Document 5LMGnzQZ4OrwqBGVypwdO7EEN

Chapter 56 DUST CONTAMINATION OF PANEL/FACE INTAKE AIR Shambhu Sharan, Raman Srikanth, Peikun Liu, Guangyu Sun, Bharath K. Belle, and Raja V. Ramani Department of Mineral Engineering, The Pennsylvania State University, University Park, PA ABSTRACT The contnbution of the various outby sources to tho contami nation of the panel intake air has been the subject of a relatively small number of studies. In this paper, after a brief review of past studies, results from recent experiments on rates of contamination of intake air by outby dust sources are presented. Present study indicates that each outby source by itself may not be a major con tributor. Tho loading point in the continuous miner section did not appear to be of major concern Irom contamination point of view. Belt entry including transfer point contributes significantly to the intake air dust level, though reentrainment was not a major source of dust. In longwall panels, the stageloador-crusher was the most dominant source. The panel-to-main bolt transfer point was not a major source. Taken collectively, the contribution of all outby sources can be significant. In one longwall section, at the begin ning of the longwall face, the contribution of all the outby sources and the headgate cut-out operation was observed to be about 80% of the permissible exposure limit (2 mg/m1). In modern high production longwalls. the application ol effective dust control mea sures to reduce the dust generated from tho outby sources is es sential to achieve compliance with the dust standards. INTRODUCTION The concern over the high incidence of fires in the belt and trol ley haulage entries led to the regulation of tho air quantity and velocities in these entries under the Federal Coal Mine Health & Safety Act of 1969 (MSHA. 1989). With regard to the belt entry ventilation, the regulation further specified the isolation of the belt entry from intake and return aircourses, and the dumping of air in the belt entry directly into the return. In addition to the immediate impact on the air distribution system, this provision affected mine ventilation planning as well. The use of belt entry as an intake air way for ventilating tho working faces has been a matter of discus sion between MSHA. mine operators and mine workers since the early days of the legislation. Several petitions were filed by the operators requesting permission to use tho belt ontry to ventilate the active workings; several were approved contingent upon In creased monitoring of the ambient air quality in the belt entry. An MSHA committee, appointed by the Assistant Secretary of Labor to review the major aspects of tho belt entry ventilation is sues, concluded the following among others (MSHA. 1989). Safety improvements can be made in the belt conveyor entries of the underground coal mines, particularly in the area ol fire protection. Directing belt entry air to the working face can at least be as safe as other ventilation methods provided carbon monoxide monitors or smoko detectors aro installed in the belt entry. Proper design of ventilation system can protect escapeways from rapid smoke contamination in the event of belt fire. There is no reason to relax the requirement of separating belt haulage entries from return air courses. The review committee identified other issues those arc rel evant to tho use of belt entry for ventilation including the impact on airborne respirable dust concentration, and fighting fires in the belt entry, but found that the contribution of belt air to the respi rable dust concentration in the face is not significant oven though the belt air is more dusty than the primary intake air. An Advisory Committee appointed by the Secretary of Labor on the use of air in belt entry to ventilate production areas concluded that velocity limits (minima and maxima) in belt ontry should bo based on methane layering and dust entrainment such that methane and dust levels are at or below the levels specified in the standards (MSHA. 1992). BACKGROUND According to MSHA, longwalls in continuous compliance of federal dust standards decreased from 40% in 1990 to 28% in 1995. Although dust levels have remained relatively unchanged over this period, averaging 1.7 mg/m3, approximately 