Document Lp4mbjQ078GB7ejEM23m1xvGb

FILE NAME Brakes BRK DATE 1981 Apr 7 DOC BRK077 DOCUMENT DESCRIPTION US Dept of Health Industrial Hygiene Report Assessment of Asbestos Exposure to Mechanics Performing Brake Service Operations ve U.S. DEPARTMENT OF HEALTH AND AND Public Health Service Service INDUSTRIAL HYGIENE ASBESTOS REPORT ASSESSMENT OF ASBESTOS EXPOSURE / MECHANICS PERFORMING BRAKE SERVICE OPERATIONS REPORT WRITTEN BY Dennis R. Roberts Ralph D. Zumwalde DATE OF REPORT April 27 1981 REPORT # 32.4 Industrial Hygiene Section Industrywide Studies Branch Division of Surveillance Hazard Evaluations and Field Studies National Institute for Occupational Safety and Health Cincinnati Ohio INTRODUCTION A major objective of the National Institute for Occupational Safety and Health NIOSH is to determine environmental exposures of working populations through occupational health research field surveys and industrywide epidemiologic studies Accordingly NIOSH conducted comprehensive industrial hygiene surveys to characterize dust exposures resulting from vehicle brake servicing operations and to make a thorough assessment of work practices utilized as well as document the types of personal protective equipment used Of particular interest was the potential for exposure to asbestos fibers which could be generated by these types of operations Limited studies of workers involved in brake servicing have suggested that their related exposures may be asso- ciated with asbestos diseases NIOSH estimates that a workforce of 151,000 brake mechanics and garage workers in the U.S. is potentially exposed to asbestos Potential exposures are a re- sult of 128 million pounds of asbestos used annually in the U.S. for the pro- duction of brake friction materials Besides asbestos other materials e.g. binders friction modifiers fillers etc. are used in the manufacture of brake linings which can likewise have potential for exposure As noted in one study thirty materials or compounds that make up the binders fiber reinforcers property modifiers etc. were identified during brake lining manufacturing rate en aoe Re = TERA oe ne oon BRAKE MATERIALS PRODUCTS AND USAGE Friction 4 Historical Development of Friction Products The requirements of early automobile friction materials were relatively mini- mal Passenger cars were light and designed for low speed operations Brakes were of an external contracting type and utilized a variety of materials this included leather and impregnated cotton products which were commonly used along with wool and felt In 1903 woven asbestos friction materials were first marketed in the United States by the Keasbey and Mattison Company of Ambler Pennsylvania Because of its superior heat resistance and durability they rapidly increased in use and soon dominated the market The Model T Ford pro- vides an example of the changing use of materials Initially cotton bands reinforced with zinc copper or brass wire and impregnated with oils and bituminous material were used for the brake bands These were soon replaced by mixed asbestos materials and finally by woven asbestos products The woven asbestos brakes continued to be the dominant product used in automobiles until about 1930. They typically contained 70 or more cored asbestos yarn impregnated with drying oils such as linseed and bituminous material Molded brake linings were developed in the early 1920's and gained increasing use with the introduction of internal shoe brakes in 1927. By 1940 virtually all automobiles were equipped with molded brake linings although woven products continue to be used in trucks heavy equipment and for specialized applications The molded linings in use were cut to length usually by the manufacturer and mounted on brake shoes using rivets Until the mid 1920's brakes were only mounted on rear wheels However with the development of internal shoes four wheel mountings soon became standard and by 1930 were generally operated hydraulically As automobiles were designed for use at even higher speeds brake linings im- Various new materials were introduced proved in both quality and performance as fillers binders and friction modifiers In 1948 bonded brake linings were developed and soon accounted for approximately 40 of the original equipment brake market However they rapidly dominated the replacement market because of the considerable savings in labor during installation In 1965 the first disc brakes were introduced on American automobiles and rapidly increased in use In 1975 virtually all original equipment front wheel brakes on cars were of this type However because of less stringent braking requirements and the difficulty of adapting mechanical parking brakes to the disc configuration the rear wheel brakes on 95 of currently sold cars are still of the drum variety Requirements for Brake Linings A constant or slightly decreasing coefficient of friction C.F. with tempera- tures up to about 1000 is required for an efficient brake lining values of from 0.30 to 0.45 C.F. are normally sought Lower values produce brakes requiring excess pedal pressure and those with higher values are too sensitive to pressure and develop excess wear Ideally the desired frictional qualities should be maintained throughout the life of the lining material During braking chemical and physical changes occur in the material at the braking surfaces These changes may produce an increase build or a decrease fade in friction Satisfactory linings will fade slightly upon repeated applications but will return to their initial stat~ upon cooling Low wear of the linings is obviously desirable for economical and practical considerations However high wear resistance can be associated with the tendency of the lining to glaze with a concomitant reduction in the coefficient of friction This can be overcome by allowing a slow alteration of the brake lining material to occur Pyrolysis of the organic binders and thermal decomposition of the chrysotile fibers under braking provide the necessary continuing renewal of the lining surface The lining should be abrasive to the drum surface In addition to causing rapid drum wear abrasive linings score the drums which in turn leads to a rapid wearing of the lining Drums made of cast iron and steel are common with steel being the more susceptible to scoring Since brake drums have a hardness of from 3.5 to 4.0 on the MOH scale virtually all lining materials used have lower hardness values Other necessary or desirable properties of brake linings include physical strength dimensional stability quiet operation and safe and offensive degradation products Of the various properties desired in the linings greatest attention is paid to build and recovery characteristics Wear problems are not as serious and can more readily