Document 8RaRNGoKR4VNw0Rn7pg2BMwyK

James D. Callaghan Vice President HILL ^TSTD KNOWLTON, Iisre. Public Relations Counsel 150 EAST FORTY-SECOND STREET NEW YORK, N. Y, 10017 212-697 - 5600 Environmental Health Unit August 27, 1971 Dr. E.P. Stefl Vice President Raybestos-Manhattan 205 Middle Street Bridgeport, Conn. 06603 Dear Gene: Bill Raines has asked me to send you the enclosed packet of materials dealing with brake linings to help in preparations for your meeting with Illinois Pollution Control Board personnel. For a quick rundown on what the scientific papers contain I am attaching to each of them a copy of the Summary and Evaluation sheets prepared at the time they were received in this office. The papers enclosed are: , Bentley, M.L., "Control of the Use of Asbestos-Containing Friction Materials" Hatch, D., "Possible Alternatives to Asbestos as a Friction Material" Hickish, D.E. and Knight, K.L., "Exposure to Asbestos During Brake Maintenance" Knight, K.L. and Hickish, D.E., "Investigations into Alternative Forms of Control for Dust Generated During the Cleaning of Brake Assemblies and Drums" Lee, G.L., "Removing Dusts from Brake Assemblies During Vehicle Servicing -- Alternative Cleaning Methods" Luxon, S., "Technical Implementation of the New Asbestos Regulations" Roach, S.A., "Hygiene Standards for Asbestos" Smither, W.J., "Asbestos and Asbestosis" Although you probably have it, I am also enclosing a copy of the Lynch paper on brake linings. In addition you will find a selection of pages from a docu ment, "National Inventory of Sources and Emissions: Cadmium, Nickel, and Asbestos - 1968. Asbestos, Section III," that deal with friction materials. This report was prepared for the old Air Pollution Control Administration and was presented to them in February 1970. It has only recently become available to the public through a printing by the U.S. Department of Commerce Clearinghouse. If we can be of any further help, please let us know. JDC:nml Enc. cc: W.P. Raines Sincerely, X{Tames D. Callaghan FMSI 06472 SUMMARY AND EVALUATION Subject: Brief account of the work of the British Asbestosis Research Council in setting hygiene standards in asbestos friction products plants. Of some interest. Evaluation: This paper runs only two pages, of which the first is devoted to the background and organization of the ARC. A Working Group on Friction Materials has been conducting studies of dust exposure in factories making brake linings. The studies are not yet complete, and there is no report as to preliminary findings. Author: Journal: Annals of Occupational Hygiene (British), January 1970. Title: "Control of the Use of Asbestos-Containing Friction Materials." Summary: As given above. -xxx- FMSI 06473 . .- Ann. Occup. llyg. Vol. 13, pp. 31-32. Pcrgumon Press 1970. Printed in Great Brilain l *. I CONTROL OF THE USE OF ASBESTOSCONTAINING friction materials* M..L. Bentley Mintex, CIcckheaton, 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 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 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 & Ncwall, 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 arc 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 w'orking environment, dealing with those areas where it had only This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood, Essex, March, 1969. 31 ` FMSI 06474 11 I t t1 / i ti 32 I . 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 or these Working Groups is being devoted to the field of frictioi^matcrials, and has, as its constituent members. Small & Parkes (makers of Don materials), Fcrodo 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 further line of study is being followed to see whether a satisfactory surface sealing agent can be found in order to cut down the amount of dust given off in hand ling a new lining, even though this amount is already small. It is not possible for us to take dust counts in every service garage in the country and the work of the Friction Materials Group has been directed to dealing with, and giving advice on, situations which are likely to be typical of those found 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. I ! Ann. Oecup. J I R it I i i I Whatevei deny that the total t an operati be judged in using tl veloping a time requ concede fi inevitable. When pressed:-aii sation aloi objective 1 mental co fibre coun evaluate d considerat simple mei dusts are i with the ci method is is importai MHTl When < the clouds Tyndall Be work. This pai Clutch Main ) SUMMARY AND EVALUATION Subject: Discussion of the possible use of materials other than asbestos for auto brakes. Of interest and importance. Evaluation: The conclusion of the author is that asbestos is practically indispensable for auto brakes at the present time. If asbestos were not available, we could "eventually find a substitute, but it could well be at the expense of a considerable loss in performance, and also at a con siderable increase in cost." The author also emphasizes that there is no valid health reason why asbestos should be abandoned at the present time. He cites the tests demonstrating the very small percentage of asbestos fiber in brake lining dust and concludes that "the wear products from friction materials are probably no more dangerous to health than many other dusts and can be treated as 'merely dirty.'" He also mentions that technical developments have reduced the quantities of asbestos needed in the pro' '` " "Eicient brakes and clutches. Author: Ferodo Company). Journal: Annals of Occupational Hygiene (British), January 1970. Title: "Possible Alternatives to Asbestos as a Friction Material." Summary: As given above. -xxx- FMSI 06476 ic industry red, in the figures for ihat over a level of 12 crhaiils on licular in jures even described tic univerrake dust. Industrial We have diffraction although ere seems eh occurs tween the >) Hygiene ^/ui. Occi/p. Hyg. Vol. 13, pp. 25-29. Pcrgamon Press 1970. Printed in Great Britain January 1970 POSSIBLE ALTERNATIVES TO ASBESTOS AS A FRICTION MATERIAL* D. Hatch Ferodo, Chapcl-en-Ie-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 arc 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 front 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 heal 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 i f5 \ FMSI 06477 . ff ^A^4vi l 8<to>Wj ' J.iv> -- .U.' -, 26 . D. Hatch ... asbestos to maintain the necessary strength and flexibility. This made possible the inclusion of heavy loadings of mineral and metal fillers which imparted greater heat resistance than could be obtained from resin and asbestos alone, and did so at the expense of a reduction in asbestos content. The last point is important in the context of asbestos substitutes. The question is often asked, "why can't asbestos be replaced by something like glass fibre which, after all, must surely impart sufficient strength?" The answer is possibly "it can", if merely the performance of a textile lining is required, but at the temperatures commonly met in modern brakes, the glass fibre melts even in depth below the operating surface. Furthermore, as a result of the embrittling effect of mineral and other fillers needed in today's brake lining, glass fibre is inadequate in imparting the necessary strength and flexibility. The same car. be said to a greater extent, of the various types of rock wools and mineral fibres which have appeared on the market over recent years. It is interesting to note that not oply is the ultimate strength of asbestos almost three times that of glass fibre, i.e. 550,000 lb/in.