TN 295 No. 9148 .0* V **T.T*' A ^cr "oV" «bv* :£mf%&. *W «\^»*- «.** *. ,0* *•"•• ^O ^ o > ■>' .. G^ ^ * (V t • • • . "*b ^* . t '• +* *+ .^VaV >. c^ » 4 ' • ***** •* .vV>"V ^rf V •bv* » • • r. o- 9 ,!/'% %> ^^ +*. j SuFWSX- <*>- J> *j*m&s. r tiu j o^^mPft^ o J*s£fer\ c°*.^^% ^/J^k/^ c ' v^^-y %^\^ v^-\/ ^ •;U:-.^ J*yJM:S*+. ,y^:o%\ V*3a^%^ 'bV' <£%> '.Warn:* ^ v ^ ; m^\vj Bureau of Mines Information Circular/1987 Reducing Dust Exposure of Workers During Bag Stacking in Enclosed Vehicles By Andrew B. Cecala, Anthony Covelli, and Edward D. Thimons UNITED STATES DEPARTMENT OF THE INTERIOR Information Circular 9148 Reducing Dust Exposure of Workers During Bag Stacking in Enclosed Vehicles By Andrew B. Cecala, Anthony Covelli, and Edward D. Thimons UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES David S. Brown, Acting Director Library of Congress Cataloging in Publication Data: Cecala, Andrew B. Reducing dust exposure of workers during bag stacking in enclosed vehicles. (Information circular ; 9148). Supt. of Docs, no.: I 28.27: 9148. 1. Loading and unloading- Safety measures. 2. Dust- Removal. I. Covelli, Anthony. II. Thimons, Edward D. III. Title. IV. Series: Information circular (United States. Bureau of Mines) ; 9148. TN295.U4 [TS180.5] 622 s [699'.00289] 87-600118 CONTENT Page Abstract • 1 Introduction 2 Laboratory-scale testing 3 Laboratory-scale results 5 Field testing 6 Discussion 11 Cost considerations 12 Conclusions 12 Appendix. — Curtain evaluation 13 ILLUSTRATIONS 1. Product leakage from bag valve while on conveyor 2 2. Laboratory test setup 4 3. Fan directions and location used for blowing system tests 5 A. Dust monitoring locations used for field evaluation 7 5. Ventilation system used for test 2 8 6. Ventilation system used for test 3 9 TABLES 1. Average concentration from four sampling locations during laboratory testing 6 2. Dust reductions of field testing exhaust ventilation system 10 A-l. Effect of blowing ventilation system with and without curtain 13 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT cfm cubic foot per minute min minute ft foot mg/m- 5 milligram per cubic meter hp horsepower mm millimeter in inch pet percent lb pound ppm part per million REDUCING DUST EXPOSURE OF WORKERS DURING BAG STACKING IN ENCLOSED VEHICLES By Andrew B. Cecala, 1 Anthony Covelli, 2 and Edward D. Thimons 3 ABSTRACT The Bureau of Mines has evaluated a number of ventilation systems for potential application in lowering the dust exposure of workers who stack bags of mineral product material in enclosed vehicles. Workers who stack these bags in enclosed vehicles usually have the highest dust ex- posure among all workers in processing plants. This is because dust liberated while the vehicle is being loaded has no means of exiting the vehicle or being diluted with fresh air and thus, dust concentrations increase to substantial levels. Laboratory-scale testing was performed in a railcar to compare the effectiveness of a number of different ven- tilation systems in reducing the bag stacker's dust exposure. The most effective system was taken into the field to optimize its performance. The final and recommended system exhausted about 2,000 cfm through 10-ft-long, 12-in-diam fiberglass tubing located 3.5 ft past the slinger at a 6.5-ft height so as to not interfere with the bag stacker's job. A 6-in-diam tube exhausted approxmately 300 cfm at the snake conveyor- slinger transfer point to capture the dust generated there. With this system, dust reductions in and around the bag stacker ranged between 65 and 95 pet when loading both 50- and 100-lb bags of product into rail- cars and trailer trucks. 1 'Mining engineer. ^Mining engineer technician. ■^Supervisory physical scientist. Pittsburgh Research Center, Bureau of Mines, Pittsburgh PA, INTRODUCTION This report describes work the Bureau of Mines performed to determine a cost- effective system for ventilating enclosed vehicles as they exist today. Laborato- ry-scale testing was performed to deter- mine the most effective system. This system was then tested at a mineral pro- cessing plant to optimize the technique in a working environment and to determine its effectiveness in lowering dust con- centrations in enclosed vehicles during loading of bagged mineral product material. Many mineral products are packaged in 50- or 100-lb paper bags. These bags are shipped to the customer on pallets, ei- ther in railcars or trailer trucks. Bags are either loaded by full pallets using a forklift, or directly by workers inside the vehicle, using a snake conveyor. The latter case is discussed in this report. Loading bags directly into enclosed vehi- cles is advantageous because it elimi- nates the forklift and operator. Howev- er, it is disadvantageous from a health standpoint because of the dust exposure to the stackers. With direct loading, the bags travel down a flexible snake conveyor before passing onto a device called a slinger, FIGURE 1.