Document 7RGxjB89oyz9Jr112Ky16k5qa

FILE NAME: Ford (FD) DATE: 1970 DOC#: FD027 DOCUMENT DESCRIPTION: Journal Article - Asbestos and Asbestosis - The Annals of Occupational Hygiene i-- pJTIntIfps ( t EXHIBIT J A B - 182 The Annals of Occupational Hygiene AN INTERNATIONAL JOURNAL PUBLISHED FOR THE BRITISH OCCUPATIONAL HYGIEN3 SOCIETY AUTHOR/CONTENTS U ST Volume 13, 1970 i 1 Pretacb NUMBER 1 D. E. Hicxish: Exposure to asbestos during brake and dutch maintenance . W. I Smithex: Asbestos and a s b e s t o s i s .................................................... S. A. Roach: Hygiene standard for .......................................................................... D. E. Hickish and K. L. Knight: Exposure to asbesto* during brake maintenance S. Luxon: Technical implemenution of the new asbesto* regulations . D. Hatch: Possible alternatives to asbestos as a friction material . . M. L. Bentley: Control of the use of asbestos-containing friction materials . G L. Lee: Removing dust from brake assemblies during vehide servidnr-altemativ deaning m e t h o d s .............................................. ... ' ' ' K. L. Knight and D. E. H ickish: Investigations into alternativeform s of control for dus generated during the deaning of brake assemblies and drums . PAGE 1. 3 7 17 23 23 31 33 S. Luxon: Respirators for protection against asbestos . " K. R. ATCU1J5 ind l . Li. Rial: lowards a criterion lor impulse noise m mousssy J. G . Walker: Tem porary threshold shift from impulse noise A. M. M artin, G. R. C. Atherley and T. I. Hemstooc: Recurrent impact noise from 39 pneumatic hammers ................................................................ 69 W. G. N oble: A new concept of damage risk c r i t e r i o n .......................................... LetteHrs. tAo. tBhae mEbdeirtoarn: d R. Butterworth: Asbestos hazard from protecti.ve. clothing 77 M. G reenberg: Asbestos release from battery b o x e s .......................................... 79 81 News I t e m s .................................................................................................................. 83 Book R e v i e w .................................................................................................................. NUMBER 2 A. Black and M . Walsh: The preparation of bromine-82 and iodine-131 abelled poly styrene microsphercs with diameters from 0-1 to 30 m icrons..................................... R. M orley and S. J. Silk: The industrial hazard from nitrous fumes . PAGE 87 101 R. A. Bentley and I. Bergman: Candle or oil soot as a cause of pneu.no niosis in coal A,, . O'*". Hn. Voi. IJ. p. I. P*"0" * n n - Printed In O r t Britain PREFACE Exposure to Asbestos during brke and clutch maintenance THE PAPERS which follow were originally Central Office, Ford M o to r Co Brentwood, of the Conference was Dr G. H. Chanmng, Chief Medical umcer r of Britain, who opened the proceedings by outlining the events wh.ch had led to the arranging f the proposed Asbestos Regulations by the Department of Em ployment and Productivity had r a i s e d p r e m i s e s and * ^ ^ r r u W acome within the requirements of the Regulations. There was a general desire that the subject should be investigated, and any n e e w y Te^diT m easures sought, in advance of the advised and servicing procedures modified where this might be necessary., lnvesuga t o W e n made by .he Industrial Hygiene Units of U 2 " ' tion, and of Ford of Britain, and their findings would be reported to the m ating. These would be preceded by papers on the medical aspects' of and later in the programme there would be papers indicating po the problems involved. E> H|CKISH Ann. Occup. H rt' Vol. 1). p p .--J . Per*mei> h tt* 1970. Printed in C r u t Britain ASBESTOS AND ASBESTOSIS* W. J. Smither Group Medical Adviser, Cape Asbestos Company, 114 Park Street. London W.l. THE FORMS AND USES OF ASBESTOS Commercially important asbestos fibres fall into two main groups. The first of these is chrysotile, and the second comprises the amphiboles. Both groups are fibrous silicates, but they differ in geological origin, in chemical composition, in molecular structure, in fibre size and strength, and in other characteristics. Chrysotile, white asbestos, comes from many different places. There are slight ciemical and physical variations in the fibres from different sources, but basically all have the same molecular structure. On the other hand, the amphiboles comprise ai least three separate types, whose molecular structure is very similar, but whose cnemical and physical properties differ more widely. Amosite (amber) and crocidolife (blue) are of commercial importance in this country, whereas anthophyllite is a Finnish fibre not used here.,- . . The relative amounts of each fibre in world production is shown in Fig. 1 and the areas of main use in Fig. 2. Asbestos Annuo) world ou tput -3 ,0 0 0 ,0 0 0 ton* ---------------------- -- C h ry s o tile (white ) . 2 ,8 0 0 .0 0 0 tons 93% C ro c id o lite (blue) (South Africo) 110,000tons 31% 1 ----------- r -------------------1 A ntlio phyllite (F in la n d ) . I0.C00 tons Amosite (South Atnco) * 9 0 ,0 0 0 ton* 3% Canada USSR S Atnco USA Europe Others 1,250,000 7 3 0 ,0 0 0 2 5 0 ,0 0 0 10 0,00 0 1 0 0 ,0 0 0 3 5 0 ,0 0 0 T * Fio. 1. World production of asbestos. 4 W. J. Smithir Asecsios Annuo! consum0lion-3,OOO,OOO*ons When it it used O lh e rs Belqiu" H o ly Fionce JAPAN UK Germony Chrysolite Others USA Southern A fric a Where <t i t mined USSR USA USSR Conada Blue C ro cid o lite S Africo Am otite A n th o p h y llite I S.AInco j Firlond In ,. 2. Areas of use of asbestos. The dillcre! characteristics of asbestos fibres dictate their uses, their applications and their mode of packing and handling. For example, amositc can be pressure packed and palletized, whereas chrysotilc lends itself more readily to containerization. Ily far the greatest use of chrysotilc is in the asbestos cement industry. Amosite is used mainly in insulation and building products. Crocidolite, due to its excellent acid resistance, finds its major application in the manufacture of .battery boxes in this Ce-ioTP.y'. T t I- ~h Thu pdc-h-'Yuli u) UtJftVfJ. ' /Ilsi'CliihU Asbestos and asbestos v ~ it can be said that current friction materials, whether they be disc brake" pads, passenger f ant[ ^ e n d f o ' f de^lopment!1p a r iic u lS Sow 'contaifapproximately 40 per cent asbestos, and newer m^ cs ca" h ,, estimated that more and more passenger earn produced .he U.K. *.U m mture be equipped with disc brakes, particularly on the front wheels. t h e b io l o g ic a l e ffe c t s o f a sbesto s The variation esisting in the bio,ogical[effects of ^ fs being investigated. The role of trace elements and contam.nants assoca.ed are conhned ,0 .he lung apd .he pleura or ^^ " nnha.ed in fair,, high eoneen.ra.ions . . -- period of time, may cause fibrosis of the lungs. This d.sease, called ast* S Z rists of thickening of the lung membranes with resultant st.ffemn; o[ d interference with oxygen uptake. The interference w.th gas tr*n*'er the shortness of breath which causes the disability associated with asbest s,s- The amount of exposure required to produce fibrosis o f thc plf "raL ^ o r t c r less calcium deposition in the scars, is more debatable. may . ' In concentrated exposures, particularly in youth, leave th.s ma;k P "nl^ " ;v `n any event this particular effect of asbestos inhalation causes little or no disability in '^E xposure to asbestos may lead to further complications, e.g., of the lung, or, rarely, to malignant changes in the pleura or ^ " mesothelioma. Cancer of the lung has been shown to be more common in asbes workers who smoke, just as it is in the general population uncommon throughout thc world, but in some areas they have been ^ o 'a ^ more frequently with exposure to