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JC 9118 
 
 Bureau of Mines Information Circular/1986 
 
 Face Ventilation for Oil Shale Mining 
 
 By Edward D. Thimons, Carl E. Brechtel, Marvin E. Adam, 
 and Joseph F. T. Agapito 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
{riJdmu. u*** 
 
 T 
 
 Information Circular 9118 
 
 vi A 
 
 Face Ventilation for Oil Shale Mining 
 
 By Edward D. Thimons, Carl E. Brechtel, Marvin E. Adam, 
 and Joseph F. T. Agapito 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 

 Library of Congress Cataloging in Publication Data: 
 
 Face ventilation for oil shale mining. 
 
 (Bureau of Mines information circular : 9118) 
 
 Bibliography: p. 21-22 
 
 Supt. of Docs, no.: I 28.27: 9118. 
 
 1. Mine ventilation. 2. Oil-shales. I. Thimons, Edward D. U. Series: Information circular 
 (United States. Bureau of Mines) ; 9118. 
 
 TN295.U4 [TN301] 622 s [622'.42] 86-600361 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 1 
 
 Acknowledgments 2 
 
 Face ventilation requirements 2 
 
 Diesel engine emissions 3 
 
 Oil shale dust and diesel particulates 4 
 
 Blasting 5 
 
 Methane occurrence in oil shale raining 6 
 
 Sudden inflow of methane-saturated water or free methane 7 
 
 Blast-released methane 8 
 
 Maximum length of deadheading 9 
 
 Fan system design 9 
 
 Design of the jet fan system 9 
 
 Phases 1 and 2 10 
 
 Phase 3 10 
 
 Phase 4 10 
 
 Design of the ducted fan system 12 
 
 Applications of tracer gas testing results 12 
 
 Tracer gas determination of dilution efficiencies 13 
 
 Test results 14 
 
 Impact of fan recirculation 15 
 
 Impact of fan outlet locations 15 
 
 Case studies of performance in projected operating conditions 17 
 
 Blast-produced pollutants 17 
 
 Diesel emissions 18 
 
 Methane emissions 18 
 
 General conclusions on face ventilation 20 
 
 References 21 
 
 ILLUSTRATIONS 
 
 1. Ventilation velocities required to achieve methane layering numbers of 2 
 
 and 5 versus methane inflow 8 
 
 2. Typical curve of methane concentration in exhaust air after blasting oil 
 
 shale in the saline zone at Horse Draw 9 
 
 3. Schematic of dead-end heading ventilated by jet fan 9 
 
 4. Plan view of freely expanding turbulent jet illustrating McElroy's dif- 
 
 ferent phases of velocity decay 10 
 
 5. Approximate distance to transition zone (phase 4 flow) as a function of 
 
 outlet velocity normalized to outlet diameter for fans located adjacent 
 
 to a wall 11 
 
 6. Jet fan penetration versus velocity curve for large jet fan tested in oil 
 
 shale mining 11 
 
 7. Schematics of the ducted fan system operating in deadheading 12 
 
 8. Schematic of Colony Mine showing mine ventilation system and location of 
 
 test room in crosscut 7 13 
 
 9. Test room grid system showing location of fans during tracer gas tests.... 14 
 
 10. Schematic showing tracer gas sampling points and tracer gas release point 
 
 for various simulations 15 
 
 11. Ducted system operating in blowing mode with jet fan to assist methane 
 
 plume mixing 20 
 
 12. Reorientation of jet fan to minimize inlet recirculation and reduce 
 
 effective room airflow rate for methane dilution 20 
 
TABLES 
 
 Page 
 
 1. Threshold limit values of air pollutants expected in oil shale mining.... 2 
 
 2. Comparison of engine exhaust production and required ventilation 3 
 
 3. Comparison of measured respirable dust concentration and TLV 4 
 
 4. Quartz content of dust sample collected during simulated loading 
 
 operations 5 
 
 5. Estimated proportions of oil shale dust, diesel particulates, and pro- 
 
 jected production rates 5 
 
 6. Comparison of estimated and measured concentration of gases produced by 
 
 full-face blast at Colony pilot oil shale mine 6 
 
 7. Summary of publicly available data on methane occurrence in oil shale.... 6 
 
 8. Comparison of dilution efficiencies measured in tracer gas tests 14 
 
 9. Potential increase in dilution efficiency resulting from elimination of 
 
 inlet recirculation 16 
 
 10. Locations, orientations, and face air velocities for jet fan 16 
 
 11. Duct discharge locations and face sweep velocities for the ducted 
 
 fan-blowing 16 
 
 12. Estimated time to clear blast-produced pollutants to TLV's 17 
 
 13. Comparison of required fan outlet flow rates 18 
 
 
 UNIT OF MEASURE ABBREVIATIONS 
 
 USED IN 
 
 THIS REPORT 
 
 bhp 
 
 brake horsepower 
 
 hp 
 
 horsepower 
 
 Btu/h 
 
 British thermal unit per 
 hour 
 
 in 
 
 inch 
 
 
 
 in w.g. 
 
 inch, water gauge 
 
 ft 
 
 foot 
 
 
 
 
 
 lb 
 
 pound 
 
 ft 2 
 
 square foot 
 
 
 
 
 
 lb/ft 3 
 
 pound per cubic foot 
 
 ft 3 
 
 cubic foot 
 
 
 
 
 
 mg/m 3 
 
 milligram per cubic meter 
 
 f t/min 
 
 foot per minute 
 
 
 
 
 
 mg/min 
 
 milligram per minute 
 
 ff min/ ft 
 
 foot per minute per foot 
 
 
 
 
 
 min 
 
 minute 
 
 ft 3 'min/bhp 
 
 cubic foot per minute 
 
 
 
 
 per brake horsepower 
 
 Um 
 
 micrometer 
 
 ft 3 /st 
 
 cubic foot per short ton 
 
 pet 
 
 percent 
 
 gal 
 
 gallon 
 
 ppm 
 
 part per million 
 
 h 
 
 hour 
 
 ppt 
 
 part per trillion 
 
FACE VENTILATION FOR OIL SHALE MINING 
 
 By Edward D. Thimons, 1 Carl E. Brechtel, 2 Marvin E. Adam, 3 and Joseph F. T. Agapito 4 
 
 ABSTRACT 
 
 This Bureau of Mines report presents expected levels of air pollu- 
 tants in the face areas of oil shale mines, based upon data collected by 
 the authors and previous investigators. Ventilation requirements to 
 maintain these pollutant levels below their threshold limit values and 
 Federal and local mine air quality standards are discussed. Two practi- 
 cal face ventilation systems are discussed in terms of actual in-mine 
 test experience. 
 
 INTRODUCTION 
 
 Oil shale mine entries typically will have cross-sectional areas of 
 1,500 ft 2 or more. Face ventilation systems, to effectively dilute and 
 remove pollutants from the face area of these mines, will be critical to 
 the successful operation of the underground oil shale industry. The 
 large diesel-powered equipment and heavy face blasting needed in oil 
 shale mines create substantial ventilation requirements. Furthermore, 
 it is possible that some oil shale mines will be classified as gassy, 
 which will introduce additional ventilation problems and requirements. 
 
 For ventilation personnel to deal with these problems, they must un- 
 derstand the levels of pollutants to be expected and the threshold limit 
 values (TLV's) of these pollutants. It will also be most helpful to 
 them to have some knowledge of what face ventilation systems have 
 already been tested and of how these systems performed. The purpose of 
 this report is to provide this information. 
 
 Under a Bureau of Mines contract, J. F. T. Agapito & Associates con- 
 ducted a detailed study to establish face ventilation requirements for 
 oil shale mines, design face ventilation systems to satisfy these 
 requirements, and test and evaluate the most promising of these designs 
 in an oil shale mine. The information presented in this report was 
 obtained under that program. 
 
 Supervisory physical scientist, Pittsburgh Research Center, Bureau of Mines, 
 Pittsburgh, PA. 
 
 ■"•Associate, J. F. T. Agapito & Associates, Inc., Grand Junction, CO. 
 ^Senior engineer, J. F. T. Agapito & Associates, Inc. 
 4 President, J. F. T. Agapito & Associates, Inc. 
 
ACKNOWLEDGMENTS 
 
 The authors wish to acknowledge both 
 the technical and financial contributions 
 to this work provided by the Colorado 
 Mining Association and the U.S. Depart- 
 ment of Energy, who acted as joint spon- 
 sors of this work with the Bureau of 
 Mines. Special thanks are directed to 
 the following members of the Oil Shale 
 Advisory Committee of the Colorado Mining 
 
 Association: David Cole, president, Col- 
 orado Mining Association; L. A. Weakly, 
 Exxon Co., USA — Committee Chairman; Sam 
 Vera, Mobil Oil Co.; David Starbuck, 
 White River Shale Oil Corp.; John Shaler, 
 Cathedral Bluffs Shale Oil Co.; Alan 
 Salter, Union Oil Co. of California; and 
 Dr. Art Hartstein, U.S. Department of 
 Energy. 
 
 FACE VENTILATION REQUIREMENTS 
 
 This section reviews background data on 
 mine air pollutant production to help 
 establish air quantities. The quality of 
 air at the face must meet regulatory re- 
 quirements. In some cases, there may be 
 multiple requirements. For example, Col- 
 orado State law requires that 75 ft 3 /min 
 of fresh air be used to ventilate each 
 brake horsepower of engine capacity; it 
 also requires the maintenance of TLV's 
 for various air pollutants, as specified 
 by the Mine Safety and Health Administra- 
 tion (MSHA). The main sources of air 
 pollutants expected to impact face venti- 
 lation requirements follow: 
 
 Loading operations . — Noxious gases, 
 diesel particulates, and dust are pro- 
 duced during loading operations at the 
 face. These are especially severe for 
 
 mines designed for front-end loaders with 
 truck haulage. 
 
