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fi!??cg;;7;'.gl / in mines and industry trUf' Vi^r-.v*^ V^ D?rQ? -- K'Q F<-rP-Pr r^c;v. ^-; La-'' O'* W u C W V~ bL S*^ ' v - i* it * p>r.r! *** L s.*# PLAINTIFF'S EXHIBIT UC-1435 c rr rWs.* nb I vWrirVtJ> GY,111' S. RAJHANS, Dust Control Specialist, Occupetional Health Service, EnviroPiriental Health Branch. Ontario Department ot Health, Toronto, Ontario ABSTRACT The strategy of fibrous dust sampling is discussed, various sampling methods are critically reviewed and their application to coal dust is demonstrated. Fibre courting is described in detail. An attempt is made to explain the basis of determining the threshold limit value of asbestos and other du-ts. The paper also discusses such dust control methods as cne!c~;'iv of the process, effective local exhaust ventila tion, sc-gregrlinn, substitution, vet processing and con tinuous monitoring of the xeturn air for recirculation. INTRODUCTION The liN'or:ot_e- inthease in the production and in dustrial use of asbestos and fibrous glass during the past 50 years 1m.- resulted in markedly widened ex posure to fibrous dust for a great number and variety of workers. In recent years, a great number of re ports have been published which discuss the effects of fibrous glas- dust in the lungs. The evidence de- GYAN S. RAJHANS was born in Bihar, India, in 19-12. He received his B.Sc. (Hons., i degree in mining engi. net-ring fi ora the Indian. School of .Vires, Phanbad in 1993. From July M'CS to July 196-1. ho worked as ar, assistant ventilation engineer at Western Bengal Coal-Fields Limited. In August 1901. Mr. Rajhan- was awarded the George C. Bateman Fel, I lc.wcl.ii-, at Queen's University. KingsMl.., .........t ton. O.-itmio, to pursue his postgrad uate studies in mine ventilation and dust control. On. eor.-pli lion of his studies at Queen's (M.Sc.), he joined th- staff of the Elliot Lake Research Labe-, ;.to: y. Pep..: ucviit of Energy, Mines and Resources, a- a scientific officer. During- hi; stay at the Elliot Lake Research Laboratory, Mr. Rajhans carried out studies on vaiic-us dust sampling instiiiments, on surface area measurements and on the cm relation of electronic scanner counts with the visual counts of konimetc-r slides. In 1967, he icturned to Queen's Univci sity tc resume his studies on critical velocities of mineral dud; and the development of a techr.inuc to mear-m ; radon daughters in uranium mines. In July 190S, he joined the Occupational Health Service of the Ontario Department of Hcr.ltii, whcic, at present, ho is it; charge of the dust control section. Mr. Rajhans is ;. member of the Ante, ican Industrial Hygj-n.. Association arJ the American Confeiente of Go\ f-riniu-nt d Industrial Hygienists. RARER PRHSEXTLD: at the 7?nd Annual General .'lo.-T t:.e Cl.M. Toronto, April. 1970. KEY'Vi.,l:jiy: l'ibi.u.s dust, Dust me.isui ement. Pu.-t con- t:ol. Bair,;,lii.g iiiC'.t.nJs. Filue cotintii.g. ThteshoM limit vah.e, .A.-ne-toS. Er,..iosin es, Yen illation. f-si egntion. Wet pfecesf .r.g, Recife .'latior.. Konimeter. Impingcrs. Ther mal ..It: M.-inb:a.nr- filter--. M'-dii-n! supervision. Cm. hi:.,. B. g, i,,v rived from these investigations indicate; that inhala tion of fibrous glass particles causes only respiratory tract irritation and doe? not produce permanent lung damage. In contrast, asbestos fibres have been known, since the beginning of the century, to cause fibrosis of the lungs. The greater threat from asbestos, how ever, lies in its possible association with lung cancer. In the last decade, several authors'151*' have called attention to the association between long-term (?) exposure to asbestos dust (especially crocidolite! and mesothelioma? of the pleura and peritoneum. Hence, we are far more concerned about asbestos dust than any other fibrous material. The word asbestos refers to a variety of hydrated silicate minerals which can be split into relatively soft silky fibres. The known varieties of asbestos can be divided into two main groups or, the basis of their crystalline structure: 11 > pyroxenes (serpentine) -- chrysotile; '2i amphiboles -- crociduiiie, amosite. tremolite. actinoRte and anthophyllite. The type- most commonly used are chrysotile yit accounts for 95 per cent of aii the asbestos produced today >. amosite and crocidolite. The fibrous form of chrysotile (chiefly produced in Canada and Russia; is retained ever, when broker, into small particles; the fibres are long and needle-like, with a thickness of about 0.5-j. and a length of 10-20-j.. The diameter of the finest fibre is in the range of txn to 4n0A:' ;lA - 10` cm.. Cr,,d- rioliie, the- blue ;--berms, is found in Cape Town and Transvaal, Smith Africa. It breaks Jcwr. to give, enor mously strong, fine fibres which are used mostly as a thermal insular w. Amosite is similai to civ.-id,elite in chemical comp, sitioii, but is not as strong:. It fuses at higher temperature " than crocidolite, and is often blended with other fibre.-. The world production of asbestos in 1968 was over 3 million tons per year, which is five times more titan twenty years ago. Workers now art not onh- exposed m mining arid textile industries, as in the past, but also in many other industries using asbestos-containing pi','ducts. There are more titan 3.000 recorded uses'1' of asbestos. The uses range from floor tile, which consume- hun dreds of thousands of tons, to special filtration appli cations which may consume a relatively snail tonnage annually. Thus. v. ith the increasing use of asbestos minerals, titcrc bus cone the ,cr1:tv. 1 uti of some very real haaurd- which must be clearly understood and controlled. The object of this paper is to offer up-to-date knowl edge on various methods of measuring asbestos dusti- ne-s iii order to provide usufu! and reasonably ac curate information for achieving adequate dust con trol. As the author is an engineer, the neveria! in this paper is presented with an engineer's paint of view. In the past, it has been difficult for engineers to un derstand the language and interpretations of nicclice- . The liter Lr:;re I ov : has fC- vealed l" the author hit there exists a !Litr j-Up be- tween the tv o group.-, Engineer.- v. ho are S.'V.* i. ing for answers to "why'', here" and "when'' Pi e. fore, completely lost before tin?y r.<" y ; ! C'..'1 .'or. *j "how" and "wliat". A tswers to thvst Cj.iv to be fc.ur.d. A 20 /"v /*- "T 0- .s have STRATEGY OF ASBESTOS DUST SAMPLING The main objects of asbestos dust sampling are: . <i > To determine whether an atmosphere is poten tially dangerous; and (ii.i to ascertain whether the dust control measures are working efficiently to maintain safe working conditions. How does one define "potentially dangerous" and "safe working conditions"? Epidemiological studies are not only confusing but contradictory. Although there is now considerable acceptance of a causal rela tionship between asbestos dust and asbestosis, lung cancer and mesotheliomas, scientists still do not agree as to what levels of dust exposure are required for the production of the various diseases'". A dose too small to produce fibrosis may, nevertheless, lead to lung cancer. A dose large enough to produce asbesto sis may cause malignancy if the worker does not die first from his pneumoconiosis'". Again, it is not known precisely how asbestos fibres cause disease or if all forms and sizes of asbestos fibres are equally hazardous. The reason that no definite answers to these questions have yet been found is due to the dif ferences in experimental and human asbestosis. In spite of extensive research on experimental asbestosis, it has r.ot been possible so far to reproduce the dis ease exactly"'. The marked variations in respiratory tract response by various animal species and the dif ference in