REFERENCE

NBS

PUBLICATIONS

A 1 1 1 4 433TLE

NBSiR 86-3498

J

x

'r Summaries of Center for Fire

Research Grants and In-House

Programs - 1988

Sonva M. Cherry, Editor

U S. DEPARTMENT OF COMMERCE

(National Sureau of Standards

National Engineering Laboratory

Center £ or F; re Research

Gaithersburg, MD 20899

December "986

‘q^ ^tment of commerce

100

• U56

#86-3498

1986

EAU Or STANDARDS

NBS

RESEARCH

INFORMATION CENTER

NBSIR 86-3498

SUMMARIES OF CENTER FOR FIRE

RESEARCH GRANTS AND IN-HOUSE

PROGRAMS - 1986

Sonya M. Cherry, Editor

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

December 1986

U.S. DEPARTMENT OF COMMERCE. Malcolm Baldrige. Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

TABLE OF CONTENTS

ABSTRACT ..ou..o.....ooo.eeooe.. ........ 1

CENTER FOR FIRE RESEARCH PROGRAMS

Ad Hoc Working Group on Mathematical Fire Modeling .......... 2

Compartment Fire Modeling Research . . © © . . © © © . . © . © © © . © 3

Fire Growth and Extinction . © 8

Fire Performance and Validation. © . ... ....... © 14

Fire Research Information Services .................. 17

Fire Simulation. ........................... 18

Flammability and Toxicity Measurement. ................ 21

Hazard Analysis « « • . . ....... ©o.©. •.••©. ....o 27

Polymer Combustion Research. ..................... 31

Smoke Dynamics Research Group 36

GRANTS

Argonne National Laboratory

Feasibility of Field Detection and Analysis of the Toxic

Products of Combustion. ............. 40

Brown University

A Study of the Effects of Oxygen Transport and Temperature

History on the Chemistry of PMMA and Cellulose Pyrolysis. .... 44

Brown University

Burning of Charring Materials ...... . . 48

Brown University

Soot Dynamics in Flames ................ 51

California Institute of Technology

Experimental Study of Environment and Heat Transfer in a Room Fire .......... ........... 54

Case Western Reserve University

Experimental and Analytical Study of Fire Sprinkler

Scaling Laws. .......................... 58

i
Page

Clemson University

Graphical Presentation and Numerical Analysis of Fire

Data for Model Validation. ................... 64

Clemson University

Ternary Reactions Among Polymer Substrate-Organohalogen-Antimony

Oxides in the Condensed Phase Under Pyrolytic, Oxidative and

Flaming Conditions ............... 66

Factory Mutual Research Corporation

Development of a Model to Provide Comprehensive Fire Property

Data 70

Factory Mutual Research Corporation

Prediction of Fire Dynamics 75

The George Washington University

Chemical Pathways to Soot Formation in Diffusion Flames. .... 88

Marquette University

Thermal Stabilization of Polymers by Cross-Link Formation. ... 92

Michigan State University

Effect of Water on Ignition of Cellulosic Materials . . 96

The Pennsylvania State University

Vertical Wall Fire in a Two-Layer Stratified Atmosphere 100

Rutgers, The State University of New Jersey

Negatively Buoyant and Penetrative Flows Generated in

Enclosure Fires 103

Southwest Research Institute

Analysis of Hazards to Life Safety in Fires: A Comprehensive

Multi-Dimensional Research Program —• Second Year 107

University of California, Berkeley

Fire Modeling 108

University of California, Berkeley

Fire Propagation in Concurrent Flows 112

University of California, Berkeley

Flame Radiation 116

University of Dayton Research Institute

Mathematical Modeling of Furniture Fires 120

University of Maryland

Interaction of Radiation and Conduction in Polymeric Materials . 124

ii
128

University of Maryland

Transient Cooling of a Hot Surface by Droplets Evaporation., .

University of Maryland

Transient Heat Transfer in Ceiling Jets ...........

The University of Michigan

Radiation from Turbulent Luminous Flames. ..........

University of Montana

Kinetics of Oxygen Chemisorption and Desorption of Combustion

Products in the Smoldering Combustion of Cellulosic Material.

University of Pittsburgh

Toxicity of Plastic Combustion Products ...........

Texas A&M University

Computer Verification, Validation and Use of Selected Stateof -the-Art Fire Safety Model for One-Story Multi-Compartment

Buildings ...» ............. .........

132

136

140

142

144

iii
-
Summaries of Center for Fire Research Grants

and In-House Programs - 1986

Abstract

This report was prepared for distribution at the Annual

Conference on Fire Research, November 3-7, 1986. It

contains extended abstracts of grants for fire research

sponsored by the Center for Fire Research, National

Bureau of Standards, as well as descriptions of the

internal programs of the Center for Fire Research.

Key words: Cellulose; charring; combustion; fire

models; flame spread; ignition; polymers; smoke;

soot; toxicity.

1
AD HOC WORKING GROUP ON MATHEMATICAL FIRE MODELING

CENTER FOR FIRE RESEARCH

FY 86

Professional Personnel

Robert S. Levine, Chairman of Steering Committee

John A. Rockett, Chairman of Computer Committee

James G. Quintiere, Chairman of Models Subcommittee

NOTE: The Modeling Committee is chaired by Professor Howard Emmons,

formerly of Harvard University, the Subprogram Committee by John de Ris

of Factory Mutual, and the User's Needs Committee by Irwin Benjamin of

Benj amin-Clarke

.

A number of CFR personnel are members of the technical committees.

Program Objectives

The objectives of this committee are to facilitate the development and use

of mathematical models of fire and to coordinate and facilitate research

needed to improve the models. The Steering Committee includes members

from other government agencies who have influence on their agencies'

research and development in this field. The coordination, of course, is

voluntary

.

Project Areas

Each applicable area is included in another program abstract. The major

portion of the CFR effort is in the Fire Modeling Program.

Associated Grants

Several grants are listed elsewhere.

Activity

During FY 86, the Working Group held a workshop on "Experimental Aspects of

Measuring and Controlling Burning Rate by Radiation to the Fuel Surface" and

a workshop on "CO Formation in Fires".

2
COMPARTMENT FIRE MODELING RESEARCH

FIRE SAFETY TECHNOLOGY DIVISION

FY 86

Professional Personnel

Leonard Y. Cooper, Head

Henri E. Mitler, Physicist

William Davis, Physicist

Glenn P. Forney, Computer Scientist

David W. Stroup, Fire Protection Engineer

John A. Rockett, Guest Worker

Masahiro Morita, Guest Worker (Tokyo Science Univ„)

Vahid Motevalli, Guest Worker (Univ. of Maryland)

Program Objectives

(1) Develop, maintain, improve and provide assistance in the use of

benchmark Compartment Fire Model computer codes

(2) Develop and maintain a catalog of submodel algorithms and subroutines

for general use in compartment fire models.

(3) Formulate, develop, and establish the validity of new and improved

analytic/computational compartment -fire -phenomena submodel algorithms

for use in compartment fire simulations.

Scone

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.

While the benchmark computer code(s) would be up-to-date in the sense of

including algorithms which describe the details of fire phenomena currently

under investigation in the fire research community, they would not be

responsive to forecasts of future research thrusts. In terms of the

complexity of compartment configurations, the capability of the new generation

of benchmark code(s) would be limited to the simulation of fire - generated

environments only in those compartment spaces which affect actual fire

development, e.g., in rooms of fire involvement and "freely connected"

adjacent spaces. In terms of the level of "user-friendliness”, the code(s)

would be useful to researchers and practitioners with relatively high levels

of commitment and technical skill.

Projects and Products

1. Compartment Fire Models

The Benchmark Compartment Fire Model (3CFM) . With a variety of objectives in

mind, many different compartment fire model computer codes have been developed

3
within the fire safety/research community. Yet, no one of these can be

described as being a "benchmark" model in the sense that it is reliable enough

to be accepted as a standard of reference for the performance of designoriented fire models. It is the major objective of the Compartment Fire

Modeling Research (CFMR) Group to develop such a BCFM computer code. During

the last year a program for the development of the BCFM was established and

initiated.

Single -Room Fire Simulations . The Harvard single -room model has been

operational at NBS for some years. It has been used both for demonstration

calculations and as a test bed for new modeling concepts. The "official"

Harvard 5 model has been enriched successfully. The results of this have led

to two new and different versions of the model; namely, NBS/Harvard 5.2, 5.3,

and subversions of these. The first stage effort in the above-mentioned BCFM

development program has been to consolidate the advances of these Harvardbased codes. The product of this effort, a BCFM prototype one -room

compartment fire model is complete and is in review. The new consolidated

code, named FIRST (Fire Simulation Technique) is supported by a comprehensive

user's manual. Both software and manual will be issued in the first quarter

of FY87

Under support of the Nuclear Regulatory Commission (NRC) the development of an algorithm to model the effect of burning in the vitiated air of the upper

layer is near completion and is being tested in an advanced development

version of FIRST. Also supported by the NRC was a comparison of the

capabilities of several different compartment fire models.

An advanced version of the ASET (Available Safe Egress Time) computer program

was developed to include simulation of the response of thermal fire detectors

in two -layer compartment fire environments. This work is continuing as a joint activity with the Fire Simulation Laboratory Group of CFR.

Multi-Room Fire Simulations. The Harvard 6 code was brought to NBS in 1983.

It was made operational on the CFR computer, made to conform strictly to the

ANSI I FORTRAN 77 standard, and a series of minor errors were corrected.

Several enrichments have been added to the code. As a part of this effort, an extensive debugging capability was also added. A separate plot package,

originally developed for NBS/Harvard 5.2, has been adapted. Comparisons are now being made between simulations of the resulting code and data from a series of full-scale multi-room tests which were carried out at NBS in 1980.

Under support from the Navy, an initial study was completed which identifies

means of using deterministic compartment fire modeling to improve the risk

analysis of the Navy's Fire Damage Simulation Model.

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, NBSIR 85-3252,

to appear in Proceedings of 1986 ASTM International Symposium on Mathematical

Modeling of Fires and Related Test Methods, Dec., 1986, New Orleans.

User's Guide to FIRST, A Prototype Benchmark Fire Model, Mitler, H.E. and

Rockett, J.A., to appear as NBSIR.
Simulating Fires on a Computer, Hitler, H.E., presented at 1986 Joint Meeting

of the Society of Plastics Industry and the Fire Retardant Chemicals

Association, March 21, 1986.

Comparison of Several Compartment Fire Models: An Interim Report, Mitler,

H.E.

NBSIR 85-3233.

The NBS/Harvard Mark VI Multi -Room Fire Simulator, Rockett, J.A. and Morita,

M. , NBSIR 85-3281.

The Harvard Fire Model, Mitler, H.E., 1984 SFPE Symposium on Computer

Applications in Fire Protection: Analysis, Modeling and Design, Fire Safety

Journal, 9, 7 (1985).

ASET: A Computer Program for Calculating Available Safe Egress Time, Cooper,

L.Y. and Stroup, D.W.

1984 SFPE Symp. on Computer Applications in Fire

Protection: Analysis, Modeling and Design, Fire Safety Journal, 9, 29 (1985).

Naval Fire Fighting Trainers - Effect of Ventilation on Fire Environment

(Model Calculations for 19 F3 FFT) , McCaffrey, B.J., Rockett, J.A. and Levine,

R.S., NBSIR 85-3238.

Fire Growth in Combat Ships, Rockett, J.A., to appear as NBSIR.

Implementing Life Safety Through Designed Safe Egress, Cooper, L.Y. and

Nelson, H.E., to appear in the Chapter on Fire in Monograph on Planning and

Design of Tall Buildings, Council on Tall Buildings and Urban Habitat.

The Need and Availability of Test Methods for Measuring the Smoke Leakage

Characteristics of Door Assemblies, Cooper, L.Y.

Fire Safety: Science and

Engineering, ASTM STP 882, Harmathy, T.Z., Ed., American Society for Testing

and Materials, Philadelphia, 1985, pp . 310-329.

Comparisons of NBS/Harvard 6 Simulations and Full-Scale, Multi -room

Compartment Fire Test Data, Rockett, J.A., Morita, M. and Cooper, L.Y. to

appear as a NBSIR.

Thermal Response of Interior Aircraft Ceilings During Fuel Spill Fire

Scenarios, Cooper, L.Y.

Proceedings of 1st International Symposium on Fire

Safety Science, Oct. 7-11, 1985, Gaithersburg, Hemisphere Publishing.

2. Compartment Fire Model Catalog of Submodel Algorithms and Associated

Computer Subroutines

This project involves a series of short- and long-term activities. These

involve: a) reviewing the subroutine algorithms and associated computer

subroutines of existing compartment fire model, computer codes, and identifying

those which are of "benchmark" quality; b) merging these into a single,

portable, algorithm/subroutine library, making improvements and developing

additional entries as appropriate; and c) developing a format for a Catalog of

Compartment Fire Submodel Algorithms/Subroutines, and a mechanism for

publication, distribution and revision of the Catalog. The Catalog will be

for general use in zone compartment fire models. The first edition of the

5
Catalog is complete and is in review. Distribution in the first quarter of

FY87 is anticipated.

The Establishment of a Catalog of Compartment Fire Model Algorithms and

Associated Computer Subroutines, Stroup, D.W. , NBSIR 85-3263.

A Catalog of Compartment Fire Model Algorithms and Associated Computer

Subroutines, Stroup, D.W. , to appear as NBSIR.

3. Compartment-Fire-Generated Flow Dynamics, Flame Spread/Growth and Heat

Transfer: Submodel/Algorithm Development and Verification.

A theoretical study of the structure and upward spread rate of wall fires is

near completion. This work was undertaken from the point of view that the

results be consistent with available experimental data, and useful in an algorithm which is simple enough for use in zone compartment fire models.

Experimental programs complement continuing theoretical activities which are being carried out to formulate, develop and validate algorithms for

simulating compartment- fire generated flow dynamics and heat transfer. The

ability to simulate such phenomena is necessary 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

completely the extent of hazard. In one example of such an activity a reducedscale, experimental program and supporting analysis was completed where the

thermal response of different ceiling constructions positioned above fires of

different strengths and fire ceiling separations was measured. In another

example, details of the flow characteristics of ceiling jets are being

established in a manner that will allow one to simulate the response of

arbitrarily deployed fire detection system components in developing

compartment fires.

A study has been initiated with the objectives of mathematically modeling the

smoldering of cigarettes on furniture, describing the influence of furniture

on the burning of a cigarette, and predicting whether furniture will ignite

for a particular cigarette configuration and furniture composition. This work

is part of a larger program which includes extensive experimental work and is

supported by the Consumer Product Safety Commission.

Heat Transfer in Compartment Fires Near Regions of Ceiling Jet-Wall

Impingement, Cooper, L.Y.Proceedings of 1985 Fall Technical Meeting of

Eastern Section of Combustion Institute, Nov. 4-6, 1985, Philadelphia.

Ceiling Jet Properties and wall Heat Transfer in Compartment Fires Near

Regions of Ceiling Jet-Wall Impingement, Cooper, L.Y.

NBSIR 86-3307.

A Bouyant Source in the Lower of Two Homogeneous Stably Stratified Layers,

Cooper, L.Y.Proceedings of 20th Symposium (International) on Combustion, The

Combustion Institute, p. 1567 (1984).

An Experimental Study of the Transient Thermal Response of Unconfined Ceilings

Above Fire Plumes, Woodhouse, A., Marks, C.H. and Cooper, L.Y.

Proceedings of

1985 Fall Technical Meeting of the Eastern Section of the Combustion

Institute, Nov. 4-6, 1985, Philadelphia, submitted for presentation and

6
publication in Proceedings of 2nd ASME-JSME Thermal Engineering Joint

Conference, March, 1987.

Burning of a Plume in the Upper Layer, Mitler, H.E., to appear in Proceedings

of 1986 ASTM International Symposium on Mathematical Modeling of Fires and

Related Test Methods, Dec., 1986, New Orleans.

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, presented at

1986 ASME International Computers in Engineering Conference, July 23, 1986,

Chicago

Heat and Mass Transfer Research Topics in Fire and Controlled Combustion

Systems, Cooper, L.Y.

and Kennedy, L.A.to appear in Mechanical Engineering.

The Thermal Response of Unconfined Ceilings Above Growing Fires and the

Importance of Convective Heat Transfer, Cooper, L.Y. and Stroup, D.W., to

appear in Journal of Heat Transfer.

The Buoyant Plume-Driven Adiabatic Temperature Revisited, Cooper, L.Y. and

Woodhouse, A., to appear in Journal of Heat Transfer.

Associated Grants and Contracts

Negatively -Buoyant and Penetrative Flows Generated in Enclosure Fires,

Jaluria, Y. , Rutgers - The State University of New Jersey.

Transient Heat Transfer in Ceiling Jets, Marks, C.H., University of Maryland.

7
FIRE GROWTH AND EXTINCTION

CENTER FOR FIRE RESEARCH

FY 86

Staff

James Quintiere, Head

Betty Thames , Secretary

Howard Baum, NBS Fellow

Edward Budnick, Fire Protection Engineer

Dan Corley, Physicist

David Evans , Research Engineer

Margaret Harkleroad, Physicist

Randy Lawson, General Physical Scientist

Bernard McCaffrey, Mechanical Engineer

Ken Steckler, Physicist

Wenhao Meng, Guest Worker, Univ. of MD

Phil DiNenno, Research Associate, Hughes Associates

James Jackson, Research Associate, Armstrong World Industries

Larry Buffington, Fire Protection Engineering Student

James Morehart, Mechanical Engineering Student

Dan Madrzykowski , Engineering Technician

William Rinkinen, Engineering Technician

Robert Vettori, Engineering Technician

Henry Wheelock, Engineering Technician

Ji-Jen Chiou, -Guest Worker, (Taiwan)

Hideo Ohtani, Guest Worker, IHI (Japan)

Program Objectives

Through research we aim to develop predictive methods to describe the

processes of growth and extinction related to natural fire phenomena and fire

safety systems.

Scope

The work addresses the processes of fire growth and decay associated with

fires within structures and with free burning fires. 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 its predictive

methods for specific applications.

Project Areas

Suppression

Research is being conducted to understand extinction dynamics associated with

water spray suppression of a variety of fires and the performance of fire

protection sprinkler systems. These included detailed studies of extinction

8
of lifted gas jet diffusion flames, room fire suppression of laboratory liquid

fuel spill fires , heat transfer between solid surfaces and evaporating

droplets, quantification of droplet sizes and trajectories from commercial

sprinkler devices, and studies of the thermal response of heat sensitive

elements used in sprinkler and heat detection systems.

Large scale blowout fire suppression tests were conducted cooperatively with

the Blowout Fire Prevention School at Louisiana State University. Methane jet

flames up to 1/2 GW were tested.

An analysis of the stability of methane jet flames was completed. This

showed, for the first time, flame blow-off characteristics at flow rates

relevant to gas -well blowouts.

The performance of new technology fast response sprinkler systems and plastic

pipe was evaluated in a series of tests conducted cooperatively with the

General Services Administration and the National Institutes of Health.

Our shadowgraphic drop size analyzer system is being utilized to characterize

the initial spray characteristics for several European and U.S. sprinkler

devices . This is part of a cooperative effort on sprinkler performance with

the Fire Research Station at Borehamwood, England and Polytechnic of the South

Bank in London under support from Brandforsk in Stockholm, Sweden.

Measurement and analysis of droplet evaporation from hot metal surfaces have

been completed. The extension of the analysis and measurements to low thermal

conductivity solids is underway in this cooperative study between CFR and the

Mechanical Engineering Department at the University of Maryland.

Temperature measurements were made above and below the penetration plane of a plume flowing from a cool lower layer to a heated upper layer of gas. This

was done using a specially designed microcomputer controlled probe positioning

device and data acquisition system to automatically record data within a cylindrical enclosure. The measurements were used to check the accuracy of

models for transition conditions in two-layer plume flow calculations. The

best fit to the data was achieved by assuming continuity of centerline plume

temperature and integrated excess enthalpy.

An analysis of thermal response of Fire Detection Systems was completed. The

results of this analysis were published in tabular form to allow fire

protection engineers easy access to design calculations that yield expected

response time for thermally activated sprinkler and heat detection systems at

a given spacing. The two volume set (SI and English Units) can be considered

companion volumes to the already in use tables published as part of NFPA 72E

Standard on Automatic Fire Detectors that yield results in terms of detector

spacing for a given response time.

Publications :

McCaffrey, B.J. and Evans, D.D., Very Large Methane Jet Diffusion Flames,

Proceedings of the 21st International Symposium on Combustion, Munich, West

Germany, August 3-8, 1986.

9
Morehart, J. and Evans, D. , Investigation of the Effects of a Stratified Two

Layer Environment on Fire Plume Temperatures, NBSIR in preparation.

Stroup, D. , Evans, D. , and Martin, P. , Evaluating Thermal Fire Detection

Systems NBS Special Publication 712 (English Units) and 713 (S.I. Units),

April 1986.

Evans, D.D.and McCaffrey, B.J., Recent Advances in Suppression of Wellhead

Fires Using Water Sprays, MMS Technical Assessment and Research Program

Seminar, November 1986.

Evans, D.D. and Stroup, D.W.

"Methods to Calculate the Response Time of Heat

and Smoke Detectors Installed Below Large Unobstructed Ceilings", Fire

Technology, Vol 22, No. 1, February 1986.

Evans, D.D., Ceiling- Jets , chapter for SFPE Quantitative Methods Handbook to

be published.

Di Marzo, M. and Evans, D.D.Evaporation of a Water Droplet Deposited on a Hot High Thermal Conductivity/Diffusivity Solid Surface to be published

International Journal of Heat and Mass Transfer, and NBSIR 86-3384, Aug. 1986.

Gore, J.P., Faeth, G.M.Evans, D. , and Pfenning, D.B., Structure and

Radiation Properties of Large-Scale Natural Gas/Air Diffusion Flames to be

published in Fire and Materials

Stroup, D.W., Development of an Automated Probe Positioner for Measurements in

Fire Generated Plumes and Ceiling Jets, NBSIR 86-3379 May 1986.

Di Marzo, M. and Trehan, A.K.Transient Cooling of a Hot Surface By Droplets

Evaporation, NBS-GCR-86-516 , July 1986.

McCaffrey, B.J., Momentum Diffusion Flame Characteristics and the Effects of

Water Spray, NBSIR 86-3442, June 1986.

McCaffrey, B.J., Radiation Measurements of Large Methane Diffusion Flames and

the Effects of Water Sprays, Eastern States Combustion Institute,

Philadelphia, PA, November 4-6, 1985.

Trehan, A.K.

Di Marzo, M. and Evans, D.D., Transient Cooling of a Hot Surface

by Droplet Evaporation, Eastern States Combustion Institute, Philadelphia, PA,

November 4-6, 1985.

Turbulent Burning

This work combines the use of theoretical, computational and experimental

methods to resolve phenomena associated with turbulent reacting flows.

Single, plume flow patterns generated by dynamically and kinematically

consistent use of experimental plume correlations were imbedded into a computational scheme that was used to predict flows generated by urban

conflagrations consisting of thousands of individual fires randomly

distributed in space and size spread over tens of square kilometers.

10
Diffusion and mixing of reactants of general configurations in a vortex field

under isothermal conditions in two dimensions were completed. Current work is

emphasizing three dimensional configurations and non- isothermal effects.

Measurements of soot yield and morphology from a variety of fuels in pool

fire and crib configurations were made. Optical extinction measurements were

also made. This will be supplemented by velocity and temperature measurements

in continuing work.

Modeling of soot agglomeration and transport phenomena using realistic soot

structures has been carried out. This will be continued and supplemented

with optical extinction analyses in future work, and applied to the Nuclear

Winter study.

Publications and Presentations

Baum, H.R. , Corley, D.M. , and Rehxn, R.G., "Time -Dependent Simulation of Small

Scale Turbulent Mixing and Reaction", Twenty-First Symposium (International)

Combustion, Munich, W. Germany, August 3-8, 1986.

Rehn, R.G. , Baum, H.R. , and Lozier, D.W. , "Two-Dimensional Flame in a Vortex

Field", SIAM 1986 National Meeting, Boston, July 21-25, 1986.

Evans, D. , Baum, H.R. , McCaffrey, B. , Mulholland, G. , Harkleroad, M. , and

Manders, W. , Combustion of Oil on Water", Proceedings of the Ninth Arctic

Marine Oilspill Program Technical Seminar, Edmonton, Alberta, June 10-12,

1986, pp. 301-336, (1986).

Baum, H.R. , "Multiple Plume Flow Fields", Defense Nuclear Agency Program

Technical Review, Moffett Field, CA, February 25-27, 1986.

Mulholland, G.W., "Smoke Emission and Properties", Defense Nuclear Agency

Program Technical Review, Moffett Field, CA, February 25-27, 1986.

Mountain, D.R. , Mulholland, G.W. , and Baum, H.R. , "Simulation of Aerosol

Agglomeration in the Free Molecular and Continuum Flow Regimes", J. Colloid

and Interface Science (in press)

Pitts, W. and McCaffrey, B.J., Response Behavior of Hot-Wires and Films in

Different Gases, Journal of Fluid Mechanics, August 1986.

McCaffrey, B.J., " Flame- he i ghts " , SFPE Quantitative Methods Handbook to be

published.

Ftre__ Dynamics of Systems and Materials

This area of activity represents the exploration of complex phenomena in fire

and the application and development of engineering approaches for their

prediction.

The analog technique of using salt and fresh water to yield the motion of

smoke in complex structures is being further developed. The measurement of

salt concentration to predict smoke concentration is being examined.

11
The energy release rates of an extensive series of shipboard cable fires were

deduced from oxygen and temperature measurements . This work was done to - support the development of safe materials and their selection for use on

combat ships.

The enclosure fire behavior caused by the burning of a discrete wall slab of

PMMA showed a dramatic affect of the enclosure and its opening size on the

fire conditions . Enclosure mass loss rates ranged from the free bum value of

the slab to nearly seven times this value for experiments of 0.75 m in height.

A single full-scale (2.4 m high) counterpart experiment, substantiated a significant increase in the rate of burning due to the enclosure. A crude

analysis of the small-scale results shows that the mass loss rate of PMMA is

linearly related to the oxygen and incident radiative heat flux proportioned

over the upper and lower (layer) wall surfaces.

A device was designed and used to measure the bulk heat of gasification (L)

for materials. The value is determined as a function of time by determining

the net heat added (q) to the sample under radiative exposure conditions. The

measured mass loss (m) under a nitrogen atmosphere is then used to complete

the process, i.e. L - q/m. Results for PMMA show a distinct dependence of L

on time and incident heat flux.

A study was initiated under the sponsorship of the Minerals Management

Services (Dol) , to determine the combustion characteristics of crude oil

burning on water.

Publications

Steckler, K. , Harkleroad, M. , and Braun, E. , Heat Release Rates from Shipboard

Cable Fires, NBS letter report to Dr. F. Williams, September, 1986.

Steckler, K.D., Baum, H.R.

,

and Quintiere, J.G., Salt Water Modeling of Fire

Induced Flows in Multicompartment Enclosures, Twenty-First International

Symposium on Combustion, Munich. West Germany, August 1986, to be published by

The Combustion Institute, Pittsburgh, PA, (expanded report issued as NBSIR 83-

3327, March 1986).

Budnick, E.K.

,

and Evans, D.D., "Hand Calculations for Enclosure Fires", NFPA

Fire Protection Handbook 16th Ed. March 1986.

Evans, D., Baum, H. , McCaffrey, B., Mulholland, G. , Harkleroad, M. , and

Manders , W. , Combustion of Oil on Water, NBSIR 86-3420, June 1986. Also,

Proceedings of the Ninth Arctic Marine Oilspill Program Technical Seminar,

Edmonton Alberta, June 10-12, 1986.

McCaffrey, B.J., Rockett, J.A. and Levine, R.S., Naval Fire Fighting Trainers

- Effect of Ventilation on Fire Environment, NBSIR 85-3238, 1985.

Flame Spread

Research is continuing in order to establish procedures for developing and

identifying the key material properties necessary to predict flame spread.

12
The test apparatus which measures ignition and lateral flame spread on a vertical sample has been produced commercially and is receiving world wide

attention. Many international laboratories now have this test apparatus.

Results from the lateral device have been shown to be applicable to predicting

flame spread on horizontal surfaces as well as vertical surfaces.

Measurements related to upward spread focused on flame heights for burning

solids as a function of their mass loss rates.

A large scale experiment of flame spread on a wall of FMMA in a room was performed and the analysis of these results will serve to evaluate the test

method strategy needed to predict the process.

A review of flame spread was prepared as a chapter for the new SFPE handbook.

Work has been done for the USCG, FAA and industry; and we have participated in

standards organizations -- ASTM, ISO and IMO.

Publications

Harkleroad, M. , "Ignition and Flame Measurements of Aircraft Lining

Materials", to be published by the FAA.

Atreya, A. , Carpentier, C. and Harkleroad, M. , "Effect of Sample Orientation

in Piloted Ignition and Flame Spread", Fire Safety Science - Proceedings of

the 1st International Symposium . Hemisphere Publishing Corporation,

1986, p. 97.

Quintiere, J., Harkleroad, M. and Hasemi, Y. , "Wall Flames and Implications to

Upward Flame Spread", Combustion Science and Technology . 1986, Vol. 88,

pp. 191-222.

'

Quintiere, J., "Surface Flame Spread", a chapter for the SFPE Handbook to be

published.

Saito, K. , Quintiere, J.G. and Williams, F.A.

"Upward Turbulent Flame

Spread" . Fire Safety Science - Proceedings of the 1st International Symposium . Hemisphere Publication Corporation, 1986, pp . 75-86.

13
FIRE PERFORMANCE AND VALIDATION

FIRE MEASUREMENT AND RESEARCH DIVISION

CENTER FOR FIRE RESEARCH

FY 86

Professional Personnel

Sanford Davis , Head

Emil Braun, Physicist

J. Newton Breese, Computer Programmer

C. Lynn Forney, Mathematician

Billy T. Lee, Fire Prevention Engineer

Richard D. Peacock, Chemical Engineer

J. Samuel Steel, Physicist

Huang Dingyi, Guest Worker (Shanghai Fire Research Institute)

Ob'] ectives

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.

