NBSIR 75-679

Measurements of the Behavior of

Incidental Fires in a Compartment

J. B. Fang

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

March 1975

Interim Report

Principal Sponsor

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410

NBSIR 75-679

MEASUREMENTS OF THE BEHAVIOR OF

INCIDENTAL FIRES IN A COMPARTMENT

J. B. Fang

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

March 1975

Interim Report

This work reported here covers work now in progress at the National Bureau of Standards

and will be superseded by a future publication.

Principal Sponsor

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D.C. 20410

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

CONTENTS

Page

1. INTRODUCTION 1

2. EXPERIMENTAL DETAILS 2 2.1. Test Compartment 2 2.2. Instrumentation 2 2.3. Test Specimens 3

3. TEST PROCEDURE 4

4. TEST RESULTS 4

4.1. Temperature and Heat Flux Levels 4

4.2. Smoke Concentration 7 4.3. Effect of Carpet 7 4.4. Wood Cribs 9

4.5. Waste Receptacle Experiment 9

4.6. Comparison Data 9

4.7. Spread of Fire 15

5. CALCULATIONS OF HEAT FLUX 15

6. CONCLUSIONS 23

7. ACKNOWLEDGEMENTS 25

8. REFERENCES 25

APPENDIX - VIEW FACTOR 26

MEASUREMENTS OF THE BEHAVIOR OF

INCIDENTAL FIRES IN A COMPARTMENT

J. B. Fang

A variety of upholstered chairs and wood cribs were

burned within a ventilated compartment. The experimental

measurements of weight loss, smoke concentration, temperature and heat flux levels are summarized. A reproducible

fire obtained from burning a standardized wood crib array was found to be capable of representing the essential

features of incidental fires of moderate intensity.

Key words: Buildings; combustibility; fire intensity;

flames; furnishings; heat release; ignition; smoke;

thermal radiation; upholstery; waste receptacle.

1. INTRODUCTION

An incidental fire which starts in a wastebasket or on a piece of

funiiture may cause ignition of adjacent combustibles such as interior

finish materials or furnishings and may grow into a fully-developed

compartment fire. Information related to the characteristics of the

environment created by such minor fires is desirable as a basis for both

the development of rational procedures for designing the needed fire

resistance of building constructions and for the establishment of design

concepts for reduction of fire hazard. An experimental study of the

burning behavior of various combustible contents of wastebaskets and

individual pieces of upholstered furniture has been reported previously

Combustible wall and ceiling finishes in fire situations are generally recognized as a primary or contributing factor in the spread of a building fire. Most building codes provide specifications to regulate

general use of interior finishes and have adopted the ASTM E-84 flame

spread tunnel furnace test as a method for hazard evaluation. However,

it is not clear to what extent the conditions presented inside the

tunnel before and during the test can rationally simulate the environment encountered in an actual fire, since material location, orientation, and the magnitude of the fire exposure have a pronounced effect on

fire behavior. To evaluate the thermal responses of different types of

interior finish materials exposed to real fire situations it is necessary to acquire information on burning characteristics of the initiating

fire such as the range of possible fire intensity, duration and flame

Numbers in brackets correspond with the literature references listed at

the end of this paper.

1
size. Such data can provide a base for developing an effective test

method as an evaluation tool for classification of materials according

to degree of fire hazard.

The present room fire study program in NBS is designed to quantify

the contribution made by interior finish materials to the growth of a fire in a compartment, to determine if a useful correlation exists

between standard laboratory and full-scale test methods for evaluating

hazard potential of materials, and to suggest improved performance

criteria of interior linings for building construction. This paper is a report of work in progress. The objectives of this phase of the compartment fire program are to characterize the fire environment to which the

interior finish materials are likely to be exposed and to develop a standardized wood crib to duplicate the conditions produced by typical

incidental fires.

This paper presents some experimental results on the burning characteristics of upholstered chairs and cross piles of wood under a wellventilated condition in a test compartment. The experimental study is

mainly concerned with a characterization of the environmental conditions

due to typical incidental fires by measurement of the levels and ranges

of temperature rise, the incident heat flux, the duration of burning,

and the rates of heat release and smoke generation.