crocidolite than to chrysot.le, amosite or an' hcPhj ' h^ The reasons for this are at present obscure, but arc being sought intensively by investigators in many different countries. Am . Ocnp. H rt. Vol. I). pp. 7-15. Ptrpunoa T ttu 1970. Printed ia Great Briuin 1 HYGIENE STANDARDS FOR ASBESTOS* S. A. R oach London School of Hygiene and Tropical Medicine, Keppel Street, London W.C.l. As long as there is any airborne asbestos dust in the work environment there may be some small risk to health. Nevertheless exposure up to certain limits can be tolerated for a lifetime without incurring undue risks. A hygiene standard for asbestos was published in the U.K. by the Ministry of Labour in 1960 and was taken from the annual list of Threshold Limit Values of the American Conference of Governmental Industrial Hygienists (ACGIH) (Committee on Threshold Limits, Annually). The British Occupational Hygiene Society formed a Hygiene Standards Com mittee in 1965 to advise on hygiene standards. This Committee recomm-mds the use of the ACGIH list of standards and supplements this with critical examinations of ACGIH and other standards considered unsatisfactory by British workers. The Hygiene Standards Committee has expert Sub-Committees, each of w iich is con cerned with a specific standard. There is a sub-committee on asbestos dust in air, one on trichloroethylene vapour and its urinary metabolites, one on airborne vegetable dusts in the textile industry, another on noise criteria for hearing const rvation and two new ones are coming into being; on cadmium oxide fume and silica dusts in air. It is important to take into account the economic consequences of any recom mendations made as well as the benefits to health, and this is one reason why on each of these Hygiene Standards Sub-committees, scientific and medical experts from industry are included. The value of a standard rises in proportion to the number of people who become protected by it. A particular advantage of direct industrial representation on hygiene standards committees is that the industry more readily identifies itself with the standards recommended. The Hygiene Standards Sub-committee on Asbestos, under the Cha rmanship of Professor Lane, has developed new hygiene standards for airborne chrysotilc dust (L ane et a!., 1968). These were based on the results from a medical ind environ mental study at an asbestos textile factory in England, in which investigations were made on 290 of the men employed at this factory in the period of 1933-1966. The Sub-committee considered that the degree and nature of the risk associated with the standards should be specified and the method of the derivation of the stan dard from the data presented should be described in detail. It was also considered that the standards should give prominence to the gradually increasing risk in relation to the concentration rather than to the single figure threshold concept. Open recogni tion should be given to the possibility that people might be adversely affected, even This paper was originally presented at a Conference on Exposure to Asbestos during Brake and r*. ........ . I. .1.1 f............* rrrar OAO S. A. Roach supplemented with medical x*m^ V " J ailable t0 the Sub-committee, and from the It was evident from the data conccntration is held constant the prevalence earlier American experience, that whc. lest duration of exposure. Over o asbcitosis was highest mm ng hosc w t ^ ^ w asbcsl0s,s. However, a period of lime, dust cumulates ." t h e ^ > E cxamp,e> by being dissolved Con som of the dust is rcmo^ ^ 2 c s amoved and exposure is limited acxordmgly. scqucntly. if * assunicd that none , ^ problem of relating prevalence with centration. ^ r -- - . n bad been measured at the textile factory con over periods from 10 years to 33 yean. ^ fibre ycars/cm., that is, the product The exposure of an individua \ P ^ e oscd during working hours and his of the average concentration o w was developed relating the prevalence of * `hiS THC PrindPlCS " ^ tWS" line (Fig. 1). There is a dose ogressively higher doses, .he response by the threshold A. I f response may be real but merely progresses correspondingly. ^ sensory manifestations. A still higher undesirable. A higher ^ sienifledbi10Bofeo ' y ,,,,,,logical changes and overt chmcal "''The degree of response may be conccitwl ^ ^ ^ T c w M be chosen linnous scale starting at rero, an ^ ta Fig , T ,,e dose-response relation- to linearise the relationship e ' line anli poipt here the line `' i r r s a t , ; ; ~ S : r p r a c t i c e to allow lb, the inevitable occasional excursions of dose above the " " TM ^ E f b c t . ,, ,, ,, ,, ,, with absolute certainty Doses which give zero respoi ' limited. A response which can since ihc sensitivity of measurements o r P Jo,, shown as threshold jus, be detected in a man corresponds to " t o and h g As w,,, B on Fig. I. Also, one n o t of , dose-response line varies ? oncTndividua* re Each m an', dose-response line ,s dilferen, with a Hygiene standards for asbestos Individual rttpoM* to dot Dot Fig. 1. Individual response to dose. lifferent threshold dose and a different slope. A particular population wider study s represented by a family of dosc-rcsponsc lines centred around the m e for the lVC]irfa rea" population the threshold dose will vary from one individual to another ibout an average value, as in other medical norms. It is to be expected tnat the size frequency distribution of threshold doses would be a hump-shaped curve tailing away on either side of the central value, as shown in the Fig. 2a. . In a real Acid study it is established whether a man has or has not bem affected. Exactly when or in what concentration he first developed the characteristic responsems usually not known. A graph showing exposure against the total number of people affected by it would be a cumulative sigmoid curve, illustrated in Fig. 2b, derived from the size frequency distribution in Fig. 2a. This tails away down to zero response at Mr An*air quality standard is still associated with a small but non-zero probability of men being affected by the contaminant in question. The risk of people being affected can be made as small as one wishes. Zero risk is the ultimate target and an air quality standard has to be a compromise between the costs of bearing a health risk and the costs of air contaminant control. - . .... A curve was fitted to the data from the textile factory on asbestosis, detected clinically and the exposure in fibre years per cm* of all the individuals under study over their years of employment up to 1966. The bottom end of the fitted curve ;s shown in Fig. 3. The three points relate to three of theigroups of workers studied. The exposure s. A. Roach Population .pon to da. n Hygiene ttandards for asbestos ^ ,, fiKre vears per cm* and the corresponding S - p-- or P - * - > - ~ .s SSIn^ 2 T & % ! 5 Z " i " - r -- * " Bt0 prev,to'" n problem arises when i ^ " t^ n e n r i, xposure. The application` of dust ^ | [ n d control the risk but is unlikely to reduce ather similar hygiene standard will lim d widely used and brings real it to zero. It has to be remembered madc so stringent that the benefits to the community at 1 g . A and se Of asbestos ceases to eost of dost control ,s be economic, production and u s ` The benefits gained by taminant exposure have benefits to the community from the and the associated benefits ate tosh 'a asbtstMis thr0ugh reducing air con- ,, ,, st the possible loss of direct and indirect tj,e material. e^ ^ to thc data was that for One conclusion from the Ps/cm.