NEW NIST PUBLICATION

December 21 , 1 988

NISTIR 88-3888

Summaries of Center for

Fire Research In-House

Projects and Grants - 1988

Sonya M. Cherry, Editor

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards)

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

November 1988

75 Yun SfeRMirtriQ Anmcit Prqqf ittJ-lfM

NISTIR 88-3888

Summaries of Center for

Fire Research In-House

Projects and Grants - 1988

Sonya M. Cherry, Editor

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards)

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

November 1988

National Bureau of Standards became the

National Institute of Standards and Technology

on August 23, 1988, when the Omnibus Trade and

Competitiveness Act was signed. NIST retains

all NBS functions. Its new programs will encourage

improved use of technology by U.S. industry.

U.S. DEPARTMENT OF COMMERCE

C. William Verity, Secretary

NATIONAL INSTITUTE OF STANDARDS

AND TECHNOLOGY

Ernest Ambler, Director

TABLE OF CONTENTS

Page

Preface 1

PART I . Basic Research and Tools for "Engineered" Fire Safety

(In-House Projects and Associated Grants Funded by

NIST)

A. Fire /Materials Interaction

Polymer Gasification (in-house) 5

Flame Radiation (grant) 9

Interaction of Radiation and Conduction

in Polymeric Materials (grant) 13

A Study of the Effects of Oxygen Transport

and Temperature History on the Chemistry

of PMMA and Cellulose Pyrolysis (grant) 17

Thermal Stabilization of Polymers by CrossLink Formation (grant) 21

Computer-Aided Molecular Design of Materials

with Improved Fire-Safety Characteristics

(in-house) 25

Flame Spread (in-house) 27

Prediction of Fire Dynamics (grant) 31

Fire Propagation in Concurrent Flows (grant) 40

Upward Flame Spread on a Vertical Wall (grant) 44

Wind-Aided Flame Spread (grant) 48

Carbon Monoxide Generation From Smoldering

Combustion (in-house) 53

Kinetics of Oxygen Chemisorption and Desorption

of Combustion Products in the Smoldering

Combustion of Cellulosic Material (grant) 55

B . Flame Dynamic Processes

Turbulent Combustion Simulation (in-house) 61

Soot Formation and Evolution (in-house) 65

Soot Morphology in Flames (grant) 69

Chemical Pathways to Soot Formation in

Diffusion Flames (grant) 73

Cooperative Research in the Kinetics of

Aggregate Formation (grant) 77

Fire Modeling (grant) 81

C

.

Compartment Fire Modeling

Wall Fire Growth in Enclosures (in-house) 87

iii
Page

Consolidated Compartment Fire Model (in-house) 91

Compartment Fire Combustion Dynamics (grant) 95

Experimental Study of the Environment and Heat

Transfer in a Room Fire (grant) 97

Negatively-Buoyant Flows Generated in Enclosure

Fires by the Downward Turning of Ceiling

Jets (grant) 101

Numerical Analysis Support for Compartment Fire

Modeling Code Development (grant) 105

Transient Ceiling Jet Characteristics (grant) 107

Ceiling Flame Length (in-house) 111

Model Accuracy Assessment (in-house) 113

Graphical Presentation and Numerical Analysis

of Fire Data for Model Validation (grant) 117

D . Hazard Modeling

Carbon Monoxide Prediction (in-house) 123

Soot Particle Formation and Destruction in

Diffusion Flames (grant) 126

Radiation from Turbulent Luminous Flames (grant) 130

Smoke Transport (in-house) 135

Toxic Potency Measurement (in-house) 139

Analysis of Hazards to Life Safety in Fires' (grant) 143

Toxicity of Plastic Combustion Products (grant) 146

Expert System Approach for Spectra/Structure

Correlation for Vapor-Phase Spectra (grant) 149

Fire Data for Materials (in-house) 153

Cone Calorimeter Development (in-house) 157

Fire Hazard Assessment (in-house) 159

Mathematical Modeling of Furniture Fires (grant) 162

E . Fire Protection Technology

Engineering Analysis System & Fire Reconstruction

(in-house) 167

Fire Suppression (in-house) 169

Effect of Water on Ignition of Cellulosic

Materials (grant) 172

Transient Cooling of A Hot Surface by Droplets

Evaporation (grant) 176

A Study of the Suppression and Extinction of

Fires by Water Sprays (grant) 180

Development of a Technique to Assess the

Adequacy of the Municipal Water Supply for

Residential Sprinkler Systems (grant) 184

IV
Page

F . Technology Transfer

Technology Transfer (in-house) 189

PART I I . Timely Response to Current Fire Problems

(Projects Funded by Other Agencies and Private Sector

Organizations

)

A. Fire/Materials Interaction

Radiative Ignition in Microgravity Environment (NASA) 193

Low Flammability Composites (Navy) 194

Fire Properties of Candidate Materials for Composite

Deckhouse (Navy) 195

Burning Characteristics of Combat Ship Compartments

and Vertical Fire Spread (Navy) 196

Prediction of Thermal Degradation and Heat Release

from Aircraft Composites (FAA) 197

Coefficient of Variation of ASTM E-648 Test for

Carpets (Carpet & Rug Institute, American Textile

Manufacturers Institute, and The Man Made Fiber

Producers Association) 198

NFPA 701 Multiple Layer Drapery Flammability (ATMI

,

MMFPA, Wool Bureau) 199

Fire Performance and Toxicity of Composite Materials

(Navy) 200

A Technical Assessment of Explosive Vapor Detection

Devices (LESEL/NIST) 201

Fire Condition Effects on Smoke Generation and

Toxicity (Industry Coalition) 202

Heat Flux Sensor Calibration (FAA) 203

B . Smoke Movement and Control

Fire Growth/Suppression within Aircraft (FAA) 207

Fire Environment in Counterflow Ventilation

(grant) 208

C . Fire Protection Technology

Fire and Thermal Characteristics of Navy Fire

Fighting Trainers (Navy Training Systems Center) 215

False Alarms from Smoke Detectors (VA and AF) 216

Safety in Offshore Drilling (MMS) 218

A Study of Oil-Slick Combustion (grant) 219

An Investigation of Simulated Oil Well

Blowout Fires (grant) 223

Quick Response Sprinklers in Office Occupancies (GSA) 227

v
Page

Foam Fire Suppression (USFA) 228

Compartment Fire Model to Simulate the Effects of

Roof Vents, Sprinklers, and Their Interactions

(AAMA Research Foundation) 229

Expert System (AF) 230

Fire Risk Assessment (NFPRF) 231

Fire Risk Analysis Methodology (grant) 232

APPENDIX (Alphabetical Listing of Grants) 237

vi
PREFACE

This report describes the research projects performed in the Center for Fire

Research (CFR) and under its grants program during FY-1988.

The Center is nationally recognized as the focal point for fire research and

is the largest and most comprehensive fire research laboratory in the world,

with an extremely competent multi-disciplinary technical staff that is

supported by an excellent fire library and extensive laboratory facilities.

The Center was created by the Federal Fire Prevention and Control Act of 1974

which authorized the Secretary of Commerce, through the Center, to conduct a

fire research program directly or through contracts or grants. Therefore, in

addition to its in-house program, the Center maintains a fire research grants

program that supplements most of the in-house programs and supports most of

the academic fire research in the country. The Center, as a component of the

National Institute of Standards and Technology (formerly the National Bureau

of Standards) , responds to the needs of other Federal agencies and private

sector organizations. This report covers work performed with funds

appropriated to the Center and work performed under contract to other

agencies

.

The goal of the Center's program is to provide the technical basis for the

reduction of losses and costs of fire. The program is designed to upgrade the

knowledge of fire and the production of usable products to meet the fire

safety needs of the public, the fire services, and the manufacturing industry.

It is comprised of three elements:

• Basic research leading to the development of tools for

"engineered" fire safety; i.e., fire protection

technologies and fire prediction methods as demonstrated

in such CFR fire models as: FIREFOAM, HAZARD, and CCFM.

• Timely response to current fire problems; for example,

smoke toxicity, hazards of upholstered furniture,

investigations support and fire reconstructions.

• Serves as a focal point for fire research in the nation

by incorporating in its program academic and foreign

Guest Researchers, collaborating and cooperating with

international work in fire research, conducting fire

simulation lab workshops; as well as technology transfer

and support activities such as standards and codes

participation, FRIS, the Computer Bulletin Board, NFRSC,

meetings, etc.

(Note: For FY-89, the Center's program has been expanded in the areas of

smoke toxicity and upholstered furniture flammability. Progress on these

projects will be reported in next year's report.)

The majority of our in-house priority projects and grants work fits into the

first category, basic research and tools for engineered fire safety, and is

1
presented in Part I of this report. Our work for other agencies fits in the

second, timely response to current fire problems, and is presented in Part II.

Activities under the third element are diverse and are not included in this

report

.

Part I is organized to reflect the way in which the grants augment and support

the in-house program. Therefore, each grant report is presented immediately

following its related in-house priority project. The projects are arranged in

five groups:

Fire/Materials Interaction

Fire Dynamic Processes

Compartment Fire Modeling

Hazard Modeling

Fire Protection Technology

Technology Transfer

The projects for other agencies, presented in Part II, although usually

related to internally funded projects, are primarily designed to meet the

missions of those agencies and organizations. The distribution of subjects

prevents them from being classified in the same way as those in Part I so they

have been organized into three groups

:

Fire/Materials Interaction

Smoke Movement and Control

Fire Protection Technology

For the convenience of the reader, an alphabetical listing of all grants is

contained in the Appendix.

Most of the material in this report was written before the National Bureau of

Standards (NBS) was renamed the National Institute of Standards and Technology

(NIST). For purposes of this publication, the names are synonymous.

2
PART I. Basic Research and Tools for "Engineered" Fire Safety

(In-House Projects and Associated Grants Funded by

NIST)

A. FIRE /MATERIALS INTERACTION
1

'
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

POLYMER GASIFICATION

Professional Personnel

Takashi Kashiwagi, Project Leader

James E. Brown, Research Chemist

Scott Dolan, Chemist

Stephen Fischer, NRC Post Doctorate

Thomas J. Ohlemiller, General Engineer

William J. Parker, Physicist

Kuniyasu Kanemaru, Guest Researcher

Atsumi Omori, Guest Researcher

Project Objectives

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

determine flammability characteristics of various types of polymeric

materials

.

(2) Develop theoretical models to be able to predict their flammabi lity

characteristics

.

Scope

The approach of this project is basic and aims to: (1) understand the

mechanisms which control material flammability characteristics, (2) determine

chemical and physical characteristics of condensed phase and gas phase

processes for selected polymeric materials, (3) develop theoretical models to

be able to predict material flammability characteristics, and (4) verify the

predicted flammability characteristics and physical and chemical quantities

with results obtained from well-defined experiments.

Technical Accomplishments

The effects of thermal stability and melt viscosity on flammability

characteristics of polystyrene and poly(methyl methacrylate) were determined

by using two different pairs of PS and PMMA samples. The difference in melt

viscosity and in thermal stability for these samples was studied by comparing

the difference in observed flammability characteristics between the two

different initial molecular weight PS or PMMA samples. The difference in the

PS samples was based on the effects of melt viscosity and the difference in

the PMMA samples was based on the effects of thermal stability and melt

viscosity. For this study, a low MW PMMA sample was more stable than a high

MW PMMA sample and both low MW samples were less viscose than high MW samples.

These effects were determined on piloted ignition, flame spreading, mass

burning rate, heat release rate, and global heat of vaporization. The results

show that thermal stability of the sample affects piloted ignition delay time,

flame spreading rate, mass burning rate, heat release rate, and global heat of

vaporization. Melt viscosity of the material affects flame spreading rate and

probably mass burning rate at low external radiant flux condition. The

5
results for piloted ignition delay time and flame spreading rate are shown in

Figures 1 and 2, respectively.

Figure 1. Relationship Between

Piloted Ignition Delay Time and

Incident External Radiant Flux.

Figure 2. Comparison of Flame Spreading Distance

Against Time Between Low MW PMMA and High MW PMMA

.

6
Changes in molecular weight and in sample weight during thermal degradation of

anionically polymerized PMMA samples with different initial molecular weights

were calculated numerically and compared with experimental results. The

comparison indicates that depropagation from primary radicals as previously

thought is questionable and a new degradation path from primary radicals is

proposed to describe the behavior of the primary radicals . The primary

radical rearranges to form the polymer molecule with the unsaturated bond at a chain end. Two different degradation paths for this rearrangement are

proposed via /3 scission at the C-C bond of the pendant group. The specific

products evolved from the proposed degradation paths, CO, C02 , and CHA

, were

experimentally measured and the experimentally observed trends of these

quantities agree well with the theoretically calculated ones.

Measurements have been made on the thermal diffusivity of Douglas fir and its

char up to 550° C. Its char contraction factors have also been determined.

Interpretation of some data in the literature has resulted in the

establishment of the specific heat as a function of temperature over this

range. These thermophysical property data along with some data on the

thermochemical properties of cellulose, mannan, xylan and lignin were used as

input to the model for the heat release rate of wood in order to calculate the

heat release rate of Douglas fir exposed to an external radiant flux of 25

kW/m2

. These calculations are compared in Figure 3 with measurements made in

the Cone Calorimeter. The agreement is reasonable at this stage of the model

development

.

v - Calculated

X 20 H 0L0 200 400 600 800 1000 1200

Time (s)

Figure 3. Comparison of Calculated and

Measured Heat Release Rate.

7
Reports and Publications

• Inaba, A. and Kashiwagi, T., "A Calculation of Thermal Degradation

Initiated by Random Scission, Unsteady Radical Concentration" European

Polymer J. , 23, 871 (1987)

.

• Ito, A. and Kashiwagi, T., "Characterization of Flame Spread Over PMMA

Using Holographic Interferometry, Sample Orientation Effects" Combustion

and Flame, 71, 189 (1988).

• Inaba, A., Kashiwagi, T. , and Brown, J.E., "Effects of Initial Molecular

Weight on Thermal Degradation of Poly(methyl methacrylate) - 1. Model

1." Polymer Degradation and Stability, 21, 1 (1988).

• Kashiwagi, T., Omori, A., and Brown, J.E., "Effects of Material

Characteristics on Flame Spreading" Second International Symposium on

Fire Safety Science, 1988 (in press).

• Kashiwagi, T., and Omori, A., "Effects of Thermal Stability and Melt

Viscosity of Thermoplastics on Piloted Ignition" Twenty- Second

International Symposium on Combustion, 1988 (in press)

.

• Parker, W.J., "Determination of the Input Data for a Model of the Heat

Release Rate of Wood," Mathematical Modeling of Fires, ASTM STP 983,

Mehaffey, J.R.,Ed., American Society for Testing and Materials,

Philadelphia, 1987, 105-115.

• Parker, W.J., "Prediction of the Heat-Release Rate of Wood", DSc thesis,

George Washington, April 1988.

• Parker, W.J., "Prediction of the Heat Release Rate of Douglas Fir",

Second Internatiional Symposium on Fire Safety Science, 1988 (in press).

Related Grants

"Flame Radiation", Chang-Lin Tien, University of California, Berkely.

"Interaction of Radiation and Conduction in Polymeric Materials ", Wing Aung,

University of Maryland.

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

Chemistry of PMMA and Cellulose Pyrolysis”, Eric M. Suuberg, Brown University.

"Thermal Stabilization of Polymers by Cross-Link Formation”, Charles A. Wilkie,

Marquette University.

8
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : University of Califomia-Berkeley

Grant No. : 60NANB4D0018

Grant Title : Flame Radiation

Principal Investigator : Dr. Chang-Lin Tien

A. Martin Berlin Professor

Department of Mechanical Engineering

University of California

6179 Etcheverry Hall

Berkeley, California 94720

Telephone: (415) 642-0877

Other Professional Personnel: S. Kumar, Post Doctoral

A.J. Stretton, Ph.D. student

S.H. Park, Ph.D. student

A. Tuntomo, M.S. student

NBS Scientific Officer : Dr. Takashi Kashiwagi

Technical Abstract:

Introduction . The purpose of this research program is to establish a simple analytical

basis for the calculation of radiative heat transfer in fires. From an experimental and theoretical investigation, approximate relations have been correlated for a practical engineering application and radiation interactions have been characterized for the verification of the heat

transfer mechanism. The present work is focused on three primary topics: (1) experimental

and theoretical determination of the infrared radiation properties of hydrocarbon gases pyrolyzed from burning condensed fuels; (2) development of a simplified methodology to investigate radiative transfer phenomena in pool fires and plumes; and (3) experimental and

theoretical investigation of the radiation characteristics of agglomerated soot particles.

Radiation Properties of Hydrocarbon Gases . The infrared radiation properties of hydrocarbon gases evolved from burning condensed fuels are important to investigate their blockage effects on the thermal radiation feedback and thus the combustion mechanism of largescale fires. The experimental data of MMA vapor have been taken by a low-resolution

infrared radiation measurement apparatus and analyzed to correlate the narrow, wide and

super-band parameters [1]. The total emissivity and Planck mean absorption coefficient were

calculated with a wide range of optical pathlengths and temperatures for engineering uses. The absorption spectra of the major infrared bands of ethylene have been measured and are being correlated into engineering models [2]. The five principal infrared bands of ethylene

are centered near 949.2 cm

-1

(10.5 pm), 1443.5 cm

-

* (6.9 |im), 1889.6 cm

-1

(5.3 pm),

2325 cm

-1

(4.3 Jim), and 2989.5 cm

-1

(3.35 pm), as shown in Fig. 1.

Thermal Radiation in Fire Plumes . The thermal radiation heat flux from a pool fire and

its associated smoke plume is one of major causes of fire spread and radiation induced ignition. The effects of radiation heat transfer on fire plumes are under investigation with the aid

of simple integral formulations.

The importance of thermal radiation in a plume can be viewed by a "radiation" Peclet

number Pe R , which is the ratio of convection energy flux to radiation energy flux at the

source of the plume. While thermal radiation plays a dominant role in the fire dynamics, its

9
effects are negligible for plumes greater than 10 m in diameter due to the large value of

PeR [3]. Figure 2 shows the effects of cumulatively including various terms to the classical

plume model [3] on the plume growth.

The Gaussian profile as an averaged temperature distribution in the conventional integral

analysis of smaller plumes generates a false radiation blockage effect at the perimeter of the

plume, since the approximate temperature close to the edge of plume structures is lower than

the real temperature. The error trends inherent in using time-averaged turbulent properties

to predict the radiant heat flux from a moving fluid structure can be demonstrated by a simple analysis of an infinite slab representing a flame layer [4]. Figure 3 shows the possible errors induced by using only the mean property profile for the calculation of radiant heat flux

from an homogeneous slab oscillating with a constant amplitude and frequency.

Properties of Soot Agglomerates . The study of radiation properties of soot agglomerates

is important to analyze radiative transfer in soot-laden systems and to introduce optical diagnostic methods for inferring particulate properties.

As soot particulates are strong absorbers and emitters of radiation, an accurate determination of their radiative properties is critical to the analysis and prediction of energy transport

in flames and combustion systems. Due to the difficulties involved in the evaluation of the

properties of such agglomerates, an equivalent sphere is introduced as one that exhibits similar radiative properties as the cluster of soot particles comprising the agglomerate [5,6]. A

simple analytical reasoning establishes the ratio of the diameter of the effective sphere to the

primary particle diameter to be proportional to the cube root of the number of particles in the

cluster [6].

The non-invasive laser diagnostics techniques employed to obtain soot characteristics are sensitive to the analytical model selected for the reduction of data. Previous analyses for data

reduction have used the independent assumption whereby each particle in the agglomerate is assumed to act independently of the others in its interactions with the laser beam. This

analysis is incapable of predicting the morphological shape of the agglomerated soot particulate. By incorporating the dependent effects [7] in analyzing the scattering from agglomerates

it is shown [6] that the scattering pattern from different morphologies is unique and can be

used to identify the structure of the agglomerate, as shown in Fig. 4. Hence, the scattering

patterns can be a good tool in the optical diagnostics of soot in flames and combustion systems as a data reduction scheme.

Reports and Papers :

1. Park, S.H., Stretton, A.J., and C.L.Tien,, “Infrared Radiation Properties of Methyl

Methacrylate Vapor,’’ Comb. Sci. Tech, (submitted for publication).

2. Tuntomo, A., Park, S.H., and Tien, C.L., “Infrared Radiation Properties of Ethylene,’’

(in preparation).

3. Stretton, A.J., Park, S.H., and Tien, C.L., “Radiation Heat Transfer in Fire Plumes,’’

(in preparation).

4. Stretton, A.J. and Tien, C.L., “Structural-Averaging for Radiation Property Profiles,’’

(in preparation).

5. Drolen, B.L. and Tien, C.L., “Absorption and Scattering of Agglomerated Soot Particulates,’’ J. Quant. Spec. Radiat. Trans. 37, pp. 433-448 (1987).

6. Kumar, S. and Tien, C.L., “Effective Diameter of Agglomerates for radiative Extinction

and Scattering,’’ Comb. Sci. Tech, (submitted for publication).

7. Kumar, S. and Tien, C.L., “Dependent Scattering and Absorption od Radiation by Small

Particles,’’ ASME/A1CHE 24th National Heat transfer Conf.( Pittsburg) , pp. 9-12 (1987).

10
SPECTRAL

ABSORPTANCE

Fig. 2. Comparison of factors affecting fire plume dynamics.

ll
150

ap = 0 1 001

O

c

hA -

100

ir*r

50

Straight chain

Random cluster. fL = 0 01

Random cluster. fL — 0 1 Fracul cluster, f = 1.78 — — < V iVv

**v

a

• T ,*“ . . 0 **

O A ^ f f » .

’ • — • • o

4

A ***»*<

O — o

^ . o m = 2.0 + s 1.0

D

C

0

N * 100 °°o 0 ^oocoodo8oggo6ooo<

.1 -i i

1 I 1 i l 1 1

Fig. 4. Scattering pattern of agglomerates.

12
CENTER FOR FIRE RESEARCH

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

FY 88

Institution: University of Maryland

Grant No.

7 0NANB8H0853

Grant Title : Interaction of Radiation and

Conduction in Polymeric Materials

Principal Investigator : Dr. Win Aung (Adjunct Professor)

Mechanical Engineering Department

University of Maryland

College Park, MD 20742

Other Professional Personnel : Yen-hao Pan, Ph.D. Student

NBS Scientific Officer : Dr. Takashi Kashiwagi

Technical Abstract :

* The objective of this research is to analyze the transient

heating of semitransparent polymeric materials exposed to radiant

fluxes from high temperature sources. The research is important

in fire development because the thermal degradation of polymeric

materials may lead to the liberation of flammable gaseous

products. To simplify the analysis, we have focused on a onedimension problem. The general model we consider is a vertical

plane layer of material with negligible scattering and in local

thermodynamic equilibrium. The collimated flux at normal

incidence at the irradiated surface of the solid is considered to

be a known quantity. The transient energy equation for combined

conduction and radiation is solved for boundaries subjected to

natural convection and surface radiation. The effects of linearly

varying thermal conductivity and specific heat are also

considered.

From a heat transfer standpoint, the complete non-flaming,

transient heating cycle for a polymeric solid consists of an

initial, combined radiative-conductive heating phase involving a

homogeneous solid, followed by heating with phase transition and

gas-product liberation. Numerical solutions for the initial

heating phase have been obtained resulting in development of

opaque, cold and re-radiating models. The results of these

studies have been summarized by Finlayson, Aung, and Kashiwagi

(1987) with details given by Finlayson (1988) . In these studies,

the re-radiating model has been compared with experimental data

taken with fused silica by means of holographic interferometry.

Good agreement has been obtained. This model, which solves the

coupled nonlinear energy equation and equation of transfer,

requires relatively long calculation time, thus diminishing the

model's usefulness in the development of the eventual

thermochemical model for the second phase heating process. To

13
get around this problem, simplifications afforded by the

Rosseland approximation have been adopted and the Crank-Nicolson

numerical scheme has. also been employed in the present study.

Efforts are underway to extend the present transient heating

computation scheme to the development of the thermochemical model

that will account for phase transformation and chemical reaction.

Rosseland Approximation : A medium is said to be optically

thick if the radiation photon mean free path is very small

compared with the characteristic dimension of the medium. In the

optically thick case, emitted radiation is largely attenuated?

hence, energy transfer depends only on the conditions in the

immediate vicinity of the position being considered. In the

Rosseland approximation the energy transfer is described in terms

of the gradient of the conditions at any given position.

Crank-Nicolson Scheme ; One other reason for the large

time consumption in previous calculations was the use of the

implicit scheme. The implicit scheme is un-conditionally

convergent, but very small time steps are necessary to maintain

accuracy. With a view towards solving this problem, we have

adopted the Crank-Nicohlson scheme. The discretization of the

energy equation is as following:

pcAx(T

p

-Tp) = fAt r VW

[ Ax

kH(T

p

-T„)

Ax

+ (l-f)At

k

e tTETP

) VT?-TSh _

.t+At re 3F

Ax Ax dx

*4 tJ w

dx dt

For an explanation of the symbols used, please see Figure 1.

» Results : Rosseland approximation is valid only for

locations that are far from boundaries; therefore, the calculated

temperature profiles near boundaries are not accurate. To improve

this approximation, we have added exponential terms representing

"external flux" as source terms in the energy equation. The

external flux approach is also used in the cold model (Finlayson

et al., 1987; Finlayson, 1988), so the present improved method is

actually the "Rosseland + Cold" approach. As indicated in Figure

2 , Rosseland approximation produces acceptable results as

compared with experiments. The results displayed in Figure 2 are

for fused silica. Sample thickness is 310 mm. The

reflectivities of the external flux are determined by the Fresnel

equation. The internally emitted radiated heat flux is assumed

to be totally reflected at boundaries. The results indicate that

the slight sacrifice in accuracy as compared with the reradiating

model gives rise to a 50% reduction in processor time (800 sec vs

2000 sec on CYBER 205 computer)

.

14
The above results concerned only Rosseland approximation.

When the Crank-Nicolson method was coupled into the above, it was

discovered that the time step sizes could be increased by up to a

factor of ten without noticeable reduction in accuracy. Further

research into this is needed, since changes of this magnitude may

reflect over-conservativeness in the choice of time step

heretofore.

Figure 3 shows a comparison of computations using the new

"Cold + Rosseland" model with existing experimental results

measured for fused silica. The experimental approach employed is

holographic interferometry. The irradiated boundary is subjected

to a heat flux of 1.98 W/cm**2. The figure displays the spatial

temperature distribution at various times inside the sample.

There are five groups of temperature profiles and they

correrspond to 30, 105, 210, 375, 465 seconds after the beginning

of heating. The results show the both re-radiating and "Cold +

Rosseland" models are acceptable as compared with experiments.

The "Cold + Rosseland" model is not as accurate as re-radiating

model, as mentioned in the previous paragraph, but the former

model is certainly an acceptable approach. It is obvious from

the figure that, at later times, the calculated temperature

profiles are steeper than the experimental results. The

discrepancies may be in part due to inaccuracy in specifying the

thermal conductivity in the theoretical models, since a higher

thermal conductivity leads to a flatter temperature profile. It

should be noticed that there are temperature maxima inside the

slab, according to the calculations, but this is not evident in

the measurements.

Figure 4 shows heat from the front boundary (x = 0) for a

radiative flux of 2 W/cm**2. The change in the sign the

conducted heat is caused by a change in the direction of the

temperature gradient. Initially, the maximum temperature is

located at the front boundary itself, and heat conduction occurs

from the boundary into the solid and is positive. Later, the

location of the maximum temperature shift to the inside of the

solid, and heat conduction at the boundary reverses direction.

This figure clearly indicates but for a very short duration at

the beginning of the heating period, heat conduction transfer

occurs in the negative direction, in contrast to the assumption

employed in many existing theoretical studies on gas generation

in solids.

References

Finlayson, E.U. , Aung, W. , and Kashiwagi, T. , "Theoretical Models

for Combined Radiation-Conduction in Semitransparent Solids

Heated by External Radiative Flux," Proc. Second ASME/JSME

Thermal Engineering Conference . Vol. 1, pp. 427-432 (1987).

Finlayson, E.U., "Interaction of Conduction and Radiation in

Polymeric Materials," M.S. Thesis, Department of Mechanical

Engineering, University of Maryland (under preparation)

.

15
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16
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

InstitutionBrown 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 : Mr. William D. Lilly, Research Engineer

NBS Sc ientific O ffi ce r: Dr. Takashi Kashiwagi

Technical Abstract : Introduction

The goal of this project is the elucidation of the effects

of several key variables on the chemistry of pyrolysis of polymethyl

methacrylate (PMMA) and cellulose . These materials are often chosen in

fire research as models for vaporizing and charring solids,

respectively. The variables studied include: the heating rate of the

sample, the partial pressure of oxygen at the surface of the sample, and

sample characteristics, such as thickness, or content of flame

retardant. Detailed analyses are performed on both the vapor- and

condensed-phase products of pyrolysis, and modeling of the processes is

conducted in order to determine when they are controlled by mass

transfer effects. In the case of PMMA, it is already well established

that the major product of pyrolysis is simply the monomer, and that

decomposition thus must proceed by a simple "unzipping" process. Gel

permeation chromatography (GPC) of the unvaporized polymer residue

provides valuable insights into the nature of the process, and the

extent to which oxygen affects it at various heating rates.

The conclusions for the part of the project dealing with

PMMA will not be discussed at length here, but they may be summarized

as follows:

1. Heating rate is not important in determining the global

kinetics of PMMA degradation, in the range from 5K/min to

1000 K/min.

2 . The presence of gaseous oxygen at the surface of the

sample affects the kinetics of pyrolysis if the heating

rate is sufficiently low (5K/min) , but when a sample

is heated at a rate of lOOK/min, the kinetics

of decomposition are indistinguishable from those seen in

an inert gas

.

17
In the case of the cellulose pyrolysis process, the products

of pyrolysis are much more complex, and consist of many different gas

species and tars or oils, as well as a char residue. The effect of the

heating rate, oxygen content, and presence of retardant is seen in the

mixture of products. The present report will focus on this aspect of the

project. Previously, we have already reported the following conclusions

concerning the kinetics of cellulose pyrolysis:

1. Variations in heating rates from 5K/min to 400 K/sec have

a rather minor effect on the global kinetics of cellulose

pyrolysis

.

2. Oxygen catalyzes decomposition (or more precisely, weight

loss) during pyrolysis of thin samples of cellulose, but

only at heating rates of lOOK/min or less. At higher

heating rates, there is apparently not enough opportunity

for the oxygen to diffuse into the sample, so that it

cannot affect the rate. Whether this is because the

surface flux of products is too high to permit oxygen to

reach the surface, or the diffusivity of oxygen in the

sample is too low for ‘it to be present in significant

concentrations, is still under investigation.

Experimental

All pyrolysis experiments were carried out in a heated wire

mesh reactor. The technique involves heating a thin strip of sample (or

fine particles) inside of a wire gauze which is suspended between two

electrodes in a controlled atmosphere chamber. The wire mesh is

resistively heated at a rate which is set in advance and controlled by a

microcomputer. The temperature of the mesh is measured by a fine

thermocouple inserted in its folds, and this temperature is assumed to

be equal to the sample temperature. The products of primary pyrolysis in

the polymer (PMMA or cellulose) escape quickly from the porous mesh, and

are quenched by mixing with the cold gas in the pyrolysis chamber--

consequently the products collected at the end of an experiment are

representative of what escapes the surface of the polymer, and are not

altered by processes in the vapor phase. The gases are analyzed by gas

chromatography. The tars and oils are collected by washing the chamber

with an appropriate solvent, and are analyzed by GPC.

Cellulose from two different sources was examined and found

to give similar behavior. The first is Whatman cellulose powder CF11,

medium length fibres, with an ash content of <0.015%. The diameter of

the fibres was in the range 10 to 30 (im. The second sample was a low ash

filter paper-- Munktell's OK/S2-80-200 , with an ash content of <0.007%.

This latter sample had a thickness of 168±8|im, and thus was an order of

magnitude thicker than the powder, in smallest sample dimension.

Nevertheless, there was little significant difference between the powder

and paper.

An experiment consists of a complete cycle of heating and

cooling the sample. Unlike experiments in a standard thermogravimet ric

device, in which the mass of the sample is recorded continuously, in the

18
present device, the sample mass loss is determined only at the end of

the full temperature cycle (the sample mass is measured before and after

the experiment). The derivation of kinetic constants requires that

samples be heated to various maximum temperatures, and that integrated

rate expressions be used for data fitting. The present procedure is thus

a bit more tedious than those available for obtaining kinetic constants

from TGA data, but the present experimental method has the major

advantage that it allows examination of a much wider range of heating

rates than can be studied by conventional TGA equipment

.

Results and Discussion

Typical pyrolysis data for samples of unretarded cellulose

are shown in Figure 1, obtained at heating rates from 5K/min to

lOOOK/min. In all cases, the cooling rates of the samples were between

200 and 300K/sec. Each datum represents the fraction of mass left after

the sample was heated to the maximum temperature indicated by the

abcissa temperature. Also shown on Fig.l are calculated kinetic curves,

assuming a single, first order global decomposition process, in which

the rate of mass loss may be represented by:

dM/dt = -MAexp (-E/RT)

where M is the mass remaining at time t, A is an Arrhenius

pre-exponential factor, E is an activation energy, R the gas constant,

and T the temperature. After integration over the full time-temperature

history of the sample, it is possible to obtain A and E from data such

as shown in Fig. 1. The curves shown were actually calclated from the

values of A and E suggested by Lewellwn, Peters, and Howard (16th

Symp.on Combustion, pl471,1977), A=6. 79x10^ sec

-

-'- and E=33.4 kcal/mol.

These values had been obtained by Lewellen et al . at heating rates of

400K/sec, and show how invariant with heating rate the kinetice of

cellulose decomposition are. To fit the data in this case, however

required assuming a certain constant small fraction of cellulose always

forms char- this fraction was roughly 0.1.

Attention has recently been turned to the question of how

retardant affects the observed pyrolysis behavior of the cellulose.

Several experiments were performed at identical conditions, under inert

gas, on retarded and unretarded cellulose. The retardant studied in this

case was NaOH, wet impregnated into cellulose. The results of the tests

performed to date are shown in Table 1 (all at 40K/min heating rate)

.

Table 1. Pyrolysis Product Distributions From Retarded and Unretarded

Cellulose. Pyrolyzed to a Maximum Temperature of 700K

Retardant Level (wt%) 0 0 0 3 3 3

Tot. Volatile Yield (wt%)

Product Yields (wt%)

90.4 91.8 94.4 72.9 67.9 68.6

CO 0.8 ND 0.9 8.0 ND 8.9

co2 2.1 ND 2.4 11.3 ND 12.5

h 2 o 18.4 ND 18.7 35.0 ND 29.1

ch 4 <0.01 ND <0.01 0.02 ND 0.02

Tar ND 60.3 ND ND 7.4 ND

ND-Not Determined

19
It is apparent that the data in Table 1 confirm the

hypothesized role of retardant in shifting the pathway of pyrolysis away

from one which favors formation of flammable tar vapors, to one in which

gases with low (or zero) heating value predominate . Retarding a sample

would also be expected to result in lowering yields of soot or smoke

precursors during non-flaming combustion, because the vaporizing species

have an inherently high 0/C ratio in the retarded case.

Work is continuing on several aspects of this problem.

Reports and Papers

Suuberg,E.M. and Dalai, V., Proc. Eastern Section of the

Combustion Institute. Fall meet ina. 1 987 . pp65-l to 65-4, Nov. 1987.

Suuberg,E.M. and Dalai, V. , "Effect of Heating Rates on the

Global Kinetics of Cellulose Pyrolysis", submitted for review for

journal publication.

20
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY88

Institution: Marquette University

Grant No. 60NANB6D0602

Title :

Principal Investigator:

Other Personnel : NBS Scientific Officer :

Technical Abstract:

Thermal Stabilization of Polymers by Cross-Link Formation

Charles A. Wilkie

Department of Chemistry

Marquette University

Milwaukee, Wl 53233

Telephone: (414)224-7239

Po-Hui Chang, Graduate Assistant

James Brown

Introduction: The objective of this research program is to understand the

chemical basis of pyrolysis reactions of polymers and to use this information to develop

suitable schemes for cross-linking of polymers to produce intractable chars. The

production of char does not proceed spontaneously, rather additives are required to

promote these reactions. Each polymer has a unique set of requirements for the crosslinking reactions and these must be elucidated for each polymer in question. The

polymers that are addressed in this research are poly(methyl methacrylate) (PMMA) and

polyethylene terephthalate) (PET).

Progress to Date

PMMA. The investigation of Wilkinson’s salt, CIRhtPPhgJg, as an additive for

PMMA has been completed. We can definitely state that this compound does effect

cross-linking of the polymer and that this cross-linking leads to an increase in the

oxygen index. The reaction proceeds by an oxidative insertion of the rhodium moiety

into a carbon-oxygen bond of the polymer. When appropriately configured rhodiuminserted species encounter each other reaction proceeds with the elimination of

rhodium-methyl and rhodium-methoxide species and the formation of anhydride. These

encounters may proceed within different chains and thus lead to char. Due to

problems with expense, color, and toxicity the rhodium compound will never be used as

a flame retardant. Analysis of the requirements for an additive to function in this

reaction leads to the following conclusions:

1. the additive must be able to interact with carbonyl, i.e. a transition metal

compound is required,

2. the additive must be able to participate in oxidative insertion, i.e. it must

be coordinatively unsaturated,

3. the compound should show some catalytic activity, and

4. the additives should be colorless and available at a reasonable price.

21
Work is underway to identify compounds that fulfill these requirements. Efficacy

of the additives will be assessed by oxygen index measurements and thermal analysis

techniques as well as from reactions.

In a separate investigation we have probed the suitability of metal carbonyl

derivatives as flame retardant additives. The additive that has been studied is [CpFe(CO)2] 2

. The observation is that great quantities of gas are produced upon

reaction between PMMA and the iron compound, the gas is CO and arises from

thermolysis of the iron compound. This reaction is of interest since char formation is

also observed. Since this reaction would be of great interest if the evolution of CO

could be suppressed, we have investigated the thermolysis of the dimer. We have

delineated the complete reaction pathway which involves an initial dissociation to

monomer radicals. The complete reaction pathway is shown in Scheme 1. There are

many potential reactants in the decomposition scheme which may interact with the

polymer, we have just begun a thorough investigation of the reaction between

[CpFe(CO)2] 2 and PMMA and PMMA models.

PET. Since there are no pendant groups on the PET chain, an initial reaction is required to generate some material which may be cross-linked. We have developed a

four-step sequence for PET cross-linking, the steps are:

1 . cleavage of the PET chain to produce a vinyl ester and a carboxylic acid,

2. vinyl polymerization,

3. chain-stripping to eliminate a polymeric carboxylic acid and generate

unsaturation in the polymer chain, and

4. cyclization of the polyene produced above to yield cyclic cross-linked

materials.

Since PET undergoes all of these reactions essentially simultaneously, it is

necessary to investigate this series of reactions with a PET model, the model that we

have chosen is vinyl methylterephthalate. We observe that vinyl polymerization

proceeds thermally at a temperature as low as 200°C. At this temperature the product

is identical with that obtained by polymerization of the monomer by standard

techniques except for the presence of a small amount of acids produced by the chainstripping process. When the thermolysis is carried out at higher temperatures, the

products of the chain-stripping reaction are present in larger quantities and one may

observe unsaturation of the polymer by infrared spectroscopy. At the highest

temperatures that we have studied, 400°C, cross-linking of the polymer chains to

produce char is obvious by gelation experiments.

It is well-established that the initial step of PET decomposition is the formation

of the vinyl ester. This material may undergo two reactions, it may be subject to

further decomposition and lead to burning or_ this intermediate may be trapped by vinyl

polymerization and lead to the cross-linking scheme noted above. This appears to be

the key step in the design of a flame retardant for PET, the additive must effect the

generation of the vinyl ester at as low a temperature as possible, in order to minimize

decomposition, yet this must be above the processing temperature of the polymer. It is also required that this, or another, additive promote the vinyl polymerization reaction

and thus feed into the above delineated scheme for PET cross-linking. Work continues

in this area.

22
[CpFe(CO)2 J2 CpFe(CO)2 (

1 )

CpFe(CO)z — • Cp

Fe(CO)2

— CO - — CO

^ > CpFe(CO) — CpFe (2)

u

[CpFe(CO)]4

Fe + CO + C *+- C02

23
Utilization in Reducing Fire Loses . The work herein presented continues the

investigation of the basic chemistry that occurs between polymers and putative flame

retardants. Every step that we are able to take provides one more information in

order to design an effective flame retardant for a particular polymer. The results of

this work will be utilized to design additional experiments that will eventually lead to

a complete understanding of the chemical reactions that are involved in flame

retardation and thus permit the rational design of effective flame retardants.

Reports and Papers

1. T. Suebsaeng, C. A. Wilkie, and C. E. Brown, "Reaction of Triphenylphosphine

with Polyethylene terephthalate) and Certain Model Compounds at Elevated

Temperature," J. Polym. Sci., Polym. Chem. Ed. , in press.

2. S. J. Sirdesai and C. A. Wilkie, "Wilkinson’s Salt: A Flame Retardant for

Poly(methyl methacrylate)," J. Appl. Polym. Sci. . in press.

3. S. J. Sirdesai and C. A. Wilkie, "Mechahism of Poly(methyl methacrylate) fire

retardation by Wilkinson’s Salt," J. Appl. Polym. Sci. , in press.

4. C. A. Wilkie and B. Huettl, "The Thermolysis of Cyclopentadienylirondicarbonyl Dimer," submitted for publication.

5. P. Chang and C. A. Wilkie, "A Mechanism for Flame Retardation of

Polyethylene terephthalate)," manuscript in preparation.

24
CENTER FOR FIRE RESEARCH

1988

COMPUTER-AIDED MOLECULAR DESIGN OF MATERIALS WITH IMPROVED

FIRE- SAFETY CHARACTERISTICS

Professional Personnel

Marc R. Nyden, Project Leader

Project Objective

Develop techniques in the computer-aided design of materials for the purpose

of achieving a better understanding of the relationships between thermal

stability and the molecular chemistry of polymers.

Scope

The thermal degradation of polymers proceeds through a complex sequence of

chemical reactions that frequently culminate in the formation of toxic and

otherwise undesirable products. A computer model of this process would allow

scientists to examine the feasibility of mechanisms proposed on the basis of

limited experimental data and to explore the new degradation pathways which

occur as the result of structural alterations in the model polymers. The

initial studies have been directed to investigations of the kinetic and

mechanistic aspects of initial events in the thermal degradation of

polyethylene and related polymers

.

Technical Accomplishments

1. The Distribution of Thermal Energy in the Polymer

Computer simulations of thermally induced movements in individual model

polymers have demonstrated that the distribution of thermal energy is

statistical. All simulations were initiated by supplying uniform

distributions of atomic velocities which equilibrated to Boltzman

distributions in less than 0.1 picoseconds. The heat capacities computed from

these velocities were approximately equal to the statistical prediction of 5/2

NkB and rates for the random scissions of carbon-carbon bonds in the model

polymers were consistent with the predictions of statistical theories of

unimolecular reactivity.

2. Thermal Stability

The thermal stability of the model polymers, as measured by the minimum

temperature which results in at least one bond dissociation in a 10 picosecond

simulation, was shown to increase with decreasing molecular weight.

25
3 . Mechanistic Studies

Studies of the detailed .motions of model polymers have revealed pronounced

coiling actions in the vicinity of bond dissociations which are consistent

with proposed mechanisms for intramolecular hydrogen transfer.

Reports and Publications

"Molecular Dynamics of Initial Events in the Thermal Degradation of Polymers,

Marc R. Nyden and Donald W. Noid, manuscript in preparation.

26
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

FLAME SPREAD

Professional Personnel

James Quintiere, Project Leader

Margaret Harkleroad, Physicist

King Mon Tu, Mechanical Engineer

Robert Vettori, Engineering Technician

Steven Fischer, Post-doc

Anil Kulkarni, Guest worker

Project Objective

Develop the methodology to predict the flame spread on products and materials

by using properties determined by practical test methods.

Scope

This project on flame spread has concentrated its attention on vertical

surfaces representative of walls. Nevertheless, the applicability of its

results to other situations has been examined. For example, past work has

demonstrated that results obtained under natural convection conditions for

opposed flow lateral spread on a vertical surface have been applied with good

accuracy to similar conditions in downward wall spread and axisymmetric

horizontal spread. We have shown that the properties for lateral flame spread

on a vertical wall surface can be derived from a radiant panel apparatus which

we call LIFT (Lateral Ignition and Flame spread Test) . Some of these

properties are also applicable to other modes of flame spread such as upward

spread. More recently we have been attempting to complete the identification

of the general properties needed to predict upward flame spread by measuring

the properties of materials and testing our ability to predict upward flame

spread for these materials. The goal of this work is to establish a complete

method for predicting the performance of a wall material in any compartment

and environment

.

Technical Accomplishments

1. Developing a Standardized Test Method for Lateral Flame

Spread

Margaret Harkleroad has been leading the efforts to develop the

LIFT apparatus as an ASTM standard, and in demonstrating its

usefulness in the ISO TC 92 working group on flame spread. This

test represents a distinct change from the tests on flammability

that are based on indices of performance to a test that measures

properties based on the physics of flame spread. A draft of a

standard test method for the LIFT apparatus has been prepared and

a first ballot has been taken by the ASTM task group, chaired by

Margaret Harkleroad. This ballot yielded approximately 2

negatives out of nearly 65 votes cast, and the resolution of

these results has led to improvements in the draft standard which

27
will be balloted on again early this year. In ISO plans for a

round robin of the LIFT procedure have been formulated, and we

have been working with users of the test apparatus to insure

uniformity and consistency in its use.

2. Demonstrating the Applicability and Accuracy of LIFT

The LIFT procedure allows the determination of several properties

that would then enable the prediction of lateral or downward

flame spread as a function of the local surface temperature of

the material under arbitrary heating conditions. We have shown

that for a number of widely different materials this has

sufficient accuracy to discriminate among materials. Also, we

have shown that results obtained for lateral spread in the LIFT

apparatus are in agreement with the normal velocity to the flame

front spreading away from the upper corner of a free standing

vertical wall of PMMA, at 0.6 and 2.4 m high. In these

experiments, measurements of the velocity of the flame front have

been made along with detailed measurements of the surface

temperature just ahead of the flame's heat transfer extent. The

LIFT allows one to predict these results by a simple test

procedure with no need to measure such temperatures. The results

of these comparisons are shown (Figure 1) for PMMA at the three

scales (the smallest in the LIFT) , and for Mahogany taken solely

in the LIFT apparatus.

CNb 2-

I

100 200 300

Temperature (C)

400 500

C4

l

1 --

VELOCfTY / TEMPERATURE CORRELATION

^ O

MAHOGANY

O Measured — Predicted

\

\

100 200 300

Temperature (C)

400 500

Figure 1. Applicability and accuracy of the LIFT predictions

3. Correlating Flame Height for Burning Wall Materials

It has been shown from theoretical analyses that the flame height for a wall fire is only a function of the energy release rate per unit width

of wall burning raised to the 2/3 power. Experimental results for

line-burner fires against a wall give approximately this same result

with the power ranging from roughly 0.6 to 0.85. Data for unsteady

wall fires were analyzed this year to investigate the applicability of

this dependence of flame height on energy release rate. This

28
characteristic is valuable because the height of a flame represents a

distinct hazard on its own, the relationship can be inverted to use the

observation to yield the energy release rate, and this relationship is

needed in models proposed to predict upward wall flame spread. The

flame height was measured for 0.3m high PMMA and wood particle board

burning under a range of radiant heating exposures. The energy release

rates were determined from the instantaneous mass loss rates of the

samples. These transient data for the various conditions and both

materials are plotted in Figure 2. The results are within 25% of

theory and line -burner data which serve to give confidence in the use

of this correlation to the modeling of the dynamic process of flame

spread.

