title: Transformer fluid fires in a ventilated tunnel
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IV . i • < -^ * ^O 5 * ^* .v q^ * o » o g ,0 b# r o '."".I* A P V > vv !^c?^: ^^ Q~ . » * « ^6* ,^ .••-".-. ^ "ov* S' » ?-^-$W ; y ,! %A^ .-S t ^ /fflfe'v W* .-isK«i-. ^.^ /Jfe\ V./ .^M» *«^ /^K\ ^ VJ A ". T * a ,. ^ v O.. 'o . » » ^V <, *' ... "*bv^ s s^y* •/ \-^?\y.. v 1 ^-/ \-^^v v^-/ \-^\/ *. o, »o. Bureau of Mines Information Circular 1986 Transformer Fluid Fires in a Ventilated Tunnel By Margaret R. Egan UNITED STATES DEPARTMENT OF THE INTERIOR Information Circular 9117 Transformer Fluid Fires in a Ventilated Tunnel By Margaret R. Egan UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES Robert C. Horton, Director Library of Congress Cataloging in Publication Data: Egan, Margaret R Transformer fluid fires in a ventilated tunnel. (Information circular; 9117) Bibliography. Supt. of Docs, no.: I 28.27: 9117. 1. Mine fires. 2. Mine ventilation. 3. Electric transformers. 1. Title. II. Series: Information circular (United States Bureau of Mines) ; 9117. TN295.U4 [TN315] 622 s [622'.8] 86-600288 CONTENTS Page Abstract 1 Introduction 2 Instrumentation 2 Fire tunnel 2 Thermocouples 2 Flow probes and pressure transducers 2 Gas monitors 3 Smoke monitors 3 Fuel-consumption monitor 4 Typical test procedure 4 Calculations 4 Product generation rates 4 Combustion yields 4 Heat-release rates 5 Production constants 5 Smoke particle diameters 5 Burning rate 6 Brand comparison results. 6 Gas concentrations and heat production 6 Smoke characteristics 8 Combustion yields 8 Production constants 8 Discussion of results 8 Conclusions 10 Fuel comparison results and discussion 10 Scaling results and discussion 11 Appendix. — List of symbols 13 ILLUSTRATIONS 1. Schematic of intermediate-scale tunnel 3 2. CO concentrations (A), CO2 concentrations (B), heat-release rates (C)» and heats of combustion (D) for three brands of transformer fluid 7 3. Particle mass concentrations (A), number concentrations (5), and mass mean diameters (C) for three brands of transformer fluid 9 4. Burning rates for gasoline and transformer fluid 12 TABLES 1. Average gas concentrations, heat-release rates, and heats of combustion for transformer fluid 7 2. Toxic-gas concentrations for transformer fluid 8 3. Smoke characteristics for transformer fluid 8 4. Mean particle sizes and obscuration rates for transformer fluid 8 5. Combustion yields for transformer fluid 8 6. Production constants for transformer fluid 9 7. Gas, heat, and smoke concentrations for the three fuels tested 10 8. Normalized gas and smoke concentrations for the three fuels tested 10 9. Particle size and obscuration rates for the three fuels tested 11 10. Production constants for the three fuels tested 11 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT cm centimeter mg/m 3 milligram per cubic meter cm/min centimeter per minute pg/m 3 microgram per cubic meter °F degree Fahrenheit min minute g gram ym micrometer g/cm 3 gram per cubic centimeter m 3 /s cubic meter per second g/(m 3, ppm) gram per (cubic meter times part per million) P particle p/cm 3 particle per cubic i g/g gram per gram centimeter g/kJ gram per kilo joule pet percent g/s gram per second p/g particle per gram kg kilogram p/kJ particle per kilojoule kJ/g kilo joule per gram ppm part per million kW kilowatt ppm/min part per million per minute In logarithm, natural psi pound per square inch m meter TRANSFORMER FLUID FIRES IN A VENTILATED TUNNEL By Margaret R. These transformer fluid measurements will be added to the existing coal and wood data that can be used as a basis of comparison for future studies of other mine combustibles. Further research into the combustion product emissions from combustible materials found in underground mines will lead to improved and realistic fire detection and suppression systems. Chemist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. INTRODUCTION The Bureau of Mines conducts research to ensure that mines are safe and healthful places to work. Exceptional circumstances, such as an underground fire, pose additional problems involving health and safety. Among these dangers are those affecting escape and rescue. Early fire detection increases the opportunity for human escape. Rescue efforts are often hampered by reduced visibility due to smoke and the potential toxicity of the combustion products. More efficient detection devices and rescue equipment can be designed once the hazardous products of combustible materials are known. Therefore, the smoke