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 No. 9173 
 
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Bureau of Mines Information Circular/1988 
 
 Investigation of Dust Sources and Control 
 Technology for Longwall Plow Operations 
 
 By John J. McClelland and Robert A. Jankowski 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 9173 
 
 Investigation of Dust Sources and Control 
 Technology for Longwall Plow Operations 
 
 By John J. McClelland and Robert A. Jankowski 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 
 David S. Brown, Acting Director 
 
TUaqs 
 i 
 
 73 
 
 Library of Congress Cataloging in Publication Data: 
 
 McClelland, John J. 
 
 
 
 
 Investigation of dust sources 
 
 and control technology for longwall plow 
 
 operations. 
 
 
 
 
 (Bureau of Mines information circular 
 
 ; 9173) 
 
 
 
 Bibliography: p. 10 
 
 
 
 
 Supt. of Docs, no.: I 28.27: 9173. 
 
 
 
 
 1. Mine dusts. 2. Longwall mining. I 
 
 Jankowski, Robert A. II. Title. 
 
 III. Series: Infor- 
 
 mation circular (United States. Bureau of Mines) 
 
 ; 9173. 
 
 
 -?N39&.e4- [TN312] 
 
 
 622 s [622 '.8] 
 
 87-600333 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Test setup 3 
 
 In situ conditions 3 
 
 Sampling strategy 4 
 
 Survey Results 5 
 
 Discussion 7 
 
 Conclusions 9 
 
 References 10 
 
 ILLUSTRATIONS 
 
 1. Longwall plow face 2 
 
 2. Typical respirable dust sources 5 
 
 3. Instantaneous roof support dust concentrations at mine B 6 
 
 4. Instantaneous dust concentrations by a plow at mine C 6 
 
 5. Enclosed stageloader-crusher with strategic location of water sprays....... 8 
 
 TABLES 
 
 1. Principal operating parameters 3 
 
 2. Gravimetric results 5 
 

 
 UNIT OF MEASURE ABBREVIATIONS USED 
 
 IN THIS REPORT 
 
 
 cfm 
 
 cubic foot per minute 
 
 mg/m 3 
 
 milligram per cubic meter 
 
 
 ft 
 
 foot 
 
 min 
 
 minute 
 
 
 f t/min 
 
 foot per minute 
 
 pet 
 
 percent 
 
 
 gpm 
 
 gallon per minute 
 
 psi 
 
 pound per square inch 
 
 
 h 
 
 hour 
 
 s 
 
 second 
 
 
 in 
 
 inch 
 
 
 
INVESTIGATION OF DUST SOURCES AND CONTROL TECHNOLOGY FOR 
 
 LONGWALL PLOW OPERATIONS 
 
 By John J. McClelland 1 and Robert A. Jankowski 2 
 
 ABSTRACT 
 
 The Bureau of Mines conducted a study of longwall plow operations to 
 identify dust sources and existing control technology. Three longwalls 
 employing either the high-speed overtaking or conventional method 
 of mining were surveyed. Principal operating parameters and on-site 
 dust control technology at the time of each survey are described. 
 Short-term gravimetric and instantaneous sampling results are discussed 
 in detail. The relationship between longwall dust levels and dust 
 control technology was examined. 
 
 'Mining engineer. 
 Supervisory physical scientist. 
 Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 
INTRODUCTION 
 
 The plow is a continuous mining machine 
 equipped with a static set of cutting 
 bits, positioned at a predetermined depth 
 and height, for mining in both directions 
 along a longwall face. The plow is 
 pulled in either direction by a heavy- 
 duty chain. The broken coal is loaded 
 onto an armored flexible face conveyor 
 which, with the aid of hydraulic rams, 
 holds the plow to the coal face, thereby 
 causing the bits to bite into the coal as 
 they are pulled along it (fig. 1). 
 
 Coal plows were initially developed in 
 the Federal Republic of Germany (FRG) in 
 the 1940' s for mining friable coal seams 
 less than 4.3 ft thick (O. 3 At the 
 present time, they are used on 50 pet of 
 
 ^Underlined numbers in parentheses re- 
 fer to items in the list of references at 
 the end of this report. 
 
 the longwalls in the FRG ( 2_) . The first 
 application of coal plow on a longwall 
 face in the United States was in 1951 at 
 a southern West Virginia coal mine (3_). 
 The growth of plows in the U.S. coal 
 market has been limited by advances in 
 thin-seam shearer technology. Today, 
 plow longwalls represent a small percent- 
 age of U.S. longwalls and are primarily 
 located in the Appalachian coal fields. 
 