Figure 2. Flame height for transient wall fire of wood and PMMA

4. Predicting Upward Flame Spread

We have begun to evaluate our ability to predict upward flame spread on

particular wall construction materials. This has been done through a

modeling strategy, collecting the needed material fire property data

for the model, and conducting tests on upward flame spread on samples

1.2 and 2.4 high. The results have been promising in two respects:

(1) all of the data can be developed that is needed for the model

(some comes from the LIFT apparatus), and (2) initial results for

previous experiments on wood particle board were able to predict the

extent of spread for various ignition flames. These results show that

the model is capable of predicting the nonsustained spread case as well

as the rate of spread in the sustained case. This is very important to

the evaluation of a product's performance since it can reveal under

what conditions sustained spread is possible. In a previous study we

found that it is necessary to preheat this particle board to permit

sustained upward spread. It required sufficient preheating at 0.42

W/cm2 or approximately a minimum surface temperature of 100° C. The

predicted results for the particle board are shown in Figure 3 for two

values of K, a coefficient in the formula for flame height. The lower

value considers a fixed flame heat flux over the continuous luminous

flame height, and the higher value corresponds to the flame tip. A

unique feature of this approach has been to derive a transient mass

loss rate for the material directly from a small scale experiment that

29
has been designed to simulate the flame heating conditions for the

early part of the process. This has to be generalized to include a flame heat transfer model that includes the radiation component

indicative of the material and size effect, and to establish a method

for interpreting material calorimetry tests, such as the Cone

Calorimeter, to permit the prediction of the transient mass burning

rate of the particular material.

Figure 3. The maximum distance spread on wood for a range of

igniting flame energy release rates, experimental results and theory.

Reports and Publications

"Upward Turbulent Flame Spread on Wood Under External Radiation", S.

Saito, F. A. Williams, I. S. Wichman, and J. G. Quintiere, ASME Paper

No. 87-HT-56, NTHC , Pittsburgh, PA, August 9-12, 1987 (to be published

J. Heat Transfer )

"The Application of Flame Spread Theory to Predict Material

Performance", J. G. Quintiere, J . of Research of the National Bureau of

Standards . 93 , 1, Jan - Feb, 1988.

"Ignition and Flame Spread Measurements of Aircraft Lining Materials",

M. Harkleroad, Nat. Bur. Stand., NBSIR 88-3773, May 1988.

"State of Fire Research and Safety", J. G. Quintiere, Second

Proceedings of the Fire Safety Science International Symposium", Tokyo,

June 13 -17, 1988.

Related Grants

"Prediction of Fire Dynamics", J. de Ris, R. L. Alpert, Factory Mutual

Research Corp.

"Fire Propagation on Concurrent Flows", A. C. Fernandez Pello, U. of

Cal . (Berkeley)

.

"Upward Flame Spread on a Vertical Wall", A. Kulkarni , Penn. St. Univ.

"Wind-Aided Flame Spread", F. Fendell, TRW Space and Technology Group.

30
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution: Factory Mutual Research Corporation

Grant No.

60NANB5D0560

Grant Title: Prediction of Fire Dynamics

Principal Investigators: John de Ris and Ronald L. Alpert

Other Professional Personnel: G.H. Markstein

M.A. Delichatsios

L. Orloff

H.W. Emmons

NBS Scientific Officer: Dr. Henri Mitler

Technical Abstract:

This work is divided into four tasks, each of which is designed to provide

essential inputs for comprehensive models of burning and fire growth. Such

predictive models will reduce fire losses through the development of sciencebased techniques for rating material flammability.

Task 1. Prediction of Fires in Buildings (H.W. Emmons)

Please see a separate summary under this title.

Task 2. Fire Radiation and Toxic Product Release - An objective of the

research conducted over the past year was to develop correlations that predict

the radiation from buoyant turbulent jet flames for a wide range of fuels in

terms of the respective fuel smoke point, chemical bonding structure, and the

ambient oxygen concentration. This is an ongoing study in which our results

will be extended into simulations of turbulent wall fires and the prediction

of incomplete combustion product generation, particularly those that are corrosive or toxic. The correlations developed in this study will provide essential inputs on flame radiation for fire growth predictions.

The experiments were performed inside a 1 .2 m dia water-cooled enclosure

which allowed us to independently control the adiabatic stoichiometric flame

temperature and stoichiometric mass ratio by adding: 1) either oxygen or

nitrogen to the supplied ambient air, and 2) nitrogen to the supplied fuel.

Measurements of the radiant fraction (of the theoretical heat release rate)

were obtained with a wide angle radiometer with parallax corrections derived

from a traversing horizontal slit radiometer. The burner nozzles were gold

plated to minimize radiative emission from their hot surfaces. Considerable

testing of various experimental conditions was performed to insure reproducibility and to minimize dependence on the specific experimental conditions.

For the measured 6-20 kW fires the radiant fractions were effectively independent of the: 1) overall heat release rate, 2) fuel-jet orifice diameter,

3) degree of oxidant over ventilation , and 4) fuel-mixture supply temperature.

Measurements were made over a very wide range of stoichiometric mass ratios,

S, ranging from 2 to 20, and adiabatic flame temperatur es, Tad , ranging from

31
1 900K to 2600K. For typical values of S _> 12, the radiant fractions were independent of S and all the fuels had a similar dependence of radiant fraction,

X Ri , on T ad described by the formula:

(T - T ) y*

ad b

x Ri

‘Ri

(T* - t ) + y* (T - T* ) ad b

; x Ri ad ad ;

where xj^ is the reference value of Xr^ "standard conditions" [T* d = 2200K

and S* = 15], and T

b

•= 1 675K was a good empirical fit for all measured fuels

( CH^j , C

2 H

2

, C

2 H^, C 2 H^, CgHg , CgHg, C^Hg). The values of x$i were ranged in

agreement with the independently measured classical laminar smoke-point values

at the identical "standard condition".

For smaller values of S < 12 the radiant fractions decreased with decreasing S. The amount of decrease was considerably greater for the alkenes (C 2 H^,

CoHg and C^Hg) and alkyne (C 2 H

2

) than for the alkanes (CH^, C

2 Hg and CgHg).

Thus for S < 12, there is some additional effect of chemical structure on Xr

beyond that included in the classical smoke point. We are currently measuring

the radiant fractions for more fuels to examine this more complicated dependence on the chemical structure of the fuels.

Publications

1. Orloff, L. , de Ris, J., Delichatsios , M.A. : "Radiation from Buoyant Turbulent Diffusion Flames," Poster Session Paper P22-156, 22nd International

Symposium on Combustion, Seattle, WA, Aug. 1^-19, 1988.

Task 3. Wall Fire Flame Radiation - The objectives are extensions of previously established relationships for fire radiation to the case of vertical walls

burning, comparison of the results with existing analyses of wall burning, and

development of improved models of wall burning based on experimental findings.

As in other related work the significance of studies of fire radiation rests

on the fact that in many fires energy transfer from the flame to the fuel and

to the surroundings occurs predominantly by thermal radiation. The rate of

fire growth and the spread of fire to new fuel elements depends critically on

this radiant energy transfer, and its quantitative assessment is thus essential for predicting fire behavior.

In the present task, wall fires of solid fuels are simulated by burning

gaseous hydrocarbon fuels on a water-cooled vertical porous metal surface

under steady-state conditions. The burner is subdivided into a number of

panels of equal height, so that the simulated pyrolysis height can be varied

by the choice of the number of fuel-supplying panels. In addition, the limiting case of zero pyrolysis height can be studied by supplying the fuel from a slot burner at the base of the wall.

Fuel is supplied to the burner by electronic flow controllers, and the

heat transferred to each panel is determined from the temperature rise of the

cooling water, measured by differential thermocouples. The total radiant

emission from the fire is measured with a wi de-vi ew-angle radiometer employing

a spectrally flat thermopile sensor. In addition, the vertical distribution

32
of radiant power per unit height emitted by narrow horizontal slices across

the width of the fire is measured with a scanning slit radiometer. The scan

along the height of the fire is obtained by the use of an electromagnet i cally

deflected plane front surface mirror operated in a linear ramp mode. A fastresponse spectrally flat pyroelectric sensor is used in this instrument. A

new version of this instrument, improved by the use of spherical-mirror

optics, has been recently evaluated, and the expected enhanced signal-to-noise

ratio and vertical resolution has been confirmed.

Initial work under this task was perf ormed with a previously developed

burner consisting of six 380-mm wide and 220-mm high sintered-metal panels

topped by a 520-mm high metal plate. Since the fine-grained sintered metal of

the burner was susceptible to clogging by soot, the work was restricted to

ethane, which produces relatively small amounts of soot. A new burner incorporating various design improvements has been assembled, and work with this

burner is about to begin. One important new feature is the use of an outer

layer of coarse-grained sintered metal that is expected to prevent permanent

clogging by soot, so that future work can be extended to fuels of greater

sooting tendency than ethane. The height of the individual panels has been

reduced to 127 mm to provide improved resolution of the simulated pyrolysis

height. As another new feature, heat transfer instrumentation has been incorporated in the metal plate above the burner panels.

Although the data obtained previously with the old burner are of a preliminary nature, they nevertheless provided valuable results which have recently

been examined in greater detail. In this recent work,"1 correlations have been

established between the radiative fraction and the convective B-number, and

between normalized values of radiant flux and height. These relationships and

their significance are being further investigated and it is planned to extend

the correlations to the data to be obtained with the new burner. The results

will also be compared with existing theoretical models of wall-fire combustion

and will also be used to extend correlations between flame radiation and fuel

smoke points to wall fires.

Concurrently with the study of wall fires, measurements of smoke points

and of radiant emission from laminar diffusion flames have been performed.

This continuing work, which is also partly supported by the Gas Research

Institute, is of interest for the wall-fire study in connection with correlations between flame radiation and smoke points and is also of importance for

the study of turbulent flames under Task 2. In recent work on laminar

flames, ’ ^ a new method for smoke-point determination based on measurement of

radiant extinction by soot in the combustion products has been developed to

replace the customary visual observation. The results of this work led to

general correlations for the smoke point and for the radiant emission, which

will be of value in the formulation of models for soot formation and radiant

emission, both of laminar flames and of turbulent flame jets and wall fires.

Publications

1. de Ris, J. , ’’Radiation from Diffusion Flames - Smoke Point,” presented at

the 9th Joint Panel Meeting of the UJNR Panel on Fire Research and Safety,

May 4-8, 1987.

33
2. Markstein, G.H., "Correlation for Smoke Points and Radiant Emission of

Laminar Diffusion Flames,” presented at the Spring Technical Meeting, Central States Section, The Combustion Institute, Argonne, IL, May 11-12,

1 987.

3. Markstein, G.H., "Correlat i ons for Smoke Points and Radiant Emission of

Laminar Hydrocarbon Diffusion Flames," to be presented at the 22nd International Symposium on Combustion, Seattle, Washington, Aug 14-19, 1988.

Task 4. Transient Pyrolysis and Flame Radiation from Charring Fuels - Measurements needed to handle the vertical fire growth problem include material pyrolysis rates (including charring materials) and flame radiation characteris tics

which are being obtained in the new flammability apparatus in the Basic Research Department of FMRC. Coupled with models for a) gaseous burning (developed for pool fires and walls at FMRC), b) heat transfer, c) pyrolysis rates,

and d) flame spread, already developed as a part of this program, the measured

flammability properties will lead to predicting the occurrence and the development of sustained flame spread on a charring, composite or laminated fuel.

The following results have been achieved during the previous reporting

period:

1) The new material flammability apparatus has been successfully used to obtain pyrolysis rates for charring materials (results for two different particle boards, Douglas fir wood and PMMA, as a baseline measurement, are contained in Reference 2). Preliminary analysis of the data shows that the pyrolysis behavior of charring materials is consistent with semi-analytical models

developed earlier at the Basic Research Department of FMRC.

2) An outline for a comprehensive upward flame spread model'1 has been assembled. Moreover, a simplified reduction of the model has allowed identification of the parameters controlling flame spread. These parameters are:

X R

radiant fraction from the wall fire

AH

c a parameter proportional to the ratio of

flame height to pyrolysis length.

X R AH

v

2 2

k it (T - T ) w p s a

w

a characteris tic ignition parameter

the chemical heat release rate from the fire

Y ratio of any external heat flux to the flame

radiation heat flux

Notice that the present program addresses the charact erization of xr and ^ch

(through the pyrolysis rate and heat of vaporization).

34
A significant achievement during the previous reporting period was undoubtedly the successful operation of the new material flammability apparatus.

Over fifty tests 2 have been conducted with the assistance of Prof. K. Saito

for four materials (2 particle boards, Douglas fir wood, and PMMA) and heat

fluxes ranging from 2 to 16 W/cm , which is a unique range of operation. In

addition to the weight loss, temperatures at four locations inside the samples

(12 cm in diameter, 1 or 2 cm thick) were measured. Flame radiation was not

measured during these tests because no steady buoyant flame-jet was established. For this reason the exit nozzle has been recently modified by using a

conical diffuser with an exit nozzle diameter of 1 in., large enough to allow

the establishment of a turbulent buoyant flame. In addition, provisions have

been made to purge the quartz plate by using methane fuel instead of heated

nitrogen through the annular sand box distributor (see Fig. 1). We have found

in preliminary experiments that a purge by methane readily stabilizes the turbulent buoyant flame of the pyrolyzing gases on the exit nozzle’s perimeter.

We plan to unravel the effects of methane on the flame radiation of the pyrolyzing gases by measuring the radiation from turbulent flames of gaseous mixtures of methane and other gaseous fuels (e.g. propane, acetylene) whose radiation properties are known. Such measurements can be made in the material

flammability apparatus by introducing fuel gases in place of a charring

sample.

After we completed the experiments with the particle board sample, we

found out that its density was not uniform: the density was thirty percent

less at its center than near its top or bottom surface. To allow a direct

comparison with theory, we plan to use a uniform charring fuel stock for additional tests by manufacturing, probably, our own cellulosic board. The assembled data are being analyzed, but it is worth sharing some of the results of a preliminary analysis:

1) By conducting tests with carbon blackened and pure particle boards, it was

shown that spectral absorption selectivity affects the "ignition” time, but

not the ensuing pyrolysis history;

2) It is encouraging that the measured pyrolysis histories are consistent

with our semi-analytical model for the pyrolysis of charring and noncharring

mat erials

3) The time to "ignition" (i.e. copious pyrolysis) is controlled by surface

reradiation losses, which are not properly accounted for in existing

analytical models and methodologies. A new semi-analytical model has been

developed to account for this important phenomenon. Our recent theoretical

analysis and experimental results have indicated that in depth radiation

absorption in "black" PMMA significantly affects the "ignition" or pyrolysis

time. We have developed a procedure to uniformly cover the surface of all

samples with a black paint which would absorb all radiation at the surface.

Such a procedure will render results which would be easy to interpret because

"ignition" times would depend only on conduction losses into the solid (plus

surface reradiation, of course).

Our immediate plans include: a) analyze the numerous experimental pyrolysis data with particle board; b) repeat experiments with black PMMA covered

35
with a thin layer of black paint; c) use cone calorimeter to document spectral

radiation effects (in comparison with quartz heaters); and d) measure flame

radiation from the burning of pyrolyzing gases.

Publi cations

1. Del ichatsios , M.A., "An Outline for a Comprehensive Model for the Burning

and Upward Flame Spread on Charring Materials in Wall Fires," Eastern Section Meeting of the Combustion Institute, NBS, November 1987.

2. Saito, K., et al . , "Transient Pyrolysis Tests of Charring Material under

External Radiation up to 16 W/cm , " Central Section Meeting of the Combustion Institute, Indianapolis, May 1988.

36
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : Factory Mutual Research Corporation

Grant No: 60NANB5D0560

Grant Title : Prediction of Fire Dynamics ~ Task 1. Prediction of Fires in Buildings

Principal Investigator: Prof. Howard W. Emmons, Retired

Division of Applied Sciences

Harvard University

Cambridge, MA 02138

NBS Scientific Officer: Dr. Henri Mitler

Technical Abstract:

Introduction The computer Fire Model for calculation of the growth of fire in an

enclosure has been under development at NBS for several years. This project has

contributed to this effort as follows:

1 . Improve the user-friendly nature of the latest update program "FIRST."

2. Examine a range of cases to find and remove "bugs."

3 . To improve the required heat transfer relations for a ceiling jet.

1 . The user friendly input. The input at user's choice can be run through completely

or input specific data introduced through a menu. Many minor improvements have been

made such as the use of the notation (Y/[NJ) which answers a question with either caps or lower case letters and for which a simple <Retum> selects the commonest response [ ].

2. Over 1 10 specific cases have been run. These runs examined the effect of many

variables, e.g., size of room, size of vent, height of fuel, height of vent, location of fuel.

A few of these results are presented in a paper at the second meeting of the International

Association of Fire Safety Science. The most important effect on fire growth are those

changes that affect the availability of oxygen.

During these runs, 18 specific problems were found. A list of all these needed

fixes has been given to NBS for future incorporation into FIRST. These problems

included items such as permit user to add or remove objects through the menu, there is a

fraction of "hydrocarbons," f(HC)> listed in the output but not in the input, sometimes a burning object is starved of O2 and unstarved every two seconds, if the user asks for a nonexistent object or vent, the program should not bomb but should return to the menu so

the user can fix it, etc. (The full list is available on request.)

This series of runs also disclosed a long list (38) of specific needed permanent (or

user selectable) phenomena additions. This list included such items as burning in the hot

layer, wall burning (now being implemented at NBS), a variable property fire (e.g., initial

fire spread and later char burning), sprinkler response and extinguishment, etc. (The full

list is available on request.)

37
The most severe "bug" is, of course, the failure of the program to complete a run

because of "Divide by Zero," "Underflow," "Overflow," or failure to converge at the

smallest time step. Time did not permit the clarification and permanent removal of most of

these problems but three types of "cures" were often effective.

a. Set a smaller tolerance. This gave greater accuracy of a converged solution

and sometimes the next time step came easier.

b. Relax the tolerance. Even a very poor tolerance as bad as 0. 1 (instead of

10~5

) gave answers to two percent except in critical regions (immediately

after target ignition) where errors might be 20% (satisfactory for many

practical fire purposes).

c. Make some small (1%) change in heat of pyrolysis, heat of combustion, or

move an object. This can remove an accidental coincidence of difficulties

such as "Divide by Zero."

Various test results, furniture calorimeter data, etc., should be made available to

FIRST via the following observations. An object or objects under test that are to be

represented as a single object in FIRST should have properties determined by:

1. x, k, p, c, Tig) set for item quickest

to ignite (as for example a cellular

plastic cushion).

2. e set high (~ 0.98) because char is

generally carbon and is black.

3. M for each component set at fraction

you expect to actually bum (there is

often a lot of char unbumed).

4. The initial burning radius depends on

the size of the ignition source (see

figure).

5. The fire spread parameter A depends

upon the spread mechanism and is

generally somewhat larger than the mass

weighted average of component A's. It sets the slope of the rapid rise (see Figure).

6. The effective fuel area sets the maximum rate of heat release (it approximates the fuel

projected area).

7. The burnout parameter B sets the time of char burnout.

8. All other parameters are the mass weighted average.

3. Ceiling jet heat transfer. When hot gas, without combustion, at temperature Ts (initial temperature To) flows at constant rate u along a ceiling at initial temperature Tw, it transfers heat to the ceiling at rate h (Ts - Tw ) and also loses heat to the ambient at the rate

ha (Ts - Ta ). The wall, too, loses heat to the ambient at the rate hwa (Tw - Ta). Thus, the

ceiling jet is cooled while the ceiling is heated. If a corridor were very long, both the

ceiling jet and ceiling would have temperature Ta at large distances.

radius

38
The solution to this heat transfer process is:

0S(X> x) = e

-(P,+ P,)x

{

e"

(p»+p«)(T"

x) Iq(2^ P*Psx(t-x) )

r T_z

"P (Pw "P Pwa) I Jo

e

(Pw+Pw*)t I0 (2VPwPsXt) dt} u(t-x)

0w(X.t) = (Pw+Pwa) eKP‘+P‘)X

J

*-x

e

~<pw

+pwa)t dt U(x-X)

es - 0w = e

a>s+Pa>x

e

(p»+pw>)(t x) Io(2^PsPwx(t-x)) u(x-x)

T -T T -T

where 6S = _

s ~a

, 9W = * ~

a

, x = x/L , x = t u/L,

1 0-1

a

1 0_I a

u(x-x) =

(X <X)

(i>X)

P= *L_ s Ps U 8SCPS p = » 1 w

hL

,Pa =

h^L

Pw u SwCpw

’ a ps u 6S Cp

P = > A wa

pw ti SwCpw

Io (z) is the modified Bessel function of the first kind. % is the fractional length, x is the

fractional location of the leading edge of the ceiling jet. If the ceiling jet has not reached the

point of interest (x < %) » 0S = 0w = 0, i.e., the jet and wall are both at ambient

temperature.

While these formulas appear complex, they can be and will be precalculated and

made available as simple algebraic expressions.

39
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : University of California, Berkeley

Grant No : 60NANB7D0737

Grant Title : Fire Propagation in Concurrent Flows

Principal Investigator : Professor A.C. Fernandez-Pello

Department of Mechanical Engineering

University of California

Berkeley, CA 94720

Other Professional Personnel : B. Amos, Doctoral Graduate Student

L. Zhou, Doctoral Graduate Student

NBS Scientific Officer: Dr. H.R. Baum

Technical Abstract :

A research program is being conducted to study the mechanisms controlling

the spread of flames over the surface of a solid combustible in an oxidizing gas

flow. The objective of the research is to provide fundamental information about

the spread of fire for its use in the development of models of fire growth in

rooms, and of test methods of the flammability of materials.

Research performed during this reporting period includes two theoretical

studies (one on ignition and the other on flow assisted flame spread) and an

experimental study of turbulent flame spread. The ignition work consists of a numerical analysis of the ignition and flame establishment over a combustible

solid that is vaporizing in a stagnation point air flow due to an externally

applied irradiance. The flame spread work is a numerical model of the spread of

flames over a thin charring combustible in a gas flow moving in the direction of

spread. The experimental work is a study of the effect of flow turbulence on

the rate of opposed flow flame spread.

Stagnation Flow Ignition of a Vaporizing Surface

In this work, an analysis is developed of the ignition of a vaporizing flat

combustible solid and of the subsequent establishment of a diffusion flame over

it, in a stagnation point oxidizing gas flow. The gasification of the solid is

produced by an external radiant flux applied perpendicular to the surface.

The vapor ignition process is modeled as follows. A planar combustible

solid at its vaporization temperature is in a stagnation point air flow at

ambient temperature. At the initial time the solid surface is suddenly subjected to a constant radiant flux perpendicular to the surface. The solid

absorbs the radiation at its surface and immediately begins to vaporize, mixing

with the ambient air. The vaporized fuel absorbs some of the incoming radiation

and eventually becomes hot enough to initiate the ignition of the fuel/air mix40
ture. After the onset of ignition, the external radiation is removed and the

chemical reaction is let to evolve until it becomes a self-sustained, steady,

diffusion flame. In the analysis it is assumed that the adsorption of radiation

by the gas is independent of the temperature, but that is directly proportional

to the fuel concentration. The combustion of the mixture is modeled using a one

step chemical reaction of the Arrhenius type.

The problem governing equations are solved numerically using an implicit

method except for the temperature in the reaction rate term which is handled

explicitly. A movable grid is used to track the propagation of the flame after

ignition. The predicted evolution of the temperature and species profiles shows

the existence of three regimes. The first regime corresponds to the period from

the instant when the external irradiance is first applied to the onset of ignition. The evaporation of the fuel causes the generation of two opposing stagnation point flows, one of fuel and the other of oxidizer, at whose interface the

fuel and oxidizer mix by diffusion. During this period the fuel vapor absorbs

radiation and heats up eventually causing the ignition of the mixture. After

ignition, the combustion reaction propagates through the mixture away from the

solid surface. This premixed propagation process leads to the generation of a diffusion flame once all the fuel ahead of it is consumed. The diffusion flame

adjusts its position until finally it reaches its steady state position near

the wall. A characteristic example of the predicted evolution of the temperature distribution is shown in Fig. 1.

Model of Concurrent Flame Spread Over a Thin Charring Solid

A theoretical model is developed of the spread of a flame over the surface

of a thin combustible solid in a gas flow moving in the direction of flame propagation. The combustion reaction and the solid pyrolysis are modeled respectively with a one-step, second order, and with a zero order Arrhenius rate.

The charring of the solid is modeled by treating the solid as a two component

material, the combustible component that gasifies, and the char that remains

occupying the initial solid volume. To simplify the mathematical solution of

the problem, a Hagen-Poiseuille flow is prescribed, thus eliminating the need

for using the momentum conservation equations. The transient, reactive, gas

phase balance equations of energy and species coupled at the interface to the

solid phase balance equations are solved numerically to describe the evolution

of the flame and solid properties, and through them to predict the variation

with time of the flame, pyrolysis and burn-out distances and their dependence on

the flow velocity.

The model is applied to the description of the spread of flames over paper

sheets in a concurrent air flow. In Fig. 2 the predicted variation with time of

the flame, pyrolysis and burn out distances are presented for several flow velocities. The experimental data of Loh and Fernandez-Pello (1st Int . Symp. Fire

Saf . Sci., 65, 1986) are included for comparison. It is seen that the predictions of the model agree well with the experiments. Particularly important is

the description of the transition of the flame spread process from an initial

accelerative stage to a final steady state. The transition is determined by the

interaction between the progress of the pyrolysis and the burn out fronts, and

their effects on the flame length. The model also predicts a flame extinction

limit due to increased concurrent velocity that is very close to the experimentally determined value.

41
Experiments of Turbulent, Concurrent, Flame Spread

Experiments are currently underway to study the effect of flow turbulence

on the rate of flame spread over a solid combustible. The experiments are

carried out in a combustion tunnel facility that has been described in a previous report. The turbulence intensity in the tunnel test section is varied by

means of grids of different sizes placed at the exit of the tunnel converging

nozzle. The velocity and turbulence intensity of the flow field are measured

with a Laser Doppler Velocimeter. The flame spread rate is obtained from the

temperature history of thermocouples placed at fixed distances along the combustible surface.

Currently we are performing experiments to measure the rate of flame spread

over the surface of thick (1/2") PMMA sheets as a function of the velocity and

turbulence intensity of an air flow opposing the direction of flame spread. The

opposed flow mode of flame spread was selected to do the initial experiments

because, it being easier to measure accurately the spread rate, it permits

better familiarization with the experimental technique. Once this initial study

is completed, the study of the effect of turbulence on the concurrent mode of

flame spread will follow.

Preliminary results of the measurements of the opposed flow flame spread

rate over PMMA as a function of the flo*w velocity for turbulent intensities of

1%, 15% and 20% are presented in Fig. 3. The results, although preliminary,

show that for a given flow velocity the spread rate decreases moderately as the

turbulence intensity increases. This result is explained by the fact that as

the flow turbulence intensity increases the transfer of heat upstream from the

flame front decreases, and consequently, so does the flame spread rate.

Reports and Papers

1. Kodama, H. , Miyasaka, K. and Fernandez-Pello , A.C., "Extinction and

Stabilization of a Diffusion Flame on a Flat Combustible Surface with

Emphasis on Thermal Controlling Mechanisms," Combustion, Science and

Technology, 94, 1-6, pp. 37-50 (1987).

2. Amos, B., Kodama, H. and Fernandez-Pello, A.C., "An Analysis of the

Ignition by Vapor Radiation Absorption of Vaporizing Fuel at Zero Gravity,"

presented at the AIAA 25th Aero. Sci. Meeting, Reno, Nevada, 1987. Also

Progress in Aeronautics and Astronautics (in press), 1988.

3. Amos, B., "Ignition and Flame Propagation Studies Over a Flat Fuel

Surface," Ph.D. Thesis, Department of Mechanical Engineering, University of

California, Berkeley, August 1987.

4. Di Blasi, C., Cresticelli, S., Russo, G. and Fernandez-Pello, A.C.,

"Predictions of the Dependence on the Opposed Flow Characteristics of the

Flame Spread Rate Over Thick Solid Fuels," 2nd Int . Symp. of Fire Safety

Sci., (accepted) Japan, June 1988.

5. Di Blasi, C., Cresticelli, S., Russo, G. and Fernandez-Pello, A.C., "Model

of the Flow Assisted Spread of Flames Over a Thin Charring Combustible,"

accepted for presentation at the 22nd Symposium (Int.) in Combustion,

Seattle, WA, August 1988.

42
3MniUM3dW31

FLAME

,

PYROLYSIS

.

BURN

OUT

DISTANCES

t [«]

TIME FROM IGNITION

FIGURE 2. FIGURE3.

43
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : The Pennsylvania State University

Grant No. : 60NANB4D0037

Grant Title : Upward Flame Spread on Vertical Wall

Principal Investigator : A. K. Kulkarni

Department of Mechanical Engineering

The Pennsylvania State University

University Park, PA 16802

Other Professional Personnel : S. Fischer, NBS

R. Vettori, NBS

Scientific Officer: K. D. Steckler

Technical Abstract :

Introduction : Upward flame spread is highly significant for fire growth

because it is more rapid than lateral or downward spread in wall fires. An

experimental and theoretical study of upward flame spread on vertical walls

was initiated this year. The overall objective is to develop a predictive

methodology to determine if there is sustained upward spread on a given

material, and if so, to calculate the upward flame spread velocity using the

known or easily measurable properties for that material. Specifically, a model

for upward spread is developed and experiments are designed and conducted in

order to provide proper input to the model and to validate the model

capabilities. Such an algorithm for the prediction of upward flame spread

will allow zone models to evaluate the fire growth and hazard in buildings and

compartments more accurately and also it will allow a quantitative assessment

of flammability of materials burning in vertical orientation.

Development of Mathematical Model : Concepts introduced in the upward

flame spread models of Saito et al.(1985) and Quintiere et al . (1986) have

been developed further to formulate a model that accepts certain measurable

"fire properties" obtained from small scale experiments in order to predict

the upward propagation of fire on a vertical wall made of a combustible

material. The present formulation differs from the previous models in

primarily two respects, (a) the present model accepts an arbitrarily specified

local mass loss rate as a function of time, unlike the previous models which

assumed m"(t) to be either a constant or an exponentially decaying function,

and (b) the present model allows as input a flame height correlation in the

form of xf = KQn (where x f is flame height, Q* is energy release rate per unit

length, and K and n are constants), unlike previous models which assumed n = 1

and simplified the analysis considerably. The other quantities required as

input to the model are, (a) the ignition temperature and the product of

thermal conductivity, density, and heat capacity for the material, which are

obtained from the LIFT apparatus (Quintiere et al. 1986), and (b) a numerical

value for flame heat feedback. Model equations are solved numerically on a

personal computer to obtain the upward flame velocity, V(t), and the

44
progression of pyrolysis and burnout fronts (x and xb ) as a function of time.

Development of the model is in progress.

Mass Loss Rate Measurements : The mass loss rate should be determined

under similar conditions as the upward flame spread situation. Specifically,

the sample must burn in the same orientation (vertical) and be uniformly

covered with flames, similar to the unburnt material above the pyrolysis

front. In order to obtain such data, a small scale test apparatus was designed

and fabricated as illustrated in Fig. 1. A 20 cm x 7.5 cm sample is held flush

in an inert, surrounding wall. The sample is subjected to flames from a

natural gas line burner positioned parallel to the lower edge of the sample,

well below the sample. Flames from the burner uniformly cover the sample

surface, simulating wall material which is covered by flames issued by the

upstream, burning surface.

One of the objectives of this series of experiments is to systematically

study the influence of burnout time, r

b , on the process of upward flame

spread. This means samples are thin for a small r b

. However, in order to

simulate a typical wall fire, the samples must burn as "thermally thick"

solids. (For example, a thin wall panel burns on the exposed surface with a

heat loss into the interior of the wall, and therefore it behaves

approximately like a thermally thick solid.) Hence, the thin samples (such as

a 1/16" PMMA sheet, a cardboard, a textile material, or a wall panel) are

first mounted on a thicker substrate, typically a 1/2" marinite panel.

The weight of the sample is continuously recorded as m(t). The data are

smoothed using a 31 -point averaging scheme and curvefitted to a fifth order

polynomial. The mass loss rate per unit area, m^t), is then expressed as,

m"(t) = a4 t

A + a 3 1

3 + a2 1

2 + a 1 1 4- a0 Materials tested in this apparatus so far are, PMMA slabs of 1/16", 1/8"

and 1/2", particle board, polystyrene, and polyvinylchloride. Some of these

samples did not yield satisfactory results because of dripping or delaminating

problems. Additional samples to be tested are, textile materials of various

types, cardboards of various thicknesses, wall panels, and foam materials.

Larger Scale Experiments : In order to verify the model, upward flame

spread experiments are being conducted on 45 cm x 240 cm samples. Here the

important tasks are

(a) to measure V(t) and V(x ) for various materials

(b) to measure forward heat flux (ahead of the pyrolysis front), q", as

a function of time and distance

(c) to conduct a systematic study with the burnout time as a parameter

(d) to classify materials that sustain/do not sustain upward propagation

(Go/No go tests) and compare the results with predictions.

Figure 2 shows a schematic of the setup. Ignition is achieved by a

linear gas burner. Heat flux to the wall is measured by five total heat flux

gages. The test run is video-taped and xf is inferred from the recording. The

pyrolysis front is followed visually during the test run, indicated with a

pointer, and recorded on the video camera. These experiments are currently in

progress

45
Upward Spread on Particle Board : An Example

Mass loss rate for a 0.5" thick particle board was measured in the small

scale apparatus described above and plotted in Fig. 3 after smoothing and

curvefitting. Using available properties and the measured mass loss rate as

input to the model described earlier, upward flame spread velocity and

pyrolysis height were calculated as a function of time. The maximum pyrolysis

height, x

p nmx , as a function of the igniter strength is compared with the

data of Saito, et al . (1985) in Fig. 4. Comparisons are made for two different

values of K (the constant appearing in the flame height correlation). The

value of K for 50 % flame tip intermittency height has been reported to be

0.0433, and for continuous flame it is reported to be 0.027, with the same

exponent of n-2/3 (all units in meters) (Quintiere et al . 1986). Using these

two values of K, predictions are found to overestimate and underestimate the

data, respectively. At 50 % intermittency, the prediction of xf is high

because the heat flux to the wall starts dropping off before x - xf

; for

continuous flame, q" is significant at least up to x - xf

. The present model

assumes a constant q" up to x - xf and then zero thereafter. Therefore, the

prediction of Xp Btx is consistent with respect to the K values and the model

appears to predict data well.

References :

Quintiere, J. and Harkelroad, M. (1984) New Concepts for Measuring Flame

Spread Properties. NBS report no. NBSIR84- 2943

Quintiere, J., Harkelroad, M. , and Hasemi , Y. (1986) Comb. Sci. Tech. 48, 191.

Saito, K. , Williams, F. A., and Quintiere, J. (1986) Upward Turbulent Flame

Spread. Fire Safety Science . Proc . First Int'l. Symp . , Hemisphere Pub., 75.

Fig. 1

IKDa.SUMOmOINC

«ALL SAXFLE

(45 o wlAt s 2.4 •

BUT rua CAGES

T*EWDC0C?1£S

Cf^^VviDEt

CAME! CAS LUG WMLS

46

Fig. 2 : Apparatus for upward spread

experiments
LOW

(CAT I

MffTICK ftOMD 1.3 In.

9.612 e.en

e.ai

• 9.969

N

e.eee

9.967

9.669

6.669

9.964

9.663

9.962

9.861

6

9 9.2 9.4 9.9 9.9 1 1.2 1.4 (Thousands

Tlltf (9)

Fig. 3 : Mass loss rate as a function of time for particle board.

(Polynomial curve fit)

Fig. 4 : Pyrolysis front height as a function of burner energy

supply rate for particle board. Symbols are data of

Saito et al. (1985) for three different definitions of

pyrolysis front; dashed lines are predictions using

present model.

47
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : TRW Space and Technology Group

Contract No .: 60NAN37D0742

Title : Wind-Aided Flame Spread

Principal Investigator : Francis Fendell

Other Professional Personnel : Gerald Butler, Co-Participant

George Carrier, Co-Participant

NBS Scientific Officer : Howard Baum

Technical Abstract : Objectives A definitive (numerical) solution is sought to a

prototypical formulation of wind-aided flame spread over a solid

fuel slab. In particular, the rate of increased involvement is

sought as a function of the (given) ambient thermohydrodynamic

environment (temperature, wind speed, air vitiation, etc.) and of

the (given) physicochemical properties of the fuel slab (density,

heat capacity, thermal conductivity, temperature for onset of

pyrolysis, endothermicity required for pyrolysis, exothermicity

released by combustion of the gaseous pyrolyzate, etc.). The

formulation is a straightforward generalization, for ignition at

the "leading edge" of a thermally thick slab, of the classical

treatment by Emmons (1956) of the steady-state diffusion-flame

burning of a fully involved slab; accordingly, the solution to the

initial/boundary-value problem treated here evolves in time to the

steady-state Emmons solution by contruction.

The motivation for pursuing careful finite-difference solution

to this three-independent-variable problem [time since ignition,

distance downwind from the leading edge, distance transverse to the

two-phase (gas-solid) interface] are several. First, it is of

interest to ascertain precisely what such a "simplest reasonable"

formulation of the physics predicts about the rate of fire spread

under forced-convective aiding of the fire propagation. This is

one of the most escape-limiting scenarios associated with fires in

structures. Second, experimental results obtained by Loh and

Fernandez-Pello (1984) are available for the problem under

theoretical study. Loh and Fernandez-Pello suggested that the

above-described formulation adequately incorporates the physics, so

that the formulation yields results consistent with the measurements reported for noncharring (PMMA-type) polymers. The present

investigators are concerned whether indeed the status of this

particular cornerstone of fire science and technology is in such a

satisfactory state: perhaps a careful solution of the formulation

will prove to be at odds with their rough approximate solution,

which agrees with the experiment. If so, then is the execution of

the experiment or the adequacy of the formulation deficient?

48
Other motivations are as follows. First, this problem is

highly reminiscent of the ASTM E84 protocol, executed in a Steiner

tunnel. Abuse and misuse of data from this protocol is irrelevant

to the present discussion. What is relevant is that the pursuit of

this modeling supports by example the contention that a useful

companion model can be developed for even seemingly intricate

protocols. Such models establish what physicochemical properties

of the test sample are central to the material performance in the

protocol. That is, the model helps to elucidate what the E84

protocol does, and does not, reveal about the fire behavior of a

sample. Ultimately, in the distant future, such models may become

sufficiently predictive to obviate the need for some testing.

Second, it is logical to have the relatively simplistic case of a

noncharring material well in hand before pursuing the additional

complications of (1) a charring and soot-forming material, with the

attendant complications of significant radiative transfer of heat,

or (2) the more closely coupled dynamics and energetics of fire

spread up a vertical wall, another wind-aided-f ire-propagation

scenario. Third, fire spread under forced-convective-flow

assistance arises in many ominous structure fires, often in

connection with ceiling-type spread along a long corridor-like

expanse, owing to effluents from flashover in an adjoining room

(e.g. the MGM Grand casino fire) . * Thus, a capacity for

parameterization of this "subscaled" phenonomenon into

multicompartment-structure-fire hydrocodes is highly desirable.

Approach A so-called Stefan problem arises from the

formulation of the gas-phase and solid-phase energetics, coupled by

constraints holding at the two-phase interface. A Stefan problem

entails a moving boundary; identifying the position of this

boundary as a function of time is a key output of the solution.

Here the moving boundary is a "separatrix" at the two-phase,

gas-solid interface. Downwind of the separatrix is the preheating

zone: the wash of hot gases raises still-uninvolved portions of

the solid slab toward the temperature at which occurs the outgasing

of combustible fuel vapor from the solid. Upwind of the separatrix

is the pyrolysis zone: the endothermic requirement for generation

of fresh pyrolyzat« is met by the exothermicity from the gas-phase

diffusion flame. Thus, the separatrix is the furthest-downwind

position along the two-phase interface at which the temperature is

the pyrolysis temperature. Alternatively, the separatrix is the

furthest-upwind position along the two-phase interface at which the

interphase mass transfer is zero.

In the present formulation, the problem admits a similarity

solution, such that the three independent variables may be reduced

to two independent variables. Explicitly, the solution depends on

two ratios of the three independent variables: the ratio of

streamwise coordinate to time, and the ratio of transverse distance

to the square root of streamwise distance. This similarity

property is not exploited, but rather is reserved as a check on the

accuracy of numerical results obtained with a three-independentvariable formulation. The reason is that numerical techniques are

being developed robust enough to treat in the future more difficult

situations in which the simplications of a similarity property no

longer are available. However, the similarity property assures

that the ratio of the propagation speed of the separatrix

49
(hereafter identified as the fire-spread rate) to the ambient wind

speed is (conveniently) constant in space and time for the

particular cases examined in this discussion. The normalized

(nondimensionalized) rate of fire spread depends on ten

dimensionless parametric ratios. Ultimately one would like to

identify the dependence of the normalized spread rate on each of

these ten parametrical ratios, but, in the interim, attention is

concentrated on those parameters varied in the available

experimental data. In fact, only one dimensionless ratio is varied

in the available data, the ambient oxygen mass fraction (in other

words, the degree of vitiation of the aiding wind) . The magnitude

of the aiding wind is also varied in the experiments, but this

dimensional parameter enters into the nondimensionalization of the

spread rate only, and into none of the dimensionless ratios (in the

present formulation, which adopts inviscid flow) . Thus, the

experimentally observed linear increase of spread rate with increase

in the ambient wind speed follows directly from dimensional analysis

(without explicit solution) of the current formulation.

Results Thus, a large fraction of the twenty executed

computational cases are dedicated to identifying how the fire-spread

rate varies with the ambient oxygen mass fraction, with the nine

other dimensionless ratios of parameters held invariant. According

to the experimental observations of Loh and Fernandez-Pello and also

according to their approximate solution of the inital/boundary-value

problem posed here, the dependence of the spread rate on the ambient

oxygen mass fraction is very nearly quadratic (over the range for

which a finite rate of fire spread is observed) . Numerical results

previously reported (Butler, Carrier, and Fendell 1985) for the

present model yielded a linear increase of spread rate with ambient

oxygen mass fraction, but these results pertained to a sample of far

less density than the density of the PMMA examined in the

experiment.

References

Butler, G., Carrier, G. , and Fendell, F. 1985 Modeling of wind-aided

flame spread. Report 39641-6001-UT-00 . Redondo Beach, CA: TRW

Space and Technology Group.

Carrier, G. F. , Fendell, F. E., and Feldman 1980 Wind-aided flame

spread along a horizontal fuel slab. Comb. Sci. Tech. 23., 41-78.

Emmons, H. W. 1956 The film combustion of liquid fuel. Z. Angew.

Math. Mech. 36, 60-71.

Loh, H.-T., and Fernandez-Pello, A.C 1984 A study of the controlling

mechanisms of flow assisted flame spread. Twentieth Symposium

(International ) on Combustion . 1575-1582. Pittsburgh, PA:

Combustion Institute.

50
asterisk denotes a dimensional quantity; absence of the asterisk, a

dimensionless quantity. The streamwise coordinate is x*; the (densityweighted) transverse coordinate in the gas phase is z*(> 0) and

z*(< 0) in the solid phase; the time since onset of heated flow is

t^. In the interfacial plane z* - z* - 0, the preheat zone extends

from the hot-gas front x* -= u* t* to the pyrolysis front x* — x*(t*)

The pyrolysis zone extends from the pyrolysis front to the leading

edge of the solid slab x* - 0 . The pyrolyzed-vapor- sustained thin

gas -phase diffusion flame attaches to the interface at x* - 0 and at

x* - x*(t*), where in general u* t* > x*(t*) > x*(t*) > 0. The flame locus

is defined by Yp « Yq - 0 , where Yp and Yq are the stoichiometri

cally adjusted mass fraction for fuel vapor and oxygen, respectively. The

temperature in the gas phase is denoted T*, and in the solid phase,

X* The ambient gas and solid are both at T*. The fuel -vapor- free heated

s

' vitiated-air flow is characterized by values Yq^ T*, and u*^ the

speed of the inviscid flow. The local values of the interfacial mass

transfer m*, in units of mass per area per time, and interfacial tempera'

ture are noted, where T*

v

is the pyrolysis temperature. The rate

of flame spread is associated with dx*/dt*.

51
.

_

.

'

-
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

CARBON MONOXIDE GENERATION FROM SMOLDERING COMBUSTION

Professional Personnel

T. J. Ohlemiller , Project Leader

S. Dolan, Chemist

Project Objectives

To further our fundamental understanding of smoldering combustion phenomena

while, at the same time, providing input data for hazard analysis models.

Project Scope

Smoldering combustion is responsible for a large fraction of residential fire

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

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

combustion for some common residential fuels. At the same time, we are

exploring the smoldering behavior of these fuels between the extinction and

flaming limits in order to obtain insights into the controlling factors.

Technical Accomplishments

The initial work has focused on the smoldering of solid wood since this

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

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

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

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

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

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

are all for the case in which the smolder zone propagates in the same

direction as the air flow along the channel. The range of air flow rates for

which stable propagation is possible in the current configuration is rather

narrow -- about 8 to 18 cm/sec referred to the initial channel cross section.

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

lower flow rates. In the range of stable smolder, CO comprises 3 to 4 mole %

of the exhaust gases evolved from the combustion chamber and 10 to 20 weight %

of the evolved mass from the wood. Other products have also been

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

modes of gasification. In addition we have obtained estimates of the rate of

heat release from this smolder situation on the basis of oxygen consumption.

Analysis of temperature profiles in the wood during smolder propagation leads

to the inference that radiation along the channel axis is a major heat

transfer mode driving the propagation. Future work includes expanding the

range of configurations for solid wood and examination of CO from the

smoldering of other residential fuels, particularly upholstery materials.

Plans also include the development of a model for smolder propagation in twodimensional slab configurations.

Reports and Publications

53
Ohlemiller, T. and Shaub , W. , "Products of Wood Smolder and Their Relation to

Wood-Burning Stoves", National Bureau of Standards NBSIR 88-3767, May, 1988

Related Grant

"Kinetics of Oxygen Chemisorption and Desorption of Combustion Products in

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

Montana

54
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : University of Montana

Grant Number : 60NANB5D0554

Grant Title : Kinetics of Oxygen Chemisorption and Desorption of Combustion

i Products in the Smoldering Combustion of Cellulosic Material

Principal Investigator : Professor Geoffrey N. Richards

Wood Chemistry Laboratory

University of Montana

Missoula, Montana 59812

(406) 243-4435

Other Professional Personnel : Dr. F.-Y. Hshieh, Postdoctoral Research

Associate

Mr. William F. DeGroot, Research Specialist

NBS Scientific Officer : Dr. Thomas Ohlemiller

Technical Abstract :

Introduction . Smoldering combustion is a major source of ignition of

highly destructive residential and forest fires. Depending on the prevailing

conditions , smoldering is propagated by oxidation of a stable char formed

either by nonoxidative thermal degradation (pyrolysis) or by oxidation

occurring simultaneously with the initial thermal degradation reactions. In

either case, the process must involve combination of oxygen with the

substrate and evolution of both pyrolysis and combustion products. 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 from cellulose under pyrolytic conditions.

The main purpose of this research was to study the kinetics of

pyrolysis and of oxygen chemisorption and desorption of combustion products

under conditions which occur in the smoldering combustion of lignocellulosic

materials, which were expected to behave differently from pure cellulose.