.•: :; -r . v. 2. EXPERIMENTAL DETAILS

• ' 2.1. Test Compartment

Experiments were conducted in a burn room measuring 2.9m by 3.2m by

2.4m high. One door measuring 1.3m wide by 2m high was located in one

of the smaller compartment walls and was kept fully open during the

test. The entire test compartment was enclosed in a large building to

provide wind and draft-free conditions. The test compartment was con- structed of reinforced concrete and the interior surfaces which were

exposed to the fires were lined with 16imn thick gypsum wallboards sprayed

with a vermiculite gypsum plaster.

2.2. Instrumentation

Commercial radiometers and heat fluxmeters, placed at selected

locations in the test compartment, were used to determine the heat flux

due to radiation alone and also due to the combination of convection and

radiation.

Direct measurements of the weight loss rate of the burning combustible materials were made with four strain-gage type load cells positioned at the corners of a 0.94 by 1.60m platform. A single layer of

painted 16mm thick gypsum wallboard nailed to wood studs extending from

2
floor to celling, was located near the fire and served to represent a typical dwelling wall and to provide an estimate of the fire intensity

by the surface area burned.

A Gardon-type heat fluxmeter was mounted on the painted gypsum

board for continuous monitoring of heat flux incident on the board from

the test fire. This heat fluxmeter was placed at a height of 730mm

above the floor, and spaced 51mm from the chair back and small sized

wood crib, or 102mm from the medium and large wood cribs. This transducer was made from a copper block with an opening of 19mm in diameter

and a 50mm blackened platinum foil screwed over the opening on the

copper body. With two fine copper wires soldered to the body and the

center of the foil, the meter thereby constituted a copper-platinum

thermocouple. The transducer output was calibrated against the radiant

flux from of a blackbody cavity placed in a muffle furnace and showed

linearity of signal output with an accuracy of + 5% over the flux range

corresponding to the blackbody temperature range of 500 to 910°C.

The temperatures of the plume gas along the flame axis above the

chair or wood crib, the surface of the finished gypsum board, and the

heated air at various locations within the compartment were determined

by bareheaded thermocouples of 0.5mm diameter Chromel-Alumel wire.

Measurement of the smoke produced by the test fire in the compartment was made by the use of the attenuation of light principle. A

photometric system which consisted of a voltage controlled light source,

appropriate lenses to collimate and focus the beam, and a photodetector

tube was used for continuous measurement of the decrease in light transmittance. The concentration of smoke buildup within the compartment was determined at two locations: one at the 1.52m above the floor with a horizontal beam parallel to the gypsum wall board, situated at a spacing

of 2.3m from the gypsum board, and covering the whole room width with a path length of 3.17m; the other at a location near the center of the

compartment, separated a horizontal distance of 1.4m from the center of

the fire with the beam collimated perpendicular to the floor and having

a path length of 2.41m.

All output signals from the radiometers, thermocouples and heat

fluxmeters were punched on paper tape for data processing as well as being recorded digitally at 1-minute intervals on a high speed digital

acquisition system. Two 2-channel potentiometric strip chart recorders

were used to monitor the outputs of smoke meters and load cell.

2.3. Test Specimens

The chairs, obtained from a local used furniture outlet, had different weights and constructions and had experienced various degrees of use and wear. Several types of upholstery fabrics were used on these

chairs, including cotton, nylon, and rayon. The cushion pads were made

of cotton batting, latex rubber, or urethane foam.

3
The standarized wood cribs were designed to duplicate the con- ditions produced by the test fires with furniture. A large crib was

used to simulate the incidental furniture fire of moderate intensity.

