^■- %,** .V" "-^^'^" .^'\ .^'\ 4 o ^^0^ **'\ »• ^^-^K. -: ,0^ \-^^*\/ %''^^'/ \'^.\/ %"'T^- *^^'. "w* .-^fe--. x/ yM£\ %y:'^^-^ x.-^^' '.' . **'% . ''-W&S j-'X '-WM^ . *«% •■ X'-^^V*. "*%''^^V* X^'^^V"* ''v^^V*°'\''^^ ._^'/ /\ '-^^*" ^^'% \^-' /\ '-^*- /% m ** ** -.^ip/ v^^ % •••w^-" ** % '-mm/ j'-x -.^p*.- «*'% IC 8894 Bureau of Mines Information Circular/1982 How To Evaluate Longwall Dust Sources With Gravimetric Personal Samplers By Steven J. Page, Robert A. Jankowski, and Fred N. Kissell UNITED STATES DEPARTMENT OF THE INTERIOR Lpformation Circular 8894 How To Evaluate Longwall Dust Sources With Gravimetric Personal Samplers By Steven J. Page, Robert A. Jankowski, and Fred N. Kissell UNITED STATES DEPARTMENT OF THE INTERIOR James G. Watt, Secretary BUREAU OF MINES Robert C. Horton, Director This publication has been cataloged as follows: A h O^ ©' Page, Steven J How to evaluate longwall c I U.St sources with gravimetric personal j samplers. ( Bureau of Mines information circular ; 8894). Includes bibliographical refe rences. Supt. of Docs, no .: I 28.27:8894. ]. ( oal mines and mining— Dust control . 2. Mine (. lusts- M ?asure- mcnt. 1. Jankowsk , Robert A » II. Kisse 11, Frt d N. III. 1 it e. IV. Series; Information circular (IJ nited States Bureau of Mines ) . 8894. TN^^&im 622s |622'.42l fTN312] 82-600229 CONTENTS Page Abstract 1 Introduction 2 Sampling method 2 Sampling strategy 2 Calculation examples of mine data 5 Mine 1 — unidirectional head-to-tall cutting sequence with support movement of shearer Intake 6 Mine 2 — unidirectional tall-to-head cutting sequence with support movement on shearer Intake 7 Mine 3 — bidirectional cutting sequence 8 Mine 4 — unidirectional tall-to-head cutting sequence with support movement on shearer return 9 Mine 5 — unidirectional head-to-tall cutting sequence with support movement on shearer Intake 10 Summary 11 Appendix A. — Sampling sequence 12 Appendix B. — Shearer operator dust source contributions for shearers in coiiq>llance 13 Appendix C. — Filter weights and error considerations 14 ILLUSTRATIONS 1 . Hand-held sampler packages 3 2. Sampler vest... 4 3. Sampling location designations 5 TABLES 1. Dust source data for mine 1 6 2. Dust source data for mine 2 7 3. Dust source data for mine 3. 8 4. Dust source data for mine 4 9 3. Dust source data for mine 5 10 B-1, Typical longwall double-drum shearer dust source contributions obtained from a survey of six longwalls regularly in compliance.... 13 i HOW TO EVALUATE LONGWALL DUST SOURCES WITH GRAVIMETRIC PERSONAL SAMPLERS By Steven J. Page, 1 Robert A. Jankowski,2 and Fred N. Kissel! 3 ABSTRACT Longwall double-drum shearers frequently have difficulty complying with the 2,0 mg/m^ dust standard and, therefore, require the use of effective dust controls. However, before dust controls can be imple- mented effectively, the major individual dust sources must be determined and their relative severity evaluated. The Bureau of Mines has recently developed a sampling strategy, based upon short-term gravimetric sampling, that can identify the major dust sources contributing to the shearer operator's exposure. This technique utilizes approved gravimetric sampling equipment already available to all mine operators and can be performed by two people in 2 days. Five examples, including data analysis, are discussed with respect to various cutting sequences. In addition, typical dust source contributions obtained from studies of double-drum shearer operations regularly in conqjliance are included. Mine operators can thereby con5)are their dust source evaluation results with those from these longwalls. 'Physicist. ^Physical scientist. ■'Supervisory physical scientist. All authors are with the Pittsburgh Research Center, Bureau of Mines, Pittsburgh, Pa. INTRODUCTION The objective of this report is to pro- vide to the mine operator a sampling strategy for evaluating longwall dust sources and the range within which the dust concentrations for these sources should lie. This is important because major dust sources must be identified be- fore dust controls can be recommended and applied correctly. The shearer operator is typically a high-risk, occupation; for this reason the sampling strategy pre- sented is aimed at the shearer operator's exposure to the major dust sources. The standard method of evaluating dust exposure is by collecting personal sam- ples over an 8-hr period. Although