Previous work (FY 87) was concerned with (1) first chemical events in

pyrolysis and oxidative pyrolysis of wood at 250°C, and (2) influence of

indigenous and of added metal ions in pyrolysis and oxidative pyrolysis of

wood from room temperature to 550°C at low heating rate (3°C/min). During

the present period of study, work was carried out in the following areas:

(1) factors influencing chemisorption of oxygen and ignition of wood chars,

(2) factors influencing chemisorption of oxygen and ignition of chars from

newsprint (newsprint was studied because it is frequently the raw material

for manufacture of cellulosic insulation)

Factors Influencing Oxygen Chemisorption and Ignition of Wood Chars . Solid discs of cottonwood have been pyrolyzed under nitrogen to an

appropriate temperature (HTT)

,

and then cooled under nitrogen to

55
chemisorption temperature for study of oxygen chemisorption activity (CSA)

Presorption of nitrogen slowed the initial rate of oxygen chemisorption, but

had no effect on long-te-rm (4 hours) chemisorption. Variation of HTT lead to

a pronounced maximum CSA at HTT 450-500°C; the causes of this effect are

assumed to be chemical in origin and have been studied further by FTIR of the

chars. Chars have also been prepared for collaborative solid-state NMR at

the University of Utah and publication of the results is anticipated in the

future. Removal of indigenous metal ions from the wood and replacement with

individual metal ions resulted in small but significant changes in CSA.

Ignition of the char samples prepared by pyrolysis in nitrogen has

been studied without removal of the char from the thermal balance. The

ignition temperatures of chars were dramatically influenced by the nature of

the cations present. The complete removal of cations was effective in

raising ignition temperature. The physical form of the wood samples (i.e.

fine and coarse powders and solid discs) also had considerable influence on

ignition temperatures, with the chars from solid wood samples igniting at

lower temperatures than corresponding chars from wood powder, either in

oxygen or in air.

Factors Influencing Oxygen Chemisorption and Ignition of Chars from

Newsprint . The oxygen chemisorption behavior of newsprint chars is similar

to that of wood chars and significantly different from cellulose chars.

Maximum chemisorption activity occurred with chars prepared at 500°C. The

black ink on newsprint has a retarding effect on the ignition of chars, but

color in newsprint enhances the ignition of chars due to the concomitant

increase in metal ion content. The lowest "minimum ignition" temperature

(i.e. without prior low temperature oxygen chemisorption) occurred with chars

of HTT 375°C. For higher temperature chars (HTT > 375°C), the ignition

temperature increased as heat treatment temperature increased. These effects

are interpreted in terms of the more ready oxidation of aliphatic than

aromatic components of chars and of the influence of HTT on chemisorption

activity.

This project was completed on April 30, 1988. A new project,

"Chemical Factors Influencing Ignition and Combustion in Lignocellulosics"

began May 1, 1988. Research funded by this project will involve (1)

contribution of cellulose, hemicelluloses and lignin to combustion and

ignition properties of lignocellulosic chars, (2) properties of low

temperature lignocellulosic char ("protochar"), and (3) interaction and

effects of oxygen chemisorption and metal ions on ignition and combustion of

lignocellulosics

Reports and Papers

1. W.F. DeGroot and G.N. Richards, "The Influence of Pyrolysis Conditions

and Ion-Exchanged Catalysts on the Gasification of Cottonwood Chars by

Carbon Dioxide," Fuel . 67 (1988) 352-360.

2. W.F. DeGroot and G.N. Richards, "The Effects of Ion-exchanged Cobalt

Catalysts on the Gasification of Wood Chars in Carbon Dioxide," Fuel , 67 (1988) 345-351.

3. T.L. Lowary and G.N. Richards, "Vacuum Pyrolysis of Bark from Pinus

56
Ponderosa," J. Wood Chem. & Tech. , in press.

4. G.N. Richards, "Effects of Impurities on Degradation of Sucrose under

Processing Conditions," book chapter in "Chemistry and Processing of

Sugar Cane," Ed. Margaret Clarke (10/19/87).

5. T.L. Lowary and G.N. Richards, "Effects of Impurities on Hydrolysis of

Sucrose in Concentrated Aqueous Solution," Int. Sugar Journal , in

press

-t 6. M. Essig, T. Lowary, G.N. Richards and E. Schenck, "Influences of

"Neutral" Salts on Thermochemical Conversion of Cellulose and of

Sucrose," Proceedings from the Biomass Conversion Conference, Phoenix,

1988.

7. F.-Y. Hshieh and G.N. Richards, "Factors Influencing Chemisorption and

Ignition of Wood Chars," submitted to Combustion and Flame . 2/88.

8. W.F. DeGroot, T.H. Osterheld and G.N. Richards, "The Influence of

Natural and Added Catalysts on the Gasification of Wood Chars,"

Proceedings from the Biomass Conversion Conference, Phoenix, 1988.

9. W.F. DeGroot, M.P. Kannan and G.N. Richards and 0. Theander,

"Gasification of Agricultural Residues (Biomass); Influence of

Inorganic Constituents," submitted to J. Agric. Food Chem. 3/88.

10. F.-Y. Hshieh and G.N. Richards, "Factors Influencing Oxygen

Chemisorption and Ignition of Chars from Newsprint," submitted to

Comb , and Flame 3/88.

11. M.D. Rahman and G.N. Richards, "Interactions of Starch and Other

Polysaccharides with Condensed Tannins in Hot Water Extracts of

Ponderosa Pine Bark," J. Wood Chem. and Tech. . 8(1) (1988) 111-120.

12. J.D. Blake, M.L. Clarke and G.N. Richards, "Determination of Organic

Acids in Sugar Cane Process Juice by High-performance Liquid

Chromatography: Improved Resolution using Dual Aminex HPX-87H Cationexchange Columns Equilibrated to Different Temperatures," J . Chromat

. 398 (1987) 265-277.

13. F.-Y. Hshieh and G.N. Richards, "Factors Influencing Chemisorption of

Oxygen and Ignition of Wood Chars," Prepr. Pap., Combined Meetings,

Eastern Section: The Combustion Institute 20th Fall Technical

Meeting, Chemical and Physical Processes in Combustion and the

National Bureau of Standards Annual Conference on Fire Research,

Washington, D.C., November 1987.

14. G.N. Richards, "Kinetics of Oxygen Chemisorption and Desorption of

Combustion Products in the Smoldering Combustion of Cellulosic

Materials," Final Report, NBS Grant No. 60NANB5D0554 , Wood Chemistry

Laboratory, University of Montana, Missoula, Montana, April 1988.

57
.

'
PART I

B

Basic Research and Tools for "Engineered" Fire Safety

(In-House Projects and Associated Grants Funded by

, NIST)

FLAME DYNAMIC PROCESSES
W.

•

.
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

TURBULENT COMBUSTION SIMULATION

Professional Personnel

Howard R. Baum, NIST Fellow, Project Leader

Daniel M. Corley, Physicist

Ronald G\ Rehm, NIST Fellow

Objective

Develop a fundamental understanding of the mechanisms which control gas phase

combustion processes in fires and a predictive capability which will allow the

evolution of these processes to be calculated from basic principles.

Scone

A theoretical and computational approach to the study of the transport,

mixing, diffusion, and reaction processes in an enclosure fire context. Each

process is considered in detail at the appropriate level of description.

Since these phenomena occur at widely different length and time scales, a large part of this effort is devoted to providing a set of overlapping

analyses in frames of reference (see figures on next page) which permit the

phenomena to be coupled together.

Support

Part of this work, (see items 2. and 3. below) is supported by the Air Force

Office of Scientific Research.

Technical Accomplishments

1. Large Scale Eddy Simulations

A three dimensional time dependent inviscid large eddy simulation of the

buoyant convection induced by an enclosure fire developed earlier has been

revived and ported to a Convex C120 mini supercomputer acquired jointly with

the Center for Applied Mathematics to support this project. The simulation, a

sample of whose output is shown in the upper figure, resolves the largest

(geometric) scales of the turbulent flow. It also calculates the hydrodynamic

transport of all subscale processes using the particles shown in the figure.

Use of the new computational facility permits flow resolution over a factor

exceeding fifty in length and time scales.

2. Combustion in a Turbulent Eddy

The small scale mixing and diffusion processes which provide the actual local

environment for the chemical heat release is calculated in the local frame of

reference. The local mixture fraction variable, representing the fraction of

gaseous material present that was once fuel, is determined as a function of

the local large scale flow quantities. The distortion of an initially

61
Buoyant Convection and

Combustion Models

Turbulent Eddy

and Chemistry Models
spherical fuel blob under the influence of local mixing is shown in the upper

and lower figures. It provides a transition from the room scales down to

those where the chemistry occurs . The model on which the solution is based

contains the effect of intense local vorticity, feedback from the local heat

release, and large density and temperature variations. It is itself a three

dimensional time dependent calculation which has also been ported over to the

new machine

3. Finite Rate Chemistry

Work has been initiated in collaboration with Dr. John de Ris of Factory

Mutual Research Corp. (FMRC) to develop a finite rate hydrocarbon chemistry

model for use in conjunction with this program. There are two tasks to be

carried out. The first, being performed by Dr. deRis , is to develop an

appropriate time dependent solution scheme using the mixture fraction variable

as the space- like coordinate. The second, being carried out at NIST, is to

imbed a given finite rate chemistry model into the turbulent eddy as indicated

in the lower figure.

Reports and Publications

"Time Dependent Simulation of Small-Scale Turbulent Mixing and Reaction" by

Baum, H.R., Corley, D.M., and Rehm, R.G., Twenty First International Symposium

on Combustion . The Combustion Institute, Pittsburgh, PA, 1263, 1988.

"Transient Combustion in a Turbulent Fire" by Baum, H.R. and Rehm, R.G., Ninth

Joint Meeting of the U.S. -Japan Natural Resources (UJNR) Panel on Fire

Research and Safety . N.H. Jason and B.A. Houston, Eds., National Bureau of

Standards Report NBSIR 88-3753, April 1988.

"Diffusion-Controlled Reaction in a Vortex Field" by Rehm, R.G., Baum, H.R.,

and Lozier, D.W., Symposium in Honor of C.C. Lin. Proceedings . D.J. Benney,

F.H. Shu, and C. Yuan, Eds World Scientific, 241, 1988.

Related Grants

1. "Subgrid Modeling of the Structure of Transient Diffusion Flames', J. de

Ris, FMRC. *

2. "Radiation from Turbulent Lumincies Fires", G.M. Faeth, U. of Michigan.

(See p. 130 for description)

*New grant with work just beginning. It is not discussed in this report

but will be described in the 1989 publication.

63
'

.
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

SOOT FORMATION AND EVOLUTION

Professional Personnel

George W. Mulholland, Project Leader

Kermit C. Smyth, Project Leader

Nelson P. Bryner, Chemical Engineer

Paul J.H. Tjossem, Physicist

James Gentry, Guest Scientist

J. Houston Miller, Associate Professor

Thomas Cleary, Guest Scientist

Project 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.

Technical Accomplishments

During hydrocarbon combustion the exothermic chemical reactions which lead to

the formation of water and carbon dioxide consume most of the fuel. However,

in many cases a significant fraction of the hydrocarbon fuel is converted into

species which participate in chemical growth reactions. These processes lead

to dramatic consequences in numerous combustion environments. For example,

the formation of intermediate hydrocarbons, such as polycyclic aromatic

hydrocarbons (PAH) , occurs under fuel-rich conditions and poses a potential

long-term health hazard since many PAH are carcinogenic. In addition, such

compounds are also involved in further growth reactions to form soot

particles. Radiation from soot dominates energy transfer from large fires,

and thus soot formation plays a key role for combustion efficiency in furnaces

and for flame spread. In turn, particle formation and radiative energy

transfer control the amount of smoke produced, which is important in fire

detection and pollutant emission. In contrast to the oxidation of simple

hydrocarbons, which is well understood, the detailed mechanisms for producing

large hydrocarbons during combustion have not been established. The

elucidation of chemical growth mechanisms continues to be one of the most

challenging research problems in combustion science today.

While -the chemical growth reactions play a key role in regard to the total

amount of smoke produced, the actual structure of the smoke leaving the flame

region is determined by a physical agglomeration process of particles sticking

65
structure. The light extinction coefficient and light scattering coefficient,

both of which affect the visibility through smoke, are not well characterized

for agglomerate structures. The aerodynamic properties, which control smoke

deposition in the respiratory tract, are also poorly characterized.

Understanding the relationship between the geometric structure of an

agglomerate and its properties is a key research topic in both aerosol

research and condensed matter physics.

1. Soot Formation

This is the ninth year of a long-term study of the fundamental chemistry of

soot formation, carried out jointly with the NBS Thermal Processes Division

and also in collaboration with the Chemical Kinetics Division. Detailed flame

structure measurements (species concentrations, temperature, and velocity)

have been made in a laminar methane/air diffusion flame using a variety of

laser-based optical techniques as well as mass spectrometric sampling. By

using all of these data, the species profiles have been analyzed to determine

production and destruction rates of intermediate hydrocarbons. The 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 suggest that a pathway involving vinyl radical addition to acetylene is the fastest route to

form benzene. Experiments have also investigated fuel structure effects on

chemical growth pathways by the addition of small amounts of ethylene,

butadiene, and toluene to the base methane flame.

Recently the first quantitative OH concentration measurements have been made

for a hydrocarbon diffusion flame. These results will enable us to determine

the most rapid production pathways for forming vinyl and ethynyl radicals,

which are thought to be key precursors in chemical growth, and to greatly

expand our analysis of proposed mechanisms for soot formation. New results

have also been obtained for detection of H, 0, C, CH , 02

, and CO by means of

multiphoton ionization spectroscopy. Profiles of these species are being

measured in our methane/air diffusion flame.

2. Smoke Agglomerates

A combined experimental and theoretical effort is focussed on the

characterization of the optical properties of smoke agglomerates. The

theoretical effort has consisted of generating simulated smoke agglomerates of

various sizes and then computing the light scattered by the agglomerates using

Rayleigh-Debye scattering theory. The most noteworthy result of this analysis

is the prospect of inferring information about the concentration and size of

the soot from the scattering measurements. It is shown that from the

scattering measurements one can infer the overall size of the agglomerate, the

size of the primary units in the agglomerate, the number of primary units in

the agglomerate, and the number concentration of agglomerates.

To study the optical properties of smoke, a combined transmission cellreciprocal nephelometer has been developed. This device allows the

simultaneous measurement of the extinction coefficient and the total

scattering coefficient of smoke. These are the key quantities needed for

studying radiation transport through a smoke cloud. From the difference of

these two quantities, the absorption coefficient of smoke can be determined.

66
The specific scattering and absorption coefficient for acetylene smoke are

found to be 2.2 m

2 /g and 6.9 m

2 /g, respectively. It was found that the smoke

can be changed to a nearly spherical structure by exposing the smoke to a

condensation/evaporation cycle. This "cloud processing" mechanism results in

a doubling of the scattering coefficient while the absorption coefficient is

unchanged. These results are consistent with the Berry-Percival theory

regarding the optical properties of smoke clusters.

A Smoke Aging/Dilution chamber has been fabricated for use in large scale fire

tests involving the furniture calorimeter. The facility allows rapid filling

of a 1 m

3 chamber within a few seconds with smoke collected just above the

fire. The chamber walls can be heated up to 150° C allowing the matching of

wall temperature to the smoke temperature as it rises in the stack.

Preliminary measurements have been performed regarding the effect of aging

over a one hour period on the extinction coefficient of crude oil smoke for

three wavelengths spanning the visible range. The results indicate that while

the agglomerates increase in size during the aging, the specific extinction

coefficient is not affected. An extensive series of smoke aging experiments

are planned for the next year including the determination of the agglomeration

coefficient, the change in the size distribution function, as well as optical

properties measurements. These measurements will be performed both at ambient

and elevated temperatures

Reports and Publications

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

Diffusion Flame" by Miller, J.H., Mallard, W.G.

,

and Smyth, K.C.,

Twenty-First Symposium ('International) on Combustion 1057 (1986) .

"Multiphoton Ionization Detection of CH, Carbon Atoms, and 02 in

Premixed Hydrocarbon Flames" by Tjossem, P.J.H. and Smyth, K.C.

"Concentrations and Production Rates of the Hydroxyl and Radical in a

Laminar Methanel Air Diffusion Flame" by Miller, J.H., Tjossem, P.J.H.

,

Hamins , A., and Smyth, K.C. submitted to Combustion and Flame.

"Methyl Radical Concentrations and Production Rates in a Laminar

Methane/Air Diffusion Flame" by Miller, J.H., and Taylor, P.H.,

Combustion Science and Technology . 52, 139 (1987).

"Measurement and Rate Law Analysis of D2 Q-Branch Line Broadening

Coefficients for Collisions with D2

, He, Ar, H2

, and CHA " by Smyth,

K.C., Roscasco, G.J., and Hurst, W.S., J

Chem . Phvs

, 87, 1001,

(1987).

"Chemistry of Molecular Growth Processes in Flames" by Smyth, K.C. and

Miller, J.H., Science . 236, 1540 (1987).

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

and Miller, J.H., Langmuir

3, 244 (1987).

-"Smoke Production and Properties" by Mulholland, G.W.

,

Society of Fire

Protection Engineers Handbook, 1988 .

67
"Fractal Analysis of Soot Agglomerates" by Samson, R.J., Mulholland,

G.W.and Gentry, J.W., Langmuir . 3, 272 (1987).

"Cluster Size Distribution for Free Molecular Agglomeration" by

Mulholland, G.W., Samson, R.J., Mountain, R.D., and Ernst, M.H.

Energy

and Fuels (in press).

"The Effect of Scale on Smoke Emission" by Mulholland, G.W., Henzel, V.,

and Babrauskas , V. , presented to 2nd International Fire Safety Science

Symposium.

"Light Scattering from Simulated Smoke Agglomerates" by Mountain, R.D.

and Mulholland, G.W., accepted for publication in Langmuir .

Related Grants

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

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

George Washington University.

3. "Soot Particle Formation and Destruction in Diffusion Flames", R.J.

Santoro, Pennsylvania State University. (See p. 126 for description)

4. "Cooperative Research in the Kinetics of Agglomerate Formation", James

W. Gentry, The University of Maryland.

3. "Fire Modeling", P.J. Pagni, University of California, Berkeley.

68
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : Brown University

Grant No : 60NANB6D0643

Grant Title : Soot Morphology in Flames

Principal Investigator : Professor R. A. Dobbins

Division of Engineering

Brown University

Providence, R. I. 02912

Other Professional Personnel : Dr.C.M. Megaridis

Post Doctoral Research

Investigator

NBS Scientific Officer: Dr. George w. Mulholland " % Technical Abstract :

Introduction : An improved knowledge of soot properties has application to

the use of smoke as an early detector of fire, to the improved prediction of

the radiation properties of flames, and through the latter, to a better

understanding of the spread of fires. The object of this study has been the

determination of the morphological character of the soot particles in

diffusion flames and the interpretation of this information in terms of the

soot dynamic processes. To achieve this goal we have developed a

thermophoretic sampling technique in which the sampling probe is rapidly

inserted into the flame, held for a controlled brief interval (ca. 30 - 100

ms), and withdrawn rapidly. The captured sample is then placed directly in the

electron microscope for TEM examination without handling or transfer

operations. The details of this technique have been reported(l,2) . To

quantitatively interpret the morphological observations we have developed a moment integral solution to the derosol dynamic equation with simultaneous

particle inception, surface growth, and coagulative growth. Using this novel

experimental method and modeling by the aerosol dynamic equation, we have made

significant progress in understanding the production, transport, and oxidation

and/or release of soot to the environment. These results are recapitulated

briefly herein and are described in fuller detail in the reports and

publications cited below.

1. Thermophoretic Sampling : The technique provides soot particle

samples for the determination of the primary particle size of agglomerated

chains. Primary particle size is a durable property which can provide valuable

information on the history of the soot field. The state of agglomeration of

the soot particle field can also be determined but agglomerate samples are

fragile, and are subject to damage during handling procedures. The variation

69
of the particle morphology - primary particle size and extent of agglomeration

- along a particle path line in the flame provides information on the particle

field and the dynamic processes to which it is subject.

Our observations have been conducted mainly in the ethene coannular diffusion

flame, and they confirm previous reports that the primary particles from any

one point of origin within the flame are highly monodisperse. This result has

important consequences in the modeling of the optical properties of the

agglomerates. Optical observations do provide an accurate measure of the

particle volume fraction which, when combined with the knowledge of the

primary particle size, can yield both the primary particle number density and

the total surface area per unit volume of space. We find values of surface

area of 6 to 15 cm2/cm3 typical of the annular region of the ethene diffusion

flame.

The thermophoretic sampling technique provides excellent data on the primary

particle diameter vs. height in the flame along a particle path line. The

size information can be combined with data on the local gas velocity to yield

specific surface growth rates of the soot particles. Our results(3) obtained

using the flame velocity measurements of Santoro et al.(Rl) are shown in

Figure 1 below. Our measurements are intermediate to the corresponding data by

Santoro(R2) for the same flame and the data reported by Harris and Weiner (R3)

in a premixed ethene flame that produces lower soot concentrations.

Along a given height in the ethene diffusion flame we find the maximum primary

particle size at the radius of maximum particle volume fraction. Primary

particles are smaller at the larger radii where the local temperature and

oxygen concentration is higher.

The decrease in soot particle size with height in the upper portion of the

nonsmoking ethene flame can be used to find the order of magnitude of the

oxidation rates. We find the soot particle burnout rate to be 10-4 gm/cm2 sec

in regions where the flame temperature ranges from 1500 to 1800 K. Values of

10-8 to 10-3 gm/cm2 sec have been reported in the literature for this quantity

which strongly depends on the particular combustion environment.

2. Soot Aerosol Dynamics : To interpret the experimental results we have

formulated a bimodal integral solution to the aerosol dynamic equation (2-4).

The experimental data are used to the maximum extent to quantify the processes

which control the soot aerosol dynamics. Some results of this modeling are as

follows:

-Soot inception is extremely intense in an annular region in the lowest

portion of the ethene diffusion flame. In this region we infer particle

inception rates of about 1x10+16 cm-3s -1

. These rates are consistent

with previous estimations in various combustion environments.

-A criterion for the development of collisional growth is formulated

that provides a test for the likehood of the presence or absence of

agglomeration when the primary particle size and particle volume fraction are

known. This test applied to our flame indicates that the presence of

agglomerates is consistent with the observed primary particle size..

-The aerosol dynamic model shows that larger particles within. the free

molecular flow regime will cause more rapid agglomerative growth. This result

can explain the anomalous lower values of the soot particle number

70
concentration at the same radial location in the soot field where both the

particle volume fraction and the mean particle size possess their maxima. In

this region the intense surface growth explains the high particle volume

fraction. The larger sizes cause a more intense agglomeration and reduce the

local soot particle number concentration.

-The moments of the volume equivalent diameters of the agglomerates are

controlled by diverse effects such as agglomerative and surface growth. Our

observations indicate that the various moments have ratios that are well

approximated by the values obtained under the self-preserving size

distribution assumption.

3. Soot Morphological Development : The morphology of agglomerates on the

path line corresponding to the maximum soot volume fraction has been studied

in detail(3). We find that the primary particle size increases to a maximum

just above the midpoint of the flame. Agglomerative growth is sustained

throughout this region including into the upper portion of the flame where

oxidation dominates. Oxidation reduces the primary particle size and burns the

agglomerates completely at the top of the flame in the case of the nonsmoking

flame. This description is displayed schematically in Fig. 2.

Only a limited statistical analysis of the agglomerates has been performed

because of the cost of this type of analysis. At z=15 mm in the nonsmoking

ethene flame we find the fractal dimension to be 1.73 and 1.85 for the two

samples which were analyzed. These values of the fractal dimension are

consistent with the occurrence of agglomerative growth by cluster-cluster

collision processes.

The investigation of a lightly sooting methane flame showed slight

agglomeration and modest amounts of surface growth.

4. Optical Properties of Polydisperse Agglomerates : A description of the

optical properties of agglomerates with an emphasis on polydispersity, i.e.,

variable chain length with monodisperse primary particles, has been

formulated(5) . This model provides the optical properties of interest in the

prediction of radiative properties and interpretation of laser scattering

experiments, as well as the prediction of agglomerate albedo and specific

extinction. This model relies on the calculations by Felske et al.(R4) for

monodisperse agglomerates. It also agrees with the model by Mountain and

Mulholland (R5) in the limit of small ratio of radius of gyration to

wavelength of light. Further comparisons of these methods with one another and

with the available experimental data are being conducted.

References :

Rl. Santoro, R. J., et al., Combustion Sci. and Tech. _53, 89, 1987.

R2 . Santoro, R. J., Twentieth Fall Technical Meeting, Eastern Section,

Paper 19, The Combustion Institute, 1987.

R3. Harris, S. J., and Weiner, A. M., Combustion Sci. and Tech. 31, 155,

_ 1983.

71
Specific

Growth

Rate f

(g/c

R4. Felske, J. D., et al., J. Quant. Spectrosc. Radiat. Transfer 3^, 447,

1986.

R5 . Mountain, R. D. and Mulholland, G. W. , "Light Scattering from

Simulated Smoke Agglomerates", NBS manuscript submitted for

publication, May 1988.

Reports and Publications :

1. Dobbins, R. A. and Megaridis, C. M. , "Morphology of Flame Generated Soot as

Determined by Thermophoretic Sampling", Langmuir _3, 254, 1987.

2. Megaridis, C. M., "Thermophoretic Sampling and Soot Aerosol Dynamics of an

Ethene Diffusion Flame", National Bureau of Standards Report,

NBS-GCR-87-532, December 1987.

3. Megaridis, C. M. and Dobbins, R. A., "Soot Aerosol Dynamics in a Laminar

Ethylene Diffusion Flame", to appear in the 22nd International Symposium on

Combustion, 1988.

4. Megaridis, C. M. , and Dobbins, R. A., "An Integral Solution of the

Aerosol Dynamic Equation Including Surface Growth Reactions", to appear in

Combustion Science and Technology.

5. Dobbins, R. A., and Megaridis, C. M., "Absorption and Scattering of Light

by Flame Generated Polydisperse Agglomerates", manuscript in preparation.

Fig. 2 Soot morphology in a flam

72
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

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) 994-7474

Other Professional Personnel: Dr. Anthony Hamins , Postdoctoral Research Assoc.

NBS Scientific Officer: Dr. Kermit C. Smyth

Technical Abstract

Introduction

Chemical growth reactions which occur during hydrocarbon combustion lead

to the formation of polycyclic aromatic hydrocarbons and soot particles. As a

consequence, many pollutants and smoke may be emitted from flames. Soot is

involved in determining energy transfer and the temperature field within the

flame environment. It is now believed that the early steps of chemical

growth, the soot inception phase, are rate- limiting and control the later

stages of growth.

The chemical steps of molecular growth from small hydrocarbon molecules

to aromatic species and eventually soot particles are not well established for

flame conditions. From several studies performed in premixed flames [1-9] and

in shock tubes [10-13], specific mechanisms have been proposed and predictions

have been compared to measured species concentrations profiles. Available

kinetic models successfully reproduce the experimental results for the major

species but serious discrepancies arise for radicals and intermediate

hydrocarbons [8,9]

Despite these shortcomings of the theory, consensus is developing on the

general scheme for this radical-based chemical growth mechanism. Fuel

molecules are rapidly converted into a number of precursor species,

predominately acetylene. After these pyrolyses reactions have run their

course, the precursor species may react together to form larger hydrocarbon

species, eventually leading to aromatic structures. Formation of subsequent

aromatic rings has been suggested to proceed by continual addition of

acetylene to a growing aromatic radical.

There have been few attempts to validate models for this subsequent PAH

growth chemistry through comparison with experimental data. An exception has

been the recent work of Frenklach and Warnatz [10] , who modelled the low

pressure acetylene oxygen flame of Bockhorn et al . [13]. Although the

agreement between peak concentrations and profile shapes is less than

completely satisfactory in this work, it represents an exciting beginning to

the application of detailed chemical models to studies of flame data.

Unfortunately, such comparisons are not possible for more flame systems

73
because of the lack of species-specific data on the concentrations of larger

molecular systems.

Cooperative research by our group at George Washington University and

workers at the National Bureau of Standards has concentrated on extending the

study of early growth chemistry described above to a laminar, methane/air

diffusion flame by making extensive concentration, temperature, and velocity

measurements [15-20]. Because a laminar flame is a steady state system,

changes in a species' concentration at given flame location balance one

another. Therefore, concentration changes due to chemical processes are

exactly the same magnitude as changes due to transport processes (convection

and diffusion) . We have exploited this relationship to calculate the net

rates of chemical processes for intermediate hydrocarbons in our flame system

[17] and can now compare these rates with the predictions of the mechanism for

benzene formation presented above [20]. In last year's report, our

experimental approach and results from the first few years of effort were

summarized. The discussion which follows will concentrate on new results from

the past year, organized according to research topics in last years proposal.

Scavenger Probe Sampling with Deuterium

The of the iodine scavenger probe which was used to profile the

concentration of methyl radicals in our methane/air flame system has the

disadvantage that iodine is somewhat corrosive. Recent literature suggested

that a superior scavenging agent might be deuterium, which had been used to

determine flame concentrations of H and 0 atoms and hydroxyl radicals [21].

We have modified our iodine scavenger probe for use with deuterium.

Unfortunately, the results from our initial work with D2 were unsatisfactory.

In these experiments, it was found that profile signals at mass 3 (indicative

of H atom scavenging) and 19 (indicative of hydroxyl radicals) showed evidence

of isotopic scrambling within the probe. Profile signals at mass 17, thought

to be indicative of methyl radical scavenging, had the same appearance as

methane profiles. Although this might also be attributable to isotopic

exchange within the probe, a more reasonable explanation would be interference

from natural abundance 13 C (approximately 1% of 12 C). Unfortunately, this

interference will be present when applying deuterium scavenging to any

hydrocarbon radical. A solution to the problem would be to try the experiment

in a diffusion flame burning isotopically enriched 12 C methane. We are

pursuing sources of funding to explore this experimental possibility.

The Effect of Fuel Additives on the Formation of Aromatics

The data set which is available from the GWU/CFR studies of a

methane/air diffusion flame represents the most complete description of a hydrocarbon diffusion flame system. An appropriate extension to the methane

flame studies would be a series of experiments in which small additions of

materials to the methane fuel flow could be used to perturb the well-known

flame structure. If the additions are small enough, their effects on flame

temperature and convective velocities will be inconsequential, and it will not

be necessary to repeat these difficult measurements. We have performed some

of the hydrocarbon addition experiments (ethylene and toluene) in the last

year. Addition of 1 to 3% ethylene to the fuel flow had very little effect on

the concentrations of acetylene and benzene, the most prevalent intermediate

hydrocarbons in the pure methane flame. However, the addition of one percent

toluene to the fuel flow had dramatic effects on the flame structure:

74
The concentration of benzene, phenyl acetylene, styrene, and

naphthalene were much higher in the toluene -doped flame.

Bibenzyl , benzaldehyde , and ethyl benzene were not observed in

appreciable concentrations.

Concentrations of acetylene and diacetylene were not appreciably

different in the flame with toluene added.

A consistent picture for the fate of toluene in this diffusion flame

emerges from this data. Low concentrations of benzaldehyde, ethyl benzene,

and bibenzyi suggest that toluene decomposition via the benzyl radical is a

minor pathway in this flame. In contrast, toluene is rapidly converted into

significant concentrations of the phenyl radical via unimolecular processes or

bimolecular reactions with radicals. If the phenyl were to decay further,

dramatic increases in the concentrations of acetylene and diacetylene (from

Ca H3 *) would be observed. Instead, our data suggests that phenyl radicals are

either rapidly converted into benzene (the dominant route) or react with

acetylene to form either phenylacetylene or styrene. These species may then

participate in subsequent growth processes which lead to the formation of the

second aromatic ring, as indicated by the marked increase in the concentration

of naphthalene

Further work is necessary to clafify the evolution from one to two ring

systems in our flame. In the case of the toluene addition experiments, this

includes evaluating this proposed reaction sequence quantitatively through a

determination of the production rates for species which might be involved in

aromatic ring formation processes. Preliminary results show dramatic

differences in the observed production rates for such important intermediates

as phenylacetylene in the me thane/toluene flame when compared to the pure

methane flame . Additional experimental work is also required and will be

discussed below.

It might be possible to distinguish between phenyl and benzyl radical

based chemistries by repeating the addition experiments with fully deuterated

toluene. If phenyl radical is formed quickly from toluene, and is rapidly

converted into benzene, it should be possible to observe a signal indicative

of the presence of Cg D5 H from the reaction of deuterated phenyl with H2 or

H2 0. It may also be possible to follow the growth of the deuterated additive

through detection of C6 D5 -C2 H (via R14) and partially deuterated naphthalene

(through R15-R17) . We presently have on hand approximately 200 ml of toluene - d6 and will soon try this experiment.

If it is correct to view the role of toluene in the methane flame as a

source of phenyl radicals, it should be possible to add other species to the

flame which might more directly perturb phenyl radical concentrations. One

possibility is the addition of nitroso-benzene (N0-C6 H5 ), which is often used

as a phenyl precursor in kinetic studies of phenyl chemistry. The vapor

pressure of this compound is relatively low (approximately one torr at 298 K)

However, the conversion of this compound into phenyl is nearly quantitative at

600 K. It is expected that the concentration of phenyl in the pure methane

flame is quite small (less than 10 ppm). Thus, addition of only one torr of

nitroso-benzene should have dramatic effects on hydrocarbon growth chemistry.

If necessary, this concentration could be boosted by heating the

nitrosobenzene in the fuel line.

75
References

1. J.D. Bittner and J.B. Howard, Eighteenth Symposium (International) on

Combustion, p. 110*5, The Combustion Institute, 1981.

2. J.D. Bittner and J.B. Howard, Particulate Carbon: Formation During

Combustion (D.C. Siegla and G.W. Smith, Eds.), p. 109, Plenum Press, New

York, 1981.

3. J.B. Howard and J.D. Bittner, Soot in Combustion Systems and its Toxic

Properties ( J . Lahaye and G. Prado, Eds.), p. 57, Plenum Press, New

York, 1983.

4. J.D. Bittner, J.B. Howard, and H.B. Palmer, Soot in Combustion Systems

and its Toxic Properties ( J . Lahaye and G. Prado, Eds.), p. 95, Plenum

Press, New York, 1983.

5. J.D. Bittner, D. Sc. Dissertation, Massachusetts Institute of

Technology, 1981.

6. J.D. Bittner and J.B. Howard, Nineteenth Symposium (International) on

Combustion, p. 211, The Combustion Institute, 1982.

7. J.A. Cole, J.D. Bittner, J.P. Longwell, and J.B. Howard, Comb. & Flame

56, 51 (1984).

8. R.J. Hennessy, C. Robinson, and D.B. Smith, Twenty- First Symposium

(International) on Combustion, The Combustion Institute, 1986 (in

press) . 9. P.R. Westmoreland, J.B. Howard, and J.P. Longwell, Twenty- First

Symposium (International) on Combustion, The Combustion Institute, 1986

( in press)

10. M. Frenklach and J. Warnatz , Comb. Sci. & Tech. 51, 265 (1987).

11. T. Tanzawa and W.C. Gardiner, Jr., J. Phys . Chem. 84, 236 (1980).

12. M. Frenklach, D.W. Clary, W.C. Gardiner, Jr., and S.E. Stein, Twentieth

Symposium (International) on Combustion, p. 887, The Combustion

Institute, 1984.

13. M.B. Colket III, Twenty-First Symposium (International) on Combustion,

The Combustion Institute, 1986 (in press).

14. H. Bockhorn, F. Fetting, and H.W. Wenz , Ber. Buns. Phys. Chem. 87., 1067

(1983).

15. K.C. Smyth, J.H. Miller, R.C. Dorfman, W.G. Mallard, and R.J. Santoro,

Comb. & Flame 62, 157 (1985).

16. J.H. Miller and P.H. Taylor, Comb. Sci. & Tech. 52., 139 (1987).

17. J.H. Miller, W.G. Mallard, and K.C. Smyth, Twenty-First Symposium

(International) on Combustion, The Combustion Institute, 1986, p. 1057.

18. K.C. Smyth and J.H. Miller, Science 236 . 1540 (1987).

19. J.H. Miller, P.J.H. Tjossem, A. Hamins , and K.C. Smyth, manuscript in

preparation.

20. A. Hamins and J.H. Miller, manuscript in preparation,

21. J.V. Volponi, W.J. McLean, and R.M. Fristrom, Combust. Flame 65 . 243

(1986).

Recent Publications

"Mechanistic Studies of Toluene Destruction in Diffusion Flames." A. Hamins,

D. T. Anderson, and J.H. Miller, Chem. Phys. Processes Comb. 1987, Paper #4.

"Concentrations and Productions Rates of Hydroxyl Radicals in a Laminar

Methane/Air Diffusion Flame." J.H. Miller, P.J.H. Tjossem, A. Hamins, and

K.C. Smyth, manuscript in preparation.

76
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution: The University of Maryland at College Park

Grant No.: COMM 70 NAN 85H0517

Grant TitleKinetics of Aggregate Formation

Principal Investigator: Dr. James W. Gentry

Department of Chemical Engineering

University of Maryland

College Park, MD 20742

Other Professional Personnel: T. G. Cleary, Graduate

Research Assisitant

NBS Scientific Officer: Dr. George W. Mulholland

Technical Abstract:

Introduction Soot agglomerates produced by the combustion of acetylene in

a coannular diffusion burner are studied. The agglomerates consist of primary

particles which have a mean diameter of about 30 nanometers. They appear to

be attached in a random fashion yielding a tenuous non-compact structure.

Single agglomerates may contain up to thousands of primary particles. The

aerodynamic properties determined from particle motion and deposition can be

related to the agglomerate structure. The structural properties and the

distribution of sizes affects light scattering and absorption of the soot

aerosol. Characterization of the aerosol stream from the burner provides a

basis for the use of the burner in other studies and yields information about

soot agglomerates in general.

Aerosol Generation The coannular diffusion burner has been described in

detail by Santoro [1]. An integral part of the soot generating system is a chimney assembly designed to eliminate the effects of room air currents and to

allow the operation of the burner at elevated pressure (up to 100 cm of water

above atmospheric pressure) . The chimney constructed of brass includes a viewing port for visual inspection of the flame. The output from the

generator is stable day after day. By varying the fuel flow rate from lower

to higher flow rate, the flame conditions change from non- sooting to visibly

sooting conditions. Particles formed in both regions have been studied.

Primary Particles In the pre- sooting conditions, experimental measurements

of the diffusion coefficients of the particles at different fuel flow rates

indicate that the source is highly monodisperse with diffusion coefficients

corresponding to spherical particles of 15-20 nanometers. At higher fuel flow

rates particle size does not increase, but the number concentration does

increase. The particle number concentration then drops off as the visible

sooting point is approached. Measurements of mass and number concentration

just below the visible sooting point yields an average volume equivalent

diameter of 25 nanometers. Some agglomeration appears to be occuring. The

unagglomerated primary particles have not been observed by electron microscopy

77
yet, but individual primary particles can be sized from electron micrographs

of the agglomerates

Size Distribution of Clusters At the visible sooting point, the mass

concentration of the aerosol increases by a factor of twenty above the presooting mass concentration. A multistage cascade impactor separates the soot

particles by inertial effects. Data analysis yields a mass mean diameter and

standard deviation corresponding to spherical unit density particles with the

same inertia as the agglomerates. From the visible sooting point to a highly

sooting flame, the mass mean diameter given by the impactor varies from 0.4 to

greater than 5 micrometers.

A sample of the soot, with the burner operating at the vislible sooting

point, was collected on transmission electron micrograph grids using a thermal

precipitator. The thermal precipitator collects the particles on a grid by a

force field driving particles to a surface due to a temperature gradient that

the aerosol stream passes through. Three different magnifications were used

when performing size distribution analysis. The size was defined as the

longest length times the width of the cluster, then the square root of the

productis taken. Figure one is a histogram of the results. Each calculated

size falls into a size range and over 650 particles were measured. At the

lowere magnification, only larger clusters were measured in order to obtain

better statistics of the larger clusters with out loking at cluster sizes

where significant numbers of clusters were counted at higher magnification.

Using the results of fractal analysis previously performed [2], the

relationship between the number of primaries and the size of the cluster (as

defined above) allows for the mass distribution of the sample to be

calculated. Figure 2 is a histogram of the mass distribution of the collected

soot

Cluster Friction Coefficient Individual clusters were examined to

determine how the agglomerate structure affects the friction coefficient of

the cluster. Odumade in his PhD study at Minnesota separated clusters by

electrical mobility [3]. With electron microscopy the number of primary

particles and the mean primary particle size for a cluster was calculated for

separate clusters. Samson has collected samples of soot classsified by

electrical mobility. Electron micrographic analysis of the clusters yields

the number of primary particles in each cluster. Figure 3 is a plot of both

odumade ' s and Samson's data. The volume equivalent sphere diameter of the

cluster is plooted against the diameter of a sphere with the same friction

coefficient as the cluster. Solid lines are theoretical curves. Further work

is being performed to extend the range of the measured values.

Conclusions The primary particle size in the pre-sooting range was

measured as a function of acetylene flow rate, and was found to be fairly

constant in diameter. The size distribution analysis by impaction and

electron microscopy was performed. Experimental measurements of cluster

friction coefficients are being compared to theoretical models based on

rarefied gas dynamics.

References

1. Santoro, R. J. et al .

Combustion and Flame . 51, 203-218 (1983).

78
2 . Samson, R. , M.S. Thesis, University of Maryland (1986).

3. Odumade , O.A.

,

Ph.D. Dissertation, University of Minn. (1983).

Reports and Papers

1. Cleary, T. , R. Samson, G. Mulholland, and J.W. Gentry, "The

Relationship Between Structure and Aerodynamic Measurements for

Clusters", Proceeding G Ae F Conference . Hanover, September 1987

2. Gentry, J. W. , and T. Cleary, "Diffusion Coefficients of Clusters",

Annual Conference on Fire Research . NBS -Gaithersburg, MD, 1987

3. Gentry, J.W., G. Mulho'lland, R. Samson, and T. Cleary, "Methodology

for Fractal Analysis of Combustion Aerosols and Particle Clusters",

Accepted by Journal of Aerosol Science and Technology . 1988

4. Cleary, T. , G. Mulholland, and J.W. Gentry, "The Experimental

Measurements of Clusters Formed From Soot Agglomerates Near the

Sooting Limit" , Paper to be presented at 12th International

Conference on Atmospheric Aerosols and Nucleation . Vienna, Austria,

1988

5. Cleary, T., G. Mulholland, J.W. Gentry, "Correlations of Aerodynamic

Diameters and Diffusion Coefficients with Geometric Structure for Soot

Agglomerates ", Paper submitted for AAAR Annual Meeting . Research

Triangle, NC. 1988

Figure 1.

Size Distribution of Soot Agglomerates

79
Figure 2

Size Distribution of Soot Agglomerates

Figure 3. Dve is the volume equvalent sphere size of the cluster, Fc is

the friction coefficient.

Dve of Cluster vs Dp Sphere with same Fc

Friction coefficient for data points

f rom e I ectr i ca i mob i I i ty measurements

Dp of sphere with same Fc

80
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 87

Institution : University of California, Berkeley

Grant No: 60NANB8D0848

Grant Title : Fire Modeling

Principal Investigator : Professor Patrick J. Pagni

Vice Chairman-Graduate Study

Mechanical Engineering Department

University of California

Berkeley, CA 94720

Telephone: (415)642-0729

Other Professional Personnel : Nab.il Elkouh (Ph.D Candidate)

Joseph Viray (M.S. Candidate)

NBS Scientific Officer : Dr. Howard Baum

Technical Abstract : The overall goal of this project is to develop chemical,

physical and mathematical models of the detailed combustion

phenomena which control a fire's growth. Our emphasis recently

has been on measurement and prediction of the soot volume fraction,

fv , in a variety of flames, on window breaking in compartment fires

and on an overview of fire physics.

Fire Radiation:

In flame radiation, the most important and least known

parameter is fv , the soot volume fraction, defined as the volume

occupied by soot per unit of flame volume. Previous summaries have

described a multi-wavelength laser extinction technique for in-situ

measurement of the local flame fv

, in free and forced boundary

layer diffusion flames(l), pool fires(2) and premixed flames(3,4).

Detailed experimental comparisons with alternative singlewavelength scattering/extinction measurement methods have been

reported (3 , 4

)

. Limited data on small pool fire mean soot volume

fractions suggest fv scales with optical thickness, kL, as

fv/fy

max

s 1.5 (kL) 1/3

, kL < 0.3

^v/^vmax ^ <L > 0.3

81
If this correlation holds for all fuels, it will permit scaling of

the mean fv in pool, fires of any size from laboratory scale

measured fv (2) . Window Cracking in Fires:

Following Professor Emmons' description of window breaking,

we developed an estimate of the typical increase in window

temperature required to break it (5)

An exposed window heats and

expands placing its cooler shaded edge in tension until it cracks

at a small defect, usually at the top inner edge. Glass can only

stand a small tensile stress ; cr - 4 * to

7

/W / c - &ooo ps 2 ) . The

stretch modulus for glass is e » ^>8 n/^o.i k \c 7 p a) . so

the strain, 6 - <-r / £ , required to crack the glass is, &,os-yc

. The temperature rise needed to produce that strain is ^ e/c*

~£-6 l c c i o4‘f), since the coefficient of linear thermal expansion for

glass is * * q,z > \ o-** l c~

1 ^ . These results appear to be

independent of scale. So compartment modelers may assume windows

act as vents after the glass reaches T"~80 e e. The energy transport

between flame, smoke layer and glass remains to be modeled.

Table 1. FIRE PHYSICS

I . FLUID DYNAMICS II. DIFFUSION FLAMES

1 . Buoyant Flames and Plumes 1 . Pyroly8ia Rates/ Flame Shapes

Flow Regimes

Transition Criteria

Near Field

Velocity and

Laminar Boundary Layers

Free, Forced and Mixed

Burning distinct

Temperature Profiles

Far Field

Entrainment Rates

Coherent Structures

from Pyrolysing

Heat Release Rate Databases

Turbulent Boundary Layers

and Other Oscillations

Droplet Dynamics

Interactions with Walls,

Ceilings, Layers and Flows

Reaction Distributions

Flame Base Field

Free, Forced and Mixed

Radiant Augmentation

Blockage Effects

Liquid and Solid Pools

Walls, Ceilings and Corners

Cribs, Carpets and Furniture

Charring

Melting

2. Flows Within Compartments

Ceiling Layer Formation

Two-Layer Temperatures

Extended Fire Plumes

Ceiling Jets

Stratification

Corridors

Mixing

2 . Excess Pyrolyzate

Production

Composition

Accumulation and

3 . Flame Radiation

Temperature, Geometry

3. Flows at Openings

Doors

Windows

Ceiling Holes

Multiple Openings

HVAC Systems

Mixing

and Composition Effects

Heat Release Rate Fraction

Wavelength Dependence

Soot as % of Fuel Carbon

Soot Volume Fraction

Measurement

Correlations

Analyses

U. Nondlmenslonalization U. Nondimens ionalizat ion

82
Table 1 FIRE PHYSICS continued

III. FLAME SPREAD

1 . On Solids /Liquids

Laminar /Turbulent

-» Thick/Thin

Up/Dovn Vertical Walls

Opposed/Aasisted Flow

Horizontal

Surface Tension Effects

Transport Mechanisms

Radiant Augmentation

Oxygen Variation

Correlations

Damk'dhler No.

