Document Y31kQXa7V2JxLXb0xpKg099K

r* \ t U. S. TREASURY DEPARTMENT HENRY MORCENTHAU. J*.. Ser*Ury PUBLIC HEALTH SERVICE THOUAS PARRAN. Surptcn A STUDY OF DUST CONTROL METHODS IN AN ASBESTOS FABRICATING PLANT BY RICHARD T. PAGE Attistant Public Health Engineer Par ult by tb Supcriawndtot ol DocuooU, Wtibiagtaa, D. C. .2 ' . -sr A- . r*i3* A STUDY OF DUST CONTROL METHODS IN AN ASBESTOS FABRICATING PLANT By Richabd T. Paok, Attulant Public Health Engineer, Bod J. J. Bloowdeld, Patted Attulant Sanitary Engineer, United Stale* 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 (5). The material contained in this paper supple ments the general study with a detailed study of the dust control methods used in an asbestos fabricating plant. It is a report on present conditions and how they have been obtained and is presented as an example of the results of the application of scientific methods of .dust control. These data should be interesting 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; consequently, these results should not be interpreted as representing the maximum possible efficiency in the control of asbestos dust, but it is believed that they are representative of the best practice in this country at this time. The dust control systems in use with the vari ous processes in each department are described. An occupational analysis of employees is presented, with a comparison of the atmos pheric dust concentrations associated with controlled and similar uncontrolled processes. FABRICATION OF ASBESTOS TEXTILES Asbestos is the class name for several different fibrous minerals, but the asbestos of commerce (I) is mainly the fibrous form of ser pentine known as chrysotile.1 Due to its fibrous nature, flexibility, and heat-resistant properties, asbestos fiber finds many practical applications. One of its important industrial uses is in the manu facture of fire-resistant textiles. In the plant studied, practically all raw material was crude Canadian or South African asbestos. Some imported short fiber was used, as well as some of the short fiber salvaged in the recovery process, but most of the short recovered fiber was shipped to other plants. Signif icant variations in atmospheric dust concentrations due to the grade ol fiber being processed were not evident in controlled processes in this plant. Consequently, the type of fiber used has not been con sidered in the analysis of the data. Each dust controlled process tended to decrease the amount of dust generated in subsequent ChryaolUa la bydroua mafttwiam iQteU cast aOica. 3.0 parcaot nufoalt, and U.9 parasol watar. *t bon, oaldun. and alumlooia aa wall aa macnasiais (f). 2 S27S6--tt or 2H0-lM|0-2Sl0i) eoouioto* .! p Otbar typaa at aabastoa oftao ooaUla tlllaeut ' DUST CONTROL IN AN ASBESTOS PLANT 3 processes. These factors must be considered when comparing dust concentrations reported in this plant with the data which have been reported for other plants. Approximately 300 persons were employed in this plant, of whom 180 worked in departments having a potential asbestos dust hazard. This study was confined to these departments; namely, preparation; carding; spinning, twisting and winding; and weaving. The occupa tional distribution of exposed workers is shown in table 1. Table I.--Occupation* and dual exposures 0} worker* in on atbaios lexiiU ptani 0ocapotion Naaber of worsen Innit doit ooncentrv Uoa, M. P. P. C. P. Nonn*l Without ti* haait tsU' UUoa TrcpsntJoa; Cardins: Spinning. twistIns, tad wladlat: Waiving: WMTtft: l Dost oxbttut trrtem tor thl operation. I Sample slier 1 bour'i operation without h*art, I gsmpie t&ken Inside bio darias kwdlaf. 1 It 1 2 (*.6 9 >6.4 9 >6.7 e 10 4.6 9 >.7 1.7 .1 e 10 16 <2 6.6 u 11.0 7 is 1Ig0 ( " 1 *-2 ( *7 1 *<> 7 1.1 a 9 1>1. 7 11 ' 40.4 *6.6 *16 111 METHOD OF STUDY This investigation included a study of atmospheric dust concentra tions in the factory workrooms and a study of the exhaust systems used to remove asbestos dust. Eighty-two atmospheric dust samples were collected at the workers' breathing level with the impinger dust sampling apparatus (5). Sixty-nine of these represented present working conditions and 13 represented conditions while exhaust apparatus had been turned of? for 1 hour. A collecting medium containing 25 percent ethyl alcohol in distilled water was found to prevent flocculation without causing excessive evaporation in either the sampling flasks or the counting L 4 DUST CONTROL IN AN ASBESTOS PLANT _ cells. Ail samples were counted the day after collection. Owing to the low duet concentrations encountered, most of the samples repre sented the dust in from 20 to 30 cubic feet of air. Samples were diluted with distilled water aDd counted according to the light-field technique described by Bloomfield and D&UaValle (3). A micrometer eyepiece having an eograved 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 cubic millimeter) per field was counted (7). The quantities of air removed through the various exhaust systems were calculated from pitot tube measurements of center-line velocities in the pipe lines (4). Average exhaust rates per process are listed in table 2 aDd discussed a little later in the description of exhaust systems. Entrance velocities at open hoods were measured with an Alnor velometer and checked with a vane anemometer. Most of the hoods were of the enclosed type designed to exhaust only enough air to pre vent the escape of asbestos dust into the workroom. Where individual measurements were impractical, air volumes exhausted through each hood were calculated from measurements of main-line velocities. Whenever differences in exhaust volumes were noted between similar hoods on the same operation, the average value is given. DESCRIPTION OP PROCESSES AND DUST CONTROL MEASURES Asbestos is received in burlap bags containing 100 pounds of fiber. Cotton is received in standard bales. . These are the only raw materials used in the preparation of asbestos yam at this plant. Unloading, 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 (fig. 1). Indi vidual processes and the measures for dust control are described below. PREPARATION DEPARTMENT Crushing.--Some of the asbestos fiber arrives at the plant as "pre crushed" fiber, but most of the crude fiber has received no treatment other than mining, sorting, and screening. This latter type is hand dumped from the bags into rim-wheel crushers and crushed from 5 to 15 minutes. These crushers have two heavy rollers attached to a radial axle, and revolve on a smooth-surfaced tray in which the asbestos ia placed. During the crushing, the asbestos fiber is constantly stirred by revolving scrapers. After being crushed, the fiber is replaced in the bags and carried to the asbestos opener. Crushers were not enclosed or exhausted in any way, but the general ventila tion in the preparation department was sufficient to prevent high concentrations of dust near this operation. Crusher men had res-  tirV-Tii-tii ' >**? '^'`j DUST CONTROL IN AN ASBESTOS PLANT RAW MATERIALS COTTON CRUDE ASBESTOS ------- j CRUSHERS MILL ASBESTOS RECOVERED MATERIALS ROVING WASTE CYCLONE A SETTLING CHAMBER WASTE BAG MOUSE WASTE COTTON* OPENERS ' A' ASBESTOS OPENERS 1 ROVING aviBRATlNG SCREENS! REOPENER '' ViflRATiNG 9CREEN TOUT iisr- * PICKERS market STOCK BINS ( CARDING OEPT.) WICKINO CARDS r TWISTED CORO MACHINES ROPE TWISTING MACHINES ROVING CAROS r1 MULE SPINNERS RING SPINNERS ' ' FOSTER WIN0ER3 (SPOOLERS) CHttt. TREATMENT ft BRAIDING DEPT COP WINDERS j-- TWISTERS ------ LOOMS UNIVERSAL WINDERS ' CHEMTR|ATMENT RUBBER 0PT inspection! W* MARKET U NOTE; UNOERUNEO PROCESSES HAVE OUST EXHAUST STSTEMS. Fiooe 1Frooos* flcw-oboot, uberio* Mxtllt pUot. pirators * and usually wore them while loading or unloading the crushers. The average exposure of a crusher man tending three crushers was 3.5 M. P. P. C. F. * AH uaployws Is the pnpr*Uoo dp*rtnjal sd sU nplns*s sd JuilUrs croH<l*d with mytrv ton oftype opprovod br tbs 0.8. Soma ol Worn ogalstt aoocoatntioat ot Au Qlc dost. a* 0 DU8T OONTBOL IN AN ASBESTOS PLANT Asbestos opening and screening.