* but the modulus of rigidity is up to ten times as high, at a value of 30,000,000 lb/in.5. Typical figures for other materials are say 100,000 lb/in.2, for steel wool and down at 60,000 lb/in.s for mineral wool. The current situation therefore, is that in drum brake linings of normal configura tion used for passenger cars and commercial vehicles, there exists no substitute for asbestos which would not result in a deterioration of performance and strength. DISC BRAKE PADS Rates of energy dissipation continue to rise and we have now passed the point where 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, does not have to stand up to handling during assembly, does 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, and 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. I ;i FRICTION MATERIALS FOR CLUTCHES As yet, I have confined my comments to brakes, but the development of friction materials for clutches has followed broadly similar lines. In recent years, however, i we have seen the start of a growing replacement of manual clutches by automatic i ! i I transm to airb sintcret feature that th Clu seded < frictioi of butt free mi Sur is a dr result i reduce' in autc The siderin subject Th< peratui becaus bccaus import white i but in( point i; of wati slow, t; produc the enc asbestc occurri One W' olivine but in ducts, by X-r, occasic has bci by verj the Jini Wh survive *tx*--1 v -c rrfj*'*'- K FNIS1 06478 j j j possible the j i greater heat did so at the in the context s be replaced j nt strength?" j lg is required, re melts even other fillers ihe necessary various types ; over recent ; jestos almost | idily is up to i ler materials \ iral wool. al configura- ; ubstitute for ! rength. ' d tl oint ff passenger uipped with be technical purely for>nger shape, supporled, 1, therefore, o withstand ii alone, be ic remains, c formation fibre is still brake pads that some years on of fiiction however, 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. t f > \ ; 'j 'j OTHER FACTORS AFFECTING EXPOSURE TO ASBESTOS There aie, 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 increasing, as is the ternperature at w'hich 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 foint 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 forsteritc. The olivine series of minerals are quite unlike asbestos, both physically .and chemically, being non-ftbrous, and in fact, w'idely occurring as the major part of many common rocks (basic and ultramafic igneous). One would not expect that a significant amount of asbestos W'ould 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 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 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 arc said to exist at the points of real contact between the lining and drum or disc, even at bulk temperatures as low as 100C. 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 ] . t ; ; ! ' : FMS1 06479 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 p 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 one-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 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 duhino brake cleaning by COMPRESSED AIR-JET - Test No. Noil-fibrous above 2 |j Fibre count 2-5 p Fibre count Above 5 p Samples 1 2 3 4 5 6 7 10 min average 2000+ 109 402 607 475 1513 628 181 306 11 17 21 . 37 49 . 35 50 5-4 2-1 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 p 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. . I1 in fric in the produ other to SU necess Glass Steel' Miner Carbc Sinter and i FMSI 06480 ,-r > j. luctions will ccausc each j proximately | ound down j; are judged mial condi- j sry 20 ft of j ires' private <: for brake cntilation, e use of a ic samples irral of the operator; ii Table 1. 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 lime 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 arc 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 100/lb currently forecast to fall to l/lb 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. iber of y small ement, is with of this itches vorse, ugher lower FMSI 06481 V SUMMARY AND EVALUATION Subject: Discussion of the preferred type of vacuum cleaner to use in cleaning auto brakes during servicing. Of some interest. Evaluation: Having determined that blowing the dust out of brake assemblies with a compressed air hose releases the most dust into the air, the authors investigated the use of vacuum cleaning equipment with two types of pick-up heads. It was determined that a brush on the end of the vacuum hose is more efficient than a funnel attachment. Authors: /'^f|ight^ K^L^knd Hickish, D. E. (Medical Services, Ford of Britain). Journal: Annals of Occupational Hygiene (British), January 1970, Title: "Investigations into Alternate Forms of Control for Dust Generated During the Cleaning of Brake Assemblies and Drums." Summary: As given above. -XXX- FMSI 06482 # i dust conccntrained but was not sought. INIQUE que was devised, eadily accessible sing the smallest vacuum cleaner, eas then used to cd in water and .missions of dust ods, as shown in IMIQUE t vere too low to leaning provides en brake assemts the discharge enables suitable rly part of 1968 itil such time as try were known nlmcnl and Mr i$JU JKajfci^Ja4u'fcSi' Ann. Oecup. Hyg. Vot. 13, pp. 37-39. Pergamon Press 1970. Printed in Great Britain January 1970 INVESTIGATIONS INTO ALTERNATIVE FORMS OF CONTROL FOR DUST GENERATED DURING THE CLEANING OF BRAKE ASSEMBLIES AND - DRUMS* K. L. Knight and D. E. Hickisii 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 (sec Fig. 1) 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-bore side-entry for the injection of compressed air. In use, the funnel was secured over the backplale 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. 37 YY FMSI 06483 t *J 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 angted 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-off method, in two separate experi ments shown in Table 1. Table. 1. Effect of cleaning methods on dust concentrations Hour ' ' Activity 1 Background 2 Blow-off 5 Background 6 Funnel cleaning 6 Brush cleaning Personal sampler Static sampler Peak sample particles/cm3 fibres/cm3 particles/cm3 fibres/cm3 particles/cm3 fibres/cm3 . 116 422 0-96 5-35 161 72 0-45 0-52 41750 87 107 0-95 162 0-41 415 3-5 210 075 759 104 Personal sampler Static sampler Peak sample parliclcs/cm3 fibres/cm3 particles/cm3 fibres/cm3 particles/cm3 fibres/cm3 125 635 . 140 0 16 0-84 009 129 155 110 - 010 016 0-20 41750 87 158 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-off. 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 en gaged 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 Dragcr pump 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 Standardfor Chrysolite Asbestos published by the British Occupational Hygiene Society (I9G8). Particle coyints were limited to particles greater than 1 p dia. pt' I FMSI 06484 Alternative forms of control for dust generated during the cleaning or brake assemblies 39 DISCUSSION The results for the vacuum funnel vr. blow-off experiment and for the vacuum brush versus blow-off arc 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 houb 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; 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 Occupationai. Hygiene Society (196S) Hygiene Standards for Chrysolite Asbestos Dust. Pergamon Press, Oxford. D FMSI 06485 SUMMARY AND EVALUATION Subject: Study of asbestos dust exposure among British auto brake mechanics. Of interest and importance. Evaluation: This paper sheds additional light on the persistent speculation concerning brake linings and asbestos dust. The study was conducted among workers engaged in the repair and maintenance of brake drums "at the Service Bay of a Ford Main Dealer in the Greater London area." During the dustiest part of the operation, the preliminary cleaning of the brake drum, workers were exposed to an average of fewer than two fibers per cubic centimeter of air. According to the recommended dose-time limits established by the British Occupational Hygiene Society, this means that a brake-maintenance worker could work for 50 years at this job with less than a one percent risk of contracting asbestosis. Authors: /^i^kish^D^E. and Knight, K. L. (Medical Services, Ford of Britain). Journal: Annals of Occupational Hygiene (British), January 1970. Title: "Exposure to Asbestos During Brake Maintenance." Summary: Brake lining mechanics in an automobile service shop worked on two passenger cars and a truck, while two types of dust-measuring devices counted the amount of asbestos dust in the atmosphere. The personal exposure of the mechanics was below the limit corresponding to 50-year exposure, the hygiene standard of the British Occupational Hygiene Society. "Samples of drum dust were examined by Dr. S. Holmes, and his tests showed that chrysotile was pre sent 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." -XXX- FN1S1 06486 January 1970Ann. Oceup. Hys. Vol. 13, pp. 17--21. Pcrg.imon Press 1970. Printed in Great Britain EXPOSURE TO ASBESTOS DURING BRAKE / MAINTENANCE* . 