A111DB 14 0335

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publications AlllOb Mlb754

Upholstered Furniture Heat Release

Rates Measured With A Furniture

Calorimeter

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Washington, DC 20234

December 1 982

S DEPARTMENT OF COMMERCE

lir- r TIONAL BUREAU OF STANDARDS

,U56

82-2604

1982

C . 2

NBSIR 82-2604

UPHOLSTERED FURNITURE HEAT RELEASE

RATES MEASURED WITH A FURNITURE

CALORIMETER

Vytenis Babrauskas, J. Randall Lawson

W. D. Walton, William H. Twilley

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Washington, DC 20234

December 1 982

RATIONAL BURi-AL OF STANDARDS

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES ' v NOMENCLATURE vi

Abstract 1

1. INTRODUCTION 1

2. ROOM TESTS VERSUS FURNITURE CALORIMETER TESTS 3

3. DEVELOPMENT OF THE FURNITURE CALORIMETER 5

3.1 Principles of Operation 5 3.2 Practical Development

3 . 3 Calibration

3.4 Maximum Apparatus Capacity

3.5 Smoke Measurement 1 3.6 Target Irradiance Measurements 1

4. IGNITION SOURCE 12

5. TEST SPECIMENS 13

6. TEST OBSERVATIONS 15

7. RESULTS OF MEASUREMENTS 16

7.1 Times to Peak 16

7.2 Peak Rates of Heat Release 17

7.3 Smoke Production 18

7.4 Target Irradiance 19

7.5 Effective Heats of Combustion 19

7.6 Convective Heat Release Fraction 20

7.7 Reproducibility 20

8. ANALYSIS FOR ESTIMATION 21

9. ON ACHIEVING BOTH CIGARETTE IGNITION RESISTANCE AND GOOD

FLAMING BEHAVIOR 23

10. SUMMARY AND CONCLUSIONS 24

ACKNOWLEDGEMENTS 26

REFERENCES 26

APPENDIX A - ADJUSTMENTS FOR 0

2 METER RESPONSE TIME 59

APPENDIX B - FLOW BEHAVIOR OF THE FURNITURE CALORIMETER 62

APPENDIX C - ESTIMATE OF LOSSES IN SMOKE SAMPLING 63

in

N

CX)

OIO

N
LIST OF TABLES

Page

Table 1. Test specimens 29

Table 2A. Summary of burning rate data 30

Table 2B. Supplementary data - values at peak 31

Table 3 . Ranked peak times 32

Table 4. Ranked peak heat release values 33

Table 5 . Effect of padding type for specimens with similar fabrics . . 3^

Table 6. Effect of fabric type for specimens of similar construction

and padding

Table 7. Effect of specimen mass on polyurethane foam padded

specimens of similar construction 35

Table 8. Effect of frame type for specimens with similar padding and

fabrics 36

Table 9. Ranked values for smoke 37

Table 10 . Effective heats of combustion 38

Table 11 . Estimated heat release rate data 39
LIST OF FIGURES

Page

Figure 1. View of furniture calorimeter 40

Figure 2. Measured wastebasket heat release rates, along with adopted

simplified representation 41

Figure 3. Wastebasket simulation burner used as the ignition source . . 1)

2

Figure 4. Fluxes measured at the wastebasket simulation burner .... 43

Figure 5. Chair F21 44

Figure 6. Chair F21 near peak burning time 45

Figure 7. Chair F31 46

Figure 8. Chair F31 near peak burning time 47

Figure 9. Chair F32 48

Figure 10. Chair F32 near peak burning time 49

Figure 11. Chair F28 50

Figure 12. Chair F28 near peak burning time 51

Figure 13. Rate of heat release for specimen F21 52

Figure 14. Effective heat of combustion measured for specimen F21 ... 53

Figure 15. Target irradiance and particulate conversion fraction for

specimen F21 54

Figure 16. Effect of specimen mass on rate of heat release 55

Figure 17. Effect of specimen padding and fabric on rate of heat

release 56

Figure 18. Relationship between mass loss rate and target irradiance

flux 57

Figure 19. Relationship between actual and estimated peak values of

rate of heat release 58

v
NOMENCLATURE

2 A - ventilation opening area (m )

2 A - smoke chamber ceiling area (m )

d - duct diameter (m)

2 D - particle diffusivity (m / s)

dp - particle diameter (m)

F - percent transmission (%)

h - ventilation opening height (m)

Ah

c

- lower heat of combustion (kJ/kg)

k - smoke extinction coefficient (m

K - deposition velocity (m/s)

L - smoke measurement path length (m)

m - stack air flow rate (kg/s)

a. mn

- stack oxygen flow rate (kg/s)

u

2 m - fuel mass loss rate (kg/s)

m

g

- smoke mass production rate (kg/s)

n - particle concentration

Nu - Nusselt number (-)

AP^ - pressure drop across fan (Pa)

Q

- rate of heat release (kW)

r

Q

- stoichiometric oxygen/fuel ratio (-)

R - uncorrected response

R

g

- Reynolds number (-)

S - corrected response

Sc - Schmidt number (-)

t - time(s)

t - time constant(s)

t - rise time(s)

At - sampling interval(s)

T - temperature (T)

U - response function to unit step input (-)

vi
NOMENCLATURE (continued)

V

V

u average duct flow velocity (m/s)

3 chamber volume (m ) 3 stack volume flow rate (m /s)

V +

- non-dimensional velocity (-)

X - mole fraction (-)

y

- distance along duct (m)

Y - length of duct (m)

6 - boundary layer thickness (m)

v - kinematic viscosity (m /s)

3

p

- density (kg/m )

t +

- non-dimensional time (-)

X

- smoke particulate conversion efficiency (-)

VI 1

Upholstered Furniture Heat Release Rates Measured

With a Furniture Calorimeter

Vytenis Babrauskas

J. Randall Lawson

W.D. Walton

William H. Twilley

Abstract

Accurate burning rate information on upholstered

furniture is important for two purposes - to predict

the room fire development history for a fire involving

the furniture, and to relatively, but adequately, rank

commercial products for a given application. Smallscale test result data not referenced to full-scale

fires lack validity, while full-scale room fires are

costly and lack generality. To enable simplified but

realistic full-scale testing to be done, a new apparatus,

termed a furniture calorimeter was developed. Rates of

heat release are measured by using the oxygen consumption

principle. Tests were conducted in the furniture

calorimeter on thirteen different specimens of upholstered

furniture, representing typical, but carefully controlled,

construction. The results showed significant heat

release differences between thermoplastic and cellulosic

fabrics, between frame types and between padding

materials. For polyurethane foam padding, however,

performance was unrelated to results of Bunsen burner

type tests on the foam. The data developed (1) can be

used directly in the calculation of room fire growth;

(2) will form some of the reference data for development

of appropriate bench-scale test procedures; and (3) can

be used in some cases to estimate burning rates of

similar but not identical furniture.

Keywords: Burning rate; chairs; fire tests; flammability

tests; furniture; plastics; heat release rate; textiles;

upholstered furniture.

1. INTRODUCTION

Concepts of fire protection in residential buildings have gradually been

changing in recent decades. Earlier, it was tacitly assumed that in case of

a fire outbreak, the room of fire origin would be lost; the concerns of fire

protection were to be the protection of adjoining spaces. The focus was on fire endurance of barriers. More recently it has come about that, in some

cases, protection of the initial room involved is feasible and desirable. In

other cases, the consequences of the initial room fire are so severe that a more detailed quantitative understanding is needed of the initial fires in

order to predict the impact on other parts of the building.

1
For discrete combustible goods (as opposed to combustible room linings)

detailed room fire prediction models are available [1,2]. These models

require data describing the fuel objects, the most important of which is the

rate of heat release. In principle, rate of heat release measurements can be

made as part of room fire tests. In practice, this has been difficult to do

well, for reasons which will be discussed below. Instead, a furniture

calorimeter was developed for making these measurements.

A second major application for rate of heat release data is in connection

with approximate prediction models. It is now also possible to estimate the

major features of a room fire, specifically the potential for flashover, by

simple, algebraic engineering rules. Use of these rules also requires rate

of heat release data.

Data will be presented in this report on the rate of burning of upholstered furniture. Because of the major role of upholstered furniture in many

room fires, the first test series conducted in the furniture calorimeter

examined upholstered furniture. By use of a carefully designed series of

experiments where specimen construction features were separately varied, it

became possible to relate quantitatively the rate of heat release to various

construction aspects.

It is generally acknowledged that flammability tests can be more easily

and cost-effectively done in bench-scale than in full-scale. Thus, the

furniture calorimeter is not intended to be established as a standard test

for rating products. Instead, the data gathered in this project will serve

as a data base for developing bench-scale techniques capable of adequately

predicting full-scale rate of heat release.

Finally, it is emphasized that the goal of the present series of tests

was to quantify the fire performance, primarily expressed as heat release

rate, of upholstered furniture subjected to flaming ignition sources. It is

quite true that most furniture fires initially start from smoldering or cigarette sources and that test methods are already available [3] to measure

the susceptibility to ignition. However, regulating cigarette ignitability

does not address two important fire aspects: first, some fires do start from

flaming sources, and these are most likely to be the ones that are fast,

intense, and have the most potential for damage. Second, many fires that

start as smoldering fires later erupt into open flaming. To evaluate this

behavior requires burning rate tests. It also should be emphasized that, in

general, there is no correlation between resistance to cigarette ignition and

good behavior in terms of burning in open flaming. Indeed, the data developed

2
here will suggest that for many simple, common materials there is, rather

trade-off. Of course, choice need not be restricted to common materials.

a

2. ROOM TESTS VERSUS FURNITURE CALORIMETER TESTS

Until now most quantitative data on the performance of furniture in

fires were gathered by means of full-scale room fire tests [e.g., 4,5].

Small-scale mockups have been used extensively [3] for cigarette ignition

studies; however, for flaming behavior studies these have been little used

because of difficulties in obtaining representative behavior [6]. A room

fire test is, by definition, the most realistic fire representation, yet it

does not necessarily yield data of generality. Measurements of the burning

rate of an item in a room can be confounded by two types of interact ions -

those between fuel items, if more than one is present; and those between the

burning item and the surrounding room. In the general case there are interactions both between multiple fuel items and between the fuel and the room. An approach to a portion of the problem of characterizing multiple fuel item

interactions has been presented [7] and will not be considered here.

A furniture item in the simplest case can be imagined burning outdoors

or in a very large building, away from any other objects and with no wind.

