NBSIR 73-199

Experimental and Analytical Studies

of Floor Covering Flammability with

a Model Corridor

Wells Denyes

Research Associate

Man-Made Fiber Producers Association, Inc. Washington. D. C. 20036

and

James Quintiere

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1973

Final Report

o

V. Q

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

o

NBSIR 73-199

EXPERIMENTAL AND ANALYTICAL STUDIES

OF FLOOR COVERING FLAFilMABILITY WITH

A MODEL CORRIDOR

Wells Denyes

Research Associate

Man-Made Fiber Producers Association, Inc. Washington, D. C. 20036

and

James Quintiere

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1973

Final Report

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

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director

PREFACE

This report describes one of several concepts examined at the

National Bureau of Standards for a floor covering f lammability test which

could be related to performance in real fire conditions. We believe that

this work provides substantial support for the critical energy concept as a measure of hazard potential for floor coverings. A test method based on this concept but substituting a radiant panel as the energy flux source

is now being investigated in detail at NBS.

J. E. Clark

Chief, Fire Technology Division

June 1973

iii
CONTENTS

Page

X. INTRODUCTION . 1

2 • OBJECTIVE •••••••••«•••«•••.•«• f • • • • • 2

3. EQUIPMENT AND INSTRUMENTATION. 2

4. EXPERIMENTAL RESULTS ...... . 4

4.1 General Description of Phenomenon ...... 4

4.2 Bimodal Distribution of Results ..... 7

4.3 Effect of Variables 11

4.3.1 Ceiling Height 11

4.3.2 Model Width 17

4.3.3 Heat Input 17

4.3.4 Air Velocity 21

4.3.5 Underlay t . 21

4.3.6 Other Variables. . . ...... 27

5. FLOOR COVERING TESTS ............ . 27

6. QUANTITATIVE EVALUATION OF CONTRIBUTING FACTORS , . 39

6.1 Ignition Flame. .................... 39

6.2 Air Flow 47

6.3 Energy Release Rate from Floor Covering 53

6.4 Radiant Preheating 63

6.5 Heat Balance Analysis ..... 72

7. OVERALL ANALYSIS AND SCALING RELATIONSHIPS 77

8. CONCLUSIONS. ....... . ..... 83

9. SUGGESTED TEST METHOD 88

APPENDIX A. REVIEW OF LITERATURE ON CORRIDOR AND DUCT FIRES . . 90

APPENDIX B. RADIANT PREHEATING CALCULATIONS . . .

f 94

APPENDIX C. ANALYSIS OF A LINE SOURCE PLUME IN A CROSSWIND. . . 98

REFERENCES ••••••• ••••••«e«a*«««**«*«« 103

iv
ILLUSTRATIONS

Page

3- 1 Model corridor apparatus V . . 3

4- 1 Factors influencing flame spread .......... 6

4-2 Distribution of results 8

4-3 * Typical flame spread characteristics . . 9

4-4 Some flame spread results for N-2/U. ........ 10

4-5a Flame spread curves. . . ......... 12

4-5b Flame spread curves ....... 13

4-6 Ceiling temperature profiles at various ceiling

heights (500 BTU/min) ........ 15

4-7 Ceiling temperature profiles at various ceiling

heights (1000 BTU/min) 16

4-8 Effect of model width on flame spread 18

4-9 Effect of heat input on ceiling temperature. .... 19

4-10 Effect of flame spread on ceiling temperature. ... 22

4-1.1. Effect of air velocity on ceiling temperature. ... 23

4-12 Effect of air flow on flame spread 25

4-13 Effect of under-lay on flame spread 26

6-1 Burner flame plume 30 seconds after ignition

V = 100 fpm, E = 500 BTU/min. 40

6-2 Burner plume characteristics ..... 41

6-3 Thermal-flow field of burner flame plume ...... 42

6-4 Example of flame spread for melting carpet pile

fibers 43

6-5 Example of flame spread for charring carpet

pile fibers . ......... 44

6-6 Initial flame spread velocity for A-4 and N-5. ... 45

6-7 Initial flame spread velocity for W-l, A-2,

and P-2 46

6-8 Nylon carpet flame displaying three-dimensionel

flow pattern. . . .......... 49

6-9 Vertical gas temperature profiles. ......... 50

6-10 Effect of air flow on flame spread ......... 51

6-11 Flame propagation map 52

6-12 Energy release characteristics of carpets based

on the NBS rate calorimeter 54

6-13 Energy release—comparison of NBS rate

calorimeter and oxygen bomb 55

6-14 Carpet incident heat flux as a function of

flame position 65

6-15 Calculated incident radiant heat flux. ....... 66

6-16 Flame spread as a function of calculated

incident radiation 67

6-17 Carpet preheating characteristics 69

6-18 Flame spread—radiation analysis .......... 70

6-19 Calculated radiant flux at flame front ....... 71

v
6-20 Theoretical flame spread with radiant heating ... 73

6- 21 Sensor locations for energy balance analysis. ... 76

(>-22 Some results of an overall energy balance 78

7- 1 Simplified preheating model 79

7-2 Partial scaling applied to model corridor

flame spread for nylon carpet N-5/U 85

7-3 Partial scaling applied to model corridor

flame spread for acrylic carpet A-4/U. ..... 86

A-l Model mine fire characteristics . 91

A-2 Estimated energy release rate from fires of

various occupancies 91

C-l Plume coordinate system 98

C-2 Plume measured results for 6' vs. Fr. . . . . . . . 102

vi
, NOMENCLATURE

a = plume thickness

A = area

B = mass transfer number '

0^ = specific heat at constant pressure

E = energy release "by combustion

= geometric shape factor, floor to ceiling

Fn = geometric shape factor, floor to surroundings

Fr = Froude number, defined by Eq. 6-2

g = gravitational force per unit mass, or convective mass

transfer coefficient

h = convective heat transfer coefficient

H = height

AH^ = heat of reaction per unit mass of fuel at reference

temperature

i = enthalpy per unit mass

^Nrap

= enersy required to vaporize fuel per unit mass of fuel

Is, - thermal conductivity

L = length

m = rate of mass flow

m , = mass

P = perimeter

q = heat transfer rate

r = mass of oxidant per unit mass of fuel

s = plume coordinate

t = time

T = temperature

vii
u = plume velocity

V

ent

= en"t ra-inment velocity

V = velocity

W = width

x,y = horizontal and vertical coordinates

= mass fraction of oxidant

o

a = thermal diffusivity, entrainment constant, parameter defined

by (6-9)

3 = entrainment constant

Y = thermal inertia, kpc

p = density

Ap = density difference

6 = thickness

6 = angle

0 = dimensionless temperature

t = dimensionless time

Subscripts

b ~ refers to "burning carpet

B - refers to gas "burner

c - refers to carpet

f - refers to final state

F - refers to flame

g - refers to gas

1 - refers to initial state

viii
L - refers

r - refers

s - refers

00 - refers

Superscripts

(

) ' - indicates

( )" , - indicates

( ) - indicates

to heat loss

to radiation

to surface

to ambient condition

per unit length

per unit area

average
EXPERIMENTAL AND ANALYTICAL STUDIES OF

FLOOR COVERING FLAMMABILITY WITH A MODEL CORRIDOR

Wells Denyes

and ' James Quintiere

ABSTRACT

An experimental model corridor facility vas designed, constructed, and

instrumented. The facility examines flame spread over floor covering

materials in a small scale corridor under a forced air flow condition.

A gas burner flame serves as the ignition source. A study vas made of the factors influencing flame spread in the model

corridor. These factors included energy release rate of the ignition

source, air velocity, and model corridor geometry. Twenty-six carpet

materials and 5 other floor covering materials -were studied in the model

corridor, and 369 flame spread runs -were conducted.

It vas found that flame spread behavior in the model corridor involves

either a rapidly accelerating flame front vhich propagates the full 8 foot

length of the test section ( "flameover" ) , or involves a decelerating flame

front vhich results in extinction a short distance from the ignition

source. Radiant heating of the floor material due to hot products of

combustion heating the ceiling is a significant factor in causing flameover. Carpet assembly vas found to affect flame spread more significantly

than pile fiber type.

The data have been analyzed to determine quantitatively the effects of the

factors influencing flame spread. Scaling relationships have been

presented to attempt to extrapolate the model corridor results to full

scale corridor fires.

Finally a procedure has been suggested for using the facility in a floor

covering flammability test method. The procedure is based on determining

the minimum energy input rate to cause flameover.

Key words: Flame spread; floor covering materials; model corridor % scaling laws; test method.

x
1. INTRODUCTION

Historically, carpets and rugs have not been considered to be

particularly hazardous materials in either residential or commercial

use. Meaningful statistics are difficult to obtain because there are

so few cases in which the involvement of carpets and rugs in fires is

clearly defined. However, during the past 15 years a revolution has

taken place in both the manufacture and use of carpets. The simultaneous

introduction of the tufting process and development of high performance,

man-made fibers has made quality carpet available at low cost with the

result that carpet usage has expanded exponentially. With billions of

square yards of carpets in use, two inevitable consequences began to

emerge: l) some carpet constructions that could be relatively easily

ignited appeared on the market and 2) vast exposure greatly increased

the probability that carpets could be involved in major fires. With

expanding usage of carpets in institutional and public buildings, some local, state, and federal authorities established arbitrary flammability

standards

.

On April l6, 1970, the Department of Commerce promulgated the first

national standard to control the flammability of carpets, DOC FF 1-T0[l].

It became effective one year later. This standard was developed by the

National Bureau of Standards in cooperation with the carpet and rug

industry. It is designed to eliminate from commerce those carpets that can be easily ignited by small ignition sources such as cigarettes,

matches, glowing embers from fireplaces, or minor electrical short

circuits. This standard was supported by both government and industry

for the following reasons: l) a national flammability standard is in

the public interest, and 2) the proposed standard is appropriate on the

basis of simplicity, reproducibility, and effectiveness in screening out

easily ignitable materials

.

During this same time there was a growing effort to develop a more

rigorous standard for carpets used in institutional buildings.. National

attention was focused on this effort on January 9» 1970, when a fire

took the lives of 31 elderly patients in a nursing home in Marietta,

Ohio. Carpet has been claimed to be at least partially responsible for

the spread of fire. This tragedy precipitated further activity to set

additional flammability standards for carpets used in institutional and

commercial buildings.

The most widely adopted method has been the ASTM E 8U-68 Tunnel

Test [2]. Although this method has been widely used to classify the

surface burning characteristics of building materials, it has not been

shown to be relevant when used for floor covering materials. Among

other methods under consideration are the E 84 Tunnel using floor

mounting of the samples, U. L. Subject 992 Floor Covering Chamber Test

[3], ASTM E 162-67 Radiant Panel Test [U], and the Armstrong Flooring

Radiant Panel [5]. At this time none of these methods has been shown to

be repeatable and reproducible, and a reliable measure of the hazard

contribution of floor coverings to building fires.

1

)
Experts in the fire field often say that the problem of flame spread

in buildings may not be solved until adequate detection and suppression

systems are developed and incorporated into buildings codes. Many

groups are urging that fully automatic sprinkler systems be required in

public buildings. Until this has been accomplished there remains the

need to define the nature of hazard presented by carpet and other floor

covering material in building fires and to develop a test method to

measure hazard potential. Recognizing this need, the National Bureau

of Standards and other organizations initiated programs to study the

burning characteristics of these materials in full scale environments.

The results of these programs should make it possible to develop a test

method that relates to actual .hazard

.

2. OBJECTIVE

With this need for a floor covering flammability test method

directed specifically towards carpets to be used in corridors and

exitways of institutional buildings, a Research Associate Program was begun at the National Bureau of Standards in July 1971. This program

was carried out under the sponsorship of Man-Made Fiber Producers

Association, Inc. and with the cooperation of the Carpet and Rug

Institute. The objective of this program was to develop a laboratory

scale test procedure which would provide a high degree of confidence in

prediction of the flammability and flame propagation characteristics of

carpeting in full-scale real-life situations.

3. EQUIPMENT AND INSTRUMENTATION

A model corridor facility was designed and constructed in Building

65 of the National Bureau of Standards in Washington, D. C. The

facility was designed with a test or burning section eight feet in • length, four feet in width and four feet in height. A moveable wall and

ceiling were used so that the cross-sectional dimension could be varied.

Construction material for this section was 3/8 inch thick asbestos board.

A curb was installed on each side of the test section which served to

hold the test material in place and to inhibit edge burning effects.

The air handling system was designed so that air velocity could be

varied from 50 to 300 feet per minute. The system is capable of

providing a uniform, stable air flow with little change in velocity

even during a fire test.

Heat input to the system is provided by a diffusion flame gas

burner which is mounted in 'the center of the upstream end of the test

section. The burner flame impinges on the floor mounted test sample.

Heat input can be varied up to 2000 BTU per minute. A schematic diagram

of the model corridor facility is shown in figure 3.1.

A 20-channel data acquisition system was assembled so that temperatures and energy fluxes could be automatically monitored throughout the

program. Outputs from thermocouples, radiometers and total heat flux

meters were scanned by the system. A computer program was used to convert

2

the paper tape output from the system into time dependent printouts.

Locations of sensors were changed from time to time throughout the

program so that the greatest amount of information would be available.

The test procedure used in most of the experiments is to run with

the gas burner "on", impinging on the carpet surface, for 12 minutes.

An additional 12 minutes with the burner "off" follows. During the

entire 2h minutes the position of the flame front is observed and

recorded. This procedure is similar to that used in the U.L. Subject 992

Floor Covering Chamber Test and investigation of many or the variables

was motivated by this test.

A detailed description of the construction, instrumentation and

operation of the model corridor facility is contained in the report,

"A Model Corridor for the Study of the Flammability of Floor Coverings",

by Denyes and Raines [6].

k. EXPERIMENTAL RESULTS

k.l General Description of Phenomenon

The phenomenon that is being investigated here can be described as unsteady flame spread over a porous composite material in a hydrodynamic

entrance region of a duct with a wind blown diffusion flame as an ignition source. Using the facility described, a flooring material is

ignited by the gas burner under the influence of a relatively steady

laminar air flow in the duct and flame propagation is observed and

examined. Propagation usually takes the form cf a uniform flame spread

velocity while under the influence of the burner flame. This is then

generally followed by a decrease in flame spread velocity which is subsequently followed by either extinguishment or more rapid flame spread.