 Blasting . — Large quantities of noxious 
 gases and dust are generated by face 
 blasting. 
 
 Strata gas . — Methane can occur both as 
 free gas in solution with groundwater and 
 as absorbed gas In solid solution with 
 the kerogen in oil shale. The existence 
 of methane has not been reported for 
 properties at the southern rim of the 
 Piceance Creek Basin, but it has been 
 observed during development mining in the 
 Uinta Basin and central portion of the 
 Piceance Creek Basin. 
 
 Specific air pollutants of concern pro- 
 duced during oil shale mining and their 
 allowable concentrations or TLV's are 
 listed in table 1. These values are 
 
 TABLE 1. - Threshold limit values of air pollutants 
 expected in oil shale mining 
 
 Pollutant 
 
 TLV 
 
 Exposure 
 criterion 
 
 Maximum 
 excursion 
 
 C0 2 
 CO. 
 NO. 
 
 .ppm. 
 .ppm. 
 .ppm. 
 
 N0 2 ppm. 
 
 Formaldehyde ppm. 
 
 H 2 S ppm. 
 
 Methane ppm. 
 
 Respirable dust 2 mg/ra 3 . 
 
 Total dust mg/m 3 . 
 
 5,000 
 
 50 
 
 25 
 
 5 
 
 2 
 
 10 
 
 10,000 
 
 1.4-0.7 
 
 3.6-1.9 
 
 TWA 
 TWA 
 TWA 
 C 
 
 c 
 
 TWA 
 C 
 
 TWA 
 TWA 
 
 ND 
 
 75 
 
 37.5 
 
 5 
 
 2 
 
 20 
 
 10,000 
 
 ND 
 
 ND 
 
 C Maximum value not to be exceeded. 
 
 ND Not defined. 
 
 TWA Time-weighted average. 
 
 1 Based upon American Conference of Governmental Indus- 
 trial Hygienists Standards of 1973. 
 
 2 Estimated based upon a range in quartz content between 
 5.4 and 12.6 pet. 
 
derived from the American Conference of 
 Governmental Industrial Hygienists Stand- 
 ards of 1973 (as specified by MSHA). 
 TLV's are generally based upon the time- 
 weighted average exposure over a speci- 
 fied time period. However, additional 
 restrictions can be imposed by the maxi- 
 mum excursion value, which is defined as 
 the maximum allowable concentration that 
 personnel can be exposed to at any time. 
 Dust TLV values listed in table 1 are 
 estimates based upon data published on 
 the particle size of oil shale dust and 
 on measurements of quartz content. The 
 parameters that affect the dust TLV's 
 include quartz content, respirable mass, 
 and diesel particulates. Diesel particu- 
 lates are counted in the total dust mass 
 and the total respirable dust mass; 
 they have the effect of reducing quartz 
 content. This impacts the TLV, be- 
 cause it is a strong function of quartz 
 content. 
 
 DIESEL ENGINE EMISSIONS 
 
 It has been generally accepted that the 
 production of nitrogen oxides (NO) and 
 carbon monoxide (CO) by the large-capac- 
 ity diesel loading equipment would govern 
 the quantity of fresh air required at the 
 face. However, studies of the production 
 of diesel particulates by Breslin (1_) 5 
 and Daniel (2) suggest that the require- 
 ment to limit particulate concentrations 
 may be the governing factor. 
 
 Gaseous emission studies by Markworth 
 (3) compared the performance of three 
 engines whose peak horsepower ranged from 
 800 to 1,200 hp for potential application 
 to oil shale mining and illustrated that 
 pollutant production rates varied over a 
 large range. Emissions for the cleanest 
 engine tested in the study are listed in 
 table 2, along with the required quantity 
 of fresh air, assuming ideal dilution. 
 The required quantity of fresh air was 
 determined for the additive effects of CO 
 and N0 X using the inequality in this 
 equation as suggested by Bossard (4): 
 
 Ceo 
 
 Cno, 
 
 < 1.0 
 
 (1) 
 
 TLVco TLV N X 
 where C = pollutant concentration, ppm. 
 
 The tests were conducted using both 
 fresh air and fresh air containing 1.5 
 pet methane in the form of natural gas to 
 compare emissions for nongassy and gassy 
 conditions. The addition of methane pro- 
 duced a large increase in CO production, 
 which required an increase of ventilation 
 air of 43 to 91 pet of the original quan- 
 tity, depending on operating horsepower. 
 The 1.5-pct methane content exceeds 
 the maximum methane concentration of 1.0 
 pet allowed under MSHA regulations, but 
 
 ^Underlined numbers in parentheses re- 
 fer to items in the list of references at 
 the end of this report. 
 
 TABLE 2. - Comparison of engine exhaust and required ventilation 
 
 
 Cone 
 
 ppm 
 
 Exhaust flow, 2 
 ft 3 /min 
 
 Required 
 
 Brake horsepower 
 
 CO 
 
 N0 X 
 
 ventilation, 3 
 ft 3 /min 
 
 With no methane: 
 
 561 
 
 100 
 150 
 
 875 
 713 
 
 488 
 538 
 
 506 
 513 
 
 1,814 
 2,257 
 
 1,830 
 2,276 
 
 36 140 
 
 823 
 
 55 330 
 
 With 1.5 pet methane: 
 561 
 
 69,060 
 79,170 
 
 
 From Markworth (_3) for a turbocharged, after-coo 
 D-348 engine with precorabustion engine and water sc 
 
 Estimated from Markworth (3) by subtracting 
 natural gas and extrapolated to 0.062 lb/ft 3 dens 
 lb/ft 3 . 
 
 Assuming ideal dilution. 
 
 led Caterpillar 
 rubber. 
 
 mass flow of 
 ity from 0.075 
 
illustrates that methane In the mine 
 air could impact pollutant production. 
 Based upon table 2, in the nongassy envi- 
 ronment the engine would require 64 to 67 
 ft 3 *min/bhp to meet the TLV's; in the 
 gassy environment it would require 96 to 
 123 ft 3 «min/bhp. 
 
 OIL SHALE DUST AND DIESEL PARTICULATES 
 
 Both diesel particulates and oil shale 
 dust must be considered in assessing the 
 impact of particulate production on face 
 ventilation requirements in oil shale 
 mining. Dust data reported by Volkwein 
 (5_) are summarized in table 3. The aver- 
 age dust mass was 1.45 mg/m 3 , and average 
 quartz content was 5.8 pet. 
 
 A group of dust measurements was re- 
 ported by Brechtel (6) which included 
 measurements of dust production due to 
 blasting and loading operations in an 
 underground oil shale mine. Dust pro- 
 duced by a face blast (1,900 lb ANFO) in 
 oil shale has an average total mass of 
 13.2 mg/m 3 , with less than 2 pet of the 
 dust having a particle diameter of less 
 than 0.7 um. The dust had a light brown 
 color. Particulates measured during sim- 
 ulated loading operations showed that the 
 fine fraction (<0.74 um) increased to 53 
 to 73 pet of the total mass and was black 
 in color. This led to the conclusion 
 that most of the fine particles were 
 
 diesel particulates. Quartz content 
 analyses listed in table 4 support this 
 conclusion in that quartz contents of the 
 fine fractions were below detection lim- 
 its. Quartz contents were similar in 
 range to the Volkwein (5) data, averaging 
 4.4 pet. 
 
 The rates of production of respirable 
 oil shale dust and diesel particulates 
 are estimated in table 5, using both 
 particle gradation measurements made dur- 
 ing the loading and the measured ventila- 
 tion flow. At an average production rate 
 of 6,220 rag/min, face ventilation capac- 
 ities in the range of 157,000 f t 3 /min 
 would be required to maintain respi- 
 rable particulates at a TLV of 1.4 mg/m 3 
 (assuming 5.4 pet quartz). These mea- 
 surements are probably not representative 
 of expected conditons because — 
 
 1 . The material being loaded was 
 partly comprised of cuttings from a road- 
 header miner and may have contained a 
 disproportionately large amount of fine 
 material. 
 
 2. The diesel equipment was very old 
 and poorly maintained. The generation of 
 particulates during loading operations 
 will be an important parameter in face 
 ventilation requirements. Oil shale dust 
 production must be limited by good mining 
 practice such as wetting the muckpile 
 and roadways, and diesel particulate 
 production must be minimized by engine 
 
 TABLE 3. - Comparison of measured respirable dust concentration 
 and TLV (5) 
 
 General location 
 
 Alpha quartz 
 content, pet 
 
 Respirable dust, mg/m 3 
 
 
 Measured cone 
 
 TLV 1 
 
 
 3.5 
 
 14.0 
 
 6.7 
 .9 
 
 2 2.7 
 2 11.1 
 
 NA 
 2 1.8 
 
 2.05 
 
 NA 
 
 2.68 
 .94 
 
 2.63 
 
 2 1.05 
 
 2.18 
 
 2 .63 
 
 1.82 
 
 Blasting: Around corner from face. 
 Scaling: 
 
 .63 
 1.15 
 
 Mucking: 
 
 2.00 
 2.13 
 
 
 .76 
 
 
 NA 
 
 Roof bolting: In or near bolter... 
 
 2.63 
 
 
 5.8 
 
 1.45 
 
 1.59 
 
 NA Not available. 
 
 'Based on quartz content. 
 