Its burning rate is then termed "free burn rate." If a room is now erected

around this item, its burning rate may change for the following reasons:

-- Instead of being able to entrain combustion air freely, the available

air will be throttled by limited size ventilation openings. These openings

may be an open doorway or window, or the room may be closed entirely. In the

latter case, a fire will die out when enough of the available oxygen is

consumed

-- A cloud of hot gases wi 11 col

cei 1 i ng surface . Together, radi ation

impinge upon the fuel item and may in

This effect may be considered n egligi

kW/m^ , measured at floor level. Surp

to be a definit ion of flashover , or c This figure is esp ecially signi f icant

bles ignite at thi s irradiance. For

force d burning can be dominant, with

the f ree burn r ate £ .

lect below the ceiling and heat up the

from the heated gas and surfaces will

crease its burning rate significantly,

ble when the irradiance is less than 20

assing 20 kW/m is customarily considered

omplete room involvement in flames.

since a large number of common combustihigher irradiances, this externally

resulting burning rates being far above

3
-- If the fuel item is near a wall surface, its burning will create a hot spot on the wall which will in turn reradiate to the fuel item. Such

wall augmentation is especially significant in a corner configuration.

-- Air inflow into a room is almost never radially symmetric. Instead,

it is usually through a single opening on one side. When this is the case,

it was early observed [8] that uniform fuel items, ignited all over, do not

burn uniformly, but rather progressively away from the opening. Surprisingly,

the number of test programs using pairs of symmetrically located ventilation

openings have been few [9,10]. Furthermore, although not yet quantified in

room fires, it is known that if the inflow airstream does not impinge upon

the center of the fuel, swirl is induced. Swirl is not present in an ideal

freeburn fire and serves to increase the burning rate. Quintiere [11]

has recently explored some quantitative effects of nonsymmetric air supply on gas flows and entrainment.

Probably the single most important engineering question that can be

asked about a room fire is whether or not it will lead to flashover. (Flashover may be considered to occur when a room becomes involved in flames

throughout its volume, the average hot gas temperature exceeds 600°C or the

2 radiant flux to the floor exceeds 20 kW/m ). Complex fire models [2] can be

used to compute this fire behavior. For design estimates, however, relatively

simple guidelines can be given. A simple expression which related the rate

of heat release required for flashover to occur in a room [12] is given by:

Q

> 750 A /K

where Q is the rate of heat release (kW) , A is the ventilation opening area

2 ^m ) and h is its height (m) . Since door or window dimensions can, for

normal rooms, be easily measured, the problem reduces to finding the maximum

rate of heat release. If a single, discrete combustible item is the primary

source of fuel, this value is obtainable from the furniture calorimeter.

Otherwise, the state-of-the-art does not yet include a quantitative test

procedure for determining Q, and more empirical testing, such as conducting a room fire test, may be needed.

If properly instrumented for determining weight loss and oxygen con- sumption, a room fire test can be used to obtain data similar to, but not

identical with, that obtainable in the furniture calorimeter. Prior to

flashover, the room burning rate and the calorimeter burning rate will be

similar, differing according to the considerations outlined above. If

flashover is reached in the test, however, the data after that point are not

4
even approximately characteristic of a free-burning fire, and thus cannot be

used in the general flashover prediction above (which is not tied to a specific opening size).

In practice, good quality rate of heat release

from room fires until recently for two reasons. Unt

oxygen consumption principle (discussed below) , sens

measured; these measurements are of high uncertainty

development of catcher hood systems for room fire te

required doorway velocity measurements, which have b

continue to be, difficult to make accurately [13].

data were not obtained

il the development of the

ib le heat flows had to be

Also, until the

st s , the techni que

een

,

and to some extent

3. DEVELOPMENT OF THE FURNITURE CALORIMETER

3.1 Principles of Operation

The objective of the calorimeter design is to measure the heat release

and mass loss of a furniture specimen while it is burning under essentially

open-air conditions. Thus, the specimen sits on a weighing platform in a large open laboratory bay while its products of combustion flow up and are collected in a hood. The oxygen levels in the hood flow are measured and

that is used to determine the rate of heat release. Oxygen consumption

measurements are based on the principle that while common combustibles may

vary substantially in their heat of combustion (energy released per unit mass

of fuel combusted) , the heat released per unit mass of oxygen consumed is a near- constant . This ratio Ah

c /rQ

, is taken as 13.1 x 10 kJ/kg and varies

only +_ 4 percent for almost any common combustibles [14]. Here Ah

c

= lower

heat of combustion (kJ/kg) and r

Q = the mass of oxygen required to fully

combust a unit mass of fuel. It can further be shown that the Ah /r constant

c o does not change significantly even if the combustion of the fuel is incomplete,

going partially into carbon monoxide (CO) or soot. In the case of CO, an analytical correction can also be applied. It is the availability of this

indirect technique that enables heat release rate measurements to be made

simply, yet with good accuracy.

Figure 1 shows the practical realization of the furni

The primary measurements are taken in a well-mixed flow se instrument stack. These include flow velocity and tempera

fractions of oxygen, carbon dioxide, and carbon monoxide,

with a paramagnetic oxygen analyzer, while the other gases

analyzers based on infra-red absorption. In this applicat

for the rate of heat release can be written as

ture calorimeter,

ction of the

ture and the volume

Oxygen was measured

were measured with

ion, the equation

5
Q

= Ah

c

where is the oxygen mass flow into the combustion region and iti n is

the oxygen mass flowing out with the exhaust. Mass flow rates of

oxygen are not directly measurable, only oxygen mole-percent being readily

measurable. Parker [15] has shown that for the present conditions -- metering

of stack air outflow, trapping out of water vapor, and correcting for CO^ and

CO in the stack gases -- the rate of heat release can be written as

where X represents mole fractions, superscript 0 denotes ambient conditions

prior to test, m is the stack mass flow rate (kg/s), and a - 1.1. The

requisite mass flow for the stack is determined with the use of a velocity

probe and thermocouple. The calculations were all performed at 5 or 10 s intervals by use of a digital data acquisition system and computer data

reduction code.

The above equations, while adequately documented [15], are not necessarily

intuitively obvious. The following conceptual model may be useful in visualizing

the effect of these measurements. We start by accepting the empirical fact

that each Joule of heat released corresponds to a nearly constant number of

molecules of oxygen used up in the combustion process, irrespective of actual

fuel composition [14]. Thus, we simply have to count up the molecules of

oxygen that are used up. It is not, of course, practical to actually measure

the oxygen flowing into the burning zone here. Instead, we can adopt a convenient point of view similar to that used in solid state physics to

describe electron motion. There, it is useful to consider motion of "holes",

which are simply the absence of an expected electron. Similarly, in oxygen

consumption measurements we can imagine that the combustion process discusses

a certain number of "oxygen-holes". The measurement task is to measure these

oxygen- holes

.

6
With this point of view certain aspects of operation become very simply

apparent. It is clear that we must capture all these oxygen holes in order

to have a valid measurement. The exhaust flow rate, however, can be speeded

up or slowed down with no error being introduced. Likewise, while no combustion

product leakage should occur, an arbitrary amount of room air can be added

into the exhaust, again with no error. Finally, the mixing in of a gas

stream other than unvitiated room air is permissible only if it remains in

constant ratio to the combustion product flow and if the combined stream is

used for the initial calibration.

3.2 Practical Development

While the principles of determining the rate of heat release are relatively

simple, the practical development of a system to do this proved to be more

difficult. A hood system is required which can collect all the products of

combustion without excessive dilution and without spillage. The burning

specimen must not be subjected to excessive velocities or cross-drafts. The

apparatus itself must not be acting as a source of radiative reflection to

the specimen. Specimens both tall and squat, fast-burning and smoldering

must all be accommodated and analyzed with a good signal/noise ratio. The

present embodiment of these concepts is shown in figure 1. The full exhaust

gas flow capacity of the system is approximately 2.1 kg/s under ambient

conditions, decreasing to about 45 percent of that for highest temperature

flows. For lower flows a provision is made to decrease the efficiency of fan

suction. A water spray arrangement was installed at the intake of the fan

to prevent exceeding its maximum rated temperature.

The collection hood is mounted on legs surmounting the weighing platform

and is adjustable in height. Studies of buoyant plumes usually show a halfangle of 8° to 10° for plume spread. This was found to be quite inapplicable

to furniture fires since the plume was seen to wander substantially, much

more than 10°. To contain this flow, a set of side curtains was provided to

the hood. These panels, made of sheet steel, were provided with a cooling

water circuit on the outside to maintain their faces at approximately room

temperature. Curtains without cooling would have been undesirable since they

would act as reradiative room surfaces. With the present arrangement (the

remainder of the exhaust system is substantially farther away from the

burning specimen and was thus judged not to need this precaution) reradiation

effects are minor, as determined by a later check against a larger test rig

(see section 7.7 on reproducibility).

7
3.3 Cal ibrat ion

In the method of operation that was used, primary reliance was placed on individual instrument calibration, with a supplementary burner calibration

using a natural gas burner. By individual instrument calibration it is meant

that the instruments used for measuring 0 ? , CCU, CO, velocity, and temperature

were calibrated internally and were checked once in place.* The rate of heat

release can then be obtained directly by the use of the equations above.

Specifically, oxygen, carbon dioxide, and carbon monoxide analyzers were

calibrated using known gas mixtures prior to each test. The stack flow

velocities were measured with a bi-directional probe connected to a pressure

transducer, which itself was calibrated using a differential pressure

calibrator. The stack velocity profile was determined from measurements at

16 locations along two perpendicular traverses. The locations were chosen to

correspond to equal-area annuli. The results gave a ratio of average to

centerline velocities of 0.85. This ratio did not change by more than 0.01

for varying fire size and was consequently taken as a constant. Flow values

during operation were based on the single point centerline measurement,

multiplied by the above shape factor.

Burner calibrations were made in the calorimeter by using a natural gas

burner constructed in the form of a rectangle 0.67 m by 1.0 m with many small

holes along the edges. The burner was located at 1.0 m above the platform to

correspond to the height of the top of a burning chair. Gas flow rates were

metered with an orifice meter calibrated against a dry test meter. At the

time of calibration, the lower heat of combustion of the natural gas used was

3 3 50.36 x 10 kJ/kg, which compares very closely to the 50.01 x 10 value for

methane (Ah

c /r was taken as 12.50 x lO -5 k.J/kg). The calibrations gave the

following results:

Q supplied

(kW)

Q computed

(kW)

Percent

Realized

m

Oxygen

Value

(%)

co

2 mCO

m

Air Flow

Rate

(kg/s)

138 125 91 20.58 0.18 <0.01 1.88

219 213 97 20.20 0.32 <0.01 T. 68

279 259 93 19.99 0.43 <0.01 1 .63

434 417 96 19.25 0.72 <0.01 1 . 53

699 646 92 16.45 2 .60 <0.01 0.97

906 873 96 14 . 07 3.94 <0.01 0.88

1343 1314 98 8.87 6.86 <0.01 0.80

This is considered to be adequate agreement.