This crib, measuring 0.56m x 0.56m x 0.55m high and weighing approximately 33kg, was constructed of cross piles of 34 pieces of nominal 51

X 102 X 560mm long hemlock sticks. A medium sized, 0.51m cubic crib

weighing about 25kg and constructed by stacking 30 pieces of 0.51m long

sticks was used to represent a lower intensity furniture fire. A smaller

0.36 X 0.36 X 0.30m high crib weighing about 6.3kg and constructed by

piling 28 pieces nominal 51 x 51 x 360mm long sticks was used to represent

an incidental fire of lower flame height and shorter duration. The

large and medium sized cribs had 8 and 7 layers, respectively, each

containing four sticks with a 64mm stick spacing for the top four layers,

and a 25mm spacing for the remaining layers, plus « bottom two-stick

layer, with successive layers laid crosswise. The small crib consisted

of six 4-stick and two 2-stick layers and the spacing between sticks

except for the bottom two layers was 51mm. The moisture content of the

wood cribs was found to be approximately 9 percent. Table 1 summarizes

the main parameters of the combustibles involved for each test. Fire

load density is defined as the weight of combustible materials per unit

projected gross area of the specimen on the floor.

. . 3. TEST PROCEDURE

For each upholstered chair test, the ignition source was a methenamine "timed burning" tablet placed at the junction of the chair back

with the seat cushion.

For the wood crib tests, the fire was initiated by application of" an open flame to ignite 150ml of ethyl alcohol in a square steel pan

placed beneath the crib. At ignition of the alcohol all recording

instruments were turned on simultaneously. The development and burning

behavior of each test fire was observed and recorded during the test.

4. TEST RESULTS

4.1. Temperature and Heat Flux Levels

Summary data on duration of burning, the maximum rate of weight

loss, hot gas temperature, rates of heat transfer to surroundings, smoke

generation at the peak of the fire, and the maximum distances at which

specimen indicators were affected for each test are presented in table 2.

Most of the upholstered chairs examined burned completely in 40 to

86 minutes with an average of 50 minutes. The duration of the chair

fire seems to correspond fairly well to the types of padding materials

used in the seat cushion, longer durations being associated with cotton

felt.

4
Table 1. Description of Upholstered Chair and Crib Tests

Materials Chair or Crib Fire Load

Test Upholstery Padding Weight Wiatn Density

NoFabric Body Cushion (Kg) (cm) (g/cm^)

47 Cotton Cotton Cotton 9.64 64 2.60

48 Rayon/Nylon Cotton Cotton 20.87 69 3.54

49 Nylon Cotton/ Cotton 12.81 56 3.23 i Hair

50 Cotton Cotton Cotton 21.32 58 4.44

51 Rayon Cotton Urethane 22.91 80 3. 70

Foam

52 Cotton Cotton Urethane 21.41 58 4.90

Foam

53 Cotton Cotton Urethane 14.52 65 3.09

Foam

54 Rayon Cotton/ Urethane 27.76" 76 4.36

Hair Foam

55 Rayon Cotton/ Urethane 29.26 102 2.36

Hair Foam

56 56% Rayon/ Cotton Latex 34.47* 97 3.86

40% Cotton/ Rubber

4% Metallic

57 75% Rayon/ Cotton/ Latex 24.81 79 3.16

25% Cotton Hair Rubber

58 60% Rayon/ Cotton/ Urethane 18.05 66 2.86

40% Cotton Sisal Foam

59 Cotton Cotton/ Latex 25.63 69 4.42

Sisal Rubber

60 50% Cotton/ Cotton/ Latex 32.43 97 4.01

49% Rayon/ Hair/ Rubber

1% Metallic Sisal

61 Rayon Cotton/ Urethane 29.26 102 2.36

Wood Foam

Fiber/

Hair

62 85% Rayon/ Cotton/ Latex 29.94* 71 4.28

15% Cotton, Hair Rubber j Cotton**

63 Wood Crib (Large Size) 32 . 89 56 1 10 . 53

64 Wood Crib (Large Size) 33.34 56 i 10.68

65 Wood Crib (Medium Size) 25.76 51

1 9.98

66 Wood Crib (Medium Size) 25.18 51 i 9.75

68 Wood Crib (Small Size) 6.35 36 1

1 4.90

Including 2.81 Kg of a 94 - by 127 cm acrylic carpet placed underneath

the chair.