--The crushed fiber is dumped froa] bags to the floor beside the asbestos openers and lifted into the fe*$1 lattice hopper with wooden band forks. Two openers of diflerecj' design were in operation, but the method of exhaust hooding was th same on both. (See schematic design, fig. 2.) The feed lattice hopper was 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 picked up by hood C 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 fine fibers entering the asbestos opener FEED HOPPER PNEUMATIC c CONVEYOR t-- Xiovrsx a.--Bciiemits8 rirr axbiost ryvUia >ppUd to o utmtoi op*o*c. was removed by hoods A and B. ClumpB of unopened fibers and pieces of rock too heavy to be lifted by the pneumatic fiber conveyor fell onto an enclosed belt conveyor serving both openers, and were carried to the recovery process. (Belt conveyor is not shown in fig. 2.) Exhaust volumes through the hoods were as follows: Hood A, 400 cfm; hood B, 400 cfm; hood C (pneumatic conveyor), 1,800 cfm; conveyor velocity, 2,730 feet per minute. .* Each opener had its own cyclone separator and enclosed and ex* hausted vibrating screen. One screen had two exhaust hoods, one beside the charging hopper drawing 400 cfm and one over the die- DUST CONTROL IN AN ASBESTOS PLANT 7 charge end of the screen and the stock car, drawing 770 cfm. The second screen had one hood only, over the discharge end, drawing 615 cfm. Short fibers and rock particles passing the screens fell through a chute to the enclosed recovery conveyor. Fiber failing to pa99 these screens dropped into a stock car. Full stock cars were pushed to a platform scale and then to the mixing beds. The same men charged the openers and filled the stock cars. The average dust exposure of asbestos-opener operators was 3.6 M. 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 percent of cotton by weight but as much as 20 percent cotton was used in lower grade yarns. The Iwo-slage Saco-Lowell cotton opener was provided with exhausts at three points; 770 cfm of air were exhausted through a canopy hood over the feed lattice, 270 cfm from the bottom of the primary opener, and 1,120 cfm from the bottom of the secondary opener. Opened cotton fiber was discharged into stock cars. No samples were taken at the cotton openers, but the operators' average exposure was about 2.4 M. P. P. C. F. (general air, preparation department). ,, Mixing.--Weighed quantities of asbestos and cotton were placed in alternate layers in the mixing beds. Occasionally, layers of rov ing waste from the carding room were reopened and added to the bed. Mixing was done in six "exhausted" booths, each 10 feet 2 inches deep by 6 feet 10 inches wide by 6 feet high. Sides of the booths were permanent, while the back consisted of a removable wood and canvas section. Each booth was covered by a pyramid hood 32 inches high, through which approximately 1,025 cubic feet of air per minute per hood were exhausted. The velocity of air motioD into these booths averaged 50 feet per minute during bed making and about 30 feet per minute during picker loading. Dust concentration averaged $.4 M. P. P. C. F. for the bed-making operation. After a bed had been placed, the picker operator removed the rear partition of the booth and forked the batch into the charging hopper of a picker (fig. 3). The picker machine mixes the fibers in revolving beaters. The four machines represented three different operations and two different types of exhaust systems. The first machine, not in operation during this study, discharged mixed fiber into a stock car. This 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 of the fourth picker was carried to the carding room by a pneumatic conveyor. Each of the first three machines had a hood over the charging lattice, exhausting approximately 500 cfm, a pipe exhausting about 1,650 cfm from the bottom-fly settling chambers * far >, i -*- 8 DUST CONTROL IN AN ASBESTOS PLANT under the main picker drum, and p hood over the end of the discharge 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 2,000 cfm of air at a velocity of 2,550 feet per minute. The picker operators wear respirators during the charg ing operation. Dust concentrations during picker charging varied from 4.0 to 9.5 M. P. P. C. F., averaging about 6.7 M. P. P. C. F. Recovery processes.--Waste roviug from the card room was returned to the preparation department for reopening. The roving reopener was exhausted only from the pit below the last beater, but the 1,780 cfm of air drawn through this hood were sufficient to prevent the escape of dust through the discharge lattice. The 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 dis placed from this 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 week end shut-down, and stored in bins in the preparation depart ment. Bag-house dust was screened on a completely enclosed and exhausted vibrating screen (background, fig. 4), 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 dust, and fibers separated by cyclones on the exhaust lines from the spooling operation and the weaving department were passed through a fly-willower and vibrating screen (fig. 4). 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 the screen were removed by the hood at the lower end of the screen (1,710 cfm) and pneumatically conveyed to a cyclone collector. Rock and other im purities not picked up by the pneumatic conveyor fell into a waste box below the end of the screen. The market for recovered fiber is limited, and such 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 was estimated at between 3 and 5 M. P. P. C. F. As a measure of the effectiveness of the dust control system in the preparation department, the exhaust fans were shut off for 1-hour. Pneumatic conveyors remained in operation. Dust concentrations increased steadily to about 50 M. P. P. C. F., at which time the ex haust fans were turned on. The samples taken during this period DC8T CONTROL IN AN ASBESTOS PLANT 9 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 cubic feet of space, from which ap proximately 34,650 cfm of air were exhausted. Consequently 6.5 air changes per hour were produced by mechanical ventilation, which was supplemented by natural ventilation through doors, windows, and roof ventilators. Fortunately heating was not a problem in this plant. CARDING DEPAflTME.VT Mixed fiber from the preparation department was dropped from pneumatic or mechanical conveyors into bins in the carding depart ment. The total volume of exhaust from four bins was 6,850 cfm, 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 M. P. P. C. F. were measured inside an active bin while the dust concentration just outside the door of the same bin was only 4.6 M. P. P. C. F. Workers, classed as 6tock rollers, fork the mixed fiber from the bin into stock cars. This opera tion 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. However, stock rollers, wearing respirators, like to push their cars under the chute and then climb into the car and "tread-down" the stock. The cards are machines having a series of revolving cylinders wound diagonally with strips of leather set with fine, sharp, steel bristles. Carding removes remaining small bits of rock and combs the fibers into a more or less parallel condition to facilitate spinning. At the time of this study, 31 roving card units and 2 wicldng cards were being operated. A roving card unit (fig. 5) consisted of two cards, a breaker, or primary card, and a finisher or roving card. 