEM PCME * Based on samples in which asbestos fibers were detected by TEM : Fig 4. Comparison of worker asbestos concentrations cc 30 min by analytical methods PCM TEM and PCME measured using PCM TEM and PCME respectively sampling times were 30 min in duration and collected during the anticipated peak times of exposure Figure 5 presents the average asbestos concentra- tions as measured by PCME for the worker bystander remote and background locations as compared to the current OSHA min excursion limit for asbestos Asbestos was not detected in more than half of the samples collected at the bystander lo- cations even though 1.2 m from the work activity as determined by TEM and average airborne asbes- tos concentrations at the bystander locations were generally less than half of those measured for the ' mechanic Airborne concentrations mechanic Airborne concentrations were 0.014 cc PCM 0.005 cc TEM and 0.009 cc PCME at bystander locations at the Stockton facility and 0.035 cc PCM 0.002 cc TEM and 0.002 cc PCME at bystander locations at the Big Rock facility Table 2 Airborne asbestos concentrations found at the remote and background locations samples were even lower than those found at the bystander locations It is interesting to note however that actinolite one fiber was detected in two ambient air samples and one worker sample although this finding is not surprising since actinolite is commonly found in ambient air Lee and Van Orden 2008 Because four pieces of equipment Eq3 Eq4 Eq6 and Eq7 had at least one assembly saturated in oil airborne asbestos concentrations found on the worker removing those brakes were compared to the concentrations found while removing dry brake assemblies The resulting average asbestos concentration during oily brake removal 0.009 cc was less than onefourth the concentration of dry brake removal 0.043 cc as measured by PCME These findings were statistically significant P ==== 0.001 by a twosample test of the transformed worker data Estimated h TWA asbestos exposures were calcu- lated for the worker and the bystander Considering the time involved in the brake removal activity and assuming three brake removal jobs are conducted per shift the resulting average h TWA was esti- mated to be 0.009 cc for a mechanic and 0.006 cc for bystander Therefore h TWA asbestos exposures for mechanics performing brake removal on heavy equipment and those standing nearby this work are not likely to exceed the current OSHA PEL of 0.1 cc Table 3 presents a summary of fiber size and mor- phology of the airborne asbestos fibers collected on 14 of 19 A. K. Madl et al 2- 1.0 pee oe oe tak ae win Hoe oe om ww re mn ne 2 FICE DONT Sm SOF OSHA 30 Minute Excursion Lim SUL FOE OU Jew JOY em on De OH Me Mh ty we ate aor ML or er oF cc 08 + cc { o Concentration Concentration Concentration 06 Concentration Concentration fi Concentration Concentration 04 04 4 Concentration ~ Maximum ~ Minimum * Average 02 of : 0.0 4 %- f - ~f 2 $ Worker Bystander Remote Background Fig 5. Comparison of worker bystander remote area and background airborne asbestos concentrations cc PCME 30 min the worker Within the worker samples there were 261 total asbestos fibers counted using the ISO methodology Of these only 36 were free fibers or bundles 18 were free fibers or bundles with diameter 0.7 mlength > 5 ...mand only % were free fibers or bundles with diameter 0.7 ...mand length 20 ...mThe remaining fibers were either in clusters % or attached to a matrix 61 Only % of the fibers however were part of a cluster that may be respirable 10 ...min width and 44 of fibers were part of a matrix that may be respirable Figure 6 is an image of fiber clusters collected in worker samples and exemplify fibers that are part of a much larger .matrix DISCUSSION This study was conducted to assess possible exposures to airborne asbestos during removal and disassembly of containing brakes from heavy construction equipment manufactured during the 1950-1980 time frame The data collected in this simulation study are believed to capture the plausible range of variables that might influence exposures during brake removal and disassembly from heavy construction equipment as well as the potential exposure associated with handling work clothes The work activities were conducted under low ventilation conditions e.g. no active local or general ventilation and low building air exchange by mechanics with varying years of experience and techniques at differ- ent maintenance service centers and on different heavy construction equipment tractors and backhoes with similar brake assembly configurations but representing a range of equipment use e.g. hours and brake lining wear The results collected from Fig 6. TEM image of a fiber cluster