 Two mining methods are commonly 
 employed in longwall plow operations: 
 
 (1) the conventional method, which uses a 
 plow speed of less than 125 ft/min, and 
 
 (2) the high-speed overtaking method, 
 which uses a plow speed of more than 300 
 ft/min. With the conventional method, 
 the plow runs more slowly than the con- 
 veyor. This method is usually used in 
 thick-coal seams, where the faster 
 conveyor clears the larger product more 
 
 FIGURE 1 .—Longwall plow face. 
 
easily. With the high-speed overtaking 
 method, the plow travels much faster than 
 the conveyor. This method is generally 
 used for seams less than 42-in thick 
 because of the high output potential. 
 Uniform loading of the face conveyor is 
 achieved by maintaining an optimum speed 
 differential of 2: 1 to 3: 1 between the 
 plow and conveyor (4). 
 
 Plows are generally considered to pro- 
 duce less dust than shearers since the 
 plow's method of attack produces a larger 
 product (5). However, it is also con- 
 sidered more difficult to control these 
 lower dust levels. A variety of control 
 techniques are available to the operator. 
 A sequentially activated spray system 
 mounted on a face conveyor is the most 
 popular and widely employed control tech- 
 nique. Its purpose is to suppress dust 
 in the vicinity of the plow; it does this 
 by operating several groups of water 
 sprays ahead of and behind the plow. 
 Another technique of interest is a hose- 
 handling, plow-mounted water-spray system 
 that has been tried repeatedly, but 
 with only limited success (6). Severe 
 
 operational problems are often en- 
 countered with the trailing water hose. 
 These problems far outweigh the marginal 
 improvements in dust reductions. Water 
 infusion, whereby water is injected into 
 the coal ahead of the face, can be a 
 beneficial supplement to existing conven- 
 tional dust control methods (7). How- 
 ever, costs and coal seam infusibility 
 often dictate whether it is a viable 
 option. 
 
 The Bureau of Mines began investigating 
 plow operations when a longwall census 
 indicated that average respirable dust 
 levels for the designated occupations 
 exceeded the 2.0-mg/m dust standard. In 
 addition, a background literature search 
 revealed that virtually no work has been 
 done on plow operations in recent years. 
 
 This report presents the results of 
 three underground studies of both high- 
 speed overtaking and conventional plow 
 operations. The purpose of each survey 
 was to identify and report on dust 
 sources and existing longwall control 
 technology. 
 
 TEST SETUP 
 
 IN SITU CONDITIONS 
 
 Three mines were surveyed to identify 
 dust sources and control technology on 
 
 conventional and high-speed overtaking 
 plow operations. The principal operating 
 parameters for the mines surveyed are 
 shown in table 1. 
 
 TABLE 1. - Principal operating parameters 
 
 Operating parameters 
 
 Plowing method 
 
 Plow speed ft/min. 
 
 Conveyor speed. .. .ft/min. 
 
 Depth of cut in. 
 
 Seam 
 
 Seam height in. 
 
 Face length f t . 
 
 Overburden f t . 
 
 Moisture content pet . 
 
 Water infused 
 
 Hardgrove index 
 
 Average face air 
 
 velocity ft/min. 
 
 Roof composition 
 
 Floor composition 
 
 Mine A 
 
 Conventional 
 
 132 
 
 274 
 
 4 
 
 Pocahontas No. 3. 
 
 48 , 
 
 548 
 
 600-900 
 
 1.47 
 
 No 
 
 >100 , 
 
 570 , 
 
 Shale , 
 
 Shale if 
 
 Mine B 
 
 High speed 
 
 354 
 
 181 
 
 3-8 
 
 Beckley 
 
 46 
 
 482 
 
 900-1,000 
 
 5.76 
 
 No 
 
 85 
 
 560 , 
 
 Shale to slate.. 
 
 Slate with coal 
 laminations. 
 
 Mine C 
 
 High speed. 
 
 356. 
 
 193. 
 
 2-3. 
 
 Lower Freeport. 
 
 45. 
 
 600. 
 