Scope

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 contribute to model development and, second, the evaluation and

validation 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.

Projects

1. Validation of Fire Models

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

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

and computational techniques for fulfilling this objective. With the large

amount of data collected during the room/corridor tests, including multiple

tests to develop statistical information on test reproducibility, the

presentation of the data in a standardized graphical form is extremely

important in the interpretation of the results.

Peacock, R.D., Davis, S., Lee, 3.T., Jones, W.W. , and Steel, J.S.,

Experimental Data for Model Validation, NBSIR in preparation.

14
2. Smoke Transport Model Development

The objective of this project is to provide support for continued development

of the toxic hazard model by implementation of full-scale tests, designed to

measure transport of smoke and toxic gases, supporting efforts to model

vertical smoke movement and to validate the horizontal transport model.

Completion of the interior and installation of the instrumentation in the

townhouse was delayed because of other projects taking precedence.

Ultimately, three tests were carried out: PMMA on one wall of the burn room,

three "chairs" (sofa, love seat, and chair) in the bum room, and a fully

furnished room. During the coming year, three series of experiments will be

performed using a square wave output from a natural gas diffusion burner - open shaft, vent only, and vent with staircase - to develop data for the

movement of smoke and other combustion products in a vertical direction.

3. Upgrade of Large-Scale Testing Facilities

The new computer based data acquisition system was further enhanced during the

past year. Along with two additional data collection stations installed on

the test floor (bringing our total to four stations and 600 channels) , a new

data acquisition system was installed and interfaced to the computer based

system to allow use of all our existing digital scanners (for a total capac ity

of 1600 channels in 100 or 200 channel blocks. Development of real-time

full-color graphics capabilities to allow simultaneous presentation of test

data and previously recorded test data or model calculations began which will

further enhance our data collection and presentation during large scale fire

tests.

Breese, J.N., and Peacock, R.D., A User's Guide for RAPID, Reduction

Algorithms for the Presentation of Incremental Fire Data, Nat. Bur. Stand.,

NBS Special Publication 722, August 1986.

4. 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 analytical models. This work

complements small-scale work on flame spread ( upward, downward, and lateral)

both before and after flasnover. The experimental study is designed to

analyze flame spread along a combustible wall surface using a controlled

ignition source along the floor, either against the back wall or in one rear

corner, or at the wall\ceiling interface. The heat release of the specimen can

be monitored to determine the combustion efficiency of the burning material as the fire develops.

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

Bureau of Standards, NBSIR to be published.

Lee, B. T. , Quarter-Scale Room Fire Tests of Interior Finishes, Fire and

Materials, Vol. 9, No. 4. 1985.

Huang, D.Y., Evaluation of Quarter- Scale Compartment Fire Modeling for

Constant and Stepped Heat Inputs, submitted to Fire and Materials.

15
5. 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

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

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 from 1981 to 1982 to slightly less than a seven percent increase. The

frequency of fire incidence stabilized between 1982 and 1983 (increasing

during this time less than one percent) and actually decreased in 1984

(dropping nearly 11 percent) . Positive actions by the Center for Fire

Research and others are believed responsible for improving the safety of these

appliances and, thus, reversing an increasing fire incidence rate. The

overall research program has included typical operating conditions of modem

heating appliances, intensity and duration of chimney fires in factory-built

and masonry chimneys, clearance reduction systems for protection of

combustible walls and ceilings, and wall pass-through systems for connection

of appliances to chimneys through combustible walls.

Efforts within the next year will focus on the safety of the use of new high

efficiency combustion devices becoming available in the wood heating industry.

The primary concerns are the buildup of creosote in chimneys (to be determined

quantitatively with a specially built chimney) and the thermal load imposed on

the surroundings by the device.

Peacock, R.D. , and Dipert, R.A. , STOVE: A Predictive Model for Heat Transfer

from Solid Fuel Appliances, Nat. Bur. Stand., NBSIR 86-3300, August 1986.

Peacock, R.D., Chimney Fires: Intensity and Duration, published in Fire

Technology, July 1986.

Peacock, R.D. , Wood Heating Safety Research: An Update, submitted to Fire

Technology.

6. Flammability of Composites for Naval Ship Use

The objective of this program is to assist the Navy in designing fireresistant ship components from fiber- and metal- reinforced composites by

systematically assembling data on 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. In addition,

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 full-scale experiments.

Brown, J.E., Loftus, J.J., and Dipert, R.A.

,

Fire Characteristics of Composite

Materials - A Review of the Literature, Nat. Bur. Stand., NBSIR 85-3226,

August 1986.

Associated Grants and Contracts

James P. Jarvis - Clemson University," Graphical Presentation and Numerical

Analysis of Fire Data for Model Validation.

16
FIRE RESEARCH INFORMATION SERVICES

CENTER FOR FIRE RESEARCH

FY 86

Project Leader

Nora H. Jason

Program Objective

The Fire Research Information Services (FRIS) is an on-going project within

the Center for Fire Research (CFR) , National Bureau of Standards. It was started in 1971 and incorporated several personal collections at the National

Bureau of Standards, as well as the Federal Fire Council collection. Over the

years, it has grown and now contains approximately 30,000 reports, documents

and books. (On an 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.

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. The first step^has been initiated towards filling

this gap. FRIS has begun to automate its collection and the on-line

bibliographic database is called FIREDOC . All new bibliographic records are added to FIREDOC. Retrospective input is being completed by modules, e.g.,

all CFR reports going back to the beginning of the NBS fire programs.

An extensive document distribution program is carried on, both on a regular

basis and on a demand basis. Hie publication and distribution of grantee

reports (in the NBS Government Contract Report series) to selected subject

interest groups is part of this program. All NBS report series are listed in

the automated bibliographic data base and available through the Government

Printing Office of the National Technical Information Service.

The journal collection contains approximately 100 titles. The focus is on the

research activities of the CFR, as well as fire-related research needs. The

titles are quite unique to FRIS.

For interested people who cannot come to the FRIS, an extensive inter-library

loan program is carried out with participating libraries through the United

States. FRIS is located at the National Bureau of Standards, Building 224,

Room A-252. The telephone number is (301)921-3249.

17
FIRE SIMULATION

CENTER FOR FIRE RESEARCH

FY 86

Professional Personnel

Harold E. Nelson, Head

Daniel Gross, Research Engineer

Richard L. Smith, Knowledge Engineer

W. Douglas Walton, Fire Protection Engineer

Proeram Objectives

To provide for the expedient transfer of scientifically based technology to

the professional applications community and provide a point of interface

between the computer based activity of the Center for Fire Research and others

doing similar or complementary work.

Scope

The work addresses development of engineering systems for design application,

and the development of expert systems, the collection of the supporting data

and programs , and the operation of a working and training laboratory dedicated

to computer modeling and other fire safety computations.

Projects

1. Engineering Method Development. The purpose of this project is to

assemble, adjust, coordinate existing data, models, physics, and other needed

elements to develop engineering methods useable by fire protection engineers

and others involved in building design. The object is a progressive evolution

of a fire protection engineering technology based on scientific investigation

and technical experiments undertaken by NBS and others in the fire research

community. The overall approach is to develop validated engineering methods

for appraising fire safety in buildings or design and the impact of specific

fire criteria proposals. The program is designed to produce a progressively

expanding set of capabilities with useful methods becoming available in the

near future. The program has a three level approach. Some work is already

underway in levels one and two. The levels are as follows:

Level One: Assessment of life safety within a reasonably

large space which includes the area of fire origin (eg:

auditoriums, hospital wards, offices, laboratories,

machine shops, and similar spaces).

Level Two: Assessment of life safety and the mitigation of

damaging fire effects in a facility involved in a series of

connected rooms and spaces on a single floor (eg. hospital

nursing unit, and similar divided spaces).

18
Level Three: Assessment of life safety, mission continuity

and property value risk covering multistory conditions.

The initial effort was supported by funds from the Air Force. A system of

fast responding models and formulas has been structured, a report published

outlining the potential system, and a number of the input and computational

subroutines organized into a consistent format. The future depends on availability of funds and resources.

2.

Fire Simulation Laboratory . For more than a decade researchers have been

developing computer programs to predict or model the growth of fire and its

effects in buildings. Although the variety of fire scenarios which can be

addressed with these computer programs is limited at present, there is a growing interest in the fire protection community in adapting these computer

programs for specific needs.

This interest, and the need for efficient transfer of recently developed

technology in computerized fire simulation, has prompted the Center for Fire

Research (CFR) to establish a Fire Simulation Laboratory (FSL) . This

laboratory is a place where individuals from the private sector, Federal,

state and local government agencies, academic institutions and others can utilize computer programs, state of the art graphics, video and reference

als

and associated data bases to:

(1) further develop computer fire modeling

integrate them with data.

programs and

(2) demonstrate the capability of computer

address fire questions and issues

models to

(3) provide training in the use and applic

simulation techniques, and

ation of fire

(4) provide answers to fire problems

During this first year the Simulation Laboratory has conducted several

workshops to introduce engineers to modeling and has served as a resource to

various researchers.

3.

Data Sources for Predictive Modeling. This project supports and

implements projects requiring data for use in fire growth and smoke transport

models . This involves determining the appropriate sources of information for

basic thermophysical property data and for measurements of the fire responses

of typical combustible contents. A specific output is a FAST 17 -compatible

data base catalog including the following types of data: (a) thermophysical

properties, (b) furniture calorimeter, (c) cone calorimeter, and (d) toxic

potency.

4.

Exnert SystemsThis project has as its objective to develop a computer

program which will make an expert estimate of the fire safety of a building

based on CFR's deterministic physical models, technical data, and expert

judgment. It will have the capability to explain any conclusions it

In addition, it should be readily ’useable by CFR's clients.

19

maxes
The approach being used is Co write a computer program using a LISP machine

and state-of-the-art expert system development software tools. The approach

is to base an expert system on a methodology similar to the one used in the

report "Credible Engineering Methodologies" by H. E. Nelson. The particular

expert systems developed will be determined by selecting appropriate subjects

for the construction of expert systems and are important to the fire

community. Our initial expert is Harold E. Nelson. The initial choice of a subject for an expert system is a general purpose warehouse. A system is

being developed that will first determine if the concepts or plans for a warehouse are in compliance with the United States Air Force regulations.

These regulations include by reference all well known fire codes. When this

phase is complete, expert engineering analysis will be added that is similar

in content to the material included in Engineering Methods Development.

Publications

Smith, R.L„ASKBUDJr: A Primitive Expert System for the Evaluation of the

Fire Hazard of a Room, National Bureau of Standards, NBSIR 86-3319,

Gaithersburg, MD, March 1986.

Smith, R.L.ASKBUDJr: A Precursor of an Expert System for the Evaluation of

Fire Hazard, Fire Technology (to be published).

Nelson, H.E., Concepts for Life Safety Analysis, The 7th Society of Fire

Protection Engineers Symposium, Quantitative Methods for Life Safety Analysis,

College Park, MD, March 5-7, 1986.

Nelson, H.E., "FIREFORM" , A Computerized Collection of Convenient Fire Safety

Computations, NBSIR 86-3308, National Bureau of Standards, Gaithersburg, MD,

1986.

Nelson, H.E., Walton, W.D., The Basic Structure of the Fire Protection Design

Assessment System, NBSIR 85-3298, National Bureau of Standards, Gaithersburg,

MD, 1986.

20
FLAMMAB ILITY AND TOXICITY MEASUREMENT

CENTER FOR FIRE RESEARCH

FY86

Professional Personnel

Vytenis Bafarauskas , Head

Richard H. Harris jr.

General Physical Scientist

Gerald King, Fire Prevention Engineer

John F. Krasny, Textile Technologist

Barbara C. Levin, Toxicologist

Gregory M. Michaels, General Engineer

Marc Nyden, Research Chemist

Maya Paabo , Research Chemist

Trudi H. Hensley, Guest Worker, University of Pittsburgh

Joshua L. Gurman, Research Associate (AISI)

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 the burning parameters of various furnishings

for use in fire hazard models

• developing an appropriate measurement methodology for the propensity of

cigarettes to ignite soft furnishings

• reinforcing the relationship of combustion in the cone calorimeter to

large scale burning and aiding the promulgation of the cone calorimeter

for engineering and code applications

Pro i 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 rate

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

21
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. As a parallel effort, in the international

community, ISO TC92 SCI WG5 (the ISO working group on heat release rate) has

made a commitment to develop the cone calorimeter into an ISO standard. The

commercial production of cone calorimeters has been started in the United

States; the initial unit was calibrated and checked out at NBS this summer. The list of laboratories equipped to do this work is growing- -in addition to a second unit built at NBS, and the half-dozen units being built commercially,

there are units in place in Japan and Belgium, and several more units are being built in Europe. In addition, a British equipment maker is to start

producing units for the European market commercially. Work has been started

this year on making real-time measurements of soot mass production in the cone calorimeter, and on correlating these measurements to full-scale measurements

in the furniture calorimeter. Finally, some very rough rules for estimating

full-scale heat release rates in the absence of a validating full-scale data

base were developed for use with the fire hazard analysis computer model, and

an initial database issued of previously unpublished cone calorimeter measurements on various materials

Babrauskas , V. , Comparative Rates of Heat Release from Five Different

Types of Test Apparatuses, J. of Fire Sciences. 4, 148-159 (1986).

Babrauskas, V. , Smoke Measurement Results from the Cone Calorimeter, pp

420-434, Proc. of the 8th Joint Panel Meeting UJNR Panel on Fire

Research and Safety . Building Research Institute, Tsukuba, Japan (1985).

2. Upholstered furniture flammability

The monograph on furniture flammability has finally been issued; however, a number of issues related to upholstered furniture flammability are still seen

to be in need of exploration. One such study was done to determine if smallscale open flame tests, such as the BSI test (BS5852) , provide additional,

unique information of furniture flammability not obtainable in cone calorimeter measurements. The results showed that, while there are still a number of

foam/fabric combinations whose behavior is not well understood, the ease of

ignition in a BS5852 type open flame test can be correlated to the time to

reach a certain critical heat release rate in the cone calorimeter. Also,

several furniture calorimeter studies were made during this year on fireresistive upholstered chair constructions; data analysis is still ongoing.

Babrauskas, V. , and Krasny, J.F., Prediction of Upholstered Chair Heat

Release Rates from Bench- Scale Measurements, pp . 268-284 in Fire Safety

Science and Engineering (ASTM STP 882), T.Z. Harmathy, ed.Amer. Soc.

for Testing and Materials (1985)

Babrauskas, V. , and Krasny, J.F., Fire Behavior of Upholstered Furniture

(NBS Monograph 173). Nat. Bur. Stand. (1985).

22
3. Toxicological effects of pure and mixed fire gases

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

whether the toxic effects of the combustion products from materials can be

explained by the biological interactions of the primary fire gases or if

minor, more obscure gases need to be considered. LC50 values for Fischer 344

rats have been calculated for the individual gases, CO, HCN, or decreased

oxygen, for 30 minute exposures plus relevant post- expo sure periods using the

NBS Toxicity Test Method. LG50 values have also been determined for CO and

HCN (as individual gases) for exposure times of 1, 2, 5, 10, 20, and 60

minutes . To date , combination experiments with CO and HCN indicate that they

act in a linearly additive manner for the 5, 10, 20, 30, and 60 minute time

periods. A comparison was also made of the concentrations of the major

combustion products generated from a number of materials at their LC 50 values

with the combined gas model. The results indicate that the observed toxicity

in 17 out of 24 cases can already be explained by the biological interactions

of the examined primary toxic fire gases. This success ratio is expected to

increase when several more primary gases can be included. These results

already provide information for the fire hazard analysis computer model.

Levin, B.C., Gurman, J.L., Paabo, M. , Baier, L. , Procell, L. , and

Newball, H.H. , Acute inhalation toxicity of hydrogen cyanide. The

Toxicologist 6. 59 (1986).

Gurman, J.L., Paabo, M. , and Levin, B.C., An improved gas chromatographic method for the measurement of blood cyanide. The Toxicologist

6. 138 (1986).

4. Analytical measurements of primary gas species

The toxicological ("N-gas") model above is predicated on the ability to

analyze the necessary gas species in a combustion environment. Gas concentrations have to be available which are valid despite the presence of a large

number of potential interferents and which are time resolved (since the

material pyrolysis process may exhibit a strong time -dependent character)

.

For CO, C02

, and 02 such an analytical capability has long been available.

For a few other gases (HCi, HCN) recent efforts have been made to validate

proposed methods. For other gases, however, time -resolved techniques with a well -characterized validity have typically not been available. To obtain this

capability (to be used in conjunction with the cone calorimeter) a Fourier

transform infrared spectrometer was installed and a concerted effort is under

way to develop robust algorithms for time-resolved multi-component quantitation.

Babrauskas, V. , Levin, 3.C., and Gann, R.G., A New Approach to Fire

Toxicity Data for Hazard Evaluation, ASTM S tandardization News . 14, 28-

33 (Sept. 1986).

5. Toxicological synergism between carbon monoxide and carbon dioxide.

The acute inhalation toxicities of CO and C02 as individual and combined gases

have been examined in rats. The 30 min LC 50 values for CO in air were 4600

23
ppm for square-wave exposures. No post-exposure deaths occurred from the CO.

Animals exposed to C02 concentrations ranging up to 14.7% for 30 min were*

neither incapacitated nor fatally injured. The addition of non- lethal

concentrations of C02 (1.7 to 17.3%) to sublethal concentrations of CO (2500

to 4000 ppm) caused deaths of the exposed rats both during and following (up

to 24 hours) the 30 min exposures. At the most toxic combination of these two

gases (2500 ppm CO plus 5% C02 ) , the rate of formation of COHb was 1.5 times

faster than that found in rats exposed to 2500 ppm of CO alone. The COHb

equilibrium levels, however, were the same (78%). In addition, exposure to

both CO and C02 produced a much greater degree of acidosis than that generated

by either of the gases singly. The results fit a mathematical model indicating a synergistic interaction within the range of the experiments

6. Reviews of the literature on the gaseous products and toxicity generated

from the pyrolysis and combustion of seven plastics

Detailed reviews of the literature on the thermal decomposition products and

inhalation toxicity of seven plastics commonly found in residential homes were

completed during the past year. A summary of all the reviews was also

published during this time. The materials that were examined were ABS (NBSIR

85-3248), nylon (NBSIR 85-3280), polyester (NBSIR 85-3139), polyethylene

(NBSIR 85-3268), polystyrene (NBSIR 85-3277), PVC (NBSIR 85-3286), and rigid

polyurethane foam (NBSIR 85-3224).

Levin, B.C., A summary of the NBS Literature reviews on the chemical

nature and toxicity of the pyrolysis and combustion products from seven

plastics: acrylonitrile -butadiene- styrenes (ABS), nylons, polyesters,

polyethylenes , polystyrenes, poly(vinyl chlorides) and rigid polyurethane foams. NBSIR 85-3267 (1986).

7. Development of an in vitro bacterial assay system to assess combustion

product toxicity

Initial studies examining the potential of an in vitro system utilizing

aerobic bacteria to assess the relative combustion product toxicity generated

from materials were made. The effects of pure toxic gases known to be

generated in fires and other fire associated factors on the growth rate of the

aerobic bacteria. Bacillus subtilis . were determined. Optical density of the

bacterial culture was measured to determine growth. The culture was demonstrated to be insensitive to CO, but was encouragingly sensitive to HCN, with

a 200 ppm concentration producing a 5 -fold decrease in growth rate.

Rutkowski, J.V. and Levin, B.C., Development of an in vitro bacterial

assay system to assess combustion product toxicity. The Pharmacologist

28- 209 (1936)

8. Toxicological comparison of large-scale room burns with small-scale

experiments

This study involved a comparison between the toxicity results and chemical

measurements obtained from small-scale tests on upholstered furniture compo24
nent materials with test data obtained from full-scale furniture systems. The

component materials were a flexible polyurethane foam with and without a fire

retardant and a cotton fabric. Both room fire tests and furniture calorimeter

measurements were conducted. Small-scale testing of the individual components

were conducted in the NBS toxicity test method and in the cone calorimeter.

The experiments, in general, showed broad agreement between bench- scale and

full-scale, but significantly more data will have to be accumulated before an engineering strategy is finalized.

9. Cigarette ignition study

This work is being done under the Cigarette Safety Act of 1984. So far, the

relative propensity of 12 currently- sold cigarettes was evaluated on a variety

of substrates simulating upholstered furniture. The substrates varied in

cover fabric and padding. The cigarettes were placed on the flat surface or into the crevice, and covered with a piece of fabric or left uncovered. The

study showed some statistically significant differences in the ignition

propensity among the cigarettes on some of the substrates. The results have

not been extrapolated to the total population of furniture and mattresses in

U.S. homes. A similar evaluation of 32 experimental filter and non- filter

cigarettes varying systematically in tobacco blend, circumference, tobacco

packing density, length, paper porosity, and smolder accelerant content has

been completed, as has an evaluation of patented cigarettes designed to have

low ignition propensity. The literature pertinent to the ignition by smoldering cigarettes of upholstered furniture and mattresses was searched. It was found that the smoldering behavior of cigarettes on substrates differs from

that of cigarettes burning in air: cigarette temperatures on substrates tend

to be lower, and burning rate slower. This reduction seems to be larger for

substrates which ignite than for those which self -extinguish after the cigarette bums out. The characteristics of soft furnishings which ensure

resistance to cigarette ignition have been established, but those of cigarettes with low propensity to ignite have not.

Krasny, J.F., and Gann, R.G. , Relative Propensity of Selected Commercial

Cigarettes to Ignite Soft Furnishings Mockups. NBSIR 86-3421 (1986).

Associated Grants

1. Argonne National Laboratory, Joseph R. Stetter - Feasibility of FieldDetection and Analysis of the Toxic Products of Combustion.

2. 3rown University, Merwin Sibulkin - Study of Effects of Material Properties on Flaming Combustion of Charring Fuels.

3. Factory Mutual, Archibald Tewarson - Development of a Model to Provide

Comprehensive Fire Property Data.

4. SRI International, Charles S. Rebert - Electrophysical Incapacitation

and Persistent Behavioral Dysfunction of Rats Associated with Combined

Exposure to Carbon Monoxide and Carbon Dioxide.

25
5. Southwest Research Institute, Gordon Hartzell - Analysis of Hazards -to Life Safety in Fires

.

6. University of Dayton Research Institute, Mark Dietenberger - Mathematical Modeling of Furniture Fires.

7. University of Pittsburgh, Yves Alarie - Toxicity of Plastic Combustion

Products

.

26
HAZARD ANALYSIS

FIRE SAFETY TECHNOLOGY DIVISION

FY 86

Professional Personnel

Richard W. Bukowski, P.E., Head

Bernard M. Levin, Research Psychologist

A. Jeffrey Shibe, Research Fire Protection Eng.

S. Wayne Stiefel, Operations Research Anal.

Walter W. Jones, General Physical Scientist

John H. Klote, Research Mechanical Eng.

Kevin Greenaugh, General Engineer

Daniel M. Alvord, Computer Specialist

Keith Wayland, IPA (Visiting Faculty)

Peter M. Dubivsky, Research Assoc. (UL)

A. Sekizawa, Guest Worker

Proppram Objectives

To develop predictive, analytical methods which enable the quantitative

assessment of hazard and risk from fires.

Scope

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 must

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. Toxic Hazard Assessment Models

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 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 of the occupants in

terms of incapacitation or lethality from temperature or toxic gases or incapacitation by second degree burns from radiant flux exposure.

27
Also included in the report is a set of nine representative example cases of

typical residential fires as established by two panels of outside experts..

These are three 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

serving 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.

Bukowski, R. W. , et . al

.

HAZARD I - Vol. 1: Hazard Assessment Method, Vol. 2:

Representative Example Cases, and Vol. 3: Data Base Listing, NBS Special

Publication, in press.

Bukowski, R. W. , Evaluation of Furniture Fire Hazard Using a Hazard Assessment

Computer Model, Fire and Materials . Vol. 9, No. 4, 1985.

Bukowski, R. W. , Quantitative Determination of Smoke Toxicity Hazard - A

Practical Approach for Current Use, Fire Safety Science - Proceedings of the

First International Symposium, Pagni, P.J. and Grant, C.E., eds . , Hemisphere

Publishing Corp. NY, NY, pp 1089-1100, 1986.

2. Building Smoke Transport Model

This work consists of development of a computer model 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. This model will consist of a number of subroutines

for smoke transport under specific conditions which can be used with other

fire models. The zone model FAST, for example will be used to simulate smoke

movement within the building compartments. Ultimately, when models of smoke

flow in corridors and shafts are developed these too will be incorporated.

A model of smoke movement through HVAC systems has been written which predicts

the flow of smoke and gases through the components at a HVAC system as a function of time. It is a network model of general nature such that the most

simple to the most complicated HVAC system can be simulated. Documentation

and numerical verification are currently underway.

In recent years, the possibility of using elevators as a means of fire escape,

particularly by the handicapped, has received considerable attention from the

fire protection community. Thus, a joint project was initiated between NBS

28
and the National Research Council of Canada to investigate the feasibility of

elevator smoke control systems.

Full scale tests are underway at the 10-story NRCC fire research tower in

Ottawa to verify the results of predictions of elevator smoke control

performance which used the computer program ASCOS developed at NBS . An

analysis of elevator piston effect without smoke control has been completed to

help answer questions about the pressures produced by elevator car motion. An

analysis of piston effect during smoke control system operation is currently

being conducted.

Klote, J.H. and Tamura, G.T.

,

"Piston Effect and Smoke Problem", submitted to

Fire Safety Journal for publication.

3. Smoke Transport Modeling

The primary objective of this project is modeling the growth of fires and the

spread of smoke and toxic gases. Interest runs the gamut 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 description for a building and the insult to which it is subjected,

then to model the course of the fire, and finally 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.

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 two 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. Recently, an important improvement has been made in the latter

aspect

.

The current suite of programs consists of an input program(MINPUT) , the

simulation model(MOST) and a program for displaying the output (MPLOT)

.

Jones, W.W. and Bodart, X., Buoyancy Driven Flow as the Forcing Function

of Smoke Transport Models, NBSIR 86-3329 (1986).

Jones, W.W.

,

A Model of Smoke Transport (MOST), submitted to Fire Safety

Journal

.

29
Jones, W.W. and DeWitt, C. , Heat Transfer through Multilayer Boundaries:

Implementation and Validation, 2nd ASME-JSME Thermal Engineering Joint

Conference, Honolulu.

Peacock, R. , Davis, S., Lee, B. , Jones, W. , and Steel, S., Experimental Data

for Modeling Validation, in review.

4. Computer Graphics

The objective of the graphics task is to support the modeling effort by

providing results of the model calculations which can be readily interpreted.

A secondary purpose is to provide in- situ visualization of experimental data

to aid in understanding the processes which occur as a fire grows and spreads.

We are working with state-of-the-art equipment and software, much of the

latter being specifically developed for this work.

Jones, W.W. and Fadell, A., A Device Independent Graphics Kemal,

NBSIR 86-3235 (1985).

30
POLYMER COMBUSTION RESEARCH

FIRE MEASUREMENT AND RESEARCH DIVISION

CENTER FOR FIRE RESEARCH

FY 86

Professional Personnel

Takashi Kashiwagi , Head

Walter M. Shaub, Research Chemist

James E. Brown, Research Chemist

Lisha Glinsman, Research Chemist

William Manders , Research Chemist

Thomas J. Ohlemiller, General Engineer

William J. Parker, Physicist

Jeffrey Didion, Mechanical Engineer

Elizabeth Finlayson, Guest Worker

Akihiko Ito, 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 and heat

and mass transport processes in the solid phase.

(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.

Scone

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 thermal properties of the material.

Project

1. Polymer Gasification and Ignition

The prediction of ignition, flame spread, steady burning and flashover

requires a knowledge of the rate of gasification of solids. The rate of

gasification is determined by the rate of energy input from an external source

and/or of energy feedback from a flame to the material, by the degradation

chemistry, and by the heat and mass transport processes in the material. The

complex coupling between degradation chemistry and heat and mass transport

processes in the material is the major reason why we cannot predict the rate

of gasification of solid materials. Therefore, the objective of this project

is to increase our understanding of the degradation chemistry, heat and mass

31
transport processes in polymeric materials (synthetic polymers as a first

step) through a carefully designed program of theoretical and experimental

research.

Careful experimental studies show that the "weak links" in PMMA are head-tohead linkages and unsaturated double bonds at the ends of polymer chains.

Their effects on degradation rates were demonstrated using specifically

polymerized PMMA samples supplied from the University of Osaka (Professor K.

Hatada) . The effects of initial molecular weight and ambient oxygen on

degradation initiation from these weak linkages were studied. Results show

that ambient oxygen stabilizes the degradation initiated from scission at

head-to-head linkages by trapping polymer radicals created from the scission.

Also, ambient oxygen slightly stabilizes end- initiated degradation but it

enhances the rate of degradation greatly at high temperatures.

Two theoretical models were developed to calculate changes in weight loss and

in the molecular weight distribution of a vinyl polymer without any transport

processes. The degradation reaction scheme consists of end initiation, random

scission initiation, depropagation, termination and transfer reactions. This

model is based on the approximation of a steady state radical concentration.

Effects of initial molecular weight on changes in weight loss and in the

molecular weight are being studied and compared between the predicted results

and the experimental data using the above PMMA samples. Another theoretical

model was developed to examine the validity of the commonly used approximation

of a steady state radical concentration. A degradation reaction scheme

consisting of random initiation, depropagation and termination reactions was used for this study. Results indicate that an unusual buildup of monomer

radicals is observed without specific treatment of the monomer radicals such

as enhanced rate of monomer radical transfer reaction or immediate

vaporization of monomer radicals. Guidelines for the approximation to be

reasonable are derived for the range of characteristic parameters such as normalized zip length and radical number per initial chain length.