**Fabric used for chair slipcover.

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The temperature of the gases within the test compartment was calculated by averaging of the room gas temperatures measured at 6 locations:

5 at mid-height and the other one at 25mm below the center of the ceiling.

Excluding one chair which only partially burned due to the upholstery

fabric, the average temperature of air in the compartment at the peak fire

conditions ranged from 45 to 420°C with a mean of 180°C. This temperature

level developed during the fire makes human occupancy untenable in a short

period. Under the conditions of these tests, the danger due to high

temperatures was in general found to precede the hazard due to smoke,

except for the burning of upholstered chairs cushioned with latex rubber.

The maximum rate of heat transfer from the fire to a vertically

oriented black surface located 0.61m from the flame axis varied from

approximately 0.5 to 5.5 W/cm^ with a mean of about 2.2 W/cm^, reflecting

the different weights and constructions of chairs tested. This level of

incident heat flux resulting from combined radiation and convection heating is capable of causing spontaneous ignition of nearby combustible

materials

4.2. Smoke Concentration

The average peak concentrations of smoke generated by the burning

of chairs containing latex rubber, urethane foam and cotton felt padded

seat cushions in the test compartment were of the order of 0.45, 0.34

and 0.30 Optical Density/m (O.D./m), respectively. The elapsed times to

reach these peak levels were found separately to be about 10, 17 and 27

minutes after initiation of the fire.

Figure 1 shows the time history of smoke concentration, expressed

in terms of optical density per metre smoke thickness, as measured horizontally at 1.53m above the floor, across the width of the test compartment, for fires with typical upholstered chairs and the standardized

wood crib. The rate of smoke production during the test was highly

variable as it strongly depended upon the nature of the fuel involved

and the size and intensity of the fire. The measurement data as shown

in the figure indicate that under well-ventilated conditions, the chairs

cushioned with latex foam generated the greatest amount of smoke, whereas

an open crib produced the least. The smoke concentration within the

compartment 1.5m above the floor averaged over the test period was found

to be 0.03, 0.29, 0.15 and 0.09 O.D./m, respectively, for fires involving

wood crib and the chairs having latex rubber, urethane foam and cotton

cushions. The development of smoke was found to occur at the peak of

these fires, and as shown in figure 1 the smoke could give rise to a highly dangerous situation.

4.3. Effect of Carpet

A preliminary study was made to determine the effect of a carpet on

fire behavior by placing a 0.94 by 1.27m acrylic carpet (random shear

7
8
type, polypropylene/jute, pile height 1.6 to 8mm, total weight 2.81kg)

underneath the chair. In two of the three tests conducted, it was

observed that the entire chair and carpet were enveloped in flames at

approximately 30 minutes after ignition and the chair burned more

rapidly than those without carpets. This flameover phenomena appeared

to result from the ignition of the carpet through direct flame contact

with burning chair fragments, however, it was undoubtedly associated with

an accumulation of combustible gases generated by the carpet exposed to

intense radiation.

4.4. Wood Cribs

The behavior of the wood cribs was similar to the upholstered

chairs in terms of a relatively low rate of weight loss at the early

stage followed by active burning and decay periods. It was found from

replicate tests that the weight loss rate, the heat transfer rate to

surroundings, and the burning time of these crib fires were fairly

repeatable. As illustrated in table 2, at peak fire conditions the

average temperature of air inside the test compartment generally increased

80 to 140°C, the air temperature near the ceiling above the crib varied

from 300 to 410°C. The total surface area of the painted gypsum board

burned was measured after each test and found to be comparable to that

of a chair fire.

4.5. Waste Receptacle Experiment

In the waste receptacle fire experiment involving the burning of

2.82kg of plasticized paper milk cartons in a nominal 120 liter steel

waste receptacle the original weight diminished relatively rapidly

during the initial stage of the fire and then at a slower rate. This was due to the change of burning conditions from unlimited air supply to

partially restricted air flow as the fire propagated lower into the waste

receptacle. In general, waste receptacle fires containing combustibles

commonly found in a dwelling or an office had a shorter buildup period

than chair or crib fires.