*The oxygen meter readings had to be corrected for response time, described

in appendix
The weighing platform was calibrated with fixed weights and re-zeroed

prior to each test. Although the problem is not often discussed, weighing

platforms used in fire tests are subject to an intrinsic error -- the pull on the platform due to the buoyancy of hot gases above it. If the fire does not

change size or temperature then this error is unimportant since then the

measured mass loss rate is not affected. Rapid fluctuations, on the other

hand, can introduce an error. It is possible to correct for this error if

the buoyancy can be measured. It can be estimated from temperature data, if

a large number of thermocouples are located in the fire volume [16]. Or, it

can be measured with a set of pressure probes located above and below the

platform. Both methods are cumbersome and detract from the simplicity of the

test. Exploratory pressure measurements, however, were made during one of

the tests (T38) . These suggest an average error of about 1.5 g/s, but with a few sharp peaks of up to 75 g/s. The effect on the mass loss rates reported

later, however, is smaller since a multi-point averaging was used to reduce

noise

.

After construction was completed and before specimen testing, a number

of tests were conducted to characterize the flow behavior of the exhaust

system. These measurements are discussed in appendix B.

3.4 Maximum Apparatus Capacity

For operational purposes, it was considered that the maximum capacity of

the apparatus is 2000 kW. The actual absolute upper limit corresponds to a zero oxygen condition in the stack and occurs at about 2500 kW. This is

accompanied by excessive stack temperatures, of approximately 1000°C and is

undesirable because the apparatus was not designed to resist these temperatures.

(Fan temperatures, however, can be successfully kept below 200°C with the

spray cooling system.) The large oxygen depletion conditions are, more

significantly, undesirable because of the possibilities for poor combustion

effi ciency and wall quenching when a large fraction of the c ombusti on t akes

plac e in the stack. Tes ts where Q values greater than 2000 kW were exp ected

were conducted under a 1 arge laboratory hood. Pr incip

1

es of operat ion there

were very similar to the furniture calorimeter: except for hi gher ai r fl ow rate ( - 3 . 0 kg/s) , hi gher capacity (>6000 kW)

,

and lower prec is ion.

A calibration p roce dure was followed for the large hood very s imil ar to

the one outlined for the furniture calorimeter:. The re suits were :

9
• Percent Oxygen

co

2 Air Flow

Q supplied Q computed Realized Value CO Rate

(kW) (kW) cd CD CD CD (kg/s)

439 427 97 20.09 0.35 <0.01 2.96

687 684 100 19.58 0.57 <0.01 3.06

884 833 94 19.33 0.70 <0.01 3.20

1297 1160 89 18. 59 1.05 <0.01 3.12

1426 1291 91 18.28 1 . 10 <0.01 3.07

Hood overflow can be a problem in the furniture calorimeter at highe

heat release rates. No reasonable way was found to quantify the spillage

since it was seen to depend on fire configuration

,

not just on Q alone.

Fires which were closer to the ground or closer to the hood edge were more

prone to exhibit spillage. A visual estimate suggests that for well-centered

fires no more than 10-15 percent would be lost at 2500 kW, with proportionately

less at lower Q. No spillage was ever observed below 800 kW. No spillage

was noted under any conditions in the large hood rig.

3.5 Smoke Measurement

An extinction-beam photometer was installed in the exhaust duct to

estimate total smoke emissions. Construction of the photometer light beam

and the associated electronics was as described by Bukowski [19]. A light

path distance of 0.32 m was used. The light source and the detector were

installed behind small panes of glass inset into the side of the duct and

installed with a slight air gap. The gap permits a small quantity of room

air to be sucked in over these windows to help keep them free of smoke

deposition. Experiments indicated that rapid soot buildup takes place if

this precaution is not taken.

Smoke measurement results can be presented in a large variety of ways.

It was concluded that for basic product characterization two quantities would

be of interest: (1) smoke particulate production rate, m

s

; and (2) conversion

efficiency of mass loss into particulate generation,

Smoke production rate can be determined as

kV n -K

m

s = TWO (k 8' s 5

based on the assumptions and constants as developed in [20], where

10
k

100

F (m

1

) 1L

is the extinction coefficient, determined by using the percent transmission,

• 3 _ i F, and smoke path length, L(m). The duct flow volume, V (m -s ) , is determined at the smoke meter location by adjusting the volume flow rate in the

control section according to temperature measurements at the photometer

location.

Even though precautions were taken to try to keep the photometer windows

clear, some soot deposition still takes place. Typically, at the end of a test, when only clear air is flowing through the duct, about 85 percent

transmission may be noted. A correction scheme was developed to minimize the

error from window sooting. At each scan time, k was expressed as

where k is the measured extinction coefficient and k is the window sooting

m s 6

term. It was postulated that at any time t,

k

s (t) = k

s (t - At) + C

1 k(t - At) At

That is, that window sooting is augmented by a term proportional to the

sootiness of the stream and to the length of time, and soot once deposited

continues to stay on the window. The proportionality constant is not

known a priori , since adhesion characteristics of the soot particles are not

known. Consequently, the suitable value of is determined iteratively for

each test by requiring that the extinction coefficient for the final

reading -- which should be free of smoke -- be close to zero,

- 0.001 < k < 0.001

Typically, only two iterations are required and a value of - 5 x 10 ^ is

found.

It is convenient to express results

X

= m / ih , where m is the specimen mass

s p p

r fraction of specimen mass converted into

lie between 0 and 1.0.

in a non-dimensional manner as loss rate. Thus x represents the

obscuring particulates, and it must

11
Results for x can, in principle, be compared to bench-scale measurements

[20] if losses are small or are similar in both cases. In the present study,

the smoke flow, for practical reasons, was measured over 10 m downstream from

the combustion zone. Thus, it can be surmised that wall losses can be

substantial (appendix C) . The relative performance of different specimens

should, however, be correctly indicated with the measurements.

3.6 Target Irradiance Measurements

While the goal of the present work was not to produce a heat flux mapping

from the burning items, as done in other tests [7], still some record of

potential target irradiance was desired. The target irradiance is irradiance

that could fall on a nearby combustible item and potentially lead to its

ignition. For that purpose, a Gardon heat flux gage was placed in front of

the specimen, 0.5 m above the platform and 0.5 m in front of the specimen.

The gage was equipped with a purged window for recording only the radiant

heat flux component.

4. IGNITION SOURCE

Since the present series of experiments was designed to test the flaming

combustion behavior of upholstered furniture, an ignition source had to be

selected which would reliably ignite the test specimens. A source corresponding to a small external fire was desired, one which would not overwhelm

the specimen. In previous testing, folded newspapers or wastebaskets filled

with combustibles were commonly employed. A recent investigation [7] determined the burning rate for small polyethylene wastebaskets filled with milk

cartons. For the present experiments, it was decided to simulate wastebasket

behavior with a natural gas burner. A good approximation to the wastebasket

heat release rate is a constant Q

= 50 kW applied for 200 s (fig. 2). A

burner was constructed which approximated the dimensions as the wastebasket,

i.e., 250 mm long, 180 mm wide, and 250 mm above the weighing platform (fig.

3).

A flux mapping of this burner is shown in figure 4. The burner was

placed with its 250 mm length flush against a noncombustible panel for making

these measurements. Visible flame height corresponded to 1600 mm for tips of

intermittent flames, with 1150 mm being the height of the solid flame core.

The ignition sequence consisted of positioning the ignition burner at

the middle of the left side arm, almost touching. The burner was lit off and

burned at a 50 kW level for 200 s. After that time, burner gas flow was shut

12
off and the burner itself was physically removed in order not to interfere

with later collapse of the specimen.

5. TEST SPECIMENS

The majority of the specimens, F21 through F26 and F29 through F32, were

procured from a single manufacturer. These were especially manufactured for

NBS according to the following guidelines.

-- Standard, typical construction details and workmanship was to be

used. A contemporary but conservative style was desired.

-- A minimum of different materials was to be incorporated into each

piece. The pieces were to have a typical wood frame (except structural foam

units), flat springs, a single type of cushioning material and a single

upholstery fabric. Other combustible materials, e.g., welt cord, dust

covers, etc., were to be kept to a minimum.

-- The pieces were, with the exception of varying the materials, to be

as similar as possible in construction. The materials chosen were systematically varied to study the dominant types available in the marketplace.

Experimental, unusual, or highly expensive types were not studied. Among

fabrics, cellulosic (cotton, rayon, linen) and thermoplastic types (polyolefins, nylon) are dominant. Since for flaming combustion all cellulosics

tend to perform in a generically similar way, cotton fabrics were chosen from

that type. Similarly, polyolefin fabrics were taken to represent thermoplastic behavior.

Specimen composition is summarized in table 1.

Chair F21 . This was chosen as the baseline case. It comprised a wood

frame, "California Foam" (a commercial polyurethane foam sold as meeting

California State Bulletin 117 [21] minimum requirements), polyolefin fabric,

and was of typical easy chair size. The California test for foams is a vertical Bunsen burner test with criteria based on burn length, afterflame

time, and afterglow time.

Chair F22 . This was a chair using fire retardant (FR) cotton batting

and Haitian cotton fabric, otherwise similar to F21. The seat cushion

batting was solid -- the cushion did not have springs nor was it tufted.

Chair F23 . This was a chair identical to chair F22, except for having a polyolefin upholstery fabric.

13
Chair F24 . This was a chair identical to chair F21 except for having a Haitian cotton upholstery fabric.

Chair F25 . This was a chair identical to chair F21 except that it had

standard, non-California polyurethane foam.

Chair F26 . This chair used all the same materials as chair F21 except

that it was designed with thinner construction and of lower weight.

Chair F27 . This chair was tested at the request of the Consumer Product

Safety Commission (CPSC) and was identical to a specimen tested for smoldering

behavior in their laboratories (manufacturer H) . The chair was of complex

construction. The seat cushion consisted of polyurethane foam, covered with

a layer of polyester batting, covered by a cotton inner fabric, then upholstered with a quilted fabric which contained a polyolefin batting layer

sandwiched between two cotton layers. The sides and back had the quilted

upholstery fabric on top of coarse olefin mesh on the outside. Inside of the arms and back were layers of cotton/polyester batting and polyolefin mesh.

The seat and back areas also had layers of pressed vinal fiber pads. (Vinal

fibers are made of vinyl alcohol polymer.) The structure was a conventional

wood frame and steel springs.

Chair F28 . This chair was also tested at the request of CPSC and was identical to a specimen tested in their laboratories (manufacturer B) . The

seat cushion consisted of polyurethane foam, covered with a thin layer of

polyester batting, covered by a cotton corduroy upholstery fabric. The back

was covered with the corduroy fabric on top of a polyolefin mesh, while the

sides also included a layer of cotton/polyester batting. Inside of the arms was padded with cotton/polyester batting and a thin layer of polyurethane

foam. The back cushion was stuffed with polyester batting, held in with a non-woven polyolefin fabric. The seat deck and inside back area were padded

with cotton batting; in addition, the seat deck contained a thin spring

insulator pad of bonded miscellaneous fibers. The structure was a conventional

wood frame and steel springs.

