Document NEQ5jGmZO70Y534Ga5d2nOpJy

PLAINTIFF'S EXHIBIT Dust Control Techniques in the Asbestos Industry JOSEPH GOLDFIELD and FREDERICK E. BRANDT Johnj-Manvillt Product! Corporation, Greenwood Plaza, Denver, Colorado S02I7 Aaltcttos fiber I* a remarkable ami mfd material is modern-day Itcfaaologj'. Long exposure and relatively Ud concentration! cause various diseases. Process cban(t*. leaknchl equipment, indotrial esbaost sjrstems aad dust fillers srt used <o control dual esposares la mining aad milling aad auaufaduriog. Examples from asbestos mills, asbutos cement pipe pfaats aad textile operations are given. Belt coovvyoca, vibrating screens, bag opening etatlnar. machine hoods, aad textile cards an dis cussed. Duct design and fitter selection are discussed. Asbestos Fiber ASlIfiSTOS I IHKri IS A REMARKA111.1- MATERIAL. Il is lilerutty u fi brous form of rock. It has the chemical composition of the rock with which it is associated. Table 1 lists some of the physical properties of the three most important types of asbestos fiber as well as those of the more common natural and man-made fibers. The greater surface area and the remark ably small fiber diameters of asbestos fiber are apparent. Two other properties that render asbestos fibers unique are their tem perature resistance and their relative inert ness to some types of chemical attack. Asbestos fibers, although rocklike in chemical composition, are flexible enough to be spun into yarns and woven into cloths with heat stability known to the ancient Egyptians and Greeks. Of the three forms of asbestoj listed in the table, chrysolite is the most valuable economically in the United Slates, where it represents 95% of the over 800,000 tons of asbestos fiber used annually. In Quebec, Canada, where most of the fiber imported into the United States is mined, the asbestos is graded by numbers from 1 through 7. Group 7 represents the shortest fiber lengths and the lowest price; both length and cost increase with each group to group 3, which is suitable for spinning into yarn. Groups 1 and 2 are hand-cobbed fibers, produced in such small quantity as to have small eco nomic importance. Health Hazards The first reports of bcstos-related dis ease were described as c. rty as 1907. How ever, it was noi till 1930, when Merewether and Price published an epidemiological study TABLE! Properties of Asbestos Fibert Compared with those of Organic Fibers Type Chrysotile Crocidolite Amosite Common natural and man-made fibers Cotton. Color White Blue Yellowish brown Surface Area (sq cm/gm) 130,000-220,000 _ -- 3,000- 10.000 Fiber Tensile Strength Diameter (P>i) (*m) 80.000 -100,000 0.02 100,000 -300.000 0.03 16,000*- 90,000 0.03 80,000* 10-20 799 ST000822I 1 American Industrial Bjfisna Association Journal Elements of Dost Control The methods used in the asbestos indus try for the control of asbestos are the classi cal mrtl>n<fa used by dust control engineers in all industry: 1. Enclose any dust source as fully as possible. 2. Place all dust-producing equipment un der negative pressure by connecting to ex haust ventilation of adequate capacity. 3. Design and install a properly designed duct system. 4. Filter the dust-laden air adequately. 5. Move the air with fans of the proper types, having adequate volume and pressure capabilities. 6. Where normal principles of dust con trol are difficult or expensive to apply, proc ess changes must be considered. Describing how all the principles of dust o ' rot arc applied to the field of asbestos mining and manufacturing is a massive job beyond the scope of one paper. Examples illustrating the principles given above will be described. Some of the methods arc unusual and may be fruitfully applied to other industries. Mining The two most widely used pieces of equipment in asbestos mills arc troughing belt conveyors and vibrating screens. In early milling operations, before about twen ty years ago, these pieces of equipment were not covered to prevent dust generation in the mills. The dust problems caused by belt con veyors are as follows: Ml dust contamination in asbestos mills. Dust carried on the bottom of the return belt is engraved on every idler carrying the return belt. Each idler becomes a source of dust generation. Conveyor Eadosnm Figure 1 shows an enclosure that is often used to enclose the top portioa of a trough ing conveyor. It is particularly used at the location of chutes feeding either from one belt to another or from other equipment onto the troughing conveyor. This enclosure nor mally has a sheet metal section that encloses the belt on three sides. Rubber skirting on the two vertical sides bean againtt the sur face of the belt. This skirting is adequate to prevent dusting from the material that rides on the belt. Of course, the belt width and the speed of the belt miut be adequate to carry the material load within the skirt boards: otherwise the value of the skirting is negated by material forcing its way un der the rubber skirting and out of the con veyor enclosure. Chutes feeding the conveyor should feed axially onto the belt. The material should not be forced against the skirting. If possi ble, the chute should also be arranged so that a rock box may be placed at the base 1. Dry materials carried on the belt con veyor, at high speed, generate dust in the mUI. 2. Chutes feeding cither from one belt to another, or from other equipment onto the belt, generate dust. _ 3. The return belt is a serious source of Figure t. Conveyor belt endonire. f'T J fin rtn i % UJ ) j-9 American Industrial ftyfitn* Association Journal finished products. Literally miles of chutes curry the material in process. 