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INDUSTRIAL HYGIENE FOUNDATION OF AMERICA, INC. 4400 Fifth Avenue Pittsburgh 13, Pa, REPORT- OF PRELBEENARY LUST INVESTIGATION FOR ASBESTOS TEXTILE II'JS'TITUTS JUNE, 1947 By \T,C,L. Heneon ' Head Engineer Juno 18, 1947 Industrial Hygiene Foundation of America, Inc. By John F. McMahon Managing Director REPORT of PKEILMIMARY DUST SURVEY ' for ASBESTOS TEXTILE INSTITUTE June, 1947 * OBJECT 0? INVESTIGATION ' This project was a preliminary investigation of the ashestosis problem in textile plants of members of the Asbestos Textile Institute, with the Immediate object of defining the specific nature and the magni tude of the problem in all its phases. From such a definition, the char . actor of a long-term project could be outlined. An original objective of most immediate importance wa3 to facilitate the exchange of information between member companies on successful methods of dust control and other wise to promote a general improvement in that field. . SUMMARY ' . The facts upon which this report is based were obtained on visits, during the past three months, to all plants of Institute members (except one, who wished the visit postponed to a later date). Complete cooperation, was extended at all plants. Dr, C. Richard `Walroer, Medical Director of 9 Industrial Hygiene Foundation, participated in visits to three plants and In development of the medical concepts of this report. The problem is seen to be composed of three aspects which arc discussed in three sections of the report and summarized herewith, as ENGINEERING, MEDICAL, and PHYSICAL TESTING. 'Preliminary Dust Survey for Asbestos Textile Institute June, 1947 Engineering, -- Mechanical methods were seen in use in ono or more plants-vhich effected practical dust control in all operations, bringing dust concentrations down to five million or lower with one or two exceptions. It is proposed to prepare formal detailed descriptions of these methods for gener al distribution to members of Asbestos .Textile Institute. Medical Sn-pervlsion of Workers. -- Only five plants have had any medical x-ray surveys of employees. In the others, therefore, there is a serious lack of information as to the incidence of asbestosis. The lack is more serious, in a sense, because in moat of these plants no compensable cases of asbestosis have occurred to draw attention of top management to the problem. While the medical survey conducted by one plant recently shows only about three per cent of the employees with asbestosis, two other plants appear to have about 20 per cent of their employees affected. ' Medical supervision of workers in this industry is of utmost im _% portance for the protection of both employee and employer, not to mention other considerations. Therefore, it is strongly recommended that each plant insti tute a program of medical and x-ray examinations of all exposed workers as early as practical. Physical Testing (Dust Counts, etc.) -- The "maximum permissible ' dustiness" for asbestos is commonly taken to be five million particles per cubic foot. This represents good attainment in the dust control program. It is em phasized, however, that dust elimination to this extent does not positively in sure that no asbestosis will develop in some workers after a long working life (greater than 20-25 years). Scientific evidence is obscure on this point. It is recommended, therefore, that studies be initiated aimed to develop another 0c000 Preliminary Dust Survey for Aobcstos Textile Institute, June, 1947 . yardstick, because it is suggested that vhon control below five million is attained, present'du3t count methods may not properly measure the remaining hazard. '' A detailed summary of recommendations for a long-term investigation *\ ` is given at the end of this report. , . 0 c- s) e 1 Preliminary Duat Survey for Asbeatos Textile Institute, ! June, 19^7 . 4 I- ENGINEERING PRESENT STATUS OP DUST CONTROL Practically all plants visited have had one or more dust count sur veys made of their operations and these data vere available for the present study. In addition, a fev samples vere taken by^the Investigator in most plants. ' These records vere studied and a range of concentrations judged to be most representative selected for the summary given in Table I. Where relative ly extreme values appear it in an indication of too fev data to permit a closer estimate. '' Figures in the last column, are selected to indicate the magnitude 'of readily attainable dust concentrations vith dust control measures now in common use; or judged to be most typical