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The Annals of Occupational Hygiene AN INTERNATIONAL JOURNAL PUBLISHED FOR THE BRITISH OCCUPATIONAL HYGIENE SOCIETY pcs ip p p AUTHOR/CONTENTS LIST Volume 13, 1970 I I i I ) Prztace NUMBER l taoe L>. E. Hicxish: Exposure to asbestos during brake and clutch maintenance ... 1. V W. J. Smjther; Asbestos and ssbestosis.............................................................................................3 S. A. Roach: Hygiene standards for asbcstoi ........ 7 D. E. Hickish and K. L. Knight: Exposure to asbestos during brake maintenance 17 S. Luxon: Technical implementation of the new asbestos regulations .... 23 D. Hatch: Possible alternatives to asbestos as a friction material........................................ 25 M. L. Bentley: Control of the use of asbestos-containing friction materials . 31 G. L. Lee: Removing dust from brake assemblies during vehicle setvidnn--alternative cleaning methods ............. 33 K. L. Knight and D. E. Hickish: Investigations into alternative forms of control for dust generated during the cleaning of brake assemblies and drums .... 37 S. Luxon: Respirators for protection against asbestos ...... 1 !C W. !fc.'7jLBS ana C. G. tuez: Towards a criterion for impulse noise in industry . . 41 43 J. G. Walker: Temporary threshold shift from impulse noise................................................... 51 A. M. Martin, G. R. C. Atkerlet and T. I. Hemstooc: Recurrent impact noise from pneumatic hammers ............................................................ 39 W. G. Noble: A new concept of damage risk criterion ...... 69 Letters to the Editor; H. A. Bamber and R. BuTterworth: Asbestos hazard from protective clothing 77 M. Greenberg: Asbestos release from battery boxes..............................................................79 News Items............................................................ 81 Book Review.................................................................................................................................... 85 NUMBER 2 pace A. Black and M. Walsh: The preparation of bromine-82 and iodine-131 abelled poly styrene microsphercs with diameters from 0-1 to 30 microns ..... 87 R. Morlby and S. J. Silk: The industrial hazard from nitrous fumes .... f R. A. Bf.ntlf.y and I. Bfroman: Candle or oil soot as a cause of pneumoci niosis in coal 101 Am. Ora<p. Hrt- Vol. I}. p. I. fentmen fnu J9?9. PHnitd In Grt*l Baum PREFACE Exposure (o Asbestos during brake and clutch maintenance The papers which follow were originally presented at a Conference held at the 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 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 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. These would be preceded by papers on the medical aspects of exposure to asbestos, and later in the programme there would be papers indicating possible solutions to the problems involved. D. E. Hickish An*. 0<c"f- Hyf. VoJ. 13. pp..>J. Ptm 1970. Pruned m Grut 3r>uui ASBESTOS AND ASBESTOSIS* - W. J. Smiiher Group Medical Adviser, Cape Asbestos Company, 114 Park Street, London W.i, THE FORMS AND USES OF ASBESTOS Commercially important asbestos fibres fall into two main groups. The first of these is chrysoliie, and the second comprises the amphibofes. Both groups are fibrous silicates, but they differ in geological origin, in chemical composition, in molecular structure, in fibre size and strength, and in other characteristics. Chrysotiie, white asbestos, comes from many different places. There are slight ctemical and physical variations in the fibres from different sources, but basically all have the same molecular structure. On the other hand, the amphiboles comprise ai least three separate types, whose molecular structure is very similar, but whose chemical and physical properties differ more widely. Amosite (amber) and crocidoljre (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. Aibtitot AnnuOl world output *3,000,000 toot Chryjoti I* (whit* J 2.600.000 ton* 93% Croeidolit* (fill*) (Soutn Alnee) 110,000 ton* Amonto (South a(mco) 90,000 ton* 3% ------ 1 Antliophytlit* (fmionO) 10,COO toft* ?* Conodo USSR S Africa USA Europe Other* 1.250,000 750.000 250,000 100,000 100,000 350,000 Fio. 1. World production of asbestos. 4 W. J. Smitihr AyoeHot io 3,000,OOU Wf*/* >t J yid Wr*r it '* <nmd Other* 8<<qgm Holy ftonce v>APafj UK GrmOy Cti'y'o'iH Other* USA Southern Africa USSR USA USSR Canada B!u CrOCiOOlitC SAfnco Amosit* S.Afnco l ui. 2. Areas of use of asbcsios. AnthophylM* Fmfand The diHercm characteristics of asbestos fibres dictate their uses, their applications am! their mode of packing and handling. For example, amositc can be pressure packed and palletized, whereas chrysotilc lends itself more readily to containerization. Uy far the greatest use of chrysotilc is in the asbestos cement industry. Amosite is used mainly in insulation and building products. Crocidolite, due to its excellent acid resistance, finds its major application in the manufacture of .battery boxes in this Cc-u/TAy. T4 TV ,J lUXfrVtl ' HlsVC\tu. tfjS- Aibestos and abui J Very broadly it can be said chat 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 'orcseen with an even lower percentage, probably down to a minimum of 30 per cAt. 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 associa;ed with the fibres has also to be considered. The chief biological effects of asbestos are confined to the lung and the p.'eura, 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, con sists 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 ot 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 failur:, 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 crocidoiite than to chrysotile, amosite or anihephyllite. The reasons for this are at present obscure, but are being sought intensively by investigators in many different countries. Xv. Ocow- Hrt- Vol. 13. pp. T-tS. Ptr^imoo Pru4 IJTO. PtiaUxi ia Gre*i Bnuia 1 HYGIENE STANDARDS FOR ASBESTOS* S. A. Roach London School of Hygiene end Tropical Medicine, Keppel Street, London W.C.l. As long as there is any airborne asbestos dust in the work environment there may be some small risk to health. Nevertheless exposure up to certain limits can be tolerated for a lifetime without incurring undue risks. A hygiene standard for asbestos was published in the U.K. by the Ministry of Labour in 1960 and was taken from the annual list of Threshold Limit Values of the American Conference of Governmental Industrial Hygienists (ACGIH) (Committee on Threshold Limits, Annually). The British Occupational Hygiene Society formed a Hygiene Standards Committee 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 Sub-Committees, each of wrich is con cerned with a specific standard. There is a sub-committee on asbestos dust in air, one on trichloroethylene vapour and its urinary metabolites, one on airborne vegetable dusts in the textile industry, another on noise criteria for hearing const rvation and two new ones are coming into being; on cadmium oxide fume and silica dusts in air. It is important to take imo account the economic consequences of any recom mendations made as well as the benefits to health, and this is one reason why on each of these Hygiene Standards Sub-committees, scientific and medical experts from industry are included. The value of a standard rises in proportion to the number of people who become protected by it. A particular advantage of direct industrial representation on hygiene standards committees is that the industry