Empirical

Ignition Temperature

Jgnition Phenomena

Remote Object

Piloted/Fire Brand

Extinction Phenomena

Melting

Charring

Critical Kinetics-Gas/Solid

2. In Solids (Smoldering)

Porous Media Flov

Heat and Mass Transport

Counter-Current (Diffusion)

Co-Current (Premixed)

Self-heating to Ignition

Surface Reactions

3. In Gases

Deflagrations /Detonations

Con fined /Unconfined

Pure Mixtures

Vitiated Mixtures

Ceiling Layer Limits

and Propagation Speeds

Ignition /Extinct ion

Stratification

k . Growth Models

Exponential/Power Law

Doubling Time

Fire Growth Rate Parameter

Growth Classification

Intensity Classification

Threat Variables

Escape Time

5. Nondlmensionalization

IV. COMPARTMENT MODELING

1 • Heat Transfer

Conduction Losses

Thermal Inertia

Convection Losses

Convection Between Layers

Flame Impingement

Smoke Layer

Visibility

Radiation

Surface Radiant Exchange

Accurately Described

Approximations

Radiation Rate Pool

2. Pyrolysis and Burning Rates

Ventilation Control

Vitiation

Radiative Feedback

3. Growth to Flashover

Ventilation

Free, Forced, None

Pressure

Characteristic Times

Temperature Field History

Species Field History

Computation

Zone

Field

Scale Effects

Stratification

Oscillations

U . Flashover

Definitions

Criteria

Approximations

Stability Analyses

Windows Breaking

Venting

Backdrafts

Air Flames

5 . Fire Spread to Adjacent Spaces

Postflashover Intensity

Flame Heights Out Windows

Flame Propagation and Lengths

along Adjacent Ceilings

Multiple Rooms

6. Nondlmensionalization

Fire Physics Overview:

Fire physics is defined as the study of the physical mechanisms by which fire is initiated, grows throughout a system, and is extinguished. An inclusive list of topics within each of four broad categories: I.) Fluid Mechanics, II.) Diffusion Flames, III.) Flame Spread and IV.) Compartment Modeling, presented in Ref.

5 is given in Table 1.

83
Other studies related to fire are underway at Berkeley with

separate support in the areas of smoldering (6) and compartment fire

characteristic times (7). A invited review paper was presented at

the Second International Symposium on Fire Safety Science. We are

assisting the Publications Committee with the Proceedings of the

Second International Symposium (8) . During this grant period I also

attended the Tenth Meeting of the United States-Japan Conference

on Development and Utilization of Natural Resources (UJNR) Panel

on Fire Research and Safety in Tsukuba, Japan in June 1988. We are

looking forward to hosting the Eleventh Panel Meeting here at the

University of California at Berkeley in October 1989.

Reports and Papers :

1. J.A. Ang, P.J. Pagni, T.G. Mataga, J.M. Margie and V.J. Lyons,

"Temperature and Velocity Profiles in Sooting Free Convection

Diffusion Flames," AIAA Journal . 26, 323-329, 1988.

2. 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).

3. V.J. Lyons and P.J. Pagni, "A Comparison of Optical

Measurements of Soot in Premixed Propane/Oxygen Flames,"

Paper No. 46, Central Section of the Combustion Institute,

1988 Spring Meeting, Indianapolis.

4. V.J. Lyons and P.J. Pagni, "Optical measurements of Soot and

Temperature Profiles in Premixed Propane-Oxygen Flames,"

Poster Paper No. 40, p. 135, in the Book of Abstracts of the

Twenty-Second Symposium (International) on Combustion,

Seattle, Washington, August 14-19, 1988.

5. P.J. Pagni, "Fire Physics - Promises, Problems and Progress,"

Fire Safety Science - Proceedings of the Second International

Symposium . pp. 49-66, Hemisphere Publishing Co., New York

(1989)

6. J.L. Newhall, A.C. Fernandez-Pello and P.J. Pagni,

"Experimental Observations of the Effect of Buoyancy on

Cocurrent Smoldering," Paper No. 88-50, Western Section of

the Combustion Institute, 1988 Spring Meeting, Salt Lake City,

Utah.

7. P.J. Pagni, N.J. Alvares and K.L. Foote, "Defining

Characteristic Times in Forced Ventilation Enclosure Fires,"

Mathematical Modeling of Fires - STP 983 . J.R. Mehaffey, ed. , pp. 68-82, American Society for Testing and Materials,

Philadelphia (1988)

8.

- T. Wakamatsu, Y. Hasemi, A. Sekizawa, P.G. Seeger, P.J. Pagni,

and C.E. Grant, eds., Fire Safety Science - Proceedings of the

Second International Symposium . Hemisphere Publishing Co. , New

York, 1989.

84
PART I. Basic Research and Tools for ’’Engineered" Fire Safety

(In-House Projects and Associated Grants Funded by

NIST)

C. COMPARTMENT FIRE MODELING
!
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

WALL FIRE GROWTH IN ENCLOSURES

Professional 1 1 Personnel r—

K. Steckler, Project leader

H. Mitler, Physicist

W. Davis, Physicist

M. Harkleroad, Physicist

Project Objective

To develop and experimentally validate algorithms which predict the behavior

of a burning wall in a room and which are usable in a zone -type compartmentfire model.

Scope

This project addresses the flammability aspect of wall fires in enclosures.

Both theoretical and experimental efforts are involved in developing and

validating algorithms for predicting the pyrolysis rates per unit area and the

flame spread rates of these materials . The algorithms are then embedded in

FIRST, a mathematical compartment-fire zone model which provides for

interaction between the burning wall and the environment it creates within the

enclosure

Technical Accomplishments

I. Reduced- Scale Experiments

The experiments conducted during the past year were designed to study the

pyrolysis rate of a fully- ignited fixed-area vertical surface in a reducedscale (1.0 x 1.0 x 0.75 m) enclosure. Flame spread effects were purposely

minimized. The experimental results provide a data base with which to compare

the results of the theoretical model (described below) for the pyrolysis rate

of a fixed-area wall fire in an enclosure. Since the theoretical effort has

focused on non- charring , homogeneous materials, the fuel in each experiment

was a 0.18 x 0.73 x 0.025 m slab of PMMA. The experimental results include

the pyrolysis rate of the wall panel; incident radiant flux; oxygen, carbon

dioxide, and carbon monoxide levels in the upper gas layer; oxygen level in

the lower gas layer; and gas temperatures all as a function of time. The

sole independent variable in the experiments was the width of the door opening

to the compartment. Door widths ranging from 2.6 to 100 percent of the room

width produced a wide range of ventilation conditions and pyrolysis rates.

II. Pyrolysis Model

1. Description

A steady-state model was developed to predict the pyrolysis rate of a noncharring, homogeneous material in a vertical orientation, given the dimensions

of the pyrolyzing zone, material properties of the wall material, some

87
properties of the flame and plume, incident external radiant flux, and oxygen

level in the adjacent gas layer. The pyrolysis rate, m" , is obtained from the

steady- state energy balance at the surface of the material;

m " ^ = aw ^in + ^rt ( 1 )

where is the effective heat of vaporization of the wall material, aw is the

absorptivity of the wall surface, <f> in the incident radiant flux, 4> c the

convective flux, and <f> rr the reradiation flux from the surface. The incident

radiant flux is the sum of the radiant flux from the flame and the external

flux from surrounding hot walls and/or hot gases. Since the radiation from

the flame depends on the mean absorption coefficient, a significant result of

the current work is the finding that this coefficient varies with height, z,

and it does so in a simple way (i.e. linear in 1/z ). The convective flux is

expressed in terms of the Spalding mass transfer number. The reradiation

flux, which varies as the fourth power of the surface temperature, is

formulated in terms of an Arrhenius expression to account for variations of

surface temperature with pyrolysis rate. More complete details of the model

and its derivation have been reported by Mitler [1,2].

2

Comparison with Experimental Data

The model, as described above, applies in the case of uniform conditions (i.e.

external flux, oxygen level, and gas temperature). A wall fire within a compartment, however, produces a stratified environment which, in turn,

establishes local conditions at the wall that vary with position. In the

context of a two- layer zone model, the pyrolyzing wall panel can be viewed as

the sum of two pieces; one in the upper layer and the other in the lower

layer. Each piece is exposed to the uniform conditions characteristic of the

layer in which it is located. The pyrolysis model can then be applied to each

piece independently.

This approach was used to predict the pyrolysis rates measured during the

reduced- scale PMMA wall-fire experiments. The measured fluxes, oxygen

concentrations, and gas temperatures were manipulated to produce - representative average values for each layer. These values were then input to

the pyrolysis model and the pyrolysis rate calculated. Figure 1 shows the

calculated and experimental results for a compartment with a door width of

0.33 m. Results are displayed for the period beginning at the time of

complete - area involvement and ending when the sample collapsed. Figure 2

summarizes the results obtained for the entire series of door widths.

Discrepancies between experimental and calculated values are believed to be

connected to the downward flow of melted material along the face on the

burning panel. Molten flows were observed, to some degree, in each of the

experiments

3. Insertion of Pyrolysis Model into FIRST

FIRST, an NBS compartment - f ire model, was chosen to be the testbed for the

wall - fire - growth algorithm. The immediate goal of this task is to predict the

results of the reduced- scale wall -fire experiments, given the properties and

88
geometries of the fuel and the enclosure. Unlike the calculations described

above, in which the environmental conditions (external flux, etc.) were input

parameters, FIRST will calculate these conditions and the pyrolysis rate

s imul t ane ous ly

The pyrolysis madel has been inserted into FIRST. Algorithms for calculating

wall-plume mass and energy transfers, external radiant flux to the wall, and

floor heating also have been inserted. Debugging is underway.

III. Upward Flame Spread and Burnout Model

A purely numerical model was developed to predict the upward spread rate of a

pyrolysis front on a vertical slab or wall that has been ignited at the

bottom. One of the advantages of a numerical approach is that heating fluxes

which vary with time and position along the surface of the slab can be taken

into account in a straightforward manner.

The first step is to divide the height of the slab into a series of equallyspaced points or nodes. At each node, the surface temperature is determined

from an energy balance at the node. This balance is between energy gained

from the wall flame and hot gases and walls of the enclosure, and energy lost

due to radiation and conduction from the surface of the slab. It is assumed

that the pyrolysis front reaches a particular node when the surface

temperature of the node reaches the critical temperature,

g

, of the wall

material. Once ignited, the pyrolysis model (described above) is activated

and the regression rate and burnout front can be determined.

The principal assumptions are that there is a well-defined ^ , a welldefined heat of vaporization, no diffusion of heat parallel to the surface,

and no charring or melting. Additional information is available in a report

by Mitler [ 3 ]

Retorts and Publications

1. Mitler, H.E., ’’Algorithm for the Mass Loss Rate of a Burning Wall", IAFSS,

Tokyo, Japan, June 1988.

2. Mitler, H.E., "Algorithm for the Mass Loss Rate of a Burning Wall",

NBSIR 87-3682, December 1987.

3. Mitler, H.E., "Upward Spread Algorithm", NBSIR in review.

Related Grants

Prediction of Fire Dynamics, J. deRis and R. Alpert, Factory Mutual Research

Corporation. (See page 31 for description)

89
TIME []

Figure 1. Comparison of calculated and measured mass loss

rates for a PMMA wall burning in a reduced- scale

enclosure with a 0.33 m vide doorway opening.

MEASURED l g/m* *2- S J Figure 2. Comparison of calculated and measured mass loss

rates of PMMA walls burning in a reduced- scale

enclosure with variable door widths.

90
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

CONSOLIDATED COMPARTMENT FIRE MODEL r Professional Personnel

Leonard Y. Cooper, Head, Building Fire Modeling Group and Project Leader

John H. Klote, Mechanical Engineer

Glenn P. Forney, Computer Scientist

William Davis, Physicist

Daniel Alvord, Computer Specialist

Duy Q. Duong, Guest Worker (National Building Technology Center, Australia)

Program Objectives

Develop a comprehensive fire model computer code to simulate all physical and

chemical aspects of fire in complex structures.

Scope

The work of the project focuses mainly on the development of the Consolidated

Compartment Fire Model (CCFM) computer code which consolidates past progress

in zone -type compartment fire modeling, and which allows readily for

integration of future advances with the greatest possible flexibility. It is

envisioned that the project will lead to a series of well -documented, userfriendly, and numerically-robust CCFM products. These would be versatile in

the sense that they would provide a capability of analyzing a particular

compartment fire problem by using any one of a range of physical-phenomena - modeling sophistication, from the most basic to the most comprehensive. One

final goal of the work is a Reference Fire Model (RFM) which, within the

context of the zone - fire -model concept, would provide the best possible

mathematical simulation of the fire environment. The project includes the

effort of developing mathematical submodels of the separate compartment fire

phenomena to be simulated. In this, concise algorithms and associated modular

computer subroutines are developed which are readily useable in zone -type

compartment fire model computer codes, in general, and in the CCFM/RFM, in

particular

Technical Accomplishments

The Consolidated Compartment Fire Model/Reference Fire Model (CCFM/RFM)

computer code development process was initiated by establishing a generic CCFM

equation set. This and other preliminary CCFM ideas were tested on the

computer model, CCFM. HOLE, which simulates the fire environment in a single

room with a hole of arbitrary area and elevation. Work then moved to multiroom model development. This has led to a prototype, multi-room code, called

CCFM. VENTS which is now being completed and which we expect to document and

release this coming year. This first-stage code involves a basic model

„ formulation and code structure that allows for the required CCFM/RFM future

growth flexibility. At this time the code is supported by a preliminary-draft

user guide. Although it is being developed and tested on the NIST mainframe

CYBER computer, the code runs also at comparable speeds on personal-computer

91
hardware. Features of CCFM. VENTS include: simulations of concentrations of

oxygen and an arbitrary number of other products of combustion; robust

numerics; unforced vent flows under both low- and high-cross-vent pressure

difference conditions; forced ventilation via simple fan/duct systems; and

wind effects. Finally, the code uses the simplest possible, point-sourceplume, smoke - filling fire physics in the rooms-of-fire-origin and a very

simple heat transfer calculation there and in other spaces. Throughout the

course of the year, progress has been made on developing new and improved

submodel algorithms and subroutines. These will be added eventually to future

CCFM/RFM products.

Funding from Other Agencies /Institutions

In addition to CFR Priority Project funding the above activities were carried

out with support from the following Other Agency funding:

Sponsor: Department of the Navy, Naval Sea Systems Command

Title: Evaluation of Smoke Control on Navy Ships

Reports and Publications

"A Plan for the Development of the Generic Framework and Associated Computer

Software for a Consolidated Compartment Fire Model Computer Code," G.P. Forney

and L.Y. Cooper, NBSIR 86-3500, Jan. 1987.

"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, Special

Technical Publication (STP) 983, pp 116-127, American Society for Testing and

Materials, Philidelphia , PA (1988).

"The Compartment Fire -Generated Environment and Smoke Filling," L.Y. Cooper,

presented at the International Symposium and Roundtable on Fire Protection

Engineering Methods, Sept. 13-16, 1988; Section 2/Chapter 7 of The SFPE

Handbook of Fire Protection Engineering . SFPE, Boston, MA and NFPA, Quincy,

MA, 1988.

"Comparisons of NBS/Harvard VI Simulations and Full-Scale, Multi-room Fire

Test Data," J.A. Rockett, M. Morita, and L.Y. Cooper, NBSIR 87-3567, July

1987; presented at 2nd International Conference on Fire Safety Science, June

1988, and to be published in the Conference Proceedings.

"Fire in a Room with a Hole: A Prototype Application of the Consolidated

Compartment Fire Model (CCFM) Computer Code," Cooper, L.Y. and Forney, G.P.,

presented at the Combined 1987 Fall Technical Meeting of the Eastern Section

of the Combustion Institute and Annual CFR Research Conference, Nov. 2-5,

1987, and published in the Proceedings.

"Thermal Response of Unconfined Ceilings Above Growing Fires and the

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

Journal of Heat Transfer, Vol.109, pp. 172-178, Feb. 1987.

"Transient Ceiling Jet Characteristics," V. Motevalli, C.H. Marks, B.

McCaffrey and L.Y. Cooper, presented at the Combined 1987 Fall Technical

92
Meeting of the Eastern Section of the Combustion Institute and Annual CFR

Research Conference, Nov. 2-5, 1987, and published in the Proceedings.

"Ceiling Jet-Driven Wall Flows in Compartment Fires," L.Y. Cooper, NBSIR 87-

3535, April 1987; to appear in Combustion Science and Technology.

"Calculating Flows Through Vertical Vents in Zone Fire Models Under Conditions

of Arbitrary Cross-Vent Pressure Difference," Cooper, L.Y. , NBSIR 88-3732, May

1988; also "A Note on Calculating Flows Through Vertical Vents in Zone Fire

Models Under Conditions of Arbitrary Cross -Vent Pressure Difference," Cooper,

L.Y. , submitted for outside publication.

"An Experimental Study of the Transient Thermal Response of Unconfined

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

presented at the 2nd ASME-JSME Thermal Engineering Joint Conference, March

1987, and published in the Proceedings.

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

Impingement," L.Y. Cooper, presented at the 1987 ASME/AIChE National Heat

Transfer Conference and published in Proceedings; to appear in the Journal of

Heat Transfer.

"Test Results and Predictions for the Response of Near-Ceiling Sprinkler Links

in Full-Scale Compartment Fires, L.Y. Cooper and D.W. Stroup, NBSIR 87-3633,

Sept. 1987; presented at 2nd International Conference on Fire Safety Science,

June 1988, and to be published in the Conference Proceedings.

"Before the Smoke Clears - Heat and Mass Transfer in Fires and Controlled

Combustion," Kennedy L.A. and Cooper, L.Y. , Mechanical Engineering, Vol.

109/No. 4, pp62-67, April 1987.

"A Catalog of Compartment Fire Model Algorithms and Associated Computer

Subroutines," D.W. Stroup, NBSIR 87-3607, August 1987.

Proceedings of Sessions on Heat and Mass Transfer in Compartment Fires,

Cooper, L.Y. and Farouk, B., Eds, Vol. 1, pp . 309-440, Proceedings of the 2nd

ASME-JSME Thermal Engineering Joint Conference . American Society of Mechanical

Engineers, New York, NY, March 23-27, 1987.

"Enclosed Buoyant Convection in a two-Layer Stratified Fluid," Rehm, R.G.,

Lozier, D.W., Baum, H.R., and Cooper, L.Y.

,

to be presented at the 1988

Technical Meeting of the Eastern Section of the Combustion Institute, Dec. 5-

7, 1988, and published in the Proceedings.

"An Algorithm for Modeling Flow Through a Simple Fan-Resistance Ventilation

System and Its Application to Fire Modeling," Cooper, L.Y.

,

Klote, J.H., and

Duong, D.Q., to appear as NISTIR.

"Model of a Simple Fan-Resistance Ventilation System and Its Application to

Fire Modeling," Klote, J.H. and Cooper, L.Y.

,

to appear as NISTIR.

"Negatively Buoyant Wall Flows Generated in Enclosure Fires, Jaluria, Y, and

Cooper, L.Y.," invited paper for publication in Progress in Energy and

Combustion Science, under review.

93
Related Grants

Compartment Fire Combustion Dynamics, C.L. Beyler, Fire Science Technologies,

and R. J. Roby, Virginia Polytechniic Institute.

Experimental Study of the Environment and Heat Transfer in a Room Fire,

Zukoski , E.E., California Institute of Technology.

Negatively-Buoyant and Penetrative Flows Generated in Enclosure Fires,

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

Numerical Analysis Support for Compartment Fire Modeling Code Development,

W.F. Moss, Clemson University.

Prediction of Fire Dynamics, J deRis - Factory Mutual Research Corporation.

See p. 31 for description)

Transient Ceiling Jet Characteristics, Marks, C.H., The University of

Maryland

94
Center for Fire Research

National Institute of Standards and Technology

FY 88

Institution: Virginia Polytechnic Institute and State University

Grant No. : 60NANB8D0829

Grant Titl e: Compartment Fire Combustion Dynamics

Principal Investigators : Richard Roby

Department of Mechanical Engineering

Virginia Polytechnic Institute and S.U.

Blacksburg, VA 24061

Tel. (703) 961-5846

Craig Beyler

Fire Science Technologies

3215 Donnybrook Lane

Cincinnati, OH 45251

Tel. (513) 522-4688

Other Professional Personnel : Michael Skelly, Graduate Assistant

NIST Scientific Officer: Dr. H.E. Mitler

Technical Abstract: As most fire fatalities are the result of exposure to toxic products of

combustion such as carbon monoxide, it is essential that methods be

devised to evaluate the toxic hazards posed by specific materials in varying

building designs. While toxic products are produced during both

smoldering and open combustion modes, the rate of generation of toxic

products such as carbon monoxide and hydrogen cyanide is greatest under

conditions where the compartment flow dynamics create oxygen deficient

combustion conditions.

The investigation will experimentally 1) determine the effect of

realistic compartment fire flows on species generation rates and their

correlation with equivalence ratio, 2) establish major toxic gas and smoke

generation rates for important fuels such as wood and TDI-based

polyurethane, and 3) determine the efficiency of external flames in

destroying major toxic gases produced in the compartment under oxygen

deficient compartment fire combustion.

The apparatus currently being constructed for this investigation

includes a 1.2 m X 1.2 m X 1.5 m compartment with two ventilation paths, a

normal window style exhaust vent and a ducted air inlet vent (see Figure 1).

Separation of the two flows allows an unambiguous measurement of the air

inflow, while leaving the exhaust flow dynamics undisturbed. Combined

with a measurement of fuel supply rate, this system will allow an accurate

determination of the compartment equivalence ratio. Exhaust from the

compartment will be collected by a hood system instrumented to allow the

measurement of gas and smoke generation rates. Routine measurements

95
will include determination of species concentrations for carbon monoxide,

carbon dioxide, oxygen, total unbumed hydrocarbons, and smoke. In

addition concentrations of other important species, such as hydrogen

cyanide and hydrochloric acid, will be determined by either gas

chromatography or FTIR analysis.

In addition to exhaust measurements, detailed measurements of

species and temperature will be made in the compartment and in the

external flame. These measurements will support species generation

modeling, modeling of the external flame based on a detailed knowledge of

the vent flow rate and composition, and evaluation of the existing model for

layer ignition under realistic compartment fire conditions. The apparatus

can be modified to study flames from external windows or flames from vent

openings to internal corridors.

Work on this project was initiated in the final two months of FY 1988

and has focused on construction of the experimental apparatus,

modification of the experimental facility, and development of species

measurement capabilities.

Instrumented

Inlet duct

anemometer

Figure 1. Compartment Layout.

96
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

INSTITUTION : California Institute of Technology

GRANT NO. :- NBS5 60NANB600638

GRANT TITLE : Experimental Study of Environment and Heat

Transfer in a Room Fire

Principal Investigator: Professor Edward E. Zukoski

Jet Propulsion Center

301-46

California Institute of Technology

Pasadena, CA 91123

Other Professional Personnel: Professor Toshi Kubota

Richard Chan, PhD Candidate

James Morehart, PhD Candidate

NBS Scientific Officer: Dr. Walter Jones

Technical Abstract :

Introduct ion . 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

are difficult to describe analytically because the flows are turbulent

and are strongly influenced by turbulent mixing between streams in which

buoyancy forces are predominant and because the chemical processes in

turbulent -buoyant flames are not understood completely.

Gravity Currents . The flow of hot gas in a gravity current in

hallways or across very wide rooms allows for very rapid transport of gas

which may be toxic and which may also be combustible. Our aim is to

understand this transport process and, in particular, the influence of

heat transfer between the current and the ceiling on the current and on

the subsequent development of the ceiling layer in the hallway or room.

Gravity currents in hallways which are horizontal and inclined up to 30

degrees below the horizontal are being investigated.

Two types of apparatus are being used: the first is a saltwater/ water facility which is a 2.4 meter long channel with a 15 cm

square cross section. This is being used to investigate the dependence

of the gravity current parameters on the Reynolds number and the

inclination angle, and to determine the nature of the return flow which

develops after the gravity current has impinged on a vertical wall

97
closing the downstream end of the channel.

Flow visualization techniques are used to measure the velocity of

the head of the current, the depth of the current, and the nature of the

return flow. Fluorescent dye techniques are being developed to measure

the concentration profiles in the flow and hydrogen bubble techniques,

and to determine the velocity profiles.

The work in this facility has now been completed and a

description of results is included in the Final Report for this grant

year

The second apparatus is an air facility 8.6 m long and 0.5 m

square. This apparatus and the experimental results obtained in it are

described in detail in the papers by Chobotov et al. Experiments in this

apparatus have shown that the rate of heat transfer between the current

and the ceiling is much higher than rates calculated for forced

convection over flat plates because of a buoyancy controlled instability

in the wall boundary layer. The rates are high enough to reduce the

overheat in the hot gas to very small values within a length

corresponding to 50 times the current depth. The effect on the velocity

of the head is smaller but the influence of the heat transfer could lead

to a strongly stratified hot gas layer in long hallways.

This apparatus has been used to investigate heat transfer effects

on currents with an initial depth of 10 to 15% of the channel deep.

Earthquake damage to this duct is now being repaired and it will be used

to study currents which initially occupy between 20 to 30% of the depth

of the channel and the reverse flow produced when the current impinges on

the closed end of the hall.

Motion of Smoke in Vertical Shafts . We are also beginning to

study the influence of heat transfer on the motion of hot gas in vertical

shafts initially filled with cooler air. We plan to use experimental

approaches similar to the two discussed here for horizontal flows in

these new experiments.

Combustion in Two-Laver -Models : We are also studying the

products of combustion and flame geometries produced by large buoyancycontrolled diffusion flames which extend from a lower layer, which

contains unvitiated air, into an upper layer which contains products of

combustion mixed with air. The results of these tests are described in

detail in Toner et al (1986) for steady state flows from the plume into

the upper vitiated layer.

Toner's measurements were made for steady flows in which the

equivalence ratio for the gas entering the upper layer in the fire plume

is equal to that for the gases which make up the upper layer <J> . P X

However, in most fires these equivalence ratios are not equal and

in general the values of 4^ will be less than the corresponding values

for (£ due the transient development of the fire plume and the upper

layer? An important question here concerns the possibility that excess

fuel or oxygen in the fire-plume will react with excess oxygen or fuel

entrained from the ceiling layer into the fire plume.

98
In order to study this situation we have constructed a new

apparatus which consists of a hood, 1.83 m square and 1.22 m deep with

windows on one side which allow photographic and visual observations of

the flame within the hood. To allow the modeling of unsteady flows, this

apparatus was built so that additional gas can be added to the hood

through an axisymmetric array of pipes located in the upper 20 cm of the

hood. The gas is injected through a large number of l/16th inch holes to

insure rapid mixing between the injected gas and the recirculating flow

produced within the hood by the fire plume. The new hood is large enough

to allow burners up to at least 0.5 m in diameter to be used in contrast

to the 20 cm burners used in the steady state measure ments made by Toner

in the old 1.2 m square hood.

Because the added gas is injected outside of the region of

flaming combustion, we believe that it can be used to model the unsteady

situation since the equivalence ratio for the gas recirculated into the

fire plume by the entrainment process will have a different value than

that in the plume at the interface.

A typical result of preliminary measurements are shown in the

accompanying figure where data for mole fractions for oxygen and carbon

monoxide measured for the ceiling layer gas are plotted as a function of

the layer equivalence ratio, <j>^ , and for a wide range of values of <|>p . Open points were obtained without air injection and closed points with

air injection; the crosses are earlier steady state data obtained by

Toner

Values of <f>p were fixed by setting the distance between the

burner and the interface, and the fuel flow rate; values of were

reduced from the corresponding steady state values by adding air to the

upper layer. We have not yet investigated the effect of adding fuel to

the upper layer.

Several interesting features are shown here: first, the measured

values of the mole fractions for oxygen and carbon monoxide obtained for

a number

values for

of fixed values for $p lie on a single curve regardless of the

depend only 6n

Thus, the species formed are independent of <j> and

This is a very welcome conclusion because it greatly simplifies

the modeling of this process and it may result from the fact that the

entrainment of upper layer gas into the fire plume is much larger than

the flow at the interface supplied by the fuel flow rate and entrained

air

Second, the mole fraction for oxygen does not go to zero for

values of <f>£ greater than one but remains a few percent above zero even

when <f>£ is greater than 2.0. This is in contrast to the data obtained

in the smaller hood by Toner, shown in these figures as the crosses. We

believe that this difference is due to the presence of surface reactions

on ceramic fiber used as insulation in Toner's experiments and the

absence of these reactions in the present hood which has bare metal

walls

99
These experiments were carried out with a 20 cm burner and with

natural gas as the fuel. We plan to extend the work to include 50 cm

burners and several other fuel types including propane and an alcohol.

Reports and Papers

Zukoski, E., Toner, S., Morehart, J., Kubota, T. (1988), "Species

Production in Two-Layer Fire Plumes," Fire Safety Sciences. Proceedings

of the Second International Suvmpos ium .

100
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY88

Institution:

Grant Noj

Grant Title:

Principal Investigator

Other Professional Personnel:

NBS Scientific Officer

Technical Abstract:

Rutgers, The State University of New Jersey

New Brunswick, New Jersey

60NANB7D0743

Negatively Buoyant Flow’s Generated in Enclosure Fires

by the Downward Turning of Ceiling Jets

Professor Yogesh Jaluria

Department of Mechanical & Aerospace Engineering

Rutgers, The State University of New' Jersey

New' Brunswick, New Jersey 08903

Telephone: (201) 932-3652

K. Kapoor (Post-Doctoral Fellow)

A. Abib (Ph.D. Student)

Dr. Leonard Y. Cooper

Introduction. The present research program extends and continues the earlier work

on negatively buoyant and penetrative flow's that arise in enclosure fires, with emphasis on

the dow'nw'ard turning of the ceiling jet at the corners. Employing and modifying the

experimental systems and facilities developed earlier, the research effort considers the flow'

of a heated two-dimensional jet over a horizontal, isothermal or adiabatic, surface, simulating

the ceiling of a compartment, and the downward turning at the corners to give rise to a negatively buoyant wall flow'. Of particular interest are the penetration distance, entrainment

into the flow' and w'all heat transfer in this flow. These are to be correlated w'ith the results

obtained earlier for a negatively buoyant w'all jet in an isothermal medium. Extensive data

have been taken on the flow' under consideration. Correlating equations have also been

derived for the heat transfer, flow' rate and penetration depth as functions of the inlet

conditions for the heated jet. The observed trends are similar to those obtained earlier for a negatively buoyant wall jet and quantitative relationships between the two flows are being

derived to provide inputs in the modeling of the transport at the early stages of the fire.

Negatively Buoyant and Penetrative Wall Flow's. A considerable amount of work has

been done on negatively buoyant wall jets in extensive media, stratification of an enclosed

region into tw'o essentially isothermal zones, penetration of a w'all jet across the interface

between the twr o zones and generation and penetration of a buoyancy induced flow across the

interface. Correlating equations have been derived for the penetration distance 6 , heat

transfer Nusselt number NuD

for an isothermal wall at temperature T

g

and the total

entrainment into the flow. These equations have been obtained for a w'all jet in an extensive

medium at temperature T^ as w'ell as for a jet in a twT o-layer, stably stratified, environment at

upper layer temperature Tu and low'er layer temperature T^ = T^. Figure 1 show's the

penetration distance as a function of the Richardson number Ri, based on the inlet slot width

D, temperature T

q

and velocity U

Q

for a jet in a two layer environment. Similarly, Figure 2

101
shows the corresponding heat transfer in terms of the local Nusselt Number. Several other

results were obtained and have been reported in the papers and reports listed at the end of

this summary.

Downward Turning of Ceiling Jets. This problem has been under detailed

investigation over the current year. Figures 3 and 4 show the resulting isotherms and the

surface heat transfer. It is seen that the downward flow is very similar to a negatively

buoyant wall jet in an extensive isothermal medium. The basic flow is sketched in Figure 5

and interest lies in correlating the inlet conditions at (c) with those at (1) and (2), so that the

ceiling jet flow may be coupled with the negatively buoyant wall jet that arises. The present

effort has also been directed at surface heat transfer rates and the entrainment into the flow.

It is found that the entrainment is a strong function of the conditions at position (2). The

ceiling jet loses thermal energy and momentum as it flows from (c) to (2). Thus, the

penetration distance heat transfer and the flow rate mout are determined by the transport

occurring at the horizontal surface and in the downward turning. This is the main concern

in the present effort and the extensive data taken so far are being analyzed to obtain a quantitative description of the flow and transport processes as the fire-plume-driven ceiling

jet spreads over the ceiling and turns downward to generate a negatively buoyant wall flow.

Reports and Papers

1 Jaluria, Y., "Buoyancy-Driven Wall Flows in Enclosure Fires,” Proc. 21st Svmp. flnt.l

Combusts Combust. Inst., Pittsburgh, PA, 151-157, 1986.

2. Jaluria, Y. and Kapoor, K., "Experimental Simulation of Penetrative Flows in a Compartment Fire," Proc. Fall Tech. Meetine. Eastern Sect.. Combust. Inst.. Gaithersburg, MD, Paper No. 89, 1987.

3. Jaluria, Y. and Kapoor, K., "Importance of Wall Flows at the Early Stages of Fire

Growth in the Mathematical Modeling of Enclosure Fires." Combust. Sci. Tech.. 59,

355-369, 1988.

4. Kapoor, K. and Jaluria, Y., "Heat Transfer from a Negatively Buoyant Wall Jet,"

NBS Report NBS-GCR-88-541, 1988, also, Int. J. Heat Mass Transfer. 1988, to appear.

5. Abib, A.H. and Jaluria, Y., "Numerical Simulation of the Buoyancy-Induced Flow in a Partially Open Enclosure," Num. Heat Transfer. 1988, to appear.

6. Kapoor, K. and Jaluria, Y., "An Experimental Study of the Generation and

Characteristics of a Two-Layer Thermally Stable Environment." Int. Comm, Heat

Mass Transfer. 1988, to appear.

7. Jaluria, Y-, "Natural Convection Wall Flows," SFPE Handbook, Sec. 1, Ch. 7, 1988.

102
Figure L Penetration depth of a negatively buoyant

jet in an isothermal and a stably stratified

two-layer environment.

Figure 2. Local heat transfer rate to an isothermal

wall due to a wall jet in a two layer

environment at Ri = 0.148. o, Tg-T^ =

-0.5 °C; A, 12°C; , 24°C.

103
<?5C Eo

(Uoc3*->

C/3 6c

_ouc33

C/3 3

C/3 Oo3<4-1 t-3

C/3 3EoO

C/3 O

.C

CD3o

C/3 c33O

•3-'

<D

t-3

U) £ 1
Center for Fire Research

National Institute of Standards and Technology

FY 88

i

Institution: Clemson University

Grant No.: 60NANB8D0857

Grant Title: Numerical Analysis Support for Compartment Fire Modeling Code Development

Principal Investigators:

William F. Moss

Department of Mathematical Sciences

Clemson University

Clemson, SC

Tel. (803) 656-5225

Other Professional Personnel: Karen Dunlap, Research Assistant

NIST Scientific Officer: Dr. G.P. Forney

Technical Abstract:

The computer code CCFM.VENTS, currently under development by the Building Fire

Modeling group, is based on past advancements in compartment fire modeling. This computer

code simulates the conditions which develop during the course of an enclosure fire. One or more

rooms or compartments are connected together or to the outside by vents such as doors, windows,

and holes. Execution of the model requires the solution of a system of ordinary differential

equations which solve for pressure, densities, smoke layer height and combustion product

concentrations in each room. This investigation will carry out research in support of the numerical

and computer science aspects of CCFM code development.

It has already been established that for some problems the system of ordinary differential

equations solved by CCFM.VENTS is stiff; that is, if the system is linearized in a neighborhood of

a point in time, then the solution of this linear system has terms which are changing rapidly with

time and terms which are changing slowly. For such systems, it is essential to use an implicit

solver. This means at each step in time a nonlinear system of equations must be solved. Most

ordinary differential equation solvers handle this nonlinear problem by using a quasi-Newton

method which requires the estimation of the Jacobian matrix associated with the right hand side of

the system of differential equations. Most of the work of implicit solvers is involved in approximating the Jacobian matrix and solving a linear system of algebraic equations with this matrix as the coefficient matrix. Methods for exploiting the structure of the Jacobian will be investigated in

order to improve the efficiency of CCFM.VENTS. This will allow more complex fire scenarios to

be simulated than otherwise would have been possible.

The ODE's in CCFM.VENTS do not always fit the classical definition of stiffness, however. For many problems the Jacobian has eigenvalues with positive real parts. Alternate solution

techniques will be investigated to exploit this property of the ODE's.

As illustrated by the peaks in Figure 1 the computer code, CCFM.VENTS, uses a disproportionate amount of computational resources during certain simulation events such as layers

crossing vent boundaries. These peaks can also be caused by the use of tabular data such as fire

size data that is represented using piece-wise linear interpolation. Both of these phenomena

introduce discontinuities into the model equations. Techniques for reducing the impact of these

105
discontinuities on the solver will be investigated.

Another source of solution inefficiency is the presence of round-off error or numerical

noise that is magnified by sub-model algorithms (plumes, vents, etc.). An error analysis of

CCFM.VENT sub-model algorithms will be performed to analyze their error propagation characteristics. For example, if the inputs to an algorithm for computing vent flows have five digits of

precision how many digits can one expect from the outputs of the algorithm? This type of

cancellation error present in some of CCFM.VENT sub-model algorithms is another source of the

peaks found in Figure 1. Work on this project was initiated in the final month of FY 1988 and has focused on

investigating the numerical properties of the CCFM.VENT differential equations.

Q.

QJ

•+* C/D

C

u

CU

Urn Q.

o

£• mm H

toa>©

C/D

time per step

200 400 600 800 1000 1200

Figure 1

Simulation Time (s)

Plot of Computer time required vs. simulation time

106
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : The University of Maryland at College Park

Grant No .: 70NANB5H0551

Grant Title : Transient Ceiling Jet Characteristics

Principal Investigator : Dr. Colin H. Marks

Mechanical Engineering Department

University of Maryland

College Park, MD 20742

Other Professional Personnel : Vahid Motevalli, Graduate Student

and Guest Worker

NBS Scientific Officer: Dr. David Evans

Technical Abstract :

Introduction This research has been concerned with the experimental determination of transient velocity and temperature profiles in the axisymmetric jet

formed by the gases from a fire plume spreading across a ceiling. The purpose

of the research is to obtain and provide data for the verification and improvement of compartment fire models, and to aid in the design of sprinkler and smoke

detector systems.

The experiments have been on a small-scale with the heat source consisting

of a flame produced by the combustion of a premixed stoichiometric mixture of

methane and air. The fire strengths ranged from 0.5 kw to 2 kw, and the burnerorifice-to-ceiling heights were 0.5 m and 1 m; this combination of five

strengths and heights produced a range of non-dimensional five strength Q (Q = Q/Pamb^p^ambS^^H^/^) 0 f from 1. 85x10- to 1.047x10“ • During a given run, the

fire strength was kept fixed. The transient effect was caused by the variation

of the ceiling temperature as it increased from room temperature to its steadystate value. The ceiling in these experiments consisted of a 2. 13m-diameter

,

1.27cm-thick disk of fiberboard. It was insulated on its upper side with a 8.26cm-thick layer of fiberglass insulation and painted black on its lower surface with an ultra-flat black paint to yield a stable and known emissivity of

0.9.

Velocities were determined from the time shift in the temperature-time

records obtained from pairs of fine (1 mill diameter) thermocouples with one

thermocouple in each pair mounted a short distance downstream from the first.

Temperatures were obtained directly from the thermocouple readings. A more

detailed description of the instrumentation and the data-reduction techniques is

given in NBS-GCR-88-540.

107
Discussion The data obtained are far too voluminous to be presented herein;

hence, only a few salient features of them will be presented. Typical temperature and velocity profiles for unconfined ceilings were shown in last years’

summary (NBSIR 87-3650) and will not be repeated here. Velocity profiles at a given position were found to be independent of time, whereas temperature profiles reflected the increase of ceiling temperature with time. Both profiles have

a maximum point located some distance below the ceiling. The location and

magnitude of these maxima is important in the design of sprinkler and smoke

alarm systems. Figure 1 shows the distance from the ceiling of the maximum

velocity, 6 vm , as a function of radial distance, r, from the plume center. Both

of these quantities have been normalized with respect to the burner-orifice-toceiling distance, H. The data shown are the average for all five strengths for

two different heights and for two different times. Some difficulty exists in

obtaining 6 vm exactly because of the scatter in the velocity data, and because

the velocity curves are not sharply peaked; however, within the scatter in the

data, it appears that 6 vm /H depends only on r/H, and is independent of time and

of H. Cooper’s model (1), which is based on momentum-driven wall jets, agrees

well with the data even in the region beyond r/H=l where buoyancy effects start

to become important.

The location of the temperature maximum in the ceiling jet is a function of

many more variables than the location of the velocity maximum since the thermal

properties of the ceiling must be considered in addition to the condition in the

plume. The normalized distance of the temperature maximum, <5xm> from the

ceiling is shown in Figure 2 as a function of r/H for various times. It is

clear that 6

i- m increases with increasing r/H and that it decreases with

increasing time. Effort is being expended to construct a model which will

correlate the 6 Xm data and so enable a better prediction of the location of the

temperature maximum location.

The maximum steady-state velocity, Vmax and maximum steady-state temperature

difference, ATmax , between the jet and the ambient air are plotted in Figures 3

and 4. As mentioned earlier, the velocity is independent of time. The data

have been normalized in a form used by Byler(2). The normalized ordinate in

each case is not non-dimensional since the fluid properties and gravity have

been left out to simplify the normalized form, kgs units have been used in

these figures. The data in each figure correlate well, and curve . fitting yields

the following equations for r/H>0.26.

V /Q

1/3

H_1/3

= 0.017(r/H) J

+ 0.113(r/H)

_1

+ 0.097 (1)

max

AT /Q

2/3H"5/3= O.^Cr/H)"2

+ 5.43(r/H ) -1

+ 2.48 (2)

max

The normalized velocity and normalized temperature decrease rapidly with

increasing r/H at small values, but become almost constant at large r/H.

Also shown in these figures are correlations due to Alpert(3), Heskestad and

Delichatsios (4) and Cooper(l). Our maximum velocity data seem to be in better

agreement with Alpert’s results than the correlations of Cooper or those of

108
Heskestad and Delichatsios, and seem to generally fall between the curves. The

maximum temperature data have the same general shape as the curves of the other

investigators but have higher values. Differences are to be expected due to

different ceiling materials and different conditions on the ceilings upper

surface. v Normalized steady-state velocity and Temperature Profiles The steady-state

ceiling jet velocity and temperature profiles, with V and AT normalized in the

same way as V^x and AT^ according to Eqs. (3 & 4), are shown for the r/H

location of 0.26 in Figures 5, and 6. The distance away from the ceiling, y, is

normalized by the floor-to-ceiling height. The velocity profiles appear to

collapse very well onto a single curve. There is some scatter in the data which

is generally due to changes in the room and variations in the experimental conditions. Some of the scatter may be due to the resolution in selecting the time

shift. The normalized temperature profiles in Fig. 6 show relatively good

agreement between the results for the range of Q’s and H’s used.

References

1. Cooper, L.Y., "Ceiling Jet-Driven Wall flows in Compartment Fires", NBSIR

87-3535, April, 1987.

2. Beyler, G.L., "Fire Plumes and Ceiling Jets", Fire Safety J. , 11, 53-75,

1986.

3. Alpert, R.L. , "Fire Induced Turbulent Ceiling Jet", Technical Report,

Factory Mutual Corp. , FMRC Serial No. 19722-2, May 1971.

4. Heskestad, G. and Delichatsios, M.A. , Proc. 17th Int’l Symp. on Combust.,

Pittsburg, 1113, 1978.

Reports and Publications

1. Motevalli, V. , C. Marks and B. McCaffrey, "Measurement of Velocity and

Temperature Profiles in Low-Speed, Turbulent, Non-Isothermal Flows", ASME

paper //87-WA/HT-16 , 108th ASME Winter Annual Meeting , Boston, Mass., Dec.

1987. Also published by National Bureau of Standards as report #NBS-GCR87-535.

2. Motevalli, V., C. Marks and B. McCaffrey, "Transient Ceiling Jet

Characteristics", Eastern Section: Combustion Institute, 20th Fall Technical

Meeting, Gaithersburg, MD, Nov. 1987, pp. 88-1 to 88-4.

3. Marks, C.H. and V. Motevalli, "Transient Ceiling Jet Characteristics",

Summaries of Center for Fire Research In-House Programs and Grants - 1987,

NBSIR 87-3650, National Bureau of Standards, Gaithersburg, MD, Oct. 1987,

pp. 137-140.

4. Motevalli, V. and C.H. Marks, "Transient Characteristics of Unconfined FirePlume-Driven Ceiling Jets", Annual Report for National Bureau of Standards

grant #70NANB5H0551 . Also published as NBS-GCP-88-540.

109
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110
CENTER FOR FIRE RESEARCH

1988

CEILING FLAME LENGTH

Professional Personnel

v Daniel Gross, Project Leader

Project Objective

To measure the extension of flames beneath ceilings under buoyancy-controlled

conditions

The two principal configurations examined were (1) an axisymmetric gas burner

flame with and without a horizontal ceiling and (2) a gas burner flame adjacent

to a corner-wall and below a confining horizontal ceiling. The natural gas

supply range corresponded to energy input rates up to 400 kW using burners of

0.61 and 0.91 m diameter in the axisymmetric configuration and a 0.54 m square

burner in the corner-wall configuration. The mean flame tip location was

estimated using several techniques: (a) visual (b) 35 mm time-exposure color

photography (c) video photography (d) temperature gradients using thermocouples

and (e) oxygen and carbon dioxide concentration gradients.

Technical Accomplishments

Measurements were made of luminous gas flame lengths with and without ceilings

under steady burning conditions and expressed in dimensional and nondimens ional

terms. The combined vertical and horizontal extension of the intermittent flame

tip in the presence of a ceiling was found to be approximately 20 % less than

the vertical flame height for the corresponding energy release rate without a ceiling. The accompanying temperature and gas concentration measurements

suggest that this was a result of higher temperatures and therefore more

complete burning, although no analysis was made of air entrainment or of the

overall heat balance.

Reports and Publications

Scope

H-0 35m

"Measurements of Flame Lengths Under

Ceilings", D. Gross, National Institute

of Standards and Technology Internal

Report NISTIR 88-3835 August 1988

(also submitted to Fire Safety Journal)

o 50 100 200 300 400

ENERGY SUPPLY RATE (kW)

rt|m 3. lorlioetal flaaa ntrealoa la ccTH«r-»all-c«n In* coaf l*ur«tloa 0.J* a a*. |U bursar

111
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

MODEL ACCURACY ASSESSMENT

Professional Personnel

Richard D. Peacock, Project Leader

Emil Braun, Physicist

Sanford Davis, Chemist

Walter W. Jones, General Physical Scientist

J. Newton Breese, Computer Programmer

C. Lynn Forney, Mathematician

Project Objective

The objective is to develop the generic methodology to provide a quantitative

assessment of the accuracy and limitations of computer based fire models.

Scope

The Center for Fire Research has been developing mathematical models for

predicting the conditions which occur as a fire develops and spreads within a room as well as to the rooms connected to it. These models must be validated

in order to become useful tools in determining and solving problems related to

fire safety. Currently work is being done to establish a methodology for assessing the validity of the mathematical models developed. This assessment problem

is likely to require as much time and effort as the model development itself.

