NISTIR 4924 

ABSTRACTS: ANNUAL CONFERENCE ON 

FIRE RESEARCH 

October 13-15, 1992 

Rockville, MD 

Sheilda B. Smith, Editor 

Building and Fire Research Laboratory 

Gaithersburg, Maryland 20899 

United States Department of Commerce 

TeCanology Administration 

National Institute of Standards and Technology 
P 
NISTIR 4924 

ABSTRACT: ANNUAL CONFERENCE ON 

FIRE RESEARCH 

October 13-15, 1992 

Rockville, MD 

Sheilda B. Smith, Editor 

October, I992 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

U.S. Department of Commerce 

Barbara Hackman Franklin, Secretary 

Technology Administration 

Robert M. White, Under Secretary for Technology 

National Institute of Standards and Technology 

John W. Lyons, Director 

i 

TABLE OF CONTENTS 

INTRODUCTION ............................................................ 

SESSION 1 Flame Spread 

Role of In-Depth Absoption in Flame Spread Under Exrema1 Radiation Over Semi- transparent Materials, S.S. Manohar, AK. Kulkami and s.?: Thynell, 

Pennsylvania State University ....................................... 3 

Mathematical Model of Cocwent Homontal Flame Spread Over Solid Combustibles, 

C.C. Hwang and C.D. Litton, US. Bureau of Mines ...................... 5 

A Model of Low-Speed Concwrent-Flow Flame Spread Over a Thin Solid Fuel, 

Paul Ferkul and James Tien, Case Western Reserve University ............. 7 

Development of an Integral Model for Prediction of Flame Spread on Horizontal 

Shipboard Sufaces, Vahid Motevalli, Yonggang Chen, Worcester 

Polytechnic Institute and Michael Delichatsios, Factory Mutual 

Research Corporation.. ........................................... 9 

Flame Spread in Microgravity - Part I.- Expefiental Study of Simulraneous Upstream 

and Downstream Propagation, S.L. Olson, NASA Lwis Research 

Center ....................................................... 11 

Flame Spread in Microgravity - Part 2: Theoretical Study on Transition from Ignition 

to Flame Bopagation, Kazuyoshi Nakabe, Howard Baum, Takashi 

Kashiwagi, BFRL/NTST .......................................... 13 

%ehents on Twbulent Upward Flame Spread Under mema1 Radiation, Ellen 

Brehob, Johnny Bao and Anil Kulkami, Pennsylvania State 

UniverSi ty.....................................................15 

Turbulent, ConcweM Ceiling and Floor Flame Spread: 272e Effects of Buoyancy and 

wen Concentration, L. Zhou, Y.H. Chao and AC. Fkmandez-Pello, 

UniversityofCalifornia ........................................... 17 

Transient Laminar Wind-Aided Flame Spread Over Hzporizing Solicts in the Ceiling 

Configuration, Sanjay Agrawal and Amhd Atreya, Michigan State 

Universi ty.....................................................19 

Calculating Flame Spread on Horizontal and 'vertical Swfaces, Gama1 Ahmed, 

Portland Cement Assoc.; Mark Dietenberger, Forest Product 

Laboratory; Walter Jones, BFRLdNIST ............................... 21 
ii 

Critical Conditions for Flame Spread and a Rational Fire Hazatrd Material Classification Method, Michael Delichatsios, Y. Chen and Mary Delichatsios, 

Factory Mutual Research Corporation ............................... 23 

SESSION II-A Fire Sinnatures 

Fire Resistant Polymer Grafi, Marc Nyden, James Brown, BFRuNlsT and Bany 

Bauer,NIST ..................................................... 

Acousric EmissiOn of Sauchrral Materials Exposed to Open I;la?nes, Wfiam 

Grosshandler and Margaret Jackson, BFRUNIST ....................... 27 

Machine Vuwn Fh Detection, Douglas Schwartz, Tpdall Air Force Base ................. 29 

Detection of Ud~und Mine Fires, Ronald Conti, U.S. Bureau of Mines ............... 31 

Session II-B Compartment Flows 

Flow Through Horizorrtal Vnts In Enclosure Fins, Y. Jaluria and Q. ‘Em, Rutgers 

U~e~i ....................................................... 33 

mhental Study of the &change Flow Through a Horkontal Ceiling Vent in Atrium 

Fins, Tokiyoshi Yamada, Fire Research Institute (Japan) and hnard 

Cooper,BF’RIJNIST ............................................ 35 

A Model of Combusrion and Convection in Enchsums of Complex Geometry, Kevin 

McGrattan, Ronald Rehm and Howard Baum, BUST ............... 37 

Modeling Backdmp Phenomersa, C.M. Fleischmann, PJ. Pa@ and RB. Williamson, 

UniversityofCalifornia ........................................... 39 

Wltat We Kitow and Don’t KiKnv About Ceiling Jets, Howard Emmons, Harvard 

UniVerrsi ~..................................................... 41 

Local Effects of Vhts, Beams and Spar Spmys on the Ceiling Jet Flow, Haukur 

Ingason, Swedish National %sting and Research Institute ................. 43 

SESSION III Flame Structure 

Entrainment in the Flaming Region of Fm Plumes, E.E. Zukoski, California Institute 

of~hnology .................................................. 45 

Scalar Mig hp& of Buoyant Turbulent Pks, 2. Dai, L-K TlLiieng and G.M 

Faeth,UniversityofMichigan ...................................... 47 

Momentum-Dii’n ControlledLaminarDifficsionFlames, H. Ban, S. Venkatesh and 

KSait0,UnbersityofKentucb .................................... 49 
iii 

Microscales of ForcedlBuoyancy Driven Turbulent Dimion Fhmes, VS. Arpaci, 

University of Michigan and RJ. Tabaczynski, Ford Motor Company ........ ; 51 

MuItzpIicity of &fig Frequencies in Buoyant Dift”Zlsr0n Flames, Baki Cetegen and 

Tarek Ahmed, University of Connecticut .............................. 53 

A Thermal Element Model for Combustion Rocesses in Fires, Ofodike Ezekoye and 

HowardBaum,BFRL/NIST ....................................... 55 

Cornpatison of l&pe&ental and Computed Species Concentration and Temperature 

Rofiles in Laminar, Two-Dimensional CHJAU Dimion Flames, 

Kermit Smyth, Thomas Norton, BFRLNST; J. Houston Miller, 

George Washington University; and Mitchell Smooke, Yale 

University ..................................................... 57 

Numerical Simulation of Themal Plumes, Soonil Nam and Robert Bill, Jr.; Factory 

Mutual Research Corporation. ..................................... 59 

The Turbulence Structure of Medium-Scale Pool Fires, EJ. Weckman and AB. Strong, 

University of Waterloo ........................................... 61 

Radiative Roperties of an Unsteady Jet Dimion Flame, Carolyn Kaplan, Seung Baek 

and Elaine Oran, Naval Research Laboratory .......................... 63 

SESSION IV-A Soot and CO Formation 

Additive Effects on Soot Formation in Laboratory Pool Fires, EJ. Weckman and C. 

Salvador, University of Waterloo .................................... 65 

Modeling the Growth of Polynuclear Aromatic Hydrocarbons in Dimion Flames, J-H. 

Miller, George Washington University.. .............................. 67 

Aerosol Dynamic Recesses of Soot Aggregates in a Laminar Ethene Dimion Flame, 

R. Puri, TE Richardson, RJ. Santoro, Pennsylvania State University; 

and R.k Dobbins, Brown University ................................ 69 

Carbon Monoxide and Soot Padcle Fomtion Studies in Undewentilated LaminarDifficsion Flames, S.G. Leonard, R Puri, RJ. Santoro, Pennsylvania 

State University; and G.W. Mdholland, BFRL/NIST ..................... 71 

A Model of Soot with Detailed Chemical Kinetics, C. Yam and Ian Kennedy, Univer 

sity of California, Davis.. ......................................... 73 

The oxidation of Carbon Monoxide and Soot in Hydrocarbon Diffusion Flames, Rahul 

Puri, Marlow Moser, Robert Santoro, Pennsylvania State University; 

and Kermit Smyth, BFRWNIST .................................... 75 
iv 

Measurements of Carbon Morrmide Concentration and Tempereture in Axially- SymmeniC Methane and Erhylene Di!n Flames, J.H. Miller, Reed 

Skaggs and Bijan Ahvazi, George Washington University. ................. 77 

Carbon Monoxide A.aiuction in Cornpa- Fins, Nelson Bryner, Erik Johnsson, 

WilliamPitts,BFRWM[ST ........................................ 79 

Applicability of the Global Qubalence Ratio for predicting Carbon Monaxide 

Generation in Enclbsure Fins, William Rtts, BFRUNIST ................. 81 

SESSION IV,B Flame Extinction 

Halon ReplacementE&@hnt Conceruhztion Requimnents: Expkntand Model, 

Ronald Sheinson and Samuel Baldwin, Naval Research Laboratory .......... 83 

Flame Suppmssbn EmiencieS of Na Generation Fire l%thguishingAgent& kR 

Hamins, WL Grosshandler and R.G. Rehwoldt, BFRUNIST .............. 85 

Flame Snucture of Inhibited Counte@wing15lames, Ix. Puri, University of Illinois at 

ChicagoandkHamins,BFRUNIST ................................ 87 

Concmation A.ofiles of Ektinguisharu3 in a Fire Environment; Gus Sampling and 

AnuEysir, H.G. Eaton, WD. Smith, J. St. Aubin, R Brown, H. 

Burchell, G. Salmon and RS. Sheinson, Naval Research Laboratory ......... 89 

Quunlii’jication of Parameters in the Assessment of Halon 1301 Replacement, W.D. 

Smith, H.G. Eaton, R Brown, G. Salmon, H. Burchell, J. St. Aubin 

and RS. Sheinson, Naval Research Laboratory ......................... 91 

Theotetical Investigation of C-H and C-X Bond Energy Correlations With OH Reactivity 

and Fire Suppmssbn Emiency, Marc Nyden, BFRLJM[ST and Karl 

Irikura,CSTUNlST ............................................. 93 

Discharge Characterktks of Fire Extinguishing Agents, J.C. Ymg, G. Linteris, W.L. 

Grosshandler, C. Presser and R Gpina, NIST .......................... 95 

Chemical and Physical Effects of Water Dwing Fire Suppression, Anhd Atreya, Todd 

Crompton and Sanjay Agrawl, Michigan State University ................. 97 

Multi-Droplet Evaprative Cooling: Experimental Results, H. Damn and M. di Mano, 

UniversityofMaxyland ........................................... 99 

SESSION V-A Soot and Radiation 

Modeling of Turbulent Flame Radiation, J. de Ris and L. OrloE, Factory Mutual 

ResearchCorporation ........................................... 101 

Wall-Fire Radiant EmissiOn, G.H. Markstein and J. de Ris, Factory Mutual Research 

Corporation .................................................. 103 
V 

Heat Feedback to a Pool Fire, k Hamins, BFRWNIST; M. Klassen, J. Gore, Purdue 

University; and T Kashiwagi, BFRLMST ............................ 105 

me Role of Reflection and Fuel VaporAbsoption in Radiative Heat Feedback to Pool 

Flames, M. Klassen, Y.R. Sivathanu, J.P. Gore, Purdue University .......... 107 

Total Radiative Heat Loss in Jet Flames porn Singe Point Radiance Measuremen< 

I? Dutta, Y.R. Sivathanu and J.P. Gore, Purdue University .............. 109 

Specific Absoption Coefficients of Soot Particles in Laminar Flat Flames, Y.R. 

Sivathanu and J.P. Gore, Purdue University ........................... 111 

Scattering by Smt Aggregates in Turbulent Dimion Flames, R. Mital, J. Dylla, Y.R. 

Sivathanu and J.P. Gore, Purdue University. .......................... 113 

Stnrcture and Optical Pt.opeities of &e@e Soot in Buoyant Turbulent Dimion 

Flames, U.O. K6ylii and G.M. Faeth, University of Michigan .............. 115 

SESSION V-B Pool Fires: 'Large Fires 

Anchoring Mechanism of Pool Fires, S. Venkatesh, k It0 and K. Saito, University of 

Kentucky .................................................... 117 

Effect of Pressure and Oxygen Concentration on Pan Fires in an Enclosed Space, Jean 

Bailey, Patricia Tatem and Frederick Wfiams, Naval Research 

Laboratory ................................................... 119 

Fire-Induced Winds in the 1991 Oakland Hfi Conflagration, Javier Belles and 

Patrick Pa@, University of California ............................... 121 

..................................................... 123 

A Lumped Parameter Model for Unburned Tree Crown Streets, M.C. Smith, Michigan 

State University and Warren Heilman, U.S. Forest Service ............... 125 

Numerical Simulation of the Rise and Diipem'on of Fire Generated Plumes, Ahmed 

Ghoniem and Xiaoming Zhang, Massachusetts Institute of Technology ...................................................... 127 

Two-Dimensional Simulations of Buoyancy-Ihduced Horizontal Roll Vortices, Warren 

Heilman, USDAForest Service.. .................................. 129 
vi 

POSTERS 

erimental Study of Forced VdriOn Glovebox Fh, Craig Beyler, Hughes 

Associates; Michelle Peatros and Richard Roby, Virginia Tech ............ 131 

Conidor Flow of Smoke jkom Pbstjlashover Fire: a pst-".FIRE SIMULATOR" 

Mbdule for FPETOOL, Harold Nelson and Scot Deal, BFRLNIST ......... 133 

Flame Retadancy of Cotton - S' Blend Fabrics, Robert Harper, Jr., George 

Ruppenicker and ARS. Sawhney, USDA Southern Regional 

Research Center, USDA. ........................................ 135 

Direct Measurement of Heat Release Rates, C. Vwelle, J.L Deb4 E Moussan, 

CNRS and C.Pham Van Cang, EDF, France .......................... 137 

Hot Su#ace Ignitions= Ionic Effects in Ipition Initiation, William Bannister, University 

of Massachusetts and Douglas Nelson, Tyndall Air Force Base ............ 139 

Ekperimental Study of Self-lgnition of Electrical Cables &posed to an &term1 Radiant 

Fha, Marie-Claude Lopez and Jacques Bergelin, IPSNEEA, 

France ...................................................... 141 

ARGOS: A Computer Rogmm for Fire Risk Evaluation, Niels Baden, Danish Institute 

of Fire Technology ............................................. 143 

Analysis of the National Fh htection Assmiahn Fn RiskAssessment FramewokExample Calculation, E Merrill Galloway, BF Goodrich Tahnical 

Center and Marcel0 Hirschler, Safety Engineering Laboratories ........... 145 

An Ekpedental Investigation of the Nation Frequency of Flames, A. Hamins, J.C. 

YangandTKashiwagi,BFRL/NIST ................................ 147 

Aqdon andAnalysh System of Bum Injhs From Flames and lhrmal Radiation, 

Bany DeCristofano, Gerald Caldarella, Brian Kimball and Joseph 

Roach, US. Army Natick RD&E .................................. 149 

Intenlatiom@ Between Heen Cyanide Gas Ekposwe Concentration, Ekposm 

Ti and Blood Cyanide Level in Rats, Arvind Chatwedi, Boyd 

Endemtt, Raxane Ritter and Donald Sanders, FAA .................... 150 

hfonnance of the Re@mcal Nephelometer, George Mulholland and Nelson Bryner, 

BmST .................................................. 152 

Correlations for Temperature and Velocity in Room Fires for ESrimating Sprinkkr 

Activation Tis, Pravinray Gandhi, Underwriters Laboratories ............ 154 
vii 

SpMer Head Response Measured and Redicted, Haukur Ingason, Swedish National 

Testing & Research Institute ........................................ .156 

Thermal Radiation Ftom Marine Fire Boundaries, LeMoyne Boyer, Southwest 

Research Institute.. ............................................ 158 

............. 160 

Ground-Fault Circuit-Intempter (GFCI) Technical Report, k Albert Biss, U.S. 

Consumer Product Safety Commission .............................. 162 

One and Two-sided Burning of T;hennally-Thin Materiab, T. Ohlemiller and J. Shields, 

BFRL/NIST .................................................. 164 

A Comparison of Numerical and &act Solution of the Creeping Flame Spread Over 

Thermally T3tin Marerial, Subrata Bhattachajee, San Diego State 

University .................................................... 166 

The Behavior of High Density Cellulose Samples Under Simulated Fire Conditiom, I. 

Milosavljevic and E.M. Suuberg, Brown University ..................... 168 

1 

INTRODUCTION 

The MST Annual Conference on Fire Research has long been the prime forum for the presentation 

and discussion of the latest advances in the science of fire and the engineering of fire safety. This 

year's Conference has been expanded to include all fire research performed within Federal 

laboratories or sponsored by Federal agencies, as well as by laboratories around the world. The 

Conference was organized with the assistance of representatives from those Federal agencies: 

Mr. Donald Bathurst 

Mr. Michael Bennett 

Dr. Thor Eklund 

Mr. Kenneth Faulstich 

Dr. Robert Friedman 

Ms. Karla Kertis 

Dr. Merrill King 

Mr. Dennis Kubicki 

Mr. Roger Lanahan 

Mr. Domenic Macaione 

Mr. Charles McGuire 

Mr. Jonas Morehart 

Ms. Margaret Neily 

Mr. Gene Sober 

Dr. Patricia Tatem 

Mr. Richard Vickers 

Dr. Robert White 

General Sexvices Administration 

Wright-Patterson Air Force Base 

Federal Aviation Administration 

Department of Veterans Affairs 

NASA Lewis Research Center 

U.S. Bureau of Mines 

National Science Foundation 

Department of Energy 

U.S. Fire Administration 

U.S. Army Materials Technology Laboratory 

Department of Transportation 

National Institutes of Health 

Consumer Product Safety Commission 

NASA Goddard Space Flight Center 

Naval Research Laboratory 

Tyndall Air Force Base 

Forest Products Laboratory 

This booklet contains the abstracts of the 64 papers and some 24 posters focussing on the 

phenomenology of fire: flame spread, flame structure, CO and soot formation, soot radiation, fire 

signatures, flame extinction, compartment flows, and large fires. Discussion sessions will consider the 

status of our knowledge and the most important understanding yet to be developed. With this, we 

hope to continue cross-pollinating the elements of the fire research community while stimulating our 

members to better our knowledge base for reducing the toll from unwanted fires. 

Richard G. Gann, Conference Chair 

Chief, Fire Measurement and Research Division 

Building and Fire Research Laboratory 

National Instiitute of Standards and Technology 
2 
3 

ROLE OF IN-DEPTHABSORprroNINFLAME SPRE4D UNDER 

by S. S. Manohar, A. K. Kulkarni and S. T. Thynell 

The Pennsylvania State University 

When radiation is incident on a semitransparent material, it is partially reflected 

and partially transmitted through the surface, which is then absorbed volumetrically 

within the material itself. Plastics, such as polymethylmethaqlate (PMMA), are often 

highly semitransparent. One of the practical problems in which the in-depth radiation 

absorption can be important is flame spread over semitransparent solid fuels, such as a 

burning wall or floor with spreading flame in the presence of a surrounding fire. Flame 

spread and $dace heating under external radiation has been studied theoretically , however, the models have used either opaque solid formulation [l] or gray in-depth 

radiation absorption [2]. When in-depth absorption is ignored, all the energy is assumed 

to be deposited on the surface. This results in a more rapid rise in surface temperature 

and consequently in a greater rate of predicted flame spread. The objective of the present 

work is to study the effect of in-depth radiation absorption on the surface temperature of 

a semitransparent material, using PMMA as exaxnple. 

Mathematical Model : The medium is modeled as a one-dimensional slab, insulated at 

one end and subjected to external radiation at the other. To examine the effect of in-depth 

radiation absorption the material is then considered to be either semitransparent or 

opaque. In a real fire situation, the surface well ahead of the pyrolysis front may be clear 

initially, but later it gets covered with a layer of soot as the combustion progresses. 

Hence, two cases are considered, one where the sul'face is clear and the other where the 

surface is covered with a layer of soot, for each of the semitransparent and opaque 

formulations. In order to accurately solve the radiation problem, a 14-band model is 

employed to simulate the spectral distribution of absorption coefficient and reflectivity, 

which were determined experimentally. 

Experiments : Two series of experiments were conducted, radiation property 

measurements for input to the model, and transient surface temperature 

measurements for a slab in the presence of strong external radiation to vew the model. 

Absorption Coeffiient and Reflectivity Measurements: The spectral radiation 

properties were measured using a standard Fourier Transform infrared (FTIR) 

spectrometer. A wavelength range from 0.67 pm to 20 pm was covered using two 

different combinations of detector and beam splitter, a potassium bromide beam-splitter 

with a mercury cadmium telluride (MCT) detector and a lead selenide detector with a 

quartz beam splitter. With the measurement of the spectral transmittance, the 

transmissivity, TX, and reflectivity, ph, were obtained using available procedure. 

Figure 1 shows absorptivity data for clear PMMA samples. It can be seen that the 

absorption coefficient is low and highly irregular in the range 1000 to 3000 cm-1, which 

may be explained by examining the molecular structure of PMMA. Also shown in Fig. 1 

is the 14-band model for the absorption coefficient. The net effect on energy absorption 

depends on both the spectral distribution of incident radiation and the spectral 

properties of the absorbing medium. Therefore, a carefidly selected multiband radiation 

model is needed to accurately account for the in-depth absorption. The radiation received 
4 

by a burning wall or floor is typically from surrounding fire which contains very little 

amount of energy below 2000 an-1 and the property data show absorption coefficient 

diminishing to almost zero above 6000 cm-1. Therefore, the range between 1775 cm-1 and 

6250 cm-1 was divided in 14 bands. The spectral radiation properties of absorptivity and 

reflectivity property data are then used as an input to the mathematical model. 

Surface Temperature Measurements : Experiments were carried out to determine 

the rise of surface temperature on two sets of PMMA samples, those with clear sdace 

and those with soot-layer covered surface. The samples were then subjected to external 

radiation at five different heat flux levels, ranging from 3.7 to 23.15 kW/xnz. 

Experimental data were recorded until either the steady state was reached or the 

surface of the sample was completely covered with bubbles. 

Model results and comparison with experiments : The predictions were compared with 

data for the four combinations of semitransparent and opaque material slabs with clear 

and blackened surfaces at different values of external heat flux. As an example, 

comparisons for blackened samples are shown in Fig. 2 at 6.8 kW/xn2. The difference 

between the opaque and semitransparent case represents the effect of in-depth radiation 

absorption. It is clearly seen that it takes longer for a semitransparent sample to reach a 

fixed bmperature than the opaque sample. 

The results have important implications for predicting flame spread under 

external radiation because the rate of flame spread depends upon the rate at which the 

surface just ahead of the pyrolysis front reaches a critical temperature. If the material 

is semitransparent, the model must adequately account for in-depth absorption, 

otherwise, an accelerated flame spread will be predicted. Additional details on the 

present work may be found in reference 131. 

R&remes: 

1. Fernandez-Pello, A. C., Comb. Sci. Tech., vol. 17, pp 87-98,1977. 

2. Park, S. H. and Tien, C. L., Int. J. Heat Mass Trans., vol. 33, pp 1511-1520,1990, 

3. Manohar, S. S., M. S. Thesis, The Penn. State Univ., University Park, PA, 1992. 

This work was partially fimded by a grant from the National Institute of 

Standards and Technology. 

-I 

V i II -I I, I 

4000 6000 8000 10000 

0 $&enumber (cm-1) 

- 

U 

0 

", 

0 

W 

E 

3 

ZSOsemitransparent 

Figure I Absorption coefficient and 

14 band model Figure 2 Effect of in-depth absorption 

on surface temperature rise 

of blackened samples 

- - 
5 

MATHEMATICAL MODEL OF COCURRENT HORIZONTAL 

FLAME SPREAD OVER SOLID COMBUSTIBLES 

C. C. Hwang and C. D. Litton 

Pittsburgh Research Center 

U.S. Bureau of Mines 

Pittsburgh, PA 15236-0070 

Introduction 

The flame spread along thermally thick fuels in the presence of a cocurrent air stream is in general 

more rapid and more hazardous than the spread in opposed-flow configurations. The interest in fire 

safety for cocurrent mode of flame spread motivated the development of flamability test methods [Steiner, 

1943; Parker, 1977; Perzak and Lazzara, 19921. de Rie (1970) obtained analytical solutions to fuel-rich 

fires spreading along fuel-lined ducts. The temperature distributions in the gas and the walls were 

obtained for the preheating zone, the combustion zone, and the burn-out zone. In the existing literature 

on the flow-aesisted flame spread, the rate of flame spread is a monotonic function of the air speed 

[Fernandez-Pello, 1979; Zhou and Fernandez-Pello, 19901. This is in contrast to our observation with 

the fire spread dong conveyor belts that a maximum spread rate occurs at the air velocity approximately 

1.5 m/s. In the experimental setup in a large-scale gallery, the hot-gas plume appears to entrain air from 

all sides, Le., the flow configuration is three dimensional. In addition, the combustion gas is stratified 

and the radiative heat transfer is the dominant mode of energy transfer. This is in contrast to the flame 

configuration in small-scale fires, i.e., the flow field is approximately two dimensional and the convective 

heat transfer is the main mode of energy transfer. In these cases, the air is entrained into the flame 

zone from the rear of the flame. It appears that the traditional, twedimeneional, boundary-layer type 

approach cannot model the flame spread for the conditions encountered in large-scale gallery fires. 

Mathematical Model 

The spread of a flame along a horizontal bed of solid fuels is considered in the present study. The 

direction of the air flow is same as that of the flame spread, and the pyrolyzed vapor from the solid 

combustibles and the combustion gases are convected ahead of the pyrolysis front enchancing the transfer 

of heat and thus assisting the spread of the flame. The spread of flame is controlled by radiative heat 

transfer from the flame zone to the fuel and by convective heat transfer from the combustion gas to the 

fuel. The heat energy entering the fuel surface is transmitted by conduction. The heating causes the 

fuel temperature to increase until it reaches the pyrolysis temperature. The pyrolyzed matter releases 

its chemical energy in the flame zone. The air in the vicinity of the flame zone is entrained into the zone 

to provide the required oxygen. The amount of entrained air is computed from the equations given by 

Delichatsios (1988). The air stream forces the flame to tilt toward the unburnt fuel. The tilt angle is 

computed from the equations given by Mudan and Croce (1988). The flame temperature is calculated 

from an energy balance for a control volume enclosing the flame zone. The soot volume fraction which 

is employed in the calculation of the flame emissivity is obtained from an experimentd correlation. 

At each time step, the surface temperature and the pyrolysis rate are computed for each cell of the 

fuel. In the present analysis, the flame front is the location on the flame surface where the temperature 

reaches ite pyrolysis temperature. The burn out of a cell occur^ when a fraction of the cell mass is 

consumed. Three flame volume shapes have been considered, a parallelepiped, a prism and a cylinder. 

The results presented are based on the prism- shaped flame volume. 

Results and Discussions 

In the modeling, a fire is initiated from a length of the combustible material. For a given air speed, 

there is a minimum initial length below which the flame dose not propagate. The length of the burning 

zone may or may not reach a final ‘steady length’ during a burn. Figure 1 shows the flame position 

versus time for several values of the air velocity. In most cases the spread ha not reached a stational 
6 

value. Figure 2 plots the spread rate as a function of the air velocity. Line A is obtained based on the 

mean spread rate for the total burneetime shown in Figure 1. A maximum spread rate is indicated at the 

air velocity of approximately 1.5 m/s. Line B is calculated from the near-straight portions of &es in 

Figure 1. For this case a maximum spread rate is at the air velocity of - 2.5 m/s. The experimental data 

are from sheets of 12.5 mm thick, 0.65 m wide by 2.4 m long PMMA and 12.5 mm thick, 1.0 m wide by 

10 m long styrene butadiene rubber (SBR) conveyor belt. It may be noted that the lengths of the fuels 

used in the experiments are short, and stational values of spread me unlikely to be reached. In general, 

the model predicts the overall trend of the flame spread observed in large-scale gallery experiments. 

References 

Delichatsios, M.A., 1988, “Air Entrainment Into buoyant Jet Flames and Pool Fires,n The SFPE 

Handbook of Fim Protection Engineering, National Fire Protection Association, Quincy, MA, 

Chapt. 1-19, p. 1-306. 

de Ris, Jone, 1970, “Duct Fires,” Combustion Science and Technology, vol. 2, pp. 230-258. 

Fernandez-Pello, A.C., 1979, “Flame Spread in a Forward Forced Flow,” Combustion und Flume, vol. 

Mudan, K.S. and Croce, P.A., 1988, “Fire Hazard Calculations for Large Open Hydrocarbon Fires,” 

The SFPE Handbook of Fim Pmtection Engineering, Nation4 Fire Protection Assodation, Quincy, 

MA, Chapt. 2-4, p. 2-45. 

Parker, W.J., 1977, “An Investigation of the Fire Environment in the ASTM E 84 ’Punnel Test,” NBS 

Technical Note 945, National Bureau of Standards, Washington, D.C., August 1977. 

Perzak, F.J. and Lazzara, C.P., 1992, “Flame Spread Over Horizontal Surf- of Polymethylmethacrylate,” Paper 190, Twenty-Fourth Symposium (International) on Combustion, Sydney, Australia. 

Steiner, A.J., 1943, “Method of Fire Hazard Classification of Building Materials,” ASTM Bulletin, 

Zhou, L. and Fernandez-Pello, A.C., 1990, “Concurreat Turbulent Flame Spread,” 23rd Symposium 

36, pp. 63-78. 

19-22, March 1943. 

(Int.) on Combustion, pp. 1709-1711, The Coanbuation Institute, Pittsburgh. 

0 

Time, s 

Figure 1: Flame front position vs time. 

0.10 

< 

E 

f! 

- 0.08 

W 

O 

g0.06 

i 

c) 0.04 

CL 

O 

Y0.02 

w 

0 

(li 

0.00, 

1 1 

A, 0: Predicted 

aa: Measured 

0 

0 0 0 

0, I I 1 I I ’ Air‘ Vel&, 4 m/s 5 6 1 

Figure 2: Flame spread rate vs air velocity 

_- _- 
7 

A MODEL OF LOW-SPEED CONCURRENT-FLOW 

. SPREAD OVER A THIN SOLID FUEL 

FLAME 

Paul V. Ferkul and James S. T’ien 

Case Western Reserve University 

Department of Mechanical and Aerospace Engineering 

Abstract 

In spacecraft cabins, low-speed flows are generated due to ventilation 

requirements. The flows can be as low as a few centimeters per second, which is 

below the velocity range typically encountered in buoyant fires on earth. The 

flame propagation and the extinction mechanisms in this low-speed regime can be 

quite different from those on earth. 

and curiosity about fundamental scientific understanding of flame behavior in 

low-speed flows prompts this investigation. 

Both the concern of spacecraft fire safety 

The model considers two-dimensional, steady flame spread in concurrent flow 

over a thin solid. Because of its thinness, the fuel bed can burn through and the 

flame is capable of reaching a constant length. Thus, following the flame, a 

steady state, with constant (and equal) flame tip velocity, pyrolysis front, and 

fuel burnout rates, can be obtained. 

The flame is assumed to be laminar because of its small size and low 

velocity. The gas-phase fluid mechanical treatment is more comprehensive than 

most works in the past. In the flame base region (where the upstream flow is seen 

first), streamwise heat and mass diffusion is included. This, together with 

finite-rate gas-phase chemical kinetics, enables us to examine the question of 

flame stabilization and extinction. The elliptic treatment of this flame 

stabilization zone entails the full Navier-Stokes equations. On the other hand, 

to save computational time, a boundary layer approximation is employed in the 

downstream region. 

location, they are also coupled indirectly through the solid by energy exchange. 

A simplified solid fuel model is used. The solid is assumed to be thermally thin 

and pyrolyzes according to a one-step Arrhenius law with no char and tar 

formation. A solid surface radiative loss term is included which turns out to be 

of critical importance in the low speed limit. 

elliptic and parabolic regions and between the gas and solid phases, the numerical 

solutions require many iterations and are computationally intensive; they are 

carried out using Cray X- MP Supercomputer at NASA Lewis Research Center. 

The two zones are coupled at an appropriate gas-phase 

Because of the coupling between 

Extensive computations have been performed using oxygen mole fraction and 

free-stream velocity as parameters. Fig. 1 gives all the points calculated and 

the extinction boundary. Some of the important results are summarized below. 

(1) A low velocity extinction limit exists. This is the consequence of surface 

radiative loss. While the maximum flame temperature remains constant at low 

velocity without radiative loss, with radiative loss the flame temperature 

drops with decreasing velocity. Without radiative loss, the model predicts 

no low-speed extinction limit. 

(2) Flames quench at low speed by shrinking in size. Near-limit flames remain 

with the fuel burnout region (flame stabilization zone). This is in contrast 

to flame blowoff at high speed (Urn > 5 cm/sec in Fig. 1) where the flame is 

unable to stabilize in the fuel burnout region and extinction is reached when 

it is blown downstream. 
8 

(3) The minimum oxygen percentage that will support a spreading flame in 

concurrent flow occurs.at Urn = 5 cdsec (see Fig. 1) which is well below, the 

buoyant flow velocity at normal gravity. 

for spacecraft fire safety. 

This can have profound implications 

(4) The computed reaction rate contours suggest short and fat flames in low speed 

flow. This is verified by recent drop tower experiments by Grayson. 

The flame spread rates are generally small, ranging, for example, from 0.08 

cm/s to 1.56 cm/s for convective velocities 0.9 to 10 cm/s in twenty-one 

percent oxygen. 

experimental results. 

present time due to the time limitations of the drop tower which prevents the 

achievement of the final steady flames. 

These computed spread rates are also roughly close to the 

A more precise comparison cannot be made at the 

(5) Using finite rate kinetics enables us to examine the percentage of fuel which 

escapes from the flame. As velocity is decreased toward the quench limit, 

this percentage increases due to increasing degree of flame tip quenching. 

The presence of unburnt fuel vapor in spacecraft can be a safety concern. 

Detailed flame structures for all the cases shown in Fig. 1 have been 

obtained but cannot be shown here due to the page limitation. Some of the most 

interesting ones will be presented at the conference. 

Acknowledgement 

This research is supported by NASA Microgravity Science and Applications 

Division through Grant NAG 3-1046. 

21 

20 

n 

be -1 9 

S 

0 

0 

Q) 

6, 

0 

21 5 

14 

0 

0 

0 STEADYFLAME 

X EXTINCTION 

0 

00 Od 

/ 

0 

Free Stream Velocity (cm/s) 

Fig. 1. Extinction Boundary for Concurrent-Flow Flame Spread 

Over a Thin Solid Fuel 
9 

Abstract submitted to: ANNUAL CONFERENCE ON FIRE RESEARCH 

Development of an Integral Model for Prediction of 

Flame Spread on Horizontal Shipboard Surfaces 

Vahid Motevalli and Yonggang Chen 

Worcester Polytechnic Institute 

Michael A. Delichatsios 

Factory Mutual Research Corp. 

A model for prediction of flame spread on horizontal surfaces is being developed for the Naval 

Research Laboratory. It is a general model for any horizontal surface, both charring and non-charring 

material, with a flexibility to incorporate the possible restrictions imposed within a shipboard 

compartment such as vitiated environment or heat transfer from adjoining compartments. This paper 

describes the components of the model being developed and the progress made during the fust year of 

this effort. 

(1) An integral transient pyrolysis model for charring and non-charring material’, (2) An integral 

combustion model, and (3) The model skeleton which includes calculation of the heat fluxes arriving 

at the surface ahead of the flame front. 

The transient pyrolysis model is based on a one-dimensional heat conduction equation solved for 

any arbitrary heat flux at the surface. The model has been tested with very good results for thermally 

thick-to-intermediate material2

. In this model, the material is divided into two layers of char and nonpyrolyzed segments and the char front propagation is tracked. The reradiation loss at the surface is 

accounted directly while the convective heat transfer at the surface is treated through use of equivalent 

properties. The integral approach and use of robust numerical techniques allows rapid computation. 

Furthermore, an approach has been developed and refined to use experimental results of a mass loss 

and surface temperature histories to derive char properties such as thermal conductivity and heat of 

As the flame spreads on the surface, the fire grows due to increased burning surface. This in 

turn will affect the rate of flame spread and has to be coupled with the flame spread model. The total 

heat flux from the flame ahead of itself is directly related to the flame geometry and heat release rate. 

A combustion model, coupled with the transient pyrolysis model is needed to address this phenomenon. 

An integral combustion model has been developed for turbulent jet diffusion flame that includes, 

as its most important component, the flame radiation and its relation to flame turbulence and the sooting 

tendency of the fuel. The soot generated by the fuel can be characterized by the laminar smoke-point 

height. This model relies both on previous integral model&59697 and more detailed k-e-g models87’. The 

main characteristics of the present integral model are the following: 

1) Instead of an entrainment equation, a dimensionless correlation for the entrainment spanning the 

range from momentum to buoyant turbulent jet flames has been employed and validated’’. 

2) A direct relationship for the fluctuation of a conserved scaler inspired by recent work of Chatwin 

and Sullivan” and validated by recent experiments’* is also used. 

3) In the present model, radial profiles for the mixture fraction and velocity are derived in order to 

preserve the strong non-linearity of the combustion process6

. 

4) Most iniportantly, a flame radiation model applicable for luminous (soot radiation) optically thin 

flames has been developed whose sooting tendency is characterized by the laminar smoke-point height. 

In order to characterize the turbulent mixing, a fl (beta) probability for the conserved scaler has 

been used which has been shown to represent the turbulent mixing process welP3. The flamelet model, 

which is based on the approximation of the turbulent diffusion flame as an ensemble of luminous 

flamelets along with known state relationships (i.e. species concentration as function of mixture fraction) 

The components of the Shipboard Horizontal Flame Spread Model (SHFSM) are as follows: 

This transient model has been incorporated into the preliminary flame spread modef. 
10 

for the various products of combustion has been applied to develop the combustion model8*'. These 

state relationships (some of which are available in chemical libraries) can be obtained by experiments 

in laminar flames8 or by detailed chemical kinetics calculations. Radiation is treated here in the 

ooticallv thin limit (as a first attempt) by making the following approximations: 

1) All radiation originates fiom deviations that are near the instantaneous maximum flame temperature. 

2) The effective temperature decreases due to radiant losses as the radiation fraction increases. 

The combustion model will provide the flame temperature, radiative loss fiaction and major 

species concentration as a function of height above the fuel surface. These are essential parameters to 

not only determine the heat flux ahead of the flame, but also provide coupling with the environment as 

well as input for a full compartment fire model. The combustion model is under development and some 

promising preliminary results have been obtained thus far. 

At the present time 

the flame spread model uses 

the surface temperature 

reaching the pyrolysis 

temperature as a spread 

criterion. The heat flux from 

the flame and any external 

flux plus heat losses are used 

to arrive at a net flux at the 

surface. The net flux is used 

as the time-varying 

(implicitly since the pyrolysis 

front position, xp=xp(t)) input 

to the transient pyrolysis 

model to determine the 

0.10 4 0 001 i=3-12 AND 0.01 FOR OTHER 

0:Ol 'FOR ALL NODES 

0.001 FOR ALL NODF,, 

x(l)=x(l-1)+0.01~1.2 

q",=25ex (- 13.246(x-x,)) 

HEAT FLUX FROM THE FLAME TO 

THE FUEL SURFACE 

t 

n 

RESULT FOR DIFFERENT SPACING X 

+ 

7 

0 2 0.04 

W 

z 

LL 

4 0.02 

,{ 

80C s~~l""""'l""""'I""""' 

0.00 200.00 400.00 600.00 

TIME (sec) 

00 

surface temperature as a 

function of time. A variable Fwre 1 - Pyrolysis front position vs. time for an arbitrary flux 

mesh spacing has been shown to produce robust and accurate results. Figure 1 shows an example of 

the results from the SHFSM for an arbitrary heat flux. 

Some preliminary experiments have been designed and performed using the LIFT apparatus in 

a horizontal orientation to attempt to define the heat flux ahead of the flame. 

References 

1. Chen, Y., Delichatsios, M.A. and Motevalli, V., Comb. Sci. and Tech., in press, 1992. 

2. Chen, Y., M.S. Thesis, Worcester Polytechnic Inst., 1991. 

3. Chen, Y ., Delichatsios, M.A. and Motevalli, V., Eastern Sect. Meeting, Ithaca, N.Y., 1991. 

4. Steward, F.R., Comb. Sci. and Tech., 2, p. 203, 1970. 

5. Tamanini, F., Eighteenth Symp. (Int'l) on Comb., p. 1081, The Combustion Institute, 1981. 

6. Delichatsios, M.A. & Mathews, M.K., 2nd Int'l Fire Safety Sci. Symp., p. 149, 1989. 

7. Cook, D.K. , Twenty-Third Symp. (Int'l) on Comb., p. 653, The Combustion Institute, 1991. 

8. Sivathanu, Y.R. and Faeth, G.M., Comb. and Flame, 82, p. 211, 1990. 

9. Gore, J.P. & Faeth, G.M., 21st Int'l Symp. (Int'l) on Comb., p. 1521, 1986. 

10. Delichatsios, M.A., Comb. Sci. and Tech., 60, p. 253, 1988. 

11. Chatwin, P.C. and Sullivan, P.J., J. Fluid Mech., 212, p. 533, 1990. 

12. Sivathanu, Y.R., Kounalakis, M.E. and Faeth, G.M., NIST-GCR-90-570, 1990 

13. Pope, S.B., Twenty-Third Symp. (Int'l) on Comb., p. 591, The Combustion Institute, 1991. 
11 

Figure 2 shows flame spread rates and 

position versus time data for the 30% oxygen 

(21, the upstream flame spread rates measthey show the same magnitude and indepentests at 0 and 2 cmk When compared with 

previous work on opposed-flow flame spread 

ured in these tests are in good agreement; 

Flame Spread in Microgravity 

S.L. Olson 

Part 1 : Experimental Study of Simultaneous Upstream and Downstream Propagation . 

7 

4.01 - 

5 3.04 

2.01 

- 

- 

z - 0 o*o------- ----- 

a. 

w > -1.0- 

5 -2.0; 

- ------ ---- 

- 

NASA Lewis Research Center 

lntroduct ion 

This summarizes the progress of the experimental portion of a collaborative experirnentaYnumericaI effort 

between NASA and NlST to study flame spread over a thermally-thin cellulosic material in low gravity. Although 

presently there are differences in conditions between experiment and model such as ignition mode and geometry, 

both aim to understand the effects of oxygen concentration and low velocity forced flow on flame spread. 

Experiment Description 

A preliminary series of tests was conducted in the 2.2 

second Drop Tower at NASA Lewis Research Center to study 

the effects of low velocity flow on flame spread over thermally 

thin solids. As shown in Figure 1, to simultaneously obtain 

both upstream and downstream flame propagation in a single 

test, the 5 cm wide by 15 cm long thermally-thin cellulosic fuel 

was centrally ignited by a straight nichrome wire run across 

the full width 7.5 cm from each end. This planar configuration 

is similar to the axisymmetric case modelled by Kushida et al 

111; the downstream gas-phase flow and atmosphere is affected by the presence of the upstream flame, which perhaps is 

more representative of a typical fire scenario than ignition at 

either end of the sample. Flow over the sample was 0',2, or 5 

cmk; molar concentrations of oxygen were 21 or 30% in N2. 

It should be noted that during the short test times, the flame never fully separated into two independent 

flames; the flame base of the downstream flame was actually still the upstream flame leading edge. The 

downstream flame spread rate is defined here as being the movement of the downstream flame tip. 

Prelim ina ry Resu Its 

WE SPREAD IN 303 OXYGEN 

5.0 ar,.,,,,,l ,,,,,,,,, I ,,.,, 

Resented at the NET Annual Coderence on Fire Research, Rodtville, MD, 06.1>16,1992 
-- * 12 

The position versus time data and flame 

spread rates for the 21% oxygen tests at 0 

and 5 cm/s are shown in Figure 3. They 

demonstrate the expected dependence on 

opposed flow velocity, but the spread rates 

are slightly faster than previous work [2]. 

Downstream flame spread rates were not 

steady in air, and the flame tips appeared to 

be retreating slightly just prior to the end of 

the 22 second test. . 

Both quiescent tests (in air and at 30% 

oxygen) revealed that the flame spread rates 

away from the central ignitor are not equal as 

they should be in a truly zero gravity environment. These results are discussed below. 

U 

-I.O] 2 -2.04 

-3.0: H Downstream Quiescent, unsteady 

-4.0Y n Downstreom 05 cm/s, unsteody 

- 

- : H Upstream Quiescent, Wr0.86 cm/s 

H Upstream OScm/s, W=1.38 cm/s -5.0, v v 0 I 1 1 1. 9 1 I ' '. ' I.. 9 ' 

0.0 0.5 1 .o 1.5 2.0 2.5 

TIME. SECONDS 

Figure 3 

Discussion 

The observation that all downstream flames are slower than the upstream flame is the opposite of normal 

gravity flame spread where co-current flame spread.rates are typically faster than opposed-flow flame spread 

rates. This may indicate that the downstream flame is weakened by the presence of the upstream flame. The 

retreating flame tips of the downstream flame in the air tests may be an indication that, given longer test times, 

the downstream flame is not viable under these atmospheric and flow conditions. It is interesting that the 

downstream flame at 30% oxygen with a 2 cm/s flow is "weaker" than the comparable downstream flame under 

quiescent conditions. This is the reverse of the upstream flame where an increase in flow velocity in low gravity 

assists the flame spread process. This may be due to the close matching of the magnitudes of the downstream 

flame spread rate and flow velocities, so the relative velocity behrveen the two is small, resulting in a reduced 

convective contribution to heat and mass transport in the flame. 

The discrepancy between upstream flame spread rates in air and previous opposed flow flame spread rates 

[2] may be due to the different boundary layer thicknesses at the 7.5 cm vs 15 cm downstream of the leading 

edge for the previous work [2]. Boundary layer effects on flame spread have been observed in normal gravity 131. 

The non-symmetry in flame spread in the quiescent tests is currently being investigated; the non-symmetry is 

attributed to a test condition that is not truly quiescent, and two possible sources of flow are 1) the chamber light 

induced buoyant flow in the chamber, or 2) there is a residual gravity level in the 2.2 second drop tower. 

Planned Work 

The gravity level during a low gravity test in the 2.2 second drop tower will be measured in the near future. 

Quiescent tests will be rerun without the light in the chamber. Further flame spread tests are to be conducted in 

the 52 second NASA Lewis Zero Gravity Facility, where longer test times may yield complete separation of the 

two flame halves or possible extinction of the downstream flame. Boundary layer effects on opposed-flow flame 

spread will also be investigated further. 

References ' Kushida, G., Baum, H.R., Kashiwagi, T., and di Blasi, C., J. Heat Transfer, Vol. 114, pp.484-502 (1992). 

* Olson,S.L.; Comb. Sci. Tech. 76, pp.233-249, (1991). ' Guerra, V.G.; M.S. Thesis (Mech. Engr), Univ. of Ky., (1981). 
13 

FLAME SPREAD IN MICROGRAVITY : Part 2 

Theoretical Study on Transition’ from Ignition to Flame propagation 

Kazuyoshi Nakabe, Howard R. Baum and Takashi Kashiwagi 

Building and Fire Research Laboratory, NIST 

Introduction 

This presentation describes the progress of the theoretical portion of 

a collaborative numerical/experbental effort between NASA and NIST to 

study flame spread mechanisms over a thermally-thin cellulosic material 

in microgravity. Although at present some differences in conditions such 

as ignition mode and geometry exist between the studies, both aim to 

understand the effects of oxygen concentration and forced slow flow 

velocity on flame spread. 

Theoretical Model 

An axisymmetric time-dependent model describing ignition and subsequent 

transition to flame spread over a thermally thin cellulosic sheet in a 

quiescent zerogravity environment has been developed. This model is 

currently being extended to a three-dimensional model including a slow 

external flow along the sample surface. The absence of gravity removes 

the buoyancy induced vorticity generation mechanism. The small scale of 

the physical size (characteristic length scale is about 1 cm which is the 

Gaussian half-width of an external radiation beam) with a quiescent 

condition or with a slow external flow implies a low Reynolds number flow 

domain. Due to the unique combination of a zerogravity environment and 

low Reynolds number flow domain, the model consists of a potential flow 

calculation coupled to mass, energy, and species conservation equations[l]. A one-step global gas phase oxidation reaction and three global 

solid phase degradation reactions[2], endothermic pyrolysis, exothermic 

oxidative degradation and highly exothermic char oxidation reaction, are 

used in the model. 

In the calculation the sample is irradiated and auto-ignited at the 

center by thermal radiant flux with a Gaussian distribution instead of 

pilot ignition for the experiment. A maximum external radiant flux of 5 

W/cm2 at 21%, 30% and 50% oxygen concentrations in a quiescent environ- ment is used in the calculation. At present development of a three- dimensional time-dependent model including an external slow flow is in 

progress. Some of preliminary results might be presented in the meeting. 

The results indicate that ignition is observed for 21% and 30% oxygen 

concentrations but the transition to flame spread does not occur. 

However, in 50% oxygen the transition is achieved as shown in Fig.1 which 

plots gas phase temperature distribution 1.0s after initiation of the 

external radiation. Each temperature isotherm line is a lOOoK interval 

starting from 35OOK. Distributions of velocity vector and oxygen/fuel 

concentrations at the same time are shown in Figs.2 and 3, respectively. 

In Fig.3 solid lines are fuel concentrations and dashed lines are oxygen 

concentrations with an interval of 2%. The energy balance at the sample 

surface at 1.0s is shown in Fig.4, where Q, is the external radiant flux, 

Qrad is the re-radiation loss, Q, is the net heat balance of the three 

degradation reactions, Qfcon is the convecting heat transfer from the gas 

phase to the sample and Qmct is the energy expressed by mass flux times 

enthalpy difference. A high energy feedback rate of nearly 6 W/cm2 is 

calculated instead of nearly 1 W/cm2 for 21% oxygen concentration case at 

1.6s after initiation of the external radiation as shown in Fig.5. This 
14 

difference in energy feedback rate is mainly caused by differences in 

flame temperature (about 1400OK for 21% vs 2000OK for 50%) and also in 

the location of peak gas phase reaction rate (closer to the sample 

surface in 50% oxygen concentration). Detailed discussion on the 

transition mechanisms and also comparison with experimental data will be 

presented in the meeting. 

Reference 

l.Kushida,G., Baura,H.R., Kashiwagi,T. and di Blasi, C., J. Heat Transfer 

2.Kashiwagi,T0 and Nambu,H., Comb. Flame 88, p345-368 (1992). 

114, ~484-502 (1992). 

10.0cm/s 

Fig. 1 

Fig.4 

Q 

6 

4 

2 

0 

-2 

-4 

E' 

Fig3 04 

N 

2 

0 I 

14 

Fig2 

Figs 
15 

by Ellen G. Brehob, Johnny Bao, and Ani1 K. Kulkarni 

The Pennsylvania State University 

The overall objective of the present project is to understand the upward flame 

spread phenomenon under simulated surrounding fire conditions. This is achieved by 

conducting experiments on upward flame spread under external radiation, developing a 

mathematical model, measuring the relevant basic material properties needed, and 

checking the validity of the model by comparing predictions with data. Emphasis is 

placed on studying and predicting the behavior of practical wall materials used in 

building and vehicle interior and textiles. This paper presents results of a 

comprehensive series of flame spread experiments conducted on Particle Board samples 

at various external radiant heat flux levels, under preheat and no preheat conditions, 

and for a range of line-burner igniter strengths. In each test, measurements were made 

as a firnction of time for total heat feedback and surface temperature at five different 

heights, and the flame height was read from the video record. Figure 1 shows a 

schematic of the experiment setup in which wall samples 0.3m wide by 1.2 m high (1' x 

4') were subjected to external radiation fluxes of up to 29 kW/mZ using two large 

electrically heated panels. 

Effect of External Radiation : Figure 2 shows an increase in flame height as a function of 

time at six different heat fluxes. The samples were not preheated and the igniter was set 

at 18 kW/m in all tests. The external flux not only enhances the upward flame spread 

significantly, but also affects whether the upward flame spread will be sustained or not. 

At 5.4 kW/m2 and above the flame spread was self-sustained; at heat flux levels tested 

below that threshold it did not. 

Effect of Preheat : When the particle board sample was preheated to steady state and 

then ignited, the flame spread was substantially greater compared to the sample which 

was simultaneously ignited and subjected extemal heat flux. (See Fig. 3.) Here, the heat 

flux was 5.4 kW/m2, and the front and back surfaces had reached an average 

temperature of 142 C and 76 C, respectively. Also shown in the figure is the scatter in the 

measurement of the flame height data, which was present in all the tests. 

Effect of Igniter Strength : The igniter strength determines the height of the flames from 

the line burner. A large ignition source can produce sufficient size of the initial 

pyrolysis zone to sustain the upward spread. Figure 4 shows interesting results of the 

effect of the igniter strength. The largest igniter flames clearly produced a sustainable 

fire, the smallest failed to do so, and the middle size initially created flames up to the top, 

however, the flames became intermittent and then dropped back to a much lower level. 

