NBSIR 76-1018

Evaluation of the Fire

Performance of Carpet

Underlayments

Susan Alderson and Leslie Breden

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

September 1976

Final Report

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBSIR 76-1018

EVALUATION OF THE FIRE

PERFORMANCE OF CARPET

UNDERLAYMENTS

Susan Alderson and Leslie Breden

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

September 1976

Final Report

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

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

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

I

CONTENTS

Page

LIST OF FIGURES iv

LIST OF TABLES vi

SI CONVERSION UNITS vli

Abstract 1

1. INTRODUCTION 1

2. EXPERIMENTAL DESIGN 1

2.1. Large-scale 1

2.1.1. Description of the Corridor 2

2.1.2. Description of Burn-Room 2

2.1.3. Description of Wood Cribs 2

2.1.4. Description of the Instrumentation 3

2.1.5. Description of the Carpet 5

2.1.6. Description of the Underlajrment 5

2.1.7. Procedure 6

2.1.8. Description of Flashover Phenomena in the

Corridor 6

3. OBSERVATION AND RESULTS 6

3.1. Crib Burning 8

3.2. Flame Spread in the Corridor 9

3.3. Gas Sampling 10

4. SMALL-SCALE TESTS 14

4.1. Pill Test 14

4.2. Smoke Density Chamber Test (NFPA 258T) 14

4.3. Thermogravimetric Analysis 17

4.4. Flooring Radiant Panel Test 17

4.5. Thermal Conductivity 19

5. CONCLUSIONS 20

6. ACKNOWLEDGMENTS 21

7. REFERENCES 21

iii

LIST OF FIGURES (cont'd)

Page

Figure 22. Temperature Profile — Corridor Celling 5 ft from

West Wall 43

Figure 23. Temperature Profile — Corridor Celling 10 ft from

Wall . 44

Figure 24. Temperature Profile — Corridor Ceiling 25 ft from

West Wall 45

Figure 25. Temperature Profile — 5 ft String 1 ft from Ceiling 46

Figure 26. Temperature Profile — 5 ft String 2 ft from Celling 47

Figure 27. Temperature Profile — 5 ft String 3 ft from Celling 48

Figure 28. Test No. 361 — Temperature at Center 5 ft down

Corridor 49

Figure 29. Test No. 357 — Temperature at Center 5 ft down

Corridor 50

Figure 30. Temperature at Center 5 ft down Corridor 51

Figure 31. Test No. 362 — Continuous Gas Monitoring Data ... 52

Figure 32. Test No. 367 — Continuous Gas Monitoring Data ... 53

Figure 33. Test No. 368 — Continuous Gas Monitoring Data ... 54

Figure 34. TGA — Hair Jute 55

Figure 35 . TGA — Virgin Urethane 56

Figure 36. TGA — Rebonded Urethane 57

Figure 37. TGA — Latex (Backing) 58

Figure 38. TGA — SBR Rubber 59

Figure 39. Flooring Radiant Panel Tester Schematic Side

Elevation 60

Figure 40. Standard Radiant Heat Energy Flux Profile 61

V
LIST OF TABLES

Page

Table 1. Corridor Instrumentation 4

Table 2. Summary of Corridor Experiments 7

Table 3. Maximum Temperature Time before Flashover 11

Table 4. Time to Reach 500 °C 11

Table 5. Grab Sample Infrared Data 12

Table 6. Comparison of Results Between the Specific Ion

Electrode Method and the Colorimetric Technique

for Hydrogen Cyanide Analysis 13

Table 7. NBS Smoke Chamber — Smoldering 15

Table 8. NBS Smoke Chamber — Flaming. 16

Table 9. Carpet Underlayment Evaluation with the Flooring

Radiant Panel Test 18

Table 10. Flooring Radiant Panel Results of Carpet and

Underlayment 19

Table 11. Thermal Conductivity Measurements 20

vi
SI CONVERSION UNITS

In view of present accepted practice in this technological area,

U.S. customary units of measurement have been used throughout this

report. It should be noted that the U.S. is a signatory to the General

Conference on Weights and Measures which gave official status to the

metric SI system of SI units in 1960. Readers interested in making use

of the coherent system of SI units will find conversion factors in ASTM

Standard Metric Practice Guide, ASTM Designation E 380-72 (available

from American Society for Testing and Materials, 1916 Race Street,

Philadelphia, Pennsylvania 19103). Conversion factors for units used in

this paper are:

Length

*

1 in = 0.0254 meter

1 ft = 0.3048* meter

Area

6.4516* X 10 ^ meter^

9.2903 X 10 meter^

Volume

1 gal 3.8 liters

Mass

1 lb = 0.4536 kg

Density

1 lb cu ft = 0.016 g/cc

Energy

1 Btu = 1054.8 J

1 Btu/lb = 2.326 kJ/kg

A

Exact Value

vii
SI CONVERSION UNITS (cont'd)

Temperature

°C = 5/9 (Temperature °F - 32)