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 as a loose blanket or web. It was carried to the finishing card by a lattice convej'or 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 condensed it into loose rovings of unspun yam. These rovings are wound on long "jack" spools to be taken to the spinning department. The rovings at the extreme ends of the cards cannot be used for spinning because they lack uniform thickness. These rovings are collected by two small hoods and pneumatically conveyed to a collection bin for return to the preparation department. 10 DUST CONTKOL IK AN ASBESTOS PLANT The exhair-t sypteiu applied (o roving cards ip shown schematically in figure 7. The quantity of air exhausted varied from 1,100 cfm to 1,800 cfm on different carding units with &n average exhaust of 1,4*10 cfm per unit. Cards are partially enclosed and only sufficient air is exhausted to prevent the escape of dust. Each breaker card is exhausted at three points. Hood B exhausts fro/o 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 Cawzl'Back CoNvtvof* m lx A -------- zj-j Bkeakkr O, 0 Feeo -sox Coycg Tj'.vhj. : r'*>" *' rvd siS%uu system O cvhet ;:t-d th*- bottom Py from the settling chamber under the carding ryiinom > Approximately cfui were exhausted tltrough each of these hoods. The finishing card had four exhaust connections besides the two small hoods G which removed the waste roving. Hoods E and F correspond to hoods A and C, respectively, on the breaker card, providing an exhaust of approximately 285 cfm each. The dofler card cylinder, doficr combs, and roving apron were exhausted from below, thro'ich hoods I)' and D* at 70 cfm each. About 40 cfm were exhausted through each roving collector. er^p1 DUST CONTROL IN AN ASBESTOS PLANT 11 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 cards were used in the manufacture of asbestos wick and* rope, since a thick roving was desired. The wick or rope was twisted from the unspun roving. The wicking cards were exhausted at three points. Approximately 380 cfra of air were drawn from under the feed lattice, 490 cfm were 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 M. P. P. C. F. Tbi6 was also the average exposure of wicking card operators and i wick and rope twisters. Samples taken near the carding department weight scales showed less than 0.5 M. 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 with the usual type of card grinders. The large roll was ground in place in the carding machine. Slightly greater quantities of air were exhausted during grinding due to the decreased loss of head resulting from removal of the wooden card covers. The small card cylinders were ground in a grinding frame. These frames were partially enclosed and covered with a canopy hood exhausting 2,330 cfm per grinder. Dust concentrations averaged 0.65 M. 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 concen trations steadily increased. At the end of 1 hour the concentration was 62.4 M. P. P. C. F. in the air. Under normal operating conditions about 64,000 cfra 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 all four sides of the room. Spinning, twisting, and winding.--The yarn as roving is twisted or * spun into compact threads on either mule or ring Bpinning frames. In this plant most of the spinning was done on mule spinners. The spun thread was transferred from the spinning spindles to spools, on Foster winding machines (spoolers). Spooled thread to be used as filler (or woof) in woven cloth was rewound on a cop winder into cops ili which will fit into the loom shuttles. The remaining spooled thread was respooled on twisters which twist several threads into a yam. The number of strands used determined the size of yam. Both plain ) and metallic yams were twisted. Metallic yam contains one or more strands of fine wire. Part of the twisted yam was used in cloth weaving while the remaining yam was rewound on Universal winding frames for the market. >_... SV irt * . y, * yy'rxrrL 12 DUST CONTROL IN AN ASBESTOS PLANT Mule opinning was separated from otbcr operations in this departs nient. by partial partitions. Natural ventilation wm good and no exhaust systems were used. The average dust concentration waa 0.85 M. P. P. C. F, with a maximum of 1.3 M. P. P. C. F. recorded. King spinning, cop winding, and Universal winding machines were located in the same room with the twisting machines. Average ex posures in the first three operations, which were not 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 not provided with exhaust. The trial system was reported to be satisfactory and is to be installed on all twisting ( * d machines. To this eyri^m. the bottom of the twisting frame was enclosed and a total of 1.700 efrn of eh per machine was drawn down ward past the twisting yams and through five conical hoods distributed along a central exhaust duct. Average dust concentrations at the various operations in this room were ring spinning, 5.0 M. P. P. C. F.; cop winding, 6.9 M. P. P. C. F.; Universal winding, 2.8 M. P. P. C. F.; and twisting, 11.0 M. P. P. C. F., with a maximum of 18.8 M. P. P. C. F. recorded beside a twisting frame. No accurate measurements of tho efficiency of the exhaust system on the single exhausted twister could bo secured, but simultaneous samples on both sides of this frame showed a dust * * . '.' <r. *, v \ Ficvii 10.