— Product leakage from bag valve while on conveyor. which can be raised and lowered to a convenient height for the workers unload- ing the bags. The stackers then take the bags from the slinger and hand-stack them onto pallets. Except for minor effects owing to out- side wind currents, there is no ventila- tion inside these vehicles. Any dust generated during the conveying and load- ing process remains within the vehicle and builds to substantial levels. This can become a serious health problem. The dust generated during loading can come from a number of different sources; the two main sources are product on the out- side of the bag and leakage from the bag valve. Product on the outside of the bag is due to blowback (dust created as air and product are forced out of the bag as a result of excess pressure release from around the fill nozzle during filling); the "rooster tail" of product from both the fill nozzle and the bag valve during ejection from the filling machine, and product on the conveyor belt. Leakage from the bag valve occurs from movement on the conveyor as the bag travels to the loading area. This leakage can be substantial at conveyor transfer points and during the pallet loading process (fig. 1). LABORATORY-SCALE TESTING Laboratory-scale testing was performed to compare the effectiveness of a number of different ventilation systems in re- ducing the bag stackers' exposure to dust. Blowing systems, exhausting sys- tems, and a combination of both (push- pull systems), were tried to determine their effectiveness at drawing the dust away from the bag stacker and out of the vehicle. Since the time needed to set and maintain the ventilating system had to be considered so as to not interfere with production, only systems that re- quired minimal maintenance time while loading the vehicle were evaluated. The ventilation system can be set up before each vehicle is loaded with only minimal effects on production, whereas a system which requires changes or maintenance during loading has a direct effect on production. An actual railcar was used to perform the laboratory-scale testing. The car was 50 ft long, 9.5 ft wide, and 11 ft high (fig. 2). Wood framing covered with brattice cloth was used to simulate a full pallet of bags. On the front edge of each pallet, a small controlled quantity of tracer gas was released to simulate dust then mixed by a small fan located in front of the simulated pal- lets. Four sampling locations were es- tablished in and around the bag stacker's work position. To compare the various techniques, gas concentrations at the sampling points were analyzed with hydro- carbon analyzers. The methane tracer gas was allowed to build to a predetermined concentration of 1,000 ppm. After reach- ing this concentration, the ventilation system was turned on. The effectiveness of each technique was based on the gas dissipation rate and the baseline con- centration, which average concentration after stabilization using the system be- ing evaluated. This analysis was not a quantitative analysis that predicted an- ticipated dust reductions in an actual work situation, but was a comparison of the effectiveness of one system versus another. A number of fan directions and fan-size variations were tested with the different techniques. For the blowing system, air from the fan was directed to either the upper left, center, or right portion of SIDE VIEW KEY • Sampling location ACH4 release points Simulated pallets TOP VIEW Door FIGURE 2.