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JC 9m 
 
 Bureau of Mines Information Circular/1986 
 
 Dust Controls To Improve Quality 
 of Longwall Intake Air 
 
 By John A. Organ iscak, Robert A. Jankowski, 
 and Jonathan S. Kelly 
 
 UNITED STATES DEPARTMENT OF THE HMTERIOR 
 
V 
 Information Circular 9114 
 
 Dust Controls To Improve Quality 
 of Long wall Intake Air 
 
 By John A. Organiscak, Robert A. Jankowski, 
 and Jonathan S. Kelly 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
t\6- VII 
 
 Library of Congress Cataloging in Publication Data: 
 
 Organiscak, John A 
 
 Dust controls to improve quality of longwall intake air. 
 
 (Bureau of Mines information circular ; 9114) 
 
 Bibliography: p. 8. 
 
 Supt. of Docs, no.: I 28.27: 9114 
 
 1. Coal mines and mining-Dust control. 2. Longwall mining. 3. Mine ventilation. 
 I. Jankowski, Robert A. II. Kelly, Jonathan S. III. Title. IV. Series: Information circular 
 (United States. Bureau of Mines) ; 9114. 
 
 TN295.U4 
 
 [TN312] 
 
 622 s 
 
 [622'.334] 
 
 86-600261 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Homotropal ventilation 2 
 
 Types of outby dust sources and controls 3 
 
 Stageloader-crusher 3 
 
 Panel belt 5 
 
 Intake roadway 7 
 
 Summary 7 
 
 References 8 
 
 ILLUSTRATIONS 
 
 1. Typical homotropal ventilation of a longwall face 2 
 
 2. Typical intake dust concentrations for antitropal and homotropal ventila- 
 
 tion systems 3 
 
 3. Ventilation curtain to keep headgate operator in clean air when headgate 
 
 is restricted 3 
 
 4. Enclosed stageloader-crusher with strategic location of water sprays 4 
 
 5. Enclosed stageloader-crusher with a water-powered scrubber 5 
 
 6. Panel belt dust contamination at a two-entry longwall system 6 
 
 7. Rotary wire brush cleans conveying side of belt 7 
 
 8. Water spray and belt wiper clean nonconveying side of belt 7 
 
 TABLE 
 
 1. Dust concentrations and reductions for stageloader-crusher dust controls.... 4 
 

 UNIT OF MEASURE ABBREVIATIONS USED 
 
 IN THIS REPORT 
 
 cfm 
 
 cubic foot per minute 
 
 mg/m 3 
 
 milligram per cubic meter 
 
 f pm 
 
 foot per minute 
 
 pet 
 
 percent 
 
 gpm 
 
 gallon per minute 
 
 psi 
 
 pound per square inch 
 
 gal/st 
 
 gallon per short ton 
 
 wt pet 
 
 weight percent 
 
f 
 
 DUST CONTROLS TO IMPROVE QUALITY 
 OF LONGWALL INTAKE AIR 
 
 By John A. Organiscak, 1 Robert A. Jankowski, 2 and Jonathan S. Kelly 3 
 
 ABSTRACT 
 
 The Bureau of Mines has recently completed a program to identify and 
 evaluate various methods that address control of dust generated outby 
 the longwall mining face. Dust generated by the stageloader-crusher, 
 the panel belt, and the intake roadway can be long-term throughout the 
 shift, contributing significantly to the dust exposure of all face 
 workers. Dust control techniques were identified and tested at a number 
 of longwall mining sections located in diverse geological conditions 
 across the United States. Dust controls investigated include (1) meth- 
 ods that eliminate the sources of intake dust contamination — homotropal 
 ventilation; (2) methods to limit the amount of respirable dust released 
 into the intake airstream — improved water application and the use of 
 curtains and enclosures; and (3) methods to clean the contaminated air 
 prior to delivery to the mining face — scrubber systems. Usually they 
 can be implemented at a low cost and can be very effective. This report 
 describes each technique and its application and presents the resulting 
 conclusions. 
 
 'Mining engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 
 Supervisory physical scientist, Pittsburqh Research Center. 
 