be overcome with the mate- rials available 7,8,9,10 Compounding Ingredients of Brake Linings To achieve the desired friction properties a wide variety of ingredients are commonly used in the manufacturer of automobile brake linings These include A Asbestos Asbestos is used for fiber reinforcement of the friction product Chrysotile is used almost exclusively and comprises from 40 to 50 percent of the brake lining Fiber grades 4 through 7 are used and occasionally several sizes are mixed or even calcined to improve performance characteristics Amosite crocidolite or other amphibole asbestos varieties are not used because they are too harsh and tend to score the brake drums Organic binders Organic binders are primarily phenolic type resins selected for high binding strength Unmodified phenolic resins when subjected to heat usually become hard and brittle To prevent this linseed cashew nut or China wood oils or cresols are added Rubber which also finds use as a binder imparts desirable friction qualities and improves the flexibility of the lining material Friction modifiers Friction modifiers are added to achieve a desirable coefficient of friction over all operating conditions These modifiers also produce a more homogeneous lining surface Included among these materials are lead zinc brass cashew nut oil graphite and oxides of iron and copper Fillers Fillers such as rubber scrap barites clays silica coke coal and other minerals are used These also have utility in achieving desired friction properties in some cases through action as abrasives to recondition braking surfaces It is important to note that one major purpose of the reconditioning agents is to retard the formation of forsterite which may accumulate on the surface of the brake lining Forsterite is a mineral not originally present in the brake material but is created by dehydroxylation and recrystallization of chrysotile asbestos at high temperatures The hardness of forsterite hardness 6.5-7.0 on the MOH Scale is such that it tends to score and gouge brake drums and discs hardness 3.5 degrading them prematurely Therefore recrystallization of chrysotile to forsterite is an unwanted effect Curing agents Curing agents and accelerators are used to assure that appropriate chemical reactions occur to produce the desired brake quality Types of Brake Linings and Manufacturing Processes In making the of different types of brake linings various manufacturing processes are utilized to achieve a wide range of potential applications .These include Wired Back These are made by a calendering process in which putty stock is formed into a ribbon about a wire backing The wire reinforcing serves to maintain strength during the curing process Further as linings of this type are invariably riveted the wire reinforcing provides long term structural strength and prevents shearing of the lining at the rivets during braking Linings of this type were extensively produced prior to World War II They are in little use today Extruded Linings These are manufactured by extruding the soft plastic stock through an appropriately sized rectangular orifice To minimize structural weakness in this lining curing agents are added to produce a hard inflexible finished product Sheet Linings These are laminated structures formed by winding a 0.001-0.002 inch film of stock about a hot roller Since the fabrication procesiss a relatively expen- sive one linings of this type are not commonly produced for general use Dry Mixed Types This process involves the dry mixing of various ingredients capable of passing a 200 mesh screen and then molding the lining under pressures of from 1000 to 3000 pounds per square inch The resulting lining is among the most heat stable of friction materials in use today and obtains wide use in the manufacture of brake blocks for heavy duty service Millboard Type The manufacture of this type of brake lining material is by a process similar to that utilized in the paper industry Wet stock is formed and passed over rollers with various drying and baking operations producing sheets of uniform lining material The equipment for producing such materials is expensive but the volume of production leads to an economically produced molded lining BRAKE LINING REPAIR AND MAINTENANCE PRACTICES To a large extent the changing character of brake lining materials has led to changing work practices and differing asbestos exposures over the years From 1920 until about 1930 when braking was done through the use of external brake bands made from woven materials the predominant exposure to asbestos would have come from the cutting and fitting of the woven lining material It is thought that airborne fiber concentrations were considerably less than those developed in later years when machining of molded materials was common From 1927 when internal brake shoes were developed using molded linings until 1948 when bonded brake linings were introduced all internal brake linings were attached to shoes using rivets The lining material for use in the replacement market would be precut to appropriate size for various brakes or obtained from rolls of indeterminate length The precut segments would usually be predrilled at the factory for rapid mounting on shoes In some circumstances however drilling for the rivets and bevelling would be done by the mechanic installing them The use of rolled linings required cutting the friction material to shape drilling holes for rivets and bevelling the edges appropriately In this latter circumstance asbestos exposure to workers could be considerable Even when shoes with predrilled and bevelled linings were installed the processes of punching out the rivets on the old shoes and riveting on of the new shoes would give rise to greater exposures than that accompanying the use of bonded linings With the introduction of bonded linings the need for drilling facing or grinding operations during installation decreased significantly However for a short period of time in the 1950's when automobile shoes were first installed with a fixed anchor some tapering was necessary on uniform thick- ness bonded linings to achieve a proper fit Previously the end of the shoe opposite to that of the hydraulic cylinder could be mechanically adjusted Shortly thereafter tapered bonded linings were available from the factory Subsequent to 1960 considerably fewer bevelling or grinding operations were performed by an automobile mechanic replacing brake linings During replacement of internal shoe brakes it was common practice to remove the brake wear dust from the housing by air blowing or brushing After 1970 increasing awareness of the hazards of asbestos and its presence in brakelining dust led to wet brushing wet wiping dry brushing or vacuuming work practices