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IC ^^""^ 
 
 Bureau of Mines Information Circular/1985 
 
 Factors Affecting Respirable Dust 
 Generation From Longwall Roof 
 Supports 
 
 By John A. Organiscak, Jeffrey M. Listak, 
 and Robert A. Jankowski 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 75j 
 
 '^INBS 75TH AVi^ 
 
Information Circular 9019 
 
 Factors Affecting Respirable Dust 
 Generation From Longwall Roof 
 Supports 
 
 By John A. Organiscak, Jeffrey M. Listak, 
 and Robert A. Jankowski 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Model, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
Library of Congress Cataloging in Publication Data: 
 
 Organiscak, John A 
 
 Factors affecting respirable dust generation from longwall roof 
 supports. 
 
 (Bureau of Mines information circular ; 9019) 
 
 Bibliography: p. 16. 
 
 Supt. of Docs, no.: I 28.27:9019. 
 
 1. Coal mines and mining— Dust control. 2. Mine roof control. I. 
 Listak, Jeffrey M, II. Jankowski, Robert A. III. Title. IV. Series: 
 Information circular (United States. Bureau of Mines) ; 9019. 
 
 TN295.U4 [TN312] 622s [622'. 42] 84-600328 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Survey description 2 
 
 Longwalls with low concentrations of support-generated dust 3 
 
 Geology 4 
 
 Supports 5 
 
 Operational procedures 5 
 
 Longwalls with moderate concentrations of support-generated dust 5 
 
 Geology 5 
 
 Supports 6 
 
 Operational procedures 7 
 
 Longwalls with high concentrations of support-generated dust 7 
 
 Geology 8 
 
 Supports 9 
 
 Operational procedures 9 
 
 Factors affecting dust generated by supports 9 
 
 Roof strength 9 
 
 Depth of cover 10 
 
 Shield design 10 
 
 Other factors 10 
 
 Support dust control technology used in the United States 11 
 
 Water application 12 
 
 Other dust control practices 12 
 
 Conclus ions 15 
 
 References 16 
 
 Appendix A. — Data from longwall survey. 17 
 
 Appendix B. — Dust-sampling strategy 19 
 
 ILLUSTRATIONS 
 
 1 . Typical longwall shield face 3 
 
 2. Instantaneous roof support dust concentrations at longwall A 4 
 
 3. Instantaneous roof support dust concentrations at longwall F 6 
 
 4. Instantaneous roof support dust concentrations at longwall G 8 
 
 5. Relationship between roof loading factor and average support dust concen- 
 
 tration at surveyed longwall faces 10 
 
 6. Relationship between panel depth and average support dust concentration 
 
 at surveyed longwall faces 11 
 
 7. Relationship between face air velocity and dust levels at the face 12 
 
 8. Spray manifold located on support canopy 13 
 
 9. Relationship between debris thickness on shield canopy and dust generated 14 
 
 10. Effectiveness of shearer-clearer system 14 
 
 11. Relationship between distance downwind of support movement and dust level 15 
 
 TABLES 
 
 A-1 . Numerical data from survey 17 
 
 A-2. Descriptive data from survey 18 
 

 UNIT OF MEASURE ABBREVIATIONS USED IN THIS 
 
 REPORT 
 
 ft 
 
 foot psi 
 
 pound (force) per 
 square inch 
 
 ft2 
 
 square foot 
 
 
 
 psig 
 
 pound (force) per 
 
 h 
 
 hour 
 
 square inch, gauge 
 
 in 
 
 inch pet 
 
 percent 
 
 mg/m^ 
 
 milligram per cubic meter ton/ft^ 
 
 ton per square foot 
 
 mm 
 
 millimeter ft/min 
 
 foot per minute 
 
 m/s 
 
 meter per second L/min 
 
 liter per minute 
 
 ym 
 
 micrometer 
 
 
 NOTE.- 
 
 -See appendix B for explanation of RAM units. 
 
 
FACTORS AFFECTING RESPIRABLE DUST GENERATION 
 FROM LONGWALL ROOF SUPPORTS 
 
 By John A. Organiscak, Jeffrey M. Listak, 
 and Robert A. Jankowski 
 
 ABSTRACT 
 
 The Bureau of Mines conducted a survey of eight shearer longwall oper- 
 ations to identify factors that affect respirable dust generation from 
 longwall roof supports. The longwalls surveyed were in coal seams lo- 
 cated in different geographic regions of the United States. Data were 
 collected on mining (geologic) conditions, support design, operational 
 characteristics, and amount of respirable dust generated from roof sup- 
 ports. Analysis indicated that mining conditions are the main factors 
 that affect the generation of dust during roof support movement. Both 
 roof strength and depth of cover above the coal seam showed relation- 
 ships with the amount of support dust generated. Several practices are 
 currently employed to effectively control roof support dust; however, 
 some of these controls are limited. More research and development is 
 needed to improve dust control technology for longwall roof supports. 
 
 ^Mining engineer. 
 ^Supervisory physical scientist. 
 Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
 
INTRODUCTION 
 
 Previous Bureau research on dust 
 sources at shearer longwall operations 
 has shown that roof support movement can 
 generate a significant amount of respira- 
 ble dust (_1).-^ Investigators found that 
 as much as 31 pet of the respirable dust 
 to which shearer operators were exposed 
 was generated by the cyclic movement of 
 longwall roof supports Q) . 
 
 On most longwalls in the United States, 
 the major source of dust is the cutting 
 action of the shearer drums , and the ma- 
 jor effort has been to control dust from 
 this source. Thus, very little research 
 has been done on the control of support- 
 generated dust in the United States (J^). 
 Some research has been done in Europe, 
 but only limited technology has resulted. 
 
 To fill this gap, the Bureau conduct- 
 ed a recent study to gain a better 
 
 understanding of conditions that contrib- 
 ute to high levels of support dust on 
 longwall mining operations. The objec- 
 tive was to identify the inherent char- 
 acteristics of longwalls having high 
 levels of support-generated respirable 
 dust. This report describes the study 
 and presents the findings. 
 
 The problem was addressed by conducting 
 dust sampling at longwalls in the east- 
 ern and western United States having a 
 wide range of dust levels generated by 
 support movement. The criteria used for 
 assessing the origins of respirable dust 
 were local geology, support design, and 
 operational procedures. The data were 
 collected and analyzed for correlations, 
 in an attempt to identify the character- 
 istics that influence dust generation. 
 