— Laboratory test setup. the back panel of the car (fig. 3). The outlet was located either at raid-height or high in the car. In tests of the ex- haust system, the inlet location was varied from on the bottom or halfway up the car. In both cases, the system was located on the door side of the car so as not to interfere with the snake conveyor. The blowing and exhaust (push-pull) ven- tilating system, incorporated the blowing system located high in the car and the exhaust system located on the floor, with both on the door side of the car. Two different fan sizes were evaluated. The first fan had a flow rate of approxi- mately 2,100 cfm, which represents one air change per min in the half of the railcar being loaded with material. The other fan had a flow rate of approximate- ly 700 cfm, which represents one air change every 3 min. One technique that was tried was to use a curtain to block off the half of the railcar that was not being loaded in con- junction with a blowing system (fig. 3). This work is described in the appendix. SIDE VIEW Curtain (used only for tests described in the appendix) TOP VIEW ^Right Center Left Door —Curtain line FIGURE 3.— Fan directions and location used for blowing system tests. LABORATORY-SCALE RESULTS The laboratory test results were used only to compare the different systems. Originally, the areas of interest were to be the dissipation of gas once the ex- haust system was turned on and the base- line concentration. However, there was no substantial difference in the dissipa- tion of gas or the decay rate from one system to another, so the baseline gas levels were used as the primary evaluation in comparing the systems. The effectiveness of the different ventila- tion systems decreased in the following order: 1. Exhaust system over snake conveyor. 2. Exhaust system on floor near pallets. 3. Blowing and exhaust system (push- pull system). TABLE 1. - Average concentration from four sampling locations during laboratory testing Ranking System type Fan position Av cone at sample loca- tions, ppm 95. 110. 127. 5 295. 310. 315. 341. 3 345. 372. 5 386. 7 427. 5 437. 5 450. 510. 532. 5 612. 5 665. 685. 707. 5 1,000. ■L. • • • • • o» • • • • 4 5 6 /•••••' 8 9 10.... 11.... 12.... 13 14 15. 16. 17...., 18...., 19 20...., Exhaust. . • • do* • • • • • • do* • • • • • • d o • • • • • Blowing. . Push-pull • • QO» • • • • Blowing. . ••do* • • • • Exhaust. . Blowing. . • • do* • • • • • • do* • • • • Exhaust. . Blowing. . Exhaust. . . .do Exhaust. . Blowing. . Exhaust. . Center, 6-f t height, even with pallet. Center, 7-f t height, even with pallet Center, 7-ft height, 8-in back from pallet Floor, right, 12-in from pallet Roof, center Blower high, left, Exhaust floor, left, 2, 100-cfm Blower high, left, Exhaust floor, left, 700-cf m. . Roof, left Middle, left Floor, left, 12-in from pallet High, right High, left Middle, center Floor, left, 8 ft from door High, center Center, 6-ft height, 8 ft from door Floor, left, 4 ft from door Floor, right, 8 ft from door High, left, 700-cf m blower Floor, right, 4 ft from door 4. Blowing system off back roof. 5. Blowing system (high or mid-height; left, center, or right). 6. Exhaust system near door (floor). The average baseline concentrations at the different sampling locations are shown in table 1 for each system eval- uated, listed in order of decreasing effectiveness. The exhaust system over the snake con- veyor, (at the center of the car) was identified as the most effective tech- nique and was therefore selected for fur- ther study. The methane release point was moved to the top of the pallets to represent dust coming from all over the pallet. To determine the effectiveness of pulling dust up and away from the bag stacker, the exhaust ventilation port was moved from being immediately above the front edge to 18 and 36 in past the front edge of the pallets. The capture effi- ciency increased with distance from slinger. Since the pallet base dimension is approximately 48 in square; 36 in was thought to be the greatest distance pos- sible, in order to maintain the necessary clearance from the back wall on the first pallet. FIELD TESTING The effectiveness of the exhaust venti- lation system located over the snake con- veyor was evaluated in an actual working environment at a mineral processing plant. An exhaust system was fabricated and installed over the snake conveyor and slinger. At this plant, both railcars and trailer trucks were loaded from the snake conveyor. To optimize the technique in the actual work environment, both types of vehicles (railcars and trailer trucks) were monitored for dust concentrations at various locations, with and without the ventilation system. The RAM-1 real-time aerosol dust monitors, built by GCA Corp., 4 Cambridge, MA, were used to evaluate respirable dust levels at var- ious locations during loading of the en- closed vehicles. The monitors use a light-scattering device to measure the dust concentration of a sample drawn in from the environment through a 10-mm cyclone. 