Power

1 Btu/min = 17.57 W

Time

1 min = 60 s

viii
EVALUATION OF THE FIRE PERFORMANCE OF CARPET UNDERLAYMENT

Susan Alderson and Leslie H. Breden

Abstract

A series of carpet underlayments was evaluated for fire

performance in a corridor configuration using the same carpet

in all tests. Carpets with underlayments flashed over during

corridor tests. In a series of small-scale tests, such as the

smoke density chamber and the radiant panel, the flammability

properties of the carpet tended to mask the flammability properties of the underlayment . The exception to this masking

effect was the results from the flooring radiant panel test

where the thermal conductivity of the underlayment influenced

the burning characteristics of the carpet. High concentrations

of toxic combustion products were observed at the time of

flashover in the corridor, with both cellulosic and synthetic

underlayments. Smoke optical density values for the various

carpet plus underlayment combinations were approximately the

same in the flaming mode, except for the integral pad system

which has a higher value.

Key words: Carpets; fire; flammability; floor coverings; pad;

underlayments

.

1 . INTRODUCTION

The current mandatory carpet flammability standard, Department of

Commerce FF 1-70, uses the methanamine pill test to keep easily ignited

carpets off the market. In some cases, however, such as in institutional

buildings, multiple occupancy buildings, and other special occupancies,

a more severe test of carpet performance may be desirable. The purpose

of this study was to determine the effect of an underlayment on the

spread of fire on carpet in a corridor when the fire originates in a room

adjacent to the corridor, and to correlate the results of these tests

with the results of small-scale laboratory tests. The corridor configuration is an experimental simulation to investigate fire spread in fullscale, and is not a test method to evaluate carpets or underlayments.

2. EXPERIMENTAL DESIGN

2.1. Large-scale

Five different carpet underlayments which were covered by the same

carpet, were evaluated for fire performance in a corridor configuration.

For example, the maximum temperature at flashover could be examined for

each underlayment as well as the products of combustion. In addition.

1
the effect of underlayments on the results of a small-scale test such as

the flooring radiant panel, could also be evaluated. A detailed description of the experiments is given below.

2.1.1. Description of the Corridor

Schematic drawings of the NBS corridor facility are shown in

figures 1, 2, and 3. The corridor has been described extensively by

other workers [1,2]-'-.

The corridor is 30 feet long, 8 feet wide, and 8 feet high. At one

end of the corridor there is a doorway connecting to a burn-room where a

crib fire is initiated. The walls and the ceiling are constructed of

1/2-inch low density cement-asbestos board on steel studs covered by

5/8- inch gypsum wall board. The subflooring consists of 1/4- inch high

density cement-asbestos board on a brick base. An exit window 70 inches

by 41 inches is located at the far end of the corridor. Part of the air

needed for combustion of the cribs enters the burn-room through the door

from the corridor. Air enters the corridor along the floor and then

into the burn room. The hot combustion products from the burn-room flow

out along the corridor ceiling and, finally, out the top of the exit

window as shown in figure 4.

A view of the burn-room is shown in figure 5. The burn-room is of

concrete block construction, 9.3 x 7.7 x 8.4 ft high, with a door opening

of 6.5 X 2.5 ft. Located 1 foot above the floor of the burn-room are two

small vents 7 x 14 in. These vents are open to the atmosphere and supply

a portion of the combustion air. The burn-room interior is sprayed with

a one-inch thick protective coating of refractory material over the concrete block. This coating has the following thermal properties:

Full-scale experimental fires for room simulation suggest that wood

cribs present a realistic fire severity [3]. Four hemlock wood cribs were

used to simulate burning objects in a room. The cribs are made of sticks

1-1/2 inches wide with a cross stick spacing of 3 inches (see figure 3).

There are 4 sticks in each layer, with 16 layers, except the bottom layer

which has 2 sticks. The 4 cribs are oven dried to a moisture content of

2.1.2. Description of the Burn-Room

Density

Thermal Conductivity

Specific Heat

Thermal Diffusivity

18.5 Ib/ft^

0.057 Btu/hr °F

0.2 Btu/hr °F

0.0015 ft^/hr

2.1.3. Description of Wood Cribs

Numbers in brackets refer to the references listed at the end of this

paper.

2
approximately ten percent. They are placed in the burn-room on a load

cell platform. To initiate the experiment, they are ignited by 250 ml of

heptane placed in a pan under each crib. Each crib weighs approximately

42.5 lbs with a total weight for the four cribs of 170 lbs. The four

cribs provided a fuel loading of 2.7 lbs per square of floor area and

each have a maximum burn rate of 12.5 lbs of wood per minute, maintaining

this rate for 8 to 11 minutes , as shown in figure 6

.

2.1.4. Description of the Instrumentation

Table 1 outlines the measurements taken in the burn-room and the

corridor. Chromel-alumel type thermocouples are used to measure temperature. Pitot tubes at the top of the burn-room and exit doors measured

the combustion product velocities while the bottom pitot-static tubes

measured the inlet airflow. Radiometers are mounted in the floor of the

corridor to monitor incident flux. In addition, there is a radiometer

mounted on the wall monitoring radiation in the burn-room. Heat flux

meters are also used to measure heat loss through the walls. Finally,

the cribs are placed on a load cell platform so that the burning rate of

wood cribs can be measured. All measurements are recorded by a high

speed digital data acquisition system. This system recorded all inputs

at 20-second intervals with seven recording points per second.