The initial conditions, namely air flow, duct cross-sectional dimensions,

and burner gas flow, along with the nature of the floor covering assembly

establish whether the fire will be propagating or non-propagating. The

term "flameover" has been employed to describe the outcome of a rapidly

propagating accelerating fire which runs the full length of the test

section.

From a practical viewpoint, the nature of the test has at least a qualitative semblance of real life. The burner diffusion flame

simulates a real fire, such as a fully developed room fire exposure

through an open doorway to a corridor with a floor covering. The test

duct geometry simulates a corridor with a unidirectional forced flow air

ventilatron pattern. Hence the system is composed in such a manner to

reflect a realistic hazard configuration which has the potential for

resultant rapid flame spread. Although the physical set-up is a rational

reflection of a real life configuration, that alone does not suffice for

its acceptance as a quantitative representation of full scale reality.

Some questions and issues remain for consideration. Two subtle points

to consider are the nature of air flow in a "typical" building corridor,

and the fact that the primary ignition burner has a prescribed fuel

output as opposed to the natural time dependent burning rate of a real
fire. Ultimately all of. these issues will have to be addressed before

one can establish by design a correlation between a laboratory

flammability test and the corresponding real life hazard.

Returning now to the phenomenon under investigation in this study,

the factors influencing flame spread are portrayed schematically in

figure h-1. In order for the flame to propagate, heat transfer at the

leading edge of the flame front must be sufficient to raise the energy

level of the floor covering material so that volatilization can occur and a combustible gas mixture can form. In the case of those

materials that pass the Pill Test this forward heat transfer is not

sufficient to propagate a fire. However, in the model corridor the

forward heat transfer is augmented by the burner plume and feedback

from heated surroundings. Also air flow, Voo

} affects the inclination

of the burner flame plume and the inclination of the leading edge of the

floor flame. This air is entrained and mixed in the combustion zone and this mixing process basically determines the extent of the combustion

zone.

At 'the initiation of a model corridor test the floor flame moves

under the direct influence of the burner flame plume. Radiant and

convective energy is transferred from the burner flame plume which

promotes a steadily spreading floor flame. Once the floor flame emerges

from the direct influence of the burner, it tends to decrease in

velocity. In this region continued flame spread is strongly dependent

on energy transfer from the surroundings. The rising plume impinges on the ceiling and results in a heated ceiling downstream of the flame

front. The gas temperature in the duct downstream of the flame tends to

be stratified, and .radiation tends to be the dominant heat transfer mode

to the floor covering material beyond several inches from the floor

flame. As flame spread becomes rapid and the flame zone grows, the

level of gas temperatures across the duct increases and convective

heating of the floor material can then become significant. Flame spread

V^, and burning rate, m^ , both can be simply related as:

[net heat transfer rate to fuel]

[energy required to vaporize fuel]

Burning rate depends on heat feedback to the burning material and heat

losses from the fuel bed. An increasing burning rate promotes higher

plume and ceiling temperatures. This in turn leads to increasing

radiant flux levels to the floor (preheating) raising the "effective"

floor temperature, T . Heat transfer, Qp, just ahead of the flame front

raises the fuel to its "vaporization" temperature, T , to sustain

flame spread. The additional energy required to vaporize the fuel has

been reduced from its initial value due to preheating. The entire

process is transient, leading to an accelerating propagation rate or extinguishment. Before continuing with a more detailed analysis of the

components of this model corridor study, some comments on past related

work will.be made. A review of the literature on fire propagation in

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model mine tunnels and "building corridors [7-15] is presented in Appendix

A. Several conclusions can be drawn from these studies:

1. Sustained flame propagation depends on the energy release of

the ignition source.

2. Steady-state fuel-rich flame propagation depends on the velocity

of forced air flow into the duct.

3. Flame spread is more likely to occur in ducts and corridors

which have combustible wall and ceiling linings than combustible

floor materials.

h. No single flammability test has been demonstrated to express the

true hazard of floor materials in building corridors.

4.2 Bimodal Distribution of Results

Results of this work and review of past experimentation both

suggest that duct fires are bimodal in nature. Depending on initial

conditions the fire will be either propagating or non-propagating. If a propagating fire develops, it will have the potential of rapid

acceleration and involvement of the total duct length. Results of the

experimental program in the model corridor confirm this bimodal

distribution.

A total of 369 floor covering tests have been made in the model

corridor. The results of these tests, illustrated graphically in

figure h-2, show this bimodal distribution. Over 90% of the tests

resulted in either flame spread of k feet or less or flame spread the

entire 8 foot length. Figure h-3 illustrates the flame spread modes

observed in the majority of tests. In the ignition zone a linear flame

spread rate occurs which is dependent on the heat input from the burner

and on the material 'being tested. Just beyond influence of the burner,

in the flame spread zone, the burn rate normally decreases. It is

within this zone that heat flux conditions develop that will result in

either an accelerating rate of flame spread leading to flameover or a decelerating flame spread. In many cases the decelerating flame front

will extinguish.

Although more than 90% of the tests demonstrate one of the two

described flame spread modes, an explanation is needed for the apparent

anomalies—those that result in ilame spread distances greater than

four feet but less than eight feet. In most cases it was found that the

initial parameters were just below the critical conditions that would

result in flameover. For example, as illustrated in figure h-h , carpet

assembly N-2/U* in a model 2h in. x 11 in. using 100 feet/minute air

flow and 600 BTU/min heat input burned at a fairly uniform rate for the

entire 2h minute test time. When initial conditions were increased in

severity (750 ETU/minute) flameover occurred. When initial conditions

^Notation defined in table 5-1 and Section 5, page 29.
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12

TIME (min)

Some flame spread results for N-2/U.

10
were decreased in severity. (-500 BTU/minute) a decelerating flame developed

and the carpet flams extinguished.

Figures U-5a and '4-5b show flame spread curves for many of the

materials tested. Most illustrate the bimodal characteristics described.

Additional flame spread rate curves are referred to in other sections of

the report

.

These results suggest that the flammability performance of floor

covering materials in a duct or model corridor should be dependent on whether or not conditions develop that lead to total involvement of the

sample. They suggest that a hazard index that is either distance or time dependent may not be appropriate. Therefore, the effect of variables

and testing procedures that will be discussed are based on the question,

"Does flameover occur?"

U.3 Effect of Variables

An initial experiment was carried out using one carpet (A-2) to get

a preliminary indication of the effects on flame spread of model dimensions,

ajlr velocity, heat input and the use of an underlay. The results of this

2 factorial experiment are shown in table h-1 . Analysis showed that

the effects of model dimensions, heat input and underlay were all

significant at the 95% confidence level. The effect of air velocity

appeared uncertain.

It was in this and other early experiments that the bimodal

distribution of results was first detected. With this fact and an understanding of the factors influencing flame spread, it became possible

to determine the effect of the selected variables. Radiant preheating

of the carpet assembly ahead of the flame front is dependent on ceiling

temperature. Therefore, ceiling temperature will be used as the primary

indicator for impending flameover. To establish a fixed reference,

blank runs were used to illustrate the effect of variables on ceiling

temperature distribution.

h.3.1 Ceiling Height

To determine the effect of varying ceiling height, blank runs (no

carpet) were made and ceiling temperatures recorded after a steady state

had been reached (about five minutes). Examples of these data are shown in figures h-6 and k-J . As was anticipated, ceiling temperatures

increased as ceiling height was reduced. This indicates that as ceiling

height is lowered, the chance of flameover occurring is greater. This

is confirmed by substantial data that will be discussed later in this

report

.

During the testing to determine this relationship it was found that

with low ceilings (i.e. 11"), very high ceiling temperatures occurred

locally in the region 12 to 18 inches from the burner. It was observed

that the luminous burner flame plume tended to approach the ceiling in

this region. With higher ceiling a much more uniform temperature

11
FLAME SPREAD CURVES

MODEL SIZE 24" X ll"

HEAT INPUT- 500 BTU/min

AIR FLOW- lOOft/min

0 4 8 12 0 4 8 12

BURN TIME (min)

Figure 4-5a. Flame spread curves.

12
FLAME SPREAD CURVES

90

A-2/U

60

30-

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A-2

MODEL SIZE 24" XII"

HEAT INPUT-500BTU/min

AIR FLOW- iooft/min

8 12

90r60

30 N-3/U

N-4/U

N-4

12 0 4

BURN TIME (min)

8

Figure 4-5b. Flame spread curves.

13
- TABLE h-1

EFFECT OF SELECTED VARIABLES ON FLAME SPREAD

CARPET - A-2

(Acrylic

)

l e st

CFT No.

Dimension

(W f x H'

)

Air

(Ft/min)

bas

(BTU/min)

Underlay Results*

3 k x h 100 500 Yes 15"

h

it it No 10" •

2

ii 1000 Yes 26"

1

ti II No 1 21"

7 200 500 Yes 18"

6

it II No 11"

8

ti 1000 Yes 29'»

5

ii II No 18"

12 2x1 100 500 Yes (3::U0)

21 II II No 19"

** II 1000 Yes

10 II It No 38"

26 200 500 Yes 57"

25

ii II No 10"

29 n 1000 Yes j (2::51)

2U it II No 61"

*Result s reported in inches burned if f lameover did not occur or in time

(min::sec) to f lameover.

**Experiment not run.

14
15
16
profile occurred. This may suggest a lover limit to ceiling height to

achieve more realistic scaled conditions.

it. 3. 2 Model Width

The width of the test section was also found to influence flame

spread behavior. Pairs of runs were made in which the only parameter

varied was model width. In every case flame spread was greater in the

narrower width and in several cases, as illustrated in figure 4-8,

flameover occurred in the narrower width model. In this figure it is

noted that flame spread rate is very similar during the first 2 1/2.

minutes, but during this time the ceiling temperature had become higher

in the narrower (24") model. At this time the flame front began to

accelerate, ceiling temperatare rose further and flameover occurred at

3::36. In the wider (48") model an accelerating flame front did not

develop and the carpet flame extinguished at 4::57 at a distance of 45".

It should be noted that throughout the experimental program the same gas burner was used. This means that burner width was not scaled

with model width. Had this been done, model width might have had a somewhat different influence on flame spread characteristics.

4.3.3 Heat Input

Heat input from the burner was varied over a wide range during the

program. As expected, increasing heat inputs caused higher ceiling

temperatures as illustrated in figure 4-9.

Tables 4-2 and 4-3 illustrate the effect of both ceiling height and

heat input. In each experiment the carpet assembly, wall separation,

and air velocity remained constant. As the test conditions were increased

in severity (conditions causing higher ceiling temperatures) by either

increasing the heat input or lowering the ceiling height the distance

burned increased gradually up to the point at which flameover occurred.

If test conditions are further increased in severity, time to flameover

decreases

.

The total heat released in the system consists of two factors; heat

input from the burner and heat released by the carpet or floor covering

system. It was found that, with any one carpet assembly, as gas supplied

to the burner increased the area of carpet burned in the ignition zone increased. No other factor influenced the area of carpet burned in the

ignition zone. This suggests that the two sources of energy vary directly,

so if the controlled energy supply (heat input from burner) is varied the

uncontrolled energy supply (heat released from carpet during the early

stage of a test) will vary directly. It must be recognized, however,

that different floor coverings do have different energy release rates

which is a part of the reason for their different flammability behavior.

Having established that the two energy sources vary directly, it was necessary to determine the relative magnitude of the two. Experimental

runs were made to compare ceiling temperatures both with and without a 17
TIME (min )

Figure 4-8. Effect of model width on flame spread.

18
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19
TABLE 4-2

EFFECT OF CEILING HEIGHT AND HEAT INPUT

ON THE EXTENT OF BURN OR TIME OF FLAMEOVER - CARPET A-4/U

Air - 100 Ft/min Model Width - 24"

CEILING HEIGHT

11" Ik" IT" 23"

H

pq

H

Uoo

1+50

500

600

750

1000

1250

1500

2000

21"

22"

(5::39) 19"

22"

(5::2U)

(U::58)

16"

73"

(3::36)

(2::U0)

17"

32"

60"

70"

TABLE 4-3

EFFECT OF CEILING HEIGHT AND HEAT INPUT

ON THE EXTENT OF BURN OR TIME OF . FLAMEOVER - CARPET N-5/U

Air - 100 Ft/min Model Width - 24"

CEILING HEIGHT j 11"

Ik" 17" 23"

HEAT

INPUT

(BTU/MIN)

300

Uoo

500

600

750

1000

1250

1500

1750

2000

23"

(17:: 08)

(11: :02)

(9::^0)

(6::32)

13"

(19::03) 28"

19"

90"

(7::2>0

25"

38"

38"

kk"

65"

20
burning carpet. An example .of these data is shown in figure 4-10. At

two minutes,, the ceiling temperature 2k" from the "burner for the one with

carpet was about 1T0°C (l40°C above the ambient). At the same time the

ceiling temperature for t'he ~b lank" "run was 100°C (T0°C above ambient).

This indicates that the energy contribution from the carpet is quite

comparable to that from the gas fuel source. Once an accelerating flame

front develops the heat release from the carpet assembly becomes dominant.

4.3.4 Air Velocity

The effect of air velocity on flame spread was investigated in a similar manner. Ceiling temperature profiles, as illustrated in

figure 4-11, show that as air velocity increases ceiling temperatures

decrease. This change in ceiling temperature, however, is quite small

at velocities of about 100 ? feet per minute and lower. Table 4-4 and

figure 4-12 show the results of one experiment carried out to determine

the effect of air velocity. Using the same carpet assembly (N-5/U)

and model size (24" x 11") runs were made with different heat inputs over a range of air velocities. In each series a critical air velocity

range was found in which the chance of flameover occurring was greatest.

As velocity is increased above this range, the flame spread was less

severe. At low velocities (below 75 to 100 feet per minute) severity

of flame spread was less. This suggests as indicated earlier, that the

mechanism of flame spread may be different at low velocity air flows.

! 4.3.5' Underlay

Throughout the program the use of an underlay was found to significantly influence flame spread characteristics. When an underlay is used

the chance of flameover occurring becomes greater, meaning that flameover

will occur with less severe conditions of heat input or model dimensions.