 SURVEY DESCRIPTION 
 
 Eight shearer longwall faces using 
 shield supports were surveyed (fig. 1).^ 
 The characteristics and dust concentra- 
 tions of these longwalls are shown in ap- 
 pendix A. The longwalls surveyed were 
 located in seven coal seams (table A-2 in 
 appendix A) at varying depths of cover, 
 in different geographic regions of the 
 United States. Geologic conditions were 
 observed during the survey, and drill- 
 core data from the vicinity of the panels 
 were obtained from mine personnel. 
 
 During the survey, four types of imme- 
 diate roof were identified. Compressive 
 strengths of these roof types were esti- 
 mated (based on observation) for use in 
 relating the support load exerted on them 
 to the dust generated (_2 ) . The four roof 
 types and their estimated compressive 
 strengths were as follows: coal, 650 
 psi; weak shale (soft), 4,000 psi; strong 
 
 -^Underlined numbers in parentheses re- 
 fer to items in the list of references 
 preceding the appendixes. 
 
 '^Frame and chock support faces were not 
 included in this survey because only a 
 limited number of these installations are 
 in use, and their application in the 
 United States is quickly diminishing. 
 
 competent shale, 10,000 psi; and weak 
 siltstone (soft), 4,000 psi. The esti- 
 mated roof strength and roof type for 
 each of the longwalls surveyed are given 
 in tables A-1 and A-2, respectively. 
 
 Supports used at the longwalls surveyed 
 were either two- or four-legged shields. 
 The pertinent characteristics of the 
 shields were setting pressures, yield 
 loads, support dimensions, and leg speci- 
 fications. From these data, the average 
 setting-load density exerted on the roof 
 by the supports at each longwall was de- 
 temnined. As an indication of the roof's 
 susceptibility to crushing under the sup- 
 port setting load, a roof loading factor 
 was devised from a ratio of the average 
 roof strength to the average support 
 setting-load density. The lower the val- 
 ue of this factor, the more likely the 
 roof was to crush under set load. 
 
 Dust samples were taken at each long- 
 wall, and operational procedures were 
 observed. Support dust was measured 
 by using GCA^ Real-Time Aerosol Moni- 
 tors (RAM's) and short-term gravimetric 
 
 ^Reference to specific products does 
 not imply endorsement by the Bureau of 
 Mines. 
 
FIGURE 1. - Typical longwall shield face. 
 
 samplers immediately upwind and downwind 
 of support movement along the face. (For 
 details of the sampling strategy, see ap- 
 pendix B) . Ventilation data were col- 
 lected at each longwall. At some of the 
 longwalls, the effect of ventilation on 
 the dilution and diffusion of support 
 dust at various distances downstream of 
 
 support movement was determined from RAM 
 measurements. (See appendix B.) Addi- 
 tional information about operational pro- 
 cedures was collected, including support 
 advance practices, support dust control 
 practices, and horizon control of the 
 roof and floor with the shearer. 
 
 LONGWALLS WITH LOW CONCENTRATIONS OF SUPPORT-GENERATED DUST 
 
 At two of the longwalls surveyed (long- 
 walls A and B, as identified in appendix 
 A), dust concentrations generated by sup- 
 port movement were very low. The average 
 respirable dust concentration was < 0.5 
 RAM unit^ as measured with the RAM's and 
 
 °Ram units are explained in appendix B. 
 
 < 0.5 mg/m-' as measured with the gravi- 
 metric samplers. 
 
 An example of low dust concentrations 
 generated by support movement along the 
 face is shown in figure 2, a plot of the 
 instantaneous measurements made at long- 
 wall A. The difference between the imme- 
 diate downwind and upwind concentrations 
 
h| 
 
 3 
 
 CO H 
 
 
 ni 
 
 
 ~: < 
 
 
 CO CO 
 
 
 => ,- 
 
 ;^ 
 
 o f{ 
 
 
 LU O 
 
 
 z P 
 
 
 < < 
 
 
 H CC 
 
 
 Z H 
 
 1 
 
 r=^ z 
 
 
 h: uj 
 
 
 CO o 
 
 
 o 0. 
 
 . 1 1 1 1 1 1 1 1 1 1 
 
 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 
 
 KEY 
 o Imnnediate downwind cone 
 ° Immediate upwind cone 
 
 ^ I//J Dust from support 
 \ movement 
 
 l^^Av downwind cone = 0.9\ £ 
 
 ! 1 1 I I J I -T— T— 
 
 Av Upwind cone _ 
 
 _ 
 
 ^SOv^ 
 
 ^/V^?}^ \'- 
 
 1 1 1 
 
 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 
 
 1 1 1 1 1 1 1 1 1 
 
 30 
 
 40 50 60 
 -* — Headgate 
 
 70 
 
 80 90 100 
 
 Tailgate — >- 
 SUPPORT MOVED 
 (Support identification number) 
 
 10 
 
 FIGURE 2. - Instantaneous roof support dust concentrations at longwoll A. 
 
 measured during support movement indi- 
 cated the dust concentration generated by 
 the supports (the shaded area between the 
 two curves). The average downwind dust 
 concentration was 0.9 RAM unit, and the 
 average upwind dust concentration was 0.5 
 RAM unit, resulting in an average dust 
 concentration of 0.4 RAM unit generated 
 by the supports. The difference between 
 the dust concentrations of the downwind 
 and upwind gravimetric samples made con- 
 currently with instantaneous sampling at 
 this longwall yielded 0.3 mg/m-^ of dust 
 generated from support movement. 
 
 Dust concentrations produced by the 
 supports at longwall B were similar to 
 those produced at longwall A; the average 
 instantaneous and gravimetric concentra- 
 tions were 0.4 RAM unit and 0.1 mg/m-^ , 
 respectively. Besides the similarities 
 in support-generated dust concentrations, 
 longwalls A and B had many similarities 
 with respect to mining conditions , sup- 
 port design, and operational procedures. 
 
