Reference

NBS

Publications

NBSIR 82-2557

NAT'L INST. OF STAND & TECH

AiiiDb

Measurement of Material Flame

Spread Properties

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Washington, DC 20234

August 1 982

Sponsored by:

QC

100

.056

82-2557

Federal Aviation Administration

Technical Center

Road

ntic City, NJ 08405

MATIUMA.L fiCJUCMm or oTAJfDjuao* - KiZBQAJffZ

NBSIR 82-2557

SEP 7 mz

(SIC MEASUREMENT OF MATERIAL FLAME

James G. Quintiere

Margaret Harkleroad

William Walton

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Washington, DC 20234

August 1 982

Sponsored by:

Federal Aviation Administration

Technical Center

Tilton Road

Atlantic City, NJ 08405

SPREAD PROPERTIES

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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MEASUREMENT OF MATERIAL FLAME SPREAD PROPERTIES

by

J. Quintiere

M. Harkleroad

D. Walton

ABSTRACT

A concept was examined for measuring flame spread parameters suitable

for predicting the performance of a material in fires. The study examines

a radiant panel test apparatus used to measure downward and lateral flame

spread, and ignition. An analysis of data from tests of Douglas fir particle

board is presented. A procedure has been identified for measuring specific

parameters useful in the general prediction of ignition and flame spread

for complex materials.

Keywords: Fire models, fire tests, flame spread, ignition, particle board

1
Table of Contents

Page

INTRODUCTION 1

THEORETICAL ANALYSIS 2

EXPERIMENTAL ANALYSIS 6

HEAT TRANSFER CHARACTERISTICS 7

MATERIALS 9

IGNITION 10

flame spread 12

CORRELATION OF RESULTS 14

CONCLUSIONS 18

ACKNOWLEDGEMENT 20
LIST OF ILLUSTRATIONS

Page

Figure 1. Components of flame spread model. 24

Figure 2. Schematic of experimental apparatus

.

25

Figure 3. Normalized radiant flux distribution. 26

Figure 4. Surface temperatures at thermal equilibrium. 27

Figure 5. Heat transfer coefficient. 28

Figure 6. Pilot flame configuration. 29

Figure 7. Time to ignite for particle board. 30

Figure 8. Surface temperature rise preceding

flame arrival for particle board.

31

Figure 9. Flame front movement for particle board tests. 32

Figure 10. Flame spread velocity for particle board tests. 33

Figure 11.

-1/2

as a function of flux for particle board. 34

Figure 12. Correlation of Ignition data for particle board. 35

Figure 13. Correlation for flame spread, F(t) by Eq. (16). 36

Figure 14. Correlation for flame spread, F(t) by Eq. (14). 37

Figure 15. Surface temperatures due to

radiant heating for particle board. 38

Figure 16. Flame spread velocity in terms of

39

surface temperature for particle

board

.

I

i iii
LIST OF TABLES

Table 1. Flame spread

Table 2. Flame spread

test conditions (particle board),

parameters (particle board)

.

Page

22

23
NOMENCLATURE

C

Gr

h

h

c k

q"

Pr

t

T

V„

h^/kpc

specific heat

flame heat transfer modulus Eq. (7)

Grashof number

heat transfer coefficient

convective heat transfer coefficient

thermal conductivity

heat transfer per unit area per unit time

Prandtl number

time

temperature

flame spread speed

horizontal coordinate

vertical coordinate

absorptivity

flame heat transfer length

heat transfer depth

emissivity

density

Stefan-Boltzmann constant

Subscripts

ig

external

flame

initial or ambient

ignition

minimum

surface

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INTRODUCTION

The purpose of this study is to develop and analyze the techniques

for the measurement of flame spread properties of materials. It does not

seek to elucidate the mechanism of flame spread. Moreover, it is restricted

to so-called "creeping” flame spread as in downward, lateral or possibly

horizontal spread. This type of flame spread is characterized by forward flame

heat transfer confined to a relatively small zone ahead of the advancing flame

front and induced or opposed air flow at the flame front. A relatively simple

procedure is considered in which flame spread is measured for a material under

the influence of external radiant heating. Both downward and lateral spread

on a vertical sample were measured. The object was to determine parameters

from these measurements and subsequent analysis which could provide general

predictions of flame spread for the materials. The extent to which these

parameters can be related to material properties or conditions of the experiment

was evaluated. Although several materials were studied, only the results for

Douglas fir particle board will be presented for illustration. In addition to

these flame spread measurements, radiative piloted ignition was studied. This

was done to show the relationship of ignition to flame spread.

This study is a continuation of work described previously by Qulntiere [1].