Chair F29 . This chair, similar to chair F25, used non- Cal if ornia foam

and polyolefin fabric. It was obtained in order to study the effects of a polypropylene structural foam frame. The shape of the chair was somewhat

more curvy and old-fashioned. (Structural foam frames are made by only a few

manufacturers and are typically not available in simple, contemporary styles.

This, we have been told, is because at present the simpler designs would not

be cost- competitive compared to analogous wood frames.)

14
Chair F30 . This cha ir was similar to c hair F2 9, except th at the frame

lade from po lyurethan e structural foam. Non -Ca lifornia foam and polyn fabi:ic we re useid .

Chair F 3 1

.

This was a loveseat (two-se ater ), identical in materials to

F21, excep t for gre ater length and wei ght.

Chair F32 . This was a sofa, identical in m ate rials to F 2

1

and F 3 1

.

Chair F 3 3

.

This was a loveseat, simila r in si ze to cha ir F31 , except of

. foam and c otton bat ting stuffing, with cot ton upholste ry fabric. A

detailed analysis is not available.

Photographs of typical furniture items are shown in figures 5, 7, 9 and

11 .

6. TEST OBSERVATIONS

The ignition source burner successfully ignited all test specimens.

Ignition times were short -- on the order of 15 s for thermoplastic fabrics -- and somewhat longer for cellulosic ones. Exact times were not recorded

because of the difficulty of observing ignition obscured by the burner flame.

As a measure of the time scale, the time to peak is considered much more

important, as discussed below. The left (occupant's view) side arm, being

adjacent to the burner, was the first to burn. From there flaming usually

progressed to the outside back of the chair. A little later flames would

start across the seat cushion and the inside back. The upholstery, on the

right side arm melted in about 80-120 s for the case of thermoplastic

fabrics. This allowed rapid fire involvement of the foam underneath. In the

case of cellulosic fabrics, the spread was much slower. The right side arm

typically ignited not from radiation at a distance, but simply at the time

when contiguous flame spread reached it, at about 250 s. The front of the

chair was the last to get involved in all cases.

Most specimens showed some pool burning underneath the chair since even

the cotton batting units had a polyolefin dust cover underneath the seat

deck. Some California foam specimens showed spurting of burning liquified

polyurethane foam in small streams at the side. Neither this phenomenon nor

the pool burning was judged to provide any significant increase in other item

ignition potential, beyond that due to high radiant heat fluxes.

15
The active burning period normally did not last beyond about 180 s, since in that time the majority of foam and fabric would be consumed. Total

burning time is very difficult to define since the last bit of smoldering may

not be extinguished for several hours. Generally by about 1800 s the heat

release rate was down to 50 to 100 kW, while at 3600 s it was around 25 kW.

For wood frames, total collapse had occurred by about 1500 s. For the polyurethane frame specimen, F30, collapse had occurred by 1200 s, while for the

polypropylene frame specimen, F29, collapse was at around 900 s. This

difference could be anticipated since the F29 frame melted during the burning

and, in fact, contributed to the fire at the peak burning time, while the F30

frame was not thermoplastic and tended instead to char.

7. RESULTS OF MEASUREMENTS

A summary of the data is presented in table 2. Detailed performance is

illustrated for specimen F21 in figures 13 through 15. For purposes of this

preliminary analysis, it was considered that there are twoprimary variables

of interest -- the peak rate of heat release and the time to reach the peak.

The reasons for concern with the peak intensity are self-evident. The time

to reach the peak is considered important because in many fires detection may

be feasible at or very shortly after ignition. Thus, occupant escape time can be controlled by the fire growth rate. In a scenario involving a specific

burn room, the appropriate method of analysis [16] would be to compute the

times in each case that are available before some defined limit of untenability

is reached. This is possible to do with the present data by using them as input to a computer room fire model. Here, however, we will merely rank the

rate

:erms of the time fr om start o f t est

7 . 1 T imes to Peak

ranked peak t ime s

Three dis t in ct

while s howing fl aming combust ion fr

substan tial rate of heat rele ase pe

! was re giste red at 910 s. Sp ecimen

: d peak t imes in the range of 420 -65

F26, F30 , F 3 1

,

and F29 burned rap

peaks in the range of 220-280 s. The relative ranking within each of these

groups is not considered significant. The differences in construction of the

specimens in each of these groups are striking, however. Clearly the slowest

fire development occurred with an all-cellulosic construction. The fastest

fire buildup happened when polyurethane foam padding is combined with thermoplastic fabric upholstery. Constructions using cellulosic fabrics with

16
polyurethane foam padding or, conversely thermoplastic fabrics with cotton

batting showed a similar, intermediate buildup time. Mixed type fillings

also fall into this category. It can be noted that foam type, i.e., whether

ordinary or "California" type, showed no effect on rankings in these

experiments

.

7.2 Peak Rates of Heat Release

Peak rates of heat release are ranked in table 4. Again, three distinct

levels of performance can be seen. The all-cellulosic specimen, F22, performed

the best, releasing only 370 kW at peak. Next came a large number of specimens

clustered in an intermediate heat release range, 700 to 1060 kW. Finally

came a group showing rates 2 to 4 times as large as the previous, with values

ranging from 1950 kW to 3120 kW. With two exceptions, the members of the

best, intermediate, and lowest groups were the same for both the time to

reach the peak and for the peak burning rate itself. The differing ones were

F26 and F30. Both of these have thermoplastic upholstery and polyurethane

foam padding. Chair F26 was a "minimum weight" specimen, so while it reached

its peak burning rate quickly it did not have as much fuel to burn as other

specimens. Chair F30 had the rigid polyurethane foam frame. The results

indicate that while replacing cotton batting padding with flexible polyurethane foam normally acts to increase the burning rate significantly,

replacing the wood frame with a comparable one of rigid polyurethane foam not

only did not increase the heat release rate but significantly decreased it.

This is perhaps not unexpected in view of the significantly different fire

behavior of rigid and flexible polyurethanes.

A detailed comparison of the effects of construction features is presented

in figures 16 and 17 and in tables 5 through 8. Table 5 shows the effect of

different padding types, for a given fabric. Type of foam ("California," or ordinary) is seen to have no effect. For a given fabric type, however,

cotton batting construction produced less than half the rate of heat release

as polyurethane foam or mixed types. Mixed type constructions can be of

various sorts but -- within a fairly wide amount of scatter -- compare in

heat release rate to the all-foam and not to the all-cotton batting types.

The effect of fabric type is explored in table 6. For

material type, the cellulosic (cotton) fabric specimens had

release of less than half of the thermoplastic (polyolefin)

a given filling

a rate of heat

fabric specimens.

17
Within a given construction type, total specimen mass can be expected to

be a major factor. The relationship is shown for polyurethane foam types in

table 7. An approximately linear dependence on specimen mass is seen. A

relationship of this type is expected of all constructions where the chair

burns in a reasonably fast way, with visible flaming, and burns up almost

completely. Highly retarded types of foams are available which burn slowly,

primarily by smoldering, and are not consumed in less than several hours, if

at all. It is expected that a linear relationship would not hold for such

chairs and that increasing their mass would increase the total heat evolution

but little. No units of this kind were tested since they are not readily

available on the commercial market. A similarly slow burning behavior can also be expected in the larger sizes of a cotton batting/cellulosic fabric

type; however, no specimens of this description were tested other than F22.

Finally, frame type is seen to have a significant effect on the peak

rate of heat release, though not on the time to reach the peak (table 8).

Traditional wood framing is shown to exhibit an intermediate behavior.

Structural plastic foam chair frames are available in two types -- thermoplastic

(polypropylene and polystyrene) and thermosetting (rigid polyurethane)

.

Polystyrene frames were not tested because they are used only in specialized

applications and are not readily available. The chair with the polypropylene

frame, F29, showed a peak rate of heat release almost identical to that of

the comparable wood frame unit, F21. It, however, had only half the mass of

F21. Thus, on a mass basis it would have to be considered twice as fast

burning. (Component weight breakdowns are not available, but table 8 suggests

that it is not unreasonable to roughly estimate peak rates of heat release on the basis of total mass.) The polyurethane frame specimen, F30, showed

considerably slower burning for a roughly similar specimen mass. A detailed

explanation is not available other than the suggestion that this frame is

not only slow to contribute to fire itself, but also that by maintaining its

integrity it can help reduce fuel contribution from the uncovering of fresh

fuel

.

7.3 Smoke Production

Smoke production values occurring near the peak burning time are reported

in table 2. It must be observed that while the numbers are expressed as non- dimensional particulate conversion efficiencies, the values are not apparatusindependent. At least one requirement for apparatus independence is that all

of the smoke flow past the measuring section. This is difficult to do since

it would require that the measurements be taken more or less at the flame

tip. In our apparatus this area is hot and not readily accessible. The

18
measurement station is located at a more accessible location further downstream,

but over this distance smoke losses occur and soot is deposited on duct walls

(if this were not the case, the photometer windows would never need cleaning).

Loss estimates are considered in appendix C.

Smoke measurements are shown ranked in table 9. The six poorest performing

specimens all had polyurethane foam padding and thermoplastic fabric upholstery.

The poorest performing specimen, F29, was distinguished by having a polypropylene

foam frame, whose rapid burning properties have been discussed above. Reliable

data could not be obtained on the all-cotton specimen, F22, nor on F33. From

the available data, however, it is evident that the polyurethane foam/thermoplastic fabric combination is more prone to smoke production than any other

combination, and that this tendency can be exacerbated by the use of a thermoplastic foam frame.

7.4 Target Irradiance

Peak target irradiance values are also given in table 2. In [7] a simplification was established by dividing target fuels into three groups.

The "especially easily ignitable" ones could ignite at an irradiance of

2 2 10 kW/m . Normal ignitability level was taken as 20 kW/m , while "difficult

2 to ignite" objects corresponded to 40 kW/m . The furnishings examined in

[7] were primarily slow-burning institutional and office furniture, as contrasted to the residential type items used in the present series. A

comparison between the maximum radiant flux values observed during the course

of the present tests and those recorded in the previous test series is shown

in figure 18. The fluxes, for a given mass loss rate, were substantially

lower in the present series. This is partly explained by the fact that the

relationship derived from the earlier tests was taken on a worst case basis.

In those tests there was a substantial difference between worst case and

average or typical performance. In the present case there is little deviation

from a single relationship, as shown by the close fit of points on figure 18.

7.5 Effective Heats of Combustion

For modeling room fires, for estimating fuel loads and for other purposes,

it is often desirable to know approximate heats of combustion for furniture.