Experiments on other types of material are in progress. This research is being 

supported by the Building and Fire Research Laboratory of the National Institute of 

Standards and Technology under grant no. NANB8DO849. 
16 

Copper Side Shields 

Marinite Panel 

1' x 4' 

Sample 

Line Burner 

Radiant Panels 

Fig. 1: Experimental Setup 

2500 

150 

1- 

100 

50 

I I I I 1 1 

0 50 100 150 200 250 300 350 

Time (sec) 

Fig. 3 : Effect of Preheat on Flame Spread; 

Heat Flux, 5.4 kW/m2; Igniter, 18.5 kW/m 

200 I 1 I I I I 

150 

100 

50 

0 

0 io0 200 300 400 500 

Time (sec) 

Fig. 2 : Flame Spread Under Various Extemd 

Heat Fluxes; Igniter, 18.5 kW/m; No preheat 

. 0 

0 100 200 300 400 500 

Time (sec) 

Fig. 4 : Effect of Igniter Strength on Flame 

Spread;Heat Flux, 5.4 kW/m2; No preheat 
17 

TURBULENT, CONCURRENT, CEILING AND FLOOR FLAME SPREAD: 

THE EFFECTS OF BUOYANCY AND OXYGEN CONCENTRATION 

L. Zhou, Y.H. Chao and A.C. Fernandez-Pello 

Department of Mechanical Engineering 

University of California 

Berkeley,' CA 94720 

ABSTRACT 

Experiments have been conducted to study the effects of forced 

oxidizer flow velocity, grid-generated turbulence, and oxygen concen- tration on the flow assisted flame spread over a flat solid combusti- ble surface in a ceiling and floor configurations. The tests are 

conducted with thick PMMA sheets as combustible material, and mixtures 

of airlnitrogenloxygen as oxidizer. Flame spread rate, flame length, 

surface heat flux and products composition are measured for air flow 

velocities ranging from 0.25 to 4.5 m/sec, turbulence intensities from 

1% to 15%, and oxygen mass fractions from 0.19 to 0.4. These parame- ters address the major heat transfer and chemistry mechanisms that 

control the spread of the flame. Comparison of the ceiling and floor 

data provides information about the effect of buoyancy on horizontal 

flame spread. Most of the experiments at oxygen concentrations differ- ent than air are performed under vitiated conditions and in laminar 

flow, and a few characteristic cases at higher oxygen concentrations 

and in turbulent flow. The experiments are carried out in a small 

scale combustion wind tunnel specially designed to conduct flame 

spread experiments under well characterized oxidizer flow conditions. 

Although the scale of the wind tunnel is too small to be representa- tive of actual fire situations in buildings, it permits to perform 

careful parametric studies of the flame spread process, and from them 

to obtain fundamental information about the controlling mechanisms of 

flame spread. 

It is found that for all oxygen concentrations, and turbulence 

intensities the flame spread rate increases monotonically with the 

flow velocity, which is in agreement with flame spread models predic- tions and is due to the decrease in the flame stand off distance with 

the flow velocity. For air and ceiling spread, the flow turbulence 

tends to reduce the spread rate for flow velocities larger than 1 

m/sec and to enhance it at lower velocities. For floor spread turbu- lence always tends to decrease the spread rate. The effect of turbu- lence on the spread rate appears primarily through the flame length, 

which decreases as the turbulence intensity is increased. Analysis of 

the products composition indicates that this effect is due to an 

enhanced burning of the fuel with the turbulence intensity. These 

results are affected somewhat by buoyancy effects at low flow veloci- ties. The flow oxygen concentration affects strongly the flame spread 

rate, which increases with the oxygen concentration. The effect of 

the oxygen concentration appears both through the surface heat flux 

and the flame length. The surface heat flux increases with the oxygen 

concentration primarily because the flame temperature increases. 

However, the flame length decreases as the oxygen concentration is 

increased due to a more complete combustion of the vaporized fuel. 

These effects are more marked under vitiation conditions and low flow 
18 

velocities because the gas phase reaction is weaker. The flame length 

and the surface heat flux exhibit power law correlations with the fuel 

pyrolyzes length, and the flame spread rate data can be correlated 

with an expression deduced from a simplified heat transfer analysis of 

flame spread. 

The experimental results indicate that in ceiling spread, buoyan- cy has two main competing effects. One is the enhancement of the heat 

transfer from the flame to the solid surface due to the flame being 

pushed closer to the surface, and the other is the flame quenching by 

the closer cold wall and boundary layer stratification. For flow 

velocity larger than 1 m/sec, the enhanced heat transfer is found to 

be the dominant mechanism and results in a faster flame spread in the 

ceiling configuration than in the floor. For flows of smaller veloci- ties, the flame quenching effect becomes more important and the oppo- site result is observed. The species concentration data show that the 

combustion reaction is less complete in the ceiling than in the floor, 

and that significant amounts of CO and unburnt hydrocarbons are pro- duced in the ceiling flame spread. 

0 

Fig. 1. Comparison of flame 

spread rate over PMMA in the 

floor and ceiling geometries. 

0.06 I 1 

d 

8 

O.O4 t I 

A I 

50 100 1 so 200 250 500 

0.00 

0 

Fig.2 .Comparison of the 

exhaust gas composition 

in ceiling and floor flame 

spread. 

__ I___- 
19 

TRANSIENT LAMINAR WIND-AIDED FLAME SPREAD OVER VAPORIZING SOLIDS 

IN THE CEILING CONFIGURATION 

Sanjay Agrawal and Arvind Atreya 

Combustion Laboratory 

Department of Mechanical Engineering 

Michigan State University 

East Lansing, MI 48823 

(Supported by USDA and NSF) 

Wind-aided flame spreadis the most hazardous type of flame spread in building fires and has been 

the most difficult to understand and quantify. An improved understanding of wind-aided flame spread will 

result in better material hazard classification and greater fire safety. 

Our previous experimental investigation' has shown that during wind-aided flame spread, the solidphase undergoes transient pyrolysis while the gas-phase remains quasi-steady. Moreover, the flame length 

and the flame tip speed are controlled by unsteady pyrolysis of the solid in the buming zone and the rate 

of progress of the pyrolysis front is controlled by heat transfer from the flame and hot gases to the solid 

ahead of the pyrolysis front. Recent model!?3 have also predicted quantitatively the effects of transient 

pyrolysis on spread rates. 

Previous studieskg of wind-aided flame spread have primarily focussed on determining the length 

of the buming zone and have assumed the local pyrolysis rate to be steady. Thus, bypassing the analysis 

of the pyrolyzing zone. As a result, the pyrolysis front location and its speed, which primarily depends 

on the ease of ignition of the as-yet-unburned material, have been extensively analyzed. In all of these 

analyses the surface re-radiation and flame/soot radiation were neglected, and hence the three coordinate 

system in the preheat zone (x,y,t) could be reduced to two coordinate system (using similarity variables 

a, y/d F), thus forcing the pyrolysis front speed to be a constant. Our flame spread experiments have 

suggested that in some cases the pyrolysis front speed accelerates, decelerates or even becomes zero. The 

fust scenario can be attributed to flame radiation and the second to surface heat losses. Inclusion of these 

in the analysis will nmlt in loss of the similarity and the analysis then demands a numerical solution. 

Recently Agrawal and Atreya2 predicted realistic flame front location as a function of steady pyrolysis 

front speed and time. As far as authors know there has been no study in this particular configuration 

which predicts both pyrolysis front speed and flame front speed as a function time. This study is an 

attempt towards this. 

Due to transient pyrolysis, the fuel production is significantly smaller than its steady state value. 

Thus, the diffusion flame moves towards the solid surface because of stoichiometry. This is the primary 

reason for the flame in the ceiling configuration to lie close to the sample surface and reduces the adverse 

effect of buoyancy. In the floor or the vertical configurations, the produced fuel itself is buoyantly lifted 

making the flame lift upwards at lower velocities. This rendets ceiling as a prefemd configuration for 

experimentally studying transient wind-aided flame spread. Much lower flow velocities are required in 

the ceiling configuration than in the floor configuration to suppress buoyant instabilities. Thus, for same 

length of the combustion tunnel, lower flow velocities provide lower heat flux and more time to study the 

acceleration or deceleration behavior of the flame front. 

During the experiments in the ceiling configuration it was observed that for nearly all the cases 

tested, the flame lies very close to the sample surface (-3mm) for the entire flame length. More 

specifically, the flame stand-off distance is not only small compared to the thermal boundary layer but is 

also nearly constant. For constant pyrolyzing temperature and constant flame temperature, the streamwise 

temperature gradient between the flame and the sample is small. Since the gas velocity next to the sample 
20 

. ~.~.~.'.'.~.~.~.'.'.~.~.'.~.~ ...... .................... .................... 

....... 

-bsurface is small, the streamwise transport of energy between the flame and the sample is negligible. 

Hence, with little error the flame may be assumed to lie on the surface thus simplifying the gas-phase 

analysis considerably and letting the variables like transient behavior of the solid, suxface re-radiation, heat 

flux shielding due to blowing to be studied in a greater detail. 

Simple integral models of ga!? and solid-phas&'o are developed in the pyrolysis zone which leads 

into the determination of transient flame front location as a function of pyrolysis hnt location. It was 

found in Ref. [2] that blowing of fuel has substantial effect on total fuel production. In the present 

analysis local blowing correction is used which makes the net surface heat flux into the solid transient 

(since fuel blowing is transient), though the surface convective heat transfer is still steady. Also with the 

measured convective surface heat flux in the preheat zone Atreya and Mekki' could predict the pyrolysis 

front speed. In this paper we use the correlation for surface convective heat flu in the preheat zdne as 

suggested in Ref. [9] and use surface re-radiative loss and the steady gas-phase and transient solid-phase 

models of Agrawal and Atreya' to predict both the flame front location and pyrolysis front location as a 

function of time, free stream velocity, oxygen mass fraction, surface emissivity and external heat flux. 

Also the maximum sample length is predicted that a non-radiating flame can travel. Future considerations 

are to include simplified flame radiation in order to predict acceleratory spread rates and also analyze 

chaning solid in the same confQuration. 

REFERENCES 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

Mekki, IC, Atreya, A., Agrawal, S., and Wichman, I.: Twenty-Third Symposium (International) 

on Combustion, p.1701, The Combustion Institute (1990). 

Agrawal, S., and Atreya, A.: Twenty-Fourth Symposium (htetnati0nal)on Combustion, The 

Combustion Institute (1992), in press. 

Delichatsios, M.M., and Delichatsios, M.A.: Comb. Flame 89,5(1992). 

Femandez-Pello, A.C.: Comb. Flame 36, 63( 1979). 

Carrier, GI., Fendell, F.E., and Feldman, P.S.: Comb. Sci. Tech. 23,41(1980). 

Loh, H.T., and Femandez-Pello, A.C.: Twentieth Symposium (International) on Combustion, 

p.1575, The Combustion Institute (1985). 

Wichman, I.S., and Agrawal, S.: Comb. Flame 83, 127(1991). 

Carrier, G.F., Fendell, F.E., Butler, G., Cook, S., and Morton, C.: Comb. Sci. Tech. 72, 17(1990). 

Atreya, A,, and Mekki, K.: Twenty-Fourth Symposium (International) on Combustion, The 

Combustion Institute (1992), in press. 

Delichatsios, M.M., Mathews, M.K., and Delichatsios, M.A.: Fire Sqfery Science - Proceedings 

of the Third Internaiional Symposium, 207(1991). 
21 

Calculating Flame Spread on 

Horizontal and Vertical Surfaces 

Gama1 N. Ahmed', Mark A. Dietenberge? and Walter W. Jones 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

The flame spread model described in this paper is a new algorithm which provides the capability 

to calculate a self-consistent fire based only on bench scale fire data. This model simulates object fire 

growth and burnout of a slab in a room and produces acceptable predictions of the spread of fire, smoke 

and production of both toxic and nontoxic gases. Thus the simulation allows a fire to grow realistically, 

possibly making a hole in the material surface. The algorithm uses empirical data, gathered from 

standard test apparatae, including the Cone Calorimeter and the LIFT (lateral ignition flame spread test 

method). By basing the transient pyrolysis description on test methods, we avoid the practical 

difficulties associated with an explicit calculation of radiation blocking and material charring. The intent 

of the project was to develop an algorithm which could be utilized in a complete model of a fie in a 

building. The three-dimensional aspects of the flame spread model include: first, panels made of 

combustible materials with different thicknesses and at various orientations; second, flames of two basic 

types, pool fire and purely wall fire. The former has a flame spreading polygon on a horizontal panel. 

The latter is used either for inclined or vertical panels; third, a radiation heat exchange between objects, 

flames, and gases. 

The first release of the Fire Hazard Methodology in 1989 was a prototype. Its focus was to 

incorporate the research which had already been done at NIST and elsewhere into a relatively small 

reference guide, along with the computer software which implemented this work. An example of such 

an approach is the requirement for a specified fue. In essence, the data used for the fire specification 

comes from free-bum data obtained in a furniture calorimeter or similar device. The fire can be 

constrained by a lack of oxygen, but is not affected by radiative feedback. Since then, the Building and 

Fire Research Laboratory has directed much of its research into improving and enhancing this product. 

The FAST (fire and smoke transport) model' utilizes the distinct gas zones concept as a 

compromise between a network model and a finite difference model. The basic predictive equations are 

derived from the laws of conservation of the mass, momentum and energy. There are usually two zones, 

or control volumes, per compartment. The two zones are referred to as upper and lower respectively. 

Transfer can occur from zone to zone or compartment to compartment in a fire driven environment. 

These equations are written so that the actual physical phenomena which affect the environment are 

couched as source terms and appear on the right-hand side. The flame spread model (FSM) discussed 

Fire Research Engineer, Portland Cement Association (PCA), Skokie, Illinois 

Research Engineer, Forest Products Laboratory, Madison, Wisconsin. 
22 

in this paper is couched simply as another algorithm. Thus, the FSM provides source terms for the 

radiative heat transfer, plume mass rate and heat id mass release rates. The numerical solution of these 

equations has been shown to be both practical and sufficiently detailed. 

The flame spread model has been applied to simulate a burning panel of HO/FRPU (heavy Olefin 

foam material/fire retarded polyurethane) in a single compartment where the fire has been specified as 

one of the constrained fires. The simulated panels have different orientations (horizontal panel and 

vertical walls), different geometries with different thicknesses, and different fii positions in the room 

of fire origin (center of the room and along a wall of the room) with different ignition locations on the 

panels. In these applications, the effect of door open (width and height of the door of the room of fire 

origin) on the flame spread rate developed on the panel, the pyrolysis rate, and the upper hot gas layer 

depth has been demonstrated and analyzed. For full size wall, the simulated wall has slightly smaller 

width and height (3.8 x 2.9 m) than the width and height of the room (4.0 x 3.0 m) to avoid some 

difficulties in shape factor and heat exchange area calculations for the transfer of heat by radiation. 

The flame spread on a horizontal 1.0 m2 panel initially proceeded at a minimum rate and then 

accelerated toward the panel edges as a result of radiative heating from the fie plume and the growing 

upper gas layer. Once the flame spread contours completely cover the panel, the fue experienced its 

greatest growth rate as indicated by the heat and mass release rates. Eventually, the fire growth reaches 

a limit dictated either by the flame soot volume fraction reaching its maximum value for the given flame 

base radius or by the bumout of some surface elements. While the panel surface is burning, the flame 

spread contours begin to recede into the cushion thickness until the whole panel material is burned out. 

Vertical flame spread from a piloted ignition source moves up rapidly until it reaches the top of 

the wall, and then moves sideways at the top in an accelerated fashion due to radiative heating from the 

growing upper gas layer. The later deceleration of the flame spread is due to much lowered preheating 

of virgin elements below the upper gas layer. Changing the door opening has negligible effect on the 

predicted flame spread. However, the door opening has a pronounced effect on the upper gas layer - 

depth. The lower the top of the door or narrower the door opening is, the higher is the pyrolysis rate 

of the burning wall. The maximum depth of the hot gas layer approximately coincides with the peak 

in the pyrolysis release of the burning wall material. Varying door opening, both the hot gas layer depth 

and the pyrolysis rate of each case have reached their limiting values, which is an important modeling 

feature. 

1. Jones, W. W., A Multicompartment Model for the Spread of Fire, Smoke and Toxic 

Gases, Fire Safety Journal 9, 55 (1985). 
23 

For Presentation, at the Annual Conference on Fire Research 

October 13-16 1992 

CRITICAL CONDITIONS FOR FLAME SPREAD AND A RATIONAL 

FIRE HAZARD MATERIAL CLASSIFICATION METHOD 

Michael A. Delichatsios, Y. Chen and Mary M. Delichatsios 

The fire hazard of a material can be characterized by two parameters: a 

maximum flame spread length scale, % These 

parameters, defined below, include a!fso the effects of the transient pyrolysis 

history of a ma 

pyrolysis is Pntroduced, 

above, dc is a char conductance le8gth and 6, is a thermal length. 

and a total spread time T&. 

ial which for non- charring materials is determined by the 

. For($nrring materials a modified f ective heat of 

where "$7 defined 

ratio L/(CQAT ) t 77 

= AHv/( ( 1+X)dC/6,) 

The maximum flame spread length scale parameter was derived starting from 

the general equations for upward flame spread, using fundamental properties 

and parameters affecting upward fire spead, such as thermal properties of the 

materials, flame height correlations and flame heat flux measurements. From 

x AH 2 

(1) 

It 

A 

this analysis, . '1 

= 1.4 10-4 (qn,t 

. I1 11 

where qnet = qt - UT 4, xA is the combustion efficiency and q 

heat flux to the wal? from the flames and/or other sources. 

time, proportional to the pyrolysis time, depends (for thermally thick 

conditions) on the material thermal inertia, the pyrolysis temperature and the 

total heat flux from the flames and/or other sources to the wall, Le., 

is the total 

the total spread 

The maximum flame spread length scale has a physical interpretation, Le., 

it is the actual maximum flame spread height, for values of Em < 1.8 m, when 

the lame heat flux can be assumed approximately constant, equal to 25 

kW/m . For larger values of Lm, the radiative component of the flames 

increases substantially and the value of gm given by Eq. (1) no longer has 

physical meaning. But even for this case, it can be used, for a relative fire 

hazard classification of materials if one includes the change in total heat 

flux (see Fig. 2). Similarly, the total spread time, -ra, is the time required 

for the flames to reach a height equal to 90% of the maximum flame spread 

length. 

as long as grD has physical meaning, Le., for Em < 1.8 m. Figures 1 and 2 

show the maximum flame spread length scale, e,, and the total spread time, 

T~, from Eq . (1) and (2) for two values of total heat flux to the wall, 25 kW/m2 

and 40 kW/m . 

5 

Obviously, the total spread time, T~, has a physical interpretation 

2 The material properties were taken from the literature. 

As can be seen from these figures, the maximum flame spread length scale 

She can be a good predictor of the relative beh vior of upward fire spread of 

different materials in small fires (25 kW/m ) and in larger fires (40 kW/m >. 

For example, polyethylene (PE), PE/PVC cables, polystyrene (PS) are materials 

on which upward fire spread is not fast and fire only spreads up to heights of 

less than one meter if the only heat flux to the wall is the heat flux from 

2 
the flames (6; = 25 kW/m 2 ). For the same conditions, (Le. qf *" - < 25 kW/mz) 

particle board and rigid foam are non-spreading materials (a, < 20 cm), 

whereas PMMA, PVC and polypropylene (PP) are fast spreading materials. 

Figure 2 shows a similar relative behavior of upward fire spread of 

different materials in larger fires when the total heat flux to the wall 

material is 40 kW/m2. A larger fire could result from external heat fluxes, a 

large ignition source (larger than 1 m), geometric configuration (i.e., a 

corner) or a high value of a (a > 1.8 m) as in PMMA, PVC and Polypropylene 

(PP). As can be seen from ths Figure, the relative behavior of the different 

materials, i.e., relative magnitude of a,, concerning upward fire spread in 

large fires, is not necessarily the same as it is in small fires. For 

example, it is worthwhile to notice that polyethylene (PE) behaves as a slowspreading material in a small fire but as a fast spreading material (similar 

to PMMA) if the fire develops to a larger, more intense fire as a result of 

external heat fluxes and/or a large ignition source (larger than 1 m). 

REFERENCES 

1. Delichatsios, M.A., Delichatsios, M.M., Chen, Y, and Hasemi, Y., 

"Similarity Solutions and Applications to Turbulent Upward Flame Spread 

on Non-charring Materials", ASME Annual Meeting, Anaheim, CA, Nov. 1992. 

Delichatsios, M.A., Chen, Y., and Motevalli, V., "Flame Spread on 

Charring Materials: Numerical Prediction of Experimental Results ,(' 

presented at the Eastern Sect ion Meeting of the Combustion Institute, 

Cornel1 University, Fall 1991. 

2. 

HEAT FLUX 25 kW/m2 

10 4 

PMMA 

PE/WC 6 PS 

0 

. Pf POM 

RED OAK 8 0 

PMTCE BOARC 

'RIGID FOAM 0 

0 

0.1 -1 ' ' ""'I 10 1 00 1000 10000 ' ' '""'1 ' ' ' '.""1 ' ' ' '-"" 

r1, TOTAL FLAME SPREAD TIME (s) 

HEAT FLUX 40 kW/m2 

100 4 

U 

PE cp * * 

PMMA 

PS * wc * .. 

RED OAK * *PE/nc 

*. 

POM 

PARTICLE* BOARD 

* 

RIGID FOAM 

I ' """I ' ' '''#''I ' ' """I 

10 1 00 . lo00 1 

T~, TOTAL FLAME SPREAD TIME (s) 

Figures 1,2. Maximum Flame Spread Length Scale, em, and Total Spread Time, T~, 

CQr Differen3 Materials for tws Flame Heat Fluxes to the Wall: 

qf = 25 kW/m and qf = 40 kW/m , respectively. 
25 

Fire Resistant Polymer Grafts 

Marc R. Nyden and James E. Brown 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

and 

Barry Bauer 

Materials Science and Engineering Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

ABSTRACT 

Flammability is a major concern when polymeric materials are used in buildings, aircraft and 

ships. This realization has provided the impetus for research into the synthesis of new and more fire 

resistant polymers. 

Fiqure 1. The thermal degradation of linear polyethylene interacting with a 

surface (white tig-zag lines). Carbon atoms involved in cross-links are 

highlighted in white. 
26 

Research conducted at 

of plastics to char when they 

BFRL and MSEL has focused on finding ways to increase the tendency 

are burned. There is a stmng correlation between char yield and fire 

resistance. This follows because char is always fomed at the expense combustible gases and because it 

protects the underlying material fmm the heat generated in gas phase combustion. Factors which promote 

the formation of char have been identified in molecular dynamics simulations of degrading polymers. The 

scene depicted in Figure 1 is representative of what happens when linear polyethylene and related 

polymers bum. The chains fragment into fuel before a significant number of cross-links can form. An 

incipient char, such as the one depicted in Figure 2, however, was produd when hydrogens were 

removed from the model polymers at the onset of the simulations. In this way, cross-linking reactions 

are given a head-start so that they can effectively compete with fragmentation. The prediction that crosslinked polymers undergo fwther cross-linking when burned and eventually form high molecular weight, 

thermally stable chars has been confinned in Cone Calorimeter flammability measurements made on both 

y and 8 - irradiated polyethylene and on chemically cross-linked poly(methy1 methacrylate). 

Firgure 2. The thermal degradation of cross-linked polyethylene. 

The behavior exhibited by the - irradiated polyethylene when it was burned was particularly 

striking. The more highly cross-linked layer on the top of the sample, charred and foxmed a large bubble 

indicating retention of the gases generated in the degradation of the interior. Eventually, the bubble broke 

and the sample ignited; leaving behind a thin carbonaceous skin. This experiment suggests that it may 

be possible to achieve significant reductions in flammability by grafting fire resistant shells on to the 

surface of processed plastics. Experiments with new materials, synthesized by grafting vinylidene chloride 

and other fire resistant monomers, to the surface of polystyrene are underway. The effect of the thickness 

and chemical nature of the graft on the relative flammabilities of these composites will be examined. 
27 

ACOUSTIC EMISSION OF STRUCTURAL 

MATERIALS EXPOSED TO OPEN FLAMES 

William Grosshandler and Margaret Jackson 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

The objective of this experimental study is to assess the viability of using the acoustic signal emitted 

by a variety of structural materials exposed to nonuniform heating as an early indicator of a fire. Beams 

of aluminum, gypsum, plywood, poly-methylmethacrylate and poly-vinylchloride, simply supported 

across a 0.5 m span, were subjected to a 0.9 kW open flame. Sensors were mounted directly on the 

beams, 0.3 m fiom the center of the flame, to record high frequency acoustic emissions. The measured 

signals varied in power and in number with the material and thickness of the specimen. 

The acoustic emission (AE) from a bulk material is associated with an abrupt change in stress following 

a microscopic dislocation. The stress relief generates an elastic wave which radiates throughout the 

material at the speed of sound. The thermal energy released by the flame impinging on the beam, plus 

the combustion of the material itself, creates a temperature gradient, and leads to thermal stresses in 

the material. A piezoelectric transducer. located remotely from source can detect the elastic wave 

created by the stress relief just milliseconds after it occurs. The strength of the acoustic source depends 

upon the suddenness with which the stress is relieved. For an instantaneous release, the source acts a 

dipole whose strength increases directly with the thermal diffusivity, elastic constant, and thermal 

energy density, and inversely with the thermal conductivity. The number of AE events will increase 

with the number of defects or discontinuities in the material; hence, a composite material is likely to 

be more active than a pure substance. 

The samples varied between 3 and 18 mm in thickness. The heat flux was maintained approximately 

constant over a circular area about 50 mm in diameter, and the time of exposure to the flame was 

adjusted between one and six minutes, depending on the temperature rise in the material, to prevent the 

AE sensors from overheating. The maximum temperature measured 0.1 m from the flame was 106 OC 

in the 2 mm thick aluminum sample, compared to only 36 "C for the 12 mm gypsum board at the same 

location. In the latter case, the increase in temperature over the ambient was 0.8 OC at the location of 

the AE sensors, 0.30 m removed from the flame. 

An acoustic emission event can be described by its rise time, amplitude, frequency, duration, and 

energy. The main distinguishing feature among the materials investigated was the event duration, which 

averaged just under a millisecond for the 12 mm thick aluminum beam and 0.15 ms for the gypsum 

board, the difference being attributable to the internal damping properties of the two materials. 

The number of AE events in a minute and the accumulated energy release during the hating cycle 

provide a good measure of the overheated state of some structural materials. The 12 mm thick plywood 

was particularly susceptible to acoustic emission, with about 43 eventdminute being recorded. The 

gypsum board produced 16 events/minute and the 12 mm aluminum just 0.5 events/minute. The 

thinnest aluminum plate did not respond above the background level (0.3 eventslminute) even though 

it reached the highest temperature. 
28 

The differences in cumulative energy were even more striking, with the plywood being four times more 

energetic than the gypsum board even though the heating period for the wood was half as long, and 30 

times more energetic than the aluminum. 

The major conclusions to come out of this study can be summarized as follows: 

1. Some common structural materials emit high frequency acoustic signals when exposed to a 

modest flame. 

2. Composite materials exhibit much higher AE activity than homogeneous materials. 

3. The use of AE transducers as early sensors of hidden structural fires remains a viable 

concept. 

4. Critical issues remain to be investigated if this technique is to be usefid for fire detection; 

eg., false signal discrimination must be verified, the maximum practical area covered per sensor 

must be determined, and durability and reliability must be examined. 
29 

MACHINE VISION FIRE DETECTION 

Douglas B. Schwartz 

Air Force Civil Engineering Support Agency 

Tyndall Air Force Base, Florida 

A new type of fire detector under development "sees" a fire visually and makes a 

reliable decision based on known visual characteristics of flames. The Machine Vision 

Fire Detection System, currently in the engineering prototype stage, has already 

demonstrated extremely high accuracy in discriminating actual fnes from false alarm 

sources, promising virtually 100% reliability at very high speed and reasonable cost. By 

dramatically reducing the false alarm rate, this technology promises to save the Air Force 

alone over $3 million per year in elimination of unnecessary releases of firefighting agent, 

while enabling improved fire protection of critical Air Force assets. 

Current technology fire detectors sense smoke, heat, or electromagnetic energy such 

as ultraviolet (vv> or infrared (IR) emissions. The latter type, optical fire detectors 

(OFDs) are used when fast, remote sensing is required. These sense electromagnetic 

emissions in particular bands emitted by hydrocarbon fires, specifically the 0.18-0.24 

micron band for UV and the 4.4 micron C02 band for IR. The disadvantage of this is that 

any emitter at these frequencies will give an indication of a fire. Ultraviolet detectors, for 

example, are commonly set off by reflected sunlight and arc welding. Infrared detectors 

can be set off by hot exhaust manifolds on aircraft ground equipment, propane torches, 

and other heat sources. Reliability of these detectors has been improved by multispectral 

detectors, including UV and IR and dual IR. 

Certain fbndamental limitations remain, though. Optical fme detectors trade off 

speed for accuracy; the faster the system is set to detect a fire, the higher the false alarm 

rate. Typically, optical detectors are slowed to 3-30 seconds detection speed from a 

theoretical speed of less than 1/100 second. OFDs cannot judge the magnitude of a fire; a 

small fire close up emits the same energy to the detector as a large fire hrther away. 

Because of the inverse square law, maximum reliable range of OFDs is about 120 feet, a 

serious limitation in large spaces such as warehouses. 

Machine vision fire detection seeks to overcome these limitations by characterizing 

the fire in the visible spectrum, using similar criteria that humans use to tell fires from 

non-fires. Detection begins with a solid-state video camera, which uses a CCD 

(charged-coupled device) to convert light into electronic information. The CCD is a square 

silicon chip, typically made up of 512 picture element, or pixels, on a side. Each pixel 

transmits the intensity of red, green, and blue light in a digital signal, which is 

transmitted into computer memory in a sequential scan. 

The image is first checked for bright areas (intensity above a certain threshold). 

These areas are then "boxed and checked for color within red, green, and blue 

parameters. The image is then compared to the next frame, taken 1/30 of a second later. 
30 

This will reveal changes in color from 

frame to frame, behavior of the.edge of 

the object, and growth rate. Actual fires 

exhibit rapid color changes from fjrame 

to fiame, have highly variable edges, 

and tend to grow outward from a 

starting point. 

Size of the fire is computed by 

counting the "fire" pixels. For a fEed 

installation, the system will be 

calibrated at installation to relate 

position within its field of view to a 

Fire Decision Criteria 

particular size. Thereafter, the pixels across the base of the fwe can be summed and size 

computed from the number of pixels fkom the lower edge of the field of view. Portable or 

mobile installations will use two cameras on a known baseline for range estimation. 

Since actual size and growth rate are known, the relative threat of the fire can be 

determined, allowing a flexible response. For example, the machine vision detector might 

be linked to an automatic suppression system capable of dispensing tens of thousands of 

pounds of fmefighting foam onto a hangar floor. This massive response would be overkill 

against a small, steady-state event such as a oil rag fire. In this case, an alarm would be 

sounded to alert personnel, who could suppress the fire with hand extinguishers. If the 

fire exceeded a certain size, or if growth rate became high, the suppression system would 

be activated. 

ENGINEERING PROTOTVPE II 

Whine Vision Hardware 

Hardware components of 

the system, including the video - 

camera, image processing 

hardware, and microprocessor, 

are all available "off the shelf." 

This drives down cost and risk. 

Current cost of the components 

is about $2500 and is expected 

to drop. Time to make the 

fme/no fire decision is 1/10 

second; ifnecessq, this can be 

reduced tenfold through use of 

a faster processor. 

The machine vision fire 

detector is currently in 

prototype stage and has undergone periodic field tests against actual fires and false alarm 

sources. At the end of 1992, fd prototypes will undergo full scale validation. The 

system is expected to be incorporated into a major Air Force upgrade of hangar fire 

protection systems. The technology will also be applied to development of portable fue 

detection and suppression systems and on-board aircraft fire protection. 
31 

DETECTION OF UNDERGROUND MINE FIRES 

By Ronald S. Conti 

U.S. Department of the Interior, Bureau of Mines, Pittsburgh Research Center 

P.O. Box 18070, Cochrans Mill Road, Pittsburgh, Pennsylvania 15236 

ABSTRACT 

An underground mine fire not only is a serious threat to life and property, 

but also results in economic losses such as injuries, mining equipment, coal 

reserves and production, and jobs. fires were reported to the Mine Safety and Health Administration (MSHA) (I). These 

fires caused 29 fatalities, numerous injuries, the sealing of several mines, and 

financial losses totaling tens of millions of dollars. During the incipient stage 

of a fire, smoke and gaseous products including CO are produced and released into 

the mine atmosphere. If not detected in the early stages of combustion, these fires 

can spread rapidly and are both difficult and dangerous to extinguish. Also, if 

they are not contained in the early stages, portions of a mine or the entire mine 

must often be sealed for long periods. This U.S. Bureau of Mines study describes the results of research conducted in 

the Experimental Mine at Lake Lynn Laboratory (2) on the response of fire-sensors to 

simulated mine fires, which include: a slowly-developing coal/conveyor belt fire, a 

rapidly burning liquid-fuel belt fire, and a liquid-fuel belt fire in the presence 

of diesel exhaust. The fire detection studies (3) to be discussed were conducted in 

A- drift. A detailed layout of a typical underground fire and detection scenario is 

shown in the perspective view in figure 1. During the experiments the airflow of 

the mine is reversed, so that the combustion products are exhausted through the main 

fan. The moveable bulkhead door in D-drift is closed and the bulkhead door in E- drift is in an open position. 

cuts of B and C-drifts. The airflows can be adjusted with one of the four positions 

of the main fan and a 0.61 m butterfly valve located in the bulkhead door of Ddrift. The airflow is monitored with a vane-type anemometer 15.2 m inby the fire 

zone . 

entry. Two pump operated, electrochemical CO sensors (see figure 1, detail I) are 

mounted 15.2 m inby the fire zone in the middle of the entry. One CO sensor is 

mounted near the roof and is labeled CO-50-Roof. The other CO sensor is mounted 

directly below, 0.66 m from the floor and is labeled CO-50-Mid. 

aluminum thermocouple is placed at the roof 0.3 m inby the fire zone and a 

continuous length of a thermal line-type fire detector (heat sensitive cable) is 

mounted at the roof from the portal of A-drift and extends 30.5 rn past the fire 

zone. A line-type fire detector is a twisted pair of insulated wires that short 

circuit when exposed to temperatures in excess of 68O C (155O F). 

Five fire sensors were mounted as shown in detail I1 of figure 1, in the entry 

cross-section at a point 274 meters (900 ft) inby the fire zone. Three diffusion- type electrochemical CO sensors are used. Two are mounted at the roof, labeled CO- Roof and CO-Roof-B, and represent two brands of CO sensors. The other CO sensor is 

mounted 0.66 m from the floor on the rib, identified as CO-Rib, and is of the same 

brand as the CO-Roof sensor. A commercially-available ionization-type smoke sensor, 

labeled smoke, was mounted on the rib, with the intake sampling point located beside 

the CO-Roof-8 sensor at the 274 m location. 

detector (4), labeled DDD, was mounted beside the intake sampling point of the Smoke 

and CO-Roof-B sensors at the 274 m location. 

calibrated before each tests. 

From 1983 to 1988, 86 underground coal mine 

Temporary stoppings are installed at the last crossProducts of combustion detectors were used at two positions along the mine 

Two thermal -contact detectors were 1 ocated near the fire source. A chrorni umA prototype diesel discriminating 

Carbon monoxide and smoke sensors are 
32 

During these tests, sever'al mine fire sensors were evaluated with respect to 

sensor placement, spacing, and type. The data indicate that smoke sensors wil.1' 

alarm several minutes before carbon monoxide (CO) sensors; and that, in the presence of diesel exhaust, a prototype diesel -discriminating smoke sensor can successfully function without being sensitive to the diesel contaminants. The vertical placement 

of sensors in the entry near the fire was also shown to be critical in terms of 

alarm times. Additional data showed that variations exist in response time and 

level of response for two types of electrochemical carbon monoxide sensors. Results 

also indicate that early detection of fires will improve the probability of miners' 

escape because of reduced smoke concentrations during the incipient stages of the 

fire. 

Entries, 1970-1988. MSHA Rep. 09-323-90, 1990, 25 pp. . 

Physical Description, and Capability. BuMines IC 8911, 1983, 40 pp. 

Evaluation. BuMines RI 9412, 1992, 13 pp. 

Developments in Metal and Nonmetal Mine Fire Protection. BuMines IC 9206, 1988, pp. 

*** REFERENCES 

1. Luzik, S. 3. and L. A. Desautels. Coal Mine Fires Involving Track and Belt 

2. Mattes, R. H., A. Bacho and L. V. Wade. Lake Lynn Laboratory: Construction, 

3. Conti, R. S. and C. D. Litton. Response of Underground Fire Sensors:An 

4. Litton, C. 0. Diesel-Discriminating Fire Sensor. Paper in the Recent 

28-32 . DETAIL I 

Figure 1 .--Perspective view of underground fire detection scenario in A-drift. Exploded views of 

sensor $lacement with respect to fires are shown in detail I and 11. 
33 

FLOW THROUGH HORIZONTAL VENTS IN 

ENCLOSURE FIRES 

Y. Jduria and Q. Tan 

Department of Mechanical and Aerospace Engineering 

Rutgers University, New Brunswicls, NJ 08903 

Introduction 

Buoyancy induced flows in enclosures, with respect to the transport induced by fires in rooms and other compartments, have received a considerable amount of attention in the literature. However, not much work has been done 

on the flow through openings or vents such as those between connecting rooms in buildings and between quarters in 

ships. The work done on the flow through horizontal vents, such as the one shown in Fig. 1, is very limited. The flow 

rate can be estimated, as done for vertical vents, by using Bernoulli’s equation (Emmons,1988 and Hinkley,1986). 

However, this model breaks down, over certain ranges of the pressure and density differences, for problems where 

both density and pressure differences exist across the vent (Cooper, 1989). 

Some experimental work has been done on the buoyancy driven flow through horizontal vents, particularly for 

the special circumstance of pressure difference across the vent Ap=O (Epstein,l988). Mercer and Thompson(l975) 

studied the flow between two fluid regions connected by an inclined circular pipe. Conditions for purging of the 

density induced flow were investigated. A total purging or flooding implies a unidirectional flow through the vent 

from one region to the other. 

The standard vent-flow model, based on Bernoulli’s equation, assumes unidirectional flow and breaks down if 

a bi-directional flow exchange occurs under the combined effects of buoyancy and pressure. This model predicts 

zero flow when Ap=O. The volume flow rate Qu at the vent into the upper region from the lower region is taken 

as uniform and given by the model as Qu = C~Avdm, where CD is the flow discharge coeacient, Av is 

the vent area of cross-section and pt is the density of the fluid in the lower region( Heskestad and Spaulding, 1989). 

Similarly, if the pressure difference is reversed, the flow QD is obtained. However, there is a flow across the vent due 

to the density difference Ap, even if the pressure difference Ap is zero, due to the fluid in the upper region being 

heavier than that in the lower region. Cooper (1989) has developed an analytical model, employing an exchange-flow 

component and has determined the steady-state rate-of-burning in a ceiling-vented room, such as the one sketched 

in Fig.1. 

Experimental Arrangement and Results 

This paper is directed at the flow through horizontal vents for nonzero pressure and density differences across 

the opening. An experimental system based on a fresh-water/salt-water flow arrangement is employed. The density 

difference ratio Ap/F is vasied from 0.0 to about 0.2, in order to cover the range encountered in typical ventedcompartment fires. The salinity is mecsured by means of a hydrometer. The pressure difference Ap across the vent 

of diameter D is obtained by keeping the upper region open to the atmosphere and pressurizing the bottom region. 

The volume flow rate across the vent is obtained by measuring the dilution of the brine solution contained in the 

upper region and the net flow rate Qo, as discussed by Tan and Jaluria( 1992). 

Several interesting and important results have been obtained. Using a shadowgraph for flow visualization, a 

bidirectional flow was found to arise across the vent at Ap=O, with denser fluid descending in the central portion 

of the opening and lighter fluid rising in the outer portion. As the opposing pressure difference Ap was increased, 

this downward flow was found to decrease, ultimately giving rise to a unidirectional upward flow. This purging, or 

flooding, pressure difference Ape is of order (gApL) for a vent of height L, g being the gravitational acceleration. 

Some typical results on the flooding pressure difference Apc are shown in Fig. 2. The measured values are in the 

range that may be derived on the basis of scale analysis. The results were found to be repeatable, within a few 

percent, of the measured values. However, the transition from bidirectional to unidirectional flow was found to be 

fairly gradual, indicating the downflow QD to gradually reduce to zero as the pressure difference Ap is increased. 

With increasing values of (gApD), at a given L/D, the purging pressure difference Apc was found to increase, as 

expected. 

The net upward flow rate Qo was also measured and the other flow rates Qu and QD determined from the 

measurements of density and overflowing fluid in the upper region. Figure 3 shows some of the characteristic results 

obtained. At zero Ap, the upward and downward flow rates are equal, yielding a zero net upward flow. As the 

pressure difference increases, the flow rate Qo increases, with the effect of the density difference Ap diminishing as 
34 

Ap becomes large. Also, at very low pressure differences, the density difference effects dominate the flow across the 

vent. Thus, clearly the basic trends indicated by Cooper (1989) axe obtained. 

The results may also be given in terms of a flow discharge coeflicient CD, as defined earlier. This discharge 

coefficient is around 0.61 for an orifice (Emmons, 1988), if buoyancy effects are neglected. However, as seen in this 

work, the flow rates decrease if the opposing buoyancy effects are increased. Therefore, the discharge coefficient may 

be correlated in terms of the buoyancy parameter B and L/D, where B = (gApD) /Ap. A correlation obtained from 

the data over the parametric ranges considered is of the fonn: 

CD = 0.61 + 0.07974Ba(L/D)b 

where the constants a and b were obtained as -0.2246 and 0.0278, respectively. As B approaches eero, the value of 

CD approaches 0.61. Also, the flow rate decreases as B incr-. This result applies 88 long as the buoyancy effect 

is not predominant, or the pressure difference is not dose to zero, Le., B .-) 00. For that case, the earlier results at 

Ap=O may be employed. 

Acknowlegments 

The authors acknGwledge the financial support provided by the National Institute of Standards and Technology, 

under Grant No. 60NANB7D0743, for this work and the several discussions with Dr. Leonard Y. Cooper on this 

problem. The help of Mr.R.Chiruvella in preparation of this manuscript and in obtaining some of the correlating 

equations is also acknowledged. 

References 

Cooper, L.Y., 1989,"Calculation of the Flow Through a Horizontal Ceiling/Floor Vent", NIST Tech. Report, 

Emmom, H., 1988,"Vent Flows", SFPE Handbook of Fire Protection Engg., Soc. Fire Protection Engg., Boeton, 

Epstein, M., 1988,"Buoyancy-Driven Exchange Flow Through Small Openings in Horizontal Partitions", J. Heat 

Heskestad, G. and Spaulding, R.D., 1989,"mow of Air Required at Wall and Ceiling Apertures to Prevent 

Hinkley, P.L., 1986,"The effect of Vents on the Opening of the First Sprinklers", Fire Safety J1, Vol.ll, pp.211-225. 

Mercer, A. and Thompson, H., 1975, "An Experimental Investigation of Some Furthex Aspects of the BuoyancyDriven Exchange Flow Beheen Carbon Dioxide and Ak Following a Depressurization Accident in a Magnox Reactor, 

Part 2: The Purging Flow Requirements in Inclined Ducts",J. Brit. Nucletzr Enqy Soc., Vo1.14, pp.335-340. 

Tan,Q. and Jaluria,Y., 1992, "Flow through a horizontal vent in an enclosure fie", 28th Nat. Heat Trans. Cod, 

August 1992,SanDiego,CA. to be presented. 

Rep. No. NISTIR-894052. Also, Ann. Con$ Pi= Res., Gaithersburg, MD (1990). 

Sec. 1, Ch.8. 

Irl).rmsfer, V01.110,~~.885-893 . 

Escape of Fire Smoke", Tech. Rep., Factory Mutual Res., Norwood, M-A. 

Fig. 1. r"7 

:, 

1 ,,,,,,,;ET,, . i/l 

,. . . j 

(L 

'1 

Fig. 1. Sketch of the fie in a room with 

Fig. 2. Measured purging pressure aerence 

Ape as a function of the buoyancy de&. 

Fig. 3. Measured Volume flow rates for 

varying Ap at L/D=0.25. 

ceiling vent. 

-__-I_ . . ..I-. --- 
35 

Experimental Study of the Exchange Flow Through a Horizontal Ceiling Vent in Atrium Fires 

Tokiyoshi YAMADA . and Leonard Y COOPER 

Fire Research Institute 

Mitaka, Tokyo, JAPAN 

National Institute of Standards and Technology 

U.S. Department of Commerce 

Gaithersburg MD, USA 

Fire Defense Agency, Ministry of Home Affairs 

Introduction. The object of this work is to study experimentally flow rates through a horizontal top vent in an atrium-type 

compartment with a fire and under relatively low cross-vent pressure differences. The results will be used to develop a 

comprehensive atrium fire model. From the point of designing atria for life safety (e.g., insuring safe evacuation from all 

threatened spaces) reliable estimates of the flow through top vents are important. For example, outward smoke movement 

generally leads to reduction of smoke layer temperature and thickness and inward flow of cool outside air enhances potentially 

hazardous mixing of the smoke through the entire atrium space. 

The physical phenomena have been studied by Epstein(l,2] and Jaluria[3] with salt-water experiments. Also, limited experimental 

work with hot/cool gas exchanges were carried out by Tu [4] who used a ethyl alcohol burner heat source. Based on Epstein’s 

experimental result, Cooper [5,6] has been developing a submodel for this kind of phenomena suitable for use in two-layer zonetype fire models. However, available data to verify and advance this kind of submodel are not adequate. The present 

experiments are designed to acquire required data and insights on the exchange flow process. This effort, which uses a reduced 

scale model with a gas burner, is similar to the liquid-fuel burner experiments of Tu [4]. 

Reduced-Scale Experiments. Reduced Scale tests were conducted to study the exchange flow rate through circular, horizontal, 

top-centered vents (diameters, 0.3 m, 0.2 m, and 0.1 m). A cubic test compartment (0.8 m side) was constructed of 0.05 m 

(0.0125 m at ceiling) thick ceramic fibre board. Fig. 1 is a sketch of the test apparatus. A 0.15 m diameter natural gas (1 1,000 

Kcal/Nm3) burner was located flush with the floor and at the center of the enclosure. Heat release rate (0.8 - 5.6 Kw) was 

controlled by a mass flow controller. Inside the test compartment was a thermocouple tree (type K with 0.127 mm beads) with 

17 measuring points to measure gas temperature versus height. Using a vertical sliding probe, 0, volume concentration was 

measured at 0.01 m, 0.40 m and 0.79m above the floor, For future experiments, the test fixture was designed with a capabillty 

for specified uniform-flux air ventilation at the floor surface. Similar preliminary tests were carried out in a smaller test 

compartment (0.43 m sides, the same size as was used in [4]) and burner (0.1 m diameter), but without any ventilation capability. 

To allow for visual observation within the compartment, both the large and small test fixtures (referred to below as large and small 

scale) were outfitted with a floor-to-ceiling glass strip in the center of one wall. During some tests, flow visualization was carried 

out with the use of smoke generating pellets placed outside the compartment and near the vent opening. 

Estimation of Flow Rate. Direct measurement of the bi-directional flow through the vent is not possible. In this experiment, 

the exchange flow rate was estimated by using the oxygen consumption method. We suppose that heat release rate calculated 

from mass burning rate is nearly equal to the estimated energy release rate obtained by oxygen consumption method. 

Neglecting the volumetric flow rate of the fuel compared to that of the vent inlet flow, vmb, and for steady state this leads to 

where p is 0, mass fraction, H is specific energy (13.1 

MJ/kgO2), Q, is the fire’s heat release rate, the subscripts amb 

and bot refer to conditions above and below the vent, respectively, or to the vent flows issuing from outside (ambient) to 

inside or from inside to outside the test fixture, respectively. 

Normalized Exchancre Flow Rate and Openinn Aspect Ratio. 

Define the dimensionless exchange flow rate, V’, 

v v* = 

@%A PIP 

where D is vent diameter, g is acceleration of gravity, p is 

density, = bmb+pbt)/2 and Ap = bamb-pbt). Experiments 

of [l] in a top-vented compartment with geometry similar to 

ours resulted in an equation correlating v&,b vs UD, where L 

is vent depth. The correlation is plotted in Fig. 2. For relatively 

small-UD, \;lZrnb is 0.055. For experiments with incompressible 

fluids (e.g., fresh-water/saMater), \ift! = vgot and the crossvent pressure difference is zero. As indicated by the second of 

Eq. (1)1 this is not generally true for steady heated-air experiments. Fig. 1 Sketch of experiment; dimensions in mm 
36 

Included in Fig. 2 are data from [l], [3], and [4]. The present 

data are listed in Table 1. The large scale data were at steady 

state, at least 2 hours after ignition. The small scale data were 

at quasi-steady-state, about 1/2 hour after increases in fuel flow 

-- lawrbu- -. 

, 

rate. The data, reduced using Eq. (l), are included in Fig. 2. 

In the latter data reduction the phot of Eq. (1) was estimated by 

the measured near-ceiling 0, volume fraction ratio, in the case 

of large scale, and by the average floor-to-ceiling 0, volume 

surements. Data is included in the table only for those tests 

Rdrmorr 

x -m,y W.rn,K Mm 

fraction ratio, in the case of small scale. In both cases, phot was 

estimated from near-ceiling time-averaged temperature meawhere 0, concentrations near the ceiling were less that 0.19. 

This insured estimates of (l-p&pamd in Eq. (1) with expected 

errors of less than 25 percent. 

Discussion. The small-scale data and the data of [4] compare 

reasonably well with the correlation of [l]. Some discrepancies 

with data from incompressible fluid experiments are to be 

expected because of the effects of large cross-vent density 

differences and non-zero cross-vent pressures. It is important 

to take these effects into account in a mathematical model of 

the exchange flow phenomena. 

The large-scale data do not correlate well with the small-scale 

data. One possible explanation for this, which has not yet been 

confirmed, is that leakage through the joints of the large focture 

plays a significant role in the present, relatively-small, crossvent pressure experiments. Leakage effects could be significant in the large scale fixture and not in the small scale 

fixture because of 1) its potentially-leaky floor-ventilation design 

feature, 2) its larger surface area, and 3) the larger crosswall/floor pressure differences (i.e., at comparable inside 

temperatures). This will be investigated prior to future tests. 

In the tests with the 0.1 m vent the burner flame always 

exhibited extended, laminar-like behavior. This was different 

from all other tests where the flame and its plume exhibited 

turbulent-like behavior. The former laminar characteristic of the 

flow persisted even near the elevation of the vent itself. 

Therefore, it is no surprise that in Fig. 2 these data do not 

correlate well with the Epstein data, which involved turbulentlike flows near the vent. (For practical interest, the objective of 

the present study is to understand the exchange flow through 

"real" vents under expected turbulent flow conditions). The 

0.1 m 'blocked flame experiments involved tests where the 

axis of the laminar flame was blocked with a small metal plate, 

0.1 L /D 0.01 

Fig. 2 Plots of Vi,, vs L,/D 

I I I 

Q.1 w*- Fka-to-Qulry 

.2 

10 0.1 1 0.66 13 185 

17.8 

17.6 

17.1 

O!! 0.66 5 2l5 17A 

1.1 375 14.5 

G L. 11 ! om 

W 1 13 1s 

292 

__ __. - - -.- 

0.88 530 15.2 

0.2 0.88 5 142 

- 192--- 

1.1 180 19.1 

13 506 18.6 

15 285 182 

Table 1. Data from the present experiments 

close to the burner surface, in an attempt to stimulate turbulent-like behavior in the plume near the vent elevation. This was 

partially successful. By simply blocking the flame, there was a significant change in the estimated vent flow conditions; the 

"blocked' data are definitely closer to the Yurbulent-flow" correlation. 

References 

1. 

2. 

3. 

4. 

5. 

6. 

Epstein, M., "Buoyancy-Driven Exchange Flow Through Small Openings in Horiiontal Partitions", J. of Heat Transfer, 

Vol.110, Nov. 1988. 

Epstein, M. and MAKenton, "Combined Natural Convection and Forced Flow Through Small Openings in a Horizontal 

Partition, With Special Reference to Flows in Multicompartment Enclosures", J. of Heat Transfer, Vol. 11 I, Nov. 1989. 

Tang, Q. and Jaluria, Y "Flow Through a Horizontal Vent in Compartment An Enclosure Fire", to appear in to Proceedings of the 1992 ASME/AIChE National Heat Transfer Conference, San Diego. 

