NBSIR 80-2085

Fire Performance of Loose Fill

Cellulosic Insulation in

Occupancies - A Progress Report

Lionel A. Issen

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

August 1980

Interim Report

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NBSIR 80-2085

f #« FIRE PERFORMANCE OF LOOSE FILL

CELLULOSIC INSULATION IN RESIDENTIAL

OCCUPANCIES - A PROGRESS REPORT

C‘>

Lionel A. Issen

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

August 1980

Interim Report

Sponsor^ in part by:

Department of Energy

Washington, D.C. 20585

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology, and Innovation

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director
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TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES v

LIST OF SYMBOLS vi

Abstract 1

1. INTRODUCTION 2

2. LABORATORY TESTS FOR CELLULOSIC INSULATION 4

2.1 Recessed Light Fixture Test 4

2.2 Divided Box Test 4

2.3 Improved Smoldering Tests 5

3. FIRE RETARDANTS 6

4. EXPERIMENTAL RESULTS 7 4.1 Smolder Tests (HH-I-515D) 8

4.2 Attic Floor Radiant Panel Tests (HH-I-515D) 9

4.3 Recessed Light Fixture Test 9

4.4 Divided Box Smoldering Test 9

4.5 Smolder Property Tests 10

5. DISCUSSION 11

6. CONCLUSIONS 12

7. RECOMMENDATIONS 13

8. ACKNOWLEDGMENTS 13

9. REFERENCES 13

APPENDIX A. CRITERIA FOR TIME OF SMOLDERING TESTS A-l

APPENDIX B. RELATIONSHIP BETWEEN HOT PLATE TEST

AND ADIABATIC FURNACE B-l

iii
LIST OF TABLES

Page

Table 1. Results of smolder tests HH-I-515D 16

Table 2. Commercial insulation - recessed light fixture test . . 17

Table 3. Laboratory insulation - recessed light fixture test . . 18

Table 4. Summary of experimental data - commercial cellulosic

insulations 19

Table 5. Summary of experimental data - laboratory cellulosic

insulations 20

iv
LIST OF FIGURES

Page

Figure 1. Cigarette smoldering test 22

Figure 2. Recessed light fixture test exterior view 22

Figure 3. Recessed light fixture test interior view 23

Figure 4. Divided box test 23

Figure 5. Blower mixer for preparing laboratory insulations ... 24

Figure 6. Average particle size distribution of boric acid

and borax 25

Figure 7. Effect of borax and boric acid on weight loss —

smoldering ignition 26

Figure 8. Effect of borax and boric acid and fineness of

grind on critical radiant flux — attic floor

radiant panel 27

Figure 9 . Divided box test — maximum temperature vs % chemical

by weight of mix for different grinds of boric acid . . 28

Figure 10. Divided box test — maximum temperature vs % chemical

by weight of mix for polybor 29

Figure 11. Hot plate tests — untreated cellulose 30

Figure 12. Adiabatic furnace test — untreated cellulose 31

Figure 13. Comparison of smolder ignition temperatures inferred

from adiabatic furnace tests and measured in hot

plate tests 32

Figure A-l. Dimensionless slope vs dimensionless time at

hot plate A5

Figure A-2. Surface heat transfer coefficient A-6

Figure A-3. Dimensionless unexposed surface temperature vs dimensionless time A-7

Figure B-l. 6^ as function of B and 0

q

[6] B-4

Figure B-2. Correspondence of adiabatic furnace and equivalent

hot plate test B-5

v
LIST OF SYMBOLS

B_^ = Biot number, LH/K (dimensionless thickness)

B = Positive roots of equation B cot B + A = 0 n

d = Effective thickness of insulation

e = Base of natural logarithms

E = Activation energy

F = Fourier number, at/L2 (dimensionless time)

g = Acceleration of gravity

H = Free convection surface heat transfer coefficient

c = Radiation surface heat transfer coefficient

H> H

T

- H

c +

“r

= Conductivity of air

K = Conductivity of insulation

L = Thickness of layer of insulation

N = Nusselt number, Hl/K

u a n = Dummy variable n = 1, 2 ,...