It includes four broad steps: 1) conceptual model validity - checking that the

theory and underlying assumptions are correct and/or reasonable, 2) computerized

model verification - ensuring that the computer programming and implementation

of the conceptual model are correct, 3) operational validity - determining that

the model's output behavior has the

accuracy required for the model's

intended purpose, and 4) data validity - checking that the data used to develop

and validate the model are adequate and

correct

Technical Accomplishments

During the current year, activity

focused in two areas: 1) continued

development and refinement of the experimental data to be compared with the

models, and 2) an analysis of the

sensitivity of one of the simpler models

which serves as a precursor to the

analysis of the more complicated models.

Figure 1 Measured rate of heat release measured by oxygen consumption calorimetry during several tests along

with estimated repeatability.

113
Several full scale experiments have

been performed for testing two-zone

fire growth and / or spread models.

The experimental arrangement

consisted of a burn room and a 12.19-

m long corridor with a target room

on one side. A diffusion flame

burner using natural gas served as

the fire source. In an attempt to

develop statistically meaningful data

for each test situation, each test

combination of fire size and corridor

configuration was repeated numerous

times. The primary data from the experiments was provided by thermocouples, smoke meters and pressure probes. Details of the methodology used

in the experiment are discussed in a

report on the experiments. Although

it is unreasonable and not particularly useful to present all of the data collected from every test conducted, figure 1 shows some of the data from one dat.a set and illustrates the data from the

individual tests together with the average and standard deviation of the set of

tests (8 in this case) as a function of time. The complete set of data from

these experiments provide an independent set of experimental data for comparison with multiple room two-zone fire growth and spread models. As a sample of

the use of the data, figure 2 shows the measured upper layer temperature and

interface height as a function of time for the three rooms in the test facility

and compares it to predictions from one of the current models.

In a sensitivity analysis, the model outputs are examined to see how they respond

to perturbations in the input parameters. Since it is often the case that the

model inputs are not known precisely, it is important to know how much the

outputs can be changed by errors in the input. To investigate methods of

determining model sensitivities, the model ASET-B was selected. ASET-B is a

fairly simple single compartment, two-zone fire model with five input parameters

and two time -dependent output variables. The relatively small size of this model

makes the investigation of sensitivity analysis methods tractable. In the

future, more complex models will be studied.

ASET-B is fairly insensitive to the uncertainty in the room area and height above

the burner, but can be quite sensitive to the uncertainty in the value of A c , the

fraction of energy from the fire which is transferred by convection. Since the

objective of ASET is to be able to determine available safe egress time, A c can

be selected according to whether time to detection or time to hazardous conditions is desired. (ASET=time to hazardous conditions - time of detection.) As

Cooper 1 suggests, select A c near .6 to obtain a conservative estimate of the time

until hazardous conditions occur and .9 to obtain a conservative estimate of the

time until detection (by occupants or detectors) occurs because the fire

progresses more quickly as A c becomes smaller. In general, if A c is thought to

Time (s) Time (s)

Figure 2 Comparison of measured and predicted upper layer

temperature and layer interface position

in a three room test facility.

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

Materials, Vol. 6, Nos. 3&4, pp 135-144, September/December 1982.

114
be within x% of A, then choose A c to be (l-x/100)A for a conservative estimate

of the time to hazardous conditions and (l+x/100)A for a conservative estimate

of the time until detection.

The decoupled direct method selected for the ASET-B analysis seems to provide

reasonable error bands on the ASET-B solution given a 10% change in area, A c , or

height above the burner and also can provide error bands on the time to reach

a particular temperature or height. The cost to provide these error bands is

that of deriving the sensitivity equations and solving a matrix equation. For

ASET-B this effort was small compared to the information provided. For other

models, it may be too difficult and complicated to derive the sensitivity

differential equations analytically; however, it may be reasonable to compute

the Jacobian of f and the partial derivatives of f with respect to the parameters

numerically instead. A shortcoming of this method is that it only provides error

bands for the case where one input is perturbed. However, a crude approximation

for perturbation of more than one variable (for the interface height in ASET-B,

f(t,v+ vi e i + v^ej) or for the temperature <f>( t,v+ vi e i + v^)) can be obtained with

f (t , v) + (3$'/3vi ) Vi+CJ^/JVj) Vj [<£(t ,v) + (d<f>/dvi ) v^d^/dv^) Vj ]

. To improve this

estimate an additional set of differential equations can be derived from the

first order sensitivity equations that would provide the second order sensitivity

coefficients. To do this, however, may be impractical as it requires solving

m

2 n additional equations where m is the number of parameters and n is the number

of original equations

It was seen that the sensitivities of the

interface height to area, height above the

burner and A c seem to behave (with respect to

shape) in the same manner across the parameter

space considered. As expected, the interface

height is initially sensitive to the height

above the burner, but becomes less and less

sensitive with time. Initially the interface

height appears to be insensitive to A c

. At

time t=180 seconds, the fuel source is jumped

from 1 kw to 25 kw making the effect of A c more

pronounced and the sensitivity of interface

height with respect to A c appears to become

linear in time. The interface height

sensitivity to area rises rapidly to .6-1.5

meters initially. It then levels off with a

slight downward trend until the interface

height reaches the burner height where it

begins to rise. When A c is at a value near .6,

the interface height is less sensitive to A c than to area; however, when A c is near .9, the

functions of sensitivity with respect to A c and

area cross each other with A c becoming the

dominant parameter. The study indicates that

the error in interface height due to a 10% change in area is bounded by approximately .1 m. The error do to a 10% uncertainty in height above the burner

is bounded by 10% until the interface height reaches the burner height. From

this point on the error is bounded by .01 m.

Figure 3. Effect of a 10% change in the input parameters

of the ASET-B model on the predicted height of the layer interface.

115
Reports and Publications

Jones, W. W. , and Peacock, R. D., Refinement and Experimental Verification of

a Model for Fire Growth and Smoke Transport , paper presented at the Second Annual

Symposium on Fire Safety Science, Tokyo, Japan (June 1988).

V Peacock, R. D. , Davis, S., and Lee, B. T. , An Experimental Data Set for the

Accuracy Assessment of Room Fire Models, Nat. Bur. Stand., (U. S.), NBSIR 88-

3752 (April 1988).

Peacock, R.D. , Status of Predicting Real Fires and Their Effects, States

Symposium on Fire Toxicity, Salt Lake City, UT, 29-35 (November 19-20 1987).

Davies, A. D. , Some Tools for Fire Model Validation, Fire Technology, Vol. 23,

No. 2, May 1987 pp 95-114.

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

Evaluation of Computer Fire Models, NBSIR in preparation.

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

International Symposium on Mathematical Modeling and Related Fire Test Methods,

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

The Journal of Fire Sciences.

Forney, C. L. , A Sensitivity Analysis of a Simple Fire Growth Model, to be

published

Related Grant

J. P. Jarvis and M. Kostreva - Clemson University, "Graphical Presentation and

Numerical Analysis of Fire Data for Model Validation."

116
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : Clemson University

.G rant .JJq 60NANB6D0627

Grant Title Graphical Presentation and Numerical Analysis

of Fire Data for Model Validation

Principal Investigator : James P. Jarvis, Professor

Department of Mathematical Sciences

Clemson University

0-104 Martin Hall

Clemson. SC 29634-1907

Telephone: (803) 656-5214

Other Professional Personnel : Michael M. Kostreva, Associate Professor

Cheryl L. Forney, Research Associate

NBS Scientific Of ficer: Richard Peacock

Technical Abstract :

Introduction . The objective of this work is the development of tools and

procedures for validation of computerized fire models. The areas of emphasis

have been (1) dimensional analysis and determination of core parameters and

(2) sensitivity analysis for physical parameters. The research has been done

in large part in the context of specific models developed at the Center for

Fire Research (CFR) at the National Bureau of Standards. The ASET model

(Available Safe Egress Time), developed by Cooper [1,2] has been of particular

interest

The validation process involves the comparison of experimental results with

model predictions. We are primarily concerned with operational validity - determining whether a model’s output behavior has the accuracy required for

the model's intended purpose. The use of dimensional analysis and determination of core parameters relate to issues of efficiency and simplification of a computer model. Sensitivity analysis deals with the nature of changes in a model’s output as a function of changes in its input.

Dimensional Analysis and Core Parameters . The main idea in dimensional

analysis is to exploit relationships among a model’s physical parameters to

produce a smaller, but still complete, set of “core” parameters. As a simplistic example, if two parameters appear in a model only as a ratio, those

two parameters can be replaced by a single new parameter, the ratio. The

advantages of dimensional analysis and reduction to core parameters are in

enhanced model simplicity and fundamental understanding of model dynamics. In

addition, computational efficiency is increased through avoidance of unnecessary duplication in ranging parameter values when applying the model. It

should be noted that the choice of a minimal set of core parameters is not

unique and that their choice is not well defined.

These concepts have been applied to the ASET model. ASET

the upper layer height and temperature in a single room fire

ables can be used to estimate the available safe egress time

is a model for

These two varifor a single room

117
fire. In the original formulation, roughly a dozen physical parameters were

reduced to four dimensionless core parameters. The current effort has further

reduced that set to two core parameters. The primary physical parameters are:

A height of fire above floor.

H height of ceiling above fire,

A area,

\c fraction of energy release rate transferred to surfaces,

Xr fraction of energy release rate radiated from combustion zone,

pa ambient density.

Cp specific heat, and

T a ambient temperature.

These are combined to produce core parameters CXi

(* 2 = (0.210) • [(l-Xr )g(A+H) 5 pa

2 C

p

2 T a

2 /Qo'] 1/3 / (1-XC ) . description of the physical parameters, see [1,2])

and CX 2 where 0C]_=A/ (A+H)

(For a more complete

and

To illustrate the advantages of the core parameter representation, we consider the effects of changing two physical parameters in the ASET model: room

height and area. Figure la shows how these two parameters might be ranged in

order to apply the ASET model in a variety of conditions. Figure lb illustrates the same values of height and area when translated to the two core

parameters. Note that the apparent uniform coverage of the physical parameter

space illustrated in Figure la is not actually realized when viewed in terms

of the core parameters.

i 1 r 800 1000

ALPHA

(b)

Figure 1.

Correspondence between physical parameters (a) and associated core parameters

(b).

Uniform coverage of the parameter space is accompl

parameters. However, uniform coverage of the model’s

not be the most appropriate method of analysis. As i

only certain values in the core parameter space might

physical parameters. In addition, in describing the

ished using the core

response surface might

llustrated in Figure 2a,

correspond to realizable

response surface of a

118
model, it is more effic

response surface is uni

output changes more rap

applied to a model to p

understanding of the mo

ient to utilize a few points

form with a larger number of

idly (Figure 2b) . All of the

rovide greater efficiency in

del’s output.

in a region where the

points where the model’s

se techniques can be

computation and greater

Figure 2

(a) Non - rectilinear region in core parameter space corresponding to physically

realizable parameters.

(b) Regions of uniform versus' rapid change in model output.

Sensitivity Analysis . Sensitivity analysis for a model generally involves

identification of dominant variables, feasible output range, and the output

range generated by a specified input range. Specifically, this information is

used in determination of the accuracy required of input variables, the number

of input variables to be studied, and the basis of comparison between model

and experimental data.

For a model having an n dimensional state vector and a k dimensional parameter vector, the sensitivity analysis problem can be stated as an estimation

problem for the nk “sensitivity coefficients” - the time-varying partial

derivatives of the output vector with respect to the input parameters.

Several approaches for estimating these sensitivity coefficients have been

investigated using the ASET model. These include finite differences and both

direct coupled and decoupled methods [3,4]. The use of finite differences is

fairly standard and will not be discussed here. The direct coupled method

combines the original system of n differential equations with an additional nk

differential equations (one for each sensitivity coefficient) and solves the

resulting system directly. The direct decoupled method involves solving the

original system of n differential equations and then using an interpolation

scheme to estimate the sensitivity coefficients from the time -dependent output

vector. For ASET, the latter is equivalent to solving k systems of n linear

equations

Figures 3a and 3b illustrate the results obtained via the direct decoupled

approach as applied to ASET. These figures show the dependence and sensitivity of both upper layer height and temperature to a 10% variation in room

height and area respectively. Again, typical sensitivity analysis information

is obtained: in this case, the output variables are relatively insensitive to

changes in room height (Figure 3a) and the upper layer temperature is fairly

sensitive to changes in room area (Figure 3b)

119
0) u3

•P

COu

0) D-e

0) H

u

<D

CO -3u

<vClCl

D

(a)

(b)

Time Time

(a)

Figure 3

Change in upper layer height /temperature with a Change in upper layer height /temperature with a

(b)

10% change in room height.

10% change in room area.

Summary . A variety of techniques are being examined for their applicability to the fire validation problem in the context of the ASET model. Future

areas for examination include incorporation of the use of core parameters into

the sensitivity analysis, further comparison of the advantages of the different approaches to sensitivity analysis, and combining these tools and techniques into procedures and software to enhance their more general applicability.

References

1. Cooper. L. Y. , "A Mathematical Model for Estimating Available Safe Egress

Time in Fires,” Fire and Materials 6, 135*142 (1982).

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

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

3. Dickinson, R. P. and R. J. Gelinas, "Sensitivity Analysis of Ordinary

Differential Equation Systems * A Direct Method,” Journal of Comp. Physics

21. 123*143 (1976).

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

Coefficients in Chemical Kinetics,” J. Chem. Phvs

81*5, 2385*2393 (1984).

Reports and Papers;

J.P. Jarvis, M.M. Kostreva. and C.L. Forney, “Tools for Validation and

Analysis of Fire Models,” Combined Proceedings, 20th Fall Technical Meeting of

the Eastern Section of the Combustion Institute & Annual Conference of the

Center for Fire Research, November 1987.

120
'
PART I. Basic Research and Tools for ’’Engineered" Fire Safety

(In-House Proiects and Associated Grants Funded by

NIST)

D. HAZARD MODELING

CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

CARBON MONOXIDE PREDICTION

Professional Personnel

v William M. Pitts, Project Leader

George W. Mulholland, Head, Smoke Dynamics Group

Nelson P. Bryner, Chemical Engineer

Project Objective

Develop scientifically- sound principals, metrology, experimental data, and

calculational procedures for measurement and prediction of carbon monoxide

(CO) production by fires and to utilize this information to assess the hazard

due to this toxic species.

Scope

This program is designed to assess the importance of CO in fire toxicology and

to provide the scientific background required to allow the prediction of CO in

real fires. Efforts range from purely empirical studies such as assessments

of CO production in full scale fire tests to fundamental studies designed to

improve the understanding of the chemically reacting turbulent flows which

ultimately produce CO. New information which is generated is incorporated

into existing CFR models of fire behavior.

Technical Accomplishments

1. CO Production in Full-Scale Enclosure Fire Tests

Results of several series of full-scale fire tests have been analyzed to

assess the concentrations of CO produced by large enclosure fires. The

production of CO is characterized by the C0/C02 ratio. The importance of

ventilation parameter on the burning behavior is clear. If a fire is fully

ventilated the C0/C02 ratio is generally low (< 0.01). However, as the fire

becomes underventilated CO levels increase greatly and the C0/C02 ratio can

approach 0.3. The final levels of CO detected for positions well away from

underventilated fires appear to depend on whether or not additional burning of

combustion products occurs outside of the enclosure. The conditions necessary

for additional burning are not well characterized and this lack of knowledge

probably represents the greatest uncertainty concerning the conditions

necessary for the production of high CO concentrations at positions far from a fire source.

2. Effects of Vitiation on Production of CO

The cone calorimeter is widely utilized for investigating the combustion of

small fuel samples under conditions of heat irradiation characteristic of

large fires. Combustion products produced are collected and analyzed. The

C0/C02 ratio is one of the parameters which is determined. In the past,

measurements have been performed under fully ventilated conditions which

generally produce low levels of CO. Modifications are in progress which will

123
allow control of the amount and composition of the "air" provided to the

combustion region of the cone calorimeter. The new design features include an

adjustable total flow through the chamber with flow straightening, variable 0 ? concentration, load cell separated from combustion chamber, overpressure panel

on back of cone, and a radiation shield for the specimen. In this way it will

be possible to investigate the production of CO for underventilated and

partially-vitiated conditions. Systematic studies utilizing this modified

cone calorimeter will provide new insights into the conditions which result in

the formation of high concentrations of CO in fires. Wood has been chosen as

the first material to be investigated because of its wide use and because of

the known effect of reduced ventilation on combustion product yields. Large

scale tests performed by Rasbash at the Fire Research Station and by

Williamson at Berkeley indicate that both CO and smoke yield increase by more

than a factor of ten as the ventilation rate is decreased.

3. Fundamental Investigations of Turbulent Combustion

The production of CO is ultimately due the entrainment, mixing behavior, and

chemical reactions occurring within the turbulent buoyant plume of a fire.

Due to the heat release there is a strong coupling of the reactions occurring

in the fire and the turbulent structure of the plume. This part of the CO

priority project is an effort to characterize the turbulent structures

responsible for mixing within buoyancy -driven plumes. Measurements are made

in isothermal, buoyancy -driven flows generated by using gases which are

lighter than air (e.g., helium or methane). During the past year flow

diagnostics developed for multi-point measurements of concentration in buoyant

plumes have been significantly improved by modifying existing equipment and

improving data acquisition capabilities. A cylindrical enclosure having a height and diameter of 2.4 m has been designed and is under construction. It

is to be utilized to provide a well-characterized environment for the

characterization of the buoyant flows.

Reports and Publications

"Development of a Line Camera for Real-Time Measurements of Concentration in

Turbulent Flow Fields, W. M. Pitts, Proceedings of the Fifth International

Congress on Applications of Lasers and Electroptics . Volume 58, The Laser

Institute of America, 1987, pp . 7-14.

"The Effects of Global Density and Reynolds Number Variations on Mixing in

Turbulent, Axisymmetric Jets -- Implications for Turbulent Jet Diffusion

Flames," W. M. Pitts, Proceedings of the 1987 ASME/JSME Thermal Engineering

Joint Conference . Vol. 1, Eds. P. J. Marto and I. Tanasawa, The American

Society of Mechanical Engineers, 1987, pp . 123-135.

"Mixing in Variable Density, Isothermal Turbulent Flows and Implications for

Chemically Reacting Turbulent Flows," W. M. Pitts and T. Kashiwagi, National

Bureau of Standards Internal Report, NBSIR 87-3550, May, 1987.

Related Grants

"Soot Particle Formation and Destruction in Diffusion Flames," Robert J.

Santoro, Pennsylvania State University.

124
"Radiation From Turbulent Luminous Fires," Gerald M. Faeth, University of

Michigan.

"Experimental Studies of the Environment and Heat Transfer in a Room Fire,"

Edward E. Zukoski , California Institute of Technology. (See p. 97 for description)

125
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution: The Pennsylvania State University

Grant No.: 60NANB7D0706

Grant Title: Soot Particle Formation and Destruction

in Diffusion Flames

Principal Investigator: Dr. Robert J. Santoro

Department of Mechanical Engineering

313A Mechanical Engineering Building

University Park, PA 16802

Other Professional Personnel: T. F. Richardson, E>octoral Student

R. Puri, Doctoral Student

NBS Scientific Officer: Dr. Kermit C. Smyth

Technical Abstract:

Introduction The formation of soot particles has important effects on energy transfer

and combustion product emissions from fires which dramatically impact loss of life and

property. The objective of the present study is to provide a fundamental understanding of the

soot formation and destruction processes which impact fire growth, spread and emissions.

The approach adopted emphasizes two elements of the problem. The first element

concentrates on the processes responsible for the conversion of fuel carbon to soot (i.e.

particle inception and surface growth) and particularly stresses the importance of fuel

molecular structure. The second element examines the destruction stage of the process which

reduces the soot concentration in the later parts of the flame. In particular, specific

information on the relationship between soot and CO production is sought. A basic thrust of

the work is to identify the overall mechanism relating the emission of CO and soot particles

from flames. In addition, fundamental information on soot oxidation processes as well as the

role of soot particles in the competition for oxidizing species such as O2 and OH may be

forthcoming.

The results of this study are of direct relevance to the problems of fire research. Soot

particle formation and destruction along with other basic phenomena such as ignition,

hydrocarbon chemistry, turbulence, radiative transfer and plume dynamics, constitute the

fundamental elements of the fire problem. Soot particles, once formed, are not passive species

in the evolution of the fire situation. Through their radiative properties, soot particles can

strongly enhance flame spread rates or the conditions necessary for "flash over" to occur. Soot particles present other complications through their role in visual obscuration and

potential effects on carbon monoxide formation. These effects represent serious problems in

terms of victim escape from fire situations and significantly contribute to fire mortality rates.

However, with a proper understanding of the fundamental controlling mechanisms, significant

improvements in the predictive capabilities of fire science modeling can dramatically improve

the present situation.

126
Experimental Approach These studies are carried out using a coannular diffusion flame

facility to which extensive laser-based diagnostics can be applied for particle and velocity

measurements. The burner, which has been previously described in detail [1], consists of a 1.1

cm diameter fuel tube surrounded by a 10 cm diameter air annulus. Flow conditioning of the

air and fuel flows is provided by a series of glass beads and fine screens. A ceramic

honeycomb at the exit of the air annulus is used to provide a uniform flow field. The fuel

flow can consist of up to three metered gases which provides for the study of fuel mixtures

as well as nitrogen dilution of the fuel for temperature control. To protect the flame from

room disturbances, a metal chimney has been incorporated into the burner facility. This

chimney translates horizontally with the burner, which slides vertically within the chimney.

Slots machined in the chimney allow for optical access. The burner is mounted on a pair of

computer controlled motorized stages which provide for vertical and horizontal motion. These

motorized stages are used to traverse the burner through the laser beam to obtain

measurements over the cross section of the flame at a particular height.

In order to accomplish the objectives of this study, a number of measurement capabilities are required. These include laser light scattering for particle sizing, laser velocimetry for

velocity measurements and intrusive probing for temperature and species concentration

measurements. Figure 1 shows a schematic representation of the laser scattering/extinction

system used to characterize the soot particle field throughout the flame. In addition to the

single scattered light detector shown in this figure, light scattering measurements can also be

obtained at 45° and 135°. Signal detection from the photodetectors is accomplished using

separate computer controlled lock-in amplifiers. This approach allows for a high degree of

user independent data acquisition and significantly eases the experimental procedures.

A similar arrangement is used for the laser velocimetry measurements. A probe system to

obtain CO, CO2 and O2 concentration measurements is presently near completion.

Instrumentation for continuous measurement of these species is available using standard online techniques (e.g. NDIR for CO and CO2 measurements). In addition, gas chromatography

and mass spectrometry techniques are available for more detailed measurements.

Technical Accomplishments The study of the effects of fuel molecular structure on the

formation of soot is one of the major elements of the present work. However, a difficulty in

studying fuel structure effects has been the wide differences in the flame size and shape

which results when various fuels are burned at, for example, a characteristic condition such as the soot point. These differences result in important variations in the temperature and

velocity fields which make quantitative comparisons impossible between the flames. In the

present studies, this difficulty is addressed by adopting a fuel addition approach involving well

characterized baseline flames in which the soot particle field is characterized in detail. The

fuel molecular structure effects are then investigated by adding an additional fuel component

to the baseline flame. However, the total carbon flow rate is held constant. This means that

an appropriate fraction of the baseline fuel is replaced with the additive fuel. With the soot

contribution from the baseline fuel known, the effect of the additive fuel on the formation of

soot particles can be determined. Under these conditions, the flame size and shape remains

similar for all flames.

Two fuels, methane and ethene, have been selected to serve as the baseline flames. The

methane flames have relatively low soot particle formation and thus provide greater sensitivity

for measuring changes introduced by varying the fuel molecular structure. The ethene flames

represent the best studied set of diffusion flames presently available and provide a significant

comparative data base [1-2]. Comparisons between the two baseline systems will also provide

a basis for examining potential synergistic effects between the fuel addition species and the

baseline fuel. Studies of the ethene and methane baseline flames have been completed and

studies of a specific series of fuels have been initiated. These studies involve comparisons

between an alkane, alkene and alkyne fuel added to a methane baseline flame. Specifically

127
butane, 1 -butene and 1,3-butadiene have been investigated.

These initial studies have concentrated on soot particle measurements using the laser

scattering/extinction approach. Analysis of the results of these measurements indicates a significant increase in the amount of fuel converted to soot as the fuel added to the flame is varied. Based on the mass of fuel added, the fuel conversion percentage increases from 12%

for butane to 35% and 44% for butene and butadiene, respectively, at the location of maximum

soot concentration in the flame. A more detailed comparison is given in Fig. 2 where the

integrated soot volume fraction is plotted as a function of axial location. The integrated soot

volume fraction, Fv, is given by

R

F = 2 r f f (r,z) rdr v v

o

where fv

is the soot volume fraction at r and z, the radial and axial positions respectively.

Thus, Fv

represents a measure of the total amount of soot at a particular axial position.

These results clearly indicate a systematic decrease in the axial position where soot is first

observed as a more sooty fuel is introduced into the flame. This indicates that the reactions

leading to the first soot particles occur more rapidly in these flames. More detailed

comparisons utilizing the velocity and temperature fields should offer the potential for

comparison with overall chemical kinetic rate information describing the pyrolysis and

oxidative pyrolysis mechanisms established for these fuels. Recent work using probe sampling

techniques have demonstrated that such comparison approaches are quite promising [3].

The results shown in Fig. 2 are limited to regions of the flame where particles are

present. As an approach to investigating the preparticle and inception regions of the flame,

laser fluorescence measurements have also been obtained. These measurements can be viewed

to be indicative of the presence of large hydrocarbon species which may be involved in the

particle inception chemistry. The objective of these studies is to provide a relative measure

of the hydrocarbon chemistry which can be compared to more fundamental chemical modeling

approaches [3].

In addition to providing a basis from which to examine fuel molecular structure effects

on soot particle inception and growth, these studies will be used to examine the effects of

soot concentration on CO emission from these flames. As the previous results demonstrate, a wide variation in soot loading can be achieved through appropriate fuel addition.

Measurements of the CO concentration will be made above these flames in order to assess the

effect of soot loading on the CO emission from fires.

The significance of these results lies in the potential to provide fundamental insights into

the soot formation and destruction chemistry. Additionally, such data can be used to identify

the important processes controlling actual fire situation. From these insights, approaches to

handling the more complicated multicomponent fuel conditions of real fires can be addressed.

References

1. Santoro, R. J., Semerjian, H. G. and Dobbins, R. A., Combustion and Flame. 51, p. 208

(1983).

2. Santoro, R. J., Yeh, T. T., Horvath, J. J. and Semerjian, H. G., Combustion Science and

Technology . 53, p. 89 (1987).

128
3. Miller, J. H., Mallard, W. G., and Smyth, K. C., Twenty-First Symposium (International)

on Combustion. The Combustion Institute, pp. 1057-1065 (1986).

Reports and Papers

R. J. Santoro and H. G. Semerjian, "The Effect of Fuel Structure on the Formation and

Growth of Soot Particles in Diffusion Flames", The Twenty Eighth Biennial Conference on

Carbon, Worcester Polytechnical Institute, (July 18-24, 1987), Worcester, MA.

R. J. Santoro, "Soot Particle Formation in Diffusion Flames", American Chemical Society

Meeting, Advances in Soot Chemistry, (Aug. 30-Sept. 4, 1987), New Orleans, LA.

R. J. Santoro, "Fuel Molecular Structure Effects on Soot Particle Growth in Diffusion

Flames", Eastern Section Meeting of the Combustion Institute, Twentieth Fall Technical

Meeting, Nov. 2-5, 1987, Gaithersburg, MD.

Laser Scattering/Extinction System

ZZ2 B

Later C

pr a

L

C • chopper, M • mirror, PR • polarization rotator, L • lent, S • spatial filter NDF • neotral denthy filler, PD • photodiode, P • polarizer, F • narrow band filter, PMT • photomultiplier,

F«(art 1 Schematic of later acatiering /exunction apparatus. Figure 2 Companion of the integrated too: volume fraction, Fv, for the butane, I -butene and

1.3-butadiene fuel addition studies The fumes had a methane flow rate of 5.6 cnJ

/s and a fuel addition flow rate of 1.05

129
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution:

Grant No:

Grant Title:

Principal Investigator

Other. Professional Personnel:

NBS Scientific Officer:

Technical Abstract:

The University of Michigan

60NANB5D0576

Radiation from Turbulent Luminous Flames

Professor Gerard M. Faeth

Department of Aerospace Engineering

218 Aerospace Engineering Building

Ann Arbor, MI 48109-2140

M. A. Kounalakis, Graduate Assistant

Y. R. Sivathanu, Graduate Assistant

Dr. David D. Evans

Introduction . This investigation is considering two aspects of thermal radiation from unwanted Fires, as follows: (1) the scalar structure of turbulent flames, emphasizing the radiation properties of soot in luminous flames;

and (2) effects of turbulence/radiation interactions, emphasizing nonluminous flames to simplify interpretation of

results. The findings have application to modeling fires in structures, developing materials test codes, and

developing fire detectors. Progress on the two phases is briefly discussed in the following, additional details can be

found in the papers and reports listed and the end of this report.

Luminous Flames . The laminar flamelet concept of turbulent nonpremixed flames implies that scalar

properties can be correlated solely as functions of mixture fraction, called state relationships, independent of local

values of flame stretch and the past history of the flow. When this concept applies, predictions of the scalar

structure of turbulent flames are vastly simplified since only governing equations for mixture fraction properties

must be solved. The laminar flamelet concept is widely accepted for gas species concentrations in turbulent diffusion

flames except near points of flame attachment where effects of finite-rate chemistry prevail. The objective of the

present investigation is to determine the conditions, if any, where the concept can be extended to soot volume

fractions - the soot property that primarily influences thermal radiation.

Measurements of soot volume fraction state relationships are being undertaken for a variety of burner sizes

(5, 50 and 250 mm diameter), fuel flow rates, and fuels. Work thus far has been limited to the overfire region.

Figure 1 is an illustration of the soot volume fraction state relationship measured for acetylene/air diffusion flames.

The data represents measurements of soot volume and mixture fractions at various points in the overfire region of

these flames. The correlation in the rich region is based on earlier measurements in laminar flames, and in the lean

region by assuming a constant soot generation efficiency (defined as the fraction of fuel carbon converted to soot).

The correlation in the lean region implies that soot reaction quenches at a fixed soot volume and mixture fraction,

followed by passive mixing in the overfire region. The measurements agree quite closely with the correlation,

implying a wide range of conditions where the laminar flamelet concept for soot volume fractions can be used for

radiation analysis of acetylene flames.

Tests have also considered propylene, ethylene and propane flames. It has been found that soot volume

fraction state relationships become progressively less satisfactory as the propensity of the fuel to soot decreases. In

effect, the soot generation efficiency appears to be constant for a given flame conditions but the soot generation

efficiencies tend to increase as flow residence times in the flame increase. These results are illustrated in Fig. 2,

where soot generation efficiencies are plotted as a function of estimated characteristic residence times for all the fuels. Clearly, soot generation efficiencies are relatively independent of residence time (for the range tested) for acetylene,

which accounts for the reasonably good soot volume fraction state relationship seen in Fig. 1. However, the other

fuels exhibit residence time effects - particularly when their soot generation efficiencies are low - although soot

generation efficiencies appear to approach an asymptotic value at long residence times. If this proves to be true, the

laminar flamelet concept for soot volume fractions would still be a viable approach for treating a wide range of

practical fires.

130
Current work is extending measurements to the 250 mm diameter burner so that the tendency to reach

asymptotic values of soot generation efficiencies at long residence times can be studied. Direct measurements of

characteristic residence times are also being undertaken so that conclusions will not be based on uncertain estimates.

The next phase of the work will involve evaluating the laminar flamelet concept for soot volume fractions in the

fuel-rich region of turbulent diffusion flames.

Nonluminous Flames . Past work has shown that radiation from turbulent flames is generally several times

larger than estimates based on mean scalar properties within the flames. This is an effect of turbulence/radiation

interactions, i.e., the fact that radiation properties are a very nonlinear function of scalar properties. Several ad hoc

stochastic methods have been developed, which have yielded encouraging predictions of effects of turbulence/radiation

interactions. The objective of present work is to extend these concepts, improving their physical basis and providing

methods for predicting the properties of radiation fluctuations.

Experiments concerning radiation properties are being undertaken in round turbulent hydrogen/air and carbon

monoxide/air flames. Measurements include mean and fluctuating spectral radiation intensities for chord-like paths

through the flames. Predictions are based on stochastic simulation of mixture-fraction variations along the radiation

paths, seeking to simulate probability density functions and spatial and temporal correlations of mixture fraction

fluctuations along the path. Given the mixture fraction distribution along the path at any instant, the state relationships yield all other scalar properties and a narrow-band radiation analysis yields the spectral radiation

intensity. Continuing the simulation in time provides predictions of the temporal variation of spectral radiation

intensity. Thus far, only a first-order temporal and spatial simulation has been studied, with points along the

radiation path spaced at the integral length scale and being statistically independent. This approach yields reasonably

good predictions of mean and fluctuating spectral radiation intensities.

Typical predictions and measurements for hydrogen/air flames are illustrated in Figs. 3 and 4. These results are for horizontal radiation paths passing through the flame axis. Figure 3 is an illustration of predicted and

measured probability density functions of radiation fluctuations: predictions are quite encouraging, including correctly

representing the increased skewness of the distribution with increasing height above the burner. Figure 4 is an

illustration of power spectra of radiation fluctuations. These predictions are also encouraging except for

overestimation of the high frequency portion of the spectra due to use of a simple first-order simulation.

Currently, measurements of radiation fluctuations are being undertaken for chord-like paths at various

distances from the axis and the stochastic analysis is being extended to higher orders. Subsequent work will involve

measurements of the statistical properties of mixture fraction along radiation paths in the flames, so that

uncertainties of predictions of these properties can be avoided while the stochastic method is being developed.

Reports and Papers :

1. M.-C. Lai and G. M. Faeth, "Turbulence Structure of Vertical Adiabatic Wall Plumes," J. Heat Transfer. Vol. 109, No. 3, pp. 663-670, 1987.

2. 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, pp. 1521-1531, 1986.

3. G. M. Faeth, J. P. Gore, S. G. Chuech and S.-M. Jeng, "Radiation from Turbulent Diffusion Flames,"

Ann. Rev. Num. Fluid Mech. and Heat Trans.. Hemisphere Publishing Corp., Washington, in press.

4. J. P. Gore and G. M. Faeth, "Structure and Radiation Properties of Luminous Turbulent Acetylene/Air

Diffusion Flames," J. Heat Trans. . Vol. 110, No. 1, pp. 173-181, 1988.

5. Y. R. Sivathanu, J. P. Gore and G. M. Faeth, "Scalar Properties in the Overfire Region of Sooting

Turbulent Diffusion Flames," Combust. Flame, in press.

6. G. M. Faeth, J. P. Gore and Y. R. Sivathanu, "Radiation from Soot-Containing Flames," 70th AGARD

Symposium on Combustion and Fuels in Gas Turbine Engines . NATO, Paris, in press.

7. M. E. Kounalakis, J. P. Gore and G. M. Faeth, "Turbulence/Radiation Interactions in Nonpremixed

Hydrogen/Air Flames," Twenty-Second Symposium (International on Combustion. The Combustion

Institute, Pittsburgh, in press.

131
8. J. P. Gore, M. E. Kounalakis and G. M. Faeth, "Temporal Properties of Radiation Fluctuations from

Nonluminous Turbulent Diffusion Flames," Proceedings of the Twentieth Fall Technical Meeting . Eastern

Section of the Combustion Institute, Pittsburgh, pp. 71.1-71.4, 1987.

9. M. E. Kounalakis, J. P. Gore and G. M. Faeth, "Turbulence/Radiation Interactions in Nonluminous

Diffusion Flames," Proceedings of the 1988 Spring Technical Meeting. Central States Section of the

Combustion Institute, Pittsburgh, pp. 135-140, 1988.

10. Y. R. Sivathanu, J. P. Gore and G. M. Faeth, "Soot Properties in the Overfire Region of Turbulent

Diffusion Flames," Proceedings of the 1988 Spring Technical Meeting. Central States Section of the

Combustion Institute, Pittsburgh, pp. 275-280, 1988.

11 G. M. Faeth, "Heat Transfer in Fires and Combustion Systems," National Heat Transfer Conference,

Houston, TX, in press.

12. M. E. Kounalakis, J. P. Gore and G. M. Faeth, "Mean and Fluctuating Radiation Properties of

Nonpremixed Turbulent Carbon Monoxide/Air Flames," ASME Winter Annual Meeting, Chicago, IL,

submitted.

13. Y. R. Sivathanu, M. E. Kounalakis, J. P. Gore and G. M. Faeth, "Radiation from Turbulent Nonluminous

and Luminous Diffusion Flames," Annual Report, NBS Grant No. 60NANB5D0576, October 1987.

132
SOOT

VOLUME

FRACTION

(PPM)

Fig. 1 Soot volume fraction state relationship in the overfire region

of acetylene/air diffusion

flames

.

Fig. 2 Soot generation efficiencies

as a function of residence

time in hydrocarbon/air diffusion flames.

Fig. 3 Probability density functions

of radiation fluctuations in

a hydrogen/air diffusion

flame

.

Fig. 4 Power spectra of radiation

fluctuations in a hydrogen/

air diffusion flame.

133
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

SMOKE TRANSPORT

Professional Personnel

John H. Klote , Project Leader

Leonard Y. Cooper, Head, Building Fire Modelling Group

Kevin Greenaugh, Engineer

William Rinkinen, Technician

Walter Jones, Computer Scientist

Project Objective

Develop physical and mathematical models to predict the motion of smoke in

buildings due to all significant mechanisms.

Scope

This program studies the motion of smoke in buildings due to any driving force

such as stack effect, wind effect, forced ventilation systems, and expansion

and buoyancy of fire gases. Studies are by full scale and scale model

experiments with initial emphasis on the influence of stack effect. The

information generated by this effort is to be used to develop mathematical

models suitable for incorporation in existing fire models.

Technical Accomplishments

1. Report on Stack Effect

In building fires, smoke often migrates to locations remote from the fire

space. Stairwells and elevator shafts frequently become smoke - logged , thereby

blocking evacuation and inhibiting fire fighting. In this report the

following driving forces of smoke movement are discussed: stack effect,

buoyancy of combustion gases, expansion of combustion gases, wind effect, and

elevator piston effect. The steady flow analysis of stack effect and some

considerations of unsteady flow are addressed. Methods of evaluating the

location of the neutral plane are presented for a number of common building

leakage configurations. The capabilities and limitations of network models

for evaluation of smoke movement do to stack effect are discussed. The steady

flow network method is applied to situations of opened and closed doors and

shaft vents likely to occur during firefighting. A number of generalizations

which could be of use to fire fighters are presented. The information in this

paper also is applicable to the migration of other airborne matter such as

hazardous gases, bacteriological matter or radioactive matter in laboratories,

hospitals, or industrial facilities.

2. Project Plan for Full Scale Smoke Control and Movement Experiments

A project plan was developed for full scale smoke control and smoke transport

experiments to be conducted at the Plaza Hotel in Washington DC. Smoke

control will be achieved by exhausting the fire zone and pressurizing

surrounding zones, and by pressurizing stairwells. The smoke control systems
were designed using the analysis methods in the NIST Smoke Control Handbook

and the design pressures recommended in NFPA 92A. The effectiveness of these

systems to limit smoke flow will be measured, and the interaction between

smoke control and fire development will be studied. Experiments without smoke

control will allow a relative evaluation of the effectiveness of smoke

control. Also, the non- smoke control tests will be used to study smoke flow

under stack effect conditions.

3. Design and Construct Scale Model Set Up

A scale model of a seven story building including the stairwell and elevator

shaft has been designed and built in a laboratory, and a forced air heating

and cooling system for the model is under design. Fires will be set under

"winter” and "summer" stack effect conditions. Several of the walls of the

model are of glass allowing video recording of the smoke flow up the stairwell

and elevator shafts and on building floors. Adjustable openings in walls and

floors simulate the building leakage paths to allow modeling of various

building leakage areas including opened and closed doors. It is anticipated

that Plaza Hotel experiments and these scale model experiments will provide an

understanding of the mechanisms involved in such smoke flow, and that this

understanding will be the basis of a mathematical model.

4. Develop Computer Graphics for Smoke Flow in Multi- Story Buildings

Computer simulation of smoke movement in multi- story buildings results in very

large quantities of data to be studied and evaluated. To aid in this

evaluation, a computer graphic routine was developed for displaying the

results of zone model simulations of smoke flow in a seven story building.

The routine can be used on IBM PC and compatible machines with CGA, EGA or VGA

graphic capabilities. The building elevation is displayed, and the depths of

smoke layers on floors and in a shaft are shown as the computer progresses

through an analysis.

Reports and Publications

Quintiere, J.G., Scaling Applications in fire Research, International

Symposium on Scale Modeling, July 18-22, 1988, Japan Society of Mechanical

Engineers

.

Klote, J.H., Project Plan for Full Scale Smoke Movement and Smoke Control

Tests, Nat. Bur. Stand. (U. S.), NBSIR 88-3800, June 1988.

Klote, J.H., Fire Safety Inspection and Testing of Air Moving Systems, Nat.

Bur. Stand. (U. S.), NBSIR 87-3660, November 1987.

Klote, J.H. and Budnick, E.K., The Capabilities of Smoke Control: Part I Fundamentals and Zoned Smoke Control, presented at SFPE tutorial at NFPA

Meeting in Portland, OR, 10 November 1987.

Budnick, E.K. and Klote J.H., The Capabilities of Smoke Control: Part II

System Performance and Stairwell Pressurization, presented at SFPE tutorial at

NFPA Meeting in Portland, OR, 10 November 1987.

136
Klote , J.H., An Overview of Smoke Control Technology, ASHRAE Transactions,

Vol . 94, Part 1, 1988, pp 1211-1222.

Klote, J.H., An Analysis of the Influence of Piston Effect on Elevator Smoke

Control, Nat. Bur. Stand. (U. S.), NBSIR 88-3751, April 1988.

Klote, J.H. and Tamura, G.T., Experiments of Piston Effect on Elevator Smoke

Control, ASHRAE Transactions, Vol 93, Part 2a, 1987, pp 2217-2228.

Tamura, G.T. and Klote, J.H., Experimental Fire Tower Studies on Mechanical

Pressurization to Control Smoke Movement Caused by Fire Pressures, Proceedings

of the 2nd International Symposium on Fire Safety Science, Tokyo, Japan.

Tamura, G.T. and Klote, J.H., Experimental Fire Tower Studies on Elevator

Pressurization Systems for Smoke Control, ASHRAE Transactions, Vol. 93, Part

II, 1987, pp 2235-2257.

OA Snoners

The work above was funded in part by the following sponsors:

American Society of Heating, Refrigerating, and

Air-Conditioning Engineers, Inc., Atlanta, GA 30329

Bell Atlantic Telephone Company

Arlington, VA 22201

New Jersey Bell Telephone Company

Newark, NJ 07101

U.S. Fire Administration

Emmitsburg, MD

U.S. Veterans Administration

Washington, DC 20420

US West Incorporated

Denver, CO 80202

137
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

TOXIC POTENCY MEASUREMENT

Professional Personnel

Barbara C. Levin, Project Leader

Maya Paabo , Research Chemist

Emil Braun, Physicist

Marc R. Nyden, Research Chemist

Richard H. Harris, Jr., Chemist

Helene M. Clark, Guest Worker, University of Pittsburgh

Lane Highbarger, Guest Worker, University of Pittsburgh

Nancy Eller, Guest Worker, University of Pittsburgh

Project Objective

To develop models and methods to predict and measure the combustion products

that evolve from burning materials and to predict the impact of those products

on living organisms.

Scope

1. Develop theoretical and analytical tools for prediction,

identification, and quantitation of toxic agents in fire

atmospheres

.

2. Develop a simplified gas model to predict the toxicity of complex

gas mixtures found in fire atmospheres

.

3. Develop a bioanalytical screening test to determine whether the

combustion products from materials are extremely toxic (i.e., low

concentrations produce toxic effect) or unusually toxic (i.e., the

toxicity of the combined major fire gases is not sufficient to

account for the observed toxicity) . This test is also designed to

minimize the use of animals.

Technical Accomplishments

The Center for Fire Research has been developing a simplified gas model (known

as the N-Gas Model) to predict the toxicity of the complex gas mixtures found

in fire atmospheres. One of the advantages of this model is the reduction in

the cost of and the dependence on animal testing without sacrificing test

accuracy. Research on the N-Gas model has progressed from the determination

of the toxicity of individual gases - CO, C02

, HCN, and reduced 02

- in

Fischer 344 rats exposed for 30 minutes and observed for at least 14 days to

the development of a four- gas model based on the combined toxicological

results of these four gases. Other exposure times ranging from 1 to 60

minutes for single gases and 5 to 60 minutes for two gas combinations - CO

plus HCN and CO plus C02

- have also been examined. With the exception of the

5 -minute CO plus C02 experiments, the additivity and synergistic effects

observed from the 30-minute animal exposures were observed at the other times.

In the 5 minute CO and C02 experiments, the LC 50 value was lower than the 5-

minute LC 50 value for CO alone, but the 95% confidence limits overlapped. The

current N-gas model appears to explain the deaths observed at the 30-minute

139
LC50 values of 17 out of 24 different cases of material thermal decomposition.

The other cases need further examination.

In the past year, experiments on the toxicity of the combined three and four

gases were performed. In addition, studies were conducted to examine if the

synergism of CO and C02 seen at sublethal concentrations of CO and C02 occurred as well at the LC50 concentration of CO. The three-gas combinations

were studied by exposing animals for 30 minutes to various concentrations of

CO, C02

, and reduced 02 (Table 1) or combinations of CO, C02

, and HCN (Table

2) . Additional experiments were performed examining 30-minute exposures to

combinations of four gases - CO, C02

, HCN, and reduced 02 (Table 3). The

additivity and synergism observed previously were still applicable for the

various three and four gas combinations.

Based on these results, equation (1) was derived to predict the combined

toxicities of these four gases:

m[C01 .[HCN] 21 - [02 1_ (1)

[C02 ] - b d 21 - LC50 02 where the values in brackets are the atmospheric concentrations of the gases

in ppm (CO, C02

, HCN) or percent (02) ; m and b are the slope and y intercept

of the C0/C02 interaction curve; and [HCN] and d are the atmospheric test and

the lethal concentrations of HCN, respectively. The value of d will vary

depending on whether it is the within-exposure deaths or the within plus postexposure deaths that are of concern. Based on all the data to date in which

some percent of the animals died (not 0 or 100%) , the mean value of equation 1

is 1.1 with 95% confidence limits ranging from 0.9 to 1.3. In other words, at

the mean value of 1.1, 50% of the exposed animals would be predicted to die;

whereas, below 0.9 or above 1.3, none or all of the animals would be expected

to die from these exposures, respectively.

When the toxicity of mixtures of sublethal amounts of CO and C02 was tested

previously, the C02 increased the uptake rate of CO and consequently, the

formation of carboxyhemoglobin (COHb) . In addition, the presence of C02 also

produced a degree of acidosis that was greater than that from CO or C02 alone;

the time of recovery from the acidosis was delayed when C02 was present in

addition to the CO. When these experiments were repeated at lethal

concentrations of CO (6200 ppm), similar effects were noted (i.e., the COHb

increased and the blood pH decreased at a faster rate when C02 was present

than when absent) . The deaths of all the animals in these experiments

prevented comparison of the recovery rates from the acidosis. However, the

mean time to death was faster when the rats were exposed to the CO in the

presence of C02 (11.9 + 3.6 min) than to CO alone (17.9 + 5.5 min).

