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The Saranac Laboratory FOR THE STUDY OF TUBERCULOSIS OF THE EDWARD L TRUDEAU FOUNDATION Saranac Lake, N.Y. February 24, 1943 */%</ is b:?r. J Mr. Vandiver Erown Johns-Kanvllle Corporation 22 East 40th Street New York, New York ,1 Dear Mr. Brown: . I have at last succeeded In analyzing nost of our VQjfljjalnous experimental data end assessing the results. I realize 'that this should have been completed before this, but the emergency has left me short-handed In the Laboratory and also necessitated my doing a good deal of extra traveling. I hope that the sponsors of our study of asbestosls will be charitable and realize that the work has far exceeded Its original scope. We have done over 40 different experiments, many of then divided Into several parts, which Involved exposure of animals for 1 to 3 years to various du6ts. The business of preparing micro scopic sections and chemically analyzing the tissues on more than 800 animals has been a Job In itself. My time for studying sections and analyzing data has been 90 limited that we are behind our sched ule. T have still not had time to write a full report of this work which will of necessity be monographic. However, for the benefit of the contributors, I am submitting a table of contents and an an notated outline to Indicate conclusions and the line of argument that will be developed. The latter Itself occupies 15 pages, but I hope they will find It sufficiently Interesting to read. I shall work on the final manuscript as I have opportunity. There ere a few.experiments still In progress which should be completed by the time ve are ready for them. x`he work on methods.of dust determination, I consider Important enough to In clude in the study. The question of cancer susceptibility now seems more significant than I had previously imagined. I believe I can obtain support for repeating it from the cancer research group. As It will take two or three years to complete such a study, I believe It would better be omitted from the present report. If It should become possible to make this study, I hope that I amy count on some of your members to supply me with enough pure, long fibre asbestos for the purpose. PLAINTIFF'S EXHIBIT II ^)\y-Qootol 060 06 00091 Mr. Vandiver Brown -2' February 24, 194. Naturally, I shall welcone any oritlolem that you or any of the other contributors would care to offer. Should any of thea want to dleouee details, I. would be pleased to Beet with then. May I take thle opportunity to thank all the sponsors through you fo the support that ve have had. Slnoerely yours, LUG:?-3H Leroy 1). Gardner, M. D. Director nnn or 00092 OUTLINE OF PROPOSED MONOGRAPH ON ASBSST03IS . Saranac Laboratory Study underGrant fron Aebeatos Association PART I HUMAN ASBEST03IS 1 Human Pathology - a study of .26 autopsy oasei^ Illustrated 2 X-ray Patterns In Asbestosls, Illustrated 3 Ash and Mineral Values In Hunan Asbestosls 4 Complications of Asbestosls (a) Susceptibility to Infection 1 Tuberculous 11 Non-Tuberculous 111 Cancer of the lung 5 Disability, causes and comparison with silicosis 6 Diagnosis (a) History of adequate exposure (b) X-ray flIn pattern (c) Physical examination (d) Asbestosls bodies In sputum, their significance ....:.................................. 060 06 00093 (2) PART II Exnrlfflental Asbestosls I Methods (a) Inhalation exposure to plant dusts. (b) Injeotlon Into lungs through traohea of pure minerals (o) Injection of pure minerals into other organs. 2 Species Susceptibility Man, guinea pigs, rabbits, oats, white mice and rats dogs. 3 Peculiar Characteristics of Asbestoels (a) Unusual looalizaion of chrysotlle fibre In lungs. (b) Rate of resultant tissue reaction more rapid than to ouartz. (c) Reaction to cbrysotlle not progressive after exposure ceases; again the reverse of the situation in silicoeli (d) Asbestoels Bodies 1 Composition and methods of formation, il Occurence in different species, ill Formation does not parallel development of flbroei lv Gradual disappearance after exposure ceases. . 