in some brake servicing facilities However even today such improvements in work practices are not universal In the 1930's and 1940's most automotive shops were relatively small and most mechanics performed all automobile maintenance and repair activities In recent years however there has been an increasing tendency towards specialization with shops existing for brakes and front end work exclusively Here while asbestos exposures during brake work on an individual job may be less than those of previous years some workers are exposed for considerably longer periods of time SELECTION OF FACILITIES SURVEYED The purpose of the industrial hygiene study was to investigate and characterize dust exposures resulting from vehicle brake maintenance and repair operations taking into account the work practices utilized Therefore it was necessary to locate facilities where a variety of brake servicing techniques were used as well as where there were differences in number of vehicles ser- viced Six of the eleven sites selected for the investigation were automobile brake service facilities which performed from 2 to 45 brake jobs per week at an average of 65 minutes per vehicle One of the facilities surveyed only serviced trucks which often required 6-9 hours per vehicle to service brakes with an average of three brake jobs per week The remaining four facilities serviced both autos and trucks and performed from 5 to 45 brake jobs per week which varied in service time depending on the type of vehicle Detailed airborne dust sampling surveys were conducted at each facility Description of Brake Servicing Operations The servicing procedures found at each facility were basically as follows The vehicle is driven into a repair stall or bay for a brake system examination Pending repairs the wheels are elevated removed and then inspected Loose dust is cleaned from the drums and brake assemblies by vacuuming wet or dry brushing using compressed air or a combination of these methods Parts are then replaced or repaired as needed and the brake systeims re- assembled and adjusted Test driving the vehicle for proper fitting and adjustment is the final phase of the servicing operation A brief description of the individual facilities is outlined as follows Industrial hygiene survey data collected at each facility are shown in Tables 1-4 10 Facility A Facility A a private fleet service garage was responsible for complete automotive maintenance and repair with the exception of internal engine repair and exterior painting The shop normally operates 8 hours per day 5 days per week Of the seven employees working at the facility only three were responsible for brake servicing Brake servicing operations were performed two to five jobs per week in either of two service stalls Facility B Facility B a municipal service garage employed there were three mechanics that specialized in brake and clutch service and three employees that operated a separate brake repair shop specializing in brake shoe and drum reconditioning The brake mechanics serviced all vehicles which included waste collection dump and light trucks autos and some 2- and 3- wheeled vehicles The shop operated 8 hours per day 5 days per week Facility C At Facility C a municipal garage there was an average of one complete brake service job per day taking about 5 hours per job with most of the vehicles consisting of cars or light trucks There were five employees responsible for brake servicing and the facility operated 8 hours per day 5 days per week 11 Facility D At Facility D a municipal garage an average of eight brake jobs per day were performed on cars and trucks Brake maintenance was performed by any of the 60 auto mechanics The hours of operation were 8 hours per day 5 days per week Facility E Facility E a private fleet service garage performed complete automotive and light truck maintenance The shop normally operated two shifts 5 days per week and there were usually four time mechanics per shift About one brake job per week per shift was performed Facility F Although Facility F was an automobile brake service shop front alignment and tire sales were also part of the shop mechanics duties The three time mechanics worked from two service stalls 12 hours per day 5 days per week Brake maintenance operations consisted of 10 to 14 brake jobs per week Facility G Major services at Facility G an automobile brake service shop consisted of front alignment shock absorber servicing and brake maintenance The normal work week was made up of five hour days and one hour day Three 12 are service stalls were used by the three time employees for brake servicing operations during the 4 to 6 brake jobs per week Facility H Major services provided at Facility H an auto brake shop were front alignment shock absorber service and brake maintenance The three time employees worked from two service stalls hours per day 6 days per week The number of brake jobs per week averaged from 20 to 30 Facility I Facility I was the largest of the automobile brake service shops surveyed Other services provided by this facility were front alignment and shock absorber replacement or repair The five time mechanics worked from four service stalls 9 hours per day 6 days per week Brake maintenance operations consisted of 35 to 45 jobs per week Facility J The major services at this facility were front alignment muffler installation and brake maintenance Automobile brake repair operations were performed by the shop's three employees and consisted on the average of 4 to 5 brake jobs per week Normal brake servicing at this facility took about 1 hour and 45 minutes per vehicle 13 Facility K Facility K a truck brake maintenance facility involved a somewhat different operatiaonnd exposure Servicing operations were more complex and therefore involved more employees with fewer vehicles serviced than Afer auto maintenance facilities The four service bays at the facility were used by seven mechanics Other service operations included pad grinding riveting and punching pad removed and replaced on shoe sand blasting of old shoes and milling of wheels SAMPLE COLLECTION AND ANALYSIS Airborne Samples Personal and general air samples were collected at each facility on different occasions during a year period Brake servicing operations and areas not in the immediate vicinity of brake work within each facility were monitored to provide asbestos exposure data Personal air samples were collected in the breathing zone of the brake mechanics using Millipore Type AA 37 millimeter mm diameter 0.8 micrometer ...mpore size membrane filters at a calibrated sampling flow rate of 2.0 liters per minute 1pm The filters were changed periodically during the work shift to prevent particulate overloading on the filter weighted average