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-out of brake shoes and drums is not included in all 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 assessment being in accordance with the technique described in the Hygiene Standard for Chrysotilc Asbestos Dust, published by the British Occupational Hygiene Society (196S). Static samples were taken by the side of.the car (Fig. 1) and composite samples were also taken in the dust-cloud during the blowing-out 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 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 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 Fibrcs/cm* 2nd period Time-weighted average By car 1-12 1-42 1-25 Dust cloud then by car 1-71 3-62 2-55 An estimate of the daily exposure of the mechanic engaged on brake cleaning was obtained by a scries of personal samples (Tig. 2V covering an entire workshift, during which brake servicing was carried out on 11 vehicles. The results arc 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 * **-'TT*P*.w*"*<"- V '*;V FMSI 06487 18 D. E. Hickisii anti K. L.'Knigiit Table 2. Personal samples during car BRAKE SERVICE - Sample Concentration (fibrcs/cm*) 1 2 3 4 5 6 Time-weighted average 063 M2 021 0-96 0-38 0-79 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/cm3) Adjacent bay 2 Bays away Centre of garage Morning Afternoon Morning Afternoon Morning Afternoon .. 0-28 0-07 0-17 0-07 049 011 Personal samples were obtained from two men--the 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 5 hr represented the remainder of the shift. The results are shown in Table 4. A *. % *' J8* * i. Zti*J/lcii "-^-riiW / ~iV > i tittr>liVt;rr r i Exposure to asbestos during brake maintenance Table 4. Personal samples--truck brake service Operator Concentration . (fibrcs/cm3) 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 19 SIGNIFICANCE OF EXPOSURE LEVELS The Hygiene Standard suggests that exposure should not exceed an accumulated level of 100 fibre-years/cm3. 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/cm3. 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 the 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. 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 Brake lining materials contain 40-60 per cent of asbestos, and it w'as somewhat surprising to find that particles 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, these 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 W'hich were fibrous in nature, and are compared in Table 5, together with a result from an incinerated thermal precipitator sample obtained during brake cleaning. I I i It i FMSI 06489 20 D. E. Hickisii and K. JL. 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 0-6 -- 12-3 16 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 bis tests showed that j 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/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 chrysotile 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-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 int be vol wo wi( Co; Hoi Lvt i ry ' TATV*TycrT FMSI 06490 ./ 'j . j>rne dust I jwed that bmpared fiat there i1 use as a I jher they ig dynarom bus instance, am tem: bi- r tng u.jremains ling and is. The different T, comteritc, a e drum ii amor' |e about ence to ibe dis- jance is srsonal jsure. jning to -cdures jrds 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 involve the filing or grinding of brake lining material, and we would envisage that these would give rise to considerably increasedaircontamination bychrysotilc asbestos, with the attendant need for strict precautions to prevent the inhalation of fibres. . REFERENCES Committee on Hygiene Standards, British Occupational Hygiene Society (1968) Hygiene Standards for Chrysotilc Asbestos Dust, Pergamon Press, Oxford. Holmes, S. (1967) Private communication. Lynch, J. R. (1968) J. Air Pollut. Control Ass. 18, 824. f | | ; \ A X* | 1 ; i. ; ! ! V <>tvi '"rt?vix****^ v*< l \ FMSI 06491 SUMMARY AND EVALUATION Subject: Comparative study of methods used for cleaning auto brakes during servicing. Of some interest. Evaluation: In British auto repair shops it has apparently be common practice to clean the dust from brake assemblies by blowing it out with a compressed air hose. The natural assumption that this process releases most dust into the air was confirmed by comparative tests using a vacuum cleaner, two types of brushes and rag wiping. However, it is noteworthy that the dust concen trations, measured by sampling devices, included relatively few fibers, which would presumably be asbestos. The author comments: "The results of fibre counts showed, that the numbers of fibres present in the high total dust con centrations obtained when an air line was used were of a low order of magnitude and hence the total dust concentration was used as a relative method to describe the dustiness of the environment." tish Leyland Company), Journal: Annals of Occupational Hygiene (British), January 1970. Title: "Removing Dusts from Brake Assemblies During Vehicle Servicing - Alternative Cleaning Methods." Summary: "Vacuum cleaning provides a useful contribution towards obtaining satisfactory dust control when brake assemblies are cleaned." -xxx- FMSI 06492 f t> jclping those 1 bcstosis Re tting on the ; ing devoted 'ill & Parkes xxn formed customers land service i exists and, jin premises | ses, by the r own dust isurcment. ' to be enintenancc. ^determine r of dust Uring two jt will be i<s of bulk : to th^se isfo j b remind jymmend -ve what osis Refe level. I over a vpes of health i;urfacet hand- jountry i K and ! service J c with l-stosis V** \ Ann. Oceitp. tfyg. Vol. 13. pp. 33-36. Pcrgamon Press 1970. Printed in Great Dritain REMOVING DUSTS FROM BRAKE ASSEMBLIES DURING VEHICLE SERVICING- ALTERNATIVE CLEANING METHODS* G. L. Lee British Leyland, Longbridgc, Birmingham PRELIMINARY CONSIDERATIONS Whatever the criticisms may be from an occupational health point of view, few would deny that the operation-of removing brake dusts with an air line is efficient in that the total time to perform the task is extremely short. The time required to perform an operation is of vital importance in industry and any process changes will always be judged relative to the time scale. In addition, the effort required from an operative in using the method should be minimal and it is easy to sec that the chances of de veloping a technique of cleaning which will reduce dust emissions but at the same time require no more time and effort are extremely slim. Quite clearly, we must concede from the very beginning that some increase in lime and effort involved is inevitable. ' When viewed under normal lighting conditions, the' result of applying a com pressed-air line to remove brake dusts is very