--Table for inspectlni, calendering, and brushing o*en doth. 1f$e1j1pPl dust com hol tn an asbestos plant 13 concentration of 18.0 M. P. P. C. F. on the side toward the unex hausted twisting frames and a concentration of 6.3 M. P. P. C. F. on the other side. Four Foster winders (spoolers) were partially separated from the other operations by partitions (fig. 6). The exhaust system con sisted of an individual conical hood around each spindle holder (fig. 8). Approximately 46.5 cfm were exhausted through each hood, or a total of 9,270 cfm through the 200 hoods on the 4 spooling frames. Dust concentrations at the spoolers averaged 2.9 M. P. P. C. F. and increased to 9.6 M. P. P. C. F. within 30 minutes after the ventilation bad been shut off. WEAVING AND INSPECTION Cloth, tape, listing, and brake 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 systems on diy tape, listing, and brake-band looms. At present these operations are mainly performed wet or partially wet. ISn'ke-band looms were not in operation during this study. Signifi cant differences could Dot- be noted between dust samples collected around the various tape and listing looms. Dust concentrations ranged from 1.2 to 4.0 M. P. P. C. F. and averaged 3.0 M. P. P. C. F. Nineteen cloth looms were in operation in this department. One of those was a wet loom not provided with exhaust hoods, 4 were dry looms provided with exhaust- hoods, and the other 14 were so provided hutcouJd he operated either wet or dry. A loom without exhaust hoods is rhown in figure 9. The exhaust system is shown schematically in M. A double f'.xhnnst hood drew air from under the warp while a second hood was attached to the top of the loom lay with exhaust ducts running down the side of each picker arm to an airtight swing joint at the bottom. The openings in the loom-lay hood consisted of four plots nine mches long by 1 inch wide extending over a space of 4 feet across the wToveo fabric at right angles to the warp. A total volume of approximately 10,500 cfm of air was exhausted from the 18 hooded looms. This averaged about 580 cfm per loom; but since it was poJdmr necessary to operate more than *0 dry looms at one time, the average quantity of air exhausted was close to 1,000 cfm per loom. J Kxhaust dampers were provided on all looms, and a sufficient number * to balance the system are closed on wet or idle looms. The average dual exposure of a weaver operating a dry loom with exhaust was U.7 M. P. P. C. F., while the average exposure in wet weaving without exhaust was 2.6 M. P. P. C. F. Samples taken beside a dry loom without exhaust showed dust concentrations of 9.6 M. P. P. C. F. * 1 14 DUST CONTROL IN AN ASBESTOS PLANT , after 45 minutes. Average dust concentrations during dry weaving have been shown as 49.7 M. P. P. C. F. fd). Woven cloth was inspected, brushed, and calendered on the inspec tion table shown in figure 10. Each of the power-driven brushes was Flop** 11.--Schematic !< of sxbsuat i^tum tppUod to brood looms. 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 cfm were drawn through the cleaning hood at the back of .. * l i DUST CONTROL IN AN ASBESTOS PLANT the table. Dust concentrations during inspection averaged 0.5 M. P. P. C. F. A sample taken while a roil of fabric was passed* across the table without benefit of exhaust showed a dust concentra tion of 11.8 M. P. P. C. F. . .. - -- - Doffing, inspection, and calendering of tape and listing were band operations end were not provided with exhaust. Dust concentrations of 5.0 M. P. P. C. F. were recorded during these operations but the exposure was intermittent. Creelers had an average exposure of about 1.3 M. P. P. C. F. while placing spools and threading looms. An exhaust of 12,200 cfm of air was provided in the weaving de partment, corresponding to approximately three air changes per hour. In cold weather, warm air was distributed through the department from a plenum 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 chemi cally treating or rubberizing fabricated cloth. No potential asbestos hazard was associated with these processes, with the exception of one braiding maeliine used to make large diameter asbestos tubing. This machine was covered with a conical canopy hood about 6 feet in diameter, which provided an exhaust of approximately 200 cfm of air. A sample takeQ beside this machine showed a dust concentration of 0.4 M. P. P. C. F. at the operators' breathing level. Table 2.-- Volumes of air exhausted per maehirte in conouJ operations in an asbestos textile plant Operation Connec tion* Tout VOluR3 Of air ubmu f*r mlnuia (co. 11./min.) Dust concen tration with ibsust. M.P.P.C.F. Du-vt orae&ntratloo witij. out tibaust. M.P.P.O.F. tlorla: ccrOv I 3 824-L 000 } l >1 11,430 1,440 1.420 - 2,744 1.700 3 | 1,040 LL1-M.0 t 1-10.0 23 44.4-74.3 " 26 . 024 * 14.1 11.0 1L8 EQuipped with pneumatic ooo*eyor--oxbauat throurb conveyor not Included. Unpublished data, other p)ou (). M. DtllaViUa, 0. 8. P. H. 8.) Fulton, el *1. Ret. If). 'Individual oon* (or oech spindle coonwtcd to axbaust maolfold. ' '.'"II.WV 1 vy >y jji i^jj, 16 DUST CONTROL IN AN ASBESTOS PLANT 6UUUART Table 2 gives a summary of the operatioDS provided with exhaust, listing the number of exhaust ducts and the rate of ventilation per machine, as well as the average dust concentrations to which operators are exposed. Average dust concentrations measured near corre sponding operations without exhaust are tabulated to show tbe effec tiveness of the control methods which have been described. . CONCLUSION This study of actual results secured by a dust control program in an asbestos fabricating plant is presented as an example of engineering control of an industrial hazard. Adequate data have not yet been published to justify tbe determination of threshold limits of dustiness which will produce asbestosis in any definite period of time. In the absence of such threshold values it is not possible to determine permis sible limits of dustiness on a medical basis. Nevertheless, any appre ciable decrease in the amount of asbestos dust will cause a decrease in the incidence and severity of the resulting asbestosis. Tbe elimina tion of ail the dust in an industrial workroom is rarely necessary from a physiological standpoint and usually economically impracticable. Consequently, actual atmospheric conditions in an industry resulting from the application of practical methods of dust control can be used as temporary standards by that industry (6). REFERENCES (1) Kies, H., and Watson, T. L.: Engineering Geology. John Wiley and Sods, Inc., New York. 1937. ` () Fulton, W. B., Dooley, A., Matthews, J. L., and Houti, R. I.: Asbestosis. Part II: Tbe nature and amount of dust encountered in asbestos fabricating plants. Spec. Bull. No. 42, Pennsylvania Dept, of Labor and Industry. Sept. 20, 1935. ' (5) Bloomfield, J. J., and DallaValle, J. M.: The determination and control of Industrial dust. Pub. Health Bull. No. 217. Govt. Priotiug Office, Washington, D. C. 1935. (4) Harding, L- A., and Willard, A. C.r Heating, ventilation, and air condi tioning. John Wiley and Sons, Inc., New York. 1932. (<5) Unpublished data. United States Public Health Service. (6) Higgins, E., Lanta, A. J., L&oey, F. B., and Rice, G. S.: Siliceous dust in relation to pulmonary disease among miners id the JopLin District, Missouri. Bull. 132, U. S. Bureau of Mines, 1917. (7) Page R. T.: Note on a new ocular micrometer for use in dust counting. Pub. Health Rep., 6: 1315-1316. o v m a. f U. S. TREASURY DEPARTMENT MEN BY MORGEMTKAU. J- 5mtwmr% PUBLIC HEALTH SERVICE THOMAS PARHAM. Sutfm A STUDY OF DUST CONTROL METHODS IN AN ASBESTOS FABRICATING PLANT IT RICHARD T. PAGE AuuianJ Pvbtic Htaiik Bnqirmr AMO J. J. BLOOMFIELD Paati Auiiiant Sanitary Enfinar Uniitd'SiaU* Public Htaltk Serna REPRINT No. 1SU non nt PUBLIC HEALTH REPORTS _ a. No. 41. NVOBB tt. irr (?iin mvmf) OWENS.COPN|NG FI3ERGUS CORP. legal a PATENT DEPT. RECO SEP 15 1941 UNTTO 9TATXS GOVXXNMENT PAINTING OFP1CX WASHINGTON: Tot Mi* br tb* Su9*n*wnd( ai Oocvaaatt. Wt*biafM. D. C. Prtv Kmm :( A STUDY OF DUST CONTROL METHODS IN AN ASBESTOS FABRICATING PLANT Bj Ricxiao T. Pass, Attiatani PiMic Haaitk tad 3. 