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NATIONAL INSTITUTE OF STANDARDS &

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Research Information Center

Gaithersburg, MD 20690

IR 87-3646

CANCELLED

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NBSIR 87-3650

Summaries of Center for Fire

Research In-House Programs and

Grants - 1987

Sonya M. Cherry, Editor

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Rre Research

Gaithersburg, MD 20899

October 1987

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBSIR 37-3650

SUMMARIES OF CENTER FOR FIRE

RESEARCH IN-HOUSE PROGRAMS AND

GRANTS - 1987

Sonya M. Cherry, Editor

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center *or .Rre Research

Gaithersburg, MD 20899

October 1987

U.S. DEPARTMENT OF COMMERCE, Clarence J. Brcwn. Acting Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Director

Table of Contents

Page No.

Abstract 1

Alphabetical Listing of Grants .... .... 2

Center for Fire Research Priority Projects .... 5

CENTER FOR FIRE RESEARCH PROGRAMS

Fire Measurement and Research Division

Fire Performance and Validation ....... 10

Grants under Fire Performance and Validation . 15

Flammability and Toxicity Measurement . 20

Grants under Flammability and Toxicity Measurement ... 25

Pol3rmer Combustion Research 47

Grants under Polymer Combustion Research 53

Smoke Dynamics Research 78

Grants under Smoke Dynamics Research 83

Fire Science and Engineering Division

Engineering Method Development .... 108

Compartment Fire Model 112

Grants under Compartment Fire Model 117

Fire Growth and Extinction 141

Grants under Fire Growth and Extinction 149

Hazard Analysis . 179

Grants under Hazard Analysis 1S3

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Summaries of Center for Fire Research In-House

Programs and Grants - 1987

Abstract

This report was prepared for distribution at the Combined Meetings

of the Eastern Section: The Combustion Institute and the Annual

Conference on Fire Research, November 2-5, 1987. It contains

descriptions of the internal programs of the Center for Fire

Research as well as extended abstracts of grants for fire research

sponsored by the Center for Fire Research.

Key words: Cellulose; charring; combustion; fire models; flame

spread; ignition; polymers; smoke; soot; toxicity

1
Alphabetical Listing of Center for

Fire Research Grants

Page No

.

Brown University

A Study of the Effects of Oxygen Transport and Temperature

History on the Chemistry of PMMA and Cellulose Pyrolysis 54

Brown University

Burning of Charring Materials 26

Brown University

Soot Dynamics in Flames 84

California Institute of Technology

Experimental Study of Environment and Heat Transfer in a Room Fire 118

Clemson University

Graphical Presentation and Numerical Analysis of Fire

Data for Model Validation 16

Factory Mutual Research Corporation

Development of a Model to Provide Comprehensive Fire Property

Data 30

Factory Mutual Research Corporation

Prediction of Fire Dymamics 122

The George Washington University

Chemical Pathways to Soot Formation in Diffusion Flames 88

Georgia Institute of Technology

Soot Formation and Corrosion in Fires 92

Howard University

Interaction of Radiation and Conduction in Polymeric

Materials 58

Marquette University

Thermal Stabilization of Polymers by Cross-Link Formation 62

Michigan State University

Effect of Water on Ignition of Cellulosic Materials 150

The Pennsylvania State University

Soot Particle Formation and Destruction in Diffusion

Flames 96

The Pennsylvania State University

Vertical Wall Fire in a Two-Layer Stratified Atmosphere 155

9
Page No

Polytechnic University

Mechanisms of Action of Metallic Smoke Suppressants and

Fire Retardants for Poly(vinyl chloride) 66

Ruggers, The State University of New Jersey

Negatively Buoyant and Penetrative Flows Generated in

Enclosure Fires 133

Southwest Research Institute

Analysis of Hazards to Life Safety in Fires: A Comprehensive

Multi -Dimensional Research Program -- Second Year 35

SRI International

Electrophysiological Incapacitation and Persistent Behavioral

Dysfunction of Rats Associated with Combined Exposure to

Carbon Monoxide and Carbon Dioxide 38

University of California, Berkeley

Fire Modeling 159

University of California, Berkeley

Fire Propagation in Concurrent Flows 163

University of California, Berkeley

Flame Radiation 70

University of California, Los Angeles

Fire Risk Analysis Methodology ’ 184

University of California, Santa Barbara

A Study of the Supression and Extinction of Fires by

Water Sprays 167

University of Dayton Research Institute

Mathematical Modeling of Furniture Fires 41

University of Maryland

Characterization of Large Scale Turbulent Structures

in Variable Density Flows 99

University of Maryland

Kinetics of Agglomerate Formation 103

University of Maryland

Transient Cooling of a Hot Surface by Droplets Evaporation 171

University of Maryland

Transient Ceiling Jet Characteristics 137

University of Michigan

Radiation from Turbulent Luminous Flames 175

3
Page No

University of Montana

Kinetics of Oxygen Chemisorption and Desorption of

Combustion Products in the Smoldering Combustion of

Cellulosic Material 74

University of Pittsburgh

Toxicity of Plastic Combustion Products 45
CFR PRIORITY PROJECTS

This year the Center for Fire Research has focussed its in house research

effort on a series of priority projects considered key to meeting its central

technical objective of providing practical quantitative tools for fire safety.

Many of these projects have involved the coordination of the efforts of

professional staff from different organizational groups within the Center.

The projects could be divided into three categories, those with short term

products, longer term projects to produce engineering tools, and those that

lead to a better understanding of fire.

Specific reports on the priority projects are not included in this volume.

Technical progress is reported instead in the organizational group technical

reports

FY 87 Priority Projects and their objectives are listed below;

CATEGORY 1 - SHORT TERM OUTPUTS

Cone Calorimeter Development

To organize an ASTM Round Robin evaluation of the Cone in order to gain

acceptance of the Cone as an ASTM and ISO Standard. To establish two

working Cone Calorimeters in CFR.

Model Accuracy Assessment

Provide the users of fire models the information needed to (1) furnish

required inputs to the model, (2) use the model without detailed

knowledge of the internal workings of the model but with some understanding of the physics involved, and (3) understand that the

degree of confidence that the physics behind the model and its output

are realistic for the use intended.

Simulation Laboratory

To transfer the hazard assessment technology to the user community

through formal courses and presentations at appropriate meetings.

CATEGORY 2 - ENGINEERING TOOL DEVELOPMENT

Engineering for Fire Protection Applications

Development and transfer of tools the practicing fire protection

engineering professional can use to incorporate applied science as a major force in his work.
Fire Hazard Assessment

To deliver a unified and verified fire and smoke hazard assessment

method.

Consolidated Compartment Fire Model

Develop generic and applications -specific software modules for a welldocumented, user-friendly, modular and easily updated CFR Consolidated

Compartment Fire Model (CCFM) Computer Code. Use these modules to

implement versions of the CCFM which address particular needs of CFR and

the Fire Science and Technology communities.

Transport Physics

To continue the development and incorporation of the physics of

transport-related phenomena into models. The selection of phenomena to

be addressed takes into account the needs of the user communities and

the applications for the models such as hazard and risk assessment.

Toxic Potency Measurement

Produce a technically sound position paper on the proper

combustion/animal test methodology for measuring smoke for the N-gas

model; expand N-gas data base to include HCi and TDI

.

CO/Soot Empirical Prediction

To produce a report on best estimates of CO and soot production for the

hazard model based on analysis of small and large scale bums.

CATEGORY 3 - BETTER UNDERSTANDING OF FIRE

Wall Fires

To develop an algorithm which predicts the behavior of a burning wall in

a room, and to embed this algorithm in a zone -type compartment fire

model

.

CO Prediction: Turbulent Flames and Smoldering

To develop an understanding of CO production in flames as a basis for

establishing a predictive model for CO production in pre and post

flashover fires. To develop, for common, smolder-prone residential

materials, a data base and a verified theoretical model for CO evolution

rates

.

Extinmishment

Develop an understanding of fire suppression processes in compartments.

6
Flame Spread with Radiation

Develop means to predict flame spread on vertical surfaces utilizing

laboratory test methods.

Mass Burning Rate /Fuel Generation

Develop a predictive model of mass burning rates of polymeric materials

in a pool burning configuration after understanding and characterizing

fire plume, heat feedback mechanism and gasification processes of the

materials

Soot Formation and Evolution

Broaden comparisons of detailed species profile measurements in

hydrocarbon diffusion flames with existing models of chemical growth;

identify fastest steps which produce intermediate hydrocarbons; identify

key intermediate hydrocarbons in chemical growth processes . Calculate

and measure the size distribution, friction force, and optical

properties of soot.

For FY 88 most of these projects will continue with the following new or modified projects added:

Toxicity SRM Development

To develop a material suitable for standard reference material use for

combustion toxicity tests.

Fire Data for Materials

To assess the fire performance of materials , components , systems , and

assemblies and to develop the protocols for obtaining, assessing, and

evaluating input data for fire models used for hazard assessment.

Turbulent Burning Theory

Mathematical modeling of turbulent combustion processes in fires.

Time Dependent Fire Plume Model

Data based fire plume flow model incorporating low frequency large scale

eddy structure.

Engineering Analysis Svstem 5e Fire Reconstruction

The development of separated and assembled fire protection analytical

(computerized) tools and the transfer of these tools to practicing

professionals. The use of these tools and other resources to recreate

and otherwise analyze one of more significant fires. To initiate

verification of the results, to evaluate the tools, and to assist

decision maker in actions to prevent recurrence.

7
Expert Systems for Model Codes

To work with model code organization, such as NFPA, to develop a generic

form of expert systems that will serve as a model for the replacements

of written model codes by expert systems.

Smart Detectors

To examine the feasibility of the application of predictive methods and

detector technologies to improvements in the response and selectiveness

of detectors.

In addition to these priority projects funded mostly by funds appropriated for

the Center, research work has been performed for other Federal agencies.

Although these "other agency" projects naturally relate directly to the

missions of those agencies, they also supplement the priority project effort

and provide a vehicle for transfer of the technology.

3
FIRE MEASUREMENT AND RESEARCH DIVISION

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CENTER FOR FIRE RESEARCH

FY 87

Professional Personnel

Richard D. Peacock, Acting Head

Emil Braun, Physicist

J. Newton Breese, Computer Programmer

C. Lynn Forney, Mathematician

Billy T. Lee, Fire Prevention Engineer

J. Samuel Steel, Physicist

Objectives

The objectives are to develop the generic methodology for assessing the

accuracy and limitations of fire models and to design and conduct tests to

evaluate the fire performance of components, systems, and structures.

Scone

This work includes two important efforts; first, the conduct of unique, highly

instrumented experiments to establish fire behavior on a realistic scale in

order to establish performance characteristics and to contribute to model

I development and, second, the evaluation and verification of fire models by

providing a mathematical tool for comparing experimental data with model

outputs utilizing expertise in facility fire test experimental design, instrumentation, and data processing and analysis.

Proi ects

1. Model Accuracy Assessment

The objective of this project is to develop the methodology for the evaluation

and verification of fire models; it focuses on the development of mathematical

and computational techniques for fulfilling this objective. A fully documented, highly instrumented collection of experimental tests was completed in

I the last year along with the development of algorithms which provide an archetypical set of calculations using experimental data for comparison with

j zone fire models. Over the next year, the procedure for model validation will

I be tested and refined on two existing fire models within CFR: ASET, a single

room model with few inputs and outputs, and FAST a multi-room model for fire

and smoke transport.

Figure 1 shows a comparison of experimental and predicted temperatures as a function of time for two rooms in a multi-room facility. The agreement is

I quite good, but deviations exist and provide insight into the limitations of

the model. Free convection is the mechanism for enthalpy flux between layers

I and compartments. In the burn room, the plume flow dominates while in adjacent

compartments the flow through the vents is most important. In the earlier

version of this model, the plume was not treated as a separate zone. Rather it was assumed that the upper layer was connected to the fire by the plume. The

implication is that the plume is formed instantaneously. Consequently, early

10
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in a fire, when the energy flux was very small and the plume length very long,

the entrainment was overpredicted. This resulted in the predicted interface

falling more rapidly than was seen in experiments. Also, the initial temperature was too low but the rate of rise was too fast. The asymptotic temperature

was correct. The latter occurred when these early effects were no longer

important. The correct sequence of events is for a small fire to generate a plume which does not reach the ceiling or upper layer initially. The fire

entrains enough cool gas to decrease the buoyancy to the point where the plume

no longer rises. When there is sufficient energy present in the plume, it will

penetrate the upper layer. The effect is two-fold: first, the interface will

take longer to fall and second, the rate of rise of the upper layer temperature

will not be as great. To this end the following prescription has been incorporated: for a given* size fire, a limit is placed on the amount of mass which

can be entrained, such that no more is entrained than would allow the plume to

reach the layer interface. The result is that the interface falls at about the

correct rate, although it starts a little too soon, and the upper layer

temperature is slightly overpredicted but after the initial phase, follows the

experimental data very well. In addition, the implementation of this model has

a place to insert an algorithm for forming a plume.

The opposite problem is encountered in the flow through vents. The entrainment

is underestimated. The difficulty lies in the use of a plume model well beyond

its nominal range of validity. The work of McCaffrey really only applies to a circular plume. In the case of vent flow an extended flat plume similar to a waterfall is encountered. However, there exists no reliable correlation as yet. Thus we must presume to use the former correlation until a better plume

model can be developed.

Upper sas layer;

Upper wail surface:

1) bum room prediction

2) corridor prediction,

3) bum room measurement

1) corridor measurement.

5) prediction and

6) measurement.

Figure 1, A comparison of the upper gas layer and upper wall surface temperatures in a multi-room large-scale test facility

Davies, A. D., "Some Tools for Fire Model Validation," Fire Technology, Vol.

23, No. 2, May 1987 pp 95-114.

11
Peacock, R.D., Davis, S., and Lee, B.T., Experimental Data for Model Validation, NBSIR in preparation.

Jones, W. W. , and Peacock, R. D., Experimental Verification of a Model for Fire

Growth and Smoke Transport, submitted for presentation at the Second .A.nnual

Symposium on Fire Safety Science.

Braun, E. , Davis, S., Forney, C. L. , and Peacock, R. D. , Procedure for the

Evaluation of Computer Fire Models, NBSIR in preparation.

Davis, S.,and Braun, E. , "Validation of Fire Models", paper presented to

International Symposium on Mathematical Modeling and Related Fire Test Methods,

American Society for Testing and Materials, December 1986. To be published in

The Journal of Fire Sciences.

3. Flame Spread on Walls

The objective of this project is to examine flame spread on selected wall

materials burning outside of a room and inside a full-size room to provide a data base for the development and refinement of a mathematical algorithm for

wall burning. This work complements small-scale work on flame spread (upward,

downward, and lateral) , both before and after flashover. The ongoing experimental study is designed to analyze flame spread along a combustible wall

surface using a controlled ignition source along the floor.

Lee, B.T., and Steel, J.S., Standard Room Fire Test Research at the National

Bureau of Standards, NBSIR to be published.

Huang, D.Y.

,

Evaluation of Quarter- Scale Compartment Fire Modeling for Constant

and Stepped Heat Inputs, submitted to Fire and Materials.

4. Flammability of Composites for Naval Ship Use

The objective of this program is to assist the Navy in designing fire-resistant

ship components from fiber- and metal-reinforced composites by systematically

assembling data on the composites flammability properties. To date, the

laboratory work performed has been using the cone calorimeter; this work is

being extended to more advanced composite materials. We have found an apparent

linear relationship between the average heat release rate during the first

minute after ignition and the external flux imposed on a polyester composite

and on a polyphenylene sulfide composite; the same was indicated for an epoxy

composite. Indications are that similar relationships hold for rate of heat

release averaged over periods where the rate is not changing extremely fast.

If this observation continues to hold, we may have a means for estimating the

heat of vaporization of the resin based on its apparent heat of combustion and

heat losses based on the material thickness and depth of material charring and

burning. In the coming year, depending on the availability of suitable

specimens, flame spread measurements will be made with the IMO apparatus. Fire

scenarios, currently being developed by the Navy, will be translated into fullscale experiments to provide large-scale verification of a predictive tool to

be develooed.

12
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ijlBraun, E., and Brown, J.E., Cone Calorimeter Characterization of Composite

!:Materials, Nat. Bur. Stand., NBSIR in preparation.

!15 . Fire Safety Aspects of Solid Fuels

. The objective of this continuing project is to study the hazards associated

with the installation, operation, and maintenance of solid fuel burning

I appliances used for space heating in single family dwellings and in similar

lij small-scale applications. Fire incidents from the use of solid fuel burning

|( equipment rose from 66,800 to 130,100 between 1978 and 1981. This trend slowed

j|| from 1981 to 1982 to slightly less than a seven percent increase. The frequenj,; cy of fire incidence stabilized between 1982 and 1983 (increasing during this

I time less than one percent) and actually decreased in 1984 (dropping nearly 11

5 percent). Positive actions by the Center for Fire Research and others are

i believed responsible for improving the safety of these appliances and, thus,

|i reversing an increasing fire incidence rate. The overall research program has

I included typical operating conditions of modern heating appliances, intensity

! and duration of chimney fires in factory-built and masonry chimneys, clearance

1 reduction systems for protection of combustible walls and ceilings, and wall

I pass- through systems for connection of appliances to chimneys through combusi tible walls. |‘ ®

|l Peacock, R. D., Thermal Performance of Masonry Chimneys and Fireplaces, Nat.

|lBur. Stand. NBSIR 87-3515 (April 1987).

[[Peacock, R.D., Wood Heating Safety Research: An Update, accepted for publica-

. tion in Fire Technology.

ii- Associated Grants and Contracts

ll

II James P.

1|^ Analysis

Jarvis - Clemson University, " Graphical Presentation and Numerical

of Fire Data for Model Validation."

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FIRE PERFORMANCE AND VALIDATION GRANTS

15

CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY87

Insriuitjon:

Grant Nq:

Grant Title:

Principal Investigator.

Other Professional Personnel:

NBS Scientific Officer

;; Technical Abstract:

Introduction. Over the past several years, the Center for Fire Research (CFR) at the National

! Bureau of Standards, has been developing mathematical models for predicting the environmental

; conditions which occur as a fire develops and spreads. Once these models are shown to be

i “valid”, they become a useful tool in determining and solving problems related to fire safety.

' Currently work is being done to establish a methodology for assessing the validity of the

I mathematical models developed. It includes four broad steps: (1) conceptual mo^l validity

checking that the theory and underlying assumptions are correct and reasonable; (2) computerized

I model verification - ensuring that the computer programming and implementation of the conceptual

I model is correct; (3) operational validity - determining that the model’s output behavior has the

j; accuracy required for the model’s intended purpose [5, 8, 9]; and (4) data validity.

I The effort described here is largely related to operational validity. It has three main

components: development of computer software tools for graphical analysis of data, sensitivity

I analysis of models, and dimensional analysis and determination of core parameters for models.

Although much of analysis has been oriented toward ASET, a model for estimating the Available

Safe Egress Time from a single room fire [1], it is hoped that the techniques will have more general

I applicability. An overview of both completed and anticipated results is given below.

Graphical Analysis. Data produced from both fire models and experiments typically include a

i number of variables and their values over time. An important aspect of model validation is the

;i capability of viewing such data in a flexible, robust manner. To this end, a computer graphics

!ii system for analysis of fire data is being developed. It will ultimately include both general scientific

[; plotting capabilities and well as numerical techniques, such as smoothing and normalization,

specifically developed for application to fire data.

Qemson University

60NANB6D0627

Graphical Presentation and Numerical Analysis

of Fire Data for Model Validation

James P. Jarvis, Professor

Department of Mathematical Sciences

Clemson University

0104 Martin Hall

Clemson, SC 29634-1907

Telephone: (803) 656-5214

Michael K. Kostreva, Associate Professor

Lynn J. Forney, Research Associate

Sanford Davis

I

i

16
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The system is being developed on an IBM PC, but is written in FORTRAN and employs the

Graphics Kernel System [6] to facilitate portability to other systems. It is anticipated that the

system will be transferred to CFR computers. The system uses a command line interface with

extensive error checking and on-line help available. The basic command strucmre includes

capabilities for varying the labeling and scaling of line and scatter plots; attaching boxes, arrows,

and text to enhance a plot; saving both data and plotting formats; displaying system status; and

changing output devices. Currently, screen, printer, and pen plotter output is supported.

Sensitivity Analysis. Sensitivity analysis of a model is a study of how changes in the model

parameters affect the results generated by the model. The parameters through which the model is studied consist of the input and internal variables and the assumptions, logic, and structure of the

computational procedures of the model. Our interest here is in the input and internal variables.

Some questions of interest to be investigated are: (1) which are the dominant variables? (2) what is the possible output range for a given input? and (3) what is the expected range in output for a given range of an input variable? Because of the number of variables in typical fire data and since

each output variable is actually a time series, a full analysis is generally infeasible and the set of

variables selected for study must be reduced.

Qassical sensitivity analysis examines the partial derivatives of a function (model) with

respect to its variables in some local region of interest A function may be sensitive to changes in a

variable in one region and insensitive to the same variable in another region; hence, a function

cannot necessarily be classified as either sensitive or insensitive to a particular variable. In performing a sensitivity analysis on a model, a global, as opposed to local, measure of sensitivity

may be more desirable.

Three methods for estimating the sensitivity of a model to its variables will be briefly

discussed and illustrated using the ASET model. The models is based on a gystem of two

differential equations used to estimate the smoke layer height from the floor and the temperamre of

the smoke layer as functions of time for a single room in which a fire develops and grows. The

equations are denoted as dzi/dt=fi(z,c,t) and dz2/dt=f2(z,c,t) where is the layer height, Z2 is the

upper layer temperature, t is time, and c is a vector of parameters. The layer height and temperature

equations depend on the height and area of the room, the height of the fire base from the floor, the

initial heat release, the heat release generation function, the fraction of the heat release lost to the

contents and surroundings, the fraction of the heat release radiated from the fire, and ambient

conditions.

In general, the sensitivity equations will not be known explicitly. Thus, the sensitivity

equations must be solved by numerical techniques. Three such techniques are being examined.

Pint, a finite difference method can be used to estimate the partial derivatives of the model z with

respect to each of its variables: c^, C2, C3, ...,c^. For this method the derivatives are estimated by

dZi/dCj={zj(ci,C2,...,Cj+Acj,...,Cn,t) - z,(ci,C2,...,Cj,...,Cn,t)}/Acj. This method requires that the

model z be run n+1 times to obtain estimates of the partial derivative of z with respect to each of its parameters. Since this method is a linear approximation, the choice of Acj is important. If Acj is selected too large, then the sensitivity estimate obtained may be very poor.

The other two methods are direct techniques but differ in their approaches. The direct method

involves deriving the sensitivity differential equations from dzj/dt=fj(z,c,t) and then solving the

sensitivity differential equations. The general form of these equations wlU be dsy/dt = 9fj/3cj +

2^(ofi/3zjj^)*Siq where Sjj=3zi/9cj. The solution of the sensitivity equations can be done in two

17
basic ways. One way is to treat dzj/dt=fi(z,c,t) and its sensitivity equations as a coupled system

and solve the system simultaneously [3]. The work involved in solving the sensitivity equations

using the direct coupled method is solving a system of m+mn equations, m original differential

equations and n systems of m sensitivity differential equations. A second way is to first solve

dzj/dt=fj(z,c,t) and then solve the system of sensitivity equations using the solution z(t) and some

interpolation scheme [4]. The work involved in solving the sensitivity equations using the direct

decoupled method is solving a system of m equations and then solving m sensitivity equations n

times.

Dimensional Analysis and Core Parameters. Model validation and interpretation are two

important steps of any application of mathematical models. In order to perform these steps in a systematic and economical manner, it is essential that the mathematical model undergo a

simplification process known as dimensional analysis, and that the minimum number of

dimensionless parameters be found. Once these parameters, the core parameters of the model, are known, the organization of the validation step and the interpretation of the model follows; e.g.,

[7]. If the validation is attempted without first determining the core parameters then many

additional experiments may have to be performed in validation, with no additional confidence

gained in the validity of the model. The reason for this is that the same experiments will be

repeated, simply in another parametric description.

For example, suppose two parameters, say a and b, occur in an unsimplified form of a model,

always as the product a»b. Then experiments which double the parameter a while halving b will

produce the same result as the base case in which both are unchanged. Since validation, including

expensive laboratory work, forms a part of fire modeling, it becomes increasingly important to nondimensionalize to the core parameters. With regard to models familiar to fire researchers.

Cooper [ 1] simplified the ASET model from twelve raw physical parameters to four parameters.

However, is four the smallest number of parameters needed to specify the ASET mo^l? Are other

models of interest in fire research currently formulated in terms of core parameters? Is there a general algorithm for obtaining core parameters? These are some questions currently under

investigation.

Mathematical models are seldom used in a manner which exploits all of the information they

convey. Whenever differential equation models are applied, such as in fire research, the solution

(functions of time and/or space) as well as several derived outputs are available (such as available

safe egress time, temperature at hazard, hazardous concentration, etc.). Once core parameters are

established, it is possible to gain significant insights into model behavior by plotting the derived

outputs against the core parameten for a large collection of model runs. Such graphs, either

surfaces or contour plots, are similar to bifurcation diagrams. Knowing regions of parameter

space in which large changes in these derived outputs occur can direct attention to areas in which

the model is especially sensitive. By the same token, knowing flat regions of these surfaces can be

a great timesaver.

Another way in which the information a model contains may be made more accessible is through the use of tables. Users without constant access to computers may derive necessary

information from tables which summarize model applications.Tables of previously computed

solutions, or values interpolated to them may be used to supplement graphical displays. For

example, consider the following; a constant size 1320kW fire may start on the floor of a room

with 10.000 feet area and ceiling height of 10 feet Which design change can increase the available

safe egress time the most; a change, in height of 1 foot or a change in area of 1000 feet? A glance at the table answers this question. (Tliis example uses data from Cooper and Stroup [2].)

18
ASET Area: 9,000 10,000 11,000

Height: 9 1 99 - 110 122

10 1 210 233 257

11 1 315 351 386

I Summary. A variety of techniques, including graphical, sensitivity, and dimensional analysis,

\i are being examined for their applicability to the fire validation problem. Although these procedures

ii are being tested in the context of the ASET model, it is hoped that the experience gained can be

p applied to other fire models as well.

! References

1. Cooper, L. Y., “A Mathematical Model for Estimating Available Safe Egress Time in Fires,”

Fire and Materials 6, 135-142 (1982).

' 2. Cooper, L. Y. and Stroup, D. W. , “ASET- A Computer Program for Calculating Available

, Safe Egress Time,” Fire Safety Journal 9, 29-45 (1985).

: 3. Dickinson, R. P. and R. J. Gelinas, “Sensitivity Analysis of Ordinary Differential Equation

Systems - A Direct Method,” Journal of Comp. Physics 21, 123-143 (1976).

I

• 4. Dunker, A. M., “The Decoupled Direct Method for Calculating Sensitivity Coefficients in

[I Chemical Kinetics,” J. Chem. Phys. 81-5, 2385-2393 (1984).

j: 5. Gass, S. L, “Concepts of Model Confidence,” NBSIR 80-2053, National Bureau of

Standards, Washington, D.C. (1980).

, 6. Graphics Software Systems. Graphics Development Toolkit. Beaverton, Oregon (1986).

7. Kostreva, M. M. and Hatton, M. B., “ROLLUBE; A Computer Package for Modeling Roller

Bearing Lubrication and Elasticity,” Proceedings of 1984 International Computers in

I Engineering Conference and Exhibit, The American Society of Mechanical Engineers, Las

I Vegas, 614-620 (1984).

,1

[

8. Sargen^ R. G., “Verification and Validation of Simulation Models,” from Progress in

Modelling and Simulation (F. E. Cellier), Academic Press, New York (1982).

9. Schruben, L. W., “Establishing the Credibility of Simulations,” Simulation 34-3, 101-110

I (1980).

19
FLAMMABILITY AND TOXICITY MEASUREMENT

CENTER FOR FIRE RESEARCH

FY87

Professional Personnel

Vytenis Babrauskas , Head

Jeffrey R. Didion, Mechanical Engineer

Richard H. Harris Jr. , General Physical Scientist

John F. Krasny, Textile Technologist

Barbara C. Levin, Toxicologist

Marc Nyden, Research Chemist

Maya Paabo , Research Chemist

Kay M. Villa, Textile Technologist

Helene Clark, Guest Worker, University of Pittsburgh

Joshua L. Gurman, Research Associate (AISI)

Marc Janssens, Research Associate (Natl. Forest Products Assn.)

Margaret Yoklavich, Guest Worker, University of Pittsburgh

Program Objectives

To develop measurement methods and the underlying principles for characterizing

the combustibility of furnishings and building materials and the impact of the

combustion products on living organisms.

Scone

Typical efforts of this group include:

• assessing the appropriate applications of the NBS toxicity screening

test method

• determining the extent to which a limited number of gases determine

the lethality of combustion products

• developing a rationale and the methodology for predicting soot and

specific gas production in full-scale fires from bench-scale methods

• exploring possible alternatives to animal testing for measuring the

impact of combustion products on people

• generating a valid, detailed model for the burning of upholstered

furniture

• producing a data base for Cone Calorimeter measured fire properties

• developing an appropriate measurement methodology for the propensity

of cigarettes to ignite soft furnishings

• reinforcing the relationship of combustion in the Cone Calorim.eter to

large scale burning and aiding the promulgation of the Cone Calorimeter

for engineering and code applications

Proi ects

1. Heat Release Rate and Related Properties of Materials

The focus in this area is measurement of materials properties in the Cone

Calorimeter. This instrument was initially developed for heat release race

20
studies. More recently, the capability was added to do smoke obscuration, soot

mass, gas species yield characterizations. In addition, data are regularly

taken on ignitability , mass loss rate, and the effective heat of combustion.

The Cone Calorimeter was recently adopted by ASTM as a tentative (grey pages)

method, P 190. The British Standards Institution (BSI) has also recently

started working on a draft method based on the Cone Calorimeter. This method

i is being put forth to ISO TC92 SCI WG5 (the ISO working group on heat release

1 rate) as a basis for developing an international standard in this area. The

j number of installed instruments has been expanding rapidly, and there are now

some 18 units in various laboratories throughout the world. A User's Guide for

the Calorimeter is in the final stages of preparation. ASTM has also organized

a round-robin for the Calorimeter and testing in being started this Fall. The

i increasing need for an accessible database in this area has been recognized and

! software development has been started. Work on smoke, soot, and gas production

correlations between bench-scale and full-scale tests has also been progressing, jointly in cooperation with the Smoke Dynamics Research Group. During

the last few years, some 40 reports and journal articles dealing with the Cone

j Calorimeter functions or analyzing data from it have been put out by staff from

{ both NBS and from other laboratories. A few of the most recent are;

i Babrauskas , V., The Cone Calorimeter- -A Versatile Bench-Scale Tool for

1 the Evaluation of Fire Properties, pp. 78-87 in New Technology to Reduce

'll Fire Losses & Costs . S.J. Grayson and D.A. Smith, eds . , Elsevier Applied

I Science Publishers, London (1986).

I; Babrauskas, V., and Parker, W.J., Ignitability Measurements with the Cone

I Calorimeter, to appear in Fire and Materials . Also issued as Nat. Bur.

I Stand. Report NBSIR 86-3445 (1986).

r

I 2. Prediction of Fire Toxicity from Analysis of the Main Gaseous Components

j (the "N-gas model")

The toxicity of single and multiple fire gases is being studied to determine

{whether the toxic effects of a material's combustion products can be explained

;f by the toxicological interactions (as indicated by lethality) of the primary

{i fire gases or if minor, more obscure gases need to be considered. LC^q values

Jl for Fischer 344 rats have been obtained for CO and HCN (as individual gases in

,|i air) for 1 through 60 min exposures plus relevant post-exposure periods using

IJ: the NBS Toxicity Test Method apparatus. The results show a constant concentra-

:'tion-time product for the various HCN exposures; for CO, however, the

concentration- time products decreased for the 1 to 5 min exposures and then

increased for the longer times. In exposures ranging from 5 to 60 min, the

I : toxic effects of CO plus HCN were additive and, except for the 5 rain exposures,

j: the presence of 5% carbon dioxide (CO^) decreased the LC^ ^ values of CO,

p indicating synergistic effects. Decreasing the oxygen concentrations in the

r presence of various mixtures of the other major fire gases increased the

toxicity even further. A pharmacokinetic study examined the formation of COHb

I

in rats during 30 min exposures to lethal concentrations of CO with and without

jp5% CO2

. The results at these high concentrations agreed with earlier results

from experiments at less than lethal concentrations (i.e., the COHb formation

I'Was faster and the pH was lower in the presence of CO2 )

. When the obser'/ed

I' toxicity for 24 cases of material decomposition was interpreted in terms of the
current N-gas model, the majority, but not all, of the cases could be correctly

predicted. These results provide necessary information for the computer model

currently being developed in the Center for Fire Research to predict the toxic

hazard that people will experience under various fire scenarios.

Levin, B.C., Paabo, M. , Gurman, J.L., and Harris, S.E., Effects of

exposure to single or multiple combinations of the predominant toxic

gases and low oxygen atmospheres produced in fires. Fundam . At>ol . Toxicol . 9, 236-250 (1987)

Babrauskas , V., Levin, B.C., and Gann, R.G. , A new approach to fire

toxicity data for hazard evaluation. Fire J. 22-71 (1987).

3. Fire Toxicity Scaling

This project, sponsored by the Consumer Product Safety Commission, involves

further studies to determine the degree to which toxicity measurements taken in

the bench scale (BS) can be used to predict full scale (FS) toxicity in fires.

For this project, the toxicity of the thermal decomposition products from two

flexible polyurethane foams (with and without a fire retardant) and a cotton

upholstery fabric was evaluated by a series of both BS and FS tests to either

the smoldering or flaming decomposition products from upholstered chairs. The

BS tests included the NBS protocol toxicity test, along with Cone Calorimeter

and Furniture Calorimeter tests. The degree of toxicity observed during and

following the FS and BS flaming tests could be explained by the current N-Gas

Model. Essentially no animal deaths were noted within the exposures to the non- flaming or smoldering combustion products produced in the BS or FS tests.

The concentrations of CO, CO2

, and HCN were also comparable. Post-exposure

deaths, however, occurred following the BS non- flaming foam or cotton tests,

but not following exposures to the smoldering phase of the FS tests. In the FS

room tests, little toxicological difference was noted between decomposition

products from the burn room and a second room 12 m away. In a second series of

FS fire tests, recently conducted, the toxicity of combustion products from

smoldering, flaming or combined smoldering- flaming tests was examined and the

results are being analyzed.

Braun, E., Levin, B.C., Paabo, M. , Gurman, J.L., Holt, T. , and Steel,

J.S., Fire toxicity scaling (NBSIR 87-3510). [U.S.] Nat. Bur. Stan.

(1987) .

4., Standard Reference Material for Small-scale Toxicity Test Methods

Several jurisdictions are presently considering legislation to address the

toxicity of smoke from the combustion of building products. As a result of

this, combustion toxicity testing has begun in many testing laboratories,

giving rise to the need of a standard reference material (SRM) for checking the

apparatus and the operating procedures. The first phase of this project

involved the selection and screening of a suitable material for combustion

toxicity evaluation. A suitable material should burn reproducibly and have a moderate level of toxicity which is not solely due to carbon monoxide. The

first material, a black polymethylmethacrylate (PMMA) , was unsatisfactory since

it was not toxic when decomposed in the non- flaming mode at the highest
I

allowable mass loading. The second material, an acrylonitrile -butadiene

styrene (ABS 1007a) , is one that has been certified as an SRM for the NBS smoke

density chamber. When tested by the NBS toxicity test method, this material

showed repeatable, satisfactory results in both the flaming and non- flaming

modes. Four outside laboratories are participating in an interlaboratory

evaluation of this material by the NBS test method to determine the

reproducibility of results among laboratories. This material, however, proved

to be unsuitable for the University of Pittsburgh test method. They are in the

process of testing a nylon material, which turns out to be more acceptable.

5. Cigarette Ignition Study

j

I This work was performed under the Cigarette Safety Act of 1984. It was

, established that the propensity to ignite upholstered furniture and mattresses

i of 12 typical commercial cigarettes varied only within a narrow range.

’ However, the ignition propensity of 41 experimental cigarettes, produced by the

cigarette industry, varied greatly. Some cigarettes which had very low

: ignition propensity combined the following design parameters; low tobacco

packing density, low paper porosity and citrate content (citrate is widely used

as an ash modifier and smolder promoter), and low circumference. Several

patented concepts (paper modification, fire stops in or additives to the

tobacco column) also showed promise, and offer directions for further investigation. Some of the low- ignition-propensity cigarettes had tar, nicotine,

and CO yields (measured by the FTC method) within the ranges of the bestselling commercial cigarettes. It was concluded that the manufacture of lowignition-propensity cigarettes is feasible, with some advances in cigarette

design and manufacturing technology. A benefit/cost study by the Center for

|i Applied Mathematics of NBS indicated that the modification needed for low

Ji cigarette ignition propensity may result only in small changes of price,

ji employment, health care cost, and the financial status of the affected

industries and professions.

A detailed experimental characterization was made of the cigarette as an

i initiator of smoldering combustion in upholstery materials. Particular

emphasis was placed on measuring the spatial distribution of heat flux passing

from the cigarette coal to an upholstery substrate. Single measures of this

I flux distribution were checked for their correlation with ignition propensity

of the experimental cigarettes. Peak fltix did not vary sufficiently among the

j|( cigarettes to reveal any correlation. The total heat input to a typical point

I on the substrate surface caused by passage of the flux distribution correlated

i| only weakly with ignition propensity. Cigarette coal area (which varies mainly

f via variations in coal length) showed a moderately good correlation with

j: ignition propensity. A shorter, less ignition-prone coal can be obtained by

I: decreasing cigarette packing density, diameter or paper porosity.

Measurement of cigarette ignition propensity on upholstered furniture mockups

was found to be reasonable indicators of the performance on full-scale

furniture. However, a standard method to measure cigarette ignition propensity/

in the laboratory could not be developed in the given time, but several

promising concepts have been identified.

23
Krasny, John F. , Cigarette Ignition of Soft Furnishings - a Literature

Review with Cominentary . NBSIR 87-3509 (1987). Also printed as a report by

the Technical Study Group, Cigarette Safety Act of 1984 to the U.S.

Congress

.

Gann, R,G., Harris Jr., R.H., Krasny, J.F., Levine, R.S., Hitler, H.E,,

and Ohlemiller, T.J., The Effect of Cigarette Characteristics on -the

Ignition of Soft Furnishings, NBS Technical Note; also printed as a report to Congress.

Technical Study Group on Cigarette and Little Cigar Fire Safety, Toward a Less Fire-Prone Cigarette, Final Report to Congress.

/ .Associated Grants

1. Brown University, Herwin Sibulkin - Study of Effects of Material Properties on Flaming Combustion of Charring Fuels.

2. Factory Mutxia.1, Archibald Tewarson - Development of a Model to Provide

Comprehensive Fire Property Data.

3. SRI International, Charles S. Rebert - Electrophysical Incapacitation and

Persistent Behavioral Dysfunction of Rats Associated with Combined

Exposure to Carbon Monoxide and Carbon Dioxide.

4. Southwest Research Institute, Gordon Hartzell - Analysis of Hazards to

Life Safety in Fires.

5. University of Dayton Research Institute, Mark Dietenberger - Mathematical

Modeling of Furniture Fires.

6. University of Pittsbxirgh, Yves Alarie - Toxicity of Plastic Combustion

Products

.
FLAMMABILITY AND TOXICITY MEASUREMENT GRANTS

25
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CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution: Brown University

; Grant No.: NBS Grant 60NANB6D0629

Grant Title: Burning of Charring Materials

Principal Investigator: Professor M. Sibulkin

Division of Engineering

Brown University

Providence, RI 02912

Telephone: (401) 863-2867

Other Professional Personnel: Y. Chen, Graduate Research Assistant

A. Frendi, Graduate Fellow

If NBS Scientific Officer: Dr. V. Babrauskas

I Technical Abstract:

I The objective of the present research program is to determine the effects of

; changes in material properties on the burning rates and extinction limits of ‘solid

fuels. In particular, we are currently looking at the effects of solid phase fire

retardants on the burning of cellulose. We wish to measure the changes in

f material properties caused by these retardants, and to use this information to

1 determine how these retardants act to suppress fires. This information will help in

[ the design of materials with improved fire safety characteristics.

In a previous investigation we studied the flaming combustion of pure and

' fire retarded cellulose, and measured the effects of retardant concentration on

If burning rates and flammability limits. In the present program we wish to measure

the major combustion related material properties for the same series of retarded

cellulose samples. Last year we reported on the heat of combustion of the volatiles

produced by the pyrolysis of cellulose under burning conditions; this year’s report

' will concentrate on measurements of the heat of gasification of the same materials.