 450. 
 
 1.4. 
 
 No. 
 
 84. 
 
 370. 
 
 Shale with occa- 
 sional sandstone. 
 Clay. 
 
The following briefly describes the 
 on-site application of existing control 
 technology: 
 
 Mine A : The primary means of con- 
 trolling dust along the face was a manu- 
 ally operated, constant fullface water- 
 spray system. Twenty-seven spray blocks 
 were mounted along the face conveyor 
 spillplate at 20-ft intervals. Each 
 block consisted of one nozzle operating 
 at 100 psi. A crusher, mounted on the 
 face conveyor located upwind of support 
 15, was equipped with three nozzles 
 on its intake side. Two sets of 10 flat- 
 fan water-sprays were mounted at the 
 f ace-conveyor-to-stageloader and stage- 
 loader-to-belt transfer points that con- 
 trolled dust in the headgate area (one 
 set of sprays at each transfer point). 
 The transfer-point sprays were enclosed 
 with brattice. Observations revealed 
 that very few transfer-point water sprays 
 worked. A Wendon 4 wetting agent was used 
 extensively throughout the section. 
 
 Mine B : An electromechanically acti- 
 vated sequential water-spray system was 
 the primary means for controlling dust 
 along the face. Ninety-six spray blocks, 
 mounted at 5-ft intervals along the face 
 conveyor spillplate, were sequentially 
 activated in groups of 12 by electric 
 solenoids. As the plow moved along the 
 face, one group of sprays closed while 
 the preceding group opened, thus keeping 
 the plow enveloped with water at all 
 times. Each spray block contained one 
 nozzle of the adjustable flat-fan type, 
 operating at 30 psi. Because the water 
 sprays were the adjustable type, orienta- 
 tion within a spray block was random. 
 Cone sprays operating at 85 psi were used 
 to control dust at transfer points. One 
 set of two sprays was mounted at the face 
 conveyor-to-stageloader transfer point, 
 and one set of two sprays was mounted at 
 the stageloader-to-belt transfer point. 
 It was observed that stageloader-to-belt 
 
 ^Reference to specific equipment does 
 not imply endorsement by the Bureau of 
 Mines. 
 
 water sprays were clogged and no sprays 
 were used at the crusher. 
 
 Mine C : A sequential water spray sys- 
 tem, similar to mine B's system, was used 
 to control dust along the face. Twelve 
 groups of 10 spray blocks were sequen- 
 tially activated by electric solenoids. 
 Spray blocks were mounted at 5 ft inter- 
 vals along the face conveyor spillplate. 
 As part of a separate ongoing evaluation 
 by the mine, three types of water sprays 
 were used along the face: (1) atomizing, 
 (2) 1/16-in jet, and (3) 3/32-in jet 
 sprays. Each block contained 3 nozzles 
 of the various types, with each nozzle 
 operating at 160 psi. Spray blocks were 
 oriented downwind, with spray coverage 
 over the conveyor and lower third of the 
 face. Eighteen water sprays, operating 
 at 25 psi, were used to control dust in 
 the headgate area. Sets of six water 
 sprays were mounted, near the f ace-con- 
 veyor-to-stageloader transfer point, at 
 the stageloader-to-belt transfer point, 
 and on the intake side of the stage- 
 loader-mounted crusher. Brattice was 
 used to cover portions of the stageloader 
 and belting was used to enclose 
 the crusher and crusher-mounted sprays. 
 Because of poor headgate roof conditions, 
 observations revealed that the crusher 
 would frequently produce high concentra- 
 tions of dust while handling the fallen 
 roof rock. 
 
 SAMPLING STRATEGY 
 
 Instantaneous and short-term gravi- 
 metric sampling methods were used to 
 isolate and quantify potential sources of 
 respirable dust. 
 
 Four gravimetric sampling stations were 
 identified along the headgate and face. 
 Sets of two gravimetric samplers each 
 were stationed in the last open crosscut, 
 at two headgate locations (approximately 
 at shields 3 and 15), and at the tailgate 
 (about 15 shields from the tail entry). 
 Face-side gravimetrics were suspended 
 from roof support canopies over the walk- 
 way. Eight gravimetric samplers were 
 used as part of each day's sampling. No 
 
8-h, full-shift sampling similar to 
 compliance sampling was performed. 
 