( it is probable that the risk of being an accumulated exposure of 100 fibr y wiU ^ less than 1 per cent. That affected to the is for example, a com-* ftbros/ens- for 50 years of inch exposure while . s. A. Roach 12 , , r, 10 vears. The British Occupa nt work, 4 fibres,'em* for 25 years, or `O i c" b-commiitee on Asbestos expressed the tional Hygiene Society Hygiene S t a n d a ^ ^ ^ reduce exposures to below view that a proper and reasonab J this level and thereby reduce he nsk f acli asbestosis to less than 1 per cent * For suCh workers who may of those who have a possibly work for 50 years the long average concentration to wh.ch they are \ QT olhcrs, who will be exposed to exposed would need to be less than 2 fibre concentration need not a t o . d u s , a i r for shorter periods. the lo"S J , h a ` 1M fibre years,cnf. be so low. a* long as .h e r exposu e w i1; ^ "" , iods of very high concentration for a The possibility was considered important in determining the risk of few wceL o, less might be d . s p r o p . . ` ^ ,, C o n c l u s i v e and the committee asbestosis. However, were satisfied that the risk m b.^sal* J concentration over 3 months and y . man s accumulated exposure ^ The exposure measured by ma g be converted into p o s u r. measmed wdh a I* In m ',T , below , pe, cent by ensuring that fibre years/enf. on membrane fdter samples can ;moineer the American method, by n m m (w0 ,ns,ruments. Such examining the results of side-by-sida" T tb lie Health Service in asbestos textde comparisons made by the United S,2 " TM of ,00 tore years/cm- corresponds plants have shown that an a c e u m "mpinger methods (A tm , Lyhch and to 15 million particle years.ft y Th hold Limit Value is a concentration of 5 Fanney, 1955). The present Antenca" TM would ,,suit in an accumulated million particles,ff (mp/ft*) **. ,f ? ^ exposure of 250 million panicle years/ft y 'taK. ' hold Umit Values, are a system These American hygiene standards, calle inants jn a convenient form for summarising published informal5' - h y g ie n e . The present American standard for the day-to-day practice of industrial hygic ^ standard for 3 monthly a v e m g e ? H X c V th c r c is p u b lish e d intention to revise the American stan ar * r a T i f which ouih' w given against asbestosis. v . 5 mt)/ft3 was recommended by Dreessen B The American Threshold Limit V alu eo r5 mp/U ^ ^ ^ ^ plants and his co-workers in 1938 a f t e . 1938). Only 3 doubtful where massive exposures to chry those cxposed to dust cases of pneumoconiosis concentrations under 5 m p,tl , ^ j Cny ^ ^ [ us well-marked cases were found above 5 mp/ft*. kinlneical effects of asbestos called attention to A conference held in 1965 on * . ,,commended by Dreessen is inade- the very real probability lhat thc tcction against all forms of asbestos quatc to give complete wor i g limits had been based were inadequate; (SaiM.L, 1965). ^ ^ i f s t u d i e d t y Dreessen and his co-workers were m0[C r i ' a n d thus had insufficient exposure time for much asbestos** Hygiene standard for asbestos W is l f e s `l mu f ^ 68) proposrf changes > h ,8S . X ^ ss t a ^ < > " A," ' ' i : , n " P?ri` n" length are couMed asm * ^ nding lo u t based" occurrence ,C " r r r t ; ; r A s ,o .hen, should be " "sideraon and sen are S e a . signs or a s h e s ,o s is ^ * " I f . h e S n , ,1m . a hygiene sundard has been ,, J 3 monlhs of 2 hbres/emh In an u some,ln.es be above S ,, s 2 m o *. " t E T S i r - * - * i " h n . h S S s /c m - . The o i T s U demons,ra.es non- mum 12 fibres/cm* 8-hr avcragc' W^ h d rcc 0f consistency between the ygte ^ r3 ?^ ? s= 14 or ,,,c W -U wiU be S. A. Roach - 1* " Will continue to dilkr. A c y y conscious 0f the slightest risks to which contaminant control. Also, a coin y ry ,, _ av w- CXncctcd to have different 1, workers may bo p c J .hrough th,r o c c r p a " " " 3 ,he greater. t o * from one which is no,, here t o t o * * prod,,e,, have workers,ha, would The British Occupational H)g.eneboc.ety on Hygiene S u n to d s standards would be suitable for Asbestos has not yet dcci c w 1 ^ th(? sufRcient protection against for amositc or crocidohte dust, aCG1H on th/other hand, make no distinction lung cancer or mesotheliomas Tire ACG1H on the otner , between different types of remembered that the Semor from the use of Asbestos cons.d " d Problems arising date on balance indicated Ute as a cause of mesotheliomas that other types of fibre 'Vh ToTeHie0lh y ^ r s t a n d a r d s for an air contaminant which provide a known dcJce or protection against a health hazard, it is necessary to have a bod)r of data showing the amount of air contaminant to which people are exposed and the corresnondine effects or lack of them in the people. It is also necessary to have a grasp the consequences to industry and users of limiting and controlling emissiMS of the contaminant. Our present information is very imprecise, particularly in tcm s fJ * c practical consequences of specific hygiene standards. In developing recommendat on Tor a hygiene standard, the British Occupational Hygiene Society Sub-committ found that knowledge of the relationship between exposure and risk was not the greatest area of uncertainty. A much more difficult and contentious problem was to decide on w h at, in fact, was an acceptable level of dust control. More information is needed, for example, on the expense of dust control. Where this is done bv ventilation it is imporumt to know what is the minimum amount and wlnt kind oriocal exhaust ventilation and dilution ventilation ,s necessary to achieve a given degree oi air cleanliness in a work place, since costs tend to climb as the cube ^ `Rcsc uih 'is needed to determine the balance between local and general ventilation which produces a specified decree of control at minimum cost. By setting down the ..... ..,,in,, . riinninc and maintenance costs, it becomes possible to is Hygiene standards for asbestos grasp more i n * ,h' " S ^ g t * X =oioUo.as .o ^ m tS T ^ c o sn o r a ^ * . mathemaltcal This does not reduce the chow ^ ^ wi$c judgment in the choice of stan- equation, nor does it avoid the little less arbitrary than at present, dard. However, the judgment can become a u r efer en c es Coi^Mi'nr^oN^rHRESHOii) H p T K S i ( M Hichsh, d . H.. Ioh* , o .. Roach. S. A4 - LANoccp. % r ' S t i . ' arising fr0m the use of asbestos. Memorandum of the Sen,or MllMedicaMnsj**tor * 132^3j ^ n<*on" Schall, E. L. (1965) Ann. N. Y. Acad. Sc. 13Z, 3to. I A w . Oca*. H rt Voi. 1>. PP 17-31. ftrftm o n Prcu l70. Printed in Otet Bri" ' exposure to asbestos d u r in g brake MAINTENANCE* D. E. H ickish and K. L. K night Medical Service*. Ford of Britain, Brentwood. Essex EXPOSURE DURING CAR SERVICING there is little maintenance of passenger vehicle brakes involved at the ^nt.facturers* p mis and therefore an investigation was carried out at the Servtce Bayof >Ford Main Dealer in the Greater London area. This Dealer " ^ a l l y se^ces .0-20 a tr per day. but blowing-out of brake shoes and drums IS ro services It is the blowing-out procedure which is the subject of the study. Air sampling was carried out using membrane filters, the sampling and subsequen assessment being in accordance with the technique described in the Hygiene Standard M c Z s o tile Asbestos Dust, published by the British Occupational Hygtene Society (I9 S8tatic samples were taken by the side of the car (Fig. 1) and composite samples were also taken in the dust-cloud during the blowing-out ]p ro c u re cnlTM 8 ^ the side of the car for the remainder of the sampling period. Normally the mechanic U t e c m to blow .ho dm . away from himself, so this sampling V" ; estimate exposure. Two sampling periods of 45 minutes were used, and (lun"8 first period one Cortina Estate and one Anglia Van received brake blow-outs, and during the second period one Cortina car was dealt with. The results are shown in T ahli I. T able 1. Atmosphere samples durino car brake service Location of samples 1st period Fibres/cm* 2nd period Time-weighted average By car M2 1-42 1- 25 1 1-71 362 2- 55 Dust