25% of the operating longwalls were in noncomplianco during any given bi monthly sampling cycle. Among the reasons attributed to the emergence of these compliance problems are higher production rates and productivity, higher gas and dust emission rates, and the increased face widths and panel lengths. To meet the in creased air quantity requirement at the face, mines are seeking permission to use the belt entry air for face ventilation. Using belt air in the face can lead to tho contamination of intake air from several outby sources including loading points, belt and transfer points. Organiscak, Jankowski and Kelly (1986) identified the stagoloader-crusher as the dominant outby dust source in a longwall panel contributing to more than 50% of dust exposure of the shearer operators. The contnbution of the panel belt was also significant representing 25% of the permissible exposure limit of 2 mg/m3. According to a recent report (Organiscak and Jankowski, 1996). the combined contribution of all outby dust sources to longwall face dust level has decreased from 51% in early 1980's to 41% in early 1990's indicating improvements in controlling contamination from outby sources. While not strictly an outby source, the headgate cut-out opera tion In a longwall face is a major source of contamination of the face intake air at tho beginning of the face. The duration of headgate cut-out operation is small in comparison to that of tho cutting cycle; however, tho potential for the contamination of in take air is significant. In a number of field evaluations (Cecala, 354 PROCEEDINGS OF THE 6TH INTERNATIONAL MINE VENTILATION CONGRESS Organiscak and Jankowski. 1987), respirable dust lovels of 20 to 30 mg/m3 have been observed at the shearer operator's location during the headgate cut-out. In high production longwalls. as the number of passes per shift increases, this source becomes even more relevant for control. According to Potts and Jankowski (1992), the average respi rable dust level in the bolt entry upwind of the feeder-breaker in a continuous miner section was 0.26 mg/m1. Feeder-breaker gen erated upto 0.2 mg/m3 of dust. On a longwall mining section, the average respirable dust level in the belt entry upwind of stageloader-crusherwas 0.59 mg/m3. Stageloader-crusher gener ated between 0.5 to 0.9 mg/m3 of respirable dust. The difference in the dust levels measured between the continuous miner section and longwall mining section was attributed to the differences in the production rates. With regard to belt entry dust levels, they found that belt entry length and production rate of the section af fected the dust levels. The entry length effect equated to roughly 0.1 mg/m3 increase in dust for 305 m (1000 ft) increase in length and the production eflect equated to roughly 0.1 mg/m3 increase in dust for 181 to 454 tonnes (200 to 500 tons) per shift increase in production. In this study, the belt speed was 2.03 m/s (400 fpm) and the air velocity varied between 0.53 m/s and 0.91 m/s (105 fpm and 180 fpm). The dust level in the belt entry was unaffected. The benefits of increased dust dilution appeared to outweigh the effects of additional dust sources in the continuous miner sec tion. Due to the increased air quantity, the respirable dust level in this section reduced by 0.1 to 0.3 mg/m3 during cutting. On the basis of a study in six longwall sections, Haney (1996) indicated that the contribution of the stageloader-crusher to face dust levels ranged from 0.5 to 1.3 mg/m3. The concentration of dust in the belt entry approached or exceeded 1.0 mg/m3. How ever, when this air was used in the face, the actual contribution to face exposure was relatively low, in the range of 0.1 to 0.3 mg/m1 because the belt air flow was a small percentage of total intake going to the face. He concluded that the use of belt air will gener ally increase the intake dust level; however, depending on the specific section, dust control and ventilation configuration, the dust exposure of face occupation could either go up, go down, or remain unchanged. DESCRIPTION OF EXPERIMENTS In the present study, two sets of experiments were conducted to study the intake air contamination. In the first set. dust surveys were conducted in three mines which were not using belt