Detection And Control Of Spontaneous Heating In Coal

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RI 9553REPORT OF INVESTIGATIONS/1995Detection and Control of Spontaneous Heatingin Coal Mine Pillars—A Case StudyBy Robert J. Timko and R. Lincoln DerickUNITED STATES DEPARTMENT OF THE INTERIORUNITED STATES BUREAU OF MINES

U.S. Department of the InteriorMission StatementAs the Nation’s principal conservation agency, the Department of theInterior has responsibility for most of our nationally-owned publiclands and natural resources. This includes fostering sound use of ourland and water resources; protecting our fish, wildlife, and biologicaldiversity; preserving the environmental and cultural values of ournational parks and historical places; and providing for the enjoymentof life through outdoor recreation. The Department assesses ourenergy and mineral resources and works to ensure that theirdevelopment is in the best interests of all our people by encouragingstewardship and citizen participation in their care. The Departmentalso has a major responsibility for American Indian reservationcommunities and for people who live in island territories under U.S.administration.

Report of Investigations 9553Detection and Control of Spontaneous Heating inCoal Mine Pillars—A Case StudyBy Robert J. Timko and R. Lincoln DerickUNITED STATES DEPARTMENT OF THE INTERIORBruce Babbitt, SecretaryBUREAU OF MINESRhea Lydia Graham, Director

International Standard Serial NumberISSN 1066-5552

CONTENTSPageAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Spontaneous heating in a Colorado coal mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Spontaneous heating detection methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Gas detection devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Handheld instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Gas chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Minewide monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Atmospheric status equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Surface temperature detection device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pressure and temperature monitoring devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pillar spontaneous heating and control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Long-term pillar spontaneous heating detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Monitoring outside the pillars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Crosscut 1 airlock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Crosscut 1 return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Monitoring inside the pillars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Boreholes 1-1 and 1-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Boreholes 2-1 through 2-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Temperature and differential pressure in test holes 2-1 through 2-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Permanent control of pillar spontaneous heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.7.8.9.10.11.12.13.14.15.Plan view of the three pillars evaluated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Detection of spontaneous heating episodes and resulting control measures implemented . . . . . . . . . . . . . . . . . . . . . .Crosscut 1 airlock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Crosscut 1 return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Locations of prototype 3.7-m boreholes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.7-m boreholes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Locations of pillar boreholes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Borehole 2-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Borehole 2-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Borehole 2-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Borehole 2-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Borehole 2-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Borehole 2-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Borehole 2-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Borehole measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .368899111112121313141516

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORTMetric UnitscmcentimeterPaPascalmmeterpctpercentm3/scubic meter per secondppmpart per millionmlmilliliterECdegree CelsiusmmmillimeterU.S. Customary Unitsftfootin3cubic inchft3/mincubic foot per minutein H2Oinch water gageininchReference to specific products does not imply endorsement by the U.S. Bureau of Mines.

Detection and Control of Spontaneous Heating in Coal Mine Pillars-A CaseStudyBy Robert J. Timko1 and R. Lincoln Derick2ABSTRACTThis U.S. Bureau of Mines study examined spontaneous heating episodes in coal mine pillars in an activeunderground coal mine. The information obtained from these incidents was then analyzed to learn whichsampling methods provided the earliest indication of pillar heating. The objective of this study was to discoverif the location of future events of pillar spontaneous heating could be inferred from the available information.The spontaneous heating-prone area in this evaluation involved pillars located just inby themine portals. Several detection methods were used to determine gas levels outside as well asinside the affected pillars.It was hoped that, by incorporating external and internal sampling methods into anorganized program, locations undergoing spontaneous heating could be determined morereadily. This study found that by drilling small-diameter boreholes into the pillars, thenobtaining gas samples from the affected pillars, the ability to locate early spontaneous heatingepisodes was improved. However, the ability to accurately predict future spontaneous heatingevents remains in question.12Physical scientist, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA.Manager, Cyprus Twentymile Coal Co., Oak Creek, CO.

