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FILE NAME Brakes BRK DATE 1970 DOC BRK033 DOCUMENT DESCRIPTION Journal - The Annals of Occupational Hygiene BAC thr 2 ty GE The Annals of wat sthFE RitSeaag Occupational Hygiene be feo 2 AN INTERNATIONAL JOURNAL PUBLISHED FOR THE BRITISH OCCUPATIONAL HYGIENE SOCIETY eae, reme fo CONTENTS LIST Volume 13 1970 PERGAMON PRESS LTD Oxford > London * New York * Paris os > eS ae me - fs Date ae E ne Z 10/10/25 No. 10/10/25 10/10/25 10/10/25 by AAC a sa = : ey eet aa ENER Eenri : des des ^' 2 & 3 85 3 4 ^' 4. H i g af 33 34 38 4d Fiat ty of ional ional : ! Brant 2 of enje enje C0 :8 SScchhooooll . 35 4 = if yy 3 ay a: ei FS. 56 z a atece iar aaa OPE gat TEAtea i OR ... ... ... ... KP KP 3 % = i 4 4 : } Fa : FORD i 10523 ; - ^' 5 ' NUMBER 1 . PAGE PREFACE and clutch maintenance . . 1 D. E. HICKISH Exposure to asbestos during brake W. J. SMITHER Asbestos and asbestosis . . . . . . . . 3 : - . 7 S. A. ROACH HyHygigene iene standards for asbestos : : : . D. E. HICKISH and K. L. KNIGHT Exposure to asbestos during brake maintenance : 17 23 S. LUXON Technical implementation of the new asbestos regulations : . . material friction friction D. HATCH Possible Possible alternatives alternatives to asbestos as a friction material : . . . 25 M. L. BENTLEY Control of the use of containing friction materials . . : G. Removing L. LEE Removing cleaning methods dust . from . brake . assemblies assemblies . . during during alternative vehicle servicing vehicle alternative . . .. . . . 31 33 K. L. KNIGHT and D. E. HICKISH Investigations into alternative forms of control for dust 37 generated during the cleaning of brake assemblies and drums . : . . S. LUXON Respirators for protection against asbestos . . ... . 41 R. COLES and C. G. RICE Towards a criterion for impulse noise in industry . . 43 J. G. WALKER Temporary threshold shift from impulse noise - : . . . 51 A. M. MARTIN G. R. C. ATHERLEY and T. I. HEMSTOCK Recurrent impact noise from 59 . . . . . . pneumatic hammers .. .. . 69 W. G. NOBLE A new concept of damage risk criterion oe . - . ese . Letters to the Editor H. A. BAMBER and R. BUTTERWORTH Asbestos hazard from protective clothing M. GREENBERG Asbestos release from battery boxes . . . . News Items . . . . ... . . . . . . Book Review . : . :. . . .. : . . 3- . 77 : 79 . 81 . ^' 85 NUMBER 2 A. BLACK and M. WALSH The preparation of bromine and iodine styrene microspheres with diameters from 0.1 to 30 microns . . e R. MORLEY and S. J. SILK The industrial hazard from nitrous fumes . labelled poly- . . . . : - pneumoconiosis coal R. A. BENTLEY and I. BERGMAN Candle or oil soot as a cause of in . . . . : . . . miners . . : : . . PAGE 87 101 109 peo ea a a . Roe = pase: RSS eeeey are ce oe % See - Boe a i re aed 4 ee z 3 - 5 : Re, 4 = 2 EEE ES as $ Shen OST te oa ie oe Ks Ser: ES 2 NEP <3 : = i ee parece: a =e Ree sees <, pars RR renee ae* 9 eR lr oe = yee Sa ss mee tenes age SES ue SE Ee ES cae Bs: a Spee a= oe ee no s eee SS. Sse eS = eee atescit tmpeh ; ee eon StS ek Ge 5h cats eee Se cs ee ek Pee Re. a eae oe 5c Seer : ven tees geen Souris ge ae eRe, ae Ann Occup Hyg Vol 13 p 1. Pergamon Press 1970. Printed in Great Britain PREFACE Exposure to Asbestos during brake and clutch maintenance kr THE PAPERS which follow were originally presented at a Conference held at the wundTm17 Central Office Ford Motor Co. Brentwood Essex on 26 March 1969. The Chairman of the Conference was Dr G. H. Channing Chief Medical Officer Ford of Britain who opened the proceedings by outlining the events which had led to the arranging Asu of the Conference Publication of the proposed Asbestos Regulations by the Department of Em- ployment and Productivity had raised queries within the motor industry as to whether Vidaubles clutch and brake maintenance activities both at the manufacturers premises and within the repair trade would come within the requirements of the Regulations There was a general desire that the subject should be investigated and any necessary remedial measures sought in advance of the legislation so that Dealers could be advised and servicing procedures modified where this might be necessary Investiga- tions had been made by the Industrial Hygiene Units of the British Motor Corpora- tion and of Ford of Britain and their findings would be reported to the meeting parumbirakan possible parumbirakan These would be preceded by papers on the medical aspects of exposure to asbestos parumbirakan indicating parumbirakan and later in the there would be parumbirakn programme papers parumbirakan solutions to m^nblues the problems involved D. E. HICKISH Bhat rae? ea On Tet re e 1 Tareas Pn Ann Occup Hyg Vol 13 pp 3-5 Pergamon Press 1970. Printed in Great Britain ete yt ABT Ta ey On ASBESTOS AND ASBESTOSIS + te n te W. J. SMITHER AS MAS Group Medical Adviser Cape Asbestos Company 114 Park Street London W.1 Potrelas fy THE FORMS AND USES OF ASBESTOS AE tact COMMERCIALLY important asbestos fibres fall into two main groups The first of b Basle er these is chrysotile and the second comprises the amphiboles Both groups are dentae fibrous silicates but they differ in geological origin in chemical composition in te molecular structure in fibre size and strength and in other characteristics Chrysotile white asbestos comes from many different places There are slight chemical and physical variations in the fibres from different sources but basically all have the same molecular structure On the other hand the amphiboles comprise at least three separate types whose molecular structure is very similar but whose chemical and physical properties differ more widely Amosite amber and crocidolite 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 Annual world output -3,000,000 tons es | co | Anthophyllite 10,0 10,000 tons Amosite ee t South Africa % |dts Crocidolite - 90,000 tons blue % South Africa egyan| Chrysotile 110,000 tons white 2,900,000 tons % 2 gag 93 UL 1,250,000 ee USSR 750,000 S.Africa 250,000 USA 100,000 100,000 Europe 100,000 Others 350,000 350,000 FIG 1. World production of asbestos This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance held at Brentwood Essex March 1969 3 4 W. J. SMITHER Asbestos Annual consumption 3,000,000 tons ae Very br a8 brake pads contain 50 } Where it is used Where it is mined - in the fields : percentage now contai Others Chrysotile mcs ley Belgium Others at Italy phe eh France Bp USA with an eve ; pads for dis It is estimat be equippe JAPAN UK Germany Southern Africa USSR USA USSR Canada a: ae ae 4 3 ig 4 ; 8 The var is the subje physical and is being inv the fibres h The chie lining of the cavity A f becoming n All type period of ti sists of thic interference the shortne The amo calcium dej concentrate any event t itself Blue Crocidolite | S.Africa S.Africa Amosite Anthophyllite S.Africo Finland FIG 2. Areas of use of asbestos : ; 3 The different characteristics of asbestos fibres dictate their uses their applications and their mode of packing and handling For example amosite can be pressure packed and palletized whereas chrysotile lends itself more readily to containerization By far the greatest use of chrysotile 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 country It is added to the pitch mixture in unopened dissoluble bags ; Exposur ofmesothelior mesothelior workers wh uncommon frequently \ The reason investigator . fab Sat aOws Be aE bt del ty serthte ea Gate Pile fala at donate ah ated dR DY a A UE UO, dete Pre a ten Sre eS en ** ** ** ** hod eae at ed cations ressure ization osite is nt acid in this Asbestos and asbestosis S Very broadly it can be said that current friction materials whether they be disc brake pads passenger car and commercial vehicle brake linings or clutch facings contain 50 per cent chrysotile asbestos The new trends of development particularly in the fields of disc brake pads and commercial vehicle brake linings indicate that the percentage of asbestos included in the mix is likely to decline Some new materials now contain approximately 40 per cent asbestos and newer mixes can be foreseen with an even lower percentage probably down to a minimum of 30 per cent The pads for disc brakes require less asbestos fibre than conventional drum brake linings It is estimated that more and more passenger cars produced in the U.K. will in future be equipped with disc brakes particularly on the front wheels THE BIOLOGICAL EFFECTS OF ASBESTOS The variation existing in the biological effects of the different types of asbestos is the subject of considerable interest and research and the extent to which the physical and chemical characteristics of the asbestos itself influence biological effects is being investigated The role of trace elements and contaminants associated with , the fibres has also to be considered The chief biological effects of asbestos are confined to the lung and the pleura or lining of the lung and chest cavity and to the peritoneum or lining of the abdominal cavity A few cases of skin corns have occured in asbestos workers but these are becoming much less common All types of asbestos if inhaled in fairly high concentrations over a considerable period of time may cause fibrosis of the lungs This disease called asbestosis consists of thickening of the lung membranes with resultant stiffening of the tissues and interference with oxygen uptake The interference with gas transfer is the reason for the shortness of breath which causes the disability associated with asbestosis The amount of exposure required to produce fibrosis of the pleura with or without calcium deposition in the scars is more debatable It may be that shorter less concentrated exposures particularly in youth leave this mark upon the pleura In any event this particular effect of asbestos inhalation causes little or no disability in itself Exposure to asbestos may lead to further complications e.g. heart failure cancer of the lung or rarely to malignant changes in the pleura or peritoneum known as mesothelioma Cancer of the lung has been shown to be more common in asbestos workers who smoke just as it is in the general population Mesotheliomas are very uncommon throughout the world but in some areas they have been associated