3. Btoourmo, Pattod Auulant Sanitary Snfiruar, (Jnitad SiatM Pudiie HtaitA Sonia* An extensive medical and engineering study of the health of asbestos workers ha* been conducted by tha United States Public Health Serrice (5). The material contained in this paper supple ments the general study with a detailed study of the dust control methods used in an asbestos fabricating plant. It is a report on present conditions and how they bare been obtained and is presented as an example of the results of the application of scientific methods of duat control. These data should be interesting not only to the asbestos industry but also to other industries haring similar dusty processes. The plant studied has only partly completed an extensile dust control program, and conditions are being unproved continually; consequently, these results should not be interpreted as representing the maximum possible efficiency in the control of asbestos dust, but it is believed that they are representative of the best practice in this country st this time. The dust control systems in use with the vari ous processes in each department are described. An occupational analysis of amployees is presented, with a comparison of the atmos pheric dust concentrations associated with controlled and similar uncontrolled processes. nsRiCATioN or ubkstos rxxmxa Asbestos is the rises name for several different fibrous minerals, but the asbestos of commerce (I) is mainly the fibrous form of ser pentine known as chrysotile.1 Due to its fibrous nature, flexibility, and beat-resistant properties, asbestos fiber finds many practical applications. One of its important industrial uses is in the manu facture of fire-resistant textiles. In the plant studied, practically all raw material was crude Canadian or South African asbestos. Some imported short fiber was used, as 'well as some of the short fiber salvaged in the recovery process, but xnoet of the short recovered fiber was shipped to other plants. Signif icant variations in atmospheric dust concentrations due to the grade oi fiber being processed were not evident in controlled processes in this plant. Consequently, the type of fiber used has not been con sidered in the analysis of the data. Each dust controlled process tended to decrease the amount of dust generated in subsequent `CAmotik ! t brdrcui u(Miaa SUom* (H.MWUO, a ISjO-lMfO BtO,) muietac M.t pv. mot lOtat, tt.6 pwokac vod lit pvaet *t* 0l& tTV* * ort*a oeouio W Uoo, aJaum. tad UumlaoA m **U m aMcaainiri (ft. 2 tun DOST CONTROL IN AN AS8EST08 PLANT 3 processes. These /sctors must be considered when compering dust concentrelions reported in this pleat with the dots which here been reported /or other pleats. Approximately 300 person* were employed in this pleat, of whom 180 worked in departments hieing e potential asbestos dust hazard. This study was confined to these departments; namely, preparation; carding; spinning, twisting and winding; and weaving. The occupa tional distribution o/ exposed workers is shows in table 1. TaBI* l.--Occupation* mnd dud epMvu /1earktr* im silerfe* itxtiU plani Owepatoae AlMlW: nihn ........ OveOttv*C: irf ...................... . ' Cv4 UcMtj--...................... Sptosiai. iWUas. aee vtasias: Vfcv*J -wen... WeWwjaaarwn: . Horn i>S9awapuiakatfalaat ItnaUaqari tooMr (/Svcituaepvanttaaorea.t < i pAftpJt ta*a lAaict btt eonas toaflia*. li `Wficrsv wnoaosa*. Kami toatosdtaewu* li 1 11 9 >1I1S.<7 14 eas M `1.7 <41 .T X7 .1 at 40.4 .* 1 IS U4 1a9* as is1 u.a as ------ -- u a* h 1 ?1 s9 7 .7 to 1.7 li 1.9 as U.I MXT809 OP STOUT This investigation included a study of atmospheric dust concentra tions in the factory workrooms and a study of the exhaust systems used to remove asbestos dust. Eighty-two atmospheric dust samples were collected at the workers' breathing level with the iznpinger dust sampling apparatus (5). Sixty-nine of these represented present working conditions and 13 represented conditions while exhaust apparatus had been turned off for 1 hour. A collecting medium oontainisg 2S percent etby! alcohol in distilled water was found to prevent flocculation without causing excessive evaporation in either the sampling flasks or the counting I i r ( fl i il \i \ V5 S\ l > 4 DOST CONTROL IN AN ASBESTOS PLANT eells. AH samples were counted the day liter collection. Owing to tbs low duet eoncentra lions encountered, most of the samples represeated the dust in from 20 to 30 cubic feet of sir. Semples were diluted with distilled water and counted according to the light-field technique described by Bloomfield and DallaValle (3). A micrometer eyepiece having an engraved square equivalent to one-fourtb the standard Whipple square *u used in counting. Since it it customary to count only one quadrant of the Whipple field, the same volume of sample (0.25 cubic millimeter) per field was counted (7), The quantities of air removed through the various exhaust systems were calculated from pitot tube measurements of center-line velocities in the pipe lines (4). Average exhaust ratea per process are listed in table 2 and discussed a little later in the description of exhaust systems. Entrance velocities et open hoods were measured with an Alnor velometer and checked with a vane anemometer. Moat of the hoods were of the enclosed type designed to exhaust only enough air to pre rent the escape of asbestos dust into the workroom. Where individual measurements were impractical, air volumes exhausted through each hood ware calculated from measurements of main-line velocities. Whenever differences in exhaust volumes were noted between similar hoode on the same operation, the average value is given. nsscBiPTXoir or rxoczsiu axd dust coxtsol kzasuxxs Asbeetoe is reeeived in burlap bags containing 100 pounds of fiber. Cotton is received is standard bales. These are the only raw materials used in the preparation of asbestos yarn at this plant. Unloading, storage, and transportation of the packed raw materials were not hazardous occupations. The progress of the material hum raw fiber to completed fabric is shown by means of a flow sheet (fig. 1). Indi vidual processes and tbs measures for dust oontrol are described below. nsraiTioN MmncwT Crushing.--Some of the asbestos fiber arrives at the plant as "precrushod" fiber, but most of the crude fiber has reeeived no treatment other than mining, sorting, and screening. This latter type is band dumped from the bags into rim-wheel crushers and crushed from 5 to 15 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. During the crushing, the asbestos fiber is constantly stirred by revolving scrapers. After being crushed, the fiber is replaced in the bags and earned to the asbestos opener. Crushers were not enclosed or exhausted in any way, but the general ventila tion in the preparation department was sufficient to prevent high concentrations of dust near this operation. Crusher men bed res- DOST CONTROL IN AN ASBESTOS PLANT RAW MATERIALS RECOVERED MATERIALS 5 NOTE: UNDERLINED PROCESSES HAVE OUST EXHAUST SYSTEMS, fitni 1 TTiti bv^ai uMa taadl* piwi. pirator* * And usually wore them while loading or unloading the crushers. The average exposure of a crusher man tending three crushers was 3.5 M. P. P. C. T. AD plars ta Um prpu*uB 4*c*rtm*et ud tU neuross mt jaaitar* *r* w*Mb4 rmv+ ten * vm tnt4 by U 0. A Bum d Kb ifflaa aaaaaaMaaai d Cat dUm 4as. 6 DUST