00

Pr = Prandtl number, 0.7 for air over range of temperatures of interest

R = Universal gas constant

R = Rayleigh number, GAT/T a v a o a

r = Half thickness of layer of insulation, i.e. r = L/2

t = Time

T = Temperature

AT = T - T

s o T^ = Temperature of unheated (top) surface of layer of insulation

T = Ambient air temperature

vi
LIST OF SYMBOLS (continued)

= Hot plate temperature

T = Dimensionless temperature (T-T)/(T - T ) o p o

X = Distance from hot plate 0 £ X _< L

X = X/L 0 < X < 1

= Diffusivity of air

a = Diffusivity of insulation

B = Hr/K

6^ = Critical self-heating parameter

e = Emissivity

v = Dynamic viscosity of air

vii

FIRE PERFORMANCE OF LOOSE FILL CELLULOSIC INSULATION IN

RESIDENTIAL OCCUPANCIES - A PROGRESS REPORT

Lionel A. Issen

Abstract

The smoldering and flame spread properties

of cellulosic loose fill insulation were examined

as a function of retardant type, particle size,

and concentration to provide a basis for the

development of improved fire test methods. A

series of laboratory insulations was prepared

whose fire performance covered an extended range

of critical radiant flux in the attic floor radiant

panel test and weight loss in the cigarette smoldering test. These materials were evaluated in a recessed light fixture test in a simulated attic

configuration. Borax and boric acid were effective

in raising the critical radiant flux (CRF) in the

attic floor radiant panel test, but borax alone,

in the cigarette smolder test, increased the

smoldering potential of loose fill cellulosic

insulation. The divided box test for smoldering

propagation appears to be a more realistic test

than the present test for smoldering ignition.

In the cigarette smoldering test, inclusion

of 10% borax increased the boric acid requirement

for passing from 7.5% to 20%. In the attic floor

radiant panel test, the finer the grind, the less

boric acid required to meet Federal -Specification

HH-I-515D. This varied from less than 10% for

vapor applied boric acid to over 35% for granular

boric acid. Above the 25% level the presence of

borax did not significantly affect the CRF level.

Passing the recessed light fixture test required

a minimum of 30% impalpable boric acid, or 40% to

50% intermediate grind boric acid.

In order to determine fundamental parameters

which could be used to characterize smoldering

ignition potential, a number of test methods have

been investigated which can be used to determine

the pre-exponential factor and the activation

energy of ignition reaction. These include the

Bowes and Townshend hot plate, thermo-gravimetric

analysis (TGA) , and the adiabatic furnace.

1
Key words: Activation energy; borax; boric acid;

cellulose; critical radiant flux; fire; fire retardants;

fire tests; loose fill insulation; smoldering ignition;

thermal analysis; thermal insulation.

1. INTRODUCTION

This report covers some of the activities to date at NBS on the

fire performance of loose fill thermal insulation as used in residential

occupancies. This effort was concentrated on an examination of the

smoldering and flame spread properties of loose fill cellulosic insulation in order to establish a technical basis for the development of

new test methods.

Since the energy crisis of 1973 there has been a markedly increased

use of insulation for both new and existing construction. This increased

use has resulted in fire incidents and has uncovered inadequacies in the

fire safety requirements and omissions in our understanding of the

unique fire behavior that may be associated with the use of these

materials.

The work reported here does not address other aspects associated

with the introduction of retardants into cellulosic loose fill insulation, e.g., reduced thermal resistance, corrosiveness, fungal growth,

mechanical separation, leaching and subliming. The work reported is

restricted to the fire properties, in particular the smolder properties

and the effect on them of chemical additives.