 GEOLOGY 
 
 The mining conditions at longwalls A 
 and B were very similar. Longwall A was 
 located in the Lower Kittanning coal 
 seam, with a mining height of about 5 ft. 
 The mining face was horizontal, with no 
 major irregularities in the coal seam. 
 The immediate roof was composed of 48 ft 
 of dark-to-medium-gray hard shale. This 
 roof was very competent in front of the 
 canopy tips and caved readily at the rear 
 of the supports. Its assumed compressive 
 strength was 10,000 psi. The floor was a 
 dark-to-medium-gray claystone of excel- 
 lent quality. The cover over the panel 
 was 320 ft deep and was formed of thick 
 sandstone and shale strata interlaced 
 with thin coal seams. 
 
 Longwall B was located in the Campbell 
 Creek coal seam. The mining height was 
 approximately 6 ft. The coal seam had no 
 major irregularities and was relatively 
 flat. The immediate roof consisted of 
 
5 ft of a gray hard shale overlain by 
 32 ft of gray sandstone. This roof be- 
 haved very well, being competent in front 
 of the canopy tips and caving readily be- 
 hind the supports. (Its compressive 
 strength was also 10,000 psi) . The floor 
 was a gray sandstone of excellent quality 
 which provided a firm surface for the 
 support bases. The cover over the panel 
 was 500 ft deep and was composed of thick 
 sandstone and shale strata interlaced 
 with coal. 
 
 Thus, both longwalls had excellent min- 
 ing conditions. 
 
 SUPPORTS 
 
 The supports used at the two longwalls 
 were identical: four-legged lemniscate 
 shield supports, each with a 55-ft^ can- 
 opy bearing area. The setting pressures 
 and yield loads of these supports were 
 4,350 pslg and 564 tons, respectively. 
 The side seals on the flushing shield 
 were spring-activated with hydraulic 
 override. The supports could be moved in 
 the contact-advance mode from a bidirec- 
 tional adjacent control. 
 
 The strong shale roof at both longwalls 
 was assumed to have had a compressive 
 strength of 10,000 psi. The load den- 
 sity set on the roof by the support at a 
 
 setting pressure of 4,350 psig was 113.9 
 psi, resulting in a roof loading fac- 
 tor of 87.7 (roof compressive strength/ 
 load density at set pressure) at both 
 longwalls. This roof loading factor in- 
 dicated that the roof had a strong re- 
 sistance to crushing under the setting 
 loads of the supports. 
 
 OPERATIONAL PROCEDURES 
 
 Both longwalls A and B used a unidirec- 
 tional cutting sequence with contact ad- 
 vance of supports in one of the cutting 
 directions. Also, each mine maintained 
 good horizon control during mining. Con- 
 tact advance and good horizon control re- 
 duce the amount of debris that is re- 
 ground and crushed into respirable dust. 
 
 Also, both longwalls applied water to 
 the roof to reduce dust entrainment when 
 supports were moved. Longwall A free- 
 wheeled the leading drum near the roof 
 during the cleanup pass to apply water. 
 Longwall B wet the roof using a venturi 
 spray mounted on the shearer body and 
 directed downstream at an angle of ap- 
 proximately 45° relative to the roof. 
 The average velocity of the air at the 
 face, traveling in a head-to-tail direc- 
 tion, was 580 ft/min for longwall A and 
 289 ft/min for longwall B. 
 
 LONGWALLS WITH MODERATE CONCENTRATIONS OF SUPPORT-GENERATED DUST 
 
 At four of the longwalls surveyed 
 (longwalls C, D, E, and F) , moderate 
 amounts of respirable dust were generated 
 by the supports. Average respirable dust 
 concentrations measured with gravimetric 
 samplers were between 0.5 and 2.0 mg/m-'. 
 Average respirable dust concentrations 
 measured with the RAM's ranged from 0.6 
 to 2.4 RAM units. 
 
 A typical example of instantaneous 
 dust concentrations measured at a long- 
 wall with moderate amounts of support- 
 generated dust (longwall F) is shown in 
 figure 3. Again, the difference between 
 the immediate downwind and upwind concen- 
 trations measured during support movement 
 (the shaded area) represented the dust 
 generated by the supports . Peak support 
 dust concentrations were measured at ar- 
 eas of the face with deteriorated roof 
 conditions. The average downwind dust 
 concentration was 2.0 RAM units, and the 
 
 average upwind dust concentration was 0.3 
 RAM unit, resulting in an average dust 
 concentration of 1.7 RAM units generated 
 by the supports. The corresponding dif- 
 ference between the downwind and upwind 
 gravimetric sample concentrations yielded 
 an average dust concentration of 1.5 
 mg/m-^. The other longwalls (C, D, and E) 
 also had moderate dust concentrations, 
 and instantaneous peak concentrations 
 similar to those measured at longwall F 
 were measured at deteriorating roof areas 
 along their faces. 
 
 GEOLOGY 
 
 Longwalls C, D, E, and F were located 
 in three different coal seams , but had 
 similar mining conditions. Longwall C 
 was located in the 6-ft-thick Eagle Seam. 
 Longwall D was located in the 6-ft-thick 
 Pittsburgh Seam. Longwalls E and F were 
 
20 30 40 50 60 70 80 
 
 -• — Headgate Tai Igate *■ 
 
 SUPPORT MOVED 
 (Support identification number) 
 
 FIGURE 3. - Instantaneous roof support dust concentrations at longwall F. 
 
 located in the 9-ft-thick Blind Can- 
 yon Seam. No major seam irregularities 
 occurred at any of these longwalls except 
 at longwall D, which had 1 ft of rock 
 parting in the middle of the seam. Each 
 of the longwalls had a fairly soft fria- 
 ble roof composed of shale (longwall C) , 
 coal (longwall D) , or siltstone (long- 
 walls E and F) . The floor at longwalls C 
 and D was a wet, soft shale; at longwalls 
 E and F, the floor was a wet, soft 
 muds tone. 
 
 Depths of cover over the longwall 
 panels ranged from 430 to 1,600 ft. In 
 general, the longwalls under greater 
 
 depths of cover had somewhat higher 
 concentrations of support-generated dust. 
 The stratigraphic composition of the 
 overburden for longwalls C, D, E, and F 
 consisted mainly of shales, sandstones, 
 limestones, siltstones, and coal seams. 
 General mining conditions for these 
 longwalls were fair to good. 
 