cloud then by car An estimate of the daily exposure of the mechanic engaged on brake cleaning was obtained by a series of personal samples (Fig. 2), covering an entire workshift, during which brake servicing was carried out on 11 vehicles. The results are shown in Table 2. This paper was originally presented at a Conference on Exposure lo Asbestos durim: Brake and D. E. UlCKISM and K. L. Knight T \ ule 2 Personal samples during car drake service Sample Concentration (fibres/cm*) 1 063 *2> 112 3 021 096 4 c 038 a0 079 Time-weighted average 068 EXPOSURE DURING TRUCK SERVICING Maintenance of truck brakeS ' ^ posure as the servicing is more ^compiex^,a i.h is less. The larger size of wheels and d ro m v m the MmbcMrfvehicles dealt makes u dlfficult ,, po5utt cooU be r the operator to avoid the d u s tc " ^ hcf mpHng was therefore earned out ghcr than that during car maintenance. d f the passenger car a large fleet workshop with equipment similar to that used p sts. . , . , , u. duration were collected during the Static samples, each of appr0*`TMa ' y ti s. at th'e bay adjacent to the one \orning and afternoon periods a r p ' j,ay and in the centre of the t which brake cleaning was earned out, at the next bay. an arage. . m,, nine but not during the afternoon. The Drakes were blown out during the morning, due n csults arc given in Table 3. . T able 3. G eneral atmosphere samples during tru ck brake service^ Location of sample Concentration (fibres/cm*) Adjacent bay AMfoternrninogon 002087 Morning 0 17 2 Bays away Afternoon 007 Centre of garage AMfoterrnninogon 0O4i9l Personal samples were oblnined from Iwo sie,dag. and r t T r f bmle elenning. and !he second period of approsimale^s'hr 'represented'll remainder of .1 sb.fl. The resul.s are shown I Exposure to asbestos during brake maintenance 19 T able 4. Personal samples- truck brake service I Operator Concentration (fibres/cm*) Brake cleaner . 709 during cleaning 008 after cleaning 1-75 Time-weighted average Clutch repair--adjacent bay 2-25 during cleaning Oil after cleaning 0-79 I SIGNIFICANCE OF EXPOSURE LEVELS 1I The Hygiene Standard s i e s t a level of 100 fibre-ycars/cm*. On ^ ' concentrations exceeding 2 fibres/cm*. rlifetime of 50 years, should not be P and the findings are summarized as foUows. somcwhat improbable in the case of ' " S V11" ' Car servicing . j !n ,ue just cloud during actual brake clean - - -- --- " 'S . ' S E d h no, exceeded away from the immediate ^ C1.m ty f aclailf basis> the personal exposure levels are vicinity do exceed the standar . brake cleaner approaches it. in . fleet workshop. brake denning operations I i- --.Aprerilv dIECC dSllV* t h e n a t u r e o f a ir -b o r n e d u s t . ft n ner cent of asbestos, and it was somewhat Brake lining materials contain P n3lurc wcrc scarce jn the air samples rprising to find that particles o a . f dust wcrc obtained by filing fleeted. >" * ' * 2 akc lining material, and a fte r! lined microscopically before a 5 MO-mesh sieve, -here were ex- incineration. Samples of dust wcrc collected . cxamjned in similar manner, im brake drums during car ' * ressed as the percentage of particles which The results of the examinatio together with a result from an cre r,b,ous in nature. b ^ i l o M u H ^ . k e ctenninn 20 D. E. H ickish and K. L. Knight T adle 5. A ssessment of fibrous fractions of dust samples Sample Percentage of panicles seen to be fibrous Sample Sample not incinerated incinerated Drake lining material Brake drum dust Air-borne dust 28 12 3 0 6 16 13 It is dearly shown that the percentage of fibres in the drum dust and airborne dust is much lower than that in the dust formed from the original lining material. Samples of drum dust were examined by Dr S. Holmes, and his tests showed that chrysotilc was present only in trace quantities, or at most at 1 per cent, compared with the original lining content of 40-60 per cent. These findings suggest that there is a change in the physical and or chemical form of the asbestos during its use as a ^ E n S e T w 'e r e made of research workers in the UK and USA as to whether they had observed a similar effect. Lynch (1968) reported that tests on brake testing dyna mometers had shown the presence of few or no fibres in the dust produced from bus and automobile brakes, except under severe braking conditions. In the latter instance, the brake temperature reached 320-370C, compared with the design maximum tem perature of 290-320C, and it appeared that, under these conditions, the binder decomposed and released part of the asbestos as free fibre. At lower bulk lining tem peratures within the normal operating range, the binder behind the surface remains intact. However, the spot temperature at the point of contact between the lining and the drum may be higher than the decomposition temperature of asbestos. The decomposition product, therefore, includes not free asbestos fibres but a different mineral, resulting from thermal metamorphosis. . Holmes (1967) in reporting the analyses described earlier in this paper, com mented that the normal thermal decomposition product of chrysotilc is forstente, a non-fibrous crystalline magnesium silicate. However, our samples of brake drum dust contained very little forstente, but rather were mainly comprised of an amor phous magnesium silicate, which is non-fibrous. Little was known at that time about the structure and composition of this substance. Whilst there was no evidence to sugecst that the material was a health hazard, this possibility could not be dis missed. and animal experimentation has been commenced in the U.S.A. CONCLUSIONS Our investigations show that exposure to asbestos during brake maintenance is not is severe as was anticipated, and in the situations wc examined, the personal exposure of the operators was below the limit corresponding to 50-ycar exposure. It is however recommended that care should be exercised during brake cleaning to avoid inhalation of the dust produced, and the development of cleaning procedures which would reduce air'eontamination is desirable. The present trend towards the Exposure to asbestos during brake maintenance 21 introduction of "ow-line" ic in g a t D eal. wotkt. in d iv id u il" * . , ninMj aimost entirely on brake servicing, emphasises this poent. be engaged . dies have not included maintenance procedures which in- | 0U|he fiJi'ne or grinding of brake lining material, and we would envisage thatthese would give rise to considerably increased air contamination by ch^ S^ ! ...leu attendant need for strict precautions to prevent the inhalation of fibres. REFERENCES c ^ u m , tu. Hvottue S u u u . n m Oecaw^oMgL Hj* Standards for ChrysotUe Asbestos Dust, Pergamon Press. Oxford. Holmes. S. (1967) Private communication. . i d nqfiRt J Air Pollut. Control Ass. 15, 8^- 4,, . Oco*. Hrt. Vot. 13. PP- -J. P n * 1970. Printed la Greet B riuia TECHNICAL IMPLEMENTATION OF THE NEW ASBESTOS REGULATIONS* S. Luxon H.M. Factory p t a t e , ^ ^ THE NEW Asbestos Regulations were signed b , 'Z S g S T - - K -- - .0 bo a. a .C wbicb wd, ievel of 2 fibres,on,-and-. Ss: S S S i r S S S S ^^ s 2 fibres/cm* over this four hour . peak concentrations which will We cannot, however, afford to ignore entire y & concentration not be'excceded during any period of 10 min. i.e. we ^a S ^ f tbC B HSh " referred to above related to conditions in the textile industry and not cnough inforaia- tion is yet available on the relationship between mass of asbestos and fibrc^ un` `n other t r i e s . To further complicate the problem, it is are biologically active and, even if this were known rejection of material not biologically active) would veiy ounts an<j totai material such as asbestos. We, ourselves, are mak.ng mass determinations by X-ray diffraction analysis in in us ri , al change industry, where degradation of the fibres may occur, resulting in a substantial ch ge in size distribution. .