the number of fibres present in relation to the degree of fibrosis make it difficult to translate any conclusion from experimental asbestosis to human asbestosis ". However, the experimental asbestosis has giver, rise to two causation theories which throw some light or. the relationship of particle size and pathoge nicity in e-bestosR These are. respectively, the theo ry of mechanical damage and the theory of chemical action. The theory of mechanical damage is supported by the observation'*' that the asbestos dust particles, smaller than 3 microns in length, had little or no reac tion on pulmonary tissues. This was very much in contrast to silicosis, which is caused by silica dust of the same size. Thus, if asbestos particles no longer than 5 microns are inhaled, very little disease would develop and the process would advance more slowly than when the airborne particles contained a predo minance of fibres of 10 to 50 microns'101. The chemical theory, on the other hand, favours the view that fibrosis is the result of the chemical action of an unknown fibrogenic agent (could be silica' re leased by disintegration of asbestos bodies'1' i sili cates '. This theory takes into account the delayed de velopment and progressive nature of asbestotic fibro sis. Nagelschmidt'"1 observed in 19G5 that in over half the asbestosis lungs from Great Britain and South Africa., practically no asbestos fibre was found, irrespective of the grade of fibrosis, and that asbes tos dust was possibly dissolved in the lungs. Knox and Beattie" studied the particle-size distribution from the insoluble residues of the lungs of twenty-seven cases of asbestosis. The fibres in excess of 2G microns were found to have almost disappeared from the lung v.he:'. the period between last exposure and death was rare than c-ight years. Significant changes in the number of fibres of less than 5 microns and those of 5 to * 1 5a were not found. Demy and Alder'151 suggest ed that the tem-'ency of the fibre to subdivide almost endlessly may account fur the failure to find asbestos in presumptive cases unless the electron microscope ic used or incineration is done. This may account for the claim that inhaled asbestos disappears from the lung, when in reality it is fragmented into submicroscopic particles. Thus, if the chemical theory is accepted, then the smaller the fibre, the greater the solubility and hence a greater biological effect. On the basis of experi ments, Holt ct a/.'1" concluded that chrysotile dust of small particle size (5a), because it was easily engulfed by phagocytes, was capable of producing fibrosis. Thompson et al.`u', in 19GG, showed that fibrosis may occur in the presence of few asbestos bodies and very small particles of asbestos dust, as well as with ultramicroscopic particles in the range of 200 - 250A. The increasing evidence of a relationship between asbestosis and carcinoma of the lung may postulate, in the future, a new dose-response relationship. We do not yet definitely know, however, whether asbestos has properties of primary carcinogenicity or whether its effect is entirely synergistic'". It has also been suggested by some authors'" that the presence of polycyclic carbon compounds and trace metals in as bestos fibre may be carcinogenic. Gross ct o2."s> ob served that the presence of trace metals (nickel, chrome and cobalt i in the asbestos dust increases by 82, 145 and 34 per cent, respectively, when the dust is subjected tu hammer milling. In 19G7, Collins'5 came up with another hypothesis. According to him. ingestion of fibres is probably as important as inhalation in the production of disease, and the 'asbestos corns' which occur in those who handle the material suggest that penetration of the skin occurs as well. The question still remains as to what we should sample -- total dust, long asbestos fibres (g: than 5a in length), short asbestos fibres (less than 5a in diameter i or metallic contents of the fibre. The obvious answer is that, in determining the dust ha zard, both the total count of asbestos particles (in cluding fibres > in the working environment and the prevalence of fibres of different lengths should be considered. The presence of trace metals and their carcinogenic qualities can, for the time being, be left to future confirmation. THE BASIS FOR DETERMINING THE THRESHOLD LIMIT VALUE The threshold limit value (TLVi is defined by the American Conference of Governmental Industrial Hy gienists (A.C.G.I.H.) as the average of the timeweighted concentrations throughout the S-liour daily operation under which it is believed that nearly all workers may be repeatedly exposed without adverse effect. Stockinger'1" in 1955 reviewed the TLY list of A.C.G.I.H. He showed that 42 per cent of the values were based on animal experiments and 11 per cent on human experiments, and that 4 per cent have the support of both, 33 per cent derive from industrial experience and 9 per cent were based on what was termed an "educated guess", with the origins of 1 per cent uncertain. In the case of asbes tos dust, it is very difficult to apply the effective values established by animal experimenting to human exposure -- due to the following reasons: H i The effect of asbestos dust causing asbestosis is recognizable only after a number of years. Hence, the animni' have to be subjected to dust concentra tions much higher than those which, occur in indus tries to pr rvide effective and rapidly assessable (2) 'There is a lack of general agreement about the theories on the formation of asbestosis. In lf*4C, the A.S.G.I.H. proposed that the TLY for asbestos dust be set at 5 mppcf (million particles per cubic foot.', as determined from impinger samples. This value was recommended by Dressen, Dallavalle, Edwards, Miller and Sayers'11' after a study of 541 employees in three asbestos textile plants using chrvsotile asbestos. In 1967, Cooper"" observed that the TLY of 5 mppcf for asbestos rests on shakier evi dence than most TLYs. His chief argument was that the impir.ger counts include all dusts and that a large proportion of asbestos fibres have diameters below the resolving power of the light microscope and are not counted at all. He further reported that asbestosis appeared in insulating workers who were exposed to concentrations much below the time-weighted aver age of 5 mppcf. Leathart and Sanderson"-' also con sidered the TLY of 5 mppcf to be too high. In Jan uary of 196$. the A.C.G.I.H. issued the following statement: "A limit to 5 mppcf. based on impinger samples counted by light-field techniques, is satisfactory to control exposures to most forms of asbestos. Croc-idolite, however, has been shown to produce, in addition to the asbestotic inflammation, also mesothelioma. Since no safe limit can be established for this form of asbestos at this time, until more definitive data are obtained, it is recommended that workers exposed to crocidclite be equipped with air-supplied helmets/' Since them it has been suggested by various inves tigators that the TLVs for known or suspected carci nogens should be established as zero, as there can be no certainty of a concentration which is harmless to man. However, a zero concentration is meaningless from :he point view cf an industrial hygienist try ing to assess the efficiency of a dust control system. By using a sufficiently insensitive method and suf ficiently impure reagents, an analyst can make almost any atmospheric concentration show no significant difference from the background concentration, which is the only meaningful definition of a zero concen tration. On the other hand, if a definite concentration is aimed at. even though it is as low as the 5 fibres per ml currently being suggested by the A.C.G.I.H., in the case of asbestos dust it is possible for a scien tist, by