Two explanations for this difference existed; the underlay contributed

additional fuel or the underlay provided thermal insulation from the

floor. To determine which of these two factors is dominant, an experiment,

illustrated in figure 4-13, was carried out. Using a model size of 24" x 11", 500 BTU/min heat input and 100 ft/min air flow, a carpet assembly

(A-4/U) was selected with which flameover had occurred at 5 : : 39

In the first experimental run a fiberglass batting (from which all

organic binder was pre-burned) was substituted for the standard rubberized

hair-jute pad. This was done to simulate an underlay with good insulating

properties but one that would contribute no fuel. Flameover occurred at

4::30. The slightly shorter time ^o flameover may have resulted because

the more porous structure of the fiberglass batting provided an oxygen

supply directly to the flame front.

The second experimental run was made using a thin sheet of aluminum

foil between the carpet and the standard rubberized hair-jute pad. The

purpose of the foil was to prevent any air supply or combustion products

released by the heated underlay from contributing to the fuel. In this

run, flameover occurred at l::0h. It is reasoned that the slightly

longer time to flameover may have resulted because of the heat sink

21

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23
TABLE k-h

EFFECT OF AIR VELOCITY

ON THE EXTENT OF FLAME SPREAD AND FLAMEOVER TIME

CARPET - N-5/U

MODEL SIZE - 2k" x 11"

HEAT, INPUT (BTU/min) . j

•• Uoo 500 600 750 1,000

50 19" (18: :00) (10: :05)

75 37" (9::15) (8::06) (6::53) (k:-M)

'min] 100 (17::08) (12: :21) (9::h0) (6::32) (9::06) i

-P 125 20" 87" (17::18) (18: :1a) (8::10)

VELOCITY 150

200

21" 21" 30"

30"

(9::h0)

82"

AIR \

300 37" 6l"

24
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26
property of even a thin foil, or blockage of flow by the foil.

In the final run in this experiment, a 1/2 inch thick aluminum plate

was substituted for a section of the rubberized hair-jute pad. It was 12 inches in length, was positioned 2^4 inches from the burner and

covered the full width of the test section (2U"). This position was selected because in the previous runs it was at this distance from the

burner that the rapidly accelerating flame front had developed which led

to flameover. In this run a rapidly accelerating flame did develop just

before the 'flame front reached the aluminum plate. When it reached the

plate it quickly decelerated and the sample extinguished a few inches

beyond the aluminum plate.

Additional experiments were carried out to reaffirm these results.

Carpet assemblies and test conditions were set that would lead to

flameover. Just before flameover occurred the tests were stopped and

the carpet assemblies extinguished. It was found, both by visual observations and weight loss measurements, that the underlay had not contributed significantly to the fuel.

These results show clearly that the dominant influence of an underlay

is the thermal insulation it provides. This thermal insulation causes a greater heat release rate from the carpet and results in higher ceiling

temperatures (as seen in figure U-9), thereby creating a greater chance

of flameover.

U.3.6 Other Variables

During the experimental work it was noticed that some of the carpets

tended to buckle. This buckling occurred locally in the area just

ahead of the moving flame front. It appeared to happen more frequently

with carpets having thermoplastic backing materials. When buckling occurs the rate of burning is accelerated leading to higher gas and ceiling

temperatures and greater chance of flameover. Several carpets which had

been found to buckle were bonded to the floor of the test section and

rerun. In every case, as illustrated in table U-5, flame spread was reduced. A bonded installation of carpeting would minimize buckling and

also would provide greater contact to the floor so that, depending on the

flooring material, there could be a greater heat loss to the floor.

Several other factors were found to influence results in the model

corridor. Changes in temperature of the intake air influenced flame

spread. Also the initial condition of the construction material in the

test section, probably mositure content, affected results. With careful

control of test conditions, good repeatability of results was obtained.

These factors are described mere thoroughly in reference [6],

5. FLOOR COVERING TESTS

The final phase of the experimental program was to determine hew a facility such as the model corridor might be used to realistically

separate or rank floor covering materials for flame spread characteristics.

27
TABLE h-5

i EFFECT OF BONDING CARPET TO FLOOR ON FLAME SPREAD

Results in time to flameover (min::sec) or distance burned (in.)

RUN NO.

CFT CARPET BONDING

TYPE OF

ADHESIVE

MODEL

SIZE

HEAT

INPUT

AIR

FLOW RESULT

OBSERVATION*

208 0-5 Yes Insulating

(in. ) (BTU/min

2Uxll 500

Xfpm)

100 17" (1)

200 0-5 No None 2Uxll 500 100 (9::56) (3) •

209 0-U Yes Insulating 2Uxll 1000 100 1*1" (1)

207 0-h No None 2Uxll 1000 100 (9::15) (3)

153 0-1 Yes Insulating 2Uxll 500 100 25" (1)

158 0-1 Yes Latex 2Uxll 500 100 (16: :20) (2)

53 0-1 No None 2l*xll 500 100 (6::12) (3)

(1) No "buckling

(2) Slight buckling

(3) Severe "buckling

28
For this purpose, 26 different carpets were provided by The Carpet and

Rug Institute. Included were carpets using each of the major types of

pile fiber (nylon, acrylic, polyester, polypropylene and wool) and both

institutional and domestic styles. The underlay used throughout the

program was a 55 oz/yd rubberized hair-jute pad. A designation, /U,

is used to identify carpet assemblies with this underlay. A designation,

/F, denotes carpets having an integral foam pad. Four resilient floor

coverings were provided by Armstrong Cork Co. Red oak flooring was included in some of the testing. Complete identification of all of the

materials' is appended in table 5-1 •

The findings of the program made it apparent that a method to

separate or rank carpets should be based on a "Go : No-Go" decision;

that .is, either flameover develops and the sample burns the entire

distance, or a decelerating flame develops and the sample does not burn

the entire length of the test section within a specified time. Therefore, to determine if floor covering materials could be ranked over a wide range it was necessary to vary one or more of the test parameters.

Two parameters that seemed practical to vary in an experimental facility

were "ceiling height" and "heat input" from the burner. Both approaches

were investigated.

A series of carpet assemblies was tested to determine the minimum

ceiling height under which each would resist flameover. Ceiling heights

of 11", 1 V , 17" and 23" were used while all other test conditions were held constant (2k" wall separation, 500 BTU/min heat input and 100 ft/min

air flow). Results of these runs are shown in table 5-2. It was found

that many of the carpet assemblies did not flameover at the lowest

ceiling height (11") while others did flameover even with the highest

ceiling (23"). Results show that it is possible to separate or rank

carpet assemblies for flame spread characteristics using this "critical

ceiling height" method.

All of the floor covering materials included in the program were tested to determine the maximum heat input each could resist without

flameover occurring. In this experiment a model dimension of 2k" x 11"

and an air velocity of 100 ft/min were used. Heat inputs selected were from 300 to 1250 BTU/min. Table 5-3 lists all of the runs made to

determine the "critical heat" value for each material. The results are summarized in table 5-k. Several conclusions can be drawn from these

data. Using a facility of this type in the manner described it is

possible to rank floor covering materials for flammability over a wide

range without encountering a biomodal distribution often associated with

other test methods. It is noted that within the group having the lowest

heat resistance there is a predominance of carpets having an underlay,

either separate pad or attached foam. Conversely, in the materials

having the greatest heat resistance there is a predominance of materials

without an underlay.

Having established that floor covering materials can be ranked for

flammability as described, other model dimensions were investigated. A

test facility to be used to measure flammability of carpets in corridors
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TABLE 5-2

"CEILING HEIGHT" TESTS

Distance Burned or Flameover Time as Influenced by Ceiling Height

LAnJrilj 1 o CEILING HEIGHT

Minimum „ , 23" 17" Ik" 11" r X axle: O V fcr I

TJ l fv IN —J. / r 18" 20" 39" ill

N-3 12" lh" 13" 111"

TJ /T T 1M — J / U 19" 21" iXX

TJ-h Vi — H 30" 51+" < 1 1 "

-1 X

TJ Ii /TT 22: ikf 6: :2l+ * t- 2> TJ-S 13" 18" < 11 "

TJ-S /TT 25" 28" 19: :03 12 •21 17" x j TJ-6 /TT 25" 12 :50 lV'

IN — [ / r 32" 8 M X1 ll" 4

A_1 23" i XX

>i— A-1X /TT / U 26" 13: :28 11: :13 17" x ( A-2 IV 19" < 11"

A_9 /TT 20" 25" 37" 3: :h0 X H 16" 20" .ill

A-? /TT 1+2" 8: : 32 3: :57 23"

11" 18" < n 11 11

A-U/U 17" 16" 19" 5 39 ll"

H—A-S5 30" 10: :h3 10 50

A — ^/TT LI: :4T 4 39 > oo M

P 1 /TT ± —X / U 1+1" 1+1" 39" 6 17

p-U 25" 15 1+1 ii+"

P ]j /tt h9" 16: :08 6 18

P-6/TT jr — \j / u 53" 20: : 1+9 ? 01 oq"

0-1 1+8" 1+9" 13: :11 6 12 ! 17"

0-1 /u LI: :03 1+ 03 > 23"

0-2 27" 37" 9 11+ i k

" • 0-3/F 52" 9 : : Ok 5 25 23"

W-l 9" 13" <11" i W-l/U 12" 9" < 11"

Test Conditions:

Model Width - 2k"

Heat Input - 500 BTU/min.

Air Velocity- 100 Ft./min.

31
TABLE '>-3 "CRITICAL HEAT'" SERIES

Influence of Gas Energy Input Pate on Flamespread

CARPET

N-1F

HEAT INPUT - BTU/MIN

300 UOO 500 600 750 1000 1250

MAXIMUM HEAT

INPU1 WITHOUT

FLAME0VER

To" 600 RTU/min 39 30 b : : 44

TTT" 10 TVTT— " 21 t ATT 52 y : : civ 1CC0

- 1 riTir £ 1 71 H rll

1 : : 5o i 600

N-3 13" 20" 32w B::55 1000

N-3/U —01 1 21 45 6 : : 14 75C

N-4 qT-n - 14: : 4 b 500

N-4/U 0 : : 24 <300

K-5 10 on" 7. .17

[ . . 1 f 750

N-5/U 7 7 . . ou L | . . UO lc: : : <_! 0.1.0 y : 4 u A . - TO 0 : : 3d Cl • • A.A y . . uo jOC

N-6 1711 1 f 2 f n. • "3 !t y *

. j 4 750

N-6/U TO. .CO ±2 :

:

tO UOO

N-7/F <- 07TI £ 1 0 : : 4 3 400

A-l 23 33 Q . , OO 3 : : 29 750

A-l/U 1 t, ..SI! 11 : : 13 300

A-2 L -iV

19 rnTT 40 2 : : 30 750

A-2/U a^"

3: :40 400

A-3 2

a." "TCT1 4 : : 50 3 : : 15 600

A-3/U

_

^ . . [j-g —V.—C7

3 : : 57 <300

A-4 1 r<" mi31 O . . oc: 2 : : 0 d. : : ui 750

A-U/U —r 57? loo

A-5 y : : 4 u 10: :^0 300

A-5/U 4::39 <300

A-b 11" —w a» 22 —TV" _.l 1250

A-b/U

1 ^ TT" 4 1 4 : : 4 j 1000

P-l 43" 0 ), C 9 : : 4b 500

P-l/U 1c . . 4 5 7: :32 6::17 <300

P-2 16" 37 5 : :10 1000

P-2/U 27" 18:: 50 8: :00 500

P-U 39" _ 15 :U1 400

P-U/U o . I, c y : : 4 5

1 e :18 <300

P-5 ! 3c

TV " n tt"" - 1 47 4 : : 5 0 750

P-5/U 14 : 39 16:04 9 <300

P-6 38" 10 : : S2 7 : : 58 500

P-6/U 20 : : 20 9: :01 <300

P-7 -1 . - TT -O 31" 7: :00 1000

P-7/U 12" : roW

59

' 0 oir 0 : : 25 750

0-1 30 20: :56 6: :12 300

0-1/u 9 • io u::03 <300

0-2 66" 8 : : 3b 9: : 44 300

0-3/F 0 : : 44 5 : : 25 <300

0-4 30

' O t T1 ^n" 29 9 : : 1

5

750

0-5 'VP1 21

... _ . 9: : 5o 400

W-l 13" 44" 1 1250

W-l/U 9" 33" 5 : : 00 750

W-2 ' 14" , ^ TT J3 1250

W — £ / U

^ a n 29" 29" 1 OCA

R-l 9" 27" 1250

R-2" 14" 36" 3: :10 1000

R-3 X T

" TT 16 : : 16 5 : : 24 500

R-U 8" 19" 1250

R-0

mrr 15"

Turn . : 31" 1250

32
TABLE 5-1*

CRITICAL HEAT

MAXIMUM HEAT INPUT WITHOUT FLAMEOVER

BTU/MINUTE v

<300 300 Uoo 500 6oo 750 1000 1 1-50

N-U/U N-5/U N-6/U N-l/F N-3/U N-2 A-6 •

A-3/U A-l/U N-T/F p-1 N-2/U N-5 N-3 W-l

A-5/U A5

A-2/U P-2/U A-3 N-6 A-6/U W-2

P 1 /tt A—A liH /TT

1 U A—A )i /TT 4/ U r—

D

A—J. P o T.T O /TT W — £1 / U

P-U/U 0-2 P-U R-3 A-2 P-7 R-l

P-5/U 0-5 k-k R-2 R-U

p-6/u P-5 ro ;

O-l /u P-7/U

0-3/F 0-U

W-l/U

33
should be designed with a shape factor (height to width ratio) more

nearly like real corridors. Additionally the data suggests that very

low ceilings in a test facility may not correlate as well with real

corridors. For these reasons tests were conducted on many of the floor

covering materials in the model corridor using cross-sectional dimensions

of both 18" x 18", and 16" x lo". Data obtained in the 16" x 16"

model corridor are shown on table 5-5. These data again indicate that

floor covering materials can be ranked for flammability over a wide

range of heat inputs. Good correlation was found between results in this

l6 M x l6" model corridor and the "ceiling height" and the "critical heat"

rankings

.