Effective heats of combustion were calculated as Q/m , averaged for several

data scan intervals to minimize noise contributions. A typical computed heat

of combustion curve is shown in figure 14 for specimen F21. In table 10, a summary is given, grouped according to type of construction. Differences in

padding and fabric do make some difference, but still for wood-framed specimens

19
most effective heat of combustion values are concentrated in the narrow range

of 14.6 to 17.9 MJ/kg. Polypropylene framed construction, however, results

in significantly higher values, due to the high value of the net heat of

combustion for polypropy lene - - 4 3 . 2 MJ/kg [22]. The average effective value

for specimen F29 was 35.1 MJ/kg, approximately double of that for the others.

Most specimens showed a behavior similar to F21--higher initial values of the

heat of combustion were followed by lower values for charring frame combustion.

7.6 Convective Heat Release Fraction

Attempts -are sometimes made to characterize materials by the fraction of

their heat release that goes into convective and into radiative heat. This

partition is possible to uniquely describe only in a completely free,

undisturbed ambient environment. Thus, while this convective quantity may be

defined simply as the sensible enthalpy leaving an imaginary hemisphere

surrounding the specimen, its actual measurement would be difficult. In a more usual situation, as in the present case, convective heat output can be

defined as the enthalpy flow measured in a collector hood. This measurement

does not represent the theoretical convective fraction because losses occur

in the duct ahead of the measuring section and because the measured temperature

is not the true gas temperature. In the furniture calorimeter the convective

fraction, measured at the velocity station, ranged from 31 percent to 58

percent. (In the large hood experiments the values were from 12 percent to

21 percent .

)

Alternatively, in truly open burning the total radiative output may be

measured with a radiometer located far away from the burning object and

viewing all its flame volume [23]. This, again, cannot be readily implemented

in the furniture calorimeter.

7.7 Reproducibility

In full-scale fire testing replicability is often an area of significant

concern. It is a general observation that to date more success is customarily

had in producing well-replicatable measurements in bench-scale tests than in

full-scale tests. In addition to the higher intrinsic variability in fullscale results, costs have to be considered. While it is usually feasible to

conduct three to 12 replicate measurements with bench-scale tests, such an endeavor is normally not affordable in full-scale testing. Instead, it has

to be sufficient to retest only one or two specimens. In the present tests,

it was decided to test reproducibility by using two different scale but same

principle apparatuses. Chairs F31 and F21 were tested twice, once in the

20
furniture calorimeter and once under the large hood. For F31, a complete

test record for the furniture calorimeter test is not available since its

capacity was exceeded at 2500 kW. Up to that point, however, the rate of

heat release curves are similar, with a time shift of about 20 s (test T37

faster than T31)

.

A complete comparison is available for chair F21, with test T19 being

conducted in the furniture calorimeter and test T45 under the large hood

(fig. 13). Agreement of both rate of heat release and time to peak is to

within 7 percent. This comparison also empirically demonstrates that up to

at least the 2000 kW level there are no systematic discrepancies in the

furniture calorimeter due to limited entrainment, incomplete combustion, or limited wall cooling (or, at least, that such errors cancel out).

8. ANALYSIS FOR ESTIMATION

The ultimate goal of the project of which this work was a part was to

produce an engineering methodology for testing upholstered furniture items to

determine their expected burning rates. To do this requires that quantitative

tests be made available and run on whole or partial specimens of the kind

considered. The bench-scale test development activities are intended to lead

to this goal.

There are certain applications, on the other hand, where it is desired

not to test and rate a specific article from a given manufacturer, but rather

to describe, in an approximate way, the typical burning behavior of a class

of articles. For this purpose we can, and indeed should, use only very

limited, easily obtainable information. During the current full-scale test

series a significant amount of information was collected on a wide variety of

upholstered furniture pieces.

A simple model is, therefore, proposed that may be used for estimating

the peak rate of heat release of some common classes of upholstered furniture

items. Material types not explicitly listed (such as metal frames) have not

yet been characterized. The model is based on a series of multiplicative

factors

:

21
Speak ’ (mass factor > x (frame factor)

x (style factor)

x (padding factor)

x (fabric factor)

The factors are computed as follows:

Mass Factor 64. x (total mass, kg)

!

1 . 0 for wood

0.6 for (rigid) polyurethane foam

2.0 for (thermoplastic) polypropylene foam

Style Factor

1.0 for plain, primarily rectilinear construction

1.5 for ornate, convoluted shapes

with intermediate values for intermediate shapes

Padding Factor

0.4

for polyurethane foam, ordinary or California

for cotton batting

for mixed materials filling

for polychloroprene foam*

1

1.0 for thermoplastic fabrics (fabrics such as polyolefin and nylon which melt prior to burning)

0.4 for cellulosic fabrics (cotton; also rayon,

linen, etc.)

0.25 for PVC/PU type coverings**

* Estimate based on extrapolation from earlier work [24]. This value would

also be applicable to the best available highly retardant treated polyurethane foams but in practice this distinction cannot be made without

detailed testing.

**This is an extension based on recent unpublished work. Into this group

of coverings are placed those which have a thick layer of polyvinylchloride (PVC) or polyurethane (PU) material supported on a fabric scrim.

The construction is often found in washable waiting room chairs and in

imitation leather chairs.

22
The estimated Q , has units 'peak

given in table 11. Figure 19

values

of kW. Computations for the test specimens are shows the agreement between actual and estimated

Time to peak can also be estimated. Here, however, it is important to

emphasize the role of the ignition source. Most upholstered furniture

items, if successfully and fully ignited, will show [5] approximately similar

peak characteristics, although their times to reach the peak may be greatly

varied. The ignition source chosen in the present series probably approaches

the shortest possible limit, without dominating the furniture fire itself.

Times from ignition to peak for most other sources would tend to be longer.

Based on these considerations, we can provide an estimate for minimum times

to reach peak burning rate:

Minimum time to peak = 250 s for polyurethane foam with

thermoplastic fabric

= 900 s for cotton batting with cotton fabric

= 550 s for all others

In addition to the limitations discussed above -- that approximate rules

of this nature are only useful for surveying and not for product acceptance -- the limited range of materials used must be emphasized. No data were gathered

on cotton/thermoplastic blend fabrics, on vinyl coverings, or numerous other

less common classes of upholstery materials. Also, consideration was only

given to furniture built with a traditional frame, although not necessarily

of traditional materials. Some modern furniture does not have a proper frame

and earlier test experience has shown [5] that there is little commonality of

fire behavior among such specimens.

9. ON ACHIEVING BOTH CIGARETTE IGNITION RESISTANCE

AND GOOD FLAMING BEHAVIOR

From furniture cigarette ignitability tests, it is seen that cellulosic

fabrics perform generally less well than thermoplastic ones and that polyurethane

foams might be preferred because, unlike cotton batting they do not have to

be specially treated to achieve cigarette ignition resistance. Thus, while

at first glance cigarette resistance and good flaming behavior might seen

antagonistic goals, this need not be the case. Some readily available

materials are known to perform well in both cases -- wool fabric and polychloroprene foams are such examples. Both of these have the drawback of

being relatively costly.

23
It is also very likely that designs can be worked out which combine

materials of modest cost in such a way as to achieve good overall performance

for both cigarette ignition and flaming situations. Polyurethane foams are,

for various manufacturing reasons, much preferred in the furniture industry.

It has been shown [241 that it is possible to produce highly fire retardant

treated polyurethane foams that have performance similar to polychloroprene

.

Unfortunately, costs and foam density are also comparable. A more fruitful

approach is to protect polyurethane foams with an interliner. Polychloroprene interliners intended for this use have recently come on the market.

While this does not reduce the fuel load, it can delay fire development and

reduce peak burning rates. When a heavy cellulosic fabric is used on polyurethane foam, it burns slowly when subjected to flames and does not

expose the foam itself to flames for some time; however, it is difficult to

achieve cigarette ignition resistance with a heavy cellulosic fabric. On the

other hand, it was seen in the present test series that common thermoplastic

fabrics tend to melt quickly when exposed to heat. Thus, they expose the

foam to rapid heating from flames and from radiation early in the fire. An

interliner may only provide a modest additional benefit when used under a cellulosic fabric but can be of significant benefit under a thermoplastic

one. The use of some early polychloroprene-based interliners has been

studied [5,24]. An extensive testing program in Great Britain resulted in

recommendation for the use of cotton cambric as an interliner [25]. Additional

cigarette resistance can be imparted to such a cambric by bonded

aluminized and thermoplastic layers, as has been done in experimental

systems

.

For the choice of fabrics, additional investigation is likely to show

modestly priced types that can have both smolder resistance and good resistance

to rapid flame propagation. Since poor flaming condition behavior is largely

attributed to the fabric melting away and opening up quickly, charring fiber

materials, such as modacrylics and matrix fabrics, should be investigated.

10. SUMMARY AND CONCLUSIONS

The advantages of open -- as opposed to room -- fire testing were

considered and were shown to motivate the construction of a furniture

calorimeter

.

A description was provided of the design of a full-scale furniture

calorimeter for making burning rate measurements. An oxygen consumption

technique was used to measure heat release, and conventional instruments were

used for measurement of mass loss, smoke production and target irradiance.

24
The primary effort was addressed to gathering comparative open flame

burning rate data on a set of upholstered furniture pieces where only one

construction feature was varied at a time. The findings showed that for the

range of constructions examined:

a -- Furniture using polyurethane foams with retardants added to meet

California state requirements did not show any reduction in rate of heat

release compared to ordinary polyurethane foams. (This finding was earlier

noted in bench-scale tests by Herrington [26].

b

-- For foam-padded chairs, rate of heat release was related to specimen

mass -- for comparable specimens, those that weighed more showed higher rates

of heat release. This indicates that any realistic testing or evaluation

procedure must take specimen mass into account and cannot be based on smallscale tests alone.

c -- Furniture using padding materials made of cotton batting showed

lower rates of heat release and slower fire buildup than those using polyurethane foams or battings of mixed fibers.

d -- Furniture using cellulosic fabrics showed lower rates of heat

release and slower fire buildup than those using thermoplastic fabrics.

Cellulosic/thermoplastic blends were not investigated.

e -- Structural foam frames showed widely differing behaviors. A frame

of a charring plastic was seen to give a lower heat release rate than a wood

frame, while a melting, thermoplastic frame material led to a substantially

greater heat release.

f -- Furniture items with more polymeric content showed significantly

more smokiness than those with primarily cellulosic content. Since the total

smoke production rate is the product of the smokiness times the burning rate,

the total release of smoke for predominantly polymeric specimens was considerably greater.

g -- A very approximate set of rules was suggested for estimating the

rate of heat release of upholstered furniture based only on known weights and

construction. This can be useful in hazards surveying work.