This year's research has been very successful and has resulted in the

development of a 4-Gas Model to predict the toxicity of combustion products

for different times and variable concentrations of gases. This 4-Gas Model is

based on the combined additive and synergistic toxicities of CO, C02

, HCN,

and reduced 02

. We have also been able to show that the synergistic effects

of C02 seen at sublethal levels of CO are applicable at higher (lethal)

concentrations of CO.

Progress this year has also been achieved in the development of methodologies

to reveal previously unknown sources of fire toxicity. Computer software has

140
been developed to simulate the degradation of materials as a function of

temperature and to make use of infrared measurements to identify the

components and measure the concentrations of these components in fire

atmospheres. Current studies have revealed unsuspected mechanisms of thermal

degradation and correlations between polymeric structure and thermally induced

product and energy distributions.

Funding from Other Agencies/Institutions

In addition to CFR Priority Project funding, the above research was partially

supported with funds from The Society of Plastics, Inc., The International

Isocyanate Institute and The U.S. Army Medical Research Institute of Chemical

Defense.

Reports and Publications

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

toxicity data for hazard evaluation. Fire Journal .81:22-71 (1987). Also

in ASTM Stand. News 14:28-33 (1986).

2. Levin, B.C., Paabo , M. , Gurman, J.L., Harris, S.E., and Braun, E.,

Toxicological interactions between carbon monoxide and carbon dioxide.

Toxicology 47:135-164 (1987).

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

exposure to single or multiple combinations of the predominant toxic

gases and low oxygen atmospheres produced in fires. Fundam. Appl.

Toxicol. 9:236-250 (1987).

4. Levin, B.C., Gurman, J.L., Paabo, M. , Baier, L. , and Holt, T.,

Toxicological effects of different time exposures to the fire gases:

carbon monoxide or hydrogen cyanide or to carbon monoxide combined with

hydrogen cyanide or carbon dioxide. Proceedings of the Ninth Meeting of

the U.S. -Japan Panel on Fire Research and Safety, Norwood, MA, May,

1987. NBSIR 88-3753, National Bureau of Standards, Gaithersburg, MD

,

pp . 368-384 (April, 1988).

5. Complex Mixture Committee, ’’Complex Mixtures: Methods for In Vivo

Toxicity Testing", National Research Council, National Academy Press,

ISBN 0-309-03778-6, 375p. (1988).

6. Levin, B.C., Paabo, M. , Gurman, J.L., Clark, H.M.

,

and Yoklavich, M.F.,

Further development of the N-Gas Model. Report to Sponsor, June, 1988.

7. Nyden, M. R. and Babrauskas, V., "Use of FTIR Spectroscopy for

Multicomponent Quantitation in Combustion Toxicology," Abstracts from

the Combined Meetings of the Eastern Section: Combustion Institute and

the National Bureau of Standards Center for Fire Research Annual

Conference for Fire Research, Gaithersburg, MD, pp 107-1 - 107-4,

(November, 1987).

8. Nyden, M. R. , Forney, G. F. , and Chittur, K. , "Spectroscopic Analysis of

Strongly Interacting Systems: Human Plasma Protein Mixtures," Applied

Spectrosc., 42: 588 - 593, (1988).

Related Grants

1. Southwest Research Institute, PI - Gordon Hartzell, Analysis of Hazards

to Life Safety in Fires.

2. University of Pittsburgh, PI - Yves Alarie , Toxicity of Plastic

Combustion Products.

3. University of California, PI - Peter Griffiths, Expert System Approach

for Spectra/Structure Correlation for Vapor-Phase Spectra.

141
TABLE 1. PREDICTABILITY OF N-GAS MODEL USING CO, C02

, AND 02 N-Gas Prediction

Valueb

Deaths

WI PE

Day0

0.84 0/6 0/4

0.89 0/6 0/4 - 0.93 0/6 1/4 0

0.96 0/5 0/4 - 1.01 3/6 0/3 - 1.06 4/6 1/2 3

1.07 3/6 1/2 0

1.12 4/6 0/5 - 1.22 5/6 0/1 -

TABLE 2. PREDICTABILITY OF N-GAS MODEL USING CO, CO

N-Gas Prediction Deaths Day0 Valueb WI PE

0.95 0/6 1/6 1

1.01 0/6 0/6 - 1.03 0/6 1/6 0

1.11 0/6 2/6 1,3

TABLE 3. PREDICTABILITY OF N-GAS MODEL USING CO, CO

N-Gas Prediction Deaths Day0 Valueb WI PE

0.77 0/6 0/6 - 0.91 0/6 0/6 - 1.06 1/6 1/5 1

1.08 0/6 0/6 - 1.22 4/6 0/2 —

that post-exposure deaths occurred

b: Based on equation (1)

WI : Within Exposure Deaths

PE: Post-Exposure Deaths

AND HCN

HCN , AND REDUCED 02

142
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution:

Grant No. :

Grant Title:

Principal Investigator :

Other Professional Personnel:

NBS Scientific Officer:

Southwest Research Institute

60NANB6D0635

Analysis of Hazards to Life Safety

In Fires: A Comprehensive MultiDimensional Research Program—Part 3

Dr. Gordon E. Hartzell

Institute Scientist

Department of Fire Technology

Southwest Research Institute

6220 Culebra Road

San Antonio, Texas 78238

Telephone: 512/522-3038

Dr. Arthur F. Grand (Staff Scientist)

Dr. Harold L. Kaplan (Manager,

Inhalation Toxicology)

Howard W. Stacy (Assistant Manager,

Inhalation Toxicology)

Valter G. Switzer (Sr. Research

Scientist)

Dr. Barbara C. Levin

Technical Abstract :

In order for a fire hazard model to be valid, it is essential that

results obtained in combustion toxicity studies on materials be predictive,

with a reasonable degree of confidence, of the effects of smoke exposure to

humans. Because of potentially significant differences between the mouse or

rat and the primate, studies were undertaken to investigate the suitability of

other rodent species or to develop methodology that would allow rodent data to

be used to better predict toxic effects in humans. The specific objective of

this work has been to investigate the suitability of the guinea pig as a model

for predicting the toxic effects of fire gases, particularly those containing

irritants, in man.

Two LC 50 values were determined for HC1 with guinea pigs. The 30-minute

exposure (plus 14-days post exposure) value was 1350 ppm, with 95-percent

confidence limits of 1000 to 1800 ppm. The 15-minute exposure (plus 14 days)

value was 2900 ppm, with 95-percent confidence limits of 1960 to 5300 ppm.

Both values are significantly lower than those for rats, showing that the

guinea pig is considerably more sensitive to HC1 in terms of lethal toxic

potency. Particularly striking was the incidence of wi thin-exposure and

same-day lethality for the guinea pig. This has never been observed with rats

over the range of HC1 concentrations used for LC 50 determinations. Further143
more, the effect appears more related to the length of the exposure, rather

than to the dose. A possible explanation may lie in the marked tendency for

bronchioconstriction by the guinea pig. Severe bronchioconstriction could

contribute to a persistent hypoxic condition, leading to death either during

or shortly after exposure.

Such bronchioconstriction does not necessarily mean, however, that the

guinea pig is a better animal model for man. The guinea pig may actually be

too sensitive. The comparison of lethal toxic potencies shown in Table I for

rodents, including mice, rats and guinea pigs, with estimated data for baboons

[1,2], would seem to indicate that the rat (and perhaps even the mouse) is a

reasonable model for primates and that the guinea pig is not.

TABLE I

LETHAL TOXIC POTENCIES OF HYDROGEN CHLORIDE

(lc

50

VALUES IN PPM)

Exposure Time

(min) Rats

a Mice

Animal ModeJ

Guinea Pigs° Baboons

5 15,900 13,745

b

17,000

10 8,370 10, 138 c 15 6,920 2,900 10,000

22.5 5,920

30 3,800 2,644° 1,350 5,000

60 2,810

a. 14-days post exposure [2]

b. 7-days post exposure [3]

c. 3-hours post exposure [4]

d. 14-days post exposure (this study)

e. These are not LC

50 values, but estimates based on conditions of animals

after exposure. The 5-minute exposure resulted in post-exposure deaths

[1]. The 15- and 30-minute exposures yielded subjects that survived

indefinitely [ 2 ]

In preparation for further studies using the guinea pig, the 30-minute

LC 50 for carbon monoxide was determined to be 17,500 ppm (95-percent confidence limits of 14,900 to 21,400 ppm). This value is about three times that

for the rat, showing the guinea pig to be remarkably insensitive to CO. Carboxyhemoglobin loading studies did show the guinea pig to load CO somewhat

more slowly than the rat, but most surprising was the guinea pig's tolerance

to CO concentrations that would easily cause lethality in rats.

A further demonstration of the guinea pig's insensitivity to CO was seen

in studies exposing these animals to mixtures of CO and HC1. These two

toxicants are normally considered additive in their effects on rats [5].

However, with guinea pigs, the 30-minute (14-days post exposure) LC

5(? of HCl,

when in the presence of both 0.3 LC

50 and 0.5 LC

50 of CO, was essentially the

same as for HCl alone. Reasonable evidence of additivity was obtained only at

a combination of 0.76 LC 50 of CO and 0.37 LC 50 of HCl. It would seem that the

144
guinea pig is so insensitive to the CO that additivity is not observed until

the CO concentration is quite high and well above that which would kill rats.

Since it has been fairly well established that the rat is a reasonable model

for CO intoxication of both baboons and humans [6], it must be concluded that

the guinea pig is actually a very poor model. It would certainly appear to be

inappropriate to use an animal model for combustion toxicity studies that is

so insensitive to the most common fire gas toxicant.

V Whether or not the guinea pig's greater sensitivity to HC1 is meaningful

in terms of human exposure is uncertain. The studies reported here address

only lethal toxic potency and may or may not be relevant to sublethal effects.

However, there seems to be mounting evidence that the rat is a reasonable

model for both asphyxiants and irritants. There is little evidence that it is

not

.

References :

1. Kaplan, H.L., A.F. Grand, V.G. Switzer, D.S. Mitchell, W.R. Rogers and

G.E. Hartzell, "Effects of Combustion Gases on Escape Performance of the

Baboon and the Rat," J. Fire Sciences , Vol. 3, No. 4, pp. 228-244 (July/

August 1985).

2. Hartzell, G.E., S.C. Packham, A.F. Grand and W.G. Switzer, "Modeling of

Toxicological Effects of Fire Gases: III. Quantification of PostExposure Lethality of Rats from Exposures to HC1 Atmospheres," J. Fire

Sciences, Vol. 3, No. 3, pp. 195-207 (May/June 1985).

3. Darmer, K.I., E.R. Kinkead and L.C. DiPasquale, "Acute Toxicity in Rats

and Mice Exposed to Hydrogen Chloride Gas and Aerosols," Am. Ind. Hyg.

Assoc. J. , 35:623-631 (1974)

4. Alarie, Y. , Proceedings of the Inhalation Toxicology and Technology

Symposium, Kalamazoo, Michigan, October 23-24, 1980, B.K. Leong, Ed., Ann

Arbor Science Publishers, Incorporated, pp. 207-238 (1980).

5. Hartzell, G.E., A.F. Grand and W.G. Switzer, "Modeling of Toxicological

Effects of Fire Gases: VI. Further Studies on the Toxicity of Smoke

Containing Hydrogen Chloride," Vol. 5, No. 6, pp. 368-391 (November/

December 1987).

6. Kaplan, H.L. and G.E. Hartzell, "Modeling ot Toxicological Effects of

Fire Gases: I. Incapacitating Effects of Narcotic Fire Gases," J. Fire

Sciences, Vol. 2, No. 4, pp. 286-305 (July/August 1984).

Reports and Papers :

1. Hartzell, G.E., A.F. Grand, and W.G. Switzer, "Studies on the Toxicity of

Smoke Containing Hydrogen Chloride," Second International Symposium on

Fire Safety Science, Tokyo, Japan, June 13-17, 1988.

145
CENTER FOR THE FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution:

Grant No.

Grant Title:

Graduate School of Public Health, University of

Pittsburgh

60NANB8D0813

Toxicity of Plastic Combustion Products

Principle Investigator: Yves Alarie, Ph.D.

University of Pittsburgh

Pittsburgh, PA 15261

Telephone: (412) 624-3047

Other Professional Personnel: D. Malek, Ph.D.

F. Esposito, Ph.D.

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

Technical Abstract

An animal model has been developed to stimulate moderate exercise as

may occur in individuals trying to escape a fire. The laboratory animal

use is the guinea pig because the effect of asphyxiants and irritants,

both always present in fire smoke, can be easily recognized in this

species. Guinea pigs will also run well in an ergometer with no need for

stimulating them to run. An ergometer was built to permit training each

animal so that they will run at a constant speed and for a period of at

least 45 minutes. The running speed was selected so that the oxygen

uptake will be about two to three times the resting oxygen uptake. This

simulate a level of activity in humans which would be described as "fast

walk". The ergometer was built so that when enclosed it can function as a whole body plethysmograph to measure tidal volume and respiratory

frequency continuously as well as oxygen uptake and carbon dioxide output.

The whole body plethysmograph/ergometer system is continuously ventilated

and therefore exposure to single toxicants such as carbon monoxide,

hydrogen cyanide etc as well as smoke from burning polymers can be

introduced at any time to study their effects on the performance of the

animal

Experiments have been completed with this escape performance model

using carbon monoxide as the first toxicant. Comparisons were made with

the effect of the same toxicant in sedentary animals. The results have

now been analyzed and furthermore comparisons made with predictions of

human performance under the same toxicant.. The results in guinea pigs

indicate that the effect of carbon monoxide in running animals occurred at

about half the concentration and in about half the time for this toxicant

to affect sedentary animals. When extrapolating these results to humans,

using literature data on the incapacitating capacity of carbon monoxide in

humans at moderate work, the data obtained in guinea pigs are in very

close agreement for distance traveled before incapacitation. Therefore,

if carbon monoxide is the principal toxicant in fire smoke these data can

146
be used with confidence in computer modeling to predict escape

capabilities. In fact, fire models including levels of carbon monoxide

generation can now use levels of carbon monoxide generated to predict how

long humans can function or travel before being incapacitated by this

toxicant.

Experiments have also been completed using hydrogen chloride as the

toxicant to test how this model can be used with irritants. With hydrogen

chloride the difference between running animals and sedentary animals is

much greater than for carbon monoxide. In sedentary animals a concentration of hydrogen chloride of 1,000 to 1,200 ppm for 30 minutes

produced no incapacitation or death. In contrast a concentration of

hydrogen chloride of 500 to 600 ppm incapacitated running animals and was

lethal within 3 minutes. The lowest no effect concentration of hydrogen

chloride in running animals is around 150 ppm. Extrapolating these

results to humans is not as easy as for carbon monoxide since very few

experiments have been conducted in humans with hydrogen chloride. The

data in humans indicate that 70-100 ppm is the highest level that can be

tolerated for a few minutes because of intense irritation and chest pains.

Since running guinea pigs are not incapacitated for an exposure period of

30 minutes at 150 ppm some correction factor will have to be developed to

take into account the fact that guinea pigs are less sensitive to this

irritant than humans are. Nevertheless this escape performance model is

the first incapacitation, model described in the literature which can

assess the effect of both asphyxiants and irritants. Also the

incapacitation effect occurs at a much lower concentration and in a much

faster time for carbon monoxide than the lethal effect which

differentiates this model from all previous models where incapacitation

and death occurred at almost the same concentration and time.

In depth investigations were conducted on the possible synergistic

effects of fire gases such as carbon monoxide, hydrogen cyanide, carbon

dioxide as well as low oxygen. Experiments at NBS used rats while

experiments at the University of Pittsburgh used mice. The results are

similar although different protocols were used. It is now clear that

carbon monoxide and hydrogen cyanide act in a simple additive manner. It

is also clear that carbon dioxide will affect the toxicity of carbon

monoxide or hydrogen cyanide but its effect is small and if the

concentration is less than 10% toxic fire models can ignore its effect.

The effect of low oxygen in combination with carbon monoxide or hydrogen

cyanide cannot be ignored as easily. When oxygen was above 16% there was

no detectable influence on the toxicity of carbon monoxide or hydrogen

cyanide. When oxygen was below 13% the toxicity of carbon monoxide did

not change greatly but the toxicity of hydrogen cyanide changed

considerably. Its effect was to change both the time of exposure to

induce a lethal effect (by a factor of 3) and to reduce the lethal blood

cyanide level. With hydrogen cyanide exposure, the lethal level of

cyanide in blood was found to be around lmg/liter. This was reduced by a factor of 3 in the presence of low oxygen. In contrast the lethal level

of carboxyhemoglobin was just slightly reduced when comparing lethal

levels obtained with exposure to carbon monoxide alone versus carbon

monoxide with oxygen levels below 13%. This finding will complicate fire

hazard modeling for toxicity when cyanide is present in fire gases.

Indeed, of all the combinations used, hydrogen cyanide and low oxygen

147
present the greatest lethal threat, rather than the combination of carbon

monoxide and hydrogen cyanide. Obviously if both carbon monoxide and

hydrogen cyanide are present the additive effect is present. However if

hydrogen cyanide and low oxygen are present this combination is both more

potent and faster acting. This combination also present more difficulties

for modeling since instead of being additive as in the case of carbon

monoxide and hydrogen cyanide the combination of hydrogen cyanide and low

oxygen is of no consequence if oxygen is above 16% but of great

consequence if oxygen is below 13%. This difference of 3% is rather small

when using fire models for prediction of oxygen levels in fire smoke.

In order to develop small scale toxicity assessment of fire smoke the

cone calorimeter developed at NBS is being investigated to potentially

replace the furnace system used to burn polymers. Preliminary experiments

conducted at NBS two years ago indicated that this approach could be used.

The instrumentation was built at NBS and delivered last September to the

University of Pittsburgh. Major problems have been encountered using this

system. So far these problems have been of a mechanical nature rather

than fundamental. This is to be expected. The design of the cone

calorimeter at NBS has been centered on the measurement of heat release

and the parameters, in some instances, are in conflict with using the

apparatus for toxicological studies. The basic cone heater and mass loss

measuring load cell will be retained but the hood, enclosure, flow

measuring devices and exhaust system are being modified. These changes

are necessary for reducing the residence time of the fire smoke generated

and to provide fire smoke at a temperature which will be compatible with

minimum heat stress on the animals. Also the enclosure system is being

changed to continuously measure airflow coming within the enclosure

containing the heating cone and oxygen level will be continuously

monitored in all exposure chambers since we have found that depletion of

oxygen can have a very significant effect when hydrogen cyanide is present

in fire smoke.

148
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU of STANDARDS

FY 88

«

Institution: The University of California, Riverside

Grant No.: 60NANB7D0736

Grant Title: Expert System Approach for Spectra/Structure Correlation for

Vapor-Phase Spectra

Principal Investigator: Professor Peter R. Griffiths

Department of Chemistry

University of California, Riverside

Riverside, CA 92521

Other Professional Personnel: Dr. Dongjin Pyo

Postdoctoral Research Associate

Mr. Hsi-Tung Lin

Graduate Research Assistant

NBS Scientific Officer: Dr. Vytenis Babrauskas

Technical Abstract :

Introduction Rapid identification of the components of the atmosphere in

the region of fires is not only important in combustion research but can also

allow to have practical benefits. For example, the potential danger to firefighting personnel because of toxicity could be ascertained on site and, in

certain cases, the cause of a fire may be found. Infrared spectrometry has

the capability of allowing both major and minor components in the atmosphere

to be identified and quantified. However, the infrared spectra of compounds

in the vapor phase are not readily interpreted. Although Nyquist has

described several correlations between vapor phase infrared spectra and the

molecular structure of the absorbing molecule [1], these rules are not readily

amenable to rapid computer interpretation. Thus they cannot yet be applied to

the identification and quantification of molecules in the atmosphere near an

actual fire. Even in laboratory studies of combustion processes, where

spectroscopic data can be analyzed after the experiment is complete, the

gaseous components would still be difficult to identify simply by measuring

the infrared spectrum of the atmosphere and applying vapor-phase infrared

spectra/structure correlation rules as they are presently understood. In this

project, we are attempting to obtain a better understanding of the correlation

between the structure of molecules and their vapor-phase infrared spectra

through the use of contemporary "expert system" software.

Spectral Database The most common application for which vapor-phase

reference spectra are used is for the identification of components of mixtures

separated by gas chromatography (GC) using on-line Fourier transform infrared

(FT-IR) spectrometry. In GC/FT-IR, spectra are usually measured at relatively

low resolution (8 cm

-

!) and computed with a sampling interval of 4 cm”l. To

reduce the time required for searching GC/FT-IR data, the spectra are then

149
"deresolved", i.e. the sampling interval is reduced to 8 cm“l. At least two

databases of deresolved reference spectra are commercially available.

However, much significant information is lost from vapor-phase infrared

spectra when they are deresolved. If expert system software is to be used for

generating useful spectra/structure correlations, there is good reason to

believe that the resolution of the spectra should be no worse than 4 cm”*.

A large database of vapor-phase infrared reference spectra has been

measured by the personnel of Sadtler Research Laboratories, Division of

Bio-Rad Laboratories (Philadelphia, PA). The original spectra in this database were measured at 4 cm“^ resolution with data points at 2 cm”* intervals,

so that these spectra appear suitable for our purpose. The original spectra

in this database are not usually made available to the public because of their

proprietary nature. Before this project was started, however, the Principal

Investigator was told that he would be able to lease the entire collection of

original spectra from Sadtler Research if this project was funded.

Unfortunately, after the project was funded, Sadtler required that a very

restrictive licensing agreement be signed. It has taken over ten months from

the start of this grant for the University of California, Riverside (UCR) and

Sadtler Research Laboratories to agree on the specific terms of the license.

Even then, the data are to be sent to UCR in an encrypted form to ensure their

protection. As yet, the database has still not been received at UCR, and a

one-year extension of this grant has been requested to enable the proposed

work to be completed.

Band Parameter Calculation For the application of most expert system

software to find spectra/structure correlations, spectra must be changed from

their usual format of (absorbance, wavenumber) pairs. We are developing techniques for accurately calculating the parameters, i.e. the center wavenumber,

peak absorbance and full-width at half-height (FWHH) , of all bands in the

spectrum, including those bands that are partially or completely unresolved

from a neighboring spectral feature. The technique that is being used

involves first narrowing each band by Fourier self-deconvolution (FSD) and

then fitting the deconvolved spectrum (in which all significant bands have

been resolved) by a series of Lorentzian-Gaussian bands.

An algorithm has been developed to find the optimum parameters for vaporphase spectra. The widths of each band in a given spectrum are progressively

reduced by an amount, y’. The series of spectra calculated in this manner is

curve fit, and the sum of the squares of the difference (SSD) between each

synthetic spectrum and the corresponding deconvolved spectrum is calculated.

The conditions for calculating the most accurate band parameters can be found

from plots of SSD against y

1 • The band parameters calculated in this way will

ultimately be used as input to the expert system programs.

Expert System Programs A listing of available expert system programs for

operation on an IBM-AT compatible personal computer was obtained. From this

list, two programs were selected as being the most appropriate for our purpose.

The first (Prolog, Arity Corp. , Concord, MA) proved to be less useful than the

second (1st CLASS, Programs in Motion, Wayland, MA, and the latter program

will be used for much of the future work on this project. In addition to the

commercial software, programs have been written at UCR for testing some simple

concepts; the early results obtained using these programs are described below.
Wavenumber-Based Spectra/Structure Correlations In infrared spectra, it

is usually impossible to determine the structure of any compound on the basis

of absorption in only one region. To determine the structural units present

in a compound by the use of group frequencies, it is therefore necessary to

examine several spectral regions. Finding the group frequencies for each

functional group is the most important step for structural elucidation using

infrared spectra. For our early studies, band parameters for the vapor-phase

spectra of several carboxylic acids were calculated in the manner described

above to give "peak table spectra". A simple routine was written to show the

feasibility of determining the characteristic regions for absorption by a certain functional group. In this approach, the peak table spectra are reformatted as binary points along the wavenumber axis, with all points one full

width at half height on either side of the band center being represented as

ones. All other points are represented as zeros. (For more specific spectral

representation, a region for each band that is bounded by a fraction of the

FWHH can obviously be selected). As an example, the high wavenumber region of

the spectrum of butyric acid would be represented as follows:

000 001111 111100000

| |2 x FWHH|

4000 cm“l 3602*****3557

(START) (O-H Stretch)

Binary Representation

.000000011111 11100000 etc.

|2 x FWHH

|

3017 2929 cm-1

(C-H Stretch)

of Butyric Acid Spectrum

By overlapping spectra that have been formatted in this way, characteristic regions for a given functional group can be selected by finding the

regions common to that class of spectra, i.e., the regions where each spectrum

contains ones. An occurrence value for every wavenumber can be calculated

simply by adding the binary spectra, so that if an occurrence value equal to

the number of spectra is computed in a given region, that region would be a candidate for the spectra/structure correlation table. Using the binary

spectral data for eight carboxylic acids whose reference spectra were

available in the EPA library of vapor-phase infrared spectra, occurrence

values for every wavenumber were calculated by overlapping and summing these

eight binary spectra. Results were obtained with threshold occurrence values

of 100% (i.e., all of the acids absorbed in this region) and 88% (i.e., 7 of

the 8 acids absorbed in this region). As would be expected, broader regions

were calculated with a threshold occurrence value of 88% than with a threshold

occurrence value of 100% and additional spectral regions, corresponding to the

vibrational modes of functional groups not associated with the COOH moiety,

were added. This approach is believed to be quite promising, and will be

investigated further when we receive the full Sadtler database.

Incorporation of Peak Intensity into the Rules In previous work,

detailed absolute or relative peak intensity information has rarely been used

in the interpretation of infrared spectra. In an attempt to get less equivocal structural information than can be found using only wavenumber-based

spectra/structure correlations, we are starting to incorporate intensity

information in the input to our expert system program for structural elucida151
tion. To show the feasibility of using intensities for this purpose, peak

table spectra of the same eight carboxylic acids used above were normalized to

the most intense band in the spectrum (which in all cases was the OO

stretching band). To characterize the band intensity in a given spectral

region, the absorbances of all spectra were averaged between wavenumbers

located between one FWHH either side of the center wavenumber; the average

relative peak intensity and standard deviation was then calculated in each

region. The best correlation was found between the intensity of the 0-H

stretching and OO stretching bands of the COOH group. Since all these compounds were carboxylic acids, these preliminary results give rise to a certain

amount of optimism that relative band intensities will prove to be more useful

in structural elucidation than has been recognized previously. We will therefore attempt to incorporate information of this type in the expert system

programs.

Reference

1. R. A. Nyquist, "The Interpretation of Vapor-Phase Infrared Spectra",

Vol. 1, Sadtler Research, Philadelphia, PA, 1984.

152
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

FIRE DATA FOR MATERIALS

Professional Personnel

Sanford Davis, Project Leader

Emil Braun , Physicist

Project Objective

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

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

evaluating input data for fire models and other predictive methods.

Scope

To conceive, develop, and implement projects relating to the evaluation and

adaptation of databases for use in hazard assessment models.

Technical Accomplishments

Two milestones were achieved this year: first, participation in the National

Fire Research Strategy Conference Hazard Database Task Group and, second, the

conceptual development of a second generation HAZARD database for CFR. The

design requirements of this database are described in a draft papaer currently

undergoing editorial review. The long-term goals of these two groups - Hazard

Database Task Group and CFR - vis-a-vis a material fire property database, are

different. These divergent goals will have to be addressed in the future and

may necessitate the design of several different databases rather than a single

database meeting the needs of both groups

.

The long-term objectives of the Hazard Database Task Group are:

1) development of standard reporting forms for a large number of test

methods

;

2) making a large body of testing information available to the fire,

design, and regulatory communities.

In contrast, the long-term objectives of CFR are to:

1) provide a collection of data needed for hazard assessment, as defined in

HAZARD I;

2) reduce the information retrieval and transfer burden for users of

HAZARD N.

The Hazard Database Task Group held two meetings during which a plan for

action was developed. Six major issues were addressed. They are:

153
• Identification of materials, products, etc.

Description

Names

Sources

• Reporting of data

Format: units, conversions

Test methods

Specimen identification, including when prepared

Independent variables: temperature and time relationships

• Terminology

• * Interfaces

Obtaining data

Evaluation of data

Measured data

Derived data (equations)

Estimated data (default values)

Validation - review board

Reliability - accuracy

"Authority" - consensus

• Management of the database

Accessability - manual

- automatic

Maintenance, enhancement

• Funding, continued support

Government, industry

A paper describing the approach to the development of a National Fire Database

has been written for publication in the model code group periodicals. The

intent is to inform code and building officials of the need for input data for

hazard assessment models. The National Fire Database would contain welldocumented data obtained from standard fire performance tests. Building codes

specify fire performance requirements for materials of construction, and for

some building contents, and governmental regulatory agencies have requirements

for materials used in aircraft, rail vehicles, and sea-going vessels. The

inclusion of fire performance data in a database would facilitate decision

making for materials and product selection. The thrust of this paper is to

describe the process and to propose a database management system for

implementation of the process.

Consideration has been given to the presentation of the data in the database.

An example of how computer-accessed data would be presented for a particular

building material is shown here for purposes of discussion.

Entry Example

Class (or intended use)

Type of product

Source

Designation

Material

Form

Density, kg/m3 Thickness, mm

wall lining

wood

Weyerhaeuser

Versaboard

Douglas fir

plywood

640

13

154
Property (1)

Laboratory

Test method

Test number (if any)

Date of test

Orientation

Ignition mode

Ignition energy, kW/m2

Ignition time, sec

Heat of combustion (aver) , kJ/kg

CO yield (aver) , kg/kg

C02 yield (aver) , kg/kg

etc

.

Extinction area (aver), m

2 /kg

Time dependent data

0

10

20

30

100

110

960

1020

Other properties ( ignitability , flame spread, etc.) are included as an

extension of this table. The user of the database calls up a product and

automatically retrieves all the data input required by the hazard model. A

specifier would have ready access to a product's fire characteristics to

fulfill his needs for procurement purposes.

Current work is in progress to enhance the pilot database developed for

HAZARDI in order to provide fire performance characteristcs for additional

products and to add to the base of thermophysical properties of construction

materials. As the next version of the hazard assessment model is being

developed, it will be necessary to reformat the available data for direct

transfer into the appropriate segment of the hazard analysis process. This

will make running of the model more "user friendly" and facilitate access to

the data. What data will be included, how they will be evaluated, what format

for the data is required, how they will be input, and how they will be

presented are currently under consideration.

Reports and Publications

"National Database for Fire Hazard Analysis", S. Davis and E. Braun, to be

published

.

rate of heat release

National Bureau of Standards

cone calorimeter/ASTM P190

1264

04/16/91

horizontal

piloted (spark)

25

26

12800

0.0008

0.0048

32.9

Heat release Mass loss CO etc.

155
•

-

.
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

CONE CALORIMETER DEVELOPMENT

Professional Personnel

Vytenis Babrauskas , Project Leader

Kay Villa, Textile Technologist

Marc Janssens, Research Associate, National Forest Products Association

Project Objective

To further develop the Cone Calorimeter as a useful engineering tool for

characterizing combustion properties of products and materials.

Scope

1. To complete the ASTM and ISO round robins

2. To achieve full operation of both NBS Cone Calorimeter units, including

FTIR hookup

3. To begin the conversion of Cone Calorimeter data files into a proper

database, suitable for modeling purposes and for inter- laboratory data

exchange

.

Technical Accomplishments

Because of slightly different interests of the laboratories concerned, the

round robins sponsored by ASTM and by ISO have evolved as closely related, but

not identical, programs. The ASTM round robin uses 6 materials: ABS , particle

board, PMMA, polyethylene, PVC, and rigid polyurethane foam (aircraft

material). The test conditions comprise 25 and 50 kW/m2 irradiances , in both

horizontal and vertical orientations (excluding those specimens which are

incompatible with a given orientation) . These specimens will be tested both by

the 6 U.S. labs under ASTM's auspices and by the 7 European and Japanese labs

under ISO. The ISO labs ( + NBS) will also be conducting tests on a series of

materials of interest to the ISO community. These are: plywood, FR plywood,

rigid polyurethane foam (for buildings) , rigid polystyrene foam, and gypsum

wallboard. Testing will be done at the same irradiances and orientations as

for the ASTM materials.

Prior to the actual start of testing, two calibration steps were taken. (1)

All the heat flux gauges used in the different laboratories were calibrated

against an NBS standard gauge. (2) A supply of calibration PMMA was issued to

the participating laboratories. Only upon verifying by NBS that credible

results were being obtained with the PMMA, would the actual round robin work

begin.

157
.

A User's Guide for the Cone Calorimeter has been prepared and issued. This

document (118 pp . ) is, by far, the most detailed operating guide ever prepared

for a fire test method. The Guide includes an extensive troubleshooting

section; further experience from users will provide an expansion of this

section in the next edition.

Some progress was made on the augmentation of Cone Calorimeter physical

facilities at NBS . Certain needed work (e.g., the installation of the FTIR

sampling system) was not started due to insufficient funds. During the year,

however, significant progress was made on the installation of the second,

controlled-atmospheres Cone Calorimeter unit. This installation is now

complete, and data will be taken with the system shortly.

About a year ago, it was realized that the value of material fire properties,

such as obtained from the Cone Calorimeter and other modern fire test devices,

is much diminished if the data cannot be conveniently exchanged among

laboratories, databased, searched, graphically manipulated, and cross-compared.

Due to incompatible hardware and data format standards (and the unavailability

of specifically tailored, yet user-friendly software), data exchange and

comparison even within one laboratory has been difficult. So has the import of

materials property data into computer fire models. To resolve this situation,

it was decided to formulate standards for a unified Fire Data Management

System. This would have the capability to access measured data from the Cone

Calorimeter, the Furniture Calorimeter, and other current-day test methods. It

would, equally well, take in simulation data, as generated from room fire

models or calculations. In turn, it would have the capability to output the

needed material fire property data into computer models. Once a standard data

format is available, interchange of data among laboratories would become easy.

So far, this work is being started up in cooperation with the Fire Research

Station (England) and the Statens Provningsanstalt (Sweden) . It is expected

that other fire laboratories will be joining the effort shortly.

Progress on the software unification has been the following so far. A set of

computer hardware to run on was selected. A programming language and

programming utilities were selected. Preliminary data formats, for both vector

and scalar data, were established. An over-all work plan was written, and

certain portions expanded into pseudocode. Routines for physical ~ data

acquisition were implemented.

Also, under the Research Associate program with NFoPA, an exhaustive survey of

wood materials was made to collect the rate of heat release data taken not only

from the Cone Calorimeter, but also from older apparatuses and in large-scale

measurements. Data analysis is underway.

Reports and Publications

Twilley, W.H.

and Babrauskas , V., User's Guide for the Cone Calorimeter.

[U.S.] Nat. Bur. Stand. (1988).

Babrauskas, V., and Wickstrom, U.G., The Rational Development of Bench-Scale

Fire Tests for Full-Scale Fire Prediction, to appear in the proceeding of Fire

Safety Science, Second International Symposium (1988).

158
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

FIRE HAZARD ASSESSMENT

Professional Personnel

Richard W. Bukowski

Walter W. Jones '

Project Objective

Develop methods for the quantitative assessment of fire hazard and support the

implementation of these methods by the fire protection community.

Scope

The project is intended to produce a fundamental capability to analyze the

hazards associated with a specified fire scenario(s). This capability will be

provided in the form of a fully- supported software package for MS-DOS personal

computers. While initially limited to residential-style occupancies, the

software design will be such that it can be used across a broad range of

applications from fire safety education to fire reconstruction.

Technical Accomplishments

1. HAZARD I Beta test

The main thrust of the project this past

year has been the user evaluation of the

prototype version of the Hazard Assessment Method - HAZARD I. This consisted

of a three volume (1000 page) report and

a set of 5 1/4 in. disks containing the

software necessary to conduct hazard

analyses of products used in residential

occupancies. All of the software provided will operate on any IBM PC (XT or AT)

or compatible computer. Figure 1 shows

the information flow among the programs,

which 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 multicompartment energy and mass transport; a graphics utility for plotting data; a detec tor/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

HAZARD I SOFTWARE

v

(T^y.

Dtfine Producl •nq Coniext, Check System Umns

(PROOUCT.OM0

Obtain Property Convert Muhipie Input Building Data Burning Item* To anc Fire Date (FlREDATA) Specified Fire r* For Moa»t

or Test (MLTFUEl) (FINPUT) w Run Tranaport Mooei

(FAST)

/ •

( CASE

Run Graphics P/ccram

(PASTPtOT)

Run Decision & Action /Evacuation Mocel

(EXITTJ

( CASE EVA )

V. Run TanabWity

Calculations (TENAB)

r*

Evaluate Results and

Recycle To Ne*t Scenari

Ottein Sprinkler/ Therm a? Detector

Activation Time (DETACT)

s Automatic Date

Transfer

- Manual Data

Transfer C T Data Ftie

(PRfyl Printer Output

Figure 1

159
of incapacitation or lethality from temperature or toxic gases or incapacitation

by second degree burns from radiant flux exposure.

The prototype software was evaluated by a group of 93 international participants

representing all aspects of the fire community. After installing the software

on their own computer, they used the supporting documentation to learn the

operation of the system and examine its capabilities to address problems within

their own area of interest. While each committed to attempt and report on an

analysis of their own choosing, only one such documented case was submitted.

Many others reported conducting a case study, only to find that they had

insufficient time to document it, or that the work done was proprietary in nature

and could not be shared at this time.

The suggestions received from the evaluators, along with our own planned

improvements were incorporated into the general release version of the software

to be made available in December. Significant improvements were made,

particularly in the user interface. The experience gained through the user

evaluation was crucial to the production of a software package which promises

to revolutionize the conduct of fire protection engineering.

Even though it is a prototype in limited release, HAZARD I is beginning to find

acceptance as a tool in the practice of fire protection engineering. A major

consulting firm reports success in obtaining waivers from code authorities based

on analyses conducted with the package. The International Conference of Building

Officials (ICBO) has requested training of their entire headquarters staff in

the use of HAZARD I to evaluate code changes and new materials or products. And

FAST was qualified as a "valid scientific tool" in a criminal (arson) trial in

state court (Minnesota)

Technical Improvements to FAST

The FAST model forms the core

of the hazard assessment

capability, and the expansion

of its capabilities are crucial to the growth of HAZARD.

To this end, several technical improvements have been

implemented in version 18 of

FAST. These include a new,

and more complete combustion

chemistry scheme than has

been included in other fire

models. As shown in the diagram of figure 2, this scheme

includes entrainment by and

burning of the fire plume in

both the lower (e : ) and upper

(e 2 ) layers. The energy release is limited by the oxygen entrained into the plume

and its concentration in the

layers. Fuel which cannot burn due to insufficient oxygen in the room of origin

is tracked through other building spaces and burns when it mixes with sufficient

160
oxygen (e.g., e 3 ) . For the

physical arrangement shown in

figure 2, figure 3 shows how

the energy from a 100 kW fire

in compartment 1 would be

distributed among the two

layers in the compartment of

origin (dashed > lines) , the

second compartment, and the

vent to the exterior.

Another new feature is the

ability to open and close,

both interior and exterior

openings at any time. This

provides a unique capability

to study the impact of changing ventilation created by

evacuation, fire fighting

operations, or even failure

of a partition. Coupled with

the vitiated combustion routine, this moves the analytical capability of FAST

squarely into the realm of the fully-developed fire. Still lacking is a more

detailed treatment of combustion, including such aspects as radiation to

combustible items, enhancing their burning rate or driving the ignition and flame

spread processes. Here, much progress has been made in the University of Dayton

model which is directly linked to FAST.

Figure 3

Presentations and Publications

1. Jones, W. W. , FAST and the Analysis of Fire and Smoke Hazard, Invited

presentation at the Annual Meeting of the Sheet Metal and Air Conditioning

Contractors Assn., Las Vegas, NV . (1988).

2. Jones, W. W. , Refinement and Experimental Verification of a Model for Fire

Growth and Smoke Transport, Second International Symposium on Fire Safety

Science, Tokyo, Japan (1988).

Related Grants

"Mathematical Modeling of Furniture Fires", Mark A. Dietenberger , University

of Dayton Research Institute.

161
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY88

Institution: University of Dayton Research Institute

Grant No .

60NANB5D0556

Grant title: Mathematical Modeling of Furniture Fires

Principal Investigator: Mark A. Dietenberger

Research Physicist

University of Dayton Research Institute

300 College Park - JPC/232

Dayton, Ohio 45469

(513) 229-4417

Other Personnel: Joyce Smith, Research Programmer

NBS Scientific Officer: Dr. Vytenis Babrauskas

Technical Abstract:

Introduction HEMFAST models time -dependent, quasi- three-dimensional

predictions of furniture fire growth and burnout in a room as well as of the

spread of nontoxic and toxic gases and smoke to other rooms. The threedimensional aspect of the fire model includes a mockup construction with

connecting panels, a flame volume with pyrolyzing polygonal base and sides, a radiation heat transfer between grey facets of objects and of the flame, and

the three zones of gaseous flows. The time -dependent aspect of the fire model

includes the flame spreading in any direction on the mockup, the scaled

burning history of burning facets on mockup panels which includes mass and

heat release as well as soot and toxic gas production, the temperature rises

of the mockup facets, walls, and gas layers, and the growth of the upper gas

layer. The predictive aspects of the fire model demonstrate recent physics

models (with appropriate numerics of material heating, flame spread, material

pyrolysis, flaming combustions, fire plumes, and gas flows. Finally, almost

any furniture material can eventually be simulated because the model relies on

effective scaling of the cone calorimeter data and of the flame spreading

data. All these features taken together make HEMFAST an unique fire model.

The highest priorities of the current research were (1) to simplify and make

clear the interfaces between FAST and the Furniture Fire Model (FFM) and (2)

to validate the second version of HEMFAST with full-scale fire tests.

HEMFAST Code Interfaces Two phases were taken to improve the interfaces

between FAST and FFM. The first was to develop a main routine to divide the

FAST code into the first part which reads in the FAST database and the second

part which executes the fire growth algorithms. The subroutines for reading

and processing the FFM database were placed between the two parts of the

divided FAST code. This is shown in Figure 1. A user interactive menu was

constructed .in the main routine to manage the combined database. In the

second phase, the interfacing subroutines were inserted into three FAST

subroutines to manage the execution of FFM modules in conjunction with FAST

fire simulation. One subroutine is used to synchronize the furniture fire

162
growth computations as a function of time with the corresponding FAST time

integrations. One other subroutine is used to convert FFM predictions to

inputs needed by, -FAST and to bypass several FAST subroutines. The third

interfacing subroutine is for printing out FFM predictions. These four

interfacing routines were absent in the first version of HEMFAST installed at

NBS. The absence of these routines gave the false impression that the FAST

program was being profoundly modified.

These interfacing routines and a substantial amount of internal

documentation has been incorporated with the second version of HEMFAST. Thus

there is a basis for incorporating the FFM code to newer versions of FAST, or

to incorporate a recent version of FAST (or even the HARVARD CFC) to any newer

versions of the FFM.

Validation Process To validate the second version of HEMFAST with full-scale

fire tests, it was necessary to revise the numerical techniques of time

integration both within FFM and in its coordination with FAST's time

integration. It was also necessary to incorporate our latest results on

scaling some recent cone calorimeter database into HEMFAST by revising the

bench scale data processors for the second version.

We acquired the furniture/room fire tests database from Dr. Vito

Babrauskas , Mr. Richard peacock, and Dr. James Quintiere in August 1987. This

database has been examined to select measured variables for comparisons with

the predictions of the second version of HEMFAST. In particular, mockup

burning rates, burning regions, and air temperatures as a function of time

will be compared between model and experiment. The comparisons will be

published in an upcoming report of the current grant and the HEMFAST (second

version) code and its input/output will be presented to NBS. There should be

no difficulty in implementing the code on NBS-CFR computers because of our

experience with the first version of HEMFAST.

Conclusion Much work still remains even after the successful model

validations, because a robust, somewhat user friendly, flexible, and

documented fire model is still needed to gain full acceptability from the fire

safety community. Thus the remaining work in the current grant period will be

to start on the third version of HEMFAST.

References

rl. M. A. Dietenberger , "Improved Furniture Fire Model Within

'FAST' ; HEMFAST- 2" , NBS -GCR- 88 - 545 , March 1988.

163
Figure 1. Revised Code Structure of Second Version of HEMFAST

164
PART I. Basic Research and Tools for "Engineered" Fire Safety

(In-House Projects and Associated Grants Funded by

NIST)

E. FIRE PROTECTION TECHNOLOGY

CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

ENGINEERING ANALYSIS SYSTEM & FIRE RECONSTRUCTION

Professional Personnel

Harold E. Nelson, Project Leader

Robert Levine, Senior Scientist

D. Stroup, Fire Protection Engineer, Fire Suppression Research

C. Arnold, Computer Programer

Project Objective

1. The development of separated and assembled fire protection analytical

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

professionals

.

2. The use of these tools and other resources to recreate and otherwise

analyze one or more significant fires. To initiate verification of the

results, to evaluate the tools, and to assist decision makers in actions to

prevent recurrence.

Scone

1. Assemble useful data, formulas, and simple models. Program these into a

common format with an accessible point of entry (menu, etc.) Develop this

into a generalized engineering approach suitable for compartmented buildings.

(This portion of the project is closely allied with aspects of the GSA

sponsored Engineered Fire Protection Assessment System project.)

2. Demonstrate procedures for fire reconstruction investigations. Prepare a kit of needed materials. Conduct a reconstruction investigation of one or

more fires of significance. Analyze the fire, determine and initiate research

or testing needs required for a satisfactory reconstruction, prepare the

appropriate report.

Technical Accomplishments

1. Engineering Analysis System.

Several internal improvements expanding the capabilities and usefulness of

FIREFORM have been added to that collection and issued as modified versions of

FIREFORM. Major work continues to produce a greatly enhanced version

(FIREFORM II) and to collect the major elements into a hazard analysis

procedure (FPETOOL.

)

2. Fire Reconstruction.

Two major fire investigations have been undertaken.

167
a. Sharon, PA fire of Sept. 1987. This two story dwelling fire (3

fatalities) has been analyzed and on Sept. 22, 1988 a full scale

simulation test was conducted. The test demonstrated the high CO, low

02

, low temperature lethal conditions suspected in our investigation and

indicated by the analysis. While the analysis predicted the ultimate

levels involved, the speed of development of lethal conditions was

faster than expected.

b. First Interstate Bank Building, Los Angles, CA fire of May 4, 1988.

While the investigation has been completed, the analysis and preparation

of the report are still in process.

Funding from Other Agencies /Institutions

In addition to CFR Priority Project funding the above activities were carried

out with significant support from the General Services Administration (GSA)

Reports and Publications

Nelson, H. E., Concepts for Life Safety Analysis, Fire Safety Journal, Vol

12, No. 3, 167-177, December 1987

Nelson, H. E., Engineering Analysis of the Early Stages of Fire Development-

The Fire at the Dupont Plaza Hotel and Casino- -December 31, 1986, NBS Report

NBSIR 87-3560.

Nelson, H. E., Engineering Fire Protection Design Assessment System. In NBS

Report NBSIR 88-3753

Nelson, H. E., An Engineering Analysis of Fire Development in the Hospice of

Southern Michigan, December 15, 1985, Presented at the 2nd Symposium of the

International Association for Fire Safety Science, Tokyo, June 17, 1988

Nelson, H. E., Overview - Numerical Grading Systems, Transcript of

Workshop/Conference on Analytical Methods of Fire Safety Design, Oct. 14-

16,1987, Building Research Board, National Academy of Sciences

168
CENTER FOR FIRE RESEARCH

PRIORITY PROJECT - 1988

FIRE SUPPRESSION

Professional Personnel

David D. Evans, ^Head, Fire Suppression Research (Project Leader)

William D. Walton, Fire Prevention Engineer

James R. Lawson, General Physical Scientist

Daniel Madrzykowski , Mechanical Engineer

Project Objective

Develop understanding of fire extinguishment processes and derive techniques

to measure and predict the performance of fire protection and fire fighting

systems

.