more frequently with exposure to crocidolite than to chrysotile amosite or anthophyllite The reasons for this are at present obscure but are being sought intensively by investigators in many different countries Ann Occup Hyg Vol 13 pp 7-15 Pergamon Press 1970. Printed in Great Britain oa Gory DU ed degprte Me PSH on at RDG a RAK SOE eee na, ee een Sate SY te ne I aby Ne vpieDt Ee ! ee Re)PE Se te oe MEO WO ne apn e ea Pie REAL ; HYGIENE STANDARDS FOR ASBESTOS S. A. ROACH London School of Hygiene and Tropical Medicine Keppel Street London W.C.1 ~ 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 recommends 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 Committees each of which is concerned with a specific standard There is a 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 conservation 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 recommendations made as well as the benefits to health and this is one reason why on each of these Hygiene Standards 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 committee on Asbestos under the Chairmanship of Professor Lane has developed new hygiene standards for airborne chrysotile dust LANE et al 1968 These were based on the results from a medical and environmental 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 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 standard 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 recognition 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 Clutch Maintenance held at Brentwood Essex March 1969 7 S. A. ROACH when the recommended standards of air cleanliness are maintained It was recognised that to protect the hypersusceptible workers environmental control would have to be supplemented with medical examinations centration instruments fibres The asbestos dust concentration had been cerned with several different measured at the textile factory con- which the number of fibres including the membrane filter method in longer than 5 ...was counted The dust which different workers had been exposedexposed varied from 1 concentration to over periods from 10 years to 33 fibre to 27 years The exposure of an individual was of the expressed as fibre years that is the product average concentration to which he was exposed during workingworking hours and his average asbestosis to exposure expressed in may be explained as follows eS An individual's response to dose of any foreign substance can be . expressed by a differen line Fig ) There is a dose which produces by the threshold A. response whatsoever This is marked is SUE If the individual is given progressively repr correspondingly The least positive response average Morea response might be associated with observable physiological effects The highest responses of all would ness or even death perhaps be signified signified by loss of conscious- Ppa The degree of response may be conceived to be measurable objectively on a con- tinuous scale starting at zero and the scales of dose and to linearise the relationship between them as in Fig 1. response response The could be chosen ship could then be described by the slope of the line response relation- strikes the dose axis The slope of the line and the point where the line In about a frequen on eith In Exactly usually affected the size zero ex greater the safety factor necessary in practice to allow for the excursions of dose above the maximum inevitable occasionaloccasional desirable Doses which give zero response are An men can be standar costs of -- clinicall their ye Fig 3 i Hygiene standards for asbestos recognised have to be Individual response to dose from the prevalence oe ure Over 4 However dower ved Con- Pan ** cordingly ence with Pee aR y that the RAR is equally et that con- Plone BIE, ctory con- te d method in hi ata tration to # He ae fibres rt ie product wer rs and his Response Threshold B Threshold A Dose valence of was based FIG 1. Individual response to dose hs sg a essed by a different threshold dose and different slope A particular population under study rere is marked es is represented by a family of response lines centred around the line for the see e response average man aes ut merely In a real population the threshold dose will vary from one individual to another thaas Se till higher ot about an average value as in other medical norms It is to be expected that the size iap nc ert clinical Sines Cee frequency distribution of threshold doses would be a shaped curve tailing away consciousSe on either side of the central value as shown in the Fig 2a be In a real field study it is established whether a man has or has not been affected giely re on a con- Corie Exactly when or in what concentration he first developed the characteristic response is heap be chosen e relation- usually not known A graph showing exposure against the total number of people lye affected by it would be a cumulative sigmoid curve illustrated in Fig 2b derived from i e the line ee! the size frequency distribution in Fig 2a This tails away down to zero response at be 1 increases zero exposure hak er i oe slope the er An air quality standard is still associated with a small but zero probability occasional of men being affected by the contaminant in question The risk of people being affected om can be made as small as one wishes Zero risk is the ultimate target and an air quality 4 bot Ol we standard has to be a compromise between the costs of bearing a health risk and the RAB costs of air contaminant control .threshold .threshold Woe A curve was fitted to the data from the textile factory on asbestosis detected iget i STASI As with all ret Ae line varies Le clinically and the exposure in fibre years per cmof all individuals under study over their years of employment up to 1966. The bottom end of the fitted curve is shown in ent with a Fig 3. The three points relate to three of the groups of workers studied The exposure Vien RS AT GE S. A. ROACH Population response to dose symptoms with indvuals of Number Threshold dose FIG 2a Population response to threshold dose symptoms with indvuals of Number Dose FIG 2b Population response to dose 3 aires is shown on prevalence i basal rales Basal ral and there is posure On rales A probl said to be al mon by ever exposure T other simila it to zero I benefits to cost of dust be economic The benefit taminant ex benefits to t One con an accumula affected to is for exam tee So pihecingreg 2 The Riawas . Hygiene standards for asbestos Response to chrysotile asbestos exposure 30 30 asbetosi of 8 incdenc Percntage ts) I 250 1 500 i 750 Exposure fibre years FIG 3. Responsteo chrysotile asbestos exposure is shown on the horizontal axis expressed in fibre years per cmand the corresponding prevalence is on the vertical axis showing the proportion of people with crepitant basal rales Basal rales is the earliest clinically demonstrable effect on the lung due to asbestos and there is a steadily increasing prevalence of basal rales with increase in dust ex- posure Only groups with near zero dust exposure show zero prevalence of basal rales . A problem arises when it is appreciated that there is no exposure which can be said to be absolutely free risk There is no single threshold exposure held in com- mon by everyone There is consequently this gradually increasing risk in relation to exposure The application of dust control to meet a TLV an MAC MAK value or other similar hygiene standard will limit and control the risk but is unlikely to reduce it to zero It has to be remembered that asbestos is very widely used and brings real benefits to the community at large A standard could be made so stringent that the cost of dust control is prohibitive that the production and use of asbestos ceases to be economic production and use is discontinued and the associated benefits are lost The benefits gained by reducing the risk of asbestosis through reducing air contaminant exposure have to be weighed against the possible loss of direct and indirect benefits to the community from the use of the material One conclusion from the exposure curve fitted to the data was that for an accumulated exposure of 100 fibre years it is probable that the risk of being affected to the extent of having early clinical signs will be less than 1 per cent That is for example a concentration of 2 fibres for 50 years of such exposure while ORR et et to ae oe ae RAL Sask. ws OL he le Digtet bade ot fits 12 S. A. ROACH a at work 4 fibres for 25 years or 10 fibres for 10 years The British Occupa- tional Hygiene Society Hygiene Standards committee on Asbestos expressed the view that a proper and reasonable objective would be to reduce exposures to below this level and thereby reduce the risk of contracting asbestosis to less than 1 per cent of those who have lifetime's exposure to the dust For such workers who may possibly work for 50 years the long term average concentration to which they are exposed would need to be less than 2 fibres For others who will be exposed to asbestos dust in air for shorter periods the long term average concentration need not be so low as long as their exposure will amount to less than 100 fibre years The possibility was considered that short periods of very high concentration for a few weeks or less might be disproportionately important in determining the risk of asbestosis However the evidence for this was not conclusive and the committee - were satisfied that the risk can be satisfactorily expressed with respect to an concentration over 3 months and can safely be kept below 1 per cent by ensurianvgertahgaet a man's accumulated exposure does not rise above 100 fibre years The exposure measured by making fibre counts on membrane filter be converted into samples can exposure measured with an impinger the American method by examining the results of side comparisons of the two instruments Such comparisons made by the United States Public Health Service in asbestos textile plants have shown that an accumulated exposure of 100 fibre years corresponds to 15 million particle years by standard impinger methods AYER LYNCH and FANNEY 1965 The present American Threshold Limit Value is a concentration of 5 million particles mp which if it persisted would result in an accumulated