TWA fiber concentrations were determined for the time spent performing brake service at all facilities and peak concentrations determined for time spent cleaning brake dust from drums and assemblies Samples for peak exposures were collected using Gast pumps calibrated at 11.0 or 10.6 1pm using identical media as above At facilities B C and D a 2.0 14 train was used for peak samples Analysis of the membrane filters 1pm sampling for asbestos fibers by the Occupational was conducted in accordance with the procedures outlined Administration Safety and Health and the NIOSH Manual of Methods CAM 12 239 These procedures require the counting of Analytical than 5 micrometers ...min length and with at least a 3 to fibers greater length to width aspect ratio utilizing phase contrast optical microscopy at a of 400-450X Concentrations are expressed as fibers greater than magnification 5 ...m in length per cubic centimeter of air fibers Random samples from each facility surveyed as well as those samples having high fiber concentrations as determined by the optical counting method were analyzed on a transmission electron microscope TEM utilizing selected area electron diffraction SAED and anenergy dispersive ray analysis EDXRA Samples were observed at 17,000X magnification with fibers > 1 aspect ratio sized by length and diameter SAED was attempted on all observed fibers for possible identification In addition EDXRA was performed on individual fibers to determine their elemental composition SAED patterns and EDXRA elemental spectrum ratios were compared with reference minerals UICC chryso- .tile and forsterite obtained from the U.S. Smithsonian Institution Sample preparation and analysis were performed using the NIOSH method described in the Technical Report Review and Evaluation of Analytical Methods for Environ- mental Studies of Fibrous Particulate Exposure General area samples for trace metals lead zinc copper iron and manganese were collected at most facilities using Staplex Type 1A volume samplers at a flow rate of 10 cubic feet per minute and also with 15 a sampling train and flow rate like that used for asbestos fiber collection Samples were analyzed for metals by atomic absorption spectrophotometry in accordance with the NIOSH methods CAM Number 222 186 S341 and S366 14,15 Bulk Samples Samples of brake wear dust were collected from the brake drums of several vehicles that were being serviced during the surveys These samples were analyzed by TEM for characterization and identification of fibrous particulates and to determine fiber size distributions Work Practice Characterization Considerable emphasis was placed during the surveys on detailing work procedures during brake servicing in order to document the types of cleaning practices i.e. vacuum compressed air brushing etc. used in replacing brakes As previously described in the section Description of Brake Servicing Operations the brake servicing work practices utilized were similar for all facilities surveyed the major difference observed was the methodology utilized for clean of brake wear dust from the backing assemblies There were six different types of clean methods observed during the study Those six methods are described as follows 1. Compressed Air Blow A compressed air stream was used to blow away brake wear dust from the brake assemblies and drums 16 2. Compressed Stoddard Solvent Mist Blow The same as # except a spray gun containing stoddard solvent was used to produce a solvent mist for blow 3. Dry Brushing Brake wear dust was brushed away with a small utility brush usually " diameter 4. Wet Brushing Basically the same as dry brushing except the brush was kept saturated with a liquid such as gasoline water or stoddard solvent 5. Squirt A liquid bottle containing water was used to wash away brake dust This was followed by drying off assemblies with a cloth 6. Vacuum Cleaning A shop type vacuum cleaner equipped with a HEPA filter was used in combination with compressed air This system included a brake encapsulation cylinder that completely enclosed the backing plate assembly The mechanic operated a compressed air nozzle fixed inside the enclosure to blow off the brake dust which was immediately drawn into the vacuum system A separate vacuum hose was used to vacuum the dust from the brake drums HEPA High Efficiency Particulate Air - 99.7 at efficiency for 0.3 ...m diameter aerosols 17 In Methods 1 to 5 and especially 1 to 3 the brake dust enter the ambient air of the facility Conversely in Metho contained by the HEPA filter which may be removed from the va system and disposed of SUMMARY OF SURVEY RESULTS The optical microscopy fiber count analysis for the TWA and peak personal background area samples collected during the study are summarized in Table 1 The TWA and peak fiber concentrations for mechanics tended to fluctuate depending task For on the brake clean example regardless of method used and the the cleaning method time spent performing the utilized peak exposures are high up to 15.00 fiber when compared to their respective TWA ex- posures and the 0.01 to 0.28 fibers The differences peak exposures are perhaps best explained between the TWA exposures by variations in work practices utilized the inconsistencies in performing brake work that existed mittently and therefore represents a small percent of the work performed during the shift For example amount the of time spent servicing brakes differed among the mechanics in addition to the number of brake jobs that were performed per shift likewise there were differences in cleaning methods e.g. compressed air brush vacuum etc. and procedural distance from brake housing to breathing zone In addition techniques there were e.g. some mechanics who of brake dust as shop size dropped the brake drums on the floor causing airborne dispersal Environmental conditions at each brake service facility such ventilation controls and open windows and doors would also affect individual worker exposure and background concentrations of airborne 18 asbestos fibers Regardless of the cleaning method utilized TWA exposures for mechanics at all facilities were relatively consistent and did not differ significantly from their respective background ambient levels in facilities TWA exposures The similarities between mechanic TWA and background exposures suggest that all individuals in the immediate work environment are potentially exposed to the same fiber concentrations during a normal work shift This observation is further supported by the fact that the mechanics spend much of the work shift away from the work site and in other areas of the facility TEM Fiber Characterization Airborne Samples rs ad ~ rrr Samples were randomly selected for transmission electron microscopy TEM with fibers