Tu, ICM., "An Experimental Study of Top Vented Compartment Fires", NlSTiR 4499, Feb. 1991. 

Cooper, LY, "Calculation of the Flow Through a Horizontal Ceiling/Floor Vent", NlSTlR 4052, March 1989. 

Cooper, LY, "An Algorithm and Associated Computer Subroutine for Calculating Flow Through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment Fire Model.", NlSTlR 4402, Oct. 1990. 
37 

1992 ANNUAL CONFERENCE ON FIRE RESEARCH 

A Model of Combustion and Convection 

in Enclosures of Complex Geometry 

Kevin B. McGrattan, Ronald G. Rehm and Howard R. Baum 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

We present a model describing diffusion-controlled combustion and convection in 2D enclosures 

of general polygonal shape at high Reynolds numbers. The model is intended to simulate the 

transport processes associated with the movement of smoke and hot gases in a fire. The combustion 

model can be described as follows. Lagrangian particles representing the fuel are introduced into 

the flow at the prescribed location of the fire. Each particle is active, acting as a heat source which 

induces buoyant convection. The trajectory of each particle is determined as part of the solution 

of the large scale convection problem. This is the high Reynolds number limit of any diffusioncontrolled combustion originating on the surface of discrete fuel parcels. The particles may .also 

serve as a visualization aid, allowing one to view the evolution of the flow field in time by following 

the trajectories of the particles, color-coded to indicate the temperature of the fluid. 

The hydrodynamics are based on the time-dependent Navier-Stokes equations in the Boussinesq 

limit [l]. Viscous dissipation and thermal conduction are included in the model, but no turbulence 

model or other empirical parameters are introduced. In the two-dimensional case, we rely on 

the high resolution of the computational mesh to achieve Reynolds numbers on the order of IO5, 

which correspond to full-scale in small room fire scenarios. To accommodate the irregular shape 

of the enclosures, the physical domain is mapped conformally onto a rectangle with the numerical 

Schwarz-Christoffel mapping package SCPACK. The transformed equations are then solved by 

finite-difference techniques [2]. Typical computations are performed on grids ranging from a quarter 

to half a million grid cells, permitting Reynolds numbers of the size described above. This approach 

allows us to consider room fire phenomena in realistic geometries, including the flow out of a window, 

combustion in a corridor with a door, and the flow generated in a representative segment of a 

building. 

Here a light fluid 

representing smoke and hot gases inside the small enclosure mixes with a heavier fluid representing 

fresh air outside. The Reynolds number for the computation is 40,000, the grid size is 1024 x 256. 

No-slip, adiabatic boundary conditions have been imposed at the walls. Computations similar to 

the one presented here have been compared with salt water experiments performed at the University 

of California at Berkeley by Charles M. Fleischmann, Patrick J. Pagni and R. Brady Williamson in 

conjunction with their investigation of backdrafts. 

The Lagrangian representation of the fuel elements will allow the incorporation of realistic subgrid combustion phenomena using models of the type described in Ref. [3]. Work is underway to 

remove the Boussinesq approximation and to incorporate radiative heat transfer into the model. 

The result of a typical computation is displayed on the following page. 
38 

References 

[l] Rehm, R.G., H.R. Baum, D.W. Lozier, H.C. Tang and J.S. Sims, “Buoyant Convection in ail 

Inclined Enclosure”, Fire Safety Science- Proceedings of the Third Internationul Symposium, 

Elsevier, London, pp. 313-323, 1991. 

[2] McGrattan, K.B., R.G. Rehm, H.C. Tang and H.R. Baum, “A Boussiaesq Algorithm for Buoyant Convection in Polygonal Domains”, NIST Internal Report, NISTIR 4831, April 1992. 

[3] Baum, H.R., R.G. Rehm and J.P. Gore, “Transient Combustion in a Turbulent Eddy”, TwentyThird Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, 

pp. 715-722, 1990. 

ugh a window. 

latic boundary conditions have been imposed. 
39 

MODELING BACKDRAFT PHENOMENA 

by 

C. M. Fleischmann, P. J. Pagni 

and R. B. Williamson 

University of California 

Berkeley, CA 94720 

Fires can produce more products of pyrolysis than the locally 

available oxygen can consume. If the fire compartment is well- ventilated, these excess pyrolyzates fuel long flames w ich extend 

out the compartment opening rapidly spreading the fire.' If the 

compartment is closed, the excess pyrolyzates accumulate, ready to 

burn when a vent is opened, e.g., by a window breaking due to the 

fire-induced thermal stress2 or by a firefighter entering the 

compartment. The ensuing deflagration moving through the 

compartment consuming the accumulated excess pyrolyzates after 

venting is called a backdraft. 

Consider a fire in a closed compartment where the only 

ventilation is provided by leakage. 

of combustion products descends around the fire causing some 

pyrolysis products to remain unburned. These products accumulate 

forming a deep, fuel-rich layer. Suddenly a vent is opened. The 

hot, vitiated atmosphere within the compartment flows out of the 

upper portion of the vent. Simultaneously, cold, fresh air flows 

into the lower portion of the vent. A mixed layer forms due to the 

instabilities at the shear interface between the outflow and the 

inflow. 

is ignited when it reaches a flame or glowing ember. After 

ignition, a rapidly propagating turbulent flame propagates back 

through the mixed layer. The resulting turbulent deflagration 

within the compartment drives the remaining accumulated excess 

pyrolyzates out the vent to be burned outside the compartment. 

A hot layer composed largely 

Much of this mixed layer is within the flammable range and 

The gravity current3 which enters the compartment is an 

important parameter in understanding backdrafts. 

current is responsible for the time delay between the compartment 

opening and the ignition of the deflagration. 

causes fire fighters to become trapped when a backdraft occurs. 

Salt water experiments were conducted to quantify the height and 

travel time of the gravity currents. 

configurations over a range of density differences, O.Ol*to 0.10, 

wpre useg. Over this density range the Froude Number, V = 

U /(g*h)5, where g' is g multiplied by lhe density difference, was 

constant. The value of the constant V varied with the geometry 

of the opening. Figure 1 shgws the results for the center 1/3 

horizontal strip oper$.ng. V was nearly constant at 0.32. Other 

geometries yielded V ranging from 0.25 to 0.50. Ignition delay 

times from the 1/2 scale backdraft experiments have compared well 

with the constant Froude Number results from these experiments. 

The average height of the gravity current was also found to be a 

constant, independent of the density difference, 

The gravity 

This time delay 

Four different opening 
40 

Half scale bac 5 draft experiments have been conducted to better 

quantify backdrafts . Measurements included species concentration 

histories of the upper layer to better characterize the conditions 

prior to opening the 'compartment. Temperature and pressure 

measurements were used to estimate the mass flow into and out'of 

the compartment prior to the deflagration. Using these results and 

an estimated flame speed, a global energy balance can be performed 

on the compartment to calculate the pressure and temperature of the 

backdraft. A comparison of the predicted results with the 

experimental results will be presented. 

. 

Density Difference 

Figure 1 - Shows constant value for V* versus density difference 

for the center 1/3 horizontal opening 

References 

(1) Pagni, P. J. , and Shih, T .M. , lgExcess Phyrolyzate, 16th 

Symposium (Int'l) on Combustion, pp. 132901343, The Combustion 

Institute, 1976. 

(2)Pagni, P.J. , and Joshi, A.A. ,llGlass Breaking in Fires," in 

Fire Safetv Science - Proceedinas of the Third International 

Svmposium, pp. 791-802, Elsevier Science Pub., London, 1991. 

(3) Simpson, J.E. , @'Gravity Currents in the Laboratory, 

Atmosphere, and Ocean,ll Annual Review of Fluid Mechanics, 14, 

213-234 (1982). 

(4)Fleischmann, C.M., Pagni, P.J., and Williamson, R.B., 

"Backdraft Experiments11, to be published. 
41 

REAT HE KNOH AND DON'T KNOH ABOUT CEILING JETS 

Howard H. Emmons 

Abstract 

The movement of fire gases along a ceiling from a fire plume or open fire 

room door appears very simp1e;just like water in a river. From this ue knon 

that the flow may be tranquil or shooting. For the leading edge of an advancing ceiling jet, the speed is close to critical i.e. Richardson Number = I. 

Rhen this spreading jet reaches the end of a corridor, the Richardson Number 

remains one if it is open or the jet hits a closed end and returns as a hydraulic jump. In any caee the corridor end nil1 determine the near source flon 

nhich may be shooting flon nith a hydraulic jump or may flood the source and 

cause a " sudden enlargement" flou. All this nould just like for water except 

that the density ratio for the ceiling jet is about 4 to 1 while for nater it 

is le@@ to 1. Thus all of the above phenomena is modified for the ceiling jet 

by a relatively large entrainment. Hater and air separate after mixing Rhile 

hot air and cold air do not. 

There is a need for extensive knowledge of the values of friction factors 

and entrainment coefficients Which will require many correlatable results or a 

large program of 3D field model calculations. This is an important use of 

field models not yet exploited because of cost. 

The most critical effect for the ceiling jet, honever, is the heat transfer. Experimental studies of this effect cannot be carried out by salt solu - 

tion tests. liquids can exchange considerable heat mith very small changes in 

density. The fire ceiling jet looses buoyancy as it cools. It often cools so 

much that it fall from the ceiling and returns beloff into the fire. During 

e#xperirnents uith cooling, the ceiling jet velocity decreases and the jet 

becomes deeper for some distance then continues further aithout change. The 

simple theory does not level off. In particular the layer cant speed up to 

critical at the transient front nor at an open end. 

To satisfy boundary conditions at the source or corridor end, it is 

necessary to use the momentum equation perpendicular to the ceiling in order 

to modify the ceiling jet pressure from the simple hydrostatic. lIhen this is 

done the controlling equation becomes third order, thus the three required 

boundary conditions can be net. Figure 1 shons the range of solutions that 

exist- Host Of the solutions contain standing Raves. One solution contains a 

constant depth section. For the simplest case f = H = E = 8, the equation can 

be integrated tuice and then reduced to an integral. This integral show that 

for any ceiling jet depth and surface slope, there is one initial surface 

Curvature nhich results in a ceiling jet of constant depth in a long corridor. 

Curiously, all Ceiling Jets can have a long constant depth section in shooting 

flow. Such constant depths in tranquil flon do not exist. Figure 2 shovs the 

constant depth YI to be reached by a ceiling jet from a source of depth yi and 

Surface Slope (Yzli. Figure 2 also ShoHS the required source surface curva - 

tures. A tranquil source has a unique shooting flox constant depth ceiling jet 

while a shooting flou source has three possible constant depth ceiling jets, 

tRO in shooting flow and one in tranquil flou. However only the shooting flows 

could reach a Richardson Number = I. The effect of friction and heat transfer 

have not Yet been studied. HOHeVer the theoretical results already obtained 

are in need of experimental verification by long corridor (perhaps model 

scale) tests. It is hoped that study of the effect of heat transfer Rill 

answer the question of how real conditions are satisfied. 

43 

LOCAL EFFECTS OF VI?NTS, BEAMS AND SPRINKLER SPRAYS ON THE CEILING . . 

JET FLOW 

Haukur Ingason 

Swedish National 'It=sting and Research Institute 

BorBs, Sweden 

A field model has many advantages compared with zone models, but there has been a lack of experimental 

data from large-scale experiments with which to verify the calculations. Therefore, large-scale experiments1 

were camed out at the Swedish National 'Itsting and Research Institute in a large test room, both with and 

without fire vents. The test room measured 7,s m x 15 m and 6 m in height. The configuration of the test 

room and the location of the fire source and the fire vents were assumed to cover about 60% of the possible 

combinations of the real cases for industrial buildings in Scandinavia. The fire source was located at the centre 

of the test room and the position of the fire vent at the ceiling was varied. The fire vent in the ceiling had 

the dimension 1 x 2 m. Rsts were also performed to provide a basis for comparison between experiments and 

zone models and field model calculations. %ts were also performed to investigate the influence of water 

spray on the outflow of hot gases through a fire vent. A number of tests were also camed out to estimate the 

influence of beams in the ceiling on the local velocity and temperature field. The temperature and velocity 

fields were measured at different locations in the room and in the fire vent opening. Both growing and 

constant heat release rates were applied. Three different fire growth rates were used, fast, medium and slow. 

Different semi-empirical relationships have been developed to predict the gas temperature and velocity at the 

ceiling for different fire and ceiling Parameters such as fire size, fire growth rate and room 

geometry in two dimensions are included in the models. The relationships assume a flat ceiling with no 

obstructions, and the ceiling jet is assumed to be radially axisymmetric. In many buildings these conditions 

are not fulfilled as obstructions and vents of different types are mounted in the ceiling. Local effects on the 

temperature and velocity fields caused by beams, smoke curtains, walls, fire vents or water spray from already 

activated sprinklers, can not be satisfactory predicted with semi-empirical models. For these cases field model 

codes are often required. There are conditions under which the response of a sprinkler are difficult to predict. 

In the Scandinavian countries most ceilings are not flat as they usually have extensive load bearing systems 

due to the high snow loads. The problems to be solved are therefore more often threeaimensional than twodimensional and should therefore be simulated by more advanced methods such as field models. Until now, 

there has been a lack of full-scale fire tests to verify simulations with field models codes. The experiments 

presented here provide the basis for the necessary verifications. 

The interaction of sprinklers and fire vents has been discussed intensively during the last decade without any 

satisfactory solution. It may be possible to elucidate this question by using a field model code. However, an 

investigation of the ability of field models to predict local effects around a fire vent opening and the effects 

of the sprinkler water spray on the ceiling jet flow must first be undertaken. Therefore, as a first step in this 

direction, extensive experimental data for the verification of a field model code for such complicated cases are 

presented here. 

The test programme was divided into four major parts: 

-test series with different fire growth rates and fire vent conditions to investigate local effects of the fire vent 

on the temperature and velocity field. 

-investigate the influence of water spray, discharged from a conventional sprinkler, on the ceiling jet. 

-investigate the effects of water spray on the outflow of hot gases through a fire vent by varying the location 

of the sprinkler. 
44 

-investigate the influence of beam constructions located in the ceiling on the velocity and temperature fields. 

The fire vents applied clearly affected the temperature and velocity field in the test room. The temperature 

reductions varied depending on distance from the fire vent The obsewed effects on the temperature and 

velocity fields are probably out of range for zone models, but possible to predict with field models. 

Experiments with sprinklers mounted at the ceiling demonstrated the effects of when the fire vent was located 

above the fire source. With the fire vent mounted ezcentric to the fire source it was not clear if the fire vent 

had any impact on sprinklers located upstream from the fire vent. From tempratwe and velocity data it could 

be observed that the fire vent clearly reduced the temperature and velocity field downstream from the fire vent. 

Measurements of total heat release rate through the fire vent show that the efficiency of the fire vent varied 

depending on the location of the fire source in relation to the fire vent. 

The impact of sprinkler spray on the ceiling jet was investigated by applying a conventional sprinkler mounted 

in a pendent pition at the centre of the test room. The fire source was moved to one end of the test room 

and the terminal wall was attached to the ceiling to force the hot gases in one direction. As could be expected, 

the water flow rate influenced the amling of the ceiling jet. At centreline instrument stations downstream 

from the sprinkler spray, the temperature reduction depended on the water flow rate. The temperatures 

upstream of the sprinkler spray tended to increase in some cases and decrease in others. Some kind of 3- 

dimensional blocking effscts are probably the reason for this but the results were not very conclusive. The 

velocities of the ceiling jet were slightly reduced downstream from the sprinkler spray. 

The results show that if the sprinkler is located upstream of the fire vent, it will have a significant impact on 

the gas flow. The experiments also demonstrated the influence of the sprinkler distance from the fire vent 

and the water flow rate on the gas flow. With the sprinkler located downstream from the fire vent the 

influence of the gas flow was negligiile. It is clear from these results that the location of the sprinkler affects 

the gas flow through the fire vent The impact on the gas flow is greatest when the sprinkler is very close to 

the fire vent and decreases with the distance. 

* 

A beam construction was mounted in the ceiling to investigate the impact on velocity and temperature fields. 

?kco 05 m high beams were mounted in the ceiling and the fire source was placed between the beams at floor 

level. The results show that the beam construction influenced the temperature and velocity field considerably. 

In the space between the two beams the increase in both temperature and velocity would definitely influence 

the sprinkler operation. In the spaces between the walls and the beams the velocity and temperature were 

reduced and the velocity was influenced more than the temperature. The thickness of the ceiling jet was not 

significantly affected. 

References 

lIngason, H. and OWn, S., Interaction between sprinklers and fire vents, SP-REPORT 1992:11, The Swedish 

National %sting and Research Institute, BorHs 1992, Sweden. 

2Heskestad, G. and JXlichatsios, MA, The Initial Convective Flow in Fire, 17th International Symposium 

on Combustion, Combustion Institute, Pittsburgh (1978). 

3Cooper, LY., Estimating the Environment and the Response of SDrinkler Links in Compartment Fires with 

Draft Curtains and Fbible Link-Actuated Ceiline Vent-Theorv, Fire safety Journal, 16, pp. 137-163 (1990). 

'hnkley, EL, The Effect of Vents on the Opening of the First Sprinklers, Fire Safety Journal, 11, pp. 211-225 

(1986)- 
45 

ENTRAINMENT IN. THE FLAMING REGION OF FIRE PLUMES 

E. E. ZUKOSKI 

CALIFORNIA INSTITUTE OF TECHNOLOGY 

A review is given of entrainment measurements made in the flaming part of fire plumes. 

Although the data studied emphasize the work of a group at Caltech (see Cetegen et al. 

1982), Toner 1989, and Morehart 1991), measurements of P. H. Thomas et al. (1963), 

McCaffrey (1979), Beyler (1982), and Delichatsios and Orloff (1984) are also considered. 

Correlations developed by Cetegen et al. (1982), Delichatsios and Orloff (1984), and 

Heskestad (1986) are described and a new correlation is presented. The study is limited 

to flames with heights in the range 1 to 6 burner diameters with Q* values between 0.1 

and 5. 

In the early work of P. H. Thomas et al. (1963), fire plumes generated by gas burners 

and wood cribs were placed beneath a hood like ceiling with short vertical side walls. The 

vitiated gas was allowed to escape through a vent in the ceiling and from under the sides 

of the containing walls, and the mass flux in the plume at the interface between hot and 

ambient gas was estimated from simple formulae used to model the flow through these two 

openings. 

In the measurements made by the Caltech group, a hood, open on the bottom side, 

was placed over the fire, like a candle snuffer. The hot products of combustion are collected 

within the hood and escape from the hood along the bottoa edges of the sides. A laminar, 

sharply defined interface develops between the products of combustion contained within 

the hood and the ambient atmosphere. This interface is penetrated only by the gas in the 

fire plume and the assumption is made that the only oxygen atoms which enter the hood 

comes from the fuel or fiom air which is entrained into the fire plume from the region 

below this interface. Measurement of the specie concentrations present within the hood 

then allow the fuel-air ratio of the gas supplying the hood to be determined and given a 

measurement of the fuel flow rate, the entrainment rate can then be determined. 

Both techniques described above measure the mass flux carried into the upper hotgas layer which is the quantity required for fire models; whether or not the presence of 

the interface substantially disturbs the entrainment process in the plume has not been 

determined. 

Data collected by the Caltech group and Beyler, who used a similar technique but 

with a different type of hood, showed unambiguously that? for elevations below the top of 

the flame, the mass flux in the fire plume was linearly proportional to the burner diameter 

and the distance above the burner, and was substantially independent of the fuel flow rate. 

Beyler’s results were qualitatively similar but differeci from the results of the Caltech 

group by about a factor of two when data. for similar fuels, heat release rates and fuels are 

compared. 
46 

The results of Thomas et al. also showed that the plume mass flux scales with the 

burner diameter, (they use the perimeter of their cribs as the scaling parameter), and was 

independent of the heat release rate in the fire. However, they scaled their dependence on 

the height of the interface with Z3I2 rather than the linear dependence found by Beyler 

and the Caltech group. The extra Z1I2 combined with the acceleration of gravity gives 

a characteristic velocity which can be used to make the correlation dimensionally correct. 

Unfortunately, data from the hood experiments show that the mass flux clearly depends 

on Z not Pa5. 

The best fit to the Caltech entrainment data shows that the entrained mass flux at 

an elevation Z above a burner with diameter D is given by C,ZD. When Q* is in the 

range between 0.1 and 6, the value for C, is a constant equal to 0.62 kg/sm2 and this 

proportionality constant decreases with decreasing Q* below 0.1 and increases linearly 

with increasing &* values above 6. A scaling parameter which has the correct dimensions 

and which depends linearly on the diameter and height, and is independent of the heat 

release rate has not been found. The parameter proposed by Thomas et al. is intuitively 

satisfactory but does not fit the Caltech or Beyler data. 

REFERENCES 

Cetegen, B. M. (1982) Entrainment and Flame Geometry of Fire Plumes, Ph.D. Thesis, California Institute of Technology, Pasadena, California. 

Delichatsios M. A. and Orloff, L. (1984) “Entrainment Measurements in Turbulent, 

Buoyant Jet Flames and Implications for Modeling,” Twentieth Symposium (International) 

on Combustion, The Combustion Institute, pp. 951-960. 

Heskestad, G. (1986) “Fire Plume Air Entrainment, According to Two Competing 

Assumptions,” Twenty-first Symposium (International) on Combustion, The Combustion 

Institute, pp. 111-120. 

McCaf€rey, B. J. (1979) “Purely Buoyant Diffusion Flames: Some Experimental Results,” NBSIR 79-1910, National Bureau of Standards, Wmhington, D.C. 

Morehart, J. H. (1991) Species Produced in Fires Burning in Two-Layered and Homogeneous Vitiated Environments, Ph.D. Thesis, California Institute of Technology, Pasadena, 

California. 

Thomas, P. H., Baldwin, R., and Heselden, A.J.M. (1965) “Buoyant Diffusion Flames: 

Some Measurements of Air Entrainment, Heat Transfer, and Flame Merging,” Tenth Symposium (International) on Combustion, The Combustion Institute, pp. 983-996. 

Toner, S. J. (1986) Entrainment, Chemistry, and Structure of Fire Plumes, Ph.D. 

Thesis, California Institute of Technology. 
47 

SCALAR MIXING PROPERTIES 

OF BUOYANT TURBULENT PLUMES 

2. Dai, L.-K. Tseng and G. M. Faeth 

Department of Aerospace Engineering 

The University of Michigan 

Ann Arbor, Michigan 48109-2140 

The scalar mixing properties of round buoyant turbulent plumes were measured in 

still air. This is an important fundamental problem that has attracted significant attention 

since the classical work of Rouse et d.;1 see List,2 George et al.3 and references cited 

therein for discussions of research during the intervening years. However, recent work in 

this laboratory has highlighted the need for additional information concerning the 

turbulence properties of scalar quantities within buoyant plumes, in order to address 

turbulence/radiation interactions in fire environments, see Kounalakis et aL4 and references 

cited therein. In particular, the response of flame radiation to turbulent fluctuations is 

particularly sensitive to the moments, probability density functions, and spatial and 

temporal correlations of mixture fraction fluctuations. While the classical work of Pitts and 

Kashiwagis provides information of this type for nonbuoyant turbulent jets, surprisingly, 

comparable information is not available for buoyant turbulent plumes. Thus, the objective 

of the present investigation was to complete measurements of mixture fraction statistics in 

round buoyant turbulent plumes, and to interpret and correlate the results in order to 

facilitate treatment of turbulencdradiation intemctions in flames. 

The experiments employed techniques developed by Lai and coworkers.6~7 This 

involved using mixtures of carbon dioxide and air, and observing the resulting negatively- buoyant plumes. Initial conditions consisted of fully-developed turbulent pipe flow, with 

mean velocities adjusted so that the flow corresponded to the asymptotic Froude number of 

round turbulent plumes,3 in order to enhance rates of development toward fully-developed 

turbulent plume conditions. Effects of room disturbances were controlled by observing the 

flow in a screened enclosure surrounded by a plastic enclosure, all within a windowless 

room, with the plume exhausted using a distributed collection system located in the comers 

of the plastic enclosure. The mixture fraction measurements were made using laser- induced iodine fluorescence &IF) based on the 514.5 nm line of a cw argon-ion laser (with 

roughly 1500 mW of optical power). The laser beam passed horizontally across the flow 

and was not focussed, so that two traversible detectors could be used to measure the radial 

spatial correlations of mixture fraction fluctuations - a rarely measured property of 

turbulent mixing that is crucial for understanding turbulence/radiation interaction^.^ 

Various positions in the flow could be studied by traversing the screened enclosure in the 

horizontal (radial) direction, and the plume generator in the streamwise direction within the 

screened enclosure. 

We expected the measurements of mean mixture fractions in the plumes to serve 

primarily as a check of the operation of the present apparatus, however, this was not 

entirely the case and these measurements were pursued more thoroughly than planned. In 

particular, while existing measurements are seemingly in the fully-developed portions of 

the plumes, based on a Monin number criterion, they all are actually at relatively low (xa Research supported by the Building and Fire Research Laboratory of the National 

Institute of Standards and Technology, Grant No. 60NANBlD1175. 
48 

xo)/d, ca. 20-30, where x and X, are the streamwise distance and the position of the vhd 

origin and d is the plume generator diametet.1-3. Thus, past flows generally are not fully- developed and present measurements indicate somewhat narrower plume widths in fully- developed portions of the flow, for (x-%)/d = O( 100). Within this regime, however, the 

classical similarity behavior proposed by Rouse et al.1 is observed and entrainment rates 

agree with results in the literature within experimental uncertainties. 

Radial profiles of mixture fraction fluctuations confirmed our findings concerning 

the development of mean property distributions with streamwise distance. Near the plume 

generator, mixture fiaction fluctuations are relatively low and exhibit a dip to a local 

minimum near the axis. With increasing distance, however, the dip disappears and 

fluctuation intensities near the axis stabilize at roughly 408, which is higher than existing 

results in the literature? Probability density functions of mixture fraction are represented reasonably well by the clippd-Gaussian functions, while the behavior of the popular beta 

function distribution is somewhat less satisfactory. Temporal power spectra exhibited a 

limited inertial range because present measurements are still at modest Reynolds numbers: 

current work is seeking to remove this limitation. Additionally, the results show that 

effects of signal noise on present measurements are small. Finally, present two-point 

measurements of radial spatial correlations are in qualitative agreement with earlier results 

for forced-flow conditions in flames.4 Work is currently in progress to develop 

corresponding infonnation for streamwise spatial correlations and temporal and spatial integral scales. 

References 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

Rouse, H., Yih, C.S. and Humphreys, H.W. Tellus 4:201-210 (1952). 

List, E.J. Ann. Rev. Fluid Mech. 14:189-212 (1984). 

George, W.K., Jr., Alpert, R.L. and Tamanini, F. Znt. J. Heat Mass Trans. 

20~1145-1154 (1977). 

Kounalakis, M.E., Sivathanu, Y.R. and Faeth, G.M. J. Heat Trans. 113:437-445 

(1991). 

Pitts, W.M. and Kashiwagi, T. J. Fluid Mech. 141:391-429 (1984). 

Lai, M.-C., Jeng, S.-M. andFaeth, G.M. J. Heat. Trans. 108:827-834 (1986). 

Lai, M.-C. and Faeth, G.M. J. Heat Trans. 109:663-670 (1987); Ibid. 109:254-256 

(1987). 
49 

CONTROLLED LAMINAR. DIFFUSION FLAMES 

SI Venkatesh and KO Saito 

Combustion and Fire Research Laboratory 

Dept. of Mechanical Engineering 

University of Kentucky 

Lezington, KY 40506 

ABSTRACT: Small laminar diffusion flames (flame height 2 2-3 mm) 

established by issuing a fuel jet into a quiescent medium are 

investigated. It was found that for these flames buoyancy effects 

disappeared as the flame size decreased (Fr >>1), and diffusive 

transport of the fuel was comparable to the momentum transport of the 

fuel. The effect of buoyancy on these flames was determined by 

examining the flame shape for horizontally oriented burners. A 

phenomenological model was developed (based on experimentally 

determined flame shapes) to compare diffusion and momentum transport 

effects. Finally, the flame shapes were theoretically determined by 

solving the conservation equations using similarity methods. It was 

seen that when the axial diffusion (viscosity) terms are included in 

the conservation equations, the calculated flame shape is in better 

agreement (as compared to without the axial diffusion term) with the 

experimentally measured flame shape. 

Studies on laminar hydrocarbon diffusion flames are always of 

interest because of their fundamental nature . Beginning with 

Faraday's pioneering work - ''Chemical History of a Candle," in 1861, 

many studies have been conducted on this subject, and that there is 

still a need to study them was further established through recent 

observations by Ban, et al. (1992), where small laminar diffusion 

flames (with flame heights of a few millimeters) were studied, by 

issuing a hydrocarbon fuel jet into a quiescent atmosphere. They 

found that the flame shape of these small flames is spherical and 

different from the more commonly observed candle -like laminar 

diffusion flames, and for sufficiently small flame sizes there were 

no buoyancy effects . These observations led to the current 

investigations on the physical characteristics of the small flames, 

since we were unable to find published literature on this class of 

flames. Experiments were conducted to collect data on the flame 

height and flame shape as a function of flow rate for three different 

fuels . It was found that the small flames have interesting 

characteristics that allow the phenomenological evaluation of the 

effects of molecular diffusion, momentum and buoyancy. 

Based on past studies, laminar jet diffusion flames can be 

classified into two main types: The Burke-Schumann (1928) flame 

controlled by diffusion, and the Roper flame (1977) controlled by 

buoyancy. The small flames studied here have the following 

characteristics: Fr >> 1 and ue uD, where ue is the fuel exit 

velocity at the burner port, uD is the molecular diffusion velocity, 
50 

Fr = uz/gd and d is the burner port diameter. A scale analysis 

reveals that for Fr 2 -1, uez 0.1 m/s and d z 1 mm the buoy.ancy 

effects can be neglected (Williams, 1985) . In addition, for small 

flames ue ,N uD implying they are momentudiffusion controlled. 

EXPERIMENTAL: The flames were established on circular- port stainless-steel burners with inner diameters 0.15, 0.25 and 0.40 mm; 

the outer diameters were twice the inner diameters. Research grade 

ethane, ethylene and acetylene were used as the feels. The flow 

rates of the fuels were calibrated using a specially designed 

soap-bubble flow meter capable of measuring low flow rates of order, 

0.01 cc/s. The fuel was issued into the quiescent ambient at 

atmospheric conditions. The flame shape was recorded by a 35 mm 

still-camera with a bellows attatchment to magnify the image. 

TIEORETICAL: To explain the observed experimental phenomena, a simple 

theoretical model was developed. The case of a combustible laminar 

jet issuing into a quiescent medium was theoretically described by 

Spalding (1979) . Spalding's analysis uses the similarity procedure described by Schlichting to develop closed form expressions for the 

flame height and flame shape for circular jet laminar diffusion 

flames. Governing equations for the small flames for axisymmetric 

geometry were derived. With the assumptions of negligible buoyancy, 

constant pressure, and constant property values, the flame height and 

flame shape of the small laminar momentum-diffusion controlled flames 

were solved using similarity analysis for two cases, one is with 

axial diffusion term and the other is without axial diffusion term. 

The comparison with experimental data proved that transport by axial 

diffusion is comparable to the convective transport and cannot be 

neglected when determining the flame height/shape in such a small 

flame . 

SUAMARY:(l)Small laminar 'momentum-diffusion controlled diffusion 

flames, with Pe numbers (uelD/D) less than 5 were investigated. It 

was observed that these flames tend to achieve a spherical shape due 

to the comparable effects of momentum and molecular-diffusion. 

(2)It was found that the effect of buoyancy in these flames is 

negligible, by rotating the burner. The Froude numbers of these 

flames were in the range 10-103. 

(3)A phenomenological model was developed to understand the flame 

shape and estimate the momentum/diffusion effects. 

(4)The flame height/shape was theoretically determined starting with 

the governing equations and applying similarity methods. It was seen 

that when axial diffusion terms are used in the governing equations, the calculated flame shape is in better agreement (as compared without the axial diffusion terms) with the experimentally determined 

flame shape. 

@)For further details of this work, see the same title paper by H. 

Ban, S. Venkatesh and K. Saito, at the 1992 ASME Winter Annual 

Meeting, November 8-13, 1992, Anaheim, CA. 
51 

MICROSC.ALES OF FQRCED/BUOYANCY DWEN 

TURBULENT DIFFUSION FLAMES 

V. S. ARPACI 

Department of Mechanical Engineering and Applied Mechanics 

The University of Michigan 

R. J. TABACZYNSKI 

Scientific Laboratories 

Ford Motor Company 

ABSTRACT 

The recent decades have seen exponential growth of research on algebraic and 

transport models for prediction of turbulent flows. The potential of these models now 

appears to be exhausted and any future research along these lines is expected to be 

mostly in the nature of "utilization" or "elaboration". A novel approach is proposed 

here to study the fuel consumption in reacting turbulent flows. The approach is 

based on the development of appropriate microscales and the use of these scales in 

the prediction of fuel consumption in furnaces and heaters. 

The Kolmogorov scale was originally introduced by intuitive arguments with two 

kinematic concepts, the dissipation of energy per unit mass, 

[ E ] L2/T3, 

and the kinematic viscosity, 

The elimination of time between these readily gives this scale, 

[4 3 L~/T. 

Extension of the Kolmogorov scale to thermal scales by Oboukhov-Corrsin and 

Bat chelor follows similar arguments. However, the microscales appropriate for more 

complicated turbulent flows (say those for pulsating or reacting flows) cannot be 

obtained by similar arguments because of the need of combinations involving more 

than two concepts such as v and E . 

During the past decade, Arpaci and co-workers originated a methodology for construction of microscales appropriate for complex turbulent heat and mass transfer 

problems and utilized these scales in the correlation of heat transfer in pulse combustor tailpipes, that of mass consumption in pool fires and from forced flames. For 

example, the Reynolds and phase averaged turbulent flows pulsating with frequency 

w leads to the Kolmogorov scale, 
52 

whose two limits for w -+ 0 and w + do axe the usual Kolmogorov and Stokes scales, 

respectively. Also, the Reynolds averaged, buoyancy driven, steady turbulent flows 

lead to the thermal Kolmogorov scales, 

and 

Of these scales, the limit of the first one for Pr-, m is the Batchelor scale, and that 

of the second one for Pr --$ 0 is the Oboukhov-Corrsin scale. Here B denotes the 

production of buoyant turbulent energy, other notation being conventional. Also, for 

the Reynolds averaged, forced, steady turbulent flows, a thermal mesomicroscale 

between the Kolmogorov and Batchelor scales 

is proposed. Here q and # respectively denote the Kolmogorov and Batchelor scales. 

It is shown by extending this methodology to microscales appropriate for reacting 

turbulent flows how these scale can be employed to predict the fuel consumption in 

pool fires and forced flames. The results of the proposed research are expected to be 

useful to present federal and industrial research programs on combustion, flame and 

fires. 

REFERENCES 

1 Arpaci, V.S., Microscales of Turbulence and Heat Transfer Correlations, Int. 

J. Heat Mass Transfer 29, 1071-1078 (1986). 

2 Arpaci, V.S., Microscales of Turbulence and Heat Transfer Correlations, Annual Review of Heat Transfer Vo1.3, 195-231,(Edited by C. L. Tien), Hemisphere Publishing Corporation, (1990). 

3 Arpaci, V.S. and Selamet, A., Buoyancy Driven Turbulent Diffusion Flames, 

Combust. Flame 86, 203-215 (1991). 

4 Arpaci, V. S., Radiative Entropy Production-Heat Loss into Entropy, Advaces in Heat Transfer Vo1.21,239-276 (Edited by Hartnett, J. P. and Irvine, 

T. F.). Academic Press, New York (1991). 

5 Arpaci, .V. S., Dec, J. E. and Keller, J. O., Heat Transfer in Pulse Combustor Tailpipes (to appear in Combustion Science and Technology). 
53 

MULTIPLICITY OF PUFFING FREQUENCIES IN BUOYANT . 

DIFFUSION FLAMES* 

by Baki M. Cetegen and Tarek Ahmed 

Mechanical Engineering Department 

University of Connecticut, Storrs, CT 06269-3139 

Abstract: 

Buoyant propane diffusion flames established on 0.05 and 0.10 m. diameter burners were 

found to exhibit splitting of puffing frequencies with changes in the fuel flow rate or total 

heat release of the flames. A series of experiments were performed with flames established 

on porous-bed pool f?re burners in quiescent surroundings to explore this phenomenon. 

Burner surface pressure fluctuations along with the static pressure at a height of 1/2D above 

the burner surface were measured to determine tihe signature of puffing as detailed in a 

recent article [ 13. At low fuel flow rates, the puffing frequency more or less scales with the 

well-known, diameter dependent frequency (fa D-ln). As the fuel flow rate is increased, 

a higher frequency emerges in both the surface and the stahc pressure frequency spectrum 

as shown in the figure. At intermediate flow rates (e.g. Qf = 6.0 kw), both frequencies 

have comparable strengths. The higher frequency that appears in the spectra is believed to 

be associated with the buoyant flame instabilities with a frequency of around 10 Hz. These 

types of flames have been extensively studied by a number of researchers [2,3]. It is also 

interesting to point out that the frequency of this instability has been experimentally fo,pnd 

to be insensitive to burner size, fuel type, etc. At even higher flow rates of fuel (e.g. Qf = 

8.4 kW), this higher frequency begins to dominate while the amplitudes of the lower 

frequency fluctuations diminish. Mu1 tiplicity of flame frequencies were also recently 

observed by Sui et a1 [4] who reported flame frequencies in coflowing propane diffusion 

flames. The existence of the lower frequency along with the higher frequencies provide 

some clues as to which modes of instabilities are in play in transitional diffusion flames. 

The discussion of these new results will center around the various instability modes and the 

flame parameters which determine the transitions in the flame behavior as a result of the 

aforementioned instabilities. 

References: 

1. Cetegen, B. M. and Ahmed, T., "Experiments on the Periodic Instability of Pool 

Fires",submitted to Comb. & Flame, June 1992 

2. Chen, D. L., Seaba, J. P., Roquemore, W. M., and Goss, L. P., "Buoyant 

Diffusion Flames", Twenty-Second Symposium (International) on Combustion, pp. 

677-684, The Combustion Institute, 1988 

3. Buckmaster, J. and Peters, N., "The Infinite Candle and its Stability-A Paradigm for 

Flickering Diffusion Flames", Twenty -First Symposium (International) on 

Combustion, pp. 1829-1836, The Combustion Institute, 1986 

4. Sui, P. C., Chen, L. D., Davis, R. W, Moore, E, and Roquemore, W. M., "Lowfrequency Flame Oscillation of a Nitrogen diluted Propane Diffusion Flame: An 

Experimental and Numerical Study", presented at the Eastern States Combustion 

Meeting, Cornell University, October 14-16, 1991 

(*) This research has been sponsored by National Science Foundation Grant CTS-8909176 
54 

'i 2 

10 20 Hz. 

10.5 Ht. 

5,O 'Hz. 8*0 1 

J 

A 

Q,= 6.0 kW 

0.. 

-. 

O2 t c 1 I 1 I I 1 1 1 

0 2 4' 6 sec. 8 

Frequency spectra and pressure fluctuation traces of propane flames 

on a 10 em. diameter burner 
55 

A THERMAL ELEMENT MODEL FOR COMBUSTION PROCESSES IN F'IRES 

Ofbdike A. Ezekoye and Howard R. Baum 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

A methodology fbr incorporating combustion and radiative processes into large eddy simulations 

of fire driven flows is presented. The mathematical models describing these processes are developed in 

a local Lagrangian frame of reference moving with the large scale convection induced by the fire. The 

gaseous fuel is represented by a large number of discrete "thermal elements" which react with their local 

oxidizing environment and exchange energy radiatively with each other and with their surroundings. 

Viewed at large scales which characterize the overall geometry of the scenario under investigation, each 

element is a point source of energy and volume. At a local scale, the thermal element is a small sphere 

of gasified fuel being consumed by a transient diffusion-controlled flame. A prescribed fraction of the 

fuel is converted to soot which can emit radiation to its surroundings or absorb radiation from other 

thermal elements. 

The large and small-scale pictures are coupled both hydrodynamically and thermally. The location 

in space and time of each thermal element requires a particle tracking computation of its Lagrangian 

coordinates. The local asymptotic expansion, the chemical and net radiative heat sources in each element 

are fed back into the computational mesh used to calculate the large scale flow. The net radiation 

absorbed by each element from all others is approximately accounted for using an optically thin model 

of radiative transport. The overall velocity field induced by the fire is decomposed into an irrotational 

expansion field and a solenoidal buoyancy induced flow. The thermal elements generate the expansion 

field and provide the thermal sources for the large scale temperature field. A large eddy simulation of 

the Navier-Stokes equations (described elsewhere) generates the solenoidal field. 

Mathematically, the local thermal element is described by an unsteady, spherically symmetric 

diffusion-convection equation fbr the mixture fraction, a transport equation (including thermophoretic 

difision) fbr the soot which is assumed to be generated at the flame sheet, and an energy equation which 

accounts for energy release at the flame sheet and distributed radiation from the soot layer. The gas 

velocity is induced by the thermal expansion using an analytical recipe derived from the conservation of 

mass. The total time to consume a fuel sphere of radius R is approximately 10 times a characteristic 

diffusion time 7, based on R. The flame sheet expands out in search of air until approximately 37, and 

then collapses when the fuel diffusion rate can no longer maintain the stoichiometric mixture fraction 

value. For a 1 cm. propane diffusion flame with 7=. 1151 seconds, Figure 1 shows the total heat release 

and radiative loss rates. At early times, the large gradients in the mixture fraction profile imply large fuel 

diffusion rates into the flame sheet and thus large heat release rates while at later times, the heat release 

rates drop due to the shallower gradients. Figure 2 shows the cumulative fraction of chemical energy lost 

through radiative transfer. In Figure 3, contours of the temperature field (solid lines), the stoichiometric 

mixture fraction value (.059, dashed line) and a soot volume fraction value (5.Ox1W8, dotted lines) are 

shown spatially and temporally. The maximum soot volume fraction during the combustion process is 

approximately 5.0~ lo-'. 

The system of equations fbr a single thermal element is solved using the package MOLlD and 

can be calculated in several seconds of computer time on a Cray Y/MP computer. 

- 
56 

n 

5 0 

Y 

Z 

v) 

z 

X 

W 

0 

d 

100 

50 

0 K - I-- - 

'+---- _ --- 

RAOlATlON 

-501.. a 1.. . 1.. . 1.. . t.. . I.. .j 

0.0 0.2 0.4 0.6 0.8 1.0 1.2 

TIME [SI 

Figure 1. Time history of chemical energy release rate 

and radiative emission for a 1 cm. propane element. : 

0.40 

0.30 

0.20 

0.10 

0.00 

0.0 0.2 0.4 0.6 0.8 1.0 1.2 

TIME [s] 

Figure 2. Cumulative fraction of chemical 

energy lost through radiation. 

3 

\1 

0 

0.0 0.2 0.4 0.6 0.8 1.0 1.2 

TIME[s] 

Figure 3. Contour plot of temperature in Kelvin (solid lines), stoichiometric mixture 

fraction (dashed line) and soot volume kction of .OS ppm (dotted line). 
57 

COMPARISON OF EXPERIMENTAL AND COMPUTED SPECIES CONCENTRATION 

AND TEMPERATURE PROFlLES IN LAMINAR, TWO-DIMENSIONAL ' CH4/AIR DIFFUSION FLAMES' 

Kermit C. Smyth and Thomas S. Norton2 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

J. Houston Miller 

Department of Chemistry 

The George Washington University 

Washington, DC 20052 

and Mitchell D. Smooke 

Department of Mechanical Engineering 

Yale University 

New Haven, CT 06520 

The last decade has witnessed significant advances in our knowledge of both the chemical reactions which 

occur under high-temperature combustion conditions and the associated fluid mechanical mixing processes. As 

a consequence, increasing attention is now focussed on improving our understanding of the typically strong 

coupling between chemical heat release and turbulent mixing, Le. chemistry-turbulence interactions. One 

approach for including chemical reactions in computational models of turbulent diffusion flames is to utilize 

libraries of strained laminar flame calculations which incorporate detailed reaction mechanisms. An alternative 

avenue is to reduce systematically the number of chemical steps in the basic oxidation mechanisms for combustion 

to as few as possible (typically three or four), while still providing an adequate description of the major species 

concentration and temperature profiles. 

Few studies have addressed the question of how well flame structure calculations reproduce experimental 

results. Recent work at Sandia, mostly in turbulent jet diffusion flames of diluted methane, has compared 

measured concentrations of the OH. radical and the major stable species to values computed for strained 

(counterflow) laminar flames. With respect to developing reduced chemical mechanisms, most of the effort has 

used a detailed flame structure calculation as the point of reference. Although both strategies are logical, to this 

point only limited comparisons have been made between experimental measurements and detailed flame structure 

computations for laminar diffusion flames, particularly for the radical species. 

In the last several years we have undertaken an extensive experimental investigation of a laminar, CH4/air 

diffbsion flame burning at atmospheric pressure, in which measurements have been made of species 

concentrations, velocity, and temperature. In addition to mass spectrometric detection of stable molecules, radical 

concentration profiles have been obtained for OH*, H atom, 0 atom, CH*, and CH3*. Beyond these results, 

profile data for radicals in laminar hydrocarbon diffusion flames are scarce. Melvin and Moss (1975) have 

reported an OH. profile in a N,-diluted CH4/air flame, Bastin et al. (1987) have used molecular beam mass 

spectrometry to sample numerous radicals in a 30-torr qHz/02/Ar flame, and Barlow and Collignon (1991) have 

obtained OH- profiles in both counterflow and co-flow airdiluted methane flames. 

The detailed experimental profile measurements which are now available in the undiluted CH4/air 

diffusion flame enable a much more complete comparison to be made with flame structure calculations than has 

been possible before. Our initial focus has been on the radical species H*, 0:, OH*, CH., and CH3*, since minor 

species concentrations generally provide more critical and demanding tests of mechanism and model predictions 
58 

than do the major species. However, in our analysis it has become evident that the major stable species also need 

attention. 

Some initial comparisons between experimental measurements and flame structure calculations have been 

carried out for twodimensional axisymmetric CH4/air diffusion flames by Smooke et al. (1989, 1990). The 

agreement is generally good for the major stable species and provides confidence in the chemical mechanism used 

in the flame structure calculations. The present effort extends the comparisons between experimental and flame 

structure predictions in two-dimensional CH4/air diffusion flames with particular emphasis on the radical species. 

Since our experimental measurements have been made on a rectangular Wolfhard-Parker burner geometry (flame 

height = 33 cm), in contrast to the axisymmetric geometry of the flame structure computation (flame height = 

3.8 cm), it is also necessary to examine the results using geometry-independent coordinates, such as the local 

mixture fraction and the scalar dissipation rate. These parameters are of interest for describing the chemical 

composition and the strain field in laminar flamelets approaches. In order to address the question of which library 

of laminar flamelets is the best to use for turbulent flame computations, comparisons will also need to be made 

between counterflow and co-flow geometries. The present study is a first step in assessing how well comparisons 

can be made for diffusion flames in geometry-independent coordinates. 

Our comparisons of temperature and species concentrations have been made by basing the analysis on 

the local flame conditions, specifically the mixture fraction and the scalar dissipation rate. The best method for 

establishing a basis of comparison for the scalar dissipation rate involves using a least-squares procedure over 

a range of mixture fraction, rather than matching at a specific point which corresponds to the stoichiometric 

surface or the temperature maximum. Good agreement between experimental measurements and calculated 

concentrations is found for the major radical species OH-, H atom, and 0 atom, while for the hydrocarbon 

radicals CH. and CH3- some features of the profiles agree well but significant areas of disagreement exist. 

Overall, the calculated positions of the peak radical concentrations are slightly more compressed in terms of the 

mixture fraction compared to the experimental results. The predicted concentration profiles for the major species 

certainly agree with the experimental measurements as well as found in investigations on premixed flames, for 

example in acetylene combustion (Westmoreland et al., 1986). The computed results are somewhat more 

sensitive to the scalar dissipation rate than are the experimental profiles. 

The most serious areas of disagreement concern the comparison of the temperature profiles and the much 

larger degree of 02 penetration in the computed flame structure. The influence of the latter, particularly in rich 

flame regions, is likely to be small and can be further investigated by carrying out onedimensional counterflow 

calculations with and without a small amount of 02 added to the fuel stream and then comparing species profiles. 

Given the importance of the temperature field in determining the chemical structure of a diffusion flame, the 

disagreement between the computed and the experimental temperature profiles certainly deserves further study 

before one can be satisfied with the generally excellent agreement for the individual species profiles. 

Submitted to Combustion Science and Technology. 

* NRC-NIST Postdoctoral Research Associate (19904991); current address: 

Morgantown Energy Technology Center, Morgantown, West Virginia 26505. 
59 

Numerical Simulation of Thermal Plumes 

Soonil Nam, Robert G. Bill, Jr. 

Factory Mutual Research Corporation 

Norwood, Massachusetts 02062, USA 

Thermal plumes generated by pool fires and heptane spray fires were simulated numerically with the 

aid of the computer code PHOENICS. The flow fields associated with the various heat release rates were 

simulated and compared with experimental results. The experimental results were obtained from five different 

fires: methanol pool fire (denoted to Test l), hydrocarbon fluid pool fire (Test S), heptane pool fire (Test 

8), Heptane Spray Fire 1 (HS1) and Heptane Spray Fire 2 (HS2). Modifications were made in the standard 

k -e model used in the PHOENICS code in order to improve the accuracy of that model in the simulation of 

turbulent thermal plumes. The modification includes an additional term related to the buoyancy generated 

turbulence kinetic energy, changing constants responsible for the turbulent viscosity and the effective Prandtl 

number in the energy equation. The results obtained with the modified code were in excellent agreement 

with experimental results and significantly improved the results obtained with the standard k - model. 

The standards of the comparison were the well established plume relations1 based on axial velocity, vzo, the 

excess temperature above ambient at the centerline, ATo, and the plume half-width based on the centerline 

temperature, C AT. Thermal plumes generated with the modified model give excellent agreements with the 

plume coefficients reported in Reference 1. Figure 1 shows the comparison based on one of the coefficients 

 CAT^ which is a constant relating AT0 with the heat release rate and elevation. 

l2 t 1 

1 

Figures 2 and 3 show the comparison between the experimental and numerical results for Heptane Spray 

Fire 2. Air entrainment rates were computed and compared with the formula developed by Heskestad5; a 

comparison is given in Figure 4. The simulation was extended to calculate the ceiling jet flow under an 

unconfined flat ceiling with 3 different ceiling heights, H, with two different fire sizes (HS1 and HS2). 
60 

0.0 0.2 0.4 0.0 0.0 1 .o 

0 

0 

I ! 

1 2 

Radius (m) Elevation (m) 

2 campuim ofthe nvdd d-td du tor .olutioqAmeamnmnt. Bs2: Fii 3 Ad Vuirtion in CenceriW Velocity in HS2: . -. mrmerjcrl 

- ds1 m, ... w1.a a - - - r=203 m, - S=~M m; apcrimmt.l+ dS1 4 -.- 

o ~~1.42 m, A zA.03 m, o z=2.64 m. 

1 .o - 

k"- 

a 

a 

\ 

k- 

. 0 '.e OO 

0 

0.1 I I 

0.1 1.0 10.0 

Fi@=SCoclrp.rimdtkmnnericrl rolutiam .Pdzr=-=-aQmlrimnm~~- r/s 

'rftm: numEial - ESI. 4 --- Bs1, Ed86 m, - - - HSI, E- 4 - 

dirnvb ruyr fmm 0.15 to .6l m,Q - h 11.6 to 

A;rmrzrr 

g52,E~W~---EXt,Ed86~--BS?,Ha5m;~~ 'doH-.od 

w2 (Pmpw 

1 2 3 4 . 382 kw, E koan 036 to Worn), A Pichrd d .Ls (&hi Elevation (z/z,) 

%are4Aktn~ * in brrs nmnaicrl- TTst 1, -.. Tat 6, - - - Vh 0.W toes- H h 1.2 to24 14 Q ~b4.S b I28 kw), 

Tat 8; * h.srnbOTd 1, A Tat 6.0 Tat 8 0-4(.taobd~~dirw~erro .a 4 Q=l@ kW, E=lX m). 

The results are shown in Figure 5 and are compared with other experimental data available. Here AT 

denotes the maximum excess temperature in the ceiling jet, AT0 is the excess temperature at the centerline 

of the undeflected plume at the level of ceiling height H, r is the radius along the ceiling, b is the half-width 

of the undeflected plume at the level of H. The simulations with the present model significantly improves 

the agreements with the experimental results of buoyant thermal plumes. 

1. 

2. 

3. 

4. 

5. 

REFERENCES 

Heskestad, G., "Engineering Relations for Fire Plumes," Fire Safety Journal, vol. 7, 1984, pp. 25-32. 