 SUPPORTS 
 
 All four longwalls used two-legged lem- 
 niscate shields that were basically 
 similar in design, but with some differ- 
 ences. The shields used at longwalls C, 
 
E, and F had extendable forepoles. The 
 canopy areas with the forepoles retracted 
 were 42.0, 42.8, and 42.8 ft2, respec- 
 tively; with the forepoles extended, they 
 were 52.7, 59.0, and 59.0 ft^, respec- 
 tively. The shields used at longwall D 
 had no forepoles and had a canopy area of 
 50.7 ft^. The setting pressure for long- 
 walls C, E, and F as 4,350 psig; for 
 longwall D, it was 4,000 psig. Yield 
 loads at longwalls C, D, E, and F were 
 426, 352, 472, and 472 tons, respective- 
 ly. The canopy areas with the forepoles 
 retracted were used for the load-density 
 calculations for longwalls C, E, and F 
 because the forepoles were not extended 
 on most of the shields at these faces. ^ 
 The side seals on the flushing shields 
 at these longwalls were spring-loaded 
 with hydraulic override, and the sup- 
 ports could be moved in the contact- 
 advance mode from a bidirectional adja- 
 cent control. 
 
 Loading densities exerted on the roofs 
 at longwalls C, D, E, and F were 134.7, 
 40.3, 108.3, and 108.3 psi, respectively. 
 At longwall D, the load density on the 
 roof was significantly lower because of 
 the fairly large canopy area and smaller 
 props on the longwall D shields. The 
 roof loading factors (roof compressive 
 strength/ average set load density) for 
 longwalls C, D, E, and F were 29.7, 16.1, 
 36.9, and 36.9, respectively. These fac- 
 tors were significantly lower than the 
 roof loading factors of longwalls A and 
 B, indicating that the roofs over long- 
 walls C, D, E, and F were more suscepti- 
 ble to crushing and grinding during sup- 
 port movement. 
 
 OPERATIONAL PROCEDURES 
 
 Each of these four mines advanced the 
 supports during the head-to-tail pass. 
 Longwalls E and F did not utilize contact 
 advance; longwalls C and D utilized con- 
 tact advance in some areas of the face 
 where the floor was strong enough to keep 
 the supports from digging in. 
 
 At all four longwalls, the floor and 
 roof were cut fairly evenly. However, 
 the supports would sink or dig into the 
 floor, and some of the weaker roof areas 
 would break off in front of the canopy 
 tips, leaving cavities on top of the can- 
 opies. These cavities developed highly 
 stressed roof-contact areas that frac- 
 tured and crushed. When the supports 
 were dropped significantly before being 
 advanced, a thick layer of debris would 
 build up on the canopy, and this debris 
 was subject to further crushing and 
 grinding during set loading. At long- 
 walls C and D, the support movers lowered 
 the front of the canopy and cleaned the 
 debris off some of the shields into the 
 panline. This was a very dusty operation 
 and was conducted upwind of the shearer 
 operators and other face personnel. If 
 debris needs to be cleaned off the can- 
 opies , it should be done downwind of all 
 workers. One longwall (longwall F) uti- 
 lized spray manifolds on the shields to 
 suppress support dust. 
 
 Ventilation ^airflow was less than 200 
 ft/min at three of these longwalls. 
 Longwalls C, E, and F had average face 
 air velocities of 167, 184, and 179 ft/ 
 min. Longwall D had an average face air- 
 flow of 402 ft/min. 
 
 LONGWALLS WITH HIGH CONCENTRATIONS OF SUPPORT-GENERATED DUST 
 
 At two of the longwalls surveyed (long- 
 walls G and H) , large amounts of res- 
 pirable dust were generated by the sup- 
 port movement, with average respirable 
 dust concentrations above 2.0 mg/m^ 
 
 'The forepoles would be utilized mainly 
 to catch loose material separated from 
 the roof in some areas of the face. 
 Therefore, there was probably very lit- 
 tle if any loading of the roof with the 
 forepoles. 
 
 as measured with gravimetric samplers. 
 Average respirable dust concentrations 
 measured with the RAM exceeded 2.0 RAM 
 units. 
 
 A typical example of instantaneous dust 
 concentrations at a longwall with large 
 amounts of support-generated dust (long- 
 wall G) is shown in figure 4. Again, the 
 shaded area between the two curves repre- 
 sents the dust generated by supports. 
 The average downwind and upwind RAM 
 measurements were 6.1 and 0.6 RAM units. 
 
< 
 
 < 
 cc 
 
 LU 
 O 
 
 z 
 O 
 o 
 
 I- 
 co 
 
 ID 
 Q 
 
 CO 
 
 3 
 
 o 
 
 LXJ 
 
 12 
 
 10 
 
 8 - 
 
 z 
 
 ~1 [ 1 I r-T I I I \ 1 I r 
 
 J — I — I — I I 1 it I I I I I I I I I I I I I I I I I I 
 
 10 20 30 
 
 -• Headgate 
 
 50 60 70 80 
 
 Tailgate — 
 SUPPORT MOVED 
 (Support identification number) 
 
 90 
 
 FIGURE 4. - Instantaneous roof support dust concentrations at longwall G. 
 
 respectively. The amount of dust gener- 
 ated by the supports varied significant- 
 ly along the face. The highest and low- 
 est dust concentrations measured dovmwind 
 of the supports were 11.8 and 2.2 RAM 
 units, respectively. Less dust was gen- 
 erated by the supports at longwall H, but 
 the amount of dust generated was still 
 significant. The average RAM and gravi- 
 metric measurements of support-generated 
 dust for both longwalls were 2.6 RAM 
 units and 3.0 mg/m^. Instantaneous RAM 
 measurements showed that support dust 
 concentrations varied at longwall H but 
 were more consistent than at longwall G. 
 
 GEOLOGY 
 
 Mining conditions at longwalls G and 
 H were similar. Longwall G was located 
 in the Hiawatha coal seam, with a min- 
 ing height of about 8 ft. The mining 
 face was horizontal, with no major 
 
 irregularities in the coal seam. The 
 immediate roof was composed of 1 ft of 
 coal overlain with 10 ft of sandstone. 
 This roof was fairly competent in front 
 of the canopy tips and caved readily at 
 the rear of the supports. The assumed 
 compressive strength of the coal roof was 
 650 psi. The floor was a dry sandstone 
 of excellent quality and provided a firm 
 surface for the support based. Overlying 
 this longwall panel was 1,600 ft of over- 
 burden composed of sandstones, mudstones, 
 siltstones, shales, and coal seams. 
 
