Document Z88xoJL9oR2Rjd1g4LkqYXZrp

FILE NAME: Raybestos-Manhattan (RBM) DATE: 1937 May DOC#: RBM118 DOCUMENT DESCRIPTION: US Public Health Report - A Study of Dust Control Methods in an Asbestos Fabricating Plant with Cover Letter from RBM General Asbestos &cRubber Division oi Rayoestos-Manhaitan, Ine. North Charleston. S. C- UM U `'ay 26, 1037 * Dr. ?.. ?. Mayors, ionior Curyeon, chief, division of Indus crin 1 Vygiene, I.atioRAi i n s t i t u t e or Health, TJ. 3. i'ublia Health Jorvica, anhingeon, i>* 0. ' Oeor Joctor- I bava received your8 of the 20th enclosing a copy of the paper allowing the results of the study oonductea at our plant during the cor.th of 'urea of this yenr. l delayed aokr.owleuging chi3 paper lr-T.edlately as I wished to rasa aerro very carefully, and after having read this report I fool that ..esars. I'aga and dluomfield have tcaua a very careful study of the conditiono existing at this plant*. -HUo, I wish to thank you for the opinion expressed as per the lust aentar.ee of the flrct paragraph of your letter of the 20th. In regard to the statement ao cade in the socond paragraph of your letter as to your desiring to publish thin report in the official organ of the Tublic Health .service (Public Health i.e?ort3), I "would like to advise that when Jr. .*ilso;i of the douth Carolina ctstc health 'department first approached ce in regard to this matter, I advi3od Jr. '..iisun chat I would have to first taka the matter up wish our fresident :T. Sumner Simpson, before I could grant hie request 0 3 to coking a study of this plant, .iftor taking the tractor up with .'hr, Cicpson, it was agreed vri th Jr, "Jilson that no publicity woula bo given as to the results of tie inspection by the 'i/f. Health spare..tent in cooperation with the Couth Carolina Ctato Department of health until after your report ha a boon submitted to ua cud v;u could pass on sumo. I u-r., chore roro, in acso run nos with that unde rs con ding, forwarding today to :r. Simpson the report which you submitted, along with your letter, and requesting -r. .ir.pgon to give consideration to your request as to the publishing of the report. Juat us soon as 1 hear frofi his:, I will ad vise you. I might also state that I heve made a copy of this roport and have turned i t o v e r to " r . J u l i a n h i t oho 11 f o r h i s consider-- t ion. .hoax ln<' you f o r L avin g s o n t m-j t L i a r u p o r t aaci a l s o f o r your l e t t e r of the 20th , s n a Wien k i n d e s t p e r s o n a l r e g a r d s to you unu a l s o to ...ggcru, l t i 6 * ana d l.'Oftfl e i d , I r e c o i n , Yours very truly, fire;!:;:. / a I.._?V-* y uJ-j,_.-\L jvUJ-- .-'o-i ..ULiJa.i JXYlilwii of^yi/;yboato3-"--nL2ttan, Inc. # a. JOiforas, Can. a s ru o Y o r cu cr j j u j h j l :.^ri{opj i n a h a s 3i:j Tub f a b r i c a t i n g ^ - I a By Richard T. Paga, Assistant Public Health Engineer, and J. J. Bloomfield, P. A. Sanitary Engineer, United 3tates Public Health Service. An extensive medical and engineering study of the health of asbestos workers has been conducted by the United States Public Health Service^/ The material contained in this paper supplements the general study with a detailed study of the dust control methods used in an a s bestos fabricating plant. The following report on present conditions and how they have been obtained is presented as an example of the results of the application of scientific methods of dust control. These data should be interestJ ing not only to the asbestos industry but also to other industries having similar dusty processes. The plant studied has only partly completed an extensive dust control program and conditions are being improved continually and, consequently, these results should not be interpreted as representing the maximum possible efficiency in the con trol of asbestos dust, but it is believed that they are representative ot the best practice in this oountry at this time. The dust control systems in use with the various processes in each department are de scribed. An occupational analysis of employees is presented with a ooracarison of the atmospheric dust concentrations associated with con- * - -* trolled and similar uncontrolled processes. FABRICAfloil OF A33iiSi\>3 fAXTILilB Agbestos is tha class nanas for govaral different fibrous rcinor'-ls but the asbestos of oommorceJk/is mainly tha fibrous form of serpentine known na chrysotile*. Due to ita fibrous nature, flexibility, and lient resistant properties, asbestos fiber finds many practical applications. One of ita important industrial uses la in tliQ manufacture of fire resis tant textiles. In the plant studied, practically all raw material was crude Canadian or South African Asbestos. Some imported short fiber was used, os well as