exposure of 250 million particle years over 50 years , These American hygiene standards called Threshold Limit Values are a for summarising published information on air contaminants in a system convenient for the day practice of industrial hygiene The present American stanfdoarrmd for hr averages is thus 17 times higher than the British standard for 3 monthly averages However there is a published intention to revise the American standard in view of recent knowledge However the difference between the American and British standard is not marily due to conflicting evidence on the adverse affects of asbestos It is because porfia- different attitude now adopted over the degree of protection which ought to be given against asbestosis The American Threshold Limit Value of 5 mp was recommended and his workers in 1938 after by Dreessen studying 541 employees in 4 asbestos textile plants where massive exposures to chrysotile occurred DRESSEN et al 1938 Only 3 doubtful cases of pneumoconiosis were found at the time of the study in those exposed to dust concentrations under 5 mp whereas numerous marked above 5 mp cases were found inadequate A conference held in 1965 on the biological effects of asbestos called the very real probability that the 5 mp limit recommended by Dreessaetnteisntiinoandet-o quate to give complete working protection against all forms of asbestos SCHALL 1965 Medical data on which the limits had been based were more than half of the asbestos workers studied by Dreessen and his workers under 30 years of age and thus had insufficient were exposure time for much asbestosis to . develop Of t 5 years and o time study r in the over The British after studying the ACGIH ] Limits 1968 while taking in and considera of the health < that the 5 m~fi years a perio~ In accorda below which a average concer often consists recommended length are cou by Impinger 12 fibres of asbestos dis The intend to them shoul given the most to take advant The standa person's accur years It clinical signs c these standard associated with The standa over 3 months equals 2 fibres this value and higher than 2 mum 12 fibres compliance T standards from Inspectorate in judgment on c mum for even probability tha There is a dusts from ma ~ ayTREOTIN TS a SE Cea: RAY . ay 2 Shits 5 Sector Se We as Sica Soe ae oe RP. 2 a cae Hygiene standards for asbestos 13 ; Occupa- ssed the TOA o below develop Of the 105 workers exposed to less than 5 mp 82 had worked less than 5 years and only 4 had more than 10 years exposure Moreover it was a point time study many of the ill were missing the dead uncounted and were not considered Se per cent AER -ho may they are Dosed to in the over evaluation of the limit The British Hygiene Standards Committee finalised its views in November 1967 after studying the British data and these views were immediately communicated to the ACGIH TLV committee In May 1968 the ACGIH Committee on Threshold pata: need not n Limits 1968 proposed changes to its hygiene standard The new asbestos limit while taking into account the British views had to be based on American experience on for SE and considerations applicable to the American industrial scene Recent evaluation bE risk of Emmittee a th of the health experience in asbestos plants in the U.S.A. had nevertheless indicated that the 5 mp limit was not sufficiently low to protect workers exposed for 30 See etials years a period rarely exceeded in America ely In accordance with these findings the 5 mp limit was made a ceiling value byt below which all concentrations should fluctuate This corresponds to a weighted rsa hp ples can hod by average concentration over a shift of 2 mp Since the count by Impinger procedure ere often consists primarily of extraneous particulates an alternative fibre count was Such textile iatmn recommended using the membrane filter method in which fibres greater than 5 in length are counted as in Britain On this basis for a weighted hr average limit esponds 3 by Impinger count of 2 mp the corresponding limit based on the fibre count is fibres This limit is intended to reduce to an insignificant risk the occurrence =2 of asbestos disease among those exposed for 30 years to all forms of asbestos Ba The intended changes in American TLVs give two years notice and objections a be) to them should be conveyed to the TLV committee of the ACGIH All objections are i given the most serious and sympathetic consideration and users are strongly advised to take advantage of this if they have reason to question the proposed changes tandard The standards of the British Occupational Hygiene Society recommend that a monthly tandard person's accumulated exposure to chrysotile asbestos should not exceed 100 fibre years It is probable that the risk of being affected to the extent of having early clinical signs of asbestosis will be less than 1 per cent if the conditions comply with not pri- use of a these standards It is believed that this is the first time a hygiene standard has been associated with such a specified degree of protection it to be The standards refer essentially to an average concentration during working hours over 3 months of 2 fibres In an environment where this 3 monthly average just Preessen os le plants Houbtful iptmetad to dust e found equals 2 fibres the concentration within this period will sometimes be above this value and sometimes below The maximum hr average will thus be somewhat higher than 2 fibres The proposed change in the American TLV is to a maximum 12 fibres hr average which if exceeded on a shift demonstrates noncompliance Thus there may be a rough degree of consistency between the hygiene standards from the two countries organisations so far as this is possible The Factory ntion to Inspectorate in their work have often only a short time during a day to come to a is inade- asbestos judgment on conditions and are considering a development of this applying a maximum for even shorter periods of a few minutes which if exceeded would indicate a dequate ers were probability that the Asbestos Regulations are not being complied with There is a growing body of information on chrysotile dust and other asbestos stosis to dusts from many countries and it is hoped that in future the views from different 14 S. A. ROACH parts of the World will be sought so that standards for testing air cleanliness as vary far as possible be held in common Even so the risks that may be tolerated cacnan from country to country and from one situation to another within a country The air quality attained in industry in different countries does differ and no doubt will continue to differ A wealthy country can afford to spend more money on air- contaminant control Also a country very conscious of the slightest risks to which its workers may be exposed through their occupation may be expected to have different standards from one which is not where other health risks may be so much the greater The benefits to the community from the use of inexpensive asbestos products have in some measure to be weighed in the balance against the benefits to the health of the workers that would accrue by reducing asbestos dust exposure : The British Occupational Hygiene Society committee on Hygiene Standards for Asbestos has not yet decided whether their chrysotile standards would be suitable for amosite or crocidolite dust nor whether they give sufficient protection against lung cancer or mesotheliomas The ACGIH on the other hand make no distinction between different types of asbestos in their standards In this country it should be remembered that the Senior Medical Inspectors Advisory Panel on Problems arising from the use of Asbestos considered that the evidence to date on balance indicated that a particular significance must be given to crocidolite as a cause of mesotheliomas Ministry of Labour 1967 That Panel recommended that other types of fibre should be substituted for crocidolite wherever possible and where this is at present impossible special precautions should be taken to reduce the risks of inhaling the material to the lowest possible level Whatever measures may be adopted to control asbestos dust the Panel urged that these be even more rigidly applied to crocidolite The Factory Inspectorate is also developing procedures for testing hygiene standards in factories and is seriously considering the adoption of especially rigid requirements where crocidolite is used To derive hygiene standards for an air contaminant which provide a known degree of protection against a health hazard it is necessary to have a body of data showing the amount of air contaminant to which people are exposed and the corre- sponding effects or lack of them in the people It is also necessary to have a of the consequences to industry and users of limiting and controlling grasp emissions of the contaminant Our present information is very imprecise particularly in terms of the practical consequences of specific hygiene standards In developing recommendations for a hygiene standard the British Occupational Hygiene Society committee 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 what 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 by ventilation it is important to know what is the minimum amount and what kind of local exhaust ventilation and dilution ventilation is necessary to achieve a given degree of air cleanliness in a work place since costs tend to climb as the cube of the air flow Research is needed to determine the balance between local and general ventilation which produces a specified degree of control at minimum cost By setting down the capital cost installation cost running and maintenance costs it becomes possible to grasp mor kind of inf be able to This do equation 1 dard How AYER H. E COMMITTEE { Trans A Ohio U. COMMITTEE C Governm DREESSEN W and TRIC Wash No LANE R. E. occup Hy MINISTRY OF Medical } SCHALL E. L 55 can as can vary . no doubt ey on airto which e different e greater Eucts have lth of the lth if ag ai : 28 Standards be suitable against distinction should be arising ms arising : indicated theliomas of fibre ~ 3% a =F oH at present haling the to control rocidolite standards quirements 15 Hygiene standards for asbestos mathematical firmly the consequences of adopting particular hygiene standards This grasp more the field of asbestos dust control so as to kind of information is needed throughout be able to weigh up the costs of achieving high air cleanliness This does not reduce the choice of an air quality standard to a does it avoid the need to exercise wise judgment in the choice of stan- edqauradtiHonowneovrer the judgment can become a little less arbitrary than at present REFERENCES J. R. and FANNEY J. H. 1965 Ann N.Y. Acad Sci 132 274 AYER H. E. LYNCH THRESHOLD LIMITS 1968 Supplemental Documentation of Threshold Limit Values COMMITTEE ON Industrial Hygienists 1968 p 188. 