It seeks to extend that work to a wider class of materials, and to refine the

procedures for deriving the flame spread parameters. The models for flame

spread and ignition are based on inert heat conduction of a semi-infinite

opaque blackbody solid and on the concept of an ignition temperature. These

models are believed adequate for fire conditions where the heat conduction

1
time is large compared to the chemical reaction times. Also their relative

simplicity allows them to be applied to complex materials in a practical

manner. They capture the bulk energies of the processes without describing

the detailed mechanisms. The following results will illustrate their

accuracy.

THEORETICAL ANALYSIS

The theoretical basis for analyzing the experimental results and

gpuerallzing them will be presented here. A heuristic mathematical analysis

will be presented based on a concept of ignition and flame spread as a

result of inert heating of a thermally thick homogeneous solid to an ignition

temperature. A more rigorous mathematical analysis based on this concept

has already been presented [1]. Also the intent of this analysis is not to

develop a complete model descriptive of all the significant mechanisms, but

to provide a framework for analyzing data for materials. This analysis

would then provide the formulae for predicting flame spread and Ignition

in fire growth models, and for evaluating these materials in quantitative

terms

Figure 1 displays a conception of the flame spread model and its

components. The following conditions are considered:

(1) One dimensional unsteady heat conduction occurs in the solid

normal to the surface.

(2) The position of the flame or pyrolysis front is identified

by x^ where the surface temperature has reached an

Ignition temperature.

2
( 3 ) External radiative heating may depend on position and

time.

(4) Flame heat transfer ahead of the pyrolysis front is considered

to occur over region 6^ with a uniform heat flux of q'^

unaffected by q".

e

In this application, the flame heating distance 6^ is assumed to be small

consistent with application to downward or lateral flame spread on a vertical

wall. Although the flame heat flux is represented as a surface flux, more

general heat transfer effects (such as conduction through the solid) could be

considered without changing the form of the final results.

The premise of the model is that the flame front exists at x = x^

provided the temperature of the surface has attained This temperature

rise to ignition must equal that due to the flame heating and that rise due

to heating from the external source. It is expressed as

T. - T, = AT. + AT at x. (1) ig 1 f e f

(This is the form of the derived result, Eq. (1) of Ref. [1].)

The temperature rise due to external radiant heating is given as

At = T - T. = q" (x.) [1 - exp(at) erfc /at]/h (2) e s 1 e f

for an infinitely (thermally) thick solid with a Newtonian heat loss in

which the radiation loss has been considered as a linear approximation.

The implication of implementing this approximation will be discussed later.

3
2

In Eq. (2) h is the linearized heat transfer coefficient and a = h /kpc.

Equation (2) is for q^ independent of time, but this is not a necessary

restriction in the analysis. Any appropriate expression for AT^ consistent

with other heating modes or solid configurations is introduceable.

Equation (2) represents the time variation of the surface temperature

while the temperature variation into the solid (y-direction) depends on time

as well. As the flame front approaches a region that has been heated by q”,

the surface temperature and its gradient in the solid change with time.

The flame then adds heat over the region 6^. It is assumed that the flame

heating only affects a depth into the solid of distance A ^kt/ p c and that

9T the temperature T is uniform over A, i.e. A is small or the gradient tt" is

S ay

small. It follows then by an energy balance on a control volume of dimensions

6^ X A X 1 fixed to the flame front that

PCA Vj - T^) = (3)

where is the velocity relative to the control volume, i.e. the flame

spread velocity, and

V

f

(4)

where here e is the time lor the flame to move 6^.

Obviously Eq . (3) is a simplification of the process. The heat losses

have been ignored, but this only gives a serious error when is small [1].

Substituting for A and combining Eqns. (3) and (4) leads to

AT = T. - T = (q” /r//^)//v7 (5)

t ig s f f f

4
which is consistent with more rigorous solutions for surface flame spread

found in the literature, eq. (1). From Eq. (1), (2) and (5) the complete solution

for flame spread velocity is found from

+ q^ (x^) [1 - exp(at) erfc /^]/h (6)

or

= C(h(T. -T.) - q"(x^) • F(t)) (7)

f ig 1 e f

where C = l/q’’ /a6 the flame heat transfer modulus,

r f

and F(t) = 1 - exp(at)erfc /aT, or a possibly corresponding transient

heating function in the form of Eq. (2), i.e. h(T-T^) = q” F(t).