4.6. Comparison Data

Typical curves of weight loss versus time for some chair, waste

receptacle and crib fires are shown in figure 2. It can be noted from

the figure that the upholstered chairs, after being ignited, required

between less than 10 to more than 20 minutes to develop into fully

involved fires. The maximum weight loss rate for chair fires was quite

variable because of diverse weights and constructions of upholstered

chairs used for each test.

Figure 3 shows a comparison plot of air temperature measured

directly above the fire and measured at 2.5 cm below the ceiling versus
TIME (minute)

Figure 2. Weight loss versus time curves for fires

involving upholstered chairs, wood crib and plasticized milk cartons in a waste receptacle.

10
TIME (minute)

Figure 3. Comparison of air temperature above the fire

and near the ceiling for upholstered chair, waste

receptacle and wood crib fires.

11
time for fires involving an upholstered chair, plasticized milk cartons

in a waste receptacle and a wood crib. The ASTM E-119 standard

temperature-time curve was also plotted in the same figure for comparison. It can be seen that the temperature of hot gases above a waste

receptacle fire increases more rapidly than either chair or crib fires

during the early stage of burning. The upholstered chair, waste receptacle, and crib fires had a relatively short duration of peak temperature

whereas the standard ASTM E-119 curve increased continuously.

The combined radiative and convective heat flux level at various

locations was obtained from commercial heat fluxmeters, which were

mounted vertically 0.73m above the floor facing the burning object. The

measured values of total and radiative fluxes at peak fire conditions

for each test are listed in table 2. The experimental data show that

radiation was the primary mode of energy transport comprising approximately 75 to 85 percent of the total energy at a distance of 0.46 to

0.61m from the vertical center line of the burning item.

The temporal distributions of the level of heat flux incident on a vertical surface located at a height of 730mm above the floor in the

proximity of the test fires and the derived heat flux-time curve for a fully-developed room fire are presented in figure 4. The latter curve

has been calculated from the ASTM E-119 standard temperature-time curve with the assumptions that the fire filling a 2.4m high room may be

considered as a black-body emitter of infinite width compared to the

dimension of a receiver located at a spacing of 0.61m and an elevation

of 0.73m measured above the floor. As shown in the figure, the waste

receptacle fire had a fairly rapid start and shorter duration in com- parison with the fires with furniture or wood arrays. The relatively

steep peaks noted in the chair fires are attributed to the high heat

release resulting from active burning of the latex rubber and urethane

padded seat cushions. The heat flux level for a fully-developed room

fire based on the ASTM E-119 test procedure, increases rapidly and

continuously with time whereas the typical furniture and crib fires

reached peak levels which were considerably lower and occurred within a 30 minute period.

A plot of combined convective and radiative heat flux incident on a vertical plane at 0.61m spacing to the center of the fuel source, is

given in figure 5 as a function of heat release rate. The heat release

rate was calculated from the rate of weight loss, the projected area of

fuel source on the floor, and the calorific values of the combustibles

involved. From visual observations, it was found that most chairs

burned fairly slowly during the early stage. Then the fire propagated

progressively over the highly flammable seat cushion and the back and

arms, producing a maximum heat output and large quantities of smoke.

Flaming reduced considerably when the upholstered materials were con- sumed and slower burning wood frames were involved. As illustrated in

figure 5, the rate of heat transfer from a freely burning fire was roughly

linearly related to the heat release rate. Its magnitude at 0.73m above

the floor and 0.61m from the flame axis was estimated to be about 2 percent of the available heat generated, based on unit area occupied by

12
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Distance from Fuel

Test No. (In cm.)

60 1 Ol VIOi

> (Chair)

59 J 61 (18) 35 (Waste Receptacle) 41 (15) 63 (Large Crib) 61 (33)

Fully Developed

Room Fire (61)

68 (Small Crib) 91 (73)

20 30

TIME ( minute)

40 50

Figure 4. The combined radiative and convective heat

flux measured at the selected location versus time

for upholstered chair, waste receptacle and wood

crib fires.