collected during a shortterm worker sample performing brake removal on Equipment 6 courtesy of EMS Laboratories this study provide information not only on airborne asbestos exposures experienced by mechanics removing containing brakes from heavy construction equipment and by persons nearby these activities but also on the extent to which chrysotile asbestos degrades into fibrous particles during braking of heavy construction equipment the influence that dry versus oily brake assemblies has on airborne asbestos exposures and the size and  Asbestos concentrations during heavy equipment brake removal 15 of 19 morphological distribution and potential respirability of airborne chrysotile fibers generated during the brake removal activities Although most of the brake removal work was conducted at the Stockton CA service center 10 dry versus oily brake assemblies Based on standard tests comparisons worker exposures were found to be significantly higher than those measured at bystander or remote locations P < 0.0001 and worker exposures while removing brakes from dry backhoes and not at the Big Rock IL facility 2 tractors worker exposures resulting from brake removal and disassembly at these two facilities assemblies were statistically greater than those associated with oily assemblies P = .0.001 Although Boelter et al 2007 evaluated airborne mechanics and types of equipment appeared to be asbestos levels during repair of heavy construction similar The most striking effect on airborne asbestos machinery they did not restrict their study to just concentrations measured on the workers lapel was brake work Boelter et al 2007 Boelter et al the internal dryness of the brake housing i.e. whether it was saturated with oil with dry assemblies resulting in worker exposures of 0.043 cc range 0.01-0.13 cc and oily assemblies resulting in worker exposures of 0.009 cc range 0.003 0.016 cc No correlation was apparent using re- gression analyses for the amount of asbestos present| in the brake wear debris when compared to the asbestos content in the drum and band linings or to the extent to which the linings were worn e.g. lining thickness It is possible that this lack of correlation 2007 evaluated asbestos air concentrations during frame maintenance and repair activities which included aggressive techniques that resulted in visible dust from work involving friction products and gaskets Further the work performed during this study included dismantling cleaning and reassembling engines and clutches Because a narrow range of work tasks were involved with brake removal only a subset of asbestos measurements from the Boelter et al 2007 study can be directly compared to our study It was observed that airborne asbestos reflects the already low chrysotile asbestos concentrations present in the brake wear debris 0.49 inability of these fibers to become airborne during manipulation and compressed air blowout of the brake assembly and similar surface area dynamics during the mechanical action of the braking process that is independent of the asbestos content The precision of airborne fiber concentrations is dependent on the fiber density and proportion of filter surface area e.g. microscope fields examined with statistical uncertainties generally being inversely proportional to the fiber density Johnston et al 1982 Ogden 1982 Cherrie and Johnston 1986 Lange et al 1996 It has been reported that the accuracy is not greatly improved for counts beyond 50 fibers and thus has been recommended that at least 50 concentrations observed during brake removal and disassembly were equal to or less than those of comparable work activities reported in the Boelter et al 2007 Work involving band brake removal rivets and friction lining removal from brake band or brake shoe and disc brake assembly removal resulted in average min airborne asbestos concentrations ranging from 0.044 to 0.045 cc PCME in the Boelter et al 2007 study The average airborne asbestos concentration for similar activities in our study was 0.016 cc range 0.001-0.090 cc PCME Boelter et al collected and analyzed debris from the brake assembly of each piece of equipment and reported detectable or % asbestos levels for every sample Because PLM was utilized as the method for bulk sample analysis of brake wear de- fibers be counted and the number of fields be only limited where the airborne fiber concentrations are so low that the accuracy is no longer important Ogden 1982 These concepts have been incorporated into the current NIOSH method for asbestos` bris and because concentrations below % are not detectable this approach did not allow for precisely quantifying the extent to which chrysotile is degraded during braking While we did not specifically