characteristics of fires in ventilated mine passageways are investigated by the Bureau. These experiments are part of a series of continuing projects in which combustible materials are burned in a simulated mine environment. Previous studies have shown that the intermediate-scale fire tunnel used for the current studies can successfully predict full-scale fire conditions. Transformers are used to produce electrical power needed to operate mine machinery. Heat, which is an inherent by-product of this process, is removed by transformer fluid. Fires are potential risks whenever petroleum oil, the basic component of transformer fluid, is used in any electrical equipment. The objectives of this study are (1) to compare three brands of transformer fluid for gas production and smoke characteristics, (2) to compare these evaluations with similar data for wood and coal, and (3) to compare fire sizes and burning rates of several pool sizes of transformer fluid. INSTRUMENTATION FIRE TUNNEL THERMOCOUPLES The transformer fluid fires were conducted in an intermediate-scale fire tunnel located at the Bureau's Pittsburgh Research Center. A diagram of the tunnel with its data-acquisition system is shown in figure 1. The tunnel measures 0.8 m wide by 0.8 m high by 10 m long and is divided into three sections. The first horizontal section begins at the air-intake cone, which gradually enlarges to a hinged portion that can be lifted to allow entrance for the placement of oil pan. Next is the fire zone in which is located the gas burner followed by the oil pan. The fire zone and the remaining horizontal section are lined with fire-brick and instrumented with thermo-couples, flow probes, and sampling ports. The diffusing grid begins the vertical section of the tunnel. Located in this section is an orifice plate that can be manually adjusted to attain the desired airflow. The final section is horizontal and ends at an exterior exhaust fan. The thermocouple arrays were located 1.57, 2.36, 3.15, 4.72, 6.30, and 7.87 m from the gas burner. Additional thermo-couples are located on the air-intake cone and at the exhaust. In all, a total of 28 The thermocouples were used to measure the temperature distributions resulting from the fires. Their locations are shown in figure 1. FLOW PROBES AND PRESSURE TRANSDUCERS The air pressure produced by the exhaust ventilation is detected by the transducer. As pressure increases, the capacitance decreases. This change is then converted to a linear electric signal. Nonlinearity is described as <±0.1 2 Lee, C. K., R. F. Chaiken, J. M. Singer, and M. E. Harris. Behavior of Wood Fires in Model Tunnels Under Forced Ventilation Flow. BuMines RI 8450, 1980, 58 pp. INTERMEDIATE-SCALE FIRE TUNNEL 10- m length 12 _ m length 0.61 _ m duct 1.22 m 0.8 -m square duct Fire zone Intake Load cell Manually adjustable orifice plate 7 exhaust Ventilation fan ( 2-speed ) 1 — Diffusing grid -Q305 - rTrdiam entrance duct ( hinged and movable) CALOUCH-DECNET- Tapered-element oscillating microbalance Condensation nuclei monitor CO meter Pressure transducers MM 48" channel data- acquisition system 3X = detector t...28— ' thermocouples i_ -Load cell - Digital input for CNM range range T...28— ' thermocouples i_ -Load cell - Digital input for CNM range Range T...28— ' thermocouples i_ -Load cell - Digital input for CNM range T...28— ' thermocouples i_ -Load cell - Digital input for CNM range T...28— ' thermocouples i_ -Load cell - Digital input for CNM range T...28— ' thermocouples i_ -Load cell - Digital input for CNM range T...28— ' thermocouples i_ -Load cell - Digital input for CNM range T...28— ' thermocouples i_ -Load cell - Digital input Control terminal VAX 11/780 Printer VAX terminal CALCOMP plotter KEY Pressure transducer (flow probe) Thermocouples Differential pressure transducer Sampling ports 3X detector FIGURE 1.— Intermediate-scale fire tunnel (top) and data-acquisition system (bottom). pet full range of the output or ±0.00001 psi differential. The locations of the pressure transducers are also shown in figure 1. GAS MONITORS The carbon monoxide (CO) sures accurately within 1 range or ±5 pm. The carbon dioxide (C0 2) sures accurately within 1 range or ±250 pm. SMOKE MONITORS The number concentration (N Q) was obtained with a condensation nuclei analyzer measure of full analyzer measure of full monitor, manufactured by Environment One Corp. The monitor measures the concentration of submicrometer airborne particles (p) using a cloud chamber. The particulate cloud attenuates a light beam that