this method is the most appropriate estimate of a worker's full-shift exposure, it is far from adequate for identifying dust sources and their severity or for evalu- ating the effectiveness of dust control techniques. The Bureau has recently developed an uncon5)licated sampling strategy, based upon short-term gravi- metric sampling, that works effectively. This technique utilizes approved gravi- metric sampling equipment already avail- able to all mine operators. The objec- tive is not to precisely define the dust source contributions, but to allow the mine operator to determine suffioiently where dust problems are in the shortest and simplest way. SAMPLING METHOD Evaluating longwall dust sources re- quires that two kinds of dust samples be taken: (1) stationary and (2) mobile. It is necessary for both kinds that a minimum of four personal samplers be used. Multiple samplers arranged in a package are necessary to insure accuracy and to obtain a valid average measurement of the respirable dust con- centration because sampling is done for short periods of time (typically 20 to 30 min).4 For stationary samples, figure 1 shows two recommended methods, as it is important to keep the cyclone samplers within a 12-inch radius. For mobile samples, two techniques are available. Either a package can be hand- carried, as shown in figure 1, or the sampler vest, shown in figure 2, can be used. The sampler vest is simply a fish- ing vest that contains four large pockets suitable for holding the sampling pumps; the four cyclone samples are located on the right and left lapels of the vest. This particular arrangement gives the wearer hand freedom to make other mea- surements, such as airflow. SAMPLING STRATEGY It is important to note that the sam- pling strategy is based upon the fact that the dust concentration measured at any location is a composite of all dust sources upstream of that location. The ■^In general, all four of the measured dust concentrations in each package should be used for determining the aver- age concentration. However, you should use your own judgment in omitting one of the values from the calculation if ( 1 ) one of the values is substantially dif- ferent or (2) a sampler was known not to be functioning properly during the test. sampling locations, designated in fig- ure 3, are the same, regardless of cut- ting sequence; they allow the mine oper- ator to determine the shearer operator's exposure to the major dust sources: A — section intake B — 15 ft on shearer intake, tail-to-head C — midpoint of shearer, tail-to-head D — 15 ft on shearer intake, head-to-tail E — midpoint of shearer, head-to-tail. FIGURE 1. = Hand-held sampler packages. FIGURE 2. = Sampler vest. I Headgate a , o \ n KEY Section intake, stationary 15 ft on shearer intal(e, tail to head pass only, mobile Midpoint of shearer, tail to head pass only, mobile 15 ft on shearer intake, head to tail pass only, mobile Midpoint of shearer, head to tail pass only, mobile Direction of shearer-sampler movement Face ventilation Stage loader i^^M^ 15 ft 1 IZZ ■ - I r-1 .1 , ,K^ Shearer |>ji^;:}; D SUTv^vT^^LC^ T C- Roof support line FIGURE 3. - Sampling location designations. The sampling strategy is carried out by a survey team consisting of two individu- als, with each collecting the mobile gravimetric samples during selected seg- ments of the mining cycle. The sampling is divided into two main phases: 1. A set of samples collected on the head- to- tail pass. 5 2, A different set of samples lected on the tail-to-head pass. col- One individual stands at the midpoint of the shearer, and the other stands approx- imately 15 to 20 ft on the intake air side of the shearer. In addition, there is a stationary sampler package, located in the last open crosscut, to measure the section's intake dust concentration. Appendix A provides a s tep-by-s tep sam- pling sequence as an example. CALCULATION EXAMPLES OF MINE DATA In the following examples, the sampling locations are those designated in fig- ure 3. At the top of each table pre- sented are the sampling locations and sampling times, as well as the dust con- centrations obtained at each location. ^A pass is defined as movement from either head-to-tail or tail-to-head. The dust concentration and sampling times at the various locations are average values for all passes. These average values are then treated as if they were obtained on one single pass. In