COKTBOL Df AX 4JMEST0* FUXT bags to the floor bead* the asbestos openers end lifted into the 1*4 lattice hopper with wooden bead forts. Two openart of diSeB design were ia operation, but the method of exhaust hooding vu the same on both. (See schematic design, fig. 2.) The feed lath* hopper vu partially enclosed sod exhausted at the top (hood A). A second hood exhausted the bottom fly aad settled dust from thi bottom of the opener (hood B). The opened fiber was picked up by hood C aad pneumatically transported to a cyclone separator when the fibers were removed and dropped onto an enclosed vibrating sere. A large portion of the dust and fine fibers entering the asbestos opeeer A A n HOfi WPH&JMATIC convey# runt 1 l^mic m atew tyrua pp(M w u mtmtm >pyr was removed by hoods A and 5. Clumps of unopened fibers and pieces of rock too heavy to be lifted by the pneumatic fiber conveyor fell onto an enclosed belt conveyor serving both openers, and were carried to the recovery process. (Belt conveyor is not shown in fig. 2.) Exhaust volumes through the hoods were as follows: Hood A, 400 cfm; hood B, 400 cfm; hood C (pneumatic conveyor), 1,800 cfm; conveyor velocity, 2,730 feet per minute. Each opener had its own cyclone separator aad enclosed aad ex hausted vibrating screen. One screen had two exhaust hoods, one beside the charging hopper drawing 400 cfm aad one over the di*> DOST CONTROL IN A>* ASBESTOS *-ANT 7 I ehvte end of tht scrota tod the flock cat, drawing 770 e/m. The second screen bed one bood only, over the discharge end, drawing 615 i efm. Short fiber* end rock particles passing the screens fell through e chute to the enclosed recovery conveyor. Fiber (siting to pass these screens dropped into e stock car. Full stock can were pushed to * platform scale and then to the mixing beds. . The seme men charged the openers sod filled the stock can. The iverage dust exposure of asbestos-opener operators was 3.6 M 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 16 percent of cotton by weight but as much as 20 percent cotton was used in lower grade yarns. The two-stage Saco-Lowell cotton opener was provided with exhausts at three points; 770 cfm of air were exhausted through a canopy hood over the feed lattice, 270 cfm from the bottom of the primary opener, and 1,120 cfm from the bottom of the secondary opener. Opened cotton fiber was discharged into stock cars. No samples were taken at the cotton openers, but the operators' average exposure was about 2.4 M. P, P- C. F. (general air, preparation department). Mixing. --'Weighed quantities of asbestos end cotton were placed in alternate layers in the miring beds. Occasionally, layers of rov ing waste from the carding room were reopened and added to the bed. Mixing was done in six "exhausted'* booths, each 10 feet 2 inches deep by 6 feet 10 inches wide by 6 feet high. Sides of the booths were permanent, while the back consisted of s removable wood end canvas section. Each booth was covered by a pyramid hood 32 inches high, through which approximately 1,025 cubic feet of air per minute per hood were exhausted. The velocity of air motion into these booths averaged 50 feet per minute during bed making and about 30 feet per minute during picker loading. Dust concentration averaged 6.4 M. P. P. C. F. for the bed-making operation. After a bed had been pieced, the picker operator removed the rear partition of the booth and forked the batch into the charging hopper of a picker (fig. 3). The picker machine mixes the fibers in revolving beaters. The four machines represented three different operations and two different types of exhaust systems. The first machine, not in operation during this study, discharged mixed fiber into a stock car. This 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 of the fourth picker was carried to the carding room by a pneumatic conveyor. Each of the first three machines had a hood over the charging lattice, exhausting approximately 500 cfm, a pipe exhausting about 1,650 cfm from the bottom-Sy settling chamber* g OUST CONTROL K AN ASBESTOS PLANT under the main picker drum, and p hood over the end ot the discharge Uttice exhausting about 400 cfm. The fourth picker had the acme hood arrangement over the charging lattice but had no bottom'd/ exhaust, and the mixed fiber was removed by a pneumatic eoQveyor exhausting approximately 2,000 da of air at a velocity of 2,550 feet per minute. The picker operator! wear respirators during the charg. mg operation. Dust concentrations during picker charging varied from 4.0 to 9.5 M. P. P. C. F., averaging about 6.7 M. P. P. C. F. Recovery process**.--Waste roving from the card room was returned to the preparation department for reopening. The roving reopener was exhausted only from the pit below the last beater, but the 1,780 efm of air drawn through thia hood were sufficient to prevent the escape of dust through the discharge lattice. The dusty air collected by the exhaust systems in the preparation and carding department waa blows into a Urge settling chamber occupying two stories in the end of a separate building. Air was dis placed from this 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 besten down by hand daily during the noon rest period. The collected dust was removed during the week end shut-down, and stored in bins in the preparation depart ment. Bag-house dust was screened on completely enclosed end exhausted vibrating screen (background, fig. 4), and the long fibers were removed to a cyclone collector by a pneumatic oonveyor. The dust from the settling chamber, the long fibers from the bag-house dust, and fibers separated by cyclones on the exhaust lines from the spooling operation and the weaving department were.passed through e fly-willower and vibrating screen (fig. 4). Approximately 250 cfm l of air were exhausted from the top of the charging Uttice sod 620 cfm from the discharge aide of the opening drum. Dirt passing the screen dropped onto an inclined tray and waa removed by an exhaust hood / drawing 730 cfm. Fibers which did not fall through the screen ware removed by the hood at the lower end of the screen (1,710 efm) and pneumatically conveyed to a cyclone collector. Rock and other im I purities not picked up by the pneumatic conveyor fell into a waste box below the end of the screen. The market for recovered fiber is limited, and such 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 was estimated at between 3 and 5 M. P. P. C. F. l I As a measure of the effectiveness of the dust control system in the preparation department, the exhaust fans were shut off for 1-hour. Pneumatic conveyors remained in operation. Dust concentrations increased steadily to about 50 M. P. P. C. F., at which time the ex ( haust fans were turned on. The samples taken during this period l L DOST CONTROL ZN AN ASBESTOS PLANT 9 i were ooly a partial measure of uncontrolled conditions, since the hoods and enclosures bad 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 approrimately 320,000 cubic feet of space, from which ap proximately 34,650 cfm of air were exhausted. Consequently 6.5 air changes per hour were produced by mechanical ventilation, which was supplemented by natural ventilation through doors, windows, and roof ventilators. Fortunately heating mas not a problem in this