Two methods of gas sampling were employed to analyze the atmosphere

in the corridor:

1. continuous measurement of O2, CO2. , and CO concentrations; and

2. grab samples which were collected in pre-evacuated 2-liter glass

bulbs for later laboratory analysis.

The continuous measurements of CO and CO2 were made with nondispersive infrared instruments. These instruments were calibrated with

known gas mixtures and calibration curves developed since the instrument

readout was nonlinear. To protect the non-dispersive infrared instruments, the sample line contained a series of traps. As the sample was

drawn from the corridor, it entered a glass wool ambient trap for removal

of the majority of particulate matter. A sub- ambient dry ice trap also

packed with glass wool was used to eliminate the water. Finally, a

third glass wool trap maintained at ambient temperatures was used as a

back-up for any overflow of particulate matter before the gas entered

the analyzers. A stainless steel line was used from the sampling point

in the corridor into the cold trap and either copper or polyethylene

tubing was used from that trap to the analyzers. The delay time was

considered insignificant with respect to the response of the instrument.

An electrolytic diffusion O2 cell was used to measure the O2

depletion. These cells have been reliable, but some problems were

encountered requiring frequent regeneration of the cell. The O2

cells, and CO2 analyzers were directly attached to a Vidar System. The

data were stored on a magnetic tape and processed by computer.

3
Table 1. Corridor Instrumentation

TC Center of Burn-Room Ceiling

TC Ceiling of Corridor 01 ft from CL of Doorway

TC Corridor CL Ceiling 02 ft from West Wall

TC Corridor CL Ceiling 05 ft from West Wall

TC Corridor CL Ceiling 10 ft from West Wall

TC Corridor CL Ceiling 15 ft from West Wall

TC Corridor CL Ceiling 20 ft from West Wall

TC Corridor CL Ceiling 25 ft from West Wall

TC Pitot Tube No. 1 TC Pitot Tube No. 2 TC Pitot Tube No. 3 TC Pitot Tube No. 4 TC Pitot Tube No. 5 TC Pitot Tube No. 6

TC Pitot Tube No. 7 TC Pitot Tube No. 8 Pitot Tube No. 1 Burn-Room Door

Pitot Tube No. 2 Burn-Room Door

Pitot Tube No. 3 Burn-Room Door

Pitot Tube No. 4 Burn-Room Door

Pitot Tube No. 5 Burn-Room Door Bottom

Pitot Tube No. 6 East Window

Pitot Tube No. 7 East Window

Pitot Tube No. 8 East Window

TC 5 ft String 1 ft from Ceiling

TC 5 ft String 2 ft from Ceiling

TC 5 ft String 3 ft from Ceiling

TC 5 ft String 5 ft from Ceiling

TC 5 ft String 6 ft in from Floor

TC 25 ft String 1 ft from Ceiling

TC 25 ft String 2 ft from Ceiling

TC 25 ft String 3 ft from Ceiling

TC 25 ft String 5 ft from Ceiling

TC 25 ft String 6 in from Floor

O2 Burn Door

O2 20 ft Ceiling

TC Ref

Load Cell

Radiometer No. 1

Radiometer No. 2 Heat Fluxmeter No. 1

Heat Fluxmeter No. 2 Heat Fluxmeter No. 3

Heat Fluxmeter No. 4 CO 20 ft

CO2 20 ft

TC Door CL .5 ft

TC Door CL 2 ft

TC Door CL 4 ft

TC Door CL 6.5 ft

CL Floor 5 ft from West Wall

CL Floor 9 ft from West Wall

CL Floor 13 ft from West Wall

CL Floor 17 ft from West Wall

CL Floor 21 ft from West Wall

CL Floor 25 ft from West Wall

Seconds

4
In addition to these measurements, a bubbler system was used to collect HCN. Two bubblers were used in series, each containing 200 cc of

0.1 N NaOH. The flow rate averaged 2 liters /minute. Analysis of the

NaOH solution was done using both specific ion electrode methods and the

colorimetric technique according to Leithe [4] . The sample point for

the HCN analysis was 20-ft from the entrance of the corridor and approximately 2 feet from the ceiling. The sample line from the bubbler to the

sampling port was 2 feet-8 inches.

The grab samples were taken at the 20-ft position: the first at

5 min, 1 inch from the ceiling; the second and third samples at 10 min,

the second 1 inch from the ceiling and the third 4 feet from the ceiling.

The fourth was taken at 15 min, or at "flashover," whichever occurred

first (1 foot from the ceiling). The flasks were attached by a 19/9 ball

joint to 2.5 inches of pyrex tubing which was approximately 1 foot long

and went through the wall. These samples were not filtered; therefore,

smoke, particulate matter, and gases were collected together.