more readily identifies itself with the standards recommended. The Hygiene Standards Sub-committee on Asbestos, under the Cha rmanship of Professor Lane, has developed new hygiene standards for airborne chrysotilc dust (Lane et a!., 1968). These were based on the results from a medical ind environ mental study at an asbestos textile factory in England, in which investigations were made on 290 of the men employed at this factory in the period of 1933-1966. The Sub-committee considered that the degree and nature of the rink associated with the standards should be specified and the method of the derivation of the stan dard from the data presented should be described in detail. It was also considered that the standards should give prominence to the gradually increasing risk in relation to the concentration rather than to the single figure threshold concept. Open recogni tion should be given to the possibility that people might be adversely affected, even This paper was originallr presented at a Conference on Exposure to Asbestos during Brake and n... .i. ti ............... ..................................... r-,., i ntr, 3 S. A. Roaci when the recommended standards of air cleanliness are maintained. It was recognised that to protect the h)persusccpiibtc workers environmental control would have to be supplemented with medical examinations. It was c\ident from the data made available to the Sub-committee, and from the earlier American experience, that when concentration is held constant the prevalence of asbc>to$is was highest among those with tire greatest duration of exposure. Over a period of lime, dust accumulates in the lungs and gives rise to asbestosis. However, some of the dust is removed from the lungs, for example, by being dissolved. Con sequently, if it is assumed that none is removed and exposure is limited accordingly, a safety factor is thereby incorporated. The problem of relating prevalence with concentration and with duration of exposure was resolved by assuming that the cumulative amount ofasbestos remaining in the lungs from a given exposure is equally dependent on the dust concentration and on the duration of exposure to that con centration. The asbestos dust concentration had been measured at the textile factory con cerned with several different instruments, including the membrane filter method, in which the number of fibres longer than 5 \i was counted. The dust concentration to which different workers had been exposed varied from 1 fibre/cm* to 27 fibres/cm` over periods from 10 years to 33 years. The exposure of an individual was expressed as fibre years/cm*, that is, the product of the average concentration to which he was exposed during working hours and his years of exposure to this average. A curve was developed relating the prevalence of asbestosis to exposure expressed in this way. The principles on which this was based may be explained as follows. An individual's response to dose of any foreign substance can be expressed by a line (Fig. 1). There is a dose which produces no response whatsoever. This is marked by the threshold A. If the individual is given progressively higher doses, the response progresses correspondingly. The least positive response may be real but merely undesirable. A higher response may have sensory manifestations. A still higher response might be associated with observable physiological changes and overt clinical effects. The highest responses of all would perhaps be signified by loss of conscious ness, or even death. The degree of response may be conceived to be measurable objectively on a con tinuous scale starting at zero, and ihe scales of dose and response could be chosen to linearise the relationship between them, as in Fig. 1. The dose-response relation ship could then be described by the slope of the line and the point where the line strikes the dose axis. The slope of the line expresses the rapidity with which increases in dose produce increases in response in this individual. The steeper the slope the greater the safety factor necessary in practice to allow for the inevitable occasional excursions of dose above the maximum desirable. Doses which give 2cro response are never, in fact, known with absolute certainty since the sensitivity of measurements of response is limited. A response which can just be detected in a man corresponds to another and higher dose, shown as threshold B on Fig. 1. Also, one is not normally considering just one individual. As with ail other characteristics of man, the position and slope of a dose-response line varies from one individual to another. Each man's dose-response line is different with a Hygiene standards for asbestos lnd`iduoi <*'' to ao 9 Fto. 1. Individual response to dose. different threshold dose and a different slope. A particular population i.nder study is represented by a family of dose-response lines centred around the ine for the average man. In a real population the threshold dose will vary from one individual to another about an average value, as in other medical norms. It is to be expected that the size frequency distribution of threshold doses would be a hump-shaped curve tailing away on either side of the central value, as shown in the Fig. 2a. In a real field study it is established whether a man has or has not been affected. Exactly when or in what concentration he first developed the characteristic response is usually not known. A graph showing exposure against the total number of people affected by it would be a cumulative sigmoid curve, illustrated in Fig. 2b, derived from the size frequency distribution in Fig. 2a. This tails away down to zero response at zero exposure. An air quality standard is still associated with a small but non-zero probability ofmen being affected by the contaminant in question. The risk ofpeople being affected can be made as small as one wishes. Zero risk is the ultimate target and an air quality standard has to be a compromise between the costs of bearing a health risk and the costs of air contaminant control. A curve was fitted to the data from the textile factory on asbestosis, detected clinically and the exposure in fibre years per cm1 of all the individuals under study over their years of employment up to 1966. The bottom end of the fitted curve :s shown in Fig. 3. The three points relate to three of the'groups of workers studied. The exposure Removing dosu from brake assemblies duriog vehicle servicing 35 A Hxed sampling period of some 5 min was chosen for the determination of mass concentrations--this being longer than required for the blowing operation but sufficient to cover that re-.; .sred for the alternative cleaning methods. The dust col lected by the static sampler dose to the brake assembly gave an equivalent concen tration of 114 mg/m* and that for the personal air sampler 42 mg/m`. 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 fibrcs/cm*. ALTERNATIVE CLEANING METHODS Initial approaches were to try the use of fixed and hand-held extractors to collect the dust particles removed by hand-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 area--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 i h.p. motor and supplied with disposable paper bags in addition to the normal cloth bag. The paper bags are fitted in a 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-layer 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-held 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 ano WITH LOCAL EXTRACTION Sample Number of brake dust partkIes/5 cm* Taken at start of process Taken about 1 min bier Taken about 2 min later Taken at end of process 1070 404 426 I 446 10 S. A. Roach Fic. 2a. Population response to threshold dose. Fio. 2b. Population response to dose. 12 S. A. RoaCU at work, -1 fibres,cm* for 25 years, or 10 fibrcs/cm* for 10 years. The British Occupa tional Hygiene Society Hygiene Standards Sub-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 l per cent of those who ha\e a 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 fibrc$/cm*. 