of an operation vhere no special dust control measures are employed, e.g., ring spinning. . ' N. Discussion of Concentrations ' The available dust count data for operations in the preparation room are highly variable and reflect .the poorer accuracy in sampling inherent in operations that are Intermittent and miscellaneous in character. These figures are, therefore, considered much less reliable than those for other departments. The figures for carding room dustiness indicate .that vith reasonably 'good enclosure and exhaust of the machines, concentrations veil below three million are obtainable. Pour of the plants visited exceed the five million limit materially, ' All the data for mule spinners exposuro indicate a vide variation in dustiness, ranging from two to eight million, but the volume of data are not Preliminary Dust Survey for Asbestos Textile Institute, June, 19^7. rc-d *0H O-i t- -* Pta *P?H OPOfj 7 f0-j 0 CIPU1 I in ip1 , cpi1- rfp-1l, X0 i-j rrt--1-tl r1 Pt CO ViOnt Ct\ pl1- CU1Pj- 1 1 in Ml H C0U Oin 1 0ip l Crrm--O1ll Crrm--O1il 1 ip. d Wl -C --77* w 1 ip O1J f CO 1 f"1 PJ-. t-- in1 O cru(- ip O1J 1 ccou1 HOCU1 rC0-U1l cu {X| C1--O1[ p-</Ir-v O1J CU rc-uIi -dCU1 in 1 --1 1 H1I--PIi1'I tfO1-i in ip1 , CinO 1 t-- cu1 ofP1\, rC-Ui Pi- 1 pr-tl cu in cu1 cu 0 .4 Cin--1 ctnu * 1 \o r0H 1 tin1 1rir--n--1ll1 ~--33sfA rtA-tl Cr-U1l r-it in r-1l in r-1l in 1 --1 -e 1 s 1 , -42> 1 CKU1\ 1 -C=}U1- VOO1J cu r-1l - pcfu1- d 0 -J00P$3i f<Dt fut d cl 0 to q2 CpO. (w0-p14 d d-r-t erll CfOt tdHo tdo -j-trwPo-*l - *td>-i(>dr0o*l M-r rPi Or-l C0POi >-*-Ctddrr-oltl 5 o*> Preliminary Duet Survey for Asbestos Toxtile Institute, June, 19^7. 6# * groat enough to yield a good average. Concentrations for ring spinning vary from ono to five million although there is no strong indication in tho available data of marked differences between this operation and mule spinning. There is a similar vide variation in data for twisting (two to eight million), but there is some Justification in these data for the opinion widely held that this is one of the dustier operations in the finishing end of the mill It is believed that occasional high values in both ring spinning and twisting reflect in some cases the sampling procedure. If the largo impinger is main tained in one location and there is a strand breakage in that immediate vicinity the resulting whipping dust will be reflected in that single sample and would not, therefore, be representative of the worker's exposure. Dustiness in weaving operations reflects the use of water for dust control in some plants and exhaust systems in others. The lowest concentra tions of ono to two million obtained in Plant A reflect highly efficient wet weaving methods there employed. Concentrations less than four to five million are readily attainable by local exhaust methods as indicated by the results in several plants. *. . The data for spooling and winding operations are included for com pleteness, but reflect miscellaneous operations and conditions. The dust re ported is often due to the effect of other machinery in the same room. These considers.tions therefore affect the reliability of these data, as in the case of operations in the preparation room, . 00304 ' Preliminary Dust Survey for Asbc3to3 Textile Institute, Juno, 19^7. 7 EXISTING DUST CONTROL PRACTICES .. . The following diacussion of duat control practices in the industry is merely an outline. To "be useful to those who are responsible for the engineering in each plant, they will need to he set forth* in the form. of detailed specifications describing details of construction, specifications for sheet metal contractors, for purchase of fans of proper capacity and for design and operation of dust collectors. Preparation . Highly variable practices prevail in different plants and the mis cellaneous character of operations within a single plant makes it impractical to formulate many general statements. However, it may be said that such con-, trol as is realized results from the use of modem equipment that is well en- ' closed and which usually incorporates pneumatic conveyors with ceiling con densers. The large movement of air involved in pneumatic transport serves the useful additional purpose of preventing the escape of dust from the primary equipment. Discharge of stock fron ceiling- condensers into bins, stock boxes, or feed hoppers is a dust usually not under control. The blending operation is another source which i3 often not satisfactorily controlled. With the ex ception of these two common operations, most of the dust control procedures re quired will