 2 Average of values from several locations. 
 
TABLE 4. - Quartz content of dust sample collected during 
 simulated loading operations (6) 
 
 Loading operation 
 
 Mass cone, 
 3 
 mg/m 
 
 Quartz con- 
 tent, mg/m 
 
 Quartz as pet 
 
 and sample type 
 
 of total mass 
 
 With truck shutdown: 
 
 
 
 
 
 4.63 
 
 0.296 
 
 6.4 
 
 Dichotomous sampler: 
 
 
 
 
 Coarse (2.5 to 15 ym).. 
 
 .72 
 
 .085 
 
 NAp 
 
 
 2.34 
 
 .030 
 
 ND 
 
 
 3.06 
 
 .115 
 
 3.8 
 
 With truck idling: 
 
 
 Dichotomous sampler: 
 
 
 
 
 Coarse (2.5 to 15 ym).... 
 
 .58 
 
 .075 
 
 NAp 
 
 
 3.16 
 
 .040 
 
 ND 
 
 
 3.74 
 3.81 
 
 .115 
 .175 
 
 3.1 
 
 
 4.4 
 
 NAp Not applicable. ND Not detectable. 
 
 TABLE 5. - Estimated proportions of oil shale dust, diesel particulates, 
 and projected production rates based upon simulated loading tests (6) 
 
 Loading 
 
 With truck shut down 
 
 Worker floor 
 location 
 
 Operator 
 location 
 
 With truck 
 idling 
 
 Height above f loot ft.. 
 
 Av dust mass, mg/m 3 : 
 
 Total 1 
 
 Respirable 
 
 Oil shale dust: 
 
 Pet of respirable mass 2 
 
 Est production rate 3 mg/min. . 
 
 Diesel particulates: 
 
 Pet of respirable mass 2 
 
 Est production rate 3 mg/min. . 
 
 Est total respirable dust production mg/min. . 
 
 2.8 
 2.5 
 
 21 
 1,070 
 
 79 
 4,030 
 5,100 
 
 '13.2 for blasting. 
 
 2 Assumes that total fine fraction (<0.7 ym) is diesel particulates. 
 
 3 Based upon measured ventilation airflow of 72,000 ft 3 /min. 
 
 12 
 
 5.1 
 3.6 
 
 18 
 1,320 
 
 82 
 6,020 
 7,340 
 
 12 
 
 5.8 
 5.1 
 
 16 
 1,660 
 
 84 
 
 8,740 
 
 10,400 
 
 selection and good maintenance in order 
 to meet governing particulate TLV's. 
 
 BLASTING 
 
 Blast rounds planned for room and pil- 
 lar operations require the detonation 
 of up to 2,000 lb ANFO. Although care- 
 ful control of explosive composition lim- 
 its air pollutant production, studies of 
 blast-produced air pollutants by Rogers 
 (_7) and Abata (8) indicate that the large 
 quantities of ANFO required for oil shale 
 
 mining will produce considerable amounts 
 of noxious gases. Table 6 compares esti- 
 mated production to measurements for a 
 full-face shot at the Colony Mine (6^). 
 The table suggests that production of 
 blast-produced air pollutants can be ade- 
 quately predicted if the mass of ANFO 
 being detonated is known. Ventilation of 
 noxious gases in the face area is not 
 a critical parameter after the shot, 
 because personnel do not enter the head- 
 ing for some time. However, if gassy 
 conditions exist, methane gas may be 
 
liberated by face blasting and require 
 implementation of special ventilation 
 practices to minimize the hazard. 
 
 METHANE OCCURRENCE IN OIL SHALE MINING 
 
 Publicly available information on the 
 occurrence of methane in oil shale sug- 
 gests that it occurs both as a free gas, 
 as gas in solution with groundwater, and 
 as absorbed gas in solutuion with kero- 
 gen. Table 7 summarizes public data on 
 methane occurrence in oil shales of the 
 Green River Formation. Oil shale mining 
 and exploration conducted in central 
 Piceance Creek Basin tracts and the 
 Uinta Basin have encountered methane. 
 The outcrop and erosional exposure at the 
 
 TABLE 6. - Comparison of estimated and 
 measured concentrations of gases 
 produced by full-face blast at Col- 
 ony pilot oil shale mine (6) 
 
 1 Based upon Abata (8) , with a total of 
 1,890 lb ANFO and an estimated dilution 
 volume of 878,400 ft 3 . 
 
 2 These concentrations would vary for 
 different blasting patterns, methods of 
 initiation, and fuel oil content. 
 
 3 Includes background atmospheric C0 2 . 
 
 southern rim apparently has allowed the 
 methane to bleed off, while in the cen- 
 tral Piceance Creek and Uinta Basins, 
 confinement due to the hydrologic system 
 may have contained the gas. 
 
 Recent work by Sapko (9) presents the 
 results of measurements of methane re- 
 leased by mining operations in the Mahog- 
 any Zone at the U-a, U-b oil shale lease 
 in the Uinta Basin, and is particularly 
 pertinent to ventilation design. Methane 
 released from oil shale rubblized by 
 blasting ranged from 2.3 to 22.5 ft 3 /st 
 with an average value of 13.3 ft 3 /st. 
 Other work by Schatzel (10) reports that 
 methane given off by core samples ob- 
 tained from the Mahogany Zone at C-b 
 tract averaged 6.2 ft 3 /st after 125 days 
 of monitoring. Total methane content of 
 the core samples was not determined, but 
 similar measurements by Matta (11) sug- 
 gested that after 21 days of monitoring 
 as much as 40 pet of the methane had been 
 released. 
 
 The deep saline oil shale sequence (Rl- 
 R5 zones) found in the Central Piceance 
 Creek Basin is known to have a much 
 higher gas content than the oil shales of 
 the overlying leached sections (R6, Ma- 
 hogany [R7], and R8 zones). Data re- 
 ported by Sapko (11) for saline oil 
 shales rubblized by blasting indicated a 
 range of 2.4 to 56.7 ft 3 /st. These data 
 are not applicable to mining in the 
 leached section because of differences in 
 stratigraphic environment. 
 
 Production of methane by groundwater 
 entering the mine and by desorbtion from 
 
 TABLE 7. - Summary of publicly available data on methane occurrence 
 in oil shale 
 
 Type of occurrence, by site 
 
 Range in magnitude 
 of occurrence 
 
 Reference 
 
 
 55 -1,600 
 5.9 - 64.8 
 
 2.3 - 22.5 
 7.6 - 33.2 
 
 .8 - 15.2 
 
 .03- 32.6 
 
 6.2 
 
 2.4 - 56.7 
 
 12 
 
 Gas absorbed by kerogen, ft 3 /st: 
 
 13 
 9 
 
 
 14 
 
 
 15 
 
 
 13 
 
 
 10 
 
 
 9 
 
the excavation boundary is expected to be 
 handled by the main mine ventilation 
 system. Two specific types of occur- 
 rence could impact face ventilation, as 
 described in the following paragraphs. 
 
 Sudden Inflow of Methane-saturated 
 Water or Free Methane 
 
 Methane inflows could result from the 
 intersection of (1) natural fractures 
 that were connected to a localized aqui- 
 fer with high methane saturation or 
 (2) a localized reservoir of free meth- 
 ane. This type of situation was reported 
 by Stellavato (12) during shaft sinking 
 operations at the C-b tract, where a sud- 
 den inflow of water and methane produced 
 initial methane release rates of 1,600 
 ft 3 /min. The water inflow dropped to 13 
 pet of its initial value within 24 h, and 
 the methane production dropped to 55 ft 3 / 
 min. There are informal reports of this 
 type of methane occurrence in drilling 
 operations during resource evaluation. 
 The apparent randomness of occurrence 
 (methane was encountered in one out of 
 three shafts sunk in close proximity at 
 C-b) and rapid reduction in water-meth- 
 ane production encountered to date sug- 
 gest small, localized reservoirs (gas 
 or groundwater) , isolated from the main 
 hydrologic system. In this case, the 
 frequency of occurrence might be small, 
 and the hazard represented would be 
 reduced. 
 
 This type of methane occurrence would 
 be most hazardous if a methane layer 
 developed owing to localized, high-volume 
 methane flow from fractures intersecting 
 the roof of a heading. Methane layering 
 results when buoyant effects due to the 
 density contrast between methane and air 
 are of greater magnitude than the turbu- 
 lent mixing energy of the airstream at a 
 given velocity. 
 
 Research on methane layering is re- 
 ported in detail by Bakke (16) , who pro- 
 posed "layering numbers" to evaluate the 
 potential for methane layering at varying 
 ventilation air velocities, methane pro- 
 duction rates, and excavation widths. 
 The layering number (L) is calculated by 
 the equation 
 
 L = 
 
 37[(V/W)'/ 3 l' 
 
 (2) 
 
 where L = methane layering number, 
 
 TI = ventilation air velocity, 
 f t/min, 
 
 V = methane flow rate, ft 5 /min, 
 
 and 
 
 W = excavation width, ft. 
 
 This expression was developed for air 
 flowing uniformly along a heading without 
 any equipment to enhance mixing. Bakke 
 (16) suggests that a layering number of 5 
 represents an optimum for limiting the 
 layer length. Further increase in air 
 velocity beyond the velocity necessary to 
 produce a value of 5 does not reduce 
 the length of the layer appreciably. At 
 layering numbers below 2, the buoyant 
 effects dominate and the methane layering 
 will be pronounced. 
 
 The methane layering problem is heavily 
 dependent upon the location of the meth- 
 ane source and the degree of localization 
 of the production. Distributing a given 
 production over a long section of roof 
 tends to reduce the layering problem. If 
 the methane is produced from the floor or 
 walls, the ventilation air can mix and 
 disperse the methane more effectively. 
 Bakke ( 16 ) notes that once the methane is 
 well mixed in air, restratif ication due 
 to the density contrast is minor. 
 