some of the short fiber salvaged in the recovery process, but most of the short recovered fiber was shipped to other plants. Signifi cant variations in atmospheric dust concentrations due to the grade of fiber being processed were not evident in controlled processes in this plant. Consequently, the type of fiber used has not been considered in the analysis of the data. Each dust controlled process tended to decree.: the amount of dust generated in subsequent processes, These factors mus> be considered when comparing dust concentrations reported in this plant with the data which have been reported for other plants. . . Approximately three hundred persons were employed in this plant, of whom one hundred and eighty worked in departments having a potential asbestos dust hazard, This study was confined to these departments, namely: preparation; carding; spinning; twisting and winding; and weavln, The occupational distribution of exposed workers is shown in Table I. (Take in Table I) * Clirysotile is a hydrous magnesium silicate ( ^ L ^ S i g Q g or 2H 2O.3 i.t3 0 .28iC^ containing 44.1$ silica, 43.0$ magnesia and 12.9$ water Other typos of asbestos often contain silicates of iron, calcium and aluminum as well a9 magnesium. -3 MiSTHOD OF STUDY This investigation included a study of atmospheric dust concen trations in the factory workrooms, and a study of the exhaust systems used to remove asbestos dU3t, Eighty-two atmospheric dust samples were collected at the workers* breathing level with the impinger dust sampling apparatus^/. Sixty-nine of these represented present working conditions and thirteen represented conditions while exhaust apparatus had been turned off for one hour. A collecting medium containing twenty-five percent ethyl alcohol in distilled water was found to prevent flooculation without causing excessiv evaporation in either the sampling flasks or the counting cells. All samples were counted the day after collection. Due to the low dust con centrations encountered, mo3t of the samples represented the dust in from twenty to thirty cubic feet of air. Samples were diluted with dis tilled water and counted according to the light field technic described by Bloomfield and DallaValle^/. A micrometer eyepiece having an engraveu square equivalent to one-fourth the standard Whipple square was used in counting. Since it is customary to count only one quadrant of the Whipple field, the same volume of sample (0.25 cu.mm.) per field was oounted. The quantities of air removed through the various exhaust systems were calculated from Pitot tube measurements of center line velocities in the pipe lines4/. Average exhaust rates per process are listed in Table II and discussed below in the description of exhaust systems. Entrance velocities at open hoods were measured with an Alnor Velometer and cheakad with a van a n e c o a s t e r . I'oat or the hooda wore of the en closed type designed to exhaust only enough air to prevent the escape of -4 - asbestos dust into the workroom. V/hero individual measurements were impractical, air volumes exhausted through each hood were calculated from ir.essure front a of main line velocities. Whenever differences in ex haust volumes were noted between similar hoods on the same operation, the average value is given. * DSSCRIPl'IOIi OF PROCESSES Ai.'D DU3f CdilTF.OI I.2A3UR2S Asbestos is received in burlap bags containing one hundred pounds of fiber. Cotton is received in standard bales. These are the only raw materials used in the preparation of asbestos yarn at this plant. -Un loading, storage and transportation of the packed raw materials were not hazardous occupations. The progress of the material from raw fiber to completed fabric is shown by means of a flow sheet (figure I) Individual 'i processes and the measures for dust control are described belov/. . (Take in Figure I) Preparation Department. Crushing, Some of the asbestos fiber arrives at the plant as "precrushed" fiber but most of the crude fiber has raceived no treatment other than mining, sorting and screening. This latter type is hand dumped from the bags into rim-wheel crushers and crushed from five to fifteen minutes. These crushers have two heavy rollers attached to a radial axle, and revolve on a smooth surfaced tray in which the asbestos is placed. The asbestos fiber is constantly stirred during crushing by revolving scrapers. After crushing, the fiber is replaced in thtf bags and carriea to the asbestos opener. Crushers were not enclosed or exhausted in any way but the general ventilation in the preparation department was sufficier to prevent high concentrations of dust near this operation. Crusher men -5 - had respirators** and usually wore them while loading or unloading the crushers. The average exposure