A number of fires have occurred in which cellulosic loose fill

insulation has been the first material ignited. These were mostly attic

fires usually started by contact with a recessed light fixture, although

a few fires involved other insulations and other heat sources. On

September 8, 1978 the Consumer Product Safety Commission (CPSC) required

that all insulation manufactured and sold in the U.S. have a flame

spread classification not to exceed 25 by the ASTM E84 tunnel test [1] . This test is a flame spread test and the results have no relation to

smoldering resistance. Furthermore, the tunnel measures the flame

spread on the underside of a ceiling mounting, while in reality flame

spread occurs on the upper surface of a floor mounting. In order to

overcome the limitations of the tunnel test in evaluating the fire

performance of insulations, in 1977 the Center for Fire Research suggested that two different tests be used to evaluate the fire performance

of insulations for the Federal purchase specification; these were the

attic floor radiant panel test [2] and the cigarette smoldering com- bustion test [2]. The attic floor radiant panel test simulates conditions

on the floor of an attic where insulation may be exposed to thermal

radiation from the underside of the roof and accidently exposed to a small flame source. The smoldering test was developed to indicate the

Numbers in brackets refer to the literature references listed at the

end of this report.

2
potential of an insulation to smolder when exposed to a local high

temperature source. These tests have now been incorporated by CPSC in

the Interim Safety Standard for cellulosic insulation covering insulation

manufactured after October 15, 1979.

An important consideration for the suitability of a laboratory test

for smoldering combustion would be its ability to predict the smoldering

potential of an insulation material as a function of thickness and

density when it is exposed to heated surfaces at various temperatures,

in particular its ability to predict the occurrence of ignition and

continued spread of smoldering when the material is in proximity to a recessed light fixture or a hot flue. In studying the smoldering

phenomenon and in evaluating the suitability of a test method, it is

necessary to examine a range of materials that range from those that

will not smolder to those that will smolder easily.

The smoldering test which is described in HH-I-515D and which is

shown in figure 1 requires only simple equipment and a lighted cigarette

to run. In this test, the material is placed in a stainless steel box

8 x 8 x 4 in high (20 x 20 x 10 cm) . A standard cigarette with the lit

end up is placed in a preformed hole at the proximate center of the

material. The material passes if the weight loss due to smoldering is

15 percent or less. During the development of this test it was noted

that insulations that had passed the ASTM E84 tunnel test with flame

spread classifications of 25 or less frequently failed this test. The

reason was that the fire-retardant chemicals used were flame inhibitors

and not smolder inhibitors.

While the requirement that an insulation must pass the cigarette

ignition test reduces the probability of smoldering, it does not eliminate it under all circumstances. The fact that the insulation passes

the cigarette ignition test is no guarantee that the insulation will not

begin to smolder after prolonged exposure to an extended area heated

surface. It is necessary to provide a more realistic test for smoldering

ignition and propagation if loose fill cellulosic insulation is to be

used safely. Ideally, this should be a property test which could be

used to predict the smoldering potential of a material under different

exposure and use conditions rather than simply a pass/fail test. This

report describes some experiments which provide part of the background

needed to develop such a test. It involves an examination of the effect

of retardant type, concentration, and particle size on the smoldering

properties of loose fill cellulose insulation under realistic conditions.

While some of the early experiments were performed with the test methods

referenced in HH-I-515D, the intent of the work is neither to verify nor

modify the present test methods but to provide part of the background

necessary for the second generation of fire tests for thermal insulations.

3
2. LABORATORY TESTS FOR CELLULOSIC INSULATION

2.1 Recessed Light Fixture Test

As part of the overall studies of the performance of insulations, a reduced scale attic mock-up with a recessed light fixture in the floor was used to evaluate smoldering ignition under more realistic conditions.

The details are shown in figures 2 and 3. The mock-up was 4 x 4 x 2 ft

6 in high (1.22 x 1.22 x 0.76 m) . The underside of the roof was lined

with 3-1/2 in (89 mm) foil backed glass fiber insulation. The light

fixture which was rated for 100 W was fitted with a 150 W light bulb.

This 150 W light bulb represents a size typical of that which may be

used in practice. The light fixture itself is an off-the-shelf residential unit^. The dimensions of the fixture are 8 x 8 x 4 in high

(20.3 x 20.3 x 10.8 cm). The test is run in the following manner: (1)

the floor joist spaces are filled with insulation to the required density

using a commercial blower; (2) the overhead air space temperature is

raised to and maintained at 60°C; (3) when the overhead air temperature

reaches 60°C, usually in about 1 hour, the electric light in the fixture

is turned on. The test is run either until smoldering occurs or for a maximum of 7 hours.