.Using the critical heat ranking established for the 26 carpets,

table 5-^, a correlation study was made to determine if any factor of

carpet construction consistently influenced flammability. It should be

realized before commenting on this analysis, that the carpets in the

program were not chosen to permit this type of analysis. Data indicate

that the wool carpets, based on only two samples, tended to rank high

for heat resistance. Polypropylene tended to rank low. The other fiber

types (nylon, acrylic, and polyester) showed no trend. Carpets with

these three fibers covered a wide range of heat resistance. Tufted

carpets having a polypropylene primary or secondary backing tended to

have lower heat resistance than those made with jute primary and

secondary. Foam backed carpets performed less satisfactorily than those

without an integral pad, whioh is consistent with results discussed

earlier regarding the influence of an underlay. No correlation was found between heat resistance and carpet style, pile or total weight,

pile height, or pile density. Results suggest that carpet flammability

performance is not associated with any single characteristic of the

carpet but is dependent on the total carpet structure.

To determine if flammability rankings for floor covering materials

obtained using the model corridor correlate with other test methods,

results were obtained and are shown on table 5-6. The samples are ordered on this table by "critical heat" values (Column A) as obtained

in the experimental program. Within each level of critical heat the

materials are not ordered. Good correlation is found between "critical

heat" and "critical ceiling height" (Column B) values. This indicates

that either method as described earlier, can be used to measure the

resistance of a carpet assembly or floor covering material to the con- ditions leading to flameover.

Each of the floor covering materials was tested using a model size

of 2U" x 11", 500 BTU/min heat input and 100 ft/min air velocity. These

results are shown in Column C of table 5-6. Results are shown in time

(minutes :: seconds ) to flameover or flame spread distance (inches) if

flameover did not occur. Obviously, those materials with a "critical

heat" resistance of 500 BTU/min or higher did not flameover in this test.

Within this group there is an indication of agreement between distance

burned in this standard test and "critical heat" value, however,

correlation is poor.

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tabu; ri-<<

COMPARISON OF TEST METHODS

Crit Iral Heat" BTU/min

S.mip 1 e No.

MMFPA Tests

"Crit icaj Cei 1 ing" Standard

Test

U.L. Chamber

E-84 Tunne

1

Kadiant Panels

Armstrong K- 1 f>2

1250

1000

750

600

500

400

300

<300

A- f% J L 1

1

W-i i 1 39 u4 W- 2 1 1 "

1 1 U- 11 /II K- I 11" 9" A 1 11" 8" 4D A A

1 1 "

1 5"1 .

0

10U 100

N-2 11" 18" 179 65 210

11" 13" 1 AO. A-6/U 11" 22"

r- ^ 1 1 " 16" r— / 11" 15" R-2 11" 14" 66

V' O / IT 11" 21" AO07 1 fi 1 N- j 11" 18" 1 .

1

AO09 am 1 N— 0 11" 17" A-l 11" 23" . 9 43 85 14 J A2

11" 19" 1.2 50 227 404

11" 18" 1 . 3

i o i 1 Jl ADA 9A9 P-5 11" 38" r- //U 11" 12" 0-4 11" 30" 70 W-l/U 11" 9" 46 119

N-l/F 11" 39" 1.1 237 86 284 N-2/U 11" 27" 90 289 A3

11" 20" 131 225

N-4 11" 54" 1.9 79 173

F-l 11" 43" P-2/U 11" 27" P-6 11" 38" 200 R-3 11" 34" 98

N-6/U 14" (12::50) N-7/F 14" (8::43) A-2/U 14" (3'.:40) 2.3 279 • 453 445 A-4/U 14" (5::39) 1.7 291 P-4 14" (15::41) 0-5 (9::56) 220

N-5/U 17" (12::21) 96 332 A-l/U 17" (.11"13) 2.6 298 131 150 A-5 23" (10::50) 385 309

0-1 17" (6::i2) 2.1 71 116 616 0-2 14" (9::44)

N-4/U >23" (6::24) 11.8 135 253 A-3/U 23" (3"57) 179 265 A-5/U >23" (4::39) 533 400 P-l/U 14" (6.-.17) P-4/U 23" (6::i8) P-5/U (14::39) P-f/U 23" (20"20) O-l /U >23" (4::03) 24.0 358 764 0-3/F 23" (5:25)

36
Those materials having "critical heat" values of ^00 BTU/min or less did, as expected, flameover in this -standard test. There is no correlation between time to flameover and the "critical heat" value

for a material. It can also be noted on tables 5-2 and 5-3 that often

a material with good flame spread resistance (high "critical heat")

reaches flameover in a short time with "a large ignition source, whereas

a material with poorer resistance may flameover in a longer time under

much lower ignition energy release rate. In general it was observed

that materials that char and burn (acrylics and wool) tend to flameover

in short time, whereas the thermoplastic materials tend to flameover in

longer times. This further confirms that a time dependent index may

not be a good measure of flammability , especially, if the real hazard is

concerned with the potential for flame spread rather than the speed of

flame spread.

A number of the materials used in the program were tested by the

Underwriters 1 Laboratory Subject 992 Floor Covering Test Method. Results

are recorded in Column D of table 5-6. These results were obtained

using one of the existing chambers. There is some question regarding

control of air flow in these units. This raises the possibility that

the indexes may be lower than would occur with more positive air flow

control. Since the index obtained is dependent on distance burned or time to burn the full distance (flameover), some lack of correlation

with "critical heat" values would be expected. Results of ASTM E 8u-68

Tunnel Test were obtained for some of the materials and are shown in

Column E. Correlation between these results and "critical heat" values

is not good. •.:

Results of two radiant panel test methods were obtained on many of

the materials used in the program and are shown on table 5-6. The

methods used were the Armstrong Flooring Radiant Panel and ASTM E

162-67 Radiant Panel Test. The numerical index in the former test was based on flame spread rate or distance burned. The latter test index

relates to spread rate and energy release. Some correlation of results

is indicated but several anomalies' exist in both methods. It appears

that in these radiant panel test methods the controlling source of

energy causing flame spread is the radiant panel, whereas in the model

corridor, U. L. Chamber and E Sh Tunnel the fuel contributed by the

specimen being tested is a significant factor.

The model corridor was designed as an experimental facility, net a test apparatus, and therefore a statistical plan for determining

repeatability and reproducibility was not developed. In the course of

the experimental program, however, many runs were replicated and are available as a measure of repeatability. These data are shown on table 5-7- Another measure of experimental reliability is available.

In many of the experiments the severity of the heating conditions was gradually increased from run to run (reducing ceiling height or increasin

heat input). As this is done, the distance burned increases slightly up

to flameover. If severity of heating conditions is further increased,

time to flameover is shortened. These results are shown on tables 5-2

and 5-3. These consistent trends imply repeatability of results within

37
TABLE 5-7

REPEATABILITY DATA

Carpet Test Conditions* Run. No. Result**

N-5/U 24x11, 500, 100 41 8

!! 50

47 7 '•••04 64 10::07

A-4/U 24x11, 500, 100 49 5 "2 8

68 4"25

107 5 ••24 129 6 ".50

W-l/U 24x11, 500, 100 51 Oil 8

139 10"

A-4/U 24x14, 750, 100 82 5::40

126 5"08

A-3/U 24x17, 500, 100 92 5::06

96 U"57

0-4 24x11, 500, 100 201 31"

202 29"

N-5/U 24x11, 750, 150 301 29"

329 31"

* Test Conditions are;

Model Size (W"xHM ), Heat Input (BTU/min) , Air Flow (Ft/min).

**Results shown in inches burned or time (min::sec) to Flameover.

38
the tolerance levels indicated.

6. QUANTITATIVE EVALUATION OF CONTRIBUTING FACTORS

In this section a closer examination of the factors which influence

flame propagation in the model corridor will he presented. A qualitative

description of the phenomenon of flame propagation has been presented.

Here the focus will he on the components and mechanisms. An effort was made to quantify the effects of these factors. This vas accomplished

from measurements, analysis, and modelling. At this point, no attempt

has been made to generalize these results. The factors influencing flame

propagation which will be discussed include: (l) the ignition flame

characteristics, (2) the thermal aerodynamics of the flow, (3) the • energy release rate by the carpet in the ignition zone, [h) radiant

preheating and (5) the results of an overall energy balance on the model

corridor.

6.1 Ignition Flame

The hardware associated with the burner has been described elsewhere

[6]. Here the concern is with the resultant diffusion flame characteristics. The general description of the flame is yellow to orange in color,

visibly turbulent a short distance from the burner ports, and tends to

expand an inch or two from its initial b inch "line" width at the ports.

A photograph looking into the burner flame prior to carpet ignition in a test is shown in figure 6-1. A series of runs were conducted without

combustible floor covering to examine some details of the burner flame.

These characteristics are shown in figure 6-2 and span the normal range

of operating conditions for the tests. Some judgment had to be used in

defining the boundary of the luminous" flame zone since it is quasisteady and irregular. The general flame shape is shown in the figure.

It is significant that flame length, L^, increased as air flow, V^,

decreased. This reflects increased mixing with increasing air flow.

Flame angle was virtually constant over the range of these parameters;

however, later test results (not shown) indicate below an air flow of

1+0 fpm the plume inclination will begin to increase towards the vertical.

In fact for all ranges of gas flow used, the burner plume would be

essentially vertical at zero forced air flow. By placing a radiometer

upstream of the flame, heat flux was measured, and later forward flame

radiant flux was calculated by modeling the flame as a sheet with a projected surface area of H x 8 inches. (Note that since most of the

flame radiation would be attributed to emission from carbon particles

the capphire window is adequate since soot has an absorption coefficient

inversely related to wave length [l6] and sapphire is transparent to

5y . ) Figure 6-3 is a schematic side view of the burner flame. The

temperatures were recorded by bare type K thermocouple (approximately

20 mils) inserted into the flow stream and the flame. The trajectory

paths that were sketched are based on observations made using titanium

tetrachloride induced smoke tracings. Finally it should be errrchasized

that in all the work burner gas flow rate was used to calculate burner

energy release rate, Eg- Although more than sufficient air is available

for complete combustion all the energy released is not necessarily

39
Figure 6-1. Burner flame plume 30 seconds after ignition,

Vro= 100 fpm, E = 500 BTU/min.

D

AO
BURNER PLUME CHARACTERISTICS

BURNER ENERGY RATE, E

Q (BTU/MIN)

Figure 6-2. Burner plume characteristics.

41
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46
convected downstream. Estimates on a

r 500 BTU/min" burner input suggested

a maximum of a 10 percent conduction vail loss and a maximum of a 20

per cent radiation loss to the local surroundings.

The effect of burner flame on floor covering flame spread is to

initiate a fairly constant flame spread and to contribute to downstream

ceiling and vail heating. Carpet pile fibers vhich melt tend to maintain

a constant flame spread rate for distances greater than the burner flame

length, L^; hovever, carpets vhich did not exhibit melting tended to

maintain a uniform flame spread velocity up to L . Nylon carpets exhibit

the former (see figure 6-h) , vhile acrylic carpets exhibit the latter

(see figure 6-5). The effect of burner energy input on initial carpet

flame spread is shovn in figures 6-6 and 6-7 for several representative

carpets tested. The numbers in parenthesis represent the distance in

inches over vhich the flame velocity maintained a constant value. These

results are based on a sample of data ranging over initial conditions of

50-200 ft/min air velocity, 11 to U8 in. for height, 2k to hti it., for

width, and vith and vithout pad underlay. It is significant that this

initial flame spread is a strong function of burner flame length, L , and energy input, ; vhile very veakly dependent (if at all) on duct,

size, air flow, and carpet underlay for the range of parameters investigated. Both Kg and affect the extent of heat transfer to the floor

material. Above a critical burner heat flux level, steady flame propagation vould be expected to be monotonically increasing vith flux. For

the results presented in figures 6-6 and 6-7 it vould not be correct to

extrapolate back to E=0 since a derinite E^ > 0 is required before steady

flame spread is possible. The width of the initial burning zone is also

controlled by the burner flame width, and flame spread to the sides of

the duct is insignificant compared to forward flame motion. However,

as flame acceleration ensues and flameover is approached, burning across

the entire duct width is likely.

6.2 Air Flow

The air flow entering the test section was unidirectional, uniform,

and laminar in character. The burner and sharp edge entrance of the

test action presented local disturbances to the inlet laminar flow.

Considering only air flow to the test section, the duct inlet Reynolds

number (Re) for all run conditions was always greater than 2000. Hence

fully developed flow should be turbulent. Since the boundary layer

development is likely to be disturbed at the inlet a turbulent boundary

layer should- persist through fully developed turbulent duct flow which

could occur within the test section length [17]. Because of the increase

in kinematic viscosity with temperature, a heated flow would have a lower Reynolds number and could relaminarize . However, once the burner

flame is introduced the inlet disturbance is increased tremendously and

buoyancy becomes a dominant factor. In fact, smoke trace observations

indicated reasonably laminar flow (V^ = 60 ft/min, H = 11 in., W = 2h in.)

with no burner on up to a distance of h feet at the center line-;

however, with the burner on, laminar flow ceased at the flame plume.

Thereafter the flow appeared turbulent.

47
Once the burner flame is ignited the inlet air flow is markedlydisturbed. Air is entrained into the flame from all sides at varying

degrees. For a spreading floor covering flame, air is swept in from

V:p Lack and sides while the leading edge of the flame front is blown

forward. This flow pattern is clearly discernible in figure 6-8,

Overall the air flow has a cooling effect on the combustion products

which is clearly apparent if the average bulk gas temperature, T , is

considered. .Neglecting radiation or other losses this is

T3 . E»

= 1

(The symbols are defined in the Table of Nomenclature.) Clearly T

decreases as V is increased. Although it is useful to think in tlrms 00 ° of an average gas temperature, it is significant that the temperature

distribution downstream of the flame zone is highly stratified with the

hot gaseous products at the top of the duct. Variations in temperature

also exist across the width of the duct due to the three dimensional

character of the burning zone. However, these are not normally significant

and diminish as distance increases from the flame zone. The vertical

temperature stratification is illustrated in figure 6-9 in which is

displayed equilibrium conditions in a duct with non-combustible materials.