ultimately produces a measurable electrical signal. The accuracy is stated as ±20 pet of a point above 30 pet of scale on the linear ranges, 3,000 to 3000,000 p/m3. The mass concentration (M Q) was obtained by a TEOM tapered-element oscillating microbalance, developed by Rupprecht & Patashnick Co., Inc. It Reference to specific equipment does not imply endorsement by the Bureau of Mines. measures the mass directly by depositing the particles on a filter attached to an oscillating tapered element. The change in the oscillating frequency of the tap-ed element is directly proportional to the change in mass. The apparatus is capable of measuring dust concentrations with a better than 10-pet accuracy at the 250-ug/m 3 level. A three-wave light transmission technique was also used to measure smoke characteristics and obscuration. White light was transmitted through a smoke cloud to the detector. The beam was split into three parts, and each passed through an interference filter centered at wavelengths of 0.45, 0.63, or 1.00 pm. Each photodiode output was amplified and recorded as a linear electric signal. This technique was developed by Bureau personnel FUEL-CONSUMPTION MONITOR The weight-loss data were obtained by a strain-gauge conditioner in conjunction with a load cell, which has a range up to 22.68 kg. The accuracy of the strain gauge is stated as 0.05 kg. TYPICAL TEST PROCEDURE The transformer fluid was poured into a stainless steel pan inside the tunnel. The shaft of the pan extended through the tunnel floor and was supported on the load cell so that continuous weight loss could be recorded. Prior to each experiment, background readings were obtained after the cone was closed and the exhaust fan was started. All instruments were continuously scanned and recorded throughout the experiment. A gas jet, located immediately upstream from the pan, was the ignition source. The burner flow rate was adjusted so that the flame licked the side of the oil-filled pan. The flash point of the transformer fluid, as stated by the manufacturers, is about 300°F. At a ventilation rate of approximately 0.65 m 3/8, the transformer fluid took about 1 min to ignite. The ventilation rate was then lowered to approximately 0.47 m 3/8 during the steady-state burning. The gas burner was turned off once the transformer fluid had ignited. The flames spread quickly, engulfing the entire pan within 1 min. The flames began to die down as the transformer fluid was consumed. The experiment was concluded when the flames were no longer visible. CALCULATIONS It is necessary to measure certain parameters in order to compare the steady-state combustion products and ultimately the hazards of various fuels. Among these values are gas concentrations, mass and number concentrations of smoke particles, ventilation rate, and mass-loss rate. Other combustion properties can be calculated once these are known. PRODUCT GENERATION RATES In a ventilated system, the generation rates (Gx) of CO2 and CO are related to the bulk average concentration increase above ambient, ACO2 and ACO, by the expressions and Geo = M C0 V A ACO, (2) Geo = M C0 V A ACO 2 (1) where MCO2 = 1.97 x 10_3 g/m 3 *ppm); M C o = 1.25 x 10 -3 g/m 3 *ppm); and V A = incoming cold gas flow, m 3 /s. COMBUSTION YIELDS Once the generated rates are known and the mass-loss rate of the fuel (Mf) is 4 Cashdollar, K. L., C. K. Lee, and J. M. Singer. Three-Wavelength Light Transmission Technique To Measure Smoke Particle Size and Concentration. Appl. Opt., v. 18, No. 11, 1979, pp. 1763-1769. calculated using the load-cell assembly, the true yield of the combustion product (Yx) can be calculated by the expression Yx = Gx/Mf. (3) The yields for mass (M) and number (N) concentrations are calculated in a similar manner by the expression Yx = AX C X V A Mf (4) where Cx = appropriate units conversion factor: 1.00 x 10" 3 when M Q is in mg/m 3 or 1.00 x 10 6 when N is Cx = appropriate units conversion factor: 1.00 x 10" 3 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m 3 or 1.00 x 10 6 when N is in mg/m In the case of smoke concentration increase above amount (when M is measured as mg/ in 3 and N is measured as p/cra 3). HEAT-RELEASE RATES It has been shown that the actual heat-release rate realized during a fire can be calculated from the expression He Kco. Geo. He - Heo (Keo) Kco Geo. (5) where Qa = actual heat release, kW; He = net heat of complete combus- tion of the fuel (40.7 kj/g for transformer fluid); Substituting the values in equations 1, 2, and 5 yields Qa = V A [0.0251 (AC0 