dramatic. Unfortunately, mere dramati sation alone is not adequate to describe the emission of dust from a process; more objective methods are needed. The conventional method of evaluating an 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, "relative" techniques of measurement have considerable advantages and part of this work is concerned with applying a fairly simple method to define certain environmental conditions which prevail when brake dusts are removed by blowing out with a compressed air line and comparing these with the conditions obtained when a dust control technique is applied. Because the method is a relative one, care to prevent errors from extraneous sources of variation is important. These sources of error are discussed later. METHODS USED TO EXAMINE ENVIRONMENTAL CONDITIONS When dusts are released in relatively small quantities it is often impossible to sec the clouds under normal lighting conditions. They can be made visible using the Tyndall Beam effect and this has been employed extensively during the experimental work. . `This paper was originally presented at a Conference on Exposure to Asbestos during Brake and Clutch Maintenance, held at Brentwood, Essex, March, 1969. 33 1 FMSI 06493 34 . G. L. Lee ' ' Mass concentrations of airborne brake dusts were determined at two positions by sampling through tarcd 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 Konimetcr, 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 magnitude and hence the total dust concentration was used as a relative method to describe the dustiness of the environment. The location selected for the experiments was in a workshop area, behind a glazed partition, and well away from access doors, so that comparisons of cleaning methods were not affected by variations in local air movement. Smoke tests were carried out at each sample period to confirm this point. CONDITIONS OBTAINED WHEN A COMPRESSED AIR LINE WAS USED TO REMOVE BRAKE DUSTS A commercial vehicle brake assembly, after removal of the brake drum prepara tory to cleaning, is shown in Fig. 1. In this particular case, the hub had also been removed for bearing replacement which facilitated cleaning operations. It should be noted that this is not always so and for the majority of our tests the inconvenience of the hub being present had to be contended with. A 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-off Sample Number of brake dust parlicles/5 cm3 Taken at beginning of operation Taken approx. 20 sec later Taken approx. 60 sec later Taken approx. 30 see later. Taken approx. 30 sec later , 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 arc approximate only, the numbers of particles collected being too high for accurate counting. FMSI 06494 3 positions by : sampler was : position was had indicated ly, a personal the sampling cathing zone, eathing zone, sequent fibre 56). Possible I by weighing t in the high low order of e method to ind a glazed ing methods carried out Nr m prepara1 also been should be venience of5 5 and also in Table 1. Asperses. led being i * (fiiciiiR p. 14) FMSI 06495 f *- Cl 'i : 4>kW Removing dusts from brake assemblies during vehicle servicing 35 ` A fixed sampling period of sonic 5 min was chosen for the determination of mass concentrations--this 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 concen tration of 114 mg/m5 and that for the personal air sampler 42 mg/m5. 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/cm5. 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 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 scaled 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 filler established that no particles passed the filter. V- . - 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 and WITH LOCAL nXTKACTION Sample Number of brake dust particles/5 cm5 Taken at start of process Taken about 1 min later Taken about 2 min later Taken at'end of process 1070 404 426 446 ' l FMSI 06496 36 G'. 1*. Lee The fixed sampler in the area of the highest concentration gave a dust concentra tion of 21 mg/m3 and the personal sampler, 2-1 mg/m3. 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--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 of Konimeter samples during modified technique Sample Brushing with standard brush Brushing with tubular brush Rag wiping Number of brake dust particlcs/5 cm3 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--The 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. Riggins, R. I. and Dewell, P. in Instruction Leaflet 3107/A1, C. F. Casella. 1 1 I i i t t n tl \s V fo pc th an du tlx Ch * FMSl 06497 SUMMARY AND EVALUATION Subject: Brief discussion of the British Asbestos Regulations as applied to brake maintenance in auto repair shops. Of interest and importance. Evaluation: This very short paper is important because the last paragraph confirms the American study by Lynch on the small amounts of asbestos in brake lining dust. The present author reports the results of tests per formed in the Industrial Hygiene Laboratory of the British Ministry of Labour: "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 of 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:" Author: 'Luxon, S./\H.M. Factory Inspectorate, British Ministry of Labour). * Journal: Annals of Occupational Hygiene (British), January 1970. Title: "Technical Implementation of the New Asbestos Regulations." Summary: The levels of asbestos exposure for brake mechanics appear safe. However, the exposure of particular individual workers will be increased if brake overhauls are conducted on a production line basis, making the ` development of adequate precautionary measures even more important. "Certainly, we should not be blowing out brake dust, even if it contains only a few per cent of asbestos." -xxx- FMSI 06498 'm"r^rin*rt`* n-- r*> if*' * Ann. Occup. Hyg. Vol. 13, pp. 23-24. Pergamon Press 1970. Printed in Great Britain January 1970 TECHNICAL IMPLEMENTATION . ' OF THE NEW ASBESTOS REGULATIONS* S. Luxon H.M. Factor)' 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 on 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;cm3 and 0-1 mg/m5 for chrysotile asbestos. A fibre is taken as being 5 p 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 is based on timeweighed 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 fibres/cm3 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 fibrcs/cm3 should not be exceeded during any period of 10 min, i.e. we might regard 12 fibres/cm3 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 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 informalion is yet available on the relationship between mass of asbestos and fibre counts in other industries. To further complicate the problem, it is not known what fibre sizes are biologically active and, even if this were known, appropriate clutriation (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. HickisiI 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 c ' `.V*-** FMSI 06499 24 S. Luxon that they 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/cm3, which is considered, in the light of past knowledge, a safe one for chrysotilc 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 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 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 . Asbestos Regulations (1969) Statutory Instrument 1969 No. 690. Committee on Hygiene Standards, British Occupational Hygiene Society (1968) Hygiene Standards for Chrysotile Asbestos Dust, Pergamon Press, Oxford. Hickish, D. E. and Knight, K. L. (1969) Ann. Occup. Hyg., 13, 17. Ann. Occup POSSI I HAVE b< The fact: shortly b then I th This i eventual! loss in pc Havin the reaso friction rri The fi pregnated which, wh The main spheric ox resulted in drying oil abrasion. As bra degrade a In other u Arount that textile neither bin conditions 