sized by length and diameter In addition fiber concentrations fibers were determined for total fibers and fibers 5 ...m in length These concentrations were compared to those found by the optical microscopy method and are reported in Table 2. In all but 3 samples the concentrations of fibers 5 ...m in length determined by optical microscopy were somewhat higher than those determined by TEM This difference could have been caused by particulate loss during sample preparation for TEM or because of the small number of fibers actually counted on each sample at low fiber counts small differences in fibers counted by both microscopy methods would have a significant effect in the calculation of fiber concentrations Besides 19 3 determining the concentrations for fibers 5 ...m in length total fibers observed were counted and concentrations calculated As would be expected the greatest proportion of fibers observed was shorter than 5 ...m in length 80 to 90. Fibers observed by TEM were identified utilizing SAED and EDXRA Approx- imately 50 of the fibers analyzed by SAED could not be identified due to ambiguous diffraction patterns The remaining fibers which were identified indicated the presence of chrysotile 30 and forsterite 20 The presence of fibrous forsterite was probably due to the dehydroxylation and recrystallization of chrysotile as a result of high temperatures 1,2 650 encountered during braking Some of the fibers which revealed ambiguous diffraction patterns appeared to have crystalline structures similar to both chrysotile and forsterite probably a transition inter- mediate while others were too small for diffraction analysis When EDXRA was performed on the fibers confirmation of the SAED analysis was made for the chrysotile and forsterite fibers Some of those fibers which gave ambiguous SAED patterns indicated magnesium silicon and iron in various elemental ratios As shown in Table 3 when a fiber size distribution was performed for all fibers observed by TEM a geometric mean length of 1.66 ...mand a geometric mean diameter of 0.14 ...m were determined Likewise for those fibers identified as asbestos chrysotile a geometric mean length and diameter of 1.70 ...m and 0.15 ...m were determined respectively 20 Brake Dust Samples of brake wear dust were analyzed by TEM in the same manner as the air- borne samples Identification was attempted on all fibers using SAED and EDXRA Approximately 45 of the fibers analyzed by SAED could not be identi- fied due to ambiguous or the absence of diffraction patterns EDXRA was performed on all fibers observed with elemental analysis being successful on about 70 of the fibers When utilizing SAED and EDXRA many of the fibers observed were positively identified as chrysotile 40 while the remaining were either forsterite 20 or unknown 40 Many of the unknowns were thought to be intermediate recrystallized forms between chrysotile and forsterite In addition a fiber size distribution was performed which indicated somewhat shorter lengths 0.24-5.88 ...m vs. 0.24-10.0 ...mand smaller diameters 0.06-0.29 ...m vs. 0.06-1.0 ...mthan those observed in the airborne samples Table ) Trace Metal Analyses Trace metal analyses were performed on airborne samples collected at Facil- ities B C D I and K with the results reported in Table 4. Samples were analyzed for the following metals lead iron zinc copper and manganese As noted in Table 4 the metals were often detectable n.d. or found in trace amounts The range of concentrations for all facilities were Pb n.d. - 63.3 m 3 mFe n.d. - 1.5 mg Zn n.d. 352 m m g; Cu n.d. - 8.7 mand Mn n.d. - 3.5 m 21 DISCUSSION The human toxicological significance for the inhalation of chrysotile asbestos fibers is well documented and instances of mesothelioma in auto repair workers have been 16,17,18 identified In a detailed examination of 90 union vehicular maintenance workers in New York City with 10 or more years of shop work 29 had decreased vital capacity the percentage increased with age and most markedly after 20 years from the outset of auto work Many of the workers examined showed signs consistent with asbestosis with observed changes noted in chest rays and indication of restrictive pulmonary function The prevalence of these changes was significantly higher after 20 years exposure a result expected after occupational exposure to asbestos Unlike chrysotile the health effects of exposure to forsterite or transition series fibers chrysotile with altered crystalline structures are not well documented In studies studies by Davis Davis and 20 Coniam Coniam and 21 Koshi in in which which fibers of chrysotile chrysotile and forsterite were injected into the pleural and peritoneal cavities of mice the results suggested varying degrees of toxic effects Fiber implantation animal studies conducted by Pott et 22,23 al and Davis et al suggest that the morphology and size of a fiber regardless of fiber type are responsible for its carcinogenicity Likewise Stanton et 25 suggests that fibers 1.5 ...m in diameter and 8 um in length pose the greatest risk in producing pleural sarcomas These studies tend to suggest that the physical morphology size dimensions and to a lesser degree chemical and surface characteristics of a fiber are the determining factor for inducing a biological effect The precise fiber dimensional characteristics required for these observed pathologic responses 22 have been difficult to determine experimentally because of the difficulties encountered in producing fibers of specific size dimensions SUMMARY The TWA airborne asbestos sample results for all facilities were within the 26 current OSHA asbestos standard This standard states The hour weighted average TWA airborne concentration of asbestos fibers to which any employee may be exposed shall not exceed 2 fibers longer than 5 micrometers in length per cubic centimeter of air fibers 5 cc The ceiling airborne concentration to which no employee may be exposed shall not exceed 10 fibers 5 cc However two of four peak sample results for samples collected at Facility I Table ) during the compressed air cleaning of brake assemblies exceeded the OSHA ceiling standard The compressed air cleaning method also indicated the highest overall peak exposures up to 15 cc for all cleaning methods examined When the overall TWA and peak sample results are compared to the NIOSH recommended standard for asbestos 8 of 13 of the TWA exposures for mechanics indicated concentrations exceeding the recommendation This standard recommends a hour TWA exposure of 0.1 fibers 5 mfibers with a ceiling exposure of 0.5 fibers for any minute sampling period 23 Many of the samples collected yielded such low fiber counts that their co- efficient of variation CV was above what is considered reliable