__.. e, rv:r ;no Hickish and Knight (1969) have described conditions dur`" 8 ^ c " ^ ng f braking systems. The figures they have quoted are, to a large extent, reassuring in This paper was originally presented at a Conference ^ Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood. Essex. March. 196V. Add. Oeeup. lift- Vol. I). pp. 23-29. Peri moo Prcu 1970. Printed In Great Britain POSSIBLE ALTERNATIVES TO ASBESTOS AS A FRICTION MATERIAL* D. H atch Ferodo, Chapel-en-le-Frith, Derbyshire INTRODUCTION > I have been asked to talk on the possible alternatives to asbestos as a friction material. The facts are that if by "alternative" we mean a new or better fibre which might shortly be available as a replacement for asbestos in conventional friction materials, then I think the chances are so remote as to be not worth considering. This is not to say that if the world supplies of asbestos dried up we would not eventually find a substitute, but it could well be at the expense of a considerable loss in performance, and also at a considerable increase in cost. THE ROLE OF ASBESTOS IN FRICTION LININGS Having started on what may appear to be a rather depressing note, let us examine the reasons why asbestos occupies the role of an almost universal constituent in friction materials at the present time. The first automotive friction linings were made from cotton textile material im pregnated with drying oils which were subsequently cured to form a strip of material which, while being flexible and conformable, still exhibited great mechanical strength. The main function of the drying oil was to protect the cotton from attack by atmo spheric oxygen, which, even at the temperatures reached by early brakes, would have resulted in the cotton burning had its surface been exposed. A second function of the drying oil was to prevent the cotton from fraying under the influence of mechanical abrasion. As brake operating temperatures increased, it was found that cotton started to degrade and lose its strength even though still protected from attack by oxygen. In other words, it suffered thermal degradation instead of oxidative degradation. Around 1910, a technological break-through was achieved when it was discovered that textiles could be woven from asbestos and used to replace cotton, because asbestos neither burns nor loses its strength below about 500C. However, as brake operating conditions became steadily more severe, a point was reached in about the middle 1940's when, despite the continual improvement of synthetic resins with which the asbestos textile was impregnated, further heat resistance was required, this time because the organic part of the composite was proving inadequate. The solution proved to be to mould brake linings from powdered resins, using short fibre unwoven This paper was originally presented at a Conference on Exposure to Asbestos during Brake and ('Mllti'h MiinlrH ftrltl 'I Mmiti'foiul tr/.n 24 S. Luxun S or ; S, kno lodge. a pcn!ul'7 l O Bmindcm "? have concentrations exceeding substantially the level of 12 ' ^ T J a i 'hltcresS'tohear*of the increasing tendency to carry out brake overhauls on i r Kick This dearlv must increase the exposure of particular in- ir X " ` .hay baaoTM * . L.liy a J .p u b la .o .ha opara.or. Catlainly wa should no. ba blowing ou. braka dusl, % ! on 1 lining and the drum. .ampaaa.u,as ganara.ed b , Mahon a . .ha in..faaa ba.waan .ha REFERENCES s r ,r r j : r r r r C Slumlords for Chryyolile VPere?mo" ^ * * S' , Xf7d' t Iickisii. D. E. and Knight, K. L. (1969) Ami. Occur. H)g,, 13. 17. -- *<*> D. H atch t . a n^ihilitv This made possible the sbestos to maintain the necessary strengt an hich mparted greater heat nelosion of heavy loadings of mme-al a TM t ot 0I alone. and did so a, .he esistancc than could be bf xnense of a reduction in asbestos content. point is important in the context ..why can't asbestos be replaced f asbestos substitutes. The qu" b af(S must surely impart sufficient strength? ,y something like glass fibre which, after all of a textile lining is required, i be answer is possibly "it can *lf ^ ^ ' dcrn brakes, the glass fibre melts even ,ut at the temperatures commonly met in mofler , depth below the operating surface. cffcct of mineral and other fillers Furthermore, as a result o iccdcd in today's brake lining, gla inadequate in imparting the necessary extent, of the various types trength and flexibility. The smc t hi/ h havc aPPeared on the market over recent ,f rock wools and mineral fibres< is thc ultimate strength of asbestos.almost .cars. It is interesting to note that no y , but the modulus of rigidity is up to l.rce times that of glass fibre, t.e. V* ^ ical figurcs for other materials cn limes as high, at a value of 30'^ ? d wnat 6o,000 lb/in.* for mineral wool, ire say 100,000 lb/in.. for^teel wol ^ drum brakc linings of normal configura- Thc current situation therefor , vehicles, there exists no substitute for on ,,sed for passenger < * T S S S S i of performance and strength. DISC BRAKE PADS . Kates of energy dissipation contmue to onri w * have now passed the point fof a ,argc percentage of passenger here moulded drum brake linings are d ^ senger car axles arc equipped with ars. In this country, nearly 50 per ce 1J , * J f a wnlury> there seem to be technical lisc brakes, and for the second time in n ^ ^ malerials. It is purely for- tossibilitics of reducing the asbestos luitous that the friction materials us ^ bfakes arc designed to a stronger shape, d sidcraWc thickness, supported, that is, more or less square " The friction material, therefore furthermore, by a metal plate of a q assembly, docs not have to withstand docs not have to stand up to hand!mg dur g ^ * cchanicai strcngth alone, be riveting, and could, from the P 'nt ^ rdnfJ ccment of any kind. There remains, made without a high loading o an(} n order t0 prevent the formation however, thermal shrinkage and therma , percentage of asbestos fibre is still ::?tcn>ile cracks normal to the operatmg s u r asgbestos in disc brake pads retained. Nevertheless, it cannot be_sad that fric(ion materials that some " t o e d c lp o s t.e s coutd ocenr to the hex. - - icchnical and performance grounds. FRICTION MATERIALS FOR CLUTCHES t n hnkes but the development of friction As yet. I have co n fu ted my co"'n'" vi tines. In reecnt years, however, ' ",an" ' Cl"" h' S ^ 27 Possible alternatives to asbestos a friction material transmissions where theclutch^ctoa^im m er^in^ ii^lj^r<1lr ^ n^ j^ 1.0^ to airborne contamination. J hj h ,he sbn. is largely cellulose. -Hus S S r J X iow^erating temperatures, due in turn. ,0 tbe , e t teded at a significant the flrm o f l thin annulus, consists of a number friction material, instead of being m couid be made from asbestos- of buttons rather like disc brake pad , (ceramic-metallic compositions), free material such as sintered metals or can be seen that there d t e l m o u n u 'oftbem os E so T d isc bnikes, and replacement b , other materials ______ tmsnemiggions and some dry clutches. OTHER FACTORS AFFECTING EXPOSURE TO ASBESTOS There are, however, several sidering the exposure to asbestos during brake and clutch m subject of this meeting. The first is that the durability of fnci .at^rials is increasing, ns is the tern* mention these facts not only perature at which they will operate in vchicle miles per year, but because they tend to offset the a d v e r s e bestos in friction materials. The second because they affect the whole chemis stos yScd n friction materials is chrysotile or important point is that the type asbestos or crocidolite, not only in colour, white asbestos, and is different from " u decomposition. The third important but in chemical composition and a s point is that under the influence