be more or less specific for each plant. . Carding . '` As has been noted, reduction of dustiness in carding to concentra tions of three million or less is easily attained by good enclosure of the machine and carefully designed exhaust. Moreover, experience of several . rears Preliminary Puat Survey for Aabeatoo Toxtilo Inotituto, June, 19^7. companies proves that it dees not interfere seriously vith manufacturing operations nor vith quality of roving produced. Our investigations indicate the superior advantages of having aide- valls of the enclosure of vood to facilitate small clearance hy rubbing con tact at the edge of the main cylinder, thus avoiding excessive air infiltra tion at that point. Wood covers have the advantage of resistance to crushing vhich ^ras evident in installations vith sheet,metal covers. . Connection of the enclosure to the exhaust system by means of cham bers of ample dimensions, i.e, large cross-sectional area is of major im portance to avoid localized high air velocities close to the vebbing in the main cylinder. This detail vas not always observed. In view of similar degrees of success, judged by dust counts, be- . tween various installations, the best criterion of superior design as to de r tails of exhaust from the machine vas in the relative economy respecting , volume of air exhausted per machine. Our observations indicated rather ex- treme variations as indicated in the following table of exhaust rates per carding set in five representative plants: Plant i/ A A is B E G E \ f \ A' Air Exhausted Per Set 1500 cfm 2200 cfm 38OO cfm 5U00 cfm 2000 cfm ! / 1I It is apparent from this investigation that 2000-2500 cfm per set of bronhor and finisher cards is ample exhaust capacity if the system is . properly designed. 0C306 Preliminary Duet Survoy for Asbestos Toxtilo Institute, Juno, 1947 . All five of the syoteas described in tho table servo thoir purpose satisfactorily from tho viewpoint of operation, hut it does not moan that they would he equally satisfactory to others. Thus the plant with high ex haust capacity (G) haa a unique interplant tunnel connection, so that excess heat from another plant supplies replacement air without added cost, for heat, or winter discomfort. ' Plant H controls dust hy completely housing each pair of cards in a . spacious room, exhausted at a rate of 2000 cfm. Sidewalls are easily remov ed for repairs. Most plants would not prefer this arrangement. As far as the dust count data can show, the card room of Plant 3 with 2200 cfm is equal if not superior to that of Plant E with 38OO cfm, a recently Installed system. The fundamental features of- best card dust control systems observed, are as follows: -' 1, Wood enclosure with hingeing arrangement. 2. Libera?, clearance between worker roils and curve of cover permitting air passage at low velocity, . 3*. Large chamber connection on cover, to duct. 4. Duct branch not over 5", preferably V'. . 5. No blast gate dampors in branch line, . * 6, Exhaust influence over comb, either by extension of main cover or by separate hoods. 7. Exhaust space under machine, not over 4" duct. - -' 8, Enclosure and exhaust of food hopper, not over 4" duct. % ' Two installations include an exhaust branch to prevent the escape of dust originating in tho space between tho ring doffers and the main cylinder. 00307 Preliminary Bust Survoy for Asbestos Textile Institute, June, 19^7 ' Spinning One plant has installed ventilation for their ring spinning frames vhich management believes has reduced dust in this operation. It consists in a series of exhaust openings under the frame, near the floor, running the length of each frame. Time did not permit demonstrating to our own satisfaction whether a measurable improvement had been effected or not. This should be done by a series of dust measurements with exhaust on and off. The volume of air exhaust is insufficient to effect a true local ex haust action, and if it is effective it must, therefore, be an effect of simple dilution. : '' . Twisting ' Interest in control of dust from twisters is widespread in the in- dustry and Plants A and B have installed an exhaust system like the one de scribed-for the spinning frames in Plant A, Here again the operators believe a marked improvement has resulted. Dust count data is needed that will, measure the degree of improvement. Winders Cop winders have beon exhausted in Plants A and B with reports of- beneficial reduction in dustiness. We do not have quantitative data on this point, The exhaust arrangement for Poster winders was developed many years ago and is veil