1940's whe asbestos t< because th proved to 1 This paj Clutch Main , iii>(-r-rvr" FMSI 06500 SUMMARY AND EVALUATION Subject: Asbestos dust control standards in Britain and the U.S. and their ' relationship to occupational health. Of some interest. Evaluation: This paper is essentially identical with the one presented by the author at the Conference on "The Control of Asbestos in the Working Environment," sponsored by the British Occupational Hygiene Society and the Asbestosis Research Council, London, June 18, 1969. That paper has pre viously been evaluated and distributed. The author is president of the British Occupational Hygiene Society. Author:/ Roach, S. A. (London School of Hygiene and Tropical Medicine). Journal: Annals of Occupational Hygiene (British), January 1970. , Title: "Hygiene Standards for Asbestos." Summary: Hygiene standards of the BOHS are discussed and compared with those of the ACGIH. The British standards apply only to chrysotile, and recommend a lower TLV than the latest recommended by the ACGIH. FMSI 06501 Ann. Occup, Hyg. Vo!. 13, pp. 7-15. Tcrgamon Press 1970, Printed in Great Britain HYGIENE STANDARDS FOR ASBESTOS* S. A. Roach London School of Hygiene and Tropical Medicine, Kcppcl Street, London W.C.l. As long as there is any airborne asbestos dust in the work environment there may be some small risk to health. Nevertheless exposure up to certain limits can be tolerated for a lifetime without incurring undue risks. A hygiene standard for asbestos was published in the U.K. by the Ministry of Labour in 1960 and was taken from the annual list of Threshold Limit Values of the American Conference of Governmental Industrial Hygienists (ACGIH) (Committee on Threshold Limits, Annually). The British Occupational Hygiene Society formed a Hygiene Standards Com mittee in 1965 to advise on hygiene standards. This Committee 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 which 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 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 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 Chairmanship of Professor Lane, has developed new hygiene standards for airborne chrysolite dust (Lane el al, 1968). These were based on the results from a medical and environ mental study at an asbestos textile factory in England, in which investigations were made on 290 of the men employed at this factory in the period of 1933-1966. The Sub-committee considered that the degree and nature of the risk associated with the standards should be specified and the method of the derivation of the stan dard from the data presented should be described in detail. It was also considered that Hie 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 a fleeted, 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 B FMSI 06502 8. S. A. Roach when the recommended standards of air cleanliness arc maintained. It was recognised that to protect the hypcrsusceptiblc workers environmental control would have to be supplemented with medical examinations. It was evident from the data made available to the Sub-committee, and from the earlier American experience, that when concentration is held constant the prevalence of asbestosis was highest among those with the greatest duration of exposure. Over a period of time, 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 of asbestos 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 p. was counted. The dust concentration to which different workers had been exposed varied from 1 fibre/cm3 to 27 fibres/cm3 over periods from 10 years to 33 years. The exposure of an individual was expressed as fibre years/cm3, 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 the 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 oY dose above the maximum desirable. Doses which give zero 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 all 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 t I I 1I j j different j is repres I average i i In a l ; about an . frequcnc; i on either \ Ina r ; Exactly w i usually m ' affected b 1 the size fr j zero expo j An ail [ of men bci ; can be ma | standard I ; costs of ai A cur\ clinically a their years Fig. 3. Tin FMSI 06503'nr* . r1 *' '4 i / ; rcct,^ .scd I liavc to be id from the ; prevalence , sure. Over However, jived. Conjccordingly, j.lcnce with ;g that the e is equally II that con- jetory connethod, in itration to j fibres/cm8 :te product j rs and his valence of was based ssed i"' a I is mi .d j response it merely j ill higher jrt clinical anscious- ii !n a con e chosen jrelation| the line increases |il ope the I'casional -`erlainty jhich can hreshold j with all I'C ..tries jt with a Hygiene standards for asbestos Individual response to dose 9 Fig. 1. Individual response to dose. different threshold dose and a different slope. A particular population under study is represented by a family of dose-response lines centred around the line for the average man.. In a real population the threshold dose will vary front 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 of people being affected can be made as small as one wishes. Zero risk is the ultimate target and an air quality standard has to be a compromise between the costs of bearing a health risk and the costs of air contaminant control. A curve was fitted to the data from the textile factory on asbestosis, detected clinically and the exposure in fibre years per cm" of all the individuals under study over their years of-employmeni up lo 1966. The bottom end of the fitted curve is shown in Fig. X The three points relate to three of the groups of workers studied. The exposure FMSI 06504 10 S. A. Roach Number of individual# with symptom# Number of individuals with symptoms ` Fig. 2a. Population response to threshold dose. Fig. 2b. Population response to dose. j is shown on t prevalence i | basal rales. 1 Basal ral | 'and there is j posure. Oni j rales, j A proble | said to be at i mon by ever; j exposure. Tl j other similar ' it to zero. It ' benefits to th j cost of dust < ; be economic, : The benefits ! ' taminant exp< ( benefits to th< | One concl ; an accumulat affected to tin ' is, for exampl FMSI 06505 Hygiene standards for asbestos 11 Exposure (fibre years/cm5) Fig. 3. Responsejo chrysotilc asbestos exposure. is shown on the horizontal axis, expressed in fibre years per cm5 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 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 con taminant 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-response curve fitted to the data was that for an accumulated exposure of 100 fibre ycars/cm3, 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/cm3 for 50 years of such exposure while ) 12 S. A. Roach at work, 4 fibrcs/cm5 for 25 years, or 10 fibrcs/cm5 for 10 years. The British Occupa tional Hygiene Society Hygiene Standards Sub-committccon 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 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 fibres/cm5. 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/cm1. 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 3 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/cm5. The exposure measured by making fibre counts on membrane filter samples can be converted into exposure measured with an impinger, 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/cm5 corresponds to 15 million particle years/ft5 by standard impinger methods (Ayer, Lynch and Fanney,. 