'Htc design of the chutes is critkul in determining the cleanliness of un asbestos mill. First and foremost, they must be designed to carry the required quantities without plugging. This specification requires that the chutes be adequate in cross section and be run at angles that cause material flow and minimize hang-ups. Long, straight drops must be avoided because a change of direc tion at the base of such a run will cause plugging or will pump large quantities of dust-laden air that will contaminate the mill. Finally, the chutes must be free of leaks yet allow ready access in case of blockage. Access doors and poke holes must be pro vided but must be leak-tight in initial con struction and remain so in use. Where only asbestos fiber is handled, chutes may be of 10-gaugc, all-welded steel, on the bottom und sides. The top cover c;m be even lighter gauge. However, the seams must be leak-tight. Coth tape may be used for this purpose. Where ore-containing rocks must be han dled in chutes, they may be 3/16-inch or Vi-inch plate bolted and gasketed. For aimstvs rasa Figure 4. Ashes.in fiber hiifop-'ninf dalion. M3 abrasion resistance, Ni-Hard linen may be tfuired, since dust leakage may be due to htk' worn in iltc chute*, a* well us other leaks. Packers Most of the mill operations in the separa tion, grading, and mixing of asbestos fibers are done without human aid. However, the packing of the finished fiber used to be a manual operation. The pressure packer, de veloped hy Johns-Manville, elimina ed moat of the human handling. The fiber it weighed, compressed, and forced into a paper bag for shipment with a minimum of human ef fort Manufacturing Most manufacturing operations receive pressure-packed bap of asbestos fiber in 100-pound hap that are palletized and shipped in boxcars. Dust control starts with the unloading operation of the boxcar. Care in shipment and unloading is required to eliminate bag breakage and contamination of the boxcar. Dirty bap should be repaired and vacuum cleaned before storage in ware house areas. The pressure-packed bap are brought to manufacturing areas and opened in bag opening stations, as shown in Figure 4. The pressure-packed bag must be put in the bagopening stations before the paper bag is slit. An in-draft of approximately 200 feet per minute is maintained in this station by the dust pipe. The fiber cake may be fed into an open ing machine or into the boot of an elevator. The opened bag may be charged into a clean hag, a shredder, or a large (16-inchdiameter) bag-conveying pipe. Machine* may be necessary to break up the pressurepacked cake so that it can be handled in the manufacturing process. This machine may feed into a large ventilated opening such os the boot of an elevator, or into a lowpressure pneumatic conveying system which controls the windage from the machine. ; ST0008225 > 1 Amerkm Industrial Bygkmt Association loamai The organic Up is fed in the form of rolls into the card, Avoiding the diffkHt problem of conveying blends containing organic fi ber to the feed box at a card machine. Scraper conveyors, installed below the card, carry accumulations of asbestos fiber blend back into the card operation. Wetting In mining operations, particularly in ore processing and crashing, wet ore "'uses much less of a dust problem than dry ore. This observation has been applied to manu facturing. In textile manufacturing, wetting the yarn reduces dust generated in twisting and in weaving. Wet cutting and fiber opening have been applied to reduce the dust generated in man ufacturing operations. Exfeanst Ventilation Equipment that handles asbestos fiber must be designed as leak-tight as possible. This includes bins, elevators, conveyor en closures, screen coven, screw conveyors, chutes, and conveying ducts. However, it is impractical to design equipment that is leaktight at installation and from then until the end of the useful life of the equipment. Ex haust connections are therefore installed to maintain all leaks and openings under nega tive pressure so that room air may leak into the asbestos system instead of dust leaking out The number of variables affecting the amount of air to be exhausted is so great that only experience can indicate the amount of exhaust to be applied to each of the dust producers in the industry. However, the principle is an important one. It is desir able to maintain all parts of asbestos control systems under negative pressure. It is more desirable to carry air under negative pres sure then to pressurize an asbestos dust system. Dwe* Design Velocities Ducts sre designed to carry air at veloci- M5 ties ranging from 3000 to 3500 feet per minute to 5000 to 5500 feet per minute. The lower velocities are used for dust control ducts where relatively small concentrations -* well-opened fiber must be carried, such as the dust control systems at textile plants. The highest velocities are used where space is restricted and where large chunks of ma terial must be carried, as in dust systems for the