air for face ventilation but employed longwalls. In these mines (Minos A1. B1 and Cl), dust surveys were limited to the longwall face area including the intake and stageloader-crusher. In the second set. dust surveys were conducted in four mines which were using Sampling station Figure 1. Layout of sampling stations In continuous miner section in Mine A2. Figure 2. Layout ot sampling stations in the longwall sections. belt entry air for face ventilation. In these mines (Mines A2, B2, C2 and D2), the survey was extended to estimate the contribution of outby dust sources viz. stageloader-crusher in the longwall sec tion, feeder-breaker in the continuous miner section (Mine A2). panel belt entry, and panel-to-main belt transfer point. Sampling Plans The sampling plans were specifically developed to isolate and quantify the dust contamination arising from the following outby dust sources: Loading point in the continuous miner section : For determin ing the contribution of the loading point in the continuous miner section, two expenments were conducted in mine A2. The layout of the sampling stations is shown in Figure 1. At each station, a gravimetric personal dust sampler was used to determine the av erage respirable dust concentration at that station for the sam pling period. In addition, at stations 1 and 2, a RAM was also in stalled to provide a continuous record of dust concentration pro file during the experiment. Stageloader-crusher: In mines A1, B1 and Cl, during the first set of experiments, one sampling station was located in the intake cross-cut and the other between shield-5 and shield-10 close to the head gate. These are indicated as stations 1 and 2 in Figure 2. Gravimetric personal dust samplers were used to delermine the airborne respirable dust concentration in the intake and the headgate station. The increase in concentration from station 1 to station 2 is attributed to the contamination from the stageloadercrusher and the headgate cut-out. In mines B2, C2 and D2, a third sampling station upwind of the stageloader-crusher was added to the earlier experimental design (station 3 in Figure 2). Gravimetric personal samplers were used to determine the average respirable dust concentration during the sampling period. Additionally RAM units were also set at station 2 and 3 in order to determine the dust generation rate of the stageloader-crusher during the time the shearer is cutting coal. This experimental setup is used to determino the contributions of the stageloader-crusher, the belt entry and the primary intake to the dust level in the intake air to the face. Panel Belt: The panel in mine A2 was a continuous miner panel whereas the panels in mines B2. C2 and D2 were longwall production panels. The length of the belt entry in the continuous miner panel was about 2440 m (8000 ft) and in the longwall pan els, it was between 915 to 1065 m (3000 to 3500 ft). A number of sampling stations (5 to 8) was established along the panel belt DUST CONTAMINATION OF PANEL/FACE INTAKE AIR 355 from the head to the tail. The stations were 90 to 270 m (300 to 900 ft) apart in longwall belt entry and 395 to 670 m (1300 to 2200 It) in the continuous miner belt entry. Gravimetric personal dust sampler was used to determine the average rospirable dust con centration at the stations. Panel-to-main belt transfer point: To estimate the contamina tion of air in belt entry by the panel-to-main belt transfer point, two sampling stations were established in mines B2. C2 and D2 one outby the transfer point in the main belt ontry and the other inby of the transfer point in the panel belt entry. Gravimetric personal dust samplers were used for respirablo dust sampling. RESULTS rable dust concentration at the three sampling stations for the two experiments in mine A2 are shown in Table 1. In both the experi ments, airborne respirable dust concentration at the sampling sta tion 2 was below 1.0 mg/m3. The increases in concentration (rom station 1 to station 2 were 0.38 mg/m1 and 0.20 mg/m3 in experi ments 1 and 2, respectively. Those can be viewed as the amount of contamination by the loading point. In exporimonl 1,70% of the soction air was flowing through the belt entry. The respirable dust concentration at station 3 was 0.5 mg/m1. Thorofore, the contribu tion of the loading point to the section intako was 0.26 mg/m3. In other words, 52% of the overall respirablo dust level of the com bined section intake is the result of contamination from the load ing point. Tabie 1. ARD corcewraiion at the t-.