Scope

This program is designed to assess the performance of fire extinguishing

methods through physical measurement of fire phenomena during suppression.

These measurements form the basis for generating the needed fire science and

engineering knowledge to allow for prediction of fire suppression events. The

predictive methods are developed to enhance CFR fire models

.

Technical Accomplishments

1. Wood Crib Fire Suppression

Data from a series of water spray suppression tests was analyzed to produce

two correlations; One for time to extinction and the other for energy release

rate during suppression. These correlations will be the basis for the future

fire suppression module to be added to the HAZARD I fire model.

The time to extinction was correlated using the method developed by Tamanini

(Comb. Sci. Tech. 1976, Vol 14, p 17-23) for large normalized water

application rates. At low normalized water application rates the correlated

dimensionless time to extinction for Tamanini ' s small wood cribs (1/2" x 5 x 8

x 10) was found to be much greater than that measured for the large cribs

(1.5" x 6 x 16 x 16, 100 kg mass and energy release rates of 460 kW) used in

this study.

Measurements of energy release rate during water spray suppression were

correlated by assuming an exponential decay from the energy release rate at

the time of initial water spray application. The time constant for this decay

in energy release rate that provided the best fit of the data was 28% of the

calculated time to extinction.

The significance of these results is that both time to fire extinction and

energy release rate during suppression can be estimated for the purpose of

hazard assessment fire modeling without detailed calculation. Of course there

remains the assumption that all fires must be reduced to an equivalent wood

crib fuel source in order to perform the analysis.

169
2 . Thermal Model of Extinction

Previous analysis and measurement of water droplet evaporation on non-porous

high thermal conductivity surfaces were extended to both porous and non-porous

low thermal conductivity solids. The analysis of droplet evaporation on low

thermal conductivity solids requires coupling of the liquid and solid phase

conduction analysis. This was avoided in analysis of evaporation from metal

surfaces by using a constant interface contact temperature. The prediction of

droplet evaporation on non-porous surfaces uses a Green's function integration

over transformed domains representing the droplet and the solid. Measurements

using both porous and non-porous ceramic solids have shown that: (1) water

droplet evaporation is quicker from porous solids than non-porous solids and,

(2) thermal recovery time and volume of droplet influence are greater for

porous solids compared to non-porous solid. An apparatus that irradiate

solids from external heat sources above the surface, simulating heat flux from

a flame, is being constructed. This apparatus will be used to extend the

study of droplet evaporation into a geometry that closely simulates burning

fuels

Reports and Publications

Suppression of Wood Crib Fires With Sprinkler Sprays: Test Results, William D.

Walton, National Bureau of Standards Interagency Report, NBSIR 88-3696,

January 1988.

Water Spray Suppression of Fully- Developed Wood Crib Fires in a Compartment,

James A. Milke, David D. Evans, and Warren Hayes Jr., National Bureau of

Standards Interagency Report, NBSIR 88-3745, June 1988.

"Progress in Modeling Sprinkler Performance," in U.S. /Japan Government

Cooperative Program on Natural Resources (UJNR) . Fire Research and Safety. 9th

Joint Panel Meeting of the UJNR Panel. May 4-8, 1987., Norwood, MA, David D.

Evans, William D. Walton, and Bernard J. McCaffrey, National Bureau of

Standards Interagency Report, NBSIR 88-3753, April, 1988 .

Cooling Effect of a Single Evaporating Droplet on A Hot Semi - Inf inite Metal

Body, Marino di Marzo, Anil K. Trehan, and David D. Evans, National Bureau of

Standards Interagency Report, NBSIR 87-3517, April, 1987.

Dropwise Evaporative Cooling of High Thermal Conductivity Materials, Marino di

Marzo, and David D. Evans, Heat and Technology . Vol.5, No. 1-2, 1987.

"Evaporation of a Water Droplet Deposited on a Hot High Thermal Conductivity

Solid Surface," Marino di Marzo and David D. Evans, Heat and Mass Transfer in

Fire, HTD-Vol 73, A. K. Kulkarni and Y. Jaluria, editors, The American Society

of Mechanical Engineers, New York, NY 10017, 1987

"Ceiling- Jet Flows," David D. Evans, SFPE Handbook of Fire Prevention, Phillip

Di Nenno , editor, National Fire Protection Association, Quincy, MA, 1988

"Use of Computer Fire Models for Analyzing Thermal Detector Spacing," David W.

Stroup and David D. Evans, Fire Safety Journal . Vol 14, 1988.

170
Measurement of Droplet Size in Sprinkler Sprays, James R. Lawson, William D.

Walton, and David D. Evans, National Bureau of Standards Interagency Report,

NBSIR 88-3715, February 1988.

Related Grants

"Effects of Water on Ignition of Cellulosic Materials," Arvind Atreya and

Indrek S. Wichman, Michigan State University.

"Transient Cooling of A Hot Surface'" Marino di Marzo, University of Maryland.

"A Study of the Suppression and Extinction of Fires by Water Sprays," Walter

W. Yuen and Wilber Lick, University of California.

"Development of a Technique to Assess the Adequacy of the Municipal Water

Supply for Residential Sprinkler Systems", John L. Bryan and James A. Milkie,

University of Maryland.

171
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution: Michigan State University

Grant No .

60NANB5D0578

Grant Title: Effect of Water on Ignition of Cellulosic Materials

Principal Investigator (s)

Drs . Arvind Atreya and Indrek S . Wichman

Department of Mechanical Engineering

Michigan State University

East Lansing, MI 48824-1226

Other Professional Personnel L-S Tzeng, Graduate Research Assistant

M. Abu-Zaid, Graduate Research Assistant

NBS Scientific Officer: Dr. David D. Evans

Technical Abstract:

Introduction The study of ignition and extinguishment of combustible

cellulosic materials is of great importance for fire safety because these

materials constitute the bulk of the fuels in many building fires. Because of

the porosity of cellulosics, water plays an important role from ignition to

extinguishment. Absorbed water delays the onset of ignition and consequently

retards the fire growth rate. Also, water is the most common agent used to

extinguish such fires. Our results will be useful for determining onset of

ignition, the fire growth rate and its subsequent containment by external

application of water.

Piloted Ignition Experiments Measurements of the time required for

ignition, surface temperature, mass evolution rate (fuel and water vapor) are

made for different levels of external radiation and sample moisture content.

The test facility is shown in Figure 1. The wood samples are instrumented

with thermocouples, dried (at 105° over phosphorous pentoxide) , weighed,

conditioned to a known relative humidity, weighed again (to determine moisture

weight), then subjected to a known external radiant heat flux. The duct

exhaust is continuously analyzed for water concentration and CO , CO

2

, and

total hydrocarbons. Thus, for a given moisture content and external radiation

the following measurements are made as a function of time (i) front and back

surface temperatures, (ii) mass evolution rate of water vapor, (iii)

production rate of combustible gases.

Theoretical Model of Piloted Ignition A simplified model of piloted

ignition is analyzed numerically. The two-dimensional couples gas and solid

phase problem is simplified by assuming that the mass evolution rate from the

combustible is a known function of time and by employing a plane (not a point)

ignition source; thus, the model problem is transient and one -dimensional

The effects of (i) ignition source location, (ii) fuel mass evolution rate

from surface, and (iii) surface temperature of solid fuel were investigated.

The experimentally-observed pre-ignition flashes are explained. A rational

criterion for positioning of the pilot flame is proposed (at equilibrium

diffusion flame location). Also, the minimum fuel flow rate, by itself, is

found insufficient for predicting inset of piloted ignition - heat losses play

an important role. Heat flux profiles, which are proportional to the local

172
temperature gradient, are shown for the propagating premixed flame stage of

piloted ignition in Figure 2. Note how quickly the premixed flame moves

through the mixture

.

Transient Cooling of Ceramic Solids bv Droplet Evaporation The effect of

a single droplet of pure water on transient cooling is studied experimentally.

The solid surface temperature ranged from 75 to 200°C; they were instrumented

with surface and indepth thermocouples. For the non-porous solid these

temperatures remain nearly constant, while for the porous solid a continuous

decrease is observed during droplet evaporation. Thus, an energy sink exists

in the porous matrix in the vicinity of the thermocouple. From the transient

measurements of surface and indepth temperatures the following quantities were

determined, (i) recovery time (larger for porous than non-porous), (ii) size

of surface and indepth zones affected by droplet (larger for porous solid)

.

Shown in Figures 3 and 4 is a comparison between indepth temperatures for

porous and non-porous solids for an initial solid surface temperature of 100°C

and a droplet volume of 30 /xL.

Reports and Papers:

1. Tzeng, L.S., Wichman, I.S. and Baum, H.R.

,

"A Combined AnalyticalNumerical Solution Procedure for Chemically Reacting Flows , " Central State

Meeting of the Combustion Institute , pp. 426-431 (1987).

2. Tzeng, L.S., Atreya, A. and Wichman, I.S., "A One -Dimensional Model of

Piloted Ignition," submitted to Combustion and Flame (1988).

3. Abu-Zaid, M. and Atreya, A., "Transient Cooling of Hot Porous and NonPorous Ceramic Solids by Droplet Evaporation," submitted to Journal of

Heat and Mass Transfer (1988).

Figure I. Schematic of the Experimental Apparatus

173
Indepth

Temperatures

(°C)

g

HEAT

FLUX

(J/sec

2.= Heat flux profiles (proportional to teaperature gradient) for the propagating

pre-alxed flaae during piloted Ignition.

Fig. 3. Indepth temperatures versus time for a non —

porous solid. Initial solid surface temperature

100°C. Droplet volume 30 pL.

174
Indepth

Temperatures

(°C)

Fig. Indepth temperatures versus time for

a porous solid. Initial solid surface temperature

100 6 C. Droplet volume 30 pL.

175
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

InstitutionThe University of Maryland at College Park

Grant No.COMM 70NANBSH0525

Grant Title: Transient Cooling of a Hot Surface

by Droplets Evaporation

Principal Investigator; Dr. Marino di Marzo

Mechanical Engineering Department

University of Maryland

College Park, MD 20742

Other Professional Personnel: F. Kavoosi, Graduate

Research Assistant

D. Madrzykowski,

Undergraduate Student

NBS Scientific Officer: Dr. David D. Evans

Technical Abstract:

Introduction The phenomena associated with solid fuel fire

extinguishment processes are related to the evaporation of water droplets

deposited on hot solids. In the previous grant periods we successfully

correlated the experimental results for droplets deposited on high

thermal conductivity solids. Extensive experimental data for a low

conductivity material were also collected. Further investigation of a different low conductivity solid will be performed in the next grant

period. The current effort is aimed at developing a model to predict the

complex thermal behavior of the liquid-solid interaction on these low

conductivity materials.

Some detailed aspects of a small droplet generator will be discussed in

the following. The droplet size characteristic of sprinkler

distributions is in the order of 1 pi. These small droplet are strongly

influenced by surface tension forces and special techniques must be

developed to disengage them from the dispenser.

Evaporative Cooling Model The governing equation for the solid transient

thermal behavior and its boundary conditions are:

& T 2 T(x,y,z,0) = prescribed

= a V T

6 t s (6 T / & r) =0

for r = 0 & r-*®

The temperature gradient at the exposed solid surface <& T / 6 z) is

prescribed. At the solid-liquid boundary under the droplet, both the

heat flux and the temperature are matched. For the liquid the governing

equation is identical with the exception of the different thermal

176
diffusivity. The boundary condition at the exposed surface of the

droplet is casted in terms of evaporative mass transfer as described in a previous paper [23.

The idea of using the Green's theorem to reduce the three dimensional

nodalization to a simpler surface description of the phenomena is

extremely appealing because ve are only interested on the area influenced

by the droplet cooling at the surface of the solid. The general solution

for the transient conduction equation is:

u ( x, t ) = a [ G(x,t,x0,t0) <7 u) - u<x0, t0) (7 G) 3 • n d s d t0

X0 X0

0 S

^ G<x,t,x0,0) u<x0, 0) dv

J V

Note thBt u is a simple transform of the temperature # T

# defined in such

a way that the volume integral is eliminated. The functions G for the

solid and the liquid are defined, in the general form, as:

2 2 2

(x - x0) + (y - y0) (z - z0)

-1.5 - G(x,t,x0,t0) = (4 n a t0) e 4 a t0

2 2 2

(x x0) <y y0) (z - z0)

-1.5 - (4nat0) e 4a t0

Further, this selections of G are such that (V G) • n at the solid surface

is zero. This simplifies the surface integral at the solid surface and

at the liquid-solid interface. The integral on the exposed surface of

the droplet will contain both terms (G and 7 G>. At this time ve have

identified the terms related to the solid surface only. In general ve

can represent these terms as a surface integral of the product of a forcing function F, vhich is the temperature gradient normal to the solid

surface, and of a veighing function W. In cylindrical coordinates this

can be vritten as:

u ( r, t

)

t a

j' F(r0, t0) W(r,r0, t0) d r0 d t0

J 0 0

vhere, for the general case, W is given by:

177
2

(r - r0)

1 -1.5 2 r r0 - W(r,r0, t0) = r0 t0 L ( ) e 4 a t0

.5 0 4 a t0

(4 n a

For the particular cases <r = 0 and/or t = 0 ) , we obtain specific forms of

the weighing function W which are integrated analytically over the

interval of concern. The interval of concern is determined by the grid

size and by the time step ' 7

' accordingly. These specific

expressions for W are:

2

-1 2r G

W(r0=r,t0) = r t0 L ( ) erf t — 3 0 4 a t0 .5

<16 a t0>

2

(r - r0)

E C ] i 4 a 7

a t . 5 €

W ( r0 = r, 0 ) = 2 < ) erf t ] n . 5

<16 a 7 )

Preliminary results for the solid were obtained and compared favorably

with the previously published data for aluminum [rl3.

Droplet dispenser The average size of the droplet generated by a sprinkler system is in the order of one pi. The droplet size used to

investigate the cooling effect due to the evaporative cooling ranges from

10 to 50 pi. This size range is most convenient for accurate

experimental measurements because such big droplets are easy to generate

and their evaporation time is long enough to carefully monitor the

transient heat and mass transfer processes. The first difficulty that

arises in the generation of one pi droplets is due to the strong surface

tension forces. The droplet does not leave the dispenser and clings to

it. We have observed that the minimum size that leaves a thin needle or

fiber is of the order of 10 pi. The addition of a surfactant brings this

minimum size down to 3-5 pi. However, the purity of the water is

compromised and the experimental data loose their significance.

The droplet must have some momentum in order to disengage from the

dispenser tip. We have designed and build a dispenser in which a thin

disk is imparting momentum to the liquid and it is pushing it through a nozzle. A schematic of the conceptual design is given in Fig. 1.

Initially we choose a piezoelectric activated disk, but the

incompatibility of water with the piezoelectric material required the

2

G G

E [ ] 2 n i 16 a t

1 . 5

W(r,r0,0) = <r0 / r)

2 n

178
system to be sealed. The constraints due to the leak proof system were

such to almost completely restrain the piezoelectric motion.

Figure One - Droplet Generator Design Conceptual

In order to pulse the thin disk we used a mechanical spring-loaded

plunger. This device was difficult to control and was used to explore

the feasibility of a mechanical pulse generator for the thin disk.

Preliminary results indicated that very small droplets (0.01 pi) were

generated and they were scattered over a 12 millimeter radius. The exact

size and position of the droplet must be controlled in order to perform

the necessary measurements during the transient. Therefore, we will

design a different device to impart a controlled pulse to the thin disk.

This new pulse generator will be activated by a solenoid driven rod

attached to the thin disk. The size of the dispenser nozzle was 150

microns in diameter. We are building various nozzles of larger size to

study the effect of the nozzle diameter on the droplet size.

Acknowledgements Dr. H. Baum suggested the approach to the numerical

computation of the coupled liquid-solid evaporative cooling problem. His

guidance has been invaluable for the progress of this research. The

Computer Science Center of the University of Maryland at College Park

provided support for the computational expenditures.

References

rl. M. di Marzo, D. D. Evans, "Dropwise Evaporative Cooling of High

Thermal Conductivity Materials", Heat and Technology. Vol. 5, Ho.

1-2, pp. 126-136, 1987

Reports and Papers:

1. M. di Marzo, Z. Y. Wang, W. H. Meng, "Transient Cooling of a Hot

Surface by Droplet Evaporation", National Bureau of Standards Report.

NBS-GCR-87-534, 1987

2. M. di Marzo, D. D. Evans, "Evaporation of a Water Droplet Deposited on

a Hot High Conductivity Solid Surface", 24th ASME/AIChE National Heat

Transfer Conference. Pittsburgh, Pennsylvania, HTD Vol. 73, pp. 11-18;

Also to appear in Journal of Heat Transfer. Transaction ASME

3. W. H. Meng, Z. Y. Wang, M. di Marzo, D. D. Evans, "Single and Multi

Droplet Evaporative Cooling", Combined Meetings: Eastern Session of

the Combustion Institute and CFR Annual Conference on Fire Research.

NBS - Gaithersburg, Maryland, pp. 42.1-42.4, 1987

179
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FT 87

Institution: The University of California

Grant No: 60NANB6D0651

Grant Title: A Study of the Supression and Extinction of Fires

by Water Sprays

Principal Investigators: Professors W. W. Yuen and W. Lick

Department of Mechanical Engineering

University of California at Santa Barbara

Santa Barbara, California, 93106

NBS Scientific Officer: Dr. Bernard J. McCaffrey

Technical Abstract

1. INTRODUCTION

The objective of this study is to determine the fundamental mechanisms by

which the spraying of water leads to fire supression and extinction. During this

reporting period, the research concentrated on three specific tasks: (1) the

numerical modelling of the general and localized circulation in a room as dependent upon door and window openings: (2) a detailed analysis and description of

the dynamics of water spray as influenced by the fluid dynamics; and (3) the

thermal quenching of a flame due to the presence of chemically-inert species.

The first two tasks contribute to the understanding of the "survivability" of the

water sprays in a fire environment after injection. The third task contributes to

the understanding of the interaction between the water droplets/vapor and the

reacting species in a combustion/extinction process.

2. MODELLING OF CIRCULATION IN A ROOM WITH DOOR AND WIDOW OPENINGS

A quite general numerical model of the time-dependent dynamics of a compressible, viscous, heat-conducting, chemically-reacting mixture of gases

has been developed and applied to the problem of natural heat convection in a room with door and window openings. A unique feature of the model is its treatment of the conditions at the doors and windows, where open boundary conditions (Licks, et. al. 1986, 1987). must he specified. Numerous calculations have

been made and are being made to investigate the general dynamics of natural

convection in a room with specific emphasis on the effects of door and window

opening.

A preliminary calculation of this type, primarily to test the open boundary

condition, is shown in Figures 1 and 2. A heat source at the middle of the left

wall causes the air to rise and a ceiling jet to develop. On the right, the hot air

escapes from the top and cool air is drawn in at the bottom. A steady-state

eventually develops and it can be shown that the open boundary condition (in its

180
nonlinear formulation) works extremely well. This type of calculation is continuing so as to investigate the effects of various flow parameters.

3. DYNAMICS OF WATER DROPLETS

The model described in section 2 is used simply to describe the general

fluid dynamics. Of primary interest is the dynamics of the water droplets as influenced by the fluid dynamics and the influence of the water droplets on the

fluid dynamics. A general numerical model of this interaction is being

developed.

Both the fluid dynamics and the droplet dynamics are developed by an

Eulerian procedure. For complex problems of droplet-fluid dynamics interaction, this seems most appropriate and numerically efficient. The basic conservation equations for the water droplets have been written in a form identical to

the fluid dynamics equations used in the model described in section 2 and are

presently being included in that model. In its most general form, this model can

then be used to describe the dynamics of water droplets of varying sizes and the

droplet’s size changes as a function of evaporation and heat transfer.

4. THERMAL QUENCHING BY CHEMICALLY-INERT SPECE5

Since water is not expected to be chemically reactive with most common

fuels, the supression and extinction of fire by water is primarily a thermal

quenching phenomenon as noted by previous investigators (Rasbash 1962, Grove

et.al. 1981, Williams 1981). A survey of the literature, however, shows that while

extensive amount of data have been collected on the relative effectiveness of

various gaseous/liquid agents on thermal quenching (Friedman and Levy 1963,

Seshadri and Williams 1975, Kent and Williams 1975, Tucker et.al. 1981), a fundamental non-empirical theoretical study of this important phenomenon has not

been reported. The development of such a theoretical model is a major objective of this research program.

A laminar diffusion flames generated by two opposing flows of fuel and oxidizer is selected as the basis of the present extinction study. The geometry is shown in Figure 3. This geometry is selected because it is one of the few cases

for which conservation equations for mass, momentum and energy can be

readily written from first principle with no empirical constants. Assuming constant thermophysical properties, density and a unit Lewis number, numerical

and approximate solutions to this problem have been reported by many investigators (Fendell 1965, Linan 1974, Krishnamurthy et.al. 1976). Many of the

reported experimental studies on extinction (Friedman and Levy 1963, Seshadri

and Williams 1975, Kent and Williams 1975, Tucker et.al. 1981) were also performed on this opposing flow configuration.

The mathematical development in the previous works is generalized in the

present work to allow a variation of the specific heat of the reactants and products as a function of composition and temperature. Numerical results are generated for a pure fuel stream (methane) and oxidizer streams consisting of oxygen and different inert gases of various proportions.

Typical ignition characteristics generated for three inert gaseous species

(A2 , 0, andi/e ) with different specific heats are presented in Figure 4a. At

600 K, the specific heat for A2 , H%0 and He are 1.0 J/gm-K, 2.0 J/gm-K and 5.2

J/gm-K respectively. As expected, for a given oxygen mass fraction in the oxidizer stream, the mixture ignites if the dimensionless Damkohler number (which

181
is a ratio of the characteristic time of the flow to the characteristic time of the

reaction) exceed a critical value. For a given inert gas, a decrease in the oxygen

mass fraction in the oxidizer stream reduces the reaction rate, the critical Damkohler number required for ignition increases. For the same oxygen mass fraction, a mixture with an inert gas of higher specific heat has a lower mixture temperature and therefore lower reaction rate. The critical Damkohler number

required for ignition also increases.

Since the Damkohler number is inversely proportional to the characteristic

flow velocity, numerical data presented in Figure 4a can be presented in terms

of the characteristic flow velocity, u as shown in Figure 4b. u0 is a characteristic velocity corresponding to the ignition of an oxygen/nitrogen mixture with

50% oxygen mass fraction. It is interesting to note that Figure 4b is qualitatively

similar to some experimental extinction curves. Since u0 is the only adjustable

parameter in Figure 4b, the present results suggest that measurement of the

extinction curves for different inert species and oxygen mass fraction can be an

effective mean in determining the various reaction constants for the reaction.

In the next reporting period, additional numerical results will be generated

for other fuels and inert gases. The model will also be expanded to allow for

variable density and Lewis number different from unity. Based on the model,

the effect of liquid inert species on the reacting mixture will be addressed.

Specifically, the fire supression/extinction Characteristics of water spray will be

illustrated.

182
^ s s

f50

Fig. 1. Computed Isotherms in an Enclosure

with a Hot Spot (1000 C) at the Wall

and an Opening.

Fig. 3. Oxidant, Fuel, and Product Particle

Lines in an Axially Symmetric

Stagnation-Region Flow.

I /

. * - ^ \ \ \ \ '

j /

'

j

" \ \ \ \ ‘

\\ v .

.

\

• . _ ..

Fig. 2. Computed Flow Field in an Enclosure

with a Hot Spot (1000 C) at the Wall

and and Opening.

Fig. 4a. Critical Damkohler Number Required fo:

Extinction for Oxidizer Streams with

Different Oxygen Hass Fraction and

Inert Gas.

LOG y/ue

Critical Characteristic Flow Velocity

Required for Extinction for Oxidizer Streams

with Different Oxygen Mass Fraction and Inert Gases.

183

Fig. 4b
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : The University of Maryland at College Park

Grant No.: 60NANB8D0814

Grant Title: Development of a Technique to Assess the

Adequacy of the Municipal Water Supply for

Residential Sprinkler Systems.

Principal Investigator Dr. John L. Bryan and James A. Milke

Fire Protection Engineering Department

University of Maryland

College Park, MD 20742

NBS Scientific Officer : Dr. David D. Evans

Technical Abstract:

This project is a continuation of work examining the

capability of a municipal water supply system to supply a

residential sprinkler system. The initial phase of work

emphasized an assessment of the costs associated with alleviating

deficiencies in the capability of the municipal water supply

system. The current phase has focused on an evaluation of the

water supply in residences as provided by the municipal system in

the Baltimore, Maryland - Washington, D.C. metropolitan area.

In the first phase, simple cost effective techniques for

alleviating water supply deficiencies in a residential sprinkler

system installed in a one or two-family dwelling have been

examined. The equipment associated with compensating for a

inadequate municipal water supply using water storage tanks,

booster pumps, and large diameter pipe have been investigated for

efficiency and cost effectiveness.

Hydraulically-designed, NFPA 13D, residential sprinkler

systems in seven residences were used to carry out this research.

The seven selected floor plans of one and two-family dwellings

included in this project were representative of a wide range of

designs currently being utilized in actual residential

subdivisions under construction at the time of the project in the

Baltimore-Washington area.

The simple technique for determining the installation cost

of a sprinkler system was formulated following an analysis of the

sprinkler system versus the key design features of the dwelling.

Emphasis was placed on developing a technique which was accurate

and easy to apply with minimal time and effort.

184
In the second phase the evaluation consisted of determining

the water supply characteristics at selected residences in the

metropolitan area. Water flow measurements were conducted using

characterized residential flow devices, e.g. faucets and hose

bibbs, which were in-place in the selected residences. An

elementary hydraulic analysis was used to determine the

characteristics of the domestic water supply at the water meter,

based on the results of the flow test. The adequacy of the

municipal water supply system can be assessed with a knowledge of

the water supply characteristics at the water meter and the

demand requirements of the residential sprinkler system also

determined at the water meter.

185
,

m

.

H

:lffl

i
PART I. Basic Research and Tools for "Engineered” Fire Safety

(In-House Projects and Associated Grants Funded by

(NIST)

F. TECHNOLOGY TRANSFER

CENTER FOR FIRE RESEARCH

PRIORITY PROJECT

TECHNOLOGY TRANSFER

Professional Personnel

James H. Winger, Project Leader

Nora H. Jason, Technical Information Specialist

W. Doug Walton, Fire Protection Engineer

Project Objective

* Facilitate the transfer of the scientific and technical output of the Center

to the user community.

Scope

The transfer of the results of fire research to the fire safety community has

been identified in several forums as one of the most important and most

neglected responsibilities of fire research organizations. Included in this

responsibility is the obligation to effectively communicate with various

segments of the fire safety community to identify their needs , provide

information on the progress and capabilities of fire research, and to provide

them with the outputs of research. The products of fire research need to be

tailored to address identified community needs. Training in the use and

usefullness of the outputs of fire research is an essential part of this

effort. Easily available information such as provided by the fire research

library and the computer bulletin board is important to the fire safety

community

.

Technical Accomplishments

1. Conducted a very successful symposium on fire protection engineering

methods with the Society of Fire Protection Engineers to recognize the

publication by them of the first handbook on fire protection engineering. The

conference was attended by over 200 engineers, scientists, and other fire

safety practitioners from around the world.

2. The Fire Research Information Service (FRIS) has over 30,000 fire research

reports, books, video tapes, etc. in its collection and is growing at the rate

of almost 2000 items per year. This is the most complete fire research

library in the world. FIREDOC , the computerized bibliographic system in FRIS,

has over 14,000 entries. FRIS is open to the public and FIREDOC is available

for searching both on site and by telephone. This service is used by many

individuals and organizations.

3. A first version prototype fire safety education computer game was developed

based on the output of CFR developed fire models to demonstrate the potential

for educational materials based on the results of fire research. Further

improvements are needed prior to dissemination to the education community.

189
4. The CFR computer bulletin board was established to provide access to all

members of the fire research community, including those in remote sites.

Since its inception last year, it already has over 800 users from around the

world including engineers, fire services, consultants, materials and products

manufacturers, and others. These users are requesting and receiving

information on the Center's activities such as meetings and workshops, recent

publications, downloading of CFR computer software, and more.

5. A first meeting of leaders of international fire research organizations was

held that has led to more effective communications, cooperation, and

collaboration. Further meetings are now planned.

6. CFR developed technologies were presented at the annual meetings of the

NFPA and the International Association of Fire Chiefs, and in many other

forums

190
PART II, Timely Response to Current Fire Problems

(Projects Funded by Other Agencies and Private Sector

Organizations)

A. FIRE /MATERIALS INTERACTION
'
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 19 88

RADIATIVE IGNITION IN MICROGRAVITY ENVIRONMENT

Funding Agency: NASA

Project Leader: Takashi Kashiwagi

Project Objective:

The objective of this study is to develop a theoretical model capable of

predicting the, radiative ignition of a cellulosic material( for example

,

filter -paper) and subsequent flame spread over the sample in microgravity

environment. This study is to lead to applications such as fire safety for

spacecraft by understanding and predicting ignition and subsequent flame

spreading behavior.

Technical Accomplishments:

The flow pattern and the temperature distribution in the gas phase during the

preheating period, which is controlled by a balance between the thermal

expansion of the gas due to the heat addition from the heated surface to the

gas phase and conduction away from the heated region, were calculated first.

The results were obtained analytically for early time and numerically for most

times of interest in the experiments envisaged for this study. The additional

complexity of convective mass transfer of the evolved degradation products

from the sample surface to the gas phase is currently being incorporated into

the preheating model. The characterization of thermal and thermal oxidative

degradation of the cellulosic material is on progress including the

measurements of CO, C02

, and H2 0 in the evolved gases. The construction of an

ignition chamber for radiative ignition experiments in a normal gravity has

been completed. The calibration of the radiant flux distribution and

preliminary ignition experiments are being conducted. Shadowgraph photography

setup to observe ignition events is being assembled. The overall design of

the flow reactor is completed and some of its components, for example high

temperature flow settling chamber, are being constructed.

Publications

H. Baum, T. Kashiwagi, and C. di Blasi, "Radiative Ignition of Solid Fuels in

a Microgravity Environment - The preheating Problem" to be presented at 1988

Eastern States Combustion Meeting, December 1988.

193
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

LOW FLAMMABILITY COMPOSITES

Funding Agency: U.S. Dept, of the Navy

Project Leader: James E. Brown

Project Objective:

To develop a bench- scale methodology for evaluating the fire performance

properties of fiber-reinforced composites in order to assist the Navy in

selecting composite materials for use on ships.

Technical Accomplishments:

1. Combustion Sensitivity Index Methodology

The dependence of rate of heat release (RHR) on external flux was determined

for a broad range of materials under constant fluxes indicative of small and

large (flash over) fires. The dependence is expressed as a thermal sensitivity

index for RHR averaged over various periods of the flaming combustion.

Additionally, the external flux requirement for sustained flaming combustion

is ascertained.

2. Ignitability

Ignition delay time as a function of external radiant heating was determined

over a broad range of fluxes. Minimum external fluxes required for ignition

in reasonably finite periods can be predicted.

3. Testing of Materials

Fire testing of Navy candidate composite materials for surface ships was

initiated. The results from these tests are being used to propose

requirements for submarine applications.

Reports and Publications:

Report of Test "Combustion Characteristics of Fiber Reinforced Panels" J.E.

Brown, Report No. FR3970, National Bureau of Standards, April 1987.

Report of Test "Cone Calorimeter Tests of Two Composite Materials" E. Braun

and J. Didion, Report No. FR3973, National Bureau of Standards, November 1987.

"Cone Calorimeter Evaluation of the Flammability of Composite Materials", J.E.

Brown, E. Braun, and W.E. Twilley, NBSIR 88-3733, National Bureau of

Standards, March 1988.

"Cone Calorimeter Method for Determining the Flammability of Composite

Materials" J.E. Brown, Proceedings of the fourth Annual Conference on Advanced

Composites: "How to Apply Advanced Composites Technology" Dearborn, MI 13-15

Sept. 1988, pp . 141 - 150.

194
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

FIRE PROPERTIES OF CANDIDATE MATERIALS FOR COMPOSITE DECKHOUSE

Funding Agency: Navy

Project Leader: T. Ohlemiller

Project Objective:

To develop a complete characterization of the flammability behavior

(ignitability , lateral flame spread, upward flame spread) of composite

materials which are candidates to be used in deckhouse structures aboard Navy

ships. This characterization is to employ a combination of bench scale,

intermediate scale and full scale tests.

Technical Accomplishments:

The Lateral Ignition and Flame Spread Apparatus (LIFT) was used to assess the

heat- flux dependent ignition delay time, the minimum heat flux for ignition,

flux -dependent lateral flame spread rate and minimum flux for lateral spread

across four composite materials. In addition, these test results were used to

infer values for certain empirical parameters which

appear in simplified models for ignition and lateral flame spread. It was

determined that these types of materials can exhibit differing flammabi lity

behavior at sample edges and at areas away from edges . This is apparently due

to a tendency for the gases generated within the sample interior during

heating to seek the path of least resistance in exiting from the sample; that

path is frequently out through the sample edge rather than out through the

sample face. Quantification of these effects will be pursued in the future

together with characterization of other flammability measures on these

materials

.

195
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

BURNING CHARACTERISTICS OF COMBAT SHIP COMPARTMENTS

AND VERTICAL FIRE SPREAD

Funding Agency: Navy (Naval Reserch Laboratory)

Project Leader: Daniel Gross

Project Objective

To perform a preliminary parametric computer modeling study of fire growth in

combat ship compartments with emphasis on vertical fire spread as a result of

heat transfer through metal decks.

Technical Accomplishments

Using the computer model FIRST (with some enhancements) , estimates of fire

development were provided over a wide range of variables, including

compartment size, vent size, combustible load and compartment enclosure

materials. Estimates were made of the heat transmitted through steel and

aluminum decks and of potential ignition of combustible contents in

compartments above the fire - involved compartment, as well as the effect of

added thermal insulation.

196
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

PREDICTION OF THERMAL DEGRADATION AND HEAT RELEASE

FROM AIRCRAFT COMPOSITES

Funding Agency : Federal Aviation Administration

Project Leader : William J. Parker

Project Objective :

Develop a theoretical and/or empirical or estimating technology for predicting

an aircraft cabin panel's heat release rate in the OSU calorimeter.

Technical Accomplishments :

A preliminary model has been constructed to calculate the temperature

distribution throughout an aircraft cabin panel. The panel consists of a Nomex honeycomb with facing sheets on each side. These sheets are of either

fiberglass or carbon fibers and are impregnated with either epoxy or phenolic.

It is assumed that the temperature is uniform in each facing sheet and that

the heat transfer through the interior is by solid phase heat conduction

through the walls of the cells and by gas phase heat conduction and thermal

radiation through the cavities. The mass loss rate at each depth is

calculated from an Arrhenius equation using measured kinetic constants and the

local temperature and density. The heat release rate is determined by

multiplying the local mass loss rate by the local heat of combustion of the

volatiles and integrating over the thickness of the panel. Most of the

thermophysical and thermochemical properties of the individual components were

determined using the TGA, the DSC, the PYROCAT, and the oxygen bomb

calorimeter. Some of the burning rate measurements have been completed. The

heat release rates at 35 kW/m2 have been measured in both the Cone Calorimeter

in CFR and in the OSU Calorimeter at the FAA Technical Center in Atlantic

City

.

PublicationsNone

197
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

COEFFICIENT OF VARIATION OF ASTM E-648 TEST FOR CARPETS

Funding Agency : Carpet and Rug Institute, American Textile Manufacturers

Institute, and the Man Made Fiber Producers Association

Project Leader : William J. Parker

Project Objective :

To provide a technical basis for recommending changes in the ASTM E-648

Flooring Radiant Test which would lead to a substantial reduction in the

coefficient of variation for carpets.

Technical Accomplishments :

This project started with a review of an industry sponsored round robin

involving five laboratories. The flame did not spread away from the ignition

area for about half of those specimens, thus yielding a high critical radiant

flux (CRF) . However, other specimens" of the same carpet spread flame over

significant distances thus yielding considerably lower values of the CRF.

Thus, uncertain propagation was identified as one of the problems, though not

the only one, leading to high coefficients of variation. In the tests run on

the same carpet at NBS the pilot was always sufficient to ignite the carpet

and sustain a flame. However, the local flame that was produced experienced

some difficulty moving down the specimen against the convectively driven air

flow. A line burner which ignites the specimen over its entire width was

constructed to replace the single flame jet used as the original pilot. This

provides a longer, more stable flame front with one dimensional spread

starting at the time of ignition. A coefficient of variation study was then

made on eight carpets in order to pick one with the lowest coefficient of

variation for use in a parametric study. This study which is just starting

is systematically examining the effects of radiant flux, preheat time, air

flow, adhesive mounting board, backing board, specimen orientation and the

purity of the gas used by the radiant panel. The selected carpet. is a 50 oz/yd2 cut pile Nylon 6,6 staple.

PublicationsNone

198
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

NFPA 701 MULTIPLE LAYER DRAPERY FLAMMABILITY

Funding Agency: ATMI , MMFPA, Wool Bureau

Project Leader: Sanford Davis

Project Objective:

To develop a flammability test method for multiple - layer fabrics, particularly

curtains and drapes for inclusion in NFPA 701. The test method will correlate

to full-scale multiple-layer fabric fire behavior.

Technical Accomplishments:

Working with the textile industry, four fire-retardant drapery fabrics

(cotton, polyester, wool, and modacrylic) and two fire-retardant linings

(cotton and vinyl-coated cotton/polyester blackout) were selected for this

study. The experimental approach is to carry out full-scale room burns

involving each of the eight combinations of double layers ignited with a

simulated wastepaper basket. The same combinations will be evaluated in the

NFPA 701 large-scale test apparatus and by the ASTM D 3659-80 semi - restraint

method; the latter is being considered for inclusion in the NFPA 701 standard.

The children's sleepwear apparatus, which is currently used for the NFPA 701

small-scale test, has been adapted for the semi -restraint method. At the time

of writing, all of the test specimens have been prepared and testing is being

initiated. Funding is being sought for extending this program to other fabric

combinations and for multiple- track curtain and drapery systems.

Publications

None to date; however, the major deliverable will be a test procedure for

evaluating the fire behavior of multiple - layer fabrics for inclusion in the

NFPA 701 standard.
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

FIRE PERFORMANCE AND TOXICITY OF COMPOSITE MATERIALS

Funding Agency: Navy

Project Leader: Emil Braun

Project Objective:

To assist the Navy in developing fire safety performance requirements and

evaluation procedures for use of composite materials aboard submarines.

Technical Accomplishments:

The scope of this work limited CFR involvement in the development of fire

safety performance requirements and evaluation procedures to an analysis of the

applicability of the NBS Toxicity Protocol and the Cone Calorimeter for

composite material aboard submarines. Several candidate materials were

supplied by the Navy and used in the evaluation of the test procedures and the

acceptance criteria contained in the second draft of the military standard.

Tests were conducted using a modified NBS Toxicity Protocol as defined in the

military standard. As a result of these tests, the Navy has been encouraged to

adopt an N-Gas Toxicity Procedure as the basis for a first estimate of

material toxic potency. Since such a procedure has never been fully developed,

we are currently drafting such a document. This calls for a modification of

the acceptance criterion for "super toxicity" as defined in the military

standard for use of composite materials aboard submarines, draft 2.

The same materials were tested for fire performance using the Cone

Calorimeter. Once an acceptable fire scenario is developed by the Navy,

suitable performance requirements can be established for this test method.

Publications

Report of Test on the Fire and Toxicological Behavior of Four Materials (report

in preparation)

Test Procedure for the Implementation of N-Gas Toxicity Protocol (report in

preparation)

200
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

A TECHNICAL ASSESSMENT OF EXPLOSIVE VAPOR DETECTION DEVICES

Funding Agency: Law Enforcement Standards Laboratory, National Institute

of Standards and Technology

Project Leader: Marc R. Nyden

Project Objective:

Report on the present and future capabilities of explosive vapor detectors for

the purpose of providing technical guidance to the representatives of local

law enforcement agencies.

Technical Accomplishments:

The major findings of this investigation were as follows:

1) Portable explosive vapor detectors are capable of detecting a limited

range of organonitrate explosives including ethylene glycol dinitrate,

nitrotoulene , di -nitrotoulene , nitroglycerine, and, in some cases, trinitrotoulene

.

2) Commercially available models are much less effective in detecting

cyclonite, pentaerythritol tetranitrate , flammable liquids, and

inorganic nitrates. The inability to detect the latter two categories

of explosives is a serious limitation as they are frequently encountered

explosive fillers.

3) Recent advances in the design of explosives detection devices have

become manifest in the form of large, complicated, and expensive

instruments which are most suitable for use as dedicated detectors at

major installations such as military bases and international airports.

Research efforts appear to be directed more at improving sensitivity

than at increasing the field-worthiness and reducing the cost of these

instruments. The possibility of improving search effectiveness by

introducing computer technology has not been fully examined.

Reports and Publications:

"A Technical Assessment of Explosive Vapor Detection Devices," Marc R. Nyden,

a report prepared for the National Institute of Justice (in preparation).

201
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

FIRE CONDITION EFFECTS ON SMOKE GENERATION AND TOXICITY

Funding Agency: Industry Coalition

Project Leader: Vyto Babrauskas

Project Objectives:

Measuring the generation rates of soot and the principal toxic gases as a function of ventilation, irradiance, fire size, and sample nature and

orientation leading to:

• Sufficient knowledge for predicting full-scale smoke generation from

small-scale data;

• Deriving a validated set of combustion conditions for toxicity

measurement

• Evaluating the usefulness of existing toxicity measurement devices as a

means of obtaining input data for fire hazard assessment.

Technical Accomplishments:

Parallel instrumentation for measuring fire smoke yield and obscuration has

been developed for both the Cone Calorimeter and the Furniture Calorimeter.

For solid and liquid combustibles, it was found that large-scale smoke

emission rates could be well represented from the Cone Calorimeter data after

matching the specimen mass loss rates per unit area. This matching was

accomplished in bench scale by exposing the specimens to a suitable level of

external irradiance. The results were expressed in terms of the specific

extinction area, which is defined as the smoke extinction cross-section per

unit mass. The specific extinction area, when computed on a smoke particulate

mass basis, was found to be independent of fuel type and of the conditions of

test

A first set of experiments has been performed to determine the sensitivity of

smoke and toxic gas yields to the combustion conditions. Operating the Cone

Calorimeter at a single irradiance, samples were combusted under various air

flows and differing oxygen concentrations in the flow. Significant variation

in the carbon monoxide yields was observed. The data are being analyzed

further to direct the next set of experiments.

Publications

Babrauskas, V., and Mulholland, G.W., "Smoke and Soot Data Determinations in

the Cone Calorimeter," ASTM Symposium on Mathematical Modeling of Fires and

Related Test Methods, New Orleans, December, 1986.

Mulholland, G.W., Henzel, V., and Babrauskas, V., "The Effect of Scale on

Smoke Emission," Second International Symposium on Fire Safety Science . Tokyo,

1988.

202
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

HEAT FLUX SENSOR CALIBRATION

Funding Agency: Federal Aviation Administration

Project Leader: Kenneth D. Steckler

Project Objective:

To evaluate the use of heat flux sensors in FAA fire tests and to establish a means for calibrating these sensors.

Technical Accomplishments:

This work focuses on the FAA proposed test method for aircraft cabin interior

materials. This test method requires a measurement of the exposure (external)

radiant heat flux incident upon the material or product to be tested. Thin

foil (Gardon) heat flux sensors are used for this purpose.

A comparative (substitution) calibration technique is being developed. This

approach entails identifying a well-characterized reference radiometer and a

stable radiant source, constructing an apparatus for aligning the source and

sensor, and assessing the accuracy and consistency of the calibration

apparatus and procedure

.

A self -calibrating electrically heated cavity radiometer (ECR) is being

evaluated for use as a reference standard. The ECR contains a small blackened

cavity which absorbs the radiative flux. This flux produces a measurable

increase of the cavity's temperature. A resistance heater wound into the

walls of the cavity and powered by a high precision power supply allows the

injection of a precise amount of energy into the cavity for calibration

purposes. The Radiometrics Physics Division of NIST has characterized the ECR

with respect to absolute accuracy, linearity, and blackness. Overall accuracy

was found to be within 2 percent up to 1 W/cm2

.

The calibration apparatus has been designed and is currently being fabricated.

It consists of a 6-inch diameter electric radiant heater capable of

establishing fluxes in the range 1 to 4 W/cm2 along its axis. Water-cooled

baffles maintained at ambient temperature insure that a heat flux sensor

positioned along the axis of and pointed at the heater "sees" only radiation

from the heater and from a well-defined ambient environment.

In addition to calibrating a sensor at various flux levels, the effect of the

spectral characteristics of the sensor's "black" surface will be assessed by

changing the temperature of the source and the source- to -sensor distance so as

to produce the same total incident radiative flux, but with different spectral

content

.

Publications

None

203
.

.

*

'

.
PART II. Timely Response to Current Fire Problems

(Projects Funded by Other Agencies and Private Sector

Organizations)

B. SMOKE " MOVEMENT AND CONTROL

CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

FIRE GROWTH/SUPPRESSION WITHIN AIRCRAFT

FundinE Agency : Federal Aviation Administration, DoT

Project Leader : King-mon Tu

Project Objective :

To evaluate and quantify the effects of changes in present aircraft

ventilation patterns on passenger cabin environment during in-flight fires.

Technical Accomplishments :

Conditions resulting from a steady state fire located in the interior of an

otherwise reasonably sealed, systematically ventilated enclosure were studied

regarding the effects of fire size, ventilation rate and location, and

ventilation direction: either having the inlet at the ceiling with the

exhaust at the floor or vice versa. Additionally, the effects on the fire

environment of having vents open to the ambient, located near the ceiling at

either end of the enclosure, were studied. For the situation w

T itn the inlet

at the ceiling and over the range of interest the rate of ventilation had

little effect on the gas, wall, and ceiling temperatures. These temperatures

varied directly with fire size (ranged from 6 to 60 kW) . Most of the energy

released by the fire was transferred to the ceiling above the fire. To first

order, the combustion product's chemical species concentrations increased

linearly with ventilation times and fire size. The introduction of small

vents had little effect on the thermal environment but a substantial effect on

chemical species concentration was noted. By reversing the flow direction,

that is, having the fresh air inlet at the floor and the exhaust at the

ceiling a substantial lowering of the environment temperature and species

concentration in the interior of the enclosure was observed.

Publications :

Fire Environment in Counterflow Ventilation (The In-Flight Aircraft Cabin Fire

Problem), B. McCaffrey and V. Rinkiner., National Bureau of Standards

Interagency Report, NBSIR 88-3086, June 1988.

Effect of Venting Through Small Hatches Near the Ceiling on CounterflowVentilated Enclosure Fires, K. Tu, W. Rinkiner., B. McCaffrey, National Bureau

of Standards Interagency Report, NBSIR 88-3834, July 1988.

Effect of Reversing Ventilation Direction on the Environment in ForcedVentilated Enclosure Fires, B. McCaffrey, K. Tu, W. Rinkiner., National Bureau

of Standards Letter Report, August 1988.

Reiated Grants :

"Fire Environment In Counterflow Ventilation," Bernard McCaffrey, University

of Maryland.