From Eq. (2) an ignition theory can be derived if T is set equal to T . s ig

This would apply to radiative ignition with a pilot flame. In that sense it

should be consistent with the flame spread result since flame spread may be

regarded as a continuous series of piloted ignitions. Also the concept of an

ignition temperature should be consistent between these two processes. Following

the notation in Eq. (7), it follows that ignition is governed by

h (T. - T.) = q" • F(t) (8) ig X ^e

Since F(t) -> 1 as t the minimum radiative heat flux for piloted ignition

is given as

5
( 9 ) q” . = h (T. - T.) o,ig ig 1

Equations (7), (8) and (9) constitute the basis for analyzing the

experimental test data, and also serve as predictive formulae where they

are applicable. The parameters that arise in the equations can be determined

experimentally. They depend both on the material and on the conditions of

flame spread. For opposed flow flame spread, the flow velocity induced by

a developing fire should be relatively small and fairly constant. Therefore,

C and h should not vary significantly. In general C will depend on the

opposed flow velocity and on the ambient oxygen concentration. It will be

shown that under circumstances of natural convection the convective component

of h is fairly constant, but its radiative component depends on surface temperature and emissivity. For most materials of interest an emlssivity of 0.8 to 0.95

can be expected for Irradiance sources of 1000 K or below. Hence an assumption

of an emissivity of one would be reasonable, but for greater accuracy variation

in surface radiation properties should be accounted for. An ignition temperature

may not be an unique material constant; however, its unique value for this

application will be valid in the context of this model. The critical flux for

ignition q" . must be considered in the same manner. o,ig

EXPERIMENTAL ANALYSIS

A schematic of the experimental apparatus is shown in Figure 2. The

sample was oriented so that either the 155 mm dimension was vertical or the

800 mm dimension was vertical. The former arrangement recorded lateral spread

while the latter arrangement recorded downward spread. The radiant panel

imposed a distribution of radiant heat flux to the face of the sample as

shown in Figure 3. The results there have been normalized in terms of the

6
incident flux measured at x = 50 mm. The incident flux was measured by

water-cooled thermopile-type total incident heat flux sensors along the centerline of the sample face, and is fairly uniform over its width. Since these

were mounted in a noncombustible board which would get hot, they could

experience a convective heat flux contribution estimated to be no more than

10 percent of their reading. The radiant panel was a porous refractory

pre-mixed natural gas-air combustor and its face temperature was changed by

varying the fuel and air flow rate.

Some characteristics of the heat transfer processes at the sample surface

were investigated. An energy balance at the surface is given as follows:

where a is the surface absorptivity,

e is the surface emissivity,

h is the convection heat transfer coefficient,

cand k is the material's conductivity.

Steady-state surface temperatures were measured under radiant heating

conditions in the apparatus with the sample holder oriented such that 800 mm

was the vertical dimension. The results are plotted in Figure 4 for a blackened

*

(£ % a 'v. 1) inert (calcium-silicate) sample board (Marinite I) and for Douglas

fir particle board. Also shown are the Incident flux-surface temperature ideal

results for a black surface with no conduction loss and h values as indicated, i.e.,

c

’

*Trade name - implies no endorsement by NBS

HEAT TRANSFER CHARACTERISTICS

aq

e

4 4 eo (TSI- t7) + h

c

( 10 )

7
q” = a(T"^SI- T^) + h (T - T.) + h (T - T.) c s ^ s

( 11 )

The departure of the actual measurements from these ideal curves reflects

the radiation and conduction losses for the materials as well as effects

due to decomposition and distortion of the materials under heating which can

result in changes in surface heat flux. The convective heat transfer

coefficient was estimated from [2]

h X

ck 0.13 (Gr^ Pr) 1/3 Gr > 10'

( 12 )

g although the Grashof number could be as low as 10 for the lateral spread

apparatus (Fig. 2, x = 155 mm). For the downward spread apparatus, h was

c measured directly at x = 325 and 575 mm. This was done with the blackened

inert specimen board at thermal equilibrium and subjected to radiant

heating. The h^ values were calculated from Eq. (10) by estimating

the conduction loss as steady one dimensional conduction from front and back

face temperature measurements and a knowledge of the conductivity. These

derived values along with those computed by Eq. (12) are plotted in Figure 5.

The derived values are higher than the theoretical natural convection results.

This is not unexpected since the temperature of the surface is not uniform,

and the disturbances in the flow due to the radiant panel can enhance the heat

transfer coefficient. Also shown is the overall heat transfer coefficient,

h, which includes the derived convective values and the radiation loss as

defined by Eq. (11). This overall coefficient is necessary for the theoretical

application; however, its departure from a constant is clearly shown. Hence,

some appropriate mean value must be used in implementing the theoretical

solution.

8
MATERIALS

The current study included six materials selected for their diverse

characteristics. They included the following:

(1) Douglas fir particle board,

(2) Polymethylmethacrylate,

(3) Rigid low density polyurethane foam (GM-31)

,

(4) Flexible polyurethane foam,

(5) Carpet with an integral pad,

(6) Aircraft lining (honeycomb composite) material.