 A MIE RAM-1 instantaneous dust monitor 
 was used to measure dust concentrations 
 generated by the plow and roof support 
 movements. RAM-] data are normally re- 
 corded on handheld audio tape recorders. 
 After the survey of mine A, tape re- 
 corders were replaced with Mine Safety 
 and Health Administration (MSHA) approved 
 solid-state digital data loggers. Each 
 logger was preprogrammed to record one 
 output voltage level from the RAM-1 every 
 second, for a total run time of 34 min« 
 The 1-s averaging and recording of output 
 voltage insured accurate and consistent 
 monitoring of dust levels at each sam- 
 pling station. A portable microcomputer, 
 in combination with communication soft- 
 ware, was later used to retrieve and 
 store logger data onto floppy disks for 
 future analysis. 
 
 Stationary instantaneous sampling was 
 conducted at locations upwind of support 
 35 during each survey. Earlier attempts 
 to sample near the tailgate were unsuc- 
 cessful because concurrent upwind activi- 
 ties produced unpredictable background 
 dust levels. By selecting two sampling 
 locations in close proximity and upwind 
 of support 35, it was possible to over- 
 come restricted visibility and conduct 
 accurately timed surveys of upwind and 
 downwind face activity. Time study re- 
 sults were used to interpret logger data 
 by identifying events that may have had 
 an adverse effect on dust levels. For 
 example, it was important to make note of 
 the start and stop times of the plow, 
 face conveyor, and support movement acti- 
 vity; changes in cut direction; and the 
 location of the plow with respect to each 
 sampling location. 
 
 SURVEY RESULTS 
 
 Gravimetric results are shown in ta- 
 ble 2 and figure 2. Table 2 presents the 
 average concentration measured at each 
 sampling station for all three mines sur- 
 veyed. Based on this information, 
 respirable dust sources have been identi- 
 fied and their contributions to face 
 workers' exposure computed. Respirable 
 dust sources fall into three groups: 
 (1) sources that occur outby and repre- 
 sent section intake dust, (2) sources up- 
 wind of support 15 (specifically stage- 
 loader and crusher-generated dust), and 
 (3) sources that occur along the face 
 
 TABLE 2. - Gravimetric results: 
 average dust concentrations 1 in 
 milligrams per cubic meter 
 
 Sampling station 
 
 Mine A 
 
 Mine B z 
 
 Mine C 
 
 Section intake.. 
 
 0.2 
 
 0.5 
 
 0.1 
 
 
 1.1 
 
 2.5 
 
 1.3 
 
 
 2.1 
 
 2.4 
 
 1.3 
 
 Support 
 
 
 
 
 
 3.1 
 
 NA 
 
 2.4 
 
 NA Not available. 
 
 Concentrations are 
 equivalents. 
 
 Data has been 
 production. 
 
 not calculated MRE 
 
 normalized 
 
 for 
 
 (namely coal transport-, plow-, and 
 support-generated dust). Figure 2 illus- 
 trates the significance or insignificance 
 
 Section intake (7.1 pet) 
 
 Coal transport 
 Plow 
 
 _ 39.3 
 
 Support movements J pct 
 
 FIGURE 2.— Typical respirable dust sources. 
 
of each group based on the survey average 
 of source contributions. 
 
 Instantaneous sampling was conducted to 
 identify the significance of group 3 dust 
 sources. Individual segments of recorded 
 instantaneous data were analyzed to iden- 
 tify source contributions from plow 
 and roof support movements. Current sam- 
 pling methodologies did not permit inde- 
 pendent evaluation of coal transport 
 dust. Figures 3 and 4 represent typical 
 time history plots of instantaneous dust 
 levels for mines B and C, respectively. 
 
 Figure 3 shows the significance of sup- 
 port movements for face dust levels; fig- 
 ure 4 presents dust levels measured near 
 the plow. 
 
 Mine A: 
 
 Gravimetric results showed 
 
 that the most significant change in dust 
 levels occurred upwind of support 15. 
 Sixty-eight percent, or 2. 1 mg/m 3 of 
 respirable dust along the face, was 
 measured at this location. Approximately 
 0. 9 mg/m 3 was generated by the stage- 
 loader upwind of support 3 and 1. mg/m 3 
 
 H 
 
 1? 
 