plant. CABDIKG DCP&ftTXCKT Mixed fiber from the preparation department was dropped from pneumstic or mechanical conveyors into bins in the carding depart ment. The total volume of exhaust from four bins was 6,850 cfm, the major portion of this sir being drawn through the one or two bin ( doors left open during the loadiog of carding room stock ears. Dust concentrations as high as 40.4 M. P. P. C. F. were measured inside an active bio while the dust concentration just outside the door of the same bin was only 4.6 M. P. P. C. F. Workers, classed as stock i rollers, fork the mixed fiber from the bin into stock cars. This opera tion 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. However, stock rollers, wearing respirators, like to push their can undey the chute and then climb into the ear and "tread-down" the Stock. : The cards are machines having a series of revolving cylinders wound diagonally with strips of leather set with fine, sharp, steel bristles. Carding removes remaining small bits of rock and combs the fibers into a more or leas parallel condition to facilitate spinning. At the time of this study, 31 roving card units and 2 wiclring cards were being operated. A roving card unit (fig. 5) consisted of two cards, a breaker, or primary card, and a finisher or roving card. The mixed fiber was fed by hand from the stock car to the feed u hopper of the breaker card. The stock roller wore a respirator during this operation. The fiber passed through the breaker card, emerging as a loose blanket or web. It was carried to the finishing card by a lattice cooveyor 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 condensed it into loose rovings of unspun yarn. These rovings are wound on long "jack" spools to be taken to the spinning department. The rovings at the extreme ends of the cards cannot be used for spinning because they lack uniform thickness. These rovings are collected by two small hoods and pneumatically conveyed to a collection bio for return to the preparation department. 10 DCST CONTROL IS .kS ASBESTOS PLANT The exhaust sysUm applied to roving cards is shown schematically is figure 7. The quantity of air exhausted varied from 1,100 efm to 1.S00 efm oo different carding units with an average exhaust of 1,440 efm per unit. Cards are partially enclosed and only sufficient air is exhausted to prevent the escape of dust. Each breaker card is exhausted at three points. Hood B 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 elm of air were exhausted through the hood. Hood A exhausted the top fij from the enclosure covering the main carding cylinder. Hood CAMtL'MMtt COMvt ro* 11 i I r il! 11UI i 1H11 l-H1^ H i 11 If ITITTTTTTT 7 t>li o' wrd <i5uk ifmra C exhausted the bottom fy from the settling chtmber under the carding rriinder^. Approximately dm were exhausted through each of these hoods. The finishing card had four exhaust connections besides the two small hoods G which removed the waste roving. Hoods E and F correspond to hoods A and C, respectively, on the breaker card, providing ax exhaust of approximately 2S5 efm each. The doffer card cylinder, doffer combs, and roving apron were exhausted from below, through hoods D' and D* at 70 efm each. About 40 efm were exhausted through each roving collector. V DOST CONTROL IN AN ASBESTOS PLANT H i The volumes of air exhausted through each hood ware estimated oo the basis of pipe areaa. Actual volumes showed wide variations oo different unite. f Single cards were used in the manufacture of asbestos wick and** rope, since a thick roving waa desired. The wick or rope was twisted from the unspun roving. The wicldog cards were exhausted at three points. Approximately 380 cfm of air were drawn from under the feed lattice, 490 cfm were 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 aversged 1.7 M. 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 showed less than 0.5 M. P. P. C. F. Card rolls were cleaned and ground at night, except in eases of emergency. Cleaning was done with hand scrapers made of strips of card cloth, and the card cylinder was turned by band. Grinding waa done with the usual type of card grinders. The large roll waa ground in place in. the carding machine. Slightly greater quantities of air were exhausted during grinding due to the decreased loss of bead resulting from removal of the wooden card covers. The small card cylinders were ground in a grinding frame. These frames were partially enclosed and covered with a canopy hood exhausting 2,330 cfm per grinder. Dust concentrations averaged 0.65 M. P. P. C. F. during grinding. A special run of a group of carding machines made with all exhaust i ventilation turned off and windows closed showed that dust concen trations steadily increased. At the end of 1 hour the concentration was 62.4 M. P. P. C. T. in the air. Under normal operating conditions r about 64,000 cfm of air are exhausted from the carding department. i This is equivalent to about 5.5 air changes per hour, disregarding natural ventilation through windows on all four sides of the room. Spinning, twisting, and winding.--The yarn as roving is twisted or 4 spun into compact threads on either mule or ring spinning frames. i In this plant most of the spinning was done on mule spinners. The spun thread was transferred from the spinning spindles to spools, on Foster winding machines (spoolers). Spooled thread to be used as I{ filler (or woof) in woven doth was rewound on a cop winder into cops . which will fit into the loom shuttles. The remaining spooled thread was respooled on twisters which twist several threads into a yam. The number of strands used determined the si2e of yam. Both plain and metallic yams were twisted. Metallic yam cootains one or more strands of fine wire. Part of the twisted yam was used in doth weaving while the remaining yam was rewound oo Universal winding frames for the market. ( t i 12 DOST CONTROL IN AN ASBESTOS PLANT Mule spinning was separated from other operation io this depart ment by partial partitions. Natural ventilation was good and no exhaust systems were used. The average dust concentration waa 0.85 M. P. P. C. F. with a maximum of 1.3 M. P. P. C. F. recorded. Ring spinning, cop winding, and Universal winding machines were located in the same room with the twisting machines. Average ex* posures in the first three operations, which were not 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 not provided with exhaust. The trial system was reported to be satisfactory aod is to be installed on all twisting r rtori* t -*<i,of `tbossr mt*s ppu*d w fmt*r wiflcJn. In this erstetr the bottom of the twisting frame was enclosed and a total of 1,700 cfm of air per machine w*s drawn down ward past the twisting yarns and through five conical hoods distributed along a central exhaust duct. Average dust concentrations st the various operations in this room were ring spinning, 5.0 M. P. P. C. F.; cop winding, 6.9M.P. P. C. F.; Universal winding, 2.8 M. P. P. C. F.; and twisting, 11.0 M. P. P. C. F., with a maximum of 18.8 M. P. P. C. F. recorded beside s twisting frame. No accurate measurements of the efficiency of the exhaust svstem oo the single exhausted twister could be secured, but simultaneous samples on both sides of this frame showed s dust I DUST CONTHOL IN AN ASBESTOS