-aa sanding In M-ne A2* Mine A2 Experi- Average ARD Concentration ment (mg/m5) No. Station 1 Station 2 Station 3 1 0.29 067 050 2 0.28 0.48 0.47 Soa Figure i The respirable dust concentration profiles recorded by the RAMs at station 1 and station 2 for experiments 1 and 2 are shown in Figure 3. Using the production, air quantity and the RAM data calibrated to the gravimetric respirable units (mg/m*), the average airborne respirable dust generation rates at the loading point can be calculated for a given time interval. For example, for two dilferent time intervals during experiment 1. the average air borne respirable dust generation ratos wore found to be 579 mg/ tonne and 237 mg/Ionne. In experiment 2. the results fortwo time intervals were 58 mg/tonne and 32 mg/tonne. The high dust genoration rates in experiment 1 are indicative of the occasional dust control problems expenenced at the loading point. The variability in the dust generation rates in experiment 2 is attributed to the normal changes in production rate and air quantity. Stageloader-crusher: The airborne respirable dust concentra tion and air quantity measured at station 1 and station 2 in mines A1.B1 and Cl are shown in the Table 2. The Increase in the con centration from station 1 to station 2 Is due to the dust generated Irom the stageloader-crusher and headgate cut-out operations. The mean contribution of the stageloader-crusher and headgate cut-out in mines A1, B1 and Cl were 0.37 mg/m\ 1.31 mg/m* and 1.34 mg/m1, respectively. Clearly, the stageloadercrusher and headgate cut-out operation in combination continues to bo a major source of contamination at the beginning of the longwall face. Data from the second set of experiments (mines B2, C2 and D2) were analyzed to determine the concentrations at stations 1. 2 and 3. These concentration data along with the air quantity data at these stations are shown in Table 3. These data are used to calculate the contributions of the belt entry, the primary intake and the stageloader-crusher/cut-out operations to the dust level at the headgate station (Figure 2, station 2). The concentration at station 3 (upwind of stageloader-crusher) is due to the contamination from the belt entry. The concentration at station 1 (intake cross cut) is due to the contamination by sources upwind in the primary intake. The concentration at station 2 (headgate station) is due to the concentrations at station 3, station 1 and the addition of dust by the stageloader-crusher and headgate cut-out operations. The belt entry contribution to the concentration at station 2 in experi ment 1 of mine B2 is shown in Table 4 as 56% and is calculated from Tablo 3 data as follows : ({(1.12)(7.438)/ (0.87)(7.438+9.713)) x 100 = 56%]. The contribution from the belt entry to the concentration of 0.87 mg/m1 at station 2 is 0.49 mg/ m3 (0.87x0.56). Similar calculations are made for the primary in take where the contribution is 0.12 mg/rn1, i.e. 14% of the concen tration at station 2. Finally, the contribution of the stageloader/ headgate cut-out operations (0.26 mg/m1 or 30%) is calculated as the difference between the concentration at station 2 and the sum of the contributions from the belt and the primary intake, I.e. (0.87(0.49+0.12) = 0.26 mg/m3]. As shown in Tablo 4, the contribution of the stageloadercrusher/headgate cut-out operations to the face intake dust level ranged from 0.26 to 0.97 mg/m* and as a percent of the dust level a! station 2. it is between 20% to 66%. and between 13% to 48% of the permissible exposure limit of 2 mg/m3. In mine B2. data was a>socollected on the face concentrations. It was observed that the contribution of the stageloader-crusher/headgate cut-out opera tions ranged from 13% to 56% of the average face concentration. During the experiments in mine B2. data was collected on the production from the longwall face and a time study was also con ducted on the shearer operation. Using the RAM data collected at station 3 and station 2 (when the shearer is downwind of