The grab samples were analyzed using a Perkin-Elmer 457 infrared

spectrophotometer. A one-meter gas cell was used. The measured percent

transmittance was sensitive to pressure; therefore, all the samples were

run at 100 torr pressure. Calibration curves were developed based upon

peak height and were used for semi-quantitative results . The gases

analyzed in this way were CO, CO2, CHi^, C2H^, C2H2, and HCN.

2.1.5. Description of the Carpet

The carpet used in this experiment was standard for all the tests

and was composed of 3-ply nylon yarn with a total weight of 56 oz/yd^

.

The face fiber has a weight of 22 oz/yd^. The pile height was .177 Inches

with a tufted gage of 1/10 inch and 7 stitches per inch. The primary

backing was polypropylene filament with a jute secondary backing. The

carpet had a potential heat of combustion of 6968 Btu/lb.

2.1.6. Description of the Underlayment

Five different types of underlayments were examined — hair jute,

virgin urethane, rebonded urethane, integral latex with alumina trihydrate

filler, and styrene-butadiene rubber containing calcium carbonate and

naphthenic oil. Their corresponding densities and thermal conductivity

were respectively, 8.8, 2.6, 5.2, 17.7, 4.2 lbs/ft ^ and 0.29, 0.18, 0.23,

0.45 and 0.38 Btu/hr/ft^/F^/in. The underlayments were 1/2 inch thick

except for the integral latex and the SBR and waffle pads which were 3/16

inch thick. The hair jute was not treated for fire retardancy while the

virgin urethane and the rebonded urethane contained a phosphorus type

flame retardant. The virgin and rebonded both had a 0.0075-inch film of

low density polyethlene on the surface. The carpet was placed directly

over the underlayment except for experiments 362, 363, and 365 where a

chloroprene type of adhesive was used to bond the carpet to the underlayment .

5
2.1.7. Procedure

A blank run (No. 355), was made with four cribs in the burn-room,

and a cement-asbestos board floor in the corridor. Metal cans filled with

250 g of heptane were used to ignite the cribs. Measurements were taken

with these burning cribs alone. This procedure was repeated with the

nylon carpet in the corridor over the cement-asbestos board (No. 356).

The experiment was then repeated with the carpet laid down over various

pads or adhered to a pad for the length of the corridor. When carpeting

was used, a piece of carpet, 2 x 4 ft, was extended into the burn-room

under the cribs. This piece provided for a continuous path for the flame

to spread into the corridor. Eleven tests were conducted. The details

are given in table 2.

2.1.8. Description of Flashover Phenomena in the Corridor

A test commences with the ignition of the four cribs in the burnroom. In several minutes the crib fire reaches a fairly steady burning

rate. Approximately half of the air required to support crib combustion

flows into the burn-room through the two floor level vents, while the

remaining air supply enters from the corridor [5]. Products of combustion flow from the room along the corridor heating its walls and ceiling.

Inlet air flows over the corridor floor. The floor is heated by radiative

transfer from upper hot walls and ceiling and the hot smoke products.

Three to four minutes after the crib is ignited, ignition occurs on a

2-1/2 ft wide floor covering runner which extends from the corridor into

the burn-room. This ignition results from a high radiant heating exposure

over this runner and from the flaming crib embers falling onto the carpet.

Once ignition occurs on the runner, rapid flame spread follows over the

entire runner in the burn-room. This flooring fire then emerges and

spreads slowly into the corridor. The flame fans out from the doorway

advancing against the incoming airflow and progresses under the radiant

heating of the floor from the walls, ceiling, and hot smoke layer.

As the fire on the floor advances it consumes some of the oxygen of

the incoming air. Flashover in the corridor occurs in the gaseous phase

and ignites the carpet. The occurrence of flashover in the corridor is

preceded by a reduction in air supply from the corridor to the burn-room

so that the crib fire becomes fuel rich. The crib fire continues to

produce pyrolysis products, but incomplete combustion products enter

the corridor followed by rapid flame spread within the corridor. The

flashover from the combustion of the carpeting produces a large increase

in the corridor temperature and heat flux.

3. OBSERVATION AND RESULTS

A series of carpet underlajnnent experiments were carried out. The

results are summarized in table 2. It should be noted that due to the

extensive building renovation at the time, extraneous variables may have

6
Table 2. Summary of Corridor Experiments

Test

No.