 Longwall H was located in the E-Seam. 
 This coal seam is characterized by local 
 thickening and thinning due to the pres- 
 ence of rolls in the coalbed. The strata 
 above the coal seam are composed of sand- 
 stone, shale, and mudstone. The seam is 
 fairly flat, with a 2° to 3° dip in the 
 northern direction. At the longwall pan- 
 el, 8 ft of coal was mined, limited by 
 the maximum support height , leaving 1 ft 
 
of coal for the immediate roof below the 
 sandstone strata above the seam. This 
 roof was fairly competent in front of the 
 canopy tips and caved readily at the rear 
 of the supports. The assumed compressive 
 strength of the coal roof was 650 psi. 
 The floor was a hard, dry shale and pro- 
 vided a firm surface for the support 
 bases. Overlying this longwall panel was 
 2,200 ft of overburden composed of sand- 
 stones, mudstones, siltstones, shales, 
 and coal seams . 
 
 Since the immediate roof at both long- 
 walls was coal, it was assumed that the 
 roof at both mines had a compressive 
 strength of 650 psi. Load densities 
 exerted on the roof by the supports at 
 longwalls G and H were 73.6 and 80.6 psi, 
 yielding roof loading factors of 8.8 and 
 8.1, respectively, indicating a tendency 
 of the roof to crush and grind under set- 
 ting loads . 
 
 OPERATIONAL PROCEDURES 
 
 SUPPORTS 
 
 The supports used at longwalls G and 
 H were similar in design. Supports at 
 longwall G were two-legged lemniscate 
 shields with a 57.6-ft^ canopy bearing 
 area. The setting pressures and yield 
 loads of the supports were 4,350 psig and 
 472 tons, respectively. Longwall H also 
 had two-legged lemniscate shields, but 
 the canopy bearing area was 54.0 ft^, the 
 setting pressure was 4,500 psig, and the 
 yield load was 440 tons. At both long- 
 walls, the side seals on the flushing 
 shields were spring-activated with hy- 
 draulic override. The supports could be 
 moved in the contact-advance mode from a 
 bidirectional adjacent control. 
 
 Longwalls G and H used a unidirectional 
 cutting sequence with contact advance of 
 supports during the head-to-tail pass. 
 Horizon control was maintained fairly 
 well. Ventilation at G and H was head- 
 to-tail, with average face airflows of 
 650 and 355 ft/min, respectively. Mining 
 conditions at these longwalls were fairly 
 good. The large amounts of roof support 
 dust seemed to be generated by the easy 
 crushing and grinding of the coal roof 
 during advance and setting of the sup- 
 ports. The airflow at longwall G was 
 quite high, which could have contributed 
 to the entrainment of support-generated 
 dust. 
 
 FACTORS AFFECTING DUST GENERATED BY SUPPORTS 
 
 Eight longwalls were surveyed and cate- 
 gorized according to the amount of res- 
 pirable dust generated by roof supports 
 (low, moderate, and high). Within these 
 categories, similarities were observed, 
 mainly with respect to mining conditions 
 (geology). Mining conditions determined 
 by the coalbed geology seemed to be the 
 main factors affecting support dust 
 generation. 
 
 ROOF STRENGTH 
 
 Strong shale roof seemed to generate 
 the least amount of dust during support 
 movement (< 0.5 mg/m^). The weaker shale 
 and siltstone roofs generated moderate 
 amounts of dust during support movement 
 (> 0.5 mg/m? and < 2.0 mg/m-'). Longwalls 
 
 that left an immediate coal roof (lowest 
 compressive strength) because of weak 
 strata above the coal or limits of the 
 longwall equipment had the highest 
 amounts of support-generated dust (> 2.0 
 mg/m^). Thus, there appears to be an in- 
 verse relationship between roof strength 
 and support-generated dust. Figure 5 
 shows the relationship of the roof load- 
 ing factor to dust concentration. Usual- 
 ly, the lower the roof -loading factor 
 (roof compressive strength/load density 
 exerted on roof by canopy) , the weaker 
 the roof. The dust concentrations plot- 
 ted in figure 5 were the average RAM mea- 
 surements of support dust at each long- 
 wall; using the gravimetric dust data 
 instead of the RAM measurements yielded 
 the same relationship. 
 
10 
 
 o 
 a: 
 
 f2 
 
 O 
 
 a. 
 
 CL 
 
 Z) 
 
 (/) 
 
 UJ >- 
 
 U DQ 
 
 O 
 O 
 
 CO 
 
 Z) 
 Q 
 
 Q 
 UJ 
 
 UJ 
 
 UJ 
 CD 
 
 < 
 DC 
 
 5 
 
 - 
 
 o 
 
 
 1 
 
 1 
 
 
 o 
 
 1 1 
 
 KEY 
 Av RAM dust cone 
 
 
 - 
 
 4 
 
 - 
 
 
 
 
 
 
 
 
 
 - 
 
 3 
 2 
 
 1 
 
 - 
 
 o "** 
 
 o 
 
 o 
 
 1 
 
 o 
 1 
 
 ^- 
 
 -. 
 
 1 T^ 
 
 o 
 
 - 
 
 
 
 20 
 
 40 
 
 60 
 
 80 
 
 100 
 
 ROOF LOADING FACTOR 
 
 FIGURE 5. - Relationship between roof loading factor and average support dust concentration at 
 surveyed longwall faces. 
 
 DEPTH OF COVER 
 
 Another geologic factor that seemed to 
 affect the amount of support-generated 
 dust was the depth of cover over the coal 
 seam. At the eight longwalls studied, 
 the support-generated dust seemed to in- 
 crease as overburden above the seam in- 
 creased. In figure 6, seam depth is 
 plotted against average RAM concentra- 
 tions of the support dust at each long- 
 wall. The gravimetric data for these 
 longwalls showed the same trend. As 
 depth of cover increases, vertical and 
 horizontal stresses in the strata in- 
 crease, usually producing more pronounced 
 fracturing of the strata. Also, deeper 
 strata usually have more in situ stresses 
 in all directions. Generally, fractured 
 and highly stressed rock, strata are weak- 
 er and less competent during mining, 
 which may make them more susceptible to 
 crushing and grinding by longwall roof 
 supports. 
 