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/cm*. 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 average concentration over 5 months and can safely be kept below 1 per cent by ensuring that a man's accumulated exposure does not rise above 100 fibre years/cm*. The exposure measured by making fibre counts on membrane filter samples can be converted into exposure measured with an impingcr, the American method, by examining the results of side-by-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/cm* corresponds to 15 mitlion particle years, ft* by standard impinger methods (Ayer, Lynch and Fanney, 1965). The present American Threshold Limit Value is a concentration of 5 million particies/ft* (mp/ft*) which, if it persisted, would result in an accumulated exposure of 250 million particle years/ft* over 50 years. These American hygiene standards, called Threshold Limit Values, are a system for summarising published information on air contaminants in a convenient form for the day-to-day practice of industrial hygiene. The present American standard for 8-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 pri marily due to conflicting evidence on the adverse affects of asbestos. It is because of a diircrcnt attitude now adopted over the degree of protection which ought to be given against asbestosis. The American Threshold Limit Value of 5 mp/ft3 was recommended by Dreessen and his co-workers in 1938 after studying 541 employees in 4 asbestos textile plants where massive exposures to chrysotile occurred (Dressen cial., 1938). Only 3 doubtful cases of pneumoconiosis were foujid at the time of the study in those exposed to dust concentrations under 5 mp,ft\ whereas numerous well-marked cases were found above 5 mp/ft*. A conference held in 1965 on the biological effects of asbtslos called attention to the very real probability that the 5 mp/ft* limit recommended by Dreessen is inade quate to give complete working-lifetime protection against all forms of asbestos (ScttAt.L, 1965). Medical data on which the limits had been based were inadequate; more than half of thc*asbestos workers studied by Dreessen and his co-workers were an vivirs of nee and thus had insufficient exposure time for much asbestosis to Hygiene standards for asbestos !3 develop. Of the 105 workers exposed to less than 5 mp/ft*, 82 had woked less than 5 years and only 4 had more than 10 years exposure. Moreover, it was a "point-intime" study; many of the ill were missing, the dead uncounted, and were not considered in the over-all 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 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 and considerations applicable to the American industrial scene. Recent evaluation of the health experience in asbestos plants in the U.S.A. had, nevertheless, indicated that the 5 mp/ft* limit was not sufficiently low to protect workers txposed for 30 yean, a period rarely exceeded in America. In accordance with these findings, the 5 mp/ft1 limit was made a ceiling value below which all concentrations should fluctuate. This corresponds to a time-weighted average concentration over a shift of 2 mp/ft*. Since the count by Irapinger procedure often consists primarily of extraneous particulates, an alternative fibre count was recommended, using the membrane filter method in which fibres greater than 5 p in length are counted as in Britain. On this basis, for a time-weighted 8-hr average limit by Impinger count of 2 mp/ft*, the corresponding limit based on the fibre count is 12 fibres/cm*. This limit is intended to reduce to an insignificant risk, the occurrence of asbestos disease among those exposed for 30 years to all forms of asbestos. The intended changes in American TLVs give two years' notice and objections to them should be conveyed to the TLV committee of the ACGIH. All objections are 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. The standards of the British Occupational Hygiene Society recommend that a person's accumulated exposure to chrysotile asbestos should not exceed 100 fibre yarsfcm*. 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 these standards. It is believed that this is the first time a hygiene standard has been associated with such a specified degree of protection. The n&ndatds refer essentially to an average concentration during working hours over 3 months of 2 fibres/cm*. In an environment where this 3 monthly average just equals 2 fibres/cm1, the concentration within this period will sometimes be above this value and sometimes below. The maximum 8*hr average will thus be somewhat higher than 2 fibres/cm*. The proposed change in the American TLV is to a maxi* mum 12 fibres/cm* 8*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 Inspectorate in their work have often only a short time during a day to come to a judgment on conditions and are considering a development of this, applying a maxi mum for even shorter periods, of a few minutes, which if exceeded would indicate a probability that the Asbestos Regulations are not being complied with. There is a growing body of information on chrysotile dust and other asbestos dusts from many countries, and it is hoped that in future the views from different ;f *. \-f ' * ti? lut| * T * ~~r. rl- M S. A. Roach parts of the World will bo sought so that standards for testing air cleanliness can, as far as possible, be held in common. Even so, the risks that may be tolerated can vary from country to country and from one situation to another within a country. The air quality attained in industry in difTerent countries docs differ and, no doubt, will continue to dill'er. 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 ma> 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 Sub-committee on Hygiene Standards for Asbestos has not yet decided whether their chrysotile standards would be suitable for amositc 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 decree 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 cITccts or lack of them in the people. It is also necessary to have a grasp of the consequences to industry and users of limiting and controlling 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 Sub-committec 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 \cutiIation 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 tc determine the balance between local and general ventilation which produces a specified degree of control at minimum cost. By setting down the ,n.i it no H-iiir>n mnnine and mnintcnnncc costs, it becomes possible to Hygiene standards for asbestos 15 grasp more firmly the consequences of adopting particular hygiene standards. This kind of information is needed throughout the field of asbestos dust control so. as to 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 mathematical equation, nor does it avoid the need to exercise wise judgment in the choice of stan dard. However, the judgment can become a little less arbitrary than at present. REFERENCES Ayes. H. E., Lynch, J. R. and Fannet. J. H. (1965) Aw. ft. Y. Acad. Set. 132, 274. Committee on ThreshOU? Limits (1968) Supplemental Documentation of Threshold Limit Values. Trans. Am. Conf. Governmental Industrial Hygienists 1968, p. 188. 