 The magnitude of potential methane lay- 
 ering problems in oil shale mining is 
 difficult to estimate because of the lack 
 of operating data on methane production. 
 Figure 1 shows the relationship between 
 methane inflow rate and required air 
 velocity to achieve methane layering num- 
 bers of 2 and 5. An air quantity of 
 100,000 ft 3 /min for face ventilation in a 
 55-ft-wide by 30-ft-high opening gives an 
 average velocity of 61 f t/min. The re- 
 sulting methane layering number would be 
 below the critical value of 2 for methane 
 inflows above 50 ft 3 /min, indicating that 
 layering in the face heading area will be 
 a problem given sufficient methane in- 
 flow. The problem may be compounded by 
 the large cross-sectional area of the 
 
KEY 
 L Methane layering number 
 W Excavation width 
 
 c 
 
 1 1 ' 
 
 E 
 s 
 
 ./L = 5, 
 
 H- 
 
 X W=55ft 
 
 >- 
 
 
 H 
 
 
 5 400 
 
 / 
 
 o 
 
 /j-500,000 ft 3 /min in a 
 / ]_55- by 30-ft heading 
 
 _i 
 
 LU 
 
 > 
 
 cc 
 
 J 
 
 < 
 
 f L=2, 
 
 z 
 
 / W=55ft 
 
 o 
 
 i ^^-^ 
 
 |= 200 
 
 7 j**^*' 
 
 < 
 
 r ^^"^^^ 
 
 _i 
 
 1 s^"^ 
 
 Z 
 
 y^r-100,000 ft 3 /min in a 
 "/^ J_ 55- by 30-ft heading 
 
 i 
 
 > 
 
 1,000 2,000 
 
 METHANE INFLOW, ft 3 /min 
 
 FIGURE 1 . — Ventilation velocities required to achieve methane 
 layering numbers of 2 and 5 versus methane inflow. 
 
 openings. Ventilation using a ducted 
 system results in very high velocity 
 at the immediate face but relatively 
 low velocity throughout the heading. In- 
 creasing the average air velocity 
 requires a large increase in flow rate 
 through the duct, which would result in 
 large energy costs. An alternative would 
 be to increase local mixing by using an 
 auxiliary jet fan. The use of a jet fan 
 as the main face ventilation system would 
 be an effective way to increase air mix- 
 ing, because the jet fan uses the heading 
 itself as a duct and the average air vel- 
 ocity is higher (200 to 400 ft/min). 
 Bakke (16) emphasizes that air velocity 
 is the critical factor. 
 
 Flow in the last open crosscut is ex- 
 pected to range from 400,000 to 800,000 
 
 ft 3 /min based upon a survey by Brechtel 
 (6_) of oil shale companies. A value of 
 500,000 ft 3 /min would give air velocities 
 above 300 ft/min and result in a layering 
 number above 2 for a quite large inflow 
 of methane. 
 
 Blast-Released Methane 
 
 The magnitude of the methane concentra- 
 tion that could result from face blasting 
 in methane-saturated oil shale is diffi- 
 cult to estimate because of the lack of 
 definitive data on methane content and 
 because of the interaction of methane 
 release rate and ventilation airflow in 
 the heading. Measurements of methane 
 production during oil shale mining oper- 
 ations at the Horse Draw facility are 
 reported by Richmond (17) and Sapko (11). 
 A typical curve of methane concentration 
 in ventilation air after a blast (fig. 
 2A) indicates that the methane concentra- 
 tion reached its peak value shortly after 
 the blast. Figure 2B shows a semilog 
 plot of the data, illustrating the gen- 
 erally linear relationship expected for 
 the dilution of gas in a room of fixed 
 volume ventilated by a constant flow rate 
 of fresh air. Based upon room volume, 
 80 pet of the total methane liberated 
 by the blast was mixed with the room 
 air within 5 min after the blast. Fig- 
 ure 2 shows data for 60 st of blasted 
 shale; it is not known how a blast 
 rubblizing several thousand tons of oil 
 shale would affect the rate of methane 
 release. 
 
 A typical face heading 50 ft wide by 30 
 ft high, advancing 30 ft, would produce 
 2,808 st of rubblized shale (density of 
 approximately 124.8 lb/ft 3 ) and could 
 release a large volume of methane. 
 Assuming an average saturation of 13.3 
 ft 3 /st, a single blast could produce 
 approximately 44,000 ft 3 of methane, as 
 suggested by the data from Sapko (9). 
 If all the methane were released instan- 
 taneously in a 50-ft-wide by 30-ft-high 
 heading, 300 ft long and mixed uniformly, 
 this would result in a methane concentra- 
 tion of 8 pet. 
 
MAXIMUM LENGTH OF DEADHEADING 
 
 Regulatory guidelines govern the length 
 of the deadheading in coal mining by 
 stipulating a limit of 100 ft of advance 
 before breaking through a new crosscut. 
 For oil shale mining, this requirement 
 
 would be impractical. Based upon opera- 
 tional considerations and typical room 
 and pillar dimensions, it was estimated 
 that 300 ft would be an acceptable dead- 
 heading length before breakthrough to the 
 last open crosscut. 
 
 FAN SYSTEM DESIGN 
 
 A group of seven conceptual designs of 
 large-capacity face ventilation systems 
 was developed as part of this study. 
 
 The concepts were evaluated for mine 
 operation compatibility, projected ven- 
 tilation effectiveness, and cost. The 
 highest ranking concepts were a jet fan 
 
 — — i— i i 1 1 1 1 1 1- 
 
 A Methane concentration in ventilating 
 air after blast 
 
 5 8.0 p B Semilog plot of gas dilution 
 
 ul 60 
 
 < 4.0 
 
 X 
 
 h- 
 
 LU 
 
 2 2.0 h 
 
 1.0 
 .8 
 .6 
 
 _L 
 
 10 20 30 40 
 
 TIME AFTER BLAST, min 
 
 50 
 
 FIGURE 2. — Typical curve of methane concentration in exhaust 
 air after blasting oil shale in the saline zone at Horse Draw. Total 
 methane = 4,088 ft 3 , which represents 60 ft 3 /st oil shale. 
 
 system for nongassy oil shale mining and 
 a reversible fan with rigid duct for 
 gassy oil shale mining. 
 
 The design of each system was based 
 upon commercially available equipment. 
 Each system had a common design basis, 
 including 
 
 1. 100,000-ft 3 /min capacity. 
 
 2. Low power consumption. 
 
 3. Components that must be handled 
 with a minimum of special equipment. 
 
 4. Two-speed operation to conserve 
 power consumption when full flow was not 
 needed. 
 
 DESIGN OF THE JET FAN SYSTEM 
 
 Jet fans (free-standing, unducted fans) 
 are commonly employed in the mining in- 
 dustry. The application of the jet fan 
 for ventilation of a dead-end heading is 
 illustrated in figure 3. The fan is 
 located along the upstream corner of the 
 last crosscut and projects air in a high- 
 velocity turbulent jet along the wall 
 toward the face. The jet expands with 
 increasing distance from the fan until, 
 ideally, air is flowing toward the face 
 in half the opening and exhausting back 
 
 FIGURE 3.— Schematic of dead-end heading ventilated by jet 
 fan. 
 
10 
 
 to the last open crosscut in the other 
 half. The jet grows through the action 
 of frictional forces at the boundary of 
 the jet, where the relatively still air 
 is accelerated or entrained into the jet. 
 In this process, the initial momentum of 
 the jet of air is transferred to an ever 
 greater mass, thereby reducing the veloc- 
 ity of flow. By the process of entrain- 
 ment, the jet fan delivers a volume much 
 greater than its inlet volume to the 
 face, resulting in high air velocities 
 and enhanced mixing. The entrained por- 
 tion of the air delivered to the face is 
 recirculated; therefore the dilution ca- 
 pability of the jet fan is dependent upon 
 the amount of fresh air entering the 
 inlet. Recirculation at the inlet is 
 generally 20 to 40 pet, depending upon 
 inlet location. 
 
 The key to the design of the jet 
 fan system was characterization of the 
 complex action of the turbulent jet. 
 Although detailed analysis has been per- 
 formed by Abromovich (18) , a simplified 
 method derived by McElroy ( 19 ) from em- 
 pirical studies was chosen for this proj- 
 ect. McElroy developed a group of equa- 
 tions to describe the decay in centerline 
 velocity with increasing distance from 
 the fan outlet. These equations are 
 correlated with four phases of behavior, 
 as illustrated in figure 4. For round 
 jets, phases 1 and 2 are combined so that 
 the jet centerline decay is predicted for 
 each phase as described below. 
 
 Gaussian air 
 
 velocity 
 distribution 
 
 FamzE-^-yo 
 Phase I and I 
 2 flow I I 
 
 fan diam) 
 
 Phase 3 flow 
 (5 to 75 fan diam) 
 
 ■Transition zone 
 
 Phase 4 flow (beyond phase 3) 
 
 Phases 1 and 2 
 
 The centerline velocity, V* x , at a dis- 
 tance, X, from the fan outlet is charac- 
 terized by 
 
 V x = aV , (3) 
 
 where V Q = outlet or discharge velocity 
 
 and a = a constant (1.0-1.2). 
 
 The centerline velocities are fairly 
 well characterized by this expression for 
 a distance of up to five times the outlet 
 diameter. The constant a is apparently 
 related to outlet velocity, decreasing 
 with decreasing velocity. 
 
 Phase 3 
 
 The centerline velocity, V x , at a dis- 
 tance, X, from the fan outlet is charac- 
 terized by 
 
 V x = (KV D)/X, (4) 
 
 where K = a constant (3-10), 
 
 D = outlet diameter, 
 
 and X = distance from the outlet. 
 