i.e. greater than 0.38 Consequently the fiber concentration data are best utilized for comparing exposure variations among the different cleaning methods practices CONCLUSION The results of this and other tudies 1,2 indicate varying concentrations of asbestos fiber exposure to brake mechanics The exposure concentrations are apparently affected by the work practices utilized and the existing environmental conditions and controls at each facility The results of this study show that 8 of 13 of the mechanics engaged in brake service had TWA fiber exposures above the NIOSH recommendation however all TWA exposures were below the OSHA standard Furthermore when samples were analyzed by TEM only 30 of the fibers observed were identified as asbestos with the remaining fibers being categorized as forsterite 20 or unknowns 50 As a result of the TEM analysis the interpretation of the asbestos concentrations as determined by optical microscopy is questionable The analysis indicates that actual asbestos fiber concentrations 5 ...m length are often less than those reported see Table 2 However this does not preclude the possibility of high airborne asbestos fiber concentrations when all fiber size ranges are considered As determined analysis this 28,29 by the TEM analysis in this study and from other reported studies a significant number up to 100 of short fibers < m in length are always 24 studies present see Table 2 Likewise some epidemiologic have indicated health risk exists for asbestos fibers 5 ...m in length that a potential Additional supportive evidence has been shown from the studies which various size fibers were implanted in results animals of animal 22,23,24,25,30 22,23,24,25,30 These studies concluded that the physical morphology size dimensions and to a lesser degree chemical and surface characteristics of a fiber are the determining factor for inducing a biological effect The mechanics surveyed during this study were either time brake mechanics who performed only brake maintenance service and may have serviced to five cars per six days a week or mechanics who undertook only one up brake job per week Regardless of the number of brake jobs performed per work shift the TWA fiber exposures were similar for all the mechanics surveyed The exposures to mechanics who performed time brake work were not significantly higher than the exposures for those who did much less brake servicing Conversely the short 3 term minutes peak exposures encountered in this study during the dust clean of braking assemblies were often higher when compressed air was used All of the cleaning methods surveyed except for vacuum cleaning had peak fiber concentrations that were near or above the recommended ceiling exposure level of 0.5 fibers However the com- pressed air cleaning method was the only type which approached and in two cases even exceeded the OSHA ceiling exposure limit of 10 fibers These that brake mechanics are at a higher risk of airfindings strongly suggest borne exposure to asbestos fibers during the cleaning of brake assemblies 25 except when the vacuum cleaning methods are properly utilized The peak fiber exposures found for mechanics during the cleaning of brake assemblies were higher than most of the TWA exposure concentrations However there is some question as to the accuracy of the fiber counts from the analysis of the peak samples since the number of fibers counted were small resulting in a large coefficient of variation RECOMMENDATIONS The data from this study suggests that a potential for airborne fiber exposure exists during brake servicing operations principally during brake assembly cleaning While the fiber exposures reported do not represent 100 asbestos fiber a potential health hazard still exists since at least 30 of the fibers are asbestos Also animal studies suggest that fiber shape and size may be more important than chemical nature in terms of biological activity Further- more the possibility exists for exposure to a much higher asbestos fiber con- centrations for fibers 5 ...m length Since there is no known safe asbestos fiber exposure level and as clinical evidence suggests from a study of union vehicular maintenance workers in which over 25 had evidence of ray abnormalities consistent with asbestosis it would seem prudent to conclude that a potential health hazard exists during the performance of brake maintenance operations Therefore it is recommended that appropriate control measures for reducing exposures especially during brake assembly cleaning be instituted at brake maintenance facilities This would best be accomplished by 26 , using an appropriate vacuum cleaning system to remove all dust from brake assemblies and drums Above all any blow of brake dust by compressed air must be eliminated To further protect the health of the brake mechanics it would be advisable to initiate a personal respiratory protection program would include the wearing of NIOSH approved respirators for asbestos a This program for proper fitting and a routine maintenance program for the cleaning and replacing of respirator filters As the exposure data indicates it would only be necessary for mechanics to wear respirators while performing brake service In order to minimize asbestos dust exposures to vehicular mechanics performing brake and clutch maintenance NIOSH has prepared guidelines Recommended Procedures for Asbestos Brake and Clutch Servicing see Attachment ) to be utilized during these types of work tasks 27 REFERENCES 1. Lorimer W.V. Rohl A.N. Miller A. Nicholson W.J. and in Selikoff I.J. Asbestos Exposure Brake Repair Workers in the United States Mt. Sinai Journal of Medicine 207-218 June 1976 National 2. Occupational Hazard Survey U.S. Dept. of Health and Human Services Public Health Service Centers for Disease Control National Institute for Occupational Safety and Health estimate April 1981 Stanford Research Institute 712.1000C October 1977 1976 Chemical Economics Handbood Much of the historical information on the development of fricition products was obtained Mount Sinai School of from interviews by Dr. William J. Medicine with Edward W. Drisane Nicholson Friction Materials Standards Institute Paramus N.J. Harry H. Wagner Jr. Molded Materials Co. Ridgway Pa Keasbey and Mattison products catalog 1926. Ambler Pa Friction materials on automotive brakes Fleet Owner August 1963 Carroll W.G. The manufacture 414-417 August 1962 of brake linings British Plastics Anderson A.E. and R. Unpublished notes Gealer Ford Motor Co. Detroit MI White Andrew J. Brake Dynamics an inspection station level Motor Veh Chapter 11 463 4721968 introduction to brakes at Resh of N.H. Lee N.H. the 10. Rohl A.N. et al Asbestos exposure during brake lining 11. U.S. Code of Federal Regulations Title 29 part 1910.1001 U.S. Department of Labor Occupational Safety and Health Administration Occupational Safety and Health Standards 12. Taylor D.G. 1977 NIOSH Manual of Analytical Methods Volume 1 CAM No. 239 Publications No. 77-157 2nd Edition 13. Zumwalde R.D. and Dement J.M. 1977 Review and Evaluation of Analytical Exposures Methods for Environmental Studies of DHEW NIOSH Publication No. 77-204 Fibrous Particulate 14. Taylor D.G. 1977 NIOSH Manual of Analytical Methods Volume 1. CAM No. 222 Publication No. 77-157 2nd Edition 15. Taylor D.G. 1977 NIOSH Manual of Analytical Methods Volume 11I S186 341 366 Publication No. 77-157 2nd Edition 28 16. Newhouse M.L. and Thompson H. Mesothelioma following exposure to asbestos in the London Med 261-269 1965 of pleura and peritoneum area Brit J. Ind 17. McDonald tumors in A.D. et Canada al Epidemiology of primary Cancer 914-19 1970 malignant mesothelial Greenberg 18. M. and Lloyd Davies T.A. Mesothelioma Register . 