For these conditions the degree of stratification increases directly with

E . In general a dimensional analysis of the governing equations suggests

that a Froude number parameter (Fr),

p V

s- Fr =

is a suitable indicator for stratification. This follows since Fr is the

ratio of inertia force to buoyant force. Hence a large Fr implies weak

stratification. However, the above form for Fr is not convenient since

Ap is not an independent quantity. By introducing Ideal Gas laws and

incorporating an average bulk temperature to characterize the temperature

level it follows that an alternative expression is

Fr = 3

^*

(6-2)

48
Figure 6-8. Nylon carpet flame displaying three-dimensional Q

49

EFFECT OF AIR FLOW

ON FLAME SPREAD VELOCITY _ NYLON N-5 24"xH n DUCT

400 < £ R <750 BTU/min

INLET AIR VELOCITY, Vqq (FT./min)

Figure 6-10. Effect of air flow on flame spread.

51
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For the data presented in figure 6-9, Fr ranges from 0.30 to 0.10.

The effect of air flow on flame spread is not completely understood

hut some thoughts and observations can he made. As reported by Rhodes

and Smith [7], a critical velocity appears to exist for flame spread.

This is illustrated in figures 6-10 and 6-11. The first figure displays

the end result of tests for a nylon carpet at various air flows (V ) and burner settings (E ). In order to appropriately display propagating

and non-propagating fires an average flame front velocity (V ) has been

introduced as

V = Distance burned

Time

Also an attempt has been made to draw a family of curves based on averag

initial gas temperature, Tg. A critical zone is suggested and the inter

sections are used to plot figure 6-11. Physical reasoning led to the

extrapolated curve shown as a dashed line. Also shown are flow characterizations based on Reynolds number and Froude number considerations.

Finally a line of constant burner input (Kg) is superimposed and

following this line by varying the air flow illustrates how one can move from a propagating regime to a non-propagating regime. Although

these results are restrictive to the particular conditions in these

tests, it is suggested that the effect of air flow on duct flame spread

has this same general character.

6.3 Energy Release Rate from Floor Covering

Due to the nature of the test at least a portion of every floor

material which was under the influence of the burner flame would be

consumed. Based on initial duct temperature levels for runs with and

without floor combustibles during the same time period, it was reasoned

that energy release rate of the burning carpets was significant when

compared to that of the burner alone. Since this total initial energy

input is critical for propagation an estimate of the carpet energy

release rate was sought. This was accomplished by several techniques,

but the general intent was to arrive at results of the correct order of

magnitude. The effort was not intensive but the results are expected

to be representative for carpets.

Carpet samples were tested in the NBS rate of heat release calorimeter [l8]. The results of these tests for three sample carpets are shown in figure 6-12 [19] The samples were burned for varying times

und^er normal atmospheric conditions at an irradiation level of 6 watts/

cm . The principal interest was energy release as a function of weight

loss. By then determining the resultant weight loss during a model

corridor experiment, the energy release could be deduced. This, of

course, assumes identical burning characteristics in the chamber and

the rate calorimeter. An alternative method was to determine the heat

of combustion from an oxygen bomb calorimeter, and then repeat this

procedure for residue following a model corridor fire. The higher

heating values determined in the oxygen bomb by Kashiwagi [20] are

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TABLE 6-2

Floor Covering Weight Loss in Model Corridor

(Following Flameover)

No. Material Weight Loss

N-1 Nylon 64

N-2 Nylon 64

N-4 Nylon 74

N-5 Nylon 84

N-6 Nylon 67 - 82

A-l Acrylic 42

A4

Acrylic 47 - 49

A6

nv_ i y iil 45

P-l Polyester 77*

P-2 Polyester 69

P-4 Polyester 77

0-1 Polypropylene 62

0-2 Polypropylene 43 - 100

0-3 Polypropylene 46

W-l Wool 59* - 73*

* No flameover occurred

57
summarized in table 6-1. These values represent an upper limit for heat

release. Based on residue samplings from a model corridor test

(CFT-137) energy release per "unit initial carpet mass was determined.

These results are shewn in figure 6-13 and are compared with the NBS

rate calorimeter results. The two techniques are in general agreement

except in the low mass loss regime. This is not surprising since the

initial burning process is very different in the two methods and complete

combustion is forced in the bomb (and water vaporization was not corrected

for in the bomb). Because of non-combustible filler in the latex

backing it is not uncommon to have a significant non-combustible residue

in the bomb calorimeter. An 18 per cent residue was reported for Nylon

N-5. It is noted that beyond a 30 percent weight loss for acrylic A-h

a uniform combustion line based on 80 per cent maximum weight loss

agrees well with the data. Maximum weight loss of floor covering samples

following a model corridor burn is presented in table 6-2. These

results are consistent with maximum weight loss found in the NBS rate

calorimeter as indicated by che upper limit of the data presented in

figure 6-13.

In order to translate these energy results into an average release

rate, average burning time ( At ) must be known. The quantity At is

defined as the duration of flaming for a fixed position on the floor

covering. Although the weight loss result for a material may be

invariant following a fire above a critical intensity, the burning time

is likely to be more sensitive to surface boundary conditions (both top

and bottom). If Spaldings formulation [21] is adopted for a burning

material (directly applicable to a liquid below its vaporization temperature), then the effect of variables on burning time can be recognized.

For a material of mass per unit surface area mV , with a burning mass

flux m", then 1

mV<|> (6-3)

i m"

where <j> is the fractional mass loss. From Spalding's formulation

m" = gB (6-U)

where g includes the convective effects (h/Cp) and B is the driving force

for the flux transport.

(6-5)

At, = b

58
where i = free stream enthalpy

i = surface enthalpy

—* :— = energy of reaction per unit mass of gas mixture

In addition if radiation is significant at the surface then it must be

appropriately added to the equation (6-U). Although a floor covering is

usually thermally thick, a rough estimate of a conductive heat loss to

the substrate material below can be assessed from

(6-6)

where y = (kpc ) substrate ' Tnis followed by considering a thin material

of constant temperature T on an infinitely thick substrate of initial

temperature, T . Thus the greater y is for the substrate, the lower the

burning- rate should be. Several conclusions can be reached from the

above modeling. Since the numerator in eq. (6-5) and m." are probably

similar for carpets, it follows that burning time At is directly proportional to fractional weight loss, <j>; effective vaporization energy,

Ai ; and thermal inertia of the substrate, kpc; and inversely, proportional to air flow, (as reflected by h). Table 6-3 is a first

attempt to categorize burning time for the floor samples tested in terms

of the major variables suggested by the model. At a cursory examination

it appears that the burning is erratic, however, this is not surprising

since the initial burning process is transient and unstable. Moreover,

it should be pointed out that the times are based on thermocouple

response - the duration between a rapid rise and a pronounced drop in

temperature. This has not been correlated with observed flaming. A

more thorough review of the data should show consistent results at distances beyond the burner influence and for runs resulting in flameover.

A simple model will now be presented which is empirical in nature

and based on laboratory data and test observations. Assuming uniform

burning, the energy release flux, £

" is

(6-Ta)

where "^c L c ,

f

dt " At, (6-Tb)

0

59
H (0 00c

3

CO

rH u

<g rH C 3

•H 05 U. Cj OS

«» o o c o C o o O o U1 o O o O o o

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tsi O o o o O O O O o © o O O o o C O O O o o o o m O O

n o CO 1 "J o <T vD 1 eg i rH CM » 1 00 r~ in r-i r- co 1 rH 0"> vO X rH CM CM rH CM CM r-l rH 1—

1

rH CM CM rH cm —> rH CM pg r-i cm rg ro CM PI

t—

<

o c o o o o o •o o o o o o o o o O o o O C O o O u*> O LTl U1 o

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,' .n ro CM rH 1—

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t/5 -D3

/3

t-i U < >

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E

CO T3 C eg •a T3

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u

o o o o •J ' j o Cv u o CJ <—

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rH rH rH rH c C

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c: c

o o

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a) a, ai

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a. a. o o

i~ u

a. c

rS >,

'J! C

Xi

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o o

o

CO r*1 CO

I I I I < < < < < < < < <

-T ul i-1 "-H PI Pi

I I

I I I I < < <.< < <

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I I I I I I I I I I I I zzzzzzzzzooo

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-3 sD

\C C J vt r i co p I r—

r~. rH rH -H -T <T fv ^ O <I iA ^) c

in h o vo * vo

PI rH

in c O r-» O LTl r-l —I CM

cr. C/5 <

-K

60
and E ^ is the energy released at the final fractional weight loss,

(J)-. 8f rearranging

m (6-8)

where m." is the initial carpet mass per unit area, and (E

c f/m.) is

the maximum energy release corresponding to the representative final

weight, as given in table 6-2.

. . In order to determine a rate of energy release by the floor material

E

c

, the burning area must be known. Two cases will be considered. Case

assumes the principal carpet energy release occurs in the ignition region

under the burner influence. This initial energy input plus the contribution from the burner is significant to the outcome of the test. If a critical input is exceeded flameover will occur. Case II addresses the

slower burning materials which tend to propagate substantially beyond the

burner's influence then may cease to propagate. In both cases a constant

flame front velocity, V , will be assumed. This is justified in view of

the comments made covering figures 6-U and 6-5. For Case I the flame

front is restricted to the burner regime denoted by flame length L and

width W_.

r The results follow:.

Case I : Flame spread restricted to burner regime.

Q. *M

(6-9)

Ec -H*WFVF t ^ * ^ LB

/VF

(6-lOa)

Equation (6-10a) was then averaged over the time interval ~ +

to yield *T

^' e*«w9-~ octi ' (6-iOb)

61
b. «>1

V(6-iOc)

Et,1<9 .* E.WF LB |_— i+ i/ct J

. (6-iM)

Case II : Steady continuous flame spread

(6-11)

To illustrate the procedure Case I is considered for Acrylic A-h

under conditions of V = 100 ft/min and E = 500 BTU/rain.

= 10 in. (Fig. 6-2)

V- = 11 in/min (Fig. 6-6)

r At^ " 250 sec. (Table 6-3)

D Then

a

-

VF *th

From equation 6-8, table 6-2, and figure 6-13

.

—

_ (0.2.1 g^/cm1-) ( l\&50j|am) ^0^cc 9.48*10 BTO.

tin in jouu

(2.5"0 S*^

0.7 1 7 bTU/cw^ m'm

62
Finally from equation 6-10b,

« 29,5 BTO/min.

(Note that an 8 inch flame zone was assumed. This is consistent with

the burner characteristics). The fact that this energy release, rate

is significant when compared to E^ = 500 BTU/min is important. Thus

this initial energy input by the carpet must be considered as a contributing factor in evaluating the critical energy rate required for flameover,

If Case II is considered with the same V„ and W values, then, at most,

r r

- \70OBTU/n»m. W t>2.50sec

In this case the flame front would reach x = in t = L^/V^ = 5h

seconds. For acrylic carpets (see figure 6-5) the flame front would

normally slow down considerably for x>L until flameover ensues. Hen'ce an E slightly greater than 285 but much lower than 1700 BTU/min

wouici be representative of the carpet's contribution. In any case the

energy release from the initial burning of the carpet cannot be

neglected.

6.h Radiant Preheating

A dominant factor determining whether a propagating fire will

occur was found to be preheating of the floorcovering surface extending

over several feet from the flame front. In close proximity to the

burner flame both radiation (figure 6-2) and convection (figure 6-3) are important; however, downstream of the burner zone (figure 6-9)

radiant heating of the floor material is caused by the hotter ceiling

temperatures. Unfortunately no single device was consistently used in

the testing to accurately monitor the flame and ceiling induced floor

heat flux. Gardon type heat flux sensors were used with sapphire

windows to shield out convective heating. However, sapphire is a poor

transmitter of long wavelength radiation which predominates for

relatively low temperature sources (200-600°C) encountered. Moreover,

once the flame front passed over the sensor the heated window reradiated

to the sensor element causing an erroneous radiant heat flux measurement.

Hence an indirect method of calculating the local floor flux from

63
ceiling temperature measurements was resorted to. Before this is fully

discussed, some approximate results from a water flow designed total heat

flux gage will be reported. A 0.005 inch thick stainless steel tube

b inches long and 1/8 inch o.d. (A 1/8 in. o. d. with a 3/64 in. wall

thickness Cu-tube was also used) was inserted along the carpet surface

aligned normal to flame propagation. A controlled water flow passed

through the tube and a calibrated differential thermocouple monitored

water temperature rise. Assuming one-half of the tube circumference was

exposed to incident heat flux (the tube was blackened with a high

emissivity paint), the total heat flux could then be determined. For a water flow of about 10 ml/min, a 1/32 to 1/8 in I.D. tube has a response

time of 2 to 15 seconds. Figure 6-14 displays the results for one run.

It appears that the effect of the flame is felt when it is within about

10 inches of the sensor. Previous flux levels are soley due to radiant

heating from the ceiling. Although the cooled tube sensor probably inhibits the flame to some extent, the maximum value recorded 1.5 BTU/ft sec

is comparable to 1.77 BTU/ft sec determined by Parker [22] for downward

flame propagation along thin cellulosic materials.

Since the primary long term radiation originates from the heated

ceiling a calculation was made to determine the incident floor flux

along the centerline of the floor. Seven ceiling temperature measuring

stations were used to determine the radiant flux. The ceiling was

assumed to be a blackbody with uniform temperature across its width.

(Asbestos board and soot deposited on a solid surface both have

emissivities of 0.93 - 0.95 up to 400°C [23] .) The incident floor flux was then determined by considering the emitted flux from a diffuse

surface, and geometric considerations. The result is given in figure

6-15, Integration was accomplished by using an Aitken one-degree

interpolation for the ceiling temperatures and Simpson's Rule with a 40 point step division. The floor flux was then determined for several

tests using seven ceiling thermocouples and found as a function of

distance and time.

Having made these calculations, two points of view were taken to

examine the effect of radiant flux. The first was to view it as an instant additive of direct forward heat transfer by the flame front.