the lower portion of the table are listed the dust sources and the calcula- tion of their contributions. For exam- ple, the section intake contribution is simply the value of A; the stage loader- conveyor contribution is obtained by sub- tracting A from B and is designated (B- A), and so forth for the other dust sources. The time fraction of the mining cycle is simply the percentage of the total sampling time for both passes that a given dust source contributes to the shearer operator's exposure. avg source contribution (mg/m^) = dus X t Appendix B is provided to allow the mine operator to conqjare the provided examples, as well as sampling results from the mine, with the shearer operator dust source contributions for shearers in compliance. Appendix C provides information on filter weight requirements and sampling error considerations. Mine 1 — Unidirectional Head-to-Tail Cutting Sequence With Support Movement on Shearer Intake Mine 1 has roof support movement on the intake air side of the shearer during the head-to-tail cut. For all examples, the ventilation in- take is at the headgate, and there are no atypical operations that affect the sam- pling results. The average (tables 1-5) is equation source contribution obtained from the t source concentration (mg/m^) ime fraction of mining cycle (pet). Results of the sampling analysis are shown in table 1. According to table 1, the section intake (A) contributes 1 pet to the total source contribution 100 pet of the time; the stage loader-conveyor (B-A), operating 100 pet of the time, contributes 23 pet to the total; roof support movement (D-B),6 operating 67 pet of the time, contributes 11 pet to the total; the head-to-tail shearer cut (E- D), operating 67 pet of the time, eon- tributes 62 pet to the total; and the tail-to-head shearer cleanup (C-B), oper- ating 33 pet of the time, contributes 3 pet to the total. TABLE 1. - Dust source data for mine 1 Sampling location^ A B (cleanup) C (cleanup) D (cut) E (cut) S amn 1 i n p t imp ......... mi n . . 42 0.1 14 1.8 14 2.3 28 3.0 28 Dust concentration. .mg/m3, , 9.9 Dust source A B-A D-B E-D C-B Descriotion. •...•...•••••.. Section intake. 0.1 100 0.1 1 Stage loader- conveyor. 1.7 100 1.7 23 Support movement. 1.2 67 0.8 11 Shearer (cut). 6.9 67 4.6 62 Shearer Dust source concentration mg/m3, , Time fraction of mining cycle pet. . Average source contribution mg/m3. , Percent of total source contribution^ (cleanup). 0.5 33 0.2 3 ^See figure 3. ^Total source contribution, 7.4 mg/m3; this represents average exposure during cut- ting and not exposure for conqjliance purposes. ^Calculation of the roof support movement contribution (D-B) is based on the assumption that the stage loader-conveyor contribution is the same on both cleanup and cutting. Table 4 indicates that there is no significant difference, although this may not always be true. This mine was regularly out of compli- ance. The short-term sampling has iden- tified two problem areas: (1) the head- to-tail cut (62 pet); and (2) the stage loader-conveyor (23 pet). Referring to table B-1 (appendix B), both of these values lie outside the ranges for the cleanest longwalls. Efforts can now be concentrated on these two areas to achieve compliance. For this operation, the shearer cut the full seam on the head-to-tail pass. The effect of this cutting sequence placed the trailing headgate drum (which is cutting bottom coal) on the intake air shearer. A logical would be to employ a tional head-to-tail where the bottom coal is cut on the tail- to-head cleanup by the tailgate drum. This has the effect of putting the bottom cut on the return air side of the shearer rather than on the intake air side. side of the corrective measure modified unidirec- cutting sequence7 Mine 2 — Unidirectional Tail-To-Head Cutting Sequence With Support Movement on Shearer Intake Mine 2 has roof support movement on the intake air side of the shearer during the head-to-tail cleanup pass. Results of the sampling analysis are shown in table 2. According to table 2, the section intake (A) contributes 13 pet to the total source contribution 100 pet of the time; the stage loader-conveyor (B-A), operating 100 pet of the time, contributes 7 pet to the total; roof sup- port movement (D-B), operating 36 pet of the time, contributes 7 pet to the total; the tail-to-head shearer cut (C-B), oper- ating 64 pet of the time, contributes 20 pet to the total; and the head-to-tail shearer cleanup (E-D) , operating 36 pet of the time, contributes 54 pet to the total. TABLE 2. - Dust source data for Mine 2 Sampling location^ A B (cut) C (cut) D (cleanup) E (cleanup) Samolincr time. •.