These measured properties will then be used as inputs to a mathematical model of

flaming combustion. The results of these calculations for burning rates and

I flammability limits will be compared with the previous measurements in order to

! determine how the retardants act to suppress fires.

The heat of gasification is defined by

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,11 , M where q , is the sum of the heat inputs and losses at the fuel surface and is the mass flux of gaseous products leaving the surface. Two other terms are used in

the literature to describe energy changes which occur during pyrolysis of a solid fuel:

(i) the heat of pyrolysis h defined as the difference in enthalpy between the

products (gas plus char) at and the reactant (fuel) at T* , and (ii) the heat of

reaction h^. defined as the difference in enthalpy between the products and reactants

at To, . Whereas hp and h^. are thermodynamics quantities, h^ is not. Previously it has been shown that only for steady burning of a vaporizing fuel; for a charring material (such as cellulose) there is no simple relationship between h and

hpA schematic side-view of the apparatus developed to measure h^ is shown in

Fig. 1. The heat flux from the flame to the fuel surface is simulated by a pair of

I.R. lamps. Tungsten filament, quartz envelope lamps giving a blackbody distribution

of energy are used. The cellulose sample (in the form of a horizontal 2.5 cm

diameter cylinder) is mounted inside an extensively modified glass draft shield of a top-loading electronic balance. A nitrogen supply system is attached to the weighing

system to first scavenge air from the chamber and then maintain a reduced flow of

nitrogen around the sample during pyrolysis. Oxygen is excluded from the

atmosphere to simulate conditions at the surface of a burning material enveloped by

a diffusion flame. A combination of a quartz absorption plate, radiation shields and

cooling coils is used to prevent breakage of the front window of the chamber. In addition, air cooling (not shown) is used to keep the temperature of the chamber

window and quartz plate below 200 C so that the thermal radiation from these

surfaces can be neglected in determining the surface temperature (as described

below).

The basic measurements needed to obtain the heat of gasification [see Eq.

(1)] are the mass loss rate and the net heat flux. Values of the time-dependent mass

m(t) measured by the electronic balance are stored in a computer. A running least

squares fit to m(t) is generated, and then differentiated to obtain values of m(t).

The net heat flux is found from

’net = ^dex4 4

T... - T„ - dp ( 2 )

• n using the following procedure: (1) The value of the incident heat flux q^^ is obtained by calibration of the I.R. lamps against a water-cooled radiation flux gage;

(2) the surface temperature T^ is found from a calibration curve of the I.R. pyrometer versus thermocouple measurements of T^ made in a separate set of runs;

(3) the convective heat loss from the sample surface is calculated from heat transfer

theory; and (4) a value of €=0.96 obtained from a separate set of surface reflectance

measurements is used.

Cellulose samples which are homogeneous, free from cracks and of adequate

mechanical strength are needed for these experiments. A method for producing such

samples has previously been described. Briefly, a slurry of cellulose, distilled water

(and fire retardant) is blended in a mixer and pressed into a cylindrical shape. The

sample is then oven dried to 105 °C and stored in a dessicator until needed. The

27
fire retardant used was 0 to 3 wt. % of sodium hydroxide. A special technique was developed for determining the retardant mass concentration in the sample.

Measurements were primarily made at an absorbed heat flux of 40

kW/m'. This heat flux gives mass loss rates which are comparable to those found

for cellulose samples burning in air. Additional measurements were made at fluxes

of 35, 30 and 25 kW/m^ Average values of the mass loss rate as a function of

time are shown in Fig. 2 at 40 kW/m^ for pure cellulose (Yp^=0) and for fire

retarded cellulose (Yj^=0.03). Contrary to what might have been expected, the

addition of the retardant leads to an increase in the mass loss rate (even through the

char fraction remaining after pyrolysis also increases). The qualitative shape of the

curves, a rapid rise to a peak mass loss rate followed by a steady decline, is similar

to that predicted by theory.

The effect of retardant addition on the surface temperature at t=200 s is shown in Fig. 3. While the increase in T^ from 829 K at Yp^=0 to 861 K at Yj^=0.03 is not large, it increases the radiative heat loss from the surface enough to have a significant effect on q^^^^ (see Eq. [2]) and therefore on h^. The

combination of the increase in m'^ and the increase in surface heat loss causes a major reduction in the heat of gasification with retardant addition as shown in

Fig. 4.

Oyr current efforts are directed towards determination of the inert and

combustible fractions of the total volatiles. These measurements will be made by

passing a sample of the pyrolysate produced by the apparatus in Fig. 1 through a gas

chromatograph. Once the inert fraction of the volatiles is known, final results for

the heat of combustion and stoichiometric ratio of the "fuel" will be calculated, and

the resulting property values will be used in combustion calculations for burning

rates and flammability limits.

In order to aid in the dissemination of the results of previously sponsored

research, a review paper on the results of diffusion flame studies was presented at the 1987 ASME Heat Transfer Conference.

Publications

"Pyrolysis of Bulk Samples of Cellulose," M. Sibulkin, Int. Conf. on the Physical and

Chemical Processes Occurring in a Burning Cigarette (1987).

"Heat of Gasification of Pure and Fire Retarded Cellulose" M. Sibulkin, S. S. Tewari

and Y. Chen, Eastern Section: The Combustion Institute (1987).

"Heat of Combusjtion of Pure and Fire Retarded Cellulose", M. Sibulkin and A.

Frendi (in process).

"Free Convection Diffusion Flames: A Review of Results", M. Sibulkin, 24th National

Heat Transfer Conference, ASME Symposium Volume H392 (1987).
I.(K|

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29
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution :

Grant No :

Title:

Factory Mutual Research Corporation

60NANB4D-0043

Development of a Model to Provide Comprehensive

Fire Property Data

Principal Investigator

Other Professional Personnel

NBS Scientific Officer

Dr, Archibald Tewarson

1151 Boston-Providence Turnpike

Norwood, MA 02062

Telephone: (6l7) 762-4300, Ext. 2950

Mr, S. D. Ogden, Senior Research Technician

Dr. V. Babrauskas

Technical Abstract :

The objective of the study is to develop generalized relationships, using

existing data, for the engineering calculations of combustion properties of

materials. The combustion properties are used for the assessment of hazard

presented by various environments and protection requirements. The combustion

properties being considered are: 1) net heat of complete combustion, 4Hqq„;

2) chemical, convective and radiative heat of combustion, ana

AHo^d» respectively; 3) combustion efficiency, Xcv^enj> and its convective and

radiative components, xqop ^Rad’ ^®spectively‘; and 4) yields of chemical

compounds generated during combu^ion, Y., especially CO and particulates.

AHcj^em calculated from the yields of CO and CO2 and/or O

2 (depletion). Xj_

is defined as aH^/AHq^jjjp .

AH^, Xi and Y. depend on the chemical structures of fuels and

ventilation, but not on the size of turbulent fires; thus, effects of the

chemical structures of fuels and fire ventilation on combustion properties are being examined.

Chemical Structures of Fuels . Relationships between AH., Xi» Yj and

molecular weight (M) are being sought. Note that the majority of polymeric

materials gasify as oligomers rather than as monomers.

In the study, correlations are being sought between smoke point heights

reported in the literature and heights measured in our apparatus with

corresponding values for AH^ and Y.; aHqq„ is either taken from the

literature or calculated from the standard neats of formation of the chemical

bonds. For about 250 fuels, linear relationships are found between AH^ and M

values and between Y. and M values, within each group of fuels with similar

types of chemical bonds. An example is shown in Figure 1, where is

plotted against M for fuels with C-H-N and C-H-S types of structures.

30
The following relationships are suggested for the engineering

: calculations of ^Hchem’ ^^Con» ^%ad» ^CO ^s ^ represents

particulates).

= A^M + Bj_, (1)

I and, Yj = CjM ^ Dy (2)

I where AH. is in kJ/mole; M is in g/mole; Y. is in g/mole and A^, B., C. and D.

I are constants. A. is in kJ/g; Bj^ is in kJzmole; C. is in g/g and D. is in

I g/mole. The constants derived from the regression '^analysis of data'^for about

j: 250 fuels using Eqs. (1) and (2) are listed in Table 1. The values of AH^ and

Y., calculated using the constants in Table 1, show very good agreement with

the values calculated from the experimental data measured in large-scale

fires.

, Some examples of the data calculated from the constants listed in Table 1 are shown in Figures 2, 3 and 4, where it can be noted that AHQ^gjjj/ABr. or

I ^Chem <^®creases and Y^q and Yg increase with increase in the degree or

i3 unsaturation and aromatic nature of the chemical bonds. Xi values are

lij strongly dependent on M for smaller molecules. In terms of the dependency on

M and chemical structures, x^on Xr^em' Xf^^j shows an opposite

/; dependency; for example, x^hem lowest for aromatic fu^s, whereas Xr^cI

Ij' highest. Since most of the polymeric materials gasify as oligomers ratner

ii: than as monomers, the effect of M on combustion properties may be

ll| insignificant.

}

Fire Ventilation .. Relationships between AH^, x^j ] and fire ventilation

are being sought. Fire ventilation is expressed in termS of air-to-fuel

i{ stoichiometric fraction, 4>.

,

1

- Data are being measured in our apparatus for AH^ and Y^ at various 4> values, where changes are made by varying air flow rate, oxygen concentration

and generation rate of fuel vapors. Data for enclosure fires, concentration

I' profiles in flames and downstream region of the flame, data from the toxicity

! tests, etc., reported in the literature are also being used. In addition, the

.] generalized relationships in combination with the N-Gas Model of the National

Bureau of Standards are being used to extend the application of the

I engineering calculations to the assessment of toxicity of fire environments

I and extent of dilution required to reduce the hazard.

|i

j The data show that Xc^em ^Con decrease and xp^p t Yqo ‘s

increase

I with decrease in 4>. The extent of variations in Xj_ and Y. due to changes in

is significantly larger than variations due to changes in“^the chemical

I structures.

Some examples of the data are shown in Figures 5 and 6. In Figure 5,

AHchem i'on propane and propylene, is very close to the flame

extinction limit. The maximum value of Yqq in Figure 6 is in the range of

about 0.23 to 0.30 g/g of fuel vapors, which is in the range reported in the

literature for the ceiling layers of highly under-ventilated enclosure fires.

31
It is hoped that the study will continue: 1) to refine the values of the

constants reported in Table 1 and demonstrate the applicability of the data to

large-scale fires, and for the modification of materials to enhance passive

fire protection; 2) to develop relationships for under-ventilated fires; 3) to

seek combined relationships for combustion property and N-Gas Model of NBS;

and 4) to understand the fire behavior of materials in terms of their chemical

structures and fire ventilations.

Reports and Papers

1. Tewarson, A., "Generation of Heat and Chemical Compounds in Fires,"

Society of Fire Protection Engineers (SFPE) Handbook (in Press)

.

2. Tewarson, A., "Correlation for the Generation of Carbon Monoxide in

Small- and Large-Scale Fires," 9th Meeting of the United States/Japan

Panel of Fire Research and Safety, May 1987 (to be Submitted to the

J. Fire Science).

3. Tewarson, A., "A Study of Diffusion Flames of Hydrocarbons to Understand

Fire Behavior of Materials," (Submitted to the Fall Technical Meeting of

the Eastern Section of the Combustion Institute, November 1987).

4. Newman, J.S., and Tewarson, A., "Ventilation Effects on Particulate

Generation," (Submitted to the Fall Technical Meeting of the Eastern

Section of the Combustion Institute, November 1987).

5. Tewarson, A., "Prediction of Fire Properties of Materials," Technical

Report Grant 60NANB4D-0043, National Bureau of Standards (to be issued).

32
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CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

I nstitution :

Grant No. :

Grant Title :

Principal Investigator :

Other Professional Personnel:

NBS Scientific Officer:

Southwest Research Institute

60NANB6D0635

Analysis of Hazards to Life Safety In Fires:

A Comprehensive Mul ti-Dimensi onal Research

Program--Second Year

Dr. Gordon E. Hartzell

Director, Department of Fire Technology

Southwest Research Institute

6220 Culebra Road

San Antonio, Texas 78238

Telephone: 512/522-3038

Dr. Arthur F. Grand (Staff Scientist)

Dr. Harold L. Kaplan (Manager, Inhalation

Toxi cology

)

Howard W. Stacy (Assistant Manager,

Inhalation Toxicology)

Walter G. Switzer (Sr. Research Scientist)

Dr. Barbara C. Levin

Technical Abstract :

The overall objective of this research program has been to develop data

and methodology to assess toxicological hazards from the time course of analytical data on fire gases. A previous project resulted in the development of

methodology for the Fractional Effective Dose model, a method by which the

time to a toxicological effect could be estimated for asphyxiant gases from

analytical data. That project also yielded considerable LC^g data on exposure

of rats to hydrogen chloride. The major focus of this current project has

been to conduct further studies on the toxicity of smoke containing HCl

,

particularly in combination with CO.

The mechanism of action of HCl is so very different physiologically from

that of CO, that it would be anticipated that these two toxicants should be

considered separately in predicting hazardous exposure conditions through the

use of the Fractional Effective Dose model. Fractional doses would not be

expected to be additive, as in the case of CO and HCN. However, the LC^g data

on mixtures of CO and HCl tempt one to consider additivity on an empirical

basis. In Table 1 are shown data for some limited mixtures of CO and HCl in

which the summation of fractional lethal doses approximates unity for

50-percent lethality with 30-minute exposures (14-day observation). In

Table 2 is shown a comparable treatment of data using PVC as the source of

HCl. It would appear that the increased lethal toxicity of HCl as contained

in smoke from the flaming combustion of PVC may be attributed only in part to

35
the contribution of CO produced. The full explanation may be quite complex

since the gas/aerosol /particul ate nature of real smoke may result in a different pattern of respiratory penetration. For example, particulate deposition

in the upper respiratory tract may obstruct breathing of rodents and further

stress an already compromised oxygen transport system.

TABLE 1 SUMMATION OF FRACTIONAL EFFECTIVE (LETHALJ DOSES FOR 30-MINUTE EXPOSURE

OF RATS TO MIXTURES OF CO AND HCl

CO HCl I

PED ppm {50X Lethality)

Fractional Lethal Dose ppm

Fractional Lethal

Dose

6400 1.0 — 1.0 5700 0.89 600 0.16 1.05

5300 0.83 1000 0.26 1.09

4150 0.65 1900 0.50 1.15

3000 0.49 2100 0.55 1.04 — — 3800 1.0 1.0

TABLE 2 SUMMATION OF FRACTIONAL EFFECTIVE (LETHAL) DOSES FOR 30-MINUTE

OF RATS TO MIXTURES OF CO AND HCl AS PRODUCED FROM PVC

CO HCl

EXPOSURE

I

eed

ppm (50* Lethality)

Fractional Lethal Dose ppmFractional Lethal Dose

ca. 700 ca. 0.11 2100 ( fl aming) 0. 55 ca. 0.66

7100 1.11 1000 (nonflaming) 0.26 1.37 — — 2900 ( nonfl ami ng) 0.76 0.76

Smoke from the nonflaming decomposition of PVC would appear to be more

irritating that expected from the HCl content. Thus, in the case of CO being

the major toxicant, the summation of FED' s was found to be considerably

greater than unity when HCl from nonflaming PVC smoke was present at the

sensory irritation level. Although smoke from the nonflaming combustion of

PVC would appear, based on summation of HCl FED's, to be more toxic (as a pulmonary irritant) than expected, the significance of the difference is

questionable.

Particularly striking, both in the case of the flaming combustion of PVC

(with wnich up to 1680 ppm CO was produced) and in the case of HCl in tne

presence of 3000 ppm CO supplied from a cylinder source, was the incidence of

postexposure deaths the same day as the exposure, usually within an hour.

This is rare, except at hign concentrations, for HCl, alone. Data showing the

incidence of these early postexposure deaths are shown in Table 3.

36
TABLE 3 COMPOSITE LETHALITY OF RATS EXPOSED TO ATMOSPHERES

CONTAINING HYDROGEN CHLORIDE*

Atmosphere

Animals

Expos ed Exposure

Number

Day 0

of Deaths

Days 1-4 Days 5-14

'-‘'50 HCl in ppm

HCl 60 0 0 21 9 3800

PVC Smoke-Nonfl aming 36 0 0 10 8 2900

PVC Smoke-Flaming 30 1 4 5 19 2100

HCl + 3000 ppm CO 30 1 2 8 17 2100

* At nominal approximate HCl concentrations of 1800, 2600, 3500, 4300, 5500 and 6500 ppm.

Attempts to elucidate the effect of CO on the postexposure lethality of

HCl were inconclusive, but did suggest somewhat impaired ability of rats to

return to homeostasis following exposure. Exposure of rats to a mixture of

5300 ppm HCl and 3000 ppm CO was characterized by a relatively rapid initial

drop in blood pH and slower than normal postexposure unloading of COHb. Even

with these data (compared with those for CO alone), it is difficult to speculate as to the cause of the incidence of same day postexposure lethality. The

observations reported with rodents may pose some significance in the case of

immediate postexposure complications following human exposures to mixtures of

CO and HCl (e.g., prolonged hypoxemic conditions after rescue or escape).

In summary, it would seem that the lethal toxicity of combinations of CO

and HCl can be predicted from an FED model. However, only limited success was obtained when applied to real smoke from PVC. This may be due to complications in respiratory penetration patterns involved with the complex gas/

aerosol /parti cul ate mixtures found in smoke.

Reports and Papers

1. "Analysis of Hazards to Life Safety in Fires: A Comprehensive Multi

Dimensional Research Program," Final Report, NB3 Grant No. 60NANB6D0635,

Southwest Research Institute, San Antonio, Texas, March 1987.

2. Hartzell, 6. E., A. F. Grand and W. G. Switzer, "Modeling of Toxicological Effects of Fire Gases: VI. Further Studies on the Toxicity of

Smoke Containing Hydrogen Chloride," J. Fire Sciences (In Press).

37
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY87

Institution

:

SRI International

Grant: No. : 60NANMB6D0644

Grant Title : Electrophysiological Incapacitacion and

Persistent Behavioral Dysfunction of Rats

Associated with Combined Exposure to

Carbon Monoxide and Carbon Dioxide

Principal Investigator : Charles S. Rebert, Ph.D.

Director, Neuroscience Program

SRI International, LA1 17

333 Ravenswood Avenue

Menlo Park, CA 94025

Other Professional Personnel: Debra E. Sutter

Biologist

SRI International

Gordon T. Pryor, Ph.D.

Director, Department of Psyc.hobiology

SRI International

MBS Scientific Officer : Dr. Barbara C. Levin

Technical Abstract :

The primary objective of this project is to characterise the effects of

carbon monoxide (CO) alone or CO in combination with 5'7a carbon dioxide (COt) on sensory-evoked potentials of Fischer 344 rats. Interactive effects of

these gases are of interest because, as shown by other investigators, CO

intoxication alone cannot account for all smoke-related deaths, typical

levels of hydrogen cyanide are also insufficient to account for deaths, but

the presence of 5% CO 2 exacerbates the lethality of CO at about 2500 ppm

when Fischer 344 rats are exposed in a nose-only exposure aooaratus.^

However, using a multiple-animal exposure chamoer without restraining the

rats, we found the presence of 5» CO 2 to decrease CO lethality. This could

be mediated by an increasec Pa02 due to C02-induced hyperventilation and

greater O 2 release to tissues oecause of the COi-induced rightward shift of

the oxyhemoglobin dissociation curve. Potential differences in the interactive effects of CO and CO- in restrained and unrestrained rats requires

additional study.

‘Levin et al., Funa. Appi. Toxicol., 1987, in press.

38
We have begun studying the effects of CO and CO + CO 2 on visual,

auditory, and somatosensory evoked potentials of male Fischer 3^4 rats

prepared with chronic recording electrodes implanted in the skull. The rats

are restrained in a head-only exposure apparatus which is placed inside a chamber containing a strobe lamp, speaker, and device for electrically

stimulating the tail. Potentials evoked by the visual and somatosensory

stimuli reflect activity in cerebral cortex, whereas the response to

auditory stimulation reflects neuronal activity in the brainstem auditory

pathway. In previous independent studies of hypoxia and hypercapnea the EPs

were affected when PaO^ was less than 30 mm Hg, and by an FiC02 of 3% (the

lowest level studied).

In this current study we first determined that exposure (30 min) to

about 1500 ppm CO was required to affect the EPs and exposure to about 2500

ppm CO almost abolished the cortical responses, without much effect on the

brainstem auditory evoked response (BAER). A formal study of 11 rats

involved exposure first to 5% CO 2 and then to 2000 ppm CO alone or 2000 ppm

CO + 5 % CO 2 , followed by exposure to the opposite CO condition in a third

test. The tests were separated by several days, and no deleterious

consequences were observed due to the multiple exposures. No rats died.

1

t The waveforms have not yet been quantitatively analyzed, but judging

I from the group average waveforms (Fig. 1), there was a slight effect of 5%

I CO 2 , involving increased interwave time in the BAER (suggesting slowed conduction velocity in the brainstem auditory pathways) and slight decreases in

amplitudes of the somatosensory and flash evoked potentials (SEP and FEP,

respectively). The effects of 2000 ppm CO alone* on the BAER was about the

same as the 5 % CO 2 alone. Amplitude decreases for the SEP and FEP were much

more pronounced with the 2000 ppm CO alone than for 5f» CO 2 alone, and certain components of the waveforms also increased in latency. The combined

gases had about the same effect as CO alone, except for a possible slightly

larger effect on FEP amplitude.

Colonic temperature declined from baseline by 0.6 and 0.3°C in exposure

and recovery conditions, respectively, in the 5)5 CO 2 condition, and by 0.9

and 1.7°C (exposure and recovery) in the CO and CO + 5 % CO 2 conditions.

Recovery of the EPs was complete for the SEP in all conditions, but was slightly less complete for the FEP when combined gases were used compared to

the CO-alone condition —the waveform for combined gases was flatter than

when CO alone was administered. This may not be a statistically significant

1 effect, however. The general recovery noted for the SEP and FEP indicates

that the effects in exposure were not due to the decline in colonic temperature, as temperature declined even further in the recovery phase. In conj trast, increases in the latency of BAER components were more pronounced

during recovery than during exposure, indicating the te.mperature dependence

of these changes.

! In this study we roughly estimated the threshold of effect for CO on

] EPs and determined a level (about 2500 ppm) that caused a large effect on

I them. This might oe related to the finding noted above that the CO-CO 2

I interaction on lethality is maximal at 2500 ppm. Using a CO level causing a

39
moderate effect on EPs, we also determined that the combination of 2000 ppm

CO and 5)S CO 2 had only slightly more effect on EPs than did CO alone, and

the enhanced effect was confined to the FEP. It would be interesting to

determine if combinatory effects would be greater when a higher level of CO

is used, and, given the apparent special sensitivity of the visual system to

the combined gases, if a more sophisticated test such as the pattern-reversal

EP would be more affected than the FEP.

^sT' EXPOSURE ^ C02 CO; Ac RECCN^ERY ^ AFTER CO OrJLY

A2 GhSELINE BEFORE CO) A 5 PECOC'EFy < AFTER CG2 CO;

A 1 BASELINE BEFORE C02 CO) A4 EXPOSURE ( CO ONLY .1

yV (50/div.)

TIME (45 msec/div.)

FIGURE 1 CHANGES IN THE GROUP AVERAGE FLASH-EVOKED

POTENTIAL INDUCED BY 30-MIN EXPOSURES TO

2000 PPM CO or 2000 PPM CO + 5% CO^ (DOTTED LINES)

Early components (P1-N2) of the response were not

affected, but CO produced a decrease in amplitude

of middle and late components (P3-N5) . The effect

during exposure and recovery was only slightly

greater with the combined gases than with CO alone.

40
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : University of Dayton Research Institute

Grant No. ; 60NANB5D0556

Grant Title; Mathematical Modeling of Furniture Fires

Principal Investigator : Mark A. Dietenberger

Research Physicist

University of Dayton Research Institute

300 College Park - JPC/232

Dayton, Ohio 45469

(513) 229-3921

Other Personnel: Joyce Smith, Research Programmer

NBS Scientific Officer : Dr. Vytenis Babrauskas

Technical Abstract:

Introduction . The objective of this work is to improve a working

computer model of a furniture fire in a room environment which only uses the

cone calorimeter and the flame spreading apparatus database for description

of the material properties. Although the primary prediction of the model is

the furniture burning rate as a function of time, the combustion products

such as carbon monoxide, water vapor, soot, etc. that can be measured in the

cone calorimeter can also be predicted as a function of time. Since the

furniture fire model has been merged with a room fire model, FAST, resulting

in a program now called HEMFAST, the focus during this contract period was to improve the HEMFAST model. The first version of HEMFAST has been

implemented on the Center of Fire Research computers and now provides

qualitative predictions of a particular furniture fire.

The current research has concentrated on two areas of improvement in

I the HEMFAST code with the goal towards quantitative predictions: (1) Revise

I the bench scale data processing routines to take advantage of the recent

upgrades in the cone calorimeter apparatus and of the consequentual new

scaling relationships for the material burning rates and combustion

products. (2) Improve the predictability of the furniture fire modules by

restructuring the code to improve the time integrations of virgin surface

temperature, of the flame front positions, and of the local burn history.

Other improvements include a model of convective heat transfer on burning

areas and a new soot formation model.

New Scaling Relationships. Past work has demons tratea the cone

calorimeter database could not be used directly by the f’urniture fire model

unless the data was processea into a useable form. The reason is that the

material is burned at constant conditions and at much smaller scale in a cone calorimeter than in a f’urniture fire. However, the cone calori.meter can

be made to simulate varying scales by adjusting the cone irradiances. Under

these conditions the measurements of burning rate, mass loss race.

41
combustion products rate, and the soot formation rate as a function of time

are made in the cone calorimeter. To be used in a furniture fire model these

data are rescaled into intrinsic variables of the material. For a very

simple material an intrinsic variable would be the heat of pyrolysis, for

example, and is the mass loss rate divided by the net surface heat flux.

Thus instead of burning rate, mass loss rate, combustion product rate, and

soot formation rate we could have the corresponding variables of heat of

combustion, the heat of pyrolysis, the combustion product mass fraction, and

the soot mass fraction of the fuel. Instead of the time variable we could

have the total mass loss of the material as the intrinsic variable. For a complicated material such as that of the furniture, the conversion of the

measured variables to the intrinsic ( or scaled) variables was not obvious

and has been a subject of research by other investigators.

Our attempt at the conversions of the measured variables was found

to be successful for several furniture materials and it turns out to be a simple scheme as follows. The cone calorimeter measurements of carbon

monoxide and of soot are used to directly convert the burning rate

measurements to the st iochimetri c heat release rate. The numerical time

integration of the stiochimetri c heat release rate with a small time

stretching parameter is used to define the burning history of the material

instead of the actual time. Next a net surface heat flux is calculated

taxing into account the convective heat flux, the flame radiative heat flux,

the cone irradiated heat flux as attenuated by the flame, the burning

surface radiance, and a constant heat flux, attributed to glowing

combustion, fitted for different cone irradiances. These surface heat fluxes

are computed in the same way as it is done in the furniture fire model. The

scaled heat release flux is computed as the stiochometri c heat release flux

divided by the calculated net surface heat flux. This scaled variable can be

thought of as the complete heat of combustion divided by the effective heat

of pyrolysis. By choosing a proper value for the constant surface heat flux,

it was found the data points of the scaled heat release flux at different

cone irradiances coalesce into a single well-behaved curve as a function of

the burn history for many materials. Now that both the vertical and the

horizontal scales for the burn rate data are in intrinsic dimensions we can interpolate and extrapolate from the scalea database for direct use in the

furniture fire model.

Similarly, the scaled fuel loss flux curve is computed as the fuel

mass loss flux divided by the same net surface heat flux as above as a fionction of the burn history, also as defined as above. The scaled fuel loss

can be thought of as the inverse of the effective heat of pyrolysis. Again, we observed a single well-behaved curve at different cone irradiances for

many materials. The combustion products mass rate likewise can be divided by

the net surface heat flux as a function of the burn history to also ootain

the combustion products in intrinsic aimensions for scaling up to the

f'urniture fire dimensions. The scaling of soot production rates is not as straight forward because the formation of soot is known to be affected by

the structure of the fire plume and by the thermal radiation intensity in

tne flame.

Since the cone calorimeter can now measure the time resolved values

of the exiting soot extinction coefficient and of the soot mass formation,

and also measure the time to ignition of the materials at different cone
I

irradi ances , means that the database for input to the furniture fire model

from the cone calorimeter and the flame spread apparatus should be

sufficient. Eventually no reliance will be made on any other material

database except for deriving and/or validating the model equations in the

furniture fire model.

The successful scaling of the cone calorimeter database and its

j] completeness and comprehensiveness had a significant effect on the

jj' modification of the bench scale data processors and of the furniture fire

llj modules in the HEMFAST code. For one thing the scaled database with their

j? intrinsic dimensions has allow us to closely coupled the solution of the

I thermal radiation field with the solution of the fuel mass loss^rates, which

directly controlls the size of the fire plume. Meanwhile it allows the

si: explicit time integration of the burn history to be done separately from the

I coupled solutions of the radiative heat fluxes, the convective heat fluxes,

I and the fuel heat release and mass loss rates.

Ill

j Code Restructuring. The HEMFAST code was restructured to improve the

numerical time integrations of virgin surface temperature, flame front

positions, and local burn history, to accomodate coupled solutions of

radiative and convective heat fluxes and the fuel heat release and mass loss

I rates, and to simplify the interfaces between the furniture fire model and

FAST. These changes were sufficient to described the restructured code as the second version of HEMFAST. This version of HEMFAST would be appropriate

( for validation with full scale furniture and room fire experiments, but it

!: would hardly accomodate the novice user. Current and future efforts with the

. second version is debugging and validating.

The time integration of the flame front positions and of the local

burn history by the Euler method so far has not show any appearance of

II instability in their solutions. Meanwhile, instability in the virgin surface

temperature predictions were noted. Since the furniture material was deduced

to behave like a thermally thin material at least during the time it takes

to ignite, the temperature solution is the integration of a first order

nonlinear differential equation with irradiant heat flux as the only input

from the other furniture fire modules. 3y considering the irradiant heat

jj flux to be a constant during a time step and linearizing the ODE, an

ji analytic solution was derived for a stabilized surface temperature

I prediction over a time step. In fact for a very large time step the

predicted surface temperature approaches the equilibrium value, which is a basis for predictors designed for stiff ODE’s. Since the FAST code has a general first order ODE solver which should be accurate and stable, it may

be worth while to incorporate it into the furniture fire model to avoid any

future problems with time integration of furniture fire variables.

i A vitally needed model equation is the functional relationship

between the exiting soot extinction coefficient and the flaming soot

absorption coefficient, which is critical in calculating the thermal

radiation field. Such a relationship has been developed for application to

r the f'urniture fire model and comparison with the data shows it has good

(j' prospects. Because Bard and Pagni reported a nearly constant soot volume

/ fraction within the solid flame and a flame temperature of 1200 °K for

: several fuels for pool fires; our- analysis of the fire pl'ume model from

' McCaffrey shows that the soot mass formation rate within the solid flame is

43
a CO ns tan*:. Tnus the amount of soot mass increases with vertical height in

the solid flame hut the air entrainment is just enough to result in a fairly

coriStant soot volume fraction.

This result seem to imply that a good approximation to the chemical

kinetics is tnat rapid soot formation occurs near 1200 °K and that the- net mass rate of soot formation is controlled by the thermal radiation from the

soot as a mechanism of thermal sinx (.rather than the heat of chemical

reaction as a thermal sink). It is also suggested the thermal radiation

field has a catalytic role in reducing the soot activation energy by photo

absorption in the fuel, thus insuring rapid soot reactions. The radiation

cooling of a newly formed soot par.ticle would tend to prevent the soot

particle from disintegrating unless the particle has passed through the

combustion zones. However, it seems just as likely that the soot particle

migrates from the soot reaction zones to the center of a burning fuel

parcel. A mechanism proposed for quenching the soot formation would be the

bursting of the burning fuel parcel by vigorous turbulent action or by

partial fuel burnout. This occurs at the top of the solid flame region,

which according to McCaffrey’s correlations correspond to the plume mass

flow rate divided by the pool fire heat release rate ratio of 0.00266 g/J.

This assumption leads to the exiting soot extinction area as proportional to

the product of the heat of combustion and the flaming soot absorption

coefficient for cor.stant flame and ambient air temperatures. Using Bard and

Pagni correlation for the flaming soot absorption coefficient and no fitting

parameters, we obtained good comparisons with the exiting soot extinction

areas obtained from the cone calorimeter database of a few furniture

materials. Complete details will be in the next yearly report and in a article submitted to a journal.

The above results on soot formation modeling were incorporated into

the second version of HEMFAST and it also had an impact on restructuring the

code. Direct calculation of the local surface convective heat transfer for

both horizontal and inclined burning surfaces were incorporated into the

second version to improve the code predictability in the early phase of the

furniture fire. All the essential physics of a furniture fire growth are now incorporated in the model. Each physical phenomena, such as tne flame spread

rate, the flame height, the soot production, the burning rate, etc are all

described with an analytical equation of approximately equal complexity. The

most complex part of the model are in the geometries of the furniture and

the fire and in the thermal radiation analysis associated with it.

Recort

1. M.A. Dietenberger , ’’Description and Results of Furniture Fire Modules

Within FAST (HEMFAST)", Interim Technical Report on NBS Grant No.

60MANBSD0557 , University of Dayton Research Institute, UDR-TR-87 -29 , Jan. 1937.
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution: Graduate School of Puoiic Health, university of Pittsburgn

Grant No.: 60NANB4D001

Grant Title: Toxicity of Plastic Combustion Products

Principal Investigator: Yves Alarie, Ph.D.

University of Pittsburgh

Pittsburgh, PA 15261

Telephone: (412) 624-3047

Other Professional Personnel : M. Schaper, Ph.D.

D. Malek (Ph.D. Student)

F. Esposito (Ph.D. Student)

NBS Scientific Officer: B. C. Levin, Ph.D.

Technical Abstract:

One of the current objectives of this project is to establish animal

models of escape performance which can be used to provide a data base suitable

for inclusion in toxic hazard analysis in fire situations. A guinea pig

ergometer has been developed for this purpose. Using this apparatus, guinea

pigs were trained to run at a constant speed. The running speed selected is

such that it resulted in an increase in oxygen uptake of three times above

baseline resting conditions. This running speed can be considered "moderate"

exercise since this level of increase in oxygen uptake is approximately one

third of the maximum oxygen uptake that guinea pigs can achieve. Each animal

is trained for several days to run at this speed for a period of at least 35

to 40 minutes prior to exposure to toxicants commonly found in smoke from

burning polymeric materials. This guinea pig ergometer is so constructed that

room air can flow through it on a continous basis. Therefore, known concentrations of toxicants can also be added to study their incapacitating effects

on running animals.

So far, the effects of two toxicants have been studied. With carbon monoxide,

incapacitation occurred at one-half the concentration and twice as fast in

running animals as in sedentary animals. With this toxicant, incapacitation

occurs in sedentary animals due to narcosis, and animals fall on their side

unconscious. The effect in running animals is quite different. Here,

incapacitation is their inability to continue to run. Although the animals

are no longer capable of running, they are still conscious and even alert

since the concentration of CO is too low to induce narcosis. Thus, they can remain alert but are incapable of muscular movement. With HCl, incapacitation

is much more dramatic than with CO. At concentrations between 550 and 600

ppm, HCl produces incapacitation of running guinea pigs within 45 sec which is

followed by death within 3 min. The animals cough, choke and they die of

suffocation. This is in contrast to the effect of this toxicant in sedentary

guinea Digs where incapacitation or death did not occur during 30 min. of

exposure at concentrations up to 1,300 ppm. Thus the guinea pig ergometer
model can be used to study the effects of two types of toxicants found in

smoke, namely the asphyxiants and the irritants. The data available from this

model will include the distances traveled prior to incapacitation and the

time-concentration relationships for incapacitation with each toxicant and

thus provide the necessary data for toxic hazard analysis in fire situations.

Reports and Papers

1. Kennah, H.E., Stock, M.F. and Alarie, Y. Toxicity of thermal

decomposition products from composites. J. Fire Sciences _5, 3-16.

2. Malek, D.E., Stock, M.F. and Alarie, Y. Performance under intoxicating

atmospheres. Fund. Appl. Toxicol. 8_, 335-345.

3. Malek, D.E. and Alarie, Y. A model for physiologic and behavioral evaluation of animal performance during toxic inhalation exposures.

Toxicologist 7., 31 (1987).

4. Esposito, F.M. and Alarie, Y. Lethal blood concentrations of cyanide and

carbon monoxide in mice following inhlation of these gases or thermal

decomposition products of polymers containing these toxicants.

Toxicologist _7, 12 (1987).

^6
POLYMER COMBUSTION RESEARCH

CENTER FOR FIRE RESEARCH

FY 87

Professional Personnel

Thomas J. Ohlemiller, Head

James E. Brown, Research Chemist

Scott Dolan, Chemist

Takashi Kashiwagi, Materials Engineer

William J. Parker, Physicist

Elizabeth Finlayson, Guest Worker

Atsumi Omori, Guest Worker

Program Objectives

(1) Improve the understanding of the chemical and physical processes which

underlie macroscopic fire phenomena. The research embraces broad areas covering both solid and gas phase processes, with particular attention

to phenomena in the solid phase such as degradation chemistry as well as heat and mass transport processes.

(2) Devise new techniques and methods for studying these phenomena.

(3) Furnish fundamental scientific information to support the other

activities within the Center for Fire Research.

Scope

Chemical and physical processes associated with ignition, flame spread and

smoldering of polymeric materials are being studied. The approach of this

group is basic and aims to understand the mechanisms of polymer degradation

(natural and synthetic polymers) , heat and mass transport processes in the

solid phase and to obtain appropriate thermal properties of the material.

Projects

Carbon Monoxide Generation from Smoldering Combustion

Smoldering combustion is responsible for a large fraction of residential fire

deaths and it appears that CO poisoning is a major underlying cause. We have

thus undertaken a program to characterize the emissions from this mode of

combustion. The initial work has focused on the smoldering of solid wood

since this dovetails with prior work for DOE. A first set of experiments has

been completed in which samples of red oak and white pine were made to undergo

self -sustained smolder under conditions of controlled air supply. Achievement

of self -sustained smolder over solid wood requires a configuration which

limits the heat loss rate from the oxidizing char surface; propagation along

the interior surface of a U-shaped channel was used here. The first results

are all for the case in which the smolder zone propagates in the same direction as the air flow along the channel. The range of air flow races for
which stable propagation is possible in the current configuration is rather

narrow -- about 8 to 22 cm/sec referred to the initial channel cross section.

Transition to flaming occurs with higher flow rates and extinction occurs with

lower flow rates. In the range of stable smolder, CO comprises 3 to 4 mole % of the exhaust gases evolved from the combustion chamber and 10 to 20 weight % of the evolved mass from the wood. Other products are also being

characterized and compared with those evolved from the same woods in other

modes of gasification. Future work includes expanding the range of

configurations for solid wood and examination of CO from the smoldering of

other residential fuels, particularly upholstery materials. Plans also

include the development of a model for the rate of evolution of CO from char

forming materials

.

Related Publications:

"Wood Gasification at Fire Level Heat Fluxes" by T. Ohlemiller, T. Kashiwagi

and K. Werner, Combust. Flame 69; 155-170 (1987)

"Effects of External Radiant Flux and Ambient Oxygen Concentration on Nonflaming Gasification Rates and Evolved Products Of White Pine" by T.

Kashiwagi, T. Ohlemiller and K. Werner, Combust. Flame 69: 331-345 (1987)

Related Grants

:

"Kinetics of Oxygen Chemisorption and Desorption of Combustion Products in

the Smoldering Combustion of Cellulosic Material", G. Richards, U. of

Montana

"A Study of the Effects of Oxygen Transport, and Temperature History on the

Chemistry of PMMA and Cellulose Pyrolysis", E. Suuberg, Brown Univ.

Mass Burning Rate and Gasification

The objective of this new project is to understand and characterize fire

plumes, the heat feedback mechanism from the plume to a burning fuel surfa.ce

and the gasification processes of burning polymeric materials. Ultimately the

aim is to develop a predictive model for the mass burning rate of polymeric

materials in a pool burning configuration by combining the above results.

This project consists of the following subsets; (1) characterization of fire

plumes and the development of theoretical models for plume properties (this is

done by Fire Growth and Extinction Group.), (2) characterization of energy

feedback rate from the plume to the fuel surface, and (3) experimental and

theoretical analysis of the gasification process of synthetic and natural

polymeric materials. The last two subsets are being addressed by the Pol}Tner

Combustion Research Group under the following headings.