Heskestad, G. and Hamada, T., "Ceiling Flows of Strong Fire Plumes," FMRC Technical Report, J. I. 

OKOEl.RU, Factory Mutual Research Corporation, Norwood, MA, 1984. 

Pickard, R.W., Hird, D., Nash, P., Note No. 247, Fire Research Station, Boreham Wood, Herts, UK, 

1957. 

Thomas, P.H., Note No. 141, Fire Research Station, Boreham Wood, Herts, UK, 1955. 

Heskestad, G., "Fire Plume Air Entrainment According to Two Competing Assumptions," Twenty-first 

Symposium (International) on Combustion, The Combustion Institute, 1986, pp. 11 1-120 
61 

THE TURBULENCE STRUCTURE OF MEDIUM-SCALE POOL FIRES 

E.J. Weckman and A.B Strong 

Department of Mechanical Engineering 

University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1 

Introduction 

Explanations of mixing and entrainment in pool fires, and therefore full mathematical models of fire behaviour, 

are only in their formative stages. The reasons are twofold. First, only a very limited number of detailed measurements of local velocities, temperatures and species concentration have been reported due to difficulties in making 

measurements near the base of the fire. Secondly, the data that are available typically consist of measurements 

of only one or two parameters (i.e., mean temperature and concentration [l], or mean temperature and velocity 

[2,3,4,5]) over restricted regions in the fire flow field. Determinations of the correlations between parameters, the key 

to understanding mixing and entrainment, have been limited to some autocorrelations [2] and only a few Reynolds 

stress and axial velocity and temperature correlations [2,4,5]. 

In this study, the flaming regions of 0.31 m diameter methanol pool fires were measured. A full set of simultaneous velocity and temperature measurements were made in and around the continuous and intermittent flame zones 

of the fires. Mean and rms values were calculated for each parameter from time series of data. In addition, time 

correlations, u'v'(T), UT(~) and v'T'(T), turbulence length and time scales, turbulence Reynolds number, Ret, and 

flux Richardson number, Ril, were estimated throughout the measured flow domain. The combined results were 

used to examine the mechanisms of production of turbulent energy for various points in the fire. 

-- 

The Experiment 

The fires were established in the existing University of Waterloo pool fire test facility [4]. Axial and radial 

components of velocity were measured using two component LDA operated in the forward scatter configuration, 

while temperature was measured with a 50 pm diameter bare wire Pt/Pt-lO%Rh thermocouple. The data acquisition 

system allowed simultaneous sampling of four channels of velocity and temperature data. Time series of data 

consisting of 40,000 measurements were analysed to provide mean and rms values, correlations, length and time 

scales for each parameter. 

Results 

The mean temperature and velocity fields substantiate existing descriptions of the fire flow field [5,7,8]. The 

development of the mean velocity and temperature fields closely parallel one another since buoyancy resulting from 

heat release in the fire is the major source of vertical momentum in the flow. The velocity profiles are narrower than 

the temperature profiles, so that regions of highest radial gradient of axial velocity are closer to the fire centreline 

than the highest radial temperature gradients. In this respect, the development of the mean flow field in the pool 

fire parallels that in a burning gas jet, suggesting strong similarities in the overall mixing and entrainment processes. 

In order to discuss the role of buoyancy in development of the flow, as well as its link to turbulence properties, 

contributions to turbulent energy production due to the mean flow were considered as distinct from those due to 

buoyancy. Measurements of the most significant terms in the kinetic energy balance indicate that,in the fire, the 

dominant path for buoyant production of turbulent kinetic energy is the indirect route fiom pgTI2 production-of 

the u'T' scalar flux, feeding buoyant production of kinetic energy through Pgu'T'. 

The magnitude of PgF is fairly uniform throughout the fire flow field, except very near the pool rim. There, 

enhanced mixing due to entrained ambient air feeds the flapping flame fronts which cause large relative temperature 

intensities. These intensities directly feed the generation of scalar flux u'T' and buoyant generation of turbulent 

kinetic energy. Contrary to the uniform axial production of energy through temperature intensity, the net buoyant 

contribution to turbulent kinetic energy rises rapidly with height above the fuel surface and falls off in the radial 

direction (Fig. 1). Evidently, the - mean flow production terms, through the mean flow gradients, play a significant 

role in the balance of scalar flux, u'T'. 

The relative importance of buoyancy and shear production of turbulent kinetic energy was also examined. 

The contribution to shear production of turbulent kinetic energy (Fig. 2) via -u1v'8U/ar is dominant through 

most of the flow, with -u'u'aV/t3x contributing significantly (up to 30%) only in the outer regions of the fire 

well above the fire base. The topology of the shear and buoyancy production terms are similar, with the highest 

- - 

- 

- 

- 

'Research supported through individual NSERC Operating Grants to E.J. Wedanan and A.B. Strong 
62 

levels of shear production corresponding to regions of highest mean velocity gradient. The flux Richardson number, 

Rij = -Gbuqancy/Pihsar, is approximately -1.0 throughout the fire flow field, much larger than would be expected 

in a typical buoyant jet and approaching values seen in largescale atmospheric flows. 

A turbulence Reynolds number, Ret =.&Au4/v, was calculated based on temperature corrected viscosity, and 

calculated Taylor microscales for u'. Levels of turbulent kinetic energy increase with height above the fuel but 

decrease toward the edges of the fire, while the Taylor microscale for length increases in value in the radial direction. 

The combination of these effects lead to fairly uniform values of R,et radially, but increasing with height above the 

fuel. Choosing a critical value of Ret of 100 for fully turbulent flow, the data indicate that the fire is turbulent 

over most of the domain and suggest a very limited region (less than 0.1 m above the fuel surface) where laminar 

diffusion could be considered an appropriate mechanism controlling combustion. 

Conclusions 

The velocity and temperature data presented here substantiate many of the observations made in previous 

studies of medium-scale pool fires. 

New information is provided through calculations of velocity and temperature turbulence properties. A preliminary evaluation of these mezsurements shows that high values of some properties initially occur in regions of 

flapping flame fronts. The profiles of all turbulence properties evolve in a manner consistent with those in a buoyant 

shear flow but for the relatively higher negative values of flux Richardson number which suggest aspects of large 

scale environmental flows. Clearly, the flow is turbulent through most of the &e. 

The detailed data presented contribute to a complete mapping of the coupled, fluctuating velocity and temperature fields in a liquid pool fire. They provide an entirely consistent description of fire flow field development and 

contribute to the data base required to improve and validate existing explanations of fire development. 

References 

1. 

2. 

3. 

4. 

5. 

Fischer, S.J., Hardouin-Duparc, B. and Grosshandler, W.L.: Comb. Flame 70, 291 (1987). 

Gengembre, E.: Ph.D. Thesis, E.N.S.M.A., University of Poitiers (1983). 

Crauford, N.L.: Ph.D. Thesis, University of Southhampton (1984). 

Weckman, E.J.: Ph.D. Thesis, University of Waterloo (1987). . 

Annaruma, M., Most, J.M. and Joulain, P.: 12th ICDERS, Michigan (1989). 

Fig. 1: Buoyancy production of turbulent 

kinetic energy due to scalar flux U'T' 

- Fig. 2: Total contribution of shear production 

to the balance of turbulent kinetic energy due 

-au -av 

ar 62 to (- u'v' - - u'v' -) 
63 

RADIATIVE PROPERTIES OF AN UNSTEADY JET DIFFUSION FLAME 

Carolyn R. Kaplan, Seung W. Baek., and Elaine S. Oran** 

Navy Technology Center for Safety and Survivability 

Naval Research Laboratory 

Washington, D.C. 20375 

INTRODUCTION 

Numerical simulations otan axisymmetric buoyant ethylene jet diffusion flame have been carried 

out to study the effects of radiation transport on the development, structure and dynamics of the flame. 

The numerical model is based on one originally developed by Ellzey et al. [l] for hydrogen jet diffusion 

€lames. Now, it has been modified to examine hydrocarbon flames, so that it includes new models for 

chemical reactions and energy release, soot formation and radiation transport. In this paper, we simulate 

a low-velocity laminar ethylene diffusion flame for which experimental data are available in the literature 

[2]. These simulations serve as a benchmark for validation of these new algorithms. 

NUMERICAL METHOD AND MODEL FORMULATION 

The numerical model solves the time-dependent equations for conservation of mass density, 

momentum, energy, individual species number densities, soot number density and soot volume fraction. 

These equations include terms for convection, thermal conduction, molecular diffusion, viscosity, gravity, 

chemical reaction and energy release, soot formation and thermal radiation. The equations are then 

rewritten in tern of finite-volume approximations on an Eulerian mesh and solved numerically for 

specified boundary and initial conditions. The model consists of separate algorithms for each of the 

individual processes, which are then coupled together by the method of timestep splitting [3]. A thorough 

description of the algorithms for convection, thermal conduction, molecular difCusion, Viscosity and the 

coupling of the individual processes have been previously described in detail [l]. The chemical reaction. 

and energy release process for ethylene oxidation is modeled phenomenologically using a finite-rate, quasiglobal Arrhenius expression from Westbrook and Dryer [4]. The evolution of soot number density and 

volume fraction is represented by two coupled ordinary differential equations derived by Moss et al. [5] 

which includes terms for soot nucleation, surface growth and coagulation. The radiative heat flux is found 

from a solution of the radiative transfer equation using the Discrete Ordinates Method [6]. The radiation 

transport model spans twelve directions and includes radiative effects from soot, CO, and H20. Scattering 

is neglected since it is negligiile in comparison to absorption. 

We simulate a case in which undiluted ethylene fuel flows at 5.3 cm/s through a 1 cm diameter 

burner into a coflowing air stream. The computational domain covers a region of 10 cm x 15 em for a grid 

consisting of 64 x 88 cells. The left hand boundary is an axis of symmetry, while the right hand boundary 

is a free-slip wall. The bottom boundary represents an inflow condition, while the top is an outflow 

boundary where the pressure is adjusted to atmospheric conditions. Boundary conditions for the radiation 

transport model include diffusely emitting-reflecting surface conditions at the inflow, outnow and right hand 

boundaries. At the axis of symmetry, the specularly reflecting boundary condition is used. Timesteps are 

on the order of 10 ps. 

*Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology, 373-1 

8. Gusung-dong, Yusung-ku, Daejon, Korea 

Laboratory for Computational Physics and Fluid Dynamics, Naval Research Laboratory, 

Washington, D.C. 20375 

Prepared for submission to the Annual Conference on Fire Ra&, Oct. 13-16, 1992, Rockville, MD. 
64 

RESULTS 

Figure 1 shows instantaneo& contours of mixture fkaction, soot volume fraction, temperature, 

radiative intensity and the radiative heat flux vectors at 4oooO timesteps. Mixture fraction is defined as the 

mass fraction of fuel elements found in the mixture at any location in the flow. The maximum flame 

temperature, 2100 %, is located 4 cm from the base of the flame. The maximum soot concentration is 

16x10d, and is located within the region where the mixture fi-action ranges from approximately 0.05 to 0.1. 

The maximum mole fractions of H20 and CO, (not shown) are 0.11 and 0.12, respectively, and are located 

in the high-temperature region. The temperature contours show the low-frequency buoyancy-driven outer 

structures which are assoCiated with flame flicker. 

The radiative intensity is greatest near the sooting region, with a maximum value of 1000 kW/m2, 

and then decreases with distanue from that region. The contours show the strong attenuation of radiative 

intensity in the heavily sooting region. The length of each of the radiative heat flux vectors is proportional 

to the magnitude of the vector. The vectors with the largest magnitude are located near the sooting region 

and decrease with distance from that region. Although the radiative flux vectors point predominately in 

the radial diredon, there is a strong axial componemt which follows the curvature of the sooting region. 

This indicates that the axial component of radiation transfer cannot neceSSarily be neglected, which is 

common practice in many radiation transport models. 

REFERENCES 

1. Ellzey, J.L, Laskey, KJ., and Oran, E.S., Combrut Flame 84:249 (1991). 

2. Kent, J.H. and Honnery, D.R, Combust Flame 79287 (1990). 

3. Oran, E.S. and Boris, J.P., Nwnerical Simulation of Reactive Flow, Elsevier, 1987. 

4. Westbrook, C.K. and Dryer, F.L, Comb. Sci. Tech 27:31 (1981). 

5. Moss, J.B., Stewart, C.D., and Syed, KJ., Twenty-Second S- (IntdnaI) on Combustion, p. 

6. Kim, J.S., Baek, S.W., and Kaplan, COR, Comb. Su Tech. (to appear, 1992). 

413, The Combustion Institute, 1988. 

15 Q11 

0 3.1 cm 

Fig 1. Instantaneous contours at timestep 4oooO (0.4 s) 
65 

ADDITIVE EFFECTS ON SOOT FORMATION IN LABORATORY POOL FIRES 

E.J. Weckman and C. Salvador 

Department of Mechanical Engineering 

University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1 

Introduction 

The effects of additives on soot formation and burnout in flames have been studied for many 

years [l-61. It has been determined that inorganic alkali and alkaline earth salts [l-31, as well 

as organo-iron compounds [4-61 can have marked effects on the overall soot production in both 

premixed and diffusion laboratory-scale flames. In the case of organo-iron compounds, it appears 

that soot formation initially is enhanced, with large numbers of small soot particles being produced 

[4]. Following this, depending on the total residence time of the soot in the flame, the additive 

appears to have either increased [4] or decreased [5] the total amount of soot produced in the flame. 

Recently, it has been demonstrated that organo-iron compounds decrease total soot emission from 

both small-scale kerosene and crude oil fires [5,6] and larger-scale crude oil fires [7]. Chemical 

mechanisms have been proposed to explain the effects of these additives on the soot formation 

mechanisms in these open fires, but no quantitative measurements were made in the fire flow field. 

Therefore, further study is required in order to verify details of the additive/fire interactions' in 

open diffusion flames or to predict the effects of an additive on soot production in larger-scale fires. 

In this study, the flaming regions of highly sooting (kerosene) and less sooting (methanol, acetone and ferrocene-doped kerosene) pool fires are examined and compared. Flow visualization is 

combined with mean and rms temperature and velocity measurements to chart the overall development of the fire flow fields. In addition, the nature and distribution of the soot is examined 

throughout the continuous and intermittent flame zones of 6.5 and 31 cm diameter pool fires. 

The Experiments 

The fires were established in the existing University of Waterloo pool fire test facility, which 

has been described in detail in reference 8. Velocities were measured (where possible) using two 

component LDA operated in the forward scatter configuration, while temperatures were measured 

with a 50 pm diameter bare wire Pt/Pt-lO%Rh thermocouple. Soot loading was estimated gravimetrically, and the nature of the particles examined by collecting samples onto small discs and using 

both optical and scanning electron microscopy with image analysis equipment. 

Preliminary Results and Discussion 

The overall development of the mean temperature and velocity fields in all of the fires are 

very similar to those that have been reported previously [8]; however, details of the distribution of 

temperature, and therefore the velocity field, do exhibit some variations in the fires with ferrocene 

added. The overall structure and visible flame height of small kerosene fires appeared unchanged 

with and without ferrocene added to the fuel; however, generally higher centreline temperatures 

were observed in small kerosene fires doped with ferrocene. In the larger kerosene fires, on the other 

hand, the visible flame heights appeared shortened when ferrocene was added to the fuel and the 

fire changed in colour and shape, indicative of the changes in soot formation and therefore radiation 

distribution within the flow field. 

'Research supported through individual NSERC Operating Grant to E.J. Weckman 
66 

In general, the soot collected from kerosene fires with ferrocene added was much finer than that 

collected in the base kerosene fires. Similarly, there appeared to be higher soot particle loadings in 

the lower regions of the fire. Both these observations are consistent with previous work *[3,4] and 

the theory that soot agglomeration processes are hindered by the addition of the additive. 

Ferrocene added to the kerosene fire reduced total soot emission, as measured in the upper 

regions of the smaller fires, by about 30%. This is of the order suggested in reference 2 for alkali 

earth additives in polymer diffusion flames, but less than the amount predicted in reference 6 for 

ferrocene additions to crude oil fires. This discrepancy is still under investigation. 

Conclusions 

Results of this study provide the first quantitative data on the effects of ferrocene addition 

for soot suppression in small and medium-scale open pool fires. Addition of ferrocene does not 

affect the overall development of the fire flow field; however, there is an effect on the details of the 

temperature and velocity fields. 

Soot collected in the fires with ferrocene added is finer and the soot particle loading is higher 

near the base of the fires. In the upper regions of the fires, total soot emission has been reduced, 

by about 30% for small kerosene fires. 

In the smaller fires, the addition of ferrocene, and consequent reduction in soot loading, does not 

appear to affect either the flame height or visible structure of the fire. In the larger diameter fires, 

on the other hand, flame heights are shortened and the fire appears less luminous with ferrocene 

addit ion. 

References 

1. Howard, J.B. and W.J. Kausch: 

2. Ndubizu, C.C. and B.T. Zinn: 

3. Bonczyk, P.A.: 

4. Ftitrievi, K.E., J.P. Longwell, and A.F. Sarofim: 

5. Mitchell, J.B. and J.M. Miller: 

6. Mitchell, J.B.: 

7. Mitchell, J.B.: Personal Communication. 

8. Weckman, E.J.: 

Prog. Energy Combust. Sci. 6, 263-276 (1980). 

Comb. and Flame 46, 301-313 (1982). 

Comb. and Flame 67, 179-184 (1987). 

Comb. and Flame 70, 17-31 (1987). 

Comb. Flame 75, 45-55 (1989). 

Comb. and Flame 86, 179-184 (1991). 

PhD Thesis, University of Waterloo, Canada, 1987. 
67 

Modeling the Growth of Polynuclear Aromatic Hydrocarbons in Diffusion Flames 

J.H. Miller 

Department of Chemistry 

The George Washington University 

Washington, DC 20052 

We have developed a model which describes the physical and chemical processes that control PAH 

and soot concentrations along stream lines in laminar methane/air and ethylene/air diffusion flames. The 

development is similar in spirit to that presented in a recent paper by kMedy et al. [l]. In both models, 

soot processes are divided into three broad classifications: inception, chemical and physical growth 

(agglomeration), and oxidation. Both models assume that the rates of the soot processes depend on mixture 

fraction. In our model, we attempt to rationalize the choice of these rates from a knowledge of the 

fundamental chemical processes which are occurring in the flame combined with detailed measurements of 

species concentrations. 

Growth 

The growth chemistry in our model is based on the work of Frenklach et al. who proposed a model 

for ring growth based on the successive addition of acetylene to a growing aromatic radical core [2,3]. In 

Frenklach's simplified mechanism parent PAH (4) are converted into a phenyl-like radical by hydrogen 

abstraction. The resulting radical reacts with acetylene to form a radical addition product. A subsequent 

acetylene addition irreversibly forms the next largest parent PAH. In this reaction scheme, using steady-state 

estimates for the concentrations of phenyl and phenylactylene radicals, the rate of formation of the h+l 

PAH can be written as 

where keE is dependent upon the concentrations of qH2, H,, and He. In addition to this chemical growth 

process, agglomeration of PAH is also considered [4], 

Inception 

As seen above, aromatic growth is treated as an irreversible sequence of acetylenic addition steps to 

a growing aromatic core whose initial source is the one ring species A, @e., benzene). Although, there have 

been a number of models proposed for the chemistry of the formation process of benzene (invoking either 

reactions of species [SI), no clear consensus exists for the 

dominant channel in hydrocarbon flames. Because of this uncertainty, we will adopt a different approach 

for deriving an inception rate. Over the past few years an extensive data base for species concentrations, 

temperature, and velocity in a laminar methane/air diffusion flame has been collected. These data have 

included measurements of the concentration of stable species such as acetylene, benzene, and molecular 

hydrogen [6] and has been recently extended to include profile measurements of radical species [7,8]. With 

this data base, we have demonstrated how the overall rates for a species' chemistry may be calculated by 

solving its conservation equation directly. For the work presented here, we will use the correlation of the 

benzene formation rate with mixture fraction as calculated using this technique [9]. For mixture fractions 

where this net rate is negative (such as at the high temperature reaction zone), the inception rate will be set 

to zero. 

with C4 species [2] or the reaction of two 

Oxidation 
68 

In combustion systems, Soot and PAH may be oxidized by a number of species with 0-atoms, 

molecular oxygen, and hydroxyl radical believed to be dominant. In the model we include both .hydroxyl 

radical reactions with parent PAH and the reaction of molecular oxygen with radical PAH 

Mixture Fraction Libraries 

Concentration profiles for qH2, H2, He, OH; 0, temperature, and mixture fraction (derived from 

these and other species profiles) collected in a laminar methane/air diffusion flame supported on a WolfhardParker burner were used to build a library of growth and oxidation species. With the exception of qH2, the 

concentrations of these species showed little variation with flame height. Acetylene concentrations grow with 

height for the first 9 mm above the burner surface and then appear to level off. All profiles used in 

developing the library were collected at this 9 mm height. Much less chemical data is available for 

ethyleneair diffusion flames. Therefore, estimates based on equilibrium (full, super, and partial) must be 

made for the radical species concentrations. 

Flame Field Calculations 

We have modeled the structures of both methane/air and ethylene/air diffusion flames which have 

been studied by Santoro et al. [lo]. Velocity, density, and mixture fraction fields throughout the flame were 

obtained using a computer code which has been described previously [ll-131. 

Results and Discussion 

These results will be 

compared with experimental measurements of soot volume fractions, carbon monoxide concentrations, and 

flame temperature [ 141. 

Results for both methane/air and ethylene/air flames will be presented. 

References 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

Kennedy, I.M., KObaM, W. and Chen, J.-Y.: Combust. and Flame 81, 73 (1990). 

Frenklach, M., Clary, D.W., Gardiner W.C., Jr. and Stein, S.E.: Twenty-First Symposium (International) on Combustion, p. 1067, The Combustion Institute, 1986. 

Frenklach, M.: Twenty-Second Symposium (International) on Combustion, p. 1075, The Combustion 

Institute, 1989. 

Miller, J.H.: Twenty-Third Symposium (International) on Combustion, The Combustion Institute, 91 

Stein, S.E., Walker, J.A, Suryan, M.M. and Fahr, A: Twenty-Third Symposium (International) on 

Combustion, The Combustion Institute, (1990). 

Smyth, KC., Miller, J.H., Dorfman, R.C., Mallard, W.G. and Santoro, RJ.: Combust. Flame 62, 157 

(1985). 

Smyth, KC., Tjossem, PJ.H., Hamins, k and Miller, J.H.: Combust. and Flame 79,366 (1990). 

Smyth, KC. and Tjossem, PJ.H.: Twenty-Third Symposium (International) on Combustion, The 

Combustion Institute, 1829 (1990). 

Miller, J.H., Mallard, W.G., and Smyth, KC.: Twenty-First Symposium (International) on Combustion, 

p. 1057, The Combustion Institute, 1986. 

Santoro, R.J., Yeh, TT, Horvath, J.J. and Semerjian, H.G.: Combust. Sci. and Tech. 53, 89 (1987); 

Santoro, R.J. and Semerjian, H.G.: Spring 1984 Meeting of the Western States Section of The 

Combustion Institute, paper 84-49. 

Bilger R.W. and Sther, S.H.: Combust. and Flame 51, 155 (1983). 

Honnery, D.R. and Kent, J.H.: Combust. and Flame 82,426 (1990). 

Kent, J.H. and Honnery, D.R.: Combust. Sci. and Tech. 54,383 (1987). 

J.H. Miller, Reed Skaggs, and Bijan Ahvazi,"Measurements of Carbon Monoxide Concentration and 

Temperature in Axially-Symmetric Methane and Ethylene Diffusion Flames," Annual Conference on 

Fire Research (1992). 

(1990)- 
69 

AEROSOL DYNAMIC PROCESSES OF SOOT AGGREGATES IN A LAMINAR 

ETHENE DIFFUSION FLAME 

R. Puri, T.F. Richardson, and R.J. Santoro 

Department of Mechanical Engineering 

Pennsylvania State University 

University Park, PA 16802 

and 

R.A. Dobbins 

Division of Engineering 

Brown University 

Providence, RI 02912 

Introduction 

Soot particles consist of aggregates of a variable number of 

smaller primary particles which are uniform in size and more or less 

spherical in shape. The optical cross sections of these polydisperse 

aggregates have been formulated [l] and were used by Dobbins et al. [2J 

to reduce laser light scattering/extinction measurements in an 

ethene/air diffusion flame. In the present work, the intensity of the 

scattered light was measured simultaneously at three angles - 45O, 90° 

and 135O rather than sequentially [Z]. This improved data allows the 

determination of the fractal dimension D, by an iterative procedure, The 

new data (in conjunction with existing information on the local 

extinction, the primary particle size and velocity field information) 

allow a more detailed analysis of the observations. The current 

analysis provides a global description of the physical processes 

associated with formation, growth and oxidation of soot aggregates. 

ExDerimenta1 

A coannular burner [3 J , having a 1.1 cm diameter fuel tube and a 

concentric 10.2 cm diameter air annulus, was supplied with ethene and 

air at flow rates of 3.85 and 713 cm3/s respectively, The vertically 

polarized laser beam from an Argon ion laser having a wavelength of 

514.5 nm and incident power of 0.5 W was modulated at 1015 Hz before 

being focussed onto the flame. Scattered light receivers (comprising a 

polarizer, a 12.7 mm circular aperture, collection lens, a i mm pinhole 

aperture, laser line filter and a photomultiplier tube) were located at 

45O, 90° and 135O. The detectors were connected to lockin amplifiers 

and to a computer employing a GPIB interface; thus providing near 

simultaneous data acquisition from each detector. The detectors were 

calibrated using a Rayleigh scattering technique [3]. 

Results and Discussion 

Analysis of the light scattering data, when combined with 

Transmission Electron Microscopy (TEM), employing an approach previously 

reported by Dobbins et al. [2 J yields information on the aggregate size, 

primary particle size, aggregate number concentration, aggregate surface 

area, and average number of primary particles per aggregate. The light 

scattering results indicate that the aggregates can be described as 

fractal-like [4] with a fractal dimension of D, = 1.74. Figure 1 shows 

the measured results obtained for the soot volume fraction, f,, the 

primary particle diameter, d,, (as determined from TEM images) and volume 
70 

1 o-' 

I I *--.A ..-----+---~-........... 200 - 100 

....... A*-..- ' . \ 

4 - 80 

- 150 

4. . .A' 

........ v ..... 

A 

.... .... '\. :. n 

E -6OT ..... .. .-.- *..* ' ... c- r *'*. A - loow v 

c;" - 40 

.. .... 

'V. 0. a A ; 

V' 

,/ V 

......... 0 ....... 0 ......................... v ...... .. ,....o O .., 50 

- 20 */' 0 ..- -*. ,. .... 0- <;:.*** 

P 

- - a a a a a I - - a . a I a a a a - I - - - - 1 a a a a - - - 0 - 0 

mean diameter, D, of the aggregates. These three curves show maximum 

values at about 56 ms which corresponds to a height in the flame of 50 

nun from the burner exit. This point marks the transition from the 

growth region, where surface growth and cluster-cluster aggregation are 

contributing to particle size increases, to the oxidation region where 

oxidation reactions oppose aggregate growth. For this same region of 

the flame, the number concentration of the primary particles remains 

constant while the number concentration of aggregates monotonically 

decreases with time (or height in the flame). This aggregation process 

occurs at a rate similar in magnitude to theoretical calculations for 

the coagulation of spherical particles in the free molecular limit. The 

data reduction of the soot particle field that is based on the presence 

of aggregate morphology presents an internally consistent picture of the 

development of the soot particle field in laminar diffusion flames. 

Acknowledaement 

This research was performed under the sponsorship of the U.S. 

Department of Commerce, National Institute of Standards and Technology, 

Center for Fire Research under grant number 6ONANBOD1035 to the 

Pennsylvania State University and grant numbers 60NANB9D0975 and 

60NANBlD1110 to Brown University. 

References 

1. Dobbins, R.A. 8 and Megaridis, C.M.: Applied Optics, 30:4747, 1991. 

2. Dobbins, R.AOI Santoro, R.J., and Semerjian, H.G.: Twenty-Third 

Symposium (International) on Combustion, The Combustion Institute, 

3. Santoro, R.J., Semerjian, H.G., and Dobbins, R.A., Combustion and 

Flame, 51: 203, 1983. 

40 Megaridis, C.M., and Dobbins, R.A.: Combustion Science and 

Technology, 71:95, 1990. 

pp. 152591532, 1990. 
71 

Carbon Monoxide and Soot Particle Formation Studies in Underventilated Laminar Diffusion Flames. 

S..G. Uonard, R. Puri and R.J. Santoro 

Department of Mechanical Engineering 

Pennsylvania State University 

University Park, PA 16802 

and 

G.W. Mulholland 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

Introduction Carbon monoxide (CO) has been identified as one of the most serious products of 

incomplete combustion resulting from fires. Since the severity and the rapidity of its effect depend on 

concentration [l], a better understanding of its formation with respect to other species is of great interest. 

Studies of the fundamental process of CO formation and its relationship to soot have recently been 

reported [2]. However, the use of overventilated diffusion flames for these studies limited the range of 

fuel equivalence ratio which could be studied. Underventilated flames offer the opportunity to study 

much richer fuel conditions, but previous studies of this flame configuration are lacking. In the present 

study a series of underventilated laminar diffusion flames have been investigated with respect to the CO 

and soot yields as a function of fuel and oxidizer ratio and flow rate. Based on the analysis of soot 

samples collected on filters, information on the organic carbon content of the soot has also been 

obtained. Preliminary results for these studies are presented here to provide an overview of CO and soot 

formation under underventilated flame conditions. 

Experimental ApDroac h Underventilated diffusion flames refer to conditions where the amount of 

oxidizer flow is insufficient to result in the oxidation of all of the fuel to carbon dioxide and water. In the 

following study, the fuel to oxidizer ratio is characterized by the overall equivalence ratio, CP, based on 

the ratio of the inlet fuel and air flow rates, where CP greater than one correspond to fuel rich conditions. 

The burner consists of two concentric tubes which could be varied in size to investigate the sensitivity of 

the results to burner geometry effects. In the present work, results for a single burner will be presented 

which are representative of the general behavior obsemed for the CO and soot yields. This burner had a 

fuel tube of 0.73 cm i.d. and outer air annulus with a 2.88 cm i.d. Both methane (Ca) and ethene 

(C2H4) fuels were studied. For the methane flames, fuel flow rates of 10 cm3/s and 20 cm3/s were . 

examined, while for ethene, flow rates of 3.2 and 6.4 cm3/s were considered. The air flow rates were 

selected in each case to allow the overall equivalence ratio, a, to be varied between 0.5 and 4.0. 

Measurements of CO and CO2 concentrations were obtained using individual NDIR instruments while 

soot particles were collected separately using filters and analyzed for mass deposited by a weighing 

procedure. Yields for CO and soot on a mass basis were determined from the measured concentrations 

and known flow rates of the gases supplied to the burner. Samples were withdrawn near the top of a 

glass chimney enclosure at a location approximately 50 cm above the burner exit. A large nitrogen 

dilution flow of 472 cm3/s was introduced in a mixing section of the enclosure to cool the product gases 

and aid in achieving uniform concentration profiles across the exit where sampling occmed. A tripper 

plate was placed at the connection between the main burner and the mixing section to assist in this 

process. 

Results and Discussion Figure 1 shows the CO and soot yields as a function of equivalence ratio for the 

ethene flame with a fuel flow rate of 6.4 cm3/s. It should be noted that this fuel flow rate corresponds to 

conditions well above the smoke point for ethene [3]. For these conditions, the soot yield is observed to 

initially increase slightly as CP is increased from one-half. However this quantity then is observed to 

decrease for greater than one with the soot yield varying by about one order of magnitude as CP is 

varied from lean to rich conditions. For @ greater than one, CO is qualitatively observed to follow a 

similar although somewhat smaller variation. For lean overall equivalence ratios (0.5 I Qr e 1 ) the 

yields of CO are observed to be quite low. These trends are consistent with previous observations 

regarding the behavior of soot and CO in overventilated laminar diffusion flames. Analysis of the 

elemental and organic carbon content of soot formed in these underventilated flames reveals for 0 2 2 

that the organic to elemental carbon ratio exceeded one for both the methane and ethene flames. Such 
72 

large amounts of organic carbon in the soot particles is viewed to be quite interesting and differs from 

observations for soot formed in overventilated flames where the organic carbon content is usually much 

lower. 

Future work will emphasize more detailed comparisons with overventilated flame results as well 

as further analysis of the fuel structure and burner geometry effects. 

0 

0 - 

0 

0.5 

0.4 

0.3 

0.2 

0.1 

0 

0.06 

0.05 

0.04 

0.03 

0.02 

0.01 

0 

3 

0 

r, 

0 1 2 3 4 5 

Overall Equivalence Ratio Q, 

Figure 1. Yield of CO (+) and soot (+) for the ethene flame at a fuel flow rate of 6.4 cm3/s. Yield of CO 

is in grams of CO per gram of fuel (C2H4) and yield of soot is in grams of C per gram of fuel. 

Measurements of CO are based on a dry analysis. The lines of the graph are only to indicate trends and 

are not curve fits. 

cknowledeement The work done at the Pennsylvania State University was supported under grant 

60NANBOD1035 from the National Institute of Standards and Technology. 

References 

1. 

1986. 

2. 

Symposium, p. 595, 1991. 

3. 

Technology, p. 235, 1980. 

Purser, D.A.: Fire Safety Science - Proceedings of the First International Symposium, p. 1101, 

Puri, R., and Santoro, R.J.: Fire Safety Science - Proceedings of the Third International 

Schug, K.P., Manheimer-Timnat, Y., Yaccarino, P. and Glassman I.: Combustion Science and 
73 

A MODEL OF SOOT WITH DETAILED CHEMICAL KINETICS 

Clement Yam and Ian Kennedy 

Department of Mechanical, Aeronautical and Materials Engineering, 

University of California 

Davis CA 95616 

Introduction. Thermal radiation from fires is an important aspect of fire spread and 

ignition. Fires are usually highly luminous i.e., much of the radiation is due to the 

presence of particles of carbonaceous soot in the flames. The prediction of luminous 

radiation continues to be a difficult problem in combustion research because of the 

inherent difficulty in predicting the amount of soot that is present in a flame. Several 

approaches to the prediction of soot and its radiation have been explored over the last 

decade. Some methods rely on scaling approaches or on empirical correlations of 

radiation while others attempt to solve conservation equations for the amount of soot in a 

flame. Among the latter approaches there are two methods. One method attempts to 

predict the production of soot with detailed chemical kinetics from acetylene to the first 

aromatic ring and upwards in molecular weight. This approach is strictly a research tool; 

it will not be possible to implement the complex kinetics in an engineering prediction in 

the near future. The other possible method is a semi-empirical approach in which 

knowledge of the soot process that is derived from experiments is used to develop a 

comelation of soot production and oxidation rates. The rates are then used in conservation 

equations that are solved numerically. This semi-empirical approach to soot formation 

and oxidation has been explored in this project. 

Model for Soot Formation and Oxidation The basis for the model of soot that we have 

developed is a correlation between soot surface growth rates and the local equivalence 

ratio in a flame Le., the mixture fraction. This correlation was obtained from experiments 

in a counterflow diffusion flame. An Anhenius dependence on temperature is also 

assumed for the surface growth rate. The rate of growth is assumed to depend on the total 

surface area of the soot aerosol. It was found that the details of the nucleation step were 

not necessary in order to achieve satisfactory predictions of soot volume fractions. Rapid 

coagulation of freshly nucleated particles collapsed the number of particles to low values 

and there was a resulting insensitivity to the nucleation step when soot volume fractions 

were high. Therefore, calculations were performed with only the soot volume fraction 

equation as part of an integrated flow field prediction. The other equations that were 

solved included the continuity equation, the momentum equation and an energy equation. 

The latter equation included a radiative heat loss term to account for the energy lost by luminous radiation from soot. 

The equation for the soot volume fraction included two source terms and two sink terms. 

The source terms were the contribution to the soot volume fraction due to the nucleation 

of new material and the formation of soot due to surface growth. The sink terms included 

oxidation due to attack by OH and by 02. Equilibrium values of OH and 02 at the local 

mixture fiaction and enthalpy were used in the original predictions that are reported in 

detail in the 24th Symposium on Combustion. 

Recent measurements by Pun et al. of OH concentrations in a sooty ethylene flame have 

raised doubts about the validity and accuracy of the modeling that has been used for the 

oxidation step in the soot process. The LIF measurements indicate that OH concentrations 

are up to an order of magnitude higher than the equilibrium values that have been used in 
74 

the soot modeling. Furthermore, the model that we have developed has shown that the 

loss rate of OH on soot is comparable to the estimated net production rate of OH in the. 

flame. Therefore, a goal of the project has been the relaxation of the equilibrium 

assumption regarding OH ( and other radicals such as 0). The impact of soot burnout on 

the flame chemistry and the inverse problem of the impact of finite rate OH kinetics on 

soot oxidation have been investigated. 

A model has been developed for the co-flow 

erning equations were solved in boundary layer 

form. Hence, the parabolic system of pde's could be solved with considerably greater 

speed than can be achieved if the full elliptic problem is solved. For example, the 

calculations that are presented here were obtained on a UNIX workstation in about 7 

hours; the elliptic problem requires many hours on a Cray. Neglecting phenomena such 

as diffusion in the axial direction is unlikely to be important in the present situation in 

view of the inaccuracies surrounding the soot model. A detailed kinetic scheme for 

methane and air has been used. The "short" mechanism from Sandia with forty six 

reactions was adopted. Seventeen species equations were solved along with the 

momentum equation, the energy equation and the soot volume fraction equation with the 

same source terms as before. However, in the present treatment of oxidation, the actual 

pmhcted OH and 02 mole fractions are used. In addition, a sink term in the equation for 

OH has been included in order to model the loss of OH on soot particles. In a sense, the 

model as it stands at present is a hybrid model with detailed chemistry for methane but 

surface growth rates that apply to an ethylene flame. In the near future, C2 chemistry will 

be incorporated into the model so that true ethylene-air chemistry can be treated. 

Predictions of Soot. OH and 0 with Finite Rate Kinetics The axisymmetric ethylene 

diffusion flames of Santoro et a1 have been calculated. The amount of soot increases 

along each of the flames until oxidation becomes important towards the end and the soot 

volume fractions begin to decrease. The soot layer lies within the flame envelope. The 

peak Soot distribution is in reasonable agreement with the levels that were reported by 

Santoro et al from laser extinction measurements. 

Equilibrium values of OH were obtained by running STANJAN with the calculated 

temperature at each radial point and the calculated N, 0, C, and H atom ratios. Large 

superequilibrium values of OH are predicted. At the peak OH location the calculated OH 

mole fraction can exceed the equilibrium value by as much as a factor of 10. This value is 

accord with the measurements of Pun, Moser, Santoro and Smyth in an ethylene flame. 

Further work needs to be done with ethylene kinetics to be certain of this result but it is 

not likely to be greatly different. The peak OH mole fraction decreases along the flame, 

pharily as a result of the drop in temperature due to radiation. 

Another potentially important oxidant of soot is the 0 atom. Large superequilibrium 

concentrations are obtained, in this case up to a factor of 60 larger than equilibrium. The 

Soot model does not include 0 as an oxidant at present. These results suggest that it may 

be potentially important. The assumption of equilibrium concentrations for OH are also 

inaccurate. It is not clear at present how these non-equilibrium effects can be incorporated 

into the basic soot model whilst retaining its potential for use in turbulent flame 

calculations. 

Acknowledgement This work was performed with the support of NIST through Grant 

6ONANBOD1055. 
75 

THE OXIDATION OF CARBON MONOXIDE AND SOOT 

IN HYDROCARBON DIFFUSION FLAMES 

Rahul Puri, Marlow Moser and Robert J. Santoro 

Department of Mechanical Engineering 

Pen ns y I va n ia Stat e University 

University Park, PA 16802 

and 

Kermit C. Smyth 

Building and Fire Research Laboratory 

Gaithersburg, MD 20899 

National Institute of Standards and Technology 

Introduction Since CO inhalation is one of the major causes of fire fatalities, significant effort 

has been directed towards obtaining an understanding of the increased CO production in fires. 

Numerous workers have observed a correlation between the amounts of CO and soot produced 

in diffusion flames [I] as well as compartment fires [21. 

Our earlier work [3] sought to obtain a fundamental understanding of the relationship 

between the production rates of CO and soot in diffusion flames. The effects on the CO 

depletion rates of lower temperatures (due to radiation heat loss from the soot particles) and 

competition between CO and soot for the oxidizer species OH. were examined using equilibrium 

estimates of the OH- concentration. Based on the rates of CO and soot oxidation due to OH., 

competition between these species for OH* was found to be plausible in both fuel lean and fuel 

rich regions of the flames studied. While radiation quenching (through reduction of OH. radicals) 

seemed important in the fuel lean regions, the equilibrium concentrations of OH- did not 

correlate with the observed CO destruction rates in the fuel rich regions. 

Our recent work [41 has shown that equilibrium estimates of OH. concentrations are not 

reliable, with the departure from equilibrium depending upon the soot loading. Therefore, in 

order to carefully evaluate the interaction between CO and soot, OH- concentration 

measurements were extended to the flames of our earlier study [3]. 

Experimental Amroach Laminar diffusion flames burning fuel mixtures were used to vary the 

soot concentration while keeping the total carbon flow rate constant. Flames burning methane 

(9.8 cm3/s) and methane (5.6 cm3/s) doped with either butane (1.05 cm3/s) or 1-butene (1.05 

cm3/s) were studied. The OH* concentrations were measured in the soot oxidation region of 

these flames using laser-induced fluorescence. The experimental arrangement and the 

measurement procedures are described in detail elsewhere [4]. 

Results And Analvsis Figure 1 presents the OH* concentration as a function of the axial 

centerline position in the three flames, with the error bars showing the estimated uncertainty. 

The pure methane flame and the methane/butane flames have maximum centerline soot volume 

fractions of 0.76 and 2.55 ppm respectively and completely oxidize all the soot produced within 

the flame. Consequently these flames have a closed flame tip at axial locations of 10.7 and 

1 1.7 cm respectively. The methane/l-butene flame has a maximum centerline soot volume 

fraction of 5.46 ppm and does not have a closed flame tip since it emits smoke. This figure 

clearly shows that as the soot concentration increases, the centerline OH. concentration 

decreases. The most noteworthy feature is that the pure methane and the methane/butane 

flames have approximately the same OH. concentration along the flame centerline once the soot 

particles are completely oxidized. Thus, the decrease in the OH. concentration in the presence 

of soot particles can be attributed to chemical consumption by soot particles. 
76 

In addition to the soot 

concentration the OH* 

concentration can be expected' 

to depend on the local 

stoichiometry (9) 8 tem perature 

(T) and the CO concentration 

(which may not be uniquely 

related to @ [3]). Equilibrium 

calculations reveal that the OH* 

concentration is not very 

sensitive to tp for tp 5 0.95. 

The lean flame region, with the 

elimination of the @ 

dependency, is amenable to a 

simple analysis for the 

evaluation of the relative 

contributions of thermal and 

chemical effects to the 

observed OH. concentration. 

Along the centerline the 

Methane/Butane 

h Methane/l -Buten 

I A 

e 

1 

I 

5 10 15 

Centerline Position (cm) 

Figure 1. Centerline OH. concentration profiles in the soot 

oxidation region of the flames studied. 

OH. concentration depends upon the temperature and the concentrations of CO and soot, Le. 

[OH.] = f(T,[Soot],[CO]). However, on the lean side of the flame front, where there is no soot 

and little CO, the OH- concentration depends only on the temperature, i.e. [OH-] = f(T). A 

comparison for flames with different soot concentrations allows a simple estimate to be made 

of the relative contributions of thermal and chemical effects on the CO depletion rates. If 

then the relative contribution of radiative quenching to the observed decrease of the OHconcentration in the methane/l -butene flame is the ratio F,/F,. This analysis indicates that 

radiative quenching makes only a 6% f 2% contribution to the observed lower OHconcentration along the centerline in the methane/l -butene flame. Thus, the OH. concentration 

in the presence of soot particles is suppressed primarily due to oxidation reactions as opposed 

to thermal quenching effects. 

Acknowledaement The work done at the Pennsylvania State University was supported under 

grant 6ONANBOD1035 from the National Institute of Standards and Technology. 

References 

1. 

2. 

3. 

4. 

Koylu, ii.b.8 Sivathanu, Y.R., and Faeth, G.M.: Fire Safety Science - Proceedings of the 

Third International Symposium, p. 625, 1 99 1 . Fischer, S.J., and Grosshandler, W.L.: Twenty-Second Symposium (International) on 

Combustion, p. 1241, 1988. 

Puri, R., and Santoro, R.J.: Fire Safety Science - Proceedings of the Third International 

Symposium, p. 5958 1991. 

Puri, R., Moser, M., Santoro, R.J., and Smyth, K.C.: to appear in the Twenty-Fourth 

Symposium (International) on Combustion, 1 992. 
77 

Measurements of Carbon Monoxide Concentration and Temperature 

in Axially-Symmetric Methane and Ethylene Diffusion Flames 

J.H. Miller, Reed Skaggs, and Bijan Ahvazi 

Department of Chemistry 

The George Washington University 

Washington, DC 20052 

Carbon monoxide is an important flame species. A substantial fraction of the heat release in a flame 

occurs from the CO oxidation reaction: 

In many combustion systems this reaction is essentially irreversible, which serves as the basis for the development 

of global oxidation kinetics relationships of the form 111: 

CO + OH. -+ C02 + H* 

where bv represents the effective, overall rate constant for the process. In other combustion systems, this 

reaction is close to equilibration, which may explain the correlation of carbon monoxide concentration with local 

equivalence ratio (or, alternatively, mixture fraction) [2]. 

Because of the effectiveness of its binding with hemoglobin, carbon monoxide is largely responsible for 

the loss of life in fire situations 131. In efforts aimed at the development of a predicative capability for carbon 

monoxide emissions from fires, various workers have found that CO concentrations can be correlated against 

overall stoichiometry in the ceiling layers of room fues. Of course, although similar in overall appearance, these 

correlations are quantitatively different from those observed within the flame itself [Z]. Because the carbon 

monoxide oxidation reaction may effectively be frozen below a certain temperature (due to a decrease in hydroxyl 

radical concentrations), the conceptual link between in-flame and global correlations will be established via a 

coupling of a carbon monoxide oxidation model with a turbulence code capable of predicting the occurrence of 

this thermal quenching. Although this task may be far into the future, the data required to validate such a model 

must come from measurements of CO concentrations in both laminar and unsteady diffusion flame conditions. 

This will eventually require not only quantitative accuracy, but also fast temporal response, as can be provided 

by tunable diode laser diagnostics. 

The emission of soot particles from flames is likely to also affect the concentration of emitted carbon 

monoxide. There are two reasons for this assertion. First, large soot particles radiate considerable energy, thus 

cooling the local flame environment. If the cooling is substantive enough, the rate of carbon monoxide oxidation 

will decrease. Secondly, copious amounts of carbon monoxide accompany the oxidative pyrolysis of aromatic 

compounds [4]. Since soot has essentially an aromatic structure, carbon monoxide might be an expected product 

of the soot oxidation process. 

Measurements of carbon monoxide concentrations in Wolfhard/Parker diffusion flame systems have been 

accomplished in three ways: a laser-induced fluorescence technique [5], which gives only a relative determination 

of concentration, a quartz microprobe/mass spectrometric technique [6], and tunable diode laser absorption 

spectroscopy QDLAS) [8]. For the mass spectrometric technique, profiles of signal at molecular weight 28 were 

collected at three different ionization energies. In this flame, there are three species which occur at this mass to 

charge ratio: CO, N2, and ethylene. Because carbon monoxide has a slightly higher ionization potential than 

ethylene and a slightly lower one than nitrogen, CO concentrations can be calculated by subtraction of profiles 

combined with the application of molecule and ionization-energy specific calibration factors. This is a somewhat 
78 

cumbersome process and is appropriate only for laminar flames. It should also be noted that this technique is 

only possible when soot concentratio& are quite low because of clogging of the microprobe orifice by particles 

[7,9]. Because light scattering intensity is proportional to X4, absorption spectroscopy in the mid-infrared 

spectral region is free from interference by particulates. Thus, the quantitative determination of carbon monoxide 

concentration in the presence of soot is most easily accomplished with TDLAS. 

Much of the available data on soot concentrations in diffusion flames has been collected in axially 

symmetric jet burners [lo]. In the work described here, we apply TDLAS to measurements of both carbon 

monoxide concentration and local flame temperature in axial ethylenelair and methane/air diffusion flames. 

Because TDLAS is a line-of-sight technique, tomographic reconstruction of the flame structure is required to 

obtain radial profiles [ 1 1-14]. The results of these measurements are compared with computed flame structures 

and soot concentration maps for these flame systems [ 151. 

References 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

15. 

R.A. Yctttr, F.L. Dryer, and H. Rabitz, "Complications of One-Step Kinetics For Moist CO Oxidation," in Twenty-fmt 

Symposium (Intnl.) on Combust., 749-760 (1986). 

R.E. Mitchell, A.F. Sarofun, and L.A. Clomburg, "Experimental and Numerical Investigation Confined Laminar Diffusion 

Flames, " Combust. Flame 37, 227-244 (1 980). 

W.M. Pitts, "A Long Range Plan for a R-h Project on Carbon Monoxide Production and Prediction," NISTIR 894185 (1989). 

K. Brczinsky, "High Temperature Oxidation of Aromatic Hydrocarbons," Prog. Energy Combust. Sci. 12, 1-24 (1986). 

P.J.H. Tjosscm and K.C. Smyth, "Multiphoton Excitation Spectroscopy of the B'C' and CIC+ Rydberg States of CO," J. Chem. 

A. Hamins and J.H. Miller, (1989); unpublished results. 

K.C. Smyth, J.H. Miller, R.C. Dorfman, W.G. Mallard, and R.J. Santoro, "Soot Inception in a Methanelk Diffusion Flame as 

Characterized by Detailed Species Profiles," Combust. Flame 62, 157-181 (1985). 

J.H. Miller, S. EWy, B. Ahvazi, F. Woldu, and P. Hassanzadeh, "Tunable Diode Laser Measurement of Carbon Monoxide 

Concentration and Tempexature in a Laminar MethanclAir Diffusion Flame," Applied Optics, in press. 

R.J. Santoro, (1989); penronal communication. 

R.J. Santoro, T.T. Yeh, J.J. Horvath, and H.G. Semcrjian, Combust. Sci. and Tech. 53, 89 (1987); R.J. Santoro and H.G. 

stmcrjian, Spring 1984 Meeting of the Western States Section of The Combustion Institute, paper 8449. 

P.J. Emmennan, R. Goulard, R.J. Santoro, and H.G. Scmcrjian, "Multiangular Absorption DiilgnosticsofaTbxtuhAxpnMethane Jet", J. Energy 4, 70 (1980). 

R.J. Santoro, H.G. Stmtjian, P.J. Emmcnnan, R. Goulard, and R. Shabahang, "Multiangular Absorption Measurements in a 

Methane Diffusion Jet", Lascr Probes for Combustion Chemistry , Ed: D. Crosley, ACS Symposium Series 134; American 

Chemical Society, Washington D.C., 1980, P. 427. 

J.Y. Wang, "Laser Absorption Methods for Siultaneous Determination ofTemperature and Species Concentration through a Cross 

Section of a Radiating Flow", Applied Optics 15, 768 (1976). 

C.J. Dasch, "Onedimensional tomography: a comparison of Abel, onion-peeling, and fdtered backprojection methods", Applied 

Optics 31, 1146 (1992). 

J.H. Miller, "Modeling the Growth of Polynuclear Aromatic Hydrocarbons in Diffusion Flames," Annd Conference on Fire 

Research (1992). 

Phys. 91, 2041-2048 (1989). 

Acknowledgment 

Institute of Standards and Technology and The National Science Foundation. 

This work was supported through grants from the Building and Fire Research Laboratory of the National 
79 

Carbon Monoxide Production in Compartment Fires 

Nelson P. Bryner, Erik L. Johnson, William M. Pitts 

Building and Fire .Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 301-975-6868 

* 

Introduction 

Recent studies attribute a large percentage of fire injuries and deaths to the products of incomplete 

combustion such as smoke and carbon monoxide (CO). Carbon monoxide has been implicated as the major 

toxicant by investigations [l-31 which indicate that more than half of all fire victims have fatal levels of 

carboxyhemoglobin in their blood. In an effort to understand and predict how CO is produced in enclosure 

fires, a long-term project [4] has been implemented within the Building and Fire Research Laboratory. The 

findings of the study will be used to create more realistic fire models and in the development of strategies 

for reducing the number of deaths attributed to CO. This paper describes the construction and operation 

of a reduced-scale enclosure (RSE) fire facility. This enclosure was designed to model important physical 

phenomena of a fire located in a compartment. Natural gas was the fuel source for over 140 fues with heat 

release rates (HRR) ranging from 7 to 650 kW. Fires of greater than 150 kW HRR created post-flashover 

conditions within the RSE. Temperatures inside the RSE and CO, CO,, and 0, concentrations inside and 

outside the RSE were measured at different elevations and positions for each fire. 