of hea chrvsotile asbestos decomposes by loss , [Jund ^ c . The process is rather of water of crystallization at a tempera of the asbestos to its degradation slow, taking well over an hour lo con^ ' l 5 ^ i s| licatc materials known as olivine, products. These form a series of iron ies ofmincrals are quite unlike the end member of which is forstente. The non.fibr0us, and in fact, widely asbestos, both physically and ks (basic and ultramafic igneous), occurring as the major part of many t cf asbestos would be converted to One would not expect that a " * * Vere duty such as a fade test, olivine during braking cxccPl u " de[ . but in fact it is exceedingly difficult to t asbcstos in friction material wear pro dctect asbestos in wear products ducts. It has only on rare occasions been p j ^ | q dectron diffraction, selecting by X-ray diffraction methods, and one h cx;stence. This rather surprising fact occasional individual small fibres 1 s 0 h suggests that it is accounted for has been known for several years * * J ^ * TM & " nts 0f real contact between by very high temperatures low as 100'C. the lining and drum or disc, cv rcmains a,fact that very little asbestos W h e th e r th is e x p l a n a t i o n i s c o c . r "- h , ~ i ~ n --- ----------------- survives in the wear products after . 28 D. Hatch penning conditions. As the durability of brakes improves, further reductions will occur in the percentage of asbestos which survives the wear process, because each particle of asbestos is then subjected to more heat treatment. Of the approximately I per cent of asbestos remaining in wear products, a large proportion is ground down during the wear process to much less than the 5 u length at which particles are judged to he fibres. This is easy to understand when one considers that under normal condi tions a lining will lose about one-millionth of an inch of thickness for every 20 ft of sliding. , . Over recent weeks l have had regular tests performed in which employees private cars, and trucks from the Company Hect have been brought into the garage for brake cleaning. The drums have keen removed and in a garage with no forced ventilation, all loose dust has been removed from the drums and back plates by the use of a compressed air jet. As each brake was cleaned, instantaneous atmospheric samples were rapidly taken by a hand-pump from the centre of the dust cloud. Several of the . dust clouds were visibly filthy, and would, in my view, be avoided by the operator; the dust counts taken at the point of maximum dust density were as given in Table 1. T able I. D ust counts during brake cleaning by COMPRESSED AIR-JET Test Non-fibrous Fibre count Fibre count No. above 2 |i 2-5|i Above 5 |i Samples 1 2 3 4 5 6 7 10 min average 2000+ 109 402 607 475 1513 628 181 , , 306 It 21 17 2 5 21 3'7 37 5-3 49 8 2 35 3-2 50 U- -'8 The interesting points from this exercise are, firstly, the ratio of the number of particles of asbestos to the total dust particles of a similar size, showing a very small percentage of asbestos, and, secondly, the distribution of size of the fibrous clement, suggesting that those particles over 5 ;i must have been only just over. 1am not sucucsting for a minute that the practice of blowing out brake drums with a compressed a"ir line is to be recommended, merely that an intense dust cloud of this composition is a lot less harmful than one might think. Unfortunately, at the present time, no corresponding data is available from clutches but one would expect the situation to be better than in brakes rather than worse, because on the one hand, surface rubbing speeds are higher, giving rise to higher point contact temperatures, and on 4hc other hand, wear rates are very much lower resulting in an even liner subdivision in the wear products. Possible alternatives to asbestos as a friction material 29 POSSIBLE ALTERNATIVES TO ASBESTOS "crrlis,o^T^n:nX% Glass fibre Lo * 8 ^ . cost_ i 0w strength-damage to drums. Mineral wool Very low strength-brittle to the extent of limiting m.x.ng pro Carbon fibres Sintered metals 100/Ib currently forecast to fall to l/lb in several years time. Still ten times too expensive. Probably the best possibility eventually, but cost will always be ^ k io K 1 H ,, . V o ,.,, PP.3,-. '" 0 ~ ` B' iUia rnNTROL OF THE USE OF ASBESTOSCONTAINING FRICTION MATERIALS M. L. Bentley Mint, Qeckhealon, York* . INTRODUCTION TH,S paper outlines the measures nature and causes of asbestos, and t control. Particular reference is m sequent handling and machining pe rSSTLTWSLSTTSiSS--. "it is rather less than 40 Inv^onmenlS during the manufacture and sub of friction materials containing asbestos, control of asbestos dust in large Regulations --*ofptople which became law been dramatic, cases of as S i" wcrc introduced and it was also apparent that " " K h i s the three Group, Cape Asbestos and Turner & Ne ' T 2 ^ and thcy fe n c e d and set up the the nature and causes of as.^ St S1.SJ s ' biective.^Since then the Asbestosis Research Asbestosis Research Council wi d rcscarch at Cambridge, Reading and ,,s on -- * -- - - stems from these research projects " J 1 and have been consulted regular y, y lions both in this country and overseas. T tic on the handling of ^ Departments and other orgamsa- ARC has drawn up some Codes of Prac- ARC asbestos dust svas an active pari in the forntu- " bS usc o , its considerable cxpenenM^in^usingJ^bestos^and^as^stos^oducIs itself and its concern that thas'PTM h bj f nl,, !if>i,,g the study of prob- tionalcontntitteeJ" ' * * h" e U^ ,,tns a,,s,ng m the or 8 ,, , ^ ,, , 0 ^ .,..d K n .B ,a l eand This paper w a .o w n a y P ^ . H F w T M,, , h <o<n Clutch Mmntcvtnro hrl.l It 32 M. L. Bentley recently become apparent that some control might be necessary and helping those concerned with satisfying the requirements of the new regulations. This Committee is the Environmental Control Committee of the Asbestos Re search Council and it consists of a number of working groups concentrating on he special problems oi particular areas. One of these Working Groups is being devoted loathe Ikld of friction materials, and has. as its constituent members Small & Parkes (makers of Don materials), Ferodo and Mintex. This Group which has been formed recently, is concerned with the users of friction materials, both at its major customers I t h e brake, clutch and car manufacturers-and also in the replacement and serv.ee flC,d,,s concern has been, first of all, to establish whether or not a problem exists and, if so how big a problem it is. To this end dust counts have been taken both in premises where friction materials are handled and serviced, and at customers premises, by the three Companies principally involved. These tests have been taken by their ow n dust counting teams who have many years' experience m accurate dust measurement. This work is continuing and a picture is being bu.lt up of dust counts likely to be en countered whilst carrying out typical operations during brake and clutch mamtenanw. Analysis of the dust found in brake drums is being earned out also to determine whether all the fibrous dust is asbestos or not. r . In addition to gathering and collating information on a large number of dust rcadincs in various types of service premises, the Working Group is PTMP",n? codes 'o f practice for users of asbestos-based friction materials which will be issued by the Asbestosis Research Council. One of these is for the H a n c e users in factory premises carrying out, in some cases, operations similar to hose carried out in our own factories, such as drilling and grinding, and the other is for the guidance of those engaged in servicing of brakes and clutches. The purpose of these Codes of Practice or Notes for Guidance will be to remind users of die principal requirements of the new Asbestos