48
(a) Characterization of the Energy Feedback Rate from a Fire Plume

i A new experimental setup to measure energy feedback rates from a flame to the

[' fuel surface in a pool burning configuration is being constructed. Also,

^ detailed radiation absorption-emission measurements and distribution

( measurements of key chemical species concentrations and temperature throughout

ij the plume are planned. Aliphatic and aromatic liquid fuels (some of which are

ij the monomer of vinyl polyroers) will be used. The design and most of the

j construction of the pool burning facility are completed. The installation of

j measurement devices is in progress.

I Related Grant

i

i': "Flame Radiation", Chang-Lin Tien, University of California, Berkeley.

(b) Gasification of Synthetic Polymers

Ij The rate of gasification(burning rate) is determined by the rate of energy

i feedback from a flame to a fuel surface, by the degradation chemistry, and by

I the heat and mass transport processes in the material. Therefore, the

I objective of this subset of the project is to understand the degradation

I chemistry, coupled with the heat and mass transport processes and to develop

[ theoretical models to be able to predict the gasification rate at the

|l specified rate of energy input to the material.

j| Theoretically calculated molecular weight and sample weight during the

isothermal degradation of anionically polymerized PMMA having three different

r initial molecular weights were rigorously compared with experimentally

[: determined results. In this calculation, the degradation scheme consists of

If random initiation, depropagation and termination reactions without any

transport processes. The comparison raises a question about the validity/ of

the commonly-used approximation of equal reactivity between primary polymer

I radicals and tertiary polymer radicals. A new model based on rearrangement of

the primary polymer radicals was developed and solved numerically. The

ii results indicate that molecular weights and sample weights calculated from the new model agree with the experimental results better than those calculated

from the previous model and furthermore they provide consistent values for

I

degradation kinetic constants.

In another phase of this subset, temperature distributions inside a PMMA

.1 sample near a traveling flame front were measured using holographic

: interferometry at various sample orientations, from vertical downward to

'r vertical upward. Streamwise and normal to streamwise heat flux distributions

.j and heat flow vectors in the sample were calculated from the temperature

i! distributions. It was found that the contribution of streamwise heat

(i: conduction through the sample to flame spreading decreases with increase in

Ml inclination angle from vertically downward through horizontal angle to

vertical upward angle. The same technique was applied to measure timewise

temperature distributions inside a fused silica sample (first step toward a

f! polymer sample) at four different external radiant fluxes. Two theoretical

I

models were developed to calculate temperature distribution of a diathermic

material. The first model is a rigorous model based on an integraldifferential equation for radiative and conductive heat transfer (including

49
internal reradiation) and the second model approximately calculates

reradiation in the sample. The results of the first model agree with the

experimental data within 4“C through the sample, except near the backside of

the sample. The results of the second model tend to overestimate at most 4‘’C

over that of the first model.

Related Publications:

"Effects of Weak Linkages on Thermal and Oxidative Degradation of Poly(methyl

methacrylate)” by Kashiwagi, T. , Inaba, A., Brown, J.E., Hatada, K. , Kitayama,

T. , and Masuda, E. , Macromolecviles , 19, 2160 (1986).

"A Calculation of Thermal Degradation Initiated by Random Scission. 1 Steady

State Radical Concentration”, by Inaba, A., and Kashiwagi, T. , Macromolecules,

19, 2412 (1986).

"A Calculation of Thermal Degradation Initiated by Random Scission. Unsteady

Radical Concentration" by Inaba, A., and Kashiwagi, T. , European Polymer

Journal (in press).

"Effects of Initial Molecular Weight on Thermal Degradation of Poly(methyl

methacrylate) - Model 1” by Inaba, A., Kashiwagi, T. , and Brown, J.E., Jotimal

of Polymer degradation and Stability (submitted).

"A Measurement Technique for Determining the Temperature Distribution in a Transparent Solid Using Holographic Interferometry" by Ito, A., and Kashiwagi,

T. , Applied Optics, 26, 954 (1987).

"Characterization of Flame Spread over PMMA Using Holographic Interferometry - Sample Orientation Effects" by Ito, A., and Kashiwagi, T. Combustion and Flame

( in press )

.

R.elated Grants:

1. "Thermal Stabilization of Polymers by Cross-Link Formation", C. Wilkie,

Marquette University.

2. "Mechanisms of Action of Metallic Smoke Suppressants and Fire Retardants

for Poly(vinyl chlorid" , W. Stones, Polytechnic University.

3. "Interaction of Radiation and Conduction in Polymeric Materials", W. Aung,

Howard University.

(c) Rate of Heat Release from Wood

In order to understand and predict the heat release rate, flame spread rate

and charring rate of char forming materials, it is necessary to be able to

predict their mass burning rate. A model has been under development for the

prediction of the mass burning rate and heat release race of wood as function

of the incident radiant flux, thickness, moisture content, rear surface

boundary conditions and the thermophysical and thermochemical properties. The

thermophysical properties include the density/, thermal conductivity and

specific heat. The chermochemical properties include the heat of combustion of

50
the volatiles, the heat of pyrolysis and the kinetic parameters which describe

the rate of mass loss. These properties are taken to be a function of the

temperature and the residual mass fraction. The thermochemical properties

must be determined separately for all of the major chemical components of the

wood. A critical element in the model development is the determination of the

required material properties so that the predictions can be compared with

measurements in the Cone calorimeter.

During this past year the concentration has been on the determination of the

thermophysical properties up to 550° C and their incorporation into the model

along with the thermochemical properties that were measured earlier on this

project. In particular a method for measuring the thermal diffusivity of wood

char has been devised. The thermal diffusivity of Douglas fir and its char

was found to have a relatively constant value of about 2.1 m^/s x 10"^ °p to a temperature of 550° C for mass retention fractions above 0.30. The comparison

of the predictions of the model with measurements on instrumented specimens in

the Cone calorimeter have been encouraging. At 25 kW/m^ the overall agreement

with the heat release rate is within 20 percent over most of the burning time.

For the higher incident heat fluxes the time scale of the calculated heat

release rate curves become progressively longer than the measured ones. The

reason for these differences may be due to the lack of property data above

600° C. Some measurements are presently being made to overcome this

deficiency

The measurement of the required property data for every type of wood would be

a tedious process. However, all woods are, to a reasonable degree of

approximation, made up of some combination of a small number of chemical

components in different proportions and the thermal conductivity of wood, at

'least near room temperature, is a well known function of the density.

Therefore, the possibility exists for predicting the required properties of

the wood and their temperature and residual mass fraction dependence from a small set of more easily determined parameters such as the density and the

chemical composition. Thus future research on this project will include the

development of models for the properties themselves. Since wood is a very

complex material, this can only be done in an approximate way, but it may be

adequate for fire modeling purposes.

Due to a project on the heat release rate of aircraft cabin materials soon to

be initiated for the FAA the present work on wood will be extended to

composites including honeycomb materials.

Related Publications:

Parker, W.J., "Prediction of the Heat Release Rate of Wood", Proceedings of

the First International Symposium on Fire Safety Science, Hemisphere

Publishing Corporation, 1986, pp 207-216.

Parker, W.J., "Determination of the Input Data on a Model of the Heat Release

Rate of Wood," International Symposium on Mathematical Modeling of Fires and

Related Test Methods, Sponsored by ASTM, New Orleans, Dec 1986.

Parker, W.J., "Determination of the Kinetic Parameters and the Heat of

Combustion of the Volatiles for Wood," (presented at the UJNR Panel on Fire

Research and Safety, May 1987)

51
Hi

fd arker, W.J., "Prediction of the Heat Release Rate of Douglas Fir," (submitted

or presentation at the Second International Symposium on Fire Safety Science

in 1988)

.

Parker, W.J. and LeVan, S.L. , "Kinetic Properties of the Components of Douglas

Fir and the Heat of Combustion of their Volatile Combustion Products ,"* (to be

submitted to Wood Fiber Science)

.
POLYMER COMBUSTION RESEARCH GRANTS
I.,

.

,V<X "':

%''
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : Brown University

Grant No.: 60NANB4D0036

t Grant Title: A Study of the Effects of Oxygen Transport and Temperature History

j[l On the Chemistry of PMMA and Cellulose Pyrolysis

I

j:l Principal Investigator: Professor Eric M Suuberg

P Division of Engineering

I Brown University

I Box D

? Providence, Rhode Island 02912

1; Telephone: (401) 863-1420

Other Professional Personnel: Viraf Dalai, Postdoctoral Assistant

p William Lilly, Research Engineer

r;; NBS Scientific Officer: Dr. Takashi Kashiwagi

li: Technical Abstract:

0

si; Introduction: The goal of this project is an elucidation of the effect of several

^ key variables on the chemistry of pyrolysis of polymethyl methacrylate (PMMA) and

j. cellulose. These variables include the heating rate of the sample, the partial pressure

h of oxygen at the surface of the sample, and sample characteristics as affect the

U transport of pyrolysis products out of the sample. Detailed product analysis of both

j>| vapor and condensed phase products of pyrolysis are used to infer under what

pi conditions already established or suggested chemical mechanisms may or may not be

applied to fire modeling situations. In the case of PMMA, vapor products mainly

i' consist of monomer. The condensed phase products are characterized by gel

; permentation chromatography (GPC), providing information concerning the degree of

! polymerization as a function of cited variables. The analysis of vapor and liquid

products of cellulose pyrolysis is somewhat more complex. Particular attention will

i| be given to characterization of what are commonly called "tar" products, since these

j are the products that represent the most combustible vapor products. GPC is being

. used to characterize these materials, providing information about molecular weight

(distributions and hence, vapor pressures of the products.

This project is presently at the midpoint of its third year. The initial focus

? was the pyrolysis of PMMA and the effects of heating rate and oxygen partial

' pressure on observed kinetics.

These results were reported on last year and the following conclusions drawn:

1. Heating rate was not important in determining the kinetics of PMMA

degradation in the range 5K/min to 1000 K/min.

2. Oxygen affects the kinetics of PMMA degradation only at low heating rates

(5 K/min). At 100 K/min heating rates, the relevant kinetics are the same

as in inert gas.

: 54 I

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The remainder of this report will focus on similar issues in cellulose pyrolysis.

Experimental

Pvrolvsis Experiments

All pyrolysis experiments were carried out in a heated wire mesh reactor.

Samples are heated in a wire gauze which is stretched between two electrodes. The

reactor shell was designed for near atmospheric pressure and vacuum work. It consisted of a stainless steel cone with a narrow neck (a modified funnel). The base

of the funnel was about 20 cm in diameter and was sealed with a flange containing

various feedthrough for the electrodes and for gases. The cone was about 15 cm

high and had a neck of 2.54 cm in diameter. The conical shape facilitates collection

of condensible products of pyrolysis, not discussed in this paper. The large volume

of the reactor ensures that gaseous products of pyrolysis are dilute and can quickly

escape the hot region in the reactor, and thus are quenched.

Cellulose from two different sources was examined and showed no difference in

behavior. The first was Whatman cellulose powder CFll, medium length fibers

(ash content 0.015 wt %). The diameter of the fibers was typically 10 to 30^m. As an

alternative to the powder, cellulose samples were also cut from an acid washed filter

paper (MunktelTs OK/S2-80-200) which had an average ash content of 0.007%. These

papers had a thickness of 168 ± 8ixm, and thus were an order of magnitude thicker

than the powder, in smallest sample dimension. Nevertheless, there was little significant difference between the behaviors of the powder and paper during

pyrolysis, so the majority of results reported here are for the paper samples. For most

experiments, paper samples were cut into a rectangular shape (approximately 2 cm x

1 cm, and mass less than 20 mg). They were placed in a folded strip of 400 mesh

stainless steel screen positioned between two relatively massive aluminum electrodes.

In the experiments performed thus far, the pyrolysis was carried out under (1) a pure

helium atmosphere, (2) air, or (3) a mixture of 1% oxygen in helium. It has been

verified by chromatographic analysis, that in the experiments in "pure" helium, the

oxygen level in the vessel is about 10 ppm.

The temperature history of the samples (actually, the mesh) was controlled

through a thermocouple sensor signal which was fed into a control computer.

Calibration of the thermocouples assured a temperature measurement uncertainty of

not more than about 5K.

The total mass loss during pyrolysis was determined as the difference between

the mass of the mesh plus sample before and after heating. Thus, one experiment

could lead to only one single mass loss datum, compared to TGA-type analysis which

yields a continuous record of mass vs temperature (or time). This makes the

experimental procedure for determining reaction kinetics rather tedious compared to other methods. However, the advantage of the present method is almost unlimited

control of heating rate, not available in thermogravimetric analysis techniques.

Results and Discussion

The data for mass loss in inert gas are shown in Figure 1, for three different

heating rates--5 K/min, 100 K/min, and 1000 K/min. Again, each datum represents

the mass loss from one experiment in which the sample was heated at the indicated

rate to the indicated temperature, and then immediately permitted to cool at a rate of between 200 and 300 K/s. Also shown on Figure 1 are calculated kinetic curves.
The assumed model is based on a single, simple first order process:

dMp/dt = kQexp(-E/RT)Mp

Where Mp is the mass of pyrolyzable material left at any time t, is the

Arrhenius pre-exponential, E is the activation energy, R the universal gas constant,

and T is temperature. If the initial mass of the pyrolyzable fraction is (fM^), then

the above may be integrated using well known approximations for linear heating and

cooling rates, to give

M/M, = f^exp|- (ko RT^EKl/mij + 1/m^) exp(-E/RT)| + ( 1-0

where M is the remaining mass of cellulose, M = M^ + Mp, where M^ is the char

forming fraction = [1-OM^, m^ is the heating rate and m^ is the cooling rate of the

sample.

While obviously the approximation of the very complex mechanism of cellulose

pyrolysis by a single first order rate law is quite crude, the excellent fit achieved

with quite a narrow range of k^ and E values over a range of heating rates of 5 to 1000 K/min is surprising. Figure 1 shows a comparison of the calculated and

measured mass losses using k^ = 6.79 x 10® and E = 33.4 kcal/mol, as suggested

earlier by Lewellen et al. at based on experiments performed at heating rates of 400 K/s. The fact that constant kinetic parameters apply reasonably well

irrespective of variations of the heating rate over many orders of magnitude suggests

that despite the crudeness of the model, it may indeed be reflecting a basic,

fundamental, rate controlling step. The poorest fit is seen at 5 K/min heating rate, at which the pseudo constant kinetic parameters underpredict rate. This is, on the

surface, not particularly surprising in light of the generally accepted view that the

decomposition can proceed along two competitive pathways--a low temperature

mechanism dominated by dehydration reactions and a high temperature mechanism

dominated by depolymerization. However, the fact that the char yield is about the

same regardless of heating rate is inconsistent with that sort of mechanistic

explanation, since the dehydration route should lead to higher char yields; f seems to be about 0.9 in all cases.

Certainly for any fire modeling it appears that the use of kinetics of mass loss

that are independent of heating rate seems reasonable (at least when oxygen is excluded from the surface, and mass transfer of products from the pyrolyzing zone is fast). There remains a question of what value to use for f, the fraction of char

formed. It has been shown previously that f is somewhat sensitive to heating rate. Here, we have observed no such heating rate dependence, and f is taken as constant.

It would, of course, be expected that the composition of the starting cellulose,

particularly with respect to catalytic inorganic matter, will affect f. As has earlier

been pointed out, the ease of mass transfer of decomposition products from the

surface will also affect char yields.

Figure 2 shows similar data to those shown in Figure 1, but obtained in air. Comparison of these data with the curves from Figure 1 shows that (1) at 5 K/min,

air does significantly accelerate the rate of decomposition, over that in inert gas; (2) at 100 K/min, air accelerates the rate only at higher extents of conversion; and (3) at 1000 K/min, the rates in inert gas and helium are virtually identical.

Figure 3 shows that small amounts of oxygen in inert gas (1%) have an effect

56
.1 which is comparable to that of air. Thus, the oxygen partial pressure dependence of

rate of decomposition (at low heating rates) is quite significant.

' Conclusions

- Variations in heating rates from 5 K/min to 400 K./sec have a negligible effect on the global kinetics of weight loss during cellulose pyrolysis in inert gas.

- Oxygen catalyzes decomposition (or more precisely, weight loss) at heating rates of 100 K/min and below, but not at 1000 K/min.

I Reports and Papers

i 1. "A Study on the Effects of Heating Rate and Ambient Oxygen on the Global

I Rates of Cellulose Pyrolysis," submitted to the Eastern Section of The Combustion

Institute. E. M. Suuberg and V. F. Dalai.

JOO »O0 7 00 000 TEMPERATURE (1C)

»uo TKMHLRATUkt !IU
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY87

Institution: Howard University

Grant No.

:

70NANB5H0529

Grant Title: Interaction of Radiation and

Conduction in Polymeric Materials

Principal Investigator : Dr. Win Aung (Adjunct Professor)

Mechanical Engineering Department

Howard University

Washington, DC 20059

Other Professional Personnel : Elizabeth Upson Finlayson

( Guest Worker

)

Hamid Moghadam ( Guest Worker

)

NBS Scientific Officer: Dr. Takashi Kashiwagi

Technical Abstract : The objective of this combined theoretical and experimental

study is to obtain a fundamental understanding of the transient

heating process for polymeric materials. Such an undersatnding

is necessary in order to describe the pre-ignition heating

mechanisms of semitransparent solids. In the course of the

present study, a numerical model has become available that is

capable of predicting the temperature profiles in a solid heated

by a high temperature radiation source. The model accounts for

combined radiation and conduction, and is formulated in nondimensional terms [1, 2].

During the past year, efforts were concentrated on the

verification of the numerical scheme through comparison with

experimental measurements, and on documentation of a user's guide

for the computer code. The latter is described in [3]

.

Experimental verification was carried out by measurements on

fused silica samples by means of holographic interferometry. The

experimental data were compared with those obtained theoretically

by specializing the model to the physical situation.

The solid considered is a plane, one-dimensional solid.

Thermal radiation from a graphite plate, modelling the thermal

energy emitted by a fire, strikes one face of the plane solid at

normal incidence. The flux from the external source has a spectral distribution consistent with Planck's law. Convection

heat transfer from the faces of the solid is computed using the

usual correlation for laminar free convection heat transfer from

a vertical plate. The solid is homogeneous, and hence scattering

of radiation is negligible. The reflection of radiation at the

58
I

air-solid interfaces is assumed to be purely specular. A portion

'i is the incoming radiation is at wavelength bands over which the

^ solid is opaque; this flux is absorbed at the surface. Radiative

i; energy in the wavelength range in which the solid is

^semitransparent is in part absorbed within the solid and the rest

Lis transmitted through the solid with no interaction.

t

i In the theoretical model, a numerical method is employed to

i‘ I solve the unsteady form of the energy equation using an implicit

(finite difference scheme. The solution to the equation of

\ radiative transfer is divided into two contributions. The

[ [Contribution from the external source is calculated once and is a

1 (Constant function of the spatial variable. The contribution from

i||the internally emitted flux must be recalculated for each

temperature profile. Thus, there is a nonlinear coupling between

I lithe energy equation and the equation of transfer. In the

.(solution procedure, an iterative method is employed in which the

^temperature distribution at any time step is used to solve the

.(equation of transfer. The resultant flux distribution is

: (substituted into the energy equation to obtain a new temperature

.[(profile. The new temperature profile is again used to obtain an

updated expression for the radiative transfer, with which a new

I I temperature field can again be ascertained. The process

icontinues until the temperature distributions from successive

nUterations meet a predetermined convergence criterion.

[Convergence is aided by the Newton-Raphson method.

' Solutions for the above model, called the "hot model" since

it incorporates internal re-radiation, are obtained using the

: Cyber 205. When re-radiation is ignored, the model is known as

(the "cold model", and here the problem becomes a decoupled,

!, linear problem. Results for the latter model can be readily

i obtained using a small computer.

Consideration has been given to several factors that can

influence the response of fused silica to heating. The first

factor is the temperature dependence of the material physical

properties. A linear variation with temperature of the thermal

'conductivity and specific heat is considered. This

ie ^representation is in agreement with the behavior of fused silica

over the temperature range of interest.

j le ! The second governing factor is the spectral dependence of

,y the physical properties. Data for the spectral variation of the

(absorption coefficient of fused silica are obtained by infrared

[spectroscopy. The spectral dependence of the index of refraction

lis obtained from manufacturers' data which are supplemented by

additional data obtained during a previous NBS study. The

material is assumed specularly reflecting, and spectral values of

the reflectivity are calculated from the refractive index using

lithe Fresnel equations. Owing to the lack of information, the

ithermal dependence of these properties is not considered.

ii

1

1

ig

I In many theoretical studies conducted date on combined

I

Ii

59
radiation and conduction, the authors have posed the problem in

terms of frequency. This simplifies the analysis because the

frequency of thermal radiation, an electromagnetic phenomenon,

remains unchanged when passing through materials of different

indices of refraction. We have chosen to formulate our problem

in terms of the wavelength. Care has been taken to match the

spectral variation of optical properties measured corresponding

to radiation emitted into air with the internal radiation emitted

into a solid whose index of refraction is typically not equal to

unity.

Traditionally, the spectral variation of the optical

properties is treated using a rectangular band model. This

method divides the spectrum of thermal radiation into regions

over which the optical properties are considered constant. The

result is therefore a summation of gray solutions. It was

desired to develop a method that would more accurately account

for the spectral dependence of the optical properties. This

variation was considered to be especially important in regard to

the external flux. Originating at 1300 K, the magnitude of this

flux varies greatly over the spectral range. Thus, the solution

to the equation of transfer for the external contribution was

integrated using 800 intervals in the wavelength range 2-10

microns. The internally radiated flux is emitted by a lower

temperature body (at roughly 400 K). The magnitude of this flux

is a much flatter function of the wavelength. A rectangular band

model is used to model this flux.

Typical dimensionless temperature distributions as a

function of the dimensionless distance have been obtained. The

effect of optical length has been investigated, as are the

effects of the temperature dependence of the thermal conductivity

and specific heat. Discussion of these results may be found in

[ 2 ] . Typical results showing comparisons between the theoretical

results and the measurements for fused silica are given in Fig.

1 . The agreement between prediction and experiments is

encouraging, with the re-radiating model showing better agreement

with the measurement. The better agreement, however, is obtained

at the expense of a significant increase in computer time. The

use of numerical integration for the external flux leads to an

improvement of the results by a maximum of 2 K. The experimental

uncertainty is one fringe line, equal to- approximately 3 K.

Papers and Reports :

1. Win Aung, E.U. Finlayson, T. Kashiwagi, "Interaction of

Radiation and Conduction in Polymeric Materials, " Summaries of

Center for Fire Research Grants and In-House Proqrams-1986 , U.S.

Department of Commerce, National Bureau of Standards,

Gaithersburg, MD, September, 1986, pp. 124-127.

2. E.U. Finlayson, W. Aung, and T. Kashiwagi, "Theoretical

60
Models for Combined Radiation-Conduction in Polymeric Solids

Heated by External Radiative Flux,'" Proceedings of 1987 ASME-JSME

Thermal Engineering Joint Conference , ASME, New York, N.Y., ed.

P.J. Marto and I. Tanasawa, Vol. 1, pp. 427-432.

3. H. Moghadam, E. Finlayson, and W. Aung, "User's Guide to

CONRAD Program," Technical Report ME/TR-87-1, Howard University,

Department of Mechanical Engineering, Washington, DC, August 15,

1987.

FUSED SILICA - COMPARISON OF PROFILES AT LATER TIME

FIGURE 1

61
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : Grant No. : Title : Principal Investigator:

Marquette University

60NANB6D0602

Stabilization of Polymers by Cross-Link Formation

Charles A. Wilkie

Department of Chemistry

Marquette University

Milwaukee, WI 53233

Telephone (414) 224-7239

Other Professional Personnel : S. J. Sirdesai, Postdoctoral Fellow

T. Suebsaeng, Graduate Assistant

B. Chang, Graduate Assistant

NBS Scientific Officer: James Brown

Technical Abstract:

Introduction. The objective of this research program is to understand the

chemical basis of pyrolysis reactions of polymers and to use this information to

develop suitable schemes for cross-linking of polymers to produce intractable chars.

The production of char does not proceed spontaneously, rather additives are required in order to promote these reactions. Each polymer has a unique set of

requirements for the cross-linking reactions, these must be elucidated for the

polymers in question. The polymers that are addressed in this research are poly(methyl methacrylate) (PMMA) and poiy(ethylene terephthalate) (PET).

PMMA. The pendant groups on the PMMA chain provide a convenient site for

cross-linking reactions. If these esters can be converted to a more reactive

functionality then they may undergo reaction with each other and lead to crosslinking. Two approaches may be identified for this reaction: 1) Conversion of the

ester to an anhydride linkage and 2) oxidative addition of a metallic compound to

the ester and subsequent coupling of this metal compound.

We have found that it is possible to convert the ester to an anhydride by

reaction with a strong acid. The reaction is presumed to proceed by the

intermediate formation of a carboxylic acid followed by dehydration of a pair of

acid moieties to produce anhydrides. This anhydride forming reaction could occur

between adjacent pairs of esters, between pairs within the same polymer strand or between pairs in different chains. Only the last reaction leads to true crosslinking, however the other reactions do provide some increase in thermal stability

since a second bond must be broken in order to produce monomer. It is well-known

that the formation of anhydride increases the glass transition temperature of PMMA.

Since It Is established that Wilkinson’s salt, Rh(PPh2

) 3

CI, reacts with the

carbonyl moiety in acyl halides, we have chosen to examine the reaction of this

compound with PMMA. This reaction proceeds by an oxidative addition of the

rhodium species to a C-0 bond of the ester to give a transitory rhodium species.

Coupling of this rhodium species results in the elimination of various organorhodium

compounds with the concomitant formation of anhydrides. As above, we observe

anhydride formation within the same polymer chain and between polymer chains.

Progress to Date

62
The reaction is presented in Scheme 1. The oxygen index is measured at 20, for

PMMA the oxygen index is near 14 (bottom ignition). The glass transition

temperature has increased by 14°C and approximately 25% of the material is nonvolatile at 600°C. It is unlikely that this compound will ever be used as a flame

retardant due to cost, color and toxicity. The value of the investigation lies in the

ability to identify other materials that may undergo similar reactions and that do

not have the same liabilities.

-CH.

CH,

I j

I c=o

I OCH

3

ClRh(PPh2)3

>

CH.

- C

c I c=o ClyRh(PPh3)^

OCH.,

CH.,

•CH, - C-^

c=o ClyRh(PPh3)^

CH.,

•CH

CH,

I J

i c=o

I ClyRh ( PPh

OCH3

CH.

3^x

CH, - C

c Ic=o

I 0

ClyRh(PPh,)

CH.

3^x

CH.

CH,

I J

c=o

I 0

I c=o

CH,-C''-"-^

C- I CH3

ClyRh(PPh3)^ OCH3

ClyRh(PPh3)^

CH3

SCHEME 1
PET. Unlike PMMA, PET offers no pendant groups as sites for cross-linking

reactions. It is necessary either to use an additive to participate in this reaction

or to make use of the initial decomposition reaction. We have chosen to utilize the

vinyl ester that is produced in the initial step of PET decomposition as a reactive

intermediate to promote cross-linking of the polymer. Scheme 2 presents a series

of reactions that we believe are operative in the cross-linking and flame retardation

of PET. There are four steps in this reaction scheme. In the first step the vinyl

ester is produced, this undergoes vinyl polymerization in the second step. The third

step is chain-stripping of this polymer and, in the last step, this polyene cyclizes to

produce the final cross-linked char.

SCHEME 2

0 CH ,C H,0

COCH=CH,

-CH-CH,- -CH=CH-CH=CH0

1 c=o

/

64
We have investigated the formation of the vinyl ester, its polymerization and

the subsequent chain-stripping reaction. The decomposition of PET is promoted

both by red phosphorus and zinc chloride. This -vinyl ester immediately

participates in the subsequent reactions and it is impossible to study this reaction

in isolation from the other steps. The use of vinyl methyl terephthalate as a mode!

of PET allows the study of the second and third reactions. At 250°C vinyl methyl

terephthalate produces only polymer, at higher temperature the chain-stripping

reaction also occurs. We have polymerized this vinyl species using conventional

techniques at modest temperatures and have studied the chain-stripping reaction by

the use of this polymer. It appears that the production of the vinyl ester and its

subsequent polymerization are the most critical steps in the process, the last two

reactions *iikely will proceed under thermal conditions from the vinyl polymer.

There are rigid temperature requirements on the production of the vinyl ester.

Suitable additives must be identified that will allow this reaction to proceed at a temperature only a little above the normal processing temperature of PET. Work

continues on ail aspects of the reaction scheme.

In a separate investigation we have examined the reaction of PET with

triphenylphosphine. This reaction proceeds by the formation of a zwitterionic

intermediate which produces a phosphonium ylid. This ylid then attacks another

molecule with the production of triphenylphosphine oxide and ethylene. All flame

retardant activity of triphenylphosphine may be attributed to the formation of

triphenylphosphine oxide, the co-production of ethylene renders triphenylphosphine a

less-effective retardant than is triphenylphosphine oxide.

This investigation will lead to additives that will significantly Increase the

thermal decomposition temperature of the target polymers. It is not possible to

render polymers totally non-flammable but it is feasible to change the nature of the

polymer, in the presence of a suitable additive and by the application of heat, to

require much greater thermal input to cause burning. This would remove the fuel

for the flame and eliminate the possibility of combustion.

Reports and Papers

1. S. Sirdesai and C. A. Wilkie, "RhCI(PPh3

)o: A Flame Retardant for

Foly(Methyl Methacrylate)", presented at the American Chemical Society

Meeting, Denver, CO, April, 1987, POLY 097.

2. T. Suebsaeng, C. A. Wilkie, and C. E. Brown, "Flame Retardant Chemistry.

The Reaction of Triphenylphosphine with Poly(Ethylene Terephthalate",

submitted for publication.

3. S. Sirdesai and C. A. Wilkie, "Wilkinson’s Salt: A Flame Retardant for

Poly(Methyl Methacrylate)", submitted for publication.

4. S. Sirdesai and C. A. Wilkie, "A Mechanistic Study of the Reaction of

RhCl(PPh3)3 and Poly(Methyl Methacrylate)", manuscript in preparation.

65
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87 -

Institution s Grant No. ; Grant Title s

Principal Investigator s

Other Professional Personnel

s

Polytechnic University

6onanb6do647

Mechanisms of Action of

Metallic Smoke Suppressants

and Fire Retardants for

Poly (vinyl chloride)

Professor W. H. Starnes, Jr.

Head, Department of Chemistry

and Life Sciences

Polytechnic University

333 Jay Street

Brooklyn, NY 11201

C.-H. Oliver Huang, Predoctoral

Scholar

N3S Scientific Officers Dr. Thomas Ohlerailler

Technical Abstract s

j

1 Introduction . This research is directed toward the elu- ! cidation of the mechanisms of action, at the molecular level, of I certain metal-containing smoke suppressants and/or fire retardants i for poly(vinyl chloride) (PVC). Our initial studies, s\immarized | here, have been concerned with substances containing copper. Such

materials are of particular interest because copper compounds, as

a group, probably are the most effective metal-based PVC smoke

suppressants that have been discovered to date.^ Cur investigative procedure involves detailed studies of the products (and, ; subsequently, the rates) of reactions between copper species and

simple organic compounds that are models for structural segments

of virgin PVC or PVC that has been degraded thermally. Similar

investigations carried out earlier with the additive, Mo03 ,^*-^

have shown that this approach is capable of providing remarkable

amounts of information about the mechanistic chemistry that operates in PVC itself. The present work will provide basic facts

that should facilitate the design of improved smoke suppressants | and/or fire retardants for this very useful polymer.

J. Kroenke, J. Apnl. Polym. Sci. 26, 1167 (1981)*

2

V/. H. Starnes, Jr., L. D. IVesco-^t, Jr., 'J. D. Reents, Jr., R. E.

Cais, G. M. Villacorta, I. M. Plitz, and L. J. Anthony, in

"Polymer Additives"; J. E. Kresta, Ed.; Plenum; New York, IpS^; ! ?. 237.

'L. 1. Nescott, Jr., '.V. H. Starnes, Jr., A. M. Mujsce, and r. A.

t J. Anal. Aool. Pyrol. 3, 163 (1925)*
Results and Discussion . Reactions with model compounds

were carried out in sealed tubes under anaerobic conditions using

(w/v) of metallic additive. Product mixtures were analysed

by gas chromatography and IR spectroscopy.

(a) Gis-trans Isomerization . In partially dehydrochlorinated PVC, conversion of cis alkenes into trans alkenes would

prevent the formation of benzene, which is a major source of

smoke and flame under low-enthalpy- input conditions. 2 We find

that CuClp# CuCl, CuO, and CU2O do not catalyze the isomerization

of cis-5~aecene into trans- 5-aecene during 60 min of heating at

350 ^C. However, the isomerization is catalyzed by MoO^ under

these conditions (though not at 250 oc)2 and by MoOpCl^'^at a

temperature of only 100 °C. ^ d

(b) Dehydrochlorination . In the case of PVC, this process

produces polyene sequences that can lead to crosslinking via alkylation reactions and intermolecular Diels-Alder cyclisations.

Crosslinking prevents the formation of volatile species that are

sources of flame and smoke. 'T’herefore, dehydrochlorination catalysis might lead indirectly to fire retardance and smoke suppression. We have examined the effects of various copper species

on the dehydrochlorination of 3-chloropentane and 7-chlorotridecane, and we have compared these effects with those produced by

1^003 and Mo02C1^. Conditions for the gc analyses were optimized

very carefully in order to prevent dehydrochlorination of the

substrates while these analyses were being performed.

In reactions carried out with 3-chloropentane at 200 °C

for 10 min, the following dehydrochlorination percentages were

determined from several replicate runs: no additive, ca. 0; CuCl,

ca. 0; Cu, 1. 3-1.8? CU2O, 1.6-2. 1; CuCl2» ^.^-6.3; CuO, 6. 2-9. 2;

MoOo, (ca. 0)-8,7; Mo02Cl2t ca. 40. In similar experiments performed with 7-chi orotridecane at 200 oc for 60 min, the extents

of dehydrochlorination were much greater, qualitatively (ranging

up to ca. 50/^) » when the copper additives (including CuCl) were

used, as compared to ca. kfo of dehydrochlorination when no additive was present. However, the quantitative reproducibilities

of the 7-chlorotridecane data were not satisfactory, apparently

owing to the heterogeneity of the reaction mixtures. By way of

contrast, in parallel experiments with 7-chlorotridecane at 200

^C for 60 min, 1.1003 and M0O2CI2 gave very complex mixtures containing both lighT (cracking) and heavy (condensation/oligomerizaticn) products, as expected.^

(c) Alkylation . In thermally degrading^ PVC , polyene alkylation by alkyl chloride or allyl chloride moie'^ies would lead

to crosslink formation. In order to investigate •’•he ca-f-alysis of

alkylation in a more ’rac^able sys*''em, we have examined the effects of metal species on the Priedel-Crafts alkylation of benzene by 3-chloropentane or 7-chlorotridecane.

In a representative series of runs carried out with 3:1

(v/v) benzene ; 7-chlorotridecane mixtures at 255 ^cr 30 min,

67
dehydrochlorination of the alkyl chloride was the only reaction observed in the presence of^CuCl 2 . CuCl, CuO, CU2 O, or Cu. On

the other hand, under identical conditions, M0 O 3 and MoOpClo oro- duced a mixture of tridecylbenzenes (at least four isomers) in

total yields of about 60-65/^, based upon the starting amounts of 7“Chlorotridecane . Analogous results were obtained in experi- ments performed with (v/v) benzene

:

3 ~chloropentane mixtures

at 200 C for 60 minj i,. e. , only dehydrochlorination was observed with CuCl 2 » CuCl, CuO, CU2O, or Cu, while good- yields of pentyl- benzenes were produced when MoO^ or M0 O

2CI 2 was used.

(d) Reductive Coupling. Crosslinking via reductive coup- ling (equation 1 ) has been suggested to be a possible means of

2RC1 + 2M"^^ > R-R + 2M'^^'^^C1 (1)

(RCl = PVC; M = a metal ion)

smoke suppression in PVC formulations containing certain metal

species. j However, in keeping with earlier findings for M0 O

3 and

Mo02Cl 2 »^ we have observed no reductive coupling products in any

of our experiments (see above) with alkyl chlorides and copper

additives.

(e) Cracking . Model-compound experiments (see part b,

above, and reference 2 ) have strongly suggested that metal-catalyzed cationic cracking of the char into volatile products is

responsible, at least in part, for the accelerated flame spread

observed at very high temperatures with PVC formulations containing M0 O3

. In similar high-temperature experiments with CuCl 2

t CuCl, CuO, CU2 O, and Cu, we now have found that all of these substances are much less effective as cracking catalysts •'han the

M0O 2CI 2 which is formed situ from M0 O3 and alkyl chlorides.

^en after 60 min at 350 OC, orJLy minor amounts of cracking have

been observed with the copper species and cis- 5 -decene , for example. Interestingly, CU 2 O did cause some cracking of 7-chlorotridecane at 250 °C, but the total yield of cracking products

was much less than those obtained in parallel experiments with

MoO^ or M0 O

2

CI

2

. Conclusions . Our findings lead us to conclude that the

copper additives we have studied are relatively weak Lewis acids.

Under the conditions of our experiments, they did not catalyze

cis - trans isomerization, alkylation, or reductive coupling, and

only one of them (CU 2O) had any significant activity as a cracking catalyst. However, they did accelerate the dehydrochlorination of simple sec -alkyl chlorides. Such acceleration would increase the rate of crosslinking in the case of PVC itself. Thus

the dehydrochlorination catalysis could lead to smoke suppression

with the polymer, and the absence of cracking produces also would

be beneficial in this regard. What remains to be decidea is

?. Lattimer and J. Kroenke, J. Arnl. Polym. Sci. 26, 1191

( 1981 ).

68
whether these effects are sufficient to account for the smokesuppression activity of typical copper additives. Our investigations of this problem are continuing.

Report i

W. H. Starnes f Jr. i "Mechanisms of Action of Metallic Smoke Sup

pressants and Fire Retardants for PVCs Current Status," Gordon

Conference on Analytical Pyrolysis, Plymouth, NK ( 1987 ).

o

69
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution: Grant No. : Grant Title :

Principal Investigator:

Other Professional Personnel:

NBS Scientific Officer:

University of California - Berkeley

60NANB4D0018

Flame Radiation

Professor Chang-Lin Tien

Department of Mechanical Engineering

University of California

Berkeley, California 94720

Telephone: (415) 642-0877

AJ. Stretton, Ph.D. smdent

S. Kumar, Ph.D. student

S.H. Park, Ph.D. student

A. Tuntomo, M.S. student

Dr. Takashi Kashiwagi

Technical .Abstract:

Introduction. The objective of this research is to develop a simplified methodology of calculating radiation heat transfer in moderate to large-scale fires, while retaining the fundamental physical framework of the problem. From the careful experimental investigation and theoretical analysis,

convenient and useful calculational methods are established for applications. During the past year, three primary topics were studied: (1) experimental and theoretical determination of the infrared

absorption properties of several hydrocarbon gases which are major pyrolysis products of PMMA;

(2) development of a simple method to calculate thermal radiation in pool fires and plumes; and (3)

theoretical investigation into the radiative properties of agglomerated soot particulate.

Radiation Properties of Hydrocarbon Gases. The infrared absorption properties of hydrocarbon gases evolved from the degradation of burning condensed fuels are important in determining

the characteristics of large fires (L>0.7m), which are primarily controlled by radiant feedback from

the flames. The radiation properties of methyl methacrylate C5H8O2 (MMA) and ethylene C2H4

have been under investigation in the past year [1,2].

The experimental measurements and property correlations have been completed for the eight

significant infrared absorption bands of MMA vapor [1]. The spectra obtained were relatively

insensitive to both pressure broadening effects and temperature variations, which are due in turn to the high spectral line density of the many superimposed bands within each major band structure and

the large number of atoms in the MMA molecule which tends to constrain the bond freedom of

interior atoms. The properties are reported in terms of correlated parameters for the Goody statisti- cal narrow-band model for spectral calculations, the Edwards exponential wide-band model for band-averaged calculations, and the super-band model for total propeny applications. Figure 1 shows the total emissivity of gaseous MMA in the standard chart format of emissivity versus temperature with various pressure pathlengths. The monomer vapor of PMMA is highly absorbing in the infrared and should be always considered in the study of radiation transfer in PMMA fires.