1014 Broadway, Cincinnati, Ohio, U.S.A. Committee on Threshold Limits (1969) Threshold Limit Values for 1969. Americas Conference of ' Governmental Industrial Hygienists. 1014 Broadway, Cincinnati, Ohio, U.S.A. Drecssen, W, C-, Dalla Valle, J. M., Edwards, T. I., Mhxex, J. W., Sayexs, P. R., Eason, H. F. and Trice, M. F. (1938) A study of asbestosis in the asbestos textile industry. Publ. HUH Bull., Wash. No. 241. Lane, R. E., Barnes, J. M., Hicxish, D. E., Jones, J. G.t Roach, S. A., and Xjno, E. (1968) Am. occup. Hyg. 11.47. Ministry or Labour (1967) Probtems arising from the use of asbestos. Memorandum of the Senior Medical Inspector's Advisory Panel. HMSO, London. SchaLL, E. L. (1965) Anti. N. Y. Acad. Sci. 132, 316. { Aim. Oca*. Hy%. Vol. 1). pp. H-JI. Per|mofl Preu UTO. Primed In Gr<i( Briuia EXPOSURE TO ASBESTOS DURING BRAKE MAINTENANCE* D. E. Hickjsh and K. L. Knight i ! Medical Services, Ford of Britain, Brentwood, Essex EXPOSURE DURING CAR SERVICING There is little maintenance of passenger vehicle brakes involved at the manufacturers' j premises, and therefore an investigation was carried out at the Service Bay of a Ford j Main Dealer in the Greater London area. This Dealer normally services 10-20 cars I per day, but blowing-out of brake shoes and drums is not included in f.ll routine ! services. It is the blowing-out procedure which is the subject of the study. Air sampling was carried out using membrane filters, the sampling and subsequent j assessment being in accordance with the technique described in the Hygiene Standard \ for Chrysolite Asbestos Dust, published by the British Occupational Hygiene Society ; 0968). Static samples were taken by the side of the car (Fig. 1) and composite samples I were also taken in the dust-cloud during the blowing-out procedure, continuing by j 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 over< estimate exposure. Two sampling periods of 45 minutes were used, and during the | first period one Cortina Estate and one Anglia Van received brake blow-outs, and i during the second period one Cortina car was dealt with. The results are shown in f Table 1. Tabu 1. Atmosphem sampus durinq car 8rakc service Location of samples 1st period Fibres/cm* 2nd period Time-weighted average By car M2 142 1*25 ' Dust cloud then by car 1-71 362 255 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. i This paper was originally presented at a Conference on Exposure to Asbestos during Brake and IX D. E. Hickisu and K. L. Knight Taule 2. Personal samples during car DRAKE SERVICE Sample Concentration (fibres/cm*) t 2 3 4 J 6 Time-weighted average 0-63 M2 0 21 096 038 079 0 68 EXPOSURE DURING TRUCK SERVICING Maintenance of truck brakes involves a somewhat different type of operator exposure as the servicing is more complex, and therefore the number of vehicles dealt with is less. The larger size of wheels and drums, on the other hand, makes it difficult for the operator to avoid the dust cloud produced, and personal exposure could be higher than that during car maintenance. Further sampling was therefore carried out in a large fleet workshop with equipment similar to that used for the passenger car tests. 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 of sample Concentration (fibres/cm*) Adjacent bay 2 hays away Centre of garage Morning Afternoon Morning Afternoon Morning Afternoon 0-28 007 017 007 049 0 11 Personal samples were obtained from two men--the m3n 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 lUc period of brake cleaning, and the second period of approximately 5 hr represented the remainder of the shift. The results are shown )I )I Fig. 1. Suite sampler by side of car. 'u4 I it.. 2. IVrvmal wimpkf. * Exposure to asbestos during brake maintenance 19 Tabu 4. Personal samples--truck brake service Operator Concentration (fibrts/cm1) Brake cleaner during cleaning after cleaning Time-weighted average Clutch repair--adjacent bay during cleaning after cleaning Time-weighted average 7-09 0-08 1-75 2-25 Oil 0-79 i SIGNIFICANCE OF EXPOSURE LEVELS ! The Hygiene Standard suggests that exposure should not exceed an accumulated ; level of 100 fibre-ycars/cm\ On this basis, a man exposed for the whole of his working j lifetime of 50 years, should not be exposed to concentrations exceeding 2 fibres/cm*. [ 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, 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 th'5 standard. Truck servicing The standard is not exceeded during brake cleaning in the general atmosphere away from the immediate vicinity of the operation, but personal exposures in the vicinity do exceed the standard. On a daily basis, the personal exposure levels are below the standard, although that of the brake cleaner approaches it.. 1 It should be noted, however, that in a fleet workshop, brake cleaning operations do not necessarily take place daily. THE NATURE OF AIR-BORNE DUST Rrake lining materials contain 40-60 per cent of asbestos, and it was somewhat surprising to find that panicles of a fibrous nature were scarce in the air samples collected. In a laboratory investigation, specimens of dust were obtained by filing brake lining material, and after sieving through a 200-mcsh sieve, 'hesc were ex amined microscopically before and after incineration. Samples of dust were collected from brake drums during car servicing and examined in similar manner. The results of the examination were expressed as the percentage of particles which were fibrous in nature, and are compare^ in Table 5, together with a result from an incinerated thermal precipitator sample obtained dnrine brake elennini*. 20 D. E. Hickish ami K. L. Knight Table 5. Assessment of fibrous fractions of dust samples Sample Percentage of particles seen to be fibrous Sample Sample not incinerated incinerated Brake lining material Brake drum dust Air-borne dust 28 12-3 0 1-6 13 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 chrysotilc was present only in trace quantities, or at most at 1 per cent, compared with the original lining content of 40-60 per cent. These findings suggest that there is a change in the physical and 'or chemical form of the asbestos during its use as a 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 or no fibres in the dust produced from bus and automobile brakes, except under severe braking conditions. In the latter instance, the brake temperature reached 320-370C, compared with the design maximum tem perature of 290-320C, and it appeared that, under these conditions, the binder decomposed and released part of the asbestos as free fibre. At lower bulk lining tem peratures within the normal operating range, the binder behind the surface remains intact. However, the spot temperature at the point of contact between the lining and the drum may be higher than the decomposition temperature of asbestos. The decomposition product, therefore, includes not free asbestos fibres but a different mineral, resulting from thermal metamorphosis. Holmes (1967) in reporting the analyses described earlier in this paper, com mented that the normal thermal decomposition product of chrysotilc is forsterite, a non-fibrous crystalline magnesium silicate. However, our samples of brake drum dust contained very little forsterite, but rather were mainly comprised of an amor phous magnesium silicate, which is non-fibrous. Little was known at that time about the structure and composition of this substance. Whilst there was no