Then, using the calculated flux and recognizing the position of the

flame front permitted the ceiling induced radiant flux to be derived at

the moving flame front. This is illustrated in figure 6-16 where two

similar runs are compared. They differed only in ceiling height and

had two distinct outcomes. At the time of incipient flameover in run

68 the flux attained 0.5 watts/cm", while the flux never exceeded 0.15

watts/cm^ for. run 76. Adopting the second point of view the calculated

flux is examined at a fixed point downstream of the burner flame

influence. Again the two runs show distinct differences in the resulting

flux. If the carpet surface temperature is also compared a distinct correlation is seen with the radiant flux calculations implying a cause and

effect relationship. Moreover, gas temperatures 1 inch above the surface

considerably lag the surface temperatures, supporting the contention that

direct radiation causes surface temperature rise. (Run 49 is shown since

it is identical to run 68 to illustrate the lagging gas temperature. The

64
roas) 3wu

(09s

2 u/ni8) ^ovddns no xnid ivbh

65
CALCULATED INCIDENT CARPET

RADIANT HEAT FLUX , q'j

(CEILING SOURCE ONLY)

T2 (x)

q

0rT2 COS 9 i COS 92

A

7T

dA

W/2

M[M + (f)

2

]

+

tan-'(^)

M

3/2

.4

T2 (x)dx

M=(D-x) 2 +H 2

Figure &-15. Calculated incident radiant heat flux.

66
(•"!) lNOdd 3WVU JO NOIllSOd

o _ _

<1- —

II X

J

n si X X

I I

( 3

uio/m) *HOMI IV Xflld

iNviavd a3iv"ino~ivo

o CO ct>

r^. io

z

ZD

ICQ

lO

IIffl

o

o

II >

8

m D

s

I <

o

>-cro

<

( 3 uio/M) 9NIH30 WOHd INOdd

3WVU iv xnu iNviavH

asivinoivo

CO •H

ca

CD •H

CJa

•HT3

Co

•H

•ui a

G

w

ca -a

ctj <uu

CO

0)e

cO

i—

I

r-H

I vO

01D

oo

•H

67
N

^0 second shift is most likely due to differences in initial conditions.)

TV support the radiant induced surface temperature response, a one- dimensional heat conduction model was considered for run 68 at x=2h

.es. The radiant heat flux was approximated as a linear function of

time up tc the point of ignition. Three cases were considered - a thermally thin carpet ("back insulated), a thermally thin pile (hack

insulated) and a thermally thick carpet. The details are presented in

Appendix B'. The results are shown in figure 6-17. Although the temperature is generally overestimated, it is apparent that the flux level is

more than adequate to cause the temperature rise observed. Some additional

runs were examined for the same carpet (Acrylic A-^). The flux at the

flame , front appears to be in excess of 0.3 watts/cm to permit a propagating fire (see figures 6-l8 and 6-19).

A semi-quantitative model is described to link flame spread to

radiation pre-heating. A thin bed horizontal steady state flame spread

is considered. A suitable representation is expressed as

dt

- vF

1 VAY 1 ©

(6-12)

derived by de Ris [2h] or Parker [22] prefixed by a constant of about

1.5. Assume the gas phase transport processes are fast compared with

radiant preheating. In this quasi-steady approximation T is the fuel

bed temperature "far" ahead of the flame which is responding to a uniform and constant radiant flux q^. For no heat losses the radiant

preheat model yields

* * 4-

(6-13)

Substituting for T and solving for the flame position as a function of

time yields

(6-lU)

68
CARPET PREHEATING

TIME (seconds)

Figure 6-17. Carper preheating

69

characteristics

.
114

120 240 360 480

TIME (sec)

Figure 6-18. Flame spread—radiation analysis.

70
RUN E B (BTU/min) H (IN)

68 500 1

1

76 500 14

CARPET A-4 113 1000 17

ACRYLIC 114 1500 17

WITH PAD

AIR 100 FPM DECREASE IN FLUX

IS DUE TO RAPID ACCELERATION

OF FLAME FRONT INTO ZONE

WITH LOWER CEILING TEMPERATURE

!20 240 360

TIME, Sec.

Figure 6-19. Calculated radiant flux at flame front.

71
For a reasonable choice of parameters the model gives the results as shown in figure 6-20. Of course, the carpet is not a thin "bed and an infinite flame spread rate is impossible. Moreover, the quasi-steady

assumption and preclusion of losses must he questioned at some point

before the physically impossible solution is reached. However, the

character and magnitude of the results has a striking similarity to the

observed phenomenon (see figure 6-5). The model, of course, does not

include the burner effect on flame spread; however, this could be

included by a step change in flux level over the thin bed to simulate

the initial burner input.

Several other observations and facts should be pointed out. Carpet

fibers which form a melt (nylon, polypropylene, polyester) upon

exposure to heat displayed a noticeable melt leading the flame front by

1 to 2 inches. Carpet fibers' which basically char (acrylic, wool)

displayed a much shorter decomposition front ahead of the flame front.

No further evidence of carpet transformation was apparent ahead of the

flame front up to the start of flameover. Also insignificant fuel

contribution could be attributed to the pad substrate before flameover.

Carpet fiber pyrolysis analysis by McCarter [25] indicated the results

shown in table 6-h based on a heating rate of 60°C/min. In general the

observed carpet surface temperatures preceding ignition were always

below the fiber decomposition (vaporization) temperatures. This supports

the observation that carpet degradation occurs only over a short distance

ahead of the advancing flame. That is, pyrolysis products are not

evolved as a direct result of carpet preheating "far" ahead of the flame.

Since radiation was found to be a dominant factor in this work, and

radiation is felt to be important in the NBS corridor fire studies, some similarly calculated floor fluxes were determined from the corridor

ceiling temperature data. Because of the low scanning rate of the data

system (30 sec) it was not possible to determine a distinct correlation

with flame spread. In addition the response of carpet surface thermocouples indicated possible pyrolysis ahead of the flame front. From

the results of the NBS corridor studies [15] 333, 337, 3^0, 3^2-3^5, a calculated floor flux at the time the carpet surface temperature

attained 200°£ ranged from 0.30 to 1.70 watts /cm and averaged about

0.60 watts/cm . The flux usually steadily increased then accelerated

rapidly to values as high as 3 watts/cm . It is significant that the

same radiant flux levels precede flame spread in the model corridor test

work.

6.5 Heat Balance Analysis

An attempt was made to monitor the heat transport and energy source processes during several test runs. This is difficult due to the

rapdily transient behavior and sharp thermal variations within the

system. The test duct was modified with baffles and a square 5 in x 5 in

orifice at the exit. This did not affect initial air flow and produced

a well mixed flow at the exit. The exit orifice did cause a substantial

decrease in inlet air flow just before flameover or with a fire which

propagated more than 2h inches. High temperature thermopile type heat

72

COo

•H

co •H

>-i 01 4J

CJ

CO

CO <* J= I U vD c W o

rJ •H

CQ 4-1 <! •H H COO

txeoO

OJ Q

01 XI

•H

Co

•H J-i 4-1 O

4-» •r-l T)

Ol c •H G, • 00 Vj C »rl )-4 CO E O

O o o o o CU 00 CJ C_> o 00 o 1 u C o CNI CNI rH CO

•rl i—1

CU T3 0)

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0) U-l <J E

CO i-i CU rO 3 V-i

C o co a. H

CO •H

QJ CO 3 CNI CNI CO o

•a

U rH 60 • • • o o o • H CU o E l—1 o CN| CO 4-J U rH rH

cu

co a.

CO •H rH CO CO cu vO St CNI o rH rH rH

•H rH i—1

60

4-1 o a CO E i-H

O o o CO

O rH

rl ri E CO CN CNI CNI CNI rH CNI CM C ^ CO cd H a. co E

E* * - CU o

rJ o r*-J

4-1 SN? r-l

m

m o mm

O CO m co CO X) U <r 00 m CO vO <r

>-i 4-1 CO cu o co co CNI -ci- <r -cr <r

01 o >

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cu 0) c c

0) cu rH rH vO >, >,

u

CU a. a. cu JO CJ U vO o o 4-1 •H •H •H M r4 CO rH rH rH C Ou CU >> rH O >. >>

rJ

uO rH rH rH rH

U o o >>

O o o < < z CU - 0-i P_

rH rH rH rH in <r rH o 1 1 1 1 l i 1 25 < <c 3 z o o 0i 74
flux sensors were used to examine heat transfer through the walls, floor,

and ceiling. They can be regarded as within 20 per cent accurate at

high temperature and have a response time of about 10 seconds. The sensors were positioned as shown in figure 6-21. By applying mass and

energy conservation equations to a control volume enclosing the duct

space and the floor covering (carpet only) the following equations result

MASS

(6-15)

ENERGY

©c +

^

CT"T-} = ^ - iv

- V . ( 6-16

)

Combining and rearranging, yields

(6-17)

The terms on the right-hand side could be determined.

E^ = burner energy release rate

q = wall conduction loss measured by heat flux sensors

K. m c (T-T ) = convected energy rate

oo p 00 D^

The terms on the left-hand side could only be inferred not determined

directly.

(a) E

c = carpet energy release rate

(b) q^ q = radiation loss out ends of duct

(c) (m, + m_,)c (T-T ) = convected energy rate of burner and carpet ^ 3 P fuel

(d) (d\J\ . _ *dt"J c = ener^y ra-te increase of carpet

75
76
Terms (a) and (d) are probably dominant. Some results are shown plotted

in figure 6-22. The "blank "run falls below the zero datum due to

radiation losses (ci ) and unaccounted conduction losses (no heat flux sensor covered the last 8 ft of the floor area). An oxygen cell was used in several runs to measure oxygen concentration in the exhaust gases.

Difficulty was encountered with calibration- and determination of response

time for this cell. However, it can be stated that for no flameover

(CFT 190) 0

2

concentration did not fall below 15 per cent while near the

time of flameover (CFT 191) the 0 o concentration dropped below 5 per cent.

It appears that flameover can lead to a fuel rich fire propagation

domain.

7. OVERALL ANALYSIS AND SCALING RELATIONSHIPS

In the previous sections both quantitative and qualitative characteristics of the test system and floor covering flammability have been

addressed. Here a simple model to characterize the system behavior will

be considered. It will be concerned with the development processes

which lead to flameover, and couched in terms of a "critical" preheating

temperature to sustain a propagating flame. Hence heat transfer

mechanisms will be emphasized and not the thermophysical and chemical

processes directly connected with flame spread. Thus a first order

overview will be achieved and effects such as carpet construction, phase

transition and pyrolysis, and gas phase composition and kinetics will be

put off to future analyses. Assuming that the factors ignored are independent of scale changes, then any scaling relationships developed

from such a model will have wide spread application. In the least, it

will present a more concise view of the variables involved.

Basically, the simplified model considers a wind blown flame plume

emanating from a line source which heats the duct ceiling which in turn

heats the duct floor covering via radiation. This idealization is

portrayed in figure 7-1. As an analysis is developed additional assumptions will be introduced as the need arises. The goal is to arrive at an approximate relationship for floor covering temperature during

preheating. Then the dimensionless groups contained in this relationship

will be assessed. The dominant groups can then be used to determine

scaling relationships.

The first step in analyzing this model is to develop a relationship

for the plume temperature at the point it intersects the ceiling. This

is based on a simplification of the work of Escudier [26]. His analysis

is based on two entrainment constants a and ft for a one-dimensional

turbulent plume in a uniform cross wind, . The constant a is

associated with the relative tangential external wind flow and reduces

to the pure free convection entrainment constant for no wind flow. The

constant ft is associated with the normal wind velocity component and

accoants for vortex mixing within the plume. Further discussion and

details of the derivations of the results can be found in Appendix C.

The results given here in dimensionless form for the gas temperatures

at (z = H) are:

77

SIMPLIFIED PREHEATING MODEL

\\\\\\\\\ \\'\\\\\

L

ASSUMPTIONS:

1. Preheat length, L -> 00

2. Carpet thermally thin, insulated back.

3. Ceiling serai-infinite.

A. Blackbody surfaces.

5. Surrounding walls cold, T^

6. Energy rate from a line source and constant.

7. Flow thermally stratified and invariant over L,

Figure 7-1. Simplified preheating model.

79
where

and

(7-la)

Co == (7-lb)

(7-lc)

or

W 9 = ^

1 -»/3

v

(T-ld)

Fr 2=

3

05 (7-le)

80
The "Combustion number" (Co) represents the ratio of the rate of energy

released during combustion to the rate of convective transfer of energy.

The Froude number, Fr, has been defined before as the wind to buoyancy

effect.

The ceiling temperature will now be determined as a result of the plume

intersecting the ceiling. Assume that the temperature is independent of

x and that the expansion of the ceiling jet fills the full width, W, of

the duct. The latter effect will be accounted for by replacing with

W in (T-'d). The ceiling is considered infinite in thickness and an approximate conduction analysis is employed. The conductive flux is

given by:

a* £ iLRT^XoH]

(7-2)

It is further assumed that the ceiling radiates as a blackbody to

surroinidings which are at temperature T^. An energy balance at the

ceiling surface yields

(T-3)

In dimensionless form, the solution is:

Gc

where

and the non-linear radiation term has been linearized for convenience.

The ceiling heat-up time is usually more rapid than the floor

heating so that a mean temperature, G

2

, will be used to decouple the

floor heating problem from the ceiling temperature. Assuming the floor

is a thin bed and L -* °° 1 then:

81
at

(7-5a)

where

(7-5*)

The solution in dimensionless form is

1 v

1 -

7-6)

These equations, 7-1, 7-^, and 7-6, form the solution for the preheating

problem. In general (neglecting flame radiation, and thermal

non-uniformities):

Q^function V w

rr

> S / VTTA ^ * ^

J (7-7)

The heat transfer coefficients, h and h^ , are not explicitly

independent since they must be calculated. For this reason it is

convenient to eliminate h from all but one of the dimensionless groups.

Where h occurs, it can be considered as proportional to pCpV which

holds for rough wall turbulent flows. A new set of dimensionless groups

is given as

•> — )

(7-8)

This form has the advantage of separating cut the velocity effect, and

the second parameter is directly related to the gas temperature for a line plume with no wind.

82
Assume nov that a "critical" floor temperature is required to

sustain flame spread. Consider the floorcovering material as fixed and

the duct material fixed. Then some observations can be made. The first

three dimensionless parameters are compared for several flammability

tests and full scale experiments of real fires in table 7-1. The time

scale is identical for all cases provided h is assumed to be invariant.

For similarity with real fires the three parameters must be equal to

their counterparts in the flammability tests. For ASTM E8U to be

applicable in this comparison the test sample is considered to be floor

mounted; Moreover, the energy contribution from the test sample in

small scale experiments may be comparable to the burner values listed in

table 7-1 and should be absorbed into E for a correct comparison. Thus,

a more rational form of comparing test methods to full-scale fire

conditions is presented.