PLANT J3 coocentratioo of 18.0 M. P. P. C. F. on the tide toward the unex hausted twisting frames and a concentration of 6.3 M. P. P. C. F. on tbe otbar aide. Four Foster winders (spoolers) were partially separated from the other operations by partitions (fig. 6). Tbe exhaust system eon* listed of an individual conical hood around each spindle bolder (fig. 8). Approximately 46.5 cfm vert exhausted through each hood, or a total of 9,270 cfm through the 200 hoods on the 4 spooling frames. Dust concentrations at the spoolers averaged 2.9 M. P. P. C. F. and increased to 9.6 M. P. P. C. F. within 30 minutes after tbe ventilation bad bees abut off. WtAVINO AND JNSrtenON Cloth, tape, listing, and brake bends were woven on different types of looms. ln.this pleot, exhaust systems bad bean applied to the dry cloth looms, since these were considered to be tbe most important source of dust. Tbe dust control program calls for installation of exhaust systems oo dry tape, listing, and brake-band looms. At prorut these operations are mainly performed wet or partially wet. F-nU;t"htnd 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 M. P. P. C. F. and avsraged 3.0 M. P. P.C.T. Nineteen cloth looms were in operation in this department One of these was a wet loom not provided with exhaust hoods, 4 were dry luoms provided with exhaust hoods, and the other 14 were ao provided but could be operated either wet'or dry. A loom without exhaust hoods is shown is figure 9. Tbe exhaust system is shown schematically in fir<re '!. A double exhaust hood drew air from under the warp while a second hood was attached to the top of the loom lay with exhaust ducts running down tbe side of each picker arm to an airtight swing joint at tbe bottom. The openings in tbe loom-lay hood consisted of four slot* nine inches long by 1 inch wide extending over a apace of 4 feet across the woveo fabric at right angles to the warp. A total volume of approximately 10,500 cfm of air ws exhausted from the 13 hooded looms. This averaged about 580 cfm per loom; but since it was seldom necessary to operate more than 10 dry looms at one time, the average quantity of sir exhausted was close to 1,000 cfm per loom. Exhaust dampers were provided on ell looms, and a sufficient number to balance tbe system are closed on wet or idle looms. The average dust exposure of a weaver operating a dry loom with exhaust was 0.7 M. P. P. C. F., while the average exposure in wet weaving without exhaust was 2.6 M. P. P. C. F. Samples taken beside a dry loom without exhaust showed dust eooceotmioos of 9.6 M. P. P. C. F. ( l kl I l\ .1 i -jf: fmobs u4 mu mrtt. ftoeit fui viodi&c swtisa (fpeokn>. feUk %hU kpu. Km~ N* MU. PUAT* 111 ( Fiant trwinm K4 \mm. riectt 10.--TW for ioipruac caMadtriac. ud bnudiat *'* data. 1 ) r 14 DOST CONTROL Of AN ASBESTOS PLANT , iftar 45 minutes. ATerage dust concentrations during dzy weaving hare been shown u 49.7 M. ?. P. C. F. (5). Woveo doth u inspected, brushed, sod calendered on the inspectlon tab!* shown in figure 10. Each of the power-driven brushes wet f r partially enclosed and exhausted. Approximately 750 dm of air were drawn through each of the two hoods at the front of the table and i about 200 cfm were drawn through the cleaning hood at the bade of i [ 'nww . i r - I f r i i i ! t. 1 I DOST CONTROL IN AS ASBESTOS PLANT 15 the table. Dust concentrations during inspection averaged 0.5 M. P. P. C. F. A sample taken while a roll of fabric was passedacross the table without beoeht of exhaust showed a dust concentra tion of 11.3 M. P. P. C. F. Doffing, inspection, and calendering of tape and listing were hand operations and were not provided with exhaust. Dust concentrations of 5.0 M. P. P. C. F. were recorded during these operstioos but the exposure was intermittent. CreeJers bad an average exposure of about 1.3 M. P. P. C. F. while placing spools and threading looms. An exhaust of 12,200 cfm of air was provided in the weaving de partment, corresponding to approximately three air changes per hour. In cold weather, warm air was distributed through the department from s plenum system, while in warm waather 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 chemi cally treating or rubberizing fabricated cloth. No potential asbestos hazard was associated with these processes, with the exception of one brsiding machine used to make large diameter ashestoe tubing. This machine was cowered with a eonical canopy hood about 6 feet in diameter, whieh provided an exhaust of approximately 200 cfm of air. A sample taken beside this machine showed e dust concentration of 0.4 M. P. P. C. F. at the operators* breathing level. T*sut 2.--Vtlumm > 'czAaiutW per maekint in eoriew spwetiefw m a IlifBW UfTlt fttfU c c. 1 Eeuipoad ufe paraaafle aoo*?cr--t&rvQfft aoB*jor tm UMo44. tOPsumnabsu. iaa4di. d*Rwjf..oiita:.r puou <). U. C. I. t. S. I.} tspjviduAJ mi tor mes ipistfjt wasaetotf to tift**** miUfold. 16 DOST CONTROL IN AN ASBESTOS PLANT SUMMABT Table 2 gives * summary of tbs operations provided with exhaust listing the number of exhaust duets and the rate of ventilation per macbioe, u well as the average dust concentrations to which operators are exposed. Average dust eoneentratioos measured near corre sponding operations without exhaust are tabulated to show the effec tiveness of the control methods a-hich hare been described. CONCLUSION C This study of actual results secured by a dust control program ia lh asbestos fabricating plant is presented as an example of engineering control of an industrial hazard. Adequate data hare sot yet bees published to justify the determination of threahold limits of dustiness which will produce asbestosis in any definite period of time. In the absence of euch threshold values it is not possible to determine permis sible limits of dustiness os a medical basis. Nevertheless, any appre ciable decrease is the amount of asbestos dust will cause s decrease in the incidence and severity of the resulting asbestosis. The elimina tion of all the dust in as industrial workroom is rarely necessary from a physiological standpoint and usually economically impracticable. Consequently, actual atmospheric conditions in as industry resulting from the application of practical methods of duat control can be used as temporary standards by that industry ($). ureuNcta (I) Riet, B., aad Watson, T. L: Engineering Geology. Joha Wiky aad Seas, lac., KrrVort. IS3?. (*> Fulton, W. B,, Dooley, A., Matthews, J. L-, sad Bouts, R. 1.: Asbestaeis. Part IX: The aature aod* aaouat of dust encountered la asbestos fabricating gUato^ Spot. Bull. No. 42, Pennsylvania Dept, of Laber aad Industry. Sept. (3) Bloomfield. J. J., aod DalleVeils. J. M.: The determination eod control ot iadusthal dust. Pub. Health Bull. No. 21?. Govv Printing OSes, Washington, D. C. 1933. (4) Harding. L. A., aad Willard, A. C.: Beating, ventilation, end air eoadt- tiooittg. John Wiley and Sobs, lac.. New York. 1932. (3) unpublished date. United States Public Health Service. _ (t) Biggins, ., Ltnaa, A J., Laacy, F. B., and Rice, G. 8.: Siliceous dust in relation to pulmonary disease among aineri in the Joplin District, Missouri. Bull. 132, U. S. Bureau of Miocs. 1917. (?) Page R. T.: Note on a ne ocular micrometer for uee in dust counting. Pub. Health R*p,, St: 1323-1316. o ( C