the selection of a sensitive method, to produce an answer with the agreed precision at this level. In May, ]PC8. the A.C.G.I.H. proposed a TLY of 12 fibres per ml for asbestos fibres greater than 5 microns in length, as determined by the membrane filter technique"'. Obviously, the committee accepted the theory of mechanical damage rather than the che mical action described earlier in this paper. Our experience"' showed that even in those places where visual impression sufficed to document the ex tremely dusty conditions and where impinger counts showed 10 to 15 times the TLY (proposed 2 mppcf -- for tot;:! dust', the average fibre concentrations were much belov. the proposed TLY of 12 fibres ml. The British ' have long been using a concentration of 4 fibres per millilitre (fibres longer than 5;jO as a goal in dust control. The A.C.G.I.H.. however, did not allow sufficient time- for various investigators to critically analyse the TLY of 12 fibres ml. Now they are proposing to low er it to 5 fibres ml. The author, however, is inclined t" agree with Ger man inve-tigatf us"' . who decided to determine 'dust fact';s' ratin'- than TLYs to evaluate working conditions. The 'dust factor' is determined by the fol lowing formula: where F = dust facto: Kc = total concentration of all dust particles in ppcc of air ippcc -- particles per cubic centimeter > Ka = asbestos fibre concentration in ppcc of air. Resting'54' suggested the following categories of de scribing safe limits: F i = 0 -- 20....................... no hazard F- = 20 -- 40....................... low hazard F3 = -JO -- 60....................... medium hazard Fj = above 60.......................high hazard According to him, an asbestos disease should not be expected with the range of F = 0-20. The proposed A.C.G.I.H. TLYs of 5 fibres per ml (membrane) or 2 mppcf (impinger), if and when substituted in equa tion (1), give: F = 3.5, which is within the range of F (0-20;. Hence, the author strongly suggests that the TLY committee of the A.C.G.I.H. should follow the German concept of `dust factor' and recommend both the total dust and fibre counts, in the case of asbestos dust, until we are reasonably sure about the relative hazards of fibres and other dust particles. Furthermore, the `dust factor' could be more ap plicable in the mining industry, where the total dust exposure may be higher than in the asbestos textile industry (mostly fine fibres'), although $0-95 per cent of the dust may be parent rock dust which could be biologically relatively inert. Before we finish discussing the subject of threshold limit values. I have one final comment to make: The TLYs, cr the safe limits established in various countries, are onlv meant to be used as a guide and should not be given a legal connotation. However, in my opinion., so long as these TLYs exist, there wj> be misinterpretations by those not fully informed of their nature. The TLY committee of the A.C.G.I.H. is aware of the fact that the TLYs have been used more absolutely than the recommendation justified. It should further be understood that the values of TLYs have been, in some cases, decreased in the past and there is every possibility that they may be fur ther reduced as fresh information becomes available, especially in the case of known or suspected carcino gens like asbestos. SAMPLING INSTRUMENTS & TECHNIQUES It has long been apparent that because the tech niques of dust counting vary considerably, they need to be standardized. The writer has no intention to involve himself in the theories of commercially or otherwise available dust sampling instruments. Sev eral comprehensive reviews on sampling instruments have been published in recent years"' . An attempt is made here to describe an instrument which is not only very practical but also reasonably accurate in the case of fibre and total dust counting. Instruments measuring mass concentrations have very little appli cation in the asbestos industries due to the follow ing reasons: (1) In most asbestos exposure, the asbestos is mixed with other (lusts. (2; When asbestos is shredded, the fibres tend to clump into balls which float around in the air; whether or not one of these balls are ce"ected by the sampler w ould have a great iiifh.eiictvpn-'ljge /-} mass concentration. A <_ U O <~ r-- Kut thermo:'-.:-. the threshold limit for asbestos dust, as mentioned earlier, is expressed in terms of fibre or total dust counts. The instruments capable of giv ing1 number counts are: (at Konimeter <bi Impinger (ci Thermal Precipitator (d > Membrane Filter The number counts are generally expressed in terms of either million particles per cubic foot (mppcf) or the number of particles per cubic centimeter (ppcc). In the case of fibres, the unit commonly used is fibres per cubic centimeter (fpcc). All of the instruments mentioned above have been described many times'55*'"'. A common characteristic is the aspiration of a quan tity of air for measurement and its subsequent exam ination and counting under the microscope. The aspi ration volume could vary from 2.5 cc in the case of the konimeter to about 500,000 cc in the case of the impinger. Let us now examine the advantages and disadvantages of these instruments in fibrous dust counting. Fibres are almost universally defined as those particles with a length three or more times thenwidth; that is, they have an aspect ratio of at least three. Konimeter leads to major errors. He also observed that the per centage of asbestos fibres in the total dust counts varied from 1 to 50 per cent, depending on the various stages of the working process l e.g. preparation, card ing, spinning and wearing!. Counting and sizing under the optical microscope inherently leads to erroneous results, particularly with konimeter counts. Because the slides of this instru ment are coated with a more or less thick layer of vaseline as an adhesive agent, the particles are less visible than in the samples of other number counting instruments. For example, the thermal precipitator samples, which do not have such a layer, permit the recognition and counting of particles smaller than can be recognized in konimeter samples'111 when stud ied under identical optical conditions. The konimeter, however, could be a very practical instrument if the sampling is to be carried out in the respiratory zone of the worker. The instrument is especially valuable if a microscope is attached to the konimeter (e.g. Bausch and Lomb dust counter). An instant and rough estimate of dust concentration in the working place can then be obtained. In any case, the konimeter slides should not be heattreated before counting asbestos fibres. An experi ment'"1' in the past has shown that asbestos fibres, when heated to 700CC, lose their crystalline and fi brous form and become amorphous. In the case of the konimeter. the entire sampling pre-vess takes only a fraction of a second fsnap samp ling) and can lead to quite erroneous results in situa tions of varying concentrations. Various authors''11' have tried to correlate konimeter counts with other instruments. The results of several tests on coal dust show, on ?'-ev:-.gc. twice the dust concent!alien as compared to that determined with the thermal precipitator. The higher counts were mainly due to the shattering effect of the impacting velocity. The instantaneous values of the konimeter results in the case of fibrous dust were observed by Kesting'5** in 10GG. He concluded that: "The extraordinary diver gence of individual results obtained from measure ments near a spinning machine were repeatedly not ed. A single break in a thread occurring at a spindle rotating at several thousand rpm shortly before meas urement produced such high values that the total pic ture of dust concentration is negatively distorted. On the other hand, a period with few thread breaks can supply excessively favourable data. Furthermore, in two plants with almost identical machinery, it was by no means rare that results were favourable in one and alarming in the other. This was due to the dif ferent quality of the raw materia! processed, and also to the different degree to which different factories approach the spinning limit of the materials." Wai te:'-''' found fibres up to 100y. in length in the sus pended dust samples taken with the konimeter at plants proee.