5 Dust was monitored at four locations inside the enclosed vehicles (fig. 4): Location 1 — On the lapel of the bag stacker (to give a direct reading of per- sonal dust exposure while stacking bags onto pallets). Location 2 — At the right side of the end of the slinger. This was the bag valve side. This location gave a direct reading of dust levels where the stacker catches the bags. Location 3 — At the transfer point be- tween the snake conveyor and the slinger. Location 4 — Over the snake conveyor, approximately 8 ft back from the con- veyor-slinger transfer point. This loca- tion gave a measurement of the dust buildup inside the main portion of the enclosed vehicle. The signal from the RAM-1 dust monitor was fed directly into a strip-chart ^Reference to a specific manufacturer does not imply endorsement by the Bureau of Mines . ^Williams, K. L., and R. J. Timko. Performance Evaluation of a Real-Time Aerosol Monitor. BuMines IC 8968, 1984, 20 pp. recorder as a function of time, which provides the notation of the starting and finishing times. Any downtime associated with loading the vehicle was also noted and excluded from the dust calculations. Dust concentrations for each vehicle were calculated* A planimeter was used to calculate the area under the curve, which was then divided by the sampling time. This yielded dust concentration values in milligrams per cubic meter. The following factors were taken into account in comparing loading using the ventilation system with the conventional loading process (with no ventilation): Vehicle type (railcar or trailer truck). Bag size (50- or 100-lb). Product size (290 or 390 mesh). Comparisons are only made among tests for which these factors are identical. Three variations of the exhaust venti- lation system on the snake conveyor were evaluated, in each case for a 1-week per- iod. In each case, a 2, 100-cfm fan lo- cated outside of the vehicle was used. Flexible tubing was attached to the fan and extended to the snake conveyor sling- er transfer point. The systems differed as follows: Test 1: The flexible tubing was con- nected to a section of 10-ft-long, 12-in-diam rigid fiberglass tubing that extended past the end of the slinger by Snake conveyor FIGURE 4.— Dust monitoring locations used for field evaluation. FIGURE 5.— Ventilation system used for test 2. approximately 3. 5 ft. The bottom of the tubing was 6. 5 ft above the floor, which allowed the bag stackers to perform their job without interference. Test 2: The flexible tubing was con- nected to a special transition composed of two 8-in-diam outlets (main exhaust) and one 6-in-diam outlet (transfer point exhaust). The two 8-in lines ran under the slinger, on either side of the dis- charge. The 6-in line was extended to the bag valve side of the snake conveyor- slinger transfer point to capture the dust generated at this point (fig. 5). Test 3: As in test 1, the flexible tubing was connected to 12-in diam rigid fiberglass tubing that extended up and out past the bag slinger. Six-inch-diam- eter tubing was extended to the bag valve side of the snake conveyor-s linger trans- fer point, as in test 2 (fig. 6). Every enclosed vehicle loaded during the test period was monitored, although there was no control with respect to the vehicle type, mesh size, or bag type; these were based on customers' orders. The first vehicle was monitored without a ventilation system. When a vehicle was ready to be loaded with an identical load, the exhaust ventilation system was installed. FIGURE 6.— Ventilation system used for test 3. 