4 Comparative Effects of Different Asbestlform minerals. ' (a) Canadian Chrysotlle. (b) Arizona Chrysotlle, low iron. (c) Crooldolite 1 Bolivian specimen, stiff and elastic. . 11 South Afrioan, soft and flexible. (d) Anthophylllte (e; Amoslte. (f) Tremollte. 5 Effects of Control Minerals (a) Grannular Serpeatine, same ohemioal composition as chrysotlle. (b) Glass Wool, a synthetic silicate fibre. (o) Bruoite, a fibrous magnesium hydroxide almost free of -silica 6 Chemical Composition of Asbestlform minerals in Relation tc Irritation. (a) Nothing in composition correlated with relative lrrltat capacity. (b) Preliminary acid treatment i Hydrochloric aoid 11 Carbonlo aoid A(c-tr3> 0B0 06 00004 w. - ^ (3) (c) Effeots of Aluminum 7 Physioal Properties In Relation to Irritation (a) Length of fibre (b) Effeot of Crushing (o) Heat treatment 6 Nature and Significance of Asbeatosla Body (a) Formation (bj Protective effect preventing further Irritation (o) Ultimate solubility In tissue 9 Theories of Action of Asbestlform Minerals !a) Chemical - reasons for considering Invalid b) Meohanloal - experimental demonstration of. 10 Complications (a) Infeotlon, tuberculosis and other varieties (b) Cancer of lung - experimental data suggestive but not proven 11 Disability 12 Essential Features of Hazardous Exposure (a) Nature of dust - fibrous component and size factors . (b) Atmospheric Concentrations - probably lover than for quartz 1 Inadequacy of standard impinger sampling method ' vhlch does not collect the dangerous fibres 11 Eleotrostatlc preclpltatafsampling preferable but method must be modified s * (c)`Duration of Exposure 13 Recommendations for a New Standard of Safe Atmospheric Con oentratlone of Asbestos Dust (a) The Quael-offlcial standard of 4 to 5 million partlole; per cui ft. (b) York upon better method of sampling (c) Necessity for comparison of results with X-ray finding in employees 14 Prevention (a) Chemical means not practical f)R0 flR nnnat; *I 1 Acidosis necessary to dissolve fibre in lungs worse ' than Aabestosle = 11 Aluminum Therapy inapplicable Hi Chief reliance still upon dust prevention with epeoial etaph&aie upon the fibrous components ' ................. .. ............................... .................................... ----------- ---- ... -.......-.................... ncn nc n ^ ^ A3BEST03IS - AN'cOTED OUTLIWE INDICATING RESULTS PART I - HUMAN ASBEST0SI8 1 Human Pathology and X-ray Patterns - Desorlptlon Baaed upon 28 human autopaloe 2 Aeh and Mineral Valuea In Human Lunge. 3 Complication of Asbestosle (a) Susceptibility to Znfeotlon 1 Tuberoulous- High lnoldenoe In English experience cot duplicated In surveys of American Plants. Available autopsy statistics deceiving because of sel ection of material. 11 Non-Tuberouloua- "The same reason probably applies should be checked, by analysis of ab senteeism among asbestos workers. Ill Cancer of Lung Ditto, but there are now on record 10 cases of. lung cancer in asbestos workers. Compared to the total number of autopsies on asbestosls, this inoldence is exoeeslv . No such frequency has been discovered in silicosis r other forms of pneumoconio sis exoept^the 8ohneeberg mine's of radio active ores. The evidenoe is suggestive but not conclusive that asbestosls may precipitate the development of oancer in susceptible individuals. 4 Disability Clinical experience suggests that truly disabling asbestosls is manifested' by less striking X-ray ohanges than a corresponding degree of siliooeis. 