-sing asbestos textiles. The still longer fibres, which arc usually present at higher concen tration*. are not aspirated by the konimeter. He count ed both the total dust and a>be.*tos fibres (with an average length of l-2y! under the konimeter micro scope. It was shown that optical evaluation was cost ly and time-consuming for the ever-expanding seiies n.tc.-cieir.ents because of the considerable fluctua tion* of the dust situation. Two konimeter sample* wi`h an equal number of particles differed greatly in fibre (oar.:. Walter''1-' then concluded that the use of the sectional counting method !*') such konimeter sam ple.* >.-f asbestos fibre* is highly problematical ar.tl Impingers There are two types of impingers currently being used in the industries -- the Greenburg-Smith (rate of flow 1 cu.ft min \ and a smaller version, the mid get impinger ' rate of flow 0.1 cfmi. Figure 1 shows the Greenburg-Smith impinger, which is ext^-sively used by the Environmental Health Branch of the On tario Department of Health. The technique of samp ling, which was originally developed for the evalua tion of siliceous dust, has been well described by r n iC t `I. O A us 3 c: FIGURE 1 -- Sampling with the G rec nb u rg-Smith 1 : pi it go r. (Ci.V.) Cm'::*.!.- ftr August, 1970 nent. The instrument was first developed by Ban croft''1' in 1920, and in 1936 a modified form, was pa tented by Green, V.'atson, Whvtlaw, Gray and Lo- mar':i>. Since then, several modifications to the stand ard design have beer, introduced'" . The Long Dunning Thermal precipitator tL.R.T.P.j, developed by Ha milton'1" in 19-36, is supposed to be the most suitable for particles abo\e 0.5 to ly.. The instrument has long been used for coal dust sampling in the U.K. It is considered to be of uniformly high efficiency for cca! / dust particles below a 5-micron aerodynamic size. The results obtained are in close agreement with those obtained with the membrane filler (described lateri. For fibre counts, the instrument is very useful be cause it uses the principles of both settlement and L___________ ; ...\ . i*. thermal precipitation, in contrast to thermal preci pitation only, as used by the standard thermal preci FIGURE 2 -- Electronniicrograph of Asbestos Fibres. pitator, which rarely collects fibres above 10 mi crons'"'. Holmes'11' observed fibres up to 300 microns in length in the samples collected by the L.E.T.P. Fur thermore. the deposit covered an area :j inch square Drinker and Hatch Davie# 'it alobserved that and was therefore easier to count than the standard with c.-Tt"! "diist the "ir.'.'iinger was apt to give erroneous thermal precipitator deposit. ly high dust-concentrations due to the breaking up of cp-; dust aggregate# originally present in the air. The count- were five to eight times higher than those det'-rnvired by the thermal precipitator for the same envii omr-mt. This compares favourably with our expe rience considering that Davits made high-power, dark.field counts on cell# evaporated to dryness. One great advantage of a thermal precipitator is that the sample? are mounted dry and, therefore, very large magnification can be used to see the fibres. This is in contrast to impir.gers, where, because the mount ing medium is a liquid, the limit is a 16-mm objec tive. Holmes'1'' has used a 4-mm objective to count - fibres between 5y. and 100y. in length. Roach'3*' re - V.'hei: the met!.:.;! was first applied to determine ported u.'iug a 2-rnnt oil immersion objective success asb.-stes ?x'-osu nih tota.l dm a no flures were fully. His conclusion was that the higher the resolving emm1 Decause toe. few fibres were seen, due to the power of the microscope, the more fibres are seen. light-field c-our.t tag mmlied and a law magnification The mean of forty thermal precipitator results, in ; ]6-m -y. r-'Aocf've . Ayer >* a1. ''- observed; in 2963 that mppcf r;r.u pp:c. is shown m comparison re re- eve-: when :! : -: vXth r. lpngt'- P whlth mfir. ,,f 3 or gi;eater wet t? i." ' . i ' t L'ti 1 i'u- the fibre c c unt was . thermal precipitator counts are higher than other usu;-!'; lev* Thm. ]f> !-er <en * <' f tiic total 1 wringer ' counts. However, the thermal precipitator is effec dust c t. The- f' ` ;*t h'-i' si a Ter] that "most airborne. tive only at a siw rate (2 cc 'min.'i and therefore re fibres c. r. ur.dve t}\) . to tent 'ns of a micron ir. diam- quires a long time '30 minutes or morel to take a etcr et en v hen ru: micron * 1. mg". - Am e!eetri'mrii- sample considered reasonable for counting. crop-'a ;-h of a ehr' r* T: f i le ashes tos dust sample is shown in F-g "fi 2. "F." of suelii >n diameter may not 1-e off icieiit !y c-h o:iv::! by th:e : myinger. Of the col- lectc-ih n\?r* of t hew. would settle to the bottom of the.counting cell, in the allotted settling time, and iho;e tliat did settle would usually not be visible by the n.icrcscojiic technique employer!. Thus, it is not surprising that fibre counts with, a lC-rr.m objective It has also been suggested that a horizontal elutriator be used on the intake side of a thermal precipita tor. The purpose of this elutriator is to pass only the respirable fraction of dust to the collector side. The validity of this elutriator is, however, doubtful when sampling fibrous dust, as the shape factor becomes important. are Our t:-.p-euifci.ee' ' with the im'pingtr tech- nkjnc in the ha# shown that the fibres have a A 2063 i tend,to cuil up in the water suspension and look like.particles. '~-T7"7- 7L T'."l17.1- . .' In 11 ">. Lynch and Ayer - aur-.ly-ed the results uf cn\irormicr.ir.l surveys of nine asbestos textile plants. Tjteir cm.-uhision wi,,- that the impingor is as conve nient as any liber in>ti umeni and. in' view 'of the 'urge '.ariante f.i:; the environment, no less accu rate than other instruments. They, howevc-r. agreed that the impiuger counts aie dominated by grains and that determining a hygiene criteria based on these counts could be misleading, because the fibres are thought to l.e the causes of disease. TABLE I--Number of Airborne Particles -- Disintegrator Plant Instru nient Midget hupinuc-r Membrane Filter Microsco)>e Objective 16 mm 16 mm 4 mm 2 mm All Visible Particles mppcf ppcc 1.1 38 C.4 13 0>.6O 21 ,t 'I berm,-.! Precipitator The therm;.! precipitator is regarded in many counti'ics. including the U.K., as the standard instrument nr atn:'-;!,ber:c dust estimation. For some reason, h.ov. o. it hits r ,t been very popular on this ennti- Thermal I'li-cipltato: ! 16 nun A mm 2 mm 3? Z).D 10.s Foyco Counter -- 2( 9 X. B. mppcf - nr': };. .if p:u tick 5 pi.:' cubic i ppec - part: civ.; per cubic ccr.r MlX'vC' 9S 195 382 740 . r" i Membrane Filler Technique A comprehensive review of the properties of various type;- of membrane filters has been published recent ly by the writer'571. Fraser'5'1, in 1053, was probably the first to apply the membrane filter technique to the sampling and measurement of dust particles. In 1050, Kruse and Eianconi'5'1 applied the technique to coal dust. The coal particles were made visible under the microscope oy treating a portion of the filter with immersion oil having a refractive index of 1.5. It was established that, by using a flow rate of 0.01 cfm and 950.x magnification for counting, accurate counts of as high as 500 mppcf could be made. In fifty-three comparative tests, coal dust concentrations agreed closely with those obtained using the thermal precipi tator but were, on the average, one-third of those determined by the midget impinger and one-half of those determined by the konimeter. The detailed tech nique for fibre counts was, however, first reported in 19G5 by Ayer et a!.'1" and Holmes'5" simultaneous ly. The main variations are shown in Table II. Holmes'55'- gave the following formula for the eval uation of the dust sample: ^Dus', concentration = --Do-: x --Xn--- x -\r1r-......................... (2 D = Diameter of the membrane sample area d = Diameter of each field of v;-.