station 2) and assuming that the primary Intake concentration does not change during these periods, it was possible to determine the contribution of the stageloader-crusher alone to the concentration at station 2. Knowing the production during these periods, total air quantity (sum of air quantity at station 1 and station 3) and the contribution of the stageloader-crusher alone, the dust generation rate of the stagoloador-crusher was calculated in terms of mg/ tonne. The dust generation rates of the stageloader-crusher dur ing experiments 1,2 and 3 were 14,60 and 47 mg/tonne, respec tively. Difference in tho cutting rates of the shearer and changes in the air quantity (primary intake and belt air) are some of tho reasons for the variation m the dust generation rates. Panel Belt Entry: In mines A2. B2, C2, and D2. for all the sam pling stations along the panel belt entries, the respirable dust con centrations and the air quantities flowing in the entry at these lo cations were obtained. In all the panels, the belt speed was ap proximately 3.25 m/s; the air velocities ranged from 0.81 m/s to 2.50 m/s. Air quantity flowing through belt entry ranged between 34% to 69% ol the total quantity delivered at the face. The respi rable dust mass flow rates at the stations (the product of tho air quantity at the station (m*/s) times the average airborne respirable dust concentration (mg/m1) at the station) is used to determine the rate of contamination of the air flow along the belt entry. Shown in Figures 4 and 5 the airborne respirable dust (ARD) concentra tion. air quantity and ARD mass flow rate for stations in the con tinuous minor section (Mine A2), and the longwall production pan- 356 PROCEEDINGS OF THE 6TH INTERNATIONAL MINE VENTILATION CONGRESS Figuio 3. ARD concentration* Time (hr:mm) and downwind ot the oadng pdnIn Mine A? el in mine C2. respectively. In the continuous miner section (Fig ure 4), the airborne respirable dust concentration remained al most unchanged and the air quantity decreased as the air moved towards the face due to leakage into the return. This resulted in a decrease in the airborne respirable dust mass flow rate. Insignifi cant change in the dust concentration coupled with a decrease in the air quantity indicates that there was no significant net addition of dust to the air in the belt entry. In all the longwall panels, the air quantity increased as the air moved towards the face due to leak age from the primary intake. The respirable dust concentration either remained unchanged or increased from the head of the belt towards the face. As a result, the average respirable dust mass flow rate increased towards the face as shown in Figure 5. The incremental mass flow rate of respirable dust in the belt entry air for every 305 m (1000 ft) length is calculated for all the experi ments (Table 5). Increasing mass flow rate of respirable dust in the belt entry air flowing towards the face can be duo to dust en trained from the belt, walking or other movements in the belt en try. As the floor was generally wet, contribution of walking and other movements can be considered negligible. In the continuous miner section, the contribution of the belt entry was 0.2 mg/m\ This is 40% of the combined intake dust level, and 10% of the permissible exposure limit of 2.0 mg/m'. As discussed oarlior, the contribution of the belt entry in contaminat ing the face intake ranged from 0.24 to 0.49 mg/m3 (Table 4) in the longwall production panels. This contribution ranged from 15% to 56% of face intake dust level, i.e. 12% to 24% of the permissible exposure limit of 2 mg'm1. PaneMo-main Belt Transfer Point: The respirable dust con centrations at the sampling stations established to quantify the dust generated by the panel-to-main belt transfer point in mines B2, C2 and D2 are shown in Table 6. Dust generated at this outby source rangod from 0.017 mg/m3 to 0.1 mg/mJ. In mine B2. the air in belt entries travel all the way from the surface through the main belts to panel belts. This may be the reason for the comparatively higher rate of contamination in mine B2. Cumulative Effects: In longwall production panels, the cumu lative effect of all the outby sources can be quite substantial. The DUST CONTAMINATION OF PANEL/FACE INTAKE