1014 Broadway Cincinnati Trans Am Conf Governmental Ohio U.S.A. Threshold Limit Values for 1969. American Conference of . ON THRESHOLD LIMITS 1969 Cincinnati Ohio U.S.A. COMMITTEE Governmental Industrial Hygienists 1014 Broadway J. W. SAYERS P. R. EASON H. F. Valle J. M. EDWARDSEDWARDS T. I. MILLER Publ Hlth Bull DREaEnSdSETNRIWC.ECM..DFa.ll1a938 A study of asbestosis in the asbestos textiletextile industry LANWEasR.h EN.o.BA2R4N1ES J. M. HICKISH D. E. JONES J. G. ROACH S. A. and KING E. 1968 Ann ; MINoIcScTuRpY HOFygLA1B1OU4R71967 Problems arising from the use of asbestos Memorandum of the Senior Medical Inspector's Advisory Panel HMSO London SCHALL E. L. 1965 Ann N.Y. Acad Sci 132 316 , a known Ta dy of data the corre- ieee a grasp of ions of the Arms of the Inendations committee as not the lem was to rol Where mount and y to achieve as the cube ventilation g down the possible to PRAE ost Ann Occup Hyg Vol 13 pp 17-21 Pergamon Press 1970. Printed in Great Britain EXPOSURE TO ASBESTOS DURING MAINTENANCE BRAKE D. E. HICKISH and K. L. KNIGHT Medical Services Ford of Britain Brentwood Essex EXPOSURE DURING CAR SERVICING THERE is little maintenance of passenger vehicle brakes involved at the manufacturers premises and therefore an investigation was carried out at the Service Bay of a Ford Main Dealer in the Greater London area This Dealer normally services 10-20 cars per day but blowing of brake shoes and drums is not included in all routine services It is the blowing procedure which is the subject of the study Air sampling was carried out using membrane filters the sampling and subsequent assessment being in accordance with the technique described the Hygiene Standard for Chrysotile Asbestos Dust published by the British Occupational Hygiene Society 1968 Static samples were taken by the side of the car Fig ) and composite samples were also taken in the cloud during the blowing procedure continuing by the side of the car for the remainder of the sampling period Normally the mechanic takes care to blow the dust away from himself so this sampling procedure should overestimate exposure Two sampling periods of 45 minutes were used and during the first period one Cortina Estate and one Anglia Van received brake blow and during the second period one Cortina car was dealt with The results are shown in Table 1 TABLE 1. ATMOSPHERE SAMPLES DURING CAR BRAKE SERVICE Location of samples 1st period Fibres 2nd period = weighted average By car 1.12 Dust cloud then by car 1-71 1-25 2.55 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 to Asbestos during Brake and Clutch Maintenance held at Brentwood Essex March 1969 17 Sawe | as meso piers aa aga ret sar Ce ERS dni bad eldest Dish ich hd, 33: D. E. HICKISH and K. L. KNIGHT TABLE 2. PERSONAL SAMPLES DURING CAR BRAKE SERVICE Sample Concentration fibres 1 0.63 1.12 Ae 23456 0.21 0.96 haate 0.38 RAT 0.79 weighted average 0-68 GSMRE Ds cat 5 EXPOSURE DURING TRUCK SERVICING tahhin a ac Maintenance of truck brakes involves a somewhat different type of operator b nnd exposure as the servicing is more complex and therefore the number of vehicles dealt Hat with is less The larger size of wheels and drums on the other hand makes it difficult dere for the operator to avoid the dust cloud produced and personal a could be higher than that during car maintenance Further sampling was theerxepfoosruercearried out a a= in large fleet workshop with equipment similar to that used for the Se tests passenger car 7 y Static samples each of approximately 3 hr duration were collected during the morning and afternoon periods at three positions at the bay adjacent to the one at which brake cleaning was carried out at the next bay and in the centre of the garage Brakes were blown out during the morning but not during the afternoon The results are given in Table 3 , TABLE 3. GENERAL ATMOSPHERE SAMPLES DURING TRUCK BRAKE SERVICE Location Location of sample Concentration fibres Adjacent luy 2 Bays away Centre of garage Morning Afternoon Morning Afternoon Morning Afternoon 0-28 0.07 0.17 0.07 0.49 0.11 Personal samples were obtained from two men man engaged on brake cleaning and the man engaged on clutch repair work at the adjacent bay The first period of 1-5-2 hr included the period of brake cleaning and the second period of approximately hr represented the remainder of the shift The results are shown in Table 4 e> 1 ER a Mapi<A ada Bon A . et 56 ON dealt operatoorperatoroperator les dealt PE x Be ead les dealt dificult dificult Sos could could could couldrireided operatoout ngerngnergecrar ringring ring the onethe the the one e ofof the onon The The . rat PG ERNIE ME ATAIT | Hey , on brake period brakebrake first first of periodperiod umo sumo sumos RO. i ha ^' F : F F FIG 1. Static sampler by side of car S82.0e FS mage Neb cakiplbnder t s J Pergi ion. Cake i! Atmakee uslnbotax s ine vet nat asp A . ie aioe hanes Bent rent abt ry ty te aoLd TT SaneERE S VINTOcNapionapteet NL pare ShemxT E iTStrsaE saieanbel facing p 18 Y den hal bikesEe ae a a Sapxticusii dates I. SH at wheat pees foe kat EL wag ee feo wig eats ope Sine alt: achat FIG 2. Personal sampler FETT ETE Ry. eS ee2 ss Eee Brake cle Ti Clutch re Ti The Hygiene ; level of 100 fibrelifetime of 50 yea While an exposu motor mechanics and the findings Car servicing While the sta ing the personal Truck servicing The standard away from the i vicinity do excee below the standa It should be do not necessaril Brake lining surprising to fin collected In a brake lining ma amined microsc from brake dru The results o were fibrous in incinerated ther Exposure to asbestos during brake maintenance TABLE 4. PERSONAL SAMPLES BRAKE SERVICE Operator Concentration fibres Brake cleaner during cleaning after cleaning weighted average Clutch adjacent bay during cleaning after cleaning weighted average 7 7.09 0.08 1-75 2-25 0-11 0-79 SIGNIFICANCE OF EXPOSURE LEVELS The Hygiene Standard suggests that exposure should not exceed an accumulated level of 100 years On this basis a man exposed for the whole of his working lifetime of 50 years should not be exposed to concentrations exceeding 2 fibres While an exposure to asbestos of this length is somewhat improbable in the case of motor mechanics nevertheless the results have been interpreted against this value : Pkt and the findings are summarized as follows = Car servicing = While the standard may be exceeded in the dust cloud during actual brake clean- ing the personal exposure of the operator studied was well below the standard eet Truck servicing Whe The standard is not exceeded during brake cleaning in the general atmosphere AOL from the immediate vicinity of the operation but personal exposures in the ald away Ne vicinity do exceed the standard On a daily basis the personal exposure levels are ecae below the standard although that of the brake cleaner approaches it nat Sabpd It should be noted however that in a fleet workshop brake cleaning operations CO be Abed do not necessarily take place daily tats eas thot THE NATURE OF BORNE DUST cr aribtesy Brake lining materials contain 40-60 per cent of asbestos and it was somewhat surprising to find that particles of a fibrous nature were scarce in the air samples | tee collected In a laboratory investigation specimens of dust were obtained by filing brake lining material and after sieving through a mesh sieve these were ex- onda amined microscopically before and after incineration Samples of dust were collected rSaey from brake drums during car servicing and examined in similar manner The results of the examination were expressed as the percentage of particles which BEa were fibrous in nature and are compared in Table 5 together with a result from an incinerated thermal precipitator sample obtained during brake cleaning DY wea ene ats Sai - ES ener RES NT Ste ner in poe iamtgnhbnirtond ot e Pier Tae nerigmreNee coartangnm Tapricoa, mansoni Bf ae ae Seat w fs paren aeFo SNAK: NI apa en aad ane maa Se rh + ch Lhe 20 D. E. HICKISH and K. L. KNIGHT TABLE 5. ASSESSMENT OF FIBROUS FRACTIONS OF DUST SAMPLES Sample Percentage of particles seen to be fibrous Sample not incinerated Sample incinerated Brake lining material Brake drum dust borne dust 28 0.6 _ 12-3 1.6 . 