•••••• .mln. • 55 0.6 35 0.9 35 2.3 20 1.6 20 Dust concentration. . .mg/m^. . 8.5 Dust source A B-A D-B C-B E-D Description Dust source concentration mg/m3. . Time fraction of mining cvele. ..••....••••••• .net. • Section intake. 0.6 100 0.6 13 Stage loader- conveyor. 0.3 100 0.3 7 Support movement. 0.7 36 0.3 7 Shearer (cut). 1.4 64 0.9 20 Shearer (cleanup) . 6.9 36 Average source contribution mg/m3. . Percent of total source contribution^ 2.5 54 ^See figure 3. ^Total source contribution, 4.6 mg/m^; this represents average exposure during cut- ting and not exposure for con5)liance purposes. 'U.S. Bureau of Mines. Modifieci Cutting Sequence Reduces Longwall Shearer Oper- ators' Dust Exposure. Technol. News, No. 116, 1981. 8 This mine was regularly in conqjliance. However, notice that the head-to-tail cleanup, which was only a third of the mining cycle, contributed more than one- half of the shearer operator's dust ex- posure. The reason for this is that, on the cleanup pass, the headgate drum was cutting bottom rock on the intake air side of the shearer. It is well known that cutting rock creates a much larger amount of dust. Similar to that for mine 1, a corrective measure would be to use a modified unidirectional tail-to-head cut where the entire seam is cut on the tail- to-head pass. This would place the bot- tom cut (rock grinding) on the return air side of the shearer. Mine 3 — Bidirectional Cutting Sequence tail-to-head cut and on the intake air side of the shearer during the head- to-tail cut. Results of the sampling analysis are shown in table 3. According to table 3, the section intake (A) contributes 43 pet to the total source contribution 100 pet of the time; the stage loader-conveyor (B-A) , operating 100 pet of the time, contributes 19 pet to the total; the roof support movement (D-B), operating 55 pet of the time, contributes 7 pet to the total; the tail-to-head shearer cut (C- B), operating 45 pet of the time, con- tributes 31 pet to the total; and the head-to-tail shearer cut (E-D) , operating 55 pet of the time, contributes pet to the total. Mine 3 has roof support movement on the return air side of the shearer during the TABLE 3. - Dust source data for Mine 3 Sampling location-^ A B (cut) C (cut) D (cut) E (cut) Samolinc time •••••••••••••• .min. • 47 1.8 21 2.6 21 5.5 26 3.2 26 Dust concentration mg/m^. . 3.1 Dust source A B-A D-B C-B E-D Descriotion. ••••••••••••••••••.•• Section intake. 1.8 100 1.8 43 Stage loader- conveyor. 0.8 100 0.8 19 Support movement. 0.6 55 0.3 7 Shearer (cut). 2.9 45 1.3 31 Shearer Dust source concentration mg/m3. . Time fraction of mining cycle pet, . Average source contribution mg/m3. . Percent of total source contribution^ (cut). 20.0 55 is actually negative: see section "Mine 3" and Appendix C for ^See figure 3. ^Quantity (E-D) explanation. ^Total source contribution, 4.2 mg/m^; this represents average exposure during cut- ting and not exposure for con^jliance purposes. Notice that, although roof support movement occurs on both passes, that is, 100 pet of the time, only 55 pet of the time is attributed to it. The reason for this is that the shearer operators are exposed to roof support dust only on the head-to-tail cut. The roof supports are moved on the return air side of the shearer during the tail-to-head cut, and, thus, do not contribute. Another apparently strange result is the 0-pct contribution (see appendix C) of the shearer on the head-to-tail cut. Inspection of the quantity (E-D) shows that it is actually slightly negative. This says that since the sample 15 ft on the shearer intake air side is slightly greater than the value at the shearer midpoint, the dust at the shearer mid- point is essentially a combination of only coal transport dust and roof support movement dust. This physically makes sense because on the head-to-tail pass, the tailgate drum is cutting most of the coal (and making the most dust) and is on the return air side of the shearer. The headgate drum is on the shearer intake air side but is cutting very little coal and, therefore, making very little dust. This mine was regularly out of compli- ance. Inspection of the results shows where the problem