known. The tendency to elimination of this machine makes the problem one of little practical interest now. '. In mo3t plants, dust from other equipment, ouch as spinning and twisting which are commonly In the same room. Is of greater Importance than that from winding operations. Preliminary Tmat Survey for Asbestos Textile Institute, Juno, 1947 11, . Weaving One plant has a superior method of suppressing dust in weaving by vet methods and dust count records indicate a complete suppression of dust, ^ ' , I-' It involves a water spray head mounted above the varp at the rear of the- harness with a mechanical screw arrangement for constant movement of the spray head transversely to the warp. They believe it to be more effective than the system common in several plants wherein the warp is passed over wetted rolls. ' It is apparently not practical to recommend 100 per cent vet weaving throughout the industry. Moreover, wo are satisfied that it ia practical to control dust in this operation by local exhaust, where dry weaving is consider ' cd imperativefor special properties of the cloth. One of the best exhaust arrangements includes an exhaust opening directly under the warp at the rear of the harness frame with a slot exhaust opening carried by the lay beam, the latter connected to the stationary part of the exhaust system, either by flexible hose arrangement or by an all metal swivel joint. Duct Work . . ' ' The actual arrangement of duct work and exhaust fan present no un usual problems where good practice in sheet metal fabrication is followed. Two - points are of sufficient importance to require emphasis. . Special care should be exercised in the fabrication to avoid sharp projections on the Inside that create points of lodgement for fibers. Secondly, it must be designed to pro vide adequate transporting velocities. Velocities below 2000 fpn, in the experience of the industry, may permit settlement of material and gradual clogging. Therefore, allowing a margin of safety, the design should provide for velocities of 300 fpm. 00909 Prcliiainary Dust Survey for Asbcotoo Textile Instituto, Juno, 19^7 ig The problem of distribution of planned air flows to tho different branches of tho system is of importance in the design of all dust exhaust systems. The use of dampers in branches to adjust air flows is avoided in tho best systems. Their function in effecting balance between branches is best attained in the original design. Design procedures to effect this ob- Jective are available but will not be elaborated at this point. . Dust Collectors , ' . Five plants in the survey employ the well-known burlap dust house for filtering air from various exhaust systems. The favored filtering area is determined on the basis of one square foot for each air flew of 2 cfm.V Most arrangements are such as to permit cleaning by whipping with a bamboo pole or a buggy whip by men who remain on the clean air side of the filter . cloth. In one system, the men are required to enter the dust side for clean ing purposes, and final cleaning is carried out once weekly with the use of a central station vacuum cleaner. Practices in different plants are variable as to frequency with which the burlap filter is freed of. its dust load by whipping, While these dust collectors work well, we are not prepared to recom- ' mend them to the exclusion of some commercial types of filters having automatic shaters, Several engineering elements enter into the design of a dust collect-, or system, involving principally a proper estimate of pressure drop in all ele ments of the system and especially that through the filter proper (back pressure.}. If the pressure drop estimate in the filter is incorrect, the system will not ` operate properly. If the basic resistance of the filter, i.e., that immediate ly after shaking tho cloth, is subjoct to a constant increase over a period 0Cyl 0 Preliminary Duat Survey for Asbestos Textile Institute, Juno, 1947 '. 