of a crusherman tending three crushers wa3 3 *5 y . p . p . c . r . Asbestos Opening and Screening. The crushed fiber ia dumped from bags to the floor beside the asbestos openers end lifted into the feed latica hopper with v/ooden hand forks. Two openers of different design were in operation but the method of exhaust hooding was th8 earns on both (See Schematic Design - Figure II). The feed latice hopper v/as partially enclosed and exhausted at the top. (Hood A). A second hood exhausted the bottom fly and settled dust from the bottom of the opener (Hood B). The opened fiber was packed up by hood 0 and pneumatically transported to a cyclone separator where the fibers were removed and dropped onto an enclosed vibrating screen. A large portion of the dust and fin9 fibers entering the asbestos opener was removed by hoods A and B. Clumps of unopened fibers and pieces of rock too heavy to be lifted by the pneu matic fiber conveyor, fall onto an enclosed belt conveyor serving both openers, and were carried to the recovery process. (Belt conveyor not shown in Figure II). Exhaust volumes through the hoods were: hood A- 400 ofm, hood B- 400cfm, hood C- (pneumatic conveyor) 1800 ofm, conveyor velocity 2730 ft,/minute. (Take in Figure II) Each opener had its own cyclone separator and enclosed and ex hausted, vibrating screen. One screen had two e'xhaust^hoods, one beside 4*A11 employees in the preparation department and all repair men and Jnintors were provided with respirators of a type approved by tho U. 3. Bureau of Hines against high concentrations of fine silica dust. -6 tha charging hopper drawing 400 cfm and one over the discharge end of the screen and the stock car, drawing 770 cfm. The second screen had one hood only, over the discharge end, drawing 615 ofa. Shbrt fibers end rock particles passing the screens fell through a chute to the en closed recovery conveyor. Fiber failing to pass these screens dropped into a s^tock car. Full stock' cars were pushed to a platform acale and then to the miring beds. The same men charged the openers and filled the stock cars. The average dust exposure of asbestos-opener operators was 3.6 LI.P.P.C .F* Cotton Openers, The best grades of insulation contain very small amounts of cotton if any, but in all other cases, cotton fiber is mixed with asbestos fiber to improve its spinning qualities. At this plant the batch seldom contained more than 15; cottoniby weight but as high as 20> cotton were used in lower grade yarns. The two stage, Saco-Xowell, cotton opener was exhausted at three points.' 770cfa of air were exhausted through a canopy hood over the feed latice, 270 cfm from the bottom of the primary opener and 1120 cfm from the botton of the secondary opener. Opened cotton fiber was discharged into stock cars. Bo samples were taken at the cotton openers but the operators average exposure was about 2.4 U.P.P.C.F. (General air - preparation department). Uixing. Weighed quantities of asbestos and cotton were placed in alternate layers in the mixing beds. Occasionally, layers of roving waste from the carding room were reopened and added to the bed. fixing was done in six exhausted booths, eaoh 1 0 t- 2 rt deep by 6 f-10Tt wide by 6 1 high. Sides of the booths were permanent while the baok consisted -7 - of a removable wood and canvas section. Zach booth was covered by a pyranid hood 32" high through which approximately 1025 cu. ft. air per minute per hood wero exhausted. The velocity of air mo tier!) into these booths averaged 50 ft. per minute during bed making and about 30 ft. per minute during picker loading. Dust concentrations averaged 5.4 i:..P,r.C .F, for thej bed making operation. After a bed wag placed, the picker operator removed the rear partition of the booth end forked the hatch into the charging hopper of a picker (Figure III). The picker machine mixes the fibers in revolving beaters. The four machines represented three different operations and tvfo different types of exhaust systems. The first machine, not in operation during this study discharged mixed fiber into a'Stock car. Thi3 material was then passed through a second picker for-remixing. 