area is: the section intake (43 pet). Mine 4 — Unidirectional Tail-to-Head Cutting Sequence With Support Movement on Shearer Return Mine 4 has roof support movement on the return air side of the shearer during pass. the tail-to-head cut Results of the sampling analysis are shown in table 4. According to table 4, the section intake (A) contributes 15 pet to the total source contribution 100 pet of the time; the stage loader-conveyor on the cut pass (B-A), operating 71 pet of the time, contributes 10 pet to the to- tal; the stage loader-conveyor on the cleanup (D-A) , operating 29 pet of the time, contributes 8 pet to the total; the tail-to-head shearer cut (C-B), operat- ing 71 pet of the time, contributes 63 pet to the total; and the head-to-tail shearer cleanup (E-D), operating 29 pet of the time, contributes 5 pet to the total. TABLE 4. - Dust source data for Mine 4 Sampling location 1 A B (cut) C (cut) D (cleanup) E (cleanup) Sampling time .......... .min. . 51 0.6 36 1.2 36 4.7 15 1.6 15 Dust concentration. .. .mg/m3. . 2.2 Dust source A B-A D-A C-B E-D Description. ................. Section intake. 0.6 100 0.6 15 Stage loader- conveyor (cut). 0.6 71 0.4 10 Stage loader- conveyor (cleanup) . 1.0 29 0.3 8 Shearer (cut). 3.5 71 2.5 63 SViPP fPT" Dust source concentration mg/m3. . Time fraction of mining cycle pet. . Average source contribution mg/m3. . Percent of total source contribution^ (cleanup) . 0.6 29 0.2 5 ^See figure 3. ^Total source contribution, 4.0 mg/m^; this represents average exposure during cut- ting and not exposure for con5)lianee purposes. Since the support movement is on the return air side of the shearer, it does not contribute to the shearer operator's exposure and is, therefore, not being measured. However, although there is no roof support dust measurement, there is an additional stage loader-conveyor dust measurement. Although the majority of the dust (63 pet) is from the headgate drum (in- take air side of shearer) on the tail- to-head cut, this mine was regularly in co^^)liance. 10 Mine 5 — Unidirectional Head-to-Tail Cutting Sequence With Support Movement on Shearer Intake Mine 5 has roof support movement on the intake air side of the shearer during the head-to-tail cut. Results of the sampling analysis are shown in table 5. According to table 5, the section intake (A) contributes 5 pet to the total source contribution 100 pet of the time; the stage loader- conveyor (B-A) , operating 100 pet of the time, contributes 58 pet to the total; roof support movement (D-B), operating 56 pet of the time, contributes 30 pet to the total; the head-to-tail shearer cut (E-D), operating 56 pet of the time, contributes pet to the total; and the tail-to-head shearer cleanup (C-B), operating 44 pet of the time, contributes 7 pet to the total. TABLE 5. - Dust source data for Mine 5 Samn line loration^... .......... A B (cleanup) C (cleanup) D (cut) E (cut) Samnl i np t ime .......•..>. .mi n. . 41 0.3 18 3.6 18 4.5 23 6.6 23 Dust concentration mg/m^.. 6.4 Dust source. ................... A B-A D-B E-D C-B Descriotion. ••.•••••••..•••••.. Section intake. 0.3 100 0.3 5 Stage loader- conveyor. 3.3 100 3.3 58 Support movement. 3.0 56 1.7 30 Shearer (cut). 20.0 56 0.0 Shearer Dust source concentration mg/m3. . Time fraction of mining cycle pet. . Average source contribution mg/m3. . Percent of total source contribution 3 (cleanup) . 0.9 44 0.4 7 ISee figure 3. 2Quantity (E-D) is actually negative: see Appendix C explanation. ^Total source contribution, 5.7 mg/m^; this represents average exposure during cut- ting and not exposure for compliance purposes. This mine was regularly out of compli- ance. It is obvious that the two largest dust sources for this operation are the stage loader-conveyor (58 pet) and the roof support movement (30 pet). Refer- ring to table B-1, it can be seen that both stage loader-conveyor dust and roof support dust contributions fall outside the range for the longwalls in conqjli- ance. Note that the stage loader- conveyor dust is on the intake air side of the roof support movement and there- fore is a major contributor to the sup- port operator's as well as the shearer operator's exposure. The reason that the shearer operator exposure is so low is that the shearer was equipped with the Bureau-developed "shearer-clearer". 