 Phase 4 
 
 After phase 3, a transition zone occurs 
 in which the centerline velocity, V x , 
 decays rapidly to the range that is 
 predicted using the flow rate and one- 
 half the area of the opening. After the 
 transition zone, the centerline velocity 
 appears to follow the equation 
 
 V x = fV_D/109X, 
 
 (5) 
 
 FIGURE 4.— Plan view of freely expanding turbulent jet il- 
 lustrating McElroy's different phases of velocity decay. 
 
 where f = a constant related to the ra- 
 tio of outlet diameter to 
 opening dimension 
 
 and g = 0.026f. 
 
11 
 
 The constants f 
 developed, with 
 
 and g are empirically 
 
 100 
 
 f = 12.2 (DS)/W 
 
 (6) 
 
 where 
 
 and 
 
 S = aspect ratio of the fan outlet 
 (1.0 for a round jet) 
 
 W = large dimension of the 
 opening. 
 
 McElroy's equations were developed for 
 jets expanding freely in all directions. 
 Placement of the fan along the wall, 
 as illustrated earlier in figure 3, 
 constrains the growth of the jet and 
 increases the distance in which phase 3 
 behavior is observed. This is incorpo- 
 rated into the predictive equation 3 by 
 increasing the value of the constant K. 
 
 McElroy's (19) equations are similar to 
 work reported by Krause ( 20 ) and were 
 checked by fitting the relationships 
 to experimental data from Lewtas ( 21 ) 
 and Spendrup (22). K values were found 
 to vary between 5.0 and 11.3 for fans 
 located within three fan diameters from 
 the wall. Distance from the fan outlet 
 to the transition zone was found to be an 
 approximately linear function of outlet 
 velocity divided by discharge diameter, 
 as shown in figure 5. 
 
 The zone of the heading that is of 
 critical importance in mining applica- 
 tions is the transition zone and beyond. 
 At this point, the entrainment action in- 
 creases rapidly, causing a rapid decrease 
 in flow velocity. The design process 
 must ensure that the jet can force air to 
 the face with sufficient velocity to 
 provide good mining and face sweep. 
 
 Application of the design equations was 
 compared to field measurements for a 39- 
 in-diam fan tested at Union Oil Co. of 
 California's Parachute Creek shale oil 
 project by Spendrup (22). Figure 6 shows 
 good correlation of the predictive equa- 
 tions and measured data near and beyond 
 the transition zone. 
 
 Design of a jet fan for this work was 
 based upon the following: 
 
 y=0.0064 X+40.7 
 1**0.75 
 
 2,000 4,000 6,000 8,000 
 
 OUTLET VELOCITY / DISCHARGE DIAMETER 
 (Vo/D), ft.mln/ft 
 
 FIGURE 5.— Approximate distance to transition zone (phase 
 4 flow) as a function of outlet velocity normalized to outlet 
 diameter for fans located adjacent to a wall. 
 
 I ' I 
 KEY 
 Fan diam = 39 in 
 Outlet vel = 6,800 ft/min 
 Flow rate =56,760 ft 3 /min 
 • Measured data 
 Predicted 
 
 25 50 75 
 
 DISTANCE/ FAN DIAMETER (X/D) 
 
 100 
 
 FIGURE 6.— Jet fan penetration versus velocity curve for large 
 jet fan tested in oil shale mining. 
 
 1. Flow capacity based upon expected 
 rates of pollutant emissions at the face. 
 
 2. Fan diameter selected such that the 
 jet reaches the face with 100-ft/min 
 velocity. 
 
 Using K = 5.0, a flow rate of 100,000 
 ft 5 /min, and opening dimensions of 55 ft 
 wide by 30 ft high, fans with diameters 
 between 48 and 60 in were predicted to 
 project air in the range of 300 ft with a 
 
12 
 
 minimum velocity of 100 ft/min. Based 
 upon this, a 55-in-diam fan was selected. 
 
 DESIGN OF THE DUCTED FAN SYSTEM 
 
 Design methods for ducted fan systems 
 are described elsewhere by Hartman (23) , 
 Jorgensen (24), and Daly (25). The pri- 
 mary design concerns in this work were 
 whether to use a blowing or exhausting 
 system and the size of ducting needed 
 to optimize power consumption yet allow 
 handling without special equipment. 
 
 A reversible system was selected for 
 this work to establish a relative compar- 
 ison between blowing and exhausting ven- 
 tilation. This selection required rigid 
 duct, and from practical considerations, 
 it appeared that 54-in-diam round or 62- 
 by 40.5-in oval ducts were as large 
 as could be handled conveniently by a 
 two-member crew without specialized 
 equipment. This size was also a practi- 
 cal minimum, since a system ventilating a 
 distance of 300 ft would be operating at 
 approximately 5.0-in-wg total pressure, 
 requiring around 120 hp. 
 
 Operation of this type of system for 
 ventilation of a dead-end heading is 
 illustrated in figure 7, for both blowing 
 and exhausting modes. Positioning of the 
 inlet is a critical parameter in elim- 
 inating recirculation. In the blowing 
 mode, the inlet should be around the cor- 
 ner and upstream in the last open cross- 
 cut. For the exhausting mode, this sys- 
 tem was designed to project the jet of 
 
 Fresh 
 air 
 
 320 ft 
 
 
 ■A 
 
 Rigid duct 
 
 Reversible 
 ventilation fan 
 
 '^ 
 
 mmmmm 
 
 J 
 
 DUCTED FAN- BLOWING MODE 
 
 Fresh 
 air 
 
 320 ft 
 
 Rigid duct 
 
 * 
 
 ^ 
 
 /— Kigia auci 
 
 _ Reversible 
 ventilation fan 
 
 *) 
 
 I \ 
 
 DUCTED FAN- EXHAUST MODE 
 
 FIGURE 7.— Schematics of the ducted fan system operating 
 in dead heading. 
 
 exhaust air downstream but across the 
 opening of the deadheading. The high 
 velocities of the jet were expected to 
 minimize recirculation of the exhaust 
 air. If this approach were unsuccess- 
 ful, exhaust mode operations would have 
 to utilize auxiliary ducting at the roof 
 to carry the exhaust downstream past the 
 opening. This would require a more com- 
 plicated dampered control system with 
 a branching duct to pass the exhaust 
 duct up along the roof to the downstream 
 side of the face heading in such a way 
 that it did not interfere with mine 
 traffic. 
 
 APPLICATIONS OF TRACER GAS TESTING RESULTS 
 
 Sulfur hexafluoride (SF 6 ) tracer gas 
 was used to measure the average per- 
 formance of the face ventilation systems. 
 Different models of tracer gas release 
 were designed to simulate the production 
 of diesel emissions, blast fumes, and 
 methane in the face area. Measurements 
 of the tracer gas concentration through- 
 out the room, and especially in the face 
 area, provided data on the uniformity 
 of mixing and the average ability of 
 the systems to dilute air pollutants. 
 These tests were described in detail by 
 Brechtel (6). 
 
 The results of the tracer gas testing 
 are compared using a uniform measure of 
 the efficiency of the face ventilation 
 system, called dilution efficiency. For 
 a perfect system, all of the air passing 
 through the fan would be uniformly mixed 
 with all of the tracer gas released in 
 the face area. The resulting dilution 
 efficiency would equal 1.0. Dilution ef- 
 ficiency is calculated using equation 7: 
 
 E d = Qe /Of » 
 where E d = dilution efficiency, 
 
 (7) 
 
13 
 
 Q E = quantity of air actually ven- 
 tilating the room, as mea- 
 sured by tracer gas dilu- 
 tion, ft 3 /min, 
 
 and Q F = measured outlet flow rate 
 the fan, ft 3 /min. 
 
 of 
 
 In an actual mining situation, the 
 value of the dilution efficiency would be 
 less than 1 .0 because of recirculation, 
 efficiency of mixing at the pollutant 
 source, turbulence, last open crosscut 
 flow, and measurement error. The tracer 
 gas tests measured the combined effects 
 of these parameters and allowed these 
 effects to be accommodated in the design 
 of ventilation capacity. 
 
 TRACER GAS DETERMINATION OF 
 DILUTION EFFICIENCIES 
 
 The tracer gas tests were conducted in 
 Exxon's Colony pilot mine in crosscut 7, 
 shown in figure 8. The mine ventilation 
 system was capable of supplying 124,000 
 ft 3 /min of fresh air, and a brattice wall 
 channel was constructed to bring the air 
 past the test room at velocities between 
 250 and 300 ft/min. The test room was 
 nominally 55 ft wide by 30 ft high and 
 was closed at a depth of 320 ft by a 
 
 Brattice 
 
 
 
 wall 
 
 LEGEND 
 Fresh air 
 
 \<X 
 
 /&^ Brattice wall 
 
 Exhaust air 
 
 Full-height extraction (60 ft) 
 
 Pillar numbers 
 
 /% 
 
 S\ ^^_ Brattice 
 )*v\ wall channel 
 
 e 
 
 /(- 
 
 
 PI 
 
 Fan 3 
 (exhaust) 
 
 &£>t 
 
 5® 
 
 Fan 2 
 2 48-in rigid ducts 
 
 £2 
 
 Scale, ft 
 
 FIGURE 8.— Schematic of Colony Mine showing mine ventila- 
 tion system and location of test room in crosscut 7. 
 
 brattice wall constructed on top of an 
 existing muckpile. 
 
 The tracer tests were designed to simu- 
 late different types of mine air pollu- 
 tant production. The tests included — 
 
 Simulation of blast clearing . — This 
 test was designed to simulate the fan's 
 effectiveness at clearing a heading after 
 blasting. The test room was sealed, and 
 SF 6 gas was released to give a uni- 
 form concentration of approximately 1 
 ppb. The fan was run for a short time to 
 mix the gas uniformly. The mine ventila- 
 tion system was then started, and the 
 fans were used to clear the tracer gas 
 from the room. 
 