evidence to suggest that the material was a health hazard, this possibility could not be dis missed, and animal experimentation has been commenced-in the U.S.A. CONCLUSIONS Our investigations show that exposure to asbestos during brake maintenance is not as severe as was anticipated, and in the situations we examined, the personal exposure of the operators was below the limit corresponding to 50-ycar exposure. It is however recommended that care should be exercised during brake cleaning to avoid inhalation of the dust produced, and the development of cleaning procedures which would reduce air contamination is desirable. The present trend towards the Exposure to asbestos during brake maintenance 21 introduction of "flow-line" servicing at Dealers works, in which one individual may be engaged almost entirely on brake servicing, emphasises this point. Our environmental studies have not included maintenance procedures which in* volve the filing or grinding of brake lining material, and we would envisage that these would give rise to considerably increased air contamination by chrysotile asbestos, with the attendant need for strict precautions to prevent the inhalation of fibres. REFERENCES Committee on Hygiene Standards, British Occueationac Htciene Society (1969) Hytiene Standards for Chrysotile Asbestos Dust, Pergamon Press, Oxford. Holmes, S. (1967) Private communication. Lynch, J. R. (1968) J. Air Poilut. Control Ass. 18, 824. \ i Ami. Occur. Hft. Vo). 1). pp. 2J-2*. pcrfamoo Frw 1970. Printed In Greet Briteia TECHNICAL IMPLEMENTATION OF THE NEW ASBESTOS REGULATIONS* S. Luxon H.M. Factory Inspectorate, Department of Employment and Productivity, Chepstow Place, Westboume 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 on May 14 1970. They are based on the concept that asbestos dust must be so controlled as to be at a level whicb 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/cm* and 0*1 mg/m* for chrysotile asbestos. A fibre is taken as being 5 n or over in length with an aspect ratio of at least 3:1. This is of course the standard proposed by the British Occupational Hygiene Society (1968) and b based on 'ime* weighed average concentrations. There is a practical limit on the time over which samples can be taken if the exercise is not to become unnecessarily cumbersome and , 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 j fibres/cm* 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 ftbres/cm* should not be exceeded during any period of 10 min, i.e. we i might regard 12 fibres/cm* as a ceiling value. It must be remembered that we are using the fibre count not as an absolute measure of concentration but rather as a conveniently measurable parameter to indicate the j 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! (ton is yet available on the relationship between mass of asbestos and fibre counts in i other industries. To further complicate the problem, it is not known what fibre sizes are biologically active and, even if this were known, appropriate eiutriation (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 X-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. HtCKisH 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 or\ Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood, Essex, March, 1969. Aim. Ottvp. Ilyf. Vot. 13. pp. 25-29. Pergjmoo Preu 1970. Printed in Great Briuia POSSIBLE ALTERNATIVES TO ASBESTOS AS A FRICTION MATERIAL* D. Hatch Ferodo, Chapel-en-le-Frith, Derbyshire INTRODUCTION I have been asked to talk on the possible alternatives to asbestos as a friction material. The facts are that if by "alternative" we mean a new or better fibre which might shortly be available as a replacement for asbestos in conventional friction materials, then I think the chances are so remote as to be not worth considering. This is not to say that if the world supplies of asbestos dried up we would not eventually find a substitute, but it could well be at the expense of a considerable loss in performance, and also at a considerable increase in cost. THE ROLE OF ASBESTOS IN FRICTION LININGS Having started on what may appear to be a rather depressing note, let us examine the reasons why asbestos occupies the role of an almost universal constituent in friction materials at the present time. The first automotive friction linings were made from cotton textile material im pregnated with drying oils which were subsequently cured to form a strip of material which, while being flexible and conformable, still exhibited great mechanical strength. The main function of the drying oil was to protect the cotton from attack by atmo spheric oxygen, which, even at the temperatures reached by early brakes, would have resulted in the cotton burning had its surface been exposed. A second function of the drying oil was to prevent the cotton from fraying under the influence of mechanical abrasion. As brake operating temperatures increased, it was found that cotton started to degrade and lose its strength even though still protected from attack by oxygen. In other words, it suffered thermal degradation instead of oxidative degradation. Around 1910, a technological break-through was achieved when it was discovered that textiles could be woven from asbestos and used to replace cotton, because asbestos neither burns nor loses its strength below about 500C. However, as brake operating conditions became steadily more severe, a point was reached in about the middle 1940's when, despite the continual improvement of synthetic resins with which the asbestos textile was impregnated, further heat resistance was required, this time because the organic part of the composite was proving inadequate. The solution proved to be to mould brake linings from powdered resins, using short fibre unwoven This paper was originally presented at a Conference op Exposure to Asbestos during Brake and Cllltrh M Tl Nr.-iil.1-..AV M Am. 0*p- Hyt- Vo). 13. pp. 23-29. Periimea Pieu 1970. Printed in Great Britain POSSIBLE ALTERNATIVES TO ASBESTOS AS A FRICTION MATERIAL* D. Hatch Ferodo, Chapel-ende-Frith, Derbyshire INTRODUCTION I have been asked to talk on the possible alternatives to asbestos as a friction material. The facts are that if by "alternative" we mean a new or better fibre which might shortly be available as a replacement for asbestos in conventional friction materials, then 1 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-OP 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 ficxible and conformable, still exhibited great mechanical strength. The main function of the drying oil was to protect the cotton from attack by atmo spheric oxygen, which, even at the temperatures reached by early brakes, would have resulted in the cotton burning had its surface been exposed. A second function of the drying oil was to prevent the cotton from fraying under the influence of mechanical abrasion. As brake operating temperatures increased, it was found that cotton started to degrade and lose its strength even though still protected from attack by oxygen. In other words, it suffered thermal degradation instead of oxidative degradation. Around 1910, a technological break-through was achieved when it was discovered that textiles could be woven from asbestos and used to replace cotton, because asbestos neither burns nor loses its strength below about 500C. However, as brake operating conditions became steadily more severe, a point was reached in about the middle I940'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 oft Exposure to Asbestos during Brake and dllli-H tw*M M Rivru.M > lonn 24 S. Luxon that (hey indicate that the levels likely to be found in many sections of the industry engaged in this work arc below the level of 2 fibres/cm*, which is considered, in the light of past knowledge, a safe one for chrysotile asbestos. Their highest figures for the time-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 w as 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, f hope the devices which will be described later to-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 X-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. REFERENCES .Uhestus Regulations (!