AIR 357 Table 2. ARD cotvcenlratfon and air quantity at station t and station 2' Mine Experi ARD Concentration Air Quantity CTC7 ment mg/m3 m3/s mg/m3 No. Station 1 Station 2 Station 1 Station 2 (Ci) (C,) A1 1 0 38 0.42 25.485 11.706 0.04 2 0.07 0.32 N.A. 14.358 0.25 3 0.13 0.75 21.252 14.231 0.62 4 0.25 0.45 25.018 11 291 0.20 5 011 0.80 16 914 9.836 0.69 6 0.09 0.62 14.619 11 964 0 53 7 0.11 0 34 26.775 6.584 0.23 8 0.09 0.47 19 326 14.111 0.38 Mean 0.15 0.52 0.37 B1 1 0.56 1.75 N.A. 11.235 1.19 2 1.34 3.44 18.972 12.833 2.10 3 0.45 1 08 15.004 13.148 0.63 Mean 0.78 2 09 1.31 Cl 1 021 1 51 3.874 4 165 1.30 2 1.00 3.13 6.387 3276 213 3 0.45 2.91 8 187 7.148 246 4 0.83 1.32 5 124 NA 0 49 5 1.51 1.82 10 660 5.697 031 Mean 0 80 2.14 1.34 Grand mean 0.47 1.32 085 RAM dust profile from one of the experiments in mine B2 is shown in Figure 6. The RAM was mounted on shield 8. There were 162 shields at the face and, therefore, the shearer was up wind of the RAM for loss than 5% of the operating timo. Yet. the RAM profile indicates significant peaks in the concentration pro file when the shearer is downwind of RAM. presumably from all sources outby the face. The contribution of the loading point and the belt air to the in take air dust level in the continuous miner section did not appear to be a matter of concern. -4- S 0.3 e . I 0.2 - - . 2 a- 2 < 0.0 - -------------- 1------------1-------------- 1--------------- 1------------- 2500 2000 1500 1000 500 0 Distance from face (m) DISCUSSION This study has quantified the contributions of the outby sources such as stageloader-crusher/feeder-breaker, panel belt, and panel-to-main belt transfer point to the contamination of the Table 3. ARD concentration arid air quantity at the throe sampling stations In tongwull production panels' Mme Expen- ARD Coneentrnt.cn (mflW') Ar Cuanlity (rn'ts) men! No Station 3 Slaton 1 Station 2 Station 3 Staton 1 Staten 2 tJ2 1 1.120 0 220 0 070 7 438 9713 14.161 2 0 700 1.600 1 020 7 810 15 038 19.040 3 0916 0 280 1 400 8 814 17 481 14 704 C2 1 0 437 0 302 0 481 15 223 N A 0 527 0 242 1.021 15.223 NA. 26051 2 0.541 0 348 0960 16.915 7 646 22.895 'See Figure 2 Table 4. ContibuDonol stageloader-au9herand panel beltin corenminafoK) iniake air Mm. U2 U2 E>ponman! 1 7 3 2 Milan Contnmr.cn |%) Dell Primo'y St^oEnty 56% 14% 30% 15% 65% 20% 21% 13% 65% jy% 11% 50% 33% 26% 42% CcntiSxflon (marm'i Hell Prim ;r* aa,,Entr, Intake irn/J.ir 0 44 0.12 026 0 2A 1.05 0 33 031 019 097 0 3/ 0 11 04B 0 35 037 0 61 Cont'tiution (% irf PEL'J b-t I'lrmry Staflc- (rntiy IfiU-e 24i 6% Icadsr 13% 12% 53% 16% 15% 9% 48% 14% 5% 24% 18% 18% 25% PermlstUblo Exposure Limit ot 2 m^'m' 2500 2000 1500 1000 500 0 Distance from face (tn) Figure 4. ARD concentration, air quantity ar-d ARD mass tlow rote In tho bolt entry ot mine A2. intake air. The results of the study indicate that outby dust sources have significant potential to contaminate the intako air. In the continuous miner section, the airborne respirable dust level in the combined intake was less than 0.5 mg/m3. The load ing point does not appear to be a major contnbutor. The respirable dust level in the belt entry remained almost unchanged indicating very little contamination. This may be due to low production rate from the section resulting in low rate of coal transport through tho section belt. In the longwall production panels, the slageloader-crusher was found to be the most significant source. The control of dust from this source needs considerable attention irrespective of whether the belt air is used for face ventilation or not. Experiments in mines B2, C2 and D2 indicated that the contribution of fhe stageloader-crusher and headgate cuf-out varied from 20% fo 66% of the face intake dust level, and between 13 to 48% of the permissible exposure limit for face workers. The control of dust 358 PROCEEDINGS OF THE 6TH INTERNATIONAL MINE VENTILATION CONGRESS "I 1.0 - E 0.8 - c0 1 0.6- ouc 0.4 u 0.2 - o.o 800 *______ --1--------------- 1---------------- 1--------------- 000 400 200 0 Distance from face (m) table 5 Increase In ARD mass How rate evory 305 m (100II) In Iho bell entry Mine B2 C2 D2 Expertment No. 1 2 3 1 1 2 Increase in ARD mass flow rate (mg/s) 1.638 0.875 1.445 1.713 1.003 0.612 Table 6 ARD concentration near the