13 of weeks, the system operation will suffer. Apparently, some of the older commercial flat hag type of collectors did exhibit that difficulty. Modifi- . cations in the design of such units have, however, been incorporated in more recent models and those difficulties may have been eliminated. Two plants employ commercial collectors of the flat bag or envelope type. Another plant uses a cloth' tube commercial collector and also one whose ' filtering element is of paper, which is replaced at intervals of several veelcs. A study of operating details of these commercial collectors is indicated in this study, including considerations- of original coot and operating coot, Recirculation .' ! Several plants return air from the dust collectors to the workroom to : conserve heat in the cold weather. We are not prepared at this point either to condone or to condemn this practice except in cases where there is obvious- .1 _ - ly leakage of dust through the filter and consequent re contamination of the air inside the plant. The practice is generally frowned upon where dusts . that are hazardous to health are being handled. We believe there are certain circumstances where the practice Blight be permissible provided adequate safe- guards are incorporated in operating procedures. ' The large volumes of air involved in dust control represent a tremendous problem as to heat loss and ' boiloi- capacity which cannot be passed over lightly. I oc^n , * ' ,, Preliminary Dust Survey for Asbestos Textile Institute, .. Juno, 1947 . II - MEDICAL PRESENT MEDICAL FACILITIES AND PRACTICES Every plant has connections with a local specialist In radiology vho is employed for diagnostic work oh an:irregular basis. Three have their own x-ray machines used by the local specialist,* but only one has a well- established schedule of periodic medical examinations. . Half of the plants have no positive information as to' the Incidence of asbestosis among their workers. The situation is these-respects is in dicated In Table II. TABES II. PRESENT PRACTICES AND FACILITIES AS TO MEDICAL X-RAY EXAMINATIONS IN VARIOUS PLANTS ' * ' Plant A B C D E F G H I J Recent X-ray'1' Survey Made ' Yes No ` Yes Yes ' No No No ` Yes No Yos Periodic X-ray Examinations Made No ' No No ` 'No No . No No Yes ' ' No No ` Have Own X-ray Machin0 Yes f ' i *fV, 4- No. (f r. if ' ' No No ' No . No `No Yes vl-M, No Yes ^Vithin last few yearB, and results available to plant or Its physician 0 fO d xf <<0n Preliminary Dust Survey for Asbestos Textile Institute June, 19^7 15 ESTIMATED INCIDENCE OF ASBESTOSIS The incidence of asbestosis among employees of those plants vhere employees vere examined in recent years, shows a marked variation as indicat ed by the following: . Plant A has recorded cases diagnosod as asbestosis to the extent of about 20 per cent, and in the past nine years ha3 compensated, on the average, two cases per annum. Total textile employment about 400. . ' Plant C on the basis of a recent systematic survey, estimates asbestosis incidence'to be about three to four per cent, - Plant P has results from an incomplete survey in which four cases were found among those volunteering for examination with a total textile em ployment of around 150, They have compensated one case in about 10 years. Three more are pending, Plant 5 with a textile employment of 300 finds five or six cases ^ ' . ' annually that the physician believes show early changes due to asbestos. Plant J has counted potential cases of asbestosis amounting in . number to about 20 por cent, comparable with Plant A, ' The other plants have conducted no systematic x-ray surveys of their own and have no information as to incidence among their employees. None of these has had cases requiring condensation. Whilo wo havo no complete data on history of employment and labor turnover in the soveral plants, it is apparent that there is, at least super ficially, a marlcod inconsistency in this picturo. Also, it is clear that -Preliminary Dust Survey for Asbestos Toxtile Institute, Juno, 1947 16 a eorious lack of informtion prevails generally an this aspect of tho problem, Iho story in North Carolina is vorth special mention. This state instituted 10 yearn ago, a system of periodic medical examinations for an vorkers in dusty industries and, hence, all asbestos textile workers have been x-rayed and clinically examined for a longer period, on a periodic basis, than any other asbestos textile plant in this group. If the state examination finds that workers should discontinue their employment because of rapidly developing asbeetosio they have tho authority to effect this change. They also see to it that vorkors vho should receive -workman's compensation due to dis- ' a'bling asbeetosio are processed. So far as ve have been able to ascertain neither event ba3 occurred to any employee of the two North Carolina asbestos plants in this group. These observations suggest that there may veil be a marked divergence in medical procedures, interpretations, and attitudes respecting the diagnosis of asbestocis. , ' There is a very urgent noed for a concerted cooperative medical effort to develop improved diagnostic procedures and uniformity of interpre tation, . 