8uch disability in asbestosls is due to disease within the lunge and not to secondary heart disease. As In silicosis, associated pulmonary infection increases the amount ey severity of the dust fibrosis with resultant accentuation of disability. There is urgent need for a oareful physiological study of pulmonary function in asbestosls of varying severity. Undoubtedly, there are many dlagnosable oases with no significant disability. 5 Diagnosis depends upon three factors. (a) History of adequate exposure, usually 6 to 6 years, some times longer, at work where both the concentration and character of the "asbestos* dust are hazardous. t C') 060 06 00097 , ... (b) Evidence of disease-tin a characteristic X-ray pattern. '`-HSj-SigS (c) ' A physical exanlnatlon vhlch reveals oertaln characteristic signs and nay reveal evidences of disability If present.:U <d) Asbestosie bodies In" the sputun are oonflrnatory when the " previous faotors are: all positive.' However, the bodies v&- nay be absent / particularly In the absence of bronchitis' lnfeotlon. ; Asbestoeobodies unsupported by other evidence do not make'^ a diagnosis.' 'Occasional ones have been found in about 15 ^ autopsy epecinens of/persons with no known exposure and no fibrosis, probably "of<non-ocoupational origin. l f.v* -Vi".?*--'.. PART II- Experimental Asbestosie -- I . Methods m (a) Inhalation Exposures .to Plant Duett >.Speciflc fibrosis .in-'*U,i lungs, but no ohanges elsewhere.#:' r-.-= *'. r ..VgMEfc (c) Injection of Suspensions of 'lPwe-'iifinerai*lPto*^ther organs* . Fibres dissolved; no asbestosie bodies; tissue reaction"con II Species Unlike free silica; asbestosidoes.not'pro'duoe its iepebiflo effe'c .in any organ of any: speoies.^bf.-anlnair^It pauses fibrosis 'only- tka InnffB' Af nan anA thasa 'afVa au `af .`tha Vaas < as Guinea Pig 2+3+ Rabbit +_______- - jf [ + = vprv Hnall atvnlsfil nsbeatofl"bodies .......... Ill Peculiar Characteristics p0g ^^'^.--.0 :V*.--* ta) non on 3- 1 Fibres like ohryeotlle having a certain degree of flexibility "7 and elasticity accumulate within the finest air tubes; granular S dust Is carried further on and la widely scattered through the ' ' terminal air spaoes. (b) Rate of tissue reaotion to asbestos Is muoh more rapid than to an active dust like quartz. Evidences of formation appear as soon as sufficient concentration of fibres has localized *ln speolflo areas; with quartz, there la a latent period of months. (c) Reaction to asbestos does not progress on oeseatlon of expos ure. Xoung soar tissue that may have formed, contracts and becomes more denes but the area of Involvement decreases in. size. In sllloosls, the-young nodules become larger after exposure oeasee. (d) , Asbestosle Bodies are..a specific conoommltant of this form of pneumoconiosis. They are due to a deposit of protein and Iron upon the eurfaoe of Inhaled fibres. In guinea pigs'they form after about 60 days of oontaot with the tissue. They ere abund ant in man and guinea pigs, (See paragraph 2 above) but much larger In the former probably because the larger sized air tubeE admit larger fibres. In cats,- rabbits and mloe, there Is an atypical ooatlng of a few of the fibres after muoh longer resi dence In the lungs; In rate and dogs no bodies could be dis covered. From paragraph 2 It la apparent that their occurence does not parallel development of fibrosis. In lung Injection experiment*, the bodies have Jtta.6 developed Hftff 1 after fibrosis Ve-^iall-advanced. The number of bodies seems to decrease several years after exposure ceases. 1 Comparative Effeots of Different Asbestosle Minerals (a) Canadian Chrvsotlle " highly Irritating. (b) Arizona chrvaotlle (low In Iron) equally Irritating and pro duces just.