A technique to measure the time -dependent temperature distribution in a transparent polymer was developed. This technique is based on holographic

interferometry. The technique was applied to measure the temperature

distribution in PMMA when flame spreads over the surface. Conductive flux

distributions (along and perpendicular to the surface) in PMMA were derived to

understand how the flame spread over the polymer surface. This technique is

being applied to measure time dependent temperature distributions in PMMA

which is headed by external radiation.

"A Model Describing the Steady-State Pyrolysis of Bubble- Forming

Polymers in Response to an Incident Heat Flux” by Wichman, I. Combustion

and Flame, 63, 217 (1986).

"Differences in PMMA Degradation Characteristics and their Effects on

its Fire Properties" by Kashiwagi, T. , Inaba, A., and Brown, J.E.,

Proceedings of First International Symposium, Hemisphere, 483 (1986).

"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. , Macromolecules, (in press).

32
"A Calculation of Thermal Degradation Initiated by Random Scission.

1. Steady-State Radical Concentration" by Inaba, A., and Kashiwagi, T.

Macromolecules (in press).

"A Calculation of Thermal Degradation Initiated by Random Scission.

2. Unsteady Radical Concentration" by Inaba, A., and Kashiwagi, T.

Macromolecules (submitted)

"A Measurement Technique for Determining the Temperature Distribution in

a Transparent Solid Using Holographic Interferometry" by I to A. , and

Kashiwagi, T. Applied Optics (submitted).

"Temperature Measurements in PMMA During Downward Flame Spread in Air

Using Holographic Interferometry" by Ito A., and Kashiwagi, T. Twenty

First International Symposium on Combustion (in press)

2. Smoldering Combustion of Cellulosics

The propensity for smoldering exhibited by cellulosie materials continues to

be a subject of major concern. Smoldering combustion is driven by exothermic

oxygen attack on the surface of organic materials; wood-based materials such

as cellulosie insulation are particularly prone to this attack. The process

is slow but self-sustaining once initiated. It poses a life threat as a copious source of toxic gases. Also, it provides a relatively easy pathway to

flaming combustion that may not be precluded by flame retardants. It is this

latter aspect- -smoldering as an initiator of flaming- -which has been examined

recently for cellulosie insulation materials. Smolder to flaming tests were

conducted using unretarded cellulosie insulation material and insulation with

either boric acid (a smolder -retardant) or borax (a flame retardant) . Both

suppress flaming effectively when the smoldering insulation is isolated from

other flammable material. Much of their effectiveness is lost when unretarded

wood abuts the smoldering insulation since the wood itself ignites.

Smolder spread over solid wood is to be examined in a series of experiments

now getting underway. Initial emphasis will be on the effective equivalence

ratio and major gasification products. The details of the degradation of wood

and its components are also of continuing interest. Solid-state NMR is being

used to characterize the early steps of degradation of lignin and hemicelluloses

"Forced Smolder Propagation and the Transition to Flaming in Cellulosie

Insulation", by Ohlemiller, T. , NBSIR 85-3212, October 1985.

"Modeling of Smoldering Combustion Propagation" by Ohlemiller, T.,

Progress in Energy and Combustion Science, 11, 277 (1985)

3. Fundamentals of Wood Gasification and Combustion

This work is aimed at clarifying and quantifying the physical and chemical

processes underlying gasification of wood at fire level heat fluxes and the

conditions required to oxidize the resultant gases. Major support comes from

the Department of Energy.

33
An extensive set of one -dimensional radiative heating tests on thermally thick

wood samples has been completed; these included the effects of wood type,

grain orientation, water content, thickness, flux and ambient oxygen level on gasification rate and product composition. The conditions required to fully

oxidize certain of these products are currently being explored in a laminar

flow reactor. Also a modeling study is underway to develop time- temperature

plots which describe the combustibility of representative gasification

products under oxidative and pyrolytic conditions. To construct these plots,

rate constants for oxidation and pyrolytic degradation of specific organic

compounds have either been extracted from the literature or estimated.

"Products of Wood Gasification" by Ohlemiller, T. , Kashiwagi, T. and

Werner, K. , NBSIR 85-3127 (April 1985).

"Wood Gasification at Fire Level Heat Fluxes", Ohlemiller, T.

,

Kashiwagi, T. and Werner, K. , submitted to Combustion and Flame.

4. Heat Release Rate of Wood

A preliminary model has been developed for the heat release rate of wood as a 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 thermochemical properties include the

heat of combustion of the volatiles, the heat of pyrolsis 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 and in the

case of the thermochemical properties must be determined separately for all of

the major chemical components of the wood. The model has been setup on IBM

computer and the major thrust of the project for the past year has been to

experimentally determine the required input properties for checking out the

model against heat release rate measurements in the cone calorimeter.

A combination pyrolyzer and catalytic converter (PYROCAT) was constructed and

used at the Forest Products Laboratory during the summer of 1985 to obtain

data on the heat of combustion of the volatiles and the kinetic parameters for

the chemical components of Douglas fir heartwood. These components included

cellulose, lignin, mannan and xylan. This was followed by a period of data

interpretation and a rebuilding of the apparatus in order to improve upon the

precision of the results. Some preliminary work has been done on the

development of a method for measuring the thermal diffusivity of the char at

elevated temperature.

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

34
complex material this can only be done in an approximate way but it may be

adequate for fire modelling purposes.

"Development of a Model for the Heat Release Rate of Wood - A Status

Report" by Parker, W. , NBSIR 85-3163, Nat. Bur. Stand. (U.S.), (May

1985).

"Prediction of the Heat Release Rate of Wood" by Parker, W. , Proceedings

of the First International Symposium on Fire Safety Science, Hemisphere

Publishing Corporation, 1986, pp 207-216.

Associated Grants and Contracts

1. "Ternary Reactions Among Polymer Substrate -Organohalogen- Antimony Oxides

in the Condensed Phase Under Pyrolytic, Oxidative and Flaming

Conditions", Michael J. Drews and Christine W. Jarvis, Clemson

University

2. "A Study of the Effects of Oxygen Transport, and Temperature History on

the Chemistry of Polymethyl Methacrylate and Cellulose Pyrolysis", Eric

M. Suuberg, Brown University.

3. "Flame Radiation", Chang -Lin Tien, Lawrence Berkeley Laboratory.

4. "Kinetics of Oxygen Chemisorption and Desorption of Combustion Products

in the Smoldering Combustion of Cellulosic Material", G. Richards, U. of

Montana

5. "Thermal Stabilization of Polymers by Cross-Link Formation", C. Wilkie,

Marquette University.

6. "Interaction of Radiation and Condition in Polymeric Materials, W. Aung,

University of Maryland.

35
Smoke Dynamics Research Group

Fire Measurement and Research Division

Center for Fire Research

FY 86

Professional Personnel

George W. Mulholland, Head

Nelson P. Bryner, Chemical Engineer

W. Gary Mallard, Research Chemist

William M. Pitts, Research Chemist

Kermit C. Smyth, Research Chemist

James Gentry, Guest Worker

Victor Henzel, Guest Worker

J. Houston Miller, Faculty Research Associate

K. C. Muck, Guest Worker

Roberto Samson, Guest Worker

Program Objectives

Develop scientifically sound principles, metrology, data, and predictive

methods 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. Despite

this importance, there is little understanding at the molecular level of the

soot formation process; i.e., how small molecules grow rapidly to become soot

particles. We are now in the seventh year of a long-term study of the

fundamental chemistry and physics of soot formation, carried out jointly with

the NBS Thermal Processes Division in the Center for Chemical Engineering and

also in collaboration with the Chemical Kinetics Division in the Center for

Chemical Physics.

A series of optical and mass spectrometric profile measurements have been

completed for methane/air diffusion flames on our Wolfhard- Parker burner. We

have used fluorescence to monitor OH, C2

, and polycyclic hydrocarbons (three

ways) , multi-photon ionization to detect methyl radicals and small soot

36
particles and Rayleigh -mie scattering to observe the emergence of large soot

particles. In addition, mass spectrometric profiles of C02 , H2 0, methane,

acetylene, butadiene, benzene, toluene, diacetylene, triacetylene, vinyl

acetylene, 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

products. Velocity measurements using laser Doppler velocimetry and thermocouple temperature profiles have also been obtained. The combined data

provide the most detailed description of the chemical structure in a 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

flame. These results show that acetylene plays the major role in surface

growth on particles (as found in premixed flame studies). Furthermore, direct

tests of proposed models of chemical growth can now be made which strongly

suggests that a pathway involving vinyl radical addition to acetylene is the

fastest route to form benzene.

In addition to species characterization studies, physical properties of soot

are being investigated. The kinetics of cluster aggregation and structure of

the resulting clusters have been studied using a "Brownian dynamics" computer

simulation of conditions appropriate for soot growth. These simulations are now being extended with the new NBS Cyber 205 to increase the number of

particles in an agglomerate from about 200 to 2000 and to include rotational

diffusion as well as translational diffusion. The observed microstructure of

soot produced by a coannular diffusion flame with acetylene was found to be in

good agreement with the computer simulations. Theoretical and experimental

work is in progress to study the optical and aerodynamic properties of soot.

The smoke emission coefficient and the light extinction coefficient have been

measured for smoke produced by free burning propane, heptane, wood cribs,

rigid polyurethane, Prudhoe Bay crude oil, and upholstered chairs. The fires

range in scale from about 50 to 500 kw. The elemental carbon content and the

optical properties of the smokes appear to be independent of the material

burning. This study is in support of the Defense Nuclear Agency study of the

global climatic effects of a major nuclear exchange.

"Soot Inception in a Methane/Air Diffusion Flame as Characterized by

Detailed Species Profiles" by Smyth, K.C., Miller, J.H., Dorfman, R.C.,

Mallard, W.G. and Santoro, F.J., Comb. & Flame . 62 . 157 (1985).

"Detection of the Methyl Radical in a Me thane/Air Diffusion Flame by

Multiphoton Ionization Spectroscopy" by Smyth, K.C. and Taylor, P.H.,

Chemical Phvsics Letters . 122 . 518 (1985)

"Multiphoton Ionization Spectra of trans-1, 3 -Butadiene: Reassignment

of a Rydberg Series" by Taylor, P.H., Mallard, W.G., and Smyth, K.C., J

Chem. Phvs . 84, 1053 (1986).

"The Chemical Structure of Methane/Air Diffusion Flames: Concentrations

and Production Rates of Intermediate Hydrocarbons" by Miller, J.H. and

37
Smyth K.C., Symposium on Chemical Mechanisms Associated with Combustion,

American Chemical Society National Meeting (April, 1986).

"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 (in press).

"Chemical Production Rates of Intermediate Hydrocarbons in a Methane/Air

Diffusion Flame" by Miller, J., Mallard, W.G. , and Smyth, K.C., Twenty

First Symposium (International) on Combustion (in press).

"Reactions of Phenyl Radicals with Ethene, Ethyne , and Benzene" by Fahr,

A., Mallard, W.G.

,

and Stein, S.E., Twenty- First Symposium

(International) on Combustion (in press)

"Soot Particle Formation in Laminar Diffusion Flames" by Santoro, R.S.

and Miller, J.H., Langmuir (submitted for publication).

"Global Soot Growth Model" by Mulholland, G.W.

,

Proceedings of the First

Intemation Fire Safety Science Symposium, edited by C.E. Grant and P.J.

Pagni (Hemisphere Publishing Corp.

,

Washington), 709. (1986).

"On the Applicability of Smoluchowski ' s Equation with a Constant Kernel

to Covalescence" by Mulholland, G.W. and Mountain, R.D.

,

JChem . Phys

84, 4109 (1986).

"Simulation of Aerosol Agglomeration in the Free Molecular and Continuum

Flow Regimes" by Mountain, R.D.

,

Mulholland, G.W., and Baum H. , J.

Colloid and Interface Science (in press).

"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 (submitted).

2. Estimation of CO Emission in Room Fires

It is known that CO is a major contributor to most fire related deaths. The

goal of this new project is the prediction of CO emission both pre and post

flashover. Available data on room bums is now being analyzed along with

results from the Cone Calorimeter.

3. Turbulent Chemically-Reacting Flow

In a large fire plume, the combustion region is turbulent and is characterized

by highly variable (both spatial and temporal) distributions of temperature

and species concentration. In such cases the flame properties are dominated

by the substantial temperature and species concentration fluctuations. Due to

the scarcity of measurements on such systems and the complexity of the

phenomena, the understanding of turbulent fire plumes is poor. This project

is designed to be a basic experimental study of chemically reacting flow in

which the effects of density differences due to composition, temperature, and

heat release on turbulent mixing are elucidated.

38
The project has required the development of new experimental diagnostic

techniques as well as the applications of these techniques to measurement in

turbulent flow fields. Up to the present time we have been primarily

concerned with the effects of density differences due to composition on the

mixing behavior of an axi symmetric jet flowing into a slow coflow of a second

gas. The findings of these studies are being used in attempts to better

understand turbulent mixing in certain types of combustion systems.

Rayleigh light scattering has been shown to be a particularly powerful

technique for monitoring real-time, spatially- resolved concentration

fluctuations in these flow fields. By combining the light scattering

technique with hot-wire anemometry a new diagnostic for simultaneous

concentration and velocity measurement has been developed. As a part of this

work an extensive experimental study of the responses of hot-wire and film

anemometers to flows of different gases was initiated. This study has not

only improved our understanding of these velocity measurement devices, but has

also yielded a much improved understanding of heat transfer from cylinders.

As part of our diagnostic development a digital line camera has been designed

and fabricated at NBS . This camera is designed to be sensitive enough to

allow real-time measurements along a line in these turbulent flow fields using

Rayleigh light scattering. Preliminary measurements have shown that this goal

has been achieved. The use of this camera will allow a much improved

characterization and understanding of entrainment and mixing in turbulent

flows

An extensive study of turbulent mixing behavior along the centerline of the

axisymmetric jet has been completed. Both flow visualization using

shadowgraphy and Rayleigh light scattering point measurements have been used

to investigate flows having jet/coflow density ratios covering the range from

0.14 to 37. The availability of measurements over such a wide range of

densities has enabled many density effects to be discerned. A manuscript

describing this work is available.

"Response Behavior of Hot-Wires and Films to Flows of Different Gases"

by Pitts, W.M. and McCaffrey, B.J., NBSIR 85-3203 and Journal of Fluid

Mechanics . 169 (1986) , to Appear.

"Effects of Global Density and Reynolds Number Variations on the Mixing

in Turbulent Axisymmetric Turbulent Jets" by Pitts, W.M. , NBSIR 86-3340

and submitted to the Journal of Fluid Mechanics .

"Chemically Reacting Turbulent Flow" by Pitts, W.M. and Kashiwagi, T.

,

NBSIR 85-3299.

Associated Grants and Contracts

1. "Soot Dynamics in Flames", Richard A. Dobbins, Brown University.

2. "Chemical Pathways to Soot Formation in Diffusion Flames", J. Houston

Miller, George Washington University

39
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 1986

Institution: Argonne National Laboratory

Grant No. : 40NANB5 1 1448

Grant Title : Feasibility of Field Detection and Analysis of the Toxic

Products of Combustion

Principal Investigator : Dr. Solomon Zaromb, Electrochemical Engineer

Environmental Research Division

Argonne National Laboratory

9700 South Cass Avenue

Argonne, Illinois 60439

Telephone: (312) 972-6423

Other Professional Personnel : Dr. W.J. Buttner, Electrochemical Engineer

Dr. V.C. Stamoudis, Program Manager

D. Domin, Research Participant

J. Privette, Research Participant

NBS Scientific Officer: Dr. Emil Braun

Technical Abstract:

Introduction . The primary objective of this work is to evaluate the

applicability of chemical parameter spectrometry (CPS) and allied

techniques to the design and construction of an instrument for the

detection and analysis of the toxic products of combustion. The

capability sought in the near term is field detection and selective

quantitation of at least five toxic compounds of primary interest in the

presence of other combustion products. Ultimately, the instrument will be

expanded to provide analyses of all or most of the toxic products formed

during combustion that present a danger to human health.

CPS consists of measuring a number of different "chemical parameters"

obtained from sensor responses to a given analyte and thus developing a characteristic response pattern or "parameter spectrum." A comparison of

that spectrum with previously determined parameter spectra for a variety

of compounds may then permit identification of an unknown compound in the

analyte.

The fundamental problem is to determine how CPS can be usefully

applied to the identification of toxic components in complex gaseous

mixtures of possibly 20 or more compounds. This problem has been

addressed, after reviews of the instrument design goals and of the

potentially usable instrumental techniques, by the following two-pronged

approach: (1) extension of the capabilities of CPS to mixtures of up to

three or four detectable compounds, and (2) fractionation of complex

combustion product mixtures into simpler mixtures of not more than three

or four of such compounds.

40
Applicability of CPS to Simple Mixtures . A portable instrument based

on CPS has been recently developed for detecting, identifying, and

monitoring any one of 20-30 compounds in air at concentrations in the

parts per-million range. This instrument utilizes the relative strenghts

of 16 sensor responses, obtained by operating four different

electrochemical sensors in four different modes, to generate response

patterns characteristic of each compound. Sensor responses to

electrochemically inactive compounds are obtained in three of the four

operating modes. Such compounds are partly preoxidized or pyrolyzed by

passing them over a noble-metal filament heated to an elevated

temperature. Response patterns obtained for 16 combustion product

compounds permit easy identification of each of these compounds, when

present singly in air, by means of a pattern-matching algorithm. An

algorithm has also been developed that extends the capability of CPS to

mixtures of detectable compounds. It uses preliminary screening steps

that reduce the number of candidate compounds to the number of Independent

simultaneous equations obtainable from the sensor response data. The

concentrations of the detected compounds are then computed by solving the

simultaneous equations. Error analysis is used to evaluate the probable

errors in the computed concentrations. To test the effectiveness and

reliability of this algorithm, sensor response patterns generated by all

possible ternary and binary combinations of six representative components

of combustion products (CO, SO2

s ’ ^2^0, and CH0 -CN) have been

gathered on disk files. These patterns are entered into the computer as unknown samples, and the computed concentrations are compared with the

actual composition of each tested mixture. The data and comparison

results are currently being evaluated.

Fractionation of Complex Combustion Product Mixtures . To achieve the near term goal of field detection and quantitation of five selected

compounds, e.g., CO, C0F2*

^

2

* ^CN, and SO2

» it may suffice to remove

most of the other combustion products by means of selective chemical

filters, and use an array of sensors that are specifically responsive to

these five compounds. However, such an approach could not easily lead to

a field instrument that could provide analyses for all or most of the

toxic compounds in combustion products.

A fractionation technique that has been successfully applied to

complex mixtures is gas chromatography (GC), and several portable GC

instruments are commercially available. By replacing or supplementing the

non-selective detector in present GC instruments with a selective CPS

sensor array, it becomes possible to unambiguously identify each simple

chromatographic peak and to resolve overlapping peaks of not more than

three or four components. While it may be difficult to obtain a single GC

column or even a pair of columns that could fractionate a combustion

product mixture into single-compound peaks, it appears to be relatively

simple to obtain a single column capable of fractionating such a mixture

into peaks of fewer than four compounds, and usually even fewer than three

or two compounds. The previously developed pattern-matching algorithm can then serve to verify that any observed single-compound peak does indeed

correspond to that deduced from its retention time. Any observed

4 L
overlapping peak may be resolvable by the algorithm that has been

developed for the analysis of simple mixtures.

Current efforts consist of passing various mixtures of compounds

encountered in combustion products through a packed GC column and hence

through a CPS sensor array. The results of these experiments will be used

to evaluate the practicality of a portable GC/CPS instrument for the field

analysis of combustion products. Figure 1 shows the non-selective

response of a flame ionization detector (FID) to a mixture of benzene and

acetonitrile (Fig. IB), as well as the responses of electrochemical

sensors in two modes of operation (Figs. 1A and 1C). Although two

distinct peak maxima were observed with the FID, baseline resolution was

not obtained. In contrast, the response depicted in 1A is due almost

solely to benzene, whereas that depicted in 1C is due to acetonitrile.

Thus the use of the electrochemical array improves the selectivity of the

detector. Such selectivity will be crucial for mixtures whose components

cannot be easily resolved by retention times alone.

Papers i

1. S. Zaromb and J.R. Stetter, "Theoretical Basis for Identification and

Measurement of Air Contaminants Using an Array of Sensors Having

Partly Overlapping Selectivities , "Sensors and Actuators, _6_:225-243

(1984).

2. S. Zaromb, D. Domin, and R. Battin, "Experimental Evaluation of

Mixture Analysis Using an Array of Amperometric Sensors," 13th Annual

Meeting of the Federation of Analytical Chemistry and Spectroscopy

Societies (1986).

42
B

Figure 1 . Illustrative CPS responses to a benzene-acetonitrile mixture®

(A) Current-time response of a commercial CO detector when the

GC eluent was passed over a heated platinum filament® (B) FID

response. (C) Current-time response of a gold sensor (biased

to +300 mV vs. an air reference electrode) to the eluent from

the FID.

43
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution: Brown University

Grant No.: 60NANB4D0036

Grant Title: A Study of the Effects of Oxygen Transport and Temperature History

On the Chemistry of PMMA and Cellulose Pyrolysis

Principal Investigator: Professor Eric M. Suuberg

Division of Engineering

Brown University

Box D

Providence, Rhode Island 02912

Telephone: (401) 863-1420

Other Professional Personnel: Tracy Kelly, Graduate Student

William Lilly, Research Engineer

NBS Scientific Officer: Dr. Takashi Kashiwagi

Technical Abstract:

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

cellulose. These variables include the heating rate of the sample, the partial pressure

of oxygen at the surface of the sample, and sample characteristics as affect the

transport of pyrolysis products out of the sample. Detailed product analysis of both

vapor and condensed phase products of pyrolysis are used to infer under what

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

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

be given to characterization of what are commonly called "tar" products, since these are the products that represent the most combustible vapor products. GPC will be

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 second year. The initial focus

has been the pyrolysis of PMMA, and the effects of heating rate and oxygen partial

pressure on observed kinetics. This work has been directed to complement the

ongoing work at the Bureau, as will be described below. The work on cellulose has

been initiated, but will be only briefly discussed here..

Effect of Heating Rate on Kinetics of PMMA Pvrolvsis: Among the motivating

factors for further work on the global kinetics of PMMA pyrolysis was the spread of

kinetic constants seen in the literature, and the concern that this might possibly be

44
due to an effect of heating rate employed in the different studies. This was

particularly of concern to those using slow heating rate TGA techniques of order (1

K/min) in which the resolution of distinct kinetic steps is easy: Could the

mechanisms and kinetics observed at these low rates be extrapolated to fire

conditions, involving orders of magnitude higher heating rates?

The data in Figure 1 suggest that heating rate is apparently not an important

consideration at heating rates of 5 K/min to 1000 K/min, and even up to 1000

K/sec. These data were obtained by heating thin films of PMMA (20-30*an Plexiglas

G) in the folds of an electrically heated wire mesh, under an atmosphere of inert gas

(He). The constants shown in Figure 1 are for a global model of pyrolysis in which

PMMA degrades by two parallel first order steps. The first step involves 10% of the

material, and the second step 90% of the material. This two-step behavior is consistent with the results obtained at the Bureau on similar, though not identical,

samples, and reflects the existence of at least two distinct initiation steps. The

constants obtained in this study suggest a slightly faster rate than obtained by the

Bureau, but the reasons for this are not entirely clear and may have to do with the

difference in samples studied.

To summarize, these data clearly show no effect of heating rate on the global

kinetics of pyrolysis of PMMA, from 5 K/min to 1000 K/min, and perhaps higher.

Effect of Oxvgen Partial Pressure on Kinetics of PMMA Fvrolvsis: The Bureau

had already shown that oxygen generally accelerates the rate of PMMA pyrolysis,

although it has a slightly retarding effect very early in the process. The question

raised was— how sensitive to oxygen partial are the kinetics of PMMA pyrolysis?

In the present study, the presence of oxygen was likewise found to have a retarding influence early during pyrolysis and an acceleratory influence throughout

the main portion of the process. It was found that the kinetics were sensitive to the

presence of anv oxygen, down to the 1% levels examined thus far, but not

particularly sensitive to concentration above 1% levels. The activation energy of the

main, random scission process in the presence of any oxygen drops to about 24

keal/mol, in low heating rate cases. In fact, it is impossible to fit data obtained at different heating rates with a single set of rate constants (in marked contrast to inert gas pyrolysis). This naturally implies a change in the global process as a function of heating rate, which in turn may imply that oxygen transport becomes

limiting at higher heating rates. This is illustrated in Figure 2, which shows

constants yielding a good fit to 5 K/min data considerably overpredicting rates at 100 K/min and 1000 K/min. In fact, at 100 K/min heating rates, there is little difference between rates measured in air and in inert gas, as is easily seen in

comparing Figures 1 and 2. The conclusion is that when the heating of the sample

is so rapid, the oxygen cannot play a role in the degradation chemistry. Thus, the

relevant rate in fire modeling situations in which heating rates exceed 100 K/min

would likely be the pvrolvsis rate in inert gas .

Measurements of molecular weight distributions of the residue largely

corroborate the above conclusions.

Rates of Diffusion of Monomer in PMMA: Some very simple experiments were performed in order to obtain estimates of the diffusivitv of MMA monomer in

PMMA. The rate is important in that it can determine whether mass loss is transport

or kineticaly controlled, and whether the surface properties of the PMMA might be
altered by bubble formation due to slow escape of MMA. Thus far, diffusion rates

have only been examined at temperatures below the glass transition temperature of

105°C Not surprisingly, the diffusion in this glassy regime seemed to be matrix

relaxation controlled rather than true Fickian. The rates are very sensitive to the

physical characteristics of the starting sample. Naturally, in real fire situations,

transport through a section of PMMA above the glass transition temperature will be

of more relevance, and these measurements are now being pursued.

Cellulose Pvrolvsis Kinetics: Measurements on cellulose pyrolysis kinetics have

only recently begun. The work involves exactly the same techniques as those

employed in the PMMA pyrolysis work. The sample of cellulose examined is identical to that in another NBS supported project at Brown under the direction of

Professor Merwin Sibulkin. This is a very low ash filter paper pulp. Results thus

far indicate that when pyrolyzed in a system which allows for very rapid transport

of the tars away from the surface, the extent of char formation is only 3 to 4% by

mass, independent of heating rate in the range 5 K/min to 100 K/min. The very

important interplay of mass transport and chemical kinetics will be examined in

future work, since it is important in fire modeling to predict the fraction of mass which is retained as char as opposed to released into the vapor phase. This question

is being examined by using various thicknesses of sample, in an effort to promote

intrasample cracking of the tars as happens in thick, bulk samples.

Reports and Papers:

"The Effect of Oxygen Concentration and Heating Rate on the Pyrolysis

Kinetics of PMMA," M.S. Thesis, Tracy Kelly.

Papers based on this M.S. thesis, which is in preparation, are expected to be

completed this fall.

46
gure 1 . Degradation of

PMMA in helium at various

heating rates . Indicated

temperature is the peak

temperature of a nonisothermal experiment,

and ordinate is mass remaining relative to initial mass.

# 1000 K/see f < 1 ) a 0.

f(2) = 0.9 a 1000 K/min A(1) a 2E!3 M2) - 1 E 1

A 100 K/mjn E{ 1) s 35 keal/mol E(2) = 45 kcal/mol

® S K/min

Calculated

Figure 2 . Degradation of

PMMA in air at various

heating rates. ( )

5K/min, (A) 100 K/xnin,

(#) 1000 K/min. Calculated curves, as explained

in text.

47
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

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

NBS Scientific Officer: Dr. V. Babrauskas

Technical Abstract:

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

material properties caused by these retardants, and to use this information to 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 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. 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 flammability limits will be compared with the previous

measurements in order to determine how the retardants act to suppress fires.

The major properties to be obtained are the heat of combustion of the

combustible fraction of the volatile products of pyrolysis Ah[comb vol], the heat of

gasification of the pyrolyzing fuel h

g

, and the mass fraction of the volatiles which

are combustible Yp-p Measurement of the heat of combustion is being done with

the use of a standard calorimeter and has progressed rapidly. The determination of

the heat of gasification is not a standard measurement and requires the development

of special apparatus and techniques; it is progressing slowly. The combustible

fraction of the volatiles will determined by future measurements of the inert gases

(CO->, H-»0) in the pyrolysate stream using gas chromatography.

48
The heat of combustion of the (total) volatiles Ah[vol] is determined using

Hess’ Law in the form

Ah[vol]

{

Ah[cel+ret] » Yq

Ahfchar] (

1 )

In this formulation is the mass fraction of char remaining after pyrolysis, and it has been measured using the following technique. A thin (3mm) disk is cut from

the end of the 25 mm diameter cellulose test specimen. The disk is replaced at the

end of the test specimen and held there by a spring-loaded clamp to maintain tension

during sample shrinkage. The composite specimen is placed in the gasification

apparatus and subjected to a radiant heat flux of the same magnitude as the heat

transfer rate during flaming combustion. Values of Yq are calculated from

measurements of the disk weight before and after pyrolysis. For cellulose retarded

with sodium hydroxide, the char fraction increases from Yq - 0.11 for pure cellulose

to Yq = .32 for a retardant mass fraction Y^ - .03. These char yields are somewhat greater than those found by Thermogravimetic Analysis at comparable

temperatures. The difference is attributed to the effects of passing the products of

pyrolysis through a hot char layer in the present experiments. This results suggests

the need to study bulk samples of charring materials to determine their behavior in

fires.

The heat of combustion Ah[cel+ret] of retarded cellulose samples was

measured using a Parr Semimicro Calorimeter, and the results are shown in Fig. 1. For pure cellulose the result is in agreement with literature values. The linear drop

in Ah is equal to that calculated by assuming the retardant acts as an inert material.

The char samples prepared for the measurements of Yq were then tested in the

calorimeter, and the values measured for Ah[char] are shown in Fig. 2. The results

show that a maximum of Ah[char] occurs at Y^ = 0.01. Calculations based on an assumption that the retardant remained in the char as an inert material do not

explain the shape of this curve.

Combining these measurements using Eq. (1) gives the values of Ah[vol]

shown in Fig. 3 at 25 °C Standard thermodvnamic methods were used to calculate

the corresponding results for Ahfvol] at 400 C. The major conclusion from this

work is that retardant addition causes a drop of up to 30 percent in the heat of

combustion of the (total) volatiles.

