Document 1y0M4Z98aM6J3gvo3bq28geMZ

.. ^pct. Ocagi, Hyf. Vet, II, pp. 33-OS. FetBaiwm Press iTlO. Printed In Gnat Britain -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 airline 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 graces 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 aad it is easy to see that the chances of de veloping a technique of cleaning which will reduce dust emissions but at the same time require no more time and effort are extremely slim. Quite clearly, we must .vneede from the very beginning that some increase io time and effort involved is `turntable. -_ "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 coaventiooaLmethod of evaluating an environ mental condition is the measurement of the appropriate parameter (in this case-- ibie. counts), referring the results to hygiene standards, fn 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 ample method to define certain environmental conditions which prevail when brake justs are removed by blowing out with a compressed air iine-and comparing these "ith 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 In important These sources of error are discussed later. METHODS USED TO EXAMINE ENVIRONMENTAL CONDITIONS When dusts are released in relatively small quantities it is often impossible to see ire clouds under normal lighting conditions. They can be made visible using the Tyndall Beam effect and this has been employed extensively during the experimental' vorlc. *TbIs paper was originally presented at a Conference an Exposure to Asbestos during Brake and Gulch Maintenance, held at Brentwood, Essex, March, 1969. - -- . 33 ' IIII -T ir-'f'i'i * !*s ^ v.iilr *I 5ij ii! . JU# 'mm ifll'i p iff iWi'li / 34 Q. L. Leh . Mass concentrations of airborne brake dusts were determined at two positions by sampling through taxed 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 ofTyndall Beam examinations had indicated that the highest dust concentrations were likely to be obtained. Secondly, a personal air sampling device was worn by the operative in such a manner that the sampling ` head was attached to the wearer's lapel, as near as practicable to the breathing zone. Samples for particle counting were taken, again in the operative's breathing zone, using a Konimeter, and membrane filter samples were also takea 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 REMOYE 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 biir 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 Tabic I. TAnm I. Results op Konimeter samples during blow-off Sample ... Number of brake dust particles/5 cm ' Taken at beginning ofoperation Taken appro*. JO sec Inter . Taken approx. 60 sec later Taken approx. 30 sec later ' Taken approx. 30 sec Inter ' 5000 4500 ` 4000 1S00 . 580 " r* .. It is seen that there is a progressive fallin., count as the local dust doud disperses. The first three figures are approximate only, the numbers of particles collected being too high for accurate counting. * ~ . . ~ . jM ROCK 001404' Removing dusts from brake assemblies during vehicle servicing 35 . A feed sampling period of some 5 min was chosen for the determination of mass- concentrations--this being longer than required for the blowing operation but sufficient to cover that required for the alternative cleaning methods. The dust col lected by the static sampler dose to the brake assembly gave an equivalent concen tration of 114 mg/m` and.,that for the personal air sampler 42 mg/ma. 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 oirder 3-5 fibres/cmB. ./ . . ALTERNATIVE CLEANING METHODS Initial approaches y/ere 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 exf tractors, although reasonably efficient, were rejected because of restrictions wbidji these placed upon the work by confining it to one .area. Hath operatives and super?vision were unhappy about being confined to one work ai*ea--preferring to retain flexibility and carry out the work as they had previously done, wherever the vehicle happened.to be. Portable extraction equipment was dearly required and alter 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 paperhags are fitted in a manner which allows them to he sealed fairly easily before removal. To trap any particulates which might pass through the'paper and. cloth bags, an ex ternal, multi-layer filter was provided for fitting to the air outlet end of the cleaner. Preliminary experiments established that some brake dust particles were passing the paper and cloth bag3 but these were trapped bythe externally fitted filter,. Sampling at the exit side of the filter established thatno particles passed the filter. CONDITIONS OBTAINED USING THE VACUUM CLEANER ' - AS A SOURCE* OF .EXTRACTION . The first technique tried was to use the nozzle of the deaner, hand-held as a source of local extraction whilst, the dust deposits were dishirbed. 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 i Results of Kgnimhtzr. sampies duiunq brushinq and wtth local extracnoK Sample ' Number of brake dust particles/5 cm* ' Taken atstart of process Taken about 1 mm later Taken about 2 min later Taken at end of process - .. 1070 404 42fi`446 ' ROCK 0014047 V'| w'4 ;i!l!i| r :i ; v.Fli* The fixed sampler in the area of the highest concentration gave a dust concentra tion of 21 mg/m* and tie-personal sampler, 2*7 mg/m*. An improvement in. controlling the release of dust had been obtained but was not considered completely satisfactory and an alternative approach was sought CONDITIONS OBTAINED USING A MODIFIED TECHNIQUE After some preliminary experiments, the following general technique was devised. Firstly, the loose deposits of dusts inside the brake drum and on- readily accessible surfaces of 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 'ce.KqNiMEim samples during modified technique Sample \ Brushing with standard brush Brushing with tubular brush Rag wiping Number of brake dust particles/5 cm 16-25 20-25 1-5 . ' No fibres were detected and the mass concentrations involved were too low to determine. '' . CONCLUSIONS The objective measurements made seem, to confirm that vacuum cleaning provides a useful contribution towards obtaining satisfactory dust control when brake assem blies are-cleaned. The design of the particular cleaner chosen prevents the discharge ofparticles back into the environment and the collection in apaperbag 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 ofthe Industrial Hygiene Department and Mr Young, Works Engineers, is gratefully acknowledged. ft 8 4m.nesap.Hi IN! OF TtJ The most ul ai'iembliesi ;t dust cloud being deane' ceaerated at! men likely ^ Enquirie? is to allow ij! in nself. Ou the parts of total deaniir Tfiecritei method did that it was nd was needed. 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