%9) Statutory Instrument 1969 No. 690. OwtMitm os Hygiene Standards. British Occupational Hygiene Society (1968) Hygiene Siaiufartfs fur Chrysotile Asbestos Dust, Pergamon Press, Oxford, f lic'Kisit, D. E. and Knight, K. L. (1969) Ann. Occup. Hyg., 13,17. D. Hatch shcsios to maintain the necessary strength and flexibility. This made possible the Delusion of heavy loadings of mineral and metal fillers which imparted greater heat cMsiuncc than could be obtained from resin and asbestos alone, and did so at the \pcnsc of a reduction in asbestos content. The last point is important in the context f asbestos substitutes. The question is often asked, "why can't asbestos be replaced >y something like glass fibre which, after all, must surely impart sufficient strength?" i lie answer is possibly "it can", if merely the performance of a textile liningis required, >ut at the temperatures commonly met in modern brakes, the glass fibre melts even u depth below the operating surface. Furthermore, as a result of the embrittling effect of mineral and other fillers iccdcd in today's brake lining, glass fibre is inadequate in imparting the necessary trength and flexibility. The same can be said to a greater extent, of the various types >f rock wools and mineral fibres which have appeared on the market over recent . cars. It is interesting to note that not only is the ultimate strength of asbestos almost I tree times that of glass fibre, i.e. 550,000 lb,in.* but the modules of rigidity is up to en times as high, at a value of 30,000,000 lb/in.*. Typical figures for other materials tre say 100,000 lb,'in.*, for steel wool and down at 60,000 lb/in.* for mineral wool. The current situation therefore, is that in drum brake linings of normal configuraion used for passenger cars and commercial vehicles, there exists no substitute for isbostos which would not result in a deterioration of performance and strength. DISC BRAKE PADS Kates of energy dissipation continue to rise and we have now passed the point a here moulded drum brake linings are adequate for a large percentage of passenger cars. In this country, nearly 50 per cent of the passenger car axles are equipped with disc brakes, and for the second time in nearly half a century, there seem to be technical possibilities of reducing the asbestos content of friction materials. It is purely for tuitous that the friction materials used in disc brakes are designed to a stronger shape, that is, more or less square or circular pads of considerable thickness, supported, furthermore, by a metal plate of adequate stiffness. The friction material, therefore, docs not have to stand up to handling during assembly, docs not have to withstand riveting, and could, from the point of view of bulk mechanical strength alone, be made without a high loading of fibrous reinforcement of any kind. There remains, however, thermal shrinkage and thermal shock, and in order to prevent the formation of tensile cracks normal to the operating surface, a percentage of asbestos fibre is still retained. Nevertheless, it cannot be said that the use of asbestos in disc brake pads remains a technical necessity, ami it is in this field of friction materials that some departure from resin-asbestos based composites could occur in the next few years on technical and performance grounds. FRACTION MATERIALS FOR CLUTCHES As yet, I have confined my comments to brakes, but the development of friction materials for dutches has followed broadly similar lines. In recent years, however, wc h;nc seen the sum of a growing replacement of manual clutches by automatic 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 super* seded 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 (ceramic-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 con sidering 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 increa&ingt as is the tem perature 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 the influence of heat alone, chrysotile asbestos decomposes by loss of water of crystallization at a temperature of around 600C. 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 non-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, i but in fact it is exceedingly difficult to detect asbestos in friction material wear pro ducts. It has only on rare occasions been possible to detect asbestos in wear products by X-ray diffraction methods, and one has to resort to electron diffraction, selecting occasional individual small fibres to show Us 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 lOO^C. Whether this explanation is correct or not, it remains a,fact that very little asbestos survives in the wear products after hrnfcrs or rhitrho* hm'i* K/\-n umW normal 28 D. Hatch operating conditions. As (he durability of brakes improves, further reductions will occur in the percentage of asbestos which survives the wear process, because each partieJe of asbestos is then subjected to more heat treatment. Of the approximately ) 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 Ik fibres. This is easy to understand when one considers that under normal condi tions a lining will lose about one-millionth of an inch of thickness for every 20 ft of sliding. Over recent weeks 1 have had regular tests performed in which employees' private cars, and trucks from the Company ilect 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 hand-pump from the centre of the dust cloud. Several of the dust clouds were visibly filthy, and would, in my view, be avoided by the operator; the dust counts taken at the point of maximum dust density were as given in Table 1. Table 1. Dust counts during brake cleaning by COMPRESSED AIR-JET Test Non-fibrous Fibre count Fibre count No. above 2 2-5 ft Above 5 jt Samples 1 2 3 4 5 6 7 10 min average 2000+ 209 402 607 475 1513 628 181 306 11 17 2t 37 49 35 50 5-4 21 2-5 3-7 5-3 8-2 3-2 0-8 The interesting points from this exercise are, firstly, the ratio of the number of particles of asbestos to the total dust particles of a similar size, showing a very small percentage of asbestos, and, secondly, the distribution of size of the fibrous element, suggesting that those particles over 5 ;i must have been only just over. I ain 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 corrcspondingdata is available from clutches hut one would expect the situation to be better than in brakes rather than worse, because on the one hand, surface rubbing speeds are higher, giving rise to higher point contact temperatures, and on 4hc other hand, wear rates are very much lower resulting in an even liner subdivision in the wear products. Possible alternatives to asbestos as a friction material 29 POSSIBLE ALTERNATIVES TO ASBESTOS I have confined my comments to an account of changes which are taking place in friction materials at the present time in the normal course of technical development, in the belief that, although the use of raw asbestos must be tightly controlled, the wear 