1-3 It is clearly 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 chrysotile 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 chemical form of the asbestos during its use as a brake material Enquiries were 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 no fibres in the dust produced from bus and automobile brakes except under severe braking conditions In the latter instance the brake temperature reached 320-370 compared with the design maximum temperature of 290-320 it appeared that under these conditions the binder - decomposed and released part of the asbestos as free fibre At lower bulk lining temperatures 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 commented that the normal thermal decomposition product of chrysotile is forsterite a fibrous crystalline magnesium silicate However our samples of brake drum dust contained very little forsterite but rather were mainly comprised of an amorphous magnesium silicate which is fibrous Little was known at that time about the structure and composition of this substance Whilst there was no evidence to suggest that the material was a health hazard this possibility could not be dismissed and animal experimentation has been commenced in the U.S.A. cats te aMt AA + i 3 CONCLUSIONS Our investigations show that exposure asbestos during brake maintenance is not as severe as was anticipated and in the situations we examined the personal exposure of the operators was below the limit corresponding to year 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 contamination is desirable The present trend towards the introduction be engaged a Our envi volve the filii would give I with the atte COMMITTEE ON Standards ] HOLMES S. 19 LYNCH J. R. ( orne dust wed that ompared hat there use as a ther they ng dyna- from bus instance num tem- ic binder ning tem> remains ining and tos The i different per com- ,rsteritea ake drum an amor- ime about idence to ot be dis- 21 Exposure to asbestos during brake maintenance introduction of flowline servicing at Dealers works in which one individual may almost entirely on brake servicing emphasises this point be engaged included maintenance procedures which in- Our environmental studies have not and we would envisage that these volve the filing or grinding of brake lining material rise to considerably increased air contamination by chrysotile asbestos would give the inhalation of fibres with the attendant need for strict precautions to prevent REFERENCES HYGIENE STANDARDS BRITISH OCCUPATIONAL HYGIENE COMMITTEE ON Pergamon Press Oxford Standards for Chrysotile Asbestos Dust HOLMES S. 1967 Private communication LYNCH J. R. 1968 J. Air Pollut Control Ass 18 824 SOCIETY 1968 Hygiene itenance is e personal xposure cleaning to procedures owards the Ann Occup Hyg Vol 13 pp 23-24 Pergamon Press 1970. Printed in Great Britain TECHNICAL IMPLEMENTATION OF THE NEW ASBESTOS REGULATIONS S. LUXON H.M. Factory Inspectorate Department of Employment and Productivity Chepstow Place Westbourne Grove London W.2 THE NEW Asbestos Regulations were signed by the First Secretary of State on May 13 1969 and will therefore come into operation May 14 1970. They are based on the concept that asbestos dust must be so controlled as to be at a level which will ; not be liable to cause injury to health For the purposes of our discussion today I believe we should take this to be a level of 2 fibres and 0-1 mg for chrysotile asbestos A fibreis taken as being 5 p or over in length with an aspect ratio of at least 3 Thisis of course the standard proposed by the British Occupational Hygiene Society 1968 andis based on time- weighed average concentrations There is a practical limit on the time over which Co samples can be taken if the exercise is not to become unnecessarily cumbersome and Pt SPSS expensive On this basis a sample of 4 hr duration seems a reasonable compromise If we accept this as a practical sampling time then the overall standard becomes 2 Cans fibres over this four hour sampling period We cannot however afford to ignore entirely peak concentrations which will occur during this period and it seems reasonable to expect that a concentration of say 12 fibres should not be exceeded during any period of 10 min i.e. we might regard 12 fibres as a ceiling value It must be remembered that we are using the fibre count not as an absolute measure of concentration rather as a conveniently measurable parameter to indicate the total asbestos in the air The work leading to the formulation of the BOHS Standard referred to above related to conditions in the textile industry and not enough informa- tion is yet available on the relationship between mass of asbestos and fibre counts in the other industries To further complicate the problem it is not known what fibre sizes with are biologically active and even if this were known appropriate elutriation i.e. the rejection of material not biologically active would be very difficult with a fibrous material such as asbestos We ourselves are making both fibre counts and total mass determinations by ray diffraction analysis in industries such as the motor industry where degradation of the fibres may occur resulting in a substantial change in size distribution HICKISH and KNIGHT 1969 have described conditions during the servicing of braking systems The figures they have quoted are to a large extent reassuring in This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance held at Brentwood Essex March 1969 23 7 ey ot mar * oig Be Scbe Ee! Rb. aciac salt Aimesun at ed imeat he RA yen aie,ha= Bi ca cr oh Peres te oil aed Sh or + asec ree Lteid 5 Lincs PROCee Lruatt Sa 24 S. LUXON Ann Occup Hyg Voi that they indicate that the levels likely to be found in many sections of the industry engaged in this work are below the level of 2 fibres which is considered in the light of past knowledge a safe one for chrysotile asbestos Their highest figures for the weighted average concentration over 4 hr however clearly show that over a period of 10 min we may have concentrations exceeding substantially the level of 12 fibres which are quoted above I was interested to hear of the increasing tendency to carry out brake overhauls on a production line basis This clearly must increase the exposure of particular in- dividual workers making the development of adequate precautionary measures even more important and in this connection I hope the devices which will be described later day can be improved and developed to the point where they become univer- sally acceptable to the operator Certainly we should not be blowing out brake dust even if it contains only a few per cent of asbestos . In regard to this latter statement perhaps I should say that work at our Industrial Hygiene laboratory confirms the figures indicated in the previous paper We have found that samples of dust from brake drums when subjected to ray diffraction analysis contained between 1 per cent and 3 per cent of chrysotile asbestos although the original lining material contained more than 40 per cent asbestos There seems little doubt that this is due to the considerable thermal degradation which occurs consequent on the high temperatures generated by friction at the interface between the lining and the drum POSSIBLE I HAVE been as The facts are shortly be ava then I think th This is not eventually finc loss in perform REFERENCES Having sta the reasons w Asbestos Regulations 1969 Statutory Instrument 1969 No. 690 COMMITTEE ON HYGIENE STANDARDS BRITISH OCCUPATIONAL HYGIENE Standards for Chrysotile Asbestos Dust Pergamon Press Oxford HICKISH D. E. and KNIGHT K. L. 1969 Ann Occup Hyg 13 17 SOCIETY 1968 Hygiene friction mater The first a pregnated wit which while t oe The main fun tESe spheric oxyge supe resulted in the a te drying oil wa ae abrasion Bs 0 As brake pos degrade and In other word Around 1 that textiles c neither burns conditions be 1940's when asbestos text because the . proved to be This paper Clutch Mainter dustry in the NA res for V over a . 1 of 12 makNG auls on lar in- es even -sikal scribed -sikal univer- e dust lustrial e have raetion though : seems occurs een the Ste Higiene Higiene dade Atal dapgren. bel gat care De NOE ESSATGTN toe MTDyay ODT E PSR SPUR . Ati weaPoca AC ty types RETA MEV 4cv b Ann Occup Hyg Vol 13 pp 25-29 Pergamon Press 1970. Printed in Great Britain POSSIBLE ALTERNATIVES TO ASBESTOS AS A FRICTION MATERIAL D. HATCH Ferodo Chapel 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 atmospheric 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 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 500 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 Clutch Maintenance held at Brentwood Essex March 1969 25 rer 8 PEG Bia Bin e dhe aore oe Bay Atytaeee a PSO a5 co a rsOTR ot a oe one ge el eh ota Tg RTE o's fees byt ete D. HATCH 26 and flexibility This made possible the asbestos to maintain the necessary strength heat of mineral and metal fillers which imparted greater inclusion otfhhaenacvoyullodadbiengosbtained from resin and asbestos alone and did so at the resistancoef a reduction in asbestos content The last point is important in the context asbestos be replaced eoxfpaesnbseestos substitutes The question is often asked why can't by something like glass fibre which after all must surely oimfpatretxtislueffliicniienngt isstrreequnigrtehd The answer is possibly it can if merely the performance fibre melts even but at the temperatures commonly met in modern brakes the glass in depth below the operating surface of mineral and other fillers Furthermore as a result of the embrittling effect needed in today's brake lining glass fibre is inadequate in imparting the necessary The same can be said to a greater extent of the various types strength and flexibility the market over recent of rock wools and mineral fibres which have appeared osntrength of asbestos almost It is interesting to note that not only is the ultimate years but the modulus of rigidity is up to three times that of glass fibre i.e. 550,000 in at a value of 30,000,000 in.Typical figures for other materials taerne staiyme1s0a0s,0h0i0gihn.for steel wool and down at 60,000 in.2 for mineral wool situation therefore is that in drum brake linings configura- The current and commercial vehicles there exists no substitute for tion used for passenger cars asbestos which would not result in a deterioration of performance and strength DISC BRAKE PADS second Rates of energy dissipation continue to rise and we have now passed the point moulded drum brake linings are adequate for a large percentage of passenger where 50 cent of the passenger car axles are equipped with cars In this country nearly per there seem to be technical disc brakes and for the time in nearly half a century materials It is purely for- possibilities of reducing the asbestos cionndtiesnctborfakfersicatrieondesigned to a stronger shape tuitous that the friction materials used less or circular pads of considerable thickness supported that is more or square The friction material therefore furthermore by a metal plate of adequate stiffness not have to stand up to handling during assembly does not have to withstand does mechanical strength alone be riveting and could from the point of view of bulk made without a high loading of fibrous reinforcement of any kind There remains thermal shrinkage and thermal shock and in order to prevent the formation however of asbestos fibre is still of tensile cracks normal to the operating surface a percentage retained Nevertheless it cannot be said that the use of asbestos in disc