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 10 
 
 3 
 
 
 3* 
 
 8 
 
 o< 
 
 
 lu tr 
 
 6 
 
 z „ 
 
 
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 4 
 
 ZLU 
 
 
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 2 
 
 CO , 
 
 
 
 
 KEY 
 
 ESS Dust from support 
 movement 
 
 Support movement 
 begins 
 
 Arv^ ^tmtrnn^^* * 
 
 I 
 
 8 
 
 10 
 
 TIME, min 
 
 FIGURE 3.— Instantaneous roof support dust concentrations at mine B. 
 
 \- 
 
 \? 
 
 CO c/> 
 
 
 3 +- 
 
 
 Q c 
 
 10 
 
 3 
 
 
 3:> 
 
 8 
 
 o< 
 
 
 LU <T 
 
 6 
 
 Z „ 
 
 
 < CO 
 
 4 
 
 Z LU 
 
 
 iZ uj 
 
 2 
 
 CO i 
 
 
 Dust plume 
 
 KEY 
 Plow passes sampler location 
 during head-to-midface cut 
 
 4 5 6 
 TIME, min 
 
 FIGURE 4.— Instantaneous dust concentrations by a plow at mine C. 
 
by a crusher mounted on the face conveyor 
 upwind of support 15. Coal transport, 
 the plow, and roof support movements gen- 
 erated 1.0 mg/ra of dust along the face 
 as measured at the tailgate support. 
 
 Plow-generated dust is identified as 
 the computed difference between dust lev- 
 els measured on the intake and return-air 
 sides of the plow. Instantaneous results 
 indicated that plowing generates, on 
 average, less than 0.2 RAM^ units of 
 dust, regardless of cut direction. 
 
 Concentrations measured downwind of two 
 support operators were averaged, and 
 intake levels subtracted to identify dust 
 contributions from support movements. 
 Roof support movements generated 1.8 RAM 
 units of dust, with peak concentrations 
 as high as 37.2 RAM units. 
 
 Mine B ; Once again, a significant 
 amount of dust was generated at the head- 
 gate by the stageloader-crusher. Based 
 on available gravimetric data, results 
 showed that 2.0 mg/m of respirable dust 
 was generated inby the last open cross- 
 cut and upwind of support 3. This is a 
 significant contribution by any measure. 
 Because of equipment malfunctions, gravi- 
 metric data are not available for the 
 tailgate sampling location. 
 
 Figure 3 shows a typical time history 
 profile of instantaneous dust levels 
 before and after the start of upwind sup- 
 port movements. Best estimates are that 
 support movements generated an average 
 of 1.4 RAM units of dust. Figure 3 
 also illustrates the insignificance of 
 
 plow-generated dust. During the first 
 4-1/2 min of sampling, and before the 
 start of upwind support movements, there 
 was virtually no measurable change in 
 dust levels, despite the fact that the 
 plow made two complete passes of the face 
 (a pass equals one cut from head to tail 
 plus one cut from tail to head). 
 
 Mine C ; Results from this survey were 
 essentially the same as the first two 
 surveys. Forty-six pet of the respir- 
 able dust along the face (1.2 mg/m 3 ) 
 was generated upwind of support 3 by 
 the stageloader-crusher. An additional 
 46 pet was generated along the face (as 
 measured at the tailgate support) by coal 
 transport, plowing, and roof support 
 movements. 
 
 Figure 4 shows a typical profile of 
 instantaneous dust levels measured while 
 a plow was mining in the vicinity of the 
 stationary sampling location. Unlike 
 plows in the other mines surveyed, this 
 plow was found to produce a measurable 
 difference in respirable dust levels. 
 During the head-to-midface cut, a plume 
 of dust was observed traveling with and 
 on the intake air side of the plow. At 
 times, dust levels reached instantaneous 
 peaks of 7.0 RAM units. Since dust is 
 generated in only one cut direction and 
 exposure to this dust is of short dura- 
 tion, it is safe to assume that the plow 
 was an insignificant dust source. Sup- 
 port dust was generally found to be 
 insignificant, except where clay veins 
 were present. 
 