 SHIELD DESIGN 
 
 The longwall roof supports at the eight 
 longwalls were either two- or four-legged 
 lemniscate shields. Their designs did 
 not seem to be as strong a factor in dust 
 generation as roof strength. The only 
 
 major difference between the two-legged 
 and four-legged shields was that the 
 four-legged shields distributed floor 
 loads more evenly throughout the bases. 
 Other differences between the shields 
 were their prop sizes and canopy areas, 
 which produced different load densities 
 exerted on the roof with approximately 
 the same setting pressures. However, 
 there seemed to be no relationship be- 
 tween the load densities alone and 
 support-generated dust. A relationship 
 did appear when the load densities exert- 
 ed on the roof and the roof strength were 
 utilized together to determine the roof- 
 loading factor. 
 
 OTHER FACTORS 
 
 Other factors that may influence the 
 generation of support dust are horizon 
 control, contact advance, water applica- 
 tion, and face airflow. Good horizon 
 control should be maintained by the 
 shearer or plow. When irregularities 
 occur in the roof and floor, the bearing 
 areas of the supports make contact with 
 only a portion of the roof or floor and 
 will crush out these areas due to high 
 stress. All the longwalls included in 
 this study maintained good horizon con- 
 trol. However, at longwalls C, D, E, and 
 
11 
 
 Q 
 
 DC 
 LlI 
 
 ID 
 
 O 
 
 < 
 
 HO 
 
 CL 
 CL 
 
 Z) 
 
 >- 
 
 00 
 
 2 - 
 
 0, 
 
 1 1 1 1 1 1 1 1 1 
 
 o 
 
 KEY 
 
 o Av RAM dust cone 
 
 
 _ — '"^ 
 
 ^^^^ 1 
 
 ^<r^ Y 
 
 -^-^ 
 
 -^"^^ o 
 
 -^-""^^^ 
 
 ^i*."** o 
 
 ^.-^ 
 
 -- 1 1 1 1 1 1 1 1 1 
 
 LlI 
 O 
 
 Z 
 
 o 
 
 CJ 
 
 H 
 CO 
 
 g "200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 2,200 
 
 PANEL DEPTH, ft 
 
 FIGURE 6. - Relationship between panel depth and average support dust concentration at surveyed 
 longw/all faces. 
 
 I 
 
 F, the roof broke off in front of the 
 canopies, leaving cavities in the roof 
 and above the support canopies after they 
 were advanced. The smaller contact area 
 between the roof and support canopies was 
 highly stressed and fractured. When the 
 support was lowered to be moved, debris 
 accumulated on the canopy and was further 
 crushed under setting loads, producing 
 respirable dust. To reduce debris build- 
 up, contact advancement of the supports 
 should be utilized to scrape the debris 
 off the canopies as the supports are 
 advanced. 
 
 Water application on the immediate roof 
 may also help reduce support-generated 
 dust. The residual moisture on the roof 
 should suppress some of the dust during 
 the crushing and grinding action of roof 
 supports. At longwalls A and B, which 
 had the least support-generated dust, the 
 roof was wet with the shearer. However, 
 
 it was difficult to determine what effect 
 the water had on the roof support dust 
 because these longwalls had the strongest 
 roofs and the best mining conditions. 
 
 Airflow can also affect dust concen- 
 trations. If the air velocity along 
 the face is maintained in a moderate 
 range, from 350 to 600 ft/min, good dust 
 diffusion and dilution can be achieved 
 some distance downwind from the generat- 
 ing source, as shown in figure 7 (_3 ) . 
 Below this range, dust levels can be sig- 
 nificantly higher because of inadequate 
 dilution and diffusion. Above this 
 range, dust levels can also be signifi- 
 cantly higher because of dust entrainment 
 at higher airflows. However, this trend 
 was not observed in the present study be- 
 cause support dust measurements were made 
 adjacent to support movement, not allow- 
 ing sufficient time for diffusion and 
 dilution. 
 
 SUPPORT DUST CONTROL TECHNOLOGY USED IN THE UNITED STATES 
 
 Several support dust control techniques 
 were observed to be in use or on trial in 
 the United States. These techniques in- 
 volve water application and/or support 
 
 movement practices. The effectiveness of 
 some of these techniques is unknown, and 
 some of them may be impractical for cer- 
 tain longwall operations. 
 
12 
 
 AVERAGE FACE AIR VELOCITY, m/s 
 
 2 3 4 
 
 200 400 600 800 
 
 AVERAGE FACE AIR VELOCITY, ft/min 
 FIGURE 7. - Relationship between face air velocity and dust levels at the face (3). 
 
 000 
 
 WATER APPLICATION 
 
 Several water application techniques 
 for longwall support dust control cur- 
 rently practiced in U.S. coal mines are 
 discussed briefly below. 
 
 Support Washdown . - One shearer opera- 
 tor uses a shearer water hose to hose 
 down the supports and roof during the 
 head-to-tail or tall-to-head pass. The 
 residual moisture reduces dust entrain- 
 ment when the supports are moved. For 
 this procedure to be effective, suffi- 
 cient water must be supplied to the 
 shearer so that its internal and external 
 water systems are not affected during 
 washdown. 
 
 Wetting Immediate Roof With Shearer 
 Water . - This can be done in several 
 ways. One way is to maintain suffi- 
 cient water pressure at the drum sprays 
 to wet the roof while it is being cut. 
 Also, during the cleanup pass in a uni- 
 directional operation, the lead drum, 
 which typically will not be cutting much 
 material, can be freewheeled near the 
 roof, allowing the water sprays to wet 
 the roof. Another alternative is to 
 spray the unsupported roof using one or 
 
 several water sprays mounted on top of 
 the shearer body, directing the water 
 with the airflow and upward at an angle 
 of approximately 45°. 
 