brake pads remains a technical necessity and it is in this field of friction materials that some departure from asbestos based composites could occur in the next few years on technical and performance grounds FRICTION MATERIALS FOR CLUTCHES I have confined my comments to brakes but the development of friction As yet lines In recent years however materials for clutches has followed broadly similar we have seen the start of a growing replacement of manual clutches by automatic ssible the ater heat so at the e context replaced rength required helts even her fillers necessary ous types er recent os almost y is up to materials wool configura- titute for gth the point passenger pped with : technical urely forger shape upported therefore withstand alone be ^ remains formation ibre is still rake pads that some years on of friction . however automatic vos Possible alternatives to asbestos as a friction material 27 transmissions where the clutch packs are immersed in oil and therefore do not give rise to airborne contamination The friction materials used are in any case made from sintered metals or paper based facings in which the fibre is largely cellulose This feature is made possible by the low operating temperatures due in turn to the fact that the materials are immersed in oil Clutches for heavy duty manual shift gear boxes are in the U.S.A. being superseded at a significant rate by the spider clutch This is a type of clutch in which the friction material instead of being in the form of a thin annulus consists of a number of buttons rather like disc brake pads and these again could be made from asbestosfree material such as sintered metals or cermets metallic compositions Summarizing the situation at the present time therefore it can be seen that there is a drift towards the use of smaller quantities of asbestos in friction materials as a result of a number of purely performance considerations and design changes that is reduced amounts of asbestos in some disc brakes and replacement by other materials in automatic transmissions and some dry clutches OTHER FACTORS AFFECTING EXPOSURE TO ASBESTOS There are however several other factors which enter the equation when considering the exposure to asbestos during brake and clutch maintenance which is the subject of this meeting The first is that the durability of friction materials is increasing as is the temperature at which they will operate satisfactorily I mention these facts not only because they tend to offset the adverse effect of increase in vehicle miles per year but because they affect the whole chemistry of asbestos in friction materials The second important point is that the type of asbestos used in friction materials is chrysotile or white asbestos and is different from blue asbestos or crocidolite not only in colour but in chemical composition and also in chemical decomposition The third important point is that under influence of heat alone chrysotile asbestos decomposes by loss of water of crystallization at a temperature of around 600 The process is rather slow taking well over an hour to convert 50 per cent of the asbestos to its degradation products These form a series of iron magnesium silicate materials known as olivine the end member of which is forsterite The olivine series of minerals are quite unlike asbestos both physically and chemically being fibrous and in fact widely occurring as the major part of many common rocks basic and ultramafic igneous One would not expect that a significant amount of asbestos would be converted to olivine during braking except under conditions of very severe duty such as a fade test but in fact it is exceedingly difficult to detect asbestos in friction material wear products It has only on rare occasions been possible to detect asbestos in wear products by ray diffraction methods and one has to resort to electron diffraction selecting occasional individual small fibres to show its existence This rather surprising fact has been known for several years and current theory suggests that it is accounted for by very high temperatures which are said to exist at the points of real contact between the lining and drum or disc even at bulk temperatures as low as 100 Whether this explanation is correct or not it remains a fact that very little asbestos survives in the wear products after brakes or clutches have been used under normal > > o Pees cont t hyp Webige FT aes Laue Ti 8 - I i : | i Hi i 4 H \ wy | ite Hea || " roy: { 1 |e 4 . 3 28 D. HATCH operating 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 1 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 be fibres This is easy to understand when one considers that under normal condi- tions a lining will lose about millionth of an inch of thickness for every 20 ft of sliding Over recent weeks I have had regular tests performed in which employees private cars and trucks from the Company fleet have been brought into the garage for brake cleaning The drums have been 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 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 TABLE 1. DUST COUNTS DURING BRAKE CLEANING BY COMPRESSED JET Test No. Samples 1 2 3 4 S 6 7 10 min average fibrous above p Fibre count 2-5 2-5 Fibre count Above 5 ... 2000+ - 109 402 607 475 1513 628 181 306 WARNIER WARNIER WARNIER WARNIER WARNIER WARNIER 5.0 5.4 2.1 2.5 3-7 5-3 8.2 3.2 0.8 I have co in friction ma in the belieft products fro other dusts a to suggest th necessity a 1 Glass fibre Steel wool Mineral woo Carbon fibre moe . Sintered met and cermets : 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 element suggesting that those particles over 5 ...must have been only just over I am not suggesting for a minute that the practice of blowing out brake drums with a compressed air 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 the other hand wear rates are very much lower resulting in an even finer subdivision in the wear products abit Fh Aa ed bhi BE Os ek hak sy cee ye "Bees Possible alternatives to asbestos as a friction material ions will POSSIBLE ALTERNATIVES TO ASBESTOS use each I have confined my comments to an account of changes which are taking place ximately in friction materials at the present time in the normal course of technical development SS nd down in the belief that although the use of raw asbestos must be tightly controlled the wear ST ONE re judged al condi- products from friction materials are probably no more dangerous to health than many other dusts and can be treated as merely dirty If further evidence comes to hand ; 20 ft of to suggest that a substitute for asbestos must be found then under the pressure of pceats op necessity a list of possible replacements could be drawn up as follows - pera) s private Glass fibre Low strength melting severe frictional instability for brake Steel wool Low availability cost strength to drums ntilation Mineral wool Very low strength to the extent of limiting mixing pro- use of a cesses C samples Carbon fibres 100 currently forecast to fall to lb in several years time 28 ral of the Still ten times too expensive - operator Sintered metals Probably the best possibility eventually but cost will always be , 1 Table . and cermets relatively high . op One RACUR ple ot number of very small 5 element rums with ud of this clutches ian worse to higher uch lower TN MEIR TERE a AN URES 7teprynmaepn i lane Uae TAT Spie sp Ree Sa WW TT TRIME REL TSI eanmoritn: COPTER mena Caen) nares ke ira oe Ann Occup Hyg Vol 13 pp 31-32 Pergamon Press 1970. Printed in Great Britain i | | . e e j CONTROL OF THE USE OF ASBESTOS- CONTAINING FRICTION MATERIALS , M. L. BENTLEY Mintex Cleckheaton Yorks . , . INTRODUCTION THIS paper outlines the measures taken by the industry to find out the nature and causes of asbestosis and the work it has carried out on environmental control Particular reference is made to dust created during the manufacture and subsequent handling and machining operations of friction materials containing asbestos It rather less than 40 years ago that the need for control of asbestos dust in large quantities was first recognised and the Government Regulations which became law in 1933 have resulted in a considerable improvement in the health record of people employed in asbestos factories In the 1950's however it became apparent that although the improvement had been dramatic cases of asbestosis were occurring in people who had joined the industry since the dust control measures were introduced and it was also apparent that 1 certain users of asbestos products such as thermal insulation engincers or laggers were also deing affected As a result of this the three leading Companies in the asbestos industry B.B.A. ; Group Cape Asbestos and Turnet & Newall decided that further investigation into the nature and causes of asbestosis was necessary and they financed and set up the Asbestosis Research Council with this objective Since then the Asbestosis Research : Council ARC has continuously sponsored research at Cambridge Reading and ' other centres and has ordinated the work of its own research medical and en- \ gineering teams concerned with this problem Much of the increased awareness of health problems connected with asbestos stems from these research projects and the industry's own experts are acknowledged and have been consulted regularly by Covernment Departments and other organisa- tions both in this country and overseas The ARC has drawn up some Codes of Prac- tice on the handling of asbestos in those areas where the control of asbestos dust was thought advisable at that time The ARC has also played an active part in the formu- lation of the new Asbestos Regulations which are expected to become law in about 12 months Because of its considerable experience in using asbestos and asbestos products itself and its concern that these products should be used without risk it set up an additional committee last year with the principal object of intensifying the study of problems arising in the working environment dealing with those areas where it had only This paper was originally presented at a Conference on Exposure to Asbestos during Brake a: nd Clutch Maintenance held at Brentwood Essex March 1969 