In this test it was noted that smoldering would start in commercial

insulations that had passed the smoldering test referenced in HH-I-515D.

Hence, the development of a more severe and realistic test for the

smoldering potential of thermal insulation appears to be needed.

2.2 Divided Box Test

The recessed light fixture test requires a day to set up and a day

to run. In order to reduce the number of these tests, a rapid screening

test that would identify those insulations that would likely pass or fail

the recessed light fixture test was developed for this project. The

apparatus, which is shown in figure 4, is called a divided box tester

and consists of a stainless steel box 8 x 8 x 4 in (20 x 20 x 10 cm)

with a removable barrier in the middle. On one side of the barrier is

placed untreated insulation, on the other the insulation material to

be tested. A single thermocouple is placed in the insulation being

tested with the bead 50 mm from the barrier and 20 mm above the base at

the centerline of the box. The thermocouple was made of 22 gauge

chromel-alumel (type K) material, with the end 25 mm oriented more or less parallel to the bottom of the box. To run the test: (1) the

barrier is placed in the box, (2) untreated insulation is placed in one half of the box to the specified density, and the test insulation

(treated) is placed to the specified density in the half with the

thermocouple, (3) the barrier is removed, (4) a lit cigarette with the

lit end up is placed in the middle of the untreated insulation, and (5)

the temperature is monitored until the smoldering ceases or the temperature has reached a maximum and then decreases. The complete test can

By coincidence this test is similar to that of the Oklahoma City

recessed light fixture tests, in which a 200 W bulb was placed in a 150 W fixture [3]. a
be run in about 30 to 60 minutes. If temperatures develop in the test

insulation in excess of about 250°C, it indicates that the material

will support the propagation of a smoldering front and the material is

considered to have failed.

In these tests the untreated cellulose was placed at a density of

2.2 pcf (35.2 Kg/m^) . This was selected on the basis of a nominal total

density of 3 pcf (48.1 Kg/m3) for the insulations, less a nominal 25

percent chemical content.

From the testing that has been done, any material that has passed

this divided box smolder test has also passed the recessed light fixture

test. The converse does not always hold, as materials that have passed

the recessed light fixture test may fail the divided box test. Twelve

materials were tested in the divided box tester.

2.3 Improved Smoldering Tests

The cigarette smoldering test, the recessed light fixture test, and

the divided box test are all pass/fail tests. They simulate different

scenarios and each provides somewhat different information which is

difficult to extrapolate to conditions other than those of the test. An

ideal test would provide information that would permit extrapolation of

the smoldering performance to other conditions, and could also be used

for other types of insulation than cellulose. With this as a guiding

principal, several test methods were examined that could provide the

fundamental parameters that would permit extrapolation to conditions

other than those of the test.

The first candidate test was the hot plate smoldering test. This

test was suggested by the work of Rogers, Ohlemiller, and Summer field

[4] at Princeton and is based on the work of Bowes and Townshend [5] and

Thomas and Bowes [6]. The test method, which appears deceptively simple,

requires that the minimum hot plate temperature to produce smoldering be

determined for a number of different thicknesses of insulation. In this

work the density of the insulation should also be controlled. With the

assumption that the smoldering ignition reactions follow an Arrhenius

temperature dependence, the effective pre- exponential factor and activation energy may be calculated. These in turn can, in principle, be

used in a thermal ignition theory model to determine whether smoldering

is likely to occur under a given set of field conditions.

The difficulties with this method are that the rate of char formation

is a function of the heating rate [7], the thickness of the insulation

layer, and the air circulating over and through the insulation. The

formation of a char layer having different thermal properties than the

insulation alters the rate and amount of heat that reaches the uncharred

insulation. The ratio between the diameter of the hot plate and the

depth of the insulation also affect the rate of char formation. These

factors may have caused some of the observed differences in the results

for different hot plates and different operators.