 3 Project engineer, Foster-Miller, Inc., 350 Second Avenue, Walthan, MA. 
 
INTRODUCTION 
 
 Many longwall mine operations are still 
 experiencing difficulty maintaining con- 
 sistent compliance with mandatory Federal 
 dust standards that limit the personal 
 dust exposure of longwall face workers. 
 The predominant dust source is usually 
 the shearer; however, several dust 
 sources outby the mining face can also 
 contribute significantly to personal ex- 
 posure levels. Past surveys by the Bu- 
 reau (1_)4 have shown that on a specific 
 operation as much as 75 pet of the 
 shearer operators' dust exposure came 
 from contaminated intake air, while in 
 many instances, approximately 25 pet of 
 face workers' respirable dust exposure 
 was generated outby the mining face. 
 
 This study showed that these sources in- 
 cluded the stageloader-crusher, panel 
 belt, and intake roadway, with the 
 stageloader-crusher being the most common 
 and significant source. 
 
 Outby dust sources can contribute sig- 
 nificantly to worker dust exposure at a 
 longwall face. Dust levels generated by 
 these sources can be long-term throughout 
 the shift and can affect all face 
 workers. This report presents the ef- 
 fects of homotropal ventilation, water 
 application, and equipment design for re- 
 ducing outby generated dust. Usually, 
 these dust controls can be implemented at 
 a low cost and can be very effective. 
 
 HOMOTROPAL VENTILATION 
 
 The most effective method for con- 
 trolling intake dust is homotropal venti- 
 lation, which routes air in the direction 
 of coal transport along the face; i.e. , 
 tailgate-to-headgate (fig. 1). This 
 places the outby dust sources downstream 
 of the face workers, eliminating their 
 dust exposure from these sources. Intake 
 dust levels are reduced in the walkway by 
 as much as 90 pet (fig. 2) GO. More- 
 over, the tailgate-to-headgate cutting 
 cycle used in homotropal ventilation can 
 increase productivity, since most of the 
 coal does not have to pass through the 
 shearer underframe. 
 
 Homotropal ventilation has the drawback 
 that the headgate operator works down- 
 stream of the mining activities (shearer 
 or plow), and tailgate entries must be 
 kept in good condition. The headgate 
 operator's dust exposure can be prevented 
 by an auxiliary intake air split brought 
 up the headgate entry next to the belt 
 entry, with at least 100 fpm of airflow 
 directed over the headgate operator (fig. 
 1). The gob at the headgate must remain 
 open so that the dust-laden face air and 
 the clean auxiliary air combine at the 
 headgate end of the face and flow through 
 
 ^Underlined numbers in parentheses 
 refer to items in the list of references 
 at the end of this report. 
 
 the corner of the gob into the return or 
 directly into the return crosscut. This 
 may require additional cribbing in the 
 crosscut, and between the last headgate 
 shield and pillar. It is also recom- 
 mended that the headgate operator con- 
 trols be located as far outby the face 
 
 < Return air 
 Stopping 
 I Curtain 
 i — b — i Belt 
 ii i ' iiii Stageloader 
 
 FIGURE 1.— Typical homotropal ventilation of a longwall 
 face. 
 
< 
 
 E 
 E 
 
 rr 
 
 UJ 
 
 o 
 o 
 
 CO 
 Q 
 
 d.UU 
 
 
 1 
 KEY 
 
 i 
 
 1 
 • 
 
 
 1.60 
 
 - •- 
 
 - Headgate to 
 
 tailgate 
 
 
 - 
 
 
 ■ - 
 
 - Tailgate to 
 
 neadgate 
 
 
 
 1.20 
 
 - 
 
 • • 
 
 • 
 
 • 
 
 - 
 
 0.80 
 
 
 • m 
 
 • 
 • 
 
 • • 
 
 - 
 
 0.40 
 
 
 
 
 
 _ 
 
 
 
 __■ f 
 
 ■ m~~ 
 
 i 
 
 ■ 
 l 
 
 ■ 
 
 
 I 
 
 Curtain 
 
 20 40 60 
 
 FACE LOCATION, support number 
 
 80 
 
 FIGURE 2.— Typical intake dust concentrations for anti- 
 tropal and homotropal ventilation systems. 
 
 as practical. This helps to keep the 
 operator clear of contaminated air if the 
 headgate gob should be closed up or seri- 
 ously restricted, thus temporarily forc- 
 ing the face air through the headgate to 
 the return. A brattice curtain may have 
 to be installed to insure clean intake 
 air over the headgate operator when the 
 face air is directed through the headgate 
 to the return (fig. 3). 
 