2 ) + 7.07 x 10~ 3 (ACO)]. (6) Since measurements of V A , ACO2, and ACO were made continuously, the actual heat-release rates could be calculated using equation 6. A typical fire rarely realizes the state of complete combustion. For this reason, the actual heat of combustion (Ha) during a fire is usually less than the total heat of combustion (He). By measuring both the actual heat-release rate, equation 6 above, and the fuel mass-loss rate (Mf), the actual heat of combustion can be calculated from the expression H A = QA/Mf. PRODUCTION CONSTANTS (7) In an actual mine fire, it is often difficult, if not impossible, to calcu- late the actual heat of combustion. Moreover, since the true yield of a com- bustion product depends upon this infor- mation, significant errors can result in predicting the resultant concentration increases. For flaming fires, the rel- ative hazards tend to increase with the actual heat-release rate that results. For this reason, production constants or beta values (Bx) can be calculated for a given product by the expression 3x = Gx/Qa« (8) Kco 2 = stoichiometric yield of CO2 = 3.19 g/g; Heo = heat of combustion of CO =10.1 kJ/g; and Kco = stoichiometric yield of CO = 2.58 g/g. 5 Tewarson, A. Heat Release Rate in Fires. Fire and Mater., v. 4, No. 4, 1980, pp. 185-191. Using the rate of formation of gas or smoke as a function of the fire size is also beneficial in comparing the combustion hazards of different fuels. SMOKE PARTICLE DIAMETERS Measurements of both number and mass concentrates of the smoke provide important information relative to the yields, equation 4, and production constants, equation 7. They can also be used to calculate the average size of the smoke particles, with the expression In T (XI. 00) In T (XI. 00) Td m 3 p p N = 1 x 10 3 M, (9) where p p = individual particle density, g/cm 3; particle, ym; and 1 x 10 3 = the appropriate units conversion factor. Assuming a value of p p = 1.4 g/cm 3, then the mass mean diameter of the particles can be calculated from d m = 11 (10) where the particle diameter is expressed in micrometers. Using the three-wavelength smoke detector, the transmittance of the light through the smoke can be calculated for each wavelength. The extinction coefficient can be calculated for each pair of wavelengths by the following log-transmission ratios: or In T (X0.63) In T (X0.45) In T (X0.45) In T (X0.45) Using these extinction coefficients and the curve found by Cashdollar, the mean particle size (d 32) can be determined. The smoke-obscuration rate is the percentage of the ratio of the light detected after passing through the smoke compared with the background light. BURNING RATE It is difficult to compare the hazards from liquid-fuel fires with those of fires involving solid fuels such as coal and wood. The major reason for this difficulty is the speed with which liquid-fuel fires develop compared with that for solid-fuel fires. However, liquid-pool fires can be compared by using the total burning rate, which is calculated by dividing the depth of the fuel (in centimeters) by the burning time (in minutes). This information can then be used to compare various pan diameters. BRAND COMPARISON RESULTS All the values listed in this report are an average of steady-state burning stage that was arbitrarily selected to be the 20th to the 30th minute after ignition. Ten experiments were completed using three brands of transformer fluid: four with Texaco 7 fluid and three each with Shell and Gulf fluids. All three brands showed similar results for gas production, heat release, and heat of combustion. However, the tested brands showed somewhat different results for smoke characteristics. GAS CONCENTRATIONS AND HEAT PRODUCTION The CO and CO2 concentrations, heat-release rates, and heats of combustion 6 Figure 9 of work cited in footnote 4. graphs for an average test of each brand of transformer fluid are found in figure 2. The initial spike found on the CO2, heat-release rate, and heat of combustion was caused by the natural gas burner. The CO2 concentration gradually rose at an average rate of 22. The coal was consumed. The heat-release rate remained fairly constant for most of the experiments, increasing slightly just before the flames died. The average mass loss was 2.026 g, at a rate of 0.866 g. The heat of combustion also remained fairly constant throughout the steady-state burning but rose sharply just before the fuel was completely consumed. The average values for each brand and the grand average (which includes all experiments) are listed in table 1. During a 30-min period after ignition, six gas samples were taken, each 5 min apart. All brands showed a slight decrease in oxygen and a slight increase in heat-release rates. 