1965). The present American Threshold Limit Value is a concentration of 5 million particles/ft5 (mp/ft5) which, if it persisted, would result in an accumulated exposure of 250 million particle years/ft5 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 different 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 Drcessen and his co-workers in 1938 after studying 541 employees in 4 asbestos textile plants where massive exposures to chrysotile occurred (Dressen etal, 1938). Only 3 doubtful cases of pneumoconiosis were found at the time of the study in those exposed to dust concentrations under 5 mp/ft5, whereas numerous well-marked cases were found above 5 mp/ft5. A conference held in 1965 on the biological effects of asbestos called attention to the very real probability that the 5 mp/ft5 limit recommended by Dreessen is inade quate to give complete working-lifetime protection against all forms of asbestos (Schall, 1965). Medical data on which the limits had been based were inadequate; more than half of the asbestos workers studied by Drcessen and his co-workers were under 30 years of age and thus had insufficient exposure time for much asbestosis to dcvclc 5 yeai time" in the The after i the A Limit: . while and c of the that t years. In below avera; often recoil lengtl by In 12 fib of as! . T1 to the given to tal T1 ! perso j years, I clinic ( these t j assoc j ' ' T1 j over: j equal j this v ; highe | mum ! comp ; !. stand Inspc i judgr j mum : prob; !T ` dusts f i i i f.-*rY^r.'nr <*;'t'T*"vr^? FMSI 06507 i ish Occupa1 pressed the i os to below j i I per cent ., who may ; eh they are I exposed to in need not <cm'. S -ation for a j the risk of j committee * an average suringthat impics can : nethod, by I nts. Such ; itos textile : atresponds YNCit and | ration of 5 cumulated leas, cm lient fonn i standard 5 monthly t standard ] is not priI 'cause of a ; ght to be j ' Drccssen | tile plants I 3 doubtful ed to dust ere found i tention to | 1 is inadcI asbestos , adequate; | *'Cis were >estosis to -4 A*.W **.A*im Hygiene standards for asbestos 13 develop. Of the 105 workers exposed to less than 5 mp/ft*, 82 had worked less than 5 years and only 4 had more than 10 years exposure. Moreover, it was a "point-in time" 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 ACG1H 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/ft1 limit was not sufficiently low to protect workers exposed for 30 years, 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/ft1. Since the count by Impinger 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/ft1, the corresponding limit based on the fibre count is 12 fibres/cm1. 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 ycars/cm1. 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 standards refer essentially to an average concentration during working hours over 3 months of 2 fibres/cm1. 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/cm1. The proposed change in the American TLV is to a maximirm 12 fibrcs/cm1 8-hr average, which if exceeded on a shift demonstrates non compliance. 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 I f I l \ f i l i ii f \ rit i FNISI 06508 14 S. A. Roacii parts of the World will be 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 different countries does differ and, no doubt, will continue to dilfer. 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 Sub-committee on Hygiene Standards for Asbestos has not yet decided whether their chrysotilc 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 w'hicli people are exposed and the corre sponding effects 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-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 mo i kind of in be able to This d equation, dard. Ho Ayer, H. E. Committee Trans. / Ohio, U Committee Governr Dreessen, V and Trii Wash. 1> Lane, R. E. oectip. H Ministry oi Medical Schall, E.! FMSI 06509 ] incss can, as i ted can vary i -ry. I d, no doubt, i nney on airJ .ks to which j nve different | i ihc greater. oductshave j icalth of the i. I a Standards i I be suitable | tion against ] i distinction j ;i should be 1 iems arising ee indicated ' sotheliomas jcs of fibre j i at present i nhaling the J to control croc 'ite. c stanaards j `quirements ; c a known "dy of data i i the corre a grasp of ions of the I crms of the inendations i -committee : 'as not the i 'lent was to j ' rol. Where | mount and j >o achieve j as (he cube j ventilation ] - down the j possible to i | Tt.. ..,,.^.l-.*.t.>w. <v,-iVrrt'-*n^^*1V" JVr iir Sift liTnf-t^~iiY' -- rtitn",rrutrtWiftaiT-inr . 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 Aver, H. E., Lynch, J, R. and Fanney, J. H. (1965) Ann. N. Y. Acad. Sci. 132, 274. Committee on Threshold 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 Llmits (1969) Threshold Limit Values for 1969. American Conference of Governmental Industrial Hygienists, 1014 Broadway, Cincinnati, Ohio, U.S.A. Dreessen, W. C., Dalla Valle, J. M., Edwards, T. I., Miller, J. W., Sayers, P. R,, Eason, H. F. and Trice, M. F. (1938) A study of asbestosis in the asbestos textile industry. Pub!. Hlth Bull., Wash. No. 241. Lane, R. E,, Barnes, J. M., Hickish, D. E., Jones, J. G., Roach, S. A., and King, E. (1968) Ann. occup. Hyg. 11,47. Ministry of Labour (1967) Problems arising from the use of asbestos. Memorandum of the Senior Medical Inspector's Advisory Panel, HMSO, London. Schall, E. L. (1965) A mi. N. Y. A cad. Sci. 132, 316. , I FMSI 06510 SUMMARY AND EVALUATION Subject; Brief discussion of the various forms of asbestos and their effects on health. Of some interest. Evaluation: This very short paper, running to three printed pages, was presented to provide background information to a conference on possible asbestos exposure to maintenance workers on auto brakes and clutches in Britain. The author points out that currently disc brake pads, brake linings and clutch facings contain 50 percent chrysotile asbestos. However newer developments indicate that the percentage of asbestos in the mix is likely to decline, perhaps down to a minimum of 30 .percent asbestos. Disc brakes require less asbestos fiber than drum brake linings, and it is estimated that more and more passenger cars produced in the U.K. will be equiped with disc brakes. Author: Smither, W. J. (Group Medical Adviser, Cape Asbestos Company). Journal: Annals of Occupational Hygiene (British), January 1970, Title: "Asbestos and Asbestosis." Summary: As given above. -xxx- FMSI 06511 r lr'V*I>-- 3 i 'WwtiaVr&tf tfji a: ua's Anti, Occup. Hyx. Vol. 13, pp. 3-3. Pcrgamon Press 1970. Printed in Great Britain ` ASBESTOS AND ASBESTOSJS* W. J. Smither Group Medical Adviser, Cape Asbestos Company, 114 Park Strecl, London W.l. THE FORMS AND USES OF ASBESTOS Commercially important asbestos fibres fall into two main groups. The first of these is chrysotile, and the second comprises the amphiboles. Both groups arc fibrous silicates, but they differ .in geological origin, in chemical composition, in molecular structure, in fibre size and strength, and in other characteristics. Chrysotile, white asbestos, comes from many different places. There arc 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 anthophyllile 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. Annuol world output *3,000,000 tons j l j j ! ! ! J ; ; ' I Chrysolite (while) 2,800,000 tons 93% Conodo USSR S. Africa USA Europe Others 1,250,000 750,000 250,000 100,000 100,000 350. 