 On homotropal ventilated faces, the 
 tailgate entries must be kept in good 
 condition. Intake air travels up these 
 entries, which are under additional roof 
 loading from the adjacent mined-out 
 panel. Some additional cribbing may be 
 required, but this should not be regarded 
 
 FIGURE 3.— Ventilation curtain to keep headgate operator 
 in clean air when headgate gob is restricted. 
 
 as an additional task, since both head- 
 gate and tailgate entries are considered 
 escapeways and must remain passable ac- 
 cording to Federal regulations. 
 
 TYPES OF 0UTBY DUST SOURCES AND CONTROLS 
 
 STAGELOADER-CRUSHER 
 
 Although homotropal ventilation is the 
 most effective dust control method for 
 all outby dust sources, it can be diffi- 
 cult and expensive to implement. Many 
 other dust source controls can be imple- 
 mented at a lower cost and be very ef- 
 fective in reducing outby generated dust. 
 
 The stageloader-crusher is usually the 
 most significant outby dust source on 
 most longwalls. At several longwalls 
 surveyed by the Bureau, more than 50 
 pet of the shearer operators' dust expo- 
 sure came from the stageloader-crusher 
 ( 1_) . Significant dust reduction can 
 be achieved with water sprays lo- 
 cated strategically on an enclosed 
 
manufacturers ' 
 
 not enclosed, 
 in the crusher 
 
 stageloader-crusher, or with a water- 
 powered scrubber that cleans the air 
 inside it (3). 
 
 Enclosing a stageloader-crusher and 
 locating water sprays for optimum dust 
 knockdown was evaluated at an underground 
 longwall where a stageloader-crusher gen- 
 erated a significant amount of respirable 
 dust. Four different dust control sys- 
 tems (3) were investigated as follows: 
 
 1. Baseline condition, stageloader- 
 crusher not enclosed and four hollow cone 
 sprays in the crusher (waterflow, 10 
 gpm). This is typical 
 dust controls. 
 
 2. Stageloader-crusher 
 four hollow cone sprays 
 (waterflow, 10 gpm), spray bar with two 
 hollow cone sprays directed at the intake 
 of the crusher (waterflow, 2 gpm), spray 
 bar with three hollow cone sprays di- 
 rected down on the chain conveyor on the 
 discharge side of the crusher (waterflow, 
 5 gpm), and a spray bar with three hollow 
 cone sprays directed on and with coal 
 movement on the conveyor belt immediately 
 after the stageloader dump point (water- 
 flow, 3 gpm). Total system waterflow was 
 20 gpm. 
 
 3. Enclosed stageloader-crusher (brat- 
 tice enclosure) with only crusher sprays 
 operating (10 gpm total waterflow). 
 
 4. Enclosed stageloader-crusher (brat- 
 tice enclosure) with all sprays operating 
 (20 gpm total waterflow (fig. 4)). 
 
 As can be seen from table 1, the over- 
 all highest dust concentration occurred 
 with the baseline dust control system: 
 
 TABLE 1. - Dust concentrations and 
 reductions for stageloader-crusher 
 dust controls 
 
 Conveyor belt 
 
 Crusher 
 sprays 
 
 Brattice hood 
 
 Control system 
 
 Av dust cone, RAM units: 
 
 Belt entry 
 
 Stageloader 
 
 Headgate operator 
 
 Support 20 2 
 
 Reduction in dust cone, 
 pet: 
 
 Belt entry 
 
 Stageloader 
 
 Headgate operator 
 
 Support 20 2 
 
 1 
 
 1.2 
 2.7 
 2.4 
 1.7 
 
 BL 
 BL 
 BL 
 BL 
 
 0.9 
 2.4 
 1.0 
 1.4 
 
 25 
 11 
 58 
 18 
 
 1.5 
 2.8 
 0.9 
 1.3 
 
 -25 
 -4 
 63 
 24 
 
 1.0 
 0.7 
 0.5 
 1.0 
 
 17 
 74 
 79 
 41 
 
 FIGURE 4.— Enclosed stageloader-crusher with strategic 
 location of water sprays. 
 
 BL Baseline. 
 
 'As defined in Stageloader-Crusher sec- 
 tion of text: 
 
 1 — Stageloader-crusher open, crusher 
 
 sprays only. 
 2 — Stageloader-crusher open, all 
 
 sprays. 
 3 — Stageloader-crusher enclosed, 
 
 crusher sprays only. 
 4 — Stageloader-crusher enclosed, all 
 sprays. 
 2 This face location chosen for compari- 
 son because the airflow had ample face 
 distance to stabilize from a directional 
 change. 
 