1,871 1,784 20.3 22.2 21.0 22.9 25.3 24.5 124 1,769 21.1 24.1 in argon and nitrogen concentrations. These samples were also tested for hydro-carbons C1-C3. The brands showed very little variation. The concentrations increased slightly as combustion proceeded. Table 2 lists the averages for each brand. SMOKE CHARACTERISTICS The number concentration slowly in- creased until the fuel was almost completely consumed, then it started to drop. The mass concentration varied throughout the experiments. An average was taken during the steady-state burning when it was the most stable. Using these values, the mass mean diameter was calculated. The average values for each brand are listed in table 3. The mass number concentrations and the mass mean diameters for an average test of each brand are found in figure 3. Using the three-wavelength smoke de- tector, the average mean particle size (d32) was calculated for each wavelength. These averages and the obscuration rates for each brand are listed in table 4. COMBUSTION YIELDS The gas concentration yields, as ex- pected, showed little variation. How- ever, the mass and number concentration yields of smoke particles showed a wide variation between brands. The average yields are listed in table 5. PRODUCTION CONSTANTS The production constants or beta values were calculated as a function of the fire size. For the tested brands of trans- former fluid, the fire sizes were very similar. Therefore, it is expected that the beta values reflect the same vari- ability as the gas and smoke concen- trations. Table 6 lists the average pro- duction constants for each brand. DISCUSSION OF RESULTS The Shell transformer fluid generated a slightly larger CO2 concentration, thus increasing the corresponding fire size TABLE 2. - Toxic-gas concentrations for transformer fluid, ppm Brand Methane Ethane Ethy- lene Acety- lene Texaco. .. Shell.... Gulf 22.1 15.3 22.5 4.5 1.7 .9 19.0 11.5 16.9 9.8 16.6 16.2 TABLE 3. - Smoke characteristics for transformer fluid Brand Texaco. . .. Shell Gulf Average, No, p/cm 3 1,567,250 1,126,900 416,533 1,089,930 Mo, mg/m 3 40.6 9.0 58.1 35.3 dm, ym 0.309 .223 .601 .386 TABLE 4. - Mean particle sizes and obscuration rates  pet 0.302 .339 .336 0.351 .395 .431 0.391 .440 .538 0.348 .391 .435 39.9 Shell 40.8 59.6 .323 .388 .450 .387 46.1 TABLE 5. - Combustion yields for transformer fluid Brand Yco, g/g V C0 2, g/g 10^°p/g g/g Brand Yco, g/g Yco 2 » g/g Yn, 10H°p/g g/g 0.083 .0 64 1.829 1.952 8.85 5.92 0.021 .005 Average.. 0.081 1.894 2.23 0.031 .077 1.885 5.99 .019 2.0 1.8 A A S 1.8 1.6 A A S 1.4 1 VI A E 1.6 A A S 1.4 1 VI A E 1.0 10 20 30 40 50 TIME, min FIGURE 3.— Particle mass concentrations (A), number concentrations (B), and mass mean diameters (C) for three brands of transformer fluid. TABLE 6. - Production constants for transformer fluid Brand Bco 10~ 3 g/kJ Bco?  m, while the d 32 approximates the average. The low number and high mass concentrations for the Gulf fluid resulted in the largest calculated d m. By either method, the Gulf fluid produced the largest particles. This was corroborated by its high obscuration rate. CONCLUSIONS The results of these experiments showed little variation between the transformer fluid brands for CO and CO production, heat release, and heat of combustion. However, the smoke-characteristic calculations indicate that the Gulf fluid produced the heaviest and thickest smoke, while the Shell fluid generally produced the lowest toxic-gas concentrations. FUEL COMPARISON RESULTS AND DISCUSSION Earlier wood and coal experiments were conducted in the same intermediate-scale fire tunnel. Since the same instrumentation was used in the collection of all the data, it was possible to compare them. The gas, heat, and smoke concentrations for the three fuels studied are found in table 7. In these experiments, wood produced the most heat relative to the fuel consumed. For better comparison, the other fuels were normalized to this fire intensity. Table 8 has these normalized values. Burning coal produced the most hazardous smoke and gas concentrations. TABLE 7. - Gas, heat, and smoke concentrations for the three fuels tested Fuel CO, ppm co 2, ppm kW No. 10 6 p/cm 3 mg/m 3 145 76 113 6,759 909 1,769 110.2 5.4 21.1 6.04 1.68 1.09 49.1 7.7 35.3 TABLE 8. - Normalized gas and smoke concentrations for the three fuels tested Fuel CO, PPm CO 2, PPm N, 10 6 p/cm 3 Wood Coal Transformer fluid. 