NBSIR 75-967

Radiative Ignition of Some

Typical Floor Covering Materials

Karen Den Braven

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

December 1975

Final Report

U S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

0* 0F

NBSIR 75-967

RADIATIVE IGNITION OF SOME

TYPICAL FLOOR COVERING MATERIALS

Karen Den Braven

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

December 1975

Final Report

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

CONTENTS

Page

LIST OF FIGURES iv

LIST OF TABLES iv

Abstract 1

1. INTRODUCTION 1

2. EXPERIMENT 2

3. DISCUSSION OF RESULT 3

4. REFERENCES 5

iii
LIST OF FIGURES

Page

Figure 1. Schematic of Apparatus 8

Figure 2. Ignition Delay Time (t^ ) vs Incident

Radiant Heat Flux (q") for a White Acrylic

Carpet (A-5) 9

Figure 3. Ignition Delay Time (t^ ) vs Incident

Radiant Heat Flux (q") for 0.6 cm Thick

Hardboard 10

Figure 4. Ignition Delay Time (t^ ) vs Incident

Radiant Heat Flux (q") for a Vinyl-Asbestos

Floor Tile 11

Figure 5. Transient or Unsustained Ignition Time (t. ) vs Incident Radiant Heat Flux (q") for an

" Aromatic Polyamide Carpet 12

Figure 6. Ignition Delay Time (t^ ) vs Incident

Radiant Heat Flux (q") for a Red Acrylic

Carpet 13

Figure 7. Ignition Delay Time (t^ ) vs Incident

Radiant Heat Flux at Various Pilot Distances

for a White Acrylic Carpet 14

LIST OF TABLES

Table 1. Materials Tested 15

Table 2a. A Comparison of Ignition and Flashover

Times for Several Floor Coverings 16

Table 2b. Material Identification Code 17

iv
RADIATIVE IGNITION OF SOME

TYPICAL FLOOR COVERING MATERIALS

Karen Den Braven

Abstract

The ignition time for some typical floor

coverings was measured at varying incident radiant flux levels. A large radiant panel was used

as a heat source, with a non- impinging pilot flame

1.0 cm above the sample as an ignition source.

Each material was subjected to flux levels varying

from 0.5 - 2.4 W/cm2

. Samples were 5 cm square,

mounted horizontally below the radiant panel. A

critical flux level, below which ignition did not

occur, was determined for each material. No correlation was observed between the ignition time of

flooring samples and the time to flashover in fullscale corridor experiments in which the same flooring materials were used.

Key words: Carpets; floor coverings; horizontal;

ignition; ignition time; pilot ignition; radiant

heat flux.

1. INTRODUCTION

Ignition experiments have been done using a large

radiant panel and a non-impinging pilot diffusion flame on

small samples of various floor coverings. The purpose of

the experiments was to determine the ignition delay time

(t^g) as a function of incident radiative heat flux (q") i a low velocity (room) environment with an ambient temperature of 24+2 °C. The radiant flux level ranged from the

1
minimum value to cause ignition for a given material to generally 2.5 W/cm 2

. The results from these preliminary experiments could give some indication of the ignition hazard of

floor coverings. For example, these results could indicate

when a room floor covering might ignite when exposed to the

radiant heating of a developing fire.

2. EXPERIMENT

A radiant panel was oriented horizontally with the

sample placed below. The samples themselves were 5 cm

square, and were mounted in a steel box which exposed the

sample surface to radiation from the radiant panel. They

were kept at the surface by a 0.6 cm thick asbestos-cement

board (2,100 kg/m 3

) which was epoxied to a set of five small

springs which bore against the bottom of the box. These

springs promoted good contact between the asbestos-cement

board and the rear face of the sample and pressed the front

face of the sample against the top lip of the steel box.

The distance from the radiant panel was measured to the

sample surface. The pilot flame was approximately 0.7 cm in

diameter and its lower edge was kept 1.0 cm above the center

of the sample. The radiant panel described by Kashiwagi [1]

was 38 cm x 84 cm in size, and was kept at a constant temperature of around 870 °K. A schematic of the apparatus is

shown in figure 1. Radiant flux levels were changed by

varying the distance from the sample to the panel. A heat

flux meter was used to calibrate these distances and also to

determine the time at which the panel temperature stabilized,

after which a test was begun.

After the sample holder had been placed under the radiant

panel, the sample was kept from exposure to the panel by an

2
aluminum shatter. Timing with a stop watch began when the

shutter was removed. The sample was then allowed to heat

and ignite. Unnecessary time under the panel was kept to a minimum to avoid unwanted preheating. The gas pilot was

just large enough to insure the life of the flame in the

stream of hot pyrolysis gases from the samples. In most

cases, gas evolution would begin shortly after exposure to

the panel.

3. DISCUSSION OF RESULT

Many times recurrent flashes from the pilot to the

sample surface would occur before ignition. In such cases

the time noted was that of sustained ignition. The exception

to this rule was the aromatic polyamide carpet, which would

not sustain ignition. In this case, the times recorded were

those at which the first flashing occurred. With this

material, as well as with other samples that would not

ignite, gas evolution would reach a peak, then taper off and

eventually subside.