 An open stageloader-crusher with crusher 
 sprays, representing a typical manufac- 
 turers' dust control system. The overall 
 lowest dust concentration occurred for 
 the enclosed stageloader-crusher with all 
 the water sprays operating. The combina- 
 tion of additional water sprays and 
 enclosing the stageloader-crusher reduced 
 dust concentrations considerably at the 
 headgate operator (79 pet), stageloader 
 (74 pet), and at support 20 (41 pet); 
 modest dust reductions were observed in 
 the belt entry (17 pet). 
 
 In further limited testing of the en- 
 closed stageloader-crusher with addi- 
 tional water sprays, the waterflow was 
 increased from 20 gpm to 30 gpm, with 
 most of the additional water applied 
 through the crusher-sprays. A 30-pct 
 additional improvement in dust levels 
 was achieved at the headgate operator's 
 
** 
 
 position and at support 20. No addi- 
 tional improvement was recorded at the 
 belt entry, indicating that the belt 
 spray bar was responsible for most of the 
 panel belt dust reduction. 
 
 With all the sprays turned off, regard- 
 less of whether the stageloader-crusher 
 was open or enclosed, conditions deterio- 
 rated, particularly in the belt entry, 
 with a 100-pct increase in dust concen- 
 tration at support 20. 
 
 An enclosed stageloader-crusher with 
 additional water sprays placed in stra- 
 tegic locations is one of the most cost 
 effective headgate dust control systems. 
 The materials and labor-hours needed to 
 build and maintain the system are minus- 
 cule compared with the benefits gained. 
 
 Another means of control is a water- 
 powered scrubber (4^ (Jet Spray Air 
 Mover, JSAM) that cleans the air inside 
 an enclosed stageloader-crusher and dis- 
 charges the clean air into the mine en- 
 vironment (fig. 5). In this case, the 
 stageloader-crusher is enclosed, but with 
 an opening or ducting for the scrubber 
 intake located as close as practical to 
 the crusher discharge. Water sprays 
 should again be added under the brattice 
 hood on the intake side of the crusher, 
 to knock down or contain the dust gener- 
 ated by the crusher and prevent it from 
 boiling out of the crusher intake. The 
 scrubber should be installed on the 
 stageloader to draw the air from the duct 
 or opening on the discharge side of the 
 crusher. The scrubber exhaust should 
 discharge air in the direction of coal 
 movement. 
 
 This type of system was tested at an 
 underground coal mine where the scrubber 
 was supplied with approximately 9 gpm 
 
 Water-powered 
 scrubber 
 
 Crusher intake f 
 (with brattice hood 
 and water spray) I — r 
 
 Crusher 
 
 FIGURE 5.— Enclosed stageloader-crusher with a water- 
 powered scrubber. 
 
 water at 500 psi for an airflow of ap- 
 proximately 2,000 cfm through the unit. 
 With all controls operating, dust re- 
 ductions of approximately 75 pet were ob- 
 served at the headgate operator's 
 position, with a 50-pct reduction in in- 
 take dust along the longwall face. The 
 water pressure should be maintained at 
 ~500 psi for most effective results. 
 
 PANEL BELT 
 
 For three- and four-entry longwall 
 systems, there should be no dust contami- 
 nation at the face from the longwall 
 panel belt, unless immense quantities of 
 ventilation air are needed for methane 
 control. The belt entry at most of these 
 systems should be on a neutral split of 
 air with perceptible airflow directed 
 away from the face, and into the air re- 
 turn. A properly isolated and regulated 
 belt entry with a check curtain just 
 outby the stageloader can provide this 
 neutral split. 
 
 It is not unusual to find longwalls 
 with an inadequately regulated belt entry 
 and a poorly maintained or nonexistent 
 check curtain where the belt entry air- 
 flow is towards the face, contaminating 
 the intake air. On some two-entry long- 
 walls, where a portion of the intake air 
 is brought up the belt entry to ventilate 
 the face (under an MSHA variance), dust 
 contamination can be significant. 
 
 The significance of belt panel dust 
 contamination of the intake air to the 
 face can be shown by some data from a Bu- 
 reau study of stageloader-crusher dust 
 controls ( 3) ■ The longwall was a two- 
 entry system and brought 20 pet of its 
 intake air up the belt entry. Figure 6 
 shows the longwall headgate area includ- 
 ing measured dust concentrations and air 
 quantities. As a result of panel belt 
 dust contamination (2.4 mg/m 3 in 13,500 
 cfm air) , the face intake dust concen- 
 tration was 0.5 mg/m 3 , based on intake 
 air dilution [(13,500 cfm/70,000 cfm) 
 x 2.4 mg/m 3 ] . 
 