000 Crocidolite (blue) (South Africa) 110,000 tons 3-4% * I Amosite (South Africa) 90,000 tons 3% Fig. I. World production of asbestos. Anthophyllile (Finland) 10,000 tons j., 20 This paper was originally presented at a Conference on Exposure lo Asbestos during Brake and Clutch Maintenance, held at Brentwood, Essex, March, 1969. . ' 3 .. f f I -t "Vv*; T* *3 V ^ fly*: * FMS1 06512 lr i .11 4 W. J. Smither * Asbestos Annual consumpfion-3,000,000tons Where it is used Where it is mined Others Belgium Itoly France JAPAN UK Germany Chrysotile Others USA Southern Africa USSR USA USSR Conodo Blue Crocidolite S.Africa Amosite Ant hophy Hite | S.Africa | Finland Fig. 2. Areas of use of asbestos. The different characteristics of asbestos fibres dictate their uses, their applications and their mode of packing and handling. For example, ainosite 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. V brake conU in the pcrcc now with pads It is c be eq Ti is the physit is bei the III TI lining cavity becon A1 pcrioc sists o interfc the sh Th calcim conee i any ev itself. Ex of the mesotl workei uncom frequei The re investi; r? C' r. W*"t FMSI 06513 ' -h cations "css tire ization. wile is -nt acid Asbestos and asbestosis 5 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, 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 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 crocidolile than to chrysotile, amosilc or anthophyllitc. The reasons for this arc at present obscure, but arc being sought intensively by investigators in many different countries. BRAKE LINING DECOMPOSITION PRODUCTS In recent years, some individuals have pointed at brake lining wear as a pro bable source of asbestos contamination of the ambient air. In this paper, Jeremiah R. Lynch of the National Center for Urban and Industrial Health, HEW, refutes this theory by showing that in all but a few extremely severe automobile braking tests, less than one percent asbestos fiber could be found in the collected dust. He concludes that brake lining wear is "an inconsequential health factor in urban air pollution." Jeremiah R. Lynch I Brake Lining National Center for Urban and Industrial Health DeCOITIpOSitiOn PfOdlJCtS A number of investigators have found asbestos bodies in the lungs of urban residents who were not oc cupationally exposed to asbestos. A relationship between the carinogenic properties of asbestos and the urban excess of lung cancer has been suggested. The decomposition products of brake linings have been described as a possible source of these fibers. Brake testing laboratory methods were used to test fiber emission from a variety of friction products. Only a very small fraction of the asbestos escaped as free fiber while the remainder was transformed into some other, nonfibrous, mineral. A significant release of free fiber occurred only under conditions extreme enough to produce brake failure. Table I. Asbestos bodies in human lungs. Location Cape Town (2) Miami (2) Pittsburgh (3) Johannesburg (4) Finland (5) Montreal (6) San Francisco (1) Year 1963 1965 1965 1965 1966 1966 1966 % Positive 26 . 27 41 ,39 58 48 42 Table II. Brake lining composition. Ingredient Automobile Truck Asbestos Resins and polymers Oxides and pigments Metals Carbon, graphite. etc. 55 28 9 3 5 100% 33 45 16 2 1 100% Mr. Lynch is Chief uf the L.-ihoratory of Engineering, Occupa tional Health Program, Public. Health (service, Department of Health, Education, ami Welfare, 1014 Broadway, Cincinnati, Ohio 45202. 824 The occurrence of coated fibers re ferred to as "asbestos bodies'" in the lungs of urban populations not oc cupationally exposed to asbestos has been noted by several investigators. The results of several autopsy series, as summarized by Cooper,1 are shown in Table I.1-* Thompson,7 in suggesting possible modes of exposure that could account for these bodies, stated: The average private motor vehicle wears out three or four sets of brake linings and one or two clutch linings in its lifetime, and commercial and public transport vehicles wear out many more. These linings consist largely of asbestos which is ground to dust as the linings wear, and most wear occurs in built-up areas. This alone in most cities would involve the discharge of many tons of asbestos dust and fibers in the streets each year. Since asbestos has been implicated as a carcinogen9 and lung cancer has a higher incidence9 among urban popula tions, the fate of the asbestos worn from brake linings becomes significant. Brake Lining Composition The average composition of typical brake linings of the type tested is shown in Table II. Individual mixes may vary considerably from these averages. Each of these ingredients performs a particular function. The asbestos pro vides strength, beat resistance, and selec tive decomposition under stress. The resins and polymers hold the other in gredients together. Various oxides are added as pigments and to improve the grip of the lining on the drum. Soft metals such as lead and brass improve wear while carbon and graphite serve as friction modifiers. Brake lining quality depends to a large extent on the type of binder used. Linseed oil, which begins to decompose at about 450F, is used for light service brakes. More demanding service re quires brakes made from cashew type resins or oil modified phenolic resins. These ingredients are mixed, either dry or with a solvent added, formed into shape, and cured in an oven. The hardened lining is then cut, ground, and sanded to the precise dimensions of the finished linings. The dust produced by the abrading operations in asbestos friction product factories (Figure 1) contains free asbestos fibers that are similar to those in industries where can cer is known to be in excess.10 The question to be resolved, therefore, is whether the dust produced by the normal w;ear of brake linings contains this same type of free asbestos fiber. Test Methods In an initial exploratory survey, the dust obtained from inside automobile brake drums removed for brake refining was examined by electron micrograph. Figure 2, which is typical of the series, does not reveal any free fibers. How ever, this finding did not eliminate the possibility that free asbestos fibers were released and that they had escaped into the atmosphere. To examine this hy pothesis a scries of experiments was devised to permit .sampling decomposi tion products of the fining under simu lated operating conditions. The tests (Tabic III) were performed with the brake testing machines in the laboratory of a major brake lining manufacturer. Most of the tests were performed on a nal of the Air Pollution Control Association FMS1 06516 -I Figura 1. Brake lining factory dust. Figure 2. Dust removed from brake drum. Figure 3. Decomposition product from nor mal wear of brake lining. friction-testing machine which used one-inch-square samples of the test lining. Heating and cooling apparatus permitted control of drum temperature from those encountered with inter mittent brake use to the maximum temperature which occurred only in extremely rapid or "panic" stops from high speed. Other tests were performed on a brake-testing dynamometer which subjected a complete brake assembly to a series of stops and starts from different speeds and at different deceleration rates to simulate actual driving con ditions. In these tests the drum tem peratures varied according to the driv ing condition simulated. During each run at a test condition, a sample was collected on an 0.8 n pore size membrane filter. Electron micrographs of these filters were examined to determine the presence of free asbestos fibers and to quantify these fibers when more than a few occurred. ' Results The object of the tests was to deter mine what proportion of the asbestos known to be present in the lining ap peared as free fiber in the decomposi tion product. No attempt was made at a mass balance between the material worn from the lining and the decom position product since it was not pos sible to collect all of the decomposition product. However, the percentages obtained in the fraction of decomposi tion product examined are applicable to the total material worn from the brake and may be compared to the percentage of asbestos originally present. In all but a few tests the automobile drum brake linings showed less than 1% free fiber in the decomposition product as compared to about 50% in the lining. An electron micrograph of the decomposition product obtained from a typical test in this group is shown in Figure 3. In those tests where a sig nificant mass of free fiber was released (Figure 4), the temperature was in an extremely high range