panet-tO-mam bet) transferpoint Mine Expert- Upwind of Downwind of Increase in ment transfer point transfer point concentration No (mg/nr) (mg/m!) (mg/m3) B2 1 2 0.430 0 280 0.470 0.380 0.040 0.100 3 C2 1 D2 1 0.410 0.545 0.461 0.430 0.562 0.488 0.020 0.017 0.027 at a maximum relative air ve'ocity of 5.75 m/s with respect to coal over belt. At higher relative velocities (either higher belt speed or higher air velocity or both), the situation can be different. The contribution of the panel-to-main belt transfer point was found to be the lowest among all the outby dust sources. In all the experiments, respirable dust generated at the transfer point ranged from less than 1% to 5% of the permissible exposure limit of 2 mg/m'. Fortunately, the impact of most of outby sources of intake air contamination is small. However, in longwall faces, sources like stageloader-crusher and headgate cut-out seem to have a dispro portionately large impact. Since high production longwalte are ex periencing severe problems of staying under the mandated dust levels, the adoption of appropriate engineering control for reduc ing the intake air contamination is particularly important for these longwall faces. Figure 5. ARD concentration, air quantity and ARD mass now ralo in the belt entry o mine C2. generated and entrained from this source, which occurs at the be ginning of the face, will have considerable beneficial impact on longwall face concentrations. The high variability in the dust gen eration rates of the loading point (32 mg/tonne to 579 mg/tonne) and the stageloader-crusher (14 mg/tonne to 60 mg/tonne) re veals the need for monitoring the conditions that cause theso vari abilities. and ensuring all dust control measures are effectively de ployed. Although entrainmont of respirable dust was noticed in the panel belt entry, the contamination was not significant. The abso lute respirable dust level upwind of the stageloader-crusher in longwall panels in all experiments, excepting one, was less than 1 mg/m3. The contribution of the belt entry varied from 12 to 24% of the permissible exposure limit of 2 mg/m3. The contamination of belt air depends on several factors viz. production rate, belt speed, air velocity, wetness of coal, belt maintenance and clean ing practices. In the present study, experiments wore conducted REFERENCES Cecala, A.B., Organiscak, J.A. and Jankowski. R A , 1987. "Meth ane and dust controls for headgate cutouts". Mining Science and Technology. Vol. 4. No. 3, pp. 307-313, Haney. R A., 1996, "Effect of belt air on dust levels in under ground coal mines', Applied Occupational and Environmental Hygiene, Vol. 11, No. 7. pp. 826-829. Jankowski. R.A. and Organiscak, J.A., 1996, "An overview of re search experience as it relates to shearer dust control in the United States', Proceedings of the International Scientific and Technical Conference on Respirable Dust Hazard Control in the World Mining Industry, KOMAG Mining Mechanization Centre, Gliwice, Poland, pp. 5-10. MSHA, 1989, "3e!t entry Ventilation Review: Report of Findings and Recommendations', U.S. Department of Labor, Washing ton, D.C., 42 pp. MSHA, 1992, "Final Report of the belt air Advisory Committee on the use of air in the bolt entry to ventilate the production areas of underground coal mines and related provisions", U.S. De- DUST CONTAMINATION OF PANEUFACE INTAKE AIR 359 Figure 6. ARD concentration profile recorded by RAM at shield 8 in the longwall face In Mine B2. Experiment 1. partment of Labor, Washington, D.C., 82 pp. Organiscak, J.A. and R.A. Jankowski, 1996, "US longwall prac tices (or controlling respirable dust sources outby the shearing machine', Proceedings ol the International Scientific and Tech nical Conference on Respirable Dust Hazard Control in the World Mining Industry, KOMAG Mining Mechanization Centre, Gliwice, Poland, pp. 19-25. Organiscak, J.A., Jankowski, R.A. and Kelly, J.A., 1986, "Dust controls to improve quality of longwall intake ait-, Information Circular 9114, United States Department of Interior, Bureau of Mines, 8 pp. Potts, J.D. and Jankowski, R.A., 1992. "Dust considerations when using belt entry air to ventilate work areas'. Report of Investi gations (RI-9426), United States Department of Interior, Bu reau of Mines, 12 pp.