70
Modeling of Large Pool Fires and Fire Plumes. Pyrolysis rates and radiative heat fluxes of

moderately sized PMMA pool fires have been successfully predicted using a simple zone model

cl with two discrete homogeneous conical volumes for the core and flaming regions [3]. The core

; properties were assumed to be constant and estimated from the available experimental data in the

original published model, but an improved version for PMMA fires is now possible since the

; infrared absorption properties of MMA are available. The new analysis adds several simple

features which improve the correspondence of the model to the physics of an acmal fire. The radiajitive flux to the ftiel bed is calculated using the Chan-Tien scaling method to accommodate the

I differing properties of the two zones. Figure 2 shows the excellent agreement between the predic1 tion of the average radiant heat flux to the fuel bed by the two-zone model and experimental measiurements [4].

Simple models for radiative heat transfer in the lower regions of the plume for large pool fires

, are currently under development. An integral formulation for the plume, including the effects of

t| radiation heat transfer within the flow and to the environment, is linked to the two-zone model to provide initial conditions for the simulation. Preliminary investigation reveals that the radiant flux

I in the plume can be accurately estimated from simple homogeneous cylinder calculations.

I Radiative Properties of Agglomerated Soot Particulate. The phenomenon of agglomeration by

^

small spherical particles into large clusters is encountered in flames and in combustion systems that

:* contain ash and soot particulates. The study of the effect of conglomeration on the radiative

I characteristics is imponant from the standpoint of computing heat transfer in such systems, as well

;|as from the aspect of experimental determination of radiation properties. To obtain simple analytical models for this study, the concept of an effective diameter is suggested [5], which can be

I defined as the diameter of a sphere that has the same specified characteristics as the agglomerated

I cluster, where this equivalent sphere is made up of the same material as the primary particles. Fig-

|ure 3 presents the effective diameter based on the extinction and scattering cross-sections for two

I

common soot morphologies, straight chains and random clusters. The scattered radiation from all other particles that is incident on each particle increases the net energy incident on the individual

particles. Thus the net energy absorbed and extinguished by the system of panicles increases. This

increase is more pronounced in large dense systems [6] but is negligible when the particles are few. This trend is theoretically predicted for large systems [6] and confirmed by expenmental

observation [7].

Absorption of radiation is the dominant mechanism of radiation extinction by small absorbing

panicles in the Rayleigh regime. A method to model the dependent absorption characteristics of

dense particulate systems as well as a complete model for evaluating the dependent scattering has

been established [6]. Statistical averages based on the random character of particulate medium are

I inu-oduced to obtain simple expressions for the model. The evaluation of radiative transfer in such

_ systems is shown to be more sensitive to the variations in the absorption characteristics than those

i in the scattering,

i

71
Repons and Papers

1. Park, S.H., Stretton, A.J., and Tien, C.L., “Infrared Radiation Properties of Meiiiyl

Methacrylate Vapor,” Comb. Sci. Tech. , submitted.

2. Tuntomo, A., Park, S.H., Stretton, A.J., and Tien, C.L., “Infrared Radiation Properties of

Ethylene,” in preparation.

3. Brosmer, M.A. and Tien, C.L., “Radiation Blockage in Large Pool Fires,” Comb. Sci.

Tech. 51, pp. 21-37 (1986).

4. Park, S.H., Stretton, AJ., and Tien, C.L., “Radiative Heat Transfer in Plastic Fires,” Twentieth Fall Technical Meeting, Eastern Section of the Combustion Institute, Gaithersburg,

MD, submitted.

5. Kumar, S. and Tien, C.L., “Effective Diameter of Agglomerates for Radiative E.xtinction and

Scattering,” Twentieth Fall Technical Meeting, Eastern Section of the Combustion Institute,

Gaithersburg, MD, submitted.

6. Kumar, S. and Tien, C.L., “Dependent Scattering and Absorption of Radiation by Small Particles,” Fundamentals and Applications of Radiation Heat Transfer, HTD-Vol. 72, pp. 1- 7 (1987T

7. Drolen, B.L., Kumar, S., and Tien, C.L., “Experiments on Dependent Scattering of Radiation,” AIAA 22nd Thermophy. Conf. (Honolulu), Paper 87-1485, June 8-10 (1987).

Fig. 1 Total emissivity of MMA vapor for an effective pressure of unity.

72
73
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : University of Montana

Grant Number ; 60NANB5D0554

Grant Title ; Kinetics of Oxygen Chemisorption and Desorption of Combustion

Products in the Smoldering Combustion of Cellulosic Material

Principal Investigator ; Professor Geoffrey N. Richards

Wood Chemistry Laboratory

University of Montana

Missoula, Montana 59812

(406) 243-4435

Other Professional Personnel ; Dr. F.-Y. Hshieh, Postdoctoral Research

Associate

Mr. William F. DeGroot, Research Specialist

NBS Scientific Officer ; Dr. Thomas Ohlemiller

Technical Abstract :

Introduc ti on . The tendency of a material to support smoldering

combustion has previously been correlated with the kinetics of oxygen

chemisorption at low temperatures on stable chars formed under pyrolytic

conditions. This investigation commenced in January, 1986 and aims to extend

the analysis of chemisorption kinetics to chars formed at lower temperatures

and includes kinetic analysis of gasification reactions which occur

simultaneously with or subsequent to oxygen chemisorption. In the preceding

year, methods were developed to study the volatile pyrolysis and combustion

products evolved by wood and wood chars over temperatures from 250-550°C by

the combined techniques of thermogravimetry and Fourier transform infra-red

(TG/FTIR). The same techniques were also used to study the effect of

"natural" and of i on -exc ha ng ed cations on thermal behaviour. Wood was selected as raw material because many substances whose thermal decomposition

and smoldering combustion are of importance are, like wood, 1 ignocel 1 ul osi cs

.

Commonly used cellulosic insulation prepared from newsprint is in this class

and its combustion behavior, and that of its chars, is likely to be

significantly different from pure celluloses. Preliminary results, described

briefly in the previous report, indicated that the 1 ow-temperature oxidative

pyrolysis of wood, which is likely to be a major factor 'in smoldering

combustion, involves first the degradation of hemicel luloses and lignin, while

the cellulose survives to higher temperatures. The nature of the trace

amounts of cations in the wood has major effects on these processes. These

preliminary indications have now been confirmed and are detailed below.

First chemical events in pyrolysis of wood . Wood has been heated at

250°C on a thermal balance and the evolved gases analyzed by FTIR. The heated

wood has been analyzed for glycoses, uronic acids and by nitrobenzene

oxidation to vanillin and syri ngal dehyde.' About 60% of the weight loss is

74
accounted for by five compounds, which are the only products detected in the

,]i gases by FTIR. These products are water, carbon dioxide, methanol, acetic

acid and formic acid. By relating the rates of formation of these compounds

(, to weight loss, the following major conclusions are reached regarding the

i

first chemical events in pyrolysis of wood. Uronic acids in the

hemi cel 1 u 1 OSes and pectic substances decompose very readily to yield carbon

dioxide, water, char (or char precursors) and perhaps some methanol. This

decomposition may lead to further pyrolysis of the xylose units to which the

uronic acids are attached in the hemi cel 1 u loses. Acetyl ester groups in the

hemi cel 1 u loses are much more resistant to pyrolysis, but are released slowly

j as acetic acid. A small proportion of the potential methanol product is

1 released very readily and at least part of this product is derived from

i

! lignin. Formic acid is released at a slow and continuing rate at 250°C by

, unknown mechanisms and is probably derived from degradation of hemicelluloses.

Influence of cations on oxidative pyrolysis of wood . The indigenous

!

l cations of wood are predominantly potassium and calcium. These have been

removed by mild acid-washing and replaced by single cation species by ion

exchange without any other change in the chemistry or morphology of the wood.

The results from TG/FTIR studies of the resulting woods show that potassium

I catalyzed pyrolysis of all three major components of wood (viz. cellulose,

I' hemicelluloses and lignin), while calcium retards the same processes. The

p same generalizations apply to oxidative pyrolysis, with especial emphasis of

j low temperature (e.g., 280°C) catalytic effects of potassium. The influence

I of the trace amounts of cations on oxidation of the char in air is dramatic.

I Above 430°C the char oxidation is highly catalyzed by potassium but strongly

[

suppressed in char from acid-washed wood, with the char from calcium-exchanged

wood being intermediate. These effects confirm earlier results and indicate

promising leads for future wor^ on smolder control in 1 ignocel lulosics. The

I C02 '.C 0 ratio formed from char oxidation changes from 2:1 for original wood to

I 1:1 for acid-washed wood. This effect should be of considerable importance in

heat balance in oxidizing chars and hence probably in smolder behavior,

because of the greater heat of formation of CO2 compared with CO.

|i Oxygen chemisorption on chars . The chars used have been prepared in the

|i thermal balance from wood discs under nitrogen and all subsequent measurements

of chemisorption activity (CSA) made without removal from the balance, in

i'|t order to avoid intermediate exposure of the char to air or mechanical effects.

Ijf After some difficulties, procedures have been designed to give reproducible

'f CSA measurements. These have shown that the char, as it forms from slowly

!; heated wood, begins to develop significant CSA at about 370°, peaks at 500°

( and by 600°C the CSA has fallen to about a quarter of the maximum. This type

(I of maximum in char reactivity had been indicated in previous studies with

I chars from pure celluloses. The effect may be of considerable importance in

E smoldering combustion and also in the phenomenon of spontaneous ignition of

I

1 ignocel 1 ulosics. The mechanism is not known and will be further studied.

The influence of cations on CSA has been measured using chars from ionI exchanged wood and shown to be small but significant. The CSA appears to be

catalyzed by potassium and to a smaller extent by calcium and is lowest in

I

acid-washed wood.

I Influence of cations on ignition . The study of ignition has been

: commenced by heating chars from ion-exchanged wood after chemisorption of

75
oxygen in the thermal balance. The preliminary results show increase in i ignition temperature from 377° for potassium-exchanged wood, through 384° for j untreated wood to 393°C for calcium-exchanged wood, but most dramatically, the i char from acid-washed wood oxidized without ignition in these experiments.

•In general, the detailed results for the current period have demonstrated ' quite separate and different influences of cations in wood respectively upon

pyrolysis, oxygen chemisorption, combustion, and ignition.

Reports and Papers

1. G.N. Richards, "Kinetics of Oxygen Chemisorption and Desorption of

Combustion Products in the Smoldering Combustion of Cellulosic Material,"

Annual Report, NBS Grant No. 60NANB5D0554, Wood Chemistry Laboratory,

University of Montana, Missoula, MT, February 1987.

2. G.N. Richards, "Volatile Products of Low-temperature Oxidative Pyrolysis

of Wood - Influence of Cations," Annual Conference on Fire Research, NBS

Center for Fire Research, 1986.

3. W.F. DeGroot, W.-P. Pan, M.D. Rahman and G.N. Richards, "Early Products

of Pyrolysis of Wood," Prepr. Pap., 193rd National ACS Meeting, Division

of Fuel Chemistry, Denver, 32(^), (1987) 36-43.

4. W.F. DeGroot and G.N. Richards, "The Influence of Pyrolysis Conditions

and Ion-Exchanged Catalysts on the Gasification of Cottonwood Chars by

Carbon Dioxide," Fuel , in press.

5. W.F. DeGroot and G.N. Richards, "The Effects of Ion-Exchanged Cobalt

Catalysts on the Gasification of Wood Chars in Carbon Dioxide," Fuel , in

press.

6. F,-Y. Hshieh and G.N. Richards, "Factors Influencing Chemisorption of

Oxygen and Ignition of Wood Chars," Prepr. Pap., Combined Meetings,

Eastern Section: The Combustion Institute 12th Fall Technical Meeting,

Chemical and Physical Processes in Combustion and the National Bureau of

Standards Annual Conference on Fire Research, Washington, D.C., in press.

7. W.F. DeGroot, W.-P. Pan, M.D. Rahman and G.N. Richards, "First Chemical

Events in Pyrolysis of Wood," J. Anal, and Appl. Pyrol. , in press.

8. M. G. Essig and G.N. Richards, "1 , 5-Anhydro-S-L-arabi nofuranose from

Pyrolysis of Plant Cell Wall Materials (Biomass)," submitted to

Carbohydr. Res.

9. M.D. Rahman and G.N. Richards, "Interference by Flavonoids in PhenolSulfuric Acid Analysis of Carbohydrates, " Carbohydr. Res. , in press.

10.

M.D. Rahman and G.N. Richards, "Interactions of Starch and Other

Polysaccharides with Condensed Tannins in Hot Water Extracts of Ponderosa

Pine Bark," J. Wood Chem. and Tech., in press.

76
n. W. F. DeGroot and G.N. Richards, "The Effects of Ion-exchanged Cobalt

Catalysts on the Gasification of Wood Chars in Carbon Dioxide," Prepr.

Pap. 194th National ACS Meeting, Division of Fuel Chemistry, New Orleans,

32(4), (1987) 193-202.

12. G.N. Richards, "Synthetic Applications of Thermal Degradation of

Sucrose," 3rd New Orleans Carbohydrate Symposium, 1987.

13. G.N. Richards, "Interactions between Condensed Tannins (Polymeric

Proanthocyanidin Glucosides) and Polysacchari des, "1 94th National ACS

Meeting, Cellulose, Paper and Textile Division, New Orleans, 1987.

14. *G.N. Richards, "Studies of Thermal Degradation of Sucrose and Influences

of Impurities at Processing Temperatures, " 194th National ACS Meeting,

Agricultural and Food Division, New Orleans, 1987.

77
Smoke Dynamics Research Group

Center for Fire Research

FY 87

Professional Personnel

George W. Mulholland, Head

Nelson P. Bryner, Chemical Engineer

William M. Pitts, Research Chemist

Kermit C. Smyth, Research Chemist

Paul J.H. Tjossem, Physicist

James Gentry, Visiting Scientist

Victor Henzel, Visiting Scientist

J. Houston Miller, Faculty Research Associate

K. C. Muck, Visiting Scientist

Thomas Cleary, Visiting Scientist

Program Objectives

Develop scientifically sound principles, metrology, data, and predictive

methojis for the formation/evolution of smoke components in flames for use in

understanding and modeling general fire phenomena.

Scope

This work embraces broad areas underpinning CFR programs with focussed study

in the areas of hot gas physics and chemistry. Effects are directed toward

improved understanding of the chemical and physical processes which underlie

macroscopic fire phenomena and include development of new techniques and

methods for studying these processes.

1. Soot Formation Chemistry and Physics

Flame radiation from incandescent soot dominates flame spread and heat

transfer in large fires. Escaping particulates hinder vision and impair

breathing, as well as being a sensitive signature for fire detection. It has

been predicted that smoke from mass fires ignited by a major nuclear exchange

would absorb enough solar radiation to reduce the ambient temperature by 10°

C

or more on a global scale. Despite the importance of soot, there is little

understanding at the molecular level of the soot formation process; i.e., how

small molecules grow rapidly to become soot particles. There is also little

information on the amount of soot emitted from fires and on the properties of

the soot particles. We are engaged in a broad program to provide information

and understanding regarding soot formation and properties.

This is the eighth year of a long-term study of the fundamental chemistry of

soot formation, carried out jointly with the NBS Thermal Processes Division

and also in collaboration with the Chemical Kinetics Division. A series of

oDtical and mass spectrometric profile measurements have been completed for

methane/air diffusion flames on a Wolfhard-Parker slot burner. we have used

fluorescence to monitor OH, C 2

, and polycyclic hydrocarbons (three ways),

multiphoton ionization to detect methyl radicals and small soot particles and

73
! Rayleigh-Mie scattering to observe the emergence of large soot particles. In

, addition, mass spectrometric profiles of CO2 , H2O, methane, acetylene,

I butadiene, benzene, toluene, diacetylene, triacetylene, vinyl acetylene,

1 methylacetylene , and allene have been taken. These results clearly delineate

the region of soot nucleation: soot particles first appear on the high

temperature, radical-rich side of a zone containing numerous pyrolysis

I products. Velocity measurements using laser Doppler velocimetry and thermoI couple temperature profiles have also been obtained. The combined data

t provide the most detailed description of the chemical structure in a

I hydrocarbon diffusion flame obtained to date.

! The species profiles have been analyzed to determine production and

destruction rates of intermediate hydrocarbons in our methane/air diffusion

I flame. These results show that acetylene plays the major role in surface

growth on particles (as found in premixed flame studies). Furthermore, direct

[

I tests of proposed models of chemical growth can now be made which strongly

suggest that a pathway involving vinyl radical addition to acetylene is the

fastest route to form benzene. Recent experiments have investigated fuel

structure effects on chemical growth pathways by the addition of small amounts

[j of ethylene, butadiene, and toluene to the base methane flame. In addition,

r measurements have been obtained in an ethylene/air diffusion flame which

kj further clarify the key role of acetylene in molecular growth reactions.

I e In addition to species characterization studies, physical properties of soot

are being investigated. The kinetics of cluster agglomeration and structure

l\\ of the resulting clusters have been studied using a "Brownian dynamics"

p computer simulation of conditions appropriate for soot growth. The average

[i cluster size is found to be proportional to the square of the time while

I

I previous models of soot growth predicted a much slower growth based on

1 particle coagulation and coalescence. We have shown that using a kinetic rate

L'l kernel based on the fractal geometry of soot leads to a size distribution in

ji good agreement with the self -preserving distribution obtained with the

i| computer simulation. An experimental study of the size distribution of soot

1'; leaving the flame is now in progress

'i Parallel instrumentation for measuring fire smoke aerosols has been developed

1 in bench scale, as part of the Cone Calorimeter, and in large scale, in a

'll specially built measuring rig. Since the principles of design were similar,

data could be directly compared. For solid and liquid combustibles, it was

I found that large-scale smoke emission rates could be well represented from

J Cone Calorimeter data if the specimen mass loss rates, per unit area, were

i matched for the two cases. The matching of the mass loss rates was accomplished in bench scale by exposing the specimen to a suitable level of

external irradiance. For gaseous fuels, a similar clear conclusion could not

be drawn, and further studies are seen to be necessary. • The specific

! extinction area, when computed on a smoke particulate mass basis, was seen to

!' be independent of fuel type and of the conditions of test.

"Chemical Production Rates of Intermediate Hydrocarbons in a Methane/'Air

Diffusion Flame" by Miller, J.H., Mallard, W.G., and Smyth, K.C.,

Twenty-First Symposium (International) on Combustion (in press).

79
"Methyl Radical Concentrations and Production Rates in a Laminar

Methane/Air Diffusion Flame” by Miller, J.H. and Taylor, P.H.,

Combustion Science and Technology . 52, 139 (1987).

"Measurement and Rate Law Analysis of D2 Q-Branch Line Broadening

Coefficients for Collisions with , He, Ar, , and CH^ " by Smyth,

K.C., Roscasco, G.J. and Hurst, W.S., J. Chem. Phvs

,

, 87, 1001,* (1987).

"Chemistry of Molecular Growth Processes in Flames" by Smyth, K.C. and

Miller, J.H., Science . 236, 1540 (1987).

"Soot Formation in Hydrocarbon Diffusion Flames" by Miller, J.H.,

Hamins , A., Kohout, T.A.

,

Smyth, K.C. and Mallard, W.G., Energy and

Fuels (in press).

"Soot Particle Formation in Laminar Diffusion Flames" by Santoro, R.S.

and Miller, J.H., Langmuir

.

3, 244 (1987).

"Simulation of Aerosol Agglomeration in the Free Molecular and Continuum

Flow Regimes" by Mountain, R.D., Mulholland, G.W. , and Bavim H. , J.

Colloid and Interface Science. 114, 67 (1986).

"Smoke Production and Properties" by Mulholland, G.W.

,

Society of Fire

Protection Engineers Handbook (in press).

"Fractal Analysis of Soot Agglomerates" by Samson, R.J., Mulholland,

G.W.

,

and Gentry, J.W., Langmuir . 3, 272 (1987).

"Cluster Size Distribution for Free Molecular Agglomeration" by

Mulholland, G.W., Samson, R.J., Mountain, R.D., and Ernst, M.H.

,

Energy

and Fuels (in press)

.

"The Effect of Scale on Smoke Emission" by Mulholland, G.W., Henzel, V.

,

and Babrauskas , V., submitted to 2nd International Fire Safety Science

Symposium.

1. Prediction of CO

This multi - discipline , long-range program is designed to provide the basic

understanding necessary to allow the prediction of CO in both pre- and postflashover room fires. Flame chemistry, fluid mechanics, and their

interactions must all be considerexi. Experiments here at NBS and in other

laboratories supported by the grants program are being coordinated to address

this fundamental problem.

Work at NBS has focused on the area of chemically- reacting turbulent flow.

The goal is to provide the experimental foundation for theories designed to

calculate the behaviors of these complex flow fields. Such theories are necessary if the formation of incomplete products of combustion, such as CO

and soot, are to be predicted.

During the past year a new experimental diagnostic has been developed in

cooperation with workers from the University of Maryland for the study of

variable density turbulent flows. This technique combines Rayleigh light

80
i scattering (concentration measurement) with an array of hot-wires (velocit3/

C measurements) to allow simultaneous, real-time, spatially-resolved

I

measurements of velocity and concentration along a line in the flow field.

Preliminary measurements have demonstrated the role of large scale turbulent

structures in the entrainment behavior of an axisymmetric jet of propane

flowing into air. A new flow facility is under development which will allow

this powerful diagnostic to be employed for the investigation of buoyancydriven turbulent plumes

Experimental findings of variable density flows have been utilized to predict

the lift-off and blow out behaviors of turbulent jet diffusion flames. These

flame extinction processes , which are relatively easy to experimentally

characterize, serve as tests of various chemically reacting flow theories.

I

' Our work has shown that the large scale entrainment behaviors of isothermal

jets of the fuel are sufficient to predict lift-off and blow out behaviors for

the corresponding turbulent jet diffusion flames. This finding suggests that

models based on mixing in large scale turbulent structures may provide a means

for the prediction of chemically reacting turbulent flow.

"Development of a Line Camera for Real-Time Measurements of

I Concentration in Turbulent Flow Fields," Pitts, W.M. , Proceedings of the

I Fifth International Congress on Applications of Lasers and Electrontics .

j! Volume 58, The Laser Institute of America, 1987, pp. 7-14.

f

|, "The Effects of Global Density and Reynolds Number Variations on Mixing

s|; in Turbulent, Axisymmetric Jets- -Implications for Turbulent Jet

Diffusion Flames," Pitts, W.M. , Proceedings of the 1987 ASME/JSME

i'l Thermal Engineering Joint Conference . Vol. 1, Eds. P.J. Marto and I.

I' Tanasawa, The American Society of Mechanical Engineers, 1987, pp . 123-

l\\ 135.

i'

: "Mixing in Variable Density, Isothermal Turbulent Flows and Implications

;; for Chemically Reacting Turbulent Flows," Pitts, W.M. and Kashiwagi, T.,

( National Bureau of Standards Internal Report, NBSIR 87-3550, May, 1987.

|i "Importance of Isothermal Mixing Processes to the Understanding of Lift-

| Off and Blow Out of Turbulent Jet Diffusion Flames," Pitts, W.M. , submitted to Combustion and Flame.

Associated Grants

I

I 1. "Soot Dynamics in Flames", R.A. Dobbins, Brown University.

i.

i| 2. "Chemical Pathways to Soot Formation in Diffusion Flames", J.H. Miller,

' George Washington University.

3. "Soot Particle Formation and Destruction in Diffusion Flames", R.J.

ji Santoro, Pennsylvania State University.

ij

I 4. "Soot Formation, Smoke and Corrosion Hazards in Fires", B. Zinn and J.

Jagoda, Georgia Institute of Technology.

5. "Characterization of Large Scale Turbulent Structures in Variable

Density Flows", J. Wallace, University of Maryland.

6. "Kinetics of Agglomerate Formation", J.W. Gentry, University of Marvland.

81
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33

CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 1987

Institution ;

Grant No. ;

Grant Title ;

Principal Investigator ;

Other Professional Personnel;

Brovn University

60NANB6D0643

Soot Dynamics in Flames

Professor R. A. Dobbins

Division of Engineering

Brown University

Providence, R.I. 02912

Telephone; (401) 863-1422

Dr. Constantine Megaridis,

Postdoctoral Research Associate

NBS Scientific Officer ; . Dr. George Mulholland

Technical Abstract;

This research has resulted in the development of a thermophoretic

sampling technique for the extraction of soot particles from flames. The

technique has been described in detail in a recent journal article. Electron

microscope analysis of soot particles sampl*ed from the ethene diffusion fla.me

shows them to be highly aggregated chains of essentially monodisperse spheres.

' This result implies that the particles grow predominantly by surface growth.

Modeling of the process by the aerosol dynamic equation has led to an understanding of the relative contributions of the various phenomena involved.

The variation of primary particle size with height and the velocity

measurements of others allow the determination of the specific surface growth

rate of the soot particles. These important results are reported in detail

below. The availability of information on actual soot morphology in the

ethene flame allows an attack on the calculation of soot extinction and

scattering properties with particle shape properly considered. This aspect of

t the work will be reported at a later date.

I. EXPERIMENTAL; The combustion system studied in the current work is a coannular laminar ethylene/air diffusion flame under atmospheric pressure. The

burner consists of two concentric brass tubes of 11. 1 mm and 101. *6 mm i.d. The

fuel flows through the inner tube while the ventilating air flow passes

through the annulus between the two tubes. The flow rates adopted for ethylene

and air are 3.85 and 713.3 cm^/s respectively. These flow rate's result in a nonsmoking laminar flame with definite shape and height (-88 mm) which

' displays the yellow incandescence characteristic of soot. The structure of the

j soot field of the above flame has been previously investigated using laser

light-scattering and extinction measurements^’**, as well as a thermophoretic

sampling technique^ with remarkably short sampling times. The current study

is a continuation of the latter work on soot particle morphological

characteristics using the same technique. A detailed description of the

thermophoretic sampling method is given in ref. 6.

84
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II. RESULTS AHD DISCUSSION: The thernophoretic sampling technique, combined

with electron microscopy for high quality observations, was used to study the

mcrohology of soot aggregates collected from the coannular ethylene diffusion

flame. " These aggregates consist of individual particles, called primary

oarticles, of approximately spherical shape and rather uniform size. A

vertical survey of primary particle size has been performed for particles

corresponding to radial positions of maximum soot volume fraction (annular

region). A variety of probes was used to collect the particles

thermophoretically from the flame environment and a high consistency of the

measured primary particle size was observed.

1 The current results refer to the intermediate region of the flame,

i.e. heights (z) from 10 mm to 50 mm. These regions are characterized by

,, intense particle growth, which occurs by both mechanisms (agglomeration and

i' surface growth) simultaneously as depicted in Figure 1. Examining a series of

I electron micrographs, we produced quantitative data on the primary particle

diameter D of soot particles corresponding to the annular region (r=r^). These

I values of vs the axial coordinate z for a variety of thermophoretic probes

are plotted^^in Figure 2. The maximum size shown occurs at z=40 mm which marks

the lower boundary of the oxidation region. The evolution of the primary

| particle size distribution with height, for particles transported on the

I

annular region can be characterized by the ratio o/D^, where a is the standard

deviation of the primary particle diameter. From our measurements we obtained

that o/Dp = 0.22, 0.18, 0.15 and 0.13 corresponding to heights z=10, 20, 30

and 40 mm respectively. These values show that the distribution of the

; primary particle size narrows considerably with height above the burner mouth,

j' This behavior clearly illustrates the dominant effect of surface growth

;; reactions on soot particle morphology at low and intermediate heights of the

I flame.

I

:j Figure 2 provides additional information on the specific surface

growth rate f of soot particles corresponding to the annular region. This

I: rate is defined as the mass deposition rate per unit of particulate surface

ji area and it is generally a function of the axial location z. The dependence

:i( on z translates into a dependence on the residence time t of the particles',

1 ' through a series of particle trajectory measurements reported by Santoro et

al.‘‘ for the identical flame. The specific surface growth rate is related

I

with the material density p^, the axial velocity component v^ and the

i|; z-gradient of the primary particle diameter through

I 2 dz

I

111 The axial velocity values are taken from ref. 4. A soot density of 1.S6

; gr/cm^ was used in Eq. (1). Thus we retrieve the values of f given in the

following table

85
TABLE 1 Selected Data for the Ethene Diffusion Flame

t^ (m s) 25 31 36 44 47

z (mm) 10 15‘ 20 30 35

fxlO ^ (gr/cm^s)

9.4 10.5 10.1 6.2 3.1

*From ref. 7.

In the above calculations no assumptions were adopted on the size distribution

of the soot aggregates or the regime these particles belong to. These

calculations resulted in a maximum value of f=10.5xl0'“ gr/cm^s corresponding

to z=15 mm above the burner mouth (t=3lms). Harris and Weiner^ reported a maximum value of f=6xl0*® gr/cm^s for a series of rich premixed ethylene/air

flat flames. This value was calculated by them using purely optical

obervations, adopting Rayleigh scattering theory and assiiming a self -preserving size distribution of smooth spheres.

Some recent studies^ suggest that acetylene may be the soot growth

species in a diffusion flame environment. Under this assumption the surface

growth rate can be expressed as

f = K[c,K,] (2)

where K is the rate constant for the surface reactions that convert C..H, into

soot and [C,H,] the mole fraction of acetylene. In Eq. (2) we have” already

assumed first order surface growth reaction kinetics. Using the mass spectrometric measurements by Miller^° for our diffusion flame system we have

=0 .022 corresponding to the annular region at a height z»9 mm. The

corresponding value for f at z=10 mm from our measurements derives through Eq.

(2) the surface growth reaction constant K=»4xl0*^ gr/cm*s atm corresponding to

the annular region at a height of z=9mm above the burner mouth where the

temperature^ is T-1700K.

REFERENCES

1. Santoro, R.J., Semerjian, K.G., and Dobbins, R.A.: Combustion and Flame

51, 203 (1983).

2. Santoro, R.J., Semerjian, H.G., and Dobbins, R.A. : AIAA Eighteenth

Thermophysics Conference, Montreal, Canada (1983).

3. Santoro, R.J., and Semerjian, H.G.: Twentieth Symposi’^m (International)

on Combustion, The Combustion Institute, 997 (1984).

4. Santoro, R.J., Yeh, T.T., and Semerjian, H.G.: 23rd ASME/AIChE National

Heat Transfer Conference, Denver, CO (1985).

36
5. Dobbins, R.A., and Megaridis, C.M.: Langmuir 3, No 2, 254 (1987).

6. Megaridis, C.M.: Ph.D. thesis, Brown University, Providence, RI (1987).

To be released as an N.B.S. report.

7. .Santoro, R.J., Personal communication, 1984.

8. Karris, S.J., and Weiner, A.M.: Comb. Sci. and Technology 31, 155 (1983).

9. Smyth, K.C., and Hiller, J.H.: Invited paper C, Technical Meeting,

Eastern Section of the Combustion Institute, San Juan, Puerto Rico

(1986).

10. Miller, J.H.: Paper 33, Technical Meeting, Eastern Section of t.he

Combustion Institute, San Juan, Puerto Rico (1986).

Figure 1 Mechanisms of soot particle growth.

Height above burner Z(mm')

Figure 2 Primary particle size as function of height, near f’r.. for :hc ethylene diffusion flame. Eaeh size measurement is an average over about ICO primary particles. Various thcrmophorctic probes were used to obtain the abo\c

data points.

87
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

Institution: The George Washington University

Grant Number: 60NANB6D0625

Grant Title: Chemical Pathways to Soot Foraation in Diffusion Flames

Principal Investigator: Professor J. Houston Miller

Department of Chemistry

The George Washington University

Washington, DC 20052

(202) 994-7474

Other Professional Personnel: Dr. Anthony Hamins , Postdoctoral Research Assoc

NBS Scientific Officer: Dr. Kermit C. Smyth

Technical Abstract

The chemistry of the combustion of simple hydrocarbons to form carbon

dioxide and water has been extensively studied and is generally well

established. Our level of understanding of the chemistry which leads to the

formation of polynuclear aromatic hydrocarbons (PAH) and soot particles is

less fully developed. Because of the importance of radiation from soot

particles in flame spread, a predictive capability for particle generation

rates in fires is an essential component of any useful fire model. However,

simple schemes which attempt to correlate soot production with global flame

properties (such as stoichiometry) are unlikely to be able to account for new

and puzzling* data which is being collected in laminar diffusion flames. For

example, Hura and Classman have observed an increase of more than an order of

magnitude in the soot volume fraction with addition of 10% oxygen to the fuel

stream of a counterflow ethylene/air diffusion flame [1], Addition of oxygen

to other fuels did not show nearly as dramatic an effect. Clearly, effects

such as these will only be understood from a knowledge of the dominant

chemical pathways which lead from fuel pyrolysis to particle inception. The

goal of our work is to develop a data base of flame structure information for

laminar diffusion flames. This data is then used to calculate the rates of

chemical processes which lead to the formation and growth of aromatic ring

structures

.

During the past year, we have performed experiments on two flame

geometries: an axial burner supporting ethylene/air diffusion flames and

methane/air diffusion flames on a Wolfhard- Parker slot burner. The results of

these studies are summarized below.

Ethylene/Air Flames:

Over the past few years, work in this laboratory has been concerned with

detailed flame structure measurements in laminar methane/air diffusion flames

There are many important questions which remain unanswered from our previous

investigations. These include:

1) Are the conclusions which have been derived concerning

the early chemical steps leading to aromatic formation

88
unique to the methane/air flame or are' they generally

applicable to hydrocarbon diffusion flames?

2) Can correlations be made between the chemical structure

of a flame (species concentrations and production rates)

and the evolution of the soot particle field?

To address these questions we performed a study of an ethylene/air diffusion

: flame supported on an axially symmetric burner. This particular flame system

I was chosen because of the wealth of information which is available on the

I evolution of the soot particle field in this flame, and the availability of

; temperature and velocity field data for this system [2]

The experimental /

1 details and results of this study have been reported previously [3]. Although

I microprobe sampling in highly sooting environments such as the ethylene/air

diffusion flame leads to relatively high uncertainty in species

- concentrations, these studies have led to a characterization of flame

conditions for soot particle growth. In work published during the past few

I years this region has been characterized through laser light scattering

i I measurements [4,5]. By comparing molecular concentrations with contours of

I soot volxome fraction the area of fastest soot particle growth in the

I ethylene/air flame is characterized as follows:

I 1500 - 1700 K

! Relatively high concentrations of acetylene (> 1 %)

Near flame region where acetylene is produced with

II maximum rate

I

ji These results suggest that acetylene, or a reactive species that may be

i equilibrated rapidly with acetylene (vinyl or ethynyl radicals) , participate

in the rapid growth of young particles.

I

ii' Methane/Alr Diffusion Flame:

' Although comparisons of concentration data with measurements of the soot

" particle field are a tremendous advantage for the ethylene flame system,

; experimental sampling difficulties have precluded the collection of as complete a data base as that available for the methane/air flame supported on

the Wolfhard- Parker burner. We have therefore concentrated most of our efforts

li during the past year on collection of a more refined data set for the

' methane/air flame. In the past few years in our laboratory, production rates

;; for stable flame species have been determined from measurements of the

ji concentration of chemical species, velocity and temperature [6,7], The

; production rate for benzene has been compared to estimated forward rates for

the formation of small (two-carbon) free radicals from hydrogen atom attack on

I acetylene and ethylene. For these calculations, the hydrogen atom

concentration was estimated from the equilibrium of methane with methyl

|i radicals [8]. The results of this study indicate that the vinyl radical

jj (C2H3 • ) plays the dominant role in benzene formation processes. However, if

hydrogen atom abstraction from acetylene by hydroxyl radicals is included as

I an initiation pathway, both vinyl and ethynyl (C2H- ) reactions are fast enough

ij' to account for the observed rate of benzene formation [9]. Therefore, the

bottleneck in the formation of benzene in diffusion flames probably occurs at

I larger molecular sizes than ethynyl or vinyl radical.

89
To investigate these subsequent steps in the formation mechanism of

benzene it is necessary to have estimates for concentrations of the radicals I which are involved in these elementary steps. To this end, radical I concentrations can be calculated from elementary reaction equilibria if the I reactions are sufficiently fast in both the forward and reverse directions

j|| relative to the rates of transport processes. Concentrations calculated in jl this way can be used to evaluate the relative importance of specific r-eactions

in the overall benzene formation mechanism. The calculated chemical rates for I specific species can be compared with those found experimentally. Further, the

set of estimates of radical concentrations can be iterated to improve the '4 agreement between experimental and calculated rates . 1

This approach is likely to be subject to inaccuracies; radical J

concentrations calculated from equilibria may be off by an order of magnitude :ia in even the most favorable cases. It is therefore necessary to have a gauge |jj for the impact of specific concentration estimates on the calculated rates. To j this end, sensitivity analysis can be used to determine the impact of radical

concentrations on calculated rates. Moreover, this analysis can be used to ! rank the importance of specific reaction pathways toward a common product. t

For these calculations it is important that the magnitude and position of ,, features in the species production rate profiles be as accurate as possible. |‘ During the past year we replaced our mass spectrometer electronics so that it

is now possible to collect concentration data with a dynamic range spanning

four orders of magnitude. With the new data chemical rates can be calculated ,|j with much greater accuracy particularly for flame regions where oxidation I; processes are important and species concentrations fall rapidly. I'

We have also recently initiated a study or methane/air diffusion flames

with small additions of other hydrocarbons to the fuel flow. Addition of one

to three percent ethylene had very little effect on the concentrations of ^ acetylene and benzene. However, addition of one percent toluene to the fuel i flow led to dramatic increases in the concentrations of both one and two ring j aromatics. The results of the toluene addition experiments have been [ summarized as an Eastern States extended abstract for this meeting.

I

s References

:

1. H.S. Hura and I. Classman, Combust. Sci. Tech. 53 . 1 (1987). j 2. R.J. Santoro, H.G. Semerjian, and R.A. Dobbins, Combust. Flame 37 . 227 j (1980).

3. J.H. Miller, Chemical and Physical Processes in Combustion . Fall Meeting of i the Combustion Institute (1986). | 4. R.J. Santoro, T.T. Yeh, J. Horvath, and H.G. Semerjian, Combust. Sci. Tech, i 52, (1987). I 5. Kent and Wagner, Combust. Sci. Tech. 41 . 245 (1984).

6. Smyth, K.C., Miller, J.H., Dorfman, R.C., Mallard, W.G. and Santoro, R.J..

Combustion and Flame 62 . 157 (1985).

7. Miller, J.H., Mallard, W.G., and Smyth, K.C., Twentv-First Symposium

(International) on Combustion . The Combustion Institute, in press.

8. Miller, J.H., and Taylor, P.M., Combust. Sci. Tech. 52 , 139 (1987). | 9. Smyth. K.C., and Miller, J.H., Science 236 , 1540 (1987).

90
Publications during the Fast Year:

1) "Soot Inception in Hydrocarbon Diffusion Flames."

K.C. Smyth and J.H. Hiller, Chemical and Physical Processes During

Combustion . Fall 1986 Meeting of the Eastern States Section. Paper C.

2) "The Chemical Structure of an Atmospheric Pressure Ethylene/Air Diffusion

Flame .

J. H. Miller, Chemical and Physical Processes During Combustion . Fall 1986

Meeting of the Eastern States Section. Paper C.

3) "Chemistry of Molecular Growth Processes in Flames."

K. C. Smyth and J.H. Miller, Science 236 . 1540 (1987).

4) "Soot Formation in Hydrocarbon Diffusion Flames."

J. H. Miller, A. Hamins , T.A. Kohout, K.C. Smyth, and W.G. Mallard, Fuel

Division Preprints: Advances in Soot Chemistry, American Chemical Society,

August 1987.

91
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Insti tution : Georgia Institute of Technology

Grant No. : 60NANB6D0650

Grant Title : Soot Formation, Smoke and Corrosion in Fires

Co-Principal Investigators : Dr. J. I. Jagoda

Dr. E. A. Powell

Dr. B. T. Zinn

Georgia Institute of Technology

School of Aerospace Engineering

225 North Avenue

Atlanta, Georgia 30332

NBS Scientific Officer: Dr. Richard Burkowski

Technical Abstract :

Introduction . The objective of the proposed study is to determine the

importance of ions in the soot formation process and to obtain information on the sooting and corrosive behavior of various commonly used materials in fire

situations. This study is divided into three major tasks to be carried out

simul taneously

.

In Task I the effect of flame ions on the nucleation and growth

processes in diffusion flames will be determined. These tests will be carried

out on an opposed flow diffusion flame at sub-atmospheric pressure. The

reduced pressure will spread out the reaction zone resulting in better

spatial resolution of the optical measurements. The ion concentration in the

flame will be varied using a charged probe. This technique has the advantage

of permitting a change in local ion concentration without inducing a significant electric field in the flame. Such a field has in the past been

found to manipulate the charged soot particles causing a significant change

in the soot formation process which would interfere with the measurements.