-\v V = volume of sample co N = number of fibres counted n = number of fields observed A slight modification over Ayer et af.'s technique was published by Edwards and Lynch"1'' in 196S. The Oeeup.'.t ion a! Health La be rat or;/ of the Ontario De partment of Health closely -follows the technique de scribed by F.hv.d and Lynch. Ho,ve'. =r, Seveial modifications, based on experience and difficulties encountered in industry, have been introduced. The pivce.-s i- described here in detail. Air Sampling Air is drawn through, a 37-nim-diameter cellulose acetate filter i Metrical. GA-G, pore size 0.45y.; Gelman Instrument Co. at a flew rate of approximately 25 litres per minute. The face of the plastic filter holder is cut away, permitting air to strike the whole area of the membrane filter. In this -way, an equal distribution of fibres is obtained on the filter. The holder, filter and pump a'-e shown, in. Figi'rt 3. Fig ure 4 shows a close-up of the filter, with the collected samtde on it.' ~77. T * TL.'7."'~ZrT7'~--i.---------- Asbestos Fibre Count Method A microscope fAmerican Optical Co.) equipped with phase-contrast optics is used to count the fibres. The magnification is 400. Fig-'rt 3 shows the microscope, with the photomicrograph equipment attached. The filter containing the fibres is placed on a hard surface and a wedge-shaped section, representing about one-tenth of the total area, is cut out with a lazor blade 'see Figure 4 i. The section is placed on a g:,-..-' n-.'cr.-.'Oopc slide and a few drops of the solvent mixture is added to cover the entire wedge (Fiai'ec c The solvent mixture is a 1:1 solution of diethyl oxyli-.te : dimethyl phth.tlate containing about 0.1 gram of the n.e-ybr.-.ne filler per ml of the above solution. TABLE II--Comparison of Detailed Techniques for Fibre Counts Ayer et al.i31, \ Holmes'3'; HI Sampling Medium -- \ il i "Millipore". Type "HA1", "Millipore". Type "AA", pore size 0.45 0.02y pore size 0.8 y. (2.1 Sampling Head -- (2j Aluminum holder with a Plastic holder containing a ! 20-mm-diameter filter 37-mni-oiameicr filler with 1 an open area approxi- 1 mately 850 mm-'. (3) Sampling Rate -- 2000 (31 2C0cc/min. cc.'min. (4) Liquid used for making >4; A few drops of glycerol the filter transparent -- a 1 triacetate mixture of 50 per cent di- | methyl phthalate and 50 per cent diethyl oxylaie ! f5; Mounting Technique: [ (5: The dust deposited on the A segment was cut from i MF surface was fixed by the filter, placed face upon I applying a drop of Pers a microscope slide, ren- | pex solution (0.05 per cent dered transparent and a 1 in chloroform) to the covershp placed on top. ! membrane and evaporat ing it quickly by pulling clean air through. A few drops of clearing agent (as mentioned in (4.1 placed on a clean microscope slide, then place the filter on top of the clearing agent and cover with a clean 1-in.- diameter covcrslip. :6. Covin ting Technique: A 4-nm (43-x- phase- ; contrast objective, sup- ' >6 The cleaned samples were posed to have the resolu- ] observed at a magnifica tion-iim.it of fi nucron. A tion of 500x. The sizing I'orton oyepivre 10x> was carried out b\ inn-- gratia:'. was uscc. to de porating a "Patterson fine ti'.e counting field and Globe and Circle" grati to assi?' in making length cule in one of the cvc- judgment of fibres. I'hasc- pitces. The graticule was co.ntrar illumination was calibrated against a suit used for all counts. Three able stage micrometer. modes of counting were The size ranges counted used: . were: (a-1 counting all fibres ! with length to width ia 5 -- ICj. ratios of 3 or greater: 'b 10 - 2C-jl ib' counting only those ic- 20 - 5C-i fibres longer than 5 : :d 50 - ICC-i microns: I ic counting only those . fibres longer than 10 1 microns. 1 A The index of refraction of this medium is about 1.3. The wedge of filter containing the sample dissolves in about 10 minutes. A faint shadow of the wedge is visible after dissolution. This shadow is used to line tip fhe field on the microscope. ' A cover glass is placed over the sample on the slide and placed on the microscope stage (see Figure T). All fibres greater than 5 microns in the eyepiece gra ticule (5.000 y: areai are counted. Five different fields, selected at random, are counted and the results averaged. Total fibres > 5 microns per cc of air = Ave.au. uraticv.le count x 107! mm3 cc of air s: tuple x 51X0 y- or 0.CC5 rr.ai- Figure S shows a microphntograph of a slide sect: through the pha<e-contrast microscope at a magnifieation of 400. (Cl-''> '-.r fn-'x' 197*1 To .summarize, the 3IF technique has the following advantages over other dust counting methods: (1 i The membrane filter has a pore size of 0.45 mi cron, which is quite adequate for trapping fibres in the length range of 5-100 microns. It has also been reported'5' that membrane filters can collect particulates as small as 0.1* in diameter with . practically 100 per cent efficiency. (21 The fibres are collected on the surface and the filter can be examined directly with incident light, rendered transparent and examined by high-resolution transmitted-light microscopy; or the par ticles may be transferred to an electron micro scope grid and examined by electron micro scopy""'. The electron microscope gives about four times as high a fibre count as the 4-mm objective with phase contrast. (3.i Higher sampling rates than are possible with the other instruments can be used, enabling large volumes of air to be filtered in a reasonable time. Addingley'"' reported that a variation in air -'."sampling rate between 10 cc and 500 cc. min. does not effect the results. This enables samples to be taken over short or long periods, and is quite convenient as compared to the rather long periods of at least 30 minutes required with a thermal precipitator. (4) The sampling head is smail enough for incorpo ration in a personal sampler to give a more rep resentative assessment of the true health hazard to which an operator is subjected. A personal sampler with a pump and motor which can be carried in a pocket and a membrane filter which can be mounted in the lapel of a coat is described by Hunt and Ellisch'4". (51 Hand pumps can be used where electric supply is inconvenient. (6) According to Addingley<::', the MF technique is of particular value in the estimation of mixed dusts containing asbestos, such as those found in the manufacture of brake linings. The asbestos component can be distinguished from that of the _ resins and fillers and counted fairly accurately under the microscope. FIG I RE -- Membrane Filter Sampling Technique Used by the Oc cupational Health Service of the On tario Department of Health. FIGURE 4 -- A Close-Up of the Membrane Filter, with the Asbestos Sample on it. A piece is cut for view ing under the microscope (see text). FIGURE 5 -- Phase-Contrast Micro scope, with Photomicrograph Equip ment Attached. A 2 OS 3 3 \ FIGURE 0 -- A Vi'edge-Shnpec! Section (about ]/I0tli FIGURE 7 -- A Cm or Glass Placed on the Trar.spari r.t of the total MF area) placed on a Micro-cope Slide. MF Sample. TABLE III--Number of Airborne `Fibres4-- Disintegrator Plant Instrument Microscope Objective Length > 5> Particle length > 3 x width mfpcf fpcc M:dcet Impinger . .. . 