Handbook for Methane Control in Mining - AMMSA

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155DEALING WITH METHANE IN METAL/NONMETAL MINESDealing with methane in metal/nonmetal mines requires anunderstanding of five important issues:1. The differences between coal mines and metal/nonmetalmines, and recognizing why explosions happen evenwith low gas emission rates.2. How to monitor for gas and what gas concentrationsrequire action.3. The importance of continuously diluting methane withventilation air.4. The importance of eliminating all ignition sources.5. Avoiding outburst hazards.Although the regulations discussed in the previous section are important to preventing methaneexplosions in metal/nonmetal mines, they represent only a starting point in achieving a safemine. A broader understanding of five important issues is necessary, which are detailed below.1. Why metal/nonmetal mines are different from coal mines. Unlike coal mines, methaneemission rates in metal/nonmetal mines are not consistent. This irregularity often makes anaccumulation of methane an unexpected event, and an unexpected event by definition is difficultto anticipate. 8 Methane can be detected in coal mines everywhere and almost all the time; therefore,monitoring becomes a regular pattern of activity. Ventilation controls are rigorously maintained,and large quantities of ventilation air are blown through the mine to sweep the gas away.Permissible equipment is used to minimize ignition sources, and workers are constantly on noticethat coal mines are potentially dangerous places. All of these factors lead to a constant awarenessof the potential methane hazard, promoting consistent efforts to reduce the risk of an ignitionor explosion.By contrast, workers in metal/nonmetal mines may never detect methane gas or only encounter itinfrequently. It is easy to become complacent, testing for gas in a cursory or offhand fashion,or not even bothering to test at all. Also, the same attention to ventilation controls is lacking,with series 9 ventilation circuits and recirculation being common practices.See Chapter 14 for a parallel discussion on ventilationcontrols. Poor ventilation allows for a dangerousaccumulation of gas in a location where little to nogas had been previously detected.8 In the manufacturing industry, quality inspections have recognized the problem of unexpected events, which is whydeliberately faulty parts are slipped into an inspection line to keep the inspectors on their toes.9 In series ventilation, the return from one working area is used as the intake to the next one downstream.
1562. Monitoring for gas and taking control measures.An important part of methane monitoring is knowingwhat control measures to take when gas is detected.The actions described here for methane testing areonly a summary. For complete details, consult theCode of Federal Regulations.Metal/nonmetal mines with a history of gas emissions are already on notice that they have amethane problem. The U.S. regulatory standards have very specific monitoring requirementsand actions to be taken depending on the category of mine and its methane history. These providea good, commonsense approach to methane monitoring and control measures.Those mines that liberate significant quantities of gas must monitor for it each shift in a preshiftexamination similar to that for coal mines (30 CFR 57.22226 and 57.22228). No testing is mandatedfor those mines where methane is not expected to be present, but there are action levels andprescribed actions when gas is detected at certain levels, 10 as follows:Actions at 0.25% methane: If the mine had never before measured 0.25% or more or never had anignition, then changes must be made to improve ventilation, and MSHA must be notified immediately.Actions at 0.5% methane: Ventilation changes are required to reduce methane below 0.5%.In the meantime, depending on the category of mine, one or more of the following are necessary:electrical power must be deenergized, diesel equipment must be shut off or removed, and/orwork must stop.Actions at 1.0% methane: Ventilation changes are required to reduce the methane. In themeantime, depending on the category of mine, one or more of the following are necessary:all workers from the affected areas must be withdrawn except those needed to make the ventilationchanges, electrical power must be deenergized, and/or diesel equipment must be shut off orremoved.All persons must be withdrawn from the mine if the 1.0% accumulation results from a main fanfailure or if 1.0% is measured at a main exhaust fan.Actions at 2.0% methane: Ventilation changes are required to reduce the methane, and all personsmust be withdrawn except those necessary to make the ventilation changes. Depending onthe category of mine, one or more of the following are necessary: MSHA must be informed, themethane must be reduced to below 0.5%, and/or the methane must be reduced to below 1.0%.For all of the above scenarios, the mine category also impacts (1) the frequency and location ofmethane testing, (2) the use of atmospheric monitoring systems, (3) the use of methane monitorson mining equipment, and (4) whether explosion-proof electrical equipment is used, among otherfactors.10 Keep in mind that one needs to regularly test for gas only in the mine atmosphere, not in boreholes. Chapter 2contains more information on sampling for methane.