The objective was to determine whether measurements of ignition and

flame spread on these materials could be described by the analysis under

consideration. It was also of interest to determine how mechanisms not

included in the analysis, such as melting and dripping, delaminating, etc.,

might be interpreted. This report, however, will only consider the results

for particle board. In this way, a test of the analysis would be performed

for a reasonably homogeneous material which is somewhat complex due to its

charring nature during combustion.

The materials were maintained before testing at 55 percent relative

humidity by storing them in a conditioning room or in a desicator. The

particle board was found to have a moisture content of approximately 5 percent

under these conditions. Its other properties were estimated by measurement

or from literature values [3] to be:

3 density, p = 650 kg/m

thermal conductivity, k = 0.110 x 10 ^ [1 + 2.18 x 10~^(T-T^)] kW/m-K

9
specific heat, c = 1.97 [1 + 2.18 x 10 ^(T-T^)] kJ/kg-K

where T is in K, and here T. = 295K.

1

Degradation effects at high temperature will alter these relationships.

Effects of moisture content at this level (5%) are much less significant

than property dependence on temperature [3].

IGNITION

Ignition experiments were conducted with sample face dimensions of

155 X 110 mm. The back and sides were wrapped with aluminum- foil. This was

mounted in the sample holder such that the back side was bounded by 12.8 mm

thick calcium silicate board and the exposed face was 130 x 90 mm. The

sample was mounted at the hot end of the lateral spread apparatus. It is

seen from Figure 3 that the flux was nearly constant over the face of the

2 sample. The flux was varied at the face over a range of 1.5 to 6.5 W/cm .

With the pilot flame on, the sample holder was moved into place to initiate

the radiant exposure. The time to Ignite was then recorded. A definition

of ignition, most relevant to flame spread, would be the onset of sustained

surface burning. Any departure from this was noted.

The onset of ignition may depend on the location and temperature

of the pilot flame. Simms [4] found that the distance from the surface

of a vertical specimen under laminar conditions affected the time to Ignite.

Kashiwagl [5] found that the temperature of a heated wire for an upward

facing horizontal sample had an effect. Different pilot flame configurations

and locations were used in this study. In general each seemed to give

equivalent results for most conditions. Typically when a peculiar ignition

10
behavior occurred, variations with the pilot flame were made to determine

whether the pilot was responsible. If it was, a new pilot arrangement was

adopted, and the anomolous data discarded. In this fashion an optimum

pilot flame was developed and subsequently used. The additional criterion

for the pilot was that it should not provide any heat transfer to the surface

of the specimen. It should only act as a source of heat to the mixture of pyrolysis

products and air. The optimum pilot flame consisted of a premixed flame

positioned above the specimen to intercept the hot boundary layer plume generated

by sample decomposition. For this sample configuration that boundary layer

was expected to be turbulent or in the transition region. The best pilot

configuration consisted of an acetylene (C

2H

2

)-air flame supplied through

two 1.5 mm diameter openings in a ceramic cylinder mounted as shown in

Figure 6. A vertical flange flush with the sample face was included to

promote flame propagation downward through the boundary layer to the material.

Without the flange, a low velocity wake region occurred which retarded or

prevented flashback to the material. The pilot tube was positioned 5 mm

from the flange surface and its conical blue flame extended about 140 mm

horizontally.

The ignition results for the particle board are shown in Figure 7.

Results for various pilot flames are shown. They include variations in

fuel (acetylene, natural gas) and configuration (flange, no flange, and a

vertical pilot displaced from the face of the specimen) . The ignition data

from the flange configuration was developed from the flame spread tests

explained subsequently. The wake effect (no flange) can be seen by the data

which distinguishes between the ignition time of the wake ("upper gases") and

the surface ignition time. Other than this differentiation, the effects due to

pilot flame appear to be contained within the normal scatter of these data. The

11
two lowest flux data points did not result in full surface ignition since the

flame did not propagate to the leading edge of the specimen. The dashed

2 line in Figure 7 at 1.55 W/cm denotes the flux below which ignition would

not occur (q” . )

o,ig^

FLAME SPREAD

The samples for flame spread had a 155 x 800 mm face dimension. Their

back and edge surfaces were covered with aluminum-foil, and they were backed by

a 12.8 mm thick calcium silicate board. Their exposed face in the sample

holder was 130 x 775 mm. Two apparatuses were used so that lateral and

downward spread could be measured on a vertical sample. The initial heat

flux with its corresponding distribution and the application time of the

pilot flame were two conditions varied in the experiments. Flame position

was visually recorded. An extensive series of experiments investigating the

effect of these conditions was done for the lateral flame spread mode. This

was done less extensively in dovmward spread; however, surface temperatures

were measured during those flame spread experiments. The thermocouples were

0.13 mm diameter chromel-alumel wire slightly pressed into the surface of the

material and held in place by drawing the wires out the back of the sample

holder to a junction position. These thermocouples recorded the temperature

rise due to radiant heating bt'fore the arrival of the flame front. As heat

transfer from the flame occurred, followed by ignition, their validity as a surface