Partial use of the sealing relationships were applied to some of

the model corridor data -which represented a wide range of experimental

conditions. A presentation of this analysis was motivated by equation

(7-6) and flame spread was expressed as final distance burned (D^)

divided by burner flame length (L ) . The dependent dimensionless

parameter was based on the product of the first two terms on the righthand-side of eq. (7-6). This parameter, <J> , is based on plume temperature and radiation exchange. It is reasoned that these factors are strong variables compared with the ether parameters in eq. (7-6). The

results of this approach is shown in figure 7-2 for nylon carpet N-5/U

and in figure 7-3 for acrylic carpet A-h/U. Each designated point on the figures represents the outcome of experiments summarized in tables

k-2 and U-3. It is apparent that when flameover does not occur, the

distance burned is primarily influenced by the length of the burner

flame. Also the results clearly demonstrate a critical region beyond

which flameover will occur for the appropriate combination of energy

input rate and geometry. Moreover this critical value for <J> is seen to

be dependent on the material properties of the test specimen as one would

expect. An increase in $ beyond its critical value should lead to

flameover in shorter time, however, this trend is not completely evident.

Finally this use of partial scaling appears to be helpful in generalizing

the data. However, general extrapolation of these results will have to

await more extensive scaling studies.

An experimental model corridor facility was designed, constructed

and instrumented. Good control of selected variables was obtained. A

testing procedure was developed that has given reliable results.

Using the model corridor many of the factors which control flame

spread on carpets have been defined and are reasonably well understood.

The dominant factor is radiant preheating of the carpet surface ahead of

the flame front. If the critical level of preheating is exceeded an accelerating flame front will develop and the total length of sample

becomes involved. This phenomenon has been termed flameover. If

sufficient preheating does not occur, a decelerating flame front develops

8 CONCLUSIONS

83
' TABLE 7-1

Comparison of Test Methods and Fire Conditions

Based on Scaling Relationships

Parmeter Proposed

Model

Corridor

Test

UL

Chamber

Test

ASTM

E-84

Tunnel

Test

Full*

Scale

Corridor

E (BTU/Min) 600 500 5,000 100,000

VooCFT/Min) 100 100 240 200

H (FT) 1.33 1 1 8

W (fT) 1.33 2 1.5 8

[E/WH 3/2

] 293 250 3,330 550

[V^/H 172

] 87 100 240 71

[H/W] 1 0.5 0.667 1

* Based on energy estimates of rea] fires by Waterman and Christian [14]

Air flow is based on extreme ventilation conditions [27,28],

84
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86
which leads to very slow burning or extinguishment. The intensity

of the radiant preheating is related to the energy supplied both from an external source and the burning carpet, the cross-sectional dimensions

of the model corridor and air velocity.

The total floor covering assembly is shown to affect flame spread

behavior. The thermal insulation provided by an underlay can increase

severity and a "bonded" installation can reduce severity. This suggests

that a test method should be designed to evaluate total floor covering

assemblies and not components.

Mathematical modeling yields scaling relationships which allow the

model corridor to be compared, with some qualifications, to the burning

characteristics of floor covering materials in full-scale situations.

Several factors remain to be clarified. The effect of air velocity

in the model corridor, and its relationship to real situations, is not

clearly understood. In the model corridor the heat released by the

initially burning carpet is a significant part of the total energy. It

is not known whether this is the case in real fires. It is recommended

that further experimentation be directed to these questions.

Dr. Clayton Huggett [32] of the National Bureau of Standards characterized carpet behavior in building fires as follows:

1. Rapid flame spread over- the pile surface is the primary hazard

mechanism.

2. This flame spread is controlled by a time and intensity

dependent energy input to the carpet surface ahead of the flame front.

3. This energy is supplied by the ignition source and feedback

from the burning carpet.

h. The magnitude of the energy input necessary to cause rapid

flame spread is a measure of hazard potential.

This behavior is supported by findings of the full-scale corridor

program being carried out at the National Bureau of Standards, results

of previous corridor and duct experiments, and by reports from witnesses

to real building fires. It describes well the findings of this program,

although correlation has not yet been established between the results

obtained in the model corridor and full-scale experiments.

It is -concluded that the major hazard that should be addressed by

a test method is the rapid total involvement or flameover of a carpet

assembly. Radiant preheating of the carpet surface, which is controlled

by the energy supplied by both the ignition source and energy released

by the burning carpet, determines whether flameover will occur. The

energy input to a model or test facility can be scaled to simulate

full-scale rt.il-life conditions.

87
9. SUGGESTED TEST METHOD

Based on the findings reported, it seems practical to develop a te~t facility and procedure that can provide a measure of the potential

hazard of floor coverings in "building fires. The following design and

operating conditions are suggested for consideration.

1. A test section with cross-sectional dimensions of l6" x l6" and

8 ft. in length. This shape will be similar to real corridors.

2. Construction materials for the test section that have thermal

properties similar to materials used in real corridors and that provide

rapid cooling to facilitate short time between tests. Asbestos hoard

(conforming to Canadian specification 3^-g p. 18) is suggested for this

material

.

3. Water cooled curbs to inhibit edge burning.

h, A forced air flow with adequate control to insure a stable,

uniform flow during testing. An air velocity of 100 ft/min is suggested

This is higher than scaling relationships suggest but practical if good

flow control is desired.

5. A heat input to the test section supplied by a diffusion flame

gas burner mounted to impinge on the surface of the floor covering

material. A heat input of 600 BTU/min is suggested. Using the scaling

relationship, E/WH this would simulate about 53,000 BTU/min in a real

corridor with cross-sectional dimensions of 8 ft x 8 ft and about 93,000

ETU/min in a corridor 10 ft x 10 ft. If consideration is given to

energy release by the floor material in the test, then higher full-scale

values for E will be estimated.

6. Preconditioning of samples and control of intake air temperatur

and humidity should be considered and studied in future work.

7. A test time of 12 minutes with the burner "on" followed by 12

minutes with the burner "off".

8. Testing of total floor covering assemblies as they are to be

used in actual situations. This would include both the use of underlayments and bonded installations.

9- The test result should be a "pass-fail" decision. This is

consistent with the results of the program and should be based on whether or not the test specimen burns the entire 8 foot length in the

2h minute test time.

Some of these parameters are not fully quantified at this time. As

additional results of full-scale and laboratory experiments become

available, some test conditions could be modified to more closely

approximate true hazard conditions. It is not anticipated that major

changes in the test facility or procedure would be required.

88
It is suggested that a test method, based on the concepts presented

in this report, would be suitable for use in regulating floor covering

materials to be used in corridors and exitways of institutional buildings.

To accomplish this recommendation it is suggested that one such test

facility be designed and constructed. With this unit, the concept

presented could be confirmed and repeatability established. Following

this, several additional test facilities would be required so that interlaboratory reproducibility could be established.

89
APPENDIX A. REVIEW OF LITERATURE ON DUCT AND CORRIDOR FIRES

Past studies motivated "by mine fire considerations and flammability

test development projects have been concerned with flame spread in ducts.

Typically these ducts have varied in size, have been oriented

horizontally, have involved forced air flow, and have included a variety

of ignition sources and arrangements of fuel loadings. Although the

conditions may differ, there is sufficient commonality upon which to

base some general conclusions.

Rhodes and Smith [Tl^describe experiments with model mine fires.

The test duct was U8 feet long and had a cross section of 6.5 by U . 75

inches. The ignition source vac- small and only when wood lagging

covered both sides and roof did a fire propagate the full fuel length.

Floor fuel covered ducts did not propagate beyond 7 feet. They also

found that for hardwood fuel lagging along the duct sides and roof air

flow had a marked effect on fire propagation. This is shown in figure

A-l in which a critical air flew speed is apparent for fires which

propagate. They explained this critical zone as associated with the

fully developed transition Reynolds number for laminar to turbulent flow.

Roberts and Clough [8] conducted similar experiments in a wood

lined passage 30 cm square and about 30 meters long. They studied steady

propagating fuel rich fires. These fires produce an excess of fuel

gases due to intense preheating downstream of the flame zone, consume

all available oxygen in the air stream, and propagation rate depends on ventilation air speed. The fuel rich case developes from an oxygen rich

fire which in turn requires a critical ignition source to be sustained.

They put forth a one-dimensional flame spread model which incorporates

convective preheating to develop a pyrolysis zone ahead of the flame zone Basically they found that if the ignition source is insufficient to

generate a critical rate of fuel per unit rate of air flow then no propagation or an oxygen rich propagation mode is possible. On the

other hand, above this critical condition, acceleration to the more

intense fuel-rich steady propagation limit would result. In this fuelrich zone an increase in air flow would lead to an increase in flame

propagation. Roberts [9] has re-iterated these findings along with

additional experimental investigations of duct fires.

de Ris [10] has presented a detailed analysis of fuel-rich duct fires

and his predicted results are in reasonable agreement with some of the

findings of reference [8]. de Ris correctly qualifies his analysis to cases excluding secondary backflow upstream or downstream of the combustion zone, and excluding stratification which permits oxygen to bypass

the fire. He adopts the criterion

Pm \&

1 Figures in brackets indicate literature references at the end of this

report

.

90
160

140

120 e

E 100

g

10 3o

* 60

U40

20

l

!

1 \ *

»

I * \ FIRES PROPAGATED CONTINUOUSLY

FIRES DID NOT

PROPAGATE

1. FIRES

1 PROPAGATED 1

J SPASMODICALLYJ

50 100 150 200 250 300 350 400 450 500 550 60O 650 700 Airspeed : ft/min

Figure A-l. Model mine fire characteristics [7].

180,000

160.000

c 140,000

— Reference Fire

120,000

I Low Intensity y

-Reference Fire Bedroom I

or 100,000

« 80,000

x 60,000

40.000

20,000

High Intensity

/Kitchen |>. 3]

[10.6] Storeroom

[6 . 3] Linen Room

[7. OjOffice

Closet o Closet Peak Fire [l 1 . f) Reference Fire Lcw ventilation Fires

8 10 12 14 16 18 Time- Min.

4.0

3.5 &

CO

3-0 i

o

a: 2.5 |

2.0 5

1.5

20

Figure A-2. Estimated energy release rate from fires of various

occupancies [14].

91
to insure that no backflow or stratification occurs. P. H. Thomas [ll]

used a similar criterion; i.e.

to denote the onset of upstream movement of smoke from a line fire in a ventilated duct. The two relationships should he regarded as estimations

and not as exact, and they are essentially equivalent.

Although the duct flow literature is closest in physical scale to

the study herein, the ultimate application is fire propagation in

building corridors. Corridor studies have typically "been full scale and

have investigated the effect of a room fire on adjoining corridor. All

studies, generally, have had a similar configuration. A doorway connects

the fire room to the corridor, and the corridor has a window at its far

end. Vents have been distributed in various locations, and usually no forced air flow has been imposed. Although much data gathering and

categorizing has been done here, no detailed analysis has been put forth,

and only one study been primarily directed to floor covering materials.

McGuire [12] reports on full-scale and quarter-scale model results

in which various lining materials have been used along walls, floor, and

ceiling. He also displays the ratings given to the various materials

used as determined by ASTM E-8U and ASTM E-162 flammability tests. He

concludes that floor coverings with a rating below 220 made little con- tribution to fire spread in the full scale corridor but were more

significant in the quarter-scale work. The critical rating for ceiling

material appeared to be 130 and for wall linings 35.

Tests conducted at the Danish State Testing Laboratory in Denmark

are reported on by Christensen, Lohse, and Malmstedt [13] . The room and

corridor were full scale and no combustible floor materials were investigated. Although no floor covering materials were studied, their

overall results are of direct relevance here if one is to understand real

fires versus controlled fires. With caution, some of their conclusions

have been abstracted as follows:

(1) Wood crib fires have different developments than furnished rooms

(2) The ignition process depends not only on a time-gas temperature

relationship but also on the heat transfer and thermo-physical conditions

of the ignition environment.

(3) "Comparison between various small scale laboratory methods

disclosed such great differences between the results found by these

methods that it must be established that they neither reflect the

regularity found in the full-scale tests nor the limitation of influences.

< 1

92
It must be an indispensable requirement to the applicability of a testing method that it depends on effects that are probable in practice,

and that it affords a criterion of the degree of ignitability that is

connected with one of the thermo-physical conditions to which the

materials may be brought by influences existing in practice."

The room and corridor experiments of Christian and Waterman [ih]

appear to be the only reported work which attempts to classify the

energy output of fully developed room fires for various occupancies.

Although much data was gathered in these tests, it is significant to

review the energy release rates for the rooms. This is displayed in

figure A-2. The numbers [ ] indicate fuel loading in lb/ft of floor

area, and^all the rooms had a volume of 1200 ft except the closet which

was 72 ft . In addition gas temperature measurements imply a fire duration of about 30 minutes. It should be emphasized that these energy

release rates were calculated from air flow measurements and involve

several assumptions on fuel type and fuel-air mixing. Thus they should

not be accepted as exact but only approximate.

Finally, work is in progress at NBS [15 ] to characterize room-corridor

fires and assess the fire hazard with respect to floor covering materials.

In summary several observations can be made with respect to both

duct and corridor fires. The strength of the ignition source is

significant. With respect to the room-corridor arrangement, the room is

the primary ignition source with regard to corridor flame spread. A

critical input energy is required to sustain flame spread in a corridor

or duct. The flame spread has a potential to propagate indefinitely if

it becomes a fuel rich fire. Flame spread in ducts and corridors is

more likely with wall or ceiling combustible linings than combustible

floor coverings. Insufficient quantitative data and analysis have been

put forth to generalize the spectrum of real fires and to provide a direct relationship to any established flammability test.

93
APPENDIX B. RADIANT PREHEATING CALCULATIONS

In order to determine if the observed incident radiant heat flux is

sufficient to cause the measured surface temperature rise on the carpet

pile some calculations were made. Two models vere considered. The

first considered a thermally thin floor material. Although this is not

a good assumption "based on the low thermal conductivity of carpets, in

depth radiant absorption in the pile fibers would tend to result in a uniform temperature distribution in depth. Moreover a thermally thin

assumption is a limiting case in which all the energy is distributed

uniformly in depth. Alternately, the second model considers an infinitely

thick material. In both models the material is assumed to have uniform

properties, is an opaque black body, and is subjected to incident radiant

heating with convective cooling. No other losses, such as reradiation or conduction into the underlay, are accounted for. A linearly varying

radiant flux was prescribed.