31 Or ar r orm mi ergee Baea enl en PO A ALI OTT OL RR EIN HOON OM yap t Salad CEETETON IN 5 TA YT CPR TT NG T EET! HET LEE IRD othe: Ldvammetinnds cans 0a tod ie-eistentiae teint. Caer ne eee ET Brn rare arden vey 1 ee mn - 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 Asbestosis Re- search Council and it consists of a number of working groups concentrating on the special problems of particular areas One of these Working Groups is being devoted to the field 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 the brake clutch and car manufacturers also in the replacement and service field - ; Its 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 own dust counting teams who have many years experience in accurate dust measurement This work is continuing and a picture is being built up of dust counts likely to be en- countered whilst carrying out typical operations during brake and clutch maintenance Analysis of the dust found in brake drums is being carried out also to determine whether all the fibrous dust is asbestos or not 1 In addition to gathering and collating information on a large number of dust 1 readings in various types of service premises the Working Group is preparing two | codes of practice for users of asbestos iricuon materials which will be ' issued by the Asbestosis Research Council One of these is for the guidance of bulk i } users in factory premises carrying out in some cases operations similar to those i 5 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 the principal requirements of the new Asbestos Regulations to recommend the action that they should take to meet their requirements The aim is to achieve what is after all the whole purpose of the Asbestos Regulations and the Asbestosis Re- ath search Council's work reduce concentrations of asbestos dust to a safe level d^' The long experience of the manufacturers of friction materials in dust control over a antl wide variety of operations will enable them to recommend measures and types of sthenta equipment to help the users to comply with the Regulations and protect the health of their employees pon A further line of study is being followed to see whether a satisfactory surface- wre sealing agent can be found in order to cut down the amount of dust given off in hand- Se 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 ae 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 in service Cee garages It is however the intention to give as much help and advice as possible with Oe the facilities that are available and requests for help or advice directed to the Asbestosis Te PERI Research Council will be passed on to the Working Group for action SA Tm eR er eeE Par . oe incik saith deck en 3 STEEN UTE i OT LSR PTY ON a ORR ' epmmeres ree Eng those tosis Reng on the I devoted & Parkes n formed -ustomers and service xists and premises 2s by the own dust surement to be enintenance determine er of dust - aring two h will be ce of bulk - to those is for the to remind commend nieve what stosis Re- safe level trol over a d types of 4% the health z zi r V surface- betes Ye fi fi in hand- Bb Hy he country r with and . in service ssible with Asbestosis Ann Occup Hyg Vol 13 pp 33-36 Pergamon Press 1970. Printed in Great Britain REMOVING DUSTS FROM BRAKE ASSEMBLIES DURING VEHICLE SERVICINGALTERNATIVE CLEANING METHODS G. L. LEE British Leyland Longbridge Birmingham PRELIMINARY CONSIDERATIONS and 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 the method should be minimal and it is easy to see that the chances of de- ivneluospiinngg a technique of cleaning which will reduce dust emissions but at the same time and effort are extremely slim Quite clearly we must time require no more concede from the very beginning that some increase in time effort involved is , inevitable When viewed under normal lighting conditions the result of applying a compressed line to remove brake dusts is very dramatic Unfortunately mere dramatisation alone is not adequate to describe the emission of dust from a process more methods are needed The conventional method of evaluating an environmobejnetcatlivecondition 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 method to define certain environmental conditions which prevail when brake sdiumstpsleare 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 are 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 at a Conference on Exposure to Asbestos during Brake and This paper was originally presented Clutch Maintenance held at Brentwood Essex March 1969 33 BN 2 re] ' PAT ee sh Vn ot TT ta predic Ae. arntS)d EET Lt ~ PE nop eT en he be Ce Tew,res aa aig) Reiko ad OEE T permnatbenWaren intearge Fok pgnros TT onreset anegs ay 2 ATOTTIOTR 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 Konimeter 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 HIGGINS and DEWELL 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 a to magnitude and hence the total dust concentration was used as describe the dustiness of the environment relative method 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 preparatory 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 series of Konimeter samples were taken during typical operations and also after the process had ceased The counts for these samples are summarized in Table 1 TABLE 1. RESULTS OF KONIMETER SAMPLES DURING BLOW Sample Taken at beginning of operation Taken approx 20 sec later Taken approx 60 sec later Taken approx 30 sec later Taken approx 30 sec later Number of brake dust particles cm 5000 4500 4000 1800 580 It is seen that there is a progressive fall in count as the local dust cloud disperses The first three figures are approximate only the numbers of particles collected being too high for accurate counting ndicatedwasiolerns was ion ndicated Personal Personal ampling ampling ng zone entfibreamplingngng zone fibre Possible Possible eigeihgiehniigngghingeighing eighing Che highhighorder of ethodethodethod PCB a An glazemdthodsglazed methodsmethods methods out fry AGIA RE Iv NP TP Sty % r ROS Cre oe Pe rear repara- repara2 ould Ckee ould ience iencbee nience TabTlaebleTablealso . , sperses sperses sperses d beingbeing being . papgeint sedy fi wae FIG 1. Brake Brake Brake assembly assembly assemblyasembly assembly assembly as embly before before cleaning cleaning facing p 34 mn bona Ptpe ee PE ae ures aero SRT Te PUES sear Cora eee aORChae a pacemn ded ARAN Bt we ak . eee ioe aha ine ee atase taFe ar nt wel ScotiagesIe: tei Seat puaateae e bbe 1S e ad 3s 8Pele29 * set dielatnr) i: mery INTEL bs a e lipatiantrandheta 2 meyr prem fA at Pld en cetirsTy ae nalRieteh e pbb ter danda UD| 1 Anion 7 tt er is tna etPt OY ELE eundatharen dhs CS Be RA OL 4 Aa GORE Ct nis s^'Soanah 4 cg q oad 2 aed a a = ES & & Es: #8 a = S : Ze a: ~ # ak az e x =z vt 4 AEP ATA on oti Removing dusts from brake assemblies during vehicle servicing 35 A fixed sampling period of some 5 min was chosen for the determination of mass concentrations being longer than required for the blowing operation but sufficient to cover that required for the alternative cleaning methods The dust col- lected by the static sampler close to the brake assembly gave an equivalent concentration of 114 mg and that for the personal air sampler 42 mg It is probable that many of the particles included were larger than respirable size The few asbestos fibres counted on membrane filter samples gave a concentration of the order 3-5 fibres ALTERNATIVE CLEANING METHODS Initial approaches were to try the use of fixed and hand extractors to collect the dust particles removed by brushing with a small paint brush Fixed ex- tractors although reasonably efficient were rejected because of restrictions which these placed upon the work by confining it to one area Both operatives and super- vision were unhappy about being confined to one work preferring to retain flexibility and carry out the work as they had previously done wherever the vehicle happened to be Portable extraction equipment was clearly required and after some preliminary enquiries a BVC industrial vacuum cleaner was selected for use in experimental work It is of fairly conventional type powered by a 2 h.p. motor and supplied with disposable paper bags in addition to the normal cloth bag The paper bags are fitted in manner which allows them to be sealed fairly easily before removal To trap any particulates which might pass through the paper and cloth bags an ex- ternal multi filter was provided for fitting to the air outlet end of the cleaner Preliminary experiments established that some brake dust particles were passing the paper and cloth bags but these were trapped by the externally fitted filter Sampling , at the exit side of the filter established that no particles passed the filter CONDITIONS OBTAINED USING THE VACUUM CLEANER AS A SOURCE OF EXTRACTION The first technique tried was to use the nozzle of the cleaner hand as a source of local extraction whilst the dust deposits were disturbed with a small paint brush held in the other hand The Tyndall Beam showed that some dust was escaping into the environment Objective measurements are summarized in Table 2 TABLE 2. RESULTS OF KONIMETER SAMPLES DURING BRUSHING AND WITH LOCAL EXTRACTION Sample Taken at start of process Taken about 1 min later Taken about 2 min later Taken at end of process Number of brake dust particles cm 1070 404 426 446 gawd! Semmens at A br Ladsatienianl se sar ehitine asihe R bee y teh ben he n a ae WAS BE T STR at Sc It SoTR sre 36 G. L. LEE The fixed sampler in the area of the highest concentration gave a dust concentration of 21 mg mand the personal sampler 7 mg An improvement in controlling the release of dust had been obtained but was not considered completely satisfactory and an alternative approach was sought CONDITIONS OBTAINED USING A MODIFIED TECHNIQUE After some preliminary experiments the following general technique was devised Firstly the loose deposits of dusts inside the brake drum and on readily accessible surfaces of brake shoes and the brake assembly were removed using the smallest brush supplied with the cleaner equipment being used as a vacuum cleaner A much narrower tubular brush made from available materials was