'The second and third machines discharged mixed fiber onto a belt conveyor which transported it to bins in the carding room. The product rof the fourth picker was carried to the carding room by a pneumatic conveyor* Saoh of the first three machines had a hood over the charging lattice exhausting approximately 500 cfm, a pipe exhausting about 1650 cfm from the bottom-fly settling chambers under the main picker drum, and a hood over the end of the disoharge lattice exhausting about 400 cfm. The fourth picker had the same hood arrangement over the charging lattice but had no bottom-fly exhaust and the mixed fiber was removed by a pneumatic conveyor exhausting approximately 2000 cfm of air* at a velocity of 2550 ft. per minute. The picker operators wear respirators during the charging operation. Oust concentrations during piokor charging varied from 4,0 to 9.5 M.P.P.C.F. averaging about 6.7 M.P.P.C.F. (Take in Figure III) -3 - Recovery Processes. Yiaste roving from the card room wag re turned to the preparation department for reopening. The roving reoponer was exhausted only from the pit below the last beater, but 'the 1730 cfm of air drawn through this hood were sufficient to prevent the escape of dust through the discharge lattice. iThe dusty air collected by the exhaust systems in the preparation and carding department was blown into a large settling chamber occupying two stories in the end of a separate building. Air was displaced from thi3 room to a bag house occupying the second floor on the other end of this building. Dust was filtered out by burlap filters stretched on "A" frames. The filters were beaten down by hand daily during the noon rest period. The' collected dust was removed during the weekend shutdown, and stored in bins in the preparation department. Bag house dust was screened on a completely enclosed and exhausted vibrating screen (Background Figure 17) and the long fibers were removed to a cyclone collector by a pneumatic conveyor. The dust from the settling chamber, the long fibers from the bag house dU3t, and fibers separated by cyclones on the exhaust lines from the spooling operation and the weaving department were passed through a fly-wi'llower and vibrating screen (Figure 17). Approximately 250 cfm of air were exhausted from the top of the charging lattice and 620 cfm from the discharge side of the opening drum. Dirt passing the screen dropped onto an inclined tray and was removed by an exhaust hood drawing 730 cfm. Fibers which did not fall through tlib screen were removed by the hood at the lower end of she screen (1710 cfm) and pneumatically conveyed to a oyolone collector. Rock and other impurities not picked up by the pneumatic conveyor fell into a waste box below the end of the screen. The market for recovered fiber 3 limited and suoh fiber is usually too soiled for use in high grade textiles. Consequently only part of the collected dust was passed through this process. Average exposure of operators wa3 estimated at between 3 an& 5 M.P.P.C.F. (Take in Figure IV) As a measure of the effectiveness of the dust control system in the preparation department, the exhaust fans were shutt off for one hour. Pneumatic conveyors remained in operation. Dust concentrations increased steadily to about 50 M.P.P.C.F. at which time the exhaust fans were turned on. The samples taken during this period were only a partial measure of uncontrolled conditions since the hoods and enclosures had a definite control value. While the location and design of hoods were the most important factors in dust control in the preparation department, general ventila tion helped prevent high dust concentrations. This department* occupied approximately 320,000 cu. ft. of space, from which approximately 34,650 cfm of air were exhausted. Consequently 6.5 air changes per hour were produced by mechanical ventilation which was supplemented by natural ven tilation through door3, windows, and roof ventilators. Fortunately heating was not a problem in thi3 plant. Carding Department. Mixed fiber from the preparation department was dropped from pneumatic or mechanical conveyors into bins in the carding department. A total volume of 6850 cfm was exhausted from four bins, the major portion of this air being drawn through the one or two bin doors left open during the loading of carding room stock cars. Dust concentrations as high as 40.4 ^.P.P.C.F. were measured inside an aotive bin while the dust ooncentration Just outside the door of the same bin was only 4.6 M.P.P.C.F. Workers, classed as stock rollers, 10- fork the mixed fiber from the bin into stock cars, 'fills operation is supposed to be performed with, both stock car and stock roller outside the bin door. This rule of keeping out of the bins should be strictly enforced. Howdver,stock rollers, wearing respirators, like to pu3h their cars under the chute and then climb into the car and "tread-down" the stobk. The cards are machines having a series df revolving cylinders wound diagonally with strips of leather set with fine, eharp, steel bristles. Carding removes remaining small bits of rook and combs -the fibers into a more or less papalled condition to facilitate spinning. At the time of this study, thirty-one roving oard units and two wicking cards were being operated, A roving card unit (Figure V) `consisted of s two cards, a breaker or primary card and a finisher