Work in progress includes measurements of char composition using an

elemental analyser. These results will show to what extent the elemental

composition of the char is affected by retardant addition, and will also be used to calculate the elemental composition of the volatiles [by a subtraction technique

analogous to Eq. (1)]. The final determination of Ah[comb vol] = Ah[vol]/Yp-p will

be made after the future measurements of Yp-p.

COMPLETED PUBLICATIONS

"Heat of Gasification for Pyrolysis of Charring Materials," M. Sibulkin, Fire Safety

Science-Proceedings of the First International Symposium, Hemisphere, pp. 391-400

(1986).

49
50

Eli. 3
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 1986

Institution: Division of Engineering

Brown University

Providence, R.I. 02912

Grant Title: Soot Dynamics in Flames

Grant No.: NB83NADA4025

Principal Investigator: Professor R. A. Dobbins

Division of Engineering

Brown University

Providence, R.I. 02912

Telephone: (401) 863=1422

Other Professional Personnel: Mr. Constantine Megaridis, Research Assistant

NBS Scientific Officer: Dr. George W. Mulholland

Technical Abstract:

We seek a deeper understanding of the dynamic processes which

control the behavior of the soot aerosol present within flames as well as in

the smoke which they release. The presence of the soot aerosol in low

concentrations is a widely used signal for the presence of fire. The soot

released from flames in higher concentrations is a hazard to victims of

uncontrolled fires. We have developed sampling methods based on thermophotetic attraction of small particles to a cold surface. These methods

allow us to sample the soot aerosol in regions of the flame where the process

of coagulation acts in concert with new particle formation, surface growth,

oxidation or release to the environment. Morphological features which are readily determined include spherule size and state of agglomeration and size

distribution in the regions where single particles are observed. Observations

are compared with the predictions of solutions to the aerosol dynamic equation

that include terms which describe the above processes.

I. Experimental Work

Thermophoretic sampling is accomplished by inserting a cold probe

surface for a brief instant into a precisely defined region of a particle laden

flame. Thermophoretic probes are fabricated from the materials normally used

in electron microscopy, viz., circular grids and bulk specimen carriers and by

combinations of these two devises. The probe is inserted into the flame by

51
an electro-pneumatic probe control system in an interval of 15 ms and can be

held by in a precisely defined region for times that vary from 30 to several

hundred milliseconds. From observations conducted with this technique we are able to examine particles from three regions of the flame: A. The

nucleation region in which the smallest particles are first formed. B. The

agglomeration-growth region where intense agglomeration occurs and wherein

primary particles that make up the agglomerates grow to their largest size. C.

The oxidation region where the primary particles within the agglomerates

contract even though agglomeration continues unabated. To date we have

concentrated most effort on measuring the regional extent and aerosol

properties low in the flame in the nucleation region. The dynamic behavior

of the size distribution in this region has considerable significance and

provides the initial data with which to start the simulation calculations.

Two effects have been consistently observed with a variety of probes

that have been exposed for various residence times. The first of these is the

strong manifestation of surface growth in the agglomeration-growth region at heights above the burner (z) varying from 10 to 40 mm (The flame height we

use for this non smoking flame is 88 mm.) The primary particle size of the

agglomerates is observed to grow systematically from 14 to 36 nm. This size

has a maximum at z = 40 mm where soot oxidation stants to play a more

important role (sec Figure 1 below). For 40 mm < z < 88 mm the degree of

agglomeration continues to increase while the primary particle size decreases.

The maximum of the primary particle size coincides with the height at which

optical measurements (Ref. 1) show the maximum soot concentration in the

same flame.

A second interesting feature, which is found to occur in a variety of

probe samples, is the presence of fine unagglomerated soot particles in the

region outside the annulus of highest particle volume fraction. The region

of fine particles thus coincides with this layer external to the surface of high

luminosity where C>2 is present and where temperature has a maximum. These

fine particles can in principle be transported from lower levels where they are formed or may be created and oxidized locally by the diffusion of fuel across

the streamline from the central portion of the flame. We present

experimental and theoretical arguments relating to these two viewpoints on the

origin of the fine particles.

II. Coagulation Theory

The aerosol dynamics in the lower portion of the flame are described

by the aerosol dynamic equation when expanded to include the effects of new

particle formation, coagulation, and surface growth. In order to implement

this solution we have chosen the integral methods which have an appropriate

degree of accuracy and which have the potential to yield insight into the

observed data. To describe the formation of the aerosol it is advantageous to employ a bimodal distribution in which a smaller mode is used to describe the

population of the nucleation mode and a larger group is used to account for

the growth mode. Initially this formulation posed algebraic complexities

which prevented our achieving solutions in an efficient fashion. These

difficulties were overcome by introducing the variables representing the

number concentrations of the two modes as primative variables in the set of

52
ordinary equations describing the aerosol dynamic behavior. This

modification has lead to a formulation that is compact and robust to a wide

variety of input variables* The bimodal solution decays to the monomodal

solution and it also reduces in turn to the asymtotic solution corresponding the

self preserving size distribution function. A publication is in progress

describing this method in detail. The application of this theoretical model to the soot aerosol dynamics will be discussed.

III. Oral Presentations and Publications

During the past calendar year the following oral and written reports

authored by R. A. Dobbins and C. M, Megaridis have been presented:

"Regional Soot Morphology in a Laminar Diffusion Flame", Annual Meeting of

the American Association for Aerosol Research, November 20, 1985.

"Soot Morphology in a Laminar Ethene Difffusion Flame", Sixtieth Annual

Meeting of the American Chemical Society, Division of Surface Chemistry,

Atlanta, June 19, 1986.

"Morphology of Flame Generated Soot as Determined by Thermophoretic

Sampling", submitted for publication to Langmuir, July 1986.

Reference

1. R. J. Santoro, H. G. Semerjien and R. A. Dobbins, "Soot Particle

Measurement in Diffusion Flames", Combustion and Flame 5JL, 203 * 218 (1983).

Figure 1

53
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Inst itut ion : California Institute of Technology

Grant No. : NBS Grant NB82NADA3033

Grant Title : Experimental Study of Environment and Heat

Transfer in a Room Fire

Principal Investigator : Professor Edward E. Zukoski 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 Moreheart, Research Assistant

California Institute of Technology

Pasadena, CA 91125

NBS Scientific Officer : Dr. Walter Jones

Technical Abstract :

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 burn 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 cannot be described analytically because the

flows are turbulent and are strongly influenced by turbulent mixing

between streams in which buoyancy forces are predominant. The aim of

the research work described here is to develop sufficient

understanding of the fluid dynamic and chenical processes so that

rational models can be developed for the use in two layer fire codes.

54
FLOW AND HEAT TRANSFER IN GRAVITY CURRENTS

During the past year we have been primarily involved in an experimental investigation of the flow field produced by the transient

motion of smoke in a horizontal hallway-like structure. The aim of

this work is to obtain an understanding of the flow of hot smoke along

a ceiling during the transient period in which the smoke moves as gravity current. Heat transfer from the current to the wall can affect these flows and studying the heat transfer process is an important part of the present work. A final report on the current

status of this work will be available in October and a qualitative

description of the apparatus and results is given here.

We have carried out experiments in which a gravity current of salt

water flows through a duct filled with fresh water and a second set of

experiments in which the gravity current of hot air flows through a duct filled with cool air. The tests in air included both viscous and

heat transfer effects and they will be discussed first.

AIR TESTS: The tests in air were carried out by creating a transient

flow of hot gas along the ceiling of a square duct with a constant

temperature ceiling. The velocity of the front produced by this flow,

the rate of heat transfer to the ceiling, and the velocity and

temperature fields of the flow are being measured.

The channel used in the gas flow experiments is a duct 0.5m in height

and width, and S.6 meters in length. Hot gas can be supplied to this

duct at one end from a small furnace at temperatures up to 500 K and

with a large range of metered flow rates. Cool air in the tunnel

which is displaced by the hot "smoke" can be withdrawn from the tunnel

at a number of positions so that a number of interesting flow

situations can be modeled. In the work reported here, the downstream

end of the duct is completely open. The side walls of the channel

have been made of heat treated glass to allow observation of the flow

through shadowgraph photography or direct observation of . smoke which

is added to the hot gas.

We have developed, for our application, a smoke-wire technique for

velocity measurements which gives a good qualitative measure of the

local gas speed. However, the measurements are affected by the

buoyancy of the smoke relative to the cooler gas in the flow and do

not give a precise measure of the gas speed.

Thermocouples, with a diameter of about 0.01 mm and consequently with

a fast time response, are used alone or in a rake to determine the

arrival of the head of the current and to make gas temperature

measurements in the current; thin film heat transfer gages have been

installed on the wall to measure heat transfer rates.

The ceiling of the apparatus in its current state is a 1.27 cm thick

aluminum plate which was used because conduction into the plate is

fast enough to keep the plate temperature rise below one degree.

Thus, the surface temperature is kept far below the initial

temperature of the gas in the duct and does not enter the problem.
Given the heat transfer rates observed in these experiments, the

temperature rise at the surface of a wall composed of an insulator,

say one with the propertiers of plaster board, would be in the range

of 20 to 50 degrees after a period of 10 to 15 seconds. Thus, the rise

would still be small after the period required for the front to reach

the end of our test section. However, we are very much interested in

the effects of the temperature of the wall and the wall boundary layer

on the heat transfer process and are modifying our apparatus to allow

measurements of this type.

The initial conditions for a typical experiment include, temperature

of 520 K, initial layer thickness of 6 cm and an initial velocity of

the front 0.5 m/s. At the downstream end of the duct, the

corresponding conditions are a temperature of 280 K, a thickness of 12

cm, and a velocity of the front of 0.2 m/s. The Richardson number

based on layer thickness is about 0.9 throughout the length of the

duct and the initial value is about one 30 that there is no initial

hydraulic jump. The large velocity change observed as the current

moves across the duct was the result of the change in temperature of

the current produced by heat transfer to the ceiling.

The rate of heat transfer from the current to the constant temperature

wall was measured in these experiments and it varies from values as large as 3000 W/m to values as low as 60 W/m , and the maximum values

are observed at the upstream end of the duct where the hot current is

introduced. Because the total enthalpy flux in the current is

typically 1.0 to 2.5 kW, it is not surprising that the heat flux to

the wall has a large influence on the temperature of the current and

its motion.

Heat transfer rates, expressed in the form of a Nusselt number based

on distance from the origin of the flow, have been found to vary

linearly with the Reynolds number based on the same length scale and

the local velocity; the proportionality constant is about 0.013. These

Nusselt numbers are some ten times higher than the values estimated

for a laminar wall jet with the same Reynolds number and about 3 times

larger than the corresponding turbulent wall jet.

We believe that the large heat transfer rates result from natural

convection within the boundary layer which develops between the cool

boundary layer flow next to the wall and the hotter flow in the

current below it. Large two- dimensional rolls develop which have

their axis parallel to the wall and the direction of the flow, a two

dimensional 3enard cell. These rolls greatly enhance the heat

transfer by transporting cool material away from the wall and hot

material to the wall. The velocity of the front of the current depends

strongly on local gas temperature and hence is strongly affected by

the heat transfer.

SALT WATER TESTS: In addition to the experiments described above, we

are investigating similar gravity current flows in which the current

is formed between salt and fresh water. The hallway is a 15 cm square

channel which is about 250 cm long and the channel can be tilted so that the long 3ide makes an angle with respect to the horizontal of 0

56
to 35 degrees. The influence of the angle and of the fluid dynamic

variables on the resulting gravity currents are being investigated.

When the channel is horizontal, the flow is similar to that described

above except that heat transfer effects are absent and consequently

the velocity of the head is constant. The influence of Reynolds

number and the development of the boundary layer between the current

and the wall are under investigation.

The angle makes a qualitative difference in the flow even when it is as small as one degree. For large angles, the mixing between the

current and the fluid under it becomes important and for angles of 20

degrees can completely fill the duct behind the head of the current

with mixed fluid. In the horizontal case, the current mass flux and

velocity and head geometry were constant; in contrast, when the

ceiling was tilted, these parameters grow rapidly with distance from

the origin.

MODELING: We are developing a computational scheme which will be used

to describe the flow described above and the data are being used to

guide its development. The model uses an integral method based on the

Howarth transformation of the vertical dimension to describe the

conditions in the flow behind the head of the gravity current. The

boundary layer approximation is used in the description of the flow

and the effects of buoyancy, heat transfer, and viscosity are taken

into account. The model gives a good prediction of the flow when the

experimental correlation for the heat transfer coefficient is used and

successfully predicts that the local Richardson number will be close

to one.

Reports and Papers

Zukoski, E. E. , Cetegen, B. M. and Kubota, T., "Visible Structure of

Buoyant Diffusion Flames," presented at 20th Combustion Symposium,

Aug. 12-17, 1984.

Zukoski, E. E., "Fluid dynamic aspects of room fires," Fire Safety

Science - Proceedings of the First International Symposium, 1-33, 1986

57
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY86

Institut ion : Case Western Reserve University

Contract Numb e

: NB82NADA3028

Contract Title : Experimental and Analytical Study of Fire Sprinkler

Scaling Laws

Principal Investigator : Joseph M. Prahl, Ph.D., P.E.

Professor of Engineering

Department of Mechanical and Aerospace

Engineering

Case Western Reserve University

Cleveland, Ohio 44106

Other Professional Personnel ; Brnce Wendt, M.S.

Htun Win, M.S.

Case Western Reserve University

Cleveland, Ohio 44106

NBS Scientific Officer : David D. Evans

Technical Abstract

The objective of this project is to develop an experimental base

that will delineate the relevant scaling parameters that govern the

performance of a wide class of fire sprinklers. The sheet trajectory,

sheet breakup, and subsequent droplet size distribution and droplet

trajectories are related to the mechanical and thermal properties of the

liquid and gaseous fluids, the geometry and the initial dynamics of the

liquid and gaseous streams.

Experimental data for water has been obtained on an apparatus

developed to study the axisymmetric jet impingement on a flat disk which

can be vibrated axially at a given frequency and chosen amplitude, shown

schematically in Figure 1. The sheet of water leaving the disk is allowed

to breakup without interference over the full 360 °, whereas the discharge

subsequent to sheet breakup is masked off to a 22.5 0 sector for the

purpose of determining the droplet radial discharge distribution. The

sheet breakup radius is determined by direct observation and the radial

discharge from the sector is collected in a series of rain gutters spanning

the floor of the sector normal to the midangle radial direction. Variation

of disk size and disk surface characteristics show no measurable effect on either sheet breakup radial location or on the measured discharge distribution.

58
Figure 1. Schematic Representation of the Experimental Set Up

Sprinkler flow distributions as shown in Figure 2 are presented in a non-dimensional form which emphasizes the sprinkler's ability to uniformly

spread the volume flow rate of water over the maximum possible floo r area . The maximum radial extent of the sprinkler system is represented U / 2y/g , where U is the jet velocity, y, the distance of the disk from the floor and

g, gravity, see Figure 1. The non-dimensional application rate is the

measured 'rain rate' from the gutter collection system, normalized with

respect to the 'ideal rain rate', the total flow rate from the nozzle

divided by the maiximum possible floor area.

By driving the disk at various frequencies and amplitudes, dramatic

differences in flow distribution can result from the nature of the liquid

sheet breakup induced by the choice of driving frequency as illustrated in

Figure 2. If the driving frequency is near 1/4 the frequency for largest

growth of sinuous waves on the sheet, large waves appear before sheet

breakup occurs and a broad distribution of droplets results from the flapping sheet. If the sheet is driven at frequencies greater than or equal to

those for maximum growth of sinuous waves, the sheet remains quite flat

until breakup. Since the sheet is not flapping, the droplet distribution

is far narrower under these conditions.

59
Figure 2. Flow Sate Patterns as a Function of Disk Disturbances

Figure 3 illustrates the point that the ratio of the sheet breakup

radius at a given driving frequency to that at zero driving frequency

appears to correlate with the ratio of the driving frequency to the

frequency for maximum growth of sinuous waves, for a given amplitude of

disk oscillation. Figures 4a—b illustrate the apparent correlation of flow

distribution with ratio of driving frequency to frequency of maximum growth

of sinuous waves.

The droplet trajectory model combined with a Ro s in— Ramm 1 e

distribution function for the droplet diameters gives qualitative agreement

with measured flow distributions. The model is sensitive to the initial

conditions of the droplets at the point they leave the sheet breakup

location. If the sheet is flapping sinuously with large amplitude, it

causes the flow distribution to be much broader than if the sheet is

relatively flat at the breakup point as can be seen by predicted flow

distributions from the computer model shown in Figures 5a-b.

60
Nondlmen6ional

Breakup

Amplitude

a.

/a

Reports and Publications :

1. B„ Wendt and J. M. Prahl, 'Discharge Distribution Performance for an Axisymmetric Model of a Fire Sprinkler Head' Department of Mechanical

and Aerospace Engineering, Case Western Reserve University, Cleveland,

Ohio 44106, Aug. 1986, FTAS/TR-86-184.

1 is 1111 ® 3. Experimental Discription of the Sheet Structure. Nondimens iona 1 Breakup Radius and Nondimens iona 1 Breakup Amplitude of Dominant

Sheet Waves Plotted Versus Frequency Ratio

61
Figure 4. Flow Distribution Curves for Frequency Ratios of 1/4 and 1/2.

62
ar?srt3«se«aiy loearala«4 now ?*esera e*pv®e fo* » sosrj* flow .-*ew of

Figure 5. A Cocparison of Analytical and Experimental Flow Patterns

63
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution: Clemson University

Grant No. : 60NANB6D0627

Grant Title : Graphical Presentation and Numerical Analysis of Fire Data

for Model Validation

Principal Investigator: James P. Jarvis

Department of Mathematical Sciences

Clemson University

0-104 Martin Hall

Clemson.SC 29634-1907

Telephone: (803) 656-5214

Other Professional Personnel : Melissa Bowers, Graduate Assistant

NBS Scientific Officer: Sanford Davis

Technical Abstract :

Introduction : The primary objective of this research is the development of

computational procedures for graphical and numerical analysis to assist in the

validation problem for fire models. The validation problem concerns the question of

whether fire models are in sufficient agreement with experimental data to be of use in

predicting fire behavior in alternative scenarios. Validation is a difficult, but essential,

part of mathematical modeling with no universally applicable procedures. In the

context of fire modeling, the validation problem is further complicated in two respects.

First, large scale fire models and experiments typically generate enormous amounts of

data. Data collected from a single burn conducted at NBS might consist of one

hundred fifty independent channels and one hundred derived channels of 250

observations each. Second, fires are described by a multiplicity of variables. In one

context, smoke and toxic gases might be the most important consideration; in another,

temperature and neat flux. Hence, validation of a fire model must include some

provision for dealing with differing assessments of the importance of each variable.

The effort is focused on three areas: (1) completion of flexible graphics software to

facilitate examination and presentation of fire data; (2) systematic treatment of

statistical uncertainties associated with experimental data and sensitivity analysis of

the fire simulation models in conjunction with the development of well-defined,

systematic validation procedures; and (3) a preliminary investigation of how subjective

assessments can be incorporated into the validation process.

As a test case, these approaches are being investigated in the specific context of

the "FAST model for the transport of fire, smoke, and toxic gases developed by the

Center for Fire Research and empirical data gathered from instrumented burns

conducted at NBS.

64
Graphical Analysis : An important tool in validating a model is the visual inspection

of data. The volume of data generated by an instrumented burn experiment or a

computer simulation must be handled in a consistent and flexible framework to permit

a comprehensive examination. Typical problems which must be addressed are the

compatibility of units of measurement and manipulation and display of subsets of

variables over specified time frames. In order to address these issues, a software

package for graphics analysis is being developed. The initial version of this software is designed to run on an IBM PC with screen displays and hardcopy output to a

Hewlett-Packard pen plotter or dot matrix printer. The software is written in FORTRAN

to maintain portability to mini and mainframe computers.

It is important to note that while the graphics software will be useful for general

scientific plotting, its focus is analysis specific to the fire validation problem. The

software will accept data in the format generated by FAST and RAPID (the software

developed at CFR for reduction of experimental data). A simple use of the graphics

software would be simultaneous display of corresponding model and experimental

data. In addition, any validation procedures which affect how data should be displayed

could be incorporated into the graphics software. For example, data smoothing,

normalization, or weighting techniques developed as part of the validation process

could be incorporated directly into the graphics routines to facilitate examination of the

data.

Data Manipulation : The basic issue in the validation problem is the comparison of

experimental and model data. This involves the preparation of both experimental and

model data for comparison. In the case of the experimental data, some smoothing to remove noise will be required. Also, estimates of statistical uncertainty in the observed

values must be made. Finally, the data will require some "normalization ' 9 to adjust for

biases introduced by ambient conditions or starting times. Since the initial conditions

can be specified for FAST, the same problems do not arise for model data. However,

model sensitivity must be considered. If the model was particularly sensitive to

changes in certain parameters, that information should be included in the decision as

to whether model and experiment are in satisfactory agreement. Effects of statistical

uncertainty of data, model sensitivity, and comparison of multidimensional data will be

integrated into a flexible framework and interfaced to the graphics routines.

Validation Procedures : The effort outlined here is somewhat speculative. Fires are described by a multiplicity of variables, not all of which are relevant in every

situation. For this reason, it does not appear appropriate to attempt to produce a single

number which would measure the "accuracy" of a fire model. A more useful approach

is to establish which variables are important in a particular situation and then ask

whether the model accurately predicts those variables. To this end, techniques of

decision analysis and multi-attribute utility theory will be investigated in the context of

the fire model validation problem. Such techniques can be used to incorporate

individual assessments of risk into a unified measure. The important idea is reflecting

the model user's priorities in the validation process.

Research Status : An initial version of the graphics software has been completed.

Techniques for data analysis are being incorported into the software. Research in model validation and incorporation of subjective assessments is continuing.

65
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution: Clemson University

Grant No. : 60NANB4D0033

Grant Title : Ternary Reactions Among Polymer Substrate-Organohalogen-Antimony

Oxides in the Condensed Phase Under Pyrolytic, Oxidative and

Flaming Conditions

Principal Investigator : Dr. M. J. Drews

School of Textiles

Clemson University

Clemson, South Carolina 29634-1307

Other Professional Personnel : Dr. C. W. Jarvis, Co-Principal Investigator

Dr. G. C. Lickfield, Research Associate

Ms. K. McCoy, Graduate Assistant

NBS Scientific Officer: Dr. W. Schaub

Technical Abstract :

The objective of this work was to determine the chemical mechanisms for

the solid phase interactions which occur in antimony oxide /organohalogen/

thermoplastic polymer substrate compositions during combustion. The formation

of intermediate flame retardant decomposition products and the role of the

polymer substrate in the generation of the volatile antimony compounds were of

special interest, with regards to the relative importance of the solid state

chemistry to the overall chemistry of degradation and combustion. Data on the

combustion chemistry were obtained from laboratory scale flaming combustion

experiments conducted at the Center for Fire Research of the National Bureau of

Standards

The small scale degradation studies employed isothermal and dynamic

thermal analysis, as well as isothermal tube furnace experiments. Sample sizes

ranged from the milligram to the gram scale depending on the apparatus.

Antimony analysis and bromide ion monitoring were used in the initial stages of

the work to develop a temperature profile for the antimony volatilization and

extent of reaction. In the latter stages of this work, capillary gas chromatographic analysis of the trapped volatiles was used to more completely define

the extent of reaction. Throughout the course of this investigation a basic

experimental sequence consisted of the study of the individual components,

followed by a study of component mixtures under identical degradation conditions .

Initially, three polymers and three organobromine compounds of significantly different thermal stabilities and primary decomposition pathways were chosen as model polymer substrates and halogen sources. The polymer substrates

were poly (ethylene terephthalate) (PET), polypropylene (PP) and poly(methyl

methacrylate) (PMMA) . The organobromine compounds were decabromodiphenvl oxide

66
(DBDPO) , tetrabromobisphenol-A (TBBPA) and hexabromocyclododecane (HBCD) . As

the work progressed, two additional polymer substrates, linear high density

polyethylene (HDPE) and poly (butylene terephthalate) (PBT) and additional

halogen sources including an acyclic organochlorine compound and the chlorine

analog to DBDPO were included. The study was also extended to include

additional antimony compounds and other metals.

In the previous antimony /halogen synergism literature, at least three

different mechanisms have been proposed to account for the antimony volatilization which has been observed in degradation and combustion studies. These

reaction mechanisms could generally be separated into two categories according

to whether or not the organohalogen component could undergo an intramolecular

dehydrohalogenation. For those compounds which could undergo intramolecular

loss of halogen and form HX directly, the principal route to the generation of

volatile antimony species has been thought to involve the reaction of the HX

with antimony oxide. In the absence of a simple intramolecular reaction to

form HX, alternative reaction schemes involving either the indirect formation

of HX or unspecified intermediates have been proposed. Even in these alternative reaction schemes, the necessity for HX formation is implied if not

explicity included.

Based on the results of the small scale degradation experiments with

DBDPO, it was concluded that at least one previously unreported mechanism

exists for the antimony volatilization which does not involve HX formation.

Confirmation of this was obtained from experiments with antimony metal/DBDPO

mixtures at temperatures measured for the pyrolyzing polymer

substrates during combustion C 400C) . In this experiments, the measured

antimony volatilization was comparable in magnitude to that observed for

polymer /antimony oxide /organohalogen mixtures at the same temperatures.

Attempts to identify the presence and measure the concentration of Sb in

pyrolysis mixtures of polymer substrate and antimony oxide using Mossbauer and

ESCA were unsuccessful. Similar experiments with bismuth and zinc have indicated

that the proposed reaction is not unique to antimony and may be rather general

for certain organohalogen structures.

Based on a comparison of the results obtained from tube furnace experiments

to those from thermogravimetric analysis experiments, it would also appear that

the extent of reaction in organohalogen/antimonv oxide/polvmer substrate

mixtures can be significantly influenced by physical factors related to the

preparation of the sample. In particular, these results may be interpreted in

such a manner as to possibly explain some of the observations which have

previously been made in the literature regarding the difference in the

efficiencies of antimony trioxide versus antimony pentoxide. Finally, the data

from a series of experiments with several organophosphorus compounds has

provided some insight into the nature of the phosphorus /antimony antagonism

which has been proposed in the literature.

Three partial sets of laboratory scale combustion experiments were completed during the course of this work. In addition to the burning parameters

which have been measured during these combustion experiments, smoke samples

have been collected for condensable volatiles analysis by capillary GC. This

work will be completed as soon as the necessary mass spectral confirmation of

the tentative degradation product GC assignments is obtained. These data will

form the basis for a comparison of the combustion efficiency of not only the

67
polymer substrate, but also the organohalogen volatiles generated during the

burns. These data are potentially very significant for certain organohalogen

sources from an overall fire safety, risk and hazard assessment perspective.

The most important conclusion which has been drawn from the analysis of the

available combustion data is that there are clearly small, but significant,

differences in the combustion efficiencies of the different halogen sources in

the different polymer substrates. Consequently, it can also be concluded that

antimony/halogen flame retardant systems are not completely substrate independent, as has often been implied in the flame retardant literature.

The results of this systematic investigation into the solid state

chemistry of organohalogen/antimony oxide flame retardants have yielded new,

basic information with respect to fire retarded and fire resistance thermoplastics; the mechanisms for the formation of volatile antimony species from

the reaction of antimony oxides and other antimony compounds in the presence of

organohalogens ; the controlled combustion of thermoplastics containing this

important class of flame retardants. It was also the first work to identify

the presence of the potentially hazardous degradation products of DBDPO which

are given off during combustion, which have been the subject of such interest

in the recent literature.

Reports and Papers :

1. "Or ganobromine /Antimony Oxide/Polymer Substrate Interactions in the Solid

Phase. Part I. Binary Interactions," Second Chemical Congress of the

North American Continent, Las Vegas, Nevada, August 1981.

2. "Antimony Oxide /Organohalogen Flame Retardant Systems, Are they Really

Synergistic?", Polymer Products Res., DuPont, Wilmington, Delaware,

February, 1981.

3. "Organohalogen/Antimony Oxide /Polymer Substrate Interactions in the Solid

Phase. Part I. Binary Interactions," M. J. Drews, C. W. Jarvis, and E. A.

Leibner, Organic Coatings and Plastics Preprints, 43, 181 (1981).

4. "Fire and Smoke Retardants," Prepared for Director Snell for the 1982

U.J.N.R. Conference, M. J. Drews.

5. "Progress Report. Organobromine /Antimony Oxide/Polymer Substrate

Interactions in the Solid Phase," M. J. Drews and C. W. Jarvis, Fifth

Annual Conference on Fire Research, National Bureau of Standards,

Washington, D.C., August 19-21, 1981.

6. "Thermally Initiated Solid State Reactions in Polymer Substrates

Containing Antimony Trioxide," T. L. Gilstrap, Masters Thesis, Clemson

University, May 1984.

7. "A Thermal Analysis and Calorimetric Investigation of Antimony

Oxide/Organohalogen Flame Retardant Systems," Great Lakes Chemical Corp.,

West Lafayette, Ind., July 1985.

8. "Organohalogen/Antimony Oxide/Polymer Substrate Interactions in the Solid

Phase. Part I. Small Scale Degradation Studies of Simple Mixtures," M. J.

Drews, C. W. Jarvis, and E. A. Leibner, in preparation for submission to

J. of Fire Sciences, 1986.

68
9 . "Organohalogen/Antimony Oxide/Polymer Substrate Interactions in the Solid

Phase. Part II. A Thermal Analysis Study of the Thermally Initiated

Reactions," M. J. Drews, C. W. Jarvis and t. L. Gilstrap, in preparation

for submission to J. Appl. Polyrn. Sci. , 1986.

10. "The Use of Cone Calorimetry to Measure the Efficiency of Antimony Oxide/

Organobromine Flame Retardants in Polypropylene and Poly (methylmethacrylate)," M. Jo Drews and C. W. Jarvis, in preparation for submission to the

J. of Fire Sciences, 1986.

11. "Polymer Substrate Interactions with Metal Oxide /Organohalogen Flame

Retardant Additives," Annual Conference on Fire Research, National Bureau

of Standards, Washington, D,C. , November 3-7, 1986.