1967-1968 Brit J. Ind Med 91-104 1974 19. Bader M.E. Bader R.A. Teirstein A.S. Miller A. and Selikoff I.J. Pulmonary function and radiographic changes in 598 workers with varying duration of exposure to asbestos Mount Sinai J. of Med 492-500 1970 20. Davis J.M.S. and Coniam S.W. Experimental of Heated Chrysotile Asbestos and Automobile into the Body Cavities of Mice Experimental Volume 19 pp 339-353 1973 Studies on the Effects Brake Lining Dust Injected and Molecular Pathology 21. Koshi K. Hayashi H. and Sakabe H. Studies on Serpentine Minerals in Heat Volume 7 pp 66-85 1969 Biological and Mineralogical Treated State Ind Health 22. Pott F. Huth F. and Friedricks K.H. Tumorigenic Effect of Fibrous Dust in Experimental Animals Environmental Health Perspectives Volume 9 pp 313-315 1974 23. Pott F. Dolgner R. Friedricks K.H. and Huth F. Animal Experiments Concerning the Carcinogenic Effect of Fibrous Dusts Interpretation of Results Considering the Carcinogenesis in Humans Annales d'Anatomie Pathologique Paris 1976 Volume 21 pp 237-246 24. Davis J.M.G. The Fibrogenic Effects of Mineral Dusts Injected the Pleural Cavity of Mice British Journal Exp Pathology Volume 53 pp 190-201 1972 into 25. Stanton M.F. Layard M. Tegeris A. Kent E. The Carcinogenicity of Fibrous the Rat in Relation to Fiber Dimension 587-603 March 1977 Miller E. May M. and Glass Pleural Response in J. Natl Cancer Institute U.S. Code of Federal Section 1910.1001 Regulations Title 29 Part 1910 Leidel N.A. Bayer S.G. Zumwalde R.D. and Busch K.A. NIOSH Technical Report NIOSH Membrane Filter Method for Evaluating Airborne Asbestos Fibers DHEW NIOSH Publication No. 79-127 February 1979 29 28. Bayer S.G. Zumwalde R.D. and Brown T.A. Equipment and Procedures for Mounting Millipore Filters and Counting Asbestos Fibers by Phase Contrast Microscopy Available from U.S. Department of Health and Human Services National Institute for Occupational Safety and Health 29. Gillam J.D. Dement J.M. Lemen R.A. Wagoner J.K. Archer V.E. and Blejer H.P. Mortality Patterns Among Hard Gold Miners Exposed to an Asbestiform Mineral Annals of the York Academy of Sciences 336-344 1976 Rock New 30. Stanton M.F. Carcinogenesis 1969 Blackwell R. with Asbestos and Am Miller E. Experimental Pulmonary Ind Hyg Assoc J. 236-244 31. U.S. Department of Health and Human Services Public Health Service National Institutes of Health Asbestos An Information Resource DHHS Publication Number NIH 79-161 May 1978 30 cswrqgdayduesMt aUN [TOA O9L 992 SY gel = 3250INSdXy | | =f | | | | | | | | | YML atdwesawtyLCut) O8e cer Lee "6 | | ff { | | [ | | | | punorsyg /sxteqd PER) eloro o1'o g0.o0 <t*o | || | 29% y | tez zzz | 7070 c00 8c8 VOL oce OzL vee 062 9G || | | || | O oly c8E oot O9E ove S6E BLE | || | 0O0o Lovo Lovo for.e goo 1o o |f | i | || i || | Sampleay aun dures [OA 709 99 96S O4s 989 9 96 76E z09 269 BEL ote z69 ORY Fiber | I Mechanic Mechanic eyerg } | | f[ | | | { | | | | | Air Peak Peak Sample Sample Fibers | | | <82 862 Ole Exposures Sample /szeqra 180 00 | 34 34 | | C8 . z1 0 oT.o 61 00 oro || | * Sample cot Background Background Background TWA Exposures ** Time Time | | Volume Volume Volume | L00 020 61 O 708Z"0 veo. wo 100 , | || ayduwes BUNT OA 20 o 9 Ly o 7 2.5 2.5 crot o 8 < eS s J| | on o-s < s zl 9ev o 9 o 9 ST 81 oz 91 91 91 . | 14.54 atdurs awI 30 ost gc 9E 5.3 5.3 09 0.19 0.19 oe 270 SY o < Ost OeL 0.13 ost ost O4S 94 009 188 188 oct ajtdwesg Yead || {|| | | | =| | | | | || | | | | | | IL |G aty 45 72 1 Ot02 69 Z 98 2 0.08 0.08 oT o ct 343 sto 9O 686 0.04 0.04 79? Zze B0231 *0 462 462 <00 /saeqra paTdues | ||| |] | JO l# lf T# T# T# TH 0.07 0.07 <# 283 T# cH cH 0.03 0.03 If t# 222 222 T# 444 444 {TH a kot asvtuws dug180 2Tueyo druvyoa oTueyo 2 DTueYyoN DTURYON 0.20 0.20 OTUEYOW 197 2TueYoay DpUeYyON DFUBYIOR 0.7 0.7 2tUeYOR STUEYIOW DPURYOaW 414 DTUeYIaR 828828DrUCyoa| seus 0.61 | vagus Aryproe1g 80 5 5 900005 I1II 540 I I I I 0.07 0.07 i) ] 360 ) a q 720 i) seu . qareug - 7 ~ ~ 120 ity ATy ity 16 ay ATV aty ATTY Ipy ity TEY aty FIV wy eqa30g ue yee 756 756 PUTLITD pasa pasa 16 pasa 240 pasa ISEW IST 480 ISTW 0.01 0.01 qsnig ysnig 378 378 arnbs unm tbteh 120 pasiduo9 pasidung 0.10.1 pasizduoy 240 pasiduc) idus) idungidung iduing 5 warps rowedIWaATOS Wosa}ypos iuWodapos 41gA1q 29M 10% 204 Tay pynbiy wnoea ec, ee Table 2 Comparison Air Sample Results For Fibers Between TEM and Optical Microscopy Analysis | Optical Microscopy Transmission Electron Microscopy | | 5 ...m in length 5 ...m in length | Total Fibers % Fibers | | fibers | | 0.54 | 6.0 | 0.58 | 1.18 | 0.13 | 6.84 | 5.59 | 0.82 | 0.01 | 0.01 fibers | 0.25 | 5.97 | 0.17 | 0.67 | 0.10 | 0.07 | 0.33 | 0.02 | 0.0 | 0.0 : ! fibers > um in length | | | 0.50 | 50 | | 11.33 | 53 | | 1.01 -| 17 | | 2.35 | 29 | | 0.74 | 14 | | 0.43 , | 17 | | 0.39 | 83 | | 0.02 | 100 | | 0.11 | | 0.0 0 | | 0.02 | 0.19 | 2.72 14 | | 0.38 | 0.16 | 0.48 | 33 | | 1.44 | 0.0 | 0.08 | ) | 0.01 | 0.0 1.43 0 | 0.26 | 0.09 0.09 100 | | 0.24 | 0.04 | 0.16 | 25 | | 0.06 | 0.0 | 0.0 | 0 | 0.12 0.01 | 0.01 | 0.0 0.01 | 100 | - 0.03 | 0 | | 0.03 | 0.0 | 0.0 | 0 | | 0.0 Blank | 0.0 | 0.0 | | 0.12 | 0.42 | 0.86 | 48 | 0.17 | 0.10 | 0.20 | 50 | 0.18 | 0.14 | 0.43 | 33 | 0.06 | 0.05 | 0.15 | 33 | | 0.12 | 0.50 | 0.73 | 68 | | [ | L * Note Fibers counted by TEM represent asbestos fibers onol nly y 32 D1AVawoDH saogd or 672 eorz Sovl Pas | || | | | | || || | | | | wi ueay oLt 99 T Brake Fiber DEAyewoa = ~ y suay | 1 | =| | | =|. | | | | | ||. | 94" ort-7z"0 Fiber 8"S-47Z0 Dev 19qTYy asuey Diametr | | | Range Range Range | | | | | | | Std Std 2.36 sioyrtd 8 raquny Ist ezs_ 601 jo |||||| ||||| dtayewog 1.53 eqeg Aad Only 0.6-0.18 0.6-0.18 0.10 Es" Fibers pas | | ||| | Dust Only 1.53 wi 3sng fiber fiber data detrmined by Al Al Transmion aye1g | | =| | =| | =| | = 8T*0-90 6z*0-90 oT ot elep 19qig