13
CALCULATED RATE OF HEAT RELEASE (W/cm2)

Figure 5. Relationship of combined radiative and

convective heat flux incident at 0.61m location

and rate of heat release for chair and crib

fires.

14
the fire load. This relationship is expected, since for a given burning

source an increase in the burning rate would produce an increase in the

flame size, thereby yielding a higher rate of radiative and convective

heat transfer.

4.7. Spread of Fire

In order to obtain some information concerning the minimum separation distances at which incidental fires would not spread to nearby

combustible items, three types of cellulosic materials commonly found in

dwellings and offices were studied. These indicator specimens were

0.19mm thick white cotton cloth, 0.08mm thick white paper, and 6.4mm

thick cedar wood. All of the specimens were 100mm x 150mm in dimension

and were mounted on stands; specimens were mounted on stands at heights

of 0.43 and 0.71m above the floor and at fixed distances of 15, 30, 45

and 60 cm from the chair or wood crib. The maximum distance at which

the specimen was ignited, charred or scorched by the test fire is given

in table 3. There are obvious variations in the distance at which the

test fires caused spontaneous ignition. Some fires were unable to

ignite white paper as close as 15 cm. These differences are primarily

due to the wide variations in fire intensity and periods of exposure to

the fluctuating flame. As illustrated in the table, the ignitability of

the cotton cloth and white paper used were not much different from that

of the wood specimens, and all three seem to provide equal sensitivity

as indicators. This is primarily due to low absorptivity of the irradiated surfaces and reduction of the temperature gradients within these

thin specimens.

The maximum distance at which the various effects were produced in

the specimens of wood, cloth and paper is shown in figure 6 as a function

of the maximum fire intensity expressed in terms of the maximum incident

heat flux. This heat flux was measured at a horizontal distance of

0.61m from the center of the chair and at a height of 0.73m above the

floor. The ignition distances found ranged from 0.15m for light weight

upholstered chairs to 0.60m for moderate sized chairs with a carpet

beneath. Most chair fires caused ignition of wood at a separation

distance of 0.15m, char at 0.30m and scorch at a distance of 0.60m

within 30 minutes after ignition of the furniture item.

5. CALCULATIONS OF HEAT FLUX

Since radiation is found to be the dominant mode of energy transport,

the magnitude of radiant heat flux impinging on a neighboring object

from a fire depends upon temperature, total emissivity of the flame, and

the view factor between the flame emitter and the receiver.

Calculations of the radiant flux distribution around a radiating

flame generally involve complex integration procedures and numerical

techniques [2,3]. A mathematical model of free-burning fires [4] has

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MAXIMUM FIRE INTENSITY (W/cm2)

Figure 6. Fire intensity and distances at which

specimens were affected.

17
been recently developed to relate the burning rate and fuel properties

to the flame physical and geometrical properties, which are essential

information required in radiative analysis. In order to estimate heat

flux levels at various locations, the freely burning fire is assumed to

be a finite cylinder having a diameter equal to the fuel source width,

a height identical to the visible flame height, a constant emittance, and

a constant temperature. Figure 7 presents calculated curves of view factor for radiant exchange between a differential plane receiver and a right circular cylinder, as a function of the dimensionless separation

distance for two typical dimensionless flame heights, and two heights of

the receiver measured above the flame base. An analytical expression of

the view factor for the configuration illustrated in the figure is given

in appendix A.

Experimental data on heat flux measured at different locations are plotted and presented in figure 8, where the incident heat flux at peak

fire conditions is plotted against the geometric view factor calculated

on the basis of the relative location of the heat fluxmeter, the width

of the combustible item and the measured flame height. It can be seen

that all the data in each test fall adjacent to a regression line, and

the resultant heat flux conditions produced by the fires from the developed

simple wood arrays lie within those created by incidental fires.