 DISCUSSION 
 
 Instantaneous and short-term gravi- 
 metric sampling methods were used to 
 identify respirable dust sources along 
 high-speed overtaking and conventional 
 plow operations. Gravimetric results 
 provided information on three dust source 
 
 C ; — 
 
 -"A RAM unit is the relative numerical 
 output from the RAM-1 and approximates 
 respirable dust levels in milligrams per 
 cubic meter. 
 
 groups: section intake; stageloader- 
 crusher; and coal transport, plow, and 
 support movements. Instantaneous results 
 helped to identify the significance of 
 plow- and support-generated dust. 
 
 The impact of a dust source on face 
 workers' exposure is directly related to 
 its frequency of occurrence (or time 
 fraction of the mining cycle) and to the 
 workers' location along the plow face, 
 with respect to the dust source. For 
 
example, a stageloader- crusher operates 
 100 pet of the actual mining time, and 
 regardless of the operators' location 
 along the face, they are exposed to this 
 dust source 100 pet of the time. On the 
 other hand, upwind support movements 
 occur only 25 to 50 pet of the mining 
 time. Although exposure to this dust 
 source is less frequent, a tailgate 
 worker on a plow face is exposed to many 
 more upwind roof support movements than a 
 worker located near the headgate. Theo- 
 retically, dust exposure levels for the 
 tailgate worker should be higher. The 
 logic is the same for exposure to plow- 
 generated dust as it is for exposure to 
 support dust; the longer a worker stays 
 on the return air side of a plow, the 
 greater the exposure. 
 
 On the longwall plow faces surveyed by 
 the Bureau, the stageloader-crusher was 
 found to be the most common and signifi- 
 cant source of dust. Typically, 54 pet 
 of the dust responsible for face worker 
 exposure comes from the stageloader- 
 crusher. Despite the mines' efforts to 
 control this dust source, existing con- 
 trol systems were inadequate. 
 
 A number of low-cost alternatives are 
 available for controlling stageloader- 
 crusher dust. Strategically located 
 
 water sprays mounted on an enclosed 
 stageloader-crusher, or a water-powered 
 scrubber that cleans the air inside it, 
 can be very effective in reducing dust 
 levels. An enclosed stageloader-crusher 
 spray system consisting of twelve hollow- 
 cone sprays (20 gpm total water flow) lo- 
 cated in the crusher, at the intake and 
 discharge side of the crusher, and im- 
 mediately after the stageloader dump 
 point, can reduce dust concentrations by 
 74 pet at the stageloader (fig. 5) (8). 
 A water-powered scrubber mounted on a 
 stageloader and supplied with approxi- 
 mately 9 gpm water at 500 psi, for an 
 airflow of approximately 2,000 cfm, can 
 reduce intake dust along the face by 
 50 pet (JJ). Although a water-powered 
 scrubber offers excellent dust control, 
 its application to plow operations may be 
 limited by seam height. 
 
 Plow, coal transport, and support move- 
 ments typically account for 38 pet of the 
 dust responsible for face workers' 
 exposure. Support-generated dust was a 
 problem at mines A and B. Support dust 
 problems normally occur when coal or 
 some other highly friable roof material 
 is ground and crushed during the advance 
 and setting of roof supports (10). At 
 mine A, the problem was a combination of 
 
 Conveyor belt 
 
 Crusher 
 sprays 
 
 Brattice hood 
 
 Crusher intake 
 sprays 
 
 FIGURE 5.— Enclosed stageloader-crusher with strategic location of water sprays. 
 
poor roof conditions and failure of the 
 uncut coal to fall freely away from the 
 roof. At mine B, the problem was pri- 
 marily roof coal. The solution to this 
 problem is not quite clear. For plow 
 operations, it is common and often neces- 
 sary to mine at a cutting height that is 
 lower than the seam height, to prevent 
 the plow from riding into the roof and 
 interrupting production. However, if the 
 remaining uncut coal fails to break and 
 fall freely away from the roof prior to 
 the movement of supports, it can create a 
 dust problem. Alternatives may include 
 adjusting the cutting height, at the risk 
 of interrupting production, or to intro- 
 duce modified support-setting techniques. 
 Attempts have been made to attach water 
 sprays to roof support canopies and to 
 
 wet the zone ahead of the support along 
 the roof. Maintenance often becomes a 
 problem, and it is usually difficult to 
 prevent the sprays from being torn off. 
 