25
Further quantification of the burning rates of upholstered furniture

will be carried on in three directions: (1) burning of simplified mock-ups

in the furniture calorimeter; (2) rate of heat release tests on small specimens

cut from test chairs; and (3) the development of a laboratory flame spread

test suitable for testing upholstered furniture samples. The eventual development

of a test protocol is then envisioned which will enable the relative fire

risk of furniture items to be quantified using actual measured properties.

Finally, it is emphasized that limited heat release during flaming

exposure and good cigarette ignition resistance are not necessarily mutually

exclusive and that reasonable designs can be evolved suited to both.

11. ACKNOWLEDGEMENTS

David E. Swanson participated in the construction of the calorimeter;

Charles F. Veirtz assisted in the operation; David P. Klein provided computer

programming assistance.

The project was partly funded by the Consumer Product Safety Commission

as Project 154, Paul Lancer, technical monitor. The development of the

furniture calorimeter was also partly funded through the Department of Health

and Human Services, Jonas Morehart , project officer.

12. REFERENCES

(1) Pape, R. , Waterman, T.E., Understanding and modeling preflashover

compartment fires, Design of Buildings for Fire Safety (ASTM STP 685),

pp 106-138, E.E. Smith, T.Z. Harmathy, eds. American Society for Testing

and Materials, Philadelphia, PA (1978).

(2) Mitler, H.E., Emmons, H.W., Documentation for CFC-V, The fifth Harvard

computer fire code, Nat. Bur. Stand. (U.S.), NBS-GCR-81-344 (1981).

(3) Loftus, J.J., Back-up report for the proposed standard for the flammability (cigarette ignition resistance) of upholstered furniture, PFF6-

76, Nat. Bur. Std. (U.S.), NBSIR 78-1438 (1978).

(4) Pape, R. , et ahl. , Semistochastic approach to predicting the development

of a fire Tn a room from ignition to flashover. Program documentation

and users guide, RFIRES. IIT Research Institute, Chicago (1976). NTIS

No. PB- 278643

.

(5) Babrauskas, V. , Full-scale burning behavior of upholstered chairs, Nat.

Bur. Std. (U.S.) Tech. Note 1103 (1979).

(6) Bard, S., Clow, K.H., Pagni, P.J., Combustion of Cellular Urethane,

Combustion Science and Technology. 1_9, 141-150 (1979).

(7) Babrauskas, V., Will the second item ignite? Fire Safety J. (1982).

(8) Gross, D., Ward, D., Shoub , H. , Fires in model rooms. Results of

preliminary experiments under an international cooperative program, Nat.

Bur. Std. (U.S.), unpublished report (1960).

26
(9) Tewarson, A., Some observations on experimental fires in enclosures,

Part I, cellulosic materials; Part II, alcohol and paraffin oil.

Factory Mutual Research Corp., Norwood, MA (1971).

(10) Croce, P.A., Modeling of vented enclosure fires, pp 23-37, vol. 1, Fifth

International Fire Protection Seminar, Karlsruhe, Germany (1976).

(11) Quintiere, J.G., Rinkinen, W.J., Jones, W.W., The effect of room openings

on fire plume entrainment, Combustion Science and Technology. 2_6, 193-

201 (1981).

(12) Babrauskas, V. , Estimating room flashover potential, Fire Technology.

16, 94-103, 112 (1980).

(13) Tu, K-M. , Babrauskas, V. , The calibration of a burn room for fire tests

on furnishings, Nat. Bur. Std. (U.S.) Tech. Note 981 (1978).

(14) Huggett, C., Estimation of rate of heat release by means of oxygen

consumption measurements, Fire and Materials. _4 , 61- 5 (1980).

(15) Parker, W.J., Calculations of the heat release rate by oxygen consumption

for various applications, Nat. Bur. Std. (U.S.), NBSIR 81-2427 (1982).

(16) Babrauskas, V. , Combustion of mattresses exposed to flaming ignition

sources, part I. Full-scale tests and hazard analysis, Nat. Bur. Std.

(U.S.) NBSIR 77-1290 (1977).

(17) Croce, P.A., A method for improved measurement of gas concentration

histories -in rapidly developing fires, Combustion Science and Technology,

14_, 221- 228 (1976).

(18) Evans, D.D., Breden, L.H., A numerical technique to correct heat release

rate calorimetry data for apparatus delay, Nat. Bur. Std. (U.S.) NBSIR

77-1302 (1977).

(19) Bukowski, R.W., Smoke measurements in large- and small-scale fire

testing, Fire Technology. 15 , 173-9, 271-281 (1979).

(20) Babrauskas, V. , Applications of predictive smoke measurements, J. Fire

and Flammability. 12 , 51-64 (1981).

(21) Requirements, test procedure and apparatus for testing the flame retardance

of resilient filling materials used in upholstered furniture (Technical

Information Bulletin 117) . State of California Department of Consumer

Affairs, Bureau of Home Furnishings, Sacramento (January 1980).

(22) Fire Protection Handbook, p 4-122, National Fire Protection Assn.,

Quincy, MA (1981).

(23) Modak, A.T., Thermal radiation from pool fires, Combustion and Flame.

2_9 , 177- 192 (1977).

(24) Babrauskas, V., Combustion of mattresses exposed to flaming ignition

sources, Part II. Benchscale tests and hazard analysis, Nat. Bur. Std.

(U.S.) NBSIR 80-2186 (1981).

(25) Fire research on cellular plastics: The final report of the Products

Research Committee, Washington, D.C. (1980).

(26) Herrington, R.M., The rate of heat, smoke and toxic gases release from

polyurethane foams, J. Fire and Flammability. )Q0, 308-325 (1979).

27
(27) Friedlander, S.K., Smoke, Dust and Haze, Wiley, New York (1977).

(28) Bankston, C.P., et al., Review of Smoke Particulate Properties Data for

Burning Natural and Synthetic Materials, Georgia Institute of Technology

(1978) . NT I S No. PB- 292066.

(29) Liu, B.Y.H., Ilori, T.A., Aerosol Deposition in Turbulent Pipe Flow,

Environmental Science and Technology, Vol. 8, 351-356 (1974).

(30) Standard Test Method for Specific Optical Density of Smoke Generated by

Solid Materials (ANSI/ASTM E662) . American Society for Testing and

Materials, Philadelphia, PA.
Test

Specimens

bo

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03 to to CN] CNI rH CNI CNI rH CNI

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(NJ to

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29

F33

T18

39.2

Foam,

Cotton

Cotton

Wood

(Loveseat)
Summary

of

Data

a>

C

X E O U *H

•h

C

H

tO 0)

C'HO, O Pi

a. uu *j u J-< *rH r-£ /• \ • o fH cn or

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t-n <vi

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a> cs <ni X<X

<Jo

E-1 <z H E O \ CT> CnJ to cn nO (NJ (NJ cn r-. lo cn < <

03 H- r* r-H rH to (NJ f-H to rH to cn

SX

A z z P wo > 00 DO

as

X rH Cn r-H vO o o to Cn rH cn • LO cn cn

Si \ < • 0) >-3 OO OC H" VO r- OO O LO o oo to > S r-H r-H r-H r-H i-H r-H f-H (NJ i-H to (NJ Z --H f-H r-H <X

03 /—>v

<D OC X X 00 00 r-H 00 (NJ r- (NJ rH o • (NJ LO cn X < • < • • Si >-j • \D nO LO to LO r-- r^. NO • (NJ rH r-H rt 2 Z rH i-H r-H (NJ r-H i-H rH (NJ (NJ Z <N! (NJ rH

as '-i z O to LO r-H CTl CT) o cn cn NO to < to ^ ^1- (NJ vO vO r-H o i-H NO NO • f-H i-H LO s H- ‘‘Cf to to LO to to Z vO H- o o o o o O o o o o o o o o O

•O' Si IX to IX o o CT) r-H (NJ to LO NO o cn (NJ H" X Cn r-H to r- cn 00 cn cn o LO 00 rH O'. N

/ r-H (NJ r-H i-H i-H (NJ (NJ to A

in •E ^ < fO LO (NJ no

O i-H oo (NJ (NJ i-H < o LO LO 00 • 00 (NJ "3- OO NO LO H • to H" z Z iH rH o o o o o o O o o o LO < O O o

rt io OO \0 r-H LO LO NO (NJ (NJ to . to LO NO

<D '-I (NJ (NJ Cn H" nO (NJ (NJ LO (NJ (NJ Z <-'i (NJ LO Pi

to r—N

CNJ tO or (NJ to OO (NJ o (NJ o (NJ o -S' LO (NJ to bO

rt

X oo oo r-H i-H oo tx cn cn Cn LO cn o rH cn S V J (NJ (NJ to to (NJ CNJ i-H (NJ (NJ i-H (NJ tO LO to H * •K •K to cn lo to (NJ or LO NO 00 o i-H oo oo 0 i-H (NJ (NJ CNJ (NJ (NJ (NJ (NJ (NJ to to to to rH

E- E- E- E-i E-i

H E-i E-i E-i E-i E-i E-I E— E-i E-i E-i

Si

•rH r-H (NJ to LO NO I"-. OO cn o i-H (NJ to

03 (NJ (NJ (NJ (NJ (NJ (NJ (NJ (NJ (NJ to to to to X PL, Ph u- UP PH PL, Ph PP PP PP Pp Ph Ph I

CJ 30 -

Not

Available

Test

conducted

in

large

test

rig.
Table 2B

Supplementary Data -- Values at Peak

°2 C0

2 CO m

a Specimen Test m CD CD (kg/s)

F 2

1

T19 7.54 10.51 0.11 1.07

T4 5 * 17. 31 2.85 <0.001 3.84

F22 T24 19.65 0.64 <0.001 1 .82

F23 T23 17.12 3.27 0.015 1 .27

F 2 4 T22 17.23 3. 52 <0.001 1 . 33

F25 T29 7.80 7. 06 0.12 1.08

F26 T25 16.93 3.95 <0.001 1.44

F27 T27 15.45 4.49 <0.001 1 . 16

F 2 8 T28 17.47 2 .57 <0.001 1.42

F 2 9 T27 5 .12 11.35 0.46 0.88

F30 T30 15. 53 2.38 0.06 1.28

F 3

1

T 3

1

N.A. N.A. N.A. N.A.

T37* 16.02 3.86 0.11 4.06

F 3 2 T38* 16.06 3.81 0. 12 4.42

F 3 3 T18 12. 78 7. 22 0.06 0.84

N.A. - Not available

* - Test conducted in large test rig.