0G9 j4 Preliminary Dust Survey for Asbestos Textile Institute, June,`19^7 17 IMPORTANCE OF ISPIODIC MEDICAL EXAMINATIONS One of the most important elements of a program of protecting health of -workers in dusty occupations is the periodic medical examination. The lack of scientific information regarding all aspects of ashestosi3 is serious. This cannot he over-emphasized. The obvious procedure to help overcome this deficiency is to employ every tool now available that will throw more light on the facts. The importance of the periodic medical x-ray examination can per haps best bo emphasized by stating that dust count investigations cannot, in the present state of knowledge, give U3 assurance as to the extent of our suc cess in eliminating the hazard. Regular examinations serve to protect the worker by giving early in dication of health impairment due to dust, and permit intelligent action to be taken to avoid further serious health deterioration. This is particularly true if the detection is early enough and there is no progression to late stage asbestosi3. '' More important, for the long tern, the accumulation of factual in formation regarding the health status of exposed workers, statistically inter preted in relation to dustiness studies and to mechanical developments in dust control equipment, will eventually indicate when the battle of asbestosis con- ' trol is being won. This aspect of the problem is elaborated in the following . section. ` `. The inventory providod by such a medical program is Just as important to intelligent action in this problem, a3 material inventories are to the propor conduct of business. Preliminary Bust Survey for Asbestos Textile Institute), June, 1947 . 18 The question as to whether a plant should purchase its own x-ray equipment is an economic ono involving consideration of cost of local outside medical and x-ray facilities and of loss of employee time in travel, etc. Diagnostic Panel '- - To furthor the objective, of improvement and uniformity in diagnostic procedures, a medical section of the program is proposed in the form of a MEDICAL ASBESTOSIS PAEEL to be composed of outstanding medical men in this field, and of the physician designated by each company as the one responsible for its medical and diagnostic work. The composition, as' to outside medical personnel, of this panel would be determined by its objectives: the assembling of the best possible medical brains and the mutual education in diagnostic procedures that comes from exchanges of scientific experiences and information. .' The panel would meet, perhaps semi-annually, and consider the sig nificance of x-ray films and other clinical data brought to the group by each participating physician. Dr. C. Diehard Walmer's services would be available for the organization and other details. ' Preliminary Dust Survey for Asbestos Textile Institute June, 19^7 19 STATISTICAL STODIES OF MEDICAL RECORDS There are two very important questions concerning the physiological nature of asbestos that have not yet been answered by any published investi gation: . . ' 1, . What is the expectation of asbestosis in workers exposed more than 15-20 years to low concentrations of asbestos dust? Among the 500-odd workers who composed the subjects in the U,S. Public Health Service study, there were abnormally few who, had been exposed for more than 15 years and practically none over 20 years. These facts seriously affected the conclu sions that could be drawn, . .' 2. Is there a progression to advanced asbestosis after exposure or an Individual has been discontinued or has been reduced to very lew levels, due to action of dust deposits from earlier exposure? This question is of very great importance to intelligent medical supervision of workers in these plants . It is virtually certain that statistical investigations of existing records would throw valuable light on these questions. . ' None of the plants visited during this inquiry have sufficiently extensive and systematic records to provide satisfactory.answers to these ` questions, but the medical department of Metropolitan Life Insurance Company, under* Hr. A. J. Xanza, have x-rays of a number of men obtained^ in the early 1930's which could provide the nucleus of some useful information, depending on hair many of the original group are available for re-x-ray, _ OCJj.7 Preliminary Du3t Survey for Asbestos Textile Institute, Jjme, 19^7 20 The most outstanding store of information is in the records of the Division of Industrial Hygiene of the North Carolina Department of Health who, in accordance vith state law have x-rayed workers in