-as many asbestosle bodies as the Canadian product with over 11 times' as much Iron. (c) Crocldollte - The South African blue asbestos Is known to cause asbestosle. Only a limited supply of this material In pure forn was available, most of It was used earlier In the work In non-productive experiments. For the later-crltloal Injection tests Into the lunge, a Bolivian variety was substituted be cause of Its high purity. Its fibres were much etraighter, etlffer and more elastic than the cottony South African variety. Perhaps because of these peculiarities, it has not given reactions oomparable to ohrysotile. It produced asbestosle bodies but -did not localize in the terminal air tubes nor cause ' any fibrosis. Tests now being repeated with a typical South African crocldollte with physical characteristics simulating chrysotile. , - L- tc G)  "m. (d). Anthoohylllte - stiff, straight fibres - atyploal aebestosls ' bodies forms slowly but nolocalization or fibrosisIn lunge.''': 4 #. (e) Aaoalte - Ditto. (f) Anohlbole - Ditto. . -'l: - (g) Treoollte - Ditto but very few aebestosls .bodies'p Observation' beingoontlnued. w- . V Control Mineral . ** .* - & ,*.,'} v;v (a) Granular 8ernentlne of same chemloal composition as ohryeotll< la Inert causing no fibrosis in lungs or other organs. <ut attracts Iron from the lungs but' of oourse, no 'bodies* develop (b) Glass Vool(a synthetlo silicate) fibres are not inhalabl'e from, air-borne suspensions^ apparently beoauee of their stiffness/. (the diameter Is not responsible as some used were less .than'fS1 1 micron thick) On Injection into the lungs, they do hot jjlvf localize In the air .tubes but are widely scattered. 'They oause no flbroels. After 3 or 4 months In oontaot with lung fluid, a few glass fibres take up iron but remain smooth. They never. show the swollen ends and lateral projections of the true aebestosls bodies. . -j. (c) Bruclte of Interest beoause it is a fibrous mineral praotically free of silica (o.9). Cryetallographioally the arrangement of Its Mb ar.d OH groups in eaoh unit oell is similar to that in chrysotlle. The sample used also oontalned about 16>. iron, pro bably from contaminating magnetite. The fibres are stiff and needle like. Observalons not yet oompleted but after 2 months In the lungs, typical asbestoels bodies develop but there is as yet no fibrosis. *he fibre are scattered through the lung lnste of being, localized inside the terminal air tubes and tissue reactlon'..qccur8 around, instead of within the tubes. VI Chenlcsl Corn-position In Relation to Irritation (a) Nothing in the following chemical compositions can be cor related with variations In capacity to provoke tissue reaction. (See Table Next Page) s-to - b i* oO 0G0 06 ooion Chrys- Crooldotlle olite ` 37.43* 2.35*_________ 0 54.99* 16.27* 4.29* .. -.V-- >:* 0.51* '-`"'r."',4.06*'" O 1 lach :.o 0.36* 0.055 1.02*' - . 0.25* 0.79* 0.44* .- 1:69* %-0.56* " 0.'46*'-?ft% 2:61*' 12.22* -1: *. 4.45* -^a-'53v 0 "40* 'tm. ^0 iaa. 0 t.o 38.775 .12:25* 0.29 6.92 0.08 0.57 29 ."64* 0.62 0.15 '8.29* " 23C29* #*20.62*^.8s"s9*>^ 0:33 0.40 -V*- 6.78 %-.S13Sf5S': 0.10 - 4>X*' - .1 0.120.99 ' `0.16 *** C*s4105 4.30 0.02 0.62 ' 0.66 V 0.'32''3s&-0.34 0l53^^ ' >105 14.92 2.56 2.42 1.51- ^3.89 *>^ 2.78 '26.66 (b) Acid treataent of ohrysotile 1 One hour In dilute or conce-n4t&ra3t8eWd HtSCL:do:es not alter-ap^ pearance of fibre but after euoh .treaitoent it rapldly^dls eolvee and disappears on injeotinglnto living tleeuea5v-` **.%*/.$& ii Treatment with CO2 bubbled through water or lung juice ~.%i euepenaiona of chryeotile fibres oauees partial solution with liberation of silica aind magnesia/; (c) '`-.-'v't*.