16 mm 0.11 4 Membrane Filter ....... 16 mm 0.06 2 . 4 man 0.37 13 2 mm 0.48 17 Thermal Precipitator . 16 mm 4 mm 2 mm 0.31 11 0.54 19 0.57 20 Reyco Counter........... -- (0.12i (4) N'.B. tr.fncf = millions of fibre; per cubic fool fpcc = fibres per cubic centimeter (A i t _ : - -_ . . FIGl KE S -- Microphotogr.aph of a Sample Seen Through the Phase-Contrast Microscope. -Ore common disadvantage of all these methods has always been the laborious and time-consuming'assess ment of the'samples under the microscope. It is diffi cult to eliminate human errors in counting and siz ing- particles. Fatigue or boredom probably affects the results. Hence, there is liable to be a rapid turn over _cf operators. Lynch and Aver'"' compared fibre count' by the impingev and membrane filter. The counts at 430x phase contrast were eight times those found on comparable impir.ger samples at 100.x light field. In 19G7, G. Xnight ct al."-' observed that the tc:a! dust counts by the midget impinger were usually cr.s cyunrter those of the therma1 precipitator. The fi bre ce nt; if the'impinger. on the other hand, were half those ' the thermal precipitator. Roach'''', often comparing various instruments, concluded that, in the case of fibrous dust iTnb'e IIIi. the thermal precipi tator had the greatest collecting efficiency. His reas oning was that the thin fibres were not collected effi ciently by the impinger. and in the membrane filter the' contrast between the filters and the mounting medium is poor, making them difficult to sec. .This difficulty was later eliminated by using a phase-cuntras: microscope in the membrane filter technique. -Thu.-, from the above di.-cussion. one may conclude that the MF technique using the phase-contrast mi croscope is the most practical developed to date for fib: c- dust counting. Dl*$T CONTROL METHODS Because asbestos exposures are of infinite types and intensities, each problem must be studied indivi dually before dust control measures, requiring consideral-e engineering experience and ingenuity, can hr ch-igned or recommended. Their control presents a"n\;.yy problem. Applications of various dust control methods to specific asbestos industries are discussed elsewhere in this paper. The following are general principles sugg-. -A d by cur service to minimize asbestos dust ex; re: (1) Substitution: The only sure way to prevent acbe-n. s disease is not to use asbestos. Thus, in all cas-:-. extor.-'r.e efforts should be made to find sub tit..tr-. A large number of non-asbestos-containing mat?: lal.-. sw-h a> nek v- o .! and glass wool, may be used.: Cork and expanded polystyrene can be used for low-temperature insulation and, as one scientist has said, "This is the age of synthetic materials, and matt surely can develop a substitute for asbestos which has all its useful properties without its harmful effects." Harries reported in 1967 that hot and cold water pipes and ventilation ducts in naval ships can very effectively be insulated with glass fibre cloth, felt canvas or polyurethane insulation rather than with asbestos cloth. Sound-insulating asbestos boards were replaced by those made of glass fibre and this mate rial also had taken the place of sprayed asbestos as an environmental insulation for steel deckheads and bulkheads. In those places when.- immediate substitutes cannot be found < e.g. machines subjected-to long periods cf intense heat, vibration and mechanical trauma), an attempt should be made to use asbestos cloth treated with a dust suppressant or coated with an imper meable plastic film. (2) Segregation: It is possible, with suitable planning, to arrange that work producing high con centrations of asbestos dust be dene in isolation. This reduces the exposure of `neighbourhood workers' to a minimum. This is especially useful in the case of asbestos spraying operations, where the chances of contaminating adjacent areas are considered to be maximum. A study'4" has shown that the dust counts 15 to 30 feet from the spraying operation were found to range from 5 to 10 times the TLV. j.4'Asbestos worker" and "neighbourhood worker" should be clearly defined. "Asbestos worker" is a man directly employed using asbestos materials continu ously or frequently. "Neighbourhood workers" are these who work in close proximity to the former with out -being directly involved with the use of asbestos. 'One such case in which both substitution and se gregation could have been effectively used was inves tigated by the writer last summer (1969). The case history is published in the March, 1970 issue of Occu pational Health in Ontario. Humidifier plates for use in domestic boilers Mere being made from blue as bestos i cn cidolite i. The area where the crocidnb'te was being used was located in the east end of a cafe teria. Tli? cafeteria, which had r. coffee mach'r.c. a cigarette machine and a coke machine, was used rmily by ab:ut 1C persons. The floor ar.d the machines in the area were found to be covered with blue fibres. When'the company was asked to find a substitute, jj;ov said that, after IS months of research, they had A.;::u! crocidolite to be best suited for making humid ifier plates. However, the company agreed to provide j.dori.atc dust control measures including segregation i.f the area. (3) Dust Suppression: This includes such meth ods as enclosure of the process, as far as is possible, installation of adequate and effective local exhaust ventilation, automation of the process and wet pro cessing. In some cases, materials containing or made from asbestos are impregnated with dust-binding agents. This helps reduce the dissemination of dust to a considerable degree. As a rule, it is not enough to take only one of the above steps. It is necessary often to apply two or more in combination: for example, wet processing and dust extracting (local exhaust). Our experience is that the proper enclosure of the process and the provision of a dust extracting system at the enclosure makes a real conlribution_to the control of the airborne dust.. How ever, Twcrthings we invariably notice in asbestcs-uslng industries are: ia'The dust control systems are seldom maintained in good operating condition. In most cases, they are never checked after installation. The design and main tenance of dust control systems js so complex that this review can do-no better than refer to the many texts which adequately cover the subject"'-'"1'"7'. fb1 The operators are not instructed to use dust exhaust systems properly; e.g. turning on the fan before the start of a process or adjusting the damper to ensure adequate exhau>t capacity. One other problem we often are faced with in the j' descry to ccnvince n-.ar.ng emeu* nut to >ceimilate the air exhausted front any process using asbestos or other toxic material. The obvious disadvantage of re circulation is a continuous exposure of fine dust to the workers in the plant. The /mlm-trial Safety Act of the Ontario Department of Labour 'Section 201 requires that all the air exhausted from any process using sili ca, asbestos and other toxic material be exhausted to atmosphere. Tice main argument against this is the tremendous cost of providing heated make-up air in winter. In 1965, Hills"5' reported that, for 1.000,000 cu.ft of air per minute, the running costs cf the dust-ex traction. system, including electric power, labour, plant depreciation am; other overhead charges and the extra heating cost becaiu-e the filtered air cannot be recir culated. come to about $250,000 a year. This figure could go very high in the case of asbestos mines and mills, many of which are located in northern climates, where the winter is long and very cold. We have, however, from