2INTRODUCTIONBecause of previous spontaneous combustion episodeswithin another Colorado mine operating in the same coal seamas the mine studied, portal pillars at the study site had to beclosely monitored for signs of spontaneous heating. Thepurpose of this study was to document various detectionmethods and to show that, even when using many of thesetechniques, results could be difficult to interpret. This work wasin support of the U.S. Bureau of Mines (USBM) program tominimize underground fire hazards by employing betterventilation methods.Spontaneous heating in underground coal mines involves theoxidation of coal deposits. Factors affecting the likelihood ofspontaneous heating include coal rank, moisture content,temperature, ventilation, oxygen concentration, particle size,impurities, friability, geological factors, and mining practices (14).3All coals oxidize to some extent when exposed to theatmosphere. Since oxidation is an exothermic reaction betweencoal and the oxygen component of the atmosphere, heat isconstantly being released. This reaction is directly related totemperature; if the heat released by the oxidation reaction is notdissipated, the temperature of the mass increases. In somereactive coals this oxidation can increase to the point that, ifremedial control measures are not instituted, the heating cancontinue and the temperature will rise at an increasing rate untilsmoldering combustion occurs.Mine operators usually know if their coal is prone tospontaneous heating. This understanding may have come froma previous heating discovered in their mine, from heatings inother nearby mines within the same coal seam, or frompublished USBM research that defines a coal's propensity forself-heating (5).Spontaneous heating typically occurs when the quantity ofair passing through the coal is sufficient to support oxidation butis inadequate to carry off the heat produced by the oxidationreaction. Some ways to generate spontaneous heating include;continuing to ventilate a heating-prone area once the miningcycle is completed, air leaking around poorly built seals, or bypermitting pressure differentials across weathered or previouslyoxidized pillars.If spontaneous heating is permitted to continue untilsmoldering combustion, it is often necessary to seal a largevolume underground to control the fire. This can be an expensive decision, not only because of the loss of valuable coalreserves, but also because sealing is typically an expeditedprocess. This usually means that all coal extraction and haulagemachinery remain within the sealed volume.When coal is prone to spontaneous heating, a problem canarise within pillars that remain after the mining cycle has beencompleted. This is especially true in main or submain entrieswhere large quantities of ventilation air continually flow.Differential pressures exist across the pillars as well as acrossany structures, such as stoppings, that are used to separateentries. These pressure differences tend to induce air leakagenot only through stoppings but also through the pillarsthemselves. Under certain conditions, this airflow can generatespontaneous heating within the pillar. The volume of airflowing past a pillar in a main or submain entry is sufficient todilute combustion products being emitted. Thus, spontaneousheating in a main or submain entry pillar is more likely tocontinue undiscovered. At times, a strange odor is detected or"sweating" is seen on cooler surfaces near the heating.However, control procedures are normally begun only aftereither carbon monoxide (CO) is detected or smoke is observed.This report is divided into four sections. The first involvesan overview of the detection methods used. The second sectionlooks at the discovery and control of the initial pillar heatings.The third studies the long-term evaluation of control methodeffectiveness. This section includes a description of theboreholes that were drilled into the pillars to obtain additionalinformation on spontaneous heating. The final sectiondocuments methods developed to permanently controlspontaneous heating within the pillars in question.SPONTANEOUS HEATING IN A COLORADO COAL MINEThe D seam in Colorado's western slope coal fields is proneto spontaneous heating. Coal from the D seam contains aneasily fractured vertical cleat (6),4 which creates a multitude3Italic numbers in parentheses refer to items in the list of references at theend of this report.of airflow paths through it. These fractures, and their attendantheatings, are especially4Cleat is defined as the main joint in a coal seam along which it breaksmost easily. Cleat runs in two directions, along and across the seam.

3prevalent near outcrops. In this area outcrops are common because of the wide variation in surface elevation. Many of thesecoal outcrops have spontaneously heated, a reaction that resulted in burned coal from the exposed outcrop to some depth.The coal in these locations has been chemically changed tomore closely resemble coke.This study evaluated diverse sampling methods that wereused to monitor pillars prone to spontaneous heating. Thesetechniques were routinely employed by engineers of theColorado Westmoreland Coal Co., which later became theCyprus Orchard Valley Coal Co. This company is currentlyoperating the Orchard Valley West Mine, located in the D seamin Colorado's western slope coal region just north of Paonia,CO. Orchard Valley West was developed as a replacementfacility for the Orchard Valley East Mine, which was sealed in1986 after an uncontrolled spontaneous combustion fire.Because of previous pillar spontaneous heating incidents thatoccurred just inby the East mine portal, three pillars in theOrchard Valley West Mine were of particular interest.Orchard Valley West is a drift mine having coal extracted bythe room-and-pillar method. Coal cleat alignment was offsetfrom initial entry drivage by about 23E. The mine has threeparallel entries driven from three separate portals. Averageentry height was 2.1 m (7 ft); entry width was 5.5 m (18 ft).The entries consisted of a beltline flanked by an intake and areturn entry. When this study began, a vane-axial fan waslocated at the return-entry portal. It exhausted approximately80 m3 /s (170,000 ft 3/min). The belt entry was ventilated bylow- velocity intake air.The three pillars examined in this study and their associateddimensions are seen in figure 1. Two pillars, A and B, werelocated between the belt and the return entries and weresubjected to differential pressures of 175 Pa (0.7 in H2 O) acrossthem. Pillar C was separated by intake and belt entries and,since both entries were on intake air, had no measurabledifferential pressure across it.