207
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY88

Institution : The University of Maryland Baltimore County

Grant No. : 70NANB8H0819

Grant Title : Fire Environment In Counterflow Ventilation

Principal Investigator : Prof. Bernard J. McCaffrey

Department of Mechanical Engineering

University of Maryland Baltimore County

Baltimore, MD 21228

Other Professional Personnel : Scot P. Deal, Graduate

Research Assistant

NBS Scientific Officer : Dr. King-Mon Tu

Technical Abstract :

Introduction - The work described herein involves the study of the effects

of forced ventilation on the fire environment in an enclosed volume. A unique

aspect concerns the direction of the ventilation flow which is opposed to the

buoyancy forces of the fire - generated hot gases, that is, fresh air is forced

into the enclosure at the ceiling and exhausted at the floor of the otherwise

sealed "box" . The study is primarily experimental although a future

analytical component is planned in an effort to generalize the experimental

results. The findings of a previous NBS study using the same facility, Ref.

rl, describe the complete thermal field in the enclosure as a function of fire

size and ventilation rate. The conclusions indicated that the ventilation

rate within ranges considered had little effect on the ability of the system

to promptly remove energy generated by the fire. The ventilation did little

to prevent the buoyancy forces from tending to keep the enclosure quite

stratified. Most of the heat released by the fire was absorbed by the ceiling

above the fire. In this work the chemical species concentrations in steady

state at various positions throughout the enclosure will be described for the

present ventilation configuration and range of ventilation flow rates. We

hope to gain some insight into the large scale eddy mixing associated with

this kind of strongly buoyant, weakly f orced-ventilated environment. Future

studies of changes in ventilation patterns, rates, etc. will be compared to

these baseline results. Additionally, a study aimed at elucidating the

near-wall or confinement phenomena associated with diffusion flames is taking

place concurrently.

Experimental - The enclosure is 4. 8x2. 4x1. 2 m high, made of galvanized

sheet and containing a ceiling and floor plenum constructed of calcium

silicate board (marinite) which allowed for two separate pairs of air inlet

configuration positions in the ceiling and a single pair for exhaust in the

floor. The inlet and outlet slits run the full length of the longer dimension

of the box. (See Fig. 1) For the experiments described here 32 simulated

208
seats of aluminum and marinite were symmetrically arranged in the box. The

fire, a constant feed of propane through a diffusive burner at the floor, was

located in the geometric center of the enclosure and exhibited heat release

rates between 10 and 60 kW. Ventilation flow rates varied between two and six

minutes for one enclosure volume exchange. Approximately 60 channels of data

were recorded in time during each test. Complete details of this facility are

contained in [rl]

.

Results - Fig. 2 shows a scatter plot of all the data for normalized C02 (+) and 02 ( Q ) gaseous concentration for five positions in the enclosure and

also for an additional 02 (a) sample in the exhaust gas. Positions near the

ceiling exhibit higher concentrations, data from lower points in the box are

similar to values in the exhaust. The abscissa is a non-dimensional

generation to ventilation rates ratio and the straight line shows a

calculation of what a well stirred reactor would exhibit. These are steady

state values and represent concentration averages of the data from 450s to

800s. A typical transient plot can be observed on Fig. 3.

Assuming complete combustion of propane, the reaction with excess dry air

is illustrated in the following:

C 3 H8 + 5(l+x) [02 +3.76N2 ]= 3C02 + 4H2 0 +5x02 + 5(l+x)3.76N2 The mole fraction of C02 in the exhaust is [C02 ]=3/(25 . 8+23 . 8x)

The mole fraction of 02 in the exhaust is [02 ] =5x/(25 . 8+23 . 8x)

Or if it is assumed that at the instant before introduction of C 3 Hg that the

mole fraction of 02 is 0.21 then,

0.21 - [0 2 ] = 5 . 42/(25 . 8+23 . 8x) and hence,

the Normalized Concentration is defined as:

[C02 ]/3 = (0 . 21- [02

] )/5 .42 = 1/(25. 8 + 23. 8x)

This is the method for plotting the data in Fig. 2 and provides a consistency

check since these are results from two independent instruments. Note the small

amount of CO and soot present in these experiments hardly affects the accuracy

of the equality at all. The extent of agreement can be observed in Fig. 2 by

comparing any pair of data sets. For clarity in subsequent plotting and

analysis we can observe the average of the two as representative of that

particular point.

Through a similar analysis the right hand side of the above can be

evaluated in terms of heat release rate of the fire (the generation of the

chemical species) and the ventilation rate (the dilution). In the absence of

sources and sinks, after the transient, the average for the box or the well

stirred reactor result is approximately equal to the volume flow rate of

chemical species to that of the ventilation flow

0/ H = Q(kW) / (46343*1 . 92 ) (kJ /m*m*m) = 4.7*E-5 Q(kw)*t (min)

V 14 . 5m*m*m / 60 / t(min)

where Q is the heat release rate of the fire and t is the time for one volume

exhaust. In Ref. r2 Pagni , et al . formalized and generalized the above

including the transient portions.

Figure 4 contains all the date seen in Fig. 2 showing the vertical

distribution in the box and plotted alongside a steady state temperature

profile for TC tree "C" . From the results of Fig. 2 we can factor out first

order effects of fire size and ventilation rate by dividing the Norm.

Concentration by the right hand side of the above equation. The scale then

209
varies about the value of 1, the well stirred result. The filled symbols are

results for the "wall" ventilation configuration (Fig. 1) and the others

correspond to the "central" configuration. In general the "wall" yields

higher concentrations for the centerline positions shown in the figure.

Whether it is due to a simple local increase in dilution since the source of

the fresh air is closer to the sampling position (the cold air in the wall

case could travel down adjacent to the wall and exit at the floor) or to a

more complex flow pattern is not clear from Fig. 4. The data symbols

represent averages of the data at the particular position; the bars represent

high and low values and the numbers below the symbols is the number of data

sets. In general the lower end of the bar corresponds to longer ventilation

times and the upper end of the range corresponds to higher heat release

experiments. These second order effects then would dictate steady state

concentrations varying with Q to somewhat greater than linear and the

variation with ventilation time to a somewhat less than a linear relation.

Again one might speculate that with lower flow velocities in the longer time

cases there is less penetration through the hot upper layers yielding more

dilution

Preliminary results indicate that for 7.5X15 cm holes placed at the top

center of the two end walls a 7% reduction at the top position and a 16%

reduction in exhaust concentration could be attained. For 15X15 cm holes the

reductions increase to 16% at the top and 24% in the exhaust. For hole size

double again reductions increase to 22% and 40% respectively.

References - rl . McCaffrey, B. and Rinkinen, W. , Fire Environment In Counterflow

Ventilation (The In-Flight Aircraft Cabin Fire Problem) NBSIR 88- (in

preparation)

r2 . Pagni , P. , Alvares , N., and Foote, K. , Defining Characteristic Times in

Forced Ventilation Enclosure Fires, American Society for Testing and

Materials, STP 983 (1988).

'Central' _ Wall'

Fig. 1: INTERIOR VIEW OF ONE-HALF OF SYMMETRIC ENCLOSURE (SEATS NOT SHOWN)

210
nxi.' l>G">MOCJ

N

o

o 05 co ^ 6 d

r-o

cd uq

d d

H/z o

t —

r

cq

o

cvo

4- »—i O

o d

211

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

Temp.

(C*.0l)

Norm.

Conc./rGen/Venl

Fig.

4:

VERTICAL

VARIATION

OF

TEMPERATURE

AND

NORM.

CONCENTRATION
'

-

.

.
PART II. Timely Response to Current Fire Problems

(Projects Funded by Other Agencies and Private Sector

Organizations)

C. FIRE PROTECTION TECHNOLOGY

CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

FIRE AND THERMAL CHARACTERISTICS OF NAVY FIRE FIGHTING TRAINERS

Funding Agency : Navy Training Systems Center, Orlando, Florida

Project leader : R. S. Levine

Project Objective :

Support the development and implementation of prototype fire fighter

trainers at Mayport Naval Station, Jacksonville, Florida.

Technical Accomplishments :

Using fire compartment models, wall and gas temperatures, radiant fluxes,

oxygen concentrations, and ceiling layer heights were predicted for the trainer

compartments with large fires in them. Measurements will be made during Navy

acceptance tests of these trainers, and the results used to validate or improve

the models as design tools for the sponsor and for related CFR use.

In addition, the project leader has acted as a consultant on safety and

other concerns on the pre -prototype trainer at the Norfolk, Virginia Navy Fire

Training School

.

Reports and Publications :

Most results to date are incorporated in project letters to the Naval

Training Systems Center.

NBSIR 88- 3755, Stroup, D.V. , Naval Fire Fighting Trainers -Thermal Radiation

Effects Associated with the 19F4 FFT

.

215
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

FALSE ALARMS FROM SMOKE DETECTORS

Funding Agency Veterans Administration and U.S. Air Force

Project Leader Richard W. Bukowski

Project Objective

To conduct a field study of false alarms produced by smoke detectors installed

within VA Medical Centers to identify causes and mitigation strategies.

Technical Accomplishments

In 1987, a survey of 133 VA Medical Centers (VAMC) , out of a total of 172

throughout the U.S., coupled with visits to 20 facilities, was conducted to

gather data on false alarms of smoke detectors.

Information requested for the study included name of the detector manufacturer

and model number, control unit manufacturer and model number, number and type

of detectors installed, where installed, number of false and real alarms for

preceding year, date of installation, and policies on smoking, testing,

cleaning, and maintenance. VAMC personnel involved with the installations

were requested to indicate the maximum level of false alarms that could be

tolerated and to provide any recommendations to reduce their occurrence.

The study included a total of approximately 37,000 system type smoke detectors

of which 69 percent were of ionization (ion) type and 31 percent photoelectric, 3000 duct detectors (90 percent ion and 10 percent photo), and 1100 smoke

detector modules (80 percent ion and 20 percent photo) integral with door

holder closers (DHC) . Also, included are approximately 100 single station

smoke alarms

In 1988, a (~250 page) report of the study was produced, encompassing the

following subject areas:

1. Background information which includes a history of smoke detectors from

prior to World War II up to the present as well as the roles played by

evaluation and installation standards.

2. Technical background information describing: (a) principle of operation

and susceptibility to false alarms resulting from their use, (b) method

of measurement of the detector sensitivity (threshold response) , and (c)

production window.

3. Review of previously-conducted false alarm studies.

4. Analysis of the various causes of false alarms.

5. Effect of sensitivity, environmental factors, misapplication, smoking,

lack of testing and cleaning, and other miscellaneous VAMC operational

procedures on false alarm rates.

216
6. Discussion of the various testing procedures employed at the VAMCS

.

7. Suggested short-term remedies for presently installed detectors including use of alarm verification, presignal operation, detector replacement, cross zoning, and the like. Long term remedies are also included

through changes in product performance and installation standards.

8. Recommendations for reducing false alarms are included for: the VAMCS,

VA Central Office, testing agencies, NFPA 72E committee, detector

manufacturers, system designers, and industry associations. A number of

these recommendations have been presented to the appropriate

organizations, and are being adopted.

9. Evaluation of sensitivity tests conducted on detector samples removed

from VAMC installations that were visited.

10. Discussion of the shared responsibility of the various parties involved

with smoke detectors including the design, manufacture, evaluation,

installation, and inspection by the local authority having jurisdiction.

11. Numerous tables are included documenting false alarm prevalence by;

VAMC, detector manufacturer, detector model, type of detector, principle

of operation, frequency of cleaning and testing, location, sensitivity,

and the like.

12. Attachment of a practical false alarm goal, design of future detectors,

and remaining activities

.

The report is written as a reference document for the VAMC staff involved with

the fire alarm system on a daily basis. It will hopefully provide them with

the information necessary to minimize false alarms from their systems while

not sacrificing system performance. The draft document has been reviewed by

VA Headquarters staff, and praised for its comprehensive treatment of the

subj ect

.

217
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

SAFETY IN OFFSHORE DRILLING

Funding Agency : Minerals Management Service, Dol

Project Leader : David Evans

Project Objective :

Examine technologies that can mitigate the effects of fire and oil spills from

offshore platform accidents.

Technical Accomplishments :

Measurements of the effects of water spray on methane jet flames that simulate

gas -well blowout fires were continued and expanded to include mixed methane - heptane flames. Through a grant to Professor Gore at the University of

Maryland, the laminar flamelet concept for analysis of turbulent flames

developed by Professor Faeth with CFR Grants Program support, is being used by

Professor Gore to predict jet-flame structure and emitted radiation. Previous

analysis of methane flames has been extended to methane -water flows and

investigations of flame extinction.

Experiments completed two years ago by Professor Bourgoyne at Louisiana State

University were reported. This report documents extension of natural gas jetflame water spray extinction conditions, previously measured by CFR, to energy

release rates of 400 MW. For these large flames the water to natural gas mass

flow rate ratio of 2.0 produces flame extinction when the water is sprayed

along the edge of the vertical flame envelope. Measurements on obstructed

flames showed that the ratio for extinction is 15.0 or greater.

Measurements of crude oil spill pool fire combustion energy release rates and

smoke production were completed. Polycyclic Aromatic Hydrocarbon content of

the smoke was found to be equal or less than that in the original oil.

Publications :

An experimental study of suppression of obstructed gas well blowout fires

using water sprays, M. Chauvin and A. Bourgoyne, National Bureau of Standards

Government Contract Report, NBS -GCR- 88 - 547 , June, 1988.

Environment Effects of Oil Spill Combustion, D. Evans, G. Mulholland, D.

Gross, H. Baum and K. Saito, National Institute of Standards and Technology

Interagency Report, NISTIR 88-3822, September 1988.

Related Grants :

"An Investigation of Simulated Oil Well Blowout Fires," Jayavant P. Gore,

University of Maryland.

"A Study of Oil-Slick Combustion," Koso Saito and Robert A. Altenkirch,

University of Kentucky.

218
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution: The University of Kentucky

Grant No.

:

60NANB7D0739

Grant Title: A Study of Oil-Slick Combustion

Principal Investigator: Prof. Kozo Saito

Department of Mechanical Engineering

University of Kentucky

' Lexington, KY 40506-0046

Other Professional Personnel: Prof. Robert A. Altenkirch

Dr . Masataka Arai

Visiting Scientist

Sandra K. Elam

Graduate Research Assistant

NBS Scientific Officer: Dr. David D. Evans

Technical Abstract:

Introduction Crude oil is produced in many places in the world, and

accidental spills in oceans often cause environmental problems. Combustion is

a possible useful method of removing a crude-oil slick from an ocean surface.

To develop an understanding of the fundamental combustion behavior of crude

oil, scale model tests and numerical model calculations have been carried out

by several investigators. From the results of these studies, the combustion

rate of crude oil can be estimated, but they do not allow the combustion

behavior of a crude-oil slick on water to be described accurately. For

example, under certain circumstances, the water on which a burning pool of

crude oil is supported may begin to boil. However, no model calculations that

include the boiling phenomenon of the water exist. Here, we present a method

for predicting the thermal conductivity of crude oil and experimental results

that describe the boiling phenomenon of the water sublayer. These results can

be used to guide the development of calculational models for oil-slick

combustion.

Prediction of Thermal Conductivity The thermal conductivity of Alberta

Sweet, La Rosa, and Murban crude oils was measured using the transient hot-wire

method. In this method, the thermal conductivity of the liquid is determined

by comparing the measured time dependent temperature change of a wire through

which a current is passed that is submerged in a reservoir of the liquid at

known initial temperature with the known analytical solution to the transient

conduction problem. The measured thermal conductivity, A , for the three crude

m

oils over the temperature range 0 to about 50 °C is shown in Fig. 1. By

considering the oils to consist of a mixture of aromatic and paraffinic

fractions, the A were to fit to the equation

m

219
(

1

)

(J (0 x = x ®x p

m a p

in order to determine X and X . In Eqn. (1), subscripts a and p imply the

a p

aromatic and paraffinic fraction, respectively, and w is the mass fraction of

the indicated functional group normalized such that (cj v + v ) = 1.0. The

a p

y values of X and X determined experimentally then can be used to estimate X

a p m

values for a crude oil if the composition of the oil is known. X and X do

a p

not vary much over the temperature range of the measurement, their average

values being 215 and 108 mW/m»K, respectively.

Combustion Behavior of Oil Floating on Water: A schematic of the typical

sequence of events of the combustion phenomenon is shown in Figs. 2 (a) through

(e). Boi lover of the water sublayer, step (c), occurs for fuels whose boiling

point temperature is higher than that of water regardless of whether the fuel

is pure or is a multicomponent fuel. The intensity of the boi lover depends on

the boiling point temperature of the fuel; the higher the boiling temperature

of the fuel, the more intense is the boilover. Multicomponent fuels of course

do not have a unique boiling point temperature, so we expect the intensity of

the boilover to depend on the molecular weight or density of the fuel. The

heavier the fuel, the higher the boiling point range and the more intense the

boilover will be.

For pure fuels, the sequence of events depicted in (a): the onset of

boiling, (b) : normal boiling, (d): the end of boiling, and (e): extinction is

common, except for the fact that high boiling point fuels, e.g. , n-decane,

occasionally behave as shown in step (c): appearance of a fireball-like flame.

For multicomponent fuels and crude oils, the entire sequence of events (a)

through (e) is common. When step (c) occurs, the fireball-like flame emits

intense radiation to the surroundings. The size of the fireball-like flame

depends on the intensity of the boilover and the fuel type. In an extreme

case, its size is several times larger than the diameter of the pan.

Onset of Water Boiling In Fig. 3, a peak temperature in a burning fuel

layer, T , is plotted against the time, t , required to reach T . For fuels

with a boiling point temperature, T^ less than that of water, T^ T^ is

the maximum temperature of the thermocouple near the fuel-water interface. If

boilover occurs, which happens when T, r >T, , then T is the temperature

bp , i ~ bp , w p

indicated by the thermocouple just prior to when boilover begins. Numbers

written next to the data points in Fig. 3 indicate T

bp.f'

For paraffins, T and t increase with increasing T, P , and T is nearly

P P bp.f p

T, P until T, P is approximately equal to T, . Once T, ->T, , T is not

bp.f bp.f J M bp , w bp , f bp , w p

much greater & than T, , and t decreases with increasing T, P bp.w p bp.f

situation arises because when T, r <T, bp.f bp.w

When T, P >T, bp.f bp.w

process. Just after ignition, the fuel surface temperature rapidly approaches

combustion process

This

the water has little influence on the

the water affects the combustion

220
T, resulting in in-depth heating of the fuel. But the temperature of the

bp, f

fuel near the fuel-water interface cannot substantially exceed T, because

bp, w

boiling of the water ensues. The amount of time that it takes the fuel near

the fuel-water interface to reach approximately T, decreases with increasing

bp , w

T, - because the temperature gradient and heat transfer rate into the fuel

bp, f

layer increases as the surface temperature increases. Multicomponent fuels

behave somewhat differently than either paraffins or aromatics, and this is due

to the fact that the properties of the fuel change during the progress of

combustion as the lighter fractions boil off, and the heavier fractions remain.

Temperature measurements at the onset of boiling for multicomponent fuels

are shown in Fi;g. 4. A fixed amount of superheat, 10 K, for the liquid water

is obtained, and T for these fuels seems to correlate with the fuel density as

P

we anticipated. The level that T can reach is limited by the occurrence of

boilover as discussed for pure fuels in conjunction with Fig. 3. Although a

unique boiling point for multicomponent fuels cannot be specified, the

temperature range over which boiling occurs is higher than the boiling point

for water, and so we obtain the behavior shown in Fig. 4.

Summary An experimental investigation of the boilover phenomenon for

liquid fuel burning above a water sublayer indicates that boilover occurs when

the boiling point temperature of a pure fuel is more than that of the water.

In this situation, the fuel temperature near the fuel-water interface is

somewhat limited by the presence of the boiling water and cannot reach the fuel

boiling point. The boilover behavior of multicomponent fuels is similar to

that of pure fuels except that for multicomponent fuels, after the onset of

boilover, a large, f i reball- like flame frequently appears. A thermal

conductivity prediction method for crude oil was also developed by considering

the oil to be composed of an aromatic and a paraffinic fraction and fitting

measurements to determine the thermal conductivities of these fractions.

Reports and Papers:

1. S.K. Elam, I. Tokura, K. Saito, R.A. Altenkirch, "Thermal Conductivity of

Crude Oils," submitted to Experimental Thermal and Fluid Science .

2. I. Tokura, K. Saito, R.A. Altenkirch, D.D. Evans, "A Study of Crude Oil

Combustion: Thermal Conductivity of the Condensed Phase," presented at the

Central States Section of the Combustion Institute meeting, 1987.

3. S.K. Elam, I. Tokura, K. Saito, R.A. Altenkirch, "Prediction of Thermal

Conductivity of Crude Oil for use in Oil-Slick Combustion Modelling,"

presented at the Central States Section of the Combustion Institute

meeting, 1988.

4. M. Arai , K. Saito, R.A. Altenkirch, D.D. Evans, "A Study of the Boilover

Phenomenon for Liquid Fuel Supported on Water," presented at the Central

States Section of the Combustion Institute meeting, 1988.

5. M. Arai, K. Saito, R.A. Altenkirch, "Experimental Study of Burning Liquid

Fuels on a Water Sublayer," submitted for presentation in a poster session

at the Twenty-Second International Symposium on Combustion , 1988.

221
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CENTER FOR FIRE RESEARCH

NATIONAL INSTITUTE OF SCIENCE AND TECHNOLOGY

FY 88

Institution: The University of Maryland at College Park

Grant No .

:

60NANB8D0834

Grant Title: An Investigation of Simulated Oil Well Blowout Fires

Principal Investigator: Dr. J. P. Gore

Mechanical Engineering Department

, University of Maryland

College Park, MD 20742

Other Professional Personnel: Steve Skinner, Undergraduate Assistant

NIST Scientific Officer: Dr. David D. Evans

Technical Abstract:

Introduction Radiation and extinction of large turbulent jet flames is of

interest in the evaluation of hazard to personnel resulting from oil and gas

well blowouts. Motivated by this problem, experiments concerning the

feasibility of extinguishment of large (100-200 MW) and medium (1-10 MW) scale

methane/air flames using water-sprays have been conducted in the past [rl,r2].

The objectives of the study reported here are: (1) to utilize data from

reference [r2] for medium (1-10 MW) scale flames to evaluate the effectiveness

existing analysis [r3-r5] , and (2) to extend the analysis to treat two phase

flow effects resulting from combined burning of heptane (to simulate oil) and

methane (to simulate natural gas) and also liquid water suppressant. Effects of

liquid water suppressant were considered during the first phase.

Experimental Data Existing experimental data[r2] were utilized during the

initial phase of the project. Vertical jet flames burning methane at heat

release rates between 1-8 MW were considered in reference [r2]. Six chromelalumel thermocouple junctions formed from 0.5 mm wires were used to measure

temperatures along the flame axis. Radiative heat fluxes to two representative

locations around the flames (see inset of Fig. 2) were monitored using wide

angle radiometers. All the flames considered were turbulent (Re - 30,000 to

500,000) and had some effects of buoyancy(Ri - 0.000014 to 0.00012) as per the

criterion of reference [ r 6 ]

.

Many of the flames were lifted from the burner

exit

.

Theoretical Methods Theoretical methods for flames without the addition of

water were identical to those of Jeng et al. [r3]. For flames with water

added to the fuel stream, the locally homogeneous flow (LHF) approximation

described in ref. [r7] was used. Within this approximation, it was assumed

that the transport of mass, momentum, and energy between the liquid water and

the surrounding gases is much faster than the mixing between the jet and the

ambient fluids. Based on past experimental findings [r8], it was assumed

that the addition of liquid water produced only thermal effects. These were

treated by modifying the state relationships for all scalar properties as a function of mixture fraction. The structure calculations were completed using

223
a Favre- averaged K-e-g model similar to past practice using the GENMIX

algorithm [r9]. Although, many of the flames were lifted from the burner, the

effects of liftoff were neglected due to considerable uncertainties in the

current understanding [rlO] . The radiation calculations were performed using

the RADCAL algorithm [rll] and the discrete transfer method [rl2].

Results and Discussion Measurements (represented by symbols showing the

best fit to the data from ref. [r2] and not actual data points) and predictions

of temperature along the axis of a 4.6 MW flame without water addition are

shown in Figure 1. The measurements have not been corrected for the effects of

radiation (expected to be ca. 200 K in the hottest portions). In regions near

the burner exit the predictions mimic the data. This may be fortuitous in view

of the lack of radiation corrections. In regions away from the burner, the

measurements are ca. 400 K lower than the prediction. This is probably because

of the uncertainities of the analysis concerning initial conditions and flame

liftoff

Figure 2 shows measurements and predictions of total heat fluxes

incident upon two detectors (for positions indicated in the inset) as a function of heat release rate. The shape, size, and position of the flame

relative to the detectors change due to the effects of buoyancy [r6]. The

data show that the heat flux to both detectors increases rapidly with heat

release rate in the 0.5 to 2.5 MW range, and then, due to the changing shape

and size of the flame relative to the detector positions, the rate of

increase is reduced considerably before increasing again at ca. 4.5 MW. It is

encouraging to note that the analysis mimics this behavior. Based on the small

differences in the predictions (which completely neglect radiation from soot)

and measurements, it can be concluded that soot-radiation is a minor fraction

of the total radiation for methane/air flames. The agreement between

measurements and predictions of radiative heat fluxes is much better than

those of temperatures. Part of this is due to the integral nature of radiative

heat flux, resulting in cancellation of errors in the detailed scalar

distributions. Based on the encouraging predictions for flames without wateraddition, the analysis was extended to treat the effects of water added to the

fuel

Figure 3 shows the state relationships for flames with water added to

the fuel stream. Temperature, mole fraction of liquid water, mole fraction of

water vapor, and mole fraction of carbon dioxide are plotted as a function of

fuel equivalence ratio. Liquid water is present on the fuel-rich side of all

the flames with water addition and holds the temperature at the equilibrium

value corresponding to the partial pressure of water vapor. Once all the

water is evaporated, the temperature rises rapidly, but its peak is lower due

to the heat of vaporization and sensible heating of the water. Mole fractions

of gases like carbon dioxide are reduced as shown in Figure 3 while mole

fractions of water vapor are increased, resulting in non-trivial effects on

absorption coefficients. As seen from the state relationships in Figure 3,

the present analysis implies that all the liquid water is evaporated within

the flame. In practice, due to poor atomization particularly at large waterloadings, water penetrates into the fuel- lean regions and also gets ejected

from the flame. This is expected to affect the temperature and radiation

predictions for flames with water.

Measurements and prediction of peak temperatures along the axis of

4.6 MW flames as a function of nondimensional water mass flow rate are plotted

224
in Figure 4. For a fixed methane flow (fixed heat-release rate), the location

of the peak temperature (both measured and predicted) remains almost

independent of the water flow rate due to the effects of increased momentum of

the jet. As expected both data and predictions show a reduction in the peak

temperature with increasing water-addition. Discrepancies between data and

predictions for zero water- loading have been discussed above. As waterloading is increased, the differences between data and predictions are seen to

decrease. This is not only because of the reductions in radiation corrections

but also because of the assumption of complete water- evaporation . It is

therefore expected that the radiative heat fluxes for flames with large

quantities of water will be under-predicted by the analysis. Figure 5 shows

measurements and predictions of radiative heat flux to a representative

detector (normalized by the flux with zero water- loading) as a function of

non-dimensional water flow-rate. As expected, the predictions under- estimate

the heat flux for high water- loadings . Consideration of finite evaporation

rates will be necessary for treating flames with the high water-loadings which

are required for extinction.

Acknowledgement Part of this work is supported by the Mineral Management

Service, Department of the Interior.

References

[rl] Evans, D. and Pfenning, D., Oil and Gas J .

.

83 (17), 80, 1985.

[r2] McCaffrey, B. J., "Momentum Diffusion Flame Characteristics and the

Effects of Water Spray," NBSIR 86 - 3442

.

. NIST, Gaithersburg, MD , 20899,

1986.

[r3] Jeng, S. M. , Lai, M. C., and Faeth, G. M. , Combust. Sci. and Tech, . 40,

41. 1984.

[r4] Jeng, S. M. and Faeth, G. M. , J , Heat Trans

,

106, 891, 1984.

[r5] Gore, J. P., Faeth, G. M. , Evans, D. and Pfenning, D., Fire and

Materials 10 , 161, 1986.

[r6] Becker, H. and Liang D., Comb. Flame . 32, 115, 1978.

[ r 7 ] Faeth, G. M. , Prog. Energy Combust. Sci. . 9 , 1, 1983.

[r8] Seshadri, K, Comb . Flame . 33, 197, 1978.

[r9] Spalding, D. B., GENMIX: A General Computer Program for TwoDimensional Parabolic Phenomena . Pergamon, Oxford, 1977.

[rlO] Pitts, W. , 1988, "Assesment of Theories for the Behavior and Blowout of

Lifted Turbulent Jet Diffusion Flames," Twenty- Second Symposium

(International) on Combustion . The Combustion Institute, Pittsburgh, in

press, 1988.

[ r 11 ] Grosshandler , W. , Int . J. Heat Mass Transfer 23, 1447, 1980.

[ r 12 ] Lockwood, F. C. and Shah, N. B., Eighteenth Symposium

(International) on Combustion . The Combustion Institute, Pittsburgh, Pa,

1405, 1981.

Reports and Papers

1. J. P. Gore, D. D. Evans and B. J. Mccaffrey, "Temperature and Radiation of

Large Methane/Air Jet Flames with Water Supression, " Fall Technical Meeting of

the Eastern Section of the Combustion Meeting, Stillwater, FL, submitted.

2. J. P. Gore and D. D. Evans, "Radiation from Two Phase Fires burning Heptane

and Methane," ASME National Heat Transfer Conference 1989, Philadelphia, PA,

submitted.

225
Z (in)

TM h ; o/'nCH,

Fig. 5 Radiative Heat Fluxes vith HjO

o.i j.o -lo.o

EQUIVALENCE ratio

Fig . 3 State Relationships vith HjO

226
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

QUICK RESPONSE SPRINKLERS IN OFFICE OCCUPANCIES

Funding Agency: U.S. Government Services Administration

Project Leader: William D. Walton

Project Objective

To develop a basis for a design criteria for the use of quick response

sprinklers in office occupancies.

Technical Accomplishments

The Center for Fire Research has completed the first three phases of a multiphase reserch project addressing the use of quick response sprinkler

technology in office occupancies. The major areas of the first three phases

of this project were to: (1) examine the potential applicability of quick

response technology to office occupancies; (2) characterize office fuel

packages; and (3) measure the effect of sprinkler spray density on

suppression. The work to date has demonstrated some of the potential benefits

of using quick response technology and provided part of the basis for

developing a design standard focusing on the fuel packages and the amount of

water required to extinguish these packages. The current phase of the project

focuses on the determination of the time of sprinkler actuation under

conditions found in office occupancies.

Publications

Walton, w.d., and Budnick, E.K., Quick Response Sprinklers in Office

Configuration: Fire Test Results, Nat. Bur. Stand. (U.S.), NBSIR 88-3695,

1988, January.

Walton, W.D., Suppression of Wood Crib Fires with Sprinkler Sprays: Test

Results, Nat. Bur. Stand. (U.S.), NBSIR 88-3696, 1988, January.

227
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

FOAM FIRE SUPPRESSION

Funding Agency : U.S. Fire Administration

Project Leader : Daniel Madrzykowski

Project Objective :

Examine the fire suppression effectiveness of water-based compressed air foam

relative to plain water.

Technical Accomplishments :

Ignition inhibiting and mass retention measurements were completed in which

the effectiveness of synthetic hydrocarbon surfactant foam generated with

compressed air was compared to plain water spray. Foam provided twice the

increase in ignition delay compared to plain water for Tl-11 plywood exposed

to a radiative heat flux in the range of 15 kW/m2 to 60 kW/m2 for an equal

amount of moisture per unit surface area. Measurements also showed that

moisture in the form of foam accumulated 20 times faster on vertical surfaces

than water sprayed onto the surface. Measurements of fire extinguishing

capabilities of foam relative to plain water will be performed next. Waterbased compressed air foam generated with addition of a commercial synthetic

hydrocarbon surfactant at low concentrations, typically 0.3 percent by volume,

may enhance the performance of limited water supply residential sprinkler

systems

Publications :

Study of the Ignition Inhibiting Properties of Compressed Air Foam, Daniel

Madrzykowski, National Institute of Standards and Technology Interagency

Report, NISTIR 88-3880, October 1988.

228
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

COMPARTMENT FIRE MODEL TO SIMULATE THE EFFECTS OF

ROOF VENTS, SPRINKLERS, AND THEIR INTERACTIONS

Funding Agency: AAMA Research Foundation

Project Leader: Xeonard Y. Cooper

Douglas Walton, Fire Prevention Engineer

William Davis, Physicist

Project Objective

Develop a computer code model for engineering analysis of roof vents,

sprinklers, and their interactions during fire-generated environments.

Technical Accomplishments

A complete theory for the model was developed. Coding of the equations has

been initiated, and a preliminary working computer program which illustrates

some of the features of the expected final product was prepared and

demonstrated. Submodel algor ithms /sub routines prepared for and tested in this

model will be used to enhance future CCFM/RFM products.

Reports and Publications

"Estimating the Environment and the Response of Sprinkler Links in Compartment

Fires with Draft Curtains and Fusible Link-Actuated Ceiling Vents - Part I:

Theory," Cooper, L.Y.

,

NBSIR 88-3743, April 1988.

"Estimating the Environment and the Response of Sprinkler Links in Compartment

Fires with Draft Curtains and Fusible Link-Actuated Ceiling Vents - An

Overview," Cooper, L.Y.

,

presented at the 10th Joint Meeting of the UJNR, and

to appear in the Proceedings, Tokyo, June 1988; to be presented at the 1988

Technical Meeting of the Eastern Section of the Combustion Institute, Dec. 5-

7, 1988, and published in Proceedings.

229
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

EXPERT SYSTEM

Funding Agency: Air Force

Project Leaders: Richard L. Smith, Project Leader

Harold E. Nelson, Leader, Fire Safety Engineering Team

Project Objective

To develop a computer program which will make an expert estimate of the fire

safety of a general purpose warehouse based on CFR's deterministic physical

models, technical data, and expert judgment.

Technical Accomplishments

The first phase of the project, now completed, focused on the selection of a

general purpose warehouse as the first type of building for the expert system

to analyze. This was accomplished after an initial study determined that, in

general, the knowledge base for an expert system consists of public and

private knowledge -- the public knowledge for this system being reasonably large

and its sources numerous. Therefore, it was determined that the system's

knowledge base would be constructed by first including the general public

knowledge, followed by the CFR's public knowledge, and finally the private

knowledge of our human expert, H. Nelson. (The program will be written on a

Symbolics computer (a LISP machine) using state-of-the-art expert system

development software tools.)

The second phase, which focusses on the writing of the program, is underway

and has resulted in: (1) the completion of an algorithm for protecting a building from external fire exposure; (2) the development of a computer

programming procedure using oriented programming techniques to save the state

of the reasoning process of the expert system under development; and (3) the

development of a capability to draw floor plans (exterior walls, Interior

walls, doorways, doors, and windows) with understanding.

Reports and Publications

"ASKBUDJr: A Precursor of an Expert System for the Evaluation of Fire Hazard"

by Richard L. Smith, Fire Technology 2_3, pp . 5-18, February 1987.

230
CENTER FOR FIRE RESEARCH

OTHER AGENCY PROJECT - 1988

FIRE RISK ASSESSMENT

Funding Agency National Fire Protection Research Foundation (NFPRF)

Project Leader S. Wayne Stiefel

Project Objective *-

To develop a generally applicable methodology for the proper evaluation of the

expected life-safety risk associated with the fire performance of new and

existing products.

Technical Accomplishments

The first phase of the project (now completed) focused on the development of

the general methodology and its application to a diverse set of three example

cases (upholstered furniture in residences, carpet in offices, and concealed

combustibles in hotels) . The experience gained through the case studies was

used to refine the methodology and begin to evaluate its overall validity.

Critical assumptions were also tested through sensitivity analyses.

The second phase of the work is now underway. Here we will continue the

evaluation and refinement of the methodology through further sensitivity

analyses and the conduct of a fourth case study - interior finish in

restaurants. A portion of the work in phase 2 will involve an attempt to

reduce the computational burden of the method by the substitution of

procedures which eliminate unwarranted complexities in specific situations

(e.g., limiting the use of behavioral models to certain occupancies where

occupant interactions are known to be important to the eventual outcome)

.

Another crucial activity of phase 2 is the public documentation of the work

completed in phase 1. This will consist of a detailed report on the

methodology, and the documentation of the three case studies.

The final phase of the program will produce the user documentation necessary

to transfer the method and the computer software which implements it to the

international fire protection community. From preliminary indications, it is

expected that its application to real world problems will be immediate.

Publications

Bukowski , R. W. and Stiefel, S. W. , An Overview of a Method for

Predicting Fire Risk, NISTIR, in press.

Related Grant

University of Calif. (LA), G. Apostolakis, Fire Risk Analysis.

231
CENTER FOR FIRE RESEARCH

NATIONAL BUREAU OF STANDARDS

FY 88

Institution : University of California at Los Angeles

Grant No.: 60NANB6D0649

Title : Fire Risk Analysis Methodology

Principal Investigator : Professor George Apostolakis

Department of Mechanical, Aerospace

and Nuclear Engineering

University of California

5532 Boelter Hall

Los Angeles, CA 90024-1597

Other Professional Personnel :

NBS Scientific Officer:

M.D. Brandyberry, Ph.D. student

Mr. Wayne Stiefel

Technical Abstract:

Introduction To analyze a building fire scenario from initial ignition to its

consequences, e.g., dollar losses, injuries, deaths, a necessary input is the frequency of

the initiating event (IE). For many materials, objects, building types, etc., this frequency

of ignition may be obtained from data on fires which have occurred. ; A problem of

interest, however, is what happens to this frequency of ignition if the product is changed

in some way (furniture covered in a new fabric, plastic composition changed, etc.).

Changes in a product may also affect other portions of a fire scenario such as secondary

ignitions or effects from changed products of combustion. The objective of this project

is to develop a methodology for evaluating the changes in initiating event characteristics

which may be expected due to changes in a product under analysis.

Probabilistic Interpretation of Ignition The frequency of ignition of an item in a compartment in a building is composed of two basic elements:

• The frequency with which an item is exposed to an ignition source (fr(exposure)).

• The fraction of times that the item is ignited given exposure to the ignition source

(fr(ignition | exposure)). This factor depends on

1. The physical characteristics of the item (heat transfer properties, ignition

properties).

2. The intensity and duration of the ignition source. (Is the source removed or

docs it self extinguish before ignition? Is the heat flux at the target adequate

to ignite it within the exposure duration?).

The simple equation combining these is:

232
fr(ignition) = fr(exposure) x fr(ignition | exposure)

To predict the frequency of ignition of a new product, both of the factors on the right

must be known. There are, however, no direct statistics on the frequency of exposure

of any product to an ignition source (this factor includes both exposures which have

caused fires and those which have not.) Also for a brand new product, there will be no

directly applicable evidence for the ignition of an item given exposure to an ignition

source, but evidence frQm similar products and from mathematical modeling and

experimental testing may be used.

Radiant Ignition of Products by Heating Appliances To put the problem into

perspective, we have chosen the class of ignition sources "heating appliances" as an

example to illustrate the problems involved. This class of ignition sources can ignite

materials by a number of different methods. Heat conduction by contact with the

appliance, radiation transfer by the target being too close to the target, and other

problems such as spilled kerosene from a portable liquid fueled heater igniting are all

methods by which a heating appliance may ignite a material.

We may limit our attention, however, to those ignition scenarios in which the

frequency of ignition may change due to the effects of a new material. This means that

such scenarios as those involving spilled kerosene are not of interest to us since many (if

not most) combustible materials will ignite if doused with kerosene and ignited and

changing the materials properties will have little effect on the ignition frequency of the

material due to this scenario. (Other analyses, such as analyzing the effects of changes

in human behavior when filling the heater or a new heater fuel tank design may change

the frequency, but we are not considering these here.) After studying the heater fire

problem and limiting ourselves to consumer products (as opposed to structural

materials), we have concluded that the major mode of change in the frequency of

product ignition due to heating appliances will be through changes in resistance to

radiant ignition of the target product. This is the type of scenario that we analyze.

Radiant ignition of a material by a heating appliance occurs when the material is

placed too close to that appliance or vice versa (if the appliance is portable). To assess

the frequency of exposure of the material to radiant heat flux from a heater, we must

assess how often the material will come into proximity to a heater by whatever means.

There are, as noted before, no direct statistics on this type of frequency, and thus we

must infer the value from available evidence. The result will not be a single value, but

will necessarily be a probability distribution.

Three sources of information have been identified as pertinent to the problem:

1. Reported fires caused by heating appliances [1].

2. Estimates of unreported fires caused by heating appliances [2].

3. Estimates of accidents involving consumer products [3,4].

The number of reported fires can be interpreted to be a lower bound on the frequency

of exposure of a heating appliance to a combustible (by considering a suitable portion

of the total number of heater fires; e.g., those caused by being "too close" to the heater).

We may utilize an estimate of the number of unreported heater fires caused by "human

233
carelessness" as a better estimate of the number of fires actually caused by being "too

close" to the heater (this number probably also contains kerosene spills and other such

accidents). The third value we have considered is the number of accidents involving

consumer products, restricted to those accidents in which the product did not directly

cause the accident (c.g., accidents involving chain saws were not included). This value

may be considered to be the frequency with which people do "incorrect things" with

consumer products and thus may be considered to be applicable to the act of a person

"putting a combustible too close to a heater" or visa versa. The above considerations

lead us to a lognormal distribution for the exposure frequency as shown in Figure 1.

(events per year per household)

Ignition factor The second factor, fr(ignition | exposure), is scenario and product

dependant. For a specified product under analysis, there will be certain characteristic

thermophysical properties of the material which will control heat transfer within the

solid (density, thermal conductivity, surface emissivity). The solid will also have some

specific conditions under which it will ignite, e.g., critical surface temperature, critical

heat flux, etc. [5]. Additionally, there will be a set of environmental conditions which

will affect heat transfer to and from the target solid (c.g., environment temperature,

radiant heat flux to the target from external sources, etc.) For the heater fire problem,

several numerical tools arc under development with which it will be possible to estimate

the geometrical conditions under which a solid exposed to radiant flux from a heater

may ignite. As these tools will be deterministic in nature (computer models), they will

be subject to uncertainties in both the parameter inputs and in the models themselves.

This will lead to distributions of the distance of the target from the source under which

ignition is possible. Distributions of the spatial heat flux in front of a flat-plate radiator

arc currently under study (sec Figure 2., a preliminary result for a fireplace.)

234
2.0 i

Di stance Frorn Fireplace

-o- 5cm

1 0cm

20cm

30cm

-» 40cm

-100 0 100 200

Distance across fireplace (cm)

Figure 2. Heat flux at 40 cm height in front of a 100 x 80 cm

flat plate uniformly radiating 16kW

REFERENCES

1. Hall, J.R., "Update on the Auxiliary Heating Fire Problem," Fire Journal, 80, (2),

52-62, March, 1986.

2. 1984 National Sample Survey of Unreported Residential Fires, Final Technical

Report to US Consumer Product Safety Commission (Princeton, New Jersey:

Audits & Surveys, Inc., June 1985).

3. Accident Facts, 1987 Edition, National Safety Council.

4. Vital Statistics of the United States in 1984, Center for Vital and Health

Statistics, 1987.

5. Gandhi, P.D., Kanury, A.M., "Criterion for Spontaneous Ignition of Radiantly

Heated Organic Solids, Combustion Science and Technology 50, 233-254, 1986.

235
APPENDIX

ALPHABETICAL LISTING OF

CENTER FOR FIRE RESEARCH GRANTS

Pa&e

Brown University 17

A Study of the Effects of Oxygen Transport and

Temperature History on the Chemistry of PMMA and

Cellulose Pyrolysis

Brown University 69

Soot Morphology in Flames

California Institute of Technology 97

Experimental Study of Environment and Heat Transfer

in a Room Fire

Clemson University 117

Graphical Presentation and Numerical Analysis of

Fire Data for Model Validation

Clemson University 105

Numerical Analysis Support for Compartment Fire

Modeling Code Development

Factory Mutual Research Corporation 31

Prediction of Fire Dynamics

Task 1. Prediction of Fires in Buildings 37

The George Washington University 73

Chemical Pathways to Soot Formation in Diffusion

Flames

Marquette University - 21

Thermal Stabilization of Polymers by Cross-Link

Formation

Michigan State University 172

Effect of Water on Ignition of Cellulosic Materials

The Pennsylvania State University 126

Soot Particle Formation and Destruction in Diffusion

Flames

The Pennsylvania State University 44

Upward Flame Spread on Vertical Wall

Rutgers - The State University of New Jersey 101

Negatively Buoyant Flows Generated in Enclosure Fires

by the Downward Turning of Ceiling Jets

237
Page

Southwest Research Institute 143

Analysis of Hazards to Life Safety in Fires: A

Comprehensive Multi -Dimensional Research Program-

Part 3

TRW Space and Technology Group 48

Wind-Aided Flame Spread

University of California, Berkeley 81

Fire Modeling

University of California, Berkeley 40

Fire Propagation in Concurrent Flows

University of California, Berkeley 9

Flame Radiation

University of California, Los Angeles 232

Fire Risk Analysis Methodology

University of California, Riverside 149

Expert System Approach for Spectra/Structure

Correlation for Vapor-Phase Spectra

University of California, Santa Barbara 180

A Study of the Suppression and Extinction of

Fires by Water Sprays

University of Dayton Research Institute 162

Mathematical Modeling of Furniture Fires

University of Kentucky 219

A Study of Oil-Slick Combustion

University of Maryland, Baltimore 208

Fire Environment in Counterflow Ventilation

University of Maryland, College Park 223

An Investigation of Simulated Oil Well

Blowout Fires

University of Maryland, College Park 184

Development of a Technique to Assess the Adequacy

of the Municipal Water Supply for Residential

Sprinkler Systems

University of Maryland, College Park 13

Interaction of Radiation and Conduction in Polymeric

Materials

238
Page

University of Maryland, College Park 77

Kinetics of Aggregate Formation

University of Maryland, College Park 107

Transient Ceiling Jet Characteristics

University of Maryland, College Park 176

Transient Cooling of a Hot Surface by

Droplets Evaporation

University of Michigan 130

Radiation from Turbulent Luminous Flames

University of Montana 55

Kinetics of Oxygen Chemisorption and Desorption

of Combustion Products in the Smoldering Combustion of

Cellulosic Material

University of Pittsburgh 146

Toxicity of Plastic Combustion Products

Virginia Polytechnic Institute and State University 95

Compartment Fire Combustion Dynamics

239
SS-H4A irev. 2 -eo

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NISTIR 88-3888

2. Performing Organ. Report No. 3. Publication Date

NOVEMBER 1988

TITLE AND SUBTITLE

"Summaries of Center for Fire Research In-House Projects and Grants - 1988"

AUTHOR(S)

Sonya M. Cherry (Editor)

PERFORMING ORGANIZATION (If joint or other than N BS. see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8 . Type of Report & Period Covered

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

. supplementary notes

H Document describes a computer program; SF-185, FlPS Software Summary, is attached.

ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bi bl iography or literature survey, mention it here)

This report describes the research projects performed in the Center for

Fire Research and under its grants program during FY1988.

/KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s)

cellulose; charring; combustion; fire models; flame spread; ignition;

polymers; smoke; soot; toxicity

/AVAILABILITY 14. NO. OF

PRINTED PAGES

| y | Unlimited

| j For Official Distribution. Do Not Release to NTIS 226

i 1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402. 15. Price

[Xj Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $24.95

USCOMM-DC 6 0 4 3 -P 80
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