A variety of materials were chosen for the tests. The

white acrylic carpet coded A-5 was chosen because of extensive

testing done on flame spread for this particular type by

Kashiwagi [1] . The aromatic polyamide carpet was chosen for

its fire resistant nature.

Behavior of the different materials was generally

similar, with the surface flashes noted with each type. The

white acrylic, however, would char, then form large black

bubbles on the surface. When these bubbles broke, ignition

occurred (see fig. 2) . However, with the tempered hardboard, there appears to be two different types of ignition:

3
those in which the sample cracked and those in which no

cracks occurred (see fig. 3). Cracking occurred at lower

flux levels after long heating durations. The crack would

ignite first, then the flame would spread over the entire

sample. These cracks would often continue to smolder after

extinguishment of the flame.

The vinyl-asbestos tile was also chosen as a representative floor covering that might be relatively difficult

to ignite. In these tests, however, its ignition curve (see

fig. 4) is very similar to that of the non-cracking hardboard

As the tile sample was heated, it tended to bulge away from

the support toward the flame. However, it never came in

contact with the pilot. Prior to ignition, frequent flashing

was always noted. Also the pilot flame would turn shades of

light blue and green from the volatile gases given off by

the sample.

Results from the white acrylic carpet were the most

reproducible. Separate runs at the same radiant flux level

often differred by only a few seconds. The hardboard seemed

the least consistent, due in part to the problem with the

cracking at low flux levels. The aromatic polyamide carpet

proved itself particularly difficult to ignite. Even at

flux levels well above 2 W/cm2 the samples would, after a few minutes, begin flashing with great frequency, but would

never sustain ignition. After several minutes of this flashing it would abruptly cease, with decreased gas evolution

thereafter. Thus, the curve in figure 5 records the time of

flashing, as opposed to sustained ignition. Again, the

flashing ignition curve is similar in form to the sustained

ignition curves of the other floor coverings.

4
All the materials appear to have a specific critical

flux associated with them, below which ignition will not

occur. For materials such as A-5 the curve (see fig. 2)

appears gradually to approach an asymptote of 0.97 W/cm2. For the red acrylic (see fig. 6), however, the asymptote is

abruptly reached, with the graph becoming almost vertical

below 1.24 W/cm2

. The highest flux level tested at which

ignition did not occur is noted for each material on the

figures. Thus, the critical ignition flux lies between the

"no ignition line" and the lowest ignition flux data point.

The apparent asymptote on the ignition curves yields the

critical flux.

A question was raised concerning the choice of 1.0 cm as

the distance from the pilot flame to the sample surface. It

can be qualitatively assumed that the farther the pilot is

from the sample the longer the ignition time. The question

then was whether 1.0 cm was a sufficiently short distance to

allow the determination of the correct minimum flux necessary

for ignition. A series of tests was run to determine the

effect of pilot distance on ignition time. The white acrylic

(A-5) was chosen because previous test results with this

material proved very reproducible.

Three distances were chosen, 0.5, 1.0, and 2.0 cm. At

<0.5 cm the pilot tended to impinge on the carpet surface,

causing almost immediate ignition. The data for the 1.0 cm

distance comes from the original tests (see fig. 2). The

results are shown in figure 7. Though there is some difference in ignition time between 0.5 and 1.0 cm at intermediate

flux levels, the asymptotes are the same. As can be expected,

the graph shows that 2.0 cm is not a sufficiently short

distance for establishing the proper asymptote. Ignition

times are much longer at all flux levels tested. Thus, 1.0

cm can be considered as an adequate distance for testing.

5
As a final experiment, twelve floor covering materials

used in NBS full-scale corridor fire experiments were tested

in this ignition apparatus. This was undertaken to examine

whether an ignition phenomenon might have been the mechanism

of flashover in these full-scale tests. The flooring assembly

of the ignition experiments matched in most cases the fullscale assembly configuration. The NBS corridor subfloor was

0.64 cement-asbestos board on brick which corresponds to the

support block of the sample holder. Carpet underlayment was

used in the ignition experiments as indicated by "/u" in

table 2a. However, samples were not bonded in the ignition

experiments as indicated by "g" (table 2a) for the corresponding full-scale test. Also, a plywood underlay was not

used for the wood floors as was done in full-scale. The

radiant flux level was fixed at 2.1 W/cm2

. Relative ranking

given by the resultant ignition delay times did not correlate

with the full-scale corridor flashover times [2] . The

comparison is included as table 2. It is a striking contrast

that the wool carpet with underlayment ignited in the shortest time, yet the same carpet without underlayment did not

ignite at all! These results were repeated twice with

excellent reproducibility; in fact, most of the ignition

results in table 2a were reproduced twice. The fact that a correlation between ignition times and flashover times did

not result, suggests that an ignition mechanism was not

responsible for flashover in these corridor experiments.

The mechanisms promoting flashover can be many and complex.