Regulations to recommend the action that they should take to meet their requirements. The aim is to a` h,cve is after all, the whole purpose of the Asbestos Regulations and the Asbestosis ResJirch Council's w o rk -to reduce concentrations of asbestos dust to a safe level. The long experience of the manufacturers of friction materials in dust control1over a wide variety of operations will enable them to recommend measures ^ types of equipment to help the users to comply with the Regulations and protect the health f ' AfurUi cr^ne of study is being followed to see whether a satisfactory surface scaling agent can be found in order to cut down the amount of dust given off in hand ling a'new lining, even though this amount is already small. It is not possible for us to take dust counts in every service garage in the country and the work of the Friction Materials Group has been directed to dealing with, and Giving advice on, situations which are likely to be typical of those found m service c ir iucs It is, however, the intention to give as much help and advice as possible with ^ `facilities that arc available and requests for help or advice directed to the Asbestosis Research Council will be passed on to the Working Group for action. A m . Orel. H /f. V d. 13. pp. 33-3. Prmon P ria 1970. Printed in Great Britan REMOVING DUSTS FROM BRAKE ASSEMBLIES DURING VEHICLE SERVICING- ALTERNATIVE CLEANING METHODS* G. L. Lee British Leylind, Longbridge, Birmingham PRELIMINARY CONSIDERATIONS Whatever the criticisms may be from an occupational health point of view, few would deny that the operation of removing brake dusts with an air line is efficient in that the total time to perform the task is extremely short. The time required to perform an operation is of vital importance in industry and any process changes will always be judged relative to the time scale. In addition, the effort required from an operative in using the method should be minimal and it is easy to see that the chances of de veloping a technique of cleaning which will reduce dust emissions but at the same time require no more time and effort are extremely slim. Quite clearly, we must concede from the very beginning that some increase in time and effort involved is inevitable. . When viewed under normal lighting conditions, the result of applying a com pressed-air line to remove brake dusts is very dramatic. Unfortunately, mere dramati sation alone is not adequate to describe the emission of dust from a process; more objective methods are needed. The conventional method of evaluating an wnviron- mental condition is the measurement of the appropriate parameter (in this case fibre counts), referring the results to hygiene standards. In experimental work to evaluate dust control methods, simpler, "relative" techniques of measurement have considerable advantages and part of this work is concerned with applying a fairly simple method to define certain environmental conditions which prevail when brake dusts are removed by blowing out with a compressed air line and comparing these with the conditions obtained when a dust control technique is applied. Because the method is a relative one, care to prevent errors from extraneous sources of variation is important. These sources of error are discussed later. - METHODS USED TO EXAMINE ENVIRONMENTAL CONDITIONS When dusts arc released in relatively small quantities it is often impossible to see the clouds under normal lighting conditions. They can be made visible using the Tyndall Beam effect and this has been employed extensively during the experimental work. This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood. Essex. March. I960. 34 G. L. Lee Mass concentrations of airborne brake dusts were determined at two positions by sampling through tared membrane filters. In the first position, a static sampler was placed close to the sources of dust emission. Generally, this sampling position was chosen to be in the area where the results of Tyndall Beam examinations had indicated that the highest dust concentrations were likely to be obtained. Secondly, a personal air sampling device was worn by the operative in such a manner that the sampling head was attached to the wearer's lapel, as near as practicable to the breathing zone. Samples for particle counting were taken, again in the operative's breathing zone, using a Konimctcr, and membrane filter samples were also taken for subsequent fibre counts by microscopy, using the method described by Addingley (1966). Possible weighing errors due to static charges on membrane filters were prevented by weighing in a field of ionising radiation, as described by H iggins and D ewell. The results of fibre counts showed that the numbers of fibres present in the high total dust concentrations obtained when an air line was used were of a low order of magnitude and hence the total dust concentration was used as a relative method to describe the dustiness of the environment. The location selected for the experiments was in a workshop area, behind a glazed partition, and well away from access doors, so that comparisons of cleaning methods were not affected by variations in local air movement. Smoke tests were carried out at each sample period to confirm this point. CONDITIONS OBTAINED WHEN A COMPRESSED AIR LINE WAS USED TO REMOVE BRAKE DUSTS A commercial vehicle brake assembly, after removal of the brake drum prepara tory to cleaning, is shown in Fig. 1. In this particular case, the hub had also been removed for bearing replacement which facilitated cleaning operations. It should be noted that this is not always so and for the majority of our tests the inconvenience of the hub being present had to be contended with. A scries of Konimcter samples were taken during typical operations and also after the process had ceased. The counts for these samples arc summarized in Table 1. Tadle I. R esults of Konimeter samples durino blow-off Sample Number of brake dust parliclcs/5 cm1 Taken at beginning of operation 5000 Taken approx. 20 sec later 4500 Taken approx. COsec later 4000 Taken approx. 30 sec later 1800 Taken approx. 30 sec later 580 It is seen that there is a progressive fall in count as the local dust cloud disperses. The first three figures arc appr3ximate only, the numbers of particles collected being lo o lili'h fo r accurate cotm tine. - I I 35 Riveenmwo*vin*g d--u--st, from brake assemblies during vehicie d ic in g , . A fixed sampling period of some 5 mm _i,n.n for the determination of mass h blowing opcration but concentrations-this being Waning methods. The dust cd- sufficient to cover that required fo assembly gave an equivalent concen S Sy the static sampler Close 42 mg/m*. It is P-bable tration of 114 mg/m* and that f" * than rcSpirable size. The few asbestos that many of the particles gave a concentration of the order 3-5 fibres counted on membrane filter samples g fibres/cm*. a it e r n a t iv e c l e a n in g m eth o d s ALTERNATI ^ hand.hdd extractors to collect Initial approaches wereto try t e J ub a smaU paint brush. Futcd cx' the dust particles removed by h*nd* ^ f ere8re:cctcd because of restrictions which tractors, although reasonably efficient, TM: ^ ^ Both operatives and super these placed upon the work by confining work area--preferring to retain vision were unhappy about * "** flexibility and carry out the work as had prcviously done, wherever the vehicle * clearly required and after some happened to be. P o r t a b l e W ^ d preliminary enquiries, a BVC ind"stn^ powered by a Jh.p. motor and experimental work. It 1 supplied with disposable paper baps in adddi" cloth bag. The p a p a fairly easily before removal, bags are fitted in a manner which To trap any particulates which mig P ,he pape, and doth bags, an ex` aic oullet end of the cleaner, ternal, multi-layer filter was 8 dust particles were passing the Preliminary experiments ,he ext.ro.Uy fitted filter. Sampling .aper and dothbags ^ . " S noparticles P-- " CONDITIONS OBTMrtEDcUS.NOEtxhTeR fVtCAiCioUNUM CLEANER * .he noaale of the cleaner, hand-held as a The first technique lricd, * as "" deoosits were disturbed with a small paint source ofTocal extraction that some dust was escaping brush held in the other hand. Th J are summarized in Table 2. T r 2 R * ULTS OP KONIMETER SAMPLES OUR,NO BRUSH,NO ANO Table 2. Results U)CaL extraCt,on Sample Taken at start of proceH Taken about 1 min later Taken about 2 min later Taken at end of process Number of brake dust particles/5 cm* ___________ _______ 1070 404 426 ! 