 Simulation of hot diesel exhaust . — Thi s 
 test was designed to simulate the sys- 
 tem's ability to dilute diesel emissions 
 (gaseous and particulates). A 50,000- 
 Btu/h kerosene space heater was placed in 
 the face area, with the exhaust routed 
 through a vertical stack to be released 
 15 ft above the floor. Tracer gas flow- 
 ing at a constant rate was mixed in the 
 hot gas stream before the outlet. The 
 space heater generated a stream of hot 
 gases with a buoyancy similar to that 
 of engine emissions. The mine venti- 
 lation and face ventilation systems were 
 started, and the steady-state concentra- 
 tion for SF 6 was measured. 
 
 Simulation of methane layering . — SFg 
 was mixed with 52.4 mol pet He in air to 
 simulate the density of methane gas. It 
 was released from very small holes along 
 a 50-ft-long pipe that was suspended at 
 the roof. The pipe would simulate the 
 intersection of a crack that is conduct- 
 ing methane gas into the mine at roof 
 level, with the lighter density of the 
 mixture causing the tracer gas to form a 
 layer similar to methane. The tracer gas 
 was released at a rate of 0.833 ft 3 /min 
 for 120 min, and gas samples were taken 
 to see if the tracer would form a roof 
 layer similar to that formed by methane. 
 The fans were then started to test their 
 effectiveness at breaking up the layer. 
 
 Simulation of methane emissions from a 
 muckpile . — In this test, the mixture of 
 air, helium, and SF 6 was released from 
 a group of pipes laid out in the face 
 
14 
 
 area to simulate methane desorbing from 
 freshly blasted muckpile. The tracer gas 
 was released for 45 to 60 min, and then 
 the fans were started. The steady-state 
 concentration was measured to establish 
 the effectiveness of the two systems. 
 
 Measurement of fan inlet recircula- 
 tion . — The inlet recirculation volume was 
 measured by releasing tracer gas directly 
 into the fans. The concentration in the 
 air around the inlet was measured. The 
 concentration of air coming out the fan 
 is governed by the release rate of the 
 tracer gas and the amount of tracer gas 
 recirculated into the outlet. 
 
 Figure 9 shows a schematic of the mea- 
 surement grid established in the test 
 room and illustrates the location of 
 the fans during the testing. Figure 10 
 shows the sampler locations used during 
 each type of tracer gas test. Identical 
 tracer gas concentrations, tracer gas 
 release rates, and sampler locations were 
 used for each fan in each type of test to 
 assure that the results would be directly 
 comparable. 
 
 TEST RESULTS 
 
 Dilution efficiencies measured during 
 the tracer gas tests are compared in 
 table 8. Tests were not repeated 
 because of the extensive setup required; 
 therefore, there is no measure of the 
 reproducibility of the data. In one in- 
 stance, a tracer gas of the wrong con- 
 centration was released, requiring a 
 
 \ 
 
 320 300 280 260 
 
 Scole, ft 
 
 200 ISO 
 
 100 60 60 40 20 3 
 
 V. 
 
 PLAN VIEW 
 
 c '/t^i\t-rrfi\<rrm^\\^te 
 
 •t u r- 
 
 
 ia>/»a-»am/mia» 
 
 ELEVATION 
 
 Muckpile — ' 
 
 Js iL JJJ iL J 
 
 z) 
 
 V 
 
 y^ 
 
 -J 
 
 _l 
 
 
 Ducted fan-blowing mode Ducted fan-exhaust mode 
 
 FIGURE 9.— Test room grid system showing location of fans 
 during tracer gas tests. 
 
 repetition of the test. Dilution effi- 
 ciencies for the two tests were 0.80 and 
 0.83, even though the concentration of 
 SF 6 in the released gas differed by a 
 factor of 1,000. The average values 
 listed in the tables are mean values of 
 the dilution efficiencies measured at 
 each sample point throughout the test 
 room. The values for the face area are 
 averages of the samples located 40 to 60 
 ft from the face. The jet fan delivered 
 superior performance in the diesel ex- 
 haust and methane from muckpile tests. 
 The ducted system was superior in the 
 
 TABLE 8. - Comparison of dilution efficiencies measured in 
 tracer gas tests 
 
 Simulation type 
 
 Jet fan 
 (88,400 ft 3 /min) 
 
 Ducted fan, 
 blowing 
 (90,700 ft 3 /min) 
 
 Blast clearing: Average.. 
 Diesel exhaust: 
 
 Face area 
 
 Average 
 
 Methane layering: 
 
 Face area 
 
 Average 
 
 Methane from muckpile: 
 
 Face area 
 
 Average 
 
 1 0.79 in exhausting mode (7 
 
 0.98 
 
 .63 
 
 .74 
 
 .77 
 .83 
 
 .59 
 
 .60 
 
 3,000 ft J /min) 
 
15 
 
 10ft 
 15 ft 
 
 HOT EXHAUST TEST 
 
 KEY 
 Sampling station 
 
 Tracer gas discharged 
 
 from pipe at roof 
 
 Station 
 
 3 
 
 ffLlOft 
 
 u 15 " 
 
 METHANE LAYERING TEST 
 
 Station 
 3 
 
 BLAST CLEARING TEST 
 
 10 ft 
 15 ft 
 25ft-jf 
 
 METHANE FROM MUCKPILE TEST 
 
 FIGURE 10.— Schematic showing tracer gas sampling points 
 and tracer gas release point for various simulations. 
 
 blast clearing and methane layering 
 tests. The overall performance of both 
 systems was good, and the data indicate 
 that the fans provided effective 
 ventilation. 
 
 The methane layering test showed that 
 the helium-air mixture could be used to 
 simulate the buoyancy of methane. Both 
 fan systems were effective at breaking up 
 the tracer gas layer; however, the flow 
 rate of the gas was very small (0.83 ft 3 / 
 min) . Much larger release rates would be 
 needed to gauge the effectiveness of the 
 jet fan and ducted fan in dealing with 
 significant flow rates of methane. The 
 ducted systems appear to have been more 
 effective at breaking up the tracer gas 
 layer. This is due mostly to the fact 
 that the duct outlet delivered the fresh 
 air at high velocity directly at the 
 point of tracer gas release. 
 
 IMPACT OF FAN RECIRCULATION 
 
 Inlet position and conditions are im- 
 portant because they govern the amount 
 of inlet recirculation. The field char- 
 acterization of the test systems was 
 conducted in a manner that would re- 
 flect real operating conditions. Inlet 
 
 recirculation measurements were performed 
 using the tracer gas and showed 
 recirculation volumes of 23.8 and 28.4 
 pet for the jet fan and ducted fan, 
 respectively. The jet fan value was 
 typical, but the ducted fan value was 
 higher than expected. The ducted fan 
 recirculation was caused by poor posi- 
 tioning of the inlet. The fan should 
 have been placed farther upstream in the 
 last open crosscut to eliminate recircu- 
 lation. Inlet recirculation is expected 
 with the jet fan, but care must be taken 
 to locate the fan inlet as far into 
 the last open crosscut as possible to 
 maximize performance. Efficiency of the 
 jet fan could be further increased by 
 flexible ducting on the inlet placed well 
 upstream in the last open crosscut. 
 
 Dilution efficiencies corrected for the 
 inlet recirculation are compared with the 
 measured values in table 9, which shows 
 that inlet recirculation has a strong 
 effect in the reduction of dilution effi- 
 ciency in these tests. 
 
 IMPACT OF FAN OUTLET LOCATIONS 
 
 Positioning of the jet fan is critical 
 to its performance. Previous work by 
 Lewtas (21) and Dunn ( 26 ) indicates that 
 location of the fan within three 
 diameters of the wall extends the depth 
 of penetration of the jet by constraining 
 its growth. Anemometer and smoke veloc- 
 ity measurements were made for several 
 different directions and heights of the 
 fan centerline. Results, listed in table 
 10, indicate that the fan had its great- 
 est penetration when angled slightly down 
 and into the corner. Directing the flow 
 into the corner at too great an angle 
 reduces penetration by causing the air 
 to bounce off the adjacent wall. Wall 
 roughness was probably a factor in this 
 problem. Elevating the fan above the 
 corner caused a large reduction in pene- 
 tration and velocity. 
 
 Position of the duct outlet has been 
 shown to have a major effect on the per- 
 formance of ducted systems in the exhaust 
 mode. Measurements of the effect of dis- 
 charge location on the ducted system were 
 made in this study to evaluate the effect 
 of positioning for the blowing mode. 
 
16 
 
 TABLE 9. - Potential increase in dilution efficiency resulting from 
 elimination of inlet recirculation 
 
 Simulation type 
 
 Jet fan 
 (88,400 ft 3 /min) 
 
 Ducted fan, blowing 
 (90,700 ft 3 /min) 
 
 
 With 
 recirculation 
 
 Without 
 recirculation 
 
 With 
 recirculation 
 
 Without 
 recirculation 
 
 Diesel exhaust: 
 
 0.71 
 .78 
 
 .57 
 .59 
 
 .74 
 .79 
 
 0.87 
 .97 
 
 .80 
 .82 
 
 .90 
 .96 
 
 0.63 
 .74 
 
 .77 
 .83 
 
 .59 
 .60 
 
 0.81 
 
 Methane layering : 
 
 .98 
 1.0 
 
 Methane from muckpile: 
 
 1.0 
 
 .86 
 
 
 .89 
 
 TABLE 10. - Locations, orientations, and face air velocities for jet fan 
 
 Peak velocity, 2 ft/min 
 
 Test 
 
 Distance 
 
 from face, 
 
 ft 
 
 Height 
 
 above 
 
 floor, 
 
 ft 
 
 Orientation 
 
 in vertical 
 
 plane, ft 
 
 Angle from 
 
 axial section — 
 
 line A 
 
 At 100 ft 
 from face 
 
 At 60 ft 
 from face 
 
 306.7 
 306.7 
 305.5 
 305.5 
 305.5 
 305.5 
 305.5 
 
 8.5 
 17.3 
 3 4.0 
 3 3.4 
 3 3.7 
 3 3.7 
 3 3.9 
 
 Level 
 
 1 • *uOi •••••••• 
 
 • • •QUt •••••••• 
 
 Down 5° 
 
 Down 2-1/2°... 
 