4SPONTANEOUS HEATING DETECTION METHODSPrevious research studies have shown ways to more closelymonitor for spontaneous heating (7-9). Six different detectionmethods were used during this study. These techniquessampled from three specific pillar locations; the atmospheresurrounding the pillars, the pillar surfaces, and within thepillars. Gas detection devices measured emissions from theatmosphere surrounding the pillars as well as from within thepillars. A commercially- available infrared camera was used tosurvey pillar surfaces for elevated temperatures. Pressuremeasuring instruments were used to examine the differentialpressures obtained from within the pillars. Thermocouplesmeasured pillar internal temperatures.GAS DETECTION DEVICESHandheld InstrumentsThroughout this evaluation the Industrial Scientific CMX270 handheld multigas detector was used to measure day-today oxygen (O2), methane, and CO emissions. Gas levels wereobtained by moving the instruments along the rib surfaces ofthe pillars. Of specific interest was CO. When CO wasdetected, the location was marked with spray paint for futurereference.Gas ChromatograhyMore accurate gas sample results were obtained by gaschromatography in conjunction with handheld observations.Researchers were particularly interested in CO and O 2 levels.These were considered important indicators in the progressionof spontaneous heating.Chromatographic samples were obtained by inserting a96%-air-evacuated, 20-ml (1.22-in3) Vacutainer test tube intoa plastic plunger. This assembly was similar to a device usedto extract blood for clinical testing. Inside the plunger was ahypodermic needle. This needle punctured a rubber bladder atone end of the test tube, causing a sample of gas to enter the testtube. Pulling the test tube from the plunger resealed the rubberbladder and prevented the gas sample from escaping or beingcontaminated. Each test tube was returned to the laboratorywhere gas concentrations were determined through electroncapture analysis.Gas chromatographic analysis was considered the most accurate method for determining the various gaseouscomponents. However, because of the appreciable time delaythat occurred between gas sample capture and analysis, initiallygas chromatography was primarily used to confirm orchallenge the results obtained with handheld instruments.Only after researchers were sure that the sample turnaroundtime was adequate to provide sufficient warning of spontaneousheating did they consider gas chromatography a viable day-today technique for data collection.Minewide MonitorA minewide CO monitoring system with attendantsurface-located computer peripherals was in operation. Topermit pillar emission sampling prior to the gas being diluted inthe mine ventilation airstream, the sensors were locatedbetween the pillar ribs and isolation curtains that were hungfrom roof to floor around pillars A and B. While theseinstruments did detect CO emissions from the pillar, theirresults provided only an indication that spontaneous heatingwas taking place somewhere within the pillar and did little toassist in locating the spontaneous heating episode. Because ofthis drawback, minewide monitors were used only as backupdevices.ATMOSPHERIC STATUS EQUATIONSTwo equations were used to monitor the status of the atmosphere outside as well as within the pillars. The variablesfor these equations were obtained through chromatographicanalyses of gas samples. Graham's Index (10) is also called theindex of carbon monoxide (ICO). The ICO is a dimensionlessnumber and is temperature dependent (its value rises withincreasing temperature). It makes two assumptions: any COdetected is fire generated, and the oxygen-to-inert-gas (nitrogen[N2] plus argon [Ar]) ratio is 0.265, indicating that the availableair is from a normal atmosphere. The equation is:ICO (CO 100)/({0.265 [N2 Ar]} - O2),whereandCO carbon monoxide, in pct,(0.265 [N2 Ar]) - O2 oxygen deficiency, in pct.Mitchell (11) states that the CO-CO2 ratio is an excellent toolfor determining changing atmospheric status.Whileindividually these gases can be affected by dilution, theirdimensionless ratio is not. Mitchell also contends that flamingcombustion can be expected when CO-CO2 values approach0.5.55Lecture on Mine Fires presented by D. W. Mitchell at BethEnergy MiningCompany, Eighty Four, PA, 1989.