 Mounting Water Sprays on Support Cano- 
 pies Over Panline . - Water sprays can be 
 mounted on the support canopies in sev- 
 eral ways. Usually several sprays are 
 directed down at the face and in the 
 direction of the airflow from a manifold 
 at every tenth support (fig. 8). Their 
 purpose is to humidify the face area to 
 suppress support dust generation. The 
 suppression effectiveness of these sprays 
 has not been documented; however, studies 
 indicate that they actually move air 
 and help diffuse and dilute the dust 
 from supports. Drawbacks are that these 
 sprays are difficult to maintain and tend 
 to wet the face personnel. 
 
 OTHER DUST CONTROL PRACTICES 
 
 Where water application might deterio- 
 rate the roof and floor, the practices 
 described below are employed during sup- 
 port movement to reduce the dust exposure 
 of face workers; these practices can also 
 be used in conjunction with water. 
 
13 
 
 FIGURE 8. - Spray manifold located on support canopy. 
 
 Minimizing Debris on Top of Canopies . - 
 Debris on top of shield canopies can be 
 minimized by contact advancing supports 
 (shields) so that the debris can be 
 scraped off the canopies into the gob. 
 This avoids crushing and grinding of de- 
 bris during support movement and thereby 
 generally reduces resplrable dust genera- 
 tion (fig. 9) (4^). Also, maintaining 
 good horizon control during mining yields 
 more contact area between the support 
 canopy and the roof , which reduces highly 
 stressed areas on the roof and minimizes 
 spaces or cavities where debris can build 
 up. 
 
 Advancing Supports During Pass Cycle 
 Against Airflow . - This practice can be 
 employed on unidirectional operations , 
 allowing all face personnel to work on 
 the intake-air side of support advance. 
 When the pass cycle against airflow is 
 
 used as a cleanup pass, dust levels gen- 
 erated by the shearer are low, and al- 
 though the support movers are on the 
 return-air side of the shearer, the dust 
 exposure levels they are subjected to can 
 be kept low. When the primary cut is 
 taken against the airflow, a properly de- 
 signed external shearer water-spray sys- 
 tem (shear clearer) can confine shearer- 
 generated dust against the face for 
 approximately 40 ft (fig. 10), thus main- 
 taining an acceptable dust-exposure level 
 for the support movers immediately down- 
 wind of the shearer (_5) . 
 
 Diluting and Diffusing Support Dust 
 When Supports Are Advanced With Air- 
 flow . - It is not always possible to 
 advance supports only on the return-air 
 side of the shearer. Roof conditions 
 may necessitate support advance immedi- 
 ately after the shearer cuts the face. 
 
14 
 
 1.0 1.5 2.0 
 
 DEBRIS THICKNESS ON CANOPY, in 
 
 FIGURE 9. - Relationship between debris thick- 
 ness on shield canopy and dust generated (4). 
 
 Bidirectional cutting requires support 
 advance during both directional passes. 
 In some operations, it may not be possi- 
 ble to install an external water-spray 
 system capable of confining the dust 
 against the face for any substantial dis- 
 tance downwind of the shearer. Under 
 these circumstances, the most feasible 
 method of dust control is to dilute and 
 diffuse the dust by increasing the dis- 
 tance between support movement and the 
 shearer. Figure 11 shows how dust levels 
 in the walkway decrease with increases in 
 distance downwind from support movement. 
 Based on the walkway dust levels shown in 
 figure 11, it is recommended that a dis- 
 tance of at least 50 ft be maintained 
 between support movement and the shearer. 
 Increasing the face airflow also promotes 
 dilution and diffusion (6^). However, 
 face velocities should not exceed 600 
 ft/min, to prevent dust entrainment. 
 
 < 
 
 o 
 
 z 
 o 
 
 O m 
 
 51 
 
 D 
 Q 
 CO 
 
 o 
 
 LU 
 
 z 
 < 
 
 Z 
 < 
 
 CO 
 
 10 
 8 
 6 
 4 
 2 
 
 
 Direction of airflow 
 
 < 
 
 Direction of cut 
 
 Without shearer clearer 
 
 50 40 30 20 
 INTAKE SIDE, ft 
 
 Shearer 
 
 FIGURE 10. - Effectiveness of shearer-clearer system 
 
 20 30 40 50 
 RETURN SIDE, ft 
 
15 
 
 10 20 30 40 50 60 
 
 DISTANCE DOWNWIND OF SUPPORT ADVANCE, ft 
 
 FIGURE 11. - Relationship between distance downwind of support movement and dust level. 
 
 CONCLUSIONS 
 
 I 
 
 Although several factors can affect the 
 amount of respirable dust generated by 
 longwall supports, this study indicates 
 that geologic conditions (roof conditions 
 and depth of cover) are the most signifi- 
 cant factors. The amount of support dust 
 generated was inversely related to roof 
 strength and directly related to depth of 
 cover over the longwall panel. Some 
 techniques for controlling support dust 
 generations are currently in use. Al- 
 though some of these techniques have lim- 
 itations, they should be applied if 
 support-generated dust makes up a signif- 
 icant portion of the face personnel's 
 overall dust exposure. 
 
 Further research and development are 
 needed to advance longwall support dust 
 control technology, to improving effi- 
 ciency and to overcome the limitations of 
 the existing techniques. The objective 
 
 of this research should be improved sup- 
 port design. One area that needs to be 
 addressed is reducing stresses on host 
 strata from supports while maintaining 
 acceptable roof convergence. Certain 
 roof types are more susceptible to crush- 
 ing and grinding from longwall roof sup- 
 ports , and therefore they generate more 
 dust during support movement. An im- 
 proved seal between supports needs to be 
 developed to prevent the dust from the 
 roof and gob areas from entering the face 
 area. It appears that the side seals 
 presently used on supports allow a sig- 
 nificant amount of dust to seep into the 
 face area from the gob and roof. Final- 
 ly, a reliable automated support advance 
 system would allow all face personnel to 
 be positioned upwind of the dust gener- 
 ated by support movement. 
 
16 
 
 REFERENCES 
 
 1. Jankowski, R. A., and J. A. Organ- 
 iscak. Dust Sources and Controls on the 
 Six U.S. Longwall Faces Having the Most 
 Difficulty Complying With Dust Standards. 
 BuMines IC 8957, 1983, 19 pp. 
 