or roving card. (Take in Figure V) ` The mixed fiber was fed by hand from the stock car to the feed hopper of the breaker card. The stock-roller wore a respirator during this operation. The fiber passed through the breaker card emerging aa a loose blanket or web. It was carried to the finishing card by a lattice conveyor, or camel back. The fiber was stripped from the last cylinder of the finisher onto a moving leather apron where a set of reciprocating rubbers condenses it into loose rovings of unspun yarn. These rovings are wound oh long "Jack" spools to be taken to the spinning department. The rovings at the extreme ends of the oards cannot be used- for spinning because they lack uniform thickness. These rovings are collected by two small hoods and pneumatically conveyed to a oolleotion bin for re turn to the preparation department. The exhaust system applied to roving oards is shown schematically in Figure Vi. The quantity of air -1 1 - exhausted varied from 1100 cfm to 1800 cfm on different carding units with an average exhaust of 1440 cfm per unit. Cards are partially enclosed and only sufficient air is exhausted to prevent the escape of dust, ^ (Take in Figure VI) Each breaker card is exhausted at three points. Hood "3" exhausts from the top of the feed hopper over the feed apron. This hopper was enclosed and covered, the cover being lifted during filling. About 160 cfm of air were exhausted through the hood. Hood "A" exhausted the top-fly from the enclosure covering the main carding cylinder. Hood rtC" exhausted the bottom-fly from the settling chamber under the carding j wylindsrs. Approximately 235 cfm were exhausted through each of these hoods. The finishing oard had four exhaust connections besides the two small hoods (G) which removed the waste roving. Hoods "S'1 and "F" correspond to hoods MA rt and "Cn respectively on the breaker card ex hausting approximately 235 cfm. each. The doffer card cylinder, doffer combs and roving apron were exhausted from below through hoods -and "E2 " at 70 cfm eaoh. About 40 cfm was exhausted through each roving collector. The volumes of air exhausted through each hood were estimated on the basis of pipe areas. Actual volumes showed wide variations on different units. Single oards were used in the manufacture of asbestos wick and ropesince a thick roving was desired. The wick or rope was twisted from the unspun roving. The nicking cards were exhausted at three points. Approximately 380 ofm of sir were drawn from under the feed -1 2 - lattice, 490 ofa ware exhausted from the top of the main cylinder cover to remove the top-fly and 550 cfm were exhausted from the bottom-fly settling chamber. Dust concentrations during carding averaged 1.7 K.P.P.C.F. This was also the average exposure of wicking card operators and wick and rope twisters. Samples taken near the carding department weight scales shewed le3s than 0.5 .r.P.P.C.F. Card rolls were cleaned and ground at night except in cases of emergency. Cleaning was done with hand scrapers made of strips of card cloth and the card cylinder was turned by hand. Grinding was done w i t h the usual type of card grinders. The large.roll was ground in' place in the carding machine. Slightly greater quantities of air were exhausted 4 during grinding due to the decreased loss of head resulting"from removal of the'wooden oard covers. The small card cylinders were ground- in a grinding frame. These frames were partially enclosed and covered with a canopy hood exhausting 2330 cfm per grinder. Dust concentrations averaged 0.65 J'.P.P.C.F. during grinding. A special run of a group of carding machines made with all exhaust ventilation turned off and windows closed showed that dust concentrations steadily increased. At the end o f one hour the concentration was 62.4 M.P.P. C.F. in the air. Under normal operating conditions about 64,000 cfm of air are exhausted from the carding department. This is equivalent to about 5.5 air changes per hour disregarding natural ventilation through windows on a n four dides of the room. Spinning, Twisting and winding. The yarn as roving is twisted, or spun, into compact threads on either iJiule or ring spinning frames. In this plant cost of the spinning was done on mule-spinners. Tlie spun thread was transferred from the spinning spindles to spools, on Foster Winding 13- aachinos (spoolers). Spooled thread to be u3Qd as filler (or woof) in woven cloth was rewound on a oop winder into cops which will fit into the loom shuttles. The remaining spooled thread was respooied on twister* which twist several threads into a yarn. The number of strands used determined the size of yarn. Both plain and metallic yarn were twisted. Metallic yarn contains one or more strand3 of fine V7ire. Part of the twisted