8 However, this device did not help the mine achieve con^jliance because the shearer was not the main source of dust, which can easily be seen from the data. ^Kissell, F. N. , N. Jayaraman, C. Tay- lor, and R. Jankowski. Reducing Dust at Longwall Shearers by Confining the Dust Cloud to the Face. BuMines TPR 111, 1981, 21 pp. 11 SUMMARY This report has shown: 1. How to evaluate the dust sources on your double-drum shearer longwall opera- tion, regardless of cutting sequence, and 2, How your results coii5)are with the cleanest double-drum shearer longwall operations. Since it is recognized that all opera- tions are different in some respect from each other, this paper has attempted to present enough examples to cover a variety of circumstances. Once the anal- ysis has been performed and the major dust source(s) identified, the effective- ness of any subsequent dust control tech- nique can be evaluated simply by repeat- ing the test program and con5)aring the results. The quantities to compare are the total source contributions in milli- grams per cubic meter before and after implementing a dust control technique. These quantities estimate the total shearer operator dust exposure during actual cutting of the coal. 12 APPENDIX A. —SAMPLING SEQUENCE As an example, a step-by-step sampling sequence is provided. It will be assumed for the example that a unidirectional head-to-tail cutting sequence (this sam- pling strategy will apply to all cutting sequences) is used and that the sampling locations are those as described in figure 3. 1. A sampler package (stationary) is located at A to measure the section in- take dust concentration. It is turned on just prior to testing. 2. One individual stands 15 to 20 ft on the intake air side (D) of the shearer, and the other stands at the shearer midpoint (E), between the operators. They will collect mobile samples. 3. Once the shearer has fully sumped into the face and cleared the headgate, the sampling pumps are turned on (note sampler start time). 4. Before the shearer reaches the tailgate, the sampling pumps are turned off (note sampler stop time). 5. This set of filters (set I) is changed and replaced with a different set (set 2). 6. The survey team assume their same positions (B, C) for the tail-to-head cleanup pass. 7. Once the shearer has begun the tail-to-head cleanup and has cleared the tailgate, the sampling pumps (set No. 2) are turned on (note sampler start t ime ) . 8. Before the shearer reaches the headgate, the sampling pumps are turned off (note the sampler stop time). This sequence can be repeated over and over again by simply using filter set 1 and the head-to-tail pass and filter set 2 on the tail-to-head pass. 9. When testing is finished, sampler package A is turned off. Some general instructions and comments concerning sampling should be made. a. The mobile samplers (B, C, D, and E) should not be turned on until the shearer is fully sumped into the face. b. The mobile samplers (B, C, D, and E) should be turned off just before the shearer completes the pass. The important point to be made in items 1 and 2 above is that the sampling should not include phases that are short pieces of the cutting sequence; that is, breaking out into the headgage or tail- gate, or wedge cutting at the snake. There may be minor contributions to the total dust exposure of the shearer oper- ator, and inclusion would conqjlicate the analysis. c. All sampler filters (except sam- pler A) must be changed after the sam- plers are turned off at the end of each pass. These will be used jver again for each successive and -IdenbiQai pass. Fil- ter changes can be performed in two ways. First, the filters themselves can be changed. Second, duplicate sampling packages (or vests) can be used and switched after each pass. d. All start-stop times of the sam- plers (including sampler A) must be re- corded. One convenient method of record- ing times is to use a small, permissible, minicassette voice recorder. e. It is necessary that a minimum of 0.2 mg of dust be deposited on each fil- ter to provide accurate weighing of the filters (see appendix C). f . Two days recommended. of sampling are g. Sampler package A must be located in the primary intake airway (last open crosscut). Since its function is only to provide an estimate of the dust entering the section during the testing, package A can be left turned on during the entire testing program. h. The survey team members follow the shearer, maintaining their positions with respect to the shearer (B and C on the tail-to-head pass, D and E on the head- to-tail pass). See figure 3. 