temperature measurement diminishes. Figure 8 gives an example of these temperature

measurements for the five measurement positions and their corresponding heat

fluxes in test D-7

12
Table 1 displays the conditions imposed for each of the flame spread

tests. In two experiments, L-17 and D-3, sample ignition did not occur

upon application of the pilot flame. This was apparently due to the charring

of the surface for long pre-heating times. For the downward spread tests

a pilot flame was applied directly above the surface while the pilot configuration shown in Figure 6 was used in the lateral tests. The nature of

the pilot flame is not so critical here as it is in the Ignition experiments

since the primary data of interest is after ignition occurs.

The procedure for assembling the flame spread data begins with recording

the flame front position as a function of time following exposure of the sample

to the radiant panel. For the particle board a well defined flame front

occurred; however, a slightly Inclined or curved front could occur. The front

at the center axis of the board was recorded. These results are shown in

Figure 9 for the tests tabulated in Table 1. The variety of results reflect

the variations in incident radiant flux distribution and in pre-heating times.

These data were operated on to determine the velocity as a function of time

and position. Finally, incident flux data vs. position was taken from Figure 3.

The flame spread velocity as a function of flux is shown in Figure 10. It should

be noted that as flux decreases, time Increases. Consequently as the

flame front slows to extinction, "long time" heating is experienced at "low"

flux levels. The convergence of the data at the apparent extinction flux

2 (^" p) of 0.5 W/cm is indicative of this behavior. However, the Initial

o , r velocities following ignition at "high" flux yield velocities that are not

uniquely related to flux q^. This is clear from Eq. (7). Indeed, plotting

- 1/2 the same data in the form of Eq . (7), i.e. with q'^, gives the results

in Figure 11. The "envelope" curves indicative of large and small heating

times suggests the order of the data. At long pre-heating times the surface

temperature approaches its equilibrium value corresponding to the flux and the

13
velocity approaches its maximum or steady state value. Under short pre-heating

times the flame, spreading from high to low flux positions in the apparatus,

experiences a nearly ambient material surface temperature. The time response

term F(t) of Eq . (7) has not been included here; however, at large time F(t)

- 1/2 -* 1 and q” = q"^ at V =0 according to Eqns. (7-9). The intercept on

2 Fig. 11 for t large is consistent with q” . =1.55 W/cm from Figure 7. o,ig

Evaluation and inclusion of F(t) should help to correlate and perhaps generalize

these results.

CORRELATION OF RESULTS

The framework indicated by Eqns. (7-9) can be used to develop correlations

for the ignition and flame spread data. Also the value and consistency of

the parameters in these relationships can be determined. Ignition was examined

first

The Ignition equation is given by

= F(t) (13)

The function F(t) = 1 - exp(at) erfc from conduction theory is

approximately for (at) < 0.01. This motivated the plot shown in

2 Figure 12. The value 1.55 W/cm was selected for q” , The parameter, a, 5 ^ o,ig. was chosen as 0.0045 s

^ so that F(t) from conduction theory best matched the

data for (at) small, since tiaat is where the semi-infinite conduction model

is most applicable. It is interesting that despite the fact that (at) >> 0.01

the data empirically follows /^with an alternative F(t) selected as

14
F(t) =

0.0504 s t < 393 s

\1, t > 393 s

(14)

Both of these forms for F(t) are now candidates for substitution into

the flame spread equation (Eq. (7)) for particle board. It should be realized

that both expressions for F (t) are deficient for predicting ignition. One

result is logically based in conduction theory but only valid for inert heating

durations, while the other is empirical and needs its generality established.

Nevertheless in applying these F (t) forms to flame spread, they only apply

for a level of temperature much less than This application will now be

investigated

Equation (7) is rewritten as follows:

(15)

The parameter C still needs to be determined; however F(t) from Eq. (14)

or

F(t) = 1 - exp(at) erfc 0.0045 s -1/2

(16)

and

q" . =1.55 W/cm^ (17) o,ig

have been determined. The data in the form of Eq . (15) are plotted in Fig. 13

q^ • F(t) as the abscissa. This has the effect of collapsing the data in

Figure 11 by accounting for the transient heating of the solid by the

radiant panel. The results in Figures 13 and 14 are given for the

15
functions F(t) = 1 - exp(at) erfc /at and F(t) in Eq. (14), respectivelv . Both

functions similarly collapse the data; however, they give slightly different

Results for the flame spread modulus, C, and the minimum flux for flame

spread, q” These are summarized in Table 2. The C values were estimated o,f

- 1/2 from a linear fit in the region where is small, and by initiating the

fit at 1.55 W/cm on the abscissa. The C value for the empirical F(t) is

higher than the values derived from the exact conduction solution on the

long preheat data of Figure 11; however, the variation is within the level

of uncertainty when determining these slopes. From Eq. (7) and the C of

Figure 13, a flame heat flux (q^) was estimated as 6.2 W/cm for a heat

transfer length 6^ = 2 mm (not unreasonable for this mode of flame spread) [6].