12. "Combustion Products in the Presence of Antimony Trioxide," M. J. Drews,

C. W. Jarvis and G. C. Lickfield," Fire Retardant Chemical Association

Technical Conference, Charleston, S.C. s October 19-22, 1986.

69
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution Factory Mutual Research Corporation

Grant No ; 60NANB4D-0043

Title : Development of a Model to Provide Comprehensive

Fire Property Data

Principal Investigator : Dr. A. Tewarson

Factory Mutual Research Corporation

1151 Boston-Providence Turnpike

Norwood, Mass 02062

Telephone: (617) 762-4300 x 2950

Other Professional Personnel : Ms. J. Steciak, Advanced Research Scientist

Mr. S.D . Ogden, Senior Research Technician

NBS Scientific Officer: Dr. V. Babrauskas

Technical Abstract : The objective of this research effort is to improve predictions for fire properties, which include combustion efficiency (x A

) and its convective and radiative components (xq and xr respectively) and generation efficiencies of

gaseous, liquid, and solid compounds ( f

j )

Such improvements are expected to

enhance the ability of models to assess fire hazard and protection requirements.

In this study, relationships are being sought between fire properties and 1

)

smoke point height of materials (l^) such that voluminous literature data on can be used; 2) nature of chemical bonds in materials; 3) molecular weight

of materials; 4) fire ventilation; and 5) fire size.

Reactivity in combustion of about 250 materials including polymers has been

examined. Figures 1 to 6 show some examples. The decrease in combustion

reactivity is followed by: 1) decrease in x A and Xc ; and 2) increase in xr and

f j , where j represents compounds associated with incompleteness of combustion

such as CO, total gaseous hydrocarbons (CH), particulates (S), and mixture of

unidentified chemical compounds (C).

The reactivity in combustion decreases with increase in bond unsaturation, for

example, x^ value is highest for normal alkanes and is l°we3t f°r arenes (materials with benzene rings in the structure). x A decreases from

normal alkanes ( c n^2n+^ t0 normal alkenes (C nH,

n

) to normal alkynes and

dienes (C n

H 2n-2>‘

The reactivity in combustion appears to depend on the relative degree of un- saturation in the pyrolysis compounds. A combustion reactivity parameter, £,

has thus been defined, which is the ratio of the sum of yields of alkanes,

alkenes, and H P to the sum of the yields of alkynes, dienes, arenes, and butylene. Some selected relationships are shown in Figures 5 and 6 for polymers.

This study is continuing, where a general understanding of resistance to thermal decomposition and formation of free radicals for oxidation by various monomers, oligomers, and their smaller fragments and validity of the combustion

reactivity parameter are being sought such that in conjunction with theoretical calculations, the predictions for fire properties can be established

firmly.

70
Reports ; 1. A. Tewarson, "Predictions of Fire Properties of Materials, Part I; Aliphatic and Aromatic Hydrocarbons and Related Polymers" National Bureau

of Standards, Center for Fire Research, Gaithersburg , MD , Technical Report

Grant No. 60NANB4D-0043 , July 1986.

2. A. Tewarson, "Predictions of Fire Properties of Materials, Part II;

Oxygenated Materials and Related Polymers" National Bureau of Standards,

Center for Fire Research, Gaithersburg, MD, Technical Report Grant No.

60NANB4D-0043, August 1986 (to be issued).

3„ A. Tewarson, "Predictions of Fire Properties of Materials, Part III:

Nitrogen and Sulfur Containing Materials and Related Polymers" National

Bureau of Standards, Center for Fire Research, Gaithersburg, MD , Technical

Report Grant No. 60NANB4D-Q043, October 1986 (to be issued).

4. A. Tewarson, " Fire Properties of Materials and Their Applications to

Multi-Room/Corridor Enclosures and Chemical Modeling of Gaseous Species in

Turbulent Fires" National Bureau of Standards, Center for Fire Research,

Gaithersburg, MD, Technical Report Grant No. 60NANB4D-0043, (to be issued).

71
Figure 1 Relationship between combustion efficiency, its convective and

radiative components, and smolte point height

polystyrene oligomers

72
lar weight

73
74
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution ; Factory Mutual Research Corp., Norwood, MA 02062

Grant No ; 60NANB5D0560

Title ; Prediction of Fire Dynamics

Principal Investigators ; Raymond Friedman (61 7)762=4300 , ext. 2870

Howard W. Emmons ( 6l 7)495=2847

Other Professional Personnel ; R. L. Aipert

M„ A. Deliehatsios

Je de Ris

G„ H„ Markstein

Lo Orloff

NBS Scientific Officer ; B. McCaffrey and H. Mitler

Technical Abstract ; This work is divided into four tasks

.

Task 1 • Prediction of Fires in Buildings (H.W. Emmons)

The major topic of research during this grant period has been the Theory

of the Ceiling Jet.

J

Several possible hydraulic type theories have been developed for the front

of the spreading jet. If the mechanical energy loss along the floor is n times that along the jet front interface, the velocity of the lower fluid relative to the front is given by

ii , A (2n - Ah l/2

Do n ~ A

2 where i *

J et depth

H duct heignt

,, aDo velocity

'J S . i. — «- ! r- i i , rr~ ,f, Do 7pH

If there are no losses along the bottom (ignoring bottom friction), n = 0, uhis formula reduces to UDo = 1, derived earlier on this project. While if

t - 1 , the loss along the bottom is equal to that along the separating stream- line, and the equation reduces to that of Benjamin^

The development of a suitable hydraulic type jump formula was impeded by

whe necessity of evaluating the pressure difference across the jump. The open

channel flow jump does not present this difficulty because there is atmospheric pressure on each side. In a duct, the determination of the pressure dif- ference requires an additional relation. The physical laws are not adequate

for a hydraulic type theory. A number of assumptions were tried, and those

made by Yih and Guha , and Chu and Baddour"“, '‘ were found adequate to the

extent that present experimental results are able to discern.

A report on the Transient Ceiling Jet-Part 1 has been finished. This

report presents the details of the 4 quadrants of hydraulic jumps in a two-

*luid stratified flow in a duct. This type of flow includes the ceiling jet

from a fire moving down a corridor with a cold lower layer flowing toward the fire.

75
The theory of ceiling jet flow with a jump following a front has been

computed in detail for an air "ceiling jet" entering a tube filled with water

while the water runs out below. This jump-front flow is combined with the

theoretical performance of a flow control at the open end of the tube (other

end closed) consisting of a slot above for air entry and a slot below for

water discharge.

This theory explains in a straightforward way the observed three types of

ceiling jet, observed experimentally as water is discharged from a horizontal

tube.

This theory was presented at the IUTAM Symposium in honor of G.I. Taylor’s

100th birthday. Following, my presentation, I visited Prof. Paul Linden and

retired Prof. John Simpson of the Department of Applied Mathematics and Theoretical Physics at Cambridge University. They are planning some experimental

work on the Fire Ceiling Jet. I have sent them the ceiling jet inlet flows

from the calculations of the MGM fire, and Prof. P. Linden has visited me here

in the U.S. to clarify further details.

On March 5“6, at the SFPE Symposium on "Quantitative Methods for Life

Safety Analysis", I presented a paper in which some new thoughts on fire

safety calculation were presented. The quantitative prediction of a fire can include the production of a Hazard Map (Fig. 1 ) for each escaping occupant.

On this map, the path of the escapee can be drawn, and from this the point of

incapacitation and death can be computed. By this method, the fire safety of

all occupants can be calculated.

The use of any material of construction having toxic fire products can be

checked by this method for fire safety in the proposed use. This is the

essential knowledge required for a performance code as soon as validated

computer codes are developed and sufficient handbook type data are obtained.

An important further use for this quantitative method of toxic gas analysis as 30on as it is available is the use of some of the 6,000+ fire deaths in

the U.S. each year as "toxicity tests with humans". At present, all but

qualitative accidental fire data on toxicity is lost for want of an adequate

method of analysis.

The calculation of fire in an unf irestopped wall space connected top and

bottom to another open wall space has been stalled by numerical instabilities.

These are slowly being understood and removed, but it will take some time yet

to develop a good working computer program.

The section of the SFPE Fire Science Handbook on Vent Flows submitted last

fall has been reviewed and corrected and returned to the section editor

(Craig Beyler) for publication.

References

1. Benjamin, T.B., "Gravity Currents and Related Phenomena," J. Fluid Mechanics, 31, P- 209-248 (1968).

2. Yih, C.S., Guha, C.R., "Hydraulic Jump in a Fluid System of Two Layers,"

Tellus, 7, p. 358-366 (1955).

76
3. Chu, V.H., Baddour, R.E., "Surges, Waves, and Mixing in Two Layer Density

Stratified Flow," Proe. 1? Conge Inti. Asso. Hydraulic Res., 1, p. 303=310

(1977).

Lectures

"The Needed Fire Science," First International Symposium on Fire Safety

Science, Oct. 7-11 , 1 985

"Fire Spread Beyond the Room of Origin," SFPE Symposium on Quantitative

Methods for Life Safety Analysis, March 5~7, 1986.

"The Transient Ceiling Jet," IUTAM Symposium on Fluid Mechanics in the Spirit

of G.I. Taylor, March 24-28, 1986.

"Why Fire Model?" Guise Award Lecture, SFPE Annual Meeting, May 20=21, 1986.

Reports

Fire Detectors for Public Fire Safety, Report #71

Fire Safety of Buildings and Building Occupants, Report #72

Why Fire Model? The MGM Fire and Toxicity Testing, The SFPE Guise Award

; Lecture, Report #73

The Transient Ceiling Jet-Part 1 , Report #74

77
CQjHC/i Hazard. /Hcth fi'vurg 1

78 ~

/VO//

UlH
Task 2. Radiative Properties of Vitiated Flames

(L. Orloff, M.A. Delichatsios , J. de Ris)

The main objectives are the measurement and characterization of flame

radiation from fires in a vitiated environment and the development of integral

models for fluid mechanics - combustion interactions including radiation

losses. Such models for flame radiation and turbulent combustion are needed

in advanced computer codes to predict accurately fire growth in a vitiated

environment; for example multiroom fires.

The study of vitiated flames uses gaseous buoyant jet flames burning

inside a water-cooled enclosure to eliminate any wandering of the flames and

provide the required vitiation environment. Different size nozzles (16 mm,

28 mm, 35 mm) are being used for investigating effects of the initial exit

flow on flame radiation. The vitiated burning experiment is designed to

explore the effects of various vitiation parameters on radiations 1 ) oxygen

concentration in the ambient; 2) ambient temperature; 3) fuel mixture temperature; and 4) fuel composition.

The fuel mass flow rate and its concentration by dilution is set automatically by mass flow controllers. The nozzles have been designed for preheating

the gas just before the nozzle exit. Ambient air vitiated by C0

2 and H2 Q (15”

21 oxygen mole percent) is supplied from the exhaust gases of two commercial

burners. These exhaust gases pass first through heat exchangers and filters

before entering the enclosure as a highly quiescent flow. Total radiant emission from the fires is measured by a conventional wide-view-radiometer and a slit radiometer. The burner moves vertically in front of the slit radiometer

by means of a piston automatically controlled. Because of space considerations, the radiometer requires parallax corrections. Such corrections were

established theoretically and were checked (within an error of 5 %) by integrating the output of the slit radiometer.

Figure 1 shows plots of normalized radiant output per unit height for

vitiated flames in terms of a normalized height (e.g. flame height). It is

remarkable that these plots are essentially independent of the heat release

rate and the depletion of ambient oxygen. Mote some dissimilar effects at the

lower half of these plots. The nozzle size for these experiments was 28 mm. Experiments with other nozzle sizes (16 mm, 35 mm) are planned to investigate

near source effects on the radiation field.

Figure 2 shows the variation of radiant fraction with ambient oxygen

concentration. Extrapolation of these results indicates that extinction

occurs at approximately 14.5$ 0

2

which is consistent with extinction limits

inferred from laminar smoke point measurements

This work continues in order to extend previously established relationships for fire radiation and smoke-point height to vitiated flames.

A parallel effort has been made for modeling turbulent combustion. We

have made significant progress by proposing a hypothesis for the key parameters that control the flow dynamics of turbulent fires. This hypothesis

leads to results which are corroborated by experimental data.- 1,2 -1

The key ingredients of the present model can be summarized briefly. One

may observe that in turbulent fires local turbulence is generated by two

79
buoyancy forces: 1 ) the buoyancy flow rate similar to that in buoyant thermal

plumes involving no combustion, and 2) a buoyancy force arising from hot

eddies burning near peak flame temperatures . One may argue that these two

buoyancy sources are determined by a) the maximum buoyancy flow rate, b> the

buoyancy forces at peak laminar flame temperatures, 3) the stoichiometric mass

air to fuel radio, S, and d) the turbulence length scales ~ both Kolmogorov

(molecular) and macroscale. Existing evidence, however, suggests that for

fast chemical reactions, the Kolmogorov scale does not affect the rate of heat

release, which depends only on macroscale mixing. Therefore, only the turbulent macroscales, which are determined by the fire geometry, affect the fire

dynamics. The Kolmogorov scale controls the radiative characteristics of the

flames.

The main results from this work are summarized in Figure 3 wherein theoretical entrainment predictions in the fire region are compared with experiments. Our work in this area continues with the development of integral

stochastic models for mixing and combustion (see, e.g., ref. 4)

Publications

1. Delichatsios , M.A., "Air Entrainment into Buoyant Jet Flames and Pool

Fires," to be published in Fire Science Handbook, C. Beyler, Editor.

2. Orloff, L., de Ris, j., and Delichatsios, M.A., "Chemical Modeling of

Gaseous Species in Turbulent Fires," accepted to the 21st International

Symposium on Combustion, 1986.

3. Delichatsios, M.A., "On the Modeling of Strong (Variable Density) Turbulent Buoyant Plumes and Ceiling Jets," presented at the Eastern Section

Meeting of the Combustion Institute, Philadelphia, Nov. 4,5,6, 1985.

4. Delichatsios, M.A., "A PDF Method for Predicting Major Species Concentrations in Turbulent Fires," presented at the Eastern Section Meeting of the

Combustion Institute, Philadelphia, Nov. 4,5,6, 1985.

80
Dimensionless

Rad.

Pewer/unl!

Height,

g(f) 4,44 kW CjH8 Buoyant Jot Flames

1: Normalized radiant output per unit

height vs. normalized diseance fro®

the source

CjH8 4.44 kW Vitiated

Buoyant Turbulent Flames in Red Tank

is r

1 r n2

\ 15

r

r os r

<2

F u«t 2SQC C

Fuel st eiTitsiefit tefnp.

j

—r —

|

i .A; /

1 / /

i_

i

3

...A.

15 16 17 18 19 20

Fig. 2:

2i Qj Mole Percent in Ambient

Variation of radiant fraction with

oxygen concentration in ambient air

Z/D

Fig. 3: Normalized entrainment vs. height

in the burning region of pool fires

SI
Task 3. Wall Fire Flame Radiation (G.H. Markstein, J. de Ris)

The main objective is the extension of previously established relationships for fire radiation to fires burning on vertical walls. 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 surroundings occurs 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.

The study of wall fires under this task uses gaseous fuels burning on a water-cooled, vertical porous-metal surface, permitting steady-state burning,

and, if desired, simulation of a range of mass transfer (B) numbers of solid

fuels. The pyrolysis height can be varied by a choice of the number of burner

panels that supply fuel ta the fire. The work thus far performed uses a previously developed burner*- 1

-' consisting of six 380-mm wide and 220-mm high

sintered-metal panels, individually water-cooled, stacked vertically and

topped by a water-cooled 380-mm wide and 520-mm high metal plate. Water

cooled sidewalls of 1 60-mm depth are attached over the entire height. Fuel is

supplied to the individual panels by electronic flow controllers. The heat

transferred to each panel is determined from the temperature rise of the

cooling water.

The fuel mass flow rate and the rate of heat transfer define, in turn, an effective mass transfer number, B, so that solid or liquid fuels of given Bnumber can be simulated by adjusting the flow rate of the gaseous fuel^ 1 -*. In

the present work, a digital control loop was used to set the fuel flow for

each burner panel supplying fuel independently to the specified B-number. The

number and position of burner panels supplying fuel to the fire can be se- lected arbitrarily. Total radiant emission from the fires was measured with a conventional wide-view-angle radiometer employing a spectrally flat thermopile

3ensor. In addition, the vertical distribution of radiant power per unit

height emitted by narrow horizontal 3lices across the width of the fire was measured with a scanning 3lit radiometer. The scan was obtained by means of

an electromagnetically deflected plane front-surface mirror operated in a linear ramp mode. Each scan comprised 500 data points recorded during a traverse of the height of the burner in 50 ms. A fast-response spectrally

flat pyroelectric sensor was used in this instrument. Mean profiles of radiant power per unit height were obtained by averaging 125 individual scans in

each run.

Since the fine-grained sintered metal of the present burner is susceptible

to clogging by soot, the work has been performed exclusively with ethane,

which produces relatively small amounts of soot. The 3-numbers ranged from

0.5 to 3, with fuel supplied from one to three panels. Results for a representative run are 3hown in Fig. 1. The plot shows on the left a schematic of

the burner panels with indication of the fuel flow rates, further to the right

the heat fluxes into the panels, and on the right the vertical profile of

radiant power per unit height. The total rate of heat release, total radiant

power, and radiative fraction are also indicated.

The most important result of the work concerns the radiative fractions of

total heat release rate, which were found to vary from about 12 percent to

about 17 percent, increasing both with B-number and with the number of fuelsupplying panels. These values are well below that of free-burning buoyant

82
turbulent ethane jets, whose radiative fraction is about 21 percent, independent of fuel flow rate over a wide range of flow rates. The value of 21 percent, obtained in several previous studies, was confirmed by measurements on fuel jets with the present instrumentation.

In contrast to the present results, in a wall-fire study in which the fuel was supplied by an uncooled slot burner at the base of the wall, Kulkarni 1

2

measured radiative fractions that agreed with those of free-burning fuel jets.

A slot burner, similar to that used by Kulkarni, has been built recently.

Measurements with this burner placed close to the wall at its base have yielded radiative fractions of about 19 percent, for total heat release rates

ranging from about 16 to 59 kW. Thus, although our slot-burner results are somewhat below the values for free-burning jets, they are essentially in

agreement with Kulkarni v s findings, and suggest that the amount of soot formed

in the flame depends critically on the competition between pyrolysis and

oxidation processes that occur near the fuel source, which, in turn, depends

strongly on the geometry of the fuel supply.

As shown in Fig. 2, further examination of the radiation results., including the slot burner data, showed that the total radiant emission (kW)

satisfied the empirical relationship

W °- 1905 Sot

- 2 - 4il2 L

?

/2

(,)

© where Q^qT

(kW) is the total theoretical heat release rate of the fire and

Lp (m) the pyrolysis height. The latter is defined as the total height of the

fuel-supplying panels, and was assumed to be zero for the slot-burner runs. Because of the scarcity of the present data, further work is required to

substantiate the validity of this relationship.

The present measurements of heat transfer to the wall, both in and above

the fuel-supply region, agreed well with those of various earlier studies of

wall fires. 1- 2” - Finally, as shown in Fig. 3, flame heights were obtained

from the intermittency of the scanning data by determining the height at which

half the data were below and half above a small threshold value. Fig. 4 shows

that the flame heights L* in m, including the slot burner data, satisfied the

relationship

L f

- 0.059 Q

,2/

3

(2)

where Q’ is the total heat release rate per unit burner width fkW/m). This

result agrees with other experimental and theoretical f indings

.

l4 ’ Q

J

Combining eqs. (1) and (2), one obtains an expression for radiative fraction

y * y* - L* L

1/2

l ' 3/2

x rad x L L

?

L

f

( 3 )

with the characteristic values x* 3 0.1905 and L* = 0.092 m for ethane.

Although the preceding valuable results have been obtained with the burner

described above, a new burner incorporating several improvements has been

designed and is now under construction. The most important change is the use

of an outer layer of coarse-grained porous sintered metal in front of the

fine-grain inner layer, to prevent permanent clogging of the burner surface by

soot. This design feature will permit work with more sooty fuels than ethane.

83
The height of the panels of the new burner has been reduced to 127 mm to

provide improved resolution of simulated pyrolysis height L

p

. As another new

feature, heat transfer instrumentation will be incorporated in the solid-metal

plate above the burner panels.

As a further improvement of the instrumentation, a new scanning slit

radiometer employing spherical mirror optics has been designed and built.

Initial evaluation has confirmed the expected improvement of signal-to-noise

ratio and of angular resolution in the scanning direction. Means for eliminating some nonuniform response with respect to horizontal and vertical angular deflection are currently under study.

After completion of the new burner, it is planned to continue this study,

particularly with extension to more sooty fuels. The results will be compared

with existing theoretical models of wall-fire combustion, l 3,5“7J aRCj Will be

used for possible modification of such models, as well as for extension to

wall fires of correlations between flame radiation and fuel smoke points.'-®-'

REFERENCES

1. de Ris, J. and Orloff, L., "The Role of Buoyancy Direction and Radiation

in Turbulent Diffusion Flames on Surfaces," Fifteenth Symposium (International) on Combustion, p. 175, The Combustion Institute, 1975.

2. Kulkarni, A., "Radiative Heat Transfer from Wall Fires," Fall Technical

Meeting, Eastern Section, The Combustion Institute, Paper No. 28, 1984.

3. Ahmed, T. and Faeth, G.H., "Turbulent Wall Fires," Seventeenth Symposium

(International on Combustion, p. 1149, The Combustion Institute, 1979.

4. Kulkarni, A., Harkleroad, M., and Quintiere, J., "Heat Feedback and Flame

Height Measurements on Burning Vertical Surfaces," Fall Technical Meeting,

Eastern Section, The Combustion Institute, Paper No. 33. 1983.

5. Delichatsios , M.A., "Turbulent Convective Flows and Burning on Vertical

Walls," Nineteenth Symposium (International) on Combustion, p. 1075, The

Combustion Institute, 1983.

6. Delichatsios, M.A., "Flame Heights in Turbulent Wall Fires with Significant Flame Radiation," Combustion Science and Technology, 39., 195, (1984).

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.

3. Markstein, G.H. , "Relationship Between Smoke Point and Radiant Emission

from Buoyant Turbulent and Laminar Diffusion Flames," Twentieth Symposium

(International) on Combustion.

PUBLICATIONS

1. Markstein, G.H., "Radiant Emission from Wall Fires," Fall Meeting, Eastern

Section, The Combustion Institute, Philadelphia, PA, Nov. 1985.

2. Markstein, G.H. , "Radiant Emission and Smoke Points for Laminar Diffusion

Flames of Fuel Mixtures," 21st Symposium on Combustion, Munich, Aug. 1986;

FMRC Technical Report RC86-BT-4 (June 1986).

84
Ctfcsro 44„ 30 h® 2.0

r

T©i«i P&bgp So 96 kt? 8«^i«4iw« fraction & JSg

Fig. 1: Wall” fire radiant emission and

heat transfer

Fig. 2 % Correlation between total

radiant power and total heat

release rate for ethane wall

fires
Task 4: Transient Pyrolysis and Flame Radiation from Charring Fuels

(R.L. Alpert, M.A. Delichatsios, J. de Ris)

The objective is to measure and model the following two key flammability

properties required for predicting flame spread on any material: 1) charring

pyrolysis and 2) flame radiation. These properties cannot be currently characterized in a way to be easily incorporated in an advanced fire code.

We have completed the construction of a sophisticated experimental apparatus carefully designed to obtain accurate measurements for the transient

pyrolysis rate of charring materials as well as for the flame radiation from

the burning of their pyrolysis gases. Shakedown experiments have been performed and have verified that heat fluxes onto the target area are uniform

(see Fig. 1). The external heat flux can be provided either by quartz heaters

or by a cone-shaped heater (very similar to that in the NBS cone calorimeter)

to investigate possible selective spectral absorption of imposed radiation by

a given material. (Quartz heaters emit predominantly short-wave length infrared radiation, while the cone heater emits blackbody radiation.)

Based on analytic pyrolysis models for charring and noncharring materials

as well as the experimental results from the new apparatus, we are looking for

" equivalent" properties to characterize the transient pyrolysis of charring

materials. To provide credibility and validate our analytical model, we have

developed a new numerical program to calculate transient pyrolysis of charring

materials under the assumption of a thin pyrolysis zone. Cubic splines have

been used to represent spatial variations and transform the differential

equations to FDE by collocation at the nodes. The program has been applied

successfully for predicting the transient pyrolysis rates for noncharring

materials (e.g. PMMA ) wherein an exact solution is known. The program has

been documented and debugged. Sample numerical results are shown in Fig. 2.

The flame radiation is characterized by measuring in our apparatus the

radiant fraction of a buoyant turbulent flame supplied by the fuel jet of hot

pyrolysis vapors. From these simple measurements of radiant fraction, radiant

emission in full-scale wall fires as well as the normal smoke point can be

inferred (cf with Tasks 2 and 3).

Publications

1. Delichatsios, M.A., de Ris, J. , "An Analytical Model for the Pyrolysis of

Charring Materials," Factory Mutual Research Corporation, Report RC84-BT-4

(1984).

2. Delichatsios, M.A. , "Pyrolysis of Charring and Noncharring Materials," Ad

Hoc Meeting on Charring Pyrolysis, Dec. 1984, Florida.

3. de Ris, J. , Mathews, M.K., Delichatsios, M.A., Factory Mutual Memo:

"Stefan Problem for Pyrolysis - Revised," June 15, 1986

4. de Ris, J. , "Effects of Dilution on Cooling in Flame Radiation,"

Appendix 3, NBS Proposal, "Prediction of Fire Dynamics," March 1984.

5. de Ris, J., "Flammability Testing: State of the Art," Fire and Materials,

Vol. 9, No. 2, June 1985, pp. 75-80.

86
MEDTHERM

OUTPUT

[VOLTS]

Fig. 1: Time-variation of heat flux at location of

fuel sample during initiation of experiment

Channel 1 - Radial distance of 51 mm from

axis, peak output of 8 W/crn^; Channel 2 - Radial distance of 19 mm from axis, peak

output of 8.6 W/cm^.

PYROLYSIS POSITION AND VELOCITY

<

1*4 X

Fig. 2: The pyrolysis history of a sample with

finite depth exposed to a constant heat

f lux

87
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

Institution: The George Washington University

Grant Number: 60NANB6D0625

Grant Title: Chemical Pathways to Soot Formation in Diffusion Flames

Principal Investigator: Professor J. Houston Miller

Department of Chemistry

The George Washington University

Washington, DC 20052

(202) 676-7474

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. To further our knowledge of these more complicated

processes, an extensive set of concentration data has been collected in shock

tubes and premixed flames operating under rich conditions . Chemical modelling

of this data might then help to elucidate dominant pathways for the formation

of aromatic rings. Unfortunately, in fires leading to loss of property and

life, fuel and oxidizer are initially separated from one another, and the

transport processes which bring them together influences the combustion event.

In order to build an understanding of soot formation in systems where mixing

is important, our laboratory has been studying the structure, both spatial and

temporal, of laminar diffusion flames.

So far, most of our work has concerned sampling in a laminar methane/air

diffusion flame burning on a Wo lfhard- Parker slot burner. Over the past two

years we have collected profiles of species concentrations, convective

velocity, and temperature. Because of the steady state nature of this flame,

the temporal and spatial data can be combined to calculate the net rates of

chemical reactions which affect a particular species' concentration. This

concentration and production rate data then provides a very complete data base

for the validation of proposed chemical models for the formation of aromatic

rings and soot particles. These studies have resulted in some important

conclusions about the chemistry of diffusion flames:

Harris and coworkers from the General Motors Research Laboratory have

argued the importance of acetylene addition to soot particles as the dominant

mechanism for particle growth in premixed flames. Their conclusion was based

on somewhat circumstantial evidence: only acetylene is present in high enough

concentrations to account for the observed particle mass gain. We have been

able to show through our production rate analysis that there is a loss process

observable for acetylene which spatially coincides with small soot particles,

(see Figure 1) Understanding particle growth is extremely important: the

ultimate size obtained by particles will affect the radiation from the

particles, and consequently, the temperature at the flame tip. Santoro has

shown that subtle variations in temperatures in the flame oxidation region may

determine the likelihood of soot emission from the flame.

88
The key factor which affects the variation in concentration of soot

formed in flames of different fuels is likely to be the rate at which new

particles are formed. To understand this inception process, it is important to

have a understanding of the hydrocarbon pyrolysis chemistry which leads to the

formation of aromatic rings. There are a number of detailed mechanisms which

have been proposed for this process. Presently, the most widely accepted

mechanisms involve two-carbon free radicals as key intermediates.

Specifically, the vinyl radical, C2 H3

*>, and the ethynyl radical, C2 H®, have

both been proposed as the first molecular radical formed in the reaction

pathway leading to benzene. We have been able to select between these two

species by comparing the maximum rate at which these species are formed with

the observed production rate of benzene. The results indicate the dominant

role for vinyl in particle inception in our diffusion flame (Figure 2). There

is not likely to be one mechanism for aromatic formation in all combustion

systems: under slightly different conditions of temperature and local species

concentrations, different pathways will dominate. However, it can be argued

that a laminar diffusion flame more accurately mimics the conditions found in

real fires than do shock tubes and low pressure pre-mixed flames. Thus our

results provide an important conclusion about particle inception in naturallyoccurring fires

The slot burner has proved to very useful in our studies over the last

few years. However, it suffers from stability problems which make sampling

results higher than two centimeters above the burner surface extremely noisy.

We have an interest in extending our profile measurements to the entire flame,

including soot particle oxidation regions. Further, we presently don't have a detailed understanding of the soot particle field in the methane/air flame

supported on the slot burner. For these reasons, we are presently performing

probe studies in an axially- symmetric diffusion flame burner identical to that

used by Santoro in his particle field measurements. The presence of particles

poses a serious experimental obstacle to probe sampling measurements: clogging

of the probe orifice. Over the last few months we have developed a rapid

insertion technique for the determination of species' concentrations in

sooting flames. This technique will enable us to not only extend our understanding of soot formation, growth, and burnout in methane diffusion

flames, but also extend our results to flames of different fuels.