Combined laser light scattering and absorption measurements will be used to

characterize the soot particles, in situ, in the flame. Soot particle

diameters and number densities as well as soot volume loadings will be

measured. The effect of ion concentrations on these parameters and, thus, on the nucleation and agglomeration processes will be determined.

In Task II the Combustion Products Test Chamber (CPTC) at Georgia Tech

(Fig. 1) will be used to obtain data on the physical and chemical

characteristics of smoke particulates emitted by various polymeric materials.

Physical data obtained from laser light scattering and attenuation

measurements will be the diameters, effective refractive index, and volume

fractions of smoke particles obtained under both smoldering and flaming

conditions. Also, the effect of ventilation gas temperature on the smoke

physical character! sti cs will be determined. These data will allow one to

estimate the loss of visibility caused by the materials when involved in

92
accidental fires. The chemical composition of the smoke particles will be

obtained by'GC/MS analysis of extracted samples. Emphasis will be on the

identification of toxic and corrosive compounds in the smoke oarticles.

In Task III the short and long term corrosive effects of the exhaust

gases and particulates generated under Task II on various structural and

electrical conductor materials will be investigated. The target materials

will be exposed to the combustion products in a corrosion test section (CTS)

installed above the CPTC sampling section (Fig. 2). Corrosion rates, changes

in tensile strength or electrical conductivity, and type of corrosion will be

determined for the target materials. These corrosion measurements will be

carried out immediately after the fire exposure period as well as during a post-fire period lasting up to several months during which the samples will

be stored in a controlled environment.

In the remainder of this report a brief summary of the accomplishments

during the first nine months of this project will be given.

Ions in Soot Formation (Task I) An opposed flow diffusion flame

burner inside an enclosure has been designed. Construction has almost been

completed. The enclosure, which is fitted with windows for optical access,

will permit the flame to be established under conditions of reduced pressure.

The burner will be rotatable about its central axis to permit absorption

measurements to be carried out at various angles. This is necessary to allow

deconvolution of the absorption signal using a tomographic technique. A

device has been designed and is currently being built which will allow the

ionization probe to be positioned remotely from outside the enclosure.

• Preliminary tests have been carried out on an existing counter flow

diffusion flame burner at atmospheric pressure. The applicability of the

theory to be used to determine the change in ion concentration induced by the

probe as a function of applied voltage and ion mobility has been confirmed.

Temperature measurements have been carried out using fine, coated

thermocouples and preliminary absorption measurements have been made in the

atmospheric pressure flame. The effect of introducing the probe into the

flame upon the soot formation process has been quantified. This effect was

found to be due mostly to a catalytic effect of the probe material.

Smoke Characterization (Task II) . The combustion products test chamber

and measurement systems had been inactive for approximately two years prior

to the initiation of this work. Therefore, these facilities were refurbished

and improved during the first six months of this project. Additional

modifications of the upper stack section were also accomplished during this

period. These were necessary in order to accommodate the corrosion test

section of Task III and another test section required by another concurrent

project. These modifications required considerable new design and shop work.

A system of pulleys and counterweights was also installed in order to support

the heavy upper stack section when the two test sections are being

interchanged.

During the third quarter of the project two specimens of a composite

material were received from the sponsoring agency. This material is a woven

carbon fiber composite with a bismaleimide binder. A sample of this material

was tested in the CPTC to obtain pyrolysis products for chemical analysis. A

93
thin slab of the material (7.6 x 7.6 x 0.32 cm) was exposed to a radiant flux ii: of 5 W/cm without a pilot flame in room temperature ventilation air (425 I liters/min flow rate). The horizontal sample orientation was used in this I test. Sampling was accomplished using two glass fiber filters in series with | a sampling rate of 28 liters/min. The test required sixty minutes with a four jj minute heating period before any smoke was visible. Peak light scattering and | optical density occurred at 10 minutes with a slow decline in smoke

production thereafter. The smoke appeared white like cigarette smoke and ij seemed to be issuing from cracks in the surface. Nearly 15% of the original i sample mass was evolved as gases and particulates during this test. About I 13.9 mg of a yellow-brown tarry liquid was collected on the first filter, -

while only 0.4 mg was collected on the second filter. Approximately 7% of the j mass lost during this test appeared as particulates. 1

The collected samples were subjected to analysis by gas chromatography ; and mass spectroscopy (GC/MS). At this time a preliminary report on the ] analysis has been received from the Georgia Tech Research Institute (GTRI)

' personnel who performed the analysis. About 20 high molecular weight : compounds have been identified, and about 20 more remain to be identified by

manual interpretation. Most of these compounds are polycyclic aromatic I hydrocarbons (PAH) with molecular weights ranging from 280 to 360. Many of

the remaining compounds are nitrogen containing substances, both heterocyclic

and acyclic. Most of these compounds possess varying degrees of toxicity or carcinogenicity.

The four most abundant compounds thus far identified are:

N-Prop-l-ene-3-(methyl phenyl ) acetamide (59,400 ppm)

5-

Methoxy-6-methyl —2-phenyl -7H-l-benzopyran-7-one (18,800 ppm)

6-

Hydroxy-l,2-naphtal enedione (18,200 ppm) , 2-Methyl -N-phenyl benzamide (14,800 ppm) i

The presence of large quantities of methyl phenyl -acetamide suggests that the

binder actually consists of a methylphenyl-maleimide. It should also be noted

that the benzopyran is a particularly toxic material.

Future plans call for additional tests of this material. The above test

will be repeated with cascade impactor sampling and laser scattering and

attenuation measurements to determine the particle size distribution and mean particle diameter. Tests at higher radiant fluxes, tests under flaming ; conditions, and tests with heated ventilation air will also be conducted.

Smoke Corrosivity (Task III) . A corrosion test section (CTS) was designated and the shop drawings prepared during the first quarter of the

project. This section consists of a 28 cm section of 21 cm diameter stainless

steel pipe fitted with access ports and a view port. A revolving specimen

rack within the CTS gives uniform exposure of the target materials to the

combustion products during a fire test in the CPTC. At the time of this

report the CTS was still in the shop, but it is expected to be completed

shortly.

Reports and Papers :

Three quarterly reports were submitted to the sponsor.

94

i
Figure 1. Combustion Products Test Chamber

Figure 2. Location of Corrosion Test Section

95
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : The Pennsylvania State University

Grant No. ; 60NANB7D0706

Grant Title ; Soot Particle Formation and Destruction

in Diffusion Flames

Principal Investigator ; Dr. Robert J. Santoro

Department of Mechanical Engineering

31 3A Mechanical Engineering Building

University Park, PA 16802

Other Professional Personnel; T. F. Richardson, Pre-Doctoral Student

NBS Scientific Officer; Dr. Kermit C. Smyth

Technical Abstract:

Introduction . The present study focuses on soot particle formation

and destruction processes in laminar diffusion flames. The objective of

this study is to provide an understanding of the effects of soot particle

formation which impact fire growth, spread and combustion product

emissions. The approach adopted emphasizes two elements of the problem.

The first element concentrates on the processes responsible for the

conversion of fuel carbon to soot and particularly stresses the importance

of fuel molecular structure. The second element examines the destruction

stage of the process which reduces the soot concentration in the later

parts of the flame. In particular, specific information on the

relationship between soot and CO production is sought. A basic thrust of

the work is to identify the overall mechanism relating the emissions of CO

and soot particles from flames if one does exist. In addition,

fundamental information on soot oxidation processes as well as the role of

soot particles in the competition for oxidizing species such as O 2 and OH

may be forthcoming.

The results of this study are of direct relevance to the problems of

fire research. Soot particle formation and destruction along with other

basic phenomena such as ignition, hydrocarbon chemistry, turbulence,

radiative transfer and plume dynamics, constitute the fundamental elements

of the fire problem. Soot particles, once formed, are not passive species

in the evolution of the fire situation. Through their radiative

properties, soot particles can strongly enhance flame spread rates or the

conditions necessary for "flash over" to occur. Soot particles present

other complications through their role in visual obscuration and potential

effects on carbon monoxide formation. These effects represent serious

problems in terms of victim escape from fire situations and significantly

contribute to fire mortality rates. However, with a proper understanding

of the fundamental controlling mechanisms significant improvements in the

96
predictive capabilities of fire science moaeling can dramatically improve

the present situation.

Present Status . During the first year of the present grant, efforts

have concentrated on the assemoly and testing of the experimental

apparatus. In order to accomplish the objectives of this study, a number

of experimental capabilities are required. These include a laser light

scattering capability for particle sizing, laser velocimetry for velocity

measurements and intrusive probing for temperature and species

concentration measurements. Since particle size measurements are critical

to understanding the evolution of the soot particle field in flames,

emphasis has been given to the laser light scattering apparatus. Figure 1 shows a schematic representation of the laser scattering/extinction system.

In addition to the single scattered light detector shown in this figure,

light scattering measurements can also be obtained at ^5° and 135°.

Signal detection from the photodiode (extinction) and photomultiplier

(scattered light) systems is accomplished using separate computer

controlled lock-in amplifiers. Positioning of the coannular diffusion

flame facility is also controlled by the IBM PC/XT laboratory computer

using motorized translation stages. This approach allows for a high

degree of user independent data acquisition and significantly eases the

experimental procedures. '

A similar arrangement for the laser velocimetry measurements is now being completed which will also utilize a computer based data acquisition

approach. A probe system to obtain CO, CO 2 and O 2 concentration

measurements is presently under design. Instrumentation for continuous

measurement of these species is presently available using standard on-line

techniques (e.g. NDIR for CO and CO 2 measurements). In addition, gas

chromatography and mass spectrometry instrumentation is available for more

detailed measurements.

The initial flame measurements have concentrated on a series of

laminar diffusion flames. These include a study of an ethene/air

diffusion flame which has served to validate the laser light scattering

measurement system. This particular flame has been well characterized in

past studies and provides an excellent comparative data base. Very good

agreement has been obtained between these past studies and the present

measurements

In addition to these validation studies, two raethane/air diffusion

flames have been studied. These methane flames are to serve as baseline

reference flames for the fuel molecular structure studies. In these

experiments, the various fuel species under study are added to the

baseline flame (methane), such that the additional carbon flow rats is

held constant. Under this condition, the flame size and shape remain

similar for all the flames, thus minimizing changes in burner heat loss or particle transport in the flame. This approach allows fuels of widely

varying soot propensity to be studied under similar conditions. The fuels

to be studied using this approach include acetylene, butane, butene,

butadiene and toluene. These fuels represent a systematic variation in

molecular structure while also providing a comparison between aliphatic

and aromatic structures. Specific attention will be given to fuel

structure effects on particle inception and surface growth processes.

97
Complementary velocity and temperature field measurements will also be

obtained to further characterize the particle growth and oxidation

processes. These measurements are being coordinated with related

diffusion flame measurements underway in the Center for Fire Research.

With the completion of the gas sampling system gas phase species

measurements will also be obtained to characterize CO production in these

flames. In this phase of the study emphasis will be given to the

oxidation processes which significantly reduce soot particle

concentration.

As describe above the objective of this study is to provide a detailed understanding of soot particle formation and destruction

processes. By undertaking these studies in a well defined and tractable

flame environment, fundamental insights into the processes controlling

soot particle phenomena and their relationship to other flame emission

products can be obtained.

Reports and Papers

1. R. J. Santoro and J. H. Miller, "Soot Particle Formation in Laminar

Diffusion Flames", Langmuir, March/April, 244-254, (1987).

Laser Scattering/Extinction System

C • chopper, M • mirror, PR - polarization rotator, L • lens, S - soatlal filter NDF • neutral density filter, PD - photodiode, P - polarizer, F - narrow band filter, PMT • photomultiplier.

Figure 1

98
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution:

Grant No ,

University of Maryland

60NANB6D0633

Grant Title: Characterization of Large Scale

Turbulent Structures

in Variable Density Flows

Principal Investigator:

Other Professional Personnel:

Professor James M. Wallace

Department of Mechanical Engineering

University of Maryland

College Park, MD 20742

Dr. Kin C, Muck

Engineering Consultant

University of Maryland

College Park, MD 20742

NBS Scientific Officer: Dr. William M. Pitts

Technical .abstract:

Introduction. The objective of this program is to develop a state-ofthe-art diagnostic tool which permits simultaneous, multi-point measurements

of concentration and velocity in binary gas mixtures. This complex

experimental technique combines laser- induced Rayleigh light scattering

measurement of concentration along a line in the flow field and a multi -probe

linear array of hot-wires designed to provide velocity measurements. The

technique will be used to generate detailed quantitative information

concerning the role of large scale structures in turbulent entrainment. The

experimental data generated is expected to provide much needed information on

the effects of density variations on the turbulent mixing process. Such

results will be useful to workers who are attempting to develop numerical

models to predict turbulent mixing between two gases in either momenfum- driven

or buoyancy -driven flows.

Experimental TechniquePrevious work at NBS has demonstrated that

laser- induced Rayleigh light scattering and hot-wire anemometry techniques can

be utilized to make simultaneous, real-time point measurements of

concentration and velocity in variable density flows [1]. The present program

is designed to extend these techniques to multi-probe capability so that the

velocity and concentration fields can be mapped out simultaneously at many

spatial locations along a line within the flow field.

The present integrated system is composed of two synchronized subsyste.ms. They are the laser- induced Rayleigh scattering line-scan camera

system for concentration measurement (which has been developed at NBS by Tr.

Pitts [2’), and a linear array of seven hot-wire probes for velocitv

measurement. Figure 1 shows a schematic of the overall system.

99
The line-scan camera system consists of a f/1.9 lens designed for 1:1

focusing, an image intensifier, a. 4:1 reduction fiber optic taper, and a Reticon RL128SF line scanner equipped with RC1024S-1 evaluation circuitry. j The system scans a 12.8 mm length of the focused laser beam (diameter > 50/im) . | The Reticon video detector has 128 pixels. TTL pulses are generated by the

line scanner circuitry, which indicate both the start of a line read-out and | pixel advance. An interface constructed in-house synchronizes the Nicolet j 1180 data acquisition system and the line camera so chat the sampled and held | video signal can be digitized and stored in dynamic memory. The digitizer has

twelve bit resolution, millivolt sensitivity and a maximum data rate of 333 i kHz. Memory limitations of Che Nicolet computer currently restrict the number ! of lines which can be scanned to 256 during a single run. i

1 The hot-wire system is composed of seven hot-wire probes in a linear

array, seven TSI constant temperature anemometers, and a data acquisition

system made up of a Metrabyte DASH16 expansion board and an IBM PC XT

computer. The hot-wire array was fabricated utilizing the techniques and ! facilities developed at the University of Maryland. It is designed such chat | simultaneous measurements of concentration and velocity are obtained at seven ' locations along a focused laser beam observed by the line camera (see

Photograph 1) . These probes are produced by spot-welding short lengths

(=0.8mm) of tungsten wires (5^m diameter) to sharpened tiingsten needles which

are electro-plated with nickel. The tungsten needles are held in place by

ceramic tubes and secured using epoxy resin. Initial phase of the program was confined to using (normal) hot-wires to record the axial velocity component

only. The DASH16 board utilizes a 12 bit successive approximation A/D

converter with 12 microsecond conversion time. A maximum throughput of 50 kHz

is possible via the DMA mode of the IBM XT. The present set-up uses seven

differential channels with a bipolar range of +/- 5 Volt. The maximum

sampling rate possible with the current set-up is about 7 kHz per channel.

Synchronization of the line camera system and the hot-wire s^/stem is

achieved through home designed TTL control and timing interfaces. For the

present setup, the line camera provides 256 scans per data file, giving 256 x

7 samples of hot-wire data per file. A communication link allows transfer of

data files between the Nicolet computer and the IBM XT computer for subsequent

analysis

.

Calibration Procedures. The hot-wires were calibrated according to

King's Law ( i.e. -A+BU-*^ ) for the velocity range 1 m/s to 15 m/s.

Each wire was calibrated at nine different known mixtures of propane and air

such that a smooch variation in B with concentration could be fitted to a second degree polynomial. The calibration constant A was found to be

insensitive to concentration. The overheat ratios for the individual wires

were close to 1.8 and the average frequency response was 13 kHz.

During the course of calibrating the hot-wires, it was discovered that

by scaling and normalizing the values of B ( which are different for different

wires ) as a function of concentration, it is possible to derive a universal

polynomial fit for the variations in 3 with concentration. This finding

suggests chat a vastly simolified calibration procedure can be employed, which

only requires that each wire be calibrated at the pure gas conditions. This

new calibration procedure is being evaluated further.

The line- scan camera system is calibrated by recording the Rayleigh

light scattering intensities from pure gases before each run.

100
Experiment

As a demonstration of the new diagnostic system,, an experiment was conducted to investigate the mixing behavior of a turbulent

axisymmetric jet of propane flowing into a slow coflow of air (about 0.16m/s).

Simultaneous measurements of concentration and velocity were made along a line

aligned along the radial direction. In addition to providing a severe test

for the new experimental system, this experiment also offered an opportunity

to study the entrainment properties of the large scale structures in a turbulent flow with density variations. The diameter of the jet nozzle was

6.35 mm, and the Reynolds number was 3960. Additional details cocerning the

flow and optical systems can be found in reference [3]. An Argon ion laser ( 15 W, 488 nm ) was used. The hot-wires were located about 2 mm downstream of

the laser beam. This separation between the laser beam and the hot-wires is

accounted for by the inclusion of a lag or delay time when reducing the hotwire results using the concentration data.

Sample Results. Figure 2 shows an example of the simultaneously

recorded time traces of axial velocity, U, and mole fraction, X, at z/r^ -

22.05, r/tg - -3.74 and recorded at 358 Hz. Significant correlation of

concentration variations and the fluctuating velocity is seen. Careful study

of such records has revealed frequent occurrence of pockets of fluid with high

concentration but with low velocity excursion. This observation is probably

related to the common observation that in the mean, the concentration profile

of a jet is wider thaft its velocity profile.

Figure 3 shows time averaged velocity and concentration profiles

respectively for the normalized axial distance of z/r^ - 22.05. Two different

sampling frequencies were used. Scatters of about 10% are seen. This is

attributed to the relatively short data records. The reasonably smooth

variation in the mean velocity profile offers some degree of confidence on the

proper working of the present technique.

Measurements at locations further downstream were also obtained. Both

Ug/U and Xg/X (subscript g denotes conditions at the nozzle exit) at the jet

|i centerline are found to increase linearly with axial distance. The hyperbolic

fall-off behavior of concentration and velocity is typical of such flows.

Conclusion. The preliminary ser of tests show that the present

experimental technique is capable of providing multi-point real-time

simultaneous measurements of concentration and velocity in turbulent flow

systems. When coupled with sophisticated conditional sampling analysis

techniques ( to be developed in the future ) , this new diagnostic technique

will be a powerful tool for studying the entrainment and mixing properties in

turbulent flows. This technique is applicable to a wide range of flows where

the complicating effects of density variations or buoyancy are present.

References

1. Pitts, W. M.

,

McCaffrey, B. J. and Kashiwagi T., ”A New Diagnostic

Technique for Simultaneous, Time-Resolved .Measurements of Concentration and

Velocity in Simple Turbulent Flow Systems," paper presented at the Fourth

S^tiposium on Turbulent Shear Flows. Karlsruhe, W. Germany ^ Sept. IT-l-i- '.

2. Pitts, W. M.

,

"Development of a Line Camera for Real-Time Measurements of

Soncentration in Turbulent Flow Fields." The 5th International Congress on

.Applications of Lasers and Electro-Optics Technical Digest, 19S6.

101
MUE

FRACIiOH

VUUCIIr

3. Pitts, W. and Kashiwagi, T., "The Application of Laser- Induced Ravleigh Light Scattering to the Study of Turbulent Mixing," J. Fluid Mech Vol 141

pp. 391-429, 1984.

Photograph 1. Arrangement of the hot-wire array Figure 1. Schematic of the apparatus lay-out,

with respect to the laser beam.

l. 35-r-

\.C5 —

TtiC STEF

. 450-i-

. 350-»-

Figure 2. SimuLtaneovisly recorded time craces of

the axial velocity and concentration.

30D «.

«

•a.ao .aao i.*a 4, ID

Figure 3. Radial profiles of the mean velocity

and concentration at z/z^ - 22.05.

102
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 37

Ins titution : The University of Maryland (College Park)

Grant No. : 70NANB5H0517

Grant Title ; Kinetics of Agglomerate Formation

Principal Investigator : Professor James W. Gentry

Department of Chemical & Nuclear Engineering

University of Maryland

College Park, MD 20742-2111

Other Professional Personnel : Mr. Roberto Samson, Graduate Fellow

Mr. Thomas Cleary, Graduate Fellow

NBS Scientific Officer: Dr. George Mulholland

Technical Abstract:

Introduction . The objectives of this study are to relate the properties of

aerosols consisting of clusters formed from combustion with the operating

variables of t.he burner. Specifically, the study focuses on the diffusion

coefficient and aerodynamic diameters of the soot agglomerates. We plan to

measure these properties of the clusters and relate them to their physical

structure as determined by electron microscopy.

The study represents a continuation of the work of Roberto Sampson^ The

'fractal dimension' of soot clusters was computed using four different

computational models and the mass concentration of soot was related to the

hydrocarbon fraction in the fuel. The data on the clusters obtained from

electron micrographs were consistent with the clusters being fractals.

The study described here is a continuation of this work. It focuses on the

in-situ measurement of the diffusion coefficients of the clusters. Described in

this paper are the experimental design, the analysis of data, and the

preliminary experimental measurements.

Experimental Design . The diffusion coefficient (D) of particles in a gas can readily be 'obtained by measuring the particle concentration before and after

long, circular tubes (length and diameter d ) as a function of flow rate (Q).

It is assumed that the collected particles are fixed on the walls of the channel

and that the flow in the tubes is laminar. The fractional penetration is given

by closed form expressions in terms of a single variable (the reciprocal of

the Peclet number). This variable for a circular cluster of channels (diameter

d^^ and porosity £) is given by

•a £ _A

d

103
The diffusion coefficient is the product of two terms the Stokes-Eins tein

diffusion coefficient and the Cunningham correction for non-continuum effects.

For spherical particles D is approximately equal to

D = ( kT

3TTnd

) (1 + 0.2

d (microns]

P

For clusters and indeed for non-spherical particles in general, the analogous

expressions are not known.

An experimental difficulty in diffusion coefficient measurements is that

the functional relation between the penetration and has two dissimilar zones. For large 0 (

4> >0.2) the separation is sharp and the diffusion battery is an excellent instrument. For small (p ( (p < 0.05) the separation is broad and the

instrument is not effective in determining size distributions.

. ( 2 ) The glass capillary array design_^ used in tb^s st^dy is suitable for

diffusion coefficients between 3 X 10 and 7 X 10 cm /sec. These values

correspond to spherical particles between 4 and 400 nm. The battery consists of

4 to 6 stages which can be placed in line either individually or grouped. Flow

enters a circular chamber approximately 5 cm in diameter and 2 cm in height

through the side of the chamber. The flow passes through the GCAF at the bottom

of the stage. The penetration is determined as the ratio of concentrations

through the filter and through a blank stage. The particle concentration is

measured with a TSI continuous flow condensation nuclei counter.

Data Analysis . Measurements of the diffusion coefficients of clusters

present two classes of problems - the aerosol is polydisperse and the aerosols

are not isometric. The difficulty of the second type is that the signals in

measurements are frequently ambiguous. We have developed two procedures or algorithms which can be applied to the analysis of clusters. The first

procedure designed for measuring polydisperse aerosols requires measurements of

the fractional penetration or collection efficiency over a range of

penetrations. The method called the apparent size method^ ’ has been

successfully applied to narrowly distributed combustion aerosols, particles with

adsorbed layers of hydrocarbons, and the electrical mobility of asbestos fibers

where the data are limited to the size distributions before and after the

filter. The analogs in the case are the clusters before and after the diffusion

battery.

The apparent size (diffusion coefficient) method is based on a plot of the

apparent size as a function of experimental penetration. The apparent size is

the diffusion coefficient of a hypothetical, monodisperse distribution whose

fractional penetration computed from theory or empirical correlations matches

the experimental value of penetration at the same conditions (i.e. flow rate).

This formulation has three advantages over alternative approaches:

(1) It provides a sensitive, graphic display of the degree of experimental

error and provides an indication of systematic errors.

(2) The mean value of the curve < Ln D > is the log mean_ diffusion

coefficient of the distribution. This remarkable result for < Ln D > is an experimental result independent of an assumed functional form for the

distribution while the log mean diffusion coefficient depends only on the size

L04
distribution function.

(3) The intercept as the penetration approaches one is proportional to the

variance

The unambiguous determination of two parameters is an efficient procedure

for characterizing the size distribution of an aerosol and the relation of its

properties to combustion variables.

The second algorithm supposes that the size distribution before and after

the diffusion battery and the overall penetration are known. The principal idea

is that the penetration Pt(X ) at a size X can be expressed by

Pt(X ) a

Iz h(x -X ,X))after

i i a

f N

j Z h(x,-x ,X)

V

. 1 a

where h(y,A) is a non-negative function equal to 1 at y=0 and collapsing to a c- function for an asymptotic value of X. The representation includes the commonly

used histogram method as a special case.

Its advantages are that it can be used with small samples. It can also be

used with particles characterized by multiple variables such as asbestos fibers

(diameter and length) or clusters (number of primary particles and radius of

gyration)

Experimental Results . Described in the paper are the measurements of the

diffusion coefficients and 'aerodynamic diameters' of soot clusters formed from

the combustion of ethane and acetylene. The cluster size - number of primary

particles - was found to depend on the hydrocarbon composition of the fuel. By

controlling the fuel composition the combustion aerosol could pass through the

entire range from detectable, but not visible, to the long sooty threads

associated with acetylene combustion. In the diffusion battery work discussed

here, the focus is on the smaller particles.

The base experiment consists of combustion in a diffusion burner. The

aerosol is diluted and passed through (i) an inertial impactor stage and/or (ii)

a diffusion battery stage. The penetration is the ratio of aerosol

concentration through a GCAF disc and a blank stage. The aerosol concentrations

were measured with a condensation nuclei counter. Experimental measurements

without the impactor stage could cover the range from their formation to

approximately 0.1 ym.

One thrust of the experiment is to determine the drag on the clusters. In

a prior study the fractal dependence of such small clusters was measured by

electron microscopy. If the drag had a (-1/F) dependency with the number of

primary particles rather than (-1/3) one would expect to see a significant

decrease in the mean diffusion coefficient and an increase in the variance for

relatively small clusters.

Diffusion coefficients measured as a function of fl&w rate as well as limited measurements with electron microscopy are reported.

105
Reports and Papers ;

I. Journal Articles, Book Chapters, etc.

1. Samson, R.J.,G.W. Mulholland and J.W. Gentry, "Structural Analysis of Soot

Agglomerates", Langmuir, 3, 272 (1987).

2. Samson, R.J., G.W. Mulholland and J.W. Gentry, "Analysis of Soot

Agglomerates and Their Physical Properties", Aerosols : Formation and

Reaction , ed . H. Fissan, Pergamon, 413-16 (1987).

II. Technical Presentations

1. Cleary, T., R. Samson, G. Mulholland and J. Gentry, "The Relationship

Between Structure and Aerodynamic Measurement for Clusters", presented at

GAeF Annual Meeting, Hanover, BDR, Sept. (1987).

2. Samson, R.J., G.W. Mulholland and J.W. Gentry, "Analysis of Soot

Agglomerates and Their Physical Properties", 2nd International Aerosol

Conference, Berlin, Sept. (1986).

3.

Samson, R.J., G.W. Mulholland and J. Gentry, "Structural Analysis of Soot

Agglomerates", Symposium on Fine Particles: High Temperature Synthesis,

Atlanta, GA, June 15-18 (1986).

III. Other Reports

1. Gentry, J., G. Mulholland, R. Samson and T. Cleary, "Methodology for Fractal

Analysis of Combustion Aerosols and Particle Clusters", Aug. (1987).

2. Samson, R. , M.Sc. Thesis, University of Maryland (1986).

106
FIRE SCIENCE AND ENGINEERING DIVISION

107
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ENGINEERING METHOD DEVELOPMENT

CENTER FOR FIRE RESEARCH

FY 87

Professional Personnel

Harold E. Nelson, Senior Research Engineer

Peter Lee, Cooperative Student

Program Objectives

To expedite the transfer of scientifically-based technology instruments to the practicing fire protection engineering community and similar groups.

Scope

The work addresses the development of engineering systems for design ^plication and the demonstration of the feasibility through examples of use. The prime examples of use to date have been in fire incident reconstruction.

Activities

There are two principle activities.

A. Fire Protection Hazard Analysis and Facility Assessment System

nils IS a three -year project currently sponsored by NBS and the General Services Administration to develop rational engineering methods. The methods are designed to be usable by practicing fire protection engineers in appraising fire safety of buildings and evaluating the impact of specific design proposals for improving fire safety.

A prime tenant of this project is to develop the least sophisticated, fastest responding analysis procedures that produce an adequate and dependable analysis of fire hazard impact. Many of the procedures being incorporated are built around algebraic computations and simple fire growth models.

^ Factors of safety are being included to compensate for uhe uncertainties involved. The initial scope addresses the development and growth of fire and fire products in any one story of a subdivided building, including leakage from that floor into other space (such as stairwells). It considers pre- and post- flashover fires, fire detection, sprinkler response, emergency evacuation, and areas of refuge

The program disk FIREFORM presents a portion of the routines involved.

108
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B. Fire Incident Reconstruction

Where appropriate, the procedures for the engineering analysis system

are being tested and demonstrated in analysis and reconstruction of fire

hazard incidents. To date, two such analyses have been made, one has

been reported, a paper on the other is in clearance.

These two fires were the December 31, 1986 fire in the Dupont Plaza

Hotel in San Juan, Puerto Rico and the December 15, 1985 fire in a hospice in southern Michigan. Both fires involved violent flashovers

that produced excess pyrolysis conditions. In the case of the Dupont

Plaza, the amount of combustible pyrolysis products transported from the

room of origin was massive (estimated in the range of 6-7,000 g/s) . As

these products vented, they found air and converted to flame. In that

fire, the majority of the deaths occurred as the occupants were swept by

this flame

Conversely, in the hospice fire, the fire vented to the outside and into an internal corridor that essentially had no vents to the outside. In

this latter case, venting to the outside maintained the temperature in

the room of fire origin keeping the rate of pyrolysis high. That

vented into the corridor, however, appeared to quickly consume the

available oxygen and move the combustion reaction sharply towards carbon

monoxide. It is believed that very high concentrations of carbon

monoxide (probably in excess of 50,000 parts per million) quickly

invaded chose other patient rooms open to the same corridor

In late summer of 1986 , a test was conducted in the NBS corridor to

approximate the conditions believed to have occurred in the hospice.

Figure 1 is a plan of the test corridor. The fire (5 MW propane burner) was positioned in the space immediately adjacent to the hood. This

stistained flashover. The fire was continued until a steady state in

both temperature and carbon monoxide production occurred in the

corridor. Data was taken in each of the rooms. Figure 2 is a plot of

the rate of energy release that occurred in the fire and the conditions

that occurred in the most remote room. These readings demonstrate the

consumption of oxygen, the production of carbon monoxide, the drop of

the interface, and the relatively low rise in temperature. This appears

to be very indicative of the type of conditions likely to occur in small

to modest size corridors exposed to a flashed over room that in turn is

vented to the outside.

Publications

Nelson, H.E., An Engineering Analysis

- The Dupont Plaza Hotel and Casino - of the Early States of Fire Development

December 31^, 1986, NBSIR 87-3560, 1987.

109
110

Figure

1.

NBS

Test

Corridor

(As

(;onCigured

for

'I’est)
5MW

CH4

Burner

oira)

CMUO
COMPARTMENT FIRE MODELING RESEARCH

CENTER FOR FIRE RESEARCH

FY 87

Professional Personnel

I •Leonard Y. Cooper, Head j Henri E. Mitler, Physicist j John H. Klote, Mechanical Engineer

William Davis, Physicist I Glenn P. Forney, Computer Scientist

Kevin Greenaugh, General Engineer j Vahid Motevalli, Guest Worker (Univ. of Maryland) j

I

j Proeram Objectives }

I i (1) Develop, maintain, improve and provide assistance in the use of

Compartment Fire Model computer codes.

(2) Develop and establish the validity of new and improved i analytic/computational compartment -fire -phenomena submodel algorithms

for use in compartment fire simulations.

(3) Develop, maintain, and enrich a catalog of well-docximented submodel : algorithms and subroutines for general use in compartment fire models. i

ScQ-pe

The work focuses on the development of benchmark computer codes (s) which would

be useful in simulating the phenomena which occur in compartment fire

scenarios. The term "benchmark computer code" is intended to connote a welldocumented computer code which: a) is based on physics and numerics of proven

reliability; b) is numerically robust; and c) is user-friendly in the sense

that it can be used with relative ease by researchers and professional fire

safety practitioners, and that it can be transferred to and used with computer;

hardware readily available to the fire science/technology community.

Projects and Recent Publications

1. Compartment Fire Models

The Consolidated Com-partment Fire Model (COFM) Computer Code. The main focus

of the Group is to develop generic and applications - specific software for a we 11 -documented, user-friendly, modular and easily updated CFR Consolidated

Compartment Fire Model (CCFM) Computer Code. This software will be used to

implement applications of the CCFM which address particular needs of CFR and

the Fire Science and Technology communities. CCFM development will be based

on and will consolidate the advances of the past decade of progress in zonet^y'pe compartment fire modeling research, and it will incorporate the most

advanced available Computer Science technology. The code will pass through a series of useable development stages to be designated as CCFM applications.

The first of these is a prototype application CCFM. HOLE. This code simulates

the environment which develops during a fire in a single constant area room with a single, arbitrarily placed, near-uniform-elevation vent, or horizontal

slit, of arbitrary area. Arbitrarily high room pressures are allowed, e.g.,

112
fire in a hermetically sealed compartment. The second CCFM application will

involve a multi -room code, and it is planned that subsequent CCFM advances

will build on this.

FIRST This NBS code is a consolidation of several adanced versions of the

original, single -room Harvard 5 code. The code was completed this year and is

being issued with a Users' Guide. FIRST will be used as a testbed for new

fire-growth algorithms which are now under development. It is also being used

as a working tool for carrying out single-room compartment fire analyses.

The NBS/Harvard 6 Multi-Room Code. This CFR- enriched, advanced version of the

original Harvard 6 code was used to simulate results of previously reported

full-scale, multi -room fire experiments. Comparisons between simulated and

measured fire -generated environments were reviewed.

A Model to Simulate the Effects of Roof Vents. Sprinklers, and Their

InteractionsA new computer code is under development which will be useful

in analyzing the responses and effects of roof vents, sprinklers, and their

interactions during compartment fire -generated environments.

"Fire Growth in Combat Ships," NBSIR 86-3451, J.A. Rockett.

"The NBS/Harvard Mark VI Multi-Room Fire Simulation," J.A. Rockett and

M. Morita, Fire Science Technology, Vol. 5, No . 2 , 1985, pp 149-163.

"A Plan for the Development of the Generic Framework and Associated

Computer Software for a Consolidated Compartment Fire Model Computer

Code," G.P. Forney and L.Y. Cooper, NBSIR 86-3500.

"How Accurate is Mathematical Fire Modeling?" H.E. Mitler and J.A.

Rockett, NBSIR 86-3459.

"A Program for the Development of a Benchmark Compartment Fire Model

Computer Code," L.Y. Cooper, J.A. Rockett, H.E. Mitler and D.W. Stroup,

presented at the ASTM International Symposium on Mathematical Modeling

of Fires and Related Fire Test Methods, Dec. 3, 1986 and to be published

in the Proceedings

"User's Guide to FIRST, A Prototype Benchmark Single Room Fire Model,"

H. E. Mitler and J. A. Rockett, NBSIR 87-3595.

"The Compartment Fire-Generated Environment and Smoke Filling," L.Y.

Cooper, to be published in the Fire Protection Engineering Handbook.

"Comparisons of NBS/Harvard VI Simulations and Full-Scale, Multi-room

Fire Test Data," J.A. Rockett, M. Morita, and L.Y. Cooper, NBSIR 87-

3567, and submitted for outside publication.

"Fire in a Room with a Hole: A Prototype Application of the Consolidated

Compartment Fire Model (CCFM) Computer Code," Cooper, L.Y. and Forney,

G.P., presentated at the 1987 Technical Meeting of the Eastern Section

of the Combustion Institute and published in the Proceedings.

113
2. Compartment -Fire -Generated Flow Dynamics, Flame Spread/Growth and Heat

Transfer: Submodel/Algorithm Development and Verification.

The purpose of this project area is to carry out research toward an understanding of compartment fire phenomena which are critical to the

advancement of newly developing compartment fire models. The critical

objective here is to develop results which can be expressed in the form of

concise algorithms and associated modular computer subroutines which are readily useable in zone -type compartment fire model computer codes, in

general, and in the CCFM, in particular.

Flow Dynamics. Heat Transfer, and the Response of Fire Safety Devices. This

work involves experimental and theoretical activities leading to the

development and validation of algorithms for simulating compartment firegenerated flow dynamics and heat transfer and the response of fire safety

devices to the fire -generated environment. The ability to simulate such

phenomena is neccessary for reliable predictions of the compartment fire

environment. This is the environment which defines the impact of the

compartment on fire growth development and which determines the extent of

hazard. Progress has been made in a variety of these areas and this is

indicated by the titles in the list of papers and reports which follow below.

Wall Fire Growth. The purpose of this work is to develop and validate

experimentally an alogorithm which predicts the fire behavior of a burning

wall in a compartment. A first-order model involving steady burning of non- charring solids has been completed and is now being implemented into FIRST.

Smoke Control and HVAC Systems. This work involves experimental and

mathematical modeling activities leading toward a capability of simulating the

effect of HVAC smoke control systems on the spread of fire -generated

environments in multi-room facilities. An algorithm for the simulation of a simple fan-duct subsystem is being developed which will be implemented in a relatively early CCFM application.

Cigarette Fire Safety. A preliminary study on the fire safety of cigarettes

has been completed. This work involved the development of mathematical models

of the smoldering of cigarettes on furniture. The objective of the work was

to use modeling to establish the propensity for furniture ignition of a particular cigarette configuration and furniture composition.

"The Buoyant Plume-Driven Adiabatic Ceiling Temperature Revisited,”

L.Y. Cooper and A. Woodhouse, Journal of Heat Transfer, Vol. 108, pp

822-826,' 1986.

"Thermal Response of Unconfined Ceilings Above Growing Fires and the

Importance of Convective Heat Transfer," L.Y. Cooper and D.W. Stroup,

Journal of Heat Transfer, Vol. 109, pp. 172-178, Feb., 1987.

"Measurements of the Transient Temperature and Velocity Profiles in

Ceiling Jets," V. Motevalli, C.H. .Marks, B. McCaffrey and L.Y. Cooper,

presentated at the 1986 Technical Meeting of the Eastern Section of the

Combustion Institute and published in the Proceedings.

114
87!3535® a/ 3535, to be Fires," L.Y. Cooper -iBSIE submitted for outside publication.

^ ^

"Heat Transfer in Compartment Fires Near Regions of Ceiling Jet U;,n

ProceedSgs

Transfer Conference and published in Conference

Test Results and Predictions for the Response of Near-CPi 1 1 ncr Cr^v- Links in Full-Scale Compartment Fires, Cooper, L.Y and Stroup

pl?StL°n. sub.itt;d for outside

•

- Heat and Mass Transfer in Fires and

Engineering,

ntrolled Combustion," Kennedy L.A. , and Cooper, L Y Mechanical Vol, 109/No. 4, pp62-67, April 1987,

Mechanical

The Effect of Cigarette Characteristics on the lenition of Cofe

Day,

Fu^lshings

D., to

- Chapter 5: Modeling Ignition." Mitlfr, H I, Davis „ appear as a NBS Special Publication. ’

Computer Model of a Smoldering Cigarette "HP* M-it-i j it ta j-;s

Algorithm for the Mass-Loss Rate of a Burning Wall " HE Mirlo.- e Appear as a NBSIR and submitted for outside lubUcation

' “

(SM^«r“Ilolf^°H (OMACS).

Movement by Air Conditioning Systems Klote, J.H., submitted for outside publication.

'’^iTs on Mass Transfer bv Pulsatile Flow " J.H., submitted for outside publication.

"An Overview of Smoke Control Technology," Klote J H NBSTR R 7 and submitted for outside publication.