5
A second candidate test is thermo-gravimetric analysis (TGA) . This

test is one of a group of thermal analyses [8] and can be used to determine the activation energy; a second test such as differential scanning

calorimetry (DSC) can be used to determine the heat of reaction. On some equipment the DSC can be run simultaneously with the TGA test.

A third candidate test is the adiabatic furnace. The adiabatic

furnace simulates self heating in an infinitely large mass of insulation.

The pre-exponential factor and the activation energy can be derived from

the test data [9]. Though the adiabatic furnace that is being used at

present requires that the data be reduced manually [10], it could be

modified so that the data could be reduced automatically by a minicomputer .

The lowest temperature to cause self-propagating smoldering is

undefined; given enough time and thickness of insulation even relatively

modest elevated temperatures can lead to self heating. Thus for both

the hot plate test and the recessed light fixture test, a criterion is

necessary for the time that the test should be run for determining

whether self heating will or will not occur. One such criterion was suggested by Ohlemiller for one-dimensional cases [11]. Using the

solution for an inert layer heated on one side and losing heat to the

atmosphere on the other side (Carslaw and Jaeger [12] case VI page 126),

the time for the temperature gradient in the insulation at the hot plate

to reach steady state is given approximately by (at)/L 2 < 0.5. For a 10 cm thick layer this indicates that the test should be run for 1-1/2 to

2 hours; for a 30 cm thick layer this indicates that the test should be

run for 10 to 15 hours. For the recessed light fixture test in which

the insulation covers the light fixture to a depth of 5 to 6 in (12.5

to 15 cm), this criterion would give a reaction time of about 3 hours.

In tests with the recessed light fixture at NBS smoldering has occurred

after upwards of 5 to 7 hours of heating. In this test the recessed

light fixture is surrounded by insulation, and so the assumption of one- dimensional heat transfer is violated. Thus some effective thickness

should be used, when applying this criterion, which is intermediate

between the thickness of the insulation covering the fixture (which

gives too short a time) and the total thickness of insulation in the

joist space (which gives too long a time). More work needs to be done

to define a suitable criterion for duration of smoldering tests. Based

on observations of the recessed light fixture test here at NBS, the test

should be run for a time at least twice that given by using the thickness

of the insulation over the fixture in Ohlemiller' s criterion. An analysis

of Ohlemiller 's criterion is given appendix A.

3. FIRE RETARDANTS

Until recently fire retardants were added to loose fill cellulosic

insulation for the purpose of passing the ASTM E8A tunnel test, which is

a flame spread test. These fire retardants include, but are not limited

to, ammonium sulphate, boric acid, borax, calcium sulfate, aluminum

sulfate, and sodium carbonate. In order to control the pH resulting

6
from the use of sulfates, hydrated lime or other buffers are added.

Experience has shown that such combinations of fire retardants and

buffers may have a low smolder resistance and may not pass a recessed

light fixture test or the smolder test of Federal Specification HH-I-515D.

For the initial studies described in this report, boric acid and borax

were used in the insulations made up specifically for this project. Of

all the commonly used fire-retardant chemicals, boric acid is the best

smolder inhibitor [13-15]. Boric acid and borax are frequently used

together in combination at about 20%-25% by weight of the insulation.

This generally produces a cellulosic insulation that has a flame spread

classification as low as 25 (or less) in the ASTM E84 tunnel test. A

particular insulation must, of course, be tested to insure compliance.

With the current commercial technology for cellulose insulations,

the fire-retardant chemicals are almost always added as dry crystals or powders and mixed mechanically with the ground paper. Some equipment

can mix fairly closely measured quantities of chemicals with the insulation; however, there is no way of guaranteeing that the chemicals

will not separate. When several commercial insulations were examined

under a microscope, the chemical crystals which ranged in size from

about 0.1 mm to about 0.4 mm did not appear to adhere to the fibers of

cellulose. This observation raises the question of the mechanical

separation and migration of crystals to the bottom of the installation

space and the effect this may have on the fire performance of the insulation. To overcome this problem, some members of the industry are experimenting with partially wet processes; that is, a small amount of

the chemicals are added as a wet spray. Knoepfler et al. [13] have

developed a method for adding boric acid to cellulose in a vapor process.