B.l Thin Bed Model

The energy equation is

"Vg-S-MMJ (B-l)

where m" = mass per unit area

c = specific heat

T = surface temperature

T^ = gas temperature and initial temperature

h = convective heat transfer coefficient

q^ = incident radiant heat flux

The radiant heat flux is specified by

q£ = q

Q + qjt. (B-2)

The solution is given by

T.T. 5 Mt--] + A_[xt-0-e Vi

)l (B-3)

wW« ^ — h /m"c

B.2 Thick Bed Model

In the interest of expedience, reference is made to solutions given

in Carslaw and Jaeger [29] as special cases of the more general problem

specified earlier.

91*
where

For constant heat flux with convective cooling,

• e. q^. = qQ

.

The surface temperature is given by

h

(B-U)

If 3 is small, then

-r -T «Q —•— (B-5)

s ^Nf? k

•

This corresponds to the uniform heating with no convective cooling. For

the case where

• ii _ _ + ^ " ^ - (B-6) .

1

i.33 k

These results will "be applied to acyrlic carpet A-h in CFT 68. The

incident radiant heat flux preceding ignition will be approximated by

q = 0

o and

-h 2 2

q^ = !*,3 x 10" cal/cm sec

Based on fully developed turbulent flow in^a duct £he convective

coefficient was estimated as h = 0.6 x 10 cal/cm sec°C. Carpet

properties are taken from measurements by Kashiwagi [20] and G. Robinson

[30].

k = 0.17^ x 10~3 cal/sec cm°C , Ref. [30]

a = 3.6 x 10"3 cm

2

/sec, Ref. [30]

95
m" = 0.286 gm/cm2

m"., = 0.121 gm/cm pile &

o °pile

= cai/g111 c > Ref> - [20]

Kashivagi has generally found a values about 50 per cent lover than

those of Robinson. The technique used by Robinson was based on the

transient conduction solution for radiant heating of an opaque solid.

Kashivagi ' s technique is based on steady state measurements. Unfortunately, he has not measured a for carpet A-k. However, an extrapolation

from his findings vould suggest

-3 2 a = 1.8 x 10 cm /sec

B.3 Results for a Thermally Thin Pile

Examining the parameter yt up to the time of ignition, it is found

that

(yt) = 0.22

max

Since this parameter is small it is justifiable to approximate equation

(B-3) as

T - T — q

l t

2

m c (B-7)

Then

T s 30 + 3.96 x 10"3

t

2

(°C) with t in sec.

B.U Results for a Thermally Thin Carpet

Here equation (B-T) also applies. The specific heat of the pile

fibers will be used for the total specific heat of the carpet. The

specific heat of the carpet may be about 10 per cent lower than the

pile value.

T = 30 + 1.78 x 10~3

t

2

(°C) .

B.5 Results for a Thermally Thick Carpet

Here equation (B-6) will, be used. This is justified since 6 = 0.352

at 200 seconds. Hence convective cooling is unimportant compared with

conductive heat transfer into the solid. Also the carpet acts like an infinite solid up to at least 100 seconds.

96
T = 30 + 0.113 t

3/2

(°C)

For the lower a value

T = 30 + 80 x 103t

3/2

(°C) .

97
APPENDIX C. ANALYSIS OF A LINE SOURCE PLUME IN A CROSSWIND

The interaction of the burner and carpet flame plume with the

entrance air flow establishes the temperature and velocity downstream.

It has been seen that the resulting temperature distribution is significant for determining conditions for flameover. In particular, the

temperature of the gases at the ceiling of the model corridor establish

the level of radiant preheating ahead of the carpet flame front. In

the following analysis a one-dimensional model will be used to determine

the variables influencing ceiling gas temperature. A turbulent linesource plume will be considered for simplicity. This means that the

energy released in combustion is treated as emanating from a line-source

A turbulent entrainment model considered by Escudier [26] '•'ill be used

here.

• Consider that energy is being released at a rate E over width W

in a crossflow of velocity V . A schematic is shown in figure C-l. A CO control volume is selected for the

Z

i 5

Figure C-l. Plume Coordinate Svstem

plume and the conservation equations are written.

Conservation of Mass

d_(pAn) _ p p

(C-l)

where

T

aWF

2(a*WF) %ZWf

and (C-2)

98
The entrainment velocity v is "based on the relative tangential

velocity and the normal vefocity to the plume. The parameter a and $ are noh-dimensional entrainment constants.

Conservation of Z momentum

ds

Conservation of X momentum

ds

* ds

Conservation of Energy

i[pcp

f\u(T-T^] ,Q_

ds

(C-5)

Equation of State

i>T =

Pj^oo • (C-6)

All properties except in the buoyancy term, will be taken as constant

and evaluated at T^. Also the plume -width W will be assumed constant

This is equivalent to assuming two dimensional planar flow. The

unknowns are a, u, T, p, and 9.

Equation (C-5) is integrated from s = 0 to yield

where E is the rate of energy released at s = 0.

99
Equation (C-U) is integrated from s=0 and the condition fl = 0 at

s = 0 is used to yield

or

U -

cos 9

(c-8)

Equation (C-3) is integrated from s=0 to yield

'CO

By using the equation of state (C-6), the uniform property assumption,

equation (C-7), and equation (C-8), this can he written as

cos Q

Assuming 6 is independent of s, representing a mean plume angle, then

~ ^Zvu (C-9)

Equation (C-2) is substituted into (C-l) and integrated treating

as a constant to yield

q =r 2 c<* 9 sin 6 (ctianfi + s . (C-10)

Substituting this result into (C-9) yields

3 E

100

(C-ll)
from which 6 can be determined. To obtain an explicit solution,

limiting values can be found. For 0 large, corresponding to low wind

speed,

A f *j \

4

For 6 small, corresponding to high wind speed,

-tan 9 * (—

T

9—_ . . x rA (c-i2b)

The Froude number can be defined as

3

rr = : —

It follows from equations (C-7), (C-8), and (C-10) that

For small 9 , or equivalently for Fr large,

(C-13)

T-T = — (C-15a)

For large 0 , or equivalently for Fr small,

T-Tto * (

°° V — (C-l5b)

This corresponds to the line plume solution (no crosswind) given by

Thomas [3lj.

101
If 8' is defined as then for large. Fr, 8'

approaches 8 ; and for small Fr, 8' approaches

This trend is observed in figure C-2. The data were obtained from

ceiling temperature data after long time during blank runs in the model

corridor facility. A flame width of 8 inches was used and data at x = 1 and 2 feet were used.

J_

Fr

C-2. Plume measured results for 8' vs. Fr.

102
REFERENCES

1. "Carpet and Rugs (Pill Test) Standard for the Surface Flammability

of Carpets and Rugs", DOC FF 1-70, Federal Register, Vol. 35, No. 74,

April 16, 1970, p. 6211.

2. "Standard Method of Test for Burning Characteristics of Building

Materials", ASTM E84-68, American Society for Testing and Materials,

Philadelphia, Pennsylvania (1968).

3. "Standard Method of Test for Flame-Propagation Classification of

Flooring and Floor-Covering Materials", Subject 992, Underwriters'

Laboratories, Inc., February 1971.

4. "Surface Flammability of Materials Using a Radiant Heat Source",

ASTM E162-67, American Society for Testing and Materials,

Philadelphia, Pennsylvania (1968).

5. Memorandum from Mr. Z. Zabawsky to ASTM Subcommittee IV Task Group

on Floor Covering, "Armstrong Cork Company Flooring Radiant Panel",

May 17, 1971.

6. W. Denyes and J. W. Raines, "A Model Corridor for the Study of the

Flammability of Floor Coverings", NBSIR 73-200, May 1973.

7. A. C. Rhodes and P. B. Smith, "Experiments with Model Mine Fires",

The Use of Models in Fire Research , ed. W. G. Berl, National Academy

of Sciences-National Research Council, pp. 235-55 (Washington, D. C.

1961).

8. A. F. Roberts and G. Clough, "The Propagation of Fires in Passages

lined with Flammable Materials", Combustion and Flame , Vol. 11,

No. 5, October 1967, pp. 365-76.

9. A. F. Roberts, "Fires in Ducts under Forced Ventilation Conditions",

Fire Technology , February 1970, p. 13.

10. J. de Ris, "Duct Fires", Combustion and Science Technology , Vol. 2,

1970, pp. 239-58.

11. P. H. Thomas, "The Movement of Smoke in Horizontal Passages Against

an Air Flow", Fire Research Note 723/1968, Fire Research Station,

Borehamwood, Herts, England.

12. J. H. McGuire, "The Spread of Fire in Corridors", Fire Technology , Vol. 4, No. 2, 1968.

103
13. G. Christensen, U. Lohse, and K. Malmstedt, "Full Scale Fire TestsThe Spread of Fire from a Chamber to a Corridor", The Danish

National Institute of Building Research, S.B.I. Report No. 59,

Copenhagen, 196?

.

lU. W. J. Christen and T. E. Waterman, "Characteristics of Full-Scale

Fires in Various Occupances", Fire Technology , August 1971, p. 205.

15. F. Fung, M. Suchomel, and P. Oglesby, "The NBS Frogram on Corridor

Fires", Fire Journal , May 1973, p. 41.

16. R. Siegel and J. R. Howell, Thermal Radiation Heat Transfer , Vol. 3,

NASA SP-16U, 1971, p. 336.

17. J. G. Knudsen and D. L. Katz, Fluid Dynamics and Heat Transfer , McGraw-Hill Book Co., Inc., New York, 1958, p. 232.

18. W. J. Parker and M. E. Long, "Development of a Heat Release Rate

Calorimeter at NBS" , ASTM STP 502, Ignition, Heat Release, and

Noncombustibility of Materials, ASTM, 1972, pp. 135-151.

19« W. J. Parker, Personal Communications, National Bureau of Standards,

1972.

20. T. Kashiwagi, Personal Communications, National Bureau of Standards,

1972.

21. D. B. Spalding, "A Standard Formulation of the Steady Convective

Mass Transfer Problem", Int. J. Heat Mass Transfer , Vol.1, I960,

pp. 192-207.

22. W. J. Parker, "Flame Spread Model for Cellulosic Materials", 1969

Meeting Central States Section, The Combustion Institute, Univ. of

Minnesota, March 1969.

23. S. S. Kutatedadze and V. M. Borishanskii , A Concise Encyclopedia of

Heat Transfer , Pergamon Press, New York, 1966 , pp . U69-71

.

2k. J. N. de Ris, "The Spread of a Laminar Diffusion Flame", Twelfth

Symposium (international) on Combustion , The Combustion Institute,

1969, p. 2kl. ~~

25. P. J. McCarter, Personal Communications, National Bureau of

Standards, 1972.

26. M. P. Escudier, "Aerodynamics of a Burning Turbulent Gas Jet in a Crossflow", Combustion Science and Technology , Vol. U', 1972,

pp. 293-301.

27. T. Kasuda, Personal Communications, National Bureau of Standards,

1972. .

104
28. J. Baker, Personal Communications, Urban and Environmental Systems,

Honeywell, Inc., Minneapolis, Minn. 1972.

29. H. S. Carslaw and J. C. Jaeger, Conduction of Heat in Solids , Oxford, 1959.

30. G. Robinson, Personal Communications, National Bureau of Standards,

1972.

31. P. H. Thomas, "The Size of Flames from Natural Fires", Ninth Symposium

(Inter.) on Combustion , Academic Press, New York, 1963, p. 844.

32. C. Huggett, "Carpet Flammability and the NBS Corridor Fire Program",

Standardization News , Vol. 1, No. 5, May 1973.

105

r;r; •< 5<_.1 I J* I t-V II

1 «j.s. Of-"-. OP CO'.'V. 1. PUBLICATION OK REPORT NO. 2. Gov't Accession

ti!D' ir^DADJir riAT* No. DiOi.il/wKArrlH_ DA I A W^SlR 73— 1^9

3. Recipient's Accession No.

1

j*4. 1"! ILL. AM) SUHTI ILE Experimental and Analytical Studies of Floor Covering

Flammability with a Model Corridor

5. Publication Date

6. Performing Organization Cod?

7. AUIHOR(S)

Wells Denyes and Janes Quintiere

8. Performing Organ ization NBSIR 73-199

9. PKRFORMIN'G ORGANIZATION NAME AND ADDRESS

NATIONAL BURLAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No. 490 0572

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Man-Mad e Fiber Producers Association, Inc.

1150 Seventeenth St. N.W., Washington, D.C. 20036 and

National Bureau of Standards

Washington, D.C. IVllk

13. Type of Report & Period

Covered

Final .

14. Sponsoring Agency Code

1

15. SUPPLEMENTARY NOTES

1 6. ABS J R AC. I > A J00- word or less factual summary of most significant in format 10 n. If document inc lude s a signif ic ant bibliography or literature survey, mention it here.) An experimental model corridor facility was designed, constructed, and instrumented. The

facility examines flame spread over floor covering materials in a small scale corridor

under a forced air flow condition. A gas burner flame serves as the ignition source. A study was made of the factors influencing flame spread in the model corridor. These

factors included energy release rate of the ignition source, air velocity, and model

corridor geometry. Twenty-six carpet materials and 5 other floor covering materials

were studied in the model corridor, and 369 flame spread runs were conducted.

It was found that flame spread behavior in the model corridor generally involves either

a rapidly accelerating flame front which propagates the full 8 foot length of the test

section ("f .ameover") , or involves a decelerating flame front which results in extinction a short distance from the ignition source. Radiant heating of the floor material

due to hot products of combustion heating the ceiling is a significant factor in

causing flameover. Carpet assembly was found to affect flame spread more significantly

than pile fiber type.

The data have been analyzed to determine quantitatively the effects of the factors

influencing flame spread. Scaling relationships have been presented to attempt to

extrapolate the model corridor results to full scale corridor fires.

Finally a procedure has been suggested for using the facility in a floor covering

flammability test method. The procedure is based on determining the minimum energy

input rate to cause flameover.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Flame spread; floor covering materials; model corridor; scaling laws; test method

l

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