Figure 9 compares the curves showing the time history of rate of heat

release, based on the projected area of the combustible item on the floor,

for fires with upholstered chair, wood crib and plasticized milk cartons

in a waste receptacle. As noted before, the rates of heat output from

the burning chairs are widely varied and significantly dependent upon the

types of padding materials, design and construction of the furniture item

involved. The simplified fuel arrays can be utilized to synthesize fire

buildup conditions for furniture since the heat output pattern of standardized crib fires approximately simulate that of certain furniture fires as shown in the figure. The maximum rate of heat output and the total amount

of heat energy released per unit projected area by test fires were estimated to be of the order of 120 kW and 2.7 x 10^ J/cm^, respectively, for

waste receptacle fires, 320 kW and 15 x 10^ J/cm^ for large crib fires and

130 kW and 5.8 x 10^ J/cm^ for fires involving a small wood crib, and

870 kW and 16 x 10^ J/cm2 for furniture fires of moderate intensity.

Figure 10 shows a plot of the combined radiative and convective heat

flux at the flame edge versus the computed rate of heat release at peak

fire condition. The former was estimated from figure 8 by extrapolating

the regression line to intercept with the ordinate corresponding to a view

factor equal to unity. The peak heat flux level in the proximity of the

test fire varied widely: ranging from approximately 0.9 W/cm^ for chairs

padded with cotton felt to 8.5 W/cm^ for those with plastic foam. As

shown in the figure, there was a trend of linear relationship existing

between the heat flux from the flame envelope and the computed heat release

rate. The heat flux level was estimated to correspond to approximately

4 percent of the available heat released based on unit area projected by

the combustible item on the floor.

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1 1

r-*

t-i—

.r-l u

•rH ni

rrt lU

Cj

S-i ni U

14_^ iH

•ri

(11 r \

UJ

r ^ L/

UJ U

(—

>-i

1 1 rrt (U

r \

I 1 lU n

1 1 1 ,—

j

15 fd 0) •H •H -p >

0

CD

M-l

M-i dJ H

^

:=! H

2ld aOlOVd M3IA

o

a

19
0.4 0.6

VIEW FACTOR F^2

Figure 8. Relationship between the measured

incident heat flux and the view factor

from the receiver to the fire.

20
TIME ( minute)

Figure 9. Comparison of rate of heat release for

furniture, wood crib and waste receptacle fires.

21
Figure 10. Relationship between the computed rate

of heat release and the extrapolated heat flux

at flame envelope.

22
A relationship showing flame emlsslvlty and half-v/ldth of the fuel source Is presented In figure 11. The emlsslvlty of the flame for each

test was calculated by using the extrapolated value of the heat flux at

the flame envelope and the flame temperature measured with the unshielded

thermocouples located along the flame axis. The flame emlsslvlty data

from chair fires was found to be considerably dispersed. This may be

attributed to wide variations in the concentration and composition of

the radiating gases and the presence of varying amounts of soot and

smoke particles from the burning of different types of upholstered

chairs. The attenuation coefficient k, is defined by the equation:

k = -In (1-e)

This coefficient can be estimated from flame thickness, which is

approximately equal to the source width 2r, and calculated flame emlsslvlty e. The equation of a best fit line drawn in figure 11 was obtained

by regression analysis and the average attenuation coefficient for these

test fires was found to be LlSm"-*^.

6. CONCLUSIONS

Incidental fires generally produce high fire plume temperatures and

intense heat flux in local areas and may approach the fire severity as represented by the ASTM Standard E-119 test method for fully involved room fires. However, these levels of air temperature and heat flux to

adjacent surfaces at peak fire conditions exist for only short periods.

The rate of heat transfer from a freely burning fire was found to

be roughly linearly related to the heat release rate or fuel burning

rate, and its magnitude at the flame boundary accounted for approximately 4 percent of the heat generation rate based on unit area of the

combustible item projected on the floor.

The fire with a standardized wood crib can duplicate the essential

characteristics, such as burning time, temperature and heat flux levels

and the size and shape of the flame, of typical incidental fires.