Emenmental 

The RSE is a 40% model of the standard room proposed in ISO/DIS 9705 [5]. The RSE internal 

dimensions are 0.98 m wide by 0.98 m tall by 1.46 m deep. A 0.48 m wide by 0.81 m tall door is centered 

at the bottom of the front wall of the enclosure. The enclosure consists of a steel frame with sheet metal 

sides and is lined with two layers of 1.27 cm thick calcium-silicate board. The RSE is instrumented with 

thermocouple trees located in the front and rear. Cooled and uncooled probes were positioned at different 

locations to sample the upper combustion layer. CO and CO, concentrations (NDIR analyzers) and 0, 

concentrations (paramagnetic analyzers) were measured. Attempts were made to measure air influx through 

the door with a pressure probe and aspirated thermocouples located in the doorway. 

The air flow in conjunction with fuel flow data was used to estimate a global equivalence ratio, t$g, 

for the enclosure. 9, is defined as the ratio of the mass of fuel-derived products to the mass of air-derived 

products in the upper layer normalized by the stoichiometric fuel-to-air ratio. Other researchers [6-91 have 

proposed using t$g to correlate major species concentrations, including CO, in the upper layer of a fire. 

Typically the burner was centered in the enclosure and each fire ranged from 15 to 20 minutes in 

duration. Different burner positions and a narrow door cofiguration were used in a few fires to study the 

effects on flow patterns and transient behavior, respectively. Several horizontal and vertical mappings, where 

a sample probe was moved during a fire, were also performed to characterize the species concentration 

profiles within the enclosure. Since water interfetes with NDIR measurements, it was trapped out of the 

sample gases and estimates of water concentrations were calculated. This allowed the data to be reported 

on a wet volume basis. 

Results and Discussion 

Figure 1 shows a plot of average steady-state CO concentrations for each fire versus the heat release 

rate of the fires. Figure 2 shows the corresponding 0, concentrations. Due to difficulties in measuring +g, 

the results are presented versus HRR. For reference purposes, a 200 kW fire had a corresponding 4g of 

approximately 1. At 100 kW HRR, the CO concentration begins to rise and levels off to 3 % in the front 

and 2 % in the rear for fires with greater than 400 kW HRR. Hood experiments by previous investigators 

[6-81 yielded 1-2 % CO concentrations for similar 9,. The 0, concentration drops to near zero at 200 kW 

and remains near zero for all higher HRR. CO concentrations are higher in the front than in the rear of 

the enclosure. Conversely, CO, concentrations are higher in the rear and lower in the front. Temperatures 

in the front of the enclosure during the high HRR fires are consistently 200 - 300 "C higher than in the rear. 

Cooled and uncooled probe concentration comparisons at the same locations were nearly identical suggesting 

no reactions occurred in the probes. 

A companion field modeling of RSE fires [lo] suggests that flow patterns within the enclosure 

introduce oxygen directly into the upper layer in regions between the doorway and the fire. For the high 
0 

0. . 

0 

*o 0 

oeo 

0 

(....I.. .. l....l.... 

I 

0 0 

0 

0 

: 

0 

0 " E 

gz 

Q 

e= 

-w ** I ..I. I .... I 

In 0 " 0 u) 0 01 cy F F 

e (3 cy F 0 
81 

APPLICABILITY OF THE GLOBAL EQUIVALENCE RATIO FOR 

PREDICTING CARBON MONOXIDE IN ENCLOSURE FIRES 

William M. Pitts 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

Roughly two thirds of all deaths resulting from enclosure fires can be attributed to the presence of carbon 

monoxide (CO) [1,2] which is known to be the dominant toxicant in fire deaths [3]. The mechanisms 

responsible for the generation of high concentrations of CO are poorly understood. A long-term program 

(Carbon Monoxide Production and Prediction Project) at the Building and Fire Research Laboratory is 

seeking to develop an understanding of and predictive capability for the generation of CO in fires. [4] 

The vast majority of this research effort during the past four years has focused on the following question: 

Can the generation behavior of CO observed in hood experiments designed to model two-layer 

burning be extended to predict CO generation in actual enclosure fires? 

It has been found that the major products of combustion measured in hoods located above open fires in the 

laboratory are strongly correlated with the global equivalence ratio (defined as the ratio of masses derived 

from fuel and air normalized by the ratio for stoichiometric burning) for the gases trapped in the hood. [5,6] 

These correlations are quite robust, holding even when air is injected directly into the hood instead of 

entering only through the fire plume. [6] The existence of these correlations has been termed the Global 

Equivalence Ratio (GER) concept. A dependence of the combustion products in the hoods on the upperlayer temperature has been noted. 

Recently, investigations have been completed which provide significant insights into the mechanism of CO 

formation in enclosure fires. The findings allow an assessment of the conditions for which the application 

of the GER concept to enclosure fires is appropriate. The results of the these studies are briefly summarized 

and are used to answer the above question. 

The reaction behavior of gases observed in the low-temperature hood experiments when the gases are heated 

to higher temperatures has been examined. [q It was found that the gas mixtures, which were observed to 

contain both fuel and oxygen, became reactive as the temperature was raised. For lean conditions, reaction 

results in the formation of CO, and H,O. For rich conditions the oxidation generates primarily CO in 

preference to CO, Due to shifts in the ratios of H20 and H2 produced, the calculated increases in CO are 

larger for temperatures in excess of lo00 K. 

Roby and coworkers [SI have monitored CO formation inside a reduced-scale enclosure designed to provide 

separate ventilation and exhaust pathways. The design ensures the development of two well-defined layers 

and that entrainment into the upper layer occurs only through the fire plume. Fuels used in the study include 

hexane, wood, PMMA, and polyurethane. This study has confirmed a temperature effect on the combustion 

products observed in the upper layer, but indicates that the correlations derived from the hood experiments 

provide good estimates for the concentrations of upper-layer combustion gases when the temperature effect 

is accounted for properly. 

In a separate investigation of fires within a reduced-scale enclosure (RSE), Bryner, Johnsson, and Pitts have 

investigated combustion gas production in a 2/5-scale model of a full-sized room. [9] Natural gas was used 

as the fuel with the burner centered in the room. Unlike the hood experiments [5,6] and the enclosure fire 

investigation of Roby et al. [8], significant variations in CO concentration were found with position in the 
. 82 

upper layer of the fire. In particular, for a mom having a doorway scaled for fire size and ventilation relative 

to the full-scale enclosure, CO concentrations observed near the doorway for fires having rich upper layers 

were much higher than observed in the hood experiments of Toner [q with the same fuel. Interestbgly, 

concentrations in the rear of the enclosure were very similar to Toner's observations. Oxygen concentrations 

were very low (< 0.5 %) at both locations in the RSE. 

Limited experiments were done with a narrow doorway for the RSE in which upper-layer temperatures were 

very similar to those observed in the hood experiments of Morehart 161. Upper-layer concentrations within 

the enclosure were more uniform and were consistent with those measured in the hood experiments. 

Preliminary experiments were done where the upper walls and ceiling of the RSE were lined with 6.4 mm 

thick plywood. A high heat release rate natural gas fire (600 kW) was burned. Previous experiments [lo] 

suggested that primarily carbon monoxide would be generated by wood pyrolysis for the high temperature, 

low oxygen conditions expected in the upper layer. Concentrations of CO as high as 14% were observed 

during the fire. This experiment demonstrates that pyrolysis of oxygenated polymers in the upper layer of 

an enclosure fire can be an important source of CO. Apparently, this mechanism of CO generation has not 

been recognized previously. 

A field modeling investigation characterized the flow patterns within the RSE. [ll] These calculations 

showed that air fiom the lower layer was entrained directly into the upper layer, i.e., the air did not pass 

through the fire plume. Based on the kinetic calculations [q, this air would be expected to react with rich 

upper-layer gases and generate CO instead of CO, This hypothesis provides an explanation for the higher 

CO concentrations observed in the front of the RSE for rich, high-temperature upper layers. 

The findings of the above studies allow the conditions for which the GER concept can be used to predict 

combustion gas generation in enclosure fires to be assessed. It is expected to be applicable in fires: 1) which 

are fully ventilated, 2) which have low upper-layer temperatures, and 3) which have high-temperature upper 

layers for which the only pathway for air to enter the upper layer is through the fire plume. It is expected 

to be inappropriate in fires: 1) which have rich, high-temperature upper layers and in which air can enter the 

upper layer directly, and 2) where solids capable of pyrolysis are located in the oxygen-depleted, hightemperature upper layer. 

The enclosure fires which are responsible for most CO-induced fire deaths are flashed over and 

underventilated. [4] Such fires are expected to have intense mixing in which air may be entrained directly 

into the upper layer. Additionally, these fires often have fuels which can be pyrolyzed located in the upper 

layer. On this basis, it is concluded that great care should be exercised when applying the GER concept to 

predict CO production in actual enclosure fires. 

References 

Harland, W A; Anderson, R. k Proceedings, Smoke and Toxic Gases fkom Burning Plastics; pp. 

15/1 to 15/19; Jan. 6-7, 1982, London, England. 

B. Harwood and J. R. Hall, Fire J. 83 (1989) 29. 

V. Babrauskas, B. C. Levin, R, G. Gam, M. Paabo, R. H. Harris, Jr,, R. D. Peacock, S. Yusa, NIST 

Special Publication 827 (1991). 

M? M. Pitts, NISTIR 89-4185 (1989). 

C. L. Beyler, Fire Sufkty J. 10 (1986) 47. 

E. E. Zukoski, J. H. Morehart, 'E Kubota, S. J. Toner, Combust. Flame 83 (1991) 325. 

W. M, Pitts, Twenty-Fourth Symposium (Iktemational) on Combustion, accepted for publication. 

D. ?I Gottuk, R, J. Roby, and C. L. Beyler, J. Fire Rotedon Eng., accepted for publication. 

N. P. Bryner, E. L. Johnson, and W. M. Pitts, NIST Internal Report, to appear. 

V, Arpiainen and M. Lappi, M. J. Anal. Appl. Pyroljsis 16 (1989) 355. 

W. D. Davis, Manuscript in preparation. 
83 

HALON REPLACEMENT EXTINGUISHANT CONCENTRATION REQUIREMENTS: 

EXPERIMENT AND MODEL 

Ronald S. Sheinson" and Samuel P. Baldwinb 

NAVAL RESEARCH LABORATORY 

Navy Technology Center for Safety & Survivability, Code 61 80 

Washington, DC 20375-5320, USA, (202) 404-81 01, FAX (202) 767-1 7 16 

The brominated halocarbons halon 1301 (CF,Br) and halon 121 1 (CF,BrCI) are widely used as 

efficient, clean, non-toxic, non-conducting fire suppression agents. However, their production 

will cease in the near future due to stratospheric ozone layer depletion concerns. Alternatives 

are needed to insure safety, system performance, and mission capability. 

The search for halon replacements is not new to NRL. Approximate kinetic calculations 

performed in 1976' showed that brominated halons were at least as potent potential ozone layer 

depleters as were chlorinated CFCs, and very likely to be more so. Fire suppression research 

showed a physically acting agent requirement predictive model could be constructed2

. Over half 

the effectiveness of halon 1301 was due to bromine radical chemical reactions; iodine was 

equivalent to bromine in suppression efficacy; and the CF, radical itself was a chemical 

suppressant3

. Halogen acid generation from halon extinguished fires could range from hundreds 

to thousands of parts per million in on cent ration^^^. 

No available candidate fulfilled the requirements of being clean, non-toxic, non-conducting, and 

highly efficient, while also having greatly reduced ozone depleting behavior. The tremendous 

growth in CFC and halon usage and the now known extent of stratospheric ozone layer depletion 

dictate that performance compromises must be accepted. 

NRL reinitiated halon replacement studies several years ago including flame suppression 

mechanisms and suppressant concentration requirement modeling6e7, intermediate scale total 

flooding candidate evaluation', and atmospheric lifetime studies. We also interact directly with 

manufacturers through secrecy agreements and as a United States Representative member (RSS) 

on the United Nations Environment Program, Halons Technical Options Committeeg. 

This presentation will be on laboratory burner extinction studies and resulting mechanism and 

modeling efforts. Other presentations from NRL at this meeting will describe our larger scale 

total flooding fire extinguishment studies carried out on eight candidate and model suppressants 

in a 56 m3 compartment at our Chesapeake Bay Detachment, Maryland, location. 

Minimum extinguishment concentrations for the currently available candidate replacements using 

n-heptane fuel in the NRL cup burner are listed in Table 1. The gas volume concentrations allow 

calculation of weight and liquid volume requirements relative to halon 1301 . The non-ozone 

depleting compounds are decidedly less efficient. We have extended cup burner studies to 

include suppressant mixtures and varying oxygen concentrations. Halon 1301 efficiency is a 

non-linear function of concentration''. A "free oxygen" model based on Ref. 11 has been 

developed that allows the prediction of suppressant concentration requirements in agent 

Supported in part by the Office of Naval Technology and the Naval Sea System Command. 

a Author to whom correspondence should be addressed. 

b Current address: Johns Hopkins University, Baltimore, MD. 
84 

mixtures and blends including as a function of oxygen concentration. The additional suppressant 

required to protect against reflash in a post-extinguishment, carbon dioxide rich and oxygen 

depleted environment can also be predicted. . 

Suppressant action can be characterized as physical, chemical scavenging, or chemical catalytic. 

The physical mechanism produces linear suppression effectiveness, while catalytic reactions 

involving bromine and iodine containing suppressants produce greatly increasing chemical 

effectiveness at lower agent concentrations. Weakly catalytic action involving chlorine, or 

chemical scavenging reactions involving fluorine, produce small or no deviations from linear 

behavior. Changes in effectiveness with bromine or iodine containing suppressant 

concentrations can be related to changes in hydrogen atom recombination chain length. 

References: 

1. Bogan, D. J., Naval Research Laboratory, unpublished results. 

2. Sheinson, R. s.8 Hahn, J. E., Geary, K, and Williams, F. we, "Quantification of Physical Fire 

Suppression of Heptane Pool Fires, " Paper 30, Proceedings, Eastern Section, Com bustion 

Institute Meeting, The Combustion Institute, 1 977. 

3. Sheinson, R. s.8 Gellene, G. I., Williams, F. w.8 and Hahn, J. E., "Quantification of Fire 

Suppressant Action on Liquid Pool Fires," Paper 18, Proceedings, Eastern Section, 

Combustion institute Meeting, The Combustion Institute, 1 978. 

4. Sheinson, R.S., and Alexander, J.I., "HF and HBr from Halon 1301 Extinguished Pan Fires," Paper 

62, Proceedings, Eastern Section, Combustion Institute Meeting, The Combustion Institute, 

1982. 

5. Sheinson, R.S., Musick, J.K., and Carhart, H.W., "HF and HBr Production from Full Scale CF,Br 

(Halon 1301 Fire Suppression Tests," Journal of Fire and Fhnmability, Vol. 12, pp. 229-237, 

1981. 

6. Sheinson, R.S., Penner-Hahn, J.E., and Indritz, D. "The Physical and Chemical Action of Fire 

Suppressants," Fire Safety Journal, Vol. 15, pp. 437-4508 1989. 

7. Sheinson, R.S. " Halon Alternatives Extinguishment Pathways," Proceedings, Halon Alternatives 

8. Sheinson, R.S., "Halon Alternatives - Compartment Total Flooding Testing," Proceedings, Int. . 

Conf. on CFC & Halon Alternatives, Dec. 3-58 1991 8 Baltimore, MD, pp. 629-641. 

9. Appendix F. "Combustion and Extinguishment - An Overview of the Science". United Nations 

Environment Programme, Montreal Protocol 1 99 1 Assessment, Report of the Halon Technical 

Options Committee, December 199 1. 

1 0. Sheinson, R.S., and Driscoll, D.C. Fire Suppressant Concentration Requirements: Agent Mixtures 

and DepletedEnriched Oxygen Concentrations. 23rd International Symposium on Combustion, 

Abstracts Book, Orleans, France, The Combustion Institute, July 1990, p. 204. 

Technical Conference, NMERI, Albuquerque, NM, USA, April 30-May 18 1991 8 pp. 71 -82. 

11. Tucker, D.M., Drysdale, D.D., and Rasbash, D.J., Combustion & F~w, VOl. 41 8 p. 293, 1981. 

Table I: NRL CUP BURNER, N-HEPTANE FUEL 

AGENT 

Halon 1301 

Great Lakes FM-100 

Great Lakes FM-200 

Sulfur hexafluoride 

Carbon Dioxide C02 

3M PFC-410 

Du Pont FE-25 

Du Pont FE-13 

CONC % 

CF,Br 3.1 

CF2BrH 4. I 

C4FIO 5.2 

CF,CFHCF, 6.6 

C,F,H 8.8 

SFf3 10.6 

CF,H 12 

CO, 21 

REL VVT 

1x 

1.2- 

2.7 

2.4 

2.3 

3.3 

I .8 

2.0 

REL VOL 

1x 

1 .o+ 

2.7 

2.7 

2.8 

3.0 

4- 

4. I 
85 

F'LAME SUPPRFBSION EFFICIENCIES OF NEXT GENEUTION 

FIRE EXTINGU"G AGENTS 

A.P. Hamins, W.L. Grosshandler 

and R. G. Rehwoldt 

Building and Fire Research Laboratory 

NIST 

A comprehensive experimental program is described which seeks to find a suitable replacement for the 

ozone-depleting fire suppressant, CF3Br, for in-flight aircraft protection. Because the effectiveness of 

a fire suppressant is related to the nature of the fire as well as an agent's thermodynamic properties and 

suppression kinetics, different experimental configurations are used to simulate the threat posed by a 

fire in a dry bay area of the aircraft and in an engine nacelle. The four facilities listed in the table 

below are used to rank the relative combustion suppression efficiency of various fluorinated compounds. 

Preliminary measurements in the cup burner and OFDF facilities will be presented, and the experiments 

which are planned for the detonation tube and the turbulent jet flame will be discussed. 

The cup burner consists of a 28 mm fuel cup surrounded by a 120 mm chimney. The flame 

extinguishment test developed in NIST TN 1278* forms the basis of the experimental method. The 

apparatus has been modified to bum liquid fuels, including viscous hydraulic fluids. Flames are 

buoyancy dominated and mildly turbulent. The critical flow rate of gaseous suppressant needed to 

extinguish a diffusion flame established in the cup burner is mmured. 

The suppression effectiveness of the agents are also determined by measuring the critical flow rate of 

suppressant needed to extinguish diffusion flames stabilized between counter-flowing streams of oxidizer 

and a vaporizing liquid fuel. Unlike the cup burner, the effect of the flow field (strain rate) on the 

extinction process is an independently regulated parameter in the OFDF. This facilitates a controlled 

comparison of the relative suppression effectiveness of the agents. The suppressant concentration in 

the air stram necessary to extinguish diffusion flames is measured as a function of strain rate. 

Preliminary measurements in the OFDF are compared to the cup burner results. 

An engine nacelle fire is typically a turbulent diffusion flame stabilized behind an obstruction in a high 

speed flow. Jet fuel, either as a spray or prevaporized, supplies the energy. Extinguishment occurs 

when a certain level of agent is supplied to the air upstream of the flame, and is likely to be affected 

by the turbulence intensity and velocity of the flow as well as the agent concentration. A coaxial 

turbulent burner has been designed to evaluate the various agents. The fuel is injected on the centerline 

and air is brought in parailel to the fuel in an annular region, approximately 50 mm across. The mean 

air velocity can be varied from 10 m/s to about 50 m/s, and the turbulence intensity can be controlled 

with screens placed upstream of the fuel nozzle. The flame is stabilized behind a disc located at the 

fuel outlet, and the temperature of the disc or the air can be increased to ensure that the flame remains 

stable. The agents are injected impulsively into the air stream so as to be dispersed uniformly across 

the tube before they reach the flame. Extinction efficiency will be determined with propane and JP8 

as fuels. 

Dry bay protection requires that an agent respond quickly enough to suppress the transition from a 

deflagration to a detonation. A worst case scenario will be investigated where the fuel has completely 
86 

vaporized and is well mixed with air. The mechanism for suppression may be distinct in detonations 

and diffusion flames because the chemistry may take place at different pressures and because the fuel 

and air are premixed rather than non-premixed. Many rate constants are pressure sensitive which could 

enhance or diminish the importance of particular chemical reactions. Furthermore, the structure of 

premixed and non-premixed flames are distinct, which may have a dramatic impact on the relative 

suppression effectiveness of different agents. A detonation tube has been designed to evaluate the 

suppression effectiveness of the agent in preventing a flame from accelerating into a premixed 

combustible fueVair mixture. A long, stainless steel, 50 mm diameter closed tube is fitted with an 

ignition source at one end and an over-pressure blow-out port at the other end. The tube can be filled 

with a fuel/& mixture, initially at ambient temperature and pressure. Agent will be premixed with 

propane and air in the downstream half of the tube, separated fkom the combustible region by a thin 

membrane. The progress of the flame front can be monitored with fast time response piezoelectric type 

pressure gauges and ionization gauges which are flush mounted in the tube. Suppression of a fully 

established advancing flame front will be tested as a function of agent concentration. 

Table. Flame Extinction Measurements 

1. Cup Burner 

Fuels: ' JP5, JP8, hydraulic fluids 5606 and 83282 

Agents: eleven fluorocarbons, plus sodium bicarbonate 

2. Opposed-flow diffusion flame 

Fuels: heptane, JPS 

Agents: eleven fluorocarbons, plus sodium bicarbonate 

Experimental variables: flame strain rate, agent concentration 

3. Turbulent jet burner 

Fuels: propane, JP8 

Agents: eleven fluorocarbons 

Experimental variables: turbulence intensity, agent concentration, velocity, air temperature 

4. Detonation tube 

Fuel: propane 

Agents: eleven fluorocarbons 

Experimental variables: fuel/air ratio, wave strength, agent concentration 

*NIST Technical Note 1278, R.G. Gann, J.D. Barnes, S. Davis, J.S. Harris, R.H. Harris, J.T. 

Herron, B.C. Levin, F.I. Mopsik, KA. Notarianni, M.C. Nyden, M. Paabo, and R.E. Ricker, 

"l?relhh.ry Screening Procedures and Criteria for Replacements for Halons 1211 and 1301," 1990. 

_.- 
87 

Flame Structure of Inhibited Counterflowing Flames 

I.K. Puri 

Chicago, IL 60680 

Department of Mechanical Engineering, University of Illinois at Chicago 

A. Hamins 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

Recent attention has been focussed on determining replacements for the 

ozone depleting halogenated fire suppressants currently in use. Before 

new agents can be designed, an improved understanding of the mechanism 

of halogenated compounds in non-premixed flames is necessary. Although 

a number of experimental studies have been conducted on the suppression 

effectiveness of halogenated compounds in hydrocarbon diffusion flames, 

few studies have considered changes in the detailed flame structure due 

to the introduction of these compounds. 

Numerical simulations of the structure of atmospheric counterflowing 

methane-air diffusion flames are conducted using a previously developed 

code [ 1 3. The code allows calculations of stretched laminar flames using 

a detailed model of molecular transport of chemical species, as well as 

detailed mechanisms of chemical reactions. The local temperature, 

velocity and species concentration distributions in the flame are 

calculated. In this study, attention is focussed on the differences in 

flame structure when either an inert (N,), a very simple halogenated 

species (CH,Cl) or methane (CH,) itself is added to the oxidizer stream. 

The chemical kinetic mechanism employed is a combination of chemical 

kinetic models for methane [2] and methyl chloride [3] oxidation which . 

contains 179 reversible chemical reactions for 38 chemical species and 

include C, chemistry. The chemical mechanism has been validated by 

comparison with the measured speeds of a number of premixed CH3C1/CH,/air 

flames [4]. 

All calculations are conducted for strain rates in the non-combusting 

flow field equal to 50 s-', which represents weakly stretched flames 

typical of buoyancy dominated combustion situations such as fires. 

Computations were conducted for 5 mole % agent (N2, CHJ1 or CH,) added 

to the oxidizer stream. 

The effects of an inert such as nitrogen when added to the oxidizer 

stream are two-fold, The inert behaves as a heat sink, reducing the 

temperature of the products of combustion and as a diluent reducing the 

collision probability of chemical reactions. In contrast to the inert, 

the effect of CH,C1 is both thermal and chemical. For additions of 5% 

CH,C1 to the oxidizer stream, the calculated maximum temperature 

increases nearly 200 KO The chemical effect of CH3C1 additions are 

evident through differences in the concentration of the radical pool. 

The calculated peak concentrations of 0 and H atoms decrease by nearly 

a factor of 2 for additions of 5% CH,C1 to the oxidizer stream while the 

peak OH. concentration decreases by approximately 30%. The decrease in 
88 

the radical pool is associated with the scavenging of H atom by C1 to 

form HC1. Chlorinated species other than HC1 and Cl atom are negligible 

(e.g. C1, < 1 ppm) . The peak HC1 concentration is nearly 5 mole % and is 

located on the oxidizer side of the temperature maximum. 

The addition of 5% CH, to the oxidizer stream yields a lean premixed 

flame flowing into a diffusion flame. The maximum flame temperature 

increases with CH, addition to the oxidizer as do the peak concentrations 

of the radical pool. 

Through a comparison of flame structures, the inhibiting effects of C1 

on the combustion process will be discussed. A sensitivity analysis 

examining the importance of suppressant heat capacity, thermal 

conductivity, and the chemical reactions will also be discussed. 

References 

1. Rogg, Bo, RUN-1DS: A computer program for simulation of one- dimensional chemically reacting flows. University of Cambridge, 

April 1991. CUED/A-THERMO/TR39 (1991). 

2. Miller, J.A. and Bowman, COT., Prog. Energy Comb. Sci. 15: 287-338 

(1989). 

3. Barat, R.B., Sarofim, A.F., Longwell, J.P. and Bozelli, J.W., Comb. 

Sci. & Tech. 74: 361-378 (1990). 

4. Lee, K.Y., Yang, MOHO and Puri, I.K.,"Numerical Sbnulations of 

Stoichiometric Premixed Flames Burning CH,Cl/CH,/Air Mixtures and 

Comparison of Flame Speeds with Experimental Results" , submitted to 

Comb. Flame, 1992. 
89 

Concentration Profiles of Extinguishants in a Fire Environment; 

Gas Sampling and Analysis 

H. G. Eatona, W. D. Smith, J. St. Aubin, R. Brown, H. Burchell, 

G. Salmonb, and R. S. Sheinson 

NAVAL RESEARCH LABORATORY 

Navy Technology Center for Safety and Survivability, Code 6180 

Washington, DC 20375-5320 USA, (202) 767-2766, Fax (202) 767-1 716 

The Naval Research Laboratory (NRL) halon 1301 total flooding extinguishant replacement 

program tests have been conducted in a 56 d (2000 cubic foot) cinderblock and concrete 

compartment approximately 4 x 3.4 x 4.3 m (13 x 11 x 14 feet) at our Chesapeake Bay 

Detachment. Special care had to be exercised to assure valid comparisons between 

suppressants' as both their thermodynamic and chemical properties differ significantly. Roof 

vents and a door are employed to ensure proper preburn ventilation. The compartment is 

instrumented with thermocouple arrays, radiometers, calorimeters, and video recorders including 

infrared video. Pressure transducers and thermocouples are installed at several discharge 

system points, including at the overhead 3 m high (10 ft) nozzles. 

Continuous gas samples were obtained from four compartment heights and analyzed for 

oxygen, carbon dioxide, carbon monoxide, and agent. Grab gas samples were taken at different 

locations in the compartment including near the seat of the fire at various times to obtain an 

understanding of agent addition hydrodynamics. 

The overhead nozzles were used to dispense precalculated pressurized agent concentration 

onto a burning fire pan, 30.5 x 76 cm (12 x 30 in), of n-heptane positioned 30 cm (1 ft) above 

the floor, or into an n-heptane spray fire of the same energy output. Discharge was from a tank 

pressurized with nitrogen to 600 psig. 

The extinguishants tested included CF, Br - Halon 1301, CF, BrCl - Halon 121 1, CF, H - Du 

Pont FE-13, C&F,H - Du Pont FE-25, CF,BrH - Great Lakes FM-100, CF3CFHCF3- Great Lakes 

FM-200, FM-100 and FM-200 15 Blend, and C4F,o - 3M PFC-410. 

Supported in part by the Naval Sea System Command. 

1. Author to whom correspondence should be addressed. 

2. Hughes Associates, Inc., Columbia, MD. 
90 

We observed significant concentration variation both as a function of location and time 

immediately following discharge. Therefore a concerted analysis was conducted. Agent profile 

concentrations were obtained by using evacuated 1.7 (100 in") stainless steel bottles. Five 

bottles each were connected to two cam actuated timers. One set of bottles was positioned to 

sample near the fire, the other, 3.7 m (12 ft) overhead. The timers were actuated at agent dump 

time and the bottles were filled sequentially over a 30 second period. 

Bottle sample pressure was typically less than 400 torr. A subambient pressure analytical 

sampling system was employed to extract the sample for detection by gas chromatography. 

A collection strategy similar to that used for gas components was employed to collect five 

halide acid samples for subsequent analysis by ion chromatography. This has allowed the 

generation of acid concentration profiles for the time interval during and immediately following 

suppressant addition. The detailed analysis of the agent concentration variation with time in the 

compartment is given by an accompanying paper. 

The different halon replacement agents were evaluated for their effectiveness in extinguishing 

the fire by comparing their Mean Effective Concentrations and time required to extinguishment. 

Factors affecting this determination include agent concentrations, nozzle geometry, and validity 

of the gas sampling and analysis systems. 

1. Baldwin, S.P., Brown, R., Burchell, H., Driscoll, D.C., Eaton, H.G., Salmon, G., St. Aubin, H.J., . 

Sheinson, R.S., and Smith, W.D., "Halon Replacement Agent Testing: Procedures, Pitfalls, and 

Interpretation," Proceedings, Halon Alternatives Technical Working Conference, NMERI, 

Albuquerque, MN, May 1992. 
91 

Quantification of Parameters in the Assessment of Halon 1301 Replacement 

W.D. Smitha

, H.G. Eaton, R. Brown, G. Salmonb, H. Burchell, J. St. Aubin, and R.S. Sheinson. 

Naval Research Laboratory 

Navy Technology Center for Safety and Survivability, Code 6180 

Washington, D.C. 20375-5320 (202) 767-2254 Fax (202) 767-1 716 

Introduction 

Halons are very effective chemical inhibitors of flaming combustion. They are also potent 

depleters of the stratospheric ozone layer if they can migrate through the tropopause. We are 

conducting a halon replacement program that spans from developing an understanding of fire 

suppression , ozone depletion interact ions, intermediate scale evaluation of halon replace men t 

on through full scale evaluation on our fire research ship facility, the ex-USS SHADWELL. This 

paper discusses the quantification of the operational parameters related to the use of and the 

effectiveness of a total flooding halon fire suppression system. 

Backaround 

The current doctrine for halon 1301 systems specifies that 1) the agent be discharged within 

10 seconds, 2) that a homogeneous mixture with a halon 1301 concentration equal to or 

exceeding the design concentration is achieved throughout the protected space, and 3) that the 

concentration is maintained for the length of time required to ensure complete extinguishment 

and for mitigation of persistent ignition sources (1 ,2). 

The halon fire suppression discharge time is defined by the National Fire Protection 

Association as the time between the cylinder actuation and when the flow from the nozzle 

becomes predominately vapor (3). This point in time is recognized as the inflection point on the 

nozzle pressure curve and the point in time when the nozzle temperature drops. 

Mixing rates of the considered agent and compartment resident gases are very important in 

the rapid extinguishment of a fire using a total flooding system. Mixing under these conditions 

is dominated by the turbulence driven by the rapid injection of agent and the charge gas. The 

charge gas used by the Navy is nitrogen at a pressure of 4.1 MPag (600 psig) (3). 

Model Description 

The model used for quantifying the operational parameters in the assessment of halon 1301 

replacement is a two symmetrical zone model of a total flooding compartment. The continuity 

equations for the concentration of a considered agent in each of the two zones may be written: 

U b 

a Author to whom correspondence should be addressed. 

Hughes Associates, Inc., Columbia, MD. b 
92 

where HL, H, are the concentration of the halon (lower and upper compartment respectively); 

DL, D, are the effective discharge rates into the respective zones. The effective discharge into 

the lower zone only is considered here and is taken to be a simple exponential function,.related 

to the discharge nozzle pressure decay: 

DL = aeM and D, = 0 

where a and b are constants. T L, 7 , are the lower and upper zone agent removal rates (physical 

and/or chemical), T~ is the mixing time between zones and initial conditions are t=O, HL=O, 

H,=O. H, the total cumulative concentration of agent discharged into the compartment at any 

given time t is: 

a 

b H, = - (I - e"'> (3) 

The halon 1301 concentration-time profile (4) has a high correlation with the form of equation 

(3). For sufficiently long times (-bt c c -1) the compartment mixing is readily approximated as: 

R-1 

rc - - where: R = ( ?) t-HX) b 

Le., R is the lower zone to upper zone concentration ratio at steady state. The discharge time, 

t, here is defined quantitatively as 3b'. 

Eff iciencv of a Considered Aaent 

The graphical integration of the derivative curve of the discharge concentration - time profile 

curve from cylinder activation, to= 0, to the time of fire extinguishment, te, is the measure of the 

system effective extinguishment concentration, Ce. The effective extinguishment concentration 

divided by te defined the time average effective application rate of a considered halon agent. 

Halide Acid Production 

The above simple symmetrical two-zone model coupled with a first-order assumption with 

respect to the concentration of halon agent present and the rate of halide acid production 

allowed for a parametric determination of halide acid production rate. 

Supported in part by the Naval Sea System Command 

References 

1. 

2. 

3. 

4. 

National Fire Protection Association, "Standard on Halogenated Extinguishing Agent Systems 

- Halon 1301 ,I' NFPA No 12A Batterymarch Park, Quincy, MA, 1987. 

P.J. DiNenno, E.W. Forssell, G.G. Back, 111, R.J. Quellette, C.R. Fulper, H.W. Carhart, 

"Shipboard Tests of the Halon 1301 Test Gas Simulants," Memo Report, Naval Research 

Laboratory, Washington, DC, 1990. 

H.W. Carhart, J.T. Leonard, P.J. DiNenno, M.D. Starchville, E.W. Forssell, and J.T. Wong, 

"Test of Halon 1301 Test Gas Simulants," Memo Report, Naval ,Research Laboratory, 

Washington, D.C., 1990. 

H. G. Eaton, W.D. Smith, J. St. Aubin, R. Brown, H. Burchell, G. Salmon, and R.S. Sheinson, 

Concentration Profiles of Extinguishants in a Fire Environment; Gas Sampling and Analysis," 

Annual Conference on Fire Research, October 13-16, 1992, Rockville, MD. 
93 

Theoretical Investigation of C-H and 

Reactivity and Fire 

C-X Bond Energy Correlations with OH 

Suppression Efficiency 

Marc R. Nyden 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

and 

Karl Irikura 

Chemical Sciences and Technology Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

ABSTRACT 

The major objective of this investigation is to develop a strategy, based on the 

calculation of carbon-hydrogen (C-H) and carbon-halogen (C-X) bond dissociation 

energies, to select the best candidates for the replacement of halon fire 

extinguishants. In the process, we hope to broaden the scope of agent screening 

beyond the 11 candidates already identified by the USAT?. 

The mode of action by which halons extinguish fires has never been fully 

resolved. The predominant view, however, is that they inhibit chain-branching 

reactions by promoting recombination of H and OH radicals. The formation of the 

corresponding hydrogen halide (HX) is thought to be an important step in the 

chemistry of halon extinction. Once formed, these compounds react with H and/or 

OH radicals via HX + H (OH) * & (bo) + X. An alternate hypothesis, which 

has also gained wide acceptance, is that halons work simply by absorbing heat from 

the fire. Once absorbed, this energy is dissipated in vibrational excitation 

culminating in the formation of HX and other noncombustible reaction products. 

In either case, the rate of dissociation of the halogen atom (X) from the halocarbon 

molecule (RX) is critical. Indeed, the empirical observation is that suppression 

efficiencies increase with decreasing bond dissociation energies in accordance with: 

R-F < R-Cl < R-Br < R-I. 

It is generally conceded that any compound containing C1, Br or I is a 

potential threat to stratospheric ozone. Perfluorinated compounds, however, are not 

thought to pose a problem because HF is chemically and photolytically inert in the 

troposphere. The principal determinant for ODP is whether the molecule which 

contains the C1, Br or I atoms is sufficiently stable to reach the stratosphere. This, 
94 

in turn, is largely determined by its propensity to react with OH. Once they escape 

the troposphere, halocarbons are rapidly photolyzed by high frequency UV radiation 

in the stratosphere. The halogen atoms released in this process are then free to 

catalyze the destruction of stratospheric ozone through the following reaction 

sequence: X + O3 + XO + 0,; XO + 0 3 O2 + X. 

The abstraction of H by OH to form KO and the corresponding free radical 

fragment is the rate limiting step in the chemical processes involved in removing 

saturated halocarbons from the troposphere. Thus, it is clear that ODP should 

correlate with C-H bond energies. Similar reawning suggests that the fire 

suppression efficiencies of halocarbons should correlate with C-X bond energies. 

It is possible to make qualitative assessments of these properties on the basis of 

simple structure/activity relationships. This was, in fact, the strategy employed in 

constructing the exploratory list of 103 halon alternatives (NIST TN1279) which is 

the point of departure for the additional agent screening component of the halon 

project. However, since small differences in bond energies can result in large 

differences in chemical reactivity, a more quantitative approach will be adopted in 

the final selection process. 

Recent advances in the theory and application of computational molecular 

quantum mechanics have made the calculation of chemically accurate bond energies 

(& 3 kJ/mol) in two and three carbon halons a realistic goal. Some of the most 

promising methods, including the G1 and non-local spin density approximations, will 

be reviewed. Calculations of C-H and C-X bond dissociation energies for a series 

of halon alternatives are underway. The progress we have made in developing 

accurate correlations between these bond dissociation energies and measurements of 

OH reactivity and fire suppression efficiency will be reported, along with a 

discussion of the strategy we are using to select environmentally safe fire 

extiguishants. . 
95 

DISCHARGE CHARACTERISTICS OF FIRE 

EXTINGUISHING AGENTS 

J.C. Yang, G. Linteris, and W.L. Grosshandler 

Building and Fire Research Laboratory 

and C. Presser and P. Espina 

Chemical Sciences and Technology Laboratory 

NIST 

As part of a program for the U.S. Air Force to identify alternatives to halon 1301 for in-flight aircraft fire 

protection, the physical behavior of eleven fluorinated compounds upon sudden release from a high pressure 

cylinder is being investigated. The effectiveness of these agents in suppressing a fire are thought to depend as 

much on their thermodynamic properties, their behavior during two-phase flow, and the timing of their release, 

as on their interaction with flame chemistry and the nature of the fire. A series of experiments have been 

designed to examine the fluid mechanical characteristics separate from the interaction of the agents with the 

combustion chemistry. Control of those phenomena which dominate the actual suppression process is sought, 

be they the chemical reactivity of the agent, the thermal quench or dilution provided by the agent, or the 

properties associated with the physical mixing of the agent into the fire. The adequate protection of dry bay areas 

of military aircraft requires that an agent be dispersed throughout a one cubic meter volume within 50 ms of an 

ignition event. The fire suppressant storage vessel is typically adjacent to the space being protected. The issue 

of concern in the current study is how quickly the material can exit the vessel and be dispersed throughout the 

volume at concentrations sufficient to extinguish an accelerating turbulent flame. 

A high pressure vessel equipped with a quick release opening and an internal volume of 500 ml has been built 

in order to assess the discharge dynamics of the eleven agents mixed with nitrogen. A rupture disc 18 mm in 

diameter, mounted at the opening of the vessel, is used as a quick release mechanism for discharging the contents 

of the vessel. The effect of the size of the opening on the nature of the emptying process will be assessed by 

placing various diameter orifices (from 6 mm to 18 mm) at the exit, with the constraint that the emptying time 

be less than 500 ms. 

The vessel is initially charged with a predetermined amount of agent and subsequently pressurized with nitrogen 

to 4.1 Mpa. The mass of agent is controlled so as not to exceed the safe operating pressure of the vessel (8.2 

Mpa). The pressure rating of the rupture disc is chosen to be within 5% of the value predicted from static 

pressure measurements at temperatures between 213 K and 422 K. During a test, the charged vessel is placed 

in a constant temperature bath until thermal equilibrium has been reached. The contents are discharged vertically 

upwards by impulsively injecting a small amount of nitrogen into the vessel, causing the disc to rupture. The 

internal temperature and pressure of the vessel are monitored during discharge. The tests are documented using 

high-speed cinematography. 

The fluid flow is multi-phase and choked as it passes through the exit orifice. The agent’s concentration in time 

and space outside of the vessel is strongly coupled to its thermodynamic and transport properties, and the 

turbulent entrainment of the surrounding ambient air. The near field is composed of a dense two-phase spray, 

which rapidly evaporates to form a free turbulent jet in the far field. The boundary of the two-phase region is 

determined by laser sheet illumination and schlieren photography. The schlieren photographs provide information 

about both the droplet loading and the gas density. The laser sheet illumination with digital image processing 

can provide estimates of the droplet velocities. High speed photography yields temporal information on droplet 

dispersion and vaporization. It is planned to use laser-line illumination with a linear diode array, scanning at 2.6 

lcHz, to make a small number of vertical measurements of the Mie scattering intensity. Rayleigh scattering will 

be used to characterize the gas-phase mixing. The gas phase experiments will include line and 2d imaging. 
96 

In parallel with the jet penetration experiments, the numerical code KIVA-II has been adapted to simulate the 

transient multi-phase flows typical of the agent release problem. The code is limited to the domain downstream 

of the exit orifice, and is not expected to-yield quantitative predictions because the initial state of the exiting spray 

is highly uncertain: however, the code is useful for parametric studies of the agents and for the assessment of the 

significance of such effects as cross flow and orientation on agent dispersion. 

Table. Experimental Measurements during Agent Discharge 

Chemicals to be Examined: 

Charging gases: 

Initial charging conditions: 

Pressure vessel volume: 

Maximum design pressure: 

Test conditions: 

Pressures: 

Vessel release mechanism: 

Vessel orientation: 

Dependent variables: 

Flow characterization of 

representative agent: 

Tests of other agents: 

Modeling conditions: 

nitrogen, CHF, 

4.1 ma, 295 K, variable mass 

100 ml (static), 500 ml (dynamic) 

13.7 MPa (static), 8.2 MPa (dynamic) 

213 K, 295 K, and 422 K 

equilibrium at test temperatures 

pressure actuated rupture disc, 6 mm to 18 mm diameter 

upward, downward, horizontal (with and without extension) 

pressure and temperature as function of time (dynamic tests), pressure as function . 

of temperature and mass (static tests) 

radial and axial boundary of two-phase region, radial and axial boundary 

of minimum concentration for suppression (as functions of time and initial 

temperature), bluff body and orientation effects on two-phase and suppression 

boundaries 

centerline two-phase boundary and centerline concentration at one location 

downstream after release 

two-phase transient jet flow with vaporization, gas jet in cross flow, gas-powder 

jet 
97 

CHEMICAL AND PHYSICAL EF'F'ECTS OF WATER DURING FIRE SUPPRESSION 

ARVIND ATREYA, TODD CROMPTON AND SANJAY AGRAWAL 

Combustion Laboratory 

Deparmrent of Mechanical Engineering 

Michigan State University 

East Lansing , MI 48823 

Suppression of fire results from the chemical and/or physical effect of the suppression agent on 

the burning process. Physical suppression mechanisms act by either cooling the condensed-phase to 

inhibit fuel pyrolysis (e.g. water application) or by quenching the gas-phase combustion reactions? 

The gas-phase quenching may be accomplished by simply blowing-off the flame (Le. by increasing the 

strain rate) or by diluting the fuel and/or the oxidizer streams with inerts such as H,O, CO,, and N2 

(effect of heat capacity, heat of vaporization or heat of decomposition) or by separating the reactants by 

mechanical or other means (blanketing). Clearly, combined extinguishment actions are also possible and 

in-fact desirable. These may occur naturally, as in the case of water application, where in addition to 

condensed-phase cooling, the pyrolyzed fuel is also diluted by evaporated water vapor. The chemical 

suppression mechanisms, on the other hand, are believed to interfere with the critical reaction steps 

responsible for maintaining the flame'? 

Water, the most widely used suppression agent, is thought to be chemically inert in a fire and is 

believed to have aphysical effect. However, there is little quantitative information regarding these effects 

during extinguishment by water. This work is an attempt to develop such a quantitative understanding 

of the chemical and physical mechanisms responsible for frre suppression by water. The results of an 

experimental investigation into extinguishment of a stagnation-point flow diffusion flame supported by 

a PMMA sample and a methane counterflow diffusion flame diluted by water vapor are presented. While 

other suppression agents will also be examined, initially this work focuses on water to establish a standard 

for comparison of suppression effectiveness. 

Typical experimental results of the overall species composition measurements made in the exhaust 

duct of the stagnation-point flow apparatus during suppression by water are shown in the enclosed figure. 

This figure shows an increase in the CO, production rate and the 0, depletion rate upon repeated 0.5ml 

water application (marked by arrows). This implies that the burning rate first substantially increases 

before it eventually decreases as a result of water application. For droplets less than 0.3ml, the 

subsequent decrease was found to be negligible. The increase in the burning rate was substantial and 

unexpected because it implies that instead of suppressing the flame, it is enhanced it by applying water 

droplets. This increase is also consistent with a decrease in CO and total hydrocarbon concentrations and 

visibly corresponds to the disappearance of soot. Thus, as a result of water evaporation CO, total 

hydrocarbons and soot are oxidized to CO,, depleting 0, in the process. This chemical hypothesis is 

supported by the fact that a non-sooty flame containing little CO, soot & unburned hydrocarbons does 

not show a similar increase in the burning rate due to water application. It seems that there are two 

simultaneous effects as a result of water application: (i) chemical enhancement of the burning rate (which 

is important only when the flames are sooty; Note: most fires are sooty), and (ii) physical cooling of the 
98 

solid via water evaporation. 

The results obtained in the 

stagnation-point diffusion flame 

apparatus are consistent with the 

experiments conducted in sooty 

(fuel-rich) methane counterflow 

diffusion flames'. Here detailed 

flame structure measurements were 

made. It was found that by reducing 

the 0, concentration while 

maintaining the flame temperature by 

preheating the reactants (thus 

reducing the H20 concentration in the 

reaction zone) led to an early soot 

inception and increased Soot volume 

fraction. However, direct addition of 

only 3.6% H,O (while holding all 

other conditions constant) resulted in 

delayed soot nucleation and a 

significant reduction in the soot 

0.8 

h 

E 

E 

0 

u 

4 0.4 

2 

M B 

2400 2600 2800 3000 

Time (sec) 

Measmtd e, C@, CO & HC during water appfication 

volume fraction. These observations can be consistently explained by the mechanism of OH interference 

with soot inception. An increase in the H20 concentration @rought about either by an increase in the 0, 

concentration or by direct addition) results in an increase in the OH concentration. This reduces the PAH 

and Cg, concentrations (the corresponding reduction in total hydrocarbons and CO was observed in the 

stagnation-point flow diffusion flame over PMMA) and delays soot inception. This substantially 

decreases the ultimate soot loading and increases the combustion efficiency and hence the burning rate. 

REFERENCES 

Evans, D. D., "Overview of Fire Suppression with Water," Proceedings combustion Institute - 

Eastern States Section 1988 Technical Meeting, December, 1988. 

Heakestad, G., "Role of Water in Suppression of Fire: A Review," Fire und FlammcrbiZity, Vol. 

11, pp. 254-259, 1980. 

Rashbash, D. J., "The Extinction of Fire with Plain Water: A Review," Fire Safety Science: 

Proceedings of the First International Symposium, Hemisphere, N.Y ., pp. 1145-1 163, 1986. 

Magee, R. S. and Reitz, R. D., "Extinguishment of Radiation Augmented Plastic Fires by Water 

Spray," 15th Symposium flntemational) on Combustion, The Combustion Institute, pp. 337-347, 

1975. 

Friedman, R., "Survey of Chemical Inhibition in Flames," Fire Research Abstracts Md Reviews, 

vol. 3, pp. 128-132, September, 1961. 

Pitts, W. M., Nyden, M. R., Gann, R. G., Mallard, W. G., and Tsang, W., ''Construction of 

an Exploratory List of Chemicals to Initiate the Search for Halon Alternatives," MST Technic& 

Note 1279, National Institute of Standards and Technology, Gaithersburg, MD, 1990. 

Zhang, C., Atreya, A. and Lee, K., "Sooting Structure of Methane Counterflow Diffusion 

Flames with Preheated Reactants and Dilution by Products of Combustion," Twenty-Fowth 

Srmposim flntemational) on combustion, The Combustion Institute, 1992, in press. 
99 

Multi-Droplet Evaporative Cooling: 

Experimental Results 

H. Dawson, M. di Marzo 

Mechanical Engineering Department 

University of Maryland at College Park 

The phenomena associated with extinguishment of a solid fuel fire are investigated 

experimentally. In particular, the evaporative cooling of a hot non metallic surface subjected to 

the impingement of a random array of droplets is quantified. The relevance of this study to the 

extinguishment process is two-fold: a) it describes the cooling of the surfaces exposed to fire and 

b) it quantifies the vapor generation in the fire environment. 

The experimental results reported here refer to a simplified situation with respect to the actual 

process to provide a controlled, repeatable and quantifiable set of data which will be used to 

validate the multi-droplet model which was obtained earlier (TaHarini et al., 1992). The fire 

environment is simulated by three, temperature controlled, radiant panels mounted above the 

surface of a macor square tile (0.1524 x 0.1524 x 0.0254 m). The tile is pasted onto a chilled plate 

which is kept at near ambient temperature. The heaters are controlled on a temperature feedback 

and are held at a constant temperature set point. These thermal boundary conditions are designed 

to obtain a linear temperature profile in the tile depth and to insure that the tile exposed surface 

is isothermal over the spray impingement region, prior to the initiation of the transient. 

The droplet distribution used in the experiment is random. However, all droplets are identical 

and the spray impingement region is kept constant. The water mass flux is controlled by changing 

the droplet generation frequency. The droplet dispenser is constituted of a cavity which gradually 

tapers to a small opening at the bottom where a needle pointing downward is attached. The cavity 

is bounded at its top by a plastic disk which is pulsated downward by a plunger at the desired 

frequency. The dispenser is suspended from four parallel vertical wires and is moving above the 

deposition region under the action of three pulsating bumpers which are moving toward each other 

symmetrically. To insure continuous motion of the dispenser, a periodic displacement of one of 

the four suspending wires is provided by a rotating device. Figure 1 shows a typical droplet 

distribution as recorded by a camera looking at the dispenser Erom above. 

The water used in the experiment is de-ionized and de-gassed. In order to obtain a constant 

feed of water, a mineral oil sealed reservoir and head control tank has been used. This system 

allows to control the fluid head above the distributer within 0.01 m and at the same time it keeps 

any gasses from diffusing back into the water. Experiments with de-ionized water are also being 

conducted to assess the effect of gasses coming out of solution during the evaporative process. 

Additional consideration will be given to the effect of impact momentum on the droplet shape on 

the surface, which greatly affects the evaporation rate. 

The macor tile transient surface temperature distribution is recorded with an infrared camera. 

The infrared image is correlated to a temperature distribution (see Hassen et aL, 1992 and dNmo 

et d, 1992). The 256 shades of gray are related to a temperature scale of about 120 "C. The scale 

is set by simultaneously measuring the temperature of a given surface point with a thermocouple 

probe and via the infrared camera reading. The spacial resolution is of about 0.0001 m/pixel and 

the temperature resolution is of 2 'C/gray-shade which yields an accuracy of about t 1 "C. The 
100 

transient temperature distribution is recorded on a VCR and selected frames during the transient 

are grabbed by a PC to be analyzed. The camera has a field of view of a circular area with a 

diameter of about 0.05 m. This area is viewed through a blackpainted chilled pipe which 

eliminates stray radiation from other sources than the macor surface in direct view. Figure 2 shows 

a typical snap-shot of the temperature distribution of the sprayed surface. In order to condense 

the information available, the averaged transient temperature is calculated for selected frames (e.g. 

Fig. 2) during the evaporative transient. A detailed description of the components of the 

experimental set-up will be provided along with a sample data record of the phenomena to 

illustrate the data processing. The surface averaged transient temperature for various conditions 

will be presented and qualitatively compared with preliminary results of the numerical simulation 

(Tartmini et aL, 1992). 

Acknowledgements The authors are indebted to Dr. Evans (BFRLNIST) for his guidance and to 

the Building and Fire Research Laboratory for the support of this research program. 