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 to suggest that a substitute for asbestos must be found, then under the pressure of necessity, a list of possible replacements could be drawn up as follows:-- Glass fibre Low strength--low melting point-severe frictional instability. Steel wool Low availability--high cost--low strength--damage to drums. Mineral wool Very low strength--brittle to the extent of limiting mixing pro cesses. Carbon fibres I00/lb currently forecast to fall to 1/Ib in several years* time. Still ten times too expensive. Sintered metals Probably the best possibility eventually, but cost will always be and cermets relatively high. A/ut. Oteup. H/t- Vot. 13, pp. 31-32. Pttnawi Ptew (970. Printed in Crets Briulo CONTROL OF THE USE OF ASBESTOSCONTAINING FRICTION MATERIALS* M. L. Bentley Mutex, Qeckbeaton, Yorks INTRODUCTION This paper outlines the measures taken by the asbestos-using 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 sub sequent handling and machining operations of friction materials containing asbestos. It is 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 ia 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 in dustry since the dust control measures were introduced and it was also apparent that certain users of asbestos products, such as thermal insulation engineers or laggers were also being affected. ' As a result of this the three leading Companies in the asbestos industry, B.B.A. Group, Cape Asbestos and Turner & 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 co-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 Government 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 addi tional committee last year with the principal object of intensifying the study of prob lems arising in the working environment, dealing with those areas where it had only This paper was originally presented at a Conference oil Exposure to Asbestos during Brake and Cliurb M:unt<*rvmrc hrf.t at 10*0 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--and 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. In addition to gathering and collating information on a large number of dust readings in various types of service premises, the Working Group is preparing two codes of practice for users of asbestos-based friction materials which will be issued by the Asbestosis Research Council. One of these is for the guidance of bulk users in factory premises carrying out, in some cases, operations similar to those 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 search Council's work--to reduce concentrations of asbestos dust to a safe level. The long experience of the manufacturers of friction materials in dust control over a wide variety of operations will enable them to recommend measures and types of equipment to help the users to comply with the Regulations and protect the health of their employees. A furllicr line of study is being followed to see whether a satisfactory surfacescaling agent can be found in order to cut down the amount of dust given off in hand ling u new lining, even though this amount is already small. It is not possible for us to take dust counts in every service garage in the country and the work of the Friction Materials Group has been directed to dealing with, and giving advice on, situations which are likely to be typical of those found in service garages. It is, however, the intention to give as much help and advice as possible with the facilities that arc available and requests for help or advice directed to the Asbestosis Research Council will be passed on to the Working Group for action. An*. Otw. Hyf. Vot. J3. pp. 31-36. Prs*mon Prt <970. Printed in Great BnUin I REMOVING DUSTS FROM BRAKE ASSEMBLIES | DURING VEHICLE SERVICING-- | ALTERNATIVE CLEANING METHODS* Ii G. L. Lee British LeyUnd, Longbridge, Birmingham ii I PRELIMINARY CONSIDERATIONS Whatever the criticisms may be from an occupational health point of view, few would i deny that the operation of removing brake dusts with an air line is efficient in that ; the total time to perform the task is extremely short. The time required to perform ( an operation is of vital importance in industry and any process changes will always ! be judged relative to the time scale. In addition, the effort required from an operative ; in using the method should be minimal and it is easy to see that the chances of de veloping a technique of cleaning which will reduce dust emissions but at the same j time require no more time and effort are extremely slim. Quite clearly, we must concede from the very beginning that some increase in time and effort involved is ! inevitable. When viewed under normal lighting conditions, the result of applying a com pressed-air line to remove brake dusts is very dramatic. Unfortunately, mere draraatij sation alone is not adequate to describe the emission of dust from a process; more I objective methods are needed. The conventional method of evaluating an environ mental condition is the measurement of the appropriate parameter (in this case-- fibre counts), referring the results to hygiene standards. In experimental work to evaluate dust control methods, simpler, "relative0 techniques of measurement have considerable advantages and part of this work is concerned with applying a fairly simple method to define certain environmental conditions which prevail when brake dusts are removed by blowing out with a compressed air line and comparing these with the conditions obtained when a dust control technique is applied. Because the method is a relative one, care to prevent errors from extraneous sources of variation is important. These sources of error are discussed later. METHODS USED TO EXAMINE ENVIRONMENTAL CONDITIONS When dusts arc released in relatively small quantities it is often impossible to see the clouds under normal lighting conditions. They can be made visible using the Tyndall Beam effect and this has been employed extensively during the experimental work. This paper was originally presented at a Conference on Exposure to Asbestos during Brake aod Clinch Maintenance, held at Brentwood. Essex. March. i%9. t I QUIUMlOJ OlCJiijai: Joj tj.mj uoj Suiaq psjDojjoD sapiucd jo Sjaqumu aqi `Xjuo amutxojddc ojc sajnSy aojqi isjij mjjl sasjadsip pnop isnp jcaoj oqj sc lunoa uj [jcj aAissaiSojd c si ojoqi iqi tiaas si j| 0S5 00S( OOOt' 005* 0005 joiej sas o 'xoiddu uo^cx jojc| 33$ o xojddc U3\C i J51C( 33$ 09 'xojddc ua^nx J3|C| aos 02 kojOUc uartc[. uotimodo jo 3uututS.\\ te tiu3 s/sopMJCd isnp 9)jejq jo Jsqiunjsi sjdujcs jjo-mois oNiuna ssuim mii3ivino>j jo snnntf ; 3iovj. ` 1 *RC1u! pazucuiums ojc sajduics asaqi ioj siurtoo aqx 'P^seao pcq ssooojci oqi j.njr osjc puc suoipjado jcoidX! 