89
Publications

1) Kermit C. Smyth, J. Houston Miller, Robert C. Dorfman, W. Gary Mallard, and

Robert J . Santoro

,

"Soot Inception in a Methane/Air Diffusion Flame as Characterized by

Detailed Species Profiles."

Combustion and Flame 62 . 157 (1985)

.

2) J. Houston Miller,

"Chemical Production Rates of Intermediate Hydrocarbons in Diffusion

Flames: Preliminary Results for Acetylene."

Fall Technical Meeting of the Eastern States Section of The Combustion

Institute. (1985).

3) J. Houston Miller and Kermit C. Smyth,

"The Chemical Structure of Methane/Air Diffusion Flames: Concentrations and

Production Rates of Intermediate Hydrocarbons."

Symposium entitled "Chemical Mechanisms associated with Combustion"

.

American Chemical Science National Meeting, April 1986.

4) J. Houston Miller, W. Gary Mallard, and Kermit C. Smyth,

"Chemical Production Rates of Intermediate Hydrocarbons in a Methane/Air

Diffusion Flame."

Twenty- first Symposium (International) on Combustion , to be published.

5) J. Houston Miller and Philip M. Taylor,

"Methyl Radical Concentrations and Production Rates in a Laminar

Methane/Air Flame."

Combustion Science and Technology , to be published.

6) J. Houston Miller and Robert S. Santoro,

"Soot Particle Formation in Laminar Diffusion Flames."

Langmuir, submitted for publication.

90
Figure 1: Profiles of the net chemical production rate for acetylene at two

heights in the methane/air diffusion flame. Fuel is emitted from the slot

burner from lateral positions 0 through 4 mm. Air flows out in an adjacent

slot (lateral positions >4mm) . The major destruction feature (negative

destruction rates) is due to oxidation of acetylene molecules which diffuse

outwards. At heights greater than 9 mm above the burner surface, a new

destruction feature is observed. This feature is due to acetylene addition to

rapidly growing soot particles, whose profile at the 13 mm height is shown as

a dashed line.

Figure 2: Comparison of the experimental net chemical rate of benzene (-o-)

with the maximum production rates of vinyl radicals ( —---) and ethynyl

radicals (-— _ ) at 9 mm above the burner. These results indicate the dominant

role played by vinyl in hydrocarbon growth chemistry in the methane/air flame.

91
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution: Marquette University

Grant No. : 60NANB6D0602

Grant Title : Thermal Stabilization of Polymers by Cross-Link Formation

Principal Investigator : Charles A. Wilkie

Department of Chemistry

Marquette University

Milwaukee, WI 53233

Telephone: (414) 224-7239

Other Professional Personnel : C.E. Brown, co Principal Investigator

S. Sirdesai, Research Associate

T. Suebsaeng, Graduate Assistant

B. Chang, Graduate Assistant

NBS Scientific Offices : Dr. W.G. Mallard

Technical Abstract:

Introduc tion . The objective of this investigation is to understand the

chemical basis of pyrolysis reactions of polymers and to use that knowledge to

make possible processable polymers that will convert to more stable materials

under pyrolysis conditions. The strategy that has been developed is a strategy

of cross-linking polymer chains to promote the formation of non-volatile, non- combustible char which will effectively prevent burning. Reactions are typically carried out at as low a temperature as practical, since it is desired to

intervene in one of the initial steps in the pyrolysis reaction. The polymers

under investigation are poly(methyl methacrylate), PMMA, and po ly ( e thy lene terephthalate), PET. Present research is focused on cross-linking reactions in

these two polymer systems.

PMMA . In earlier work it had been noted that PMMA forms an anhydride ring

upon reaction with red phosphorus, the phosphorus containing by-products are

me thy Lme thoxy phosphonium ions. It should be noted that this anhydride ring is

a second bond between a pair of methacrylate monomers and thus represents a type

of cross-link and this system is more thermally stable than the starting material. Current work is directed towards identifing other reagents that will also

generate this anhydride ring and probing the mechanism of this reaction. It is

very difficult to probe the mechanism of reaction of a polymer, according model

studies are utilized for this purpose. Two models are currently being used,

methyl myristate and dimethylgluturate. Both of these models contain the ester

linkage, which is the site of reactivity of PMMA. Both are also stable and have

low vapor pressures under reaction conditions, 250-325 0 C

Additives currently undergoing investigation are Wilkinson's salt,

Rh(PPh^) Cl, and [ CpFe(C0

?

] ?

. Both additives undergo decomposition under re- action conditions, the rhodium compound produces benzene, tripheny Iphosphine

92
and two, as yet unknown, rhodium compounds. The iron compound decomposes to

produce carbon monoxide, carbon dioxide, a pentadiene, ferrocene and iron. The

work is thus complicated by the necessity to also investigate the decomposition

reactions of the additives. Both materials react with PMMA to produce an an- hydride, the mechanistic pathway for this reaction is very uncertain and accordingly, model studies are under investigation. Several products are produced

for both additives with either of the model compounds. Current work is directed towards an understanding of these model studies.

It should be recognized that a rhodium compound is a very unlikely can- didate for a commercial flame retardant, this work is being undertaken to probe

the mechanism of the reaction and the chemical requirements of a putative flame

re tardant.

The formation of the anhydride is the initial step in this work, true

cross-linking requires that two or more of the polymer chains be bonded; this

is the second step of this work, no work has as yet been done on this step.

PET . The decomposition of PET has been reported, in previous work, to

produce a highly cross-linked product, formed by alkylation of a benzene ring

with a vinyl ester moiety produced from the breakdown of PET. This reaction

appears to occur spontaneously upon heating, it is also promoted by the pre- sence of additives such as red phosphorus and zinc salts. The requirement for

some decomposition to produce an additive that can then provide stabilization

(see scheme I) is less than satisfactory. A better approach is to seek an additive that will cross-link with the PET before any PET decomposition occurs. This additive will ideally be a divinyl moiety that can add to two chains of

PET and thus lead to cross-linking. As above it is desirable to model this

reaction with small molecules that can be completely characterized. The model

that has been chosen for PET is dimethyl terephtha La te , DMT, and the vinyl com- pound that has been studied is peryllic alcohol. The expected reaction is an alkylation of the benzene ring of the DMT by the vinyl moiety and this reaction

does occur. Current work is directed towards the complete mechanistic understanding of this reaction and its extension to other vinyl and divinyl systems.

The reaction of PET with some putative flame retardants is also under investigation. The goal is to understand the mechanism of the reaction. The

identification of the locus of the reaction, both for the polymer and for the

additive, will allow one to identify the functionality necessary in the additive for a successful flame retardant. Once again, model studies are helpful

in allowing the characterization of the important reaction steps.

The reaction of PET with tripheny Iphosphine produces tripheny 1- phosphine

oxide and several other, low molecular weight, products. This reaction is most

easily understood through model studies using methyl myristate. The reaction

involves either a carbene or free radical intermediates producing alkanes and

alkenes, - C . Tripheny Iphosphine is a poor flame retardant for PET, none the less" va Luao le information may be obtained from an understanding of the

reaction mechanism. Current research is extending these reactions to other

putative flame retardants.

93
-~o4<>Io-ch

2-ch

2-o.E^>E0 r—, 0

j-ZnCI2

Vc-oZnCI 4- ClI

0 0

CH2-CH

2-0-C^ \-c-0'--

" /~A ° c—5 ' ?

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Reports and Papers:

T. Suebsaeng and Co A. Wilkie, "Reactions of Tripheny Iphosphine and Related

Compounds with Poly( e thy lene terephthala te) , " 20th Great Lakes Regional

Meeting American Chemical Society, Milwaukee, WI . , June, 1986

95
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution : Michigan State University

Grant Number: 60NANB5D0578

Title: Effect of Water on Ignition of Cellulosic Materials

Principal Investigator :

Other Professional Personnel

Arvind Atreya

Assistant Professor

Department of Mechanical Engineering

Michigan State University

East Lansing, MI 48824

Tel. No. (517) 353 6356

M. Abu-Ziad, Ph.D. candidate

Lin-Shyang Tzeng, Ph.D. candidate

NBS Scientific Officer: Dr. David D. Evans

TECHNICAL ABSTRACT :

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 fundamental theoretical 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:

On the experimental side, we have primarily been involved in the design,

construction and calibration of a combustion wind tunnel that will permit

control of gas composition, gas speed and external radiation incident on the

sample. This facility has been constructed and is currently being calibrated.

It is essentially a small duct (5.75” X 4” cross-section; The cross-sectional

view is shown in Figure 1) capable of providing a flat plate boundary layer

flow on the sample surface. This wind tunnel is operated strictly at

atmospheric pressure to avoid leakage. The external radiation is provided by

electrical radiant heaters configured as shown in Figure 1. These heaters

have a maximum black body radiation temperature of 1300 K and are therefore

well suited to simulate external radiation in building fires. The temperature

of the heating elements is measured by a temperature probe shown in Figure 1.

96
Two water cooled blackened aluminum plates are used to intercept the radiation during the heater warm-up period. These plates are suddenly removed at the

start of the experiment to provide external radiation on the sample surface.

This radiation is transmitted via. the infrared optical glass windows that

form the top of the tunnel

Prior to the experiments the samples are conditioned in a temperature and

humidity controlled chamber. This chamber (Model TH-3, BMA Inc.) has a con- trollable humidity range of 10 to 98% RH ± 2% RH and a controllable temperature

range of 2 to 85 °C. The moisturg content of the sample is then determined by

the difference between its ’'dry

1 ' and '"wet" weight.

Work on studying the effect of water droplets on transient cooling of a porous solid is also under way. The objective is to simulate a porous material

like wood. Thus an inert porous ceramic sample will be casted around a matrix

of thermocouples. Preliminary tests have shown that castable MgO (KF-95) is

ideally suited for the purpose. This material has excellent water absorption

properties and its high temperature thermophysical properties ( up to 1200 °C)

are available from Sandia National laboratories^]

THEORETICAL WORK:

The basis of the theoretical model is the piloted ignition of a cellulosic

solid subjected to a constant external radiant heat flux. When exposed to

external radiation, the solid will release combustible gases and water vapor

depending on both the magnitude of the external flux and the thermophysical

and thermochemical properties and its moisture content. Once evolved, the

volatiles mix with the oxygen in the surrounding air producing a combustible

mixture that can be ignited by a pilot flame, and through which a premixed

flame may subsequently propagate. Ignition is considered to occur when a selfsustaining trailing diffusion flame exists behind the advancing premixed flame

front. This eliminates consideration of the initial transient flashes, that

are observed experimentally, as ignition events.

The problem being considered here is inherently two-dimensional and transient. For purposes of simplification, in the initial formulation, buoyancy

is discarded, the gas-phase thermophysical properties are assumed constant, a one-step irreversible Arrhenius reaction is assumed, and the surrounding gas

is assumed quiescent. Transverse velocities (normal to the plane of the

sample) are also ignored and the fuel is assumed to diffuse from the constant

temperature lower surface into the gas. The boundary layer approximation is

not employed, because streamwise diffusion is essential for both the piloted

ignition and the flame spread processes. The pilot flame is modeled as a constant-heat-flux line source located near the origin. The corresponding

nondimensional equations and boundary conditions are shown in Figure 2. Note

that the model configuration is symmetrical about the plane x - 0, and that

the far-field boundary conditions in y are applied at y

= i, since the steady

state of this system is known to be a flat one-dimensional diffusion flame.

As a check of the numerical solution, first transient calculations of the

flame speed through a premixed mixture were performed and its large-time

steady-state value was compared with the analytical results obtained by

activation energy asymptotics[2] . This comparison is shown in Figure 3. It can be seen that for Zeldovich # > 7, Vanalytical/Vnumerical approaches unity.

This result is the same as that of Rogg’s[3].

97
In addition to the numerical model, a simplified analytical model for

piloted ignition has also been developed [4]. Figure 4 shows the model calculations for three different levels of external radiation (2, 3 and 4 W/cro2) and two different values of the nondimensional pre-exponential factor ’A’ (10

3 and I0 19 ). The intersection of the curves marked gas-phase (M) and the curves marked solid-phase (M) is the ignition point which yields a unique solution

for the fuel mass flux and surface temperature at ignition. Given the surface

temperature at ignition, the time for piloted ignition is obtained from the

bottom graph. It is interesting to note that the predicted ignition temperatures lie within the measured range and that for a given set of parameters they

indeed are very nearly constant. Also even though the nondimensional fuel mass

flux f M* shows a considerable variation with external radiation, its

dimensional counterpart is almost constant and has a value of 1.8 gm/m2 sec. Furthermore, variations in the decomposition kinetics (change in A from 10 9 ’to

10 ) seems to cause a large variation in the surface temperature at ignition,

but only a minor change in the critical fuel mass flux at ignition.

REFERENCES :

1. Taylor, R.E. and Groot, H. "Thermophysical properties of cast MgO," Report

to Sandi a National Laboratories , Purdue University, August 1985.

2. Williams, F.A. " Combustion Theory ," The Benjamin/Cummings Publishing Co.

Second Edition, 1985.

3. Rogg, B. "On the Accuracy of Asymptotic Flame Speed Predictions for TwoReactant Flames," Combustion Science and Technology , 45, 1986.

4. Atreya, A. and Wichman, I.S., "Heat and Mass Transfer during Piloted

Ignitionof Cellulosic Solids," To be published in the 2nd ASME-JSME

Thermal Engineering Joint Conference , 1987.

98

nCDS 1 SPESZM9RK. F3V2UTT.
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Equations
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 1986

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 Assistant

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 first phase we analyzed the problem using a comprehensive mathematic model. In the present

research we have conducted an experimental study of the vertical wall fire in

a stratified atmosphere and extended the analysis further. Results from the

overall investigation are expected to provide a better understanding of the

behavior of a typical vertical wall fire in a compartment, which is also

useful as an input to multiroom buildings.

Experiments :

A test apparatus has been designed and built to study characteristics of

a wall fire in a stratified atmosphere. Since this is the first attempt for

investigating the problem experimentally and since the mathematical model

developed last year was for a laminar boundary layer fire flow, the scale of

experiments is small and restricted to a mostly laminar wall fire. After some

trial designs and modifications, the experimental setup was erected as shown

schematically in Figure I. The basic aim was to create a stratified

atmosphere in front of a wall fire. A sample of 15 cm x 7.5 cm x 1.27 cm is

mounted on a vertical panel. It is surrounded by a ceiling plate with an adjustable slot opening, two side panels of high temperature-resistant glass,

and a front panel. Relative positions of all the panels are adjustable in

order to create different types of stratified ambient atmosphere in front of

the sample. A vertical rake of fifteen chromel-alumel thermocouples is

10C
mounted on a sliding platform to measure the temperature profile with height

in front of the sample at various locations. Oxygen concentration is measured

by a Beckman oxygen analyzer using a water-cooled probe as a function of

height in the stratified atmosphere. A schlieren/shadowgraph optical system

using two front surface concave mirrors is also setup for flow visualization.

The sample is ignited such that the entire front surface burns simultaneously.

Figure 2 shows temperature measured at 8.0 cm in front of the sample

using the thermocouple rake, as a function of the height measured from the

leading edge of the sample at various time intervals. Also, some preliminary

measurements of oxygen concentration are shown in the same figure. A stably

stratified atmosphere is clearly apparent. The measured temperature variation

with height in trial experiments shows that we can simulate the stratified

conditions of a compartment interior reasonably well (Quintiere, et. al .

,

Comb. Sci, Tech. 26 , 1981; Cooper, et. al., J. Heat Trans. 104 , 1982).

Further tests are in progress.

In order to measure the mass burning rate, a vertical strip of

approximately 1 cm width is cut from the center of the burnt sample and then

cut into several pieces. These pieces are milled, weighed, and their

dimensions are measured carefully. Knowing the weight of pieces from a reference sample and the duration of burning, local mass burning rate is

calculated. Initial set of results for the simultaneous measurements of

ambient temperature, ambient oxidizer concentration, and local burning rates

have been obtained recently and they are being analyzed.

Analysis:

We have completed calculations for a laminar vertical wall fire in a stratified ambient atmosphere having various types of temperature and oxidizer

concentration profiles. The analytical investigation is extended to include

the following problems.

(a) Integral Solution: In order to obtain quick solutions to the problem of

a vertical wall fire in a stratified atmosphere, an integral solution is

proposed. Up to third order profiles are assumed for the vertical

velocity (u), and combinations of temperature (T) , fuel mass fraction

(Yp) and oxidizer mass fraction (Yq) . Results obtained using the

integral solution were compared with the numerical solution. Although

the comparison was not very close, further refinement of this solution is

in progress.

(b) Model for a Laminar-Transitional-Turbulent , Natural Convection Flow:

Before extending our laminar flow model for a vertical wall fire in a stratified atmosphere to include turbulence, we decided to first study a similar flow, but without the complications of fire. A model for

laminar-transitional-turbulent , natural convection flow over a hot,

isothermal wall in a stratified, quiescent ambient atmosphere was formulated. The modal adapted here is a combination of turbulence

models proposed by Cebeci and Khattab ( J. Heat Transfer , 1975, ?. 469)

and Price and Harris (NASA TM x-2453, 1972). The model was solved using

Keller Box finite difference technique and results have been obtained.

Effect of various types of stratification was studied on the velocity

field, temperature profiles and heat transfer to wall. It was found that

101
the upstream memory in the natural convection boundary layer flow in a stratified ambient atmosphere affects the velocity field more

significantly than the temperature.

Reports and Papers

1. A. K. Kulkarni, and J. J. Hwang, "Vertical Wall Fire in a Stratified

Atmosphere", presented at the 21st International Symposium on Combustion , August 1986.

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 Transfer , in press.

3. A. K. Kulkarni and S. L. Chou, "Turbulent Natural Convection Flow over a Vertical Wall in a Stratified Medium", being submitted to J . Heat

Transfer .

4. A. K. Kulkarni and J. J. Hwang, "Free Convection Vertical Wall Fire in

Various Types of Stratified Ambient Atmosphere", paper no. AIAA-86-0577

,

presented at the AIAA 24th Aerospace Sciences Meeting, Reno, Nevada,

(1986). * y (%) o ,°° 19.5 20.0 20.5 21.0

Fig. 2 Typical measured data for

Fig. 1 Sideview schematic of

oxidizer mass fraction (x) and

experimental apparatus

temperature in front of the

burning sample. Temperature

profiles are shown at t=8 min (a)

,

11 min (A) and 12 min (O) after

ignition.

102
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY86

Insti tution: Rutgers, The State University of New Jersey

New Brunswick, New Jersey

Grant No.

NB83NADA4047

Grant Title: Negatively Buoyant and Penetrative Flows

Generated in Enclosure Fires

Principal Investigator: Professor Yogesh Jaluria

Department of Mechanical & Aerospace Engineering

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 study is to study experimental ly the

negatively buoyant and penetrative flows that are generated at the early stages

in the growth of an enclosure fire. The. flow driven by the fire plume spreads

over the ceiling and turns downward at the corners, generating a two-dimensional

wall jet with opposing buoyancy effects. Similarly, wall flows generated in the

upper layer of the enclosure are injected across the interface into the lower

layer where they become negatively buoyant. The project is directed at such

negatively buoyant and penetrative flows. The present effort is focused on two main topics: (1) the characteristics of a negatively buoyant wall jet in an extensive environment, and (2) the penetration of wall flows across the

interface between a hot upper zone overlying a cooler lower layer. The first

topic has been studied in detail, providing very important inputs for the zone

model analysis of enclosure fires. A substantial amount of progress has also been

made on she second topic. The results obtained in the two cases have been

correlated with each other and with the zone model results for enclosure fires.

Negatively Buoyant Nall Jets . A. detailed experimental study of the

penetration depth s D , total entrainment of ambient fluid into the downward

di charged jet, the heat transfer at the wall which is maintained at a uniform

temperature T s and the resulting velocity and thermal fields has been carried

out. Details of the experimental arrangement are given in the publications

listed at the end of this report. Several important correlations have been

derived in terms of the mixed convection parameter Gr/Re- = ge (T q-T^ID/Uq-

where

D is the width of the discharge slot, U 0 the average discharge velocity, T 0 the

jet discharge temperature. T® the ambient temperature, a the coefficient of

thermal expansion of the fluid and g the gravitational acceleration.

Figures 1 and 2 snow some of the results obtained. The penetration

distance 5p and the total mass flow rate m0u t at the level of the jet are well

correlated bv the equations

103
( 1 ) 6 p

/0 = 4.424 (Gr/Re2

) -0 ’ 389

and,

m

out/m

in = 0.037 + 60.967 (Gr/Re

2

) - 238.056(Gr/Re 2

) 2 + 485.018(Gr/Re 2

) 3

- 381.352 (Gr/Re 2

) 4

(2)

Here, mou t = ^ent + ^in» where men t is the total entrainment into the flow and

m-j n the discharged flow rate. More extensive measurements are being taken for

a wider range of conditions and a more convenient form of the correlation for

m0ut> £d* (2) , is being derived. These results have also been applied to the

buoyancy driven wall flows in an enclosure fire, as shown in Fig. 3. A very

large amount of entrainment into the flow is observed and the penetration

distances are found to be physically realistic. Heat transfer rates at the wall

have also been measured and a correlating equation is being derived.

Pentration Across the Interface in a Two-Layer System . An extensive

modification of the present experimental system was undertaken to generate a two-layer, stably stratified environment. Employing a specially designed

diffuser, heated air was discharged at very low velocity over the entire top of

the enclosure and allowed to exit at the far end. This gave rise to a very

stable stratification in the tank, as shown in Fig. 4. The stratification is

essentially a two-layer system and can be maintained almost indefinitely. This

is a very encouraging result since such a system can be used to study a wide

variety of penetrative flows in ericlosure fires.

The penetration of a buoyancy induced flow, generated adjacent to a cooled

plate in the upper layer into the lower region was studied. The penetration

depth, the heat transfer and the resulting flow fields were studied. It was found that the flow buoys back toward the interface and stays near it, giving

rise to a thicker intermediate layer. A typical measurement of the resulting

thermal field is shown in Fig. 5. The work is being continued and it is

expected that correlating equations for the penetration deDth, entrainment and

heat transfer will be obtained. These can then be used as submodels for the zone model analysis of enclosure fires.

Reports and Papers

1. Jaluria, Y. and Goldman, D. , "Transport Due to Flows with Opposing 3uoyancy

Arising in Room Fires," Fall Tech. Meet., Eastern Sect. Combust. Inst.,

Philadelphia, PA, Paper No. 39, 1985.

2. Goldman, 0. and Jaluria, Y., "Effect of Opposing Buoyancy on the Flow in

Free and Wall Jets," J. Fluid Mech., 166, 41-56, 1986.

3. Jaluria, Y., "Buoyancy-Ori ven Wall Flows in Enclosure Fires," accepted for

publication in 21st Symp. (Int.) on Combustion, Combust. Inst., 1986.

4. Jaluria, Y., "Hydrodynamics of Laminar Buoyant Jets," in Encyclopedia of

Fluid Mech., Gulf Pub. Co., Ch. 12, 317-348, 1986.

104
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CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution: Southwest Research Institute

Grant No.: 60NANB6D0635

Grant Title : Analysis of Hazards to Life Safety in Fires:

A Comprehensive Multi-Dimensional Research

Program— Second Year

Principal Investigator :

Other Professional Personnel:

NBS Scientific Officer:

Dr. Gordon E. Hartzell

Director s 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, Applied

Envi ronmental Toxicology)

Howard W. Stacy (Sr. Research Scientist)

Walter G. Switzer (Research Scientist)

Dr. Steven C. Packham (Consultant)

Deggary N. Priest (Consultant)

e Dr. Baroara C. Levin

Technical Abstract :

The overall objective of this research program is to develop methodology

to assess toxicological hazards to human life from the time course of analytical data on fire gases.

Under funding from a previous grant, a Fractional Effective Dose (FED)

Model was developed based on carbon monoxide and hydrogen cyanide. Additionally, the effects of an irritant (HC1 ) on inhalation of CO by rats were

studied.

The FED model will now be modified as necessary to accommodate the

presence of HC1 and CO?, in addition to the asphyxiant toxicants, as may be

combined in smoke. After validation of the model using pure gas studies, it

will be tested using real smoke from burning materials. Any significant

discrepancies between model -predicted and experimental data from animal exposures will aid in identifying the presence of other toxicants requiring investi gation.

At the time of the preparation of this summary, work under this grant

had not commenced.

Reports and Papers :

None.

107
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution : University of California, Berkeley

Grant No . : 60NANB5D0552-1

Grant Title : Fire Modeling

Principal Investigator : Professor Patrick J. Pagni

Vice-Chairman

Mechanical Engineering Department

University of California

Berkeley, CA 94720

Telephone: (415) 642-0729

Other Professional Personnel : James Ang (Ph.D. Candidate)

Valerie Lyons (Ph.D. Candidate)

Corey Dunsky (Ph.D. Candidate)

Thomas Mataga (M.S. Candidate)

NBS Scientific Officer: Dr. Howard Baum

Technical Abstract :

While 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 fire

radiation, discussed first below. In addition, this grant period we have added thermal effects of fuel cracking, bouyancy, and variable

properties to sooting boundary layer analyses. Perturbation techniques have been utilized wherever possible.

Fire Radiation:

In flame radiation, the most important and least known parameter is

f

v

, the soot volume fraction, defined as the volume occupied by soot per

unit of flame volume. Previous summaries have described a multiwavelength laser extinction technique for in-situ measurement of the

local flame f v

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.

Limited data on small pool fire mean soot volume fractions suggest

fv scales with optical thickness, <L, as

fv/fx

max

A/Z^vmax

= 1 .5(<L

)

= 1

1/3

, kL < 0.3

, <L > 0.3

108

( 1 )
Equation (1) is shown in Fig. 1, where f is an experimental fuel vmax characteristic (- 3.4 ppm for polystyrene +; and - 0.62 ppm for

PMMA.), < is the soot absorption coefficient and L is the mean beam

length. If this correlation holds for all fuels, it will permit

scaling of the mean f

v in pool fires to any size from a single

measured fy For example, a 15 cm diameter pool of iso-octane gave

f

v

s 0.46 ppm. Using Tien's soot optical properties gives ic(nr')

1.5 fy (ppm). So < ^ 0.67 m“T . The mean beam length is well approximated by the pool radius, 7.5 cm here. Then from Eq. (1),

f v/f v

~ 0.85, and f

v * 0.83 ppm. This f will exist in all

max max max iso-octane pool fires for which <L > 0.3, i.e., all pool diameters >

0.5 m. By the method of Ref. 6, this volume fraction corresponds to

maximum conversion of fuel carbon to soot for iso-octane of 6.3%.

Additional experiments are underway to confirm this correlation.

Fig. 1

Universal

pool fire soot

volume fraction

correl ation

Combusting Boundary Layers:

In order to interpret our f v measurements in free and forced

boundary layers, accurate temperature and velocity fields are needed

(4). The classic solutions of boundary layer diffusion flames

neglected phenomena such as fuel cracking, property variations,

buoyancy and radiation and, therefore, produced profiles that are not

adequate for soot formation modeling. This analysis adds buoyancy,

soot radiation, wall radiation, and confinement pressure gradient

effects as perturbations (2). To maximize the utility of previous

solutions, each perturbation is broken into two parts. The first con tains the effect of the perturbation in the governing equations,

assuming no blowing at the wall. The second separately accounts for

109
the additional blowing due to that perturbation. An advantage of this

approach is that each perturbing effect can be assumed independent,

with the similarity solution incorporating fuel cracking and property

variations as the zeroth order. Summing the contributions provides

the full solution with a clear indication of the importance of each

perturbation. The effect of soot radiation is to increase the blowing

at the wall and lower the temperatures in the regions where soot is

present. The buoyancy perturbation causes velocity maxima in mixed

flow and moves the peak temperature closer to the wall. Confinement

pressure gradient effects in our system appear to be so large that

they cannot be adequately treated as perturbations.

The fact that predicted temperature profiles significantly

overestimate measured temperatures between the fuel surface and the

flame (6) even when soot radiation is included in the analysis,

implies that endothermic fuel cracking may be important (see e.g.

Nakagawa, et al., 13th Combustion Symposium, p. 813, 1971). Therefore, we have included a second reaction, Yp-j -*» Yp2 , in our analyses.

Fast kinetics are assumed so that a fuel cracking sheet exists inside

the flame sheet as shown in Fig. 2. These sheets can be expanded

using activation energy asymptotics. Similarity solutions are still

possible provided the Shvab-Zeldovich variables are redefined to

include the cracked fuel product, Yp

2

.

EXPERIMENTAL and THEORETICAL TEW>ERAnjRE PROFILES

FOR N-HEPTANE AT 4 am DOWNSTREAM

Fig. 2. Temperature (°K) profile for a free flow boundary layer

flame of n-heptane in air. Theory (-) includes a fuel

thermal cracking sheet at 1000°K and an endothermicity

there based on acetylene as the primary product. Experiment results (o) are described in Ref. 4.

no
and ( 2 )

6 - Y

F1 /v

F

M

F

Y F2

/v

F

M

F

- Y0

/v

0

M

0 a * h/Q + Q'Y F2 /v

F

M

F + (l-Q')Y A, M

q

.

Q* is the cracking endothermic! ty, Q = Q + Q

1 , where Q is the original

heat of combustion. Ypj is the original fuel. A separate simple

boundary value problem is solved for Ypg, allowing Yp*j and h to be

extracted from Eq. (2) between the fuel and the flame.

Reports and Papers :

1. C.E. Grant and P.J. Pagni , eds., Fire Safety Science - Proceedings

of the First International Symposium , Hemisphere Publishing Co.,

New York (1986).