10 Table 2 gives the average respirable dust concentration with the system off and on at the various sample locations, and the percent dust reduction for load- ing an entire vehicle. The values were measured only during actual work periods, and therefore they were higher than nor- mal for a worker's eight hour exposure level, that includes break periods and times when the system is not operating. TABLE 2. - Dust reductions of field testing exhaust ventilation system Vehicle and product size Monitoring location Dust cone, mg/m 3 Off On Reduction in dust cone pet TEST 1 Railcars 290 mesh, 100-lb bags. Trailers 290 mesh, 100-lb bags. 390 mesh, 100-lb bags. 390 mesh, 50-lb bags.. Railcars 390 mesh, 100-lb bags. Trailers 290 mesh, 100-lb bags. Stacker Slinger Conveyor. Stacker Slinger Stacker Slinger Conveyor. . . . . Stacker Slinger TEST 2 Stacker Slinger Transfer Stacker Slinger Transfer Conveyor Stacker Slinger Transfer Conveyor TEST 3 Stacker Slinger Transfer Conveyor Stacker Slinger Transfer Conveyor 2.47 1.38 2.40 2.04 2.08 1.51 1.69 1.52 1.53 1.48 68.4 63.8 88.3 63.2 71.2 49.0 63.9 84.2 1.9 ■148.6 390 mesh, 100-lb bags. 3.54 1.50 1.61 3.49 2.64 1.82 1.64 1.66 1.48 1.17 .94 1.46 1.07 .82 1.61 1.10 .71 1.07 1.33 1.07 .52 .61 58.8 28.7 49.1 53.9 58.3 61.0 34.8 19.9 27.7 55.6 35.1 Trailers 390 mesh, 100-lb bags. 390 mesh, 50-lb bags. 1.76 1.38 2.07 2.80 4.02 4.04 6.58 4.28 0.34 .45 .43 .42 1.38 1.42 .76 .24 80.7 67.4 79.2 85.0 65.7 64.9 88.5 94.4 11 DISCUSSION The intent of the laboratory-scale testing was to establish conditions that would be representative of actual field conditions and select the most effective system for field testing. The factor that was not simulated during laboratory- scale testing, but which proved to be significant during the field evaluation was the dust emitted from the bag valve at the snake conveyor-slinger transfer point. Any dust that was emitted at this point was drawn over the stacker to the exhaust ventilation inlet in front of the stacker (test 1). This can be seen from the railcar (290-mesh, 100-lb bag) and trailer truck (390-mesh, 100-lb bag) re- sults. The dust reduction at the stacker and slinger locations was not nearly as good as the dust reduction at the convey- or location. Since the conveyor sample location was behind the transfer point dust source, it was not affected. The amount of dust liberated at the snake conveyor-slinger transfer location increased with the 50-lb bags. The 50-lb bag results in test 1 showed no dust re- duction at the stacker location and an increase in dust at the slinger location. The increase in dust measured at the slinger location can be attributed to the fact that the dust generated at this transfer location flowed directly over the slinger monitor as it was drawn to the exhaust ventilation system. Because of the dust at the bag valve side of the snake conveyor-slinger trans- fer point, a small exhaust port was ex- tended to this location in test 2. The two 8-in-diam main exhaust lines were routed under the slinger because this would have been a more advantageous per- manent location for the system. Visual observations and actual dust measurements both showed the small transfer point ex- haust port to be effective in capturing the dust, with an average reduction of 55 pet. The main exhaust was not as ef- fective as in the first system because the inlet underneath the slinger was not powerful enough to pull the dust from the pallet stacking location along the floor and away from the bag stacker position. The final and recommended design (test 3) incorporated the exhaust system ex- tended over the pallets to capture the dust generated during bag loading. Vis- ual observation showed that this system was very effective in capturing the dust that rose above the pallets during the stacking process. The small transfer point exhaust port was also used because it was effective at capturing the dust generated from the bag valve, which was shown to be a substantial dust contribu- tor in test No. 1. The dust reductions achieved with this final version ranged from 65 to 95 pet at all sampling loca- tions. These reductions are substantial, considering that a 2, 100-cfm fan was used, which changed half the air in the railcar and trailer truck in 1 min. It is obvious that the use of a larger fan would increase the efficiency of the sys- tem. However, the added efficiency would have to be weighed against the accompany- ing increase in capital and operating costs. It is anticipated that a mineral pro- cessing plant, that installs a system similar to the one recommended here, as a permanent dust control technique, would run the exhaust into a baghouse dust col- lector. The only constraint on the sys- tem would be size of the tubing to be located under or over the snake conveyor. 