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TMIC 9486Information Circular/2006H
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ORDERING INFORMATIONCopies of Natio
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ILLUSTRATIONS—ContinuedPage4-6. U
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HANDBOOK FOR METHANE CONTROL IN MIN
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4Below 5%, called the lower explosi
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6reduced pressure, except at very l
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8Static electricity. Protection aga
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10Figure 1-4.—Estimated methane c
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12LAYERING OF METHANE AT THE MINE R
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14good eyesight. 24methane level.Ot
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16a material balance indicated that
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18As an example, assume that themet
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20Figure 1-10.—Relative frequency
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22Davies AW, Isaac AK, Cook PM [200
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24Margerson SNA, Robinson H, Wilkin
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CHAPTER 2.—SAMPLING FOR METHANE I
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29USING PORTABLE METHANE DETECTORST
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Out-of-range gas concentrations in
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Figure 2-3.—Recorder chart from a
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35Industrial Scientific Corp. [2004
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38peaks, not the overallmethane lev
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40hung on J-hook assemblies, which
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42Methane dilution effectiveness.Th
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44found that effective scrubber ope
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46When the scrubber exhaust is not
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48Methane monitors are usually moun
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50to use radial bits instead of con
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52Mott ML, Chuhta EJ [1991]. Face v
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54Service, Centers for Disease Cont
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56Methane accumulationsaround thesh
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58corner and by 43% at supportNo. 4
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60When using water sprays to reduce
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62Cecala AB, Zimmer JA, Thimons ED
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64DESIGNING BLEEDER SYSTEMSAs part
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66Caved area characteristics. The c
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68then move this gas into the activ
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70perform tests to determine whethe
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72A major purpose of the bleeder sy
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74• Inlets to the pillared area n
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76REFERENCESCFR. Code of federal re
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78Methane is released into each min
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80Figure 6-1.—Gas content of coal
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82Figure 6-3.—Simplified illustra
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842. In-mine inclined or vertical b
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861. Packed cavity method and its v
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88Table 6-3.—Methane capture rati
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90Early experiences with this metho
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9211. At the surface installation (
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94• Estimated cost for moderately
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96Thakur PC [1981]. Methane control
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98Anomalous, unanticipated methane
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100Vertical methane drainage boreho
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102Figure 7-2 shows a mine entry ap
Page 109 and 110: 104obvious solution to this problem
Page 111 and 112: 106Figure 7-8.—Hypothetical gas c
Page 113 and 114: 108Lama and Bodziony [1998] compile
Page 115 and 116: 110In-mine methane drainage systems
Page 117 and 118: 112Iannacchione AT, Ulery JP, Hyman
Page 119 and 120: 114More sophisticated reservoir eng
Page 121 and 122: 116coal lithotype on gas content is
Page 123 and 124: 118FORECASTING REMAINING GAS-IN-PLA
Page 125 and 126: 120⎛ y⎞⎜⎛⎞ ⎛ ⎞= ⎜
Page 127 and 128: 122emissions. The geometry and size
Page 129 and 130: 124Reservoir models require a subst
Page 131 and 132: 126King GR, Ertekin T [1989a]. A su
Page 133 and 134: 128an area of 314 ft 2 would requir
Page 135 and 136: 130In the case of the abovementione
Page 137 and 138: 132FILLING SHAFTS AT CLOSED MINESFi
Page 139 and 140: 134Hinderfeld G [1995]. Ventilation
Page 141 and 142: 136To calculate the effectiveinert,
Page 143 and 144: 138exhaust. The remaining diesel ex
Page 145 and 146: 140required only 4 min. As a result
Page 147 and 148: 142Figure 11-1.—Desorption test a
Page 149 and 150: 144enclosed in a tunnel-like struct
Page 151 and 152: 146Kolada RJ [1985]. Investigation
Page 153 and 154: 148air in a 6-ft by 9-ft by 6.5-ft
Page 155 and 156: 150represents flammable mixtures. F
Page 157 and 158: 152• In Eastern Europe, petroleum
Page 159: 154Category II applies to domal sal
Page 163 and 164: 158These mines typically have large
Page 165 and 166: 160Dave Graham is the safety and he
Page 167 and 168: 162Figure 13-2.—Examples of metha
Page 169 and 170: 164REFERENCESAndrews JN [1987]. Nob
Page 171 and 172: 166APPENDIX A.—ONTARIO OCCUPATION
Page 174 and 175: 169CHAPTER 14.—PREVENTING METHANE
Page 176 and 177: Ways to confirm the presence of gas
Page 178 and 179: 173The tunnel face is usually venti
Page 180 and 181: 175Figure 14-5.—TBM ventilation s
Page 182 and 183: face. While one of these elements a
Page 184 and 185: 179ELIMINATING IGNITION SOURCESElec
Page 186 and 187: 181INDEXAAbnormally gassy faces....
Page 188 and 189: 183NNatural ventilation, coal silos
Page 190 and 191: Delivering on the Nation’s Promis
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