 Although the stageloader-crusher was 
 the dominant dust source, the 0.5 mg/m 3 
 dust from the panel belt is significant 
 because it is usually constant throughout 
 
(Dust cone at support 20 
 = 1.6 mg/m 3 ) 
 
 ( Dust cone = 0.3 mg/m 3 ) 
 
 FIGURE 6.— Panel belt dust contamination at a two-entry 
 longwall system. 
 
 the shift and represents 25 pet of the 
 Federal compliance limit. If the belt 
 entry could be isolated and the belt 
 entry air could be routed into a return, 
 the panel belt contamination of the face 
 intake air would be eliminated. When the 
 belt entry air is needed at the face or a 
 neutral belt entry is hard to maintain, 
 panel belt dust controls are required. 
 Even if a neutral belt entry can be 
 maintained, panel belt dust should be 
 controlled to keep float dust to a mini- 
 mum and reduce the panel belt workers ' 
 dust exposure. 
 
 To prevent the fine dust particles from 
 becoming airborne during transport, the 
 coal should be wetted initially at the 
 face by drum sprays (shearer face) or by 
 sequential face sprays (plow face). A 
 useful guide for water application is 
 2 to 4 wt pet (4.5 to 9.5 gal/st) (_5). 
 Water should be sufficient to wet the 
 coal, but should not accumulate on the 
 floor. A Bureau study (6) of double-drum 
 shearers showed significant reductions 
 in shearer-generated dust, in addition 
 to a 25-pct reduction in the face intake 
 dust at support 8, when the total water 
 applied to the coal, through the drums, 
 was increased from 34 gpm to 48 gpm. The 
 reduction in dust generated by the outby 
 sources, stageloader-crusher and panel 
 belt, could not clearly be established 
 
 but the increase in water application was 
 felt to have had a positive effect on 
 both crushing and transport. 
 
 During outby transport, the water on 
 the coal may evaporate, making rewetting 
 necessary at intervals along the belt. 
 This is accomplished by spraying water 
 onto the coal, far enough inby the trans- 
 fer point to allow the coal and water to 
 mix, applying between 1 and 4 gpm water 
 at operating pressures of 50 psi or more 
 (7_). Flat fan sprays and full-cone noz- 
 zles are typically used for coal wetting 
 underground. 
 
 Rewetting of the coal can reduce the 
 amount of dust generated during trans- 
 port. In the above two-entry panel belt 
 dust contamination case, belt entry dust 
 concentration was reduced by 83 pet when 
 the coal was rewetted at the stageloader 
 (3). A spray bar with three hollow cone 
 sprays installed in an enclosed stage- 
 loader downstream of the crusher, knocked 
 down the dust in the stageloader and re- 
 wetted the coal, thus significantly 
 reducing panel belt dust generation. 
 
 Belt maintenance and belt cleaning also 
 control panel belt dust. Missing rol- 
 lers, belt slippage, and worn belts can 
 cause belt misalignment and create spil- 
 lage that gets pulverized by the drive 
 pulley on the nonconveying side of the 
 returning belt. The top and bottom of 
 the return belt should be cleaned 
 with spring-loaded or counter-weighted 
 scrapers, to prevent material adhering to 
 the return belt from being pulverized by 
 the tail-end pulley. A low-quantity 
 water spray can also be used to moisten 
 the belt slightly. Other means of clean- 
 ing the return belt are a motor-driven 
 rotary wire brush that cleans the convey- 
 ing side by rotating opposite belt travel 
 (fig. 7), and a full-cone water spray, 
 directed at the nonconveying side, fol- 
 lowed by a piece of carpeting (belt 
 wiper) positioned across the belt width 
 (fig. 8). The water spray wets the fines 
 and the carpeting removes them from the 
 nonconveying side. This system yielded 
 more than a 90-pct reduction of airborne 
 respirable and float dust, compared with 
 a dry operation (8). 
 
Conveyor belt 
 
 FIGURE 7.— Rotary wire brush cleans conveying side of belt. 
 