yarn was used in cloth weaving while the remaining yarn was rewound on Universal Winding frames for the market. L*ule spinning was separated from other operations in this depart ment by partial partitions. Natural ventilation was good and no exhaust systems were used. The average dust concentration was 0.85 L.P.P.C.P. with a maximum of 1.3 I'.P.P.C.P. recorded. i King spinning, cop winding and universal winding machines were located in the same room with the twisting machines. Average exposures in the first three operations, which were nos themselves especially dusty, were due to dust from the twisting operation. With the exception of a trial exhaust system on one twister, the remaining machines were unexhaust ed. `The trial system was reported to be satisfactory and is to be in stalled on all twisting machines. In this system, the bottom of the twisting frame was enclosed and a total of 1700 cfm of air per machine was drawn downward past the twisting yarns and through five conical hood3 distributed along a central exhaust duot. Average dust concentrations at the various operations in this room were ring spinning - 5.0 tf.P.P.C.F..; cop winding - 6,9 M.P.P.C.F., univer sal winding 2.8 M.P.P.C.P.and twisting 11.0 I.I.P.P.C.P. with a maximum of 18.8 V.P.P.C.F, recorded beside a twisting frame. Ho. acourate measurements of the efficiency of the exhaust system on the single exhausted twister could be secured, but simultaneous samples on both sides of this frame showed a dust concentration of 18.0 :,!.P.P.C.F. on the side toward the unexhausted twisting frames and a concentration of 6.3 F.P.P.C.F. on the other aide. Four Foster Winders (spoolers) were partially separated from the other operations by partitions (Figure VII). The exhaust system con sisted of en individual conical hood around each spindle holder (Figure VIII). Approximately 46.5 ofm were exhausted through each hood or a total of 9270 ofm through the 200 hoods on the four spooling frames. Dust concentrations at the spoolers averaged 2.9 M.P.P.C.F. and increased to 9.6 M.P.P.G.F. within 30 minutes after the ventilation was shut off. (Take in Figure VII & Figure VIII) Weaving and Inspection. Cloth, tape, listing and br^ke bands were woven on different types of looms. In this plant, exhaust systems had been applied to the dry cloth looms since these were considered to be the most important source of dust. The dust control program calls for installation of exhaust system on dry tape, listing and brake band looms. At present these operations are mainly performed wet or partially wet. Brake band looms were not in operation during this study. Signifi cant differences could not be noted between dust samples collected around the various tape and listing looms. Dust concentrations ranged from 1.2 to 4.0 F.P.P.C.F. and averaged 3.0 il.P.P.C.F. nineteen cloth looms were in operation in.this department. One of these was a wet loom and unexhausted, four were dry looms and exhausted and the other fourteen were exhausted but could be operated eitherwet or dry. An unexhausted loom is shown in Figure IX. The exhaust system -1 5 - is shown schematically in Figure X. A doubel exhaust hood drew air from i (Take in Figure jx oc Figure X) i under the warp while a second hood was attached to the top of the loom-lay with exhaust ducts running do-.vn the side of each picker arm to an air tight swing joint at the bottom. The openings in the loom lay hood con- sisted of four slots nine inches long by 1 inch wide extending over a space of four feet across the woven fabrio at right angles to the warp. A total volume of approximately 10,500 cfm of air wa3 exhausted from the eighteen hooded looms. This averaged about 580 cfm per loom, but since it was seldom necessary to operate more than ten dry looms at one time, the average quantity of air exhausted was d o s e to 1000 cfm per loom. Sxhau3 t dampers were provided on all looms and sufficient dampers j to balance the system are closed on wet or idle looms. The average dust exposure of a weaver operating an exhausted dry loom was 0.7 LI.P.P.C while the average exposure in unexhausted wet weaving was 2.6 i.P.P.C.F. Samples taken beside a dry, unexhausted loom showed dust concentrations of 9.6 It.P.P.C.F. after forty-five minutes. Average dust concentrations during dry weaving have been shown aa 49.7 U.P.P.C. F.5/ I Woven cloth was inspected, brushed and calendered on the inspectioi table shown in Figure XI. Sach of the power driven brushes was partially enclosed and exhausted. Approximately 750 cfm of air were drawn through each of the two hoods at'the front of the table and about 200 ofm was drawn through the cleaning hood at the back of the table. Dust concentra tions during inspection averaged 0.5 M.P.P.C.F. A sample