measure forsterite concentrations in brake wear de- NIOSH 1994a where 100 fibers or 100 micro- | scope fields whichever criterion is met first are counted For the majority of the worker samples collected in this simulation study 50 fibers were counted within the prescribed 100 microscope fields whereas far fewer fibers 10-20 fibers were observed in samples collected in bystander or remote area locations The confidence limits would as a re- bris indirectly we can determine how much chrysotile is degraded by measuring the chrysotile content in the friction lining and in the brake wear debris residing in the brake housing With TEM analysis we were able to quantify the amount of chrysotile in the brake wear debris average 0.49 range 0.008-6 and determine that 95 of chrysotile in the brake lining is degraded to fibrous asbestos particles sult be expected to be narrower for worker compared to those for area airborne asbestos concentrations Based on the data collected in this study however it was determined that the data represented a power of 100 at a 95 confidence level to detect a differ- ence between worker bystander and remote area measurements as well as worker exposures handling in the friction process These findings are comparable to those reported for passenger automobiles with reported averages being between 0.02 and 4.5 asbestos with the majority of wear debris samples containing % chrysotile Hickish and Knight 1970 Luxon 1970 Anderson et al 1973 Jacko et al 1973 Rohl et al 1977 Rowson 1978 16 of 19 A. K. Madl et al Williams and Muhlbaier 1982 Cha et al 1983 Sheehy et al 1989 We acknowledge that the degraded chrysotile may not in fact be chemically equivalent to forsterite and that it may be some other asbestos amorphous material Langer 2003 Candela et al 2007 It is also acknowledged that the material that is called chrysotile in this analysis may not possess the biologic activity of chrysotile asbestos due to dehydroxylation and other stresses ahs as been suggested by Langer 2003 Few studies have characterized the size distribu- tion and morphological characteristics of asbestos fibers associated with handling containing friction materials Atkinson et al 2004 Jiang et al 2008 Madl et al 2008 and other studies have evaluated the size and type of asbestos fibers retained within the lungs of mechanics Churg and Wiggs 1986 Dodson et al 1991 Roggli et al 2002 In the former set of studies however fiber characteristics were associated with directly handling replacement containing automobile brakes and in the latter group of studies the source of the fibers retained within the lungs can only be qualitatively associated with employment history To the best of our knowledge no studies have evaluated the size distribution and morphological characteristics of asbestos fibers in brake wear debris released during the disassembly of brakes and in particular in heavy equipment brakes We found that 61 of the airborne asbestos fibers were associated with a matrix or resin that can significantly influence the potential respirability of these fibers of the fibers associated with a matrix only % were potentially respirable using cutoff of particle diameter of 10 ...mand had fiber lengths 20 ...mOf the free fibers or bundles not associated with a matrix only % of airborne fibers were respirable cutoff of fiber diameter of 3 ...mThus even with the low concentrations of airborne asbestos fibers released during heavy construction equipment brake removal and disassembly only a small percentage of these fibers were likely to be respirable The exposure and epidemiologic literature for automobile mechanics can provide a useful benchmark for exposures measured in this study In a recent assessment of all the published and unpublished industrial hygiene data collected during asbestos brake repair by vehicle mechanics nearly 200 brake job and h TWA airborne asbestos samples were analyzed Paustenbach et al 2003 In this assessment which encompassed measurements collected in seven different countries over the last 30 years average h TWA concentrations of 0.04 cc for airborne asbestos were found with individual measurements ranging from 0.002 to 0.68 cc reported for brake mechanics servicing light trucks and passenger vehicles Paustenbach et al 2003 This value 0.04 cc is identical to that identified by US EPA in the survey that they conducted in 1984 Weil et al 1985 The values are also not dissimilar from the analysis of 200 short samples recently reported by Richter et al 2008 In addition since 1975 six epidemiologic casecontrol studies and two analyses have evaluated the risk of asbestos disease among mechanics McDonald and McDonald 1980 Teta et al 1983 Spirtas et al 1985 1994 Woitowitz and Rodelsperger 