 INTAKE ROADWAY 
 
 Respirable dust concentrations in the 
 intake air at the last open crosscut are 
 usually very low, with no significant ef- 
 fect on face personnel. On a typical 
 longwall, background respirable dust con- 
 centrations in the intake air are usually 
 less than 0.3 mg/m- 5 . However, if the 
 dust concentration in the intake is 
 higher, it will contribute significantly 
 to the dust exposure of face personnel. 
 
 Measures to control dust sources up- 
 stream of the last open crosscut can 
 be as simple as limiting construction, 
 haulage of supplies, and roadway grading 
 
 FIGURE 8.— Water spray and belt wiper clean nonconveying 
 side of belt. 
 
 in the intake air during the production 
 shift. If haulage activities must take 
 place during a production shift, the 
 moisture content of the dust on the haul- 
 ageway floor should be about 10 pet to 
 insure that it remains bound (J)* Plain 
 water dries out rapidly in the venti- 
 lation air, making repeated applications 
 necessary. Addition of calcium chloride 
 (CaCl 2 ) or another hygroscopic salt main- 
 tains the moisture content at the desired 
 level. 
 
 SUMMARY 
 
 Outby dust sources at a longwall face 
 can contribute significantly to face 
 workers' dust exposure. They include the 
 stageloader-crusher, the panel belt, and 
 the intake roadways. By using recom- 
 mended dust control practices, the dust 
 at these sources can be adequately con- 
 trolled. Sometimes several controls must 
 be utilized as a system to control dust 
 from many sources. 
 
 The most effective method for elimi- 
 nating the exposure of face workers to 
 all outby dust sources is homotropal ven- 
 tilation (tailgate-to-headgate), which 
 places all outby sources downwind of the 
 face workers. However, an auxilliary air 
 split must be maintained for the head- 
 gate operator, downwind of the mining 
 
 activity, and the tailgate entries must 
 be kept in good condition to ensure that 
 intake air reaches the face. 
 
 If homotropal ventilation is too dif- 
 ficult or expensive to implement, other 
 effective dust controls can be used on 
 the outby sources. Stageloader-crusher 
 dust controls include adding water sprays 
 or utilizing a scrubber to clean the air 
 inside an enclosed stageloader-crusher. 
 Practices to control panel belt dust are 
 proper belt entry ventilation, water ap- 
 plication, belt maintenance, and belt 
 cleaning. Control of intake roadway dust 
 involves reducing the amount of activity 
 in the roadway during the production 
 shift or wetting the roadway to allay 
 
 dust * 10287 102 
 
REFERENCES 
 
 1. Jankowski, R. A., and J. A. 
 Organiscak. Dust Sources and Controls on 
 the Six U.S. Longwall Faces Having the 
 Most Difficulty Complying With Dust Stan- 
 dards. BuMines IC 8957, 1983, 20 pp. 
 
 2. . Longwall Ventilation From 
 
 Tailgate-to-Headgate Reduces Intake Dust. 
 Technol. News, No. 145, 1982. 
 
 3. Foster-Miller, Inc. Evaluate Fun- 
 damental Approach to Longwall Dust 
 Control. Ongoing BuMines contract 
 J0318097; for inf., contact R. A. 
 Jankowski, TPO, Pittsburgh Res. Center, 
 BuMines, Pittsburgh, PA. 
 
 4. Grigal, D. , G. Ufken, J. Sandstedt, 
 M. Blom, and D. Johnson. Development of 
 Improved Scrubbers for Coal Mine Applica- 
 tions (contract HO199055). BuMines OFR 
 91-83, 1982, 124 pp.; NTIS PB 83-205385. 
 
 5. Goddard, B., K. Bower, and 
 D. Mitchell. Control of Harmful Dust in 
 Coal Mines. National Coal Board, United 
 Kingdom, 1973, 85 pp. 
 
 6. Pimentel, R. A., R. F. J. Adam, and 
 R. A. Jankowski. Improving Dust Control 
 on Longwall Shearers. Soc. Min. Eng. 
 AIME preprint 84-113, 1984, 8 pp. 
 
 7. Bituminous Coal Research, Inc. 
 Guidebook for Dust Control in Under- 
 ground Mining (contract JO199046). Bu- 
 mines OFR 145-82, 1981, 206 pp; NTIS PB 
 83-109207. 
 
 8. Courtney, W. G. Single Spray Re- 
 duces Dust 90 pet. Coal Min. & Proc- 
 ess., v. 20, No. 6, 1983, pp. 75-77. 
 
 
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