for the lining in question as evidenced by rapid drop in the coefficient of friction. Had these linings been subjected to like conditions in a vehicle, the brakes would have failed. Similar results were obtained in the bus and truck drum brake tests and in the clutch test. The experimental model disk brake tested did release some (>5%) free fibers, but no conclusion can be drawn from a single sample. Discussion Except in all but the most extreme driving conditions, only a very small fraction of the 30 to 50% asbestos pres ent in a brake lining escapes into the atmosphere as free fiber. The question remains: What happened to the as bestos? A prevalent theory of brake operation holds that wear occurs not by abrasion of the lining by the drum but by the production of minute areas of intense heat at the points of contact between the drum and the lining. De composition, not only of the binder but of the asbestos as well, occurs at these locations since the breakdown tem perature of asbestos, about 900F, is exceeded. Decomposition products will include not free asbestos fillers, but, a different mineral resulting from thermal metamorphosis of asbestos. December 1968 Volume 18, No. 12 Figure 4. Decomposition product from brake liningatfailure. FMSI 06517 825 Table III. Test results by electron micrograph. Product Brand Test Method Presence No. of Conditions of Free % Free Samples of Test-F Fibers Fiber* 1. Automobile A drum brakes Friction 6 300-800 Few <1 2. Automobile B Friction drum 6 250 - 800 None 0 brakes 3. Automobile C Friction drum brakes 5 300-700 Few <1 4. Automobile C drum Friction 1 700 - 900 Numerous -10 brakes 5. Automobile 0 Friction drum French brakes 5 300 - 800 Few <1 6. Automobile E Friction drum 5 300 - 700 Few <1 brakes 7. Automobile F Friction drum German brakes 5 300-800 Few <1 8. Automobile G Friction drum 2 100 - 500 Few <1 brakes 9. Automobile G Friction drum 1 600 - 700 Numerous --15 brakes 10. Automobile H Friction drum brakes 2 100-600 Few <1 11. Automobile J clutch ' Dynamometer 1 Normal None driving 0 12. ' Automobile disk brake K Dynamometer 1 Normal Few d living <5 13. Bus drum L Dynamometer 1 City None brake driving 0 14. Bus drum M Friction brake 2 450 - 550 None 0 15. Truck drum F Friction brake (light) 10 300 - 800 Few <1 Weight estimated from fiber volume. Some independent experiments done at a brake lining research laboratory" have shown that all of the magnesium present in the chrysotile asbestos orig inally in the lining can be accounted for in the decomposition products. How ever, the characteristic X-ray diffrac tion pattern of chrysotile asbestos had vanished. Thus, it is apparent that under conditions in which asbestos is worn from the lining of a brake, the asbestos is destroyed. Conclusion Only a very small proportion of the asbestos worn from brake linings is released as free fiber; the remainder is converted into some other mineral as a result of the extreme temperatures gen erated at small spots on the lining sur face. Thus, although urban air con tains a few free fibers as a result of brake lining wear, they represent a very small 126 . proportion of the total asbestos used in manufacture of brakes. Many sources of respirable fibers not associated with asbestos products have been identi fied,11 and free fibers from brake lining wear seem to be an inconsequential health factor in urban air pollution. References 1. Cooper, W. C., "Asbestos as a hazard to health," Arch, of Env. Health. 15: 285 (1967). 2. Thomson, J. G., Kaschula. R. O. C., and McDonald, It. 1!., "Asbestosis as a modern urban hazard," S. Afr. Med. J. 37: 77 (1962). ' 3. Cauna, D., Totten, It. S., and Gross, P., "Asbestos bodies in human lungs at autopsy," JAMA, 192: 37 (1965). 4. Webster, I., in discussion of Thomp son, S. F., "Physiological effect of 1X0 in mammals," .-1 nn. A*. }*. .-lend. Sci., 84: 736 (I960). . 5. Meurman, L., "Asbestos bodies and pleural plaques in a Finish scries of autopsy eases," Ada Path Microbiot. ScandSuppt., 181: 107 (1966). 6. Arvilrel, L and Thurlbeck, W., "The incidence of asbestos bodies in the lungs of randon autopsies in Montreal, Canada. Med. Assoc. J., 95: 1179 (1966). 7. Thomson, J. G., "Asbestos and the ur ban dweller," Ann. N. Y. Acad. Sci., 132: 196(1965). 8. SelikofT, I. J., Cliurg, J., and Ham mond, E. C., "Asbestos exposure and neoplasia," JAMA, 188: 22 (1964). 9. Buell, P. and Dunn, J. E., "Relative impact of smoking and air pollution on lung cancer," Arch, of Env. Health, 15:291 (1967). 10. Enterline, P. E. and Kendrick, M. A., "Asbestos dust exposures at various levels and mortality," Arch. Env. Health, 15: 181 (I9G7). 11. Sinclair, D., "Study of wear dust, front brake lining," .Johns-Manvillo lies and Eng Ctr., personal communication (1967). 12. Cralley, L. J., Keenan, It. G., Lynch, J. R., ami I.ainhart, W. S., "Source and identification of respirable fibers," Amer. Ind. Ifvg. Assoc. J., 29: 129 (1968). ' Journal of the Air Pollution Control Association FMSI 06518 NATIONAL INVENTORY OF N IC KEL, AND ASBESTOS - SOURCES AND EMISSIONS: 1968. ASBESTOS, SECTION CIIAI DMIUM, FMSI 06519 CLEARSNG HO USE FORFEDERAL SCIENTIFICAND TECHNICAL INFORMATION I jV; i I IV,' I%0 iI a E !1 i.i S Si 0 3 00 e t i 3 jt aa i % ^0 c0 if I ? a2 a2 2 5 3 3 a a a a g 1 i BC 5 8a n Zi *S 5. 5a I I e >aa. >. B ?! TJ tt | u 0 3 +* o S g sI* c> Sk e 1 0 e c o c 36 gV c% 0 9 25 ? * 2 21 * o g B to: a ** 0 =5 1: & t O5 E2 i f SB 30 1S 2 3 uM *J . ~ 1 o> S *3 TJ J5 1t g if 2*X5 * 0 s| 5< * I a 0 ** g < c -O 33 5 fe S 06 0 * 2c jC-* 0U0J Uo Me H2 (U O S 0 0 & 6 oo 2~ m 0 j S2 |S 2j3 u 0 | 6*3 Sob3 0 0^ ssSis* Sec _So,os 25 H-. a2 s*"* S| 3 05 -E5 g SM3<6| FMS1 06520 on fireproofing during 1968, are estim ated a t IS short to n s. |<*r- to f it the lin in g , to the drums by g rin d in g , and the amount of O O O to ooo I OiOO O N CD 0 OO N h 5 s e a I w5 5 S3 55 O' I I 2 1 ? a c o a . o 3 >>>> 0.. 0JaZ *c2 3 o> 5 fi sass ! & 5 E 8 C *3D -IHa a(00 s0a 2o 0m __ J03 *0 ** ttiot C I 1 O* C e- 1 s<B S. 5 JC 3 s 52 1 o 5 5 "O to I 0 0 3 e 0 E o s E (0 G 3 ! fib e r , w ere s o ld to a c o n tra c to r d u rin g IS 68 fo r use on ro a d s . 0 J0Z to C o *oJ co jEoC ` t1o0 to E0 0 cn O T3 0 to 0 E J8 (O <0 0 ml to E 0 3 aou. Tc3 to 10 00 0 to 5 il 0 S,, 3CQ dS >. S 52 gE oM HO 0 FMSI 06521 - Fifteen percent of the insulating cement wom away during Based on the follow ing assum ptions, an emissions factor o f 33 0a) ai GO a i a> s 0 1 8 a *m3 s OCM &u < 3 c3Oao o Io t 0 t0s v<ot B Doj o .5 s o S| u 3 I 13 i&s * m cE '*--2 0) (ft JS 8 o oc B) . *o oc * 2 ~ 0J 55 o 0 FMSI 06522 Troy American Brake Shoe Company American Brakeblock - D ivision Ambes Corp. Birmingham a> c j2 D OI V I?55 0) * in33o 5 ti IS 2 09 oO* ocn oO* sa 8 8 S-3 2o So o2 S wp *o1 3w g o id >50 OE2 3 o E AU 2 & Porter Company, Inc. stos-Manhattan, Inc. 2C Zo ess5S 3. o <yS *o U & sSl siiicj 5S? c* M 5es I3D o 8sS it>pp !3 I8*3 f|3| 2 i k- ^ w wO ^ (A U U n 22i ae 8 i " 1. e 521 3*O1 2--Mue 2_ 7Cr-! OOhS 8 2| =~ . 0" <2 E > i B2 55 3 si 888 40 =3 st.a (3(5 0. >, zp c W HE 3 ass >. c3 8 t0o* V] C1V0 so Ofca 3o o oc c a& 8 E 8 Kp> x 8 a FMSI 06523 REPROCESSING PLANTS PRODUCING ASBESTOS CEMENT PRODUCT?' e s IIV 6Ni O i! n 3 ti 1 1 $2 S 3 Din ?e >c5 ZSSsSa H a CO t g! >C c<0 Ok IS OJZ Oid OJB SJ|w8 oOk 8 C -C & 5 S'v. & ss 3EsescI| L|s ?ss58s I8SSS& afsifl 0 0& 0 mflu C0 C0 H0 H4) c eVisisisn-asi JS 10 IQ O) n00 (Thomas Register, D e c ., 1968 E d ., Fortune-1966 Plant & Product D irectory o the 1000 Largest U .S . Industrial Corporations; U .S. Department of Commerce.) 0 3#2 * l>c !% 03" 2c8 4 2qH 6 o. O8 O U *hj o> Je5 *C- So ,,tj C ^ &Z 6o al g& 5e S8 II s j 14AJSSa Troy B0 jos o e o> JS E* Sb0i O > -e 2 rOt 5Q f0t, e0 t 2 o & s 0 5 o 5 )* >c* S& E 0c " o. 8Ei c 8 s2 c la s " s,, o& s^ js e S6 Ss *26 c* c *s 1K oo 8ss tj Q* *U 0 0 0 C - E 0 <O2 > c0d JS 8 E < FMSI 06524