this, and other dusty Industries, almost annually for the past 10 years. A study of these records would undoubtedly cast much light on the question of progression. Through officials of the company members in North Carolina, we already have assurances of their full cooperation in any investigations, and although we have not discussed the matter vith then directly as to details, there is every reason to suppose that the desired information would be made available to us for the purposes described. - In addition, a general x-ray and medical survey of workers in one or two plants with a long history of high order of dust control would be of great value for this purpose. ' . Preliminary Dust Survoy for Asbestos Toxtile Institute June, 19^7 , III - PHYSICAL 21 SIGNIFICANCE OF DUST COUNTS Correlation "between development of asbestosis and some pertinent measure of dustiness, e.g., dust counts, can "be developed "by periodically ob serving and recording data on both aspects -- periodic medical examinations of exposed workers together with the periodically measured dust exposure of each. However, to be useful for preventive purposes, theseproceduros have to be extended into the past wherever data is availab.e This was the proced ure employed in the studies of the U.S,Public Health Service in North Carolina plants (Public Health Bulletin Ho, 24l, 1938). ' The main value of dust counts in asbestos plants is to obtain data on duct concentrations that can be compared with that study, and thus lead to conclusions as to probability of development of asbestosis in the particular plant being studied. ' - . In that study, dustiness of different occupations was measured in the usual manner, and also the incidence of asbestosis by medical and x-ray examinations of the men employed* A statistical comparison of the two sets of data led the investigators to the conclusion that new. cases of asbestosis would probably not occur if dust control measures were undertakento ensure that no dust exposures exceeded five million particles per cubic foot (measured in the same manner). Preliminary Dust Survey for Asbestos Textile 'Institute, June, 19^7 APPRAISAL OF DEDUCED DUST HAZARD Having reached' a degree of dust control represented by the dust count limit of five million, it is then proper to ask: 'What degree of assurance is afforded by existing knowledge that asbesto3io will not, in fact, develop in the future if dustiness is kept below that level?'' . If there are factors, at present-unknown, that will indicate a need for still better dust control,what will that limit be? ' The information available does not permit complete assurance that five million is thoroughly safe nor ha3 information been developed permitting a better estimate of safe diistiness. . It is nevertheless of the greatest importance either that such assurances be sought or a new yardstick of accomplishment be found for ac curately measuring any remaining hazard in the dust zone below five million for the elimination of future asbestosis depends upon the degree of control effected now. ' Measurement of Dustiness '. . One basis of uncertainty as to applying present conventional dust counting techniques to the measurement of asbestos dust hazards below the . five million level is summarized in the question -- are the fibers of asbestos the causative agent or the non-fibrous ''cubical" particles that look like -those of other industrial dusts? The non-fibrous particles in most textile operations comprise 80-95 per cent of the total dust seen in dust counting. Vhlle it is proven that asbestos dU3t is the cause of asbestosis, there is no cortain information as to what shape or size of dust is tho cauoativo factor. The correlation studies of tho U.S,Public Health Service 0 0939 Preliminary Duot Survey for Aobcstoa Toxtllo Institute, Juno, 19^7 ` 23. employed conventional dust count techniques yhich, in effect, related Incidence, of aabestosio to the number of non-fibrous particles of a size ranging from one to five or 10 microns. For illustration, suppose the causative dust element is something different, e.g., fibers that are less than 50-60 microns long, and less than 1-2 microns in diameter. The conventional du3t count method would be satis factory only If there were a fairly constant ratio between the two types of dust; It would, in that case, provide an adequate, index. Preliminary Studios on Qualities of Asbestos Dust With a view .to eventual development of supplementary methods for measuring asbestos dust concentrations on a weight basis, ve have conducted some preliminary studies directed to