13 APPENDIX B. —SHEARER OPERATOR DUST SOURCE CONTRIBUTIONS FOR SHEARERS IN COMPLIANCE After dust source contributions are determined, it is important to know how each source con5)ares with longwall double-drum shearers that are regularly in coii?)liance. 1 Table B-1 presents two quantities for each major dust source: (1) the range of dust concentrations, and (2) the percentage range of each dust source's contribution for the six longwalls in a recent Bureau survey of longwalls regularly in con5)liance. It is important to emphasize that the dust con- centrations in table B-1 for the dust sources are those only during the actual cutting and cleanup operations and not an 8-hr time -weigh ted average. As such, they can in no way be used for conpliance purposes. TABLE B-1, - Typical longwall ^ double-drum shearer dust source contributions obtained from a survey of six longwalls regularly in conqjliance Dust source Range of average source contributions during cutting, mg/m^ Range, pet of total contribution Section intake , Stage loader-conveyor: Cu tting ,( Cleanup Support movement , Shearer: Head-to-tail cut..,,, Tail-to-head cut.,.., Head-to-tail cleanup. Tail-to-head cleanup. 20,2-0,83 ,3- ,8 .1-1,0 ,0- ,3 ,1-2,0 ,9-2,5 .2-2,5 ,7-1,0 9-18 7-19 5-20 0- 7 4-45 20-63 5-54 16-45 ^The values in table B-1 were obtained from longwalls in which the airflow was from headgate to tailgate, 2lf an MRE equivalent is desired, multiply all concentrations throughout this paper by 1,38. This is unnecessary for the work proposed, however. 30ne longwall was in con^jliance with a section intake of 1.4 mg/m^. This value was omitted because it is not believed to be representative of longwalls in coii5)liance. ^Taylor, C. D., and R. A. Jankowski. How the Six Cleanest U.S. Longwalls Stay in Compliance. Pres. at the First Mine Ventilation Symp. , Tuscaloosa, Ala., Univ. Ala- bama, Mar. 29-31, 1982; Min. Cong. J., v. 58, No. 5, May 1982, pp. 37-40. 14 APPENDIX C. --FILTER WEIGHTS AND ERROR CONSIDERATIONS It was stated in appendix A, part e, that it is necessary that a minimum of 0.2 mg of dust be deposited on each fil- ter to provide accurate weighing of the filters. There are two reasons for this. First, the standard preweighed filter cassettes are preweighed to only one dec- imal place, and low dust weights may pro- duce unreasonable weighing errors. Sec- ond, the balances used by mine operators may not be capable of accurately weighing filters with less than 0.2 mg of dust. Generally, obtaining 0.2 mg or more of dust can be accon5)lished by using the same filters over and over again so that each filter represents four passes or more. The use of a more accurate balance will allow the mine operator to collect less dust on the filters. It is important to state that the data presented in this paper were based on dust masses less than 0.2 mg. Although the filter cassettes used were preweighed to the nearest tenth of a milligram, they were reweighed before and after use to the nearest thousandth of a milligram. If the operator wishes to collect less than 0.2 mg of dust, as the Bureau did, high accuracy balances are available from MSHA. The Code of Federal Regulations (30 CFR, Part 70.209 D) permits mine operators to collect samples for test purposes, and the mine operators can request MSHA to preweigh and postweigh the filters to the desired precision, thus reducing the amount of dust neces- sary for accurate filter weights. Considering the generally small amounts of dust collected on each filter that can produce significant weighing errors, it is recommended that sampling pumps of the flow-regulating type be used, although non-flow-regulating pumps are acceptable. The former type of pump is recommended so that sampling error due to pump airflow variations is minimized. In the sampling analysis examples pre- sented, certain dust source contributions (for example, E-D) are listed as 0.0 mg/m3, although the calculated value was slightly negative. This result can be attributed to sampling errors such as pump variation and weighing errors. How- ever, the important result is that the dust source was not a major contributor to the shearer operator's exposure. If it had been, the calculated quantity would have been positive, regardless of sampling error. 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