 2. Peters, W. C. Exploration and Min- 
 ing Geology. Wiley, 1978, p. 159. 
 
 3. Mundall, R. L. , R. A. Jankowski, 
 T. F. Tomb, and R. S. Ondrey. Respi- 
 rable Dust Control on Longwall Mining 
 Operations in the United States. Pa- 
 per in Proc. 2d Int. Mine Ventilation 
 Symp., Nov. 2-8, 1979, Reno, NV, 
 9 pp.; available upon request from Univ. 
 Reno. 
 
 4. National Coal Board (London). Re- 
 port on Visit to Houillleres du Bassin de 
 Lorraine, Freyming Merebach, for Meeting 
 of Sub-Committee on Dust From Roof Sup- 
 ports. Visit Rep. (82)7, Nov. 17-19, 
 1982, 5 pp. 
 
 5. U.S. Bureau of Mines. Reoriented 
 Shearer Water Sprays Move Dust Toward 
 Face. Technol. News 112, Oct. 1981. 
 
 6. . Reduce Dust on Longwall 
 
 Faces With a Gob Curtain. Technol. News 
 119, Nov. 1981. 
 
 7. 
 
 Improved Respirable Dust 
 
 Monitor. Technol. News 72, Oct. 1979. 
 
APPENDIX A. —DATA FROM LONGWALL SURVEY 
 
 TABLE A-1. - Numerical data from survey 
 
 17 
 
 Longwall ' 
 
 B 
 
 D 
 
 E 
 
 H 
 
 Seam thickness ft.. 
 
 Seam depth f t. . 
 
 Roof strength (est) psi.. 
 
 Canopy area f t^. . 
 
 Setting pressure pslg. . 
 
 Av set load density on roof 
 
 tons/ft2. . 
 psi.. 
 
 Roof loading factor^ 
 
 Yield pressure psig. . 
 
 Yield load tons. . 
 
 Av face air velocity f t/min. . 
 
 Av support dust cone along face: 
 
 RAM RAM units . . 
 
 Gravimetric mg/m^ . . 
 
 Av Average. cone Concentration 
 ^ See table A-2 for description of 
 ^Average roof strength/ average set 
 
 5 
 
 320 
 
 10,000 
 
 55.0 
 
 4,350 
 
 8.2 
 
 113.9 
 
 87.7 
 
 5,440 
 
 564 
 
 580 
 
 0.4 
 0.3 
 
 6 
 
 500 
 
 10,000 
 
 55.0 
 
 4,350 
 
 8.2 
 
 113.9 
 
 87.7 
 
 5,440 
 
 564 
 
 289 
 
 0.4 
 0.1 
 
 6 
 
 1,320 
 
 4,000 
 
 42.0 
 
 4,350 
 
 9.7 
 
 134.7 
 
 29.7 
 
 4,570 
 
 426 
 
 167 
 
 0.8 
 1.7 
 
 6 
 
 430 
 
 650 
 
 50.7 
 
 4,000 
 
 2.9 
 
 40.3 
 
 16.1 
 
 9,580 
 
 352 
 
 402 
 
 0.6 
 1.0 
 
 9 
 
 1,600 
 
 4,000 
 
 42.8 
 
 4,350 
 
 7.8 
 
 108.3 
 
 36.9 
 
 6,150 
 
 472 
 
 184 
 
 2.4 
 1.3 
 
 9 
 
 1,600 
 
 4,000 
 
 42.8 
 
 4,350 
 
 7.8 
 
 108.3 
 
 36.9 
 
 6,150 
 
 472 
 
 179 
 
 1.7 
 1.5 
 
 1,600 
 
 650 
 
 57.6 
 
 4,350 
 
 5.3 
 73.6 
 8.8 
 6,730 
 472 
 650 
 
 5.5 
 10.7 
 
 8 
 
 2,200 
 
 650 
 
 54.0 
 
 4,500 
 
 5.8 
 80.6 
 8.1 
 6,300 
 440 
 355 
 
 2.6 
 3.0 
 
 est Estimated, 
 longwalls. 
 load density. 
 
 I 
 
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APPENDIX B.— DUST-SAMPLING STRATEGY^ 
 
 19 
 
 Support-generated dust was sampled with 
 both instantaneous and gravimetric sam- 
 plers. The instantaneous sampler used 
 was the GCA Real-Time Aerosol Monitor 
 (RAM). This is a light-scattering in- 
 strument that measures the volume of res- 
 pirable dust in a volume of air instan- 
 taneously (_7 ) . Its numerical output is 
 in RAM units, which approximate respira- 
 ble dust concentrations in milligrams per 
 cubic meter. The gravimetric samplers 
 consisted of a pump, cylone, and filter: 
 A Dupont model P-2500 pump drew 2 L/min 
 of air through a 10-mm Dorr-Oliver nylon 
 cyclone and deposited the respirable dust 
 on a 5-ym MSA preweighed cassette filter. 
 This sampler gave an average weight per 
 unit volxome of air in milligrams per cu- 
 bic meter. 
 
 The amount of respirable dust generated 
 by support movement was measured by 
 two people, each using one RAM and two 
 gravimetric samplers. Samples were taken 
 on the immediate upwind side of each 
 
 ^Dust concentrations were measured only 
 during support movement and cannot be 
 directly related to an 8-h average expo- 
 sure for compliance purposes. 
 
 support moved and on the immediate down- 
 wind side of each support moved. Sam- 
 pling followed support movement along the 
 face, with gravimetric samplers continu- 
 ously running and RAM measurements taken 
 at every other support. The difference 
 between the downwind concentrations and 
 the upwind concentrations indicated the 
 amount of dust generated by supports 
 (shaded areas between curves in figures 
 2, 3, and 4). 
 
 RAM measurements were also made at some 
 faces to determine the effect of ventila- 
 tion on the diffusion and dilution of 
 support dust. These measurements were 
 made in an area of the face during move- 
 ment of about 12 supports. Sampling was 
 conducted from a stationary position 
 downwind of all the supports to be moved. 
 During the advance of each support , the 
 dust concentration at the stationary po- 
 sition was measured and the distance from 
 the support moved was recorded. The con- 
 centrations measured at various distances 
 from the supports were used to show how 
 support-generated dust is diluted and 
 diffused by face ventilation, yielding 
 lower dust concentrations at greater dis- 
 tances downwind of support movement. 
 
 i!rU.S. CPO: 1985-505-019/20,040 
 
 INT.-BU.OF MINES, PGH., PA. 27953 
 
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