31
Table 3

Ranked Peak Times

Time to

Specimen Peak (s) Padding Fabric

F22 910 Cotton Cotton

F24 650 PU Foam, C* Cotton

F27 570 Mixed Cotton

F33 560 Mixed Cotton

F 2 3 450 Cotton Polyolefin

F 2 8 420 Mixed Cotton

F 2 1 280 PU Foam, C Polyolefin

F25 260 PU Foam, NC Polyolef in

F32 250 PU Foam, C Polyolefin

F26 240 PU Foam, c Polyolefin

F30 235 PU Foam, NC Polyolefin

F 3230 PU Foam, C Polyolefin

F 2 9 220 PU Foam, NC Polyolefin

* PU = Polyurethane; C = California Foam;

NC = Not California Foam

32
Table 4

Ranked Peak Heat Release Values

Peak Q

Specimen (kW) Padding Fabric

F 2 2 3705 Cotton Cotton

F 2 4 700 PU Foam, C* Cotton

F 2 3 700 Cotton Polyolefin

F 2 8 730 Mixed Cotton

F26 810 PU Foam, C Polyolefin

F 2 7 920 Mixed Cotton

F 3 3 940 Mixed Cotton

F 3 0 1060 PU Foam, NC Polyolefin

F 2 9 1950 PU Foam, NC Polyolefin

F21 1970 PU Foam, C Polyolefin

F 2 5 1990 PU Foam, NC Polyolefin

F31 2890 PU Foam, C Polyolefin

F 3 2 3120 PU Foam, C Polyolefin

* PU = NC - Polyurethane; C Not California

= California

Foam

Foam

33
Effect

of

Padding

Type

for

Specimens

With

Similar

Fabrics

O cf)

CD£ cd

• H QJ E—' CL

o

oo

OO o

VO

OO o o

00 LO OO o o o oLO r-H [ OO vO Oh LO "H"

c/

/— O o

r* S CTi 03 CT) CTi CD ^

a,

rH r—i

o o

o- o

or r- o o o o

o o». oo lo

r— lo r^-

C

<

D

a

U oo

<D CL CL

CO

LOoo

CL.

rH LO

OO OO

CL, CL,

^f- OO

OO oo

Cl, CL

o- oo

oo oo

CL CL

34
Table 6

Effect of Fabric Type for Specimens of Similar Construction and Padding

Specimen

Peak Q

(kW)

Time to

Peak (s) Fabric Padding

F 2 4 700 650 Cotton California Foam

F 2

1970 280 Polyolefin California Foam

F 2 2 370 910 Cotton Cotton

F 2 3 700 450 Polyolefin Cotton

Table 7

Effect of Specimen Mass on Polyurethane Foam

Padded Specimens of Similar Construction

Specimen

Peak Q

(kW)

Time to

Peak (s)

Mass

(kg) Comments

F 2 6 810 240 19.2 Minimum Weight Chair

F21 1970 280 28.2 Standard Chair

F 3

2890 230 40.0 Loveseat

F32 3120 250 51.5 Sofa

35
c c G

•rH •H •rH

u 4-1 <p cm

•rH 0) 0 0 p rH rH rH x o o o G X X rS

Ph i-H r-H rH o O o

Cu Ph p,

4h <P CM

•rH •rH •rH

g rH r-H t—

</)

G 03

G

G

u o U

U CJ • rH Ph i 1 1 P c e G X o o O

aJ z 2 2

PhM3

(3G 0

GO 0 G G G 0

•rH

G i—

M3 0 X

X

M3

g P Ph

G

G 0 o

Ph P P p

Ph

G P, P T3 X >> G o r-H rH

rH o o o

•rH Oh a, g

•rH coX

H-> ,v 00 •rH o to p >—

<D o LO o

r-H tO 0 X v£5 t'O (NJ G g G (NJ (NJ (NJ

ct3 <3

H 0 H g H Ph • rHu

<L) Ph CO • O' tO p to o X G • • • m G S (NJ (NJ CT) 0 to 0 Ph H* rH P,X

E-i

(3S • O' G f—s o o o P X & O'* vO LO Ph G PS a* O a* 0 '—

rH r-H rH

m Ph opo0m C/J ,

v 00 (NJ

O

m 10 GO • w G Pi LO S (NJ (NJ rH P0g

•H LO o O'* o (NJ to (NJ 0 Ph Ph Ph sx

co

36
Table 9

Ranked Values for Smoke

Smoke

Particulate

Conversion

Specimen Efficiency (1) Padding Fabric

F 2 8 0.6 Mixed Cotton

F 2 3 0.9 Cotton Polyolefin

F24 0.9 PU Foam, c* Cotton

F 2 7 0.9 Mixed Cotton

F 2 6 1 .PU Foam, C Polyolefin

F 2 5 1 . 7 PU Foam, NC Polyolefin

F 22 .

PU Foam, C Polyolefin

F 3 0 2.4 PU Foam, NC Polyolefin

F31 2 .

PU Foam, C Polyolefin

F32 2 .

PU Foam, c Polyolefin

F 2 9 3.5 PU Foam, NC Polyolefin

* PU = Polyurethane; C = California Foam; NC = Not California Foam

37
Effective

Heats

of

Combustion

Heat

CD *-5 > 2

to

• H '—h o

4-* U C CD org

CD CD

<u o

4-1 -H H"

i ^r O

4-( 4-> LU (/)

r-H 1-1 CD f-H r-H rg 3 to O X>

oc £

rt o

r-H

4 U

<D> 4-i < O

I

lO

to

i

I

r ) to

Ph

r—i tO to ro w Ph Ph C

CD •* E o 00 ro rg O CD •H rg rg rg rg rg to rg o Ph Ph Ph Ph Ph Ph Ph

CDD- CO LOrg rg

Uh Ph

0/) E E E E C rt rt T3 o c, rt rt •H o o 0 o o o o

T3 Ph P- X 4-> 4-> Ph Ph T3 • rH +-> 4-> 03 E) E> o O E> E>

Oh Oh Oh CJ CJ Oh Oh

38
Table 11

Estimated Heat Release Rate Data

Specimen

Mass

Factor

Frame

Factor

Style

Factor

F21 1811 1.0 1.0

F 2 2 2042 1.0 1.0

F 2 3 1997 1.0 1 .

F 2 4 1811 1.0 1.0

F 2 5 1779 1.0 1.0

F26 1229 1.0 1.0

F27 1856 1 . 0 1 . 2

F 2 8 1869 1.0 1 . 2 F 2 9 896 2.0 1.2

F 3 0 1613 0.6 1 . 2 F 3

2560 1 . 0 1 . 0 F32 3296 1.0 1.0

F33 2509 1.0 1.0

Padding

Factor

Fabric

Factor

Estimated

Q

(kW)

Measured

Q

(kW)

1 .1 .

1811 1970

0.4 0.4 327 370

0.4 1 .

799 700

1.0 0.4 724 700

1 .1.0 1779 1990

1.0 1.0 1229 810

1.0 0.4 891 920

1.0 0.4 897 730

1 . 0 1.0 2150 1950

1.0 1.0 1161 1060

1.0 1.0 2560 2890

1.0 1.0 3296 3120

1 .0.4 1004 940

39
Exhaust Blower

All dimensions in meters

Figure 1. View of furniture calorimeter .

^40
TIME (S)

Figure 2. Measured wastebasket heat release rates, along with

adopted simplified representation

41
Figure 3- Wastebacket simulation burner used as

the ignition source

42
HEIGHT

ABOVE

BURNER

(mm)

TOTAL FLUX |kW/m 2

) IRRAWANCE (kW/m 2

)

DISTANCE FROM BURNER CENTERLINE (mm)

Figure 4Fluxes measured at the wastebasket

simulation burner

43
Figure 5 - Chair F21

44
Figure 6. Chair F21 near peak burning time

45

•H
Figure 7

Chair F31

46
Figure 8. Chair F31 near peak burning time

47
Figure 9- Chair F32

48
Figure 10. Chair F32 near peak burning time

49
Figure 11. Chair F28

50
Figure 12. Chair F28 near peak burning time

51
RATE

OF

HEAT

RELEASE

[kW]

Figure 13 . Rate of heat release for specimen F21

52
TIME (s)

Figure 14. Effective heat of combustion measured

for specimen F21

53
Figure 15. Target irradiance and particulate conversion

fraction for specimen F21

54

PARTICULATE

CONVERSION

(%)
RATE

OF

HEAT

RELEASE

(kW)

Figure 16. Effect of specimen mass on rate of heat release

55
RATE

OF

HEAT

RELEASE

(kW)

200 400 600 800 1000

TIME (s)

Figure 17 . Effect of specimen padding and fabric on

rate of heat release

56
MASS LOSS RATE, m (g/s)

Figure 18. Relationship between mass loss rate and

target irradiance flux

57
ESTIMATED

Q

(kW)

Figure 19- Relationships between actual and estimated peak

values of rate of heat release

58
APPENDIX A

Adjustments for 0 o Meter Response Time

Previous knowledge, together with analysis of raw data indicated that in an analysis system of the kind used here, slow instrument response is a problem that must be addressed. Some of the instruments used in the calorimeter (e.g., stack thermocouples) respond quickly enough that no response

correction needs to be made. However, gas measuring instruments show a slower response for two reasons: (1) a certain lag time is involved in

pumping the gases from the stack, through traps and filters, and into the gas

analyzers. In the present case, this amounts to approximately 30 s. The

appropriate correction is simply made by performing a 30 s translation of the

time coordinate; (2) instrument response itself is not instantaneous. This

can be compensated for if the response characteristics are known.

The 0 ? and CO^ analyzers were tested by using the calibration burner to

provide a square-wave heat release signal. For the turn-on portion, special

precautions are required if a pressure spike is to be avoided. It is difficult

to arrange this for flows of the magnitude needed here; consequently, only

the data from the turn-off portion of the response were used. The decay

transient is not subject to this error. Gas flow rates corresponding to 250,

500, 750, and 1000 kW fires were used. Analysis indicated that the normalized

response was identical for each of these cases and could be represented as

U(t) = 1 - e"

bt

where U(t) is the response at time t to a unit driving function, with the

steady state value being U(t -»-«>) e 1.0. The above is expressed, for simplicity, as the turn-on response. Values of 3 were constant for each instruments

and were

6 = 0.08 s (O 0 analyzer)

B - 0.25 s

^ (C0 9 analyzer)

The relation between 6 and the 10 percent to 90 percent rise time t is

expressed as

t r

= 2.197/6

59
and is equal to 27 s for the oxygen analyzer and 8.8 s for the CO-, analyzer.

The "time constant" can also be obtained as t = 1/6. The above values are largely, but not completely, a function of the analyzer alone. A slightly

different response might be obtained if the square-wave input were presented

directly at the inlet port of the instrument. The difference would be

accountable by species diffusion in the sampling lines. Measurements of 6

for the analyzers alone were not made since these data would not be used.