2. J.A. Ang, P.J. Pagni, H.R. Baum and T.G. Mataga, "Combusting

Boundary Layers Perturbed by Pyrolysis, Bouyancy and Radiation,"

poster presentation at the Twenty-first International Symposium on Combustion, Aug. 3-8, 1986, Munchen, F.R.G.

3. S.S. Dosanjh, P.J. Pagni and A.C. Fernandez-Pello, "Forced

Cocurrent Smoldering Combustion," poster presentation at the

Twenty-first International Symposium on Combustion, Aug. 3-8, 1986,

Munchen, F.R.G.

4. J.A. Ang, P.J. Pagni, T.G. Mataga, J.M. Margie and V.J. Lyons,

"Temperature and Velocity Profiles in Sooting, Free, Boundary Layer

Flames," AIAA Paper No. 86-0575, 24th Aerospace Sciences Meeting,

Reno, Nevada (1986).

5. K.L. Foote, P.J. Pagni and N.J. Alvares, "Temperature Correlations

for Forced-Venti 1 ated Compartment Fires," Fire Safety Science - Proceedings of the First International Symposium , pp. 139-148,

Hemisphere Publishing Co., New York (1986).

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 , pp. 361-369, Hemisphere

Publishing Co., New York (1986).

7. J.P. Vantelon, P.J. Pagni and C.M. Dunsky, "Cellular Flame

Structures on a Cooled Porous Burner," in AIAA Progress in Astro - nautica and Aeronautics Series: Dynamics of Reactive Systems - Part I: Flames and Configurations, pp. 131-151, AIAA, New York

(1986).

8. P.J. Pagni, "Progress Report on Materials Fire Properties and Test

Methods," in Proceedings of the Eighth Joint Meeting, United States - Japan Natural Resources Panel on Fire Research and Safety , pp. 352-

358, Building Research Institute, Tsukuba, Japan (1986).

Ill
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution : University of California, Berkeley

Grant No .: NB83NADA4020

Grant Title : Fire Propagation in Concurrent Flows

Principal Investigator : Professor A.C. Fernandez-Pell

Department of Mechanical Engineering

University of California

Berkeley, CA 94720

Other Professional Personnel : H.T. Loh, Research Assistant

B. Anos, Research Assistant

NBS Scientific Officer: Dr. H.R. Baum

Technical Abstract :

A research program is being carried out to study the mechanisms controlling

the spread of flames over the surface of a solid combustible in an oxidizing gas

flow. Because of the varied mechanisms involved in the flame spread process,

the program includes a number of studies covering different physical phenomena

from the ignition of a vaporizing fuel to the extinction of a propagating flame.

Research performed during the current research period includes a numerical ana- lysis of the flow assisted spread of flames over the surface of a thermally

thick fuel, an experimental study of the extinction and stabilization of a diffusion flame over a flat combustible surface, and a theoretical study of the

forced ignition of a vaporizing combustible surface. A significant contribution

of the flow assisted flame spread analysis is the incorporation of finite rate

kinetics in the formulation of the problem. This provides a more accurate

description of the regions with slow chemistry such as the upstream leading edge

of the flame and the flame tip. The flame extinction experiments were performed

primarily to verify the predictions of an analysis, previously developed, of the

dependence of the extinction distance on the velocity and oxygen concentration

of the convective flow. The study addresses the processes controlling the

structure and stabilization of the upstream leading edge of the flame. The

ignition study has as final objective the description of the ignition by a hot

particle (firebrand), or by gas absorption of radiation, of a vaporizing sur- face in a convective flow. During this reporting period, a one-dimensional

model of ignition has been developed. The results, although preliminary appear

to be phenomenologically correct.

Numerical Analysis of Flow Assisted Flame Spread . This work consists of a numerical analysis of the flame spread process over the surface of a thermally

thick fuel, in a concurrent forced oxidizing flow. In the analysis, the gas

phase governing equations for a laminar, reacting, boundary layer flow are solved numerically to obtain the heat flux at the burning and unburnt fuel sur- faces. The calculated heat flux is used later as a boundary condition for the

solid phase transient energy equation. The rate of flame spread is obtained

1 12
from the solution of this last equation by imposing the condition that at the

pyrolysis front the surface temperature of the solid is equal to its gasification temperature.

A modified version of the GENMIX computer code is used for the numerical

solution of the gas phase equations. The modified code includes finite rate

chemical kinetics for a one step chemical reaction of the Arrhenius type, and it

is applied for a laminar, non- radiating, boundary layer flow. The calculation

domain is divided into two regions: 1) The upstream region where the fuel sur- face is vaporizing and the gas phase domain can be solved independently from the

solid phase, and 2) The downstream region where the solid is not vaporizing and

where the solid and gas phases are coupled through their interfacial boundary

conditions and consequently have to be solved simultaneously. In Fig. 1 the

theoretical results for the rate of flame spread as a function of the flow velocity and oxygen concentration and their comparison with the experiments are presented. It can be seen that the predicted flame spread rates agree well with

the experimental results. It should be noted, however, that some of the parameters involved In the problem, in particular the pre-exponential factor in the

Arrhenius reaction rate, have been selected to improve the agreement between

theory and experiment.

Experimental Study of the Extinction of a Diffusion Flame . The main objective of these experiments is to verify the predictions of an analysis, already

completed, of the extinction characteristics of a diffusion flame on a vertical

surface, which is burning steadily in a mixed convective flow. The experiments

are carried out in a small scale combustion tunnel. The flow velocity and oxygen concentration of the flow in the tunnel are accurately controlled with

critical nozzles. Oifficulties in performing the experiments with a solid fuel

moved us to carry out the experiments with a liquid fuel (heptane). The liquid

fuel is supplied by gravity fed to a porous ceramic vertical plate. The experiment consists primarily in the measurement of the distance from the upstream

edge of the fuel surface to the point where the flame leading edge is stabilized

(extinction distance) as a function of the velocity and oxygen concentration of

the flow. The experimental results and their comparison with the theoretical

predictions are presented in Fig. 2. The agreement between theory and experiments is only qualitative. This is understandable since the analysis considers

only a simple one step, Arrhenius type, reaction to describe the gas phase

chemical kinetic processes. The experimental results, however, verify the

theoretical predictions.

Analysis of the Ignition of a Vaporizing Combustible Surface . A numerical

analysis of the forced ignition, by pilot or by vapor absorption of radiation,

and subsequent flame propagation in a gaseous mixture established over a vaporizing combustible surface in a still oxidizing environment is developed.

The model considers a flat combustible surface that starts to vaporize due to

the heat flux from a suddenly imposed external source of radiation. Two sources

of ignition are analyzed. One is a source of heat that is suddenly introduced

at a predetermined distance from the surface and that causes the ignition of the

pre-established gaseous mixture. The other is the absorption of radiation by

the vapor fuel , which increases the temperature of the gas and causes its ignition. In both cases the heat source is intense enough that once the ignition of

the mixture occurs, the combustion reaction becomes self-sustained. Conduction

of neat upstream results in the propagation of a reaction front (flame) toward

the fuel surface. Conduction and convection of heat downstream results in the

113
propagation of a second reaction front toward the outer boundary. The formation

and characteristics of these two reaction fronts depend on the initial location

and intensity of the ignition source.

In the present analysis, the transient, one dimensional, conservation

equations that describe the reacting flow are solved numerically to determine

the transient ignition of the gaseous fuel-oxidizer mixture and the subsequent

propagation of the combustion reaction through the mixture. A modified version

of the SIMPLER computer code is used in the computation. The combustion reac- tion is assumed to be described by a global one-step second order chemical reac- tion between fuel and oxidizer. The reaction rate is assumed to be of the

Arrhenius type with relatively small activation energy. The value of the

activation energy is selected to ease the difficulties inherent in the numerical computation of the ignition process while providing physical insight on the

process. A Lewis number unity is assumed so that the Shuab-Zeldovich formulation can be applied to simplify the numerical solution. A non-uniform grid

that moves with the reaction front is used to compute the velocity of propagation of the flame. The variation with time of the temperature for a characteristic case of vapor absorption ignition is presented in Fig. 3.

Reports and Papers :

1. H.T. Loh and A.C. Fernandez-Pel 1 o , "A Study of the Controlling Mechanisms

of Flow Assisted Flame Spread,” Twentieth Symposium (International) on Combustion, The Combustion Institute, 1575-1982 (1985).

2. H.T. Loh and A.C. Fernandez-Pel 1 o, "Flow Assisted Flame Spread Over

Thermally Thin Fuels,” First International Symposium on Fire Safety

Science, 65-74 (1986a).

3. R. Rangel and A.C. Fernandez-Pell o, "Convective Ignition of a Flat

Combustible Surface,” 1985 Fall Technical Meeting, Western States Section

of the Combustion Institute, University of California, Davis,

October 21-22, 1985.

4. C.-P. Mao and A.C. Fernandez-Pel 1 o , “Flame Spread in a Wall-Ceiling

Corner,” 1985 Technical Meeting, Eastern Section of the Combustion

Institute, Philadelphia, PA, November 4-6, 1985.

5. H. Kodama, K. Miyasaka and A.C. Fernandez-Pell o , "Extinction and

Stabilization of a Diffusion Flame on a Flat Combustible Surface,” submitted to Combustion Science and Technology, 1986.

6. H.T. Loh, "Concurrent Flow Flame Spread Study,” Ph.D. Thesis, Department of

Mechanical Engineering, University of California, Berkeley, 1986.

114
fAcerf

t eee

**o

i •.

PB0S vitOC?Tv y, t m/% )

Fig. 1

Fig. 2

Rodiotion Absorption Ignition

Fig. 3

ij
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 1986

Institution : University of California - Berkeley

Grant No. : 60NANB4D0018

Grant Title: Flame Radiation

Principal Investigator : Professor Chang-Lin Tien

Department of Mechanical Engineering

University of California

6179 Etcheverry Hall

Berkeley, California 94720

Telephone: (415) 642-0877

Other Professional Personnel : M.A. 3rosmer, Ph.D. completed in December 1985

B.L. Drolen, Ph.D. student

A. J . Stretton, Ph.D. student

S.H. Park, Ph.D. student

NBS Scientific Officer: Dr. Takashi Kashiwagi

Technical Abstract:

Introduction . The goal of the research sponsored by this grant is to

establish simple calculation schemes for radiation heat transfer in fires,

while retaining the fundamental physics of the problem. The products of the

research are approximate relations developed from careful experimental studies

and theoretical analyses. During the past year, three topics were addressed:

(1) radiative modeling of pool fires to determine burning rates and radiative

fluxes; (2) radiative properties of agglomerated soot particulate; and

(3) infrared radiative properties of several hydrocarbon gases which are pyrolysis products of PMMA. In addition to this research work, a chapter

reviewing the fundamentals of thermal radiation in fires for fire protection

engineers was prepared for publication [1].

Radiative Modeling of Pool Fires . The relatively cool gases evolved from

the pyrolysis of burning condensed fuels are important in determining the rate

of burning and the ignition characteristics of the fuel. Large fires (L > 0.7

m) are primarily controlled by radiant feedback from the flames, which provides the energy to pyrolyze the fuel into combustible gases. A two-zone

flame model which is capable of handling large-scale pool fires has been proposed recently, and has already been successfully used to predict burning

rates and total radiative output of moderate to large-scale PMMA pool fires

[2]

. The model is very simple in concept, consisting of two discrete, homogeneous, isothermal, conically-shaped regions: a high-temperature luminousflame region representing the turbulent combustion zone, and a cool, fuel-rich

layer near the fuel surface which acts to block radiation feedback from the

flames (see Fig. 1). Rigorous specification of the temperature and concentration profiles of the gases within the fire is not required to obtain accurate

predictions of the burning rate and various radiative fluxes. Further

116
refinement and simplification will be undertaken to mato the model a more con- venient tool for the fire engineering community. The scaling problem between

small-scale fire plumes and large-scale plumes associated with fires of disastrous proportions is also under analytical study, with special attention to

the role of thermal radiation.

Radiative Properties of Soot Particulate . The scattering and absorption

characteristics of agglomerated soot particulate has been modeled as a collection of spherical sub-units assuming that they are Rayleigh scatterers [3].

The model accounts for all electromagnetic interactions between the primary

particles via an existing analytical solution, and investigates clusters and

chains of as many as 1 36 primary particles aligned in various directions relative to the EM wave propagation (see Fig. 2). The analytical results are correlated using "equivalent” sphere models based on the disymmetry ratio, the

scattering cross-section and the absorption cross-section. The results indicate that a cluster of spheres has EM cross-sections which are similar to

those of an equivalent sphere of equal solid volume. The effective diameter

of the agglomerated particulate can be simply expressed by De ff/D = N

I/3

. The

results are in good agreement with existing laser diagnostic data of soot in

flames.

Radiative Properties of Hydrocarbon Gases . The blockage effect of the

pyrolyzed gases can significantly lower the burning rate of the fuel and

greatly influences the ignition character istics of the spreading flames. The

gases under study include methyl methacrylate (C 5 H 9 Q 2 , the liquid monomer of

PMMA) , ethylene (C 2 H„), ethane (C 2 H 6 ), and propane (C 3 H 3 ). To date, the list

of hydrocarbon gases for which infrarea properties have been published is limited to methane (CH„), acetylene (C 2H 2

) [4], and propylene (C 3 H S ) [5j. Typical spectral absorption data from ongoing work with methyl methacrylate is

presented in Fig. 3 • The experimental data are reduced and presented in a variety of formats: 1) spectral mean properties for narrow band models; 2)

average band properties for the exponential wide-bana model; and 3) total

absorption properties of the gas for the super-band model, the Planck mean absorption coefficient, and total emissivity charts.

Reports and Papers :

1. C.L. Tien, K.Y. Lee, and A.J. Stratton, "Radiation Heat Transfer", in

SFPE (Society for Fire Protection Engineers) Quantitative Methods Handbook (to appear).

2. M.A. Brosmer and C.L. Tien, "Radiative Energy Blockage in Large Pool

Fires," Comb. Sci. and Tech, (to appear).

3. 3.L. Drolen and C.L. Tien, "Absorption and Scattering of Agglomerated

Soot Particulate," J. Quant. Spectrcsc. and Rad. Trans, (under review).

4. M.A. Brosmer and C.L. Tien, "Thermal Radiation Properties of Acetylene,"

J. Heat Trans. K37, 943-948 (1985).

5. C.L. Tien and M.A. Brosmer, "Infrared Radiation Properties of Propylene,"

Comb. Sci. ana Tech. 48, 163-175 (1986).

117
ELEVATION COMPARISON WITH EXPERIMENT

PLAN

z n.>ne

Zo

Fig. 1 Two-Zone Model for Large Pool Fires

3

• X

3,0

• «

-''0

+ SPHERICAL CLUSTER

o PARALLEL CHAIN

a PERPENDICULAR CHAIN

o RANDOM CHAIN

20 40 50

NUMBER OF PARTICLES, N

80 100

Fig. 2 Equivalent Sphere Correlation for Agglomerated Soot Particulate

118
Fig. 3 Absorption Spectrum for Methyl Methacrylate

119
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution : University of Dayton Research Institute, Dayton, Ohio

Grant No.: N883NADA4056

Grant Title : Mathematical Modeling of Furniture Fires

Principal Investigator : Mark A. Dietenberger

Research Physicist

University of Dayton Research Institute

300 College Park - JPC/201

Dayton, Ohio 45469

(513) 229-3921

Other PersonnelJoyce Smith, Research Programmer

Scott Musson, Student Assistant

NBS Scientific Officer : Dr. Vytenis Babrauskas

Technical Abstract:

The objective of this work is to develop a working computer model of a furniture fire which utilizes the bench scale measurements on furniture

samples of burning rate history, flame spread rata, time to ignition, and the

fraction of fuel converted to soot. The primary prediction of the model is

the burning rate of a furniture fire as a function of time. The approach is

to design modular submodels that are simple, accurate, and highly coupled and

which can be incorporated into room fire models such as FAST and HARVARD CFC

Series.

The current research has concentrated in two areas: (1) Upgrade the

demonstrator furniture fire model, which was coded during the previous grant

period, to take into account more realistic flame shapes, to incorporate

Pagni's recent estimates of flame radiation temperature and soot volume fraction for PU foams, to fine-tune the flame spreading algorithms, and to accomodate burning rates as a function of net radiative flux to the burning surface,

and (2) Merge the resulting furniture fire model into FAST code, a current

multi-room fire model developed at NBS by Walter Jones. The design of four

modular sub-models corresponding to ignition/flame spreading, the surface

burning rate, the flame shapes and bulk properties, and the furniture fire

thermal radiation was confirmed for easy adaptability to a room fire model.

The merged program is now called HEMFAST and some interesting results were

obtained

.

120
Furniture Fire Model Improvements

The purpose of the improvements was to prepare the furniture fire

model for incorporation to the FAST program. For example, in the thermal

ignition flame spreading module a routine for calculating the temperature rise

of the furniture surface and its thermal ignition was put in place. In the

flame spread module a routine for calculating flame spreading taking into

account the preheat surface temperatures and the surface orientations was put

in place. It is noted that the user can input an ignition source location at

any time in the simulation. The module also includes a feature for merging of

overlapping flame spread polygons and to keep spacings between polygon points

at reasonable values. The surface burning rate module now calculates the

individual burning history of each surface element inside a flame spreading

"polygon" in response to a net radiative heat flux and then sums them up for

input to the flame structure module and to the FAST model.

In another example, the flame structure module no longer considers

a cylindrical or a conical flame shape because the VCR observations of mockup

furniture fires revealed a more complicated shape when the back or the arm rests became involved in burning. To keep the problem of flame shapes simple,

yet consistent with VCR observations it was assumed only pool fires exist when

both the seat and the side surfaces (back or arm rests) are involved. This

implied putting the ignition source on the seat. In all instances the

"horizontal" flame spreading polygons define the flame base while a hydraulic

diameter of the base is computed as four times the base area divided by the

base circumference. The burning rate of the "pool" fire is the sum from all

burning elements, both horizontal and vertical orientations. The flame height

then is an analytic function of the total burning rate and of the flame base

hydraulic diameter. The flame shape is thus defined by a horizontal flame

spread polygon base and a vertical length equal to the calculated flame

height. It was straight forward to calculate the flame volume and surface

area as well as to determine "squarelike" surface elements on the flame sur- face for inputs to the radiative heat flux module.

Improvements in the radiative heat flux module were mainly in the

calculation of the soot extinction coefficient and the corresponding flame

emissivity. Using the results from Bard and Pagni for radiation from soot in

any size or kind of pool fires, the inputs needed were the maximum soot volume

fraction, the mean beam length, and the flame temperature to calculate the

soot extinction coefficient. The flame temperature of the pool fire was assumed to be at 13Q0°K. The radiative heat fluxes then computed are recycled

as inputs to the thermal ignition/flame spread module and to the surface

burning rate module after stepping the simulation time.

Development and Results of HEMFAST Code

HEMFAST is a computer program which simulates the furniture fire

and the toxic gas growth in a room and its spread to the other rooms. This was achieved by incorporating the furniture fire model into the FAST model.

The furniture fire model was designed to be sel f-control 1 abl e in simulating a

121
fire source utilizing as inputs only the bench scale data of material burning

rate, flame spreading, thermal ignition, and the flame properties of the

following: soot volume fraction, CO 2 and H

2O mass fractions of fuel weight,

and gas temperatures. The Froude modeling of flame shape and of uniform fl-ame

properties was utilized following McCaffrey and Orloff and de Ris. To obtain

the self-controllability in the furniture fire model, and also in HEMFAST, it

has involved utilization of a practical 3-0 thermal radiation model in calculating the heat feedback from the flames to the flame front in the determination of the flame spread rates, and to the flame base in the determination

of the local material burning rates. In the HEMFAST program, the thermal

radiation model was extended to include the upper and lower gas layers and the

room enclosure. Since the Hottel's zoning method was used in the thermal

radiation model it was possible to consider surface emissivities less than

unity on all surfaces, and to consider three isothermal gray gas volumes which

are the high-temperature flaming plume, the sooty upper gas layer, and the

lower gas layer at 50% relative humidity.

Some salient features were noted in the simulation of a sample fire

growth on a furniture mockup. Immediately after the seat was ignited, the

pool fire was inferred to be sustained by glowing combustion within the

burning material while the flame front was spreading at its slowest rate.

This was shown by the relatively high net radiative power loss calculated for

the burning material. The simulated furniture fire tended to grow at a low

exponential rate for a slowly increasing spread rate of the flame fronts of

the octogonal flame base.

As the flame base reached the right armrest and the right side of

the backrest, a new phase in the fire growth rate developed because of the

additional burnrate of the side walls and its radiative feedback to the

burning seat. The increased burning rate led to a higher flame radiative

height and also to a higher soot volume fraction. The final phase in the fire

growth rate involved the spontaneous thermal ignition of the remaining surface

elements and also has been observed in VCR observations of mockup burning.

With all the elements burning at this time, the fire growth rate was at its

greatest. However, the peak in the furniture fire burnrate in this case was limited by the surface elements burnout as opposed to the limitation by the

maximum soot volume fraction for a given flame base size.

The upper and lower gas layers eventually gaines 37 and 39°C

respectively above the initial room temperature while the upper layer constituents for CO^, CO, and H

2

O eventually reached 4997, 217, and 19640 ppm

respectively at peak burning rate. Throughout most of the fire growth the

upper gas layer had a net radiative heat loss to the lower gas layer and wall

despite the heat gain from the furniture fire.

Although the HEMFAST program currently predicts the qualitative

behavior of the furniture fire growth in a room, it will need some specific

revisions for the quantitative comparisons with the data, especially the data

by Krasny and Babrauskas. The bench scale data available on the horizontal

122
and lateral f1 arne spreading on furniture materials is very limited. At the

present some data on the flame spread rate can only be inferred from the VCR

observations of furniture mockup burnings. Also, the data on the temperature

of the burning surface is nonexistent for some cases.

The resulting model can aid in resolving some fire safety issues

and aid in fire engineering a room. With further small improvements it can lead to a prediction of time to flashover.

Pubi icat ions

"Mathematical Modeling of Furnture Fires," NBS-GCR-86-506, Interim

Report, prepared for the National Bureau of Standards, Gaithersburg, MO,

February 1986.

12:
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY86

Institution: University of Maryland

Grant No .

7QNANB5H0529

Grant Title

Interaction of Radiation and Conduction in

Polymeric Materials

Principle Investigator

Dr. Win Aung (Adjunct Professor)

Mechanical Engineering Department

University of Maryland

College Park, MD 20742

Other Professional Personnel

Elizabeth Upson Finlayson (M.S. Candidate)

NBS Scientific Officer: Dr. Takashi Kashiwagi

Technical Abstract

The research presented has been carried out as a cooperative program

between the National Bureau of Standards and the University of Maryland. To

date the work considers a theoretical investigation of combined radiation and

conduction heat transfer in semitransparent media. The research is stimulated

by the interest to improve the general understanding of the pyrolysis and

flammability characteristics of an important class of solid polymeric

materials, namely, materials that are classified as semitransparent.

The heating of materials that are semitransparent to thermal radiation

is strongly dependent on the interaction of heat conduction with thermal

radiation. In an opaque material there is no interaction. Radiation heat

transfer is treated as a surface phenomenon in a purely conductive model. In

a semitransparent material the radiation is absorbed throughout the model.

The volumetric absorption of radiation causes increased thermal penetration.

In the early stages of radiative heating the semitransparent model is

considered cold. During this phase the temperature within the model is

sufficiently low so that volumetric emission within the solid can be

neglected. As the model temperature increases the emission as well as subsequent absorption of internal radiation must be considered; this is the

reradiating model. All three modellings of radiation heat transfer: opaque,

cold and reradiating are considered in this research. The main focus of the

analysis is based on a finite difference scheme but analytical solutions have

been obtained for the linear cases. The general model, common to all radiation cases considers a vertical

homogeneous plane layer. The homogeneous specification is applied to allow

for negligible scattering. The plane layer is in local thermodynamic

equilibrium so that Kirchhoff's laws are applicable. The model is heated by a high temperature gray body source which is used to model an intermediate to

large scale fire. The collimated flux of normal incidence at the irradiated

surface is a known quantity. The analysis considers only the early phases of

heating and does not consider the added complications of phase change or chemical reaction caused by degradation. It is assumed chat the temperatures

within the sample are below the glass transition temperature.

124
The physical properties; thermal conductivity, specific heat, and density are considered to be constant or to vary linearly with temperature. The transient

response of the model is of primary interest. The constrictions of the

analysis do not allow a steady state condition to be established.

Combinations of constant temperature; adiabatic; and conducting, convecting

and radiating boundary conditions are considered. The optical properties of

the models are considered constant with respect to wavelength resulting in a gray analysis of radiation. The optical length ,r

a dimensionless parameter

relating to the absorption coefficient and model thickness is used as a parameter to indicate relative opacity of a material. An opaque problem is one in which the optical length can be considered infinite.

The following nondimens ional form of the transient form of the transient

energy equation is used:

9 the temperature parameter normalized on the ambient temperature, x is the

spatial parameter normalized on the model thickness, k, p and c are the

dimensionless thermal conductivity, specific heat and density normalized on

the values determined at ambient temperature. t is the time parameter

normalized on the Fourier number. d F/3x is the spatial gradient of the

solution of the equation of transfer, integrated over the solid body angle,

normalized on the blackbody intensity of the ambient temperature. The

axisymetric form of the equation of transfer is solved subject to

semitransparent boundary conditions. N_ is the radiation conduction

interaction parameter defined as cTs

3 L/k.

The opaque model is the simplest model. The temperature profile is

obtained by solution to a form of the energy equation containing only

conduction and storage terms. The external radiation flux appears as a source

term in the boundary condition at the irradiated surface. Analytical as well

as numerical solutions have been obtained for the opaque model.

The cold model requires the solution of the energy equation and the

equation of radiative transfer. The energy equation includes three terms : a conductive term, a storage term, and a radiation term. The radiation term

contains only that part of the solution of equation of radiative transfer that

relates to the external flux. Because the cold model neglects internal

emission the solution of transfer is dependent only on the external source

temperature. The gradient of the flux is a simple exponent term. The cold

model has been solved using both analytical and numerical methods.

The final model considered is the reradiating model. This model

requires the simultaneous solution of the energy equation and the equation of

radiative transfer. The energy equation is of the same form as that used in

the cola model. The solution of the equation of radiative transfer, however,

is dependent on the internal temperature profile, as well as the external

source temperature. The energy equation and the equation are coupled through

the temperature profile to form a nonlinear integrodifferential equation. An

iterative technique is needed to obtain a temperature profile that satisfies

both equations. No attempt is made to find an analytical solution to this

problem. The solution for the equation of transfer has been obtained

analytically for a linear temperature profile and this result has been

compared with numerical methods. The solution to the equation of transfer is

obtained by assuming a constant temperature across each finite difference

nodal volume. At the beginning of each time step the values from the previous

time step are used. The integrations of the individual components of the

y

125
solution of radiative transfer over the entire model are substituted by a summation of integrations over each node. Since the temperature, hence the

flux, is constant over each node these integrations can be performed

analytically. The resulting solution to the equation of transfer is then used

in the energy equation to obtain a new temperature profile. The process is

repeated until the new temperature profile does not deviate significantly from

the original one. A Newton-Raphson scheme is used to aid in the convergence

of the solution.

Results

The following figures are a sample of the results that have been

obtained so far in the course of this research. Figure 1 shows a comparison

of the opaque, cold and reradiating models. The temperature profiles are recorded at the time required for the maximum temperature in the opaque model

to reach a value 2.0 times that of the ambient. The irradiated boundary is

subjected to a flux: F - 5 W/cm2

. Nr

_ c is taken as 0,1. In the opaque model

the flux appears in the boundary condition as qr - Nr

. c (Fj/aT^ 4 to allow for

comparison with the cold and reradiating models. The boundary conditions are determined using an energy balance between conduction, natural convection and

surface reradiation. The reflectivities relating to external flux are determined by the Fresnel equations based on a solid index of refraction:

n - 1.5. The internally generated flux is assumed to be totally reflected. A

value of r - 10 is used as the optical length in the semitransparent models.

Figure 1 shows the significant difference between the predicted surface

temperature of the opaque and semitransparent models. The semitransparent

models show a greater penetration of heat into the model. When volumetric

absorption of radiation is considered the maximum temperature occurs within

the solid not at the surface as in the opaque model. In this temperature

range the cold and reradiating models yield nearly identical results.

Figure 2 shows the cold and reradiating models. The temperature

profiles are recorded at the time required for the reradiating model to

achieve a maximum temperature equal to twice the ambient. The other

parameters are the same as for Fig. 1. Figure 2 shows the increased

difference between the cold and reradiating models as the model temperature

increases

Figure 3 shows temperature profiles for the opaque and reradiating

models. The reradiating model is analyzed for optical lengths of 20, 10, 5 and 2. Other conditions are as described for Fig. 1. These results show that

as the optical length becomes large the semitransparent model approaches the

opaque model.

The results obtained show that under limiting cases of very large

optical length the opaque modelling can be used to describe a semitransparent

modelling. A better modelling is the cold modelling which gives good results

for low temperature situations and requires a linear set of equations to

solve. The best modelling of a semitransparent solid is the reradiating

model. This model should be used when accurate prediction of the temperature

profile is required.

Papers

E.U. Finlayson, W. Aung, and T. Kashiwagi, "Interaction of Radiation and

Conduction in Polymeric Materials Exposed to External Radiation," submitted

for presentation at the Second ASME-JSME Thermal Engineering Joint Conference,

Honolulu, Hawaii, March 22-27,1987.

126
NORMALIZED

TEMPERATURE

NORMALIZED

TEMPERATURE

NORMALIZED

TEMPERATURE

127
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

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

Telephone: (301) 454-4994

Other Professional Personnel: A. K. Trehan,

Assistant

W. H. Meng,

Assistant

NBS Scientific Officer: Dr. David D. Evans

Technical Abstract:

Introduction. The research described hereafter

constitutes the first phase of an extensive research program

aimed at developing accurate droplet cooling models of

burning solid fuel surfaces. Many studies have been

performed to quantify the vaporization process of both single

and multi droplet arrays impacting on hot surfaces. For the

studies found in the published literature, the full span of

the droplet vaporization processes are usually reported.