 Down 1 ° 
 
 0° 
 
 0° 
 
 0° , 
 
 Left 5° 
 
 Left 2-1/2' 
 Left 1°..., 
 ...do 
 
 557 
 170 
 717 
 522 
 690 
 618 
 726 
 
 NA 
 
 NA 
 489 
 
 NA 
 439 
 
 NA 
 550 
 
 NA Not available. 
 
 'All tests were run with fan located 18.4 ft left of the room centerline. 
 
 2 Measured in lower left-hand quadrant of room cross section. 
 
 3 Fan removed from scissors lift and mounted on blocks on the floor. 
 
 TABLE 11. - Duct discharge locations and face sweep velocities 
 for ducted fan — blowing 
 
 Discharge 
 
 Offset 
 
 Height of duct 
 
 Discharge 
 
 Average face 
 
 distance 
 
 from room 
 
 centerline 
 
 duct 
 
 sweep velocity, 
 
 from face, 
 
 centerline, 
 
 above floor, 
 
 section 
 
 ft/min 
 
 ft 
 
 ft 
 
 ft 
 
 
 
 58.3 
 
 20.9 
 
 2.5 
 
 54-in-diam round.. 
 
 NA 
 
 30.5 
 
 21.0 
 
 2.6 
 
 
 532 
 
 30.5 
 
 21.0 
 
 2.6 
 
 
 456 
 
 78 
 
 21.0 
 
 13.0 
 
 
 1,095 
 
 NA Not ava 
 
 ilable. '62 
 
 by 40.5 in. 
 
 55.8 by 36.5 in. 
 
 
 Results are listed in table 11. The 
 highest face sweep velocities were 
 observed with the duct centering elevated 
 13 ft above the floor and the discharge 
 78 ft from the face. This position was 
 selected as the minimum distance at which 
 
 a rigid duct system run along the floor 
 could escape destruction during blasting. 
 Face blasting at the Colony Mine threw 
 a great deal of rubble along the floor 
 for several hundred feet. Ducting run 
 along the roof very close to the face 
 
17 
 
 suffered no damage during the same blast. 
 Installation of large, rigid ducting 
 along the roof would be more labor inten- 
 sive, and the floor installation appeared 
 to be a more desirable approach from the 
 operating standpoint. 
 
 The methane layering simulation illus- 
 trated the potential utility of being 
 able to orient the duct outlet so that 
 high-velocity flow can be directed at 
 localized pollutant production. 
 
 CASE STUDIES OF PERFORMANCE IN PROJECTED OPERATING CONDITIONS 
 
 The primary advantage of performing 
 tracer gas tests to characterize the 
 performance of a face ventilation system 
 is that the actual dilution efficiency of 
 the system is measured at the point of 
 maximum pollutant production. Once the 
 efficiency is known, the total air capac- 
 ity required to ventilate a known rate 
 of pollutant production can be calcu- 
 lated using the efficiency factor and 
 assuming linearity. Dilution efficien- 
 cies measured during the in-mine tests in 
 this project were applied to the examples 
 of projected mine air pollutant produc- 
 tion discussed earlier. This illustrates 
 the application of the results of the 
 tracer gas tests and evaluates the capa- 
 bility of the two ventilation systems to 
 perform under actual mining operation. 
 
 The dilution efficiency is the ratio 
 of the air quantity delivered to the 
 face divided by the fan outlet volume. 
 Therefore, the dilution efficiency (E d ) 
 multiplied by the fan flow rate is 
 approximately the effective flow (Qq). 
 For a given room volume (V) , the time to 
 reach TLV is given by equation 8: 
 
 T = (V/Qb) (lnC - In TLV), (8) 
 
 where T = time to reach TLV, min, 
 
 Qq = effective flow rate = E d 
 x Q Fan , ft 3 /min, 
 
 V = room volume, ft 3 , 
 
 and C = peak concentration, ppm. 
 
 BLAST-PRODUCED POLLUTANTS 
 
 Projected versus measured blast-pro- 
 duced air pollutant levels were presented 
 earlier in table 6. The dilution effi- 
 ciencies measured in the blast clearing 
 tests can be used to calculate the time 
 to reduce the concentrations of noxious 
 gases after the blast to their TLV's. 
 
 Table 12 lists estimated times for the 
 fan systems tested in this study to ven- 
 tilate the test room to TLV's for various 
 blasting fumes. The peak concentrations 
 are those observed in measurements of 
 blasting fumes produced by face blasting 
 at Colony. The maximum time of 20 min to 
 clear the dust is clearly acceptable from 
 an operating standpoint. 
 
 TABLE 12. - Estimated time to clear blast-produced 
 pollutants to TLV's 
 
 Pollutant 
 
 Est cone after 
 blast, ppm 
 
 TLV, 
 ppm 
 
 Time to dilute to TLV, 1 min 
 
 
 Jet fan 2 
 
 Ducted fan-blowing 3 
 
 co 2 
 
 Dust 4 . . .. 
 
 450 
 155 
 
 69 
 
 69 
 
 13.3 
 
 5,000 
 
 50 
 
 25 
 
 25 
 
 1 
 
 NAp 
 8.8 
 7.9 
 7.9 
 20.1 
 
 NAp 
 6.6 
 5.9 
 5.9 
 
 15.0 
 
 NAp Not applicable. 
 'Room volume (V) = 514,600 ft 3 ; Q e = E d 
 2 Q Fan = 88,400 ft 3 /min; E d = 0.75. 
 3 Q Fan = 90,700 ft 3 /min; E d = 98. 
 4 Approximate; based on weight. 
 
 Qf ; 
 
18 
 
 DIESEL EMISSIONS 
 
 Dilution efficiencies measured during 
 the tracer testing can be used to esti- 
 mate the actual air volumes the fan must 
 move in order to dilute the diesel emis- 
 sions in the face area to TLV. Earlier 
 engine emissions measured on a clean die- 
 sel engine in the 1,000-hp range were 
 listed to obtain projected ventilation 
 requirements. Actual fan flow rates can 
 be estimated by dividing the ideal air 
 requirements by the dilution efficiency. 
 
 Table 13 compares the ventilation 
 requirements based upon the combined 
 effects of CO and N0 X . Based upon the 
 engine emissions data and the measured 
 dilution efficiencies, the jet fan system 
 can effectively maintain the regulatory 
 air quality with 95 to 98 ft 3, min/bhp 
 in a nongassy mining environment. The 
 ducted fan in the blowing mode would 
 require 107 to 110 ft 3, min/bhp. This 
 assumes the use of modern, clean-operat- 
 ing, and well-maintained diesel engines. 
 If this is not the case, then the venti- 
 lation requirements will increase signif- 
 icantly. The ventilation air require- 
 ments would also be strongly affected if 
 methane concentrations in gassy mining 
 conditions are high enough to impact en- 
 gine carbon monoxide production. At 1.5 
 pet methane, which is greater than the 
 maximum allowable operating concentra- 
 tion, the ventilation requirements would 
 be increased to 136 to 173 ft 3, min/bhp 
 
 for the jet fan system and to 153 to 195 
 ft 3, min/bhp for the ducted fan system. 
 
 Data on diesel particulate emissions 
 are not definitive. In general, Bran- 
 stetter's (27) results suggest that die- 
 sel particulate emissions will not be a 
 problem with clean-burning, well-main- 
 tained engines. 
 
 The tracer gas measurements included 
 the effect of the buoyancy resulting 
 from engine exhaust temperature; however, 
 tracer flow rates in these tests were 
 well below the exhaust flow rates for 
 diesel engines in the 500- to 1,000-hp 
 range. Stratification would be a func- 
 tion of pollutant flow rate, as in the 
 case of methane layering; however, in 
 this case, stratification may help main- 
 tain air quality at the operator's level 
 by concentrating the pollutants near the 
 roof. 
 
 METHANE EMMISSIONS 
 
 Projection of the type and magnitude of 
 problems that may occur in oil shale min- 
 ing under gassy conditions is difficult 
 because there are few published data on 
 methane occurrence. Available data sug- 
 gest that methane production during min- 
 ing in the Mahogany Zone may occur in the 
 Central Piceance Creek and Uinta Basins; 
 however, the degree of methane saturation 
 appears to be well below that found 
 in many operating coal mines. The large 
 size of openings planned in oil shale 
 
 TABLE 13. - Comparison of required fan outlet flow rates (assuming 
 clean-burning diesel engine in the 800-hp range) 
 
 Brake 
 
 Cone in exhaust, ppm 
 
 Exhaust flow, 
 ft 3 /min 
 
 Ventilation flow, ft 3 /min 
 
 horsepower 
 
 CO 
 
 N0 X 
 
 Ideal 1 
 
 Actual 
 
 
 Jet fan^ 
 
 Ducted fan 3 
 
 With no methane: 
 561 
 
 100 
 150 
 
 875 
 713 
 
 448 
 538 
 
 506 
 513 
 
 1,814 
 2,257 
 
 1,830 
 2,276 
 
 36,140 
 55,330 
 
 69,060 
 79,180 
 
 54,990 
 77,910 
 
 97,270 
 111,520 
 
 61,970 
 
 823 
 
 87,810 
 
 With 1.5 pet 
 methane: 
 561 
 
 109,620 
 
 
 125,680 
 
 'Calculated using equation 1. 
 