Data on heat flux levels measured at various locations were, for a given item, correlated fairly well by a simplified derived expression

based on an assumption of considering the fire to be cylindrical in

shape and a gray-body emitter with constant temperature.

The upholstered chairs furnished with latex foam cushion produced

higher levels of smoke concentration than those with cotton felts or urethane foam.

The distances at which spontaneous ignition of wood would occur varied from 0.15m for light-weight burning chairs to 0.45m for moderate

sized ones above a carpet.

23
I

1.0

0.9

0.8

0.7

06

0.5

0.4

0.3-

0.2

0.15

ln(l-6)s-O.OII3r

Fire Type • Chair

O Wood Crib

A Waste Receptacle

10 20 30 40

HALF-WIDTH OF FUEL SOURCE r (CM)

50 60

Figure 11. Flame emissivity versus half-width of

the fuel source for furniture, wood crib and

waste receptacle fires.

24
7 . ACKNOWLEDGEMENTS

The author wishes to express his gratitude to Mr. C. F. Veirtz and

Mr. T. F. Maher for their assistance in the experimental work. The work

was supported in part by the United States Department of Housing and

Urban Development.

8 . REFERENCES

[1] Gross, D. and Fang, J. B. , The Definition of a Low Intensity Fire,

Joint RILEM-ASTM-CIB Symposium Proceedings, Performance Concept in

Buildings, Vol. 1, Nat. Bur. Stand. (U.S.) Special Publication,

361 (1972).

[2] Masliyah, J. H. and Steward, F. R. , Radiative Heat Transfer from a Turbulent Diffusion Buoyant Flame with Mixing Controlled Combustion

Combustion and Flame, Vol. 13, 613-625 (1969).

[3] Love, T. J., Shahrokhi, F. , Hood, J. D. and Tsai, Y. W. , A Method

for the Prediction of Radiative Heat Transfer from Flames, paper

No. 67-HT-47 presented at ASME-AIChE Heat Transfer Conference,

Aug. 6-9, 1967.

[4] Fang, J. B. , Analysis of the Behavior of a Freely Burning Fire in

a Quiescent Atmosphere, Nat. Bur. Stand. (U.S.), NBS IR 73-115

(Feb. 1973).

[5] Hamilton, D. C. and Morgan, W. R. , Radiant-Interchange Configuration

Factors, United States Nat. Advisory Com. for Aeronautics (USNACA)

Tech. Note 2836 (Dec. 1952).

25
APPENDIX - VIEW FACTOR

The view factor for radiant interchange between a right circular

cylinder A2 of radius r and height h, and a differential area element

dA, with its normal perpendicular to the axis of the cylinder, as shown

in the sketch of figure 7, can be expressed by the following equation [5]

P^ = (L + 1)^ + (H - N)^, P^ = (L + 1)^ +

= (L - 1)^ + (H - N)^ Q2 = (L - 1)^ +

USCOMM NRS DC

26
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR RHPORT NO. NBSIR 75-6792. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE 5. Publication Date

MEASUREMENTS OF THE BEHAVIOR OF INCIDENTAL FIRES

IN A COMPARTMENT 6. Performing Organization Code

7. AUTHOR(S)

J. B. Fang

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Projcct/Task/Work Unit No. 4926676

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Department of Housing and Urban Development

13. Type of Report & Period Covered _Interim

July 1972 - Feb. 1973

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliograpfxy or literature survey, mention it here.)

A variety of upholstered chairs and wood cribs were

burned within a ventilated compartment. The experimental

measurements of weight loss, smoke concentration, temperature and heat flux levels are summarized. A reproducible

fire obtained from burning a standardized wood crib array

was found to be capable of representing the essential

features of incidental fires of moderate intensity.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) t>,, ,• i j _ . „_„i, 4- u i 4. r • • ^ n-, ' Buildings; combustibility; fire intensity; flames;

furnishings; heat release; ignition; smoke; thermal radiation; upholstery;

waste receptacle.

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