time to time permitted the recirculation of air from the dust-collecting systems if the following requirements were complied with: (A) An acceptable monitoring device should be placed in the return air stream to continuously meas ure the dust concentration. The device should be fit ted with an alarm system to sound when the dust count exceeds 1 mppcf (half the proposed TLYj. Here again there are many difficulties, which include the absence of standardization in various counting meth ods and an ignorance of what amount of asbestos dust, if any, is safe. It is. however, hoped that by main taining the concentration at half the proposed TLV, a safe environment can be attained. (B.) The monitoring device should be calibrated at least once a month when operating against a standard dust-counting technique. ` (C) The monitoring device should be checked at least once a day when operating. CD) A dust-counting survey should be carried out by the company semi-annually, with a copy of the survey results submitted to this Branch. (E i The collector system should be equipped with a damper so that air can be directed outside during warm weather or when the alarm sounds. (Ft The collector system, monitoring equipment, calibration equipment and calibration test results may be available for inspection by a member of this Branch or the Department of Labour at any time. Dust s- ppre'-s-m becomes a special problem for asbestos milling. It is a dry process and is therefore an extremely dusty operation. The condition is fur ther aggravated by the leakage in conveyors and screens, spillage from the belts and improper enclo sure of the machines. The successful control methods are: (1) complete enclosure of the dust-producing machine <Fig,-re 9 shows a Hazemag crusher with proper enclosure1: or (2> adequate suction within the enclosure to prevent escape through openings. Figure 10 shows the bagging machines in a mill. We have always funnel dust counts at these machines to be very high. In one case, compressed air was be ing used to clean tits bagging platform. This stirred up a considerable amount of dust in the air. The dust counts during the blowing operation were too high to count. The obvious solutions to this problem were: r ' j f ;I !i 'l i } L'l ItE 9 -- llazt mag Cru-her Utul inr the Tine Cru-h- FIGl'JtE JU 1:l,- at Asb,-tc,; Ore. v . -0- 0 -O; pg Operation in an Asbe-tos Mill. (1) air-tight attachment of the bags to the machine;(2 i the use of suction rather than blowing for clean ing the platform; and (3) the installation of a dustextracting system at the machine to remove any spill of fibre when the bag is detached from the machine. (4) Persona] Protection: In places where ma chines and processes cannot be provided with effec tive enclosures and adequate local mechanical ex hausts, respiratory protection for each worker be comes an absolute necessity (e.g., dockyard workers engaged in the loading and unloading of asbestos bags:. Adequate respiratory protection in the case of asbestos involves either the use of air-line breath ing apparatus or approved respirators'**'. It should, however, be realized that the provision of approved respirators and their proper use by the operators are two different things. Unless an effective program of -educating the workers in regard to the dangers of as bestos is carried out, the persona! protection devices will not be effective. It is also necessary that, after each use, the respirators be cleaned, maintained and stored in-a.relatively dust-free place to avoid any contamin ation0*.-. (5) Good Housekeeping: This includes cleaning .of the floor and machines regularly and thoroughly. To avoid stirring up dust during cleaning, the dust must either be dampened with water or removed by means of a central vacuum cleaner. On our suggestion, a few companies have successfully used their central -dust-extracting system for vacuum cleaning. The .maintenance of good general ventilation also improves .'housekeeping. (C) Medical Supervision: For a number of years, it has been a policy of the Environmental Health Erami: of the- Ontario Department of Health to regu-larly X-ray a'l employees exposed to asbestos dust. It has also advised the industries that all employees, en gaged in 'asbestos work" should be given pre-employ ment physical examinations. In 1069. the Occupation al Chest X-ray Section of our Branch provided X-ray examination and lung function tests to a total of 2,644 asbestos workers, of whicli SIS were exposed to both silica and asbestos. An attempt is being made to main tain detailed medical records capable of yielding val uable and necessary information on statistical analy sis. This information is valuable in the early detection .of bronchia! carcinoma., and it is of value in preventfin g the progression of cases of asbestosis. -jkEFEKENCES - (1) Zaidi, S. H., Esperienentul Pneumoconiosis, The John Hopkins Pre-s, Maryland, 1909. . (2i Collins, T. F. B.. "Asbestos -- The Lethal Dust," S.A.-M~d`"'l Join net, pp. ftB D -at4 PJ, July, ] 907. (3) Mere-weather, E. R. A., and Price, C. \Y., "Report . on Effects of Asbestos Dust on the Lungs and Dust Suppression in the Asbestos Industry," H.M.S.O., London. 1930. (4) Wagner, J. C., Sieges, C. A., and Marchand, P., ``Diffused Pleura! Mesothelioma and Asbestos Ex posure in X.W. Cane Province," British J. Jndust. Med., 17: 200-271, 1900. (0) Sclikoff, I. J., Cliurgh, J.. and Hammond. C., "Ex posure to Asbestos and Mesothelioma,"' Sen: Eng. J. Med.. 2 12: 5C0-5''3, March, 1905. (Gj Cooper. VO. C., "Asbosio.- as a Hazard to Health," Arch. Err. Health, pp. 285-289, September, 19C7. (I Tabershaw, 1. It., `'Asbestos an Environmental Hazard." 'Jon mil of Occupational Medicine, Volume 19, No. 1. pp. 32-37. January. 1968. tsi kr.o>:. -J. F.. and Bcatile. J.. "Distribution of Min eral Particle.-- and Fibies in tin- Lung after F.xpo- (C1X) EXLslr f:r Arris'. 1579 sure to Asbestos Dust," Arch. Indus!, ling. Occn, Med., Vol. 10, pp. 30-36. (9) Vorv.ald, A. J., Durban, T. M., and Pratt, P. C.. `Experimental Studic*s of Asbestosis," Arch. Jndnstr. Hyy. Occnp. Med., 3: 1-43. 1951. (10) Buckup. H.. "Asbestosis". Die Bentfsgcuosscnsehaft, Bielefeld, Gcrnianv (Fed. P.ep.), No. 7, pp. 255-201, July, 1900. (11) Xagelschmidt. G., "Some Observations of the Dust Content and Composition in Lur.gs with Asbestosis, Made during Work on Coal Miners' Pneumoconiosis," Annals of the Sen: York Academy of Sciences, Vol. 132, pp. 64-7G, 1905. (12) Demy, X. G., and Alder, H., "Asbestosis and Malig nancy." paper presented at the sixt>-seventh An nual Meeting of the American Roentgen Ray Soci ety, San Francisco, California, September, i960. (13) Holt, P. F., Mills, J., and Young, D. K., "Experi mental Asbestosis With Four Types of Fibres -- Importance of Small Particles," Annals of the SenYork Academy of Sciences, Volume 132, Art. 1, pd. S7-97. (14) Thompson, J. G., Path, F. C., and Graves, W. M., Jr., "Asbestos As An Urban Air Contaminant," Arch. Path., SI: pp. 45S-464, 1900. (15) Gross, P., dcTreville, R. T. P.. Tolker, E. B., Kaschak, M., and Babyk, M. A., "Experimental Asbes tosis." Arch. Enr. Health, Vol. 15, pp. 343-355, Sep tember 1967. (16) Stokinger, H. E., "Standards for Safeguarding the Health of Industrial Worker," Pub. Health Repts., 71:1, (1955). (17) Dresse, W. C., Dallavalle, J. M. Edwards. T. I., Miller, J. W., Sayers, R. R.. Easom, H. F. and, Trice. M. F., "A Study of Asbestosis in the Asbes tos Textile Industry." Pub. Health Bull. No. 241, Washington. D.C., 1938. (18) Leathart, G. I., and Sanderson, J. T., "Some Ob servations On Asbestosis," Ann. Occnp. Hyg., 6: pp. 65-74, 1963. (19) "Threshold Limit Values of Air-Borne Contami nants." Adopted at the 30th Annual Meeting of the American Conference of Governmental Industrial Hygienists. St. Louis, Missouri. May 