5ICO and CO-O2 values were meaningful only when theywere used to develop a trend; individually these numbers wereworthless. A rule of thumb states that, if three successivesamples indicate a rise in either the ICO or CO-CO2 ratio, thesampling frequency should be increased.SURFACE TEMPERATURE DETECTION DEVICEThe surfaces of pillars A, B, and C were routinely scannedwith a Hughes Probeye infrared camera to locate elevatedtemperatures. This device was traversed across the coal surfaceand displayed the temperature as one of 10 different hues of asingle color. The camera was calibrated so that the brightesthue corresponded with skin temperature (about 34 EC). Sincethe Orchard Valley West Mine was on exhausting ventilation,scanning initially was performed primarily on the return sidesof pillars A and B.PRESSURE AND TEMPERATUREMONITORING DEVICESTo obtain information from within each pillar, several smalldiameter boreholes were drilled into pillars A, B, and C. Asmall-diameter copper sampling line was then placed withineach borehole. This line provided a means for obtaining gassamples and enabled researchers to measure the pressuredifferential between the far end of the borehole and the entryfrom which the borehole was driven. A Magnehelic-typepressure measuring instrument assessed pressures at the variousboreholes.A thermocouple was installed inside each borehole. If thearea near a borehole undergoes spontaneous heating, thermalconduction should cause the temperature within the borehole torise. Any temperature increase should be accompanied by acorresponding rise in CO at the same location.PILLAR SPONTANEOUS HEATING AND CONTROLDuring a routine survey with the infrared camera, elevatedsurface temperatures were discovered along the pillar A rib inthe crosscut 1 airlock (figure 2). Further investigations foundheatings within the airlock along pillars A and B. AMagnehelic-type device found that pressure fell 175 Pa (0.7 inH 2 O) from the belt side to the return side of the crosscut 1airlock. Since air was flowing through the pillar and then intothe airlock, the pillar A heating could have occurred anywherealong a line roughly paralleling the coal cleat between the beltentry pillar rib and the crosscut 1 rib. Conversely, the heatingalong the pillar B rib had to be near the surface because air wasflowing into the pillar at that location.A CO sensor was positioned inside the airlock on the pillarA rib and connected to the minewide monitor. A bratticecurtain was hung within the airlock along the pil-lar A rib toisolate the CO sensor from the remainder of the airlock volume.This curtain was located about 1 m (3.3 ft) away from andparallel to the pillar A rib, effectively isolating the rib. COlevels in the airlock behind the curtain stabilized at about 26ppm.An attempt was made to reduce airflow through pillar A.The doors in the airlock belt-side stopping and the belt-entrycontainment stopping were opened to provide a low-resistanceflow path between the belt and the airlock return-side stopping.A 0.6-m (2-ft) diameter duct was opened in crosscut 1 betweenthe belt and the intake entries, which effectively balancedventilation pressure between the belt and the intake entries.The belt-to-return pressure differential was now across thecrosscut 1 airlock return-side stopping. These changesincreased the flow path distance, raised the resistance, andreduced the potential for air flow through pillar A. CO levelswithin the airlock stabilized at about 10 ppm.As previously mentioned, the infrared camera also foundelevated surface temperatures inside the airlock along the pillarB rib. When the belt-side door of the crosscut 1 airlock wasopened, as described above, the flow path distance throughpillar B was reduced considerably. To limit air flow, and thusthe likelihood of spontaneous heating, a metal stopping wasbuilt along the pillar B rib extending from the belt-sidestopping to the return-side stopping. Air could then enter pillarB only upstream of the belt-side stopping. This additional flowdistance reduced the potential for air to flow through the pillar,making spontaneous heating less likely.The infrared camera was used at regular intervals to scanboth the belt- and return-entry surfaces of pillar A, the crosscut1 airlock, and the return-entry surfaces of pillar B in the vicinityof the airlock. Although no evidence of additional heating wasfound within the airlock or along pillar B, two hot spots werefound in pillar A between the return-side stopping of thecrosscut 1 airlock and the return entry. A follow-up surveywith a handheld detector found CO emissions in excess of 200ppm. It became apparent that the increased resistance throughpillar A did not eliminate the potential for spontaneous heatingbut simply moved it.To obtain CO emissions from heating in the new pillar Abefore they became diluted by the high-volume return air, abrattice curtain was hung between the return-side airlockstopping in crosscut 1 and the return entry. This curtain wasparallel to and about 1 m (3.3 ft) from the pillar A rib. A COsensor, connected to the minewide system, was then positioned