12 COST CONSIDERATIONS The evaluated exhaust ventilation sys- dust pulled from the vehicles, some type tem required minimal capital and operat- of filtration system might be necessary, ing costs. The approximate cost of the About 8 worker hours were required to set system was as follows: up the system. It required from 5 to 10 min to install 2,200-cfm vane axial fan, 5-hp the exhaust ventilation system into each motor $2,200 enclosed vehicle before loading could be- 60 ft of 12-in-diam flexible gin during the field evaluations. Since tubing 450 there is always a down time between the 10-ft length of 12-in loading of each vehicle, this did not af- fiberglass tubing 80 feet production. As the vehicle was Bracket to attach to snake loaded and the snake conveyor was con- conveyor 200 tinually backed out of the vehicle, Additional minor supplies 100 brackets and tubing were removed from on Total 3,030 top of the snake conveyor to avoid a clearance problem with the mill building. The only operating cost was the power For actual use in a plant, a more perma- needed for the 5-hp motor necessary to nent installation could be developed. It drive the fan. If the system is used in did not appear in the Bureau's interest conjunction with a baghouse system, the to pursue a more permanent installation incremental cost to operate the baghouse or a deployment system since every plant would also have to be considered. If a would require its own design, baghouse is not available to filter the CONCLUSIONS The exhaust ventilation system de- scribed in this report effectively lowers respirable dust concentrations when bags of product material are loaded directly into enclosed vehicles by workers. The final and recommended design exhausts about 2,000 cfm through a 12-in-diam tube located 3.5 ft in front of the slinger at a height of 6.5 ft. A small exhaust tube is used at the bag valve side of the snake conveyor-slinger transfer point to capture the dust generated at this loca- tion. When this system was used during loading, respirable dust reductions ranged from 65 to 95 pet in both railcars and trailer trucks. The system involves minimal equipment, installation, and op- erating costs, and can be modified by mineral processing plants for permanent installation at individual operations. APPENDIX. — CURTAIN EVALUATION 13 The technique of using a curtain ar- rangement to block off the half of a railcar that was not being loaded was evaluated. A brattice mining cloth was attached to two 5-ft-long pieces of 2- by 4-in lumber. Using extender poles to secure the 2 by 4's to the ceiling, a simple and effective curtain barrier was installed in a matter of minutes. The curtain was designed to improve ventila- tion by preventing the airflow from traveling back into the half of the car that was not being loaded. A barrier curtain would only be applicable with blowing ventilation systems when loading railcars. Tests were performed comparing the effectiveness of different blowing ventilation systems with and without the curtain. The results showed that use of the curtain barriers produced no measur- able difference in methane tracer gas concentrations. Table A-l shows the average methane tracer gas concentration for the four sampling positions and the percent reduction in methane tracer gas levels with the curtain in place. There was a 4-pct increase in the gas concen- tration measured at the stacker location with the curtain in place when the re- sults were averaged together, but it is believed that this increase was due mainly to sampling error. TABLE A-l. - Effect of blowing ventilation system with and without curtain Fan position and curtain Av cone, ppm Change, pet High, left: 437.5 585.0 532.5 492.5 427.5 377.5 372.5 397.5 450.0 451.3 With -33. 7 High, center: With 7.5 High, right: With 11. 7 Middle, left: With -6. 7 Middle, center: -.3 U.S. GOVERNMENT PRINTING OFFICE: 1 987 - 605-01 2 60087 INT.-BU.0F MINES,PGH.,PA. 28538 &1& tf> U.S. Department of the Interior Bureau of Mines— Prod, and Distr. Cochrans Mill Road P.O. Box 18070 Pittsburgh, Pa. 15236 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE 1300 j J Do not wi sh to recei ve thi s material, please remove from your mailing list. C^2 Address change* Please correct as indicated* AN EQUAL OPPORTUNITY EMPLOYER '^cr ^O* *>U.

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