the colorimetric determination of total - silica in the minute quantities of asbestos dust obtained in a typical atmos pheric sample. This requires development since it could provide a valuable tool for further investigation,. Sub-microscopic particles and fibers. ' , . ' Another aspect of the dust examination problem on which preliminary vorlc has been done involved studies with the electron microscope. We posed the two following questions: . '. ' 1, Ordinary dust particles, one to three microns in diameter, com prise moot of the particles in the dust count. They look like ordinary in dustrial dust and we refer to them as "cubical" as distinguished from "fibrous" particles. The question is: are these particles in fact non-fibrous or are they bundles of fibers? ' Preliminary Dust Survey for Aobootoo Textile Inotltute,' June, 1947? 24 2. Secondly,-- since tho limit of resolution of the microscope lenses used in dust counting does not permit seeing particlos very much smaller than one micron, one may ask if there are many filers of great length, hut of such small vidth that they are invisible? Samples of atmospheric dust vere obtained for examination by the electron microscope, by mounting the snail specimen slide used vith this instrument, in the dust collecting zone of the electric precipitator. In order to eliminate very large fibers, the air being sampled vas caused to pass first .through a glass spiral coated vith adhesive on its interior. This subjected the dust particles to centrifugal force and the largest ones vould be pre- ' * cipitated out, much as they might be in the nasal passages of man. Studies vith other industrial dusts employing this spiral indicate ", that very rarely do cubical particles larger than three to five microns suc ceed in passing through the several turns of the spiral. *. In samples obtainedvith this apparatus in a card room having a ' good dust control, ve obtained pictures, some of vhich are reproduced in the attached Figure. They demonstrate first, that the cubical particles seen by a low pever light-microscope are in fact bundles of fiber resembling e. life- size handful of partially opened fibers. ' The picture further demonstrated that there are many fibers of con siderable length, some fully 50 microns, vhose other dimension is-only a fraction of a micron; the fiber is therefore invisible in the dU3t counting microscope. . 0C922 o I sE-4 M rr 323 THIS CIRCLE 1 MICRON DIAMETER Preliminary Dust Survey for Aobestos Textilo Institute^ 'Juno, 19^7 ; 25 They also shoved sons filers a few microns in length whose diameter is only 0.01-0.02 microns, although the commonest particles are bundles of fibers about 0.1 micron in width. *. In addition to the light these oboervarion3 throw on the sub microscope character* of acbestos dust, they are cited to indicate the other qualities that might be pertinent to evaluation of dust exposure, to supple ment the dust count technique now in use. _ 00924 Preliminary Dust Survey for Asbestos Textile Institute Juno, 19^7 . 26, DfHEKSNT KJSTUSSS OF STOCK _ In investigations of the typo being presently considered, a primary aim nust bo to develop improvements in dust control with the minimum of waste notion and expensive experimentation on a plant scale. At the stage of development of the industry, causes of dust are very often not obvious. An examination of dust count records made available to us, combined with the few tests we performed ourselves, provide numerous instances of variation, the cause of which is not apparent. We undertook recently to measure the amount of dust in the roving of different manufacturers by suspending a measured quantity of roving in alcohol, then making a dust count in the same manner as with air samples. The result would be expressed in millions of particles per yard cf roving or per gram, etc... and would be of great advantage in relating differences in dustiness to the causative factor. Such a measurement technique would be essential in apprais1` ing the actual value of oil. . We do not have sufficient data on this effort on which to draw con clusions. There aro difficulties to be overcome, and the solution depends on more laboratory experimentation. . Another test method which would be of value is a standardized mech anical abuse of roving in a small vessel while sucking a stream of air with resulting dust as in the sampling for ordinary dust counts. A test of this kind, in conjunction with the dustiness index would be of value in evaluating the oiling practice, or it might take the place entiroly of the procedure previously outlined.