’ 87-3626

Co

"Fire

appear

Safety Inspection and Testing of Air Moving Systems " Klote J H as a NBSIR. ^ i-ems , Klote, J.H.,

Ind'’lT*?“ and G.T. Tamura,

^

Smoke Control," Klote J H presented at ASHRAE Symposium Julv 1 lQfi 7

' 'v published in ASHRAE Transactions.

1. 1987. and to be

loItlll^-^Klolf Effect on Elevator Smoke

- Klote, J.H., submitted for outside publication.

115
Heat and Mass Transfer in Compartment Fires, Cooper, L.Y, and Farouk,

B, , Editors, Proceedings of four sessions on Heat and Mass Transfer in

Compartment Fires in Volume 1 of Proceedings of the 2nd ASME-JSME

Thermal Engineering Joint Conference, American Society of Mechanical

Engineers, New York, NY, March 23-27. 1987.

"Methods to Calculate the Response Time of Heat and Smoke Detectors

Installed Below Large Unobstructed Ceilings," Evans, D.D. and Stroup,

D.W.

,

Fire Technology, 22, pp . 54-66, 1986.

"Evaluating Thermal Fire Detection Systems [English Units]," Stroup,

D.W., Evans D.D. and Martin, P. , NBS Special Publication 712, April

1986.

"Development of an Automated Probe Positioner for Measurements in FireGenerated Plumes and Ceiling Jets," Stroup, D.W., NBSIR 86-3379.

3 . Compartment Fire Model Catalog of Submodel Algorithms and Associated

Computer Subroutines

This work involves the maintenance and enhancement, through the development o improved and additional entries, of a Catalog of Compartment Fire Model

Algorithms and Associated Computer Subroutines. A first edition of the

catalog has been issued and several new entries to be used in the CCFM are under development.

"A Catalog of Compartment Fire Model Algorithms and Associated Computer

Subroutines," D.W. Stroup, NBSIR 87-3607.

.\ssociated Grants

Experimental Study of the Environment and Heat Transfer in a Room Fire,

Zukoski, E.E., California Institute of Technology.

Negatively- Buoyant and Penetrative Flows Generated in Enclosure Fires,

Jaluria, Y. , Rutgers - The State University of New Jersey.

Prediction of Fire Dynamics, J deRis - Factory Mutual Research Corporation.

Transient Heat Transfer in Ceiling Jets, Marks, C.H., University of Maryland.

116
COMPARTMENT FIRE MODEL GRANTS

117
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1 '^
CEOTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Inst itut ion : California Institute of Technology

Grant No : 1TBS5 60NANB600638

Grant Title : Experimental Study of Enviomment and Heat

Transfer in a Room Fire

Principal Investigator : Professor Edward E. Zukoski

Jet Propulsion Center

301-46

California Institute of Technology

Pasadena, CA 91125

Other Professional Personnel: Professor Toshi Kubota

Michael Chobotov, PhD Candidate

Stephen Toner, PhD Candidate

Richard Chan, PhD Candidate

James Mo rehart, PhD Candidate

NBS Scientific Officer: Dr. Walter Jones

Technical Abstract:

Introduction . Smoke which is produced by a fire spreading through a building can act to aid in the spread of the flame by the transport of

hot and perhaps combustible gas, and can be harmful to occupants because

of its temperature and toxicity or because its opacity hinders the rapid

movement of the occupants through the building. Under certain

circumstances, the combustion of the fuel produced in the fire can occur under conditions in which the concentration of oxygen in the ambient gas

is far below normal and a fuel rich mixture can be produced which will

bum later in an adjacent space and aid in the spread of the fire. We

are interested in developing models for the production and movement of

smoke in complex structures and have been studying several fluid dynamic

processes which will be described below. These processes are difficult

to describe analytically because the flows are turbulent and are strongly

influenced by turbulent mixing between streams in which buoyancy forces

are predominant and because the chemical processes in turbulent-buoyant

flames are not understood completely.

Gravity Currents . We are investigating the flow cf hot gas in

gravit]^ currents under circumstances which model the flow of hot gas

along long hallways or tunnels. Our aim is to understand the influence

of heat transfer on the motion of the hot gas and the subsequent

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development of the ceiling layer in hallways. Gravity currents in

hallways which are both horizontal and inclined up to 30 degrees below

the horizontal are being investigated.

Two types of apparatus are being used: the first is a salt waterwater facility which is a 2.4 meter long channel with a 15 cm square

cross section. This is being used to investigate the dependence of the

gravity current parameters on the Reynolds number and the inclination

angle, and to determine the nature of the return flow which develops

after the gravity current has impinged on a vertical wall closing the

downstream end of the channel.

Flow visualization techniques are used to measure the velocity of

the head of the current, the depth of the current, and the nature of the

return flow. Fluorescent dye techniques are being developed to measure

the concentration profiles in the flow and hydrogen bubble techniques,

and to determine the velocity profiles.

Measurements have shown several interesting features of these flows.

First , when the Reynolds number of the current, based on head velocity

and current thickness near the head, are greater than 6,000, the effects

of Reynolds numbers are small for ratios of hall length to current depth

of 100. Thus, for full scale fire situations, the influence of viscosity

on the propagation of the current will usually be negligible. Second , the velocity of the head of the current is surprisingly independent of

the inclination angle of the hallway over the whole range of angles from

0 to 90 degrees. Third , the return flow in the hallway occurs as a wave

on the interface between the current and the ambient fluid which brings

the current to a stop at the wave front without violent mixing. For

deeper currents, the return flow fills more than 50% of the channel.

Finally, we have found that the depth and frontal velocity of the

current are dependent on the method used to introduce the current into

the channel. In contrast to the prediction of several idealized flow

models that the maximum current depth which leads to a steady flow is

helf the channel height, much deeper currents can be formed when the

current is introduced with sufficient momentum. This process is being

studied now.

The second apparatus is an air facility 8.6 m long and 0.5 m square.

This apparatus and the experimental results obtained in it are described

in detail in the papers by Chobotov et al and will only be very briefly

reviewed here. Experiments in this apparatus have shown that the rate of

heat transfer between the current and the ceiling is much higher than

rates calculated for forced convection over flat plates because of a buoyancy controlled instability in the wall boundary layer. The rates are high enough to reduce the overheat in the hot gas to very small

values within a length corresponding to 50 times the current depth. The

119
effect on the velocity of the head is smaller but the influence of the

heat transfer could lead to a strongly stratified hot gas layer in long

hallways

.

Combustion in Tvo-Laver Models ; We are also studying the products

of combustion and flame geometries produced by large buoyancy-controlled

diffusion flames which extend from a lower layer, which contains

unvitiated air, into a upper layer which contains products of combustion

mixed with air. The results of these tests are described in detail in

Toner et al (1986) and which give results based on a steady state flow

from the plume into the upper vitiated layer.

The influence of the vitiated layer on the flame length has been

found to be negligible when the fuel-air ratio of the gases which burned

to form the upper layer is

less than stoichiometric.

However, when the fuel-air

is greater than

stoichiometric, the flame

length decreases

approximately as expected

because of the reduction

in the heat released in

the flame.

Typical data are

shown in the accompanying

figure where the

intermittency values are plotted against height for flame lengths measured in free air and with

the level of the interface between air and the vitiate layer at 23 and 10 cm. The fuel-air ratio of the gas which formed the vitiated layer were

0.76 and 1.92 for the latter two cases.

In accidental fires which often develop over a few minutes, the

steady state will rarely be reached and in general the gas in the upper

layer will contain much more oxygen, i.e., will have a much lower fuelair ratio, at a given time than the gas entering the layer through the

fire plume. We are examining this situation at the present time in a new

hood which is 2 m on a side and 1.25 meters deep, and which is equipped

with a gas supply system which will allow us to control the oxygen or fuel flow to the upper layer independent of the fuel-air ratio of the

plume gas.

Reports and Papers

FLflflE HEIGHT INTERHiTTflHCE FOR H FIFE

0.

0

INTERMIT

0.2

SOX

liT 10 CM-

- WITHOUT

SOX

soy.ST .. 23 cn-'

50 iOO 150 height HB07E EUFtlE' [Ol;]

1. E. E. Zukoski, "Heat Transfer in Unwanted Fires," presented at Joint

ASME-JSME Meeting on Heat Transfer, Hawaii, March 19S6.

120
2 . E. E. Zukoski, ’’Sunmary Report, Fire and Smoke Physics Session,'*

UJNR Meeting, Boston, I-Iass., May 4-8, 1987.

3. M. Chobotov, E. E. Zukoski and T. Kubota, "Heat Transfer Effects

on Gravity Currents," Density-Stratified Flow Symposium Proceedings , edited bv E. J. List and G. H, Jirka, D. Reidel Pub. Co. Boston, Mass.

(1987).

4. M. V. Chobotov, E. E. Zukoski and T. Kubota, "Gravity Currents with

Heat Transfer Effects," Report, ITBS Grant No. 60NANB6D0638, California

Institute of Technology, Pasadena, CA, Septanber 1986 .

5. S. J. Toner, E. E. Zukoski and T. Kubota, "Entrainment, Chemistry and

Structure of Fire Plumes," Report, NBS Grant No. 60NANB6D0638,

California Institute of Technology, Pasadena, CA, September 1986.

121
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STAJJDARDS

FY 87

Institution : Factory Mutual Research Oorp . , Norwood, MA 02062

Grant No : 60NAN35D0560

Title : Prediction of Fire Dynamics

Principal Invesoi gators : John de Ris (517)762-4300, ext. 2850 - Ronald L. Alpert (617)762-4300, ext. 2776

Other Professional Personnel : M. A. Delichatsios

H. W. Emmons (61 7)495-2847

G. H. Markstein

L. Orloff

NBS Scientific Officer : 3. McCaffrey and H. Mitler

Technical Abstract ; This work is divided into four tasks.

Task 1. Prediction of Fires in Buildings (H.W. Emmons)

Work on four problems has been in progress this year.

1. The fire in an 'unf ire-stopped wall space connected above and below by'

another open wall space was solved by a program in BASIC. It is too slow to

be practical with a stable solution time step. Therefore, it is to be re- written in Fortran and r'jn on a Vax, but this has not yet been done.

2. The Chapter on Vent Flows for the proposed book on the "Prediction of:

Fires in Buildings" has been published as a project report.

3. The Users Guide to the NBS computer code, FIRST, was reviewed and a n'umber

of changes to make it more user friendly were suggested. Many of these

changes have been made. The changes required in the Input Program are being

made at Harvard by an advanced graduate student, Jason Harry, 'inder the direction of the project leader.

4. Some 90 different fire cases, involving many different fires and their en- vironment, have been run with FIRST on the Harvard Physics Vax 86C0. This

effort has disclosed:

a. A number of cases that will not r’on

;

b. A n'umber of coding errors that are being corrected at NBS.

When a fire case fails to r’jn, it can often be "fixed" by a small change

of fuel location in the enclos’ure or a small change of some property, e.g.

Heat of Combustion or Vaporization. A frequently effective fix is a relaxation of the tolerance from .001 to a lower value, often .01. This results in

only small changes in most of the output.

I Publications : Home Fire Proj ect Report /^74 - Transient Ceiling Jec

Home Fire Project Report 475 - The Flow of Cases Through Vents

Experiments with an Enclosure Fire Math Model - Suomitoed co 2nd Symp.

(Incl) on Fire Safety Science.
Task 2. Correlation of T'irb’ilent Flame Radiation and CO Release with

SmoKe Point

(L. onoff, M.A. D®1 i chats i os , J. Ris)

The main oojective of tnis casK is to ootain general empirical correlations relating the radiant fraction from turbulent buoyant diffusion flames to

the laminar smoke-point values ac corresponding thermochemical conditions.

These correlations will be tested over a range of fuel chemical compositions,

inert additives to the fuel supply, fuel supply temperature, and ambient 02/Np

concentrati ons

Theory and experiment imply that properly designed buoyant t'orbulent jet

flame experiments can provide a quantitative bridge relating laminar smoke

point meas’irements of a fuel to its farbulent wall fire radiation. It is also

possible that we can extend the results to model large-scale b’crning using

laboratory experiments in enriched O2 atmospheres, and predict burning rates

in vitiated atmospheres. This concept of radiation modeling with buoyant jet

flames requires highly precise and reliable radiation meas'jrements that link

to the independently meas’cred wall fire radiation and smoke points. In order

to verify the models described here, these radiation meas'creraents must be re- producible in other laboratori es . These requirements merit particular attention, and are discussea below.

O’-iT modeling analysis indicates that t'crbulent wall fire flames and t'lrbulent buoyant jet flames will have the same local enthalpy versus fuel concentrations provided the respective mixed fuel gases and supplied fuel have identical compositions and tempera^t'jres . We fin'd that the composition of wall

fire gases adjacent to the wall can be simulated in jet fire experiments by

mixing a fraction B^/(B^ + 1) of the 'inb'crned gaseous fuel with a fraction

i/(B|^ + l) of cooled combustion gasses created by preburning this fuel with its

stoichiometric mass of oxidant, with corrections for completeness of combustion. A new premixed b'lrner will shortly be installed to permit verification

that effects of wall cooling on flame radiation can be simulated in the present buoyant jet study, and consequently, by smoke point meas'jrements

Another aspect of the present study arises from the need for a better scientific '-inderstanding of how rate of heat release (RHR) calorimeters can be

used for simulating enhanced flame radiation effects in large-scale fires. In

general fires exhibit a scale effect of increasing radiative feedback relative

to convection. C’jrrently there is a lack of information to guide the RHR

small-scale studies in prescribing the amount of externally imposed radiation

needed to supplement the enhanced radiative feedback induced by enriched O2

ambients. The range of vitiated and enriched O2 burning behavior that can be

investigated in this study has been extended by installation of nitrogen and

oxygen supplies to permit variation of the ambient oxygen concentrati on between 15 and 30 percent. This modification allows a more direct comparison

with smoke point measurements obtained in 0^/'N2 atmospheres by .’^educing the

complicating thermochemical effects of COp and HoO that would arise from vitiation with actual products of combustiorr. The experiment includes a f r’nac^

exhaust that can be supplied to the fire environment for subsequent study of

the more realistic vitiation environment.

123
Buoyant jet flames in open laboratories are subject to ambient dist'jrbances that induce unpredictaole effects on their radiative output. There appears to be no effective way to ens’ire a highly quiescent open laboratory en- vironment with adequate air supply and absence of radiative heading from ;:ne S'jrro'unding walls. In this study we use a watei—cooled 1.2 m diameter encloS’jre with a highly quiescent measured air supply filtered through the floor

and a precisely controlled rate of exhaust.

A series of baseline meas'urements were carried out with systematic variation of several experimental parameters in order to gauge their effect on flame radiation. These parameters include; ambient air flow velocity in the

immediate vicinity of the flame; overall air supply rate in terms of the stoichiometric combustion requirement; removal of soot fallout from the burning of

carbon-rich fuels; and fuel supply temperature.

Radiation measurements of laminar-to-turb'ulent transitional flames (5-

8 kW ) revealed a significant dependence on the air supply rate. Visual inspection suggests that the co-c’urrent flow affects the transition heignt oy

generating or damping entrained vortex flows. These transition variations, in

t'urn appear to affect soot production and oxidation processes.

Co-flow was substantially reduced by (1) restricting the air supply

through the enclosure floor to 30 times the stoichianetric requirement for

complete combustion, which reduces its co-flowing velocity component; and (2)

centering a water-cooled black circular plate below the nozzle to impose primarily horizontal air entrainment characteri sti c of burning in the open. Radiant fraction meas'jrements and visual inspection of the flow for six different fuels indicate that these procedures ins'ure stable, axi symmetric flames

that are not sensitive to minor variations in the air supply rate.

Aspiration of outside air through the enclos'are walls, for example through

electrical and fuel ports introduces disturbances that cause zhe flame to

lean, meander, and exhibit flame height f luctuations . These dist'ur bances have

been eliminated by tight regulation of the air supply blower and the exhausz

so that the ambient press'ure i.nside the enclos’-ire is in equilibrium witn tne

s'orro’jnding laboratory.

The radiation from carbon-rich fuels such as acetylene appears to be sen- sitive to fallout of agglomerated soot particles wnich screen the radiative

output. This interference is reduced by increasing the exhaust rate while

maintaining the desired level of air supply. The high value of radiant fraction obtained for this fuel is ascribed to its high flame temperafure and soot

production rate. Flame radiation was also found to be slightly sensitive to

fuel supply temperat'ire. The gaseous fuel filters through a bed of 2 mm diameter stainless steel balls before exiting at the nozzle lip. This flowsmoothing bed receives radiative feedback from th'^ flames, which can result ir. fuel supply temperatures controlled by feedback radiation. A regulated fuel

preheater was built into the burner to maintain the fuel at 60°C, which re- duces heat exchange between the bed and fuel supply.

124
Task 3. Wall Fire Flame Radiation (G.H. Markstein, J. de Ris)

The objectives are extensions of previously established relationships for

fire radiation to fires burning on vertical walls, comparison of the res'olts

wich existing analyses of wall burning, ana development of improved raoaels of

wall burning based on experimental findings. As in other related work, the

significance of studies of fire radiation rests on the fact that in many fires

energy transfer from the flame to the fuel and to the s’irroundings occ’jrs predominantly by thermal radiation. The rate of fire growth and the spread of

fire to new fuel elements depends critically on this energy transfer, and its

quantitative assessment is thus essential for predicting fire behavior.

In the present task, wall fires of solid fuels are simulated by burning

gaseous hydrocarbon fuels on a water-cooled vertical porous metal surface

under steady-state conditions. The burner is subdivided inbo a n'omber of

panels of equal height, so that the simulated pyrolysis height can be varied

by the choice of the number of fuel-supplying panels. In addition, the limiting case of zero pyrolysis height can be studied by supplying the fuel from a slot b'orner at the base of the wall.

Fuel is supplied to the b’urner by electronic flow controllers , and the

heat transferred to each panel is determined from the temperat’ure rise of the

cooling water, meas’ored by differential thermocouples. The total radiant

emission from the fire is measured with a wide-view-angle radiometer employing

a spectrally flat thermopile sensor. In addition, the vertical distribution

of radiant power per 'unit height emitted by narrow horizontal slices across

the width of the fire is measured with a scanning slit .radiometer . The scan along the height of the fire is obtained by the use of an electromagnetically

deflected plane front surface mirror operated in a linear ramp mode. A fastresponse spectrally flat pyroelectric sensor is used in this instr’oment. A new version of this instrument, providing improved signal-to-noise ratio and

vertical resolution by the use of spherical-mirror optics, is now ’undergoing

evaluation.

Initi,al work 'under this task was performed with a previously developed

b’urner^^-* consisting of six 380-mm wide and 22C-mm high sintered-metal panels

topped by a 520-mm high metal plate. Since the fine-grained sintered metal of

the Durner was s’usceptible to clogging by soot, the work was restricted to

ethane, which prod'uces relatively small amo’unts of soot. A new b'urner incorporating vario’us design improvements has been assembled, and work with this

b’urner is about to begin. One important new feafure is the use of an outer

layer of coarse-grained sintered metal that is expected to prevent permanent

clogging by soot, so that fut’ure work can be extended to fuels of greater

sooting tendency than ethane. The height of the individual panels has been

red’uced to 1 27 mm to provide improved resolution of the sim’ulated pyrolysis

height. As another new feafure, heat transfer instr'umentation has been incorporated in the metal plate above the b’urner panels.

Although txhe data obtained previously with the old b’urner , are of a preliminary nafure, they nevertheless provided valuable results ‘---i which have re- cently been examined in greater detail to estaolish correlations for the radiant fraction of heat release rate xpj for the vertical di stri outi cn of

radiant flux to the wall, q"(Z). For theoretical reasons, the convective 3-

n’umber 3^, given by

125
B Xr ) T ) ]

was used for correlating the radiant fraction Xr» where q" is the convective

heat-transf er rate to the fuel surface and m" is the mass transfer of the fuel

from the surface, is the fraction of fuel that participates in the flame

reaction, and S the stoichiometric oxidizer-to-fuel mass ratio. For t*he present data, incompleteness of combustion was not considered (x^ =1); thus, the

previously determined total B-numbers were converted into convective B-n'umbers

by the expression

C 1 “ Xr^ -1 '^R,loss

where Xr loss radiative fraction of the heat transferred to the fuelsupplying portion of the wall burner, which was determined from the scanning

data.

A plot of radiative fraction Xr '^'S 1/(1 shown in Fig. 1. The

values of Lp are sim’ulated pyrolysis lengths, corresponding to supply of fuel

by one, two, or three burner panels, respectively. The data point for = 0 represents results obtained with a slot burner placed at the base of the wall,

corresponding to 3^^ = ®.

The choice of the abscissa, 1/(1 + B.,), was based on theoretical arguments

which show that it r^resents the concentration of combustion products present

at the wall s’urf ace . In agreement with this theoretical arg’ument, the fig’ure shows a linear decrease of Xr with 1/(1 + B^^).

For correlating data of radiant flux to the wall, q”(z), derived from

scanning-radiometer measurements , a normalization by Xr Q’/L^= Qr/L^ was chosen, where Q' is the total heat-release rate per 'unit burner vJidth, its

raaiative portion, and the flame height. This choice was made so that the area 'onder plots q"(z) L.^/Q' vs normalized height z/L^ is equal to 1/2 due to

the fact that one-half of the total emitted radiant power is absorbed by the

'wall for an optically thin fire.

It was found, however, that 'ise of the expression for flame height previously adopted both on theoretical grounds and from the experimental scanning

data

,

L,= 0.059 (Q')^'^^ (1)

gave poor agreement among the normalized flux data for different values of

total heat release rate, even for constant pyrolysis height L^. The agreement

was greatly improved by using, instead, the empirically selected expression

L,= 0.17 (Q')^'^^ (2)

A partial reason for the fail'ure of eq (1) to correlate the scanning data properly may lie in the fact that it was obtained by using 50 percent intermittency 'with a fairly large threshold value as the criterion for flame length,

while a criterion based on the approach of q" to zero seems more appropriate

for the present p'irpose.

126
Figs. 2 to 5 show normalized plots of radiant flux vs height for the slot

burner and for one, two and three fuel-supplying panels (Lp = 0, 220 mm, mm and 660 mm, respectively). The data correlate well among each other

for each of the values of L^. In addition, it was found tnat they can be

matched closely by beta distributions

F(x) = x^"’’ (1-x)^”V2 B(n,m)

where 3(n,m) = r(n)r(ra)/r(n+m) ,

with empirically chosen best-fit values of n and m. As a consequence of the

flattening of the distributions, the values of n and m decrease with increasing Lp. The ratio of m/n also decreases with increasing Lp, reflecting the

shift of the maxim'um of q” to higher values of z/L^.

F’urther relationships can be deduced from the plots. Figs 2-5. The initial increase associated with the rate of soot formation can be seen to be

roughly linear with the same slope for all r’uns . Equal slopes for the dimensionless plots implies that the dimensional slope dq'Vdz is proportional to

X^, with a constant factor for all r'uns . A mean value

(dq'Vdz) initial

1 64 Xd kWVm^

has been determined from the data, and a plausL^^J,® explanation in terms of

initial rate of soot formation has been advanced.'-^-*

The burnout of soot in the upper portion of the flame also can be represented by a simple correlation. For any given threshold value, q"(z) = t , the corresponding heights z(t) were fo’und to correlate well with the expression

z(t) = 0.17 - i(t) (3)

Thus, the flame-length expression, eq (2), was f’orther confirmed as the asymptotic limit for vanishing intercept i(0) =0. A plot reflecting this relationship for a particular value of threshold t is shown in Fig. 6. It was also found that the intercept i(t), for thresholds t in the range from - to

14 kW/m^, is a linear f 'unction of t.

The vario'us relationships discussed above, and their signif i cance , are being f’urther investigated and it is planned to extend the correlations to the

data to be obtained with the new b'urner. The res’ults ^wllj.^ also be compared

with existing theoretical models of 'wall-fire corab'ustion- and will be used

for possible modification of such models, as well as for extensioui to, wall

fires L 3, 9j of correlations between flame radiation and fuel sraoKe ooints.

Conc’urrently with the study of wall fires, meas'urements of smoke poinos

and of radiant emission from laminar diffusion flames have been perf orm®d

This continuing work, which is also partly supported by the Gas Researcn Inscitute, is of interest for the wall-fire study in connection with correlations between flame radiation and smoke points and is also of imporcance for

the study of t’urbulent flames 'inder Task 2.

127
References

1. de His, J. and Orloff, L., "The Role of Buoyancy Direction and Radiation

in Turb’ulent Diffusion Flames on Surfaces," Fifteenth Symposium (International) on Combustion, p. 175, The Combustion Institute, 1 975.

2. Markstein, G.H., "Radiant Emission from Wall Fires," Fall Technical Meeting, Eastern Section, The Combustion Institute, Philadelphia, PA, Nov. 4-

6, 1985.

3. de Ris, J., "Radiation from Diffusion Flames - Smoke Point," presented at

the '9th Joint Panel Meeting of the UJNR Panel on Fire Research and Safety,

May 4-8, 1987.

4. Ahmed, T. and Faeth, G.H., "T'urbulent Wall Fires," Seventeenth Symposi’um

(International on Combustion, p. 1149, The Combustion Institute, 1 979.

5. Delichatsios , M.A., "T'urbulent Convective Flows and 3’urning on Vertical

Walls," Nineteenth Symposi’um (International) on Combustion, p. 1075, The

Combustion Institute, 1983.

6. Delichatsios, M.A., "Flame Heights in T’urb’ulent Wall Fires with Significant Flame Radiation," Comb’ustion Science and Technology, 39^, 1 95, (1 984).

7. Mitler, H.E., "Wall-Fire Algorithms for Mark 5.n.," Appendix C, Minutes of

Ad Hoc Mathematical Fire Modeling Working Group Meeting, Oct. 1984.

8. Markstein, G.H., "Relationship Between Smoke Point and Radiant Emission

from Buoyant T'urb’ulent and Laminar Diff'usion Flames," Twentieth Syraposi’um

(International) on Comb’ustion, p 1055, The Combustion Institute, 1 985.

9. Markstein, G.H., "Radiant Emission and SraoKe Points for Laminar Diffusion

Flames of F'uel Mixfures," 21st Symposi’um on Combustion, M’unich, Aug. 1 986.

Publications

1. Markstein, G.H., "Correlation for Smoke Points and Radiant Emission of

Laminar Diff’usion Flames," presented at the Spring Technical Meeting, Central States Section, The Combustion Instit’ute, Argonne, IL, May 11-12,

1 987.

12S
4.0 10 B

Fig. 1. Ethane wall-fire radiative fraction va

(Bg • convective B number, L_

pyrolysis height) ^

ethane wall fires

ethane wall fires

Fig. 2. Normalized plot of radiant flux vs height.

Fuel released from slot burner at base of wall

ethane wall fires

Fig. 3. Normalized plot of radiant flux vs height.

Fuel released from one panel (Lp - 220 mm)

ethane wall fires

Fig. 5. Normalized plot of

Fuel released from

radiant flux vs height,

three panels (Lp - 660 HUB

)

Fig. ii. Normalized plot of radiant flux vs height.

Fuel released from two panels (Lp • «40 mm)

129

Fig. 6. Flame height for radiant flux threshold o: 2.5 kH/m* vs
Task 4: Dynamics of Charring Wall Fires

(M.A. Delichatsios , K. Saito, R.L. Alpert, M.K. Mat.hews

)

Mathematical models for the prediction of upward flame spread rates as well as the prediction of critical conditions for flame spread require two key

material properties: 1) the transient generation rate and heating value -of the

pyrolysis vapors emerging from the material, and 2) the flame radiation from

the burning of the pjrrolysis gases. It has been the objective of this task to

improve on current techniques for predicting transient pyrolysis of materials

and to provide sufficient information for calculating the radiant feedback in

a fire situation, based on f’jndamental radiation properties of the pyrolysis

gases from any material.

To achieve these objectives, we have assembled a comprehensive program

which consists of a new flammability apparatus and a methodology to interpret

and analyze the experimental data on transient pyrolysis and flame radiation.

Emphasis has been given to charring materials because they have a transient

pyrolysis history even when exposed to a constant heat flux. For noncharring

materials (e.g. PMMA) , a steady rate of pyrolysis can be readily measured or calculated by using a heat of gasification and pyrolysis temperat 'cre

.

We have completed the construction of a sophisticated experimental apparatus caref’olly designed to obtain accurate meas'urements for the transient pyrolysis rate of charring materials as well as for the flame radiation from the

burning of their pyrolysis gases.

A systematic set of 56 experiments was r’jn in this apparatus by O'jr s'immer

scientist, Professor K. Saito. Measurements of weight loss and temperatures

at four locations inside the samples were recorded. In this phase, quartz

heaters were used for generating the external heat flux which was calibrated

for a range of 1 to 17 W/cm^. Four different materials were used; black PMMA,

two types of particle board and Douglas Fir wood. The measured weignt loss

was fitted by a rational ratio of third or fourth order polynomials for better

representing the local slope (i.e. pyrolysis rate) and c’crvat’ure of the experimental data trend. For illustration, Fig'ores la and 1b show the weight loss

and pyrolysis rate and the temperafure meas'creraents for particl^e board 12 cm in diameter and 1 . 9 cm thick, exposed to a heat flux of 5.2 W/cm~. These data

are c'crrently being analyzed'"'^ based on our previous semi-analytical and

n’omerical models. The next phase of experiments will involve the application

of a cone-radiant source for generating the external heat fluxes. These meas'urements will provide information on the effects of spectral characteri sti cs of the source on the transient pyrolysis of materials.

Finally, in conj -unction with concomitant efforts by NBS, we have ouolinea

a comprehensive model for the b-urning and upward flame spread on charring

materials in wall fires. Perhaps an important outcome of this worK is thao

upward flame spread rates (dXp/dt) may be correlated by the following expression:

TT (T - T dx

4 a Q , w ch

4/3

dt

= x;

AH

130
Tliis equation illustrates directly the main parameters which control upward flame spread; namely wall thermal properties (K,^, cl^, T^), heat release

AH ' n rate (Q ), radiant fraction (xr) and a material flammability n'umber ( x„ • Ch ^ a An

V

Refer ences

1. Saito, K., Delichatsios , M.A., and Alpert, R.L.: "Pyrolysis of Charring

Materials in an Inert Atmosphere-Implications for Modeling," submitted for

presentation at the Second International Symposi'um on Fire Science Safety,

Tokyo, Japan, June, 1988.

2. Delichatsios, M.A., "An Outline for a Comprehensive Model for the Burning

and Upward Flame Spread on Charring Materials in Wall Fires," FMRC report,

and paper submitted for presentation at the Eastern Section of the Combustion Institute, Nov. 1987, NBS.

131
Temperature

I

0TC1 +TC2 0TC3 ATC4

Fig. 1 Temperatures at the front s’jrface, 6 mm, 1 2 mm deep and at the back

surface (Fig. la) and weight loss and pyrolysis rate (Fig. ^b) of a charring particle board exposed to a 'uniform flux of 5.2 W/ cm .

132
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY87

Irrs titution

Grant No .

Rutgers, The State University of New Jersey

New Brunswick, New Jersey

NB83NADA4047

Grant Title: Negatively Buoyant and Penetrative Flows

Generated in Enclosure Fires

Principal Investigator : Professor Yogesh Jaluria

Department of Mechanical & Aerospace Eng.

Rutgers, The State University of New Jersey

New Brunswick, New Jersey 08903

Telephone: (201) 932-3652

Other Professional Personnel : K. Kapoor (Post-Doctoral Fellow)

A. Abib (Ph.D. Student)

NBS Scientific Officer: Dr. Leonard Y. Cooper

Technical Abstract:

Introduction . The objective of this project is to carry out a detailed

experimental investigation on the negatively buoyant and penetrative flows

that arise at the early stages during the growth of a compartment fire. In

particular, negatively buoyant jets in an extensive environment simulate the

ceiling jet driven wall flow and also the buoyancy- induced flow adjacent to

the walls of an enclosure. Following the establishment of the two zones typical of such fires, these wall flows penetrate across the interface, become

negatively buoyant and rise toward the interface. Extensive measurements have

been taken on negatively buoyant wall jets in an extensive isothermal medium,

as well as on their penetration in a two-layer stably stratified environment.

Correlating equations have been developed for the penetration depth, heat

transfer and entrainment into the flow, to provide inputs for the zone model

analysis of compartment fires.

Negatively Buoyant Wall Jets . The penetration depth S , the total

entrainment into the flow, given in terms of the total flow rate in the reverse flow, the heat transfer flux to the wall q and the velocity and

temperature fields have been determined experimentally. Details on the

experimental system and on the results obtained are given in the listed

publications. It is found that these results can be well correlated in terms

of the Richardson number Ri =» g/3(T -T )D/U , where D is the width of the jet

at the discharge, U the average discSarge°velocity , T the jet discharge

temperature, T^ the°ambient temperature, g the gravitational acceleration and

3 the coefficient of thermal expansion.

Several correlations have been derived. Some of the important ones, for

negatively buoyant wall jets, are:

133
5 (1. 88-14. 1aT/T^) + (2.6-8.56AT/T^)Ri ( 1 )

- 0.6

m _/m.

out^ in 38.6

13.1

8.75 Ri 0.177

for 0 < Ri < 1.0

for 0 < Ri < 0.06

for 0.06 < Ri < 0.3

for 0.3 < Ri < 0.6

( 2 )

Nu^ - ^

- 0.5 + [0. 268-3. 46AT/T^]Ri’^’^^ for 0 < Ri < 1.0 (3)

where T is in K, Nu_ is the Nusselt number, m. is the mass flow rate at the

jet inlet, h the heat transfer coefficient, k tRe thermal conductivity of the

fluid, AT » T -T , T being the wall temperature, and AT - T -T . For an adiabatic wall, the penetration depth had been found to be wall^correlated by

the expression

5 /D ~ 4.424 Ri'°-^^^ for 0 < Ri < 1.0. (4)

P

All the above correlations were found to represent the data quite closely,

with correlation coefficients of order 0.95. Some of these correlations have

been applied to typical enclosure fires. The results obtained have been found

to be physically realistic. The effects of these flows were confirmed to be

significant in the transport mechanisms that underlie enclosure fires.

Penetrative Wall Flows . An experimental arrangement was designed and

fabricated to obtain a stably stratified two- layer environment in an enclosed

region. Figure 1 shows the typical temperature profiles in the enclosure.

It was found that the temperature levels, the height of the interface and the

sharpness of stratified region between the two essentially isothermal regions

could be varied by controlling the temperature and flow rate of the lowvelocity hot air flowing through a wide diffuser into the tank at the top.

Both a downward heated jet and the buoyancy- induced flow adjacent to a cooled

plate were considered and the penetrative convection studied in such a twolayer environment.

Figure 2 shows the downward penetration of a two-dimensional heated jet

discharged at the top of the upper zone. The flow penetrates across the

interface into the lower zone, becomes negatively buoyant and rises toward the

interface. The corresponding penetration depth S is shown in Fig. 3 and the

results obtained are compared to those for a jet in an isothermal environment.

Clearly, the upper zone temperature T is more appropriate for correlating the

data than the lower layer temperature'^. - T . The penetration of the

buoyancy induced wall flow due to a cooled surface is shown in Fig. 4. Again,

the flow becomes negatively buoyant in the lower zone and rises toward the

interface, ultimately flowing out of the enclosure. The velocity and thermal

fields associated with these flows have also been measured in detail. The

resulting transport between the two zones because of these wall flows can thus

be determined.

This work is presently being continued and correlating equations are being derived to characterize the experimental results on penetration. These

equations will then be applied to typical enclosure fires to determine the

resulting effects at the early stages of fire growth, particularly in

predicting mass and energy transport rates. The results obtained so far have

indicated the considerable importance of the wall effects and the need to

incorporate these into existing models for an accurate prediction of the

changing environment in a compartment fire.

134
Reports and Papers

1. Jaluria, Y. , " Buoyancy -Driven Wall Flows in Enclosure Fires," Proc , 21st

S\’rnp. (Int.) Combust. . Combust. Inst., Pittsburgh, PA, 1987, in press.

2. Jaluria, Y. and Kapoor, K. , "Effect of Wall Flow at the Early Stages of

Fire Growth on the Mathematical Modeling of Enclosure Fires," Proc

ASME/JSME Thermal Engg. Conf. Hawaii, 1, 395-401, 1987.

3. Kapoor, K. and Jaluria, Y. , "Penetrative Convection Due to a Buoyancy

Driven Flow in a Stably Stratified Environment," Bull. Amer. Phvs . Soc. . 31, 1692, 1986.

4. Abib, A.H. and Jaluria, Y. , "Numerical Simulation of the Buoyancy- Induced

Flow in a Partially Open Enclosure," ASME Winter Ann. Meeting . Boston,

Dec. 1987, to be presented.

5. Kapoor, K. and Jaluria, Y. , "An Experimental Study of the Generation and

Characteristics of a Two-Layer Thermally Stable Environment," submitted

for publication.

6. Kapoor, K. and Jaluria, Y. , "Heat Transfer from a Negatively Buoyant Wall

Jet," submitted for publication.

Fig. 1. .Measured temperature profiles in the experimental enclosure

which simulates the environment in a compartment fire.

135
OISTANCt

ALONO

ISCrTHtRMAL

PLATE

(IN

IHCHIII

Fig. 2. Penetration of a downward,

heated, wall jet in a twolayer stratified

environment, in terms of the

isotheirms, at Ri - 0.1.

Fig. 3. Penetration depth of the

wall jet in an isothermal

and a two -layer stably

stratified medium as a function of the Richardson

number Ri.

f ( lA lACbAS

I

Fig. 4. Downward penetration of a buoyancy-driven flow

adjacent to a cooled

vertical plate at 25. 2 "C in

a stably stratified twolayer environment, with

T = 59“C and T, = 2~.0=C.

136
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : University of Maryland

Grant No.: 70NANB5H00551

Grant Title : Transient Ceiling Jet Characteristics

Principle Investigator : Prof. Colin H. Marks

Department of Mechanical Engineering

University of Maryland

College Park, MO 20742

Other Professional Personnel :

NBS Scientific Officer:

Vahid Motevalli, Graduate Student and Guest

Worker; Dr. Bernard McCaffrey, NBS

Dr. Leonard Y. Cooper

Technical Abstract:

Introduction . Measurements of the transient temperature and velocity

characteristics of ceiling jets caused by a fire plume impinging on a ceiling

are described here. The measurements provide a data base needed to support

the development and verification of compartment fire mathematical models, and

they are also needed in order to optimize the design and location of

sprinklers and smoke detectors. Measurements of ceiling-jet temperatures and

velocities have been made previ ously ^23 but except for the temperature

measurements of Veldman et al they have been made after the temperatures and

velocities have reached steady state.

Apparatus . The apparatus consists of a heat source formed by burning

a premixed amount of methane and air, an insulated fiberboard ceiling (2.13 m diameter, 1.27 cm thick), and a probe connected to a computerized data

acquisition system. In the work reported herein, the ceiling is unconfined.

The velocity is obtained by determining the time that it takes for hot

turbulent eddies present in the flow to be carried along by the fluid's mean motion from one position to another. This time is found by determining the

time shift in the temperature-time records for a pair of thermocouples, one located a short distance downstream of the other. This technique was utilized

by Cox and Chitty'^ for determining the fluid velocity in fire plumes. In

Alpert, R.L., Tech. Rpt., FMRC Ser. No. 19722, 2 , Veldman, C.C., et. al . , NBS, Rpt. No. NBS-GCR-77-98 , You, H.Z. and Faeth, G.M. , NBS, Rpt. No. NBS-GCR-79-188

,

Cox, G. & Chitty, R. , Combustion and Flame, Vol . 39, (1980).

i j /

2

34

(1971).

' 1975).

(1978).
addition, using the temperature-time records, the mean temperature of the

fluid can be determined directly from the thermocouple pairs. The probe used

to determine the fluid mean velocity and mean temperature has eight pairs of

thermocouples in order to obtain measurements at eight distances from the

ceiling nearly simultaneously. Details of ’the probe, the instrumentation and

of the cross-correl ation technique used to determine the time shift are described in (1,2). In order to construct complete velocity and temperature

profiles it is necessary to repeat an experiment several times with the probe

located at different distances from the ceiling.

Transient Temperature and Velocity . Temperature and velocity profiles

have been obtained as a function of time for fire strengthes, Q, ranging from

0.5 kW to 2.0 kW for burner-to-cei 1 i ng heights, H, of 0.5 m and 1.0 m. These

have been obtained at various radii, r, from the impingement point of the fire

plume on the ceiling so as to provide measurements for a range of values of

r/H from 0.26 to 2.0. r/H of 0.26 is just outside of the stagnation zone, and

r/H of 2,0 is in the region where buoyancy forces are becoming significant.