3uunp uaipi sjom so[duics jaiaunuo^ jo souas v qjM\ papuajuoa aq oi pcq juaswd Suioq qnq aqi jo aauaiudAuoaui aqi sisai Jno jo Xmofcui aqi joj puc os $Xca\jc iou si sup icqi poiou aq pfnoqs ij `suoucjado 3uiucop paiciypcj qaiqM luauiaacjdoj Suucoq joj poaouioj uaaq osp pcq qnq aqi `asco jcjnopjcd siqi uj \ -8ij ui UA\oqs si `Suiucap o\ Xjoi -cjcdaid rnnjp aipjq aqi jo pAOiuaj jajjc `Xiquiassc aqejq apiqoA ppjauuuoa y sisna 3*vua saows* 01 aasa sva\ 3NI1 XiV Q3SS35JdWOO V N5HA\ C13NIV.L80 SSOUIONOD juiod siqi uuyuoa oi pouad a|diucs qaca ic jno pauieo ojsav sisai aqouis luauiaAOia ap jcoof ui suoijcijca Xq paiaajjc iou aja.w spoqiaui Suiucap jo suosucduioo icqi os `sjoop ssaaoe uiojj Xc.wc ||3a\ puc `uoimicd pazc|3 c puiqaq `caac doqs^JOM c ui scm siuauiuadxa aqi joj papaps uoucxq aqx juauiuoJfAua aqi jo ssaunsnp aqi oquasap oi poqiaui aAuepj c sc pasn sc<w uoiicJiuaauoa isnp pioi aqi aauaq puc apmiuScui jo japjo mo[ e jo ajaM pasn scm auq jp us uaqM paupiqo suoipjiuaauoa isnp pioi q3iq aqi u{ luasajd sajqy jo sjaqiunu aqi icq; pa/woqs siunoo aaqy jo sijnsaj aqi 113A13Q puc SNiooJH paqtJasap sc `uoiicipcj 8uisiuot jo ppij e ut 3u;q3;aM Xq paiuaAajd 3J3a\ sjaify auejquiaui uo saSicqa aipis oi anp sjojja 3uiq3;aAv ajqissoj '(9961) xaiONiaay Xq paquosap poqiaui aqi Suisn `Xdoasojaiui Xq siunoa ajqy luanbasqns joj ua^ci osp 3J3a\ sa}duics jaqy auejquiaui puc 'jaiatuiuo>{ c Sujsn `auoz 3u;qicajq spAijCJado aqi ui u;e3c 4ua>jci ajaw Suiiunoa apiucd joj sajduics auoz 8uiqicajq aqi 01 a|qco|iocjd sc Jcau sc 4pdc( s,J3JcaA\ aqi oi paqacnc sew pcaq 3uqdiucs aqi icqi jauucui c qans u; aAiicjado aqi Xq ujoa\ sew dauop Suqdiucs jic puosjad c `Xipuooas 'pautciqo aq oi Xp)f;| aia/w suoiicJiuaauoa isnp isaq3;q aqi icqi paicaipui pcq suoiicuiuicxa lucag IPpuXx jo sijnsaJ aqi ajaqA\ caic aqi ui aq oi uasoqa scm uoijisod 3ui|diucs siqi `Xj|ejaua9 'uoissiuxa isnp jo saajnos aqi oi asop paaqd scm ja|dmes aticis c `uoijisod isjy aqi uj 'Siaiiy auejquiaui pajci qdnojqi Suj|duit:s Xq suoiipod omj ic pauiuuaiap aja-w sisnp aqcjq aujoqjp jo suoticJiuaauoa sscj\ 331 1 O n 36 G. L. Lie The fixed sampler in the area of the highest concentration gave a dust concentra tion of 2t mg.'m* and the persona} sampler, 2-7 mg/m*. 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 broke shoes and the brake assembly were removed, using the smallest brush supplied with the cleaner--the 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 ov Konimeter. samples during modified technique Sample Brushing with standard brush Brushing with tubular brush Rag wiping Number of brake dust particJes/5 cm* 10-25 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 arc 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 196S 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. Acknuu U'tk'eiticnis--The assistance of Mr D. Smith of the Industrial Hygiene Department and Mr Voung, Works Engineers, is gratefully acknowledged. REFERENCES Aodingley, C. G. (1066), Ann, occur*. Ilyg. 9, 73. I huojNS, R. 1. and Dtw m., P. in Instruction Leaflet 3I07/AI, C. F. Casclla. Am. Oetvp. /*. Vot. U. pp. 37-39. Peruaoo Press 1970. Prietrf in Orest Britsia 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 drum/assembly being cleaned. We therefore investigated two alternative methods of controlling dust generated at a maintenance operation on commercial vehicles, as representing maxi mum likely exposure. Enquiries at the beginning of the investigation indicated that the removal of dust is to allow inspection of the mechanism, rather than being a maintenance procedure 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. 1) comprised a steel cone with a connection point at ,ts apex for an industrial vacuum cleaner; a flexible skirt, with a draw string attached at its periphery; and a small-bore side-entry for the injection of compressed air. In use, the funnel was secured over the backplate of the brake assembly or over the drum and compressed air was injected to dislodge dust while the vacuum cleaner extracted dust-laden air. The assembly was rotated around the total circumference to complete the cleaning operation. This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood. Essex, March, 1969. Ann. Ottvfi. Hyf. Vel. 13. p. 41. Perjamoc Prta 1970. Printed In Great Britain RESPIRATORS FOR PROTECTION AGAINST ASBESTOS* S. Luxon H.M. Factory inspectorate, Department of Employment and Productivity, Chepstow Place, Westboume Grove, London, W.2. Over the past few years the British Standard for Respiratory Protection, BS.2091, has been undergoing a drastic revision. A new Standard, BS.2091:!969, Specification for Respiratorsfor Protection against Harmful Dusts and Cases has now been published and is of direct interest in regard to protection against dust including asbestos, as it places the standards of protection offered on a scientific basis. It does this by controlling facepiece leakage as well as filter penetration and valve slip, so enabling the overall standard of protection to be assessed. For ordinary respirators this protection factor is of the order of 20, that is, the external concentra tion is reduced to one-twentieth that inside the facepiece. If we use the standards suggested earlier such respirators should afford protection against prolonged ex posure to 40 fibres/cm* of chrysotile asbestos. This appears to be adequate to prevent danger during the operations of brake maintenance procedures, which we have been discussing today. Perhaps I should mention that there is shortly to be published a new B.S. Specifica tion High Efficiency Dust Respirators. These respirators will have a protection factor of 400 and will be suitable for short term protection against very high concentrations of chrysolite asbestos dust. Such respirators will be of the full facepiece or positive pressure type. Full facepieces are not, in general, acceptable for prolonged industrial use and the positive pressure dust respirator, while acceptable to the wearer, has a higher initial cost. A further British Standard Positive Pressure Powered Dust Respira tors is in preparation, and should be issued later this year. It is unlikely however that during normal brake maintenance operations the concentrations of dust will be such as to require the use of equipment of this type. An alternative approach is to utilise a half mask fed with compressed air from a suitable uncontaminated source. This type of apparatus offers complete protection for the wearer but suffers from the disadvantage of possible hose entanglement. Respiratory protection should in general be regarded as providing protection for work where control is difficult or where the work is intermittent and of short duration. It is hoped that the control of the dust will be achieved by the methods indicated earlier * and that respiratory protection will therefore only be needed for special work not of a routine nature. This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood, Essex. March, 1969. * Alternative forma of control for dual generated during the cleaning of brake assemblies 39 DISCUSSION The results for the vacuum funnel vs. blow-off experiment and for the vacuum brush versus blow-off are shown in Table 1. It can be seen that the background concentrations during the fifth hour had re-established at the original level after a 2 hr latent period and therefore the blow-off 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 80:1 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-off 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 80:1 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; i:$ 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. i Hygiene standards for asbestos 11 Flo. 3. Response'to chrysotile asbestos exposure. is shown on the horizontal axis, expressed in fibre years per cm* and 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 of 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 df 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 con' taminant exposure have to be weighed against the possible loss of direct and indirect j benefits to the community from the use of the material. One conclusion from the exposure-response curve fitted to the data was that for an accumulated exposure of 100 fibre years/cm*, it is probable that the risk of being affected to the extent of having early clinical signs will be less than I per cent. That is, for example, a concentration of 2 fibres/cm' for 50 years of ;uch exposure while