 Finally, plow-generated dust does not 
 present much of a problem. Only at 
 mine C was a measurable change in dust 
 levels observed. Since face personnel do 
 not travel with the plow, unlike shearer 
 operators who remain with the machine 
 at all times, exposure to a short- 
 duration dust cloud is insignificant. 
 (For mine C, exposure normally did not 
 last longer than 30 seconds for every 
 other cut). This suggests that existing 
 dust control technology is doing an ex- 
 cellent job of controlling plow-generated 
 dust, or that the plow produces very lit- 
 tle dust in the respirable size range. 
 
 CONCLUSIONS 
 
 The stageloader-crusher is a primary 
 source of dust on longwall plow opera- 
 tions. Stageloader-crushers can generate 
 over 60 pet of the dust along the face. 
 The mines surveyed had all made attempts 
 to control this dust source, but had met 
 with little success. Implementation of 
 stageloader-crusher control techniques 
 means strategically locating water sprays 
 under the brattice of an enclosed stage- 
 loader, or mounting a water-powered 
 scrubber to clean the air inside the 
 machine. Either technique is relatively 
 inexpensive and with proper maintenance 
 can produce significant dust reductions. 
 
 Support-generated dust presents a dust 
 control problem when uncut coal fails to 
 fall freely from the roof before advance- 
 ment of the supports. The residual roof 
 coal is crushed by roof support move- 
 ments, possibly producing high concentra- 
 tions of dust. This can be a serious 
 problem for many workers who must remain 
 at stationary locations along the plow 
 face. Since dust exposure is a function 
 of worker location along the face rela- 
 tive to the dust source, a tailgate sup- 
 port operator is exposed to many more 
 
 upwind roof support movements than is 
 a headgate operator, and theoretically 
 should be exposed to higher dust levels. 
 Two of the three mines surveyed had sup- 
 port dust problems. The solution to con- 
 trolling this dust source remains un- 
 clear. It may prove more cost-effective 
 to pursue control techniques for other 
 more significant sources of dust, speci- 
 fically the stageloader-crusher. 
 
 Surprisingly, plow-generated dust was 
 found to be insignificant. This suggests 
 that existing control technology, in the 
 form of constant or sequentially acti- 
 vated face-conveyor-mounted water sprays, 
 is adequate. Each system has its advan- 
 tages. A sequential system optimizes the 
 use of water by minimizing water flow and 
 maximizing water pressure in the vicinity 
 of the plow. It also reduces the amount 
 of nuisance water, in the form of mist 
 and runoff. On the other hand, a con- 
 stant full-face system would ensure 
 better saturation of the coal by wetting 
 the coal well in advance of the cut and 
 maintaining this saturated state during 
 coal transport. 
 
10 
 
 REFERENCES 
 
 1. Olson, J. J. , and S. Tandanand. 
 Mechanized Longwall Mining. A Review 
 Emphasizing Foreign Technology. BuMines 
 IC 8740, 1977, 201 pp. 
 
 2. Wyllie, B. European Coal Mining 
 Technology. Eng. and Min. J. , June 1986, 
 pp. 26-32. 
 
 3. Haley, W. A., J. J. Dowd, and L. A. 
 Turnbull. Modified Longwall Mining With 
 a German Coal Planer (Plow) in the Poca- 
 hontas No. 4 Coal Bed, Helen, W. V. Bu- 
 Mines RI 4922, 1952, 13 pp. 
 
 4. Wild, H. W. New Developments in 
 Ploughing. Gltickauf (Engl. Transl.), 
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 5. Stefanko, R. Longwall Mining - 
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 Ramani. Soc. Min. Eng. AIME, 1981, 
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 6. BCR National Laboratory. Dust 
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 OFR 34-86, 1985, 223 pp.; NTIS PB 86- 
 178159. 
 
 7. McClelland, J. J. , J. A. Organis- 
 cak, R. A. Jankowski, and B. Rao Pothini. 
 Water Infusion for Coal Mine Dust Con- 
 trol: Three Case Studies. BuMines 
 RI 9096, 1987, 17 pp. 
 
 8. Organiscak, J. A., R. A. Jankow- 
 ski, and J. S. Kelly. Dust Controls to 
 Improve Quality of Longwall Intake Air. 
 BuMines IC 9114, 1986, 8 pp. 
 
 9. U.S. Bureau of Mines. Stage Load- 
 er Dust Control Reduces Longwall Intake 
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 10. Organiscak, J. A. , J. M. Listak, 
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