adsuey -90O -900 ezTs | |||| 19qTFz UV SI9sfta 1st ezs_ 601 doquan hh jo 239I0N | | | | | | | | | | | | | | | | (Ajug (ATUQ setdwesSszeqty setdweg asng saqty asng (s18qTd exeig axe1g (s1aqid auioqt soiaqsy eurogit LIV AIN soiaqsy ALA LIV | Analyse 900 govo 7070 Metal - uy - - "a N - - 700 voro E070 Trace of =| | | | | | | | | Lv N.D Exposure0N..D2.N.D 7 sakjeuy Analysi Recomnde 1deL Not 82SvlRecomnde x0'OT Not 19.5 zo- < 0 zo 2.3 24.9 19.5 1.2 a N 1.4 - 0.8 zo) 1.5 1.8 | | CO: | 6| | | | YT 0.3[ | w/t < 0 Ceto 6S*0) N.D. 92 1,452.8 Standard N.D. uz - Cl - OSHA Exposure Standard TeIW 2 0 10,00 10,00 Recomend SIeIL | || | 5,000 Detected Analysis Fume Fume -~ oa tore HSOIN VHSO - - Mists ~zZT -<7t a'N aN | | | | || | | eg 672 g*0 < <9 [ove qd - - - - OS oot -2t Stet #0 G'N aN si| | | | | | | | | | | | | AqtyproegpaAains d rs) a I Dt | | | | | | | || | | | |||| stXyeu SIstq q auwNng aWNY pue pa32970g eptxO @PTXO s3asng IO-N UoIT DUTZ iasdoyn BUITOD *AN vx x, yxnx 34 ATTACHMENT I RECOMMENDED PROCEDURES FOR ASBESTOS BRAKE AND CLUTCH SERVICING The National Institute for Occupational Safety and Health NIOSH has con- ducted research on dust exposures which are generated during brake and clutch servicing Based on data demonstrating the potential for significant asbestos exposures during brake and clutch servicing NIOSH has investigated various work practices which are utilized in reducing asbestos exposures These inves- tigations have indicated that vacuum cleaning systems to be the most effective method for minimizing asbestos dust exposures during brake and clutch 1 servicing servicing Vacuum cleaner testing testing have have demonstrated that units these units operate reliably within design specifications Therefore NIOSH recommends vacuum cleaning as the primary method to be used for cleaning of asbestos dust during brake and clutch servicing operations The following are additional procedures recommended by NIOSH to minimize asbestos dust exposures 1. Where possible an area shall be designated for brake and clutch repairs and servicing Entrances into this area shall be posted with the following asbestos exposure warning sign printed in letters of sufficient size and contrast to be readily visible and legible Asbestos Dust Hazard Avoid Breathing Dust Wear Assigned Protective Equipment Do Not Remain in Area Unless Your Work Requires It Breathing Asbestos Dust May Be Hazardous to Your Health 35 2. Dust shall first be cleaned from brake drums brake backing plates brake assemblies and clutch assemblies using an industrial type vacuum cleaner equipped with a high efficiency particulate air filter system greater than 99efficiency for 0.3 ...m diameter aerosols After vacuum cleaning any remaining dust shall be removed using a water dampened cloth or rag Under no circumstances shall compressed air or a dry brush be used for cleaning If vacuum cleaning equipment is not available the wet brush cleaning method may be used until a vacuum cleaning system in obtained Where wet brushing is necessary for cleaning a NIOSH certified respirator approved for asbestos shall be worn 3. During brake pad grinding riveting and punching operations local exhaust ventilation and dust collection systems shall be designed installed and maintained in accordance with the American National Standard Fundamentals Governing the Design and Operation of Local Exhaust Systems ANSI Z9.2 - 1977 to meet the asbestos airborne exposure standard 4. During clutch servicing a NIOSH certified respirator approved for asbestos shall be worn during the removal and cleaning of the clutch pressure plate and housing assembly and during installation of the new clutch assembly Whenever possible cleaning shall be performed with an HEPA vacuum system as described in 2 above 5. All table and floor cleaning in areas where brakes and clutches are repaired shall be done with the HEPA vacuum cleaner as described in 2 above Grinding and riveting machines shall also be cleaned with such a 36 vacuum cleaner and the remaining dust wiped with a water dampened cloth A NIOSH certified respirator approved for asbestos shall be used during this cleaning If not in effect a respirator program shall be established in accordance with the Occupational Safety and Health Administration OSHA Standards Title 29 U.S. Code of Federal Regulations CFR Part 1910.134 Attachment 2 HEPA vacuum cleaner filters containing asbestos dust cloths or brushes used for wiping brake and clutch assemblies and all liquid used for wet brushing shall be disposed of in accordance with U.S. Environmental Protection Agency EPA regulations These regulations state that the asbestos waste shall be disposed of in sealed impermeable bags or other containers at a disposal site which meets EPA criteria for asbestos dis- posal Also the waste containers shall display the following warning label or tag printed in letters of sufficient size and contrast to be visible and legible Breathing CAUTION Contains Asbestos Fibers Avoid Breathing Dust Asbestos Dust May Cause Serious Bodily Harm The EPA regulations for proper asbestos waste disposal are detailed in Title 40 CFR Part 61 Subparts A and B. 37 8. A NIOSH certified respirator approved for asbestos shall be worn during removal of vacuum bags which contain asbestos dust 9. Consumption of food and beverages shall not be permitted in work areas where asbestos exists An area designated for food consumption shall be separate from the work area so as to provide maximum protection against asbestos dust contamination 10. If the employee is exposed to airborne concentrations of asbestos fibers which exceed the OSHA ceiling level the OSHA requirement regarding special clothing change rooms locker etc. as detailed in Title 29 CFR Part 1910.1001 D shall be followed The current OSHA asbestos standard is as follows the hour weighted average TWA airborne concentrations of asbestos fibers to which any employee may be exposed shall not exceed 2 fibers longer than 5 micrometers in length per cubic centimeter of air fibers 5 The ceiling airborne concen- tration to which no employee may be exposed shall not exceed 10 fibers 5 m OSHA in 1975 proposed an hour TWA of 0.5 fibers 5 mwith a permissible ceiling exposure of 5 fibers 5 cc for any period not exceeding 15 minutes NIOSH currently recommends that the TWA exposure to asbestos be 0.1 fibers 5 cc with a ceiling exposure of 0.5 fibers 5 cc for any minute sampling period 38 NOTE Strict adherence to the above procedures should minimize exposures to employees during brake and clutch servicing These recommendations are based on the results of research conducted by NIOSH Prepared By Division of Surveillance Hazard Evaluations and Field Studies National Institute for Occupational Safety and Health Cincinnati Ohio 39