Since the use of the correlating function F(t) depends on its ability to

predict surface temperature rise it would be useful to examine its accuracy.

This was examined for test D-3 at two positions. Since ignition did not

occur in that test this represents the effect of the external flux only.

2 Data are shown in Figure 15 for fluxes of 0.97, 1.33, 1.68, and 2.05 W/cm .

The high flux data all show a more rapid increase in temperature at about

300°C. It is believed this is due to the onset of charring near that temperature and a subsequent decrease in thermal conductivity due to vaporization and

charring. Above 400°C the unsteady response of the thermocouples suggest weak

contact with the charred surface. The predicted results based on Eq. (2) are

2 shown for q” = 0.97 and 2.05 W/cm . Variations in h and kpc with temperature

e were accounted for by relationships:

kpc = 0.141 [1 + 2.18 X 10 ^ (T-T^)]^,

h=0.01 [1+8.5x10^ (T-T^)], kW/m^K

(18a)

(18b)

16
with T-T^ < 400°C (T^ = 22°C) . Eq . (18b) Is an approximation to the curve

in Figure 5. The values were computed for reference temperatures of T-T^ =

200°C for q” = 0.97 W/cm^ and T-T . = 400°C for q” = 2.05 W/cm^. The Intent

e 1 e here is not to get an exact result but to account somewhat for these temperature

effects in the linear conduction solution. The corresponding values for

the parameter a are 0.0025 s ^ and 0.0039 s not markedly different from

a = 0.0045 s ^ derived from the ignition data fit of Figure 12. The predicted

temperatures are in reasonable agreement with the measured temperatures except

at high temperatures. A possible decrease in thermal conductivity due to

charring has not been considered in the theory. Indeed this effect could

partially explain the earlier ignition times rather than those predicted for

long times by the inert constant property heat conduction model.

Finally a consideration of flame spread as a function of surface

temperature was made. From the surface temperatures measurements described

earlier in tests D-5 and D-7. Those results are shown in Figure 16.

Equation (7) can also be converted into

= C . h (T. - T ) (19)

f ±g s'

From Eqns. (9), (17) and (18b) T. and h(T. ) can be estimated as ig ig

T. = 395°C

-g

and h(T. ) = 0.042 kW/m^ K

ig

17
3/2 Using C = 160 (nun-s) /J, it follows that

= 0.67 (395 -T ), (s/mm)^^^

t s (20a)

3/2 Alternatively, C = 240 (mm-s) /J yields

= 1.0 (395 - Tg), (s/mm)^^^ (20b)

These relationships should hold down to corresponding to

^ = 0.5 W/cm*^

so that

q’' = h (T ) (T - T.), T. = 23°C,

O , f S S I X

and from Eq . (18b), T , = 214°C. This would be the minimum surface

s ,mxn

temperature to support flame spread on the particle board.

CONCLUSIONS

A measurement technique has been examined for deriving parameters

which provide a means of computing flame spread speed. The result applies

to "creeping” (downward or lateral) spread where flame heat transfer affects

a small region ahead of the advancing flame, and the ambient conditions are

primarily controlled by natural convection and normal atmospheric conditions

This presentation has focused on the significance and interpretation of the

measurements for Douglas fir particle board. The following conclusions can

be drawn:

18
(1) Under external radiant heating, steady-state (long heating tine)

flame spread is complementary to piloted ignition. For particle

board flame spread commences at a critical flux of q” =

2 . 2 q" 0.5 W/cm and approaches an upper limit at q" . =1.55 W/cm . o,f o,ig

This flux is the minimum flux for piloted ignition; ignition

2 (2) times decreasing with flux for q” > 1.55 W/cm .

An inert heating conduction analysis or an empirical result

from ignition data can be used to correlate transient flame

spread data and reduce it to an equivalent steady-state result.

(3) Property variations and heat loss due to radiation are

temperature dependent and need to be accounted for in any

exact analysis. However, neglecting these temperature

effects leads to the evolution of "mean value" results for

the flame spread parameters sought, namely a, C, etc.

These "mean values" may be sufficiently accurate for

estimating flame spread on complex materials.

(4) Except for thermally thin, or significantly reflecting or

transmitting materials, the heat transfer coefficient results

in Figure 5 are likely to be applicable to most materials

burning in air.