6between the curtain and the pillar rib. Because of excessivecondensation within the enclosed volume, this sensormalfunctioned a few days after installation. To overcome thisproblem, the instrument was disconnected and removed betweensample periods.The effects of changing door positions on crosscut 1 COemissions were determined by alternately opening and closingthe belt-side and return-side airlock doors. With the airlock beltside stopping door open and the return-side stopping doorclosed, the handheld CO levels were 10 ppm inside the airlockand 12 ppm in the return. The belt-side stopping door was thenclosed and the return-side door opened. Handheld CO valuesrose to 17 ppm in the airlock and 30 ppm in the return. Both theairlock belt-side and return-side stopping doors were then closedto maximize resistance through the airlock. CO levels at the airlock and in the return increased to about 30 ppm. The belt-sidestopping door was then reopened and stayed in this position forthe remainder of the study. CO levels then returned to theiroriginal values.An attempt was made to isolate pillar A from the ventilationpressures thought responsible for the elevated CO withincrosscut 1. A floor-to-roof brattice curtain was hung in the beltentry from the portal to the containment stopping. A secondcurtain was hung between the containment stopping and theairlock. A third brattice curtain was suspended from the returnside stopping of the crosscut 1 airlock to just inby the fan in thereturn portal. These three curtains effectively enclosed pillar A.To monitor the status within the curtained-off volume, COsensors were installed between the curtains and pillar A. OneCO sensor was placed in the belt entry just outby thecontainment stopping. A second CO sensor was located withinthe return enclosure. Both the curtains and the CO sensorsremained in place for the remainder of the study.During a routine survey shortly after the curtains surroundingpillar A were erected, the infrared camera found two heatingsbetween the portal and the containment stopping in the belt-entryenclosed volume. Since these heatings were on the intake sideof pillar A (similar to that found in the crosscut 1 airlock at pillarB) they were expected to be just beneath the surface. After asmall amount of coal rib was removed from the pillars, theheatings were found. They were extinguished by digging out thesmoldering material and then flushing the areas with water.

7LONG-TERM PILLAR SPONTANEOUS HEATING DETECTIONMine officials believed the survival of this mine hinged onthe ability to rapidly detect, locate, and extinguish every pillarspontaneous heating episode. Following the initial heatings inpillars A and B and the subsequent ventilation changes made tocontrol these heatings, a long-term study of the atmospheresboth outside and inside pillars A, B, and C was begun.theory that oxidation was taking place somewhere in pillar A.Conversely, both ICO and CO-CO2 results (figures 4C and 4D)gave no indication that the oxidation reaction was acceleratingin the vicinity of these locations.MONITORING OUTSIDE THE PILLARSGas samples were obtained at regular intervals from thecurtained-off atmospheres in both the crosscut 1 airlock and thecrosscut 1 return location. Results of all sampling locations arepresented in four specific graphs, including: handheld results,CO and O2 data derived through gas chromatography, the ICO,and the CO-CO2 ratio.Infrared scanning of pillar surfaces and gas sampling of theatmosphere surrounding the pillar did not provide sufficientinformation to permit an accurate prediction of futurespontaneous heating events. Since additional heatings werelikely to occur within pillar A, a decision was made to test-drilltwo small-diameter boreholes into the pillar, sample theatmospheres within these holes, and determine whether thisinformation could more accurately predict future heatings.Crosscut 1 AirlockBoreholes 1-1 and 1-2As previously described, ele

1Physical scientist, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 2Manager, Cyprus Twentymile Coal Co., Oak Creek, CO. Detection and Control of Spontaneous Heating in Coal Mine Pillars-A Case Study By Robert J. Timko and R. Lincoln Derick1 2 ABSTRACT This U.S. Bureau of Mines study examined spontaneous heating episodes in coal mine pillars in an active

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