taken while a roll of fabric-wag passed acrogg the table without benefit of exhaust showed a dust concentration of 11.Q W.P.P.C.F. (Take in Figure XI) -1 6 - Doffing, inspection end calendering of tape and listing were hand operations and were not exhausted. Dust concentrations of 3.0 J.hP.P.O .F. were recorded during those operations but the exposure was intermittent. ^reelers had an average exposure of about 1.3 U.P.P.O.F. while placing spools and threading looms. A total of 12200 cfn of air was exhausted from the weaving de partment corresponding to approximately 3 air changes per hour. .In cold weather, warn air was distributee through the uepartmsnt from a premia system while in warm weather natural ventilation was secured through use of windows on all four sides of the department. Other Operations. Other operations in this plant consisted of processes in which the yarn was chemically treated and fabricated, or processes for chemically treating or rubberizing fabricated cloth* Ho. potential asbo3toa hazard was associated with these processes with th-a exception of one braiding machine used to make largo diameter aebestos tubing. This machine was covered with a conical canopy hood about six feet in diameter through which approximately 200 cfn of air were ex hausted. A sample taken beside this machine showed a dust concentration of 0.4 M.P.P.C.F. at the operators breathing level. Summary. Table II gives a summary of the exhausted operations, H e ing the number of exhaust ducts and rate of ventilation per machine, as Wi as the average dust concentrations to which operators are exposes. Avera^ dust concentrations measured near corresponding unexhausted operations are tabulated to sh?w the effectiveness of the control metho<B which have been described. (Take in Table II) r -1 7 - Conclusion;, This study of actual results secured by a dust con trol program in en asbestos fabricating plant is presented as an example if - of engineering control of an industrial hazard.ji Adequate d a t a have not yet been published to Justify the determination of threshold limits of dustiness which will produce asbestoais in any definite period of time. In Che absence of such threshold values it is not possible to determine permissible U n i t s of dustiness on a medical basis. Nevertheless, any appreciable decrease in the amount of asbestos dust will cause a decrease in the incidence and severity of the resulting asbestosis. ihe elimina tion of all the dust in an industrial workroom is rarely necessary from a physicological standpoint and usually economically impractical. Conse quently, actual atmospheric conditions is an industry resisting from the application of practical methods of dust control, can be uqed as temporary' standards by that Indus try.2J A'. ' -1 8 R3F3R3HCLS \J Rica, H . , and Hatson, x. I.; ''Engineering Geology"; John Viiloy i: Sons, Inc.; Hew York; (1937) 2/ F u lt o n , V/. 3 . , Do o l ey , A . , Matthews, J. 1 . , end Eo ut z, R. I ; "Aabestosia. Part II. The nature and Amount of Dust Encountered in Asbestos Fabricating Plants"; Spec, Bull. Ho. 42; Penna. Dept, of labor and Industry; Sept. 20, 1S35. 3 / Bloomfield, J. J., and DallaValle, J, LI.; "i1ha Determination and Control of Industrial Dust"; Pub. Health Bull. Ho. 217, April 1935. 4 / Harding, I. A., and Hillard, A. C., "Heating, Ventilation and Air Conditioning"; John 7iley and Sons., Inc.; Hew York; 19,32. 5/ Unpublished Data, U.S.P.H.S. '* . 5/ Higgins, H . , Lanza, A. J., Laney, F. B. ana Rice, G. S. "Siliceous Dust in Relation to Pulmonary Disease Amoung Miners in the Joplin District, Missouri"; Bull. 132; U. S. Bureau of Mines, 1917. (a) Sample after one hours operations without exhaust. (b) Sample taken inside bin during loading. * Dust ilxhaust system for this operation. Table II.-- Volumes of Air Exhausted per Machine In Operations In an Asbestos Textile Plant. Operation i Asbestos Opener Vi'o. Screen Cotton Opener "ixins Ceds Picker Roving Reopener Fly T/illowor Sc Screen Connections Total Volume of Oust Cone, Air -xhausts with per minue Exhaust (cu.ft./mln.) : .p.r.c.F. Dust Cone without Axhaus t 2 (*) 1 3 1 3 1 3 (*) 625-1000 ) 700 ) 2160 1025 2570 1780 1600 3.5 11.1-op.C - - 5.4 3.1-10.6 6.7 34.3-74.3 a - -- j Roving Cards Breaker (Primary) 3 Finisher ''ickins Card 3 1420 ) 1440 ) ) 1.7 1420 ) 62.4 Card Grinders 1 2330 0.7 - Foster Winders* (Spoolers} 1 (*) 2225 2.9 13.1^/ Twisters 1 1700 - 11.0 Weaving 2 (Brood looms) 1300 0.7 49.73/ Brusher - Calender 3 1650 O.o 11.8' -* -- -- ----- y * Equipped with, pneumatic conveyor - exhaust thru conveyor not include \ Individual cone for each spindle connected to exhaust manifold. \ a/ Unpublished data - other plants (J. I,{. DallaYalle - U.3.P.H.S.} b/ i\ilton, et al. ref. 2/ \