Floor

Linings Underla3nnent Subf looring

Number

of Cribs

Flashover

Time, (s)

355 None None 1/4" CementnsDcauOo A o d i~ c? TlDOarQ o n on Brick

4 No Flashover

J JO iNy xun INUIlc

II AH iNo riasn—

over

J J / Alt T i n iNyxon riaXX JUUc M AH JNO riasn—

over

J JO JNyion virgin ure~

thane

II 1, No riasnover

361 Nylon Rebonded Urethane

II 4 810

332 Nylon Rebonded Uresives

II 4 600

363 Nylon Virgin Urethane

01 AQncsivcs

II 4 720

i.Ny±on Lat ex

II oyu

365 Nylon Virgin Urethane II 4 630

367 Nylon SBR Waffle II 4 690

368 Nylon Hair Jute II 4 810

7
Table 2a.

Experiment

No. Material

Maximum Peak Temp.

at 5 ft, 1 ft

from the Ceiling

(°C)

Maximum Peak Temp,

at 25 ft, 1 ft

(°c)

361 Nylon carpet and

rebonded urethane

689 937

364 Nylon carpet and

latex

779 898

365 Nylon carpet and

virgin urethane

776 828

JO / Viy J-KJH ^cLL L. diiU. SBR

769 969

368 Nylon carpet and

hair jute

733 879

been introduced into the tests. For example, new smoke abatement equipment was intermittantly used on some of the corridor runs. Also, prior

to run No. 358, the wall temperature was not controlled because the outside air was allowed to circulate throughout the test facility before

testing. Since these experiments were carried out at various times of

the year, the temperature and humidity in the corridor was not maintained

constant before testing. Finally, due to leaks in the cooling water lines

needed for our instrumentation, such as in the heat flux meter, there may

have been some water contamination on the carpet in several of the early

runs

.

3.1. Crib Burning

The crib burning rates are shown in figures 7 and 8. Essentially,

the cribs reached a steady-state burning rate after 3 to 5 minutes. The

time variation between tests was attributed to the variable moisture content and the non-homogeneity of the wood. After this initial lag period,

the steady-state burning rate remained constant for 8 to 11 minutes.

With a fuel loading of 170 lbs of wood and a heat of combustion energy

content of 7,200 Btu/lb, the potential heat available is calculated to be

1,250,000 Btu. However, it must be assumed that incomplete combustion

occurs and the total available energy would be about half of this amount

[1]. It has been estimated by Christian and Waterman that a bedroom fire

would have a steady burning rate of 110,000 Btu/min [5].

8
A comparison of the burning rates of the cribs indicated no significant differences between runs. Fung and others have shown that with

the refractory material as the burn-room coating, it appears that the

heat loss of the cribs to the burn-room surface by conduction is only

significant during the early phase of burning. For the rest of the run,

the heat loss by conduction to the room is about 15% of the total heat

release. The radiant energy contribution to the energy supply to the

corridor is about 10% of the total energy transport into the corridor,

since the corridor only sees the burn-room fire through the doorway.

Thus, the bulk of the energy released (75%) from the cribs enters the

corridor in the form of convective energy out of the burn-room doorway.

3.2. Flame Spread in Corridor

During the period of maximum burning, the fire plume extended out

from the burn-room and licked the corridor ceiling near the burn-room.

As the fire progressed out of the burn-room, it was preceded by a melting

of the carpet just ahead of the flame front. This same melt phenomena

was observed in the flooring radiant panel tests. The nylon carpet has

a melt temperature of approximately 215 °C.

Figures 9 through 18 illustrate a comparison of corridor runs 357

and 368. The same type of nylon carpet over a hair jute underlayment was

used in both, however run 357 did not flashover while 368 did. Figure 9

shows that the rate of weight loss of the crib was approximately the same,

with the slopes being almost parallel in the steady-state region of burning. The similarity of the burning cribs is also reflected in the ceiling

temperature of run 357. Figure 11 shows the almost congruent ceiling

temperature in the corridor for the two experiments. Figures 12 and 13

also show exactly the same tracking profile for the corridor temperature

at the 5-ft and 25-ft stations. It should be noted from figure 14 that

the peak temperature on the floor 5 ft from the west wall was greater in

run 357, which did not flashover, than run 368, which did flashover. A

comparison of floor temperatures down the corridor, as illustrated in

figure 15, also indicates that the peak temperature was slightly higher

for 357 than 368. Figures 16, 17 and 18 illustrate the slight variance

between runs using other measurement parameters.

It appears that the thermal energy in run 357 should have been sufficient for flashover to occur corresponding to 368; however, run 357

did not flashover. A similar analysis showed the same results when

tests 358 and 365 are compared. That is, thermally, 358 should have had

the potential to flashover; but it did not.

A comparison was also made of runs 361 to 368 using various measurement parameters. Figure 19 illustrates the burning weight loss of the

wood cribs used in all 5 runs. The cribs with the hair jute underlayment

had a slightly higher burning rate than the other underlayment runs.

9
Generally, the steady-state burning weight loss was 10 to 12 pounds per

minute for all runs. The ceiling temperatures in the burn-room for

these 5 runs are shown in figure 20. In terms of heat input, test 364

(latex) had the highest ceiling temperature (1031 °C) while test 365

(virgin urethane) had the lowest (757 °F) . Figures 21, 22, 23 and 24

illustrate the ceiling temperature down the corridor. The burning

virgin urethane underlayment appeared to contribute some additional

heat, which may have caused the carpet to reach the flashover condition

sooner. This is evidenced by the virgin urethane having the shortest

flashover time of the nonadhered underlayments of 630 seconds compared

to 810 seconds for the rebonded and the hair jute underlayments, shown

in table 2. Figures 25, 26 and 27 show the virgin urethane underlayment

with the highest rate of temperature rise 1, 2 and 3 feet below the

ceiling at 5 feet down the corridor. The plateau region at 300 °C to

400 °C is attributed to the melting of the nylon carpet. This represents a temperature transitional zone with the melt temperature of the

nylon carpet fiber being between 216 °C and 260 °C, while the decomposition temperature was 316 °C. Tables 3 and 4 also show the relative

times to reach to maximum temperature and the time to reach 500 °C.