Hence, correlation is not necessarily to be expected for

corridors. Similarly, the relationship of ignition-controlled

flashover to room, rather than corridor, floor coverings is

a separate, and presently unresolved, question.

6
4 . REFERENCES

[1] Kashiwagi, T. , Experimental Observation of Flame

Spread Characteristics Over Selected Carpets, JFF/

Consumer Product Flammability , Vol. 1, 367-389

(Dec. 1974).

[2] Quintiere, J. and Huggett, C, An Evaluation of Flame

Spread Test Methods for Floor Covering Materials,

Nat. Bur. Stand. (U.S.), Special Publication 411, Fire

Safety Research, Proceedings of a Symposium held at

the National Bureau of Standards, August 1973, 59-89

(Nov. 1973).

7
208V

N0TE : Not to scale

Figure 1. Schematic of Apparatus

8
Figure 2. Ignition Delay Time (tj_g) vs Incident Radiant

Heat Flux (q") for a White Acrylic Carpet (A-5)

9
1500

1400

1300

1200

1100

1000

900

800 ~ 700 </> 600

500

400

300

200

100

0

i i r

NO IGNITION^

Sample cracked

before ignition

J. 1 ± J. .8 1.0 1.2 1.4 1.6

Q" (W/cm 2

)

.8 2.0 2.2 2.4 2.6

Figure 3. Ignition Delay Time (t^ ) vs Incident Radiant

Heat Flux (q") for 0.6 cm Thick Hardboard

10
1500

I400h

1300

1200

1100

1000

900

800

2 700

~ 600

500

400

300

200

100-

0

i i i i f r

NO IGNITION

I l

i

.6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

q"(W/cm2 )

Figure 4. Ignition Delay Time (t ig ) vs Incident Radiant

Heat Flux (q") for a Vinyl-Asbestos Floor Tile

11
1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

100-

0

i i r

NO IGNITION

J 1111

i i i i r

Transient Ignition

B

\

B

BJ L

.2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8

q" (W/cm2)

Figure 5. Transient or Unsustained Ignition Time

(t. ) vs Incident Radiant Flux (q" ) for an lg ^ Aromatic Polyamide Carpet

12
700

600

500

400

300

200

100

\ i i i r

NO IGNITION

J L J I

i

1 1 1 1 r

•8-

•8-

0 2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 26

q"(W/cm2)

Figure 6. Ignition Delay Time (t. ) vs Incident

Radiant Heat Flux (q" ) for a Red Acrylic Carpet

13
' ' ' I .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

q" (w/cm2)

Figure 7. Ignition Delay Time (t. ) vs Incident

Radiant Heat Flux at Various Distances for a White Acrylic Carpet

14
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15
Table 2a. A Comparison of Ignition and

Flashover Times for Several Floor Coverings

t ig at 2.1

W/cra2 (s)

NBS Corridor

* Flashover Time

(s)

W-l/u 40 460

A-2/u 53 342

0-1-g 88 840

A-l 92 No Sustained Spread

A-l/u 108 555

R-4-g 158 No Sustained Spread

N-3/u 277 440

N-IF 486 300

RO 1043 630 W mj V

RO-v 1063 444

NO 107 + 740

W-l none 312,420

* From Quintiere and Huggett [2]

Unsustained ignition, start of flashing •

16
* Table 2b. Material Identification Code

Code Material

A- 1 Acrylic carpet, woven level loop, .18 g/cm^

A- 2

2 Acrylic carpet, random shear, .23 g/cm

N- IF

2 Nylon carpet with integral foamback, .30 g/cm

N- 3

2 Nylon carpet, level loop, .23 g/cm

NO 2 Aromatic polyamide carpet, 0.17 g/cm

0- 1-g 2 Olefin carpet, level loop, bonded, .18 g/cm

R- 4-g TT 1 VinylT sheet, 1_ j_ 1bonded, "IT*inorganic'11* backing

RO Red oak flooring

RO -v Red oak flooring with spar varnish

u

2 Rubberized hair- jute underlayment , 0.19 g/cm

w- 1

2 Wool carpet, woven level loop, .25 g/cm

* Quintiere, J. and Huggett, C. [2] p. 67

17
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 75-967

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Radiative Ignition of Some Typical Floor

Covering Materials

5. Publication Date December 1975

6. Performing Organization Code

7. AUTHOR(S)

Karen Den Braven

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

UtrAR 1 MCn 1 Ur lUMMCKlt

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4915676

11. Contract/Grant No.

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

same as No. 9

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.)

The ignition time for some typical floor coverings

was measured at varying incident radiant flux levels.

A large radiant panel was used as a heat source, with a non-impinging pilot flame 1.0 cm above the sample as an

ignition source. Each material was subjected to flux

levels varying from 0.5 - 2.4 W/cm2

. Samples were 5 cm

square, mounted horizontally below the radiant panel. A

critical flux level, below which ignition did not occur,

was determined for each material. No correlation was

observed between the ignition time of flooring samples and

the time to flashover in full-scale corridor experiments

in which the same flooring materials were used.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Carpets; floor coverings; horizontal; ignition;

ignition time; pilot ignition; radiant heat flux.

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