1994 Teschke et al 1997 Agudo et al 2000 Wong 2001 Hessel et al 2004 These studies have consistently found no increased risk of mesothelioma in brake mechanics Studies that specifically evaluated mechanics involved in brake lining installation and repair also showed a rela- tive risk consistently 1.0 Spirtas et al 1985 Woitowitz and Rodelsperger 1994 Teschke et al 1997 Hessel et al 2004 It has been noted that the risk of mesothelioma in brake mechanics is sim- ilar to that of other occupations that do not involve occupational exposure to asbestos such as teachers librarians and accountants Teschke et al 1997 Based on these findings the available epidemiological data show that employment as a motor vehicle mechanic or more specifically a brake repair worker does not result in an increased risk of developing mesothelioma Paustenbach et al 2004 Taking the epidemiologic and industrial hygiene findings together we can conclude that auto mechanics who repair ascontaining brakes as a career are exposed on average to 0.04 cc range 0.002-0.68 cc of as- bestos and are therefore not at an increased risk of asbestos disease including mesothelioma Paustenbach et al 2003 The range of lifetime cumulative doses of chrysotile have been characterized by Finley et al 2007 and were reported to range from 0.16 to 0.41 cc year for facilities with no control procedures 1970s and from 0.010 to 0.012 cc year for those employing engineering controls 1980s Upper bound 95 estimates for the 1970s and 1980s were 1.96-2.79 and 0.07-0.10 cc yearr,,espectively Finley et al 2007 These data also suggest that mechanics conducting brake work on heavy construction equipment similar to that described in this simulation study are comparable to exposures of automobile mechanics Fig 7 and as a result would also not be expected to be at an increased risk of asbestos disease In summary the short airborne asbestos con- centrations measured for both a worker removing containing brakes from heavy construction equipment as well as for a bystander working in the vicinity of such activity were below both the current OSHA excursion limit for asbestos and all the previous US occupational asbestos standards Based on a collection of 44 samples this study found that short exposures 30 min of a mechanic to airborne asbestos during the removal and disassembly Asbestos concentrations during heavy equipment brake removal 17 of 19 ERESTAY 1 wets 1 - 1334783 eens ence ; H . ; fy i . ~ Vassour Recon Average ween OSA - PEL Wixtyeon 1821985 18211985 fee at me a nm tay 3 01 3 0.2112855 natn w enon ane eweene ~ 0.01 t ~ I q i * 201 chord chord Jason 1976 A Mngt 1970 1979 1976 peeest 18777 * Dow S Dow we do Tika Tika abcccva . do a ry ' Roberts Roberts Robertson Robertson Rodelsperger Store 1025 Shetty al Blake of 138361 330701 1993 Zumwalde 1979 1582 1876 5859 11888 319881887 2003 codecoots revocdo 3 bease revocdo per aby Rococoofonr so Rouces at 7707 7707 sex codecots codecoots codecoots 5 bras nemoze7tO0d, cocoky vocabe cocoky drave cono Booker and Spencer 2007 Coso Coupment Yesting Word 2005-2008 205-208 Case Equiament Teesno --flystander Fig 7. Comparison of airborne asbestos exposures for automobile mechanics to those measured by mechanics handling asbestoscontaining brakes on heavy construction equipment of containing brakes from heavy construction equipment average 0.024 cc range 0.001-0.1 cc whereas h TWA exposures average 0.009 cc range 0.005-0.23 cc based on the assump- tion that three brake assemblies could be removed within a workday The industrial hygiene data presented here should therefore prove useful for retrospective and current exposure assessments of indi- viduals and hazard assessments of work activities that involve repairing and replacing containing brakes contained in heavy construction equipment Hickish and Knight 1970 Johnson et al 1979 Roberts 1980a Roberts and Zumwalde 1982 Rodelsperger et al 1986 Moore 1988 Sheehy et al 1989 Blake et al 2003 Boelter et al 2007 FUNDING Case Holland * Acknowledgements research was supported by CaseNew Holland a manufacturer of heavy construction equipment which has been involved in litigation related to the possible exposure of brake mechanics to asbestos Some of the authors have served as expert witnesses in litigation regarding the potential asbestos health hazards to mechanics historically involved in automobile and heavy equipment repair work The authors would like to thank and acknowledge Pearl Moy Ellen Donovan and the mechanics for their participation in the simulation study as well as Paul Scott and James Keenan for their contributions to the analysis and graphical pre- sentation of these data REFERENCES . 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