-* Colloidal allumina does not neutralize' the "effects of aebeist- as it does quartz. On injecting chryeotile suspended in ... aluninun hydrate solution, fibrosis and asbestos bodies dev elop At the usual rate. It renalns to demonstrate whether t; fibre's'become ooated with a layer of aluninun nonohydrate as has been proved in the case of quartz, *f they have. the co. does not affeot their capaolty to Irritate tissue. VII Physical Properties in Relation to Irritation of Lung Tleeue (a) Length of Fibre >< Short, chryeotile fibres under 3 mlorons are practically inert.' 20 to 50 nicron fibres cause typical fibrosis. The effects of longer ones could not be tested for technical reasons. (b) Crushing completely destroys the fibrous structure of chryeotile. With loss of structure, allKoapaclty to Irritate disappears. - VXb- (abLSrt- ORO OR nnim (ej Heat - At .ignition ..J enperatureCwater^ibiirlYen^pf^uo.stne6KfaK; .. ;'> fibres structure '.la-preseiHred^Flbres become "ext'remely-'brlttlN * JvThe phyaical ohanfjeValtera..typical localizaticri^withiln 'thel^tfe lungs, no flbrosla No aabeatosla VIII Nature and Significance ua phpqw.qj.p -.v (a) Bodies, probably.result .from depoaltlonipf-;lron ',and organic matter on a slowly .'.dissolving <fibre j>f|a&beatoe .\^Ihe souroe of the iron ia more /likely .to^e^the #.ung itiseu'e'^han 'the (b) The tectlve enough purposes of bodies would (c) If they were capable of caualhg>rirrltatlon,^|the vflbroala in .the lungs .should progress after exposureToeases^which'it does not.' ->? (d) The gradual disappearance of ^bodies (and^flbres) /long after -:;V : excosur**(f'p*olnts.to ult.im..ate .s--o;l'ubilitylirtlesu-ve vfluids. ; yr[%V ,, (e) The bodies are probably a fortuitous boneomhitant rather than* a cause of fibrosis. '- . .f~ IX Theories of Irritant Action of Asbestlform Minerals (a) Chemical These experiments do* not oonfirm the theory that asbestosls is merely a form of silicosis resulting from free silica liberated in the solution of a ellioate molecule; If this were true aabestos^llke cuartz^phould cause fibrosis in any organ of any species for the experiments have shown that injected asbestos dissolves in these locations. However, it does not. c.*u3e such reaction in any. location.but the lungs of * $4&e species. (b) Mechanical Irritation We are proposing the theory of mechanical irritation whioh is manifested only in the lungs because this organ is the only one whose normal physiological functions involve a high degree of mobility. Experiments designed to prove .the necessity for moti in this tissue'have failed for technical'reasons. For this theory to be applicable,-it is "necessary that 'the fibres be concentrated in the flije terminal'air. tubes. It has been.shown that only ohryeotlle of .the ashestifora minerals thus far nas the proper physical characteristicsIto Insure such localization. It ia also essential that^the.fibre shall perele long enough before it dissolves in the ^lungs'of speoles like mice, rat8,+dogs. It apparently'dissolves-so rapidly that it exerts no irritation. Similarly.rapid^sblutlpn may explain In part, the lac:k of fibrosis, in orggaannsa^'ootthheerr.than the lungs. .1 L> - lr ' t to) .. ncn ne nn 1 r> The fibres must be long enough so that they cannot be completely ' surrounded by.phagocytic cells which-would prevent contact of these round, broken"ends with the delicate cells supporting the air tubes Observation has demonstrated that these conditions are realized in guinea plge treated with long fibre chryeotile and fibrosis results With the other asbestlform minerals that have been-tested, some or all of the prerequisite were lacking and no fibrosis developed. (c) If the Irritation were chemical, fine serpentine which has the same* chemical composition as chrysotile should have also causec fibrosis. The crushed chrysotlle shoudl have been more active than Intact fibres, because of the greater surface areas ex posed to body fluids. On the assumption that ohrysotlle, like ouartz, becomes coated'with a very thin layer of aluningza on treatment with