(5) A procedure can be executed to determine the following

parameters

^o,f’ minimum external flux for flame spread

^s,min’ minimum surface temperature for flame spread,

the minimum external flux for piloted ignition.

19
T. , an effective ignition temperature

ig

C, a flame heat transfer modulus such that

steady

state

( 21 )

and

- 1/2 V. ' = Ch(T. - T ), T

f ig s < T < Ts ,mln — s — ig ( 22 )

where h is evaluated at T

ig’

C, q" . and q” . can be derived from flame spread data alone o,f ^o,ig

provided the material is preheated to thermal equilibrium.

Since a specific preheat time is not always obvious and since

ignition problems can arise, transient flame spread data may

need to be analyzed. In that case, ignition data is necessary

to determine q" . and to estimate a or F(t) in order to corre o,ig

the transient data.

This study was supported by the Fire Safety Branch of the Federal

Aviation Administration Technical Center under DTFA 03-81-A-00141 . Thor I.

Eklund served as the technical monitor. We are also grateful to the

contributions of A. F. Robertson, who designed the flame spread apparatus.

ACKNOWLEDGEMENT

20
REFERENCES

1. Quintiere, J., "A Simiplif ied Theory for Generalizing Results

from a Radiant Panel Rate of Flame Spread Apparatus", Fire and

Materials, Vol. 5, No. 2, (1981).

2. Krieth, F. , Principles of Heat Transfer , 2nd Ed., Inter. Text

Book Co., Scranton, Pa. (1967).

3. Koch, P., Utilization of the Southern Pines , Agriculture Hdbk.

No. 420, Vol. I, U.S. Dept. Agriculture Forest Service ().

4. Simms, D.L., "On the Pilot Ignition of Wood by Radiation",

Combustion and Flame , Vol. 7, No. 3, (Sept. 1963).

5. Kashiwagi, T., private communication, Nat. Bur. Stand. (1982).

6. Fernandez-Pello, A.C. and Santoro, R.J., "On the Dominant Mode of

Heat Transfer in Downward Flame Spread", 17th Inter. Combustion

Symp., The Combustion Institute (1978).

21
Table 1 Flame Spread Test

Douglas Fir Particle Board

Test

Flux to Sample

at 50 mm position

(W/ cm^)

Pre-Heat Time

(s)

Ignition Time

(s) Plot Symbol

L-1 5.2 0. — (1)

L-2 5.2 0. 24 (2)

L-16 5.0 0. 30 (f)

L-6 4.0 40. 57 (6)

L-7 4.01 40. 62 % (7)

L-4 2.97 70. 120 A. (4)

L-5 2.95 80. 116 (5)

L-3 2.95 110. 94 (3)

L-21 2.98 140. 141 (m)

L-20 2.96 150. 151 (k)

L-22 2.98 200. 220 (P)

L-23 2.9 250. 263 (r)

L-9 2.6 120. 137 (9)

L-8 2.57 120. 128 (8)

L-13 2.3 240. 246 (d)

L-12 2.19 180. 183 (c)

L-14 2.26 300. 300 (e)

L-10 2.0 0. 225 (a)

L-11 2.0 0. 240 (b)

L-18 2.0 0. 166 (g) * L-19 1.7 0. 292 (h) * L-17 2.0 480. none - D-4 3.0 600. — (t)

D-5 3.0 600. — (u)

D-6 3.0 600. — (v)

D-7 3.0 100. — (w)

D-3 3.0 1000. none -

* Not pre-conditioned in constant humidity room (sample stored in Building 205 - relative humidity on test date ^ 44%)

NOTE: L = Lateral flame spread test

D = Downward flame spread test — = Not recorded

22
Table 2

Summary of parameters for particle board by different analyses

Analysis Figure

Flame Spread

Modulus

C

1/2 2

s cm mm W

Minimum Flux

for Ignition

4

" • o,ig

(W/cm^)

Minimum Flux

for Spread

^C.f

(W/ cm^)

Long pre-heating

time 11 1.7 1.55 0.5

F(t) by Eq. (16) 13 1 .