References 

diMarzo, M., C.H. Kidder, and P. Tartarini, 1992, "Infrared Thermography of Dropwise 

Evaporative Cooling of a Semi-Infinite Solid Subjected to Radiant Heat Input" Ekperimentd Heat 

Transfer, Vol. 5, pp. 101-114 

Klassen, M., M. diMarzo, and J. Sirkis, 1992, "Infrared Thermography of Dropwise Evaporative 

Cooling'' Experimental Thermal and Fluid Science, Vol. 5, No. 1, pp. 136-141 ' 

Tartarini, P., Y. Liao and M. diMarzo, 1992, "Numerical Simulation of Multi-Droplet 

Evaporative Cooling" Proceedings of the X UIT Nafional Heat Transfer Conference, Genova (Italy), 

pp. 123-132 

TH 0.01 m 

. 

FIGURE 1 - Droplet distribution obtained 

over 180 seconds at a frequency of about one 

droplet per second over a circular surface 

with 0.05 m of diameter. 

2 

FIGURE 2 - Typical instantaneous macor 

surface temperature distribution obtained 

after 60 seconds with a water mass flux of 

0.0015 kg/m*s and with an initial solid surface 

temperature of 140 T. 
101 

Abstract of Paper Submitted for Presentation at the Annual Conference on Fire 

Research, Rockville, MD, October 13-16, 1992 

MODELING OF TURBULENT FLAME RADIATION 

J. de Ris and L. Orloff 

Factory Mutual Research Corporation 

by 

Radiation from turbulent diffusion flames controls the burning rates of moderate 

and large - scale fires' and is therefore of central importance to she flammability 

problem. Recently we have developed a global flame radiation model which predicts 

the radiant fraction from buoyant turbulent (fuel- jet) diffusion flames in terms of 

the fuel's laminar flame smoke - point value. The model considers the separate roles of 

soot and gaseous radiation. The effective flame radiation temperature is predicted by 

the model in terms of the: 1) incompleteness of combus ion, 2) radiant heat loss and 3) turbulent mixing with good agreement with experiment. 5 

It is argued that the soot absorption coefficient (or soot volume fraction) is: 1) 

proportional to the turbulent macro-scale flow time in the soot formation region of 

the flames, and 2) inversely proportional to the chemical time for soot formation. 

The chemical time for soot formation is shown to be approximately proportional to the 

smok6-point heat release rate on the basis of the Lam'n r flame smoke - point models of 

Kent and Gulder'. Markstein's general correlations'f7 of smoke - points in terms of 

the stoichiometric oxidant to fuel mass ratio, S, and adiabatic stoichiometric flame 

temperature, Tad for nitrogen diluted fuel and oxidant mixtures show that: 1) the soot 

formation is quite sensitive to S which controls the local velocity of the gas flowing 

through the diffusion flame toward the fuel side, while 2) the soot formation is 

relatively insensitive to Tad. The latter result allows us to generalize the 

turbulent flame radiation model to include nitrogen diluted fuel mixtures and nitrogen 

diluted/oxygen enriched oxidants. 

The predicted radiant fractions are in excellent agreement with experiment for 

The 

and planar6 free-jet buoyant turbulent 

different oxidant and fuel mixtures coverrg a wide ra ge of flame sootiness. 

model is tested against both axisymetric 

diffusion flames over a range of heat release rates. 

model to wall fire flames which have smaller radiant 

heat loss to the surface, 2) significant dilution 

products of combustion diffusing back toward the fuel 

macro-scale mixing times due to wall shear stress. 

We are currently applying the 

fractions due to: 1) convective 

of the supplied fuel gases by 

source, and possibly 3) reduced 

The model requires knowledge of the fuel 

characterizes the fuel's chemical structure. Methods < 

the required smoke - point of gaseous, liquid, and solid (charring and non - charr ing) 

fuels of interest. 

smoke - point which effectively 

we now available for evaluating 

By developing algebraic curve - fit formulas for the soot and gaseous emissivities 

the model is self- contained and can be readily implemented using spread - sheet 

software. 

HE FEHENCES 

1. de His, J.: Seventeenth Symp. (Int.) on Combustion, The Combustion Institute, 

Pittsburg, PA (1979), 1003. 

2. de Ris, J. and Orioff, 1.: submitted to Combustion and Flame. 

3. Markstein, G.H. Comb. and Flame, 27, (1976), 51. 
102 

4. Kent, J.H.: Comb. and Flame, 63: 349-358 (1986). 

5. Gulder, O.L.: Comb. and Flame, 78: 179-194 (1989). 

6. Markstein, G.H.: Twenty First Symp. (Int.) on Combustion, The Combustion 

Institute, Pittsburg, PA, (1987), 1107-1114. 

7. Marksteirl, C.H.: Twenty-Second Symp. (Int.) on Combustion, The Combustion 

Institute, Pittsburg, PA (1989), 363-370. 

6. Orloff, L., de fiis, J., and Delichatsios, M.A.: Comb. Sci. and Tech., 1992 (in 

press). 

9. Markstein, G.H. and de his, J.: Twenty-Third Symp. (Int.) on Combustion, The 

Combustion Institute, Pittsburg, PA, (1991), 1685. 
103 

by 

WALL-FI RE RADIANT EMISSION* 

G.H. Markstein and J. de Ris 

Factory Mutual Research Corporation 

115 1 Boston- Providence Turnpike 

Norwood, MA 02062 

The scientific understanding of wall-f’r combustion and in particular the 

development of pertinent theoretical models”‘ require experimental data on flame 

radiation sc that these models can be applied to fires of hazardous scale where 

radiative energy transfer plays a controlling role. The purpose of the present work 

is to extend the range of such data beyond the upper li i s of fuel sooting tendency 

and flame height attained in previous investigations. ’k8 In the approach used 

here, wall fires of solid fuels are simulated by burning gaseous hydrocarbon fuels 

under steady - state conditions. The four fuels, methane, ethane, ethylene and 

propylene, are used to cover a suf’ficiently wide range of sooting tendency. 

Initially, the study concentrated on the simulated overfire region by releasing 

the entire fuel fl~~ from a horizontal slot burn r placed adjacent to a vertical 

water-cooled metkl plateg’” while more recent Hork‘l is concerned primarily with the 

pyrolysis region, simulated by supplying gaseous fuels from a water-cooled vertical 

sintered - porous- metal surface. The burner developed for this study consists of ten 

132-mm-high and 380-mm-wide vertical porous- metal panels topped by a 660 mm high 

water-cooled solid-metal heat transfer plate divided into five similar segments. To 

approach two- dimensional flow conditions as closely as possible, water-cooled side 

walls of 150 mm depth are attached to the burner over the entire height of 1980 mm. 

The water cooling passages embedded in the porous metal and the heat transfer 

plate are instrumented with differential thermocouples for measurement of the total 

heat transferred to each panel and segment by the flame. Other instrumentation 

includes a wide-visw-angle radiometer measuring total radiant emission and a slit 

scanning radiometer to determine the vertical distribution of radiant emission by 

horizontal slices across the wall fire. 

In the slot- burner w~rk~,’~ it was found that the radiative fraction of total 

heat release rate was reduced significantly by placing the burner adjacent to a 

water-cooled wall, compared to values obtained with free - burning slot- burner or jet 

flames. This work also yielded dimensionless correlations of radiant emission as a 

fraction of height independent of heat release rate, by introducing a radiation 

flame -length parameter. The latter varied with the 1/2 power of heat-release rate, 

suggesting that flame heights are controlled primarily by radiant cooling rather than 

turbulent mixing, and implying a mean volumetric heat-release rate independent of 

fire size and fuel type. 

Work with the porous- metal burner’’ showed that for any fixed fuel mass flux, the 

radiance No increases linearly with height, 2, after an initial jump at the flame 

base. At fixed z ,. ,,ifnear relationships between reciprocal radiance No1 and 

reciprocal mass flux m were obtained. For methane and ethane these relationships 

held over the entire range of mass flux, while for ethylene and propylene, an abrupt 

transition separating two regimes occurred as critical mass fluxes. The ordinate 

* Supported partly by the Building and Fire Research Laboratory, National 

Institute of Standards and Technology, and partly by Factory Mutual 

Research Corporation. 
104 

intercept N,, representing an asymptotic radiance, a!? the slope s of the linear 

relationship, are functions of height 2. N, and s increase with fuel sooting 

tendency at fixed 2. 

Heat fluxes to the porous metal panels decreased with increasing mass flux near 

the flame base, but were nearly independent of mass flux near the top portion of the 

porous-metal burner. These heat fluxes increased with fuel sooting tendency, except 

for a reversed trend between methane and ethane. At sufficiently high mass flux, a 

jump of heat flux occurred at the junction between the porous-metal burner and the 

solid-metal heat transfer plate, and the heat flux increased further with height in 

this over - fire region. In this zone, the data were separated into a lower over- lapping set fGr alkane fuels, methane and ethane, and a higher overlapping set for 

the alkanes, ethylene and propylene. 

Additional results beyond those included in Ref. 11 will be presented. In 

particular, separation of total heat flux to the wall into its radiative and 

convective components is an essential requirement for the development of a predictive 

theoretical model. Instrumentation for performing pertinent measurements is 

currently being developed. However, preliminary estimates of the separation can be 

obtained from the current data and will be reported. 

REFERENCES 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

Kennedy, L.A. and Plumb, O.A.: Sixteenth Symposium (International) on Combustion, 

p. 1699, The Combustion Institute, 1977. 

Ahmed, T. and Faeth, G.H.: Seventeenth Symposium (International) on Combustion, 

p. 1149, The Combustion Institute, 1979. 

Tamanini, F. : Seventeenth Symposium (International) on Combustion, p. 1075, The 

Combustion Institute, 1979. 

Delichatsios, M.A.: Ninetemth Symposium (International) on Combustion, p. 1075, 

The Combustion Institute, 1983, Combustion Science and Technology, 39, 195, 1984. 

Orloff L. , de Ris, J., and Markstein, G.H. : Fifteenth Symposium (International) 

on Combustion, p. 183, The Combustion Institute, 1975. 

de Ris, J. and Orloff, L. : Fifteenth Symposium (International) on Combustion, p. 

175, The Combustion Institute, 1975. 

Orloff, L., Modak, A.T., and Alpert, R.L.: Sixteenth Symposium (International) on 

Combustion, p. 1345, The Combustion Institute, 1977. 

Quintiere, J., Harkleroad, M., and Hasemi, Y.: Combustion Science and Technology, 

- 48, 191 (1986). 

Markstein, G.H. and de Ris, J.: Twenty-Third Symposium (International) on 

Combustion, p. 1685, The Combustion Institute, 1991. 

Markstein, G.H., and de his, 3.: "Wall-Fire Radiant Emission, Part 1. SlotBurner Flames, Comparison with Jet Flames,ll FMRC Technical Report, RC90-BT-2, 

August 1990. 

Markstein, G.H., and de Ris, J.: "Wall-Fire Radiant Emission, Part 2: Radiation 

and Heat Transfer from Porous-Metal Wall Burner Flames," 24th International 

Symposium on Combustion. (in press) 
105 

HEAT FEEDBACK TO A POOL FIRE 

A. Hamins, M.. Klassen*, J. Gore', and T. Kashiwagi 

National Institute of Standards and Technology 

The heat flux to the surface of a pool fire and the mass flux vaporizing 

from the pool are part of a positive feedback loop. The rate of mass 

burning depends on the heat feedback from the flame to the fuel surface 

and the mass burning rate controls the total heat release and the amount 

of heat feedback. Heat feedback, Q (W), to the pool surface is due to 

the sum of conduction ( Qcond) , convection ( Qconv) , and radiation ( Qtad). An 

energy balance at the fuel surface of a steady-state fire requires that 

the heat feedback is equal to the energy needed to vaporize the fuel and 

to overcome heat losses via reflection and re-radiation by the fuel 

surface to the surroundings (Qrerad), increased sensible heat of the 

liquid pool (Q,), and heat flux to the bottom and sides of the pool 

burner ( Qloss ) : 

Q = Qcond + Qconv i- Qrad (1) 

= M- (Hv + Cp- (Ts-Ta) ) + Qrerad + Qs + Qloss (2) 

where M (gh) is the mass burning rate, Hv (J/g) is the heat of vaporiza- tion at Ts (K), T, (K) is the pool surface temperature, C, (J/g-K) is the 

fuel heat capacity, and T, (K) is the ambient temperature. The loss terms 

(Qrerad! Q, and Qloss) diminish the fraction of energy available for fuel 

vaporization. 

Although much research has been conducted on the non-homogeneous 

properties of pool fires, most work has assumed a uniform mass burning 

rate across the entire pool surface, independent of radial location (r). 

Only a few experiments have measured localized heat transfer at the pool 

surf ace. In this study , Qrad ( r ) , Qloss , and Q, were independently measured, 

Qrerad was estimated and Q,,,, was calculated using Eqs. 1 and 2 (Qcond 

measured to be negligible). 

A steel fire pan composed of 4 concentric rings of 0.077, 0.152, 0.229, 

and 0,303 m in diameter, water cooled at the bottom, was used to measure 

the radial distribution of burning rate. The fuel flow to each ring was 

gravity fed and independently controlled such that the liquid level was 

maintained 5 mm below the rim. The fuel for each ring was stored in 

separate reservoirs, each on a load cell (0.1 g repeatability), such 

that the mass loss rates could be monitored. A typical experiment 

consisted of 10 minutes of warm-up and 45 minutes of observation. 

Experiments were repeated several times. Heat losses (Qloss and Q,) were 

monitored by Ch/Al thermocouples. The fuels tested were methanol (no 

soot), heptane (moderately sooting) and toluene (heavily sooting). 

Figure 1 shows the burning rate of methanol, heptane, and toluene in the 

annular ring pool. The burning rate profile is relatively flat for all 

fuels. 

A narrow view angle (0.004 str or f7"), nitrogen purged, water cooled 

radiometer was used to measure the radiative flux at the pool surface. 

The radiometer face was positioned 2 mm above the fuel surface. 

Measurements along the pool surface were made at 2 em intervals and 

tilted at 20" intervals from 30" to 150" (normal to pool surface = 90"). 

* supported by NIST Grant 6ONANBO9DO944. Permanent address: School of 

Mechanical Engineering, Purdue University, West Lafayette, IN 47907 
106 

Data was taken at a 30. Hz sampling rate and averaged for 90 s. The 

effect of gauge heat up was measured with the fire burning, by ptacing 

a water cooled cap over the radiometer (nitrogen purge maintained). The 

radiative intensity at each angle was numerically integrated to yield 

the total radiative flux at a particular location, The radiometer was 

calibrated using a standard flux gauge. For all fuels and all locations, 

the largest intensity incident on the radiometer was at 0 = 90°. The 

figure below shows that the integrated radiative flux was highest for 

toluene, followed by heptane and then methanol. The flux decreases from 

the pool center towards the pool rim for methanol, but was relatively 

flat for heptane and toluene, 

The measured values of the sum of Qs and Qloss amounted to 1%, 5%, and 8% 

of the energy required for fuel vaporization, [M-(H, + C *(Ts-Ta))], for 

the methanol, heptane and toluene fires respectively , Tgese values and 

the local mass burning rate data were used to calculate QCOnV. A 

comparison of the local radiative and convective heat flux shows that at 

pool center, for all fuels, the majority of the heat flux is due to 

radiation. Convective transfer plays a major role only in the methanol 

fire, where near the pool edge about half of the heat flux is 'due to 

convection and half to radiation, At the pool center, convection 

accounts for only a small amount of the heat transfer in the methanol 

fire, In the heptane fire, radiative transfer dominates throughout the 

pool. Near the pool center radiation accounts for almost all of the heat 

transfer, while near the pool edge convection plays a small role. In 

toluene, heat transfer over the entire surface is dominated by 

radiation, 

A A I 

I I 1 t I I I 

-0 3 6 9 12 15 

Radial Position, cm 

Integrated radiative heat flux as a function of radial location in 

0.30 m pool fires. 
107 

THE ROLE OF REFLECTIOB? AND FWEL VAPOR ABElORPTION IN RADIATIVE HEAT 

FEEDBACK TO POOL FLAMES 

M. Klassen, Y.R. Sivathanu and Je Po Gore 

School of Mechanical Engineering 

Purdue University 

West Lafayette, IN 47907 

Introduction 

Radiation from liquid fueled flames is an important heat transfer 

mechanism in combustion systems. Radiative heat flux from fires 

surrounding objects determines the possibility of ignition, flame spread 

and flashover. In liquid pool flames, the energy required for fuel 

vaporization is received entirely from the flame. 

Measurements of the incident radiative heat flux at the fuel surface 

in 30 cm toluene pool fires were found to be approximately 35 kW/m2 

across the radius of the pool [ 13 . Measurements of the feedback based on 

local burning rate indicate that only 31 kW/m2 are used. A similar 

discrepancy was found by Tewarson and Pion [2]. Recent measurements in 

60 cm and 1 m pool fires show an even larger discrepancy between 

measured incident radiation and heat flux required to support the 

burning rate. Important factors. which may explain this discrepancy 

include reflection of radiation off the fuel surface and the absorption 

of radiation by fuel vapor. 

Experimental Methods 

Measurements of the incident radiative heat flux at the fuel surface 

were made using a narrow-angle radiometer. Simultaneous measurements of 

the emission/absorption properties of flames were made using a three 

wavelength optical pyrometer [l]. Measurements of the fuel surface 

infrared reflection were made using a blackbody source and lead sulfide 

(PbS) detector (Fig. 1) . Toluene vapor absorption measurements were made 

in-situ in regions of no measurable emission. 

Results and Discussion 

Fig. 2 (A) shows the transmittance of fuel vapor over a 8 mm path. 

A large dip occurs between approximately 3200-3600 nm. But little flame 

emission is found at the corresponding wavelengths (Fig. 2 (B) ) . This 

indicates that fuel vapor absorption plays a minor role in radiative 

transfer in toluene flames. 

Fig. 3 presents measurements of the infrared reflectivity of several 

different liquids. Large reflectivity is found at small incidence angles 

for all fuels. However even in toluene flames where low regions (x/D <loo) of the flame dominate feedback [3] reflection proves to play only 

a minor role in the surface energy balance. Fig. 4 shows the effect that 

reflection has on predictions of radiative heat flux. 

References 

1. Klassen, M., J. Po Gore, Y. R. Sivathanu, A. Hamins and T. 

Kashiwagi, 1992, "Radiative Heat Feedback in Toluene Pool Fires", 24th 

Smp. (Into) on Combustion, The Combustion Institute, in press. 

2. Tewarson, A. and R.F. Pion,Comb. and Flame, 26:85-103 (1976) 

30 Klassen, M. So , 1992, "The Structure and Radiation Properties of 

Liquid Pool Fires", Ph.D thesis, University of Maryland 

Acknowledgements 

The authors acknowledge the contributions of Dr. A. Hamins and Dr. 

To Kashiwagi of NIST. This work was supported by NIST Grant Nos. 

60NANB09D0944 and 60NANBlD1169. 
108 

1.1op.- --- -- -- - W 

2 

0 1.00 

3 0.80 

k 0.80 

0.70 2 

* 0.50 

2 0.40 

0.50 

4 0.20 

a 0.10 

L' 0.60 

.c 

W 

TOLUENE 

I r/~ I 0 s/D m 0.01 

I 

I 

A 

c PATH LCnaTn I 01 .I) 

b 

0.00 

1000 2000 3000 4000 SOOO 

WAVELENGTH (nm) 

4000 

F 

e L 

,,I 3000 

E 

\ 

B ; 2000 

0 

n 

- 

z! 

3: 1000 W TOLUENE 

./P = 1.0 DATU ICY~ I CUYC nu- rr.n -..-... - .--- -- 

1000 2000 3000 4000 SOOO 

WAVELENGTH (nm) 

Toluono fuol vopor tronrmiftonco 

Toluono flomo omlrdon Flg. 1 fuol surfoco rofioctlon 

moasuromont sot-up 

r-----l 4aL 1 I 1 

s8 I w 

0 

0: 

YI 

z 

a 1 0.4 

0 

0.2 I 

0.0 

TOLUENE 30 am 

PRED, W/ REFLECTION 

PRCD. W/O REFLECTION 

0,oo 0,os 0.10 0.1 s 0.20 

4 

w 

z 

0 10 20 30 40 50 60 

INCIDENT RADIATION ANGLE (DEG) r/D 

Fig 3 Fuol Surfaco rofloctlon for vorlou8 IIquId8 ctg. 4 ProdIctIon8 of lncldont rodlotlro 

hoot flux with and without 

ro f I Otto n 
109 

Total Radiative Heat Loss in Jet Flames from 

Single Point Radiance Measurement 

P. Dutta, Y. R. Sivathanu, J. P. Gore 

School of Mechanical Engineering 

Purdue University 

West Lafayette, IN 47907 

ode The total energy radiated by fires (0) to the surroundings is of importance in determining 

burning rates, flame spread and evaluating safety standards for buildings and materials. The total radiative 

hction, XR, (fkaction of chemical energy radiated to the surroundings) is a characteristic of the fuel over a 

range of heat release rates, Q. The total radiative heat loss are usually estimated either by measurements 

of radiance over a semi-infinite enclosure surrounding the flames [ 1-21 or from a single pint measurement 

assuming spherical isotropy [3]. For liquid pl flames, a single point radiance measurement can provide 

reasonable estimates (within 13%) of total radiative heat loss from the flames [4]. The objectives of the 

present work are (1) to determine the efficacy of a single point technique for both single-phase and multiphase jet flames experimentally and (2) to study the theoretical basis for the estimation of total radiative 

flux from single point radiance measurements. The results would be useful in estimating the radiative 

output of large scale oil-well fires and flares. 

a eoretical - The scalar property distributions essential for radiation 

calculations were obtained from a k-e-g model coupled with the laminar flamelet concept for soot volume 

fractions and temperatures. The radiative heat flux (e) to Merent representative detector locations were 

calculated using a multi-ray approach [5]. The radiative flux were normalized using dimensional analysis 

and the results plotted in these nonnalized coordinates to seek universal curves. The experimental work 

consisted of making radiance measurements along a semi-infinite enclosure surrounding the flames. The 

resulting radiance measurements are plotted in the same normalized coordinates. The single phase jet 

diffusion flames considered were ethylene/& or methane/& stabilized on a 6 mm diameter burner. Multiphase jet flames burnt a mixture of methane and methanol, heptane ar Crude-oil in an effervescent atomized 

burner. During previous tests of crude-oil/methane flames from a pressure atomized burner, more than 

50% of the fuel was unburned due to poor atomization quality. In contrast to the above, the effervescent 

atomized burner resulted in complete combustion of the crude oil for relatively low gas to liquid mass 

ratios (GLR) Visual flame heights were obtained from high speed photographs. 

8 

ISC- Figure 1 shows the calculated heat flux, at a radial distance R and an axial 

distance x from the burner exit, plotted as a function of axial psition in the normalized coordinates at half 

the stochiometric flame height (0.5 Lfs), 1.0 Us, and 2.0 Lfs. The normalized heat flux, for the six 

different conditions shown in Fig. l., collapse to approximately a single curve showing the similarity of 

radiative fluxes fkom the turbulent jet flames. Figure 2 shows the experimental data from radiance 

measurements at half the visible flame height (Lfi) for two different flow conditions for methandair and 

ethylene/& asion flames. The experimental data far the two different fuels, with vaxying radiative heat 

loss fractions, collapse onto a single curve supporting the choice of scaling parameters. Figure 3 shows 

the experimental heat flux at a radial distance qual to the visible flame height from two-phase diffusion 

flames plotted on the nonnalized coardinates. Similar to the single phase difhsion flames, the normalized 

heat flux profiles for the two phase jets collapse onto a single curve. For all the mde-oil test conditions, 

the radiative fractions depended on the gas to liquid ratio (GLR). For fixed GLR, the radiative fiaction 

was found to be independent of fuel flow rate. The radiative fraction decreases with increasing GLR due to 

the lower sooting tendencies of the methane flames. In spite of the different radiative fiactions and the 

different GLRs, the normalized heat flux profiles collapse. Based on these findings, a single radiance 

measurement at a given R/L% and x/Lh can be used to estimate the total radiative heat loss from single 

phase and two phase jet diffusion flames using Figures 2 and 3 respectively. 
110 

-owl- This study is supparted by the National Institute of Science and Technology under 

Grant Nos. 60NANB9DO834 and 60NANBlD1172. with Dr. D. D. Evans Serving as NIST Technical 

eferewes1 . Sivathanu Y. R, (1990), Ph. D. Thesis, Aerospace Eng., University of Michigan, Ann Arbar, MI 

2. Jeng, S. M. and Faeth, G. M., 1984, 

3. Markstien, G. H., 1984, Twentieth Symposium (International) on Combustion, The Combustion 

Institute, Pittsburgh, PA, p. 1055. 

4. Hamins, A., Klassen, M., Gore, J. P., and Kashiwagi, T., 1991, 

5. Gore, J. P., Ip, U. S., and Siva.thanu, Y. R, 1992, 

vol. 106,886. 

vol. 86,223. 

voL 114,487. 

2.0 

1.6 

1.2 

0.8 

0.4 

0.0 

1.6 

Q! 

x 

0 

E 

*- 1.2 

(y\ 0.8 

e t 0.4 

+L 

= 0.0 

1.6 

1 e2 

0.8 

0.4 

0.0 

R =O .SL,, d(mm) Q,(kW) Sym. 

6 6.21 0 

6 12.5 A 

6 24.9 V 

12 42.4 0 

L 12 63.7 V 

b 12 93.6 V 

R=l .OLi, 

R=2.0 L,, 

0.0 0.5 1.0 1.5 2.0 -2.5 3.0 

x&. 

Fig. 1. Normalized heat flux profiles 

along the axis for three 

different radial locations from 

multi-ray calculations. 

C,H, 11.2 

C,H, 20.2 t CH, 12.8 

1.5 

% 

0 

\ 

a 1.0 

cr 

w 

? $ 0.5 

0.0 --- 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 

X4" 

Fig. 2 Normalized heat flux profiles along the 

axis of single phase diffusion flames. 

ICrude 0'' Q, GLR Syrn.] I r I 

14. 0 

14. .10 

t 14. .05 V 1 

1 .o 

005 

000 

0 1 2 3 

%ILf" 

Fig. 3. Normalized heat flux profiles along the 

axis of two phase diffusion flames. 
111 

Specific Absorption Coefficients of Soot Particles 

in Laminar Flat Flames 

Y. R. Sivathanu and J. P. Gore 

School of Mechanical Engineering 

Purdue University 

West Lafayette, IN 47907 

Jn troduct ions- Theoretical predictions of continuum radiation from luminous flames require 

information on volume fractions, temperatures and specific absorption coefficients of soot particles. Past 

studies [ 1-31 show that the specific absorption coefficients of soot particles are independent of fuel type 

(C/H ratio) and weakly dependent on temperatures. In contrast to the above, two recent studies [4,5] 

show substantial C/H ratio effects on the specific absorption coefficients in the infrared region making heat 

transfer calculations in strongly radiating flames intractable. These studies [4,5] involve a single operating 

condition for which the optical homogeneity of the path was not considered. The specific objectives of 

this study were: 1) to measure the specific absorption coefficients of soot particles for a wide variety of 

conditions for three different fuels, and 2) study the effect of optical inhomogeneity on the measurements. 

FxDerimental methods - Premixed methane/oxygen, propane/oxygen and ethylene/oxygen flames were 

stabilized by a ceramic disc placed 50 mm above the surface of McKenna flat flame burner of 5 cm 

diameter. A four-wavelength emission/absorption probe shown in Fig. 1, was used to measure the 

absorption soot volume fiactions (from the extinction of a He-Ne laser at 632 nm) and the emission soot 

volume fractions and temperatures (from emission intensities at 800 nm and 900 nm) at a height of 15 mm 

above the surface of the burner. Equality between emission and absorption soot volume hctions is taken 

as an indicator of optical homogeneity and for these conditions, the emission intensities measured at 2300 

nm, and 4000 nm were used to infer the specific absorption coefficients at these wavelengths. A range of 

equivalence ratios and flow rates were used to change the residence times and temperatures of the soot 

particles in the flame. 

esults and Discm ion- Figure 2 shows the specific absorption coefficients obtained using the 

refractive indices given by three investigators [1,2,5] as a function of wavelength. The present 

experimental data averaged over all optically homogeneous conditions are also shown for comparison. 

The results show that the specific absorption coefficients in the infrsued region are independent of fuel type 

(C/H ratio) even when fuel dependent refractive indices were used in the visible region. Figure 3 shows 

the specific absorption coefficients plotted as a function of optical path homogeneity defined as the ratio of 

emission to absorption soot volume fraction, Measurements outside the optically homogeneous band 

show a factor of 3 departure from the correct values. Hence, if different optically homogeneous 

conditions were used for different fuels, the results would show a spurious fuel-type effect. Figure 4 

shows the radial profdes of temperature and soot volume fraction for two different equivalence ratios 

calculated using a PDE solver, Entrainment of shroud gas due to buoyancy is the major cause of optical 

inhomogeneity. The degree of inhomogeneity and the inferred specific absorption coefficients at 4OOO nm 

are also tabulated. Higher temperatures result in greater inhomogeneity causing spuriously high value for 

the inferred specific absorption coefficients. 

. 

cknowledeements- Partial support for this study is provided by the National Science Foundation 

Grant Number CTS-8914520. 

eferenca 

1, Dalzell, W. H, and Sarofim A, F., 1969, J. Heat Trans., vol. 91, 100. 

2. Tien, C. L. and Lee, S. C., 1982, ROE. Enerm Combust. Sci., vol. 8,41. 

3. Charalampopoulos, T. T, and Felske, J. D., 1987, Combust. Flame, vol. 68,283. 

4. Ben Hamadi, M., Vervisch, P. and Coppalle, A,, 1987, Combust. Flame, vol. 68, 57. 

5. Habib, 2. G. and Vervisch, P.,1988, Combust. Sc i. Tech,, vol. 59, 261. 
112 

¶ 

Tbn and Lao 

0.3 0.7 1 3 SI 

Wavoiongth (pan) 

- - - . - - - - * - - - - * - - - - - # -- 

c X = 1000 nm c2n4. A 

Y)- 0.0 0.4 0.8 1.2 1.6 2.0 

fJf. 

TI,,~=2O0O K 

0.8 f "J f v= = 0 . 72 

0.6 1 

A 

> 

. 002 

> 

I-' Oe4 i a 

'*.. \ f (n e k)/b 1 39 

' 000 i l.... 

' I "" 

'r T,",-= 1 4OOK 1.0 -0- E b 0.8 

-. f Jf v. =o . 85 

f(nek)/X=1.29 

0.4 1 a -000000000~0000~0~000 

0.2 . 

0.0 

. '....> 

0.00 0.01 0.02 0.03 
113 

Scattering by Soot Aggregates in 

Turbulent Diffusion Flames 

R. Mital, J. Dylla, Y. R. Sivathanu, J. P. Gore 

School of Mechanical Engineering 

Purdue University 

West Lafayette, IN 47907 

Jntroduction- Radiation heat transfer studies in luminous flames have assumed negligible effect of 

scattering by soot particles due to their relatively small diameters compared to the wavelengths of interest 

[l-31. Recent morphological studies of soot aggregates in diffusion flames show that the scattering 

coefficients of soot particles may be as high as 100% [4-51. However, these experiments were conducted 

either in laminar flames [4] or in the overfire region of turbulent flames [SI. In addition, the effect of 

scattering on radiative heat transfer has not been studied. Based on these observations, the objectives of 

the present study are: 1) to measure the scattering coefficients in turbulent diffusion flames and 2) to 

evaluate the effect of the measured coefficients on radiative heat transfer. 

heoretical and Werirnenw maods- Insitu measurements of the scattering coefficients were 

conducted for a turbulent acetylene/air jet diffusion flame. The exit Reynolds number of the flame was 

9200 based on a burner diameter of 6 mm. Fig. 1 shows a sketch of the present scattering/absorption 

probe, which consists of two fixed and one movable stainless steel purged tubes. The extinction of a 

He-Ne laser was measured across a probe length of 10 mm and the intensity of the scattered light was 

measured at three different angles (450,900, and 1350) providing an estimate of the instantaneous 

scattering coefficient. The measured scattering coefficients were used in multi-ray radiative flux 

calculations [3] to estimate the effect of scattering on the radiaitive transfer fiom a representative horizontal path in the flame. 

esiilts and DISCUSS ion- Table 1 shows representative value of the scattering coefficients at an axial 

location corresponding to x/d = 50. The mean value of the scattering coefficient is the highest at 450 

(forward direction). The fluctuations are relatively low at large angles but increases to about 77% of the 

mean value at 450. Mean soot volume fiactions and temperatures obtained from a coupled k-e-g calculation 

[3] along with a mean scattering coefficient of 0.33 were used to evaluate the effect of scattering on the 

spectral radiation intensity (at 900 nm) along a diametric path in the flame. Fig. 2 shows the distribution 

of the different terms in the equation of radiative transfer along the diametric path. The emission intensity 

is symmetric since the scalar distribution obtained from the calculation is symmetric. The intensity 

absorbed along the path depends on the incident intensity and is comparable in magnitude to the local 

emission. The outscatter, similar to the absorption depends on the incident intensity along the path and is 

as high as 25% of the local emission. The inscatter of radiation intensity depends on the the incident 

intensity from all parts of the flames and is therefore symmetric. Fig3 shows the net radiation intensity 

leaving a local segment as a function of the distance along the segment. This represents the balance 

between the different terms plotted in Fig.2. At different points along the segment, the effects of 

neglecting scattering can be as high as 30%. However, the inscatter of radiation intensity into the segment 

tends to cancel the outscatter of radiation intensity from the segment. The difference between the values 

of intensity leaving the entire segment neglecting scattering and those including scattering is only about 

5%. 

cknowledggmnk This study is supported by the National Science Foundation under Grant No. 

CTS-9157920, 

References- 1. Viskanta, R. and Menguc, M. P., 1987, 

2. Gore, J. P. and Faeth, G. M., 1988, J. Heat Trans., vol. 110, 173. 

3. Gore, J. P., Ip, U. S., and Sivathanu, Y. R., 1992, J. Heat Trans., vol. 114, 487. 

4. Dobbins, R. A., Santaro, R. J., and Semerjian, H. G., 1990, Twenty-Third Symposium (International) on Combustion, The Combustion Institute, PA. p. 1525. 

Ene rw __ Co mbust. Sc i,, vol. 13,90. 
114 -N 100 

250 . 

. 200 ; 

150 ; 

100 ; 

50 : 

. 

. 

L 

D 

. 

. 

. 

. 

b 

0 

0 

0 

0 20 0 

0 

I .y80 L 0 

- 

oo 

< 

3 

SO 

4o 1 0 

oo 

0 

20 

0 OO 

10 00 0 

. oooo - 0 0 0 

0 

0 0 

0 0 

20 00 

=O E 0 

0 *o o*- . -00 

0 so 40 60 80 100 120 140 le0 

45 90 135 An,gie 

RMS 0.77 0.20 

0-33 0-11 0.09 

0.22 Me!an 
115 

STRUCTURE AND. OPTICAL PROPERTIES OF OVERFIRE SOOT 

IN BUOYANT TURBULENT DIFFUSION FLAMESa 

U. 0. Koylii and G. M. Faeth 

Department of Aerospace Engineering 

The University of Michigan 

Ann Arbor, Michigan 48109-2140 

The physical and optical properties of soot were measured within the fuel-lean 

(overfire) region of buoyant turbulent diffusion flames in still air. The study was limited to 

pool-like fires in the long residence time regime, where soot and carbon monoxide 

emission factors are independent of flame size and position in the overfire region [ 1-31. 

Both gas and liquid fuels (acetylene, propylene, ethylene, propane, tolc-qe, benzene, n- heptane and isopropanol) were studied to provide information for a range -i H/C ratios (1- 

2.67) and fuel types. Measurements included thermophoretic sampling and TEM to find 

soot structure, ultimate analysis to find soot composition, and laser scattering and 

extinction to find soot optical properties, see [4-61 for more details. 

Soot aggregate properties varied with the fuel but not with position or residence 

time in the long residence time regime. Primary particle diameters were 30-51 nm with 

average numbers of primary particles per aggregate of 255-552 - both increasing with 

increasing propensity of the fuel to soot. Aggregate size distributions were unusually 

broad (typically 30- 1800 primary particles per aggregate) but could be represented 

reasonably well using a log-normal function. The aggregates were mass fractal-like, with 

fractal dimensions of 1.7- 1.8. Elemental mole ratios of soot composition were variable, 

suggesting potential for variable refractive indices, e.g., C/H = 8-18, C/O = 58-109 and 

C/N = 242-976. 

Soot swcture and laser scattering measurements were used to develop predictions 

for soot optical properties. These predictions were based on existing Rayleigh-DebyeGans (RDG) fractal aggregate optical theories [7,8], extended to consider the broad size 

distributions of overfire aggregates. Predicted and measured angular scattering patterns 

(scattering crossections for various polarization states) are illustrated in Fig. 1 for acetylene 

soot at a wavelength of 514.5 nm. The results indicate large departures from the small 

particle (Rayleigh) scattering approximation (e.g., forward scattering is 100- 1000 times 

larger than wide angle scattering), with excellent agreement between RDG predictions and 

measurements over the accessible range of scattering angles. The performance of the 

theory for soot from other fuels was similar [6]. 

Strong scattering from soot aggregates affects both laser extinction measurements 

of soot concentrations and predictions of continuum radiation from soot. This is illustrated 

in Fig. 2, where present predictions of mean scattering to absorption crossections, psa, are 

plotted as a function of wavelength. ;sa is significantly greater than unity for wavelengths 

aResearch supported by the Building and Fire Research Laboratory of the National Institute 

of Standards and Technology, Grant No. 60NANBlD1175. 
116 

in the visible, which implies a corresponding overestimation of soot concentrations from 

laser extinction measurements’ interpreted using the Rayleigh scattering approximation. . . 

Additionally, psa remains large for heavily sooting materials in the near infrared, where 

continuum radiation from soot is most important. The implication of these findings, as 

well as the properties of underfire mot, are currently being studied in this laboratory. 

References 

1. Sivathanu, Y.R. and Faeth, G.M. Combust. Flame 81:133-149 (1990). 

2. Koylu, U.O., Sivathanu, Y.R and Faeth, G.M. Third International Symposium on 

Fire Safety Science, Elsevier, London, 1991, pp. 625-634 . 

Koylu, 0.0. and Faeth, G.M. Combust. Flame 87:61-76 (1991). 

Koylu, U. O., and Faeth, G.M. Combust. Flame 893140-156 (1992). 

Koylu, U. O., and Faeth, G.M. J. Heat Transfer, submitted. 

Koylu, U.O., Ph.D. Thesis, The University of Michigan, Ann Arbor, MI, 

1992. 

3. 

4. 

5. 

6. 

7. Martin, J.E. and Hurd, A.J. J. ADDL Crv st. 20~61-78 (1987). 

8. Dobbins, R.A. and Megaridis, C.M. &D1. Ootics, 30:4747-4754 (1992). 

IO’ t J 

ACETYLENE / AIR 

* 

hv AND rh 

I 1, Id2 

I2 

08 

04 

00 

0 45 90 I35 I a0 400 1000 4000 IO000 

e (dog) A (nm) 

Fig. 1 Angularsca~~gpattern Fig. 2 Mean ratios of scattering-to-absorpof overfire acetylene soot. tion crossections for overfire soot. 
117 

ANCHORING MECIUNISM OF POOL FI~S 

S. Venkatesh, A. Ito aadK. Saito 

Combustion and Fire Research Laborato y 

Dept. of Mechanical Engineering 

University of Kentucky 

Lmhgton, KY 40506 

ABSTRACT: This paper describes that the entire flame sheet of a pool 

fire has a diffusion dominant structure and unlike jet diffusion 

flames a special premixing mechanism is not necessary to explain the 

anchoringmechanismnearthe base. Inthe case of momentumcontrolled 

turbulent-jet diffusion flames the premixing near the burner rim 

occursduetothepresence of ashear- stress related circulationzone. 

We investigatedthethe structure ofthe flame nearthe base of a60mm 

diameter pool fires of n-hexane and 1-propanol through detailed 

measurements of the velocity and temperature fields. Our 

measurements near the base of the pool fire show that the Reynold's 

shear stresses aretwo orders of magnitude less thanthat reported for 

a turbulent-jet diffusion flame. A detailed investigation of the 

structure of the pool fire near the base indicates that the nature of 

the diffusion flame is similar to that in a counter-flow diffusion 

flame. The entrained air near the base and the rising fuel vapors 

create a stagnation plane and the fuel mixes into the oxidizer stream 

in the forward stagnation plane purely by diffusion and a flame sheet 

of finite thickness is established. It is shown that the upward 

tangential velocity of the fuel- oxidizer stream in the forward 

stagnation zone is lower than the stoichiometric f lame-propagation 

velocity,thus allowingthepoolfireto anchor, 

Air entrainment into pool fires is a key phenomenon that 

determines the thermal fluid dynamic and chemical structure of the 

pool ifre. Anumber of studies o n t h e s t r u c t u r e of pool fireshavebeen 

conducted. Recent studies by Weckman et al. have provided detailed 

information on the structure of pool fires through simultaneous 

measurements of velocity and temperature prolf iles . Bouhaf id et al. 

conducted measurements of temperature and species concentration on 

kerosene pool fires, and they suggest that air entrainment near the 

base leads to a convective-type mixing giving the flame a premixed 

character in this region. However, flame structure near the base is 

not clearlyunderstood. 

We studied in detail the mechanism of air entrainment, the 

thermal/fluid dynamic structure of the flame near the base and the 

flame anchoring mechanism. Detailed velocity and temperature 

profiles were measured near the base of pool fires of 1-propanol and 

hexane supported on a 60 mm diameter pan. We found that the pool fire 

can be divided into three distinct regions. Region 1 - a persistent laminar blue zone formed near the flame base; Region 2 - flame "neck" 

zone withwrinkled surface; andRegion3-intermittent zone abovethe "neck" zone. Our studywas forcused o n t h e r e g i o n n e a r t h e base ofthe 
118 

panwherethe flame is anchored. 

The flame base structure determines the following two aspects : ('1) 

Anchoring and stabilization of the pool fire . Common understanding 

for jet diffusion flames is that premixing occurs near the base and is 

responsible for anchoring and stabilization of the flame . Takahashi 

and Schmoll's results show mixing of the fuel and air through a 

circulation zone at the burner rim due to strong shear-stresses, 

leading to flame anchoring. Whereas, in a pool fire the fuel and 

oxidizer velocities near the base are much smaller, and insufficient 

to produce shear-stress-induced circulation zones . theref ore, the 

mechanism for fuel and oxidizer mixing in pool fires is different from jet 

diffusion flames . (2) Why and how much air entrainment occurs near the 

base ? the air entrainment mechanisms near the base and in the 

intermittent regions a r e q u i t e different . In the intermittent region 

of the flame, air entrainment is mainly by relatively large-sacle 

buoyancy-induced mixing. Near the base, by contrast, air is 

convectively entrained to satisfy mass conservation because of the 

r a p i d l y a c c e l e r a t i n g buoyant gases i n t h e flame interior . 

EXPERIMENTAL: The pool fires were established on a pyrex pan of 60 mm 

diameter. Velocity measurements were obtained using a two component 

phase doppler particle analyzer system, which consits of a 5 W 

argon-ion laser and standard transmitting, receiving and signal processing equipment . High speed data recording was achieved using a 

micro-computer, anddataanalysisbyadatamanagementsoftware ofthe 

system. Data recorded and analyzed includes instantaneous radial and 

axial velocities, mean and root mean square velocities and Reynold's shear-stresses. Outside the flame sheet, velocitymeasurements were 

made by seeding the ambient air with the talc particles. Inside the 

f lame, flow profile was visualized using Ti02. Temperature 

measurements were made using a 75 p-diamter chromel-alumel 

thermocouple. 

SUMMARY: (1) Based on our experimental measurements on pool fires and 

finite rate chemistry concepts, t h e e n t i r e flame sheet of a pool fire 

is established to have a diffusion flame structure . The counter-f low 

diffusion structure of the flame at the base was established from a 

mass balance at the flame sheet, and through a comparison of the 

locationofthe flame sheet inthe convective-airentrainmentzonefor 

fuels with different stoichiometric fuel- air requirements . (2) Air 

entrainment through the quenching zone was found to be a small 

fraction of the net air entrainment near the base. 3) The fluid 

diffusion flame is different. In a jet diffusion flame, Reynold's 

shear-stress nearthe rimofthe burner induce astagnantcirculation 

zone where the fuel and the oxidizer are mixed and the flame anchors. 

Contrary, in a pool fire the shear-stresses at the rim are two orders 

of magnitude lower compared to the jet diffusion flame , and turbulent 

mixing does not occur. Finite -rate chemistry establishes the 

presence of amolecular -diffusionmixingzonethatallowsthaflameto anchor at the base. 

I 

dynamic structure of the anchoring mechanism of a pool 4 ire and a jet 
119 

EFFECT OF PRESSURE AND OXYGEN CONCENTRATION 

ON PAN FIRES IN AN ENCLOSED SPACE 

Jean L. Bailey, Patricia A. Tatem, and Frederick W. Williams 

Navy Technology Center for Safety and Survivability 

Naval Research Laboratory 

Washington, D.C. 

Large-scale fire tests were conducted in the Naval Research Laboratory’s 324 m3 

pressurizable fire test facility, FIRE I (Alexander et a/., 1982) to determine the effect of 

pressure and oxygen concentration on 0.5 m diameter methanol pan fires in a totally 

enclosed space. Data from 14 experiments were analyzed in support of this study. Eight 

were conducted with an initial chamber atmosphere of 21 vol-% oxygen and one 

atmosphere pressure. The location of a moveable thermocouple array, designed to make 

detailed temperature measurements of the chamber interior, was varied during these eight 

experiments. The remaining six experiments began with the chamber interior as 

described in the table below. 

Initial Initial 

Oxygen Conc. Pressure 

Test #or %) [PSI) 

M425B 17 14.7 

M430A 15 14.7 

M430B 15 14.7 

M502A 21 23.9 

M503A 21 17.6 

M514A 21 20.7 

After the desired conditions were reached within the chamber, the chamber was 

sealed and the pan fire was ignited. The pan fires in all of the experiments with the 

exception of M425B, M430A, and M430B were allowed to burn for one hour before they 

were manually extinguished. The M4256, M430A, and M430B pan fires continued to burn 

until they self-extinguished. Mass loss rate, chamber gas composition (oxygen, carbon 

dioxide, and carbon monoxide), pressure, and chamber gas and wall temperatures were 

among the measurements recorded. 

Figure 1 shows mass loss rate as a function of time for the reduced oxygen tests. 

M425A is shown representing the eight experiments which had initial oxygen 

concentrations of 21 vol-% and initial pressures of one atmosphere. The lower the initial 

oxygen concentration, the smaller the initial burning rate. This order was maintained 
- 120 ' 

throughout the experiments as the mass loss rates decreased because of diminishing 

oxygen within the chamber. 

Mass loss rates versus time for the enhanced pressure experiments are shown in 

Figure 2. Again, M425a is representing the experiments conducted at 21 vol-% initial 

oxygen concentration and one atmosphere pressure. Higher initial burning rates 

correspond to higher initial chamber pressures. The mass loss rates decline with time 

as a result of the decreasing oxygen concentration. 

Analysis of the data revealed a linear relationship between the mass loss rate and 

oxygen concentration between 21 vol-% and 14 vol-% oxygen concentration. Below 14 

vol-%, the mass loss rate rapidly declined until the fire self-extinguished at approximately 

12 vol-%. Further data analysis relating mass loss rate to chamber pressure and oxygen 

concentration will be discussed. 

REFERENCES: 

Alexander, J.I., St. Aubin, H.J., Stone, J.P., Street, T.T., and Williams, F.W. (1982). LargeScale Pressurizable Fire Test Facility - Fire I, NRL Report 8643. 

a p"i 

ISL 

- M425A 

* M425B 

* M430FI 

* M4306 

AI 

cn 

m 

IT 

a 

T 

- M42SFi 

* MS02A 

* MS03R 

* M514Fl 

I 10 20 30 40 50 60 

P4 INU T E S 

Fig. 2 - Ma88 loa8 rate of fuel at different initial ch8rnber 

preasurea. 

_- I- 
131 

I 

Fire-Induced Winds in the 1991 Oakland Hills Conflagration 

Javier ’belles 

Patrick J. Pagni 

Mechanical Engineering Department, University of California, Berkeley, CA 94720 

The tragedy of the October 20,1991 Oakland HIUS “Timel’’ Fire has brought into sharp focus the role of wind in conflagrations. The effects of hot, dry, fast atmospheric winds (called “Diablo Winds” in th~s area) are well known. The magnitude 

of the fire-induced winds is not well understood and is the subject of this paper. 

1.0 Theory 

This research is based on the model developed by Howard Baum and Bernard McCaffrey [ 13. The total convected heat 

release rate 06, the ambient density pa, the ambient temperature To, the specific heat cp, and the acceleration of gravity g are 

used to determine characteristic quantities with which to nondimensionalize all physical quantities. The expressions for the 

characteristic length L, velocity U, vorticity a, potential a, and Stokes stream function Y are given in eq. (1). 

All the subsequent nondimensional quantities - superscripted with an asterick - are obtained by dividing the physical quantity 

by the characteristic one. Once one has solved for the flow field induced by a single fire, that produced by a series of fires is 

determined by physically scaling each single fire field and then vectorially adding all the influences at a point. 

The nondimensional flow field in axisymmetric cylindrical coordinates is decomposed into an expansion velocity u* *** governed by a potential @*(r*,z*) and a solenoidal velocity v* described by a stream function Y (r ,z ). The expansion field is 

determined by solving a Poisson equation (2) for @* with a normalized Gaussian heat release rate from a single fire Q*(r*,z*) 

as a forcing function. The boundary conditions subscripted by an Q refer to the asymptotic value. For the potential, this is simply the Green’s function for a point source. 

The stream function is determined by solving a different Poisson equation (3) whch has the vorticity a<(r*,z*) as the 

inhomogeneity. Empirically determined profiles for the center-line temperature O*(z*) and vertical velocity U*(z*) [2] are 

employed to determine a+ . a+ was derived by taking the curl of the velocity obtained from a Gaussian model which takes 

compressibility effects into account via the energy integral Ik (4). The quantity R* is the “width” of the Gaussian profile. IA is 

determined using the Romberg numerical quadrature routine qromb detailed in [3] for 3, = 0.866. Accuracy is verified by calculating IA for 3L = l and comparing with the exact logarithmic answer. 

** 

Y* (O,Z*) = Y* (f,o) = 0 Y* (102) = Y; (lO,Z*) Y* (r+,20) = Y:, (f*,20) 
122 

TIE form of the asymptotic stream function \y,* is complicated. It is convenient to first convert to a polar coordinate system (4, e) (5). This transformation is applied to equation (3). In order to determine the asymptotic stream function, the expression for 

the vorticity is replaced by its asymptotic value (6). The asymptotic stream function Y, is of the form (7). 

lo G = 4Q(x) with G(0.5) = 0 G(l) = 0 (7) -

d2G + . d? gX(1-x) Y: (;,z*) = f5’G (e) where 

The differential eon in(7) was solved via the collocation boundary value problem solver colnew from ODE. y/‘ is determined numerically using the fourth order FISHPACK routine sepx4. @* is calculated using the centered hte difference solver 

hwscyl also from FISHPACK. For both ai,* and ‘Pi;, Ar* = Az* = 0.1 were used. In order to determine the radial velocity %* 

and the axial velocity y* (8), appropriate numerical derivatives of the potential and stream function are taken and summed 

yielding the complete flow field for a single fire. 

a** 1 aw* 

az* r* ar* u, = - +-- (8) 

b* 1 aY* 

ar* r* az* ur = ---- 

Once the nondimensional flow field for one fire has been obtained, the velocities induced by N fires are found by scaling 

the calculated flow to physical dimensions which depend on ambient conditions and the heat release rate of the fire at (3, yi). 

To obtain the component velocities induced at a grid point (xj, Yj), simply vectonally sum all the velocities induced by the surrounding N fires at hs point. For very large fires, a sub-grid model is used. One directly sums all the velocities induced at a 

point by fires within the local cell. Fires in each cell outside th~s cell are approximated by a single fire centered at the heat 

release rate centroid of their cell. The summation is then made over the velocities induced by the centroid fires of the outside 

cells. 

2.0 Results 

The radial and vertical velocities induced by the burmng houses and vegetation will be determined at three times during 

the fire (1 1 AM, 1 PM, and 4 Ph4) at several altitudes. The heat release rate of the burning structures will be modelled as 30 

MW for the first hour of burn and 1 MW for the next six. The resulting velocities will be vectorially added to the mean ambient 

wind. The complete flow field helps to explain how a conflagration can quickly propagate. The fire induced winds will only 

subside when the fuel load is consumed. The wind that rushes in at the bottom emerges from the plume hot and laden with 

burning brands. In the fire of October 20,1991, this burning debris was conveyed by the plume into a strong Diablo Wmd 

which sent these ignition sources to fiesh areas with extremely dry fuel, propelling the fire rapidly downwind. 