machines that cut and shape Transits pipe. Most systems, including low-pressure pneumatic conveying systems, function well at duct velocities of 4000 to 4500 feet per minute. Dust Risers In multistoried asbestos mills, e practice has developed where vertical risen that have no carrying velocity are installed. The main value of these risers is to allow flexibility in the mill. Duct connections may be added in future years with no concern for settlement or overloading the riser. At the base of the riser, a rotary valve must be installed to remove settled material. Materials oj Construction Ducts are generally built of sheet steel, black or galvanized. Table 11 shows the sheet metal gauges commonly used for most duct sizes. These gauges are suitable for most average-duty dust systems. For heav ier duty and more abrasion resistance, el bows may be . tade of 14-gauge welded con struction. They may be square, with a removable back plate, sometimes protected by suitable rubber linings. Since ducts are generally round for dust TABLE H Sheet Metal Cause* Tor Duct Handling Aibeatoa Fiber biTimeier"Straight Duct U.S. Standard Gauge Steel Duct 41 II 20- JO It--to 41 k over 20 U 1C 14 14 \ ST0008227 Amrrkm Miutrial Hytto* Am*l*km Jmnal will dictate the use 0/ various synthetics de spite reduced efficiency. High-energy scrubbers are used today only when moisture problems preclude the use o( fabric filters. There are few examples of such applications. Scrubbers may be come somewhat mote prevalent, but it is not believed that they will be competitive with fabric filters. There are few instances of electrostatic precipitators in the asbestos field. In gen eral, small electrosyuic precipitators are much more expensive than fabric filters. In the old Johns-Manville Jeffrey Mills, there was a high-voltage electrostatic precipi tator that filtered about 1,400,000 cfm. Its efficiency was poor, about 70%. At present, a fabric filter is filtering about 5,000,000 cfm. Ita efficiency exceeds 99.99%. In addition to numerous small filters, there is one on the ore dryers filtering 700,000 cfm, and a normal ambient temperature filter filtering 600,000 cfm. Pans and Fan Systems It is certainly preferable to operate fan systems that control asbestos fiber dust so that the entire system is under negative pressure. All leaks would, therefore, leak room air into the system instead of leaking dust out. In that event, die system fans are located on the dean-air side of filters. Fans used in that location may be air-foil biaded or backwardly curved fans to save power. In sma" systems, material-handling fans with *W wheels are also used. In some instances, where it is desirable to aimplify syitemi or to reduce costs, filters have been operated under positive pressure with fans handling duat-laden air. Fana in that location are radial-wheel, material-han dling fans. Of course, the system following the fan, and the fan itself, must be com pletely leak-tight Vacsua Cleaning Systems Regulations recently promulgated prohibit the use of brooms and compressd air to M? clean dust off equipment in plants and mines that use or manufacture ubeatoe fibers. Effective and well-designed vacuum cleaning equipment is required. There are numerous types of portable vacuum cleaning units on the market They range from the great array of units suitable for household use to large, heavy-duty units designed primarily for industrial work. Most of the light-duty units available on the mar ket have no place in industrial plants. 1. Tools and hose must be 1 Vi or 2 inches in diameter. Smaller equipment cleans too slowly. Larger equipment is too unwieldly. 2. The static pressure in the I Vi- or 2inch pipe of a tool connected to a 25-foot length of flexible hose should be 1 to 2 inches of mercury. This pressure should not fall off rapidly with use. 3. The most important single feature of a well-designed vacuum unit is the filter. It should be a fabric filter of sufficient area to maintain good suction at the tools in use. Small single bags and paper filters are in adequate to do a good filtration job. 4. A heavy-duty, multistage centrifugal compressor, powered by a 3- to 7 Vi-horse power motor, can generate the required air flow and pressure to operate a satisfactory machine. 5. The unit must be equipped with a reasonable size dust bucket so that cleaning can go on for adequate periods. Stationary systema have been ur-d in as bestos mines and plants for ma;, years. Piping systems, carefully designed, can bring vacuum cleaning connections to every area of a mill or plant so that men equipped with a 25-foot length of hose and tools can clean everywhere. The central station equipment is similar to that desirable for portable equipment, except that the size and pres sure must be greater. The capacity depends on the number of men who will use the sys tem at any one time. The pressure must be ST0008229 < Johns-Manville Sales Corporation 2600 Campus Onvs San Matso. CA 94403 (415) 349-9500 March 18, 1981 TO: Atl CUSTOMERS Enclosed you will find three (3) articles relating to Health and Asbestos Fihre. We thought you might find these to be of interest. If you have any questions or wish additional copies, please don't hesitate to contact me. Very truly yours, Sandra Black Sr. Customer Service Coordinator Asbestos Fibre Division ST000822 D