These would include evaporation, nucleate boiling, film

boiling and Leidenfrost transition. This present research is

more limited in the span of vaporization process studied,

being only concerned with the evaporation of a single droplet

on a hot surface. This study does report very detailed

results for spacial and temporal variation of the heat flux

at the exposed surface of the droplet, and far temporal

variation of the droplet volume. Exclusive study of the

evaporative process implies that conditions are maintained

under which nucleate boiling is fully suppressed. The

cooling effect of a single droplet impinging a semi infinite

solid surface is deduced in great detail by numerical

integration of the transient energy equation written for the

solid. A simple relationship between the theoretically

predicted evaporation time and the volume of the portion of

the solid affected by the cooling induced by the droplet

evaporation is found. This important result opens the way

for a simplified model to describe the cooling effect of

sprays on hot surfaces based on the detailed modelling of the

single droplet cooling effect.

Graduate

Graduate

128
Droplet Evaporation Phenomenology. A spherical droplet

upon impacting a surface spreads on it. The final

configuration of the liquid varies a great deal and depends

on a multitude of parameters. For the case of liquid water

impinging a surface at near water saturation temperature, the

shape can be regarded as a spherical segment. It is

important to note that the wetted region of the semi-infinite

solid surface is constant in size throughout most of the

evaporation process.

The ratio of the wetted area radius to the radius of an

equivalent liquid volume spherical droplet Is identified by

the parameter 8 and it is the only experimental input to the

analysis. The complexity of the parameters influencing 8

(surface tension, surface wettability, etc. ) is such that

this semi-empirical approach was selected to formulate a reasonably simple analysis. Figure 1 illustrates the

coordinate system selected and gives a representation of the

droplet geometry and of the parameter 8.

Theoretical Evaporation Time. The temperature at the

solid liquid boundary under the droplet is considered uniform

and constant during the evaporation in accordance with the

experimental observations and with the models of hichiyoshi

C 1 3 and Seki C21. The temperature at the liquid-vapor

interface is determined from consideration of mass transfer

of the vapor in the ambient. The heat conducted from the

solid-liquid interface to the droplet liquid-vapor interface

is equated to the heat required to evaporate the liquid in a given time interval. Upon reassessing the liquid inventory

and upon determining the new droplet configuration the heat

balance calculation is performed again to yield the

evaporation rate. The overall evaporation time is determined

for various droplet volumes and initial solid surface

temperatures. Note that both the convective and radiative

heat transfer contributions are negligible with respect to

the evaporative contribution. The results of the

computations are compared with experimental data in Fig. 2

Cooling Effect. The volume of the 3olid thermally

influenced by the droplet evaporation is determined via

numerical integration of the transient energy equation

written in cylindrical coordinates for the semi - infinite

solid. The boundary conditions express the symmetry of the

body about the vertical axis through the center of the wetted

area, the prescribed value of the heat flux through the solid

in the original steady state condition, the convective heat

transfer taking place at the exposed surface of the solid and

the adiabatic condition at large distances from the axis of

symmetry in the radial direction. The volume influenced by

the droplet evaporative cooling is defined as the region

where a change in the temperature of more than ten per cent

of the maximum possible temperature change is observed. The

129
(ST

FIGURE ONE - Model and Coordinate

System

FIGURE THREE - Non-Dimesi onal Volume

of Influence

FIGURE TWO - Evaporation Time:

Computations Versus

Experimental Data

CALCULATED EVAPORATION TIE (a)

FIGURE FOUR - iion-Dimesional Volume of

Influence Versus Calculat

ed Evaporation Time

I3C
maximum temperature change is the difference between the

original solid surface temperature and the contact

temperature of the liquid and the solid as determined with

Seki's model C23.

In Fig 3, the results of the numerical integration of

the energy equation are plotted in terms of the volume of the

volume of influence ( non-dimensionalized with respect to the

droplet initial volume) for various initial solid surface

temperature and droplet initial volume.

Conclusions- By considering the overall similarity between

Fig- 1 and Fig. 2, one can deduce some interesting properties

of the volume of influence- In Fig- 4, the non-dimensional

volume of influence is plotted versus the evaporation time.

A linear trend of these data is detected. This finding is

rather significant because it allows one to deduce a simple

correlation for the volume of influence.

The implication of this simple result will be apparent

in the modelling approach to the multi-droplet case.

However, the usual solid fuels to be considered in practical

applications do not exhibit high thermal conductivity,

therefore it is required to confirm these results also for

those materials. Glass and MACQR are currently investigated

both experimentally and theoretically.

References.

1. I. Michiyoshi, K. Makino, "Heat Transfer Character istics

of Evaporation of a Liquid Droplet on Heated Surfaces",

Int. J. Heat Mass Transfer, 21. 605, 1978

2. 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

Reports and Papers

1. A. K. Trehan, M. diMarzo, D. D. Evans, "Transient

Cooling of a Hot Surface by Droplet Evaporation", Proc. Eastern Session Combustion Institute, Fall Technical

Meeting, 61-1, 1985

2. M. diKarzo, A. K. Trehan, "Transient Cooling of a Hot

Surface by Droplet Evaporation", Mech. Eng. Dept. Report

Mo. 86-7, Univ. of Maryland, 1986

3. M. diMarzo, D. D. Evans, "Evaporation of a Water Droplet

Deposited on a Hot High Thermal Conductivity Solid

Surface " , MBS-IR 86-3384, 1986

4. M. diMarzo, D. D. Evans, A. K. Trehan, "The Cooling

Effect of a Single Evaporating Droplet on a Hot SemiInfinite Metal Body", submitted to the Ilnd ASME-JSME

Thermal Engineering Joint Conference, Honolulu, 1987

131
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution: University of Maryland

Grant No. : 70NANB4H0020

Grant Title : Transient Heat Transfer in Ceiling Jets

Principle Investigator : Professor Colin H. Marks

Department of Mechanical Engineering

University of Maryland

Col 1 eye Park, MD 2U742

Telephone: (3U1) 464-4216

Other Professional Personnel : Vahid Motavelli, Fellow

NBS Scientific Officer : Dr. Leonard Y. Cooper

Technical Abstract :

Introduction : The objectives of this research are to determine the transient temperature and velocity profiles of ceiling jets produced by small

fires (up to 2<w) and to determine the transient thermal response of ceilings

to such fires. Such data is needed to support the development and verification of compartment fire models, especially models concerned with the early

growth stages of fires when convection is the main mode of heat transfer.

Transient Thermal Response of Ceilings . Extensive measurements of the

transient thermal response of unconfined ceilings were made by A. Woodhouse in

the first part of this research. The data obtained were the ceiling temperature as a function of time and position from the fire plume stagnation

point. Three ceiling materials were used: Marinite-XL, fiberboard and coldrolled steel. The lower surfaces of the Marinite and fiberboard ceilings were painted with a staole hiyh emissivity coatiny. Two sets of tests were run on the steel ceiling: first with a polished (low emissivity) surface, and then

with the same painted hiyh emissivity surface used on tne Marinite and fiberboard ceilings. The fires were produced by burning stoi chi ometri c proportions

of methane premixed witn air. On each ceiliny, tests were run at six non- dimensional fire strenyths, Q*, between U.UUU7y to U.UUyy (Q* = 0/pamb Cp T amD

yl/2 h^/ 2, where Q

= heat source strenytn, PamD = ambient air density, Cn = specific heat at constant pressure, TamD = ambient air density, y

= acceleration of gravity, h = vertical distance from heat source to ceiling). A total

of twenty-four tests are in the data base. A previously-developed model which

predicts the transient thermal response of ceilings above room fires was revised, and a comparison was made between the experimental data and the

results of the revised model.

The data base are too extensive to be reproduced here, but have been submitted for publication (Reports and Papers 1) and appear in tne final report

for NBS Grant No. 70NANB4H0 0 20 (Reports and Papers 2). Typical graphical

132
results are shown in Figures 1 and 2. Fiyure 1, which shows the smoothed

temperature-time history in fiberboard for l)* = U.UU63 for a number of values

of r/h (r = radial distance from the staynation point), is typical of all such

data. The temperature rises rapidly at first then becomes constant as steady

state is reached. The temperature is the hiyhest at the staynation point at

all times and decreases with increasiny r/h. Fiyure 2 shows the radial

distribution of temperature at two different times for painted steel and for

fiberboard for the same Q* as was used to obtain the data in Fiyure 1. In both cases, the emissivity was 0.9. Note that the temperature profiles for

the steel are flatter than for the fiberboard due to rn'yher radial tnermal

conduction in the former. Thus, at late times (e.y., time - 240 0 sec.) when

conduction throuyh the thickness is neyliyible, the fiberboard has a hiyher

temperature at the staynation point, while the opposite is true at larye r/h

(r/h * 1.1).

Ceiling Jet Temperatures and Velocities . Work is currently in progress to

obtain the transient temperature and velocity distributions in the ceiling jet

for various values of r/h and Q*. The major effort to date has been to develop the instrumentation and the data aquisition and processing hardware and

software.

Temperatures and velocities are measured simultaneously at eight different

distances from the ceiling at a given radial position. The probe used for

these measurements consists of an array of eight pairs of 0.001-inch diameter

type E thermocouples stretched between vertical supports as snown in Figure 3.

The supports are mounted vertically with thei r sides parallel to the

hori zontal ly-fl owi ng fluid (the ceiling jet). Each pair of thermocoupl es lies

in a horizontal plane, and the fluid flows across eacn one. Since the second

thermocouple of the pair is mounted downstream of the first, in the same nori

zontal plane, the turbulent eddies which pass the first thermocouple at time t will pass the second thermocouple a time interval t s later, at time t+t s , as they are carried alony by the fluid's mean motion. If i is the distance

separating the two thermocouples, the fluid's mean velocity will oe i/ t s. The

turbulent eddies are detected by the thermocouples as temperature fluctuations. Fiyure 4 snows the temperature-time records for each of the thermocouples in a pair. The temperature-time record of the rear thermocouple in

the pair is essentially the same as that of tne forward one, except that it is

shifted in time by the amount t s

. The time shift t s can oe obtained by cross correlation of the two temperature-time signals and finding the value of t s for wnicn tne normalized cross correlation factor, 0 (t s ) is the largest. Tne

temperature, of course, is obtained directly from tne forward thermocoupl e

In order to sample the temperatures at a fast enough rate to obtain

accurate velocity meansurements ano then process them, the following data

acquisition system has been assemDled:

1. A Hewlett-Packard (HP) mul ti programmer (HP 6 9 4 24) with 16 data acquisition channels.

2. A 16-cnannel signal conditioning 38 series Analog Devices amplifier.

3. A series 3U0 Hewlett-Packard computer witn 1M oyte Ram and 10 M byte

storage disc used as a controller for the mul ti programmer and for data

storage and processing activities.

133
The Hewlett-Packard multi programmer has an onboard analog-to-diyital con- verter, a scanner and a 128k byte memory for rapid data collection. It can be

expanded to accommodate up to 1024 channels. The siynals from the thermocouples are delivered to the multi programmer after amplification by a factor

of about 850 in order that they have a sufficiently nigh magnitude for the

devi ce.

The data acquisition system can collect up to 4.5 million data points at a frequency of up to 100 kHz. This capability is used to devise a procedure to

monitor the ceiling jet for a period of about 30 minutes - which is about that

needed for the transient period of our ceiling models - by sampling as fast as 32 kHz for a period of about 1 second every 10 to 15 seconds. This sampling

rate for 16 channels means a sampling rate of 2 kHz per thermocouple, which

produces a 5% accuracy in a velocity of 1 m/sec as detected by thermocouples

separated by a distance of one centimeter. If the thermocouple spacing is

larger than 1 cm or if the velocity is less, a slower sampling rate will be

needed (or greater accuracy can be obtained).

Reports and Papers :

1. Woodhouse, A., Marks, C.H. and Cooper, L.Y., "An Experimental Study of the

Thermal Response of Unconfined Ceilings Above Fire Plumes," submitted for

publication, 2hd ASME/JSME Thermal Engineering Joint Conference, Honolulu,

Hawaii, March 1987.

2. Marks, C.H. and Woodhouse, A., "A Study of the Transient Thermal Response

of Unconfined Ceilings Above Small Fire Plumes," Final Report for MBS

grant number 7UNANB4H00 20 , Oct. 1985.

3. Woodhouse, A., Marks, C.H. and Cooper, L.Y., "An Experimental Study of the

Transient Thermal Response of Unconfined Ceilinys Above Sami 1 Fire

Plumes," Fall Technical Meeting of the Eastern Section of the Combustion

Institute, Philadelphia, Pa., Nov. 1985.

4. Cooper, L.Y. and Woodhouse, A., "The Buoyant Plume-Driven Adiabatic

Ceiling Temperature Revisited" 23rd ASME/AICHE National Heat Transfer

Conference, Denver, Colo., Aug. 1985. Also National Bureau of Standards

Rpt. NBSIR-85-3134 of the same title, April 1985.

134
Di\

ia

i

<dtg

o

I • • J l*3 to I

t *3t*> « O «

300 tea IOC 1200 1500 1300 2100 2«00 3700 3000 3300 3600

time csco

!00if\ 0€rti04rd : Q*»0.QQ63

r/H-Q. 3.2, Q.6.1 .0. 2.0 T/H

Fig. 1 Temperature-time record Fig c 2 Radial temperature distribution

Fig. 3 Thermocouple probe

TIME

Fig. 4 Time shift diagram

135
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution: The University of Michigan

Qrant.Np,: 60NANB5D0576

CfrfflLliflg: Radiation from Turbulent Luminous Flames

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 PgJlQnn?!: JJ?. Gore, Pre-Doctoral Scholar

D. Hully, Undergraduate Assistant

M.-C. Lai, Postdoctoral Fellow

nb.s Sgimtifis-Offlcgr 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 fundamental problems are to determine

the scalar structure of turbulent diffusion flames and to treat effects of turbulence/radiation

interactions, with emphasis on soot-containing luminous flames. These issues are being

addressed using the conserved-scalar formalism of turbulent reacting flow, in conjunction with

the laminar flamelet concept. This methodology seeks to circumvent difficulties in predicting

complex chemical phenomena in a turbulent environment During this report period, the research

concentrated on two main topics: (1) nonluminous flames, particularly flames having high

energy release rates in order to examine effects of scale; and (2) luminous flames, particularly

ethylene/air and acetylene/air diffusion flames.

Nonluminous Flames. Past work demonstrated some success in predicting the structure

and radiation properties of laboratory-scale (flame heights ca. lm) nonluminous flames using the

conserved-scalar formalism for structure and a narrow-band radiation model for radiation

properties. Recent tests of large-scale natural gas/air diffusion flames (flame heights ca. 10m),

under the auspices of NBS, 1 provided an opportunity to test these concepts for large-scale

flames, more characteristic of practical applications.

Predicted and measured mean temperatures along the axis of 100 MW flames are

illustrated in Fig. 1. Initial conditions for these flames had to be estimated, and there are

uncertainties in the degree of density weighting of the measurements; therefore, several limiting

predictions are shown. The comparison between predictions and measurements is reasonably

good for Flame 7, which had a relatively quiescent environment, similar to the assumptions of

the analysis. Flame 1 was subjected to significantly higher ambient wind disturbances and the

1 D. Evans and D. Pfenning, Oil and Gas J. 83(17), 80 (1985).

136
performance of the analysis is worse as a result Findings for five other flames, having energy

release rates of ca. 200 MW, were similar.

Aside from effects of wind disturbances, structure predictions were reasonably good;

therefore, evaluation of radiation predictions was undertaken. The measurements included the

output of five radiative heat flux sensors, having various orientations with respect to the flames.

Past work showed that effects of turbulence/radiation interactions and continuum radiation from

soot (in spite of the yellow color of the flames) were small for natural gas/air flames; therefore,

these effects were ignored in the analysis. The resulting comparison between predictions and

measurements, for the seven flames and five sensors, was very satisfying in view of potential

theoretical and experimental uncertainties, e.g., average discrepancies between predictions and

measurements were 15 percent. This suggests that present methods developed using laboratoryscale flames are promising for application to large-scale nonluminous flames.

Luminous Flames. A major hypothesis of the structure analysis is the laminar flamelet

concept, which implies that scalar properties in diffusion flames, 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). These correlations, called state relationships, can be found from

routine measurements in laminar flames, assuming a wrinkled laminar flame structure for

turbulent flames. Past work demonstrated the viability of this concept for nonluminous flames.

Present work concentrated on the luminous flames of ethylene and acetylene in air.

Measurements of state relationships in laminar flames were completed for the two

luminous flames. The results showed that concentrations of major gas species were primarily a function of mixture fraction ~ supporting the laminar flamelet concept Moreover, soot volume

fractions, which are a major property needed to compute continuum radiation from soot, were

also crudely universal functions of mixture fraction as well. Departures from universality that were observed were felt to be due to hydrodynamic features of laminar flames that may very well

be absent for turbulent flames, however, definitive evidence of this has not yet been achieved.

Typical predictions and measurements of the structure of luminous diffusion flames

appear in Fig. 2. Mean and fluctuating streamwise velocities and the mean concentrations of

major gas species, along the axis, are shown for an ethylene/air diffusion flame. The comparison

between predicted and measured mean properties is reasonably good. Predictions of velocity

fluctuations are less satisfactory, which is attributed to neglect of turbulence/buoyancy

interactions in the analysis and differences between density weighted predictions and unweighted

measurements.

The structure analysis was subsequently used for predictions of spectral radiation

intensity and radiative heat flux distributions for the flames. Typical predicted and measured

radiative heat flux distributions are illustrated in Fig. 3. These results are for ethylene/air

diffusion flames having two different burner exit Reynolds numbers. Measurements involved a

radiative heat flux sensor directed toward the flame axis and traversed in the vertical direction at a distance of 575 mm from the axis. The comparison between predictions and measurements is fortuitously good, to some extent. The analysis ignored turbulence/radiation interactions and

effects of internal radiative energy exchange within the flames, both of which are known to be

important for these test conditions. However, the former effect increases radiative heat fluxes

while the latter decreases them, tending to compensate each other. The fact that the heat flux is maximum at the flame tip, and is strongly dependent on Reynolds number for these conditions, is represented very well by the analysis.

Structure predictions for acetylene/air diffusion flames were also reasonably successful.

This system provides a severe test of radiation analysis since roughiy 50 percent of the chemical

137
energy release is radiated to the surroundings, primarily by continuum radiation from soot The

results suggest that reliable radiation predictions for flames having such properties will required

coupled structure and radiation analysis. Work along these lines is currently in progress in this

laboratory.

RspsdS-aidZazsrs

1 . M-C. Lai, S.-M Jeng and G.M Faeth, "Structure of Turbulent Adiabatic Wall Plumes,"

IJisaLlmns*, in press.

2. M.-C. Lai and G.M. Faeth, "A Combined Laser-Doppler Anemometer/Laser-Induced

Fluorescence System for Turbulent Transport Measurements," J. Heat Trans., in press.

3. M.-C. Lai and G.M Faeth, "Turbulence Properties of Adiabatic Wall Plumes," J. Heat

Trans., submitted.

4. M.-C. Lai and G.M. Faeth, "The Structure of Adiabatic Wall Plumes," Final Report,

NBS Grant No. 60NANB4D0032, The Pennsylvania State University, University Park,

PA, November 1985.

5. J.P. Gore, S.-M. Jeng and G.M. Faeth, "Spectral and Total Radiation Properties of

Turbulent Hydrogen/Air Diffusion Flames," J. Heat Trans., in press.

6. J.P. Gore, S.-M. Jeng and G.M. Faeth, "Spectral and Total Radiation Properties of

Turbulent Carbon Monoxide/Air Diffusion Flames," AIAA J.. in press.

7. J.P. Gore and G.M Faeth, "Spectral Emission and Absorption Properties of Turbulent

Ethylene/Air Diffusion Flames," Proceedings of Eighteenth Fall Technical Meeting, pp.

73.1-73.4, Eastern Section of the Combustion Institute, Pittsburgh, PA (1985).

8. G.M. Faeth, "Heat and Mass Transfer in Flames," 1986 International Heat Transfer

Conference, San Francisco, CA (1986).

9. J.P. Gore and G.M Faeth, "Structure and Spectral Radiation Properties of Turbulent

Ethylene/Air Diffusion Flames," Twenty-First Symposium (International^ on Combustion. The Combustion Institute, Pittsburgh, PA, in press.

10. G.M. Faeth, J.P. Gore, S.G. Chuech and S.-M. Jeng, "Radiation from Turbulent

Diffusion Flames," Annual Review of Numerical Fluid Mechanics and Heat Transfer.

submitted.

11. J.P. Gore, G.M. Faeth, D. Evans and D.B. Pfenning, "Structure and Radiation

Properties of Large-Scale Natural Gas/Air Diffusion Flames," Fire and Materials.

submitted.

12. J P. Gore, G.M Faeth, D. Evans and D.B. Pfenning, "Radiant Heat Fluxes from 100-

200 MW Natural Gas/Air Diffusion Flames," Nineteenth Fall Technical Meeting, Eastern

Section of the Combustion Institute, Pittsburgh, PA, submitted.

13. J.P. Gore and G.M. Faeth, "Radiation from Turbulent Flames," Final Report, NBS

Grant No. 60NANB4D0032, The Pennsylvania State University, University Park, PA

(1985).

138
x / 4 Fig. 1 Mean temperatures along

the axis of natural

gas/air diffusion flames.

<

<

X,

= ^ED. DATA 3e A 1274C O 5270

0

0 aOO 5C3 2CC 6C: I3CO AXIAL OISTA.'JCE ! mm )

a

Fig. 2 Properties along the

axis of an etnvlene/

air diffusion flame.

Fig. 3 Radiative heat flux

distributions for

ethylene/air diffusion

flames

139
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

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. W.-P. Pan, Postdoctoral Research Associate

William DeGroot, Research Specialist

NBS Scientific Officer: Dr. Thomas Ohlemiller

Technical Abstract:

Introduction . 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 the gasification reactions which occur

simultaneously with or subsequent to oxygen chemisorption. This will be

accomplished by simultaneously recording changes in the weight of the sample

and measuring the concentration of combustion products in the gas stream

flowing past the sample using the combined techniques of thermogravimetry and

Fourier transform infrared analysis. Using the same experimental design, the

influence of specific (single) ion-exchanged cations on oxidative pyrolysis of

wood, cellulosic insulation and of chars will also be studied with the aim of

designing treatments which are fire retardant without promoting smoldering

combustion.

Equipment Design and Commissioning . The Cahn TG system has been

interfaced to mi crocomputer control and coupled to the Fourier transform

infrared system. The system has been calibrated for quantitative analysis of

CO2 , CO, H

2 O, methanol, and acetic and formic acids, all of which are known to

be produced in oxidative pyrolysis of cellulosics.

Quantitative Analysis of Volatile Products of Oxidative Pyrolysis of

Wood . Concentrations of above six compounds have been determined against time

for dynamic heating of cottonwood at 3°/m. from room temperature to 550°C in

nitrogen and air and also under isothermal conditions at 250°C. The results

show unequivocally that hemicel luloses and lignin begin to degrade first and

that the major portion of the cellulose survives to higher temperatures. The

presence and nature of trace cation components such as calcium and potassium

have dramatic effects, both on low temperature (250°C) oxidative pyrolysis and

140
on subsequent oxidation of chars.

This work will be extended to newsprint, which is the basis of most

cellulosic insulation and chemical analyses will be carried out on the heated

samples at relevant times. Related chemisorption studies will be undertaken

on chars from wood, newsprint and cellulose with various thermal histories and

with controlled cation content.

141
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 1986

Institution: Graduate School of Public Health, University of Pittsburgh

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)

NBS Scientific Officer: Dr. B.C. Levin

Technical Abstract :

The current objective of this project is to establish animal models of

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

inclusion in hazard analysis of fire situations. A first model using mice

running in a track has now been completed. A second model being developed

uses guinea pigs as test subject in an attempt to better characterize the

effects of not only the asphyxiants present in smoke but also the irritants.

In this model, both distance traveled and running time are also available as

in the model using mice. However, the investigator will have complete control

of the experimental situation in the sense that distance and time can be

varied at will (within reason as in fire situations). Thus, we anticipate

that a wide range of situations can be investigated to provide the basic

parameters of escape performance under toxic atmospheres as required by

scientists developing models for fire hazard analysis.

Preliminary work has also been undertaken using the NBS cone calorimeter

as the device to thermally decompose polymers. This is an attempt to replace

the furnace used in the University of Pittsburgh toxicity protocol. The work

done so far is limited but nevertheless indicates that this investigation

should be pursued. The advantages of using this device would be numerous,

particularly in the sense that the conditions of decomposition could be varied

much more widely than when using a furnace and secondly the relevant parameters, irradiance and mass loss rate, would be available while only mass loss

rate is available with the furnace.

Reports and Papers :

Burleigh-Flayer , H., Wong, K.L. and Alarie, Y. Evaluation of the pulmonary

effects of HC1 using CO? challenges in guinea pigs. Fund. Appl. Toxicol. 5_, 978-985, 1985.

142
Kennah, H.E., Stock, M.F. and Alarie, Y. Toxicity of thermal decomposition

products from composites. J. Fire Sciences., submitted.

Malak, D.E., Stock, M.F. and Alarie, Y. Performance under intoxicating atmospheres. Fund. Appl. Toxicol., submitted.

143
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 86

Institution: Texas A&M University

Grant No .

70NANB6H0619

Grant Title: Computer Verification, Validation and Use of Selected

State -of- the -Art Fire Safety Model for One-Story MultiCompartment Buildings

Principal Investigator: Nadir Khoudj

a

Research Associate

Texas Engineering Experiment Station

Engineering Research Center

Texas A&M University

College Station, TX 77843

Telephone: (301) 921-3242

Co-Principal Investigator: Dr. Waymon L. Johnston

NBS Scientific Officer: Mr. Harold E. Nelson

Technical Abstract:

Introduction. The objectives of this investigation are to establish

generic methodologies for a sensitivity analysis and performance validation

analysis of an analytical fire safety model. These analyses are part of the

overall model evaluation process. The expected benefit of the former goal is

to inform potential users on the sensitivity of major input parameters. The

latter objective would establish levels of confidence in the model for

predicting fire behavior. The target model of this investigation is an analytical fire safety model known as Fire and Smoke Transport (FAST)

.

Sensitivity Analysis. FAST requires a large number of input parameters:

16 of them are the focus of a sensitivity analysis. This was achieved through

the use of fractional factorial to two level methodology. It required 256

different computer runs portraying respective prescribed fire scenarios.

The 16 parameters encompassed three categories of the model's input

requirements. These are:

1. Geometrical data,

2. Fire Specifications, and

3. Thermophysical Properties.

Table 1 portrays the experimental input parameters used in the analysis. Two

dependent variables have been selected to represent a comprehensive model's

output. These are the upper layer temperature, and the depth of the upper

layer of smoke in the respective compartments.
As a result from the sensitivity analysis, sensitivity coefficients from each

studied parameters are presented as a function of their respective dependent

variable. Hence, a set of results, for each compartment, is illustrated for

temperature and smoke, respectively. The relative sensitivity of each

parameter is tracked over the simulated time. A relative ranking of

parameters was achieved through the superimposition of respective sensitivity

function as shown in Figure 2. From the same figure, one may observe that

parameter S is the most sensitive followed by L. Parameters M, P a and 0

exhibit minimal sensitivity behavior.

Performance Validation. The goal of this study is to establish criteria by

which FAST predictive capabilities are measured against full-scale fire data.

This criteria is supported by a systematic statistical analysis. The

performance validation effort is still in progress.

145
TABLE 1. EXPERIMENTAL PARAMETERS

CODE NAME VALUE LOW VALUE HIGH

Geometrical Data

A Compartment Width (m) 3.5 7.0

B Compartment Depth (m) 4.0 8.0

C Compartment Height (m) 2.5 5.0

D Number of Compartment 2 4

E Vent Width (m) 1.0 2.0

F Vent Height (m) 1.5 2.5

G Vent Sills (m) 0.0 1.0

Fire Specifications

H Heat of Combustion (KJ/kg) 25,000 50,000

J Fuel Mass Rate (Kg/s) 0.002 0.004

K Fire Position Center Comer

L Ambient Temperature (K) 273 330

M

Thermophysical Properties

Conductivity (KW/mK) 0 . 18x10"

3 5x10"

N Specific Heat^ (kJ/kgK) 0.9 1.9

0 Density (kg/m ) 790 2200

P Emissivity 0.3 0.9

S Thermal Properties (Walls/

Ceilings/Floors) Existant Inexis ta

146
300

147

I

i)’,me

1

.

Upper

Layer

Temperature

Sensitivity

Functions

of

l.aeli

Parameter

(A,

It,

S)

tor

Compartment

1.
NSS-J14A (rev. 2-ao

U.3. DEPT. OP COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

4. TITLE AND SUBTITLE

1. PUBLICATION OR 2 REPORT NO.

NBSIS-86/3498

. Performing Organ. Report No. 3. Publication Date

December 1986

Summaries of Center for Fire Research Grants and In-House Programs - 1986

5. AUTHOR(S)

Sonya M. Cherry

6. PERFORMING ORGANIZATION (If joint or other than N8S, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

&958XKKnXE£DCCCSBKXX

Gaithersburg, MD 20899

7. Contract/ Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME ANO COMPLETE ADDRESS (Street, City. State, ZIP)

10.

SUPPLEMENTARY NOTES

1" ~) Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200‘word or less factual summary of most si gniflcant information. If document includes a significant

bibliography or literature survey, mention it here

)

This report contains extended abstracts of grants for fire research

sponsored by the Center for Fire Research, National Bureau of'

Standards, as well as descriptions of the internal programs of the

Center for Fire Research.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) cellulose; charring; combustion; fire models;

ignition; polymers; smoke; soot; toxicity

13.

AVAILABILITY

| xi Unlimited

| | For Official Distribution. Do Not Release to NT1S

flame spread;

14. NO. OF

PRINTED PAGES

153

a

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402. 15. Price

Order From National Technical Information Service (NTtS), Springfield, VA. 22161 $ 16.95

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