 2 Dilution efficiency in face area = 0.71. 
 
 3 Dilution efficiency in face area = 0.63. 
 
19 
 
 mining tends to create greater potential 
 for methane layering problems. This is 
 offset somewhat by the large ventilation 
 air requirements imposed due to the die- 
 sel loading and hauling equipment. 
 
 The tracer gas simulations of methane 
 layering and methane from the muckpile 
 indicated that roof layering in large 
 openings without ventilation would be a 
 potential problem. Both the jet fan and 
 the ducted fan were effective in break- 
 ing up the roof layer and in reducing 
 the tracer concentration at very low 
 tracer flow rates. Work by Bakke ( 16 ) on 
 methane layering predicted that the 
 tracer gas layer would be broken up at 
 operating flow rates of the two fan sys- 
 tems because of the very low flow rates 
 of the tracer gas. Further testing at 
 higher tracer gas flow rates using the 
 helium-air mixture would provide a poten- 
 tial tool for extrapolating the currently 
 available work on methane layering num- 
 bers to oil shale mining. 
 
 The most clearly identified problem 
 associated with methane occurrence in 
 oil shale mining is the release of the 
 gas from a blasted muckpile. It was 
 estimated earlier that methane concentra- 
 tions of 8 pet could occur in a 300-ft- 
 long heading as a result of a face blast. 
 Clearly, this estimate Is directly de- 
 pendent upon the assumed methane satura- 
 tion (13.3 ft 3 /st), which is not well 
 defined. Other parameters that would 
 affect the peak concentration include — 
 
 1. The assumption of instantaneous re- 
 lease of the methane. 
 
 2. The volume of the room. 
 
 3. The containment of all of the 
 methane in the room. 
 
 Observations developed from work per- 
 formed on this project tend to support 
 the assumptions listed above. Blasting 
 fume concentrations measured in a face 
 blast at Exxon's Colony Mine were close 
 to projected values based upon the mass 
 of ANFO detonated and the volume of the 
 heading (55 ft wide by 30 ft high by 
 465 ft long). The fumes were vertically 
 stratified, but tended to be uniformly 
 distributed throughout the length of the 
 room. The fumes generally were contained 
 in the room until ventilation was begun. 
 
 Measurements of methane produced by 
 blasting of saline zone oil shale (11) 
 suggest that 80 pet of the total methane 
 produced by the blast had been released 
 within 5 min. 
 
 If the methane released by blasting 
 produces very high initial concentrations 
 in the face heading, the operator will be 
 required to implement special procedures 
 to eliminate the hazard. These might 
 include — 
 
 1. Reducing the size of the individual 
 blast to reduce the quantity of methane 
 released. 
 
 2. Increasing the quantity of fresh 
 air flowing in the last open crosscut. 
 
 3. Implementing special ventilation 
 procedures in the face heading. 
 
 The quantity of methane released by a 
 particular blast could be reduced by 
 reducing the depth of blastholes. This 
 approach may be undesirable, since the 
 economic aspects of oil shale mining 
 require maximum productivity. 
 
 The tracer gas tests performed In this 
 study indicated that the concentration 
 of a blast-produced air pollutant being 
 exhausted from the face area is instanta- 
 neously equal to the general concentra- 
 tion throughout the room. If the initial 
 concentrations of methane are very high, 
 operation of the face ventilation system 
 pushes methane into the last open cross- 
 cut at a high rate initially. The rate 
 decays as the concentration of methane in 
 the face area is reduced. If the face 
 ventilation system is to be operated at 
 high capacity, the last open crosscut 
 flow must be capable of diluting the 
 initial methane production to a safe 
 level. Planned open crosscut flows might 
 have to be increased, depending upon the 
 magnitude of methane saturation. 
 
 Another alternative is to control the 
 rate at which the methane is removed from 
 the face, so that the quantity of fresh 
 air in the last open crosscut is 
 always enough to dilute the methane to a 
 safe level. This could be accomplished 
 by operating the ducted system at a 
 reduced flow rate in the blowing mode, as 
 illustrated in figure 11. This configu- 
 ration might be enhanced by using a jet 
 fan blowing parallel to the last open 
 
20 
 
 Last open 
 crosscut 
 
 Jet fan 
 
 ~Dsc 
 
 Face 
 
 Plume of exhaust air 
 
 FIGURE 1 1 .—Ducted system operating in blowing mode with 
 jet fan to assist methane plume mixing. 
 
 Last open crosscut 
 
 4^" 
 
 Jet fan 
 
 MM 
 
 \ 
 
 r 
 
 FIGURE 12.— Reorientation of jet fan to minimize inlet recir- 
 culation and reduce effective room airflow rate for methane 
 dilution. 
 
 crosscut (with or counter to the flow) to 
 enhance mixing of the plume of exhaust 
 gas. 
 
 Proposed rules recently published in 
 the Federal Register ( 28 ) clarify and re- 
 vise MSHA's existing standards for gassy 
 metal and nonmetal mines. They specify 
 that auxiliary fans shall be operated so 
 that recirculation is minimized, which 
 may make the use of jet fans possible in 
 gassy conditions. A jet fan could be 
 repositioned so that it projects the air- 
 stream across the room, as illustrated in 
 figure 12. This would reduce both the 
 effective flow rate of air in the room 
 and the quantity of methane reaching the 
 last open crosscut. 
 
 The jet fan might be left running 
 during the blast. This could help to 
 reduce the magnitude of the peak concen- 
 tration reached in the face heading. The 
 overall effectiveness of this approach is 
 unknown, because it is a function of the 
 methane release rate. However, if the 
 buildup to peak concentration occurs in 
 about 5 min, a large portion of the 
 methane could be removed during the 
 initial release period. This would sig- 
 nificantly reduce both the magnitude of 
 peak concentration and the level of the 
 hazard that the methane presents. 
 
 GENERAL CONCLUSIONS ON FACE VENTILATION 
 
 Major conclusions derived from the 
 field testing of two of the large-capac- 
 ity face ventilation systems follow: 
 
 1. Face air quantities generally will 
 be governed by the requirement to main- 
 tain air quality TLV's. 
 
 2. Control of particulate concentra- 
 tions will be a critical parameter in the 
 design of face ventilation systems. 
 
 3. Both face ventilation systems 
 showed high dilution efficiencies and 
 were effective in ventilating the face 
 area at a distance of 320 ft. 
 
 4. Proper positioning of fan inlets to 
 minimize recirculation directly impacts 
 the ventilation performance. For both 
 the jet fan and the ducted fan, the inlet 
 should be placed as far as possible into 
 the last open crosscut. Flexible duct- 
 ing on the fan inlet side, which runs 
 upstream in the last open crosscut, would 
 also greatly reduce recirculation. Fan 
 inlet recirculation probably reduced the 
 dilution efficiencies between 17 and 27 
 pet in these tests. 
 
21 
 
 5. Overall performance of the two sys- 
 tems was similar. The ducted system 
 performed better in the blast clear- 
 ing and methane layering tests. The jet 
 fan performed better in the hot diesel 
 exhaust and methane from muckpile tests. 
 
 6. The superior performance of the 
 ducted fan in the methane layering test 
 was due to the fact that its outlet was 
 very near the source of the tracer gas. 
 This emphasized the fact that high air 
 velocity is the critical parameter in 
 controlling layering. 
 
 7. Both systems, in the blowing mode, 
 were effective at breaking up a tracer 
 gas layer formed with low tracer gas flow 
 rates. Further simulations at higher 
 flow rates are required to extrapolate 
 the capability of the system in dealing 
 with layering. 
 
 8. The jet fan provides a higher aver- 
 age air velocity throughout the heading. 
 This high velocity would tend to make the 
 jet fans more effective in breaking up 
 methane layers than a ducted system, al- 
 though the background concentration of 
 methane might be higher because of higher 
 fan inlet recirculation. 
 
 9. Based upon power consumption per 
 effective cubic foot per minute of air- 
 flow, the jet fan delivered similar per- 
 formance with less power consumption than 
 the ducted system. 
 
 10. The jet fan was more efficient at 
 a flow rate of 60,000 ft 3 /min than at 
 88,400 ft 3 /min and delivered similar di- 
 lution rates at both rates. This sug- 
 gests some interaction between the turbu- 
 lent jet and room dimensions that is not 
 well understood. 
 
 11. Operation of the ducted fan in 
 the exhaust mode reduced its dilution 
 efficiency by 19 pet as compared to 
 efficiency using the blowing mode. 
 
 12. The ducted fan tests indicate that 
 the blowing mode operation is more 
 efficient than the exhaust mode in the 
 large openings found in oil shale min- 
 ing; however, the exhuast mode might 
 be more effective in situations with 
 high dust production. Overall cost and 
 installation labor could be reduced by 
 using collapsible ventilation tubing and 
 operating the fan in the blowing mode 
 exclusively. However, collapsible tubing 
 has disadvantages, including being prone 
 to leakage, being more easily damaged, 
 and having its cross section reduced by 
 bends or external obstructions. 
 
 13. The design capacity of the fan 
 systems (100,000 ft 3 /min) will be suf- 
 ficient for room and pillar mining opera- 
 tions in oil shale, provided that diesel 
 engines with low emissions are used. 
 Operation of these engines in a gassy 
 environment may require an increase in 
 ventilation air requirements. 
 
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22 
 
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 June 4, 1985, pp. 23,612-23,660. 
 
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