446 G . L. Lee 36 The fixed sampler in the area of the *** * ^ CONDITIONS OBTAINED USING A MODIFIED TECHNIQUE After sonic preliminary Firstly, the loose deposits of Were rcm0ved, using the smallest surfaces of brake shoes an -nm~nt Heine used as a vacuum cleaner, brush s r * supplied " llt' ' ^ ' -- " " ^ U d e T L ^available materials was then used to r ^ r b ^ b L u f e w t a " d e s '^ d e ^ e e te d b , the deceive methods, as shown in rr. Lt- *5 Tadle 3. R esults oe Konimeter samples duaino modified technique Sample Number of brake dust particles/S cm* Brushing with standard brush Brushing with tubular brush Rag wiping 16-25 20-25 1-5 No fibres were detected and the mass concentrations involved were too low to determine. CONCLUSIONS n e objective measurements made:sem. a useful contribution towar s o ai * blies arc cleaned. The design of P ofpartic.es back into the disposal methods to be ad p d^ Th ^ ^ ^ cle^ ,cr chosen prevents the discharge ,lection jn a paper bagenablcssuitable t o early part of 1968 rccommended for usc until such time as ^ r " * i n g carried out elsewhere in the Motor Industry were known and detailed requirements subsequently formulated. .... Aodingley. I In.t.ins, R. REFERENCES (1966). Ann. occhi. If.t*. 9, 73. _ r ... Diwru.. P. in Instruction Leaflet 3107/A1. C. F. Casella. Am . Oetuf. H rt. Vol. IJ. pp. 37-39. FtrgrooA P n u 1970. Friaicd in O ru t Bhuio INVESTIGATIONS INTO ALTERNATIVE FORMS OF CONTROL FOR DUST GENERATED DURING THE CLEANING OF BRAKE ASSEMBLIES AND DRUMS* K. L. Knight and D. E. Hickish Medical Services, Ford of Britain, Brentwood, Esse* INTRODUCTION T he most usual method of removing the accumulated dust from brake drums and assemblies is by " blowing off" with a compressed air stream. This, of course, generates a dust cloud in which the operator works, proportionate in size to the drum/assembly being cleaned. We therefore investigated two alternative methods of controlling dust generated at a maintenance operation on commercial vehicles, as representing maxi mum likely exposure. Enquiries at the beginning of the investigation indicated that the removal of dust is to allow inspection of the mechanism, rather than being a maintenance procedure j in itself. Our efforts were, therefore, directed towards the removal of loose dust from f the parts of the brake mechanism which needed inspection, rather than achieving ' total cleanliness. The criteria for evaluating the two methods devised were firstly, that the alternative method did not take significantly longer than the method already in use, secondly, that it was not more difficult to carry out, and thirdly, that very little extra equipment was needed. ALTERNATIVE METHODS EXAMINED The alternative methods examined were a vacuum funnel, and a vacuum brush. Vacuum fu n n e l The funnel (see Fig. 1) comprised a steel cone with a connection point at .ts apex for an industrial vacuum cleaner; a flexible skirt, with a draw string attached at its periphery; and a small-bore side-entry for the injection of compressed air. In use, the funnel was secured over the backplate of the brake assembly or over the drum and compressed air was injected to dislodge dust while the vacuum cleaner extracted dust-laden air. The assembly was rotated around the total circumference to complete the cleaning operation. This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood. Essex. Marc^, 1969. Am . Ottur. H rf. Vol. I), p. 41. Fcrgimon P rtu 1970. Prinltd in C m ! Britain RESPIRATORS FOR PROTECTION AGAINST ASBESTOS* S. Luxon H.M. Factory Inspectorate, Department of Employment and Productivity, Chepstow Place, Westbourne Grove, London, W.2. Over the past few years the British Standard for Respiratory Protection, BS.2091, has been undergoing a drastic revision. A new Standard, BS.2091:1969, Specification for Respiratorsfor Protection against Harmful Dusts and Gases has now been published and is of direct interest in regard to protection against dust including asbestos, as it places the standards of protection offered on a scientific basis. It does this by controlling facepiece leakage as well as filter penetration and valve slip, so enabling the overall standard of protection to be assessed. For ordinary respirators this protection factor is of the order of 20, that is, the external concentra tion is reduced to one-twentieth that inside the facepiece. If we use the standards suggested earlier such respirators should afford protection against prolonged ex posure to 40 fibres/cm* of chrysotile asbestos. This appears to be adequate to prevent danger during the operations of brake maintenance procedures, which we have been discussing today. Perhaps I should mention that there is shortly to be published a new B.S. Specifica tion High Efficiency Dust Respirators. These respirators will have a protection factor of 400 and will be suitable for short term protection against very high concentrations of chrysolite asbestos dust. Such respirators will be of the full facepiece or positive pressure type. Full facepieces are not, in general, acceptable for prolonged industrial use and the positive pressure dust respirator, while acceptable to the wearer, has a higher initial cost. A further British Standard Positive Pressure Powered Dust Respira tors is in preparation, and should be issued later this year. It is unlikely however that during normal brake maintenance operations the concentrations of dust will be such as to require the use of equipment of this type. An alternative approach is to utilise a half mask fed with compressed air from a suitable uncontaminated source. This type of apparatus offers complete protection for the wearer but suffers from the disadvantage of possible hose entanglement. Respiratory protection should in general be regarded as providing protection for work where control is difficult or where the work is intermittent and of short duration. It is hoped that the control of the dust will be achieved by the methods indicated earlier * and that respiratory protection will therefore only be needed for special work not of a routine nature. This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood, Essex, March, 1969. ` 'I Alternative tom of eortlrol for * 39 c t o i "* ' ^ DISCUSSION The results for .he ..cuum funnel ... p.irnen, anti lor 1* bnrsh versus blow-off are show" >0 I ^ ^ ^ concentrations during * ' TM " ^ y " .o iroperation earned outdaring .he second 2 hr latent period and therefore the wo collected hour did no, affec, <j? in .he sixth hour. The funnelI appe X. b , 2 per een. for obltrvt<1 in the adjacent b a , are In peah concentrationsof atoutSO ilw as j e h i e . ^ brush test m a, be discoun,ed. Personal cap . use b - of he bTMsh L r X trX ? X :rS i.r e d u e .io n o fb O i, in peak concentrations was again observed. CONCLUSION The experiments den-- S " n S of X simpler pans and was mueh ,,uicKer Uian .he vacuum There are three major reasons for the r dat ' J ' S ^ i w a s difficult increased brake cleaning time (and t us CXP^" occurred between the necessary air r efer en c e - D.mu OrcuPATiONAL Hygiene Society (1968) Hygiene Persamon Press. Oxford.