13, 1968. (20) Rajhans, G S., "Asbestos Dust Sampling," unpub lished Internal Report, Occupational Health Serv ice, Environmental Health Branch, Out. Dept, of Health. October, I960. (21) Lynch. J. R., "Asbestos Study -- Procedures and Findings," Transactions of the 27th Annual Meet ing 0/ the A.C.G.I.H., Houston, Texas, pp. 62-70, May. 1905. (22) Resting. A. M., "Evaluation of the Results of Dust Measurements in Asbestos-Processing Plants in the Textile Industry," Die Bcru.fgenossenschaf, Biefield, Germany (Fed. Rep.), Xo. 8, pp. 321-323, August, 19G1. (23) Walter, E., "The Evaluation of Dust Measurements in Asbestos Textile Plants," Stauh, Germany (Fed. Rep.), Vol. 2G, Xo. 10, pp. 422-424. October, I960. (24) Resting, A. M., "Asbestos Dust Measurements in Asbestos Weaving and Spinning Plants,-" Staub, Vol. 26. Xo. 10, pp. 419-421, October, 19CG. (25) Green, II. L., and Lane. W. R.. Particulate Clouds, Second Edition, E. & F. X. Span Ltd., 11, Xew Filter Lane. E.C.4, London, 1904. (26) Davies. C. X., Aylward, M., and Leacev. D., "Im pingement of Dust From Air Jets," A.M.A. Arch. Indnstr. Hug., 4, 354, 1951. (27) Addingley, C. G., "Asbestos Dust and Its Measure ment." Annals of Occnp. Hug., Vol. 9, Xo. 2, pp. 73-82, April, 1900. (281 Winkel. A.. "Comparative Dust Measurements in Industrial Locations and Their Evaluation," Staub, Vol. 20. Xo. 1, pp. 2-8. I960. (29) Spiel, S., and Leineweber, J. P.. "Asbestos Minerals in Modern Technology," Euvironnu utal Jicscarch, 2, pp. 1G0-20S, 1909. (30) Drinker, P., and Hatch, T., Industrial Dust, Second Edition, McGraw-Hill Book Company Inc., New York, pp. 1-17-160, 1954. (31) Aver. H. E., Lynch. J. R.. and Far.ney. J. H.. "A Comparison of Impinger and Membrane Filter Tech niques for Evaluating Air Samples in Asbestos Plants," .4/i/>a(s of the Scu- For/.- Academy of Seicnr's, Vol. 132, Art. 1, pp. 274-287, December, 1965. (32) Walk H.. "Asbestos Dust Measurement." unpub lished Internal Report. Occuj ..tiona! Health. Serv ice. Environmental Health hkancli. Out. Dept, of Health. June, 1906. n T ft o ' ' -- U U O J 555 (u3) Lynch. J. R., and Ayer, H. E., "Measurement of Dust Exposures in the Asbestos Textile Industry,'' , A.I.H.A. Jomnal, Vol 27, No. 5, pp. 431-437, September-October, ]9G6. (34) Hamilton, J. R., "Portable Instrument for Respi.rable Dust Sampling," J. Sci. lust., 33. 395, 1 *5G. (357 Holmes, S., "Development in Dust Sampling ar.d Counting Techniques in the Asbestos'Industry," An nals of the Xcie York Academy of Sciences, Yol. 132, Art. 1, pp. 288-297, December, 1965. (36) Roach, S. A., "Measurement of Airborne Asbestos Dust by Instruments Measuring Different Para meters," Annals of the .Ynr York Academy of Sci ences. Yol. 132. Art. 1, pp. 306-315, December, 1065. (37) Rajhans, G. S., "Sampling of Airborne Dust," Ca nadian Mining Journal, pp. 70-81, October. 19GS. (38) Fraser, D. A., "Absolute Method of Sampling and Measurement of Solid Airborne Particles, Com bined Use ol` Molecular Filter Membranes and Elec tron Microscope," Archives of Industr. Hyg. and Occ. Med., Yol. 8, pp. 412-419, 1953. (39) Kruse, C. \Y., and Bianconi, W. 0., "A Comparison of Sampling Techniques for Measuring Airborne Coal Dust Concentrations", Tcun. Ind. Hyg. .Yens, pp. 7-14, April. 1959. (40) Edwards, G. H-, and Lynch. J. R., "The Method Used by the U.S. Public Health Service for Enu meration of Asbestos Dust cn Membrane Filters," Ann. Occii/i. Hyg., Yol. 11, pp. 1-G. 19GS. (41) Hunt, R,, and Ellison, M. J., Lab. Prod., 12. 148, 1963. (42) Knight. G., Rajhans, G. S., and Stefar.ich. IV., "Com parison of Dust Sampling Instruments: Y -- In terim Report on Asbestos Dust," unpublished Div isional Report. Dept, of Energv, Mines and Re sources, Ottawa, 1967. (43) Harries, P. G., "The Prevention of Asbestosis in X'aval Dockyards" a paper presented at the Second International Conference on the Biological Effects of Asbestos, 19G7. (44) "Construction Health Hazards," Michigan's Occ. Health, pp. 4-5, Spring, 19G3. (45) Industrial Ventilation -- A Manual of Recommend ed Practice, 10th Edition, Committee'on Industrial Yentilation, Am. Conf. of Govt. Ind. Hvg., Lansing, Michigan, 19GS. (4G) Alden, J. L.. Design of Industrial Exhaust Systems, Third Edition. The Industrial Press, 93 "Worth Street, New York, X.Y., 1959. (47) Hemeon, \Y. C. L., Plant and Process Ventilation, (Second Edition), The Industrial Press, New York, 1963. (4S) Hills, D. W., "Economics of Dust Control," Annals of the Xcie York Academy of Sciences, Yol. 132, Art. 1, pp. 322-337, 1965. (49) Revoir, \Y. H., and Yugilas, V. A., "Performance Characteristics of Dust Respirators, Bureau of Mines Approved and. Xon-Approved Types." A.l. H.A. Journal, pp. 322-332, July-August, 1968. (50) Nelson, H. M., "Respiratory Protection," Occupa tional Health in Ontario, pp. 1-S, December, 1969. Earth Sclsnce Symposium cn Offshore Eastern Canada Ottawa, Ontario. Canada. February 22-2-1. 1971 AN E.AKT!! SlYEXCL SYMPOSIUM on OrKsrioi-h; Eastern Canada will be held in Camsell Hall, 5:;S Booth Street, Department of Ener gy, Mines and Resources, Ottawa 0!) February 22-24, 1971. The Chairman, of the Program Commit tee is Dr.. Petek Hood. Room 57:3, Geological Survey of Canada, Ot tawa 4, Ontario, Canada. The main objective of the Sym posium is to summarize the present knowledge of the continental shelves and slopes of eastern Can ada so that emphasis will be on re sults rather than on techniques, although, descriptions of new tech niques will be encouraged. Areas to be discussed are the Bay of Fundy. Scotian Shelf. Gulf of St. Law rence. Grand Banks. Flemish Cap. Labrador Sea, Ungava Bay, Fo.xe Basin, Baffin Bay and Greenland Shelf. The topics will include Surficial Geology, Geochemistry. Repe titive-Source Seismic. Bedrock Geology and Tectonics, Seismic Re flection and Refraction, Gravity, Magnetics, Magnetotellurics. Crus tal Seismic, Heat Flew. Continental Drift, and Offshore Drilling. Papers are invited for this sym posium. Abstracts should be sub mitted before Xovember l, 1970. A number of papers have already been offered, mainly by govern ment agencies and the universities, and there has been some response from industry. It is recognized that the symposium will be a great er success by widespread industry participation. It is therefore urged that individuals and representa tives of exploration companies in dicate to Dr. Hood their degree of interest. A 20 53 7 Symposium on Stability in Open-Pit Mining Vancouver. British Columbia, November 23-25. 1970 A Practical Symposium on Sta bility in Open-Pit Mining will be held at the Baysliore Inn in Van couver, B.C. November 23-25, 1970. Thds symposium, part of the con tinuing education program for en gineer.' given at The University of British Columbia, has been ar ranged by an cd hoc committee representing not only the Univer sity but also the Vancouver Branch of The Canadian Institute of Min ing and Metallurgy and the Van couver Branch of the Engineering Institute of Canada. The. Symposium lectures will be directed toward mining executives, managers, operating engineers, and planning and design personnel. As the majority of these people have been out of university for many years and have largely lost contact with theory and coliege mathema tics. the emphasis of the Sympo sium will be on the practical as pects of stability and surface min ing. Speakers at the Symposium will include Drs. D. Deere. E. Hoek. N. Morgenstcrn, A. Bauer, R. Whit man. D. Pentz, H. Q. Colder, D. Coates and L. Casagrande. Mr. R. Stewart and Mr. C. O. Bfawner. The cost of Symposium registra tion will be approximately S100. For more information, please con tact Engineering Programs. Exten sion Dept., The University of Brit ish Columbia, Vancouver 8. B.C. SIC The C2ii2-i2a Firm;, tr.i MMilbrnual