It appears the temperature profile for all of the runs were similar

before flashover with the exception of the virgin urethane and the latex.

As previously described in section 2.1.8., it appears that substantial amounts of combustible products from the cribs were being generated

which were not burned. It is the accumulation of these fuels which

later become heated to above 600 °C and contribute to a flashover condition. Calculations by Quintiere [6] indicate that there is enough

oxygen in the airflow to maintain the burning of the wood cribs, but not

enough to completely burn all of the volatile fuel.

Figures 28, 29 and 30 illustrate the temperature profile 5 feet

down the corridor from the burn-room at ceiling and the floor level. The

fresh air entering along the floor acts to reduce the temperature 1 foot

above the floor; however, this cooling effect is lost with the onset of

flashover.

3.3. Gas Sampling

The results of the grab sample analysis with the materials tested

are shown in tables 5 and 6. In the first four tests, no "gas phase

flashover" occurred and the only gases detected in the grab samples in

any significant amount were CO and CO2 . From the fifth test on, "gas

phase flashover" did occur with an accompanied increase in the amount of

hydrocarbons in the grab samples. Two tests were repeated, that of

nylon carpet with virgin urethane underlayment and nylon carpet with

hair jute underlayment. The grab samples indicated that an increase in

the amount of hydrocarbons occurred earlier in the tests when flashover

took place. The buildup of these combustibles in the gas phase seems to

be a necessary element for the "flashover."

10
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Table 6. Comparison of Results Between the Specific Ion Electrode

Method and the Colorimetric Technique for Hydrogen Cyanide Analysis

Floor Covering Experiment Number

Specific Ion

Electrode Method

Colorimetric

Method

Nylon Carpet

Virgin Urethane

Pad & Adhesive 363 0 ppm 1 ppm

Nylon Carpet

Latex Pad 364 45 ppm 69 ppm

Nylon Carpet

Virgin Urethane

Pad 365 90 ppm 82 ppm

Nylon Carpet

SBR Waffle Pad 367 <1 ppm 2 ppm

Nylon Carpet

1 Hair Jute Pad 368 16 ppm 21 ppm

The correlation between the continuous monitoring shown in figure 31,

32 and 33 and the grab sample data is not apparent. Both the grab samples

and continuous monitors were positioned 20 feet away from the ignition

source — the continuous sample line being in the center of the corridor

1 foot from the ceiling, while the grab samples were taken on the left

side of the corridor at various heights. In a large-scale facility such

as the corridor there is a problem with variable and nonuniform mixing

of the gases. The gases were also handled differently. The continuous

sample traveled through at least 34 feet of tubing and three traps — two

ambient and one subambient. Most of the water and particulate matter was

removed before the sample reached the analyzers. The grab samples were

not filtered and, therefore, included water, smoke, particulate matter,

and gases which were drawn directly out of the corridor through a tube

1 foot long. These samples were then taken to the laboratory for analysis.

The comparison of the concentration values of CO and CO2 recorded

from the grab samples and continuous monitoring equipment shows a large

discrepancy in all but the last test. The different treatment coupled

with differing sampling positions might be an explanation. Test 368

(figure 33), which involved a nylon carpet with hair jute padding, grab

sample data and continuous monitoring gas data seemed to correlate much

more closely.

13
The gas analysis data in these tests Identifies some of the components present during the burning of carpet and underlayment . The hazard

associated with these components in a practical situation has not yet

been defined.

4. SMALL-SCALE TESTS

4.1. Pill Test

This test method is designed to prevent the ignition of carpets and

rugs from small sources such as matches, fireplace embers, or inadvertently

discarded lighted cigarettes. The test is extensively described in DOC

FF 1-70. A methenamine pill is placed in the center of a dried carpet

sample and ignited. The surface burning of the carpet is then measured

with a failure described when the surface burning reaches within one-inch

of an eight-inch diameter circle. The nylon carpet alone, and when placed

over any of the underlayments , passed the pill test.

4.2. Smoke Density Chamber Test (NFPA 258T)

This test method measures the attenuation of a light beam by smoke

accumulating in a closed chamber due to smoldering decomposition or flaming combustion. The results are reported in terms of maximum optical

density which is a dimensionless number expressed as follows:

^ V - 100 \ = aT^^s —

where D^ = maximum optical density

V = volume of chamber (18 ft^)

A = surface area of specimen (0.046 ft^)

L = path length of attenuation (3 ft)

T = percent transmittance

Measurements were taken from 3x3 inch specimens under a radiant

flux of 2.5 watts per square centimeter in a flaming and smoldering condition. A schematic diagram of the NBS Smoke Chamber is shown in figure

13. The smoke level of underlayments was measured individually and with

a carpet. The results are shown in tables 7 and 8.