For r/H<l, the ceiling jet is driven by the momentum of the plume. The data

are far too voluminous to be included in this short paper, but will De

included in the annual report to the National Bureau of Standards for the

grant under which this work is being supported.

Typical temperature profiles at various times for Q=2.0 kW at r/H of

0.26 and 1.0 are shown in figures 1 and 2, The temperature profiles represent

the difference between the ceiling jet absolute temperatures and the temperature of the ambient. The maximum temperature in the jet occurs below the

ceiling even at long times into the run when steady state has been reached.

This is because the ceiling has a high emissivity (0.9) and the thus looses

appreciable amount of heat by radiation to the cool surroundings . The temperature and velocity profiles are obtained by averaging the temperature

measurements over 1 or 2 and 5 minutes for the transient and steady state con- ditions respectively. Figure 1 shows that at r/H of 0.26, measured temperature profiles do not vary significantly with time despite the increase in

the ceiling temperature. At r/H=1.0, figure 2, ceiling jet temperature

variation with time is much more evident. This is mainly due to the increased

total heat transfer from the ceiling jet to the ceiling at larger radii.

Examination of the data also shows that the steady-state values of temperature

are approached more rapidly at smaller r/H. Comparison of figure 1 with

figure 2 shows that the point of maximum temperature is closer to the ceiling

at smaller values of r/H. This effect is more pronounced by examining the

temperature profiles at different r/H values, figure 3. The velocity profiles, figure 4, on the other hand, show a boundary layer directly below the

ceiling and a free jet type of flow below this layer. The maximum velocity

is located at the junction of the two and based on our measurements seems to

be somewhat farther from the ceiling than the point of maximum temperature.

In contrast with the temperature profiles, our investigation thus far shows

that the variation in velocity profiles witn time is not appreciable. As

would oe expected, the maximum variation of temperature witn time occurs at

the ceiling due to the ceiling's thermal inertia; however, the maximum

variation in the velocity always occurs at the point of maximum velocity.

Velocity profiles at different r/H values are compared in figure 5. The profiles seem to be similar beyond r/H=0.5 and the significant change in the

138
,fi ceiling , jet velocity occurs between r/H=0.26 and 0.5. Comparison of the

steady-state velocity profiles with those obtained by Alpert show general

ji. agreement as to the magnitude of the maximum velocity and its location from

ir tlie ceiling. The maximum velocity and its location reach steady state values

quickly. The variations of the maximum velocity with time for r/H=0.26 and

,j 0.5 are shown in Figure 6. It is observed that while the maximum velocity

fj fluctuates with time, its average value appears to reach the steady-state

(r value a short time after ignition of the fire.

?' Reports and Publications

. : 1. Marks, C.H, and Motevalli, V., "Transient Characteristics of Plume-Driven

i Ceiling Jets," National Bureau of Standards, Rpt. No, NBS-GCR-529, April

I 1987.

..i

.;!( 2. Motevalli, V,, Marks, C.H., McCaffrey, B., and Cooper, L.Y., "Measurements

li of the Transient Temperature and Velocity Profiles in Ceiling Jets," 1986

Fall Technical Meeting of the Eastern Section of the Combustion Institute,

|i San Juan, Puerto Rico, Dec. 1986.

; 3. Woodhouse, A., Marks, C.H., and Cooper, L.Y., "An Experimental Study of

the Transient Response of Unconfined Ceilings Above Fire Plumes," Proc. of

the 1987 ASME-JSME Thermal Engineering Joint Conference, Honolulu, Hawaii,

i March 1987, pp. 387-394.

I

;i 4. Motevalli, V., Marks, C.H., and McCaffrey, B. , "Measurement of Velocity

i and Temperature Profiles in Low-Speed, Turbulent Non-Isothermal Floes,"

f Submitted for publication at the 1987 ASME Winter Meeting.

1

TCiPC^nruPE PPoriLCS TEMPCPPTURE PPOriLES

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Figure I - Temperature Profiles

Variation with Time

2 KW Fire, r/H=0.26, H=l m

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2 KW Fire, r/H=1.0, H=1 m

139
f

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TCMPEROTURE PROriUES VELOCITY PROriLES

Figure 3 - Steady State Temperature

Profiles at Different radii,

H“1 m

CmI Figure 4 - Velocity Profiles variation

with Time

2 KW Fire, r/H=0.26, H-1 m

VELOCITY PROriLES MRXlMUn VELOCITY

Tine

Figure 5 - Steady State Velocity

Profiles at Different radii,

H-1 m

Figure 6 - Ceiling Jet Maximum Velocity

Variation with Time

140
Fire Growth and Suppression

Center for Fire Research

FY 87

Professional Staff

David Evans , Head

Howard Baum, NBS Fellow

Danny Gross, Senior Scientist

Ken Steckler, Physicist

Doug Walton, Fire Prevention Engineer

King-mon Tu, Mechanical Engineer

Dan Corley, Physicist

Randy Lawson, General Physical Scientist

Margaret Harkleroad, Physicist

David Stroup, Fire Prevention Engineer

Robert Vettori, Fire Prevention Engineer

Paula Beever, Guest Researcher (UK)

Marino DiMarzo, Visiting Scientist (Italy)

William McClain, Guest Researcher (USA)

Wenhao Meng, Guest Researcher (Peoples Republic of China)

Vahid Motevalli, Guest Researcher (Iran)

Ned Niedringhaus , Guest Researcher (USA)

Alex Robertson, Guest Researcher (USA)

John Rockett, Guest Researcher (USA)

Proeram Objectives

Through research we aim to develop predictive methods to describe the processes

of growth and suppression as related to natural fire phenomena and the performance of fire safety systems.

Scone

The work addresses the processes of fire growth and decay associated with both

free burning fires and fires within structures. It examines the overall

dynamics of fire growth and its suppression in order to identify and understand

the significant underlying processes; ignition, flame spread, burning rate,

extinction, and the related transport processes. It utilizes mathematical

techniques, experimental studies and correlations, and similitude methods to

develop accurate predictions for realistic configurations and materials. As

appropriate, it formulates and demonstrates predictive methods for specific

applications

141
Project Area

Suppression

Research is being conducted to understand the dynamics of fire suppression

using water sprays and the overall performance of fire protection sprinkler

systems. Studies include the development of predictive methods for sprinkler

actuation time, measurements of crib fire suppression with water sprays,

cooling of hot surfaces with water droplets, and the characterizations of

sprays from commercial sprinklers.

Analysis of laboratory scale measurements collected in a cylindrical enclosure

using automated probe positioning equipment showed that* time averaged plume

temperatures in the upper warm layer of a two layer stratified ambient could be

predicted using substitute fire source techniques as demonstrated in figure 1.

These substitute fire source techniques and quasi -steady fire assumptions were used to predict maximiim ceiling- jet temperatures in room fire tests of furniture items. Figure 2 illustrates the agreement between predicted ceiling-jet

maximum temperatures and measured values. Figure 2 also shows data revealing

the important effects of ceiling jet vertical temperature profile. Prediction

of these temperature profiles is underway using the results of a program

created by Guest Researcher Dr. Yamauchi from Hochiki Corporation, Japan.

UJ

S 80 <f

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. Aino>«ni 315K 0.057m o*io*> . . iniirlac*

• / • /

N?

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. -0.15 -0 10 -0 05 0 0.05 0 10 0.15 RADIAL distance from AXiSimi

Figure 1. Measured and predicted time averaged plume

flow temperature in the lower and upper

layers of a stratified atmosphere. Heat

source 1 KW. (Left) heat source 0.77 m below ceiling. (Right) heat source 0.97 m below ceiling.

1^2
Sprinkler and heat detector activation calculation depends on accurate prediction of gas flow temperatures and velocities and simulations of the heating of

the sensing element. Guest Researcher, Dr. Beever from the UK Fire Research

Station evaluated the role of conduction losses on sprinkler activation through

experiments and modeling. The present findings indicate that conduction losses

must be accounted for in situations of both slow fire growth and slow response

hardware

Furniture fire growth and suppression characteristics were simulated for the

time range of expected sprinkler response by wood cribs in a project to examine

critical water flow rates for fire extinction. Water sprays simulating

sprinkler discharges over the range of water fluxes from 0.013 to 0.13 £/s/m^ were used. Preliminary results show a systematic decrease in burning rate with

increased water flux. Measurements show that at low spray flux the crib

burning rate is reduced but after reduction continues to grow at the same rate

as observed with no water application. At large spray flux the burning rate

decreases and the crib is extinguished prior to collapse.

Figure 2. Predicted time dependent maximum ceiling-jet

temperature based on substitute fire source

method of analyzing plume flow in two-layer

ambients and measu-red gps temperatures at the

indicated dis.tances below the ceiling.

143
The simple analytical representations of the shape of water droplets deposited

on hot metal surfaces as segments of spherical lens have allowed calculation of

total evaporation time and surface heat flux rates . Evaporation times are consistent with measurements. Modeling of similar measurements completed for a low thermal conductivity glass substrate are underway. This work is directed

at the construction of a thermal model for fire extinction.

Measurement of droplet diameters and velocities in sprays from fire protection

sprinklers were completed. Extensive evaluation of the data showed a preferential selection of small droplets over larger diameters in the spray by the

instruments. This problem is being examined further.

An algorithm for a first order suppression model has been completed. This

algorithm when coded would be capable of evaluating first order effects of

sprinkler system performance in room fires. The algorithm includes a sprinkler

activation section based on DETACT-QS and a spray trajectory calculation

neglecting the effects of fire flow. Surfaces of fuel segments represented by

rectangular solids are extinguished if exposed to calculated spray fluxes

greater than a user specified critical value. Evaluation and improvement of

this first order model will guide future priorities in CFR suppression studies.

Turbulent Burning

This work combines the use of theoretical, computational and experimental

methods to resolve phenomena associated with turbulent reacting flows.

A mathematical model of combustion in a turbulent eddy was developed. The

model consists of a local flow field characteristic of turbulence (a timedependent stretched vortex characterized by an exact solution of the NavierStokes equation) , a variable property convection-diffusion equation for the

species mixture fraction, and an energy release controlled feedback modifying

the flow. Solutions illustrating 3-dimensional transient mixing and diffusion

of the mixture fraction have been obtained. This work will be extended to

include finite rate chemical processes in the future. The output will be a set

of computer codes describing a variety of small scale physical and chemical

processes in turbulent reacting flows.

The aerodynamic theory of soot agglomerates has been developed to the point

where the forces and moments on long linear chains of spherical particles of

arbitrary length have been calculated using a general method applicable to

agglomerates of any shape. The planned output will be a computer program

yielding the forces and moments for an agglomerated particle composed of

elemental spheres in any prescribed configuration. This information is needed

to study soot growth mechanisms.

The mathematical model of ground level flows induced by mass fires has been

completed. The results will be presented in an invited talk at the Second

International Symposium on Fire Safety Science. An initial model of the

process by which the multiple plumes coalesce and interact with the atmosphere

has been formulated.
Fire Dynamics of Systems and Materials

! Wall Fires

I

A series of experiments designed to characterize the fire behavior of a PMM/'.

wall element in a reduced- scale compartment were completed. A fixed-height

i variable -width doorway was used to vary ventilation conditions within the

I compartment. Door widths ranged from 2 . 6 to 100 percent of the compartment

i width. A first-cut analysis of the results shows the mass-loss rate to be

fairly linear with the oxygen and incident radiant flux proportioned over the

upper and lower (layer) wall surfaces. A wall burning algorithm for use in the

FIRST compartment- fire computer model was formulated as the stun of upper and

lower layer mass rates as

j i" - (qj" (Y„„/0.233) + (A„/A,L)

i

’j + !q," «„,/0.233) + q”„ - <7T\.p) (A,/A,L)

Figure 3 shows the agreement between calculated and measured mass loss rates

for PMMA wall sections.

F

Figure 3. Comparison of calculated and measured mass loss rates for

PMMA walls burning in an enclosure with variable door widths.

145
Flame Spread

Data for validation of material fire properties derived from the Lateral

Ignition and Flame Spread (LIFT) apparatus have been collected in medium and

large scale tests. In these tests horizontal and downward flame spread were measured on vertical PMMA walls radiated by a non- combustible wall heated by a gas flame sheet. The flame front position was tracked with sequenced photographs and video recordings. Thermocouples mounted at the fuel surface

produced local surface temperature histories during the flame spread process.

These data are the first large scale comparisons of the predictive capabilities

of the LIFT apparatus.

Standardization of the LIFT apparatus and test procedure is proceeding through

ASTM with the draft standard prepared for submission to the EOS -22 subcommit-

|| tee. ISO is planning a round robin test that may include the NBS test i

procedure. jjj Fire Driven Flows I

An experimental study of burning in spaces ventilated through ceiling openings I is being conducted through both compartment fire experiments and salt water ii analog experiments. '

A 0.43 m cube laboratory- scale enclosure with variable area ceiling vents and

side -wall vents was used to assess the effects of various ventilation condi- ii tions on the burning of a 0.1 m diameter ethyl-alcohol pool fire located in the | center of the enclosure floor. Various combustion conditions ranging from | choked and then quenched flames to strongly pulsating and finally steady fires ' were observed. Measurements of enclosure gas temperature and fuel mass loss

rate are being analyzed. | Some 1/10 scale plexiglass models were constructed to study exchange flow rates | through horizontal openings. Salt water was injected into fresh water to i simulate how hot fire gases move into fresh air environment. Salt concentrations were measured by a conductivity probe at appropriate points to determine f' front positions as a function of time as well as flow exchange rate. Test data f is being analyzed.

Fuel Pyrolysis I

A holographic- interferometric technique was used to measure the transient ; temperature distributions within a block of fused silica exposed to a radiant | heat source operating at levels typical of a fire environment. The experimental results were used to assess the accuracy of the Finlayson-Aung-Kashiwagi ' model for heat transfer in non-degrading transparent solids. The experimental

and theoretical results were found to be in good agreement. This work represents the first steps in a program aimed at characterizing the environment in

which pyrolysis products (gas bubbles) are formed and migrate in transparent

thermoplastic materials subjected to a fire environment.

.A.ssociated Grants

1. Pennsylvania State University, A. Kulkarni - Vertical Wall Fire and

Buoyant Plume in Two -Layer Stratified Atmosphere.

146
2. University of Maryland, M. diMarzo - Transient Cooling of a Hot Surface

by Droplet Evaporation.

3. Michigan State University, A. Atreya - Effect of Water on Ignition of

Cellulosic Materials.

4. University of California, Fernandez -Pello - Fire Propagation on Concurrent

Flows

5. University of California, P. Pagni - Fire Modeling.

6. University of Michigan, G. Faeth - Radiation from Turbulent Luminous Fires.

7. University of California, W. Yuen and W. Lick - A Study of the Suppression

and Extinction of Fires by Water Sprays

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FIRE GROWTH AND EXTINCTION GRANTS

149

CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : Michigan State University

Grant Number : 60NANB5D0578

Title : Effect of Water on Ignition of Cellulosic Materials

Principal Investigator :

Other Professional Personnel :

NBS Scientific Officer:

Arvind Atreya and Indrek S . Wichman

Department of Mechanical Engineering

Michigan State University

East Lansing, MI 48824

Tel. No. (517) 353-6356

M. Abu-Zaid, Ph.D. candidate

Lin-Shyang Tzeng, Ph.D. candidate

Dr. David D. Evans

TECHNICAL ABSTRACT :

Introduction . The objective of this work is to experimentally and

theoretically investigate the effect of water on the piloted ignition of

cellulosic materials. This work is divided into two parts. In the first

part, the effect of adsorbed water (which can be up to 30% of the oven- dry

weight) on piloted ignition is being experimentally investigated in a controlled atmosphere combustion wind tunnel as a function of sample moisture

content, external radiation, gas speed and gas composition. A fundamentaltheoretical model with finite rate gas and solid phase chemical kinetics is

also being developed. In the second part, transient cooling of the surface of

a hot porous solid by impingement of water droplets is being experimentally

investigated by using an instrumented porous ceramic block. This work will be

useful in determining the onset of ignition and subsequent fire growth rate

under different relative humidity conditions. It will also provide

information on the water application rate required to contain the fire growth.

Experimental Work . The experimental apparatus used for investigating

the effect of adsorbed moisture and environmental variables (e.g. external

radiation, wind speed and oxygen concentration) on piloted ignition is sho’-.nri in Figure 1. The heart of this apparatus is a controlled atmosphere and

controlled radiation combustion wind tunnel. To control the gas composition,

metered amounts of oxygen (or nitrogen) are mixed in the air stream. These

gases are metered by critical nozzles and mixed by using high speed opposed

jets. The resulting mixture is slightly above the atmospheric pressure before

it enters the tunnel test section. The tunnel exhausts into a 2':<.2':t3' metal

chamber whose pressure is maintained slightly below atmospheric by an exhaust

fan. The exhaust opening is controlled to obtain atmospheric pressure in the

test section. This minimizes any leaks into or out of the tunnel. After the

test section, the products of combustion are mixed in a heated exhaust section

and a representative gas sample is pumped via. heated sample lines to the gas

analysis equipment where the concentration of major species (CO.^, CO, H,.,0. 0.,, . and total bn/drocarbons [HC]) are measured as a function of time. Transient

measurements of weight loss, temperature in the gas and in the solid phase are also made for different levels of external radiation.

Prior to the experiments the samples are conditioned in a temperature

and humidity controlled chamber. This chamber (Model TH-3. BMA Inc.) has a controllable humidity range of 10 to 98% RH ± 2% RH and a controllable

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-emperature range of 10 to 85 °C. The moisture content of the sample is then

determined by the difference between its "dry" and "wet" weight. Before

conditioning, the test samples are instrumented by fine wire thermocouples oh

the surface and in-depth. After conditioning the instrumented samples are placed on the weighing table with their, top surface flat along the tunnel base

and exposed to the radiant heaters. The products of thermal decomposition in

the boundary layer flow across an electrically heated wire and the time

required for piloted ignition of the sample is noted.

Low Heat-Flux Moisture Desorption Experiments . First, a set of

experiments are being conducted to quantify the rate of moisture desorption

from the wood samples. Preliminary results of these experiments are very

encouraging. They also serve as a test of the capability of the entire

experimental apparatus. Figures 2a,b,c and d show various measured quantities

2 plotted against time for an experiment conducted at 1 W/cm on a sample that

was at equilibrium with the laboratory air (50% RH and 22°C). Figure 2a shows

the external heat flux along with the front and back surface temperatures of

the 1.5" thick wood sample. During this experiment N

2 with less than 0.1% H

2 O and 0,, was used as the main gas flow in the tunnel. Some room air (with 20.9%

0^ and 1.47% H

2 O) was allowed to leak into the tunnel in order to increase the

response time and accuracy to the dew-point hygrometer. The amount of leakage

was calculated from the measured 02 % in the gases and from the knowledge of

flow rate measured by the critical nozzle. Figure 2c shows the measured O

2 concentration in the gases and production of CO

2 during the decomposition

process. Figure 2b shows the meared weight loss during the experiment along

with the production rate of water vapor which is roughly 90% of the total

weight loss for this low heat flux experiment. The remaining 10% consists of

CO

2

, CO and total hydrocarbons which are shown in Figures 2c and 2d. It is

very encouraging to note chat the instantaneous mass balance over the entire

duration of the experiment is with ±5%. It is also evident that water is a significant part of the total weight loss, especially in the initial stages of

thermal decomposition where piloted ignition is expected to occur.

water Droplet Experiments . Work on studying the effect of water

droplets on transient cooling of a porous solid is also underway. The

objective is to simulate a porous material like wood. Thus, an inert porous

ceramic sample has been cast around a matrix of thermocouples. Castable MgO

(KF-95) was used for this purpose since it has excellent water absorption

properties and its high temperature thermophysical properties (up to 1200°C)

are fairly well known. The location of the thermocouples prior to casting was measured to within ±0.1 mm. However, the confidence in their location inside

the casting is only ± 0 . 5 mm because of the uncertainties introduced during

the casting process and shrinkage. Attempts at determining the thermocouple

locations radiographically by using X-rays, have thus far not been successful.

Theoretical .Model of Piloted Ignition . In a study of piloted ignition

of cellulosic materials (Ref. 1) it was shown that a gas-phase energy balance

at the instant of ignition enabled the determination of (i) the critical fuel

.mass flux for ignition, (ii) the critical surface temperature for ignition,

and (iii) the ignition time. An experimentally measured premixed flame

temperature of extinction was one of the key parameters in the balance

equation. A premixed flame temperature was used because it was believed that

the initial ignition process occurred through a premixed flame. An extinction

temperature was used because the application of the pilot alwavs produces

151
local temperatures higher than the ignition temperature in the gas; thus, the

limiting conditions governing sustained flaming are those of extinction. A

very convenient experimental result is the near constancv of extinction

temperature for most hydrocarbon fuels (near 1550°k, see Ref. 1). Since most

of the anal^/sis concentrated on processes occurring in the solid phase, the

above gas -phase analysis was mostly phenomenological. However, the for-mulas

obtained for the mass volatilization rate compare very well with previous

results (Ref. 2).

Analytical -Numerical Solution Algorithm for the Gas-Phase Equations of

Combustion . An operator- splitting procedure was formally developed, in which

a (thermal) model equation was analyzed by Green's functions, and shown to be

separable in the limit of large Damkohler number. Thus, the calculation of

the temperature at the following time step may be separated into two parts.

First, the solution of a (spatially) locally homogeneous explosion problem,

expressed as a balance between the transient and reaction terms in the energy

equation. The duration of the explosion is brief and enables use of the

calculated increment of temperature as a modified initial condition. Second,

the solution of a homogeneous (no reaction term) convection-diffusion

equation, in which the local temperature increments are now redistributed

throughout the field. The numerical solution algorithm developed under this

formulation is shown by comparison to other schemes to be extremely fast and

stable. Detailed discussions of these comparison are presented [see previous

progress reports], and where it is shown that the scheme performs well both

for premixed and diffusion flames.

One-Dimensional Model of Piloted Ignition . The numerical scheme

discussed above is used to integrate the equations for a one -dimensional

piloted gas phase flame near a porous fuel wall. The calculations show the

initial development of a premixing region, the subsequent propagation of two

premixed flame fronts, one toward the fuel surface, the other toward the

oxygen side, and the eventual development of a stable diffusion flame. The

steady state calculations agree with the theoretical predictions of previous

steady-state analyses (Ref. 3). The ignition process is shown to be highly

dependent on the premixing process, and therefore the location of the pilot

flame [see the discussion of the theoretical model of piloted ignition].

Quenching of the premixed flame by the cold wall just after the ignition spark

is the major reason that the theoretically-predicted steady-state flames are not attained. This also explains the "cold flashes" discussed in Ref. 1.

IvTten the pilot flame is moved away from the wall, closer to the asymptotic (t

-* ®) flame location, sustained flaming is more likely to occur. Comparison of

numerically and theoretically calculated flame locations and flame

temperatures are in excellent agreement (± 1%)

.

REFERENCES :

1. Atreya, A. and Wichman, I.S., "Heat and Mass Transfer during Piloted

Ignition of Cellulosic Solids," 2nd .ASME-JSME Thermal Engineering Joint

Conference . 1987.

2. wichman, I.S. and .Atreya, A.. ".A Simplified Model for the Pyrolysis of

Charring .Materials," accented for publication in Combustion and Flame

(1987).

3. Lihan, A., "The Asymptotic Structure of Counterflow Diffusion Flames for

Large Activation Energies," Acta Astronautica , 1, pp . 1007-1039 ^ 197-4.).

152
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CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution ; The Pennsylvania State University

Grant No. ; 60NANB4D0037

Grant Title ; Vertical Wall Fire in a Two-Layer

Stratified Atmosphere

Principal Investigator ; Professor A. K. Kulkarni

Department of Mechanical Engineering

The Pennsylvania State University

313 Mechanical Engineering Building

University Park, PA 16802

Telephone; (814) 865-7073

Other Professional Personnel ; J. J. Hwang, Research Assistant

S. L. Chou, Graduate Student

F. Murphy, Graduate Student

NBS Scientific Officer; Mr. Ken Steckler

Technical Abstract;

Introduction . In a typical compartment fire, the interior atmosphere

becomes stratified with a hot, oxygen-deficient layer of gases on the top

and a relatively cool, oxygen-rich layer of fresh air on the bottom. The

overall objective of this investigation is to study the effect of the

stratified ambient atmosphere on the vertical wall fire. We are

specifically interested in finding out how the burning rate and the flow

of gases are affected. Further, we wish to determine whether a linear

superposition of results based on studies assuming nonstratif ied ambient

conditions is adequate for predicting behavior of wall fire in a stratified atmosphere. In the past year, we simulated various types of

stratified ambient conditions surrounding burning vertical walls in a small scale apparatus and studied their effect on local burning rates.

Also, in an indirectly related project, we conducted experiments to

study behavior of a buoyant jet in a two-layer stratified at*..osphere

These experiments, and their outcome, are reported in a paper which is

listed below.

Wall -Fire -Experiments ; The experimental setup and the procedure for

simulating a stratified atmosphere surrounding a vertical, flat sample of

polymethylmethacrylate, and the technique of determining local burning

rates, were described in the last year’s report.

Figure 1 shows measured temperature (at three different times from

the start of a run) and oxygen mass fraction data at various heights for a set of runs (Set 1). For this specific stratified atmosphere in front of

.the samples, the local burning rates were evaluated in at least four

155
different runs which are shown in Figure 2. The measured burning rate

gradually decreases with the distance from the leading edge, x. Overall,

the burning rate is considerably less than the burning rate measured for

the uniform ambient atmosphere having an oxygen mass fraction, Yq® =

0 . 233 . The solid line, denoted by Yq®(x), represents the predicted

burning rate obtained using the temperature and oxygen mass fraction data

set of Figure 1 as boundary conditions in our previously developed

mathematical model. The solid line denoted by Yq® indicates the * theoretical results from our mathematical model using a constant value of

Yq® for O^x^L, where L is the total height of the sample. This value

represents a height -averaged, i.e., bulk mean, value of measured oxygen

mass fraction shown in Figure t. The broken curve with crosses is based

on the burning rate data measured by Kulkarni and Sibulkin ( Combustion and

Flame , JUJ, 1982) at a fixed height of M cm from the leading edge. They

measured local burning rate for vertical, flat PMMA slabs in an ambient

atmosphere having different (but constant over o^xSL) values of Yq®.

The broken curve is generated from their data by first selecting a distance from the leading edge, (say 3.5 cm); finding out the Yq® at

this distance from the present data in Figure 1 (at 3.5 cm, it is 0,21);

and then reading the burning rate at this Yq® from their experimental

data curve (at Yq® * 0.21, they measured m"^ = 0.88 x 10"^ kg/m S)^

Thus, the broken curve in Figure 2 thus represents a linear superposition

of data obtained from several Yqob * constant (uniform ambient

atmosphere) runs. A very important point must be noted here. It has

been shown that the measured limiting oxygen concentration for PMMA

vertical slabs (of the same scale and same configuration as the present

experiments) is 0 .I 8 ; i.e., a PMMA slab can not sustain burning in

atmospheres having Yq® less than 0 .I 8 . A linear superposition of

experimental results would indicate that as soon as Yq®(x) drops below

0 . 18 , there would be extinction. This means that (according to Figure 1)

for x>5 cm the burning rate should drop to zero, as shown by the broken

curve in Figure 2.

In our experiments, we observed that the PMMA samples continue to

burn vigorously over the entire height with the conditions of

stratification shown in Figure 1. The fact that the samples burn at the

trailing edge, despite having Yq® “ 0.025 at that height, shows that

there must be a very strong influence of the upstream, oxygen-rich layer

on the downstream, even up to the trailing edge. A simple linear

combination of results obtained from experiments conducted in the uniform

ambient atmosphere is not sufficient to explain the behavior of a burning

surface in a stratified atmosphere. Another contributing factor for

continued burning near the trailing edge of the sample where Yq® is well

below 0.18 may be the enhanced radiation from the upper, hot layer.

However, the upper layer gas temperature and the temperature of the

surrounding plates in the present experiments was less than 300®C. A

simple calculation would show that such a low temperature cannot add

sufficient radiation to sustain a vertical wall fire at Yq® = 0.025.

Therefore, the major mechanism must be the convection of oxygen from lower

layer to upper layer for sustaining the vertical wall fire in a stratified

atmosphere.

Figure 3 shows another set of stratification conditions (Set 2). The

measured local burning rate at these conditions is shown in Figure 4.

156
Again, the mechanism of convection of oxygen from the lower layer to the

upper layer is confirmed. The agreement of theoretical results using the

bulk mean value Yoo# and the data is purely coincidental here.

The present experimental study clearly shows that in the case of a vertical burning wall in a room having stratified atmosphere, the lower

layer has a strong effect on the wall fire and must be given careful

consideration in room fire modeling. Because the present study was

performed on a small scale, effects of turbulence must be studied before

results can be extended to full scale.

Reports and Papers

1. A. K. Kulkarni, and J. J. Hwang, "Vertical Wall Fire in a Stratified

Atmosphere", Proceedings -of the -BTst-International Symposium on

Combustion , August 1986 (in press).

2. A. K. Kulkarni, H. R. Jacobs, and J. J. Hwang, "Similarity Solution

for Natural Convection Flow over an Isothermal Vertical Wall Immersed

in a Stratified Medium", Int-*-l^-J^- Heat -and -Mass- Trans far 30 > pp.

691-698 (1987).

3. A. K. Kulkarni and S. L. Chou, "Turbulent Natural Convection Flow over

a Vertical Wall in a Stratified Medium", 198? National Heat Transfer

Conference, ANS Proceedings , pp, 216-223, (1987).

4 . A. K. Kulkarni and J. J. Hwang, "An Experimental Study of Vertical

Wall Fire in a Stratified Atmosphere", Proceedings of the 1 987 Fall

Technical Meeting, The Combustion Institute, pp. 21 . 1 -21 . 4 , (1987)

5. J. J. Hwang and A. K. Kulkarni, "An Experimental Study of Vertical

Wall Fire in Stratified Atmosphere". Submitted to International

Journal-of- Experimental -Heat -Transfer , -Thermodynamics , -and Fluid

Mechanics .

6. A. K. Kulkarni and F. Murphy, "Buoyant Jet in a Two-Layer Stratified

Medium", to be presented at the International Symposium on Natural

Circulation, 1987 ASME Winter Annual Meeting, Boston, Massachusetts.

157
158

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CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : University of California, Berkeley

Grant No. : 60NANB5D0552

Grant Title : Fire Modeling

Principal Investigator : Professor Patrick J. Pagni

Vice Chairman-Graduate Study

Mechanical Engineering Department

University of California

Berkeley, CA 94720

Telephone: (415) 642-0729

Other Professional Personnel : Valerie Lyons (Ph.D. Candidate)

Thomas Mataga (Ph.D. Candidate)

MBS Scientific Officer: Dr. Howard Baum

Technical Abstract :

The overall goal of this project is to develop chemical, physical

and mathematical models of the detailed combustion phenomena which

control a fire's growth. Our emphasis recently has been on accurate

descriptions of boundary layer flames and on measurement and prediction of the soot volume fraction, fy, in a variety of flames and on the role of fy in determining the fire radiation.

Combusting Boundary Layers:

In order to interpret fy measurements in free and forced boundary

layers, accurate temperature and velocity fields are needed. (See

e.g. Smyth, K.C. et al . Combustion and Flame , 62 , 1985, op. 157-181).

The classic solutions of boundary layer diffusion flames neglected

phenomena such as fuel cracking, property variations, buoyancy and

radiation and, therefore, oroduced profiles that are not adequate for

soot formation modeling. These analyses add those effects (1-4).

The fact that predicted temoerature profiles significantly

overestimate measured temperatures between the fuel surface and the

flame (5) even when soot radiation is neqligible, as shown in Fig. 1,

implies that endothermic fuel cracking is imoortant. Therefore, we have included a pyrolysis reaction, Yp]_-*Yr 9 , in our analyses. Fast

159
j 1/4 --.3/4

EXPERliENTAL SMIARITY VARIABLE, T^xp \ >T1

Fig. 1 Comparison of experimental (5) and theoretical streamwise

velocity and temperature profiles for ethanol. Experimental velocities are for 2 cm and 4 cm downstream. Experimental temperatures are for 2 cm, 4 cm and 6 cm downstream. The theoretical curves are shown

with and without thermal cracking.

160
kinetics are assumed so that a fuel cracking sheet exists inside the

flame sheet as shown in Fig. 1. In the future these sheets will be

expanded using activation energy asymptotics. Similarity solutions

are still possible provided the Shvab-Zel dovich variables are redefined to include the cracked fuel product, Yp 2 , as will be discussed

for the free case in the Meeting of the Eastern Section of the

Combustion Institute held simultaneously with this year's Annual

Conference.

Fire Radiation:

/ In flame radiation, the most important and least known parameter

is fy, the soot volume fraction, defined as the volume occupied by

soot per unit of flame volume. Previous summaries have described a multi-wavelength laser extinction technique for in-situ measurement

of the local flame fy in free and forced boundary layers as well as

in pool fires. Detailed experimental comparisons are underway with

alternative single-wavelength scattering/extinction measurement

methods, by my student, Valerie Lyons, at NASA Lewis Research Center.

Good progress has been made and this project should come to a conclusion during this grant period.

Limited data on small pool fire mean soot volume fractions suggest

fy scales with optical thickness, tc L, as

= 1.5(<L)

= 1

1/3

, <L < 0.3

. <L > 0.3

If this correlation holds for all fuels, it will permit scaling of the mean fy in pool fires to any size from a single measured fy. the

apparatus described in Ref. 6 is being reconstructed to perform additional experiments to evaluate the correlation.

Other studies related to fire are underway at Berkeley with

separate support in the areas of smoldering (7,8,9) and self-heating

to ignition (10). These projects were required due to the slow, con- tinuous attrition of CFR grant support. A review paper for the Second

International Symposium on Fire Safety Science is in preparation. We are also assisting the Publications Committee in planning the publication (11) of the Proceedings of the Second International Symposium.

161
Reports and Papers:

1. J.A. Ang, "Perturbed Boundary Layer Diffusion Flames," Doctoral

Dissertation, Mechanical Engineering Department, University of

Cal iforni a-Berkeley, November 1986.

2. T.G. Mataga, "Thermal Cracking and Variable Properties Effects on Free Boundary Layer Diffusion Flames," Master of Science Thesis,

Mechanical Engineering Department, University of CaliforniaBerkeley, December 1986.

/ 3. J.A. Ang and P.J. Pagni, "Forced Flow Boundary Layer Flames with

Thermal Cracking," Combustion and Flame , to appear, 1988.

4. T.G. Mataga, J.A. Ang and P.J. Pagni, "A Two Sheet Model for Fuel

Pyrolysis and Reaction," Paper No. 17, Eastern Section of the

Combustion Institute-1987 Fall Technical Meetino, November 2-6,

1987.

5. J.A. Ang, P.J. Pagni, T.G. Mataga, J.M. Margie and V.J. Lyons,

"Temperature and Velocity Profiles in Sooting Free Convection

Dif+'usion Flames," AIAA Journal , to appear late 1987/early 1988.

6. S. Bard and P.J. Pagni, "Spatial Variation of Soot Volume

Fractions in Pool Fire Diffusion Flames," Fire Safety Science - Proceedings of the First International Symposium , oo. 361-369,

Hemisphere Publishing Co., New York (1986).

7. S.S. Dosanjh, J. Peterson, A.C. Fernandez-Pel lo and P.J. Pagni,

"Bouyancy Effects on Smoldering Combustion," Acta Astronautica,

U, op. 689-696, 1986.

8. S.S. Dosanjh and P.J. Pagni, "Forced Countercurrent Smoldering

Combustion," Proceedings of the 1987 AMSE-JSME Thermal Engi - neering Joint Conference, P.J. Marto and I. Tanasawa, eds.

Vol. 1, op. 165-173, 1987.

9. S.S. Dosanjh, P.J. Pagni and A.C. Fernandez-Pello, "Forced

Cocurrent Smoldering Combustion," Combustion and Flame, 68,

op. 131-142, 1987.

10. F.C. Woters, P.J. Pagni, T.R. Frost and D.W. Vanderhoof, "Size

Constraints on Self-Ignition of Charcoal Briquets," Combustion

Science and Technology , to appear early 1988.

11. C.E. Grant and P.J. Pagni, eds.. Fire Safety Science - Proceedings of the First International Symposium , Hemisphere

Publishing Co., New York (1986).

162
CENTEE FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : University of California, Berkeley

G-rant No : NB83NADAU020

Grant Title: Fire Propagation in Concurrent Flows

Princinal Investigator: Professor A.C. Fernandez-Pello

Department of Mechanical Engineering

University of California

Berkeley, CA 9^720

Other Professional Personnel; B. Amos, Doctoral Graduate Student

L. Zhou, Doctoral Graduate Student

!TBS Scientific Officer: Dr. H, R. Baum

Technical Abstract :

A research program is being conducted to study the mechanisms controlling

the spread of flames over the surface of a solid com.bustible in an oxidizing gas

flow. The objective of the research is to provide fundamental information about

the spread of fire for its use in the development of models of fire growth in

rooms, and of test methods of the flammability of materials. Because of the

varied mechanisms involved in the flame spread process, the research program

encompasses a number of studies covering different physical phenom.ena, from the

ignition of a gasifying surface to the extinction of a spreading flame.

Research performed during this reporting period includes two theoretical

studies. One is a numerical analysis of the ignition of a combustible solid

that is vaporizing in a stagnation point air flow due to an externally applied

irradiance perpendicular to the solid surface. The analysis considers the cases when ignition is caused by absorption of radiation by the vaporized f'ael (high

irradiances) or by heat transfer to the gas from the elevated temperature

vaporizing surface (charring mn.terial) . The second study is a num.erical analysis of the influence on the spread of flame over a thick combustible solid of

the velocity and oxygen concentration of a flow opposing the direction of

spread. Both studies provide relevant information about the m.echanism.s leading

to the establishment of a flam^e and its spread over a solid combustible surface.

Ignition of a Vaporizing Combustible Solid :

In this work, an analysis is developed of the ignition of a vaporizing flat

combustible solid and of the subsequent establishment of a diffusion flame over

it, in a stagnation point oxidizing gas flow. The gasification of the solid is

produced by an external radiant flux applied perpendicular to the surface. Two

sources of ignition are considered; one the absorption of radiation by the

vaporized gaseous fuel, and the other heat transfer to the gas from the elevated

temperature vaporizing surface. The former case applies to the ignition of a

163
combust ible that is exposed to a very high radiant intensity, and the latter to

the ignition of a charring material whose char attains high temperature due to

the external irradiance.

The ignition by vapor fuel absorption of radiation is modeled as follows.

A planar com.bustible solid at its vaporization tem.perature is in a stagnation

point air flow at ambient temperature. At the initial time the solid surface is

suddenly subjected to a constant radiant flux perpendicular to the surface. The

solid absorbs the radiation at its surface and immediately begins to vaporize

mixing with the ambient air. The vaporized fuel absorbs some of the incoming

radiation and eventually becomes hot enough to initiate the ignition of the

fuel/air mixture. After the onset of ignition, the external radiation is

removed and the chemical reaction is let to evolve until it becom.es a selfsustained, steady, diffusion flame. In the analysis it is assximed that the

absorption of radiation by the gas is independent of the temperature, but that

is directly proportional to the fuel concentration. The combustion of the mixture is modeled using a one step chemical reaction of the Arrhenius type. In

accordance with related stagnation point solutions, it is assumed that the nor- mal velocity component, the temperature, and species are only functions of time

and the normal coordinate.

The problem governing equations are solved numerically using an implicit

method except for the temperature in the reaction rate term which is handled

explicitly. A movable grid is used to track the propagation of the flame after

ignition. The grid size and time steps are varied according to the characteristic lengths and times dominant during the analyzed period. A parametric

study of the effect on the ignition delay time and flame structure of the

radiant intensity, absorption coefficient, and flow velocity is performed for

PN^^A as combustible solid. A characteristic example of the predicted evolution

of the temperature profile is shown in Fig. 1, for a flow velocity of 0.5 m/sc

imrosed at a distance of 5 cm from the surface, an irradiance of 38 w/cm and an absorption coefficient of 10 m /kg. The predicted e'^’olution of the tem^-

perature and species profiles shows the existence of three regimes. The first

regime corresponds to the period from the instant when the external irradiance

is first applied to the onset of ignition. The evaporation of the fuel causes the generation of two opposing stagnation point flows, one of fuel and the other

of oxidizer, at whose interface the fuel and oxidizer mix by diff'asion. During

this period the fuel vapor absorbs radiation and heats up eventually causing the

ignition of the mixture. After ignition, the combustion reaction propagates

through the mixture away from the solid surface. This premixed propagation pro- cess leads to the generation of a diffusion flame once all the fuel ahead of it

is consximed. The diffusion flame adjusts its position until finally it reaches

its steady state position near the wall.