3.0 References 

1) Baum, H.R, and Mccaffrey, B.J., “Fire-Induced Flow Field - Theoxy and Experiment,”Fire Saf&y Science - Proceedings 

of the SecondhternatioMl Symposium, New York: Hemisphere, 129 - 148,1989. 

2) McCaffrey, B.J., “Momentum Implications for Buoyant Diffusion Flames,” Combustion am! Flame 12,149 - 167,1986. 

3) Press, N.H., et al., Numerical Recipes, Cambridge, England: Cambridge University Press, 114 - 115,1989. 
123 

PAPER WITHDRAWN 
124 

PAPER WITHDMWN 
125 

A LUMPED PARAMETER MODEL 

for 

UNBURNED TREE CROWN STREETS 

M.C. Smith 

Michigan State University 

Warren G. Heilman 

U.S. Forest Service, East Lansing, Michigan 

Strips of unburned tree crowns occur occasionally in wildland forest fires. These are 

called unburned tree crown streets in the literature and remain an unexplained 

phenomenon. Interest in these streets is based on the fire induced airflow and ambient 

winds which may produce the effect and ultimately on the hope that understanding will lead 

to better and safer fire fighting procedures. 

References (1) through (6) contain observations and discussion of the phenomenon, 

some of which include possible explanations of the causes of the appearance of the streets. 

Present explanations include horizontal roll vortices, wind shifts, firebrand throwing and 

buoyancy induced wind flow. None of these is entirely satisfactory due to the complexity 

of the three-dimensional transient problem involving fluid mechanics, heat transfer and 

combustion. 

The buoyancy induced wind flow model presented here is believed by the authors to 

account for most of the observed effects and offers a plausible explanation of the 

phenomenon. Confinnation requires further observation and perhaps instrumentation and 

data gathering. 

The induced air flow model yields Equation (1) 

m, 

dr 

m - = buoyant force - resistant force 

where m is the gas mass in the air flow column, v is the average induced flow speed, f is 

time and the buoyant and resistant forces are 

buoyant force = gl3ATpbH (2) 

resistant force = cp? (3) 

where g is gravity, 13 is the coefficient of thermal expansion, AT is the temperature rise due 

to combustion, p is air density, 4 is flow-crossection area, H is height of the flow column, 

c is a drag coefficient and v is the flow speed. 

The equation provides an oscillatory solution on the basis of heat release from 

burning tree crowns being substantially larger than heat release from understory burning. 
126 

The effect is to increase and decrease the induced flow periodically. This oscillation 

produces the unburned tree crown streets. 

It is evident that conditions must be favorable within a narrow range for the 

phenomenon to occur, which may account for the relative rarity of unburned tree crown 

streets occurring in wildland forest fires. Results of calculations show that the conditions 

for oscillation to occur depend upon the ratio of understory to crown heat release rates, a 

dimensionless induced inflow air speed, and the ratio of the crown base height to the 

maximum understory flame length. 

Analysis was by digital computer using numerical integration and data from 

References (6) through (9). Additional results obtained indicated that the major effects on 

the oscillation are accounted for by the use of these three dimensionless parameters. 

Other explanations of the occurrence of unburned tree crown streets cannot be ruled 

out. A more sophisticated and detailed model and the establishment of a wider range of 

data are desired to consider predicting the occurrence of the phenomenon. Results may 

then be reviewed for application to forest fighting and prediction. 

REFERENCES 

Haines, D.A., Horzontal Roll Vortices and Crown Fires, J. Appl. Met. 21, 751-763 

(1982). 

Luke, R.H. and A.G. McArthur, 1978; Bush Fires in Australia. Australian Goa. Pub. 

Service, Canberra, 359 pp. 

Shard, AJ., D.A. Haines, J.S. Frost and R.W. Blank, 1982 The Mack Fire, USDA 

Forest Service, North Central Forest Experiment Station, Res. Pap., 31 pp. 

Van Wagner, C.E., 1977; Conditions for the start and spread of crown fire, Canadian 

J. For. Res., 7, 23-34. 

Wade, D.D., and D.E. Ward, 1973; An Analysis of the Air Force Bomb Range Fire. 

USDA Forest Service, SE Forest Experiment Station Res. Pap. SE-105 xxx pp. 

Albini, FA, 1984; Wild Land Fires, American Scientist, Novo-Dec. pp. 590-597. 

Rothermel, R.C., A Mathematical Model for Predicting Fire Spread in Wildland 

Fuels, USDA Forest Service Research Paper INT-115, 1972. 

Nelson, R.M. Jr., Flame Characteristics for Fires in Southern Fuels, USDA Forest 

Service Research Paper SE-205, 1980. 

Albini, FA, Estimating Wildfire Behavior and Effects, USDA General Technical 

Report INT-20, 1976. 

. 
127 

Numerical Simulation of the Rise and Dispersion 

of Fire Generated Plumes 

Ahmed F. Ghoniem and Xiaoming Zhang 

Department of Mechanical Engineering 

Massachusetts Insitute of Technology 

Cambridge, MA 02139 

Abstract 

The rise and dispersion of plumes generated by massive fires are important phenomena which 

determine the environmental impact, hazards potential and possibly extend of fie spread. This is because 

massive fire plumes are strongly buoyant, are laden with unburnt hydrocarbon and carbonous particulates, 

and can induce entrainment currents of very high velocities. Because of their strong buoyancy, these 

plumes can penetrate the Planetary Boundary Layer velocities and interact dynamically with density its 

stratification. The latter complicates the modeling of large plumes but leads to a rich variety of phenomena 

which, in order to accurately assess the environmental impact of massive fires, must be examined in detail. 

We have developed a moving surface fornulation for the problem of buoyant plume dispersion in a 

stratified atmosphere, based on the parabolization of the governing equation in the major wind direction 

(Ghoniem et al., 1992). The solution, including the plume trajectory, the evolution of the plume cross 

sections, and the plume-induced flow is obtained using the transport element method. This is a 

Lagrangian vortex method extended to include the dynamic effects of density stratification. Our 

computational plume model thus is an efficient large eddy simulation, in which small scale atmospheric 

turbulence is modeled using a new interpretation of the classical K-theory. The model is flexible enough 

to accommodate other physically relevant processes such as chemical reactions between the plume material 

and the atmosphere. Solutions are compared with experimental measurement whenever possible. 

Figure 1 shows the density distribution within the plume cross section for three Werent buoyancy 

Reynolds numbers defined such that the velocity is that induced by gravity and the diffusivity is the 

combined molecular and turbulent diffusivities. In all cases, atmospheric density is uniform. Clearly the 

large scale structure of the plume is not strongly affected by small scale diffusivity. This structure, while 

strongly deforming by the action of two counter rotating streamwise vortices which form as the gravity 

generated vorticity on the plume boundary rolls-up, indicates that the dispersion of the plume material 

during the rise phase is rather limited. In all cases, the experimentally observed kidney shape of the plume 

cross section is predicted by the numerical simulation (Fanaki, 1975). The effect of the Reynolds number 

on the plume trajectory, and a comparison with the widely accepted two-third power law (Briggs, 1975, 

and Weil, 1988) are shown in Fig. 2. As found experimentally, the model shows that eddy viscosity, or 

small scale turbulence, has noteffect on the plume trajectory (Hewett et al., 1971). 

The effect of atmospheric density stratification, or inversion is shown in Fig. 3. During the 

daytime, plume rise takes place in a convective boundary layer capped by a sharp inversion which stops 

the plume from further penetration, except of its buoyancy is exceedingly strong or if the inversion layer is 

very close to the ground (Manins, 1979). This is shown by the results in Fig. 3 where the plume 

penetrates a low weak inversion layer in (a); partially penetrates an elevated weak inversion layer in (b), 

and is prevented from penetration by a low, strong inversion layer in (c). In case (b), only the middle 

section of the plume, which maintains the strongest buoyancy can penetrate the invasion while the side 

parts are reflected back. In the last case, all the plume material are reflected off the inversion and sent back 

downwards. 

References 

Briggs, G.A., "Plume Rise Predictions," Lectures on Air Pollution and Environmental Impact Analysis, 

D. A. Haugen, Ed., Amer. Meteor. SOC., Boston, 59-111, 1975. 

Fanaki, F.H., ""Experimental Observations of a Bifurcation Buoyuant Plume," Boundary-Layer 

Meterology, 9,479-495, 1975; 

Ghoniem, A.F., Zhang, X., Knio, O.M., Baum, H. and Rehm, R., "Dispersion and Deposition of 

Smoke Plumes generated in massive fires," J. of Hazardous Materials, (to be published). 
128 

Hewett, T.A., Fay, J.A. and Hoult, D.P., "Laboratory Experiments of Smokestack Plumes in a Stable 

Atmosphere," Atmospheric Environment, 5,767-789, 197 1. 

Manins, P.C., "Partial Penetration of an elevated Inversion Layer by Chimney Plumes," Atmos. Environ., 

13, 733-741, 1979. 

Weil, J.C., "Plume Rise,"Lectures on Air Pollution Modeling, Editors, Venkatram, A. and Wyngaard, 

J.C., 119-166, 1988. 

Re- td 

Figure 1. The density contours in the plume cross wind section at x=5 for different buoyancy Reynolds numbers. only half 

of the cross-section is shown due to the symmetry about the center line. 

7- j 

Figure 2. The rising plume trajectories for variou! 

buoyancy Reynolds numbex. The solid line is the extendec "two-thirds" law which includes the effect of the Wte initia 

plume size. Plume trajectories comsponding to cases (a), (b 

and (c) in Figm 3 are also included. 

Figure 3. The density contours at successive downwind location far a plume approaching an inversion layer when: (a) the 

plume is initially close to a weak inversion layer (penetration); (b) the plume is initially far from a weak inversion layex 

(partial penetration): and (c) the plume is initially close to a strong inversion layex (reflection). 
129 

Two-Dimensional Simulations of Buoyancy-Induced 

Horizontal Roll Vortices 

W. E. Heilman 

USDA Forest Service, East Lansing, MI 48823 

The intense heat associated with wildland fires can generate very strong atmospheric boundary-layer 

circulations in the vicinity of burning regions. Hot gases produced within a wildland fire lead to buoyancy-induced 

upward vertical velocities over the fire and low-level horizontal flow into the burning area. The buoyancy effect 

over and adjacent to firelines in wildland fire episodes is primary mechanism involved in the formation of 

atmospheric horizontal roll vortices, as outlined by Church et al. (1980). Evidence of horizontal roll vortices 

during wildland fire episodes has been documented by Haines (1982), and these vortices have been generated in 

numerous wind-tunnel experiments (Haines and Smith, 1987, 1992). The presence of horizontal roll vortices can 

influence the movement of flames, firebrands, and smoke, all potential hazards for fire-fighting personnel. In 

addition, horizontal roll vortices have been indicated as a possible factor in the formation of unburned tree-crown 

streets within burned forested areas (Haines, 1982). 

In this study, the buoyancy mechanism for horizontal roll vortex development is examined through the use of a 

two-dimensional, nonhydrostatic, atmospheric boundary-layer model. Prognostic equations are used to solve for 

the horizontal and vertical velocity components, the potential temperature, and the turbulent kinetic energy. 

Nonhydrostatic dynamic pressure perturbations are diagnosed from a Poisson equation derived &om the 

atmospheric continuity equation. The governing equations are numerically solved by both finite-element and 

finitedifference techniques. 

The presence of single and multiple firelines is approximated by introducing constant surface potential 

temperatures of 900°K or 1500°K at prescribed locations in the modeled domain, which spans a 2.0 km wide by 1.8 

km high vertical plane. Initial potential temperatures at all other locations in the modeled domain are set at 

298°K. In order to simulated the impact of varying crossflow wind speeds on the development of horizontal roll 

vortices, different initial logarithmic crossflow velocities are introduced into the model simulations. Simulations 

are carried out for a period of 90 s, with a time step of 0.05 s and 1800 time steps per simulation. 

Model simulation results indicate that the development and strength of horizontal roll vortices are influenced 

by the temperature of the approximated firelines, the proximity of the firelines to each other, the presence of light 

ambient winds blowing perpendicular to the firelines, and the slope of the underlying terrain. For a single fireline 

located on flat terrain under calm crossflow conditions, a symmetric vortex pair develops over the fireline. Larger 

surface temperatures at the fireline produce more vigorous vortex circulations. The presence of a light ambient 

crossflow completely inhibits the development of these symmetric vortices for the temperature scenarios performed 

in this study. However, the presence of a sufficiently light ambient crossflow results in the development of lowlevel vortices with significant vorticity immediately downwind of single firelines. If this type of buoyancy-induced 

vortex were to develop along the flank of an actual fireline, with flames and firebrands caught in the circulation, 

fire-fighters could be endangered. An analysis of the nonhydrostatic dynamic pressure perturbations near the 

region of surface heating reveals that higher surface temperatures generate larger pressure perturbations because of 

the increased low-level convergence over the firelines. Turbulence energy over individual firelines tends to 

diminish as the ambient crossflow speed increases and the fireline temperatures decrease. 

When multiple firelines are present, interesting interactions between adjacent horizontal roll vortices are 

observed. During calm crossflow periods, buoyancy-induced horizontal roll vortex pairs develop over each fireline 

if they are sufficiently far apart &om each other. Numerical simulations indicate a minimum firelhe spacing for 

vortex development to be on the order of the characteristic horizontal dimension of the vortices. The presence of 

multiple firelines increases the likelihood of vortex interaction and downdraft reinforcement between the firelines. 

Downdraft wind speeds between firelines were observed to increase by nearly 40% over the speeds simulated with 

only one fireline present. Downdraft reinforcement by adjacent horizontal roll vortices in actual wildland fire 

episodes could inhibit the burning of tree crowns and aid in the development of unburned tree-crown streets. 

Horizontal roll vortex development in the presence of light ambient crossflows over multiple firelines spaced 
130 

sufficiently far apart is much more prominent than for individual firelines. Upwind firelines tend to act as "barriers" to the flow for the downwind firelines (see Fig. 1). 

Numerical simulations also indicate the presence of significant low-level horizontal flow directly over xhe 

outermost firelines and directed toward the innermost firelines. This is due to the thermal characteristiks of the 

boundary layer inside and outside of the region bounded by the firelines. This phenomenon is more pronounced 

when the firelines are closer together. In an actual wildland fie with multiple firelines and an ambient flow 

parallel to the firelines, this phenomenon suggests a migration of flames and firebrands toward inner firelines and 

the creation of curved unburned tree-crown streets in response to the downdraft segments of the accompanying 

migrating roll vortices. 

The effect of terrain irregularities on boundary-layer circulations has been well documented. Sloping terrain 

also affects buoyancy-induced circulations associated with firelines. Present numerical simulations indicate that 

symmetric horizontal roll vortices are less likely to develop on the slopes of simple hills under calm crossflow 

conditions than over flat terrain. However, firelines located on the crests of simple hills generate horizontal roll 

vortices that become stronger as the steepness of the hills increases. Vortex activity associated with firelines on 

simple hills is very dependent on fireline location and terrain steepness when ambient crossflow wind speeds 

increase. The intensity of horizontal roll vortices associated with firelines on the crests and leeward slopes of 

simple hills is greatly diminished when ambient crossflow winds increase in speed, especially over steeper hills. 

8.0 m/s 

L 8. 

n 

€ 

Y 

II 

c3 

W 

W 

I 

5001 700 $06 i140 1300 is00 

HOR I ZONTAL 0 I STANCE (m) 

0 m/s 

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Figure 1. Simulated twodimensional wind fields resulting from a surface potential temperature of 1500°K at x = 

800 m, x = lo00 m, and x = 1200 m with (a) no ambient crossflow and @) a light ambient crossflow 

corresponding to an initial friction velocity of 0.1 m s-? 

References 

Church, C. R, J. T. Snow, and J. Dessens. 1980. Intense atmospheric vortices associated with a lo00 MW fire. 

Bull. her. Meteor. SOC, 61:682-694. 

Haines, D. A. 1982. Horizontal roll vortices and crown fires. J. AppL Meteor. 21:751-763. 

Haines, D. A, and M. C. Smith. 1987. Three types of horizontal vortices observed in wildland mass and crown 

fires. J. Climate Appl. Meteor. 2616244637. 

Haines, D. A, and M. C. Smith. 1992 Simulation of the collapse of bent-over vortex pairs observed in wildland 

fires. Forest Sci. 3868-79. 
131 

-Study of Forced Ventihtion Glovebox F'lres 

Michelle J. Peatross and Richard J. Roby 

Mechanical Engineering Department 

Virginia Tech 

Blacksburg, VA 24061 

Craig L Beyler 

Hughes Associates, Inc. 

6770 Oak Hall Lane, Suite 125 

Columbia, MD 21045 

Gloveboxes are widely used to allow processing hazardous materials without the need for direct exposure 

of workers to the materials. Fires within such gloveboxes can result in the loss of containment of the 

hazardous material and result in exposure of workers to dangerous materials. As such there is a need 

to limit combustible materials in gloveboxes and assure that the glovebox is designed to withstand the 

fires which may occur without serious loss of containment. The weak points in most gloveboxes are the 

gloves and the window assemblies. The most serious fire threats in gloveboxes are combustible liquids. 

A test series was carried out in which a glovebox mockup was exposed to a range of combustible liquid 

pool fires within the box. Due to the relatively low ventilation rates, these fires were primarily 

underventilated fires. These underventilated fires are unique in that the fire occurs in a forced ventilation 

compartment fire environment with ventilation provided from the top of the glovebox. This ventilation 

geometry is not expected to give rise to a well defined two layer fire environment [1,2]. The tests were 

designed to provide insights into the failure of glovebox components and to develop an understanding 

of forced ventilation, underventilated compartment fires. 

Experimental Apparatus and Procedures 

A glovebox mockup with overall dimensions of 12 X 4' x 4' was built and instrumented. The box 

consisted of an angle iron frame with steel panels. Four ceiling and four wall window assemblies were 

installed in the glovebox along with four pairs of gloves along the 12' length of the mockup. All window 

gaskets were floating type gaskets constructed of neoprene. The gaskets were partially protected by steel 

covers designed to prevent the window from falling into the glovebox if and when the gasket burned out. 

This protective gasket cover is known as a fireguard. Ceiling windows were 1/4' wired glass and wall 

windows were 1/2' laminated lead glass windows. Gloves were constructed of neoprene. 

Four fuel pans were used in the test series: 3 X 3, 33' diam., 24.5' diam., and 11' diameter. All pans 

were positioned in front of a window/glove pair location. The fuel used was a hydrocarbon combustible 

liquid. Air flows to the glovebox was via a 6' duct in the roof of one end of the glovebox, and exhaust was 

via a 6' duct on the roof at the opposite end of the 12' long box. The HVAC system was operated to 

provide a negative 3/4" of water inside the box while maintaining a flow of 200 cfm through the glovebox. 

The glovebox was instrumented to measure the fuel pan mass, gas and window temperatures, heat fluxes, 

and exhaust gas flow and composition. Gas temperature measurements were made with an aspirated 

thermocouple tree with a TC spacing of 6'. Floor, wall, and ceiling heat fluxes were measured. Exhaust 

gases were analyzed for carbon dioxide, carbon monoxide, oxygen, and unburnt hydrocarbons. 

Open pan burning rates and the glovebox ventilation rates indicated that all fires would be 

underventilated. The heat release rate indicated by the ventilation rate was about 150 kW and the open 
132 

pan burning rates were as high as 1.5-2 MW. Flames observed in the 3' X 3' pan were highly unsteady 

and did not cover the full surface area of the pan. The flame was sufficiently unstable that it often 

extinguished prior to consuming all the fuel. Other pans burned until the fuel was consumed. . + 

The thermal environment created in the tests was most severe for a two hour 3' X 3' pan test. 

Temperatures up to 600 C were observed in this test near the ceiling. The temperature profile over height 

was relatively linear as had previously been observed in compartment fires ventilated from above [la]. 

The gas temperatures near the floor were 300 C rising linearly to 600 C near the ceiling. Such conditions 

were maintained for as long as two hours in one test. Observations of the performance of the glovebox 

system will focus on this worst case exposure. In the first few minutes of the experiment both the wired 

and laminated glass windows cracked. The first to crack was the ceiling window above the fire and the 

first wall window to crack was also adjacent to the fire. However, neither the wired or laminated glass ever 

broke out. Only one window gasket burned out during the test and the window was maintained in place 

by the fireguard. Gloves were damaged by the fire especially those gloves directly exposed to the pan 

fire. When the hand of the glove was burned off, the remainder of the glove strank from the heat. This 

resulted in a reduction in the size of the glove hole. Gloves not inserted into the box, i.e. inthe storage 

position were not damaged sufficiently by the fire to create any openings. 

Containment of the fire gases in the compartment was maintained despite the glove leaks, except during 

puffing of the fire. During a puff, smoke was intermittently lost through the glove holes. The total volume 

of gases emitted was a small fraction of the total flow of fire gases from the glovebox. While fire 

extinguishment was not pursued in the test series, the tenuous nature of the flames indicated that 

extinguishment with portable extinguishers via a glove hole would be quite straightforward for trained 

personnel. 

While these pans would support far greater heat release rates than the ventilation rate would allow, the 

actual fuel volatilization rates and resulting heat release rates were on the order of I00 kW. The extent 

of underventilation of the fire was strongly reduced by the reduction in fuel volatilization caused by limited 

ventilation. The evidence was that the larger pans were modestly underventilated while the smaller pans 

were overventilated. These observations are based on CO and total hydrocarbon measurements in the 

exhaust. 

Despite the fact that the downward forced ventilation caused a distinctly non-two layer fire environment, 

the CO levels observed in the exhaust were similar to CO levels previously observed in very well defined 

two layer environments [5]. 

References: 

1. Beyler, C., Third International Symposium on Fire Safety Science, Hemisphere Publ. Co., pp.291- 

300, 1991. 

2. Backovsky, J., Foote, UL, and Ahrares, N.J., Second International Symposium on Fire Safety 

Science, Hemisphere Publ. Co., pp. 315-324, 1989. 

3. Foate, KL, Pagni, P.J., and Alvares, N.J., First International Symposium on Fire Safety Science,' 

Hemisphere Publ. Co., pp. 139-148, 1986. 

4. Alvares, N., Foote, KL, and Pagni, P., Combustion Science and Technobgy, 39, pp. 55-81,1984. 

5. Beyler, C., First International Symposium on Fire Safety Science, Hemisphere Publ. Co., pp. 431 - 

440, 1986. 
133 

Corridor Flow of Smoke from Postflashover Fire: 

a post-"FIRE SIMULATOR" Module for FPETOOL 

bY 

Harold Nelson and Scot Deal 

NIST 

In a siwcant number of multi-death fires in health care occupancies, the deceased were found 

in locations remote fkom the room of fire origin. Hot smoke from the fire travelled between 3 ane 

30 meters (10-100 feet) before reaching the victims. To better understand the mechanisms which 

caused these far field deaths it is necessary to more accurately predict smoke properties when the 

smoke is near the victim. Therefore, it is also necessary to predict the smoke properties as it 

travels from the room of fire origin and spreads throughout the building. This model focuses on 

predicting the properties of smoke as it travels away from a flashover room fire and proceeds down 

a comdor. 

Funding for this project was provided by our generous sponsors, the General Sewices 

Administration and the administration of the Building and Fire Research Laboratories, NIST 

(whose tithing of congressionally earmarked money we could nay do without). The effort was 

collaboratively produced by the two authors, whose names appear with respect to their 

contributions. 

The "Corridor" simulation (as this smoke flow simulation will now be called) is a first-order 

engineering method at predicting conditions in the smoke from a postflashover fire as it progresses 

down a corridor away from the room of fire origin. Corridor simulates smoke displacement with 

a first order, nonlinear, homogeneous ordinary differential equation. The solution was approached 

using first order Runga-Kutta or Euler's method in pseudo steady state. The frame of reference 

was Eulerian, but because of heat transfer (as will be explained) the smoke temperature cools with 

age, hence temperature is mildly dependent upon time in addition to its explicit dependence upon 

position. Generous assumptions and hence limitations were imposed upon the model for purposes 

of simplification and to make appropriate delivery, however, if this project had been easy--it would 

have already been completed. 

Comdor's first assumption is that the fire is postflashover. The limitation this imposes effects not 

temperature, but smoke flow. The program operates with a constant rate of smoke flow from the 

room of fire origin. The smoke flow rate is most readily obtained by the user from a room fire 

model (such as FIRE SIMULATOR or FAST); however, smoke flow rates are one of the least 

accurately predicted quantities from room fire models'. The temperature of the smoke can be 

accounted for down to to levels below 250°C, but this temperature must be constant with time for 

the duration of the simulation. 

The fire gases issuing into the corridor entrain air if they have any substantial horizontal or vertical 

momentum*. Comdor simulates vertical entrainment, not horizontal. As the height through which 

the issuing gases entrain ambient corridor gases increases, the smoke filling becomes qualitatively 

more and more similar to a zone room model. The user of Comdor is notified at a point where 
134 

this two zone filling behavior should begin to occur. The point is identified in corridor when the 

entrained air to smoke mass ratio exceeds 3.39. Gas concentrations and enthalpies are 

appropriately adjusted for ambket air entrainment. 

Heat is lost from the smoke to the ceiling and walls of the comdor. This is accounted for in an 

implicit, exponential relationship identified by Heseldon from experimental observations? Comdor 

accounts for the corridor surface area which contacts the advancing smoke wave. The impact of 

this heat loss on smoke temperatures is an exponential decay with distance and a modest cooling 

with time. 

The depth of the corridor smoke is predicted from the volume and horizontally projected area of 

the wave. The volume is obtained by dividing the cumulative smoke mass flow into the comdor 

by the average smoke temperature. The average smoke temperature is detennined from an 

average integrated over the distance of the wave. 

Results from Comdor are included in a soon to be published NISTIR by Nelson and Deal. This 

work brought to light several items of interest. First, if experiments were performed wherein the 

temperature of the flashover smoke from the burning room were increased with each successive 

experiment, we would observe, quite intuitively, an increase in the velocity of the advancing smoke. 

The depth of the smoke would decrease though. Apparently, the effect of increased travel speed 

overcomes the effect of density and increased voluminity. The second item arose from applying 

Comdor rather than from intrinsically using Comdor. The refuge room proximity to the room of 

flashover makes little difference on occupant survival. This curious fact arises from the effect of 

density. Refuge rooms close to the fire are exposed to hot comdor gases, however, the mass of 

hot comdor smoke leaking into next-door refuge rooms is not substantially greater than the mass 

of cool smoke leaking into refuge rooms located at the end of the hall. Smoke at the end of the 

hallway is much cooler, but also much denser. 

Additional features about Comdor 

1. 

2. 

3. 

4. 

5. 

There is no consideration of depositional mass loss from the smoke wave. 

Smoke flow can be split in two, to simulate a room located in the middle of a corridor. 

The heat loss factor can be user modified to simulate corridors of different frictional 

characteristics and to simulate different thermal properties of comdor lining materials. 

Corridor asks for smoke level in the opening, but most fire models give only the smoke 

interface level in the room. 

There is no consensus on door jet entrainment rates. 

1. Nelson, H., Deal, S., "Comparing Comparment Fires with Compartment Fire Data," Fire 

2. Personal Communication with Baum, H., NIST, Gaithersburg, MD, USA May 1992. 

Safety Science. 3rd International SvmDosium, pp. 719-728. 
135 

Flame Retardancy of Cotton - Synthetic Blend Fabrics 

Robert J. Harper Jr., George F. Ruppenicker and A. P. S. Sawhney 

Southern Regional Research Center, USDA 

New Orleans, La. 

ABSTRACT 

It has long been recognized that the treatment of cotton-polyester or cotton-nylon blends 

for flame retardancy is more difficult than the treatment of 100% cotton fabrics. The reason is 

that while the 100% synthetic can melt, drip, or shrink away from a flame, in a blend the 

composite forms a grid that prevents the synthetic from dripping away fiom the flame. This 

presentation reviews approaches for making cotton - blend fabrics flame retardant (FR), 

describes an unexploited approach for making these fabrics FR (1,2) and reports on the 

application of flame retardant finishes to a variety of blend fabrics. The usual approaches for 

treating blend fabrics utilize an antimony-halogen system, in which a halogen component such 

as decabromodiphenyl oxide is retained on the fabric with a polymer binder or in which a 

halogen containing polymer is employed as the halogen component (3,4). The unexploited 

approach is likewise based upon an antimony - halogen system. In this case, the halogen 

component is added to the fabric as of a reactive additive, which is fixed on the fabric via a resin 

system. The reactive halogen employed is dibromoneopentyl glycol. This approach leads to 

fabrics with durable press performance as well as FR performance. If the synthetic is a minor 

component of the blend, phosphorous = nitrogen (PN) systems can be used to make the blends 

FR. Blends in which the synthetic component is inherently flame resistant such as a cottonfiberglass blend can be readily made FR with finishes normally used on all-cotton fabrics. 

The blend fabrics studied will include intimate blends as well as fabrics in which the 

synthetic is present as a filament core with a cotton wrap on the outside (5,6). Fabrics made 

fiom a combination of cotton and filament core yarns offer advantages not only in comfort, but 

also in ease of finishing. A factor with filament core fabrics is that the extra strength conferred 

by the filament component permits the use of a smaller percentage of synthetic in the fabric, thus 

reducing the amount of f~sh add-on required for FR. The influence of the change in fiber 

content, location of synthetic in yam, and finish strength on FR performance will be noted. 

Finishing of these special blend fabrics was primarily done using the precondensate - 

NH3 finish (7,8). The precondensate is prepared from tetrakis (hydroxymethyl) phosphonium 

chloride and urea. The fabric is padded with the precondensate, dried, and given a cure with 

ammonia gas. FR perfomance is measured by the vertical flame test as well as by Oxygen 

Index. In addition to the usual cotton - polyester blends, the finishing of other blends of cotton 

with fiberglass, FR nylon, and aramids will be included (9-1 1). The finishing a fabric containing 

an intrinsic FR synthetic component verses a non-FR synthetic component in the blend will be 

discussed. Fabrics used in this study were designed for protective clothing as well as for usage in 

outdoor fabrics (tents). 
136 

REFERENCES 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

R J. Harper Jr., U.S. Patent No. 4,536,422 (Aug. 20, 1985). 

R. J. Harper Jr., U.S. PatentNo. 4,618,512 (Oct. 21, 1986). 

V. Mischutin, U. S. Patent 3,877,974 (April 15,1975). 

D. J. Donddson, F. L. Nomand, G. L. Drake, and W. A. Reeves, American Dyestuff 

Reporter 64, No. 9, p. 30 (1975). 

R. J. Harper Jr., G. F. Ruppenicker Jr. and D. Donaldson, Textile Research J. 56, pp. 

80-86 (1986). 

R. J. Harper Jr. and G. F. Ruppenicker Jr., Textile Research J. 57, pp. 147-154 

(1987). 

H. Coates, U. S. Patent 2,983,623 (May 9, 1961) (to Albright and Wilson Ltd). 

H. Coates, British Patent 906,3 14 (Sept. 19, 1961) (to Albright and Wilson Ltd). 

G. F. Ruppenicker, R. J. Harper and C. L. Shepard, American Textile International 

16, pp. 4-10, May 1987. 

G. F. Ruppenicker, R. J. Harper, A. P. S. Sawhney and K. Q. Robert,Textile Technology 

89, pp 26-39. 

G. F. Ruppenicker, R. J. Harper, A. P. S. Sawhney and K. Q. Robert,Fire Safety '91 

Proceedings, pp 3 18-328. 
137 

DIRECT MEASUREMENT OF HEAT RELEASE RATES. 

C. VOVELLE, J.L. DELFAU, F. MOUSSAN 

Laboratoire de Combustion et Systemes R6actifs - CNRS 

1C Avenue de la Recherche Scientifique, 45071 ORLEANS CEDEX 2 France. 

C. PHAM VAN CANG 

EDF Direction des Etudes et Recherches, 1 Avenue du G6n6ral de Gaulle, 921 41 CLAMART CEDEX. 

INTRODUCTION 

It is now widely accepted that heat release rate is a crucial parameter to characterize the flammable hazards of 

material (1, 2), and various calorimeters have been developped to measure this quantity. Laboratory or 

commercial apparatuses fall into two groups : (a) direct measurement (b) calculation from the amount of oxygen 

consumed. It is frequently reported that the first group methods suffer from heat losses and thermal inertia so 

that the oxygen consumption method is considered as more promising. However the use of a constant value for 

the heat released per unit mass of oxygen consumed is questionable for composite materials, especially for 

materials with fire suppressant included. 

In this abstract we describe a new calorimeter that allows heat release measurements with both techniques. 

Emphasis has been put on the measurement of both radiative and convective heat components, so that heat 

losses are negligeable and a direct comparison between both measurement techniques can be performed. 

A Preliminary study has been carried out with a methane diffusion flame to check the thermal inertia of the 

apparatus and to obtain heat release rate data in well defined conditions. To demonstrate the ability of this 

device to measure heat release rates of solid materials, experiments have been performed with PMMA and PVC 

samples as well. 

EXPERIMENTAL 

The calorimeter is derived from the Tewarson's flammabilrty apparatus (3) with, as a major change, a water 

cooled stainless steel chamber surrounding the sample. A first component of the heat release rate (QT1) is 

derived from the water flowrate and the temperature difference between the ends of a water coil tube solded 

around the the stainless steel chamber. Combustion gases are mixed with air and collected in an exhaust 

chimney and a second heat component (QT2) is calculated from air flowrate and temperature. 

Gaseous samples are withdrawn in the exhaust duct and introduced into continuous analysers that measure 02, 

CO, C02 and total hydrocarbon concentrations. A second value of the heat liberated during combustion (Q02) is 

obtained from the variation with time of the oxygen concentration in the exhaust gases. The signal delivered by 

the O2 analyser has to be corrected to take account of water condensation in a cooled trap. 

The weight loss of the sample is measured by an electronic balance and the effective heat of combustion is 

calculated by : 

HC = (QT1 + QT&mb Of HC = QOgmb. (mb : mass burning rate , kg.s-1). 

Air or air enriched by oxygen or nitrogen flows around the sample at a controlled overall flowrate. The surface of 

the sample can be heated by a radiative flux emitted by four quartz lamps. Presently, the maximum heat flux is 

close to 3.5 W.cm2 with changes with the position at the surface lower than 10%. Improvement in the efficiency 

of the lamps is under study to increase the maximum incident heat flux. 

RESULTS 

Methane-air flame 

The objective of the experiments performed with a cylindrical gas burner was both to calibrate the calorimeter 

and to control the inertia of the thermal measurements. The second point is important, especially for composite 

materials that can lead to an evolution of the effective heat of combustion due to staged thermal degradation of 

the solid. 
138 

30 - 

20 

CHI-AIR 

0 

1 I I I I 1 I I 

The very first experiments were conducted with 

a constant methane volumetric flowrate. Both 

the thermal and the oxygen consumption 

method gave effective heat of combustion in 

close agreement with the litterature value (50 

kJ.g-1). 

In a second step, the effect of step by step 

variations in the methane flow rate has been 

assessed. Temperature measurements and 

oxygen concentration evolution for a 4 steps 

experiment with methane flowrate adjusted to : 

12.6 cm3.~-~ (from 500 to 1500 s), 26.2 cm3.s-l 

(1500 to 2500 s), 51 .O c&s-1 (2500 to 3500 s), 

26.2 cd.s-1 (3500 to 4500 s), have been 

plotted on figure 1. Corrections of the signal with 

the Evans and Breden's technique (4) lead to 

time response close to 60 s for both 

measurements. Hence thermal inertia is 

considerably smaller than those reported for IS0 

(666 s) and ASTM (200 s) calorimeters (5). 

Figure 2 shows that a constant value is obtained 

for the effective heat of combustion in these 

experiments. 

Combustion of PMMA 

The effective heat of combustion of PMMA has 

been studied in air, without additional heat flux. 

Evolution of the mass burning rate shows an 

increase up to a maximum, due to an increase 

in the area of the combustion zone, followed by 

a continuous decrease corresponding to the 

consumption of the sample. 

40 

- 35 

0 

C 30 

25 

20 

15 

v 

Time (s) 

Evolution Wim time of Temperawes : gas (W), water in (o),water out (0) 

and oxygen concentration (A). 

Figun 1 

80 

-1 

30 

In spite of this non stationary character, a constant value of the effective heat of combustion is obtained from 

measurements performed during 90% of the whole experiment. Moreover this value (24 kJ.g-1) is in close 

agreement with litterature values for this material : 23 - 27 kJ.gl (67). 

Combustion of PVC 

Experiments on PVC have been conducted with oxygen enriched air (37% 02) and an external radiant heat flux 

(2.8 W.cm-9. The mass burning rate and the oxygen consumption curves exhibit a two stages evolution. Both 

measurement techniques lead to a slight increase in the effective heat of combustion (15 to 18 kJ.gl). 

REFERENCES 

1. Tewatson, A, J. Fire and Flammability, Vol. 8, 116-130, (1977). 

2. Akrares, N.J., Ford H. W. and Beason, D.G., J. Fire and Flammability, Vol. 9,337-352, (1 978). 

3.Tewarson, A., "A Laboratory-Scale Test Method for the Measurement of Flammability Parameters". Final 

technical Report, FMRC Serial No 22524, (1977). 

4. Evans, D.D., and Breden, L.H., Fire Technology, 14,85-96, (1978). 

5. Tsuchiya, Y., Fire safety Journal, 5,49-57, (1982). 

6. Walton, W.D. and Twilley, W.H., Heat Release and mass Loss Measurements for Selected Materials ", NBSlR 

84-2960, NBS, Gaithersburg, MD 20899, (1984). 

7. Babrauskas, V., "Development of the Cone Calorimeter - A Bench Scale Heat release rate Apparatus Based 

on Oxygen Consumption", NBSIR 82-2611, NBS, Washington DC 20234, (1982). 
139 

HOT SURFACE IGNITIONS: IONIC EFFECTS IN IGNITION INITIATION 

William W. Bannister, Department of Chemistry 

University of Massachusetts, Lowell, MA 01854 

[508] 934-3682 

Douglas F. Nelson, Air Force Civil Engineering Support 

Agency [RACF] , Tyndall AFB, FL 32403-6001 

ABSTRACT 

Events preceding spontaneous ignition of fuels on hot 

surfaces may be ionic rather than free radical, with 

polarizing hot surface effects and anionic stabilizing 

influences within the fuel molecules. Adsorbed oxygen and 

fuel molecules may be thermally polarized at the surface, 

with the negative end of the oxygen dipole abstracting a 

proton from the fuel molecule to form a carbanion/ 

hydroperoxy cation pair. Simple electron transfer 

mechanisms between carbanionic and hydroperoxy cationic 

moieties would then form free radical species, these then 

participating in conventional cool and hot flame free 

radical mechanistic pathways . Structure/property 

correlations for ignition temperatures for various 

hydrocarbon fuel molecules are consistent with carbanionic 

mechanisms, and inconsistent with effects typically 

associated with stabilizations of free radicals. Inclusion 

of polar compounds (e.~., water, hydrogen bromide and 

bromofluorocarbons) into fuel/air mixtures facilitates 

spontaneous ignition. Ignition temperature trends for 
140 

metallic surfaces are consistent with electron work 

functions (these being proportional to ease of electron 

migration from the metal surface): metals having lower work 

function values have lower ignition temperatures than those 

with higher work function values. Highly polar oxyanionic 

surfaces such as quartz greatly facilitate hot surface 

ignitions. These facts are all consistent with ionic rather 

than free radical effects in pre-ignition stages. 

An inverse relationship exists between molecular weight 

and ignition temperatures: up to a point, volatile higher 

molecular weight fuels have lower ignition temperatures and 

are more easily ignited by hot surfaces. Branched and 

cyclic alkanes, arenes and olefins have higher ignition 

temperature than analogous straight chain alkanes. 

Important structural parameters in governing ignition 

temperatures include: effects of molecular weight on the 

velocity of the fuel molecule near the hot surface; effects 

of rigidity of the fuel molecule on its ability to recoil 

from the hot surface; and effects of specific heat of the 

molecule with regard to ability for dissipation of heat 

energy within the molecule. 
141 

Number of 

cables 

1 cable 

2 cables 

4 cables 

8 cables 

12 cables 

EXPERIMENTAL STUDY OF SELFIIGNITION OF ELECTRICAL CABLES 

EXPOSEDTOANEXTERNALRADIANTF'LUX 

A Simplified theory for generalizing results 

Combustible Critical heat 

mass flux 

ing in wcm-2 

77 4,95 

155 4,75 

310 496 

642 396 

930 3 

Mane-Claude Lopez, Jaques Bergelin 

Institut de Protection et de Surete Nucleaire 

Departement de Protection de 1'Environnement et des Installations 

Service d'Etudes et de Recherche en Aerocontamination et en Confinement 

We present an experimental procedure to get some quantitative data on the pyrolysing and burning 

characteristics of combustible materials which may be found in nuclear facilities. In this study, the materials 

considered are only polymeric cable insulation and jacket which are flammable solids. In order to accomplish 

this goal, the experimental installation allows the testing of one to twelve cables. The cables are 50 cm long. 

They are fixed vertically on a metallic tray and exposed to irradiance levels ranging from 2 to 6 

The test is performed in a realistic fire situation i.e. unconfined normal air environment, without piloted 

ignition. Tbe results presented here concern one type of cable i.e. a 7 copper conductor cores, PVC jacket 

and PRC insulation. A schematic of the experimental set up is shown figure 1. 

The apparatus consists basically of a gas fired radiant panel (30x30 cm) which imposes a known flux 

distribution over the sample. The sample holder frame, where the cables are vertically fastened with steel tie 

wire, is put on a load cell for mass loss data collection. An insulating sliding shutter is located between the 

radiant panel and the specimen to precisely control exposure times. 

The pyrolysis and cornbustion products are collected in a hood for analysis. Cable temperatures and exhaust 

gas temperatures are measured by 'I)rpe K chromel-alumel thermocouples. Eor calculating the rate of heat 

release, the temperature, oxygen concentration and flow rate of the exhaust gases are to be measured. Oxygen 

consumption is performed by a continuous sampling paramagnetic oxygen analyzer. Exhaust gas flow rate is 

measured in the exhaust duct by the helium gas tracer technique. The measurements of the products of 

combustion such as carbon monoxide, carbon dioxide, unburnt hydrocarbons are carried out by a continuous 

sampling idhired analyzer. Data reported typically include ignition delay time, mass release rate at various 

flux levels, heat release rate and roducts of combustion. The experimental results show a linear relationship 

between the mass release rate (&at *1ngos-1.cm-2)for a stationary state and net heat flux delivered to the 

cable surface Qr in W.mi2for a given number of cables. The inverse of the slope of the straight gives us the 

heat of gasification Lg (J.g-'). 

1 m"stat=--(Qr-Qc), reibionshipproposedby Tewamn and' Pion. 

Lg 

In this relationship, Qc is the heat loss from the surface (W.cm-*). The Observation of this phenomena led 

us to the definition of a Critical exposure heat flux Qrc which can be Wed to the number of cables. 
142 

In our work, we try to confirm the approximate expression @warson and Kahn) which deduced the ignition 

delay time from the sample surfake temperature aid the external radiant flux This type of relationships 

between the exposure conditions and material behavior should prove useful in attempts to predict the 

development of fires using deterministic computer codes. 

References: 

kC. Rmandez-Pello, H.K Hasegawa, A.E. Lipslm-Quinn, N.J. Alvares, "On the use of Thermal Degradation 

Data to Predict Cable Ignition Performance", Lawrence Livermore National Laboratory, Livermore, CA, USA, 

1987. 

H.K. Hasegawa, K Staggs, AC. Rmandez-Pello, "A procedure for Ranking Fire Performance of Electrical 

Cables", Lawrence Livermore National Laboratory; UCRL, 93936,1986. 

C. Vovelle, R. Akrich, J.L Delfau, H. Mellottee, "Etude Exp6rimentale de la Dbgradation Themique de 

MatMaux solides sous l'action d'un flux radiatif". CRCCHT - CNRS, 1983. 

D. Drysdale, "An Introduction to Fire Dynamics", John Wdey and Sons, Department of Fire Safety 

Engineering, Massachusetts, 1985. 

k Rwarson, M.M. Khan, "Electrical Cables - Evaluation of Fire Propagation Behaviour and Development 

of Small-scale Rst Protocol", Factory Mutual Research Corporation, Boston, 1989. 

I? Beme, P Cassette, "Le tracage gazeux, technique d'analyse des systemes complexes"; Rents prop& en 

gWe des proc&Us NANCY 87. Proceedings: ler Congr6s national de ghie des pr-es, NANCY 21.23 

Septembre 1987. 

A. lkwarson and RP. Pion, "Flammability of plastics - 1 Burning intensity", journal 'Combustion and Flame', 

26,85-103,1976. 

FIG 1 : EXPERIMENTAL SET-UP 

-I*- - I^-_____ " 
143 

ARGOS 

A computer program for fire risk evaluation 

Niels Baden 

Danish Institute of Fire Technology, 

Datavej 48, DK-3460 Birkeroed, Denmark 

A new and user friendly software package ARGOS has been developed for fire prediction. The 

computer program is fully menu driven with full on-line, context sensitive help facility and simulation speed second to none due to high efficiency numerical methods. The central module in 

ARGOS is a zone model for simulation of fire development and smoke spread in buildings including: 

0 

0 

0 FueVventilation controlled fires. 

0 Smoke development and spread. 

0 

0 

0 

0 

Simultaneous calculation of up to five compartments. 

Unique physical models for fire growth and burn out in combustible objects. 

Temperature development in compartments and smoke layers. 

Temperature developmentheat penetration in building components. 

Automatic fire alarm, sprinkling and fire ventilation. 

Estimation of damage to buildings, stock and machinexy caused by the fire in question. 

Database with built-in or user specified background data for simulation of fire development, including: 

0 

-0 

Building components such as doors, windows, ceilings etc. 