The results indicate that in the smoldering mode, the carpet with

underlayment always had a higher smoke value than the carpet alone.

Tested alone, the waffle and the integral pads had high maximum optical

density values. It should be noted that in the smoldering mode, hair

jute, alone, had a significant loss of weight and took a long time to

reach the maximum smoke development when compared to the other underlayments . 14
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16
In the flaming mode, the smoke values of the carpet alone and with

the underlayment are about the same. The exception is the integral latex

pad system which had a significantly higher smoke value either with or

without the carpet.

4.3. Thermogravimetric Analysis

Thermogravimetric analysis (TGA) involves changes in weight of a

system under investigation as the temperature is increased at a predetermined rate. Samples of underlayments were conditioned for 24 hours at

23 °C, 50% relative humidity and placed in the TGA sample holder. The

sample was heated at 10 °C per minute in air. Figures 34 to 38 illustrate the results from the TGA. Generally, all of the underlayments had

a 50% weight loss by 300 °C. The initial weight loss of hair jute was

attributed to absorbed water loss. The virgin and rebonded urethane

underlayments gave uniform decomposition curves compared to the complex

curve of SBR rubber underlajonent

.

4.4. Flooring Radiant Panel Test

A radiant panel test has been developed which determines the critical radiant flux at extinguishment of flooring systems. This test

consists of a radiant panel placed at a 30° angle to a horizontal specimen as shown in figure 39. Measurements are taken of the distance

burned which is related to the critical radiant flux at the time of

extinguishment (figure 40). The initial flux level for the flooring

radiant panel was based on the heat flux level found in the large-scale

corridor tests prior to flashover.

The results, as shown in table 9, indicate that the underlayment

significantly lowers the critical heat flux so that the carpets burn

a greater distance. It appears that the heat transfer through the

carpet is impeded by the underlayment thereby allowing more heat to be

available for feedback in order to maintain the spread of fire. Thus,

the carpet without the underla3nnent had a critical heat flux was 0.24,

but with the underlayment it was reduced from 0.16 to 0.12.

Table 10 illustrates the effect of a hair jute pad on various types

of carpets when tested with the flooring radiant panel test, showing the

consistent decrease in critical flux when the pad is used to change the

thermal properties of the system.

Thus, it appears that the thermal conductivity of the underlayment

is one of the major factors in determining the horizontal surface flame

spread along carpets.

17
Table 9. Carpet Under layment Evaluation With the Flooring

Radiant Panel Test

Carpet Par?

Critical Flux

w/ cm mi 1 i f\ r> o L> oiumen L s

Nylon Hair Jute 0.12 Very high flames and

heavy black smoke.

38 cm.

Nylon Virgin Urethane 0.14 High flames and heavy

to an average 36.5 cm.

Nylon Rebond 0.16 High flames and heavy

black smoke. Melted

LO an dverage jd. j cm.

Nylon Integral Latex 0.13 Heavy black smoke.

Buckled after 2.5 min.

Melted to an average

LI ,3 cm.

Nylon SBR Waffle .13 Very high flames and

heavy black smoke,

ricitcci to an dveiragc

35 cm.

Nylon .24 Thick black smoke.

Melted to an average

27 cm.

18
Table 10. Flooring Radiant Panel Results of Carpet and Underlayment

Type of Material Radiant Critical Flux

(W/cm2)

Wool J- . u Wool and Hair Jute 0.66

Acrylic

HcryjLic anu 0.25

Nylon A nU /i 9 . 4Z

Nylon A and Hair Jute <.10

Nylon B U . bl

Nylon B and Hair Jute 0.35

Polyester A

Polyester A and Hair Jute <.10

Polyester B 0.24

Polyester B and Hair Jute <.10

4.5. Thermal Conductivity

Thermal conductivity measurements were made of the carpet plus the

underlayment by means of the guarded hot plate method in accordance with

the procedure described in ASTM C177. This method covers thermal conductivity measurements of dry specimens using a hot metal center plate

at 100 °C and two outside cold plates at 53 °C. A sample size of 8 x 8

inches was used with measurements taken of the carpet alone and with the

underla3mient . The heat flux, Q in the center and outside plates was

rigidly controlled while the temperature difference between the hot and

cold plates was measured. The smaller the K the better the insulation

values of the material. The apparent thermal conductivity is calculated

based upon Q = KATAX

where Q = heat flux

K = thermal conductivity

AT = temperature difference between the hot and cold

plates

AX = thickness

It appears that the thermal conductivity of the carpet alone is

significantly higher than any of the underlayments (table 11) . The effect

of lower thermal conductivity values is to prevent heat transfer out the

back of the carpet and allow for more reinforcement of the burning to

take place in the carpet. It appears that a similar situation exists in

the corridor experiments, however, in the original experimental design

of the corridor, this property of carpet or underlayment was not measured.