145 1,551 590 6,759 18,550 9,239 6.04 34.28 5.69 49.1 157.1 184.4 11 TABLE 9. - Particle size and obscuration rates for the three fuels tested Fuel d m » d32» Obs >curation rate, ym urn pet 0.223 ND 8.6 .177 0.272 18.2 .386 .387 46.1 Wood Coal Transformer fluid.. ND Not determined. TABLE 10. - Production constants for the three fuels tested Fuel Wood, Coal Transformer fluid. ND Not determined. 6co> 10- 3 g/kj 1.58 5.26 3.14 Bco 2 > 10~ 2 g/kj 10.44 8.89 7.71 10 10 p/kj 5.79 11.29 2.48 10- 1 g/kj 4.93 4.08 7.75 Transformer fluid produced a thick, dense smoke. It surpassed coal in the mass of smoke particles. It also produced the largest particle size and obscuration rate. The values can be found in table 9. Note the discrepancy between the d32 and the d32 for coal. The d32 may be less reliable because it is determined by the complex refractive index of the particles, which is not precisely known. If the refractive index used in the calculations is incorrect, then the diameter will be inaccurate. However, the obscuration rates do indicate that the particle diameter for coal should be smaller than that calculated for transformer fluid. Coal generated the most CO and smoke particles, using the formation rate of gas and smoke as a function of the heat produced. Transformer fluid produced the largest mass concentration. These values are confirmed by the normalized concentrations found in table 8 in which wood was found to generate the most CO 2 relative to the fire size. The production constants are found in table 10. Based on these experiments, coal was the most hazardous of the fuels studied. However, transformer fluid produced the thickest smoke with the largest particles. SCALING RESULTS AND DISCUSSION In liquid-fuel fires, the surface area of the pool determines the intensity of the fire. In order to study this phenomenon, three round pans (25, 50, and 71 cm diam), filled with transformer fluid, were used. These experiments followed the same test procedure as described above. Texaco transformer fluid was used for all the scaling studies. Only one experiment was completed using the 71-cm pan because the flame intensity was so great that the range of most of the smoke and gas detectors was exceeded. A 50-cm pan was used in two experiments but, again, the instruments were reaching their upper limits. In order to repeat the experiments using the larger pans, the gas and smoke monitors would have to be disconnected. The remaining four experiments were the ones previously reported in the portion on comparison of brands. Gasoline scaling studies were reported by Hertzberg. In those experiments, the burning time was plotted as a function of the pool diameter. In figure 4, the 8 Hertzberg, M. The Theory of Free Ambient Fires. Combust, and Flame, v. 21, 1973, p. 202. FIGURE 4.— Burning rates for gasoline and transformer fluid. Transformer fluid results were superimposed on his figure 3C. The two smaller pan sizes showed good agreement. But the 71-cm pan result was inconsistent with the gasoline data. The size of the pan approximated the entry width of the tunnel, which could have limited the oxygen supply to the fire. This would have reduced the combustion rate, thus increasing the burning time. To test this theory, higher ventilation rates could be used to increase the available oxygen supply. Future scaling experiments should be conducted without the delicate gas and smoke instrumentation. Geo GC0 2 GX H A H C HCO Keu Kuu 2 M co Mco, conversion factor of a combustion product mass mean diameter, ym mean particle size, ym generated rate of CO, g/s generated rate of CO2, g/s generated rate of a combustion product, g/s actual heat of combustion, kj/g net heat of combustion of the fuel, kJ/g heat of combustion of CO, kj/g stoichiometric yield of CO, g/g density of CO, g/g density of CO, g/m 3 *ppm) density of CO, g/m 3 *ppm) APPENDIX.— LIST OF SYMBOLS Mf fuel mass loss rate, g/s M particle mass concentration, mg/ra 3 N particle number concentration, p/cm 3 Qa actual heat of combustion, kW T transmission of light, volts V A ventilation rate, m 3 /s Yx 3x AX X Pp yield of a combustion product, g/g or p/g grams of product per unit kilo- joule of heat release measured change in a given quantity wavelength, ym individual particle density, g/cm 3 A U.S. GOVERNMENT PRINTING OFFICE: 1986-605-017/40.100 INT.-BU.0F MINES,PGH.,PA. 28377 U.S. Department of the Interior Bureau of Mines— Prod, and Distr. 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