The analysis and the results for the case when ignition is caused by the

high surface temperature are similar to those described above. A characteristic

example of the evolution of the temperature profiles is presented in Fig. 2. It

is seen that although in this case ignition occurs sooner and closer to the

wall, the generation of the diff'asion flame over the gasifying surface follows

the same pattern as that predicted in the previous case.

16 ^
Dependence on the Op-posed Flov Characteristics of the Flame Spread Over a Thick

Solid Conbustible

A theoretical model is developed of the effect on the spread of flames over

the surface of a thick solid combustible of the velocity and oxygen concentration of a gas flov opposing the direction of flame spread. In the analysis, the

transient, reactive, gas phase balance equations of energy/- and species coupled

at the interface to the solid phase energy equation are solved numerically to

predict the flame spread rate eind flame structure dependence on the characteristics of the flow. To simplify the analysis, the gas flov is prescribed as a constant density, Hagen-Poiseuille flow. The gas phase reaction is modeled

with a one step, second order Arrhenius reaction and the solid pyrolysis with a zero order Arrhenius rate. The problem governing equations atnd boundary con- ditions are solved numerically using a finite difference, implicit, method.

A variable integration grid is used in the normal direction to accommodate

the large temperature and species gradients near the solid surface. The time

steps are based on the lowest characteristic time of the problem.

The calculations are made for PJ^!A as combustible material. In Fig. 3, the

results are shown for the flame spread rate variation with the flow velocity for

three oxygen mass fractions. For comparison purposes, the experimental results

of Fernandez-Pello et. al. (l8th International Combustion Symposium., I98 I). are also included in the figure. It is seen that the analysis describes quantatively well the experiments predicting a spread rate that for a given oxygen

concentration, varies with the flow velocity first increasing and then

decreasing as the velocity increases. For a given flow velocity the spread rate

increases with the oxygen concentration. The results of the analysis show that

this behavior is the result of the interaction of two controlling m.echanisms. A

flame to fuel heat transfer mechanism that dominates at low flow velocities

and/or oxygen concentrations and a gas phase chemical Kinetics mechanism that

dominates at high velocities and/or oxygen concentrations. The discrepancies

between the theoretical and experimental results are explained by the simplifications used in the model, particularly the prescribed flow, the absence of

buoyancy and the one step chemical reaction.

Penorts and Paners

1. Kodama, H. , Miyasaka, K, and Fernandez-Pello, A.C., "Extinction and

Stabilization of a Diffusion Flame on a Flat Com.bustible Surface with

Emphasis on Thermal Controlling Mechanisms", Com.bustion, Science and

Technology (in press, I98T )

2. Ajuos, B, , Kodama, H, , and Fernandez-Pello, A.C., "An Analysis of the

Ignition by Vapor Radiation Absorption of Vaporizing Fuel at Zero Gravity",

Presented at the AIAA 25th Aero. Sci. Meeting, Reno, Vevada, I98 T.

Submitted for publication in Acta A.stronautics

3 . Amos, B., "Ignition and Flame Propagation Studies Over a Flat F^ael Surface",

?h.D. Thesis, Department of Mechanical Engineering, University of

California, Berkeley, August 198'^.

-i. DiBlasi, C., Cresticelli, S., Russo, G, and Fernandez-Pello, A.C.,

"Predictions of the Dependence on the Opposed Flow Characteristics of the

Flam.e Spread Rate over Thick Solid Fuels". 3ubm.itted at the 2nd Int. S;v-mp.

of Fire Safety Sci., Japan, June I988 .

165
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166
CENTER FDR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

rf Q7

Institution: The University of California

Grant No:- 60NANB6D0651

Grant Title: A Study of the Supression and Extinction of Fires

by Water Sprays

Principal Investigators: Professors W. W. Yuen and W. Lick

Department of Mechanical Engineering

University of California at Santa Barbara

Santa Barbara, California, 93106

NBS Scientific Officer Dr. Bernard J. McCaflrey

Technical Abstract

1. INTRODUCTION

The objective of this study is to determine the fundamental mechanisms by

which the spraying of water leads to fire supression and extinction. During this

reporting period, the research concentrated on three specific tasks: (1) the

numerical modelling of the general and localized circulation in a room as dependent upon door and window openings; (2) a detailed analysis and description of

the dynamics of water spray as influenced by the fluid dynamics; and (3) the

thermal quenching of a flame due to the presence of chemically-inert species.

The first two tasks contribute to the understanding of the "survivability" of the

water sprays in a fire environment after injection. The third task contributes to the understanding of the interaction between the water droplets/vapor and the

reacting species in a combustion/extinction process.

2. MODELUNGOFCERCUIATIONIN AROOHWITHDOORAND WINDOW OPENINGS

A quite general numerical model of the time-dependent dynamics of a compressible, viscous, heat-conducting, chemically-reacting mixture of gases

has been developed and applied to the problem of natural heat convection In a room -with door and -window openings. A unique feature of the model is its treatment of the conditions at the doors and windows, where open boundary conditions (Licks, et. al. 19B6, 1987). must be specified. Numerous calculations have

been made and are being made to investigate the general dynamics of natural

convection in a room with specific emphasis on the effects of door and window

opening.

A prelirmnary calculation of this type, primarily to test the open boundary

condition, is sho-wn in Figures 1 and 2. k heat source at the middle of the left wall causes the air to rise and a ceiling jet to develop. On the right, the hot air

escapes from the top and cool air is drawn in at the bottom. A steady-state

eventually develops and it can be shown that the open boundary condition (in its

167
nonlinear formulation) works extremely well. This type of calculation is continuing so as to investigate the effects of various flow parameters.

3. DYNAMICS OF WATER DROPLETS

The model described in section 2 is used simply to describe the general

fluid dynamics. Of primary interest is the dynamics of the water droplets as influenced by the fluid dynamics and the influence of the water droplets on the

fluid dynamics. A general numerical model of this interaction is being

developedBoth the fluid dynamics and the droplet dynamics are developed by an

Eulerian procedure. For complex problems of droplet-fluid dynamics interaction. this seems most appropriate and numerically efficient. The basic conservation equations for the water droplets have been written in a form identical to the fluid dynamics equations used in the model described in section 2 and are presently being included in that model. In its most general form, this model can

then be used to describe the dynamics of water droplets of varying sizes and the

droplet’s size changes as a function of evaporation and heat transfer.

4. THERMAL QUENCHING BY CHEMICALLY-INERT SPECIES

Since water is not expected to be chemically reactive with most common

fuels, the supression and extinction of fire by water is primarily a thermal

quenching phenomenon as noted by previous investigators (Rasbash 1962, Grove

et.aL 1981, Williams 1901). A survey of the literature, however, shows that while

extensive amount of data have been collected on the relative effectiveness of

various gaseous/liquid agents on thermal quenching (Friedman and Levy 1963,

Seshadri and Williams 1975, Kent and Williams 1975, Tucker etaL 1981), a fundamental non-empiricai theoretical study of this important phenomenon has not

been reported. The development of such a theoretical model is a major objective of this research program.

A Laminar diffusion flames generated by two opposing flows of fuel and oxidizer is selected as the basis of the present extinction study. The geometry is shown in Figure 3. This geometry is selected because it is one of the few cases

for which conservation equations for mass, momentum and energy can be

readily written from first principle with no empirical constants. Assuming constant thermophysical properties, density and a unit Lewis number, numerical

and approximate solutions to this problem have been reported by many investigators (Fendell 1965, Linan 1974, Krishnamurthy et.al. 1975). Many of the

reported experimental studies on extinction (Friedman and Levy 1963. Seshadri

and Williams 1975, Kent and Williams 1975, Tucker etai. 1981) were also performed on this opposing flow configuration.

The mathematical development in the previous works is generalized in the

present work to allow a variation of the specific heat of the reactants and products as a function of composition and temperature. .Numerical results are generated for a pure fuel stream (methane) and oxidizer streams consisting of oxygen and different inert gases of various proportions.

Typical Ignition characteristics generated for three inert gaseous species

(.Vj, HzO, and//e ) with different specific heats are presented in Figure 4a. .At 600 K. the specific heat for HzO and He are 1.0 J/gm-K, 2.0 J/gm-K and 5.2

J/gm-K respectively. As expected, for a given oxygen mass fraction in the oxidizer stream, the mixture ignites if the dimensioniess DamKohier number (which

168
is a ratio of the characteristic time of the flow to the characteristic time of the

reaction) exceed a critical value. For a given inert gas. a decrease in the oxygen

mass fraction in the oxidizer stream reduces the reaction rate, the critical Damkohler number required for ignition increases. For the same oxygen mass fraction, a mixture with an inert gas of higher specific heat has a lower mixture temperature and therefore lower reaction rate. The critical Damkohler number

required for ignition also increases.

Since the Damkohler number is inversely proportional to the characteristic

flow velocity, numerical data presented in Figure 4a can be presented in terms

of the characteristic flow velocity, u, as shown in Figure 4b. Uq is a characteristic velocity corresponding to the ignition of an oxygen/nitrogen mixture with

50% oxygen mass fraction. It is interesting to note that Figure 4b is qualitatively

similar to some experimental extinction curves. Since Uq is the only adjustable

parameter in Figure 4b, the present results suggest that measurement of the

extinction curves for different inert species and oxygen mass fraction can be an

effective mean in determining the various reaction constants for the reaction.

In the next reporting period, additional numerical results will be generated

for other fuels and inert gases. The model will also be expanded to allow for

variable density and Lewis number different from unity. Based on the model,

the effect of liquid inert species on the reacting mixture will be addressed.

Specifically, the fire supresslon/extinction characteristics of water spray will be

illustrated.

Ib9
Fig. 1. Computed Isotherms in an Enclosure

with a Hot Spot (1000 C) at the Wall

and an Opening.

Fig. 2. Computed Flow Field in an Enclosure

with a Hot Spot (1000 C) at the Wall

and and Opening.

Fig. 3. Oxidant, Fuel, and Product Particle

Lines in an Axially Symmetric

Stagnation-Region Flow.

Fig. 4a. Critical Damkohler Number Required foi

Extinction for Oxidizer Streams with

Different Oxygen Mass Fraction and

Inert Gas.

Loc m

ig, 4b. Critical Characteristic Flow Velocity

Required for Extinction for Oxidizer Streams

with Different Oxygen Mass Fraction and Inert Gases.
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution: The University of Maryland at College Park

Grant No .

COMM 70NANBSH0525

Grant Title: Transient Cooling of a Hot Surface by Droplets

Evaporation

Principal Investigator: Dr. Marino di Marzo

Mechanical Engineering Department

University of Maryland

College Park, MD 20742

Other Professional Personnel: W. H. Meng, Graduate

Research Assistant

Z. Y. Wang, Graduate

Research Assistant

NBS Scientific Officer: Dr. David D. Evans

Technical Abstract:

Introduction The phenomena associated with solid fuel fire

extinguishment processes are related to the eYaporation of water droplets

deposited on hot solids. Numerous investigations address the full range

of water vaporization phenomena on hot high thermal conductivity solids

More closely related to the extinguishment problem are the phenomena of

evaporation on low conductivity solid. The evaporation of gently

deposited droplet on Macor (a glasslike material) is described hereafter.

In order to develop a complete predictive method for the cooling

processes, the effect of the droplet momentum on the configuration of the

water deposited on the solid surface is quantified. Finally, a methodology to extend the single droplet results to a spray is

presented.

Data Collection With Macor Water droplets are gently deposited on a Macor block at various initial surface temperatures. The measured radius

of the wetted area is ratioed to the radius of the spherical droplet of

equivalent volume and is identified as the shape parameter 3 [i^l]*

Figure 1 shows the behavior of the shape parameter 3 as a function of the

initial solid surface temperature for various dr9plet volumes. Note that

each data point shown in the figure is the average of ten experimental

measurements. For the purpose of the analysis, a constant value of the

shape parameter 3 of 1.42 is used since most of the experimental data are within a plus or minus five per cent band about this value.

The evaporation time for various droplet sizes and initial surface

temperatures is presented in Fig. 2. The cooling is more intense and

more localized than previously measured for aluminum [1]. This means

that the evaporation time for droplet deposited on Macor is longer than

the time of evaporation of droplets deposited^XJn aluminum given the same

171
initial solid surface temperature. The reason for this result is evident

if one considers that, due to its lower thermal conductivity, the Macor

exhibits lower temperatures in the droplet proximity than the aluminum.

In line with this consideration it is also reasonable that nucleate

boiling is suppressed up to initial surface temperatures of the Macor in

t-he order of 160 °C while, for droplets deposited on aluminum, nucleate

boiling is observed at temperatures a few degrees higher than the water

saturation temperature. Indeed, if one considers the contact temperature

suggested by Seki [r2] to be present under the droplet (at least at the

initial contact time), it can be shown that, for an initial Macor surface

temperature of 160 °C and a liquid water initial temperature of about 25

®C, the contact temperature is very close to the water saturation

temperature

.

Droplet Release Height and Shape Parameter An extensive data base is

collected to identify the effect of droplet momentum on its configuration

after impact on the solid surface. A droplet that spreads on the surface

has a faster evaporation time than a droplet that spreads less. Analysis

to correlate the droplet shape parameter 8 with the droplet impact

velocity is under way. This information is paramount to extend the

softly deposited droplet studies to the cooling effect of a water spray.

Multi-Droplet Cooling A multi-droplet model is developed to determine

the minimum water mass needed to cool a hot surface. This calculation is

the basis for the future development of a thermal model of extinction

with water sprays. The model uses the single droplet experimental

results obtained for aluminum [1] and is derived under the following

assxmnptions : a) no coalescence of droplets takes place on the plate; b) a suitable frequency function can describe the distribution of droplet

sizes in the spray. Therefore, a droplet size distribution function can

be use to integrate the cooling effect induced by ail the droplets in a spray

.

The cooling effect induced by a single droplet is calculated making

use of three correlations describing: the evaporation time, the shape

parameter 8 ^nd the maximum area of the solid surface influenced by the

droplet cooling. As a result, the total maximum area of influence

contributed by a spray is expressed as a function of droplet mass flow

rate, initial surface temperature and two mean diameters. A criteria is

proposed to determine whether or not the hot surface is cooled. That is,

the ratio of the area of influence and of the surface area should be at

least larger than 1.0. Experimental determination of the value of this

ratio is one of the future task of this study.

In order to illustrate the model, three typical distribution functions

[r3] are used to calculate the water mass required to cool a solid

surface. Figure 3 shows the results of the model prediction for the

Rosin-Rammier , the Nukiyama-Tanasawa and the Log-Probability distribution

functions. The water mass is intended to be supplied in twice the

evaporation time of the average size droplet.

Conclusions The cooling effect of a single droplet gently deposited

on the surface of a Macor block is compared to the similar cooling effect

on a higher conductivity solid (aluminum). Further information is

172
provided concerning the behavior of the shape parameter 3 for droplets

impinging on a solid surface with a given momentum. A model to extend

the single droplet cooling to a spray is proposed and demonstrated for

three typical spray distributions.

References

rl. C. Bonacina, S. Del Giudice and G. Comini, "Dropwise

Evaporation", J. Heat Transfer, 101 , 441, 1979

r2. M. Seki, H. Kawamura, K. Sanokawa, "Transient Temperature Profile

of a Hot Wall Due to an Impinging Liquid Droplet", J. Heat

Transfer, 100 , 176, 1978

r3. R. A. Mugele, H. D. Evans, "Droplet Size Distribution in Sprays",

Ind. Eng. Chem. , (6), 1317, 1951

Reports and Papers:

1. M. di Marzo, A. K. Trehan, "Transient Cooling of a Hot Surface oy

Droplet Evaporation"

,

National Bureau of Standards Report , NBS-GCR-86-

516, 1986

2. M. di Marzo, "The Cooling Effect of a Single Evaporating Droplet on a Hot Semi-Infinite Metal Body", Annual Conference on Fire Research , NBS

- Gaithersburg, MD, 1986

3. M. di Marzo, D. D. Evans, "The Cooling Effect Induced by a Single

Evaporating Droplet on a Semi- Infinite Body", Proceedings of the

Eastern Session of the Combustion Institute Fall Technical Meeting , pp. 23-1-4, San Juan, Puerto Rico, 1986

4. M. di Marzo, D. D. Evans, A. K. Trehan, "The Cooling Effect of a Single Droplet on a Hot Semi-Infinite Metal Body", National Bureau of

Standards Interagency/ Internal Report , NBSIR 87-3517, 1987

5. M. di Marzo, D. D. Evans, "Dropwise Evaporative Cooling of High

Thermal Conductivity Materials", Heat and Technology , Vol. 5, No. 1-2,

pp. 126-136, 1987

6. M. di Marzo, D. D. Evans, A. K. Trehan, "The Cooling Effect of a Single Evaporating Droplet on a Semi-Infinite Metal Body", Proceedings

of the II ASME-JSME Thermal Engineering Joint Conference , Honolulu,

Hawaii, Vol. 1, pp. 409-415, 1987

7. M. di Marzo, Z. Y. Wang, W. H. Meng, "Transient Cooling of a Hot

Surface by Droplet Evaporation", Mechanical Engineering Report , No.

87-11, 1987

8. M. di Marzo, D. D. Evans, "Evaporation of a Water Dropler Deposited on

a Hot High Conductivity Solid Surface", 24th ASME/AIChE National Hear

Transfer Conference , Pittsburgh, Pennsylvania, in press. Also

submitted to Journal of Heat Transfer, Transaction ASME

173
CURE ONE - Shape Parameter 3

.CURE TWO - Evaporation Time

174
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY87

Tn^rimtion: The University of Michigan

Grant No.: 60NANB5D0576

Grant Title: Radiation from Turbulent Luminous Rames

Principal Investigator Professor Gerard M. Faeth

Department of Aerospace Engineering

The University of Michigan

217 Aerospace Engineering Building

Ann Arbor, MI 48109-2140

Other Professional Personnel: J. P. Gore, Postdoctoral Fellow

M A. Kounalakis, Graduate Assistant

Y. R. Sivathanu, Graduate Assistant

NBS Scientific Officer Dr. Bernard J, McCaffrey

Technical Abstract:

Introduction. The objective of this investigation is to establish methods for predicting the

structure and radiation properties of unwanted fires. The main research issues involve the scalar

structure of turbulent flames, and effects of turbulence/radiation interactions, emphasizing sootcontaining luminous flames. Both theory and experiment are being used to study these issues,

emphasizing the following two research topics: (1) the structure and radiation properties of luminous

flames; and (2) turbulence/radiation interactions in nonluminous flames. Progress in each of these

areas is briefly summarized in the following.

Luminous Rames. Structure calculations are based on the laminar flamelet concept, which

implies that scalar properties in diffusion flames (laminar or turbulent) can be correlated solely as a function of mixture fraction (the fraction of mass at a point, irrespective of chemical compound, which

originated from the fuel). Past work has shown that this is a reasonably good approximation for the

concentrations of major gas species - even in luminous soot-containing flames. If the same property is true for soot volume fractions, the main scalar property of soot that is needed for radiation calculations,

analysis of the radiation properties of luminous flames would be vastly simplified; therefore, this

hypothesis is being examined.

Figure 1 is an illustration of the correlation between soot-volume fractions and mixture

fractions in both laminar and turbulent ethylene/air diffusion flames. Measurements in laminar flames

for fuel-rich conditions, reported earlier, do not correlate as well as gas species concentrations, due to
effects of finite-rate chemistry and transport of soot particles by convention and thermophoresis in a ; ref laminar environment Nevertheless, a crude correlation of the data (denoted the soot-volume-fraction tm state relationship in Fig. 1) is obtained. For fuel-rich conditions, significant soot concentrations are ibi only observed for a narrow range of mixture fractions - yielding a soot spike.

’

Most practical flames are sooting; therefore, work during this report period considered soot fis volume fractions, and their correlation with mixture fraction, in the lean (overfire) portions of turbulent

diffusion flames. The findings at various points within two turbulent ethylene/air flames are also re illustrated in Fig. 1. Soot reactions are quenched in the overfire region and soot particles only i passively mix: a correlation based on this idea (called the soot mixing region) is also plotted on tiie figure. Data for the lower Reynolds number flame is correlated quite well by this plot, with departures

as the soot spike is approached due to effects of turbulent fluctuations. The latter effects are predicted ^ quite well by stochastic analysis. The higher Reynolds number flame, however, exhibits consistently j lower soot-volume fractions, which are attributed to finite-rate chemistry effects. Thus, the correlation f may only be appropriate for Icng-residence time flames: fortunately, such flames are of greatest interest j for unwanted fires. Similar results were obtained for acetylene; however, the correlation exhibited ( much less scatter in the lean region.

Applications of the soot volume fraction state relationship for calculations of radiation

properties are illustrated in Figs. 2 and 3. Predictions are based on the soot-volume-fraction state relationship illustrated in Fig. 1, using either mean properties along a radiation path, or a stochastic

method which allows for effects of turbulent fluctuations. Predicted monochromatic transmittivities

for a turbulent ethylene/air flame, illustrated in Fig. 2, exhibit little effect of turbulent fluctuations, ^d

are in reasonably good agreement with measurements. This is very encouraging, since the results were obtained using a single soot-volume-fraction state relationship for all points in the flame.

Typical predicted and measured spectral radiation intensities, for the same ethylene/air flame,

are illustrated in Fig. 3. In this case, there are significant differences between mean property and

stochastic predictions, indicating effects of turbulence/radiation interactions. The two methods of

prediction tend to bound the data, and represent effects of position reasonably well, which is very

encouraging. The stronger effect of turbulent fluctuations on emission than absorption suggests that

the nonlinearity of the Planck function is mainly responsible for turbulence/radiation interactions.

Present findings concerning the correlation between soot volume fractions and mixture fraction

suggest potential for the laminar flamelet concept for soot volume fractions. However, only a limited

range of test conditions has been considered and measurement uncertainties (shown as brackets in Fig.

1) are high. Current work is attempting to rectify these deficiencies, concentrating on the overfire

region. A range of burner geometries, fuel burning rates, and fuels are being considered; emphasizing

buoyant flames which are representative of unwanted fires.

Nonluminous Flames. Past work concerning turbulence/radiation interactions has been limited

to effects of turbulent fluctuations on mean radiation levels. A stochastic approach has been developed

which shows some promise for predictions of mean radiant intensities and heat fluxes (see Fig. 3).

The objective of present work is to extend these concepts to provide predictions of radiation

fluctuations, probability density functions, and the temporal properties of flame radiation (as

176
represented by temporal spectra). Findings will provide a better fundamental understanding of

turbulence/radiation interactions, while temporal properties of flame radiation are relevant directly to the design of fire detectors.

Hydrogen/air flames exhibit interesting effects of turbulence/radiation interactions and satisfy

flamelet concepts for scalar properties with good accuracy; therefore, work has begun with this flame

system, using flame conditions that were studied earlier. The new measurements involve timeresolved spectral radiation intensities and mixture fractions along various paths through the flames,

although only radiation measurements have been completed thus far.

Some typical radiation measurements are illustrated in Fig. 4. The temporal power spectral

densities of narrow-band spectral radiation intensities (4.8 nm slit width at a wavelength of 2491.1

nm) are illustrated- Two flames are considered, with the power spectral densities, E, and

frequencies, f, normalized by the local flame centerline velocity, Uc, the height above the burner, x, and the rms spectral radiation fluctuation intensity, i\. In these coordmates, the high-firequency end

of the spectra of both flames are the same, suggesting an inertial-like regime for radiation, where E -

f-2

The low frequency behavior illustrated in Fig. 4 is very different for the two flames. The high

Reynolds number flame has a flat energy-containing region, while the low Reynolds number flame

exhibits a distinct peak at fx/uc = 0.3, which corresponds to an actual frequency of 10 Hz. The latter behavior is probably more representative of unwanted fires, which are generally very buoyant and

often exhibit pulsitile behavior.

Radiation measurements are continuing, considering other variables: the diameter of the

radiation path, the wavelength, the wavelength range, and the position in the flame. The stochastic

analysis is also being extended to see if predictions of the temporal behavior of flame radiation can be

made. Subsequent work will involve predictions and measurements of scalar properties along the

radiation paths, and studying their relationship to radiation properties.

Reports and Papers:

1. M.-C. Lai, S.-M. Jeng and G. M. Faeth, ’’Structure of Turbulent Adiabatic Wail Plumes,' J. Heat Transfer, Vol. 108, No. 4, pp. 951-959, 1986

2. M.-C. Lai and G. M. Faeth, "A Combined Laser-Doppler Anemometer/Laser-Induced

Ruorescence System for Turbulent Transport Measurements," J. Heat Transfer, Vol. 109, No. 1, pp.

254-256, 1987.

3. M.-C. Lai and G. M. Faeth, "Turbulence Properties of Adiabatic Wall Plumes," J. Heat

Transfer, in press.

4. J. P. Gore, S.-M. Jeng and G. M. Faeth, "Spectral and Total Radiation Properties of

Turbulent Hydrogen/Air Diffusion Flames," J. Heat Transfer, Vol. 109, No. 1, pp. 165-171, 1987.

177
5. J. P. Gore, S.-M. Jeng and G. M. Faeth, "Spectral and Total Radiation Properties of

Turbulent Carbon Monoxide/Air Diffusion Flames," AIAA J., Vol. 25, No. 2, pp. 339-345, 1987.

6. J. P. Gore and G. M. Faeth, "Structure and Spectral Radiation Properties of Turbulent

Ethylene/Air Diffusion Rames," Twenty-First Symposium (International) on Combustion, The

Combustion Institute, Pittsburgh, PA, in press.

7. G. M. Faeth, J. P. Gore, S. G. Chuech and S.-M. Jeng, "Radiation from Turbulent Diffusion

Rames," Ann. Rev. of Numerical Ruid Mech. and Heat Trans., Hemisphere Publishing Corp.,

Washington, in press.

8. J. P. Gore, G. M. Faeth, D. Evans and D. B. Pfenning, "Structure and Radiation Properties of

Large-Scale Natural Gas/Air Diffusion Rames," Fire and Materials, Vol. 10, pp. 161-169, 1986.

9. J. P. Gore and G. M. Faeth, "Structure and Radiation Properties of Luminous Turbulent

Acetylene/Air Diffusion Rames," J. Heat Transfer, in press.

10. G. M. Faeth, J. P. Gore and Y. R. Sivathanu, "Radiation from Soot-Containing Rames,"

Proceedings of the 70th AGARD Symposium on Combustion and Fuels in Gas Turbine Engines,

Chania, Greece, in press.

11. Y. R. Sivathanu, J. P. Gore and G. M. Faeth, "Scalar Properties in the Overfire Region of

Sooting Turbulent Diffusion Rames," Combustion and Rame, submitted. •

12. J. P. Gore, G. M. Faeth, D. Evans and D. Pfenning, "Radiant Heat Ruxes from 100-200 MW

Natural Gas/Air Diffusion Rames," Proceedings of the Nineteenth Fail Technical Meeting, Eastern

Section of the Combustion Institute, Pittsburgh, pp. 21.1-21.4, 1986.

13. Y. R. Sivathanu, J. P. Gore and G. M. Faeth, "Scalar Structure and Soot Properties in the

Overfire Region of Turbulent Ethylene and Acetylene/Air Diffusion Rames, Proceedings of the 1987

Spring Technical Meeting, Central States Section of the Combustion Institute, Pittsburgh, pp. 49.1-

49.4, 1987.

14. J. P. Gore and G. M. Faeth, "Radiation from Turbulent Luminous Rames," Annual Report,

NBS Grant No. 60NANB5D0576, The University of Michigan, Ann Arbor, MI, 1986.

15. J. P. Gore, "A Theoretical and Experimental Study of Turbulent Flame Radiation," Ph.D.

Thesis, The Pennsylvania State University, University Park, PA, 1986.

178
HAZARD ANALYSIS

CENTER FOR FIRE RESEARCH

FY 87

Professional Personnel

Richard W. Bukowski , P.E., Head

Daniel M. Alvord, Computer Specialist

Peter M. Dubivsky, Research Assoc. (UL)

Nora Jason, Technical Information Specialist

Walter W. Jones, General Physical Scientist

Bernard M. Levin, Research Psychologist

James Raines, Computer Specialist

A. Jeffrey Shibe, Research Fire Protection Eng.

S. Wayne Stiefel, Operations Research Anal.

Richard Smith, Knowledge Engineer

Prograni Qb~iectives

To develop predictive, analytical methods which enable the quantitative

assessment of hazard and risk from fires.

Scone

The predictive methods being developed are based on numerical modeling, but

also include hand calculation methods for estimating hazards, and production

of design curves/tables for use by architects and engineers. To ensure use,

necessary data must be readily available, and data input and presentation mus

be in terms readily understandable by the average professional. Thus, the

projects include a strong emphasis on state-of-the-art computer graphics and

computer aided design techniques.

Projects

1. Hazard Assessment

The objective of this project is to develop quantitative methods to predict

the development of occupant hazard in building fires. The main thrust of the

group (and the Center) this past year has been the completion and publication

of the first version of the Hazard Assessment Method - HAZARD I. This

consists of a three volume (1000 page) report and a set of 5 1/4 in. disks

containing the software necessary to conduct hazard analyses of products used

in residential occupancies. All of the software provided will operate on any

IBM PC (XT or AT) or compatible computer. The programs include a scenario

development guidance utility; an interactive program for inputing data to the

fire model; a data base program and files of thermophysical, thermochemical,

and reference toxicity data; the FAST model for multi -compartment energy and

mass transport; a graphics utility for plotting data; a detector/sprinkler

activation model; an evacuation model which includes human decision/behavior;

and a tenability model which evaluates the impact of the predicted exposure o the occupants in terms of incapacitation or lethality from temperature or toxic gases or incapacitation by second degree burns from radiant flux

exposure

179
Also included in the report is a set of eight representative example cases of

typical residential fires as established by two panels of outside experts.

These consist of fire scenarios, selected by a panel composed of

representatives of the major fire services organizations, in each of three

single-family residences (three bedroom ranch and townhouse, and four bedroom

two -story) , which were felt to represent typical homes by a panel from the

model building codes, NFPA, and the architectural community. In addition to

ser^/ing as examples of the use of the system, these cases can be used as a baseline against which the change in hazard associated with products of

interest can be measured, and as a resource of typical buildings for

evaluating specific products, or fire scenarios for evaluating building

designs and their fire protection features.

While the scope of this first hazard assessment method is limited to

residential occupancies, the work necessary to extend it to other occupancy

classes is underway. This first version is being introduced in order to begin

the process of familiarization of the fire protection community with the

method and its use in addressing the critical issues facing them. In

addition, feedback from users, both positive and negative, is crucial to

identify the improvements necessary to maximize the usefulness of the method

in addressing these issues. This feedback is being obtained through an organized evaluation program of 100 invited reviewers representing all aspects

of the international fire community.

Bukowski, R. W. , et . al

.

HAZARD I - Vol. 1: Hazard Assessment Method (IIBSIR

87-3602), Vol. 2: Representative Example Case Documentation (NBSIR 87-3603),

and Vol. 3: Data Base Listing (NBSIR 87-3604), Nat. Bur. Stand. (1987).

Bukowski, R. W. , A Summary of the Assumptions and Limitations in HAZARD I,

Proceedings of the 9th UJNR, Boston MA. , (1987)

.

2. Risk Assessment

A new effort was initiated this past year with funding from the private sector

through the National Fire Protection Research Foundation. This three-year

project builds on the Hazard Assessment method by adding a means of

identifying the scenarios (a scenario generator) which involve a product in

any way and, as such, will influence its associated risk. The probabilities

of these scenarios derived from NFIRS data are used to weight the outcome

predicted by HAZARD, and summed to obtain a measure of the fire risk of that

product

.

/ The first phase of the project required the development of a proposed

calculation method and its demonstration on two products - upholstered

furniture in residential occupancies and carpet in office occupancies. The

second phase (for FY 88) is to finalize the method based on the phase 1 experience and review, and demonstrate the refined method on several more

products to be defined. The third phase is to submit the method into the

engineering and code arenas for potential implementation.

Bukowski, R.W., Hall, J.R., Sekizawa, A., and Stiefel. S.W.. Fire Risk

Assessment: Description of Methodology, NBSIR in press.

ISO
3 . Smoke Transport Modeling

The objective of this project is modeling the growth of fires and the spread

of smoke and toxic gases. Interest extends from the room of fire origin to

compartments which are sufficiently distant to be in the "far field" of the

fire. The goal is to provide a model which allows one to generate a general

description for a building, the fire to which it is subjected, and then to

model the course of the fire, and generate an easily understood description of

the results. A secondary objective is connecting laboratory scale experiments

with full scale fire performance of materials and buildings. The thrust is to

be able to predict the outcome of a fire given appropriate measurements which

can be conducted in a laboratory. If successful, this application of the

model will allow a great economy of scale as most materials and configurations

necessary for performance testing can be done in the laboratory.

A number of major, technical improvements are underway for this model. One

deals with the incorporation of a capability to simulate smoke movement

throughout large buildings including simulation of the effects of HVAC

systems, smoke control systems, inside to outside pressure difference, wind

and smoke buoyancy. Another major improvement is the addition of a selfconsistent algorithm for combustion chemistry to account for vitiated

combustion and deposition of a reactive species (HCi) to surfaces.

Verification and validation are ongoing projects to check the accuracy of the

model predictions. It is an important step in the acceptance of such a technique by the engineering and code communities. Recently, a series of

experimental studies was completed using the NBS full scale test facility and

the corresponding theoretical predictions. The present work is aimed at

identifying the strengths and weaknesses of the current model prior to adding

such features as ventilation systems, or self-consistent burning furniture.

The work has focused on three roots of the modeling tree. First is to develop

fast and reliable numerical software. Second, we must be sure that the

physical models to be incorporated are consistent and to the extent possible,

complete. Third, the output must be understandable.

Jones, W.W. , and DeWitt, C., Heat Transfer through Multilayer Boundaries,

Fall Technical Meeting of the Combustion Institute, San Juan (1986).

4. Fire Research Information Services (FRIS)

FRIS is an on-going project. It was started in 1971 and incorporated several

personal collections at the National Bureau of Standards (NBS) , as well as the

Fire Council collection. Over the years it has grown and now contains

approximately 30,000 reports, books, journal articles and conference

proceedings. (On the average, 1500 items are added to the collection each

year.) It reflects the programmatic needs of the Center for Fire Research, as well as developing a national and international fire research collection for use by NBS staff, researchers, fire departments, fire science students and the

fire community at large.

181
One of the major obstacles in fire research has been accessing fire research

information. Although the FRIS collection is one of the most complete, it

only has been a manual system and, therefore, not readily accessible to the

fire research community. To remove this obstacle, FRIS has begun to automate

its collection and the online bibliographic database is called FIREDOC . All

new bibliographic records are added to FIREDOC. Retrospective input is being

completed by modules; the current year being entered is 1984. People

interested in using the database may telephone (301)975-6862 for information.

For interested people who cannot come to the FRIS, an extensive interlibrary

loan program is carried out with participating libraries throughout the United

States. For more information on this program, you may write to us at the

National Bureau of Standards, Building 224, Room A252, or contact us by

telephone: (301)975-6860.

Jason, Nora H. FIREDOC Users Manual. Nat. Bur. Std. (U.S.) NBSIR 87-3562.

September 1987.

Jason, Nora H. FIREDOC Vocabulary List, 2nd Edition. Nat. Bur. Std. (U.S.)

NBSIR 87-3545. April 1987.

Jason, Nora H. Fire Research Publications, 1985. Nat. Bur. Std. (U.S.) NBSIR

87-3555. April 1987.

Associated Grants

1. University of California, G. Apostolakis - Fire Risk Analysis Methodology.

182
HAZARD ANALYSIS GRANTS

183
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CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : University of California Los Angeles

Grant No. : 60NANB6D0649

Title: Fire Risk Analysis Methodology

Principal Invesigator:

Other Professional Personnel:

NBS Scientific Officer:

Professor George Apostolakis

Department of Mechanical, Aerospace

and Nuclear Engineering

University of California Los Angeles

5532 Boelter Hall

Los Angeles, CA 90024-1597

M.D. Brandyberry, Ph.D. student

Mr. Wayne Stiefel

Technical Abstract

The objective of this work is to develop a methodology for the assessm^ent

of the types and frequencies of initiating events for the quantification of fire

risk in buildings. At present, the building types being most closely researched

are those which are in the category 'residential occupancies', nominally one

and two level houses. Within this building category, a major hazard to

life-safety are fires which involve upholstered furniture. Upholstered

furniture can be involved in fire in three general ways: initially ignited by

1) smoldering (e.g., cigarette ignition), or 2) flame (e.g., match ignition)

or (3) secondarily ignited from heat transfer from a fire already in progress.

While a large amount of statistical evidence is available on fires which have

already occured (building/ room of fire origin, types of materials first

involved, etc.), of interest is the change in the nation's overall fire risk

due to a new product for which no statistical evidence is available. We are interested in the adaptation of available statistics to a new product, coupled

with the use of mathematical ignition modeling and results from laboratory fire

tests, to be utilized to predict the ignition behavior of new products for

estimating changes in fire frequency and ultimately fire risk due to those

products.

F ire Occurance Statistics

The large amount of data available for fires

which have occured allows us to make good inferences as to what some of the major

factors affecting ignition are. For upholstered furniture, cigarettes and small

flames are major ignitors contributing to the occurance of fires. One major

fire data base (NFIRS) can prov-ide us with frequency estimates of the form

fr( ignitor i | fire ocurred on item j) (1)

184
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where fr(A|C) is the frequency of event A given that event C has occured. Thus,

since the frequency with which ignitor i contacted, but did not ignite item j is not available to us, we cannot explicitly estimate the frequency of a specific ignitor contacting an item. The value given in (1) might be used to

apply to a new product if that product will not have enough market share of item

i to affect the statistical base, but the reliability of this assumption is not

known at this time. Presently, a method for using laboratory ignition results

to update the available data to new products is being sought.

Mathematical Ignition Modeling. The detail to which mathematical modeling

of ignition phenomenon will be useful to us is restricted by the projected

availability of data. To predict differences in ignition properties purely from

a mathematical model would require lengthy modeling of the physical, heat

transfer, and chemical interactions and it is not reasonable to suppose that a new product manufacturer would be able to supply such data, nor would it be

easily attainable by experiment for a variety of new products. Our approach

is to utilize a simplified heat transfer model along with basic experimental

input to predict ignition properties in more general situations. Appropriate

ignition criteria such as surface temperature, average solid temperature, mass pyrolyzate loss rate, etc. are being considered and ultimately, the type of

criteria used may depend on the material being analyzed.

Consideration also needs to be taken of physical processes, such as shrinking

or cracking, which may greatly affect the ignition properties of a composite

surface such as a vinyl covered polyurethane cushion. An event-tree type logic

structure may be useful to incorporate these effects, since they can occur

systematically in time (heating, cover melting, cushion igniting, etc.

)

Development of requisite models for small-flame ignition is currently being

instituted.

Other Work. Throughout this modeling effort, the incorporation and

quantification of relevant uncertainties is important. Addition of the final

model(s) into existing hazard models is also of concern. Since a risk model

is probabilistic and usually a hazard model is a deterministic, physical

analysis model, attention is being given to making the results from the

initiating event analysis useful as input to the hazard model.

185
MBS-n^A IREV. 2*«C1 U.S. DEPT. OP COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. BIBLIOGRAPHIC DATA

REPORT NO.

SH£8 1 fSee instructions!

A. TfT’i c Ak.ir\ c? NBSIR 87 3650

3. Publication Date

Summaries of Center for Fire Research In-House Programs

and Grants - 1987

5. AUTHOR(S)

Sonya M. Cherry

6 - performing organization (If joint or other than MBS, see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

Gaithersburg, md 20899

7 . Concraci/Grant No.

S. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. Stote, ZIP)

10. SUPPLEMENTARY NOTES

! Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

Di bliography or literature survey, mention it here)

This report was prepared for distribution at the Combined Meetings of

the Eastern Section: The Combustion Institute and the Annual

Conference on Fire Research, November 2-5, 1987. It contains

descriptions of the internal programs of the Center for Fire Research

as well as extended abstracts of grants for fire research sponsored

by the Center for Fire Research.

17. KEY WORDS (Six to twelve entries; alohabetical order; capitalize only proper names; and separate key words by semicolons)

cellulose; charring; combustion; fire models; flame spread; ignition;

polymers; smoke; soot; toxicity

13. availability

!

' Unlimited

I i For Official Distribution. Do Not Release to NTIS

!

^ Oroer From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

m Order From National Technical Information Service (NTIS). Springfield, VA. 22161

.14. NO. OF

PRINTED PAGES

174

15. Price

$18.95

'JSCOmm.dC O043.PS0