colloidal aluminum hydroxide, capaolty .to cause fibrosis should be destroyed if the notion were ohemioal but such 15 not the case. ,** . (d) he heavy coating resulting from asbestosis body formation ap parently does stop tissue reaction but here the effects are probably nechanloal for reasons cited. (e) Heat sufficient to alter chenlcal structure d estroye power to irritate but it also alters essential phyeioal characterise that affect" localization of the fibres in the lungs. X' Complications (a) Susceptibility to Infection 1 Tuberculous - Asbestos behaves like most other mineral/], in this respect and not like ouartz which specifically Increase native susceptibility to the tubercle bacillus. This in fection may spread for a tine but then heals. The resultant fibrosis accentuates that caused by the mineral fibre. 11 Non-Tuberculous - of no greater frequency than in animals inhhllng dusts of other kinds. Occasional epidemics of pneumonia occur in our dust rooms, but these are due to methods of housing rather than to dust; they also occur in unexposed animals. ill" Cancer of Lungs Ho experiments were^designed to eluoidate this point but oertain evidence suggests that asbestosis nay actually favor development of tumors in susceptible species. 1 In guinea plgB, rabbits,-rats, cats and doge lung tumors are rare. 2 When these species were subjeoted to 2 to 3 years in halation of asbestos dust, the Incidence of lung tumor was not increased. C\Of\ nn nAi 3 Some strains of white mice do develop tumors without . . apparent oauee. f '' i 4 Such a strain of white mioe was unintentionally used in three inhalation experiments with asbestos. 5 Of 11 mice inhaling long fibre asbestos for 15 to 24 monthi 8 developed malignant tumors in their lungs and 6 of them had tumors in other organs. The Incidence rate 81.8% is excessive. 6 Of 22 mice Inhaling short fibre asbestos for not longer thi 12 months only 3 developed lung tumors. Rate 13.6% 7 As controls, we have only the experience with mioe in othei duet experiments. -- For short periods. there were 51 mice exposed to 4 othpr kinds of dust for 10 to 12 months. Zneidenoe of lung tumoi 1.9*. For long periods. there were 143 mice exposed to 4 differed kinds of dust, including pure quartz, 23 to 31 months. For all this group of mice the average incidence of lung tumor was 13.8%: the highest rate (25%; was in a subgroup exposed to flint dust'. Thus the Incidence of lung cancer In the long fibre asbestos mioe was over 16 times the average for mioe inhaling other dusts for comparable periods and over 3 times the maximum for any bther`group Rice exposed to the praotioally inert short fibre asbestos showed fewer lung tumors although 7 times more than those in short exposurt to other dusts. ^'hese observations are suggestive but not conclusive evidence of a cancer stimulating aotlon by asbestos dust. Tfcey are open to several criticisms. The strain of mice was not the same in the asbestos experiment as in many of the others olted; apparently the former were unusually susceptible. Rot enough animals survived in the dust for longer thgn the 15 months apparently necessary to produce many -tumors. Ahere were no unexposed controls of the same strain and age and no dlmilar controls exposed to other duets. It is hoped that this experiment can be repeated under properly controlled conditions to determine whether asbestos ectually favors csncer.pf the lung. XI Disability Cannot be determined in animals, ^'he accidental deaths were from the same causes met with in all our dust Inhalation experi ments. A.Xfc .-(a fc'OD npn nc-nnin/ XII .. . ___ fibres in the dust. Granular material and crushed fibre are -- inert diluents. ii *he long fibres must be thin enough (1-3 Microns) and short enough (under SO.Microns?) to be inhaled. ill Very-short fibre's (under 3 Microns) are practically inert. (b) Atnosoherlc CT oncentration Still unde`r`svtudy. ' Apparently this factor is lower .than ln'the oaee of duets ooDposed of granular minerals but methods of estimation are misleading. 