1.55 0.4

F(t) by Eq. (14) 14 2.4 1.55 0.5

23
Figure 1. Components of flame spread model

24
Figure 2. Schematic of experimental apparatus

25
Figure 3. Normalized radiant flux distribution

,

DISTANCE

ON

SPECIMEN

|mm)
=

0.01

kW/m^K

Figure 4. Surface temperatures at thermal equilibrium

T [—T

I

I II

I I\

I I

I

I

I

I

! [~T I

'

I I

i

I

I T CD

LCD

LO

un

CO

CD

CO

uo

CN

CD

CM

uo

ir>

l3ol 30niV03dN3i 33V3UnS

27

FLUX

(kw/m^l
Figure 5. Heat transfer coefficient

(M-ziu/M) 1N3I0IJJ300 a33SNm 1V3H

28

SURFACE

TEMPERATURE

(°C)
All

dimensions

in

mm

I'igure 6. Pilot flame configuration
800

700

600

500

400

300

200

100

0

Figure 7. Tic\e Lo ignite for particle board

o flCETYL£NE-RlR PILOT PT TOP - NO FLPNGE

® UPPER GPS IGNITION C PCETYLENE-P 1 R PILOT)

A NPTURPL GPS-PIR PILOT PT TOP - NO FLPNGE

« UPPER GPS IGNITION (NPTURPL GPS-PIR PILOT)

a PCETYLENE-P I R VERT I CPE PILOT

* FLPME SPREPD TEST (PCETYLENE -P I R PILOT)- FLPNGE

P

0

1 2

_ VS: O mJ O O .o o

8

Hi

3 4

EXTERNAL FLUX (W/cm^

)

6

30
Figure

8.

Surface

temperature

rise

preceding

flame

arrival

for

particle

board

TEST

#7

Vi

PARTICLE

BOARD

Ooo

C3

CDo

CO

lO

CO LU

CDO

CDO

CO

CD

CD

CM

lOol 3tinivtiadN3i

31

900

1000
800

700

600

500

400

300

200

100

0

Figure 9. Flame front movement for particle board tests.

i 1 1 2

i 1 6

n 2 7 6

i2 1 76 m 5 Lk

fl 2 76 m

n 2 6 mM<5P 3 r d ag

i 12 76 rn 8^ r d<^ a b

i 2 7B SWS p r d8g a b e

u

i 12B P r ag Ojjb u ^ a 0 p @-<dg

u

ua b

210'

i ns

21

1 10

6

2 7

u

5^

c

gj^9

9

9

i a b

9 gu d a b

u

g

ago da b h

crb

a b

a b

u

1^

d

c

a

5 8

dd

a

h

A

a

ee

V

I ^div

V

tr/

e

A*-' U , TU V

i u V

lu

125 250 375 500

TIME |s)

625 750

32
8

-

7

-

6

5

4

3

2

1

0

Figure 10. Flaine spread velocity lor particle board tests

7

5

2

h

8 9

P

2

12 3 4

FLUX (W/cm^l

33
8

7

6

5

4

3

2

1

0

Figure 11. V

- 1/2

f as a function of flux for particle board

1

FLUX (W/cm^l

34
Figure 12. Correlation of ignition data for particle board

OO• CD• Tj*

• CVJ

• CD O o CD CD

8b/3!‘0b iiT

35

0.25

0.50

0.75
Figure 13. Correlation for flame spread, F(t) by Eq . (16)

6

-

36
qeF(t) (W/cm^l

37
1.68

W/cm2

Figure 15. Surface temperatures due to radiant heating for particle board

O

CD

lO LO LO

CO

CD

CD

CO

LO

CNJ CO LO CD

CN4 'T- — LO

(3ol 38niVd3cll/tl31

38

900

1000
•

Test

D-5

o

Test

D-7

Figure 16 Flame spread velocity in terms of surface temperature for

particle board

CO

CO

CSI CO

ooo

CM

<=> Tf

CM

CM

CO

CO

CM

CO

c»

cz>

CO CM CM

^ ^

(s/uuu) z/^.(xi|0013A 3WV1J1

39

SURFACE

TEMPERATURE

(°C|
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

4.

BIBLIOGRAPHIC DATA

SHEET fSee instructions)

1. PUBLICATION OR 2 REPORT NO.

NBSIR 82-2557

. Performing Organ. Report No. 3.

TITLE AND SUBTITLE

PubI ication Date

August 1982

MEASUREMENT OF MATERIAL FLAME SPREAD PROPERTIES

5. AUTHOR(S)

J. Quintiere, M. Harkleroad, D. Walton

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State. ZIP)

Federal Aviation Administration

Technical Center

Tilton Road Atlantic City, N.J. 08405

10. SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

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

bi bliography or literature survey, mention it here)

A concept was examined for measuring flame spread parameters suitable for predicting the performance of a material in fires. The study examines a radiant

panel test apparatus used to measure downward and lateral flame spread, and

ignition. An analysis of data from tests of Douglas fir particle board is

presented. A procedure has been identified for measuring specific parameters

useful in the general prediction of ignition and flame spread for complex

materials

12. KEY WORDS (S/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Fire models; fire tests; flame spread; ignition; particle board

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

Unlimited

1 1 For Official Distribution. Do Not Release to NTIS

[jn Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

46

15. Price

Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $7.50

USCOMM-DC 6043-P80