Fire start, e.g. a three meter high stack of pallets. 

~~~ 

Coordri9ht CC) 1990, 1991 -ish Institute of Fire fecfnology 11 

I 

Database: Wmdow for specification of parameters for fire start model. 
144 

ARGOS has becn tested against three well documented full scale test series: 

0 

0 

0 

The two rooms tests -rics reported by Coopcr et al. (1982). These tests are often referred 

to for model verification, though the rooms and fires studied are relatively small.* 

The two rooms test series including fire ventilation in the roof reported by Hiigglund 

(1992). In these tests the moms and fires are relatively large. 

The three rooms test series reported by Meland & Unvik (1989)- These tests also include 

various fire detectors. 

1- 441.0 mriet <C) 1990, 1091 Wish Institute of Fire Tlbdrrolomd 

. I . . . e . I . I . . * Tim Ininl I ????9?? 

Fl+<t) F23nokc in rwns F3-S(#kr in lavers FI-Floor to lwrrc 

FS-clyar tam. F6-t radiation Fl04rint W-)kre Esc-Pnuious 

Cd&te: -n of meosuted &ta pin@fiomjW scale @e test (circles and squares) 

and simuktk~n rdts (solid lines). 

The comparisons with full Scale fire tests shows that the basic principles and implementation of 

ARGOS leads to satisfactory simulation of a wide variety of fire scenarios. 

References 

Baden, N- & S. Scherfig, Comparison of ARWS Simulations with Full Scale Mdti-Room Fire 

Tests, Danish Institute of Fire Ttchnology, Birkeroed (1992). 

Baden, N., ARGOS neory Manruzl, Danish Institute of Fire Technology, Birkeroed (1992). 

Cooper, LY., M. Harkleroad, J. Quintiere & W. Rinkinen, An werimentul Study of Uppr Hot 

Layer Stratification in Full-scale Multiroom Fire Scenarios, Jod of Heat Transfer, 104,741- 

750 (1982). 

Hiigglund, B., Comparing Fire Mdels with Ikperimental Data, FOA report C 20864-2.4, Swedish 

National Defence Research Establishment, Sundbyberg (1992). 

Meland, 8 & L.E. Unvik, Detection of Smoke. Reprtfiom Full Scale Fire Tests in Vaterskaun 

School Jan. 1989 (in Norwegian), SINTEF report STF25 A89010, Trondheim (1989). 
145 

ANALYSIS OF THE NATIONAL FIRE PROTECTION ASSOCIATION 

FIRE RISK ASSESSMENT FRAMEWORK: EXAMPLE CALCULATION .. 

F. Merri11 Gal loway' and Marcel0 M. Hirschleg 

BFGoodrich Technical Center 

P.O. Box 122 

Avon Lake, OH, 44012 

* Safety Engineering Laboratories 

38 Oak Road 

Rocky River, OH, 44116 

The National Fire Protection Association Research Foundation 

completed a project to develop a Fire Risk Assessment Methodology 

(FRAM). In order to check the validity of the software developed, the 

technical team used it to determine fire risk in four cases: upholstered 

furniture in residential environments, carpets in offices, concealed 

combustibles in hotels and motels and wall linings in restaurants. This 

project was a gr.eat technical success, since FRAM was capable of 

adequately predicting fire risk in, at least, the first three 

applications attempted. 

One of the main objectives of the development of FRAM, however, was 

to allow users to compare the fire risk associated with new products 

with that associated with the traditional products in use today. 

This work involves just such a comparison, for a sub-case of the 

first example: flaming upholstered furniture in a residential ranch 

house. A guide to the FRAM methodology software, accompanied by this 

example case, was supplied to the authors by NIST. The objective of 

supplying this was to carry out "beta testing", in order to confirm that 

the same results could be obtained by different investigators. The 

objective was achieved since the results from NIST were confirmed, 

except for a minor glitch: in the results of the beta test the risk 

appeared greater with smoke detectors than in their absence. This was 

clearly a case of one misaligned command, and is of no real consequence. 

The present work involved further analysis however. A set of eight 

additional cases were run, in which the inputs were changed. The 

changes involved the heat of combustion of the fuel (the upholstered 

chair), the time intervals specified for the fire, the mass loss rate in 

each time interval and the area of the fire. In 7 of the cases the heat 

of combustion of the fuel was decreased from 14 MJ/kg (base case) to 9 

MJ/kg and in the other case (# 5) it was raised to 35 MJ/kg. Table 1 

shows the fire risk results, which show almost no difference between all 

the cases investigated, which cover a period of 760 s. 

In view of the disappointing results, a few additional tests were 

run with the same data. Firstly, it was found that, although the 

overall fire risk result did not change much in the various cases, the 

individual causes of death changed considerably. For example in the 

base case the major cause of death was # 5 (FED Purser, involving heat 

and toxicity), while in case 5 (with high heat of combustion) the major 

cause of death was # 2 (temperature). The major cause of death in all 

the cases with lower heat of combustion was also # 5. 
146 

. 

Figure I. uppor ~ayor ~emporature 

5 

c 

L 

0 0 no0 4.0 0.4 

I 

Figure 1 

shows a 

comparison of 

upper layer 

temperatures in 

three cases (1, 

4, 5) which are 

iden t i ca 1 in 

every respect 

except for the. 

heat of 

combus tion of 

the fuel. It is 

clear that the 

temperatures are 

very different, 

both in the 

final value and 

in the time 

required to 

reach that 

value. In fact, 

in case 4 

f 1 as hover 

temperatures are 

not even reached in the time period under consideration. This is not, 

at least on its face, compatible with virtually no difference in overall 

risk. 

The results of this investigation indicate that the FRAM requires 

a very careful analysis before attempting to compare the fire risk of a 

new product with those of an existing product. The differences in fire 

hazard (for example fromtoxicity or temperature) between the two cases 

are very clearly noticeable, but they do not always translate easily 

into fire risk differences. 
147 

AN EXPERIMENTAL INVESTIGATION OF THE PULSATION FREQUENCY OF FLAMES 

A, Hamins, LC. Yang and T, Kashiwagi 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

A large number of experimental, theoretical and scaling studies have 

investigated the coherent vortical structures which are shed by 

flames [ 11, This phenomenon has been documented for a wide range of 

I 

burner diameters , heat 

vortical structures and 

of air entrainment into 

flow field, it may also 

and flame radiance, 

release rates, Reynolds numbers and fuels, The 

their shedding frequency can influence the rate 

a fire, As the pulsation frequency affects the 

affect the flame length, combustion efficiency, 

In the fire literature, the pulsation frequency (f) has been typically 

correlated with the burner diameter (D) which yields a power law-fit to 

the data such that f a D-*.’. Implicit in this correlation is the idea 

that the pulsation frequency is not a function of fuel exit velocity at 

the burner, fire heat release rate or other parameters. 

Measurements of the pulsation frequency in non-premixed flames were 

conducted for gaseous and liquid fuels, Measurements were performed over 

a wide range of Froude number to lo3), Reynolds number (10 to 10’) 

and burner diameters (0,0074 m to 0.30 m), A video camera (30 frames/s) 

was used to record the flame image for several minutes, The character- istic pulsation frequency was determined by counting the number of 

frames necessary for the vortex growth process to cycle, The standard 

deviation of the frequency measurement was approximately 0.2 Hz, 

The fuel velocity at the burner exit was found to have a weak influence 

on the pulsation frequency for some diameters whereas total heat release 

did not, Figure 1 shows that a plot of the Strouhal number as a function 

of the inverse Froude number correlates the measurements made here as 

well as measurements reported in the literature for pulsations in flames 

burning gaseous, liquid and solid fuels over 14 orders of magnitude in 

Froude number, ranging from buoyancy dominated to momentum dominated 

flames . defined 

where V 

(Fr) is 

where n 

Here the Strouhal number (S) is a non-dimensional frequency 

as: 

S = f*D/V 

is the average velocity at the burner exit. The Froude number 

defined as the ratio of inertial to buoyant forces: 

Fr = V2/(D-n-g) 

is the acceleration normalized by g (9.8 m/s2), the earth normal 

gravitational acceleration, Previous measurements [2] of the effect of 

enhanced gravitational level on the pulsation frequency were also 

interpreted in terms of the Strouhal-Froude number relationship as shown 

in Fig, 1, 
148 

A shadowgraph technique was used to measure the pulsation frequency of 

an isothermal buoyant gas stream over a range of Froude number (l.0-3 to 

1). Figure 1 also shows that the Strouhal number - inverse Froude number 

alot c-- - correlates the measurements, but yields a different power law 

exponent than the reacting flow case, 

Stability limits in flames were also investigated. The critical fuel . velocity (Vc) needed to initiate pulsations as a function of burner 

diameter for methane and propane flames was found to be: Vc a D-1*5. 

References 

1. Pagni, POL, ASME Paper Number 89-WA/FE-5, p. 26, 1989. 

2. Cevallos, N.E. : Experimental Studies of Effects of Elevated Gravity 

on Gaseous Hydrocarbon Diffusion Flames, MIS. Thesis, The 

University of Kentucky, Lexington, KY, 1976. 

1 o6 ' ' """I ' ' """I ' ' """I ' "'''''~ ' '"""l ' ""'"' ' ' ""'I ' ' ""'y ' """" ' ' """' ' ' """I ' ' "'"-I ' '"""I ' ' ""nl ' """1 ' ' 7 

X Byram & Nelson 

+ Schonbucher et al. 

2- 

I o4 

1 o2 

1 oo 

1 o-2 

1 o4 

lo-= 

1 

0 Gengembre et ai. 

A Zukoski et al. 

A Sibulkin & Hansen 

0 Cevallos 

EB Hemberg et ai. 

hl Baum & McCaffrey 

13 Chamberlin & Rose 

0 Present Study, Helium 

0 Present study 

Weckman & Sobiesiak 

I Portscht S oc (1 /Fr)Om3* He1 

o-~ I 0-7 1 o-~ I 0-3 lo-' IO' I o3 I o5 i 

1/Fr (= ng DN2) 

o7 

1. The Strouhal number as a function of the inverse Froude number for 

flames burning methane, methane diluted by nitrogen and liquid 

fuels, and previous measurements for fuels burning liquid, solid 

and gaseous fuels. Also shown are results from Ref , [2] for methane 

burning under enhanced gravitational conditions and for measure- ments made in this study for an isothermal buoyant helium flow, 
149 

Barry S. Decristofano, Gerald J. Caldarella, 

Brian Re Kimball, and Joseph F. Roach 

U.S. Army Natick R&E Gentes 

Natidk, MA 01760 

~n a- thenoal response da~ acquisition’system has been 

custom designed ard built by Natick to pravide state-of-the-art 

c3ll&ion and analysis of the actent of burns w by both flames and thermal energy transport clothing syst~lrs. Data 

can be recorded in a laboratory setting or sent for miles on a 

shgle coaxial cable, fiber optic cable or FM frequency. A tatal of 

521 sensors (124 on each of four manikhs and 25 miably located) 

provide a teqerature-versus-time mzd of the teqeratures reached 

in the skin tissue of a hypothetical wearer of the clothirg m. 

us- software tailored to the syskm, the acquires data 

to be displayed in real tirrr! or stored for analysis of burnseverity 

predictions at any oornrenient future timP_. The software in this 

process has been written by Natick specifid.ly for thennal response 

investigations. The data mrded fm the aperiment are us@ to 

generate two- rn- ’ ional represatations of the extent of 

skin burns predicted from skin sirml‘lant recordings. The 

three-dimensional manikin display is capable of showing the 

progression of skin damage as it changes with time, ?he software 

can be linked to models used by clothing and equiprent designers to 

allow projection of these articles onto the image. f-m 

system can be exposed in flanepits, vehicle aew-ts, and 

structures. This advancement of the technology used by the Army for 

mer 20 years allows for more rapid analysis an3 greater statistical 

confidence in the data obtained in thermal-injury studies. More 

qlete utilization of the areal extent of thermal sources is also 

achieved by the use of duple mnikins . ?hissystemisawmplete 

accurately ccgnprehensively the effects XZ thermal 

radiation on wearers of military ard/or civilian clathing. 

package, which gives the tmls tostudy 

This paper reports research sponsored 

by the U.S. Army Natick Research, 

Development and Engineering Center 

and has been assigned TP-31bYin the 

series of papers approved for publication. 
150 

INTERRELATIONSHIP BETWEEN HYDROGEN CYANIDE GAS EXPOSURE CONCENTRATION, 

EXPOSURE TIME AND BLOOD CYANIDE LEVEL IN RATS 

mind K. Chaturvedi, Boyd R. Endecott, Roxane M. Ritter and Donald C. Sanders 

Biochemistry Research Section, Toxicology and Accident Research Laboratory, 

Civil Aero~edical Institute, Federal Aviation Administration, 

Post Office Box 25082 (AAM-613), Oklahoma City, Oklahoma 73125-5066 

Inhalation of toxic combustion gases is a significant cause of death in aircraft 

fires, and hydrogen cyanide (HCN) gas is one of the principal toxicants generated in 

potentially lethal amounts during fires (Gad, 1990; Baud et al, 1991; Mayes, 1991; 

Veronneau et al, 1992). This gas has the ability to produce incapacitation at 

relatively low concentrations (Crane et al, 1989; Hartzell1989; Gad, 1990), and timeto-incapacitation ( ti) is an applicable toxicological index for predicting escape from 

a fire (Crane et al, 1977; Spurgeon et al, 1979; Sanders et al, 1991). In HCN 

poisonings, blood cyanide (CN') levels are frequently measured to explain the severity 

of HCN gas exposure; how blood CN' levels are related to HCN exposure concentrations 

and exposure times is not well defined. Therefore, this study on the HCN gas uptake was 

conducted to establish a possible interrelationship between HCN gas concentration, 

exposure time and blood CN' level; the uptake was measured as increases in blood CN' 

levels as a function of exposure time for 184 and 64 ppm HCN that produce nominal 5- 

and 35-min ti in rats, respectively. These HCN concentrations were selected to further 

establish the applicability of the interrelationship at these ti periods, representing 

both evacuation and in-flight-plus-evacuation periods (Crane, 1984, 1989; EUROCAE, 

1991). 

Male Sprague-Dawley rats (100-125 g) were individually exposed to HCN gas in a 

chamber equipped with a cage rotating at a circumferential velocity of 8.5 cm/sec. The 

exposure times were 1, 2, 3 and 4 min (4 rats/exposure interval) for the 5-min study, 

while they were 2.5, 5, 10, 15 and 25 min for the 35-min study (3 animals/exposure 

interval). At the end of each exposure interval, rats were removed from the chamber and 

killed by cervical dislocation for the blood collection and CK determination. Average 

HCN concentrations for each experiment were obtained by the integration of chamber HCN 

concentration (C; ppm) a5 a function of exposure time (t; min) and dividing the 

resulting Cat product by t. Chamber HCN concentrations and blood CN' levels were 

measured colorimetrically using a modification of the Technicon Industrial Method No. 

312-74W (Technicon, 1974); this method includes the conversion of complexed CN' to HCN 

by the digestive distillation of samples at 155OC and resampling the HCN condensate. 

Data were evaluated at a = 0.05 using the analysis of variance, Tukey's HSD multiple 

comparison test and Student's t-test; values are presented as the mean SD. 

HCN concentrations for the uptake studies were 183 4.4 (n - 16) and 71 i 3.4 

(n = 15) ppm. Within each set of studies, HCN concentrations for the exposure intervals 

were not different from each other (p > 0.05). The HCN gas uptakes at the two 

concentrations as represented by blood CN' levels vs exposure times were linear; there 

was no indication of a plateau effect prior to 5 min for 183 ppm HCN or 35 min for 71 

ppm HCN. Slopes indicated that blood CN' increased at 0.401 and 0.152 pg/mL/min for 183 

and 71 ppm HCN, respectively. There was a direct relationship between the HCN chamber 

concentration and uptake rate, as the decrease in the HCN concentration by a factor of 

2.6 also decreased the blood CN' uptake rate by 2.6. Calculated uptakes in (pg CN' 

/mL)/min/ppm HCN for both exposures were almost identical, Le., 2.19 x loe3 for 183 

ppm HCN and 2.14 x for 71 ppm HCN. Thus, this relationship can be described by 

which can be rearranged to the form 
151 

(CW) = 

where CN' - blood CN' 'n pg/mL; C = 

in min; K (constant) = 2.2 x 

C-t-K 

HCN chamber concentration in ppm; t = exposure time 

This equation may have some utility for predicting 

blood CN', HCN exposure concentration, or exposure time value by knowing the values of 

two of the three parameters (variables). 

In a separate study, where ti was measured as time from the insertion of rat 

until it could no longer walk in the rotating cage, blood CN' levels of 2.3 and 4.2 

pg/ml were observed at incapacitation from exposures to 184 and 64 ppm HCN, 

respectively, which corresponded to values of 2.1 and 4.4 pg/mL calculated from 

Equation (2). When K was derived from parameters obtained in the 184- and 64-ppm HCN 

experiments, a mean value of (2.3 * 0.5) x was obtained (n - 100; t = ti). This 

value is very close to the K value calculated from the uptake study, suggesting that 

Equation (1) holds true for incapacitation, as well. Therefore, blood CN-, HCN 

concentration, or t (or ti) can be predicted from the equation. However, there was no 

specific blood CN' level that could be linked to the onset of incapacitation. 

Baud FJ, Barriot P, Toffis V, Riou B, Vicaut E, Lecarpentier Y, Bourdon R, Astier A, 

Bismuth C (1991). Elevated blood cyanide concentrations in victims of smoke 

inhalation. N. Engl. J. Med., 325, 1761-1766. 

Crane CR, Sanders DC, Endecott BR, Abbott JK, Smith PW (1977). Inhalation toxicology: 

I. Design of a smdl-animal test system. 11. Determination of the relative toxic 

hazards of 75 aircraft cabin materials. Department of Transportation/Federal 

Aviation Administration, Washington, DC. Publication No. FAA-AM-77-9. 

Crane CR (1984). Inflight aircraft fires: Toxicological aspects. Panel presentation 

at the Aerospace Medical Association Scientific Meeting, May 7, 1984, San Diego, CA. 

Crane CR, Sanders DC, Endecott BR (1989). Inhalation toxicology: IX. Times-toincapacitation for rats exposed to carbon monoxide alone, to hydrogen cyanide alone, 

and to mixtures of carbon monoxide and hydrogen cyanide. Department of 

Transportation/Federal Aviation Administration, Washington, DC. Publication No. 

EUROCAE (1991). Minimum operational performance specification for passenger protective 

breathing equipment. ENROCAE Document No. ED-65. European Organisation for Civil 

Aviation Equipment, Paris, France. 

Gad SC (1990). The toxicity of smoke and combustion gases. In: Combustion Toxicology, 

SC Gad and RC Anderson, eds., pp 63-80. CRC Press, Boca Raton, FL. 

Hartzell GE (1989). Understanding of hazards to humans. In: Advances in Combustion 

Toxicology, Vol. 1, GE Hartzell, ed., pp 19-37. Technomic Publishing Co., Lancaster, 

PA. 

Mayes RW (1991). The toxicological examination of the victims of British Air Tours 

Boeing 737 accident at Manchester in 1985. J. Forensic Sci., 36, 179-184. 

Sanders DC, Endecott BR, Chaturvedi AK (1991). Inhalation toxicology: XII. Comparison 

of toxicity rankings of six polymers by lethality and by incapacitation in rats. 

Department of Transportation/Federal Aviation Administration, Washington, DC. 

Publication No. DOT/FAA/AM-91/17. 

Spurgeon JC, Filipczak RA, Feher RE, Sternik SJ (1979). A procedure for electronically 

monitoring animal response parameters using the rotating wheel. J. Combustion 

Toxicol., 6, 198-207. 

Technicon (1974). Cyanide in Water and Wastewater (Industrial Method No. 312-74W; 

March 18, 1974). Technicon Instruments Corporation, Tarrytown, NY. 

Veronneau S, Ribe JK, Sathyavagiswaran L, Lewis I, Muto J (1992). Lessons learned from 

the 1991 USAir/SkyWest collision at LAX, presented at the 44th Annual Meeting of the 

American Academy of Forensic Sciences, New Orleans, LA, February 17-22, 1992. 

DOT/FAA/AM-89/4. 
152 

Performance of the Reciprocal Nephelometer 

G.W. Mulholland N.P. Bryner 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

The optical properties of combustion generated aerosols, which we shall refer to as smoke, 

are of concern in regard to the degradation of visibility in building fires as well as in pristine areas, 

to the global climatic impact of a major nuclear exchange as well as the localized climate impact of 

forest fires and the oil well fires such as those recently extinguished in Kuwait. There is a large 

uncertainty in the optical properties of smokes including the scattering and absorption coefficients 

per unit concentration of smoke and the single scattering albedo defined as the ratio of the total 

scattering coefficient to the extinction coefficient. A comparison stud? involving simultaneous 

measurements of the optical properties of smoke generated from the combustion of propane resulted 

in values ranging from 3.8 to 11.4 m2/g for the absorption coefficient and 0.09 to 0.29 for the single 

scattering albedo. 

Gerberlq developed an instrument for simultaneously measuring the light extinction 

coefficient om, and the total scattering coefficient, as, of ambient atmospheric aerosols with a multipass optical cell. From these measurements, the single scattering albedo is obtained as the ratio, 

os/oe, and the light absorption coefficients is obtained as the difference, om - os. The total 

scattering measurement in Gerber's instrument utilizes a diffuser before the detector and is the 

inverse of traditional nephelometg, which uses a diffuser to provide a cosine distribution of the light 

source. We use the term transmission cell-reciprocal nephelometer (TCRN) to describe this 

instrument. Patterson et a1.4 developed a single pass TCRN and used it to characterize the optical 

properties of smoke generated by the combustion of lumber, various plastics, petroleum products, and 

tire rubber. 

This study assesses the accuracy of the TCRN for the total scattering measurement through 

a combination of modeling and measurement. The model calculations consist of computing the total 

flux of light scattered from particles in the laser beam to the cosine sensor/detector in the TCRNI 

The inference of the total scattering coefficient from the detector output is based on a number of 

assumptions: The area of the detector is infinitesimal, the diffUser has a perfect cosine response, and 

the acceptance angle extends from 0" - 180". In this paper we compute the effect of each of these 

assumptions on the accuracy of the inferred result. These effects are computed for monodisperse 

polystyrene spheres over the size range 0.02 - 8 pm based on Me theory and for smoke agglomerates 

ranging from 10 primary units to lo7 primary units based on the Fisher-Burford5 form for the 

scattering function. The accuracy of the model calculations is determined by comparison with exact 

solutions for the case of a detector with an infinitesimal area and for a finite area detector with a 

diffuse scattering function. 

The predicted results are compared with measured results for six different sizes of monodisperse polystyrene sphere aerosols with particle diameters in the range 0.1 to 2.35 pm. The measurements were carried out as a function of the distance between the laser beam and detector for a 1.3 

cm and a 2.7 cm diameter cosine sensor. Based on these measurements, our TCRN design with a 

1.3 cm cosine sensor positioned 2.4 cm from the detector (8-=2.4") has an accuracy for os of about 
153 

5% for spherical particles with diameters up to 1.1 (rm. We estimate similar accuracy for smoke 

agglomerates with up to 3x103 primary spheres. A table of design parameters for making awurate 

total scattering measurements are obtained for both spheres and agglomerates. 

References 

1. H. E. Gerber, "Simultaneous Measurements of Aerosol Scattering and Extinction Coefficients in 

a Multi-Pass Cell," in Light Absorption bv Aerosol Particles, ed. by H. E. Gerber and E. E. Hindman, 

Spectrum Press, Hampton, VA, 231-241 (1982). 

2. H. E. Gerber, "Portable Cell for Simultaneously Measuring the Coefficients of Light Scattering 

and Extinction for Ambient Aerosols," Appl. Opt. 18, 109-1014 (1979). 

3. R. J. Charlson, H. Horvath, and R. E Pueschel, "The Direct Measurement of Atmospheric Light 

Scattering Coefficient for Studies of Visibility and Pollution," Atmos. Environ. 1, 469-478 (1967). 

4. E. M. Patterson, R. M. Duckworth, C. M. Wyman, E. A Powell, and J. W. Gooch, "Measurement 

of the Optical Properties of the Smoke Emission from Plastics, Hydrocarbons, and Other Urban Fuels 

for Nuclear Winter Studies," Atmos. Environ. 25A, 2539-2552 (1991) 

5. M. E. Fisher and R. J. Burford, "Theory of Critical Point Scattering and Correlation. I. The Ising 

Model." J. Phys. Rev., 156, 583 (1967). 
154 

CORRELATIONS FOR TEMPERATLTRE AND VELOCITY IS ROOM FIRES FOR ESTIMATING 

SPRINKLER ACTIVATION TIMES 

PRAVIXRAY D. GANDHI, SENIOR STAFF EEGJNEER 

UNDERWRITERS LABORATORIES INC. 

ABSTRACT 

There have been significant tlevelopiiienta in the understanding of the fire initiation, fire growth, and 

suppression mechanisms. The understanding has helped the development of predictive methods that estimate 

ignition of a product assembly: tlie subseyueiit fire growth, and also estimate fire hazards. Further, methods 

are also available to predict, the activation tirne for automatic sprinklers, if present. These predictive 

methods are in the forrn of engineering correlations that provide relatively quick estimates of fire hazards [l], 

and in the form of computer fire models [2] that predict the fire initiation, its growth and fire hazards for a 

specific fire scenario considered. 

Several eiigineering correlat,ioiis hat e I,ceii tised tn clevelop coiiiputer fire iiiodels. One such model is 

DETACT-QS [3] in which the correlations of tenkperature and velocity have been used to predict the 

activation time for sprinklers located iindcr unconfined flat ceilings. This model may also be used for 

predicting activation tinies in large rooins where the influence of confining walls on temperature and velocity 

of the hot gases are negligible. However,, the use of DETACT-QS rnay not be applicable to many residential 

occupancies since these occupaiicies have relatively smaller rooms and the influence of confining walls on the 

temperature aiid velocity of hot gases is expected to be significant. Further, room ventilation is also expected 

to have a significant influence 011 the tmiperature aiicl velocity of the hot gases. Correlations that may be 

applicable for these type of occupancies are iiot currently available. 

In this paper, room fire tests conducted to develop temperature and velocity data are described. The tests 

were conducted in rooms ranging in size frorii 2.44111 s 2.44111 s '3.44111 high to 4.27m x 4.2im x 2.44m high. 

A single or a double doorway was used for ve~it~ilatioii. Soldered aiicl glass bulb sprinklers were located at the 

ceiling (pendant style) aiitl the wall (siclcwall style). h sand burner located in the center of the room was 

used as tlie fire source to provide three fire sizcs ('73 l;W, 100 kW, and 14'7 kW). The room was 

instrumented to measure the tciriperat ti re aiid veloci t) at specific locations, and monitor tlie activation of 

sprinklers. 

The temperature and velocit! data were anallvzetl and it. was found that both tlie temperature increase and 

the velocity of the gases at. the sidewall stFk sprinkler location were significantly lower than observed at the 

pendant style sprinkler 1oc.ation. This is espectecl to be due to higher heat and friction losses for the sidewall 

location. Further, the test data showed that the the for the hot gases to attain steady state temperatures 

was significant in relatioii to the sprinkler activation t.iine. 

The temperature and velocity data. were then further analyzed aiid used to develop nondimensional 

correlations for temperature, and velocit? for both the pendant and sidewall sprinklers. Additionally, the 

quasi-steady assumption used in some sprinkler activation models was examined to determine its 

applicability for residential sprinklers. aiid a iiondirnensional correlation for tlie temperature transient 

observed in the hot gas layer during the fire tests was developed. 

The nondimensional correlations were of the form 

where Q is the heat, release rate, g is acceleratioii due t.o gravity. po is density of air at ambient conditions, 

Cpo is specific heat of air at ambient. To is aint>ient teinperature. A, is the area of the vent, Ho is the 

height of the doorway. hk is the heat traiisfer coefficient for heat loss through the walls of the test room, and 

At is the totai surface area of IIIC roo111 wall^ arid ceiling). The factor I' was defined as (i) 4Ts/T0 - nondiinensional teinperat,ure iiicrr.asv ( ATs is s~~ady state 

dimensional velocity (IT is velocit?): i\ild (iii) 

increase): (ii) U/(GAo&/At) - non 

noiidirnensional temperature transient 

factor (a is a time coilstant for tocinperat9tirc increase iii thy roorii). ?'lie proportionality constant li, and the 
155 

exponents M. and N were tleteriiiiiitd usiiig the t~~c~tliocl of least squares for both the pendant style and 

sidewall style sprinklers fronl 1Jie data ohtaiiied fro111 the series of fire tests. 

The resulting correlation for teinperature for pendant style spriiiklers is in reasonable agreement with 

existing correlation developed by R4cCaffery [4] for room fires. The new correlation for velocity provides 

closer agreement to test data than current correlations. The results show that assuming quasi-steady 

conditions in the room will undcrcstimatc t ti rile for sprin1;ler activation. The paper demonstrates that the 

use of transient temperature factor developed. dIoivs for a closer correlation between the actual activation 

time and the predicted actuat.ioi-1 time. 

REFERENCES: 

1. Alpert R., L., "Calculations of Response Tiiiie of Ceiling Mounted Fire Detectors, Fire Technology, VoI. 

8, (19i2), pp. 181-195. 

2. Peacock, R., D., Jones, I\*.. I\*.. Buckowlii. IT., \\*., and Forlie>, C., L.. "HAZARD I", National Institute 

of Standards and Technology. Gaithersburg. hl 11. 20899. 

3. Stroup, D., IV.! and Evans. 11.. D.. *~,\4c..1.liotiso Calculate. the Response Time of Heat and Smoke 

Detectors Installed Below Large LTnol.)st.riict.ccl Ccilings". NBSll<,85-3l(j'i', Natioiial Bureau of Standards, 

Center for Fire Researclt, Gait,liersl,ui.g. J.1 D 208S9. ( 19S3). 

4. McCaffrey, B., J., Quintiere. .I .. G.. and Harl~le~~oacl. M.. F.. "Estimating Room Temperatures and the 

Likelihood of Flasliover Vsiiig i-irc 2'est Diit i\ C'oI'~c*liLtio11~." Fire l'~~111101og~. ( l9Sl). pp. 99-119. 
156 

SPRINKLER HEAD RESPONSE MEASURED 

Haukur Ingason 

Bords, Sweden 

Swedish National Testing and Research 

AND PREDICTED 

Institute 

Thermal response models for glass bulb sprinklers have been studied' considering the following 

thermal response parameters; the Rate of time Index (R%,3, the Conduction parameter (C)4 and 

the Change of Phase parameter (CHP)5. The RTI parameter reflects the thermal time constant of 

the glass bulb and the C parameter the heat conduction loss to the sprinkler fitting. The CHP 

parameter is thought to be a factor accounting for a time delay shortly before activation caused by 

heat absorption of the operating medium or work needed to shatter the glass bulb. 

The use of three parameters in the response model instead of two, Le. RTI and C, have been 

proposed to describe the thermal response of both glass bulb sprinklers and solder type sprinklers. 

According to the three-parameter model, the heat-sensitive element is heated by convection from the 

air stream and cooled by conduction to the sprinkler supports up to a point where the element starts 

to absorb heat energy without a corresponding rise in temperature. CHP characterizes, therefore, 

a physical sequence, starting when the element temperature has reached a value close to the 

activation tem erature. Fore solder type sprinklers the absorbed energy is assumed to arise from the heat of fusion % . 

Combinations of one, two and three parameters have been used to predict response times for various 

plunge and ramp test conditions, as well as for a wide range of growing fire conditions. These 

calculations indicate that the test results can not be fully explained in the framework of the thermal 

response models applied. Firstly, consistently different C values were obtained for ramp tests with 

different rates of temperature rise. Secondly, tests with precondition temperature of the sprinkler 

close to the operation temperature resulted in higher RTI values compared with cases with normal 

precondition temperatures. A thermal analysis with the finite element computer program SUPER- TASEF' shows that a plausible reason for the different C values is uneven heating of the sprinkler 

frame arms during different ramp tests while the higher RTI values can be attributed to a time delay 

caused by temperature gradients within the glass bulb. This indicates that the CHP parameter found 

necessary to explain some earlier test data in terms of heat absorption or work needed to shatter the 

glass bulb, more likely reflects an affect of thermal time delay. 

- 

Thermal analysis showed that the time delay will yield different RTI values in a plunge test for 

different heating conditions and consequently the glass bulbs will not respond as predicted. It was 

also found that the relative effects of the time delay on the RTI value will increase with shorter 

response times. However, the time delay is not constant for all types of heating conditions. The time 

delay was found relatively constant for the plunge test conditions, while for time varying heating 

conditions such as those in ramp tests, no time delay was found. This has been indicated earlier by 

Job et.al.'. Calculated heat release rate at sprinkler response in a growing fire condition was used 

to evaluate the thermal response models. For the fast, medium and slow fire growth rates the heat 

release rates at sprinkler response were found to be similar, whether based on calculations with two 

parameters (RTI and C) or with all three parameters @TI, C, CHP). However, when using only the 

RTI value, the predicted rate of heat release at sprinkler response decreased significantly. 

The velocity around the frame of one of the tested sprinklers has been measured at different 

orientations using Laser Doppler Velocimetry (LDV). The objective was to measure the air flow 

conditions around the sprinkler frame arms at two different orientations. A field model simulation 
157 

was carried out for same type of sprinkler to enable a comparison with the measured values. The 

comparison between measured and calculated velocities show good agreement. 

When the sprinkler frame arms are orientated parallel to the direction of air flow it is not obvious 

that the Nusselt number should correlate to the square root of the Reynolds number, as it does when 

the frame arms are perpendicular to the air flow. One of the basic assumptions in the RTI theory 

is that the heat transfer to the heat-sensitive element correlates to the square root of the Reynolds 

number and thus the square root of the air flow velocity. The heat transfer to the glass bulb is 

proportional to the Nusselt number. When the sprinkler frame arms are orientated parallel to the 

air flow, the flow conditions around the glass bulb will change due to the shadowing effect of the 

frame arms. This will alter the convective heat flow to the glass bulb compared to the case where 

the frame arms do not obstruct the flow. To investigate the correlation between the Nusselt number 

and the Reynolds number for the glass bulb when the frame arms are orientated parallel to the air 

flow indicate that the heat transfer varies with the square root of the velocity as assumed in the 

original RTI theory. The RTI theory is therefore deemed to be valid for the simulated sprinkler 

irrespective of the orientation. 

References 

'Ingason, H., Thermal Response Models for Glass Bulb Sprinklers, SP-REPOR T 1992:12, The 

Swedish National Testing and Research Institute, Bods 1992, Sweden. 

2Heskestad, G. and Smith, H.F.,Investigation of a New Sprinkler Sensitivity Approval Test; The 

Plunge Test, FMRC 22485, Factory Mutual Research Corporation, Norwood, Massachusetts, 

December 1976. 

3Heskestad, G. and Smith, H.F.,Plunge Test for Determination of Sprinkler Sensitivity, FMRC 

3AlE2,RR, Factory Mutual Research Corporation, Norwood, Massachusetts, September 1980. 

beskestad, G. and Bill, R.B., Conduction Heat-Loss Effects on Thermal Response of Automatic 

Sprinklers, Factory Mutual Research Corporation, Norwd, Massachusetts, September 1987. 

5Gustafsson, N.E., A Three Parameter Model for Characterizing Sprinkler Sensitivity and Predicting 

Sprinkler Operating Times. Part 1 and 2, Prepared for the C.E.A. Sprinkler Subcommittee, WG 3, 

1988. 

%vans, D.D. and Madrzykowski,D.,Characterizing the Thermal Response of Fusible-Link sprinklers, 

National Bureau of Standards, NBSIR 81-2329, August 1981. 

7Gustafkson, H. and Wicksttdm, U., Super-TASEF, Temperature Analysis of Structure Exposed to 

Fire, Version 1.0, Swedish National Testing and Research Institute, Bods, 1991. 

*Job, E.J., Job, N.J. and Paetow, J.R., Remarks on Theory and Testing Methods for Sprinkler 

Sensitivity, Ahrensburg, May 15,1990. 
158 

Thermal Radiation From Marine Fire Boundaries 

LeMoyne Boyer 

Research Engineer 

South west Research Institute (SwRl) 

Extended Abstract 

This paper presents the results of a study performed to determine the thermal radiation 

from the unexposed face of various classes of insulated bulkheads with one face exposed to 

a prescribed furnace exposure. The bulkheads were representative of that which may be 

found in marine vessels. Full scale Class A-60, A-30, A-I5 and A-0 bulkheads were 

evaluated in accordance with Fire Test Procedures for "A", "B" and "F" Class Divisions 

(Res.A.517( 13)) published by the International Maritime Organization. The thermal radiation 

and surface temperature measurements have defined the range of levels to which 

passengers would be exposed if the need for egress along a fire boundary became 

necessary. These results have shown that all classes evaluated to date (A-60, A-30 and A15) other than the A-0 class should provide adequate protection, Le. safe passage through a 

corridor. In addition, the information obtained forms a useful database for the thermal 

behavior of the materials used in the evaluations. In addition the results have fit expected 

scaling behavior based on dimensional analyses. Finite-element transient heat transfer 

modeling was performed to predict the effect of density and thickness of insulation on the 

thermal failure time of the bulkheads with a high degree of success, as shown by comparison 

with the actual data. 

A Class "A" fire boundary is a bulkhead which is constructed of steel or other 

equivalent material, is suitably stiffened, and is so constructed as to be capable of preventing . 

the passage of smoke and flame to the end of a one-hour duration of the test method: 

Recommendation on Fire Test Procedures for "A," "B," and "F" Class Divisions (IMO Res. 

A.517(13)) as it applies to Class "A" bulkheads. Further refinement of the classification is 

based on the time period for which the rise of temperature of the unexposed side is limited. 

In particular, an uninsulated steel bulkhead shall be Class A-0, while other classes shall be 

insulated with an approved structural insulation. The average temperature of the unexposed 

side will be less than 139OC above the initial temperature without rising, at any one point, 

including any joint, more than 180°C above the original temperature at the end of 15 minutes 

for a Class A-15; 30 minutes for a Class A-30; and 60 minutes for a Class A-60. 

To briefly describe the setup and evaluation method, the bulkheads were constructed 

of 4.5 mm thick mild steel, 2.4 m high by 1.9 m wide. Vertical stiffeners, 65 by 65 mm, were 

spaced 600 mm on center. Several configurations were evaluated, depending on the 

classification desired. Evaluations were performed with no insulation (A-0), with mineral 

wool (A-60, A-30, A-15), or a combination of mineral wool and calcium silicate marine board 

(A-30). The construction was typical of that found on marine vessels. Also, the A-60 

consisted of two configurations, one with the insulation exposed to the fire, and the other with 

the steel exposed to the fire. A minimum of three evaluations per configuration were 

performed, to provide for repeatability, as well as to allow the results to encompass the 
159 

expected performance rating. In general, the density or thickness was varied slightly so that 

the actual rating would bracket the "ideal" rating. The evaluations were performed using 

SwRl's vertical furnace, under positive pressure. The furnace was calibrated to assure a 

uniform exposure over the surface of the bulkhead. The furnace temperature curve was 

maintained in accordance with the IMO test standard, which is generally a logarithmic fit 

reaching 945OC at the end of a one hour period. 

The data obtained included thermal radiative measurements of the face of the 

bulkhead, surface temperatures, furnace temperatures, and for some of the evaluations, 

thermography (infrared thermal imaging) was used to view the entire unexposed surface. 

The most significant results obtained from these evaluations has been in the development of 

a database of unexposed surface temperature and heat flux for Class A-60, A-30, A-15, and 

A-0 bulkheads. This data contains information very useful for fully characterizing the 

behavior of insulated and uninsulated bulkhead systems. This information can be used to 

predict the actual expected levels of radiation in the event of fire, and also to determine 

regulatory guidelines for the use of these materials and alternative materials. As seen in the 

literature, the thermal radiation measured brackets the range of acceptable exposure levels, 

depending on the class and configuration of bulkhead evaluated. 

The data obtained has been submitted to dimensional analyses, with a high degree of 

correlation. This will be very useful for the prediction and modeling of fires in marine vessel 

construction. The analysis has shown that the primary factors affecting the thermal protection 

offered by mineral wool are the density and thickness of material used. Further study of the 

scaling parameters may broaden the scope of applicability of the correlations obtained. 

The thermal modeling performed has been very useful in selecting the density and 

thickness of insulation to meet the requirements of the study to bracket the thermal failure of 

each bulkhead classification. In addition, the comparison to the actual data has shown that 

the analyses in general agreed within 15% of the actual results. This provides a basis for 

validation of the finite element method, as applied to the thermal analysis of an insulated 

boundary subjected to fire conditions. 

References 

Recommendation on Fire Test Procedures for "A," "B," and "F" Class Divisions, IMO Res. 

A.517(13), in Fire Test Procedures, International Maritime Organization, London 1984. 

Acknowledgement 

This work was funded by the United States Coast Guard, and under the direction of Mr. 

Louis Nash, USCG Research and Development Center, Groton, CT. The advice and 

comments of Mr. Nash has been instrumental for the success of the current program. 
160 
161 

PAPER WITHDRAWN 
162 

GROUND-FAULT CIRCUIT-INTERRUPTER (GFCI) 

TECHNICAL REPORT 

A. Albert Biss, RE. 

U.S. Consumer Product Safety Commission 

Directorate of Engineering Sciences 

Division of Electrical Engineering 

Over 1,OOO deaths and several thousand injuries due to electrical shock and electrical fire hazards 

involving consumer products occur in the home each year. In addition to these deaths and injuries, 

propem damages due to electrical fires amount to over $1.2 billion each year. The consumer 

products involved in these incidents are the same kinds of electrical appliances, equipment and Wiring 

systems typical in households across the country. 

Considerable effort has been expended in the past by the Consumer Product Safety Commission 

(CPSC) and others to provide shock hazard protection for consumem in and around the home, First, 

with each succeeding edition of the National Electrical Code since 1973, protection against shock 

hazards is extended to various areas of newly constructed homes by requiring the installation of 

Ground-Fault Circuit-Interrupters (GFCI's). Second, Commission rule-making in the mid-70's 

required modification of particular citizen band base antennas to reduce consumer exposure to the 

risk of deadly shock should the antennas contact overhead power lines. Finally, through the voluntary 

standard system, manufacturers have provided double insulation in various power hand tools. 

As a result of these measures, the electrocutions related to consumer products have decreased by 55 

percent from 1975 to 1988. This downward trend plateaued somewhat from 1984 to 1986, but more 

recent data suggest the trend may still be continuing, albeit at a reduced slope. Nonetheless, the 

death toll is still too high, and further extension of GFCI protection for consumers can effectively 

reduce electrocutions further, particularly for those consumers residing in older homes. While the 

Commission's efforts to extend GFCI installation have resulted in shock protection for malions of 

new homes, the number of older homes left unprotected is still very substantial, amounting to 

approximately 70 percent of total U.S. households, Thus, a large segment of the population has no 

GFCI protection and remains at risk from ground fault shock hazards. 

. 

Based on CPSC studies, the highest rate of electrical fires occurs in dwellings over 40 years old. The 

deterioration of aging appliances, equipment and wiring can cause degradation of insulation resulting 

in current leakage to gro~nd, leading to fire conditions. Because GFCI's detect ground fault 

currents, they not only protect consumers from electrical shock hazards but they can also prevent 

some electrical fires form Occurring and reduce the severity of others by interrupting the flow of 

current. Thus, in addition to providing shock hazard protection, GFCI's can significantly reduce the 

potential for fires, particularly in older homes. 

The failure mode leading to ignition in an electrical fire is often difficult to determine since much of 

the evidence may have been destroyed in the fire. Two mechanisms causing deterioration and 

breakdown of insulation resulting in ground faults are "arc tracing and treeing" in insulation and 

"glowing" of loose electrical connections, Electrical tracking involves the development of a surface 
163 

conducting path between two points of different electrical potential. This current becomes greater 

as the thermal degradation of the surface progresses to greater values, leading ultimately to current 

concentration in a path or channel, sparking, and electric arc-over. 

In the opinion of one author, arc tracing or treeing is not a rare process; it is responsible for many 

electrical fires. One reason for this is that arc tracking usually occurs at low current values, low 

enough that the overcurrent protection device does not sense it. The process, therefore, continues 

unhindered until it is detected by the user of the device, until sufficient heat is generated to cause 

a fire, or until the user discards and replaces the product without realizing that there was a problem 

with it. 

Another mechanism resulting in insulation deterioration is the phenomenon of glowing electrical 

connections. In its 1977 study of glowing electrical connections, the National Bureau of Standards 

(NBS) defines "glow" as "a sustained source of light and heat emanating from the vicinity of an 

electrical connection or from the vicinity of some other place in an electrical circuit, such as where 

broken parts of a wire, are in contact. The report describes and characterizes the extent to which 

loose electrical connections in residential type branch circuits have overheated in the laboratory. In 

electrical devices where connections become loose due to creep, thermal expansion and contraction, 

corrosion, etc., they may overheat due to their high resistance and/or arcing. The resulting high 

temperatures can cause insulation to deteriorate thus causing current leakage to ground or enabling 

the line conductor to contact a grounded conductor or surface. During the Lab experiments at NBS, 

the GFCI operated twice, thus opening the circuit and disrupting the test. The GFCI was then 

removed from the circuit, permitting the experiment to proceed. 

Because the GFCI detects ground faults, it can prevent some electrical fires and reduce the severity 

of others by interrupting the flow of electric current. Early detection by GFCI's of ground leakage 

currents resulting from glowing or arcing due to loose connections and arc-tracking or treeing can 

prevent major electrical fires from starting. 

The activities initiated by the U.S. Consumer Product Safety Commission and others provides a 

foundation for expanding the participation by local groups, organizations, associations and firms to 

reach the great majority of consumers not presently protected by GFCI's and who may not be aware 

of GFCI's and their benefits in the home. 
164 

One and Two-sided Burning of Thermally-Thin Materials* 

T. Ohlemiller and J. Shields 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg MD 20899 

Abstract 

In spacecraft applications, many slab-like materials are dimension- ally thin as a result of weight considerations. In terrestrial 

applications, thin materials are encountered in clothing, draper- ies, paper, electronic circuit boards, etc. These materials may 

be expected to approach thermally-thin behavior during combustion. 

By thermally-thin is meant that heat absorbed on one surface of the 

material will penetrate its thickness sufficiently rapidly so that 

there will no significant temperature gradient through the material 

depth. 

One of the important flammability measures of any material is its 

rate of heat release per unit area; this is a function of the 

incident heat flux on the material. Rate of heat release helps 

determine how fast flames will spread over a material, particularly 

in a concurrent mode. The total rate of heat release is also one 

of the best measures of any fire involving the material. 

The rate of heat release from a thermally-thin material burning on 

both sides is shown here to be enhanced by more than the simple 

factor of two expected for thermally-thick materials. (That is, 

when both sides of a thin material are burning, there is an 

enhancement in burning rate beyond that due to the simple doubling 

of the burning area.) Two simplified models, one based on the 

artifice of a steady-state burning process and the other accounting 

for transient fuel consumption, demonstrate that this is a 

consequence of the Arrhenius temperature dependence of the 

gasification rate of the solid. In effect, the condensed phase 

responds to the increased heat input (fromthe flames on the second 

side) by raising its temperature and thus its gasification rate. 

The models, with typical parameter values as inputs, predict a two- sided rate of heat release more than three times that of one-sided 

burning; see Figure 1. (There is a complication in the experhental demonstration of this effect that lies behind the fact that 

there are two curves in Fig. 1 labelled "one-sided", The most 

appropriate comparison with the two-sided case is based on the 

lower, dotted curve; see below.) 

*Sponsored by NASA Lewis Research Center, Order #C-32003-R 
165 

In order to demonstrate this effect with real materials, it was 

necessary to modify the NIST Cone Calorimeter so as to permit two- sided irradiation of thin samples. The Cone heater was replaced 

with two identical flat radiators with a sufficient area so as to 

permit essentially uniform heating of samples that were 8.25 cm 

square. The two radiators were vertical and parallel with a gap of 

3.2 cm in the center of which was the sample, atop a weighing cell. 

The samples could be irradiated on one side and insulated on the 

back, thus giving the normal type of Cone exposure, or they could 

be irradiated and then ignited simultaneously on both sides. The 

materials used were three resin/glass fiber composites, two with 

polyester resin and one with epoxy resin. All were 0.16 cm thick. 

In this experimental arrangement there is no way to prevent top 

edge burning of the gases coming from the back of the sample during 

one-sided irradiation. That is, these rear surface gases meet the 

flames coming up from the front surface along the top edge of the 

sample holder and burn there. This burning provides no heat 

feedback to the rear face of the sample. The apparent rate of heat 

release is thus about of factor of two higher than that for true 

one-sided burning. In Figure 2 below this effect is contained in 

the data labelled "one-sided". 

The experimentally measured enhancement of rate of heat release is 

somewhat more than the factor of three predicted by the models. It 

1s inferred that this heat release enhancement means that thermal- ly-thin materials will undergo upward flame spread more readily 

when burning on two sides than when burning on one side. 

Fig. 1 TRANSIENT MODEL RESULT 

ONE-SIDED AND TWO-SIDED HEATING/BURNING 

2400 I I I I 1 I 

p200 - - 

? 1600 Two- - 

om- 1 3200 - 

- E = 62.7 kJ/mol - 

51800 - - 

21400 - SIDED - 

- 

z1000 - 

2400 

2200 

1800 

? 1600 

E = 62.7 kJ/mol 

600 

Fig. 2 

ONE-SIDED AND TWO-SIDED RATE OF HEAT RELEASE 

G-11 EPOXY/GLASS, 1.5 mm THICK 

1500 

SI 400 ci 

<I300 -1 

51 200 

:I 100 

2 1000 : 900 

800 

'S GI 700 

600 

% 500 1 -1 I 

I I I I 1 

15 20 25 30 35 40 45 50 15 20 25 30 35 40 45 

RADIANT FLUX (kW/m2) INCIDENT RADIANT FLUX (kW/m2) 
166 

A Comparison Of Numerical and Exact Solution of the Creeping Flame Spread 

Over Thermally Thin Material 

Subrata Bhattachajee 

Department of Mechanical Engineering 

San Diego State University, San Diego, CA 92182-0191 

ABSTRACT. A numerical solution of the well known de Ris (1969) problem of flame spread over 

thin condensed fuel in opposed-flow environment is presented. The problem is reformulated in A A A 

mo - - T" J7 

S CT, L CT, 

tern of four non-dimensional parameters, E -, & = AA, P3 5 A and p4 AA, 

retaining all the assumptions of the original theory. For a particular baseline case (pi = 0.45, p2 = 

26.94, f33 = 2.18, and 84 = 0.45 which correspond to a.50-50 oxygen/nitrogen environment, 

cellulosic fuel (GH10O5), and a vaporization temperature of 650K) eleven sets of calculations are 

performed to check the accuracy of the solution, the grid independence and domain-size 

independence; the resulting flame shape and the nondimensional heat flux are shown in Fig. 1. 

The results of this numerical analysis indicates that the flame is lifted despite the 

linearization of mass-flux at the vaporizing surface. The non-dimensional flame stand-off 

distance vary with the controlling parameters in a way similar to the behavior exhibited by onedimensional diffusion flames. While de Ris theory uses the approximation that the location of the 

leading edge and the location of the onset of vaporization, the eigen location, are identical, the 

present analysis treats the leading edge as part of the solution. The most important finding of this 

work is that the location of the flame leading edge is usually upstream of the eigen location, x=O, 

which has significant bearings on the spread rate formula. 

tje A ff 3" 

4 TY -T, 

The value of A in the de Ris formula for the spread rate, p E _S V = A n n , is 

found, approximately, to be about unity in the present work rather than, x/4, suggested by 

Delichatsios (1986). This is shown in Fig. 2 where the non-dimensional spread rate, p, is plotted 

against the de Ris parameter for a wide range of values of the controlling parameters. It can be 

seen that the value of A, the slope, is sensitive to the vaporization parameter, p4 E T, and to 

some extent to the stoichiometric parameter, PI = - - parameters that affect the location of 

the flame leading edge the most. When the values of the controlling parameters are so chosen that 

the flame leading edge is very close to the eigen location, the value of A approaches x/4. The 

results of the present analysis suggests that the exact solution is valid for these limiting values of 

the controlling parameters. 

CT, 

- 

S 

References: 

1. 

2. 

de Ris, J.N., Twelfth Symposium (International) on Combustion, The Combustion Institute, 

Pittsburgh, 1969, pp. 241-252. 

Delichatsios, M.A., Combust. Sn'. Technol., 44257-267 (1986). 
167 

X 

Fig. 1. Flame shape and the non-dimensional heat flux for eleven sets of calculations varying 

grid spacing, grid geometry, and domain size. 

40 1 1 

Numerical: 4 varying ’ 

o fit varying 

Fig. 2. Non-dimensional spread rate plotted against the de Ris parameter. Variation of p with p4 

does not appear to be captured well by the de Ris parameter. 
168 

The Behavior of High Density Cellulose Samples 

Under Simulated Fire Conditions 

I. Milosavljevic and E.M. Suuberg 

Division of Engineering, Brown University 

Providence, RI 02912 

INTRODUCTION 

The behavior of high-density samples pressed from high-purity cellulose powder has been 

examined under conditions that simulate those that exist in fires. The objective of this work was to 

establish what factors are most important in detennining the yields of char and volatiles, and to evaluate 

how well these can be predicted from simple TGA-type of measurements of cellulose pyrolysis. In this 

paper, the effects of density, sample size, and “grain orientation” are discussed. 

EXPERIMENTAL 

The pyrolysis behavior of pressed cellulose samples of various densities was examined in 

three different devices. The first is a standard thermogravhetric (TGA) device. This device has been 

classically used to establish the kinetics of pyrolysis of cellulose powders, from which the behavior of 

large samples under fm conditions has been predicted. Here, the technique was modified only insofar as 

slightly larger samples were used than is customary (3 mm cubes). The reason for using these large 

particles was a desire to see the effects of sample density in the TGA device. All he samples were pressed 

from the same powder, and thus the actual chemistry of pyrolysis should be invariant. 

The second device employed was a “heated wire mesh” reactor in which thin wafers of 

pressed powder could be examined. In this device, the sample is heated by placing it within the folds of a 

stainless steel wire mesh that acts as a resistance element within a circuit. Volatiles escape from the mesh 

into a cold surrounding gas, and are quenched. This device has been earlier shown to give pyrolysis 

kinetics that are in excellent agreement with those from standard TGA devices. Here, the interest was in 

the effects on devolatilization of varying a single sample dimension. 

The third experimental device was a simulated fire apparatus, in which large samples (38 mm 

diameter and about 10 mm thickness) are datively heated from the front face. The course of pyrolysis is 

followed by continuously recording the mass of the sample, as well as its interior temperatures. The 

samples in this study were exposed to a surface flux of 40 kW/m2, typical of fire level fluxes. 

The pressed cellulose samples were made in house by pressing high purity filter pulp in a 

laboratory press. The samples have been recently shown to be good surrogates for the behavior of wood, 

as they have comparable densities and show comparable behaviors’. 

RESULTS 

The experiments in the TGA device have revealed that if heating rates comparable to those in 

fires are to be used to study the kinetics of pyrolysis, there is a sigmficant danger of external heat transfer 

Milosavljevic, I. and Suuberg E.M., ACS Di v. Fuel Chem. Rem,= 1567 (1992). 
169 

limitations, with particles even a few millimeters in size. Since use of such large particles is not common 

practice in TGA studies, this is not of particular concern, unless the sample bed size itself reaches such 

dimensions. Of greater concern was the obsenation that there is a measurable effect of density on the 

yields of volatiles, even with particles a few millimeters in size. 

In the measurements performed in the heated wire mesh apparatus, it was obsemed that the 

escape of volatiles is sensitive to direction of transport. In the pressing of the high density cellulose 

samples of interest (1 g/cc), a banded structure is developed in the direction perpendicular to the pressing 

direction. This banded structure is analogous to the grain structure of wood Volatiles apparently travel for 

quite large distances along the grain, in preference to crossing it. 

Finally, in the simulated fie apparatus, the behavior is strongly influenced by both heat and 

mass transfer limitations. Heat transfer in the simulated fire situation is controlled by conduction into the 

bulk of the sample. As a result of the imposed radiative flux condition at the surface, the sample surface 

continually heats up, and the pyrolysis wave is driven at roughly constant rate into the sample, up to the 

point at which heat losses from the back balance the input from the front, and the process stops. Higher 

density samples thus pyrolyze at higher rates, by virtue of their better conductivities. These samples show 

a lesser temperature gradient across their thickness for the same reason. Mass loss rates are not 

sigmfkantly affected by grain orientation, since the rates are primarily detennined by heat transfer rates. 

The effects of mass transfer limitations are however clearly visible in these large samples. Volatiles 

produced in the hot forward zones of the sample can diffuse backward, recondense, and later act as heat 

sinks, when the pyrolysis wave reaches points further back in the sample. 

Standard TGA kinetics do not predict well the behavior of the devolatilization in the latter part 

of the process, in parts of the sample far from the surface. Earlier studies in this laboratory2 indicated 

that heating rate has only a minor effect of the global kinetics of pyrolysis of cellulose powder. The present 

study suggests that the conclusion must be carefully reconsidered, in view of the complications caused by 

the mass transfer limitations within the sample. The kinetics are, in fact, path dependent for reasons not yet 

fully understood. 

The “char yield” from the simulated fire experiments is not a well-defined quantity, influenced 

as it is by heat losses from the rear face of the sample. Char yield increases with increasing density of 

sample, in a direction opposite the trend that would be predicted from the better thermal conductivity of the 

higher density samples. Thus there is unquestionably an influence of rnass transfer on the ultimate yields 

of char. The effects of density are, again, small, as they were in the experiments from the TGA. 

CONCLUSIONS 

The results have clearly demonstrated that prediction of the behavior of cellulose pyrolysis 

under simulated fire conditions is difficult, based upon TGA results alone. There are issues related to 

correct prediction of heat and mass transfer effects that cannot be addressed from such data alone. A 

comprehensive model of the behavior of pyrolyzing bulk solids is under development and incorporates 

many of these issues. 

* Suuberg, E.M. and Dalal, V.F. n m In ,65-1,1987. 

1 NST-llIA U.S. DEPARTMENT OF COMMERCE I l- -" WuyIoI 

tunow INSTME OF STANDARDS ANDTECHNOLOGY , NISTIR 4924 

2. CORFo(uuwa ORQAWPATlOW REPORT NUMBER 

BfBLIOGRAPHIC DATA SHEtT 

Annual Conference on Fire Research. Abstracts 

5. Mow) 

Sheilda B. Smith, Editor 

'a -0- ORQAHUAnON (tF Joyn OR OTHER THAN WIST. SEE UIS~UCIIOWS) 17. ~/O~WUY~ 

a )uu#;A'Hou~n .- 

I September, 1992 

4. TITLEWD- 

~MWWTlObJNAMEAWDCOYMAD~S @~V~VSTA=~ 

10. SUWLEMENTARVWOflis 

11. AIsTMcT @ 2O0.WOC1D LESS FA- WWV OF YOST UQwlFlcAwT INFORNATION. DOCUYEWT yIcu)DES A SlQNlFlCAWT UUJO~RAPMV OR 

UTEMTURESURVEYv~cTHERE) 

The NIST Annual Conference on Fire Research has long been the prime forum for the present- ation and discussion of the latest advances in the science of fire and the engineering of 

fire safety. 

performed within Federal laboratories or sponsored by Federal agencies, as well as by 

laboratories around the world. 

This year's conference has been expanded to include all fire research 

12. IQV-S @TO 12 mmtes;- orrwrr; cam- erav mom -;AND wmn mwoluls BV SQU~OU)WS) 4 

fire research, fire plumes, flame spread, fire suppression, mathematical models, 

halons, microgravity, fire detection, polymers, Vents,sprinklers, pool fires, soot, 

toxic gases