19
Table 11. Thermal Conductivity Measurements

Floor Covering i emp V. * ^

/ J- L / r / J-ii^

Carpet & Hair Jute 7 c U 0u • J J J

L«dirp6 U 0£ V iLgXIl U ircL.IlctIlc 0. 325 ^ ^ ^

1 J » D n

LfdLUcL Of XLlUcgi-CtX J-id 71 2 0. 554

1 J » n 0 4Qfi

uarpe

L

QO • J nyj • 780

Hair Jute

* 90

Virgin Urethane

*nu • 1 ft

KeDonueu uretnane

*

Integral Latex

*

0. 45

SBR Waffle

*

0. 38

All of the thermal conductivity measurements and calculations were

carried out by Mr. Chuck Sui at NBS.

5 . CONCLUSIONS

1. Each of several underlayments used in combination with a standard

carpet caused flashover in the corridor under the conditions of

the corridor experiments described in this report

.

2. Temperature data and profiles do not appear to show significant

difference in performance of the various underlayments.

3. The proposed flooring radiant panel test demonstrated the insulating

effect of the underlayment on the extent of burning. All of the

ur derlayments lowered the critical radiant flux compared to the carpet alone.

4. High concentrations of toxic combustion products such as HCN and CO,

were observed at the time of flashover with both cellulosic and

synthetic underlayments. However, prior to flashover, and in those

cases where flashover did not occur, there was no significant buildup

of toxic gases. No attempt was made to correlate these measurements

with animal exposure.

20
5. All of the underlayments , used in combination with a standard carpet,

had a higher maximum specific optical density in the smoldering mode

when tested according to NFPA 258T than the carpet alone. In the

flaming mode, however, the smoke values from the carpet and the carpet plus the underlayment are similar. The exception is the integral

pad system which had a higher smoke value in the smoldering or the

flaming than any of the others.

6 . ACKNOWLEDGMENTS

The author gratefully acknowledges partial funding for this project

by the Urethane Foam Safety Group of the Society of the Plastics

Industries

.

7 . REFERENCES

Fung, F. C. W. , Suchomel, M. R. and Oglesby, P. L., The NBS Program

on Corridor Fires, Fire Journal, Vol. 67, 41 (1973).

Huggett, C. , Carpet Flammability and the NBS Corridor Fire Program,

ASTM Standardization News, Vol. 1, 16 (1973).

Christian, W. J. and Waterman, T. E. , Fire Behavior of Interior

Finish Materials, Fire Technology (Aug. 1970).

Leithe, W. , The Analysis of Air Pollutants, 227 (1970 ed.)

Christian, W. J. and Waterman, T. E. , Characteristics of Full-Scale

Fires in Various Occupancies, Fire Technology (Feb. 1971).

Quintiere, J., Some Observations on Building Corridor Fires,

Fifteenth Symposium (International) on Combustion, held in Tokyo,

Japan on August 25-31, 1974.

Fournier, L. B. , Standard Methods of Analysis of Water and Waste

Water, and ASTM Methods, 14th Edition.

21

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Figure 5. View in Corridor Fire Room Door Showing Wood Cribs.

Center Crib on Load Cell. Thermocouples and Pitot Tubes in Doorway.

26
200

5 0

' ' " 2 4 6 8 10 12 14 16 18 20

TIME IN MINUTES

Figure 6. Weight Loss Derived from Load Cell Data

27
Nylon Carpet

Virgin Urethane Pad

Seconds

Figure 7. Ceiling Temperature and Weight Loss of Cribs in Burn-Room.

28
Figure 8. Ceiling Temperature and Weight Loss of Cribs in Burn-Room

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NBS-IUA (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1018

2. Gov't Accession

No.

3. Recipient's Acces.sion No.

4, lliLb AINU ouDliiLc.

EVALUATION OF THE FIRE PERFORMANCE OF CARPET UNDERLAYMENTS

5. Publication Date

September 1976

6. Performing Organization Code

7. AUTHOR(S)

Susan Alderson and Leslie Breden

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

10. Project/Task/Work Unit No. 4927677

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 Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.)

A series of carpet under layments was evaluated for fire performance in a

corridor configuration using the same carpet in all tests. Carpets with

underlayments flashed over during corridor tests. In a series of smallscale tests, such as the smoke density chamber and the radiant panel, the

flammability properties of the carpet tended to mask the flammability properties of the underlayment . The exception to this masking effect was the

results from the flooring radiant panel test where the thermal conductivity

of the underlayment influenced the burning characteristics of the carpet.

High concentrations of toxic combustion products were observed at the time

of flashover in the corridor, with both cellulosic and synthetic underlayments.

Smoke optical density values for the various carpet plus underlayment combinations were approximately the same in the flaming mode, except for the integral

pad system which has a higher value.

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; fire; flammability; floor coverings; pad;

underlayments

.

18. AVAILABILITY Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

1

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