0.Vi:.' ^{&Z7rC'&\.- 1 The average standard Public gealthServloe lnpinger count in the long fibre asbestos.']duat room 'was *40 million particles per cu. ft. of air, vvrhie'.concentration'caused fibrosis visible to the naked eye in]20 to'24 ihlntha. For comparison the average implnger.counte!!in-an.experiment with pure quartz was 120 million particles perand fibrosis developed at about the 'sane'rate. :- ... v. .. ii However, impinger oounts are deceptive because by this r. - V method of sampling very few.'fibres.-which are the significant elements in the duet are .'collected; ` * ' ' ill Sampling with an electrostatio preolpit'ator is a much more efficient means of collecting .. .fibres .jfrorn air-borne sus pensions. Samples from our .'long fibre asbestos room showed that the duet in the air contained 32.5/C of fibres few of which had been colleoted or counted in the lnpinger sample. The latter sampled .largely'the inert granular parti- oles. . ' lv As ordinarily employed precipitator eaoples are weighed and the results expressed in mg. per cubic foot of air. There is no means of converting such values into numbers of particles particularly when these vary in size, shape and '`specific gravity. " ?'''. * ''&'.*? v Simultaneous sampling with precipitator and standard Im pinger yielded the respective values of 0.65 mg and 60 mil lion r: partiolee per . cublo ' foj o.t.. of air; vl theoretically the best index of hazard would be either the number or weight of fibrous elements in the dust. "3. Ip -- (p (o (.^ non nc nmn -10- (c) Duration of Exposure ::W - 1 Fibrosis visible to the naked eye after IS months exposure Increases In extent In subsequent lS^nonths. .j. 11 The span of life.of our nost susceptible"laboratory animal the guinea pie has prevented continuing exposure longer th three years. -In this period onlyi.the comparatively early stages of asbestosis have ;been"'produoed.With the know- ledge that we have gained,-it-is probable that opre extene disease could have been produced with a purer long fibre chryeotile. The-long llved ^pecles, -like:cats, dogs are u fortunately 111 ' For these reasonsu X -ray changewsW have.been,r minimal a^nd wew ' -.i'' were not able to3 fulfill one of the^objectives of this pro; . gram. s-'-'S.* ^"XIII . Recommendation for `a New ; of .Asbestos ioist. . " Concentratli While there la no official standard,'Ithe-tentative one of .v : "* 'V J * ** v *1 ' 4 or million particles per cubic foot !3of 'air. 16 frequently . quoted. -j ..>* A--i: ' ...... *&&&"< (b) This is probably unreliable because It jis -based.upon sampling. with a standard lmplnger vhlch.we heveij.Bhowoy.doe8 not collect nosf of the fibres that are `the' eource'iof.hazard. (c) We now think that a standard :should be'based upon samples collected with an electrostatlo precipitator if -it Is feasible to determine readily the relative proportion ioff-ffilbbries lr. such material. () Work is still in progress upon-the latter 'jblht'.'' t . '.'vi*.'. --. - (e) To be of-value the* new standard would3iaye^to?be.Correlated Vlth;'the'"X-rnr findings urion^innlnvMnfMtKo'eA 'tn A1 fferent. concentr, XIV Prevention of The experiments ^asbestos ' fibres rapidly like creating an acidosis awrhaicthwwoouuldldn;eboe.'e^soerf1l1ry_('ijj_ttieW_t_hH_a_g_rnir'v:otthbh.ae:i'b-`elyfrf)e'ec^. ts - of,: the fibrosis. (c - Co (o 0) <-- i......... <,. .. -'i ,1 m. V! /''.v ' non OR nnii ' ` * . - V*V-&J' ."Vi ' !* ' 4 X Uj _ (c (c (' 0 s* " '>`V.1M.-iS3V-5^i-J-.iLV:::',. _ &&V .V-, ;f " ' -iV'*;s . > -i*f-'-V. ;*..s" .*V`;5!l*?.' . x^r; non no 060 06 00108