then used to remove deposits from less accessible surfaces Finally a rag soaked in water and wrung fairly dry was used to remove adherent deposits No visible emissions of dust were observed but a few particles were detected by the objective methods as shown in Table 3 . TABLE 3. RESULTS OF KONIMETER SAMPLES DURING MODIFIED TECHNIQUE . Sample Brushing with standard brush Brushing with tubular brush Rag wiping Number brake dust particles cm 16-25 20-25 1-5 No fibres were detected and the mass concentrations involved were too low to determine CONCLUSIONS - The objective measurements made seem to confirm that vacuum cleaning provides a useful contribution towards obtaining satisfactory dust control when brake assem- blies are cleaned The design of the particular cleaner chosen prevents the discharge of particles back into the environment and the collection in a paper bag enables suitable disposal methods to be adopted This work was completed in the early part of 1968 and subsequently the method described was recommended for use until such time as the results of studies being carried out elsewhere in the Motor Industry were known and detailed requirements subsequently formulated Acknowledgements assistance of Mr D. Smith of the Industrial Hygiene Department and Mr Young Works Engineers is gratefully acknowledged REFERENCES ADDINGLEY C. G. 1966 Ann occup Hyg 9 73 HIGGINS R. I. and DEWELL P. in Instruction Leaflet 3107 C. F. Casella Ann Occup Hyg V. INVE OF C THE THE MOST usu assemblies is by a dust cloud in being cleaned generated at a mum likely exp Enquiries a is to allow ins in itself Our e the parts of t total cleanlines The criteria method did nc that it was not was needed The alterna Vacuum funnel The funnel for an industri periphery and the funnel was and compresse laden air the cleaning of This paper w Clutch Maintena st concentrad but was not ght EQUE was devised ily accessible - the smallest ruum cleaner then used to in water and ssions of dust 5 as shown in re too low to ining provides brake assem- the discharge tables suitable y part of 1968 I such time as y were known ment and Mr Ann Occup Hyg Vol 13 pp 37-39 Pergamon Press 1970. Printed in Great Britain 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 Essex INTRODUCTION THE 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 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 in itself Our efforts were therefore directed towards the removal of loose dust from 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 funnel The funnel see Fig ) comprised a steel cone with a connection point at its apex for an industrial vacuum cleaner a flexible skirt with a draw string attached at its periphery and a small 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 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 March 1969 37 baees Lien Pe s EE ST GPR AMESOPRR I IPM ekg ak LT S 1 Seta PA, adh A alias RAR te Anca by meh hie ar Oe Ee Ns naea Ses macs 3 ae che fares . . 1 SERN Seog r2 atAi Mes ot ayWe Ok wudnt Be we htna Bs ae cre Suid. 38 K. L. KNIGHT and D. E. HICKISH Vacuum brush The vacuum brush shown in Fig 2 consisted of a circular nylon bristle brush mounted on an angled handle and fitted via the handle to the same vacuum cleaner In use the brush was used to remove dust from drums and assemblies under vacuum EXPERIMENTAL PROCEDURE In order to determine which of these two methods was the better the performance of each was compared with the traditional blow method in two separate experi- ments shown in Table 1 TABLE 1. EFFECT OF CLEANING METHODS ON DUST CONCENTRATIONS Hour Activity Personal sampler Static sampler Peak sample _ particles fibres particles fibres particles fibres Personal sampler _ particles fibres Static sampler particles fibres Peak sample _ particles fibres 1 Back- ground 2 Blow S Back- ground 6 Funnel cleaning 6 Brush cleaning 116 422 0.96 5.35 161 ' 0.45 72 0.52 , 41750 87 107 0.95 162 0-41 415 3.5 210 0-75 759 1.04 125 0.16 129 0.10 . 635 0-84 155 0.16 41750 87 140 0.09 110 0-20 158 0-22 122 0.18 310 0-57 During the first hour of the day air samples were collected to determine background concentrations during this period the near side front road wheel was removed In the second hour samples were collected during dust removal from the near side brake assembly by blow Further background samples were taken during the fifth hour while the off side front road wheel was removed and during the sixth hour dust determinations were made while either the funnel or the brush cleaning methods were used The personal samples were collected from the breathing zones of mechanics engaged in the work and static samples were collected concurrently to simulate exposure of mechanics working in an adjacent repair bay Short duration samples were also collected by means of a Dr^/gerpump from the operator's breathing zone at the peak period of dust generation All the samples were subsequently analysed for fibres in accordance with the technique laid down in the Hygiene Standard for Chrysotile Asbestos published by the British Occupational Hygiene Society 1968 Particle counts were limited to particles greater than I u dia re ae pebadr Pen os vistes le NY wh SIT a eats bares Mage Rebwdie CFS ate ote Auta ah Oras ROT SC a CeTE Tare SSTS ICO ae TTR SORS SORE SOEs wr er; saentrg Sea FIG 1. Funnel method of dust control MANS RN a evar Sianicial kanamers taka 7 a Renr ar MAA et ETOP RELt eisaon dean and ti PTs: whoisae ET Sid TM na, tuiy here a soy) re Es i eo iy ~ ahs oo se < Mintek Bs eretay = sity 1ae LMPbp.ova an 21 21 b et vedtba nits 12 12 MA par Ait MY r Pn 18h suk FIG 2. Vacuum brush brush method of dust control tucing p a uty He A a! RT Redes RRNA UR Pah Rte Ra if Alternative forms of control for dust generated during the cleaning of brake assemblies 39 DISCUSSION The results for the vacuum funnel vs. blow experiment and for the vacuum brush versus blow are shown in Table 1. It can be seen that the background concentrations during the fifth hour had established at the original level after a 2 hr latent period and therefore the blow operation carried out during the second hour did not affect the concentrations observed in the vacuum funnel samples collected in the sixth hour The funnel appears to reduce personal exposure by 2 per cent for particles and 40 per cent for fibres concentrations observed in the adjacent bay are increased and a reduction in peak concentrations of about 80 was achieved During the second experiment there was more variability in the background con- centrations between the first and fifth hours but the effect of blow on the vacuum brush test may be discounted Personal exposure by use of the brush is reduced by 75 per cent for both particles and fibres and the static samples show a reduction of 20 per cent for particles but an increase of 12 per cent for fibres A reduction of 80 * in peak concentrations was again observed CONCLUSION The experiments demonstrated that the vacuum brush was better in reducing operator's exposure it had the added advantages over the funnel of being easier to handle consisted of fewer simpler parts and was much quicker than the vacuum funnel There are three major reasons for the relative inefficiency of the funnel its use increased brake cleaning time and thus exposure time by a factor of 8 it was difficult to obtain a good seal at the skirt and imbalance occurred between the necessary air input and the capacity of the available exhaust system with resulting leakage of dust REFERENCE COMMITTEE ON HYGIENE STANDARDS BRITISH OCCUPATIONAL HYGIENE SOCIETY 1968 Hygiene Standards for Chrysotile Asbestos Dust Pergamon Press Oxford ee SER id a ere Seae ae ee eaee 2 me So LET er ob BUR EAS RCM ADPAYN urets aM SRNSeds Pari org SELB 253 nest anh ay arta SP eraser anhahee t e Pop Soc y- lan! 2 AToes RLS ee WEcea St Bh Sek SWaEkRGE Je Orn Hae one rangersBic cei PRfs ay nOese BE avin!ip LNEHnp et oa I ete Raesow a crt tA alan IE A ate oy SE YS ATER MAR ATT PRET ye% * ae Big YE AulnitoadelerLR TN AeeR Wis rema a a ache. ky, Ann Occup Hyg Vol 13 p 41. Pergamon Press 1970. Printed in Great Britain RESPIRATORS FOR PROTECTION AGAINST ASBESTOS S. LUXON Productivity H.M. Factory Inspectorate Department of Employment and . Westbourne Grove London W.2 Chepstow Place OVER the past few years the British Standard for Respiratory Protection BS.2091 has been undergoing a drastic revision A new Standard BS.2091 Specification for Respiratorsfor Protection against Harmful Dusts and Gases has now been published andis of direct interest in regard to protection against dust including asbestos as a it places the standards of protection offered on 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 | wt respirators this protection factor is of the order of 20 that is the external concentra- S 4 acy tion is reduced to twentieth that inside the facepiece If use the standards aa * z suggested earlier such respirators should afford protection against prolonged ex- Hae posure to 40 fibres 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 thereis 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 ond use and the positive pressure dust respirator while acceptable to the wearer has a higher initial cost A further British Standard Positive Pressure Powered 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 Bs Ob as to require the use of equipment of this type as An alternative approach is to utilise a half mask fed with compressed air from a nyo 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 : " 41 Aches SoleHaeee 2 oe a Me Beit baapases ae Beg abd, Fhe Fie on a . AL st TOI z gat DITA ee ge Oo tenwry gem ad + ogthe Gene hoster: ahi hie Leanr 8 ot ot Beh , Sew = sebeags ce :ipe oe } p+ee oes sboae AS Bsch Kewane Wate Pit ries eitba pAb aaBere hi RINT one! Brae She Tetae Meae RT poresLe ngest Be& premy Ropes nee RRA CO ep Skee vey 7 dem GEE da T, aRbe Diag dea try ACADStoke anes HAs <a ge fee Bhat RAY E BOPGh OReINBeg AF tetast BOGENMeek meps sogtprent see ae RO bee + Brer hat bom EVIE2 ae4, ae Oe Che eee 1 eon FF EE Ate Tete IeASRSEee Al ind saa 33h A RCE TT eaTrsORE ree UN colo ' ocsreas AIG 7s, = TrcplneGt a PUREE i SDR evnsarycoven cer Saedreg we pemagn thy vencruseymar weal Raison