For a meaningful response correction to be made, BAt must be significantly

smaller than 1.0, where At is the data sampling interval. In the present

apparatus At = 10 s was used for the earlier tests, with At = 5 s for later

tests. Since At could not be reduced below 5 s, corrections for C0-, analyzer

response would not be meaningful. Thus, no C0 ? response corrections were

made beyond the lag time adjustment.

A number of corrections schemes for 0 ? were examined. The simplest

scheme is to let

The adjusted response, S, is expressed as the measured response, R, plus a term proportional to the time- derivative of R. The derivative has to be

evaluated numerically as a forward, central, or backward difference, but in

any case, uses only two data points. This method was tried and it was found

that while the response rise and fall times were sharpened up, an excessive

amount of numerical hash was introduced. This hash is not unexpected since

the correction at each step is based on only two data points, and has been

noted by others [17].

A more powerful technique is based on the superposition integral. For a linear system the response can be expressed as

where S denotes dS/dx. Evans and Breden [18] have indicated how to solve

this integral in finite-difference form to obtain S(t). The expression for

S(t) then contains a summation of R(t) terms starting at t + At and going

back to t = o. The terms near the origin, however, do not become small for t >> o, thus numerical errors near the origin propagate throughout. Also, the

summation gets very long for large t values.

S(t) = R(t) + | ||

R(t)

60
An equivalent superposition integral can be written as

R (t) S (t)U (t-r) dx

U can be obtained this way as an "impulse response" to a unit impulse at t

=

0. More conveniently, since U = dU/d(t-x) , this gives U = Be

r ^.

For convenience we will take At to be constant and define

S = S(t ) = S(nAt)

n

v nJ

A suitable finite-difference expression for then becomes

S = —q-t-t- R +1 - e"

eAt

S .. - e"

2BAt

S n ? , -BAt n+1 n-1 n-2

1 - e

-nBAt c e S

In this expression, in principle, all terms from S n to S

q would have

to be included. In practice, one can see that the experimental factors rapidly

go to zero for large kBAt. In the present case, the summation was extended

only to kBAt = 7. The expression thus has the desired propert ies - - a sizeable number of points, much greater than 2, is used to evaluate the

adjustment, but the process is damped and values near the origin are immaterial

at times much past the origin.

It can further be noted that a correction of this kind is worthwhile

only when the sampling rate is sufficiently fast compared to instrument

response time, so that BAt < 1. Thus, for the CC^ analyzer, in the

present case, no correction was used.

When both a physical lag time correction and a square-wave correction

have both to be made, as in the case of 0

? response, it can be seen that the

proper numerical lag time to be used is (physical lag) minus (At)

* This form was suggested by P. Goodeve, University of California, Berkeley.

61
APPENDIX B Flow Behavior of the Furniture Calorimeter

Some exploratory experiments were conducted at variable fan speeds and

heating rate values to determine the effect of fire size on system flow rate.

It was noted that while the standard volume flow and mass flow rates drop

with increasing Q, the actual volume flow rate--which in fan systems typically

remains constant -- rises somewhat with increasing Q. Analysis of these data

showed that, to a good approximation, the actual volume flow rate could be

expressed as

V = C

2 /AP^ + 1.091 x 10' 3 (Q - 55)

applicable over the range of 100 klv <_ Q £

500 kW. Here C ? is a constant

characterizing the fan and &P^ is the pressure drop across the fan. V is

seen to be expressable as a sum of two terms.

The actual volume flow through a fan is essentially constant when the

intake gas density changes, provided the shaft speed remains the same and

provided the system flow resistance remains constant. In the present case

introducing heat into the system decreases the flow resistance and thus the

actual volume flow rate rises with Q. The mass flow rate falls, but does not

fall as much as it would if the actual volume flow were constant. Measurements

show that an alternate expression is possible,

V = 1.4 + 0.0015 T (m

3 /s) heating

V = 1.4 + 0.0012 T (m

3 /s) cooling

where T is the stack temperature (K) measured at the location of the velocity

probe. The above pair of expressions is valid for 0 < Q< 2000 kW. Mass

flows can then be calculated as:

m = + 0.53 (kg/s) heating

3 1

m = + 0.42 (kg/s) cooling

The expressions for flow rates given above were derived only to illustrate

system performance; all flow rates used elsewhere in this report were based

on actual duct velocity and temperature measurements.

62
APPENDIX C

Estimate of Losses in Smoke Sampling

In the furniture calorimeter the smoke measuring location is quite a distance downstream of the combustion zone (approximately 13 m) . The soot

that is deposited on the duct walls is not available at the measuring station,

and thus the measurement underestimates the actual smoke production. The

stack duct flow is turbulent, so literature values for turbulent aerosol

deposition in pipe flow can be examined. No studies directly applicable to

fire smokes are available, but some data correlations are available for small

solid particles flowing in ducts with wall surfaces of perfect adherence.

As customary in this area, we use a deposition velocity K

3 K

_ particles deposited m' ms2 ’particles r

The units of K are m/s and represent the particle flux for a given freestream particulate concentration. This can be expressed non- dimens ional ly as K/u, where u = average duct flow velocity (m/s). By use of turbulence

analogies we directly use results from turbulent heat transfer by letting

K Nu

u

%

ReSc

Here Nu = Nusselt number,

Re — = Reynolds number

Sc = g- = Schmidt number

With d = duct diameter (m) , v = air kinematic viscosity

2 particle diffusivity (m / s ) . An appropriate expression

Nu = 0.0118 Re 7/8 Sc 1/3

In the present case we set

d = 0.3m

u = 18 m/s

v = 0.

5

x 10' 4 m

2 /s

Re = 1.0 x 10 5

(m

2 /s)

,

for Nu

and D =

27] is

63
For smoke from flaming fires we can take a typical particulate diameter as d

= 0.5 x 10 [28]. This corresponds to [27]

D = 6. 3 x 10' 11

Sc = 2.3 x 10 5

Thus this gives

- = 7 x 10" 7 u

A better estimate can be made by using relationships based on particle

measurements which take into account inertial effects and boundary layer

penetration by particles. A recent review by Liu and Ilori [29] provides a data correlation in graphical form. Their results can be approximated as

V+

= 0 . 2 for t +

> 50

V+

= 0. 045 Pp

'°- 56

t+

1 - 6 for x +

< 5

The non-dimensional quantities V

+ and x are defined as

The friction factor f/2 = 0.0395 Re 1 ^ 4

; p and p f are particle and fluid

3 P 1 densities (kg/m ), respectively. In our case take

pp

= 2000 kg/m^

p^ = 0.6 kg/m^

This gives

The quantity that is desired is the fraction of particulates lost over

the running length of the duct, Y = 13 m in this case. This is the ratio

n(y)/n

Q

, where n(Y) is the particle concentration at the smoke meter and n

Q

is the initial concentration. This value can be gotten by performing a mass

balance on particles,

64
u (dn) Trd‘ = Kirdn

o (dy)

Integrating from y

= 0 to y

= Y gives

n£zl = exp r- 41 h n exp l d U

J o Using K/u = 1.8 x 10" 4 this gives n(Y)/n = 0.97. In other words, only 3 percent of the particulates are removed due to wall losses. This value for

duct losses should be augmented by elbow and orifice losses, for which no convenient estimates are available. This would still be a very small loss;

further experimental work would be needed to make a better estimate.

The appropriate comparison for bench-scale smoke data would be with the

NBS smoke density chamber [30]. Here measurement errors can arise due to

oxygen depletion, incomplete mixing, and coagulation due to smoke aging, in

addition to chamber wall losses. The latter may also be augmented by thermophoretic forces. Further, in the static smoke chamber, due to thermal

stratification the deposition is not uniform but is preferential towards the

ceiling.

A rough indication of combined losses can be obtained by measuring the

decay rate of the extinction coefficient. Assume that the chamber volume is

well stirred but that deposition takes place only on the ceiling. Define an effective boundary layer thickness <5, such that

K

- D

‘

6

Then a balance on the particulates gives

V (dn) = (dt)

Integrating for a total time t gives

n (t) _= exp ( AD

V 6 t)

Here (V6/AD) is the time constant, A is the ceiling area (0.56 m in this

3 case), and V is the chamber volume (0.51 m ).

65
Measurements suggest that the decay time constant is about 500 s. This

gives

(500) (0. 56) (6. 3 x 10' 11

) _ ft -8

6 om - 3 X 10

Since this 6 is << d it does not realistically represent a physical boundary

layer thickness.

The time constant for the decay, however, may be used as an estimate for

the effect of wall losses and related errors on a smoke production measurement.

The effect will be small if the time during which active burning measurements

are taken is << 500 s. This burning period may typically be 200 s. Thus,

wall losses within the smoke chamber are only a minor source of error in

testing specimens.

The above analysis would be strictly applicable if the smoke chamber

window were always free of sooting. Smoke particles, however, are deposited

on the window as well as the walls. Particles which leave the gas phase by

deposition thus still have an effect on beam transmission since they may be

deposited on the window. This is hard to evaluate and has not been considered

in detail beyond simply assuming that all the deposition takes place after

combustion has ceased and adjusting the beam transmission accordingly.

66
BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBSIR 82 -2604

2. Performing Organ. Report No. ubhcation Date December 1982 4.

TITLE AND SUBTITLE

Upholstered Furniture Heat Release Rates Measured With a Furniture Calorimeter

5. AUTHOR(S)

Vytenis Babrauskas, J. Randall Lawson, W. D. Walton, William H. Twilley

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9.

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

10.

SUPPLEMENTARY NOTES

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

11.

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

bi bliogr'aphy or literature survey, mention it here)

Accurate burning rate information on upholstered furniture is important for two

purposes - to predict the room fire development history for a fire involving the

furniture, and to relatively, but adequately, rank commercial products for a given

application. Small-scale test results data not referenced to full-scale fires lack

validity, while full-scale room fires are costly and lack generality. To enable

simplified but realistic full-scale testing to be done, a new apparatus, termed a furniture calorimeter was developed. Rates of heat release are measured by using

the oxygen consumption principle. Tests were conducted in the furniture calorimeter on thirteen different specimens of upholstered furniture, representing typical,

but carefully controlled, construction. The results showed significant heat release

differences between thermoplastic and cellulosic fabrics, between frame types and

between padding materials. For polyurethane foam padding, however, performance was unrelated to results of Bunsen burner type tests on the foam. Thee data developed

(1) can be used directly in the calculation of room fire growth; (2) will form some

of the reference data for development of appropriate bench-scale test procedures;

and (3) can be used in some cases to estimate burning rates of similar but not

identical furniture.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Burning rate; chairs; fire tests; flammability tests; furniture; plastics; heat

release rate; textiles, upholstered furniture.

13. AVAILABILITY

Unlimited

| | For Official Distribution. Do Not Release to NTIS

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

20402.

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

14. NO. OF

PRINTED PAGES

73

15. Price

$9.00

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