At this time the method is not commercially viable, the process is

potentially hazardous3, and samples evaluated to date have not passed

either the recessed light fixture or the divided box test. Though

adding fire-retardant chemicals in a water solution might reduce the

total amount of chemicals required for a given level of smoldering

resistance the added cost of drying the insulation would make cellulose

insulation noncompetitive with other materials. Furthermore, it still

remains to show that this is more effective than mixing the dry chemicals

with the crushed paper.

4 . EXPERIMENTAL RESULTS

While a number of tests were run with commercial chemically-treated

insulations the bulk of the work was conducted with laboratory-prepared

specimens consisting of ground newsprint to which known concentrations

of retardants were added. The blower/mixer which was used to prepare

the test batches is shown in figure 5. It consists of a drum with a cone at one end, a transparent cover at the other, an electric vacuum

cleaner motor and connecting hose.

3Methyl and ethyl borates have flash points below 27°C (80°F); triethyl

borine has a flash point of -36°C (-32°F) [16].

7
Three different grinds or grades of boric acid were used in these

tests; these were granular, an intermediate grind that was ground from

the granular grade material in a ball mill, and impalpable. One grind

of borax was usedj this was similar in size to the intermediate grind of

boric acid and prepared in the same way. One grind of polybor (disodium

octaborate tetrahydrate) was used. The grain size distributions for

these materials are shown in figure 6. The ground paper was supplied by

a local insulation contractor. Since there are no standards for determining the size of the ground paper, no attempt was made to classify its

size. It was noted qualitatively that within a single batch the ground

paper seemed to be uniform, but the fineness of the ground paper varied

from batch to batch.

After trying several alternatives the following method of preparing

the samples was adopted: (1) the mixer /blower machine was cleaned out

manually, (2) about 150 grams of untreated ground paper insulation was

run through the mixer/blower for about 2 to 3 minutes and this material

was discarded, (3) carefully weighed amounts of untreated paper insulation and chemical (s) were hand mixed in the drum of the mixer /blower

,

(4) the blower /mixer was then run for 1 to 3 minutes, the time depending on whether the batch was small (about 100 grams) or large (about 400 grams)

,

(5) the contents and residue were carefully brushed out into a weighing

pail, and (6) the net weight after mixing was checked. If the weight

differed by more than 1 percent or 2 percent from the original weight

of the ingredients, the material was discarded and a new batch prepared.

A certain amount of practice was necessary for efficient operation of

the mixer/blower : too little time resulted in hard lumps of paper;

too much time resulted in excessive maceration of the paper. It was also

found that there was an optimal angle to run the machine which resulted

in efficient mixing and fluffing of the insulation.

4.1 Smolder Tests (HH-I-515D)

In the cigarette smoldering test, the observed effect of borax was

to increase the required amount of boric acid needed to inhibit smoldering. Figure 7 and table 1 show that with 10 percent borax in the mixture,

20 percent boric acid was required to pass, while without any borax,

only 7-1/2 percent boric acid was required to pass this test. Note that

these percentages are with respect to the overall final weight of the

mixture

The density of the insulations was controlled by: (1) preparing a batch of insulation of the specified composition, (2) carefully weighing

out an amount that would fill the smolder box to the required density,

and (3) gently placing and compressing the insulation in the smolder

box. In these tests the actual rather than the nominal dimensions of

each smolder box were used to determine the required weight of insulation. A material that has passed the cigarette smoldering test at a particular density will also pass at all lower densities. Conversely, a material that has failed the cigarette smoldering test at a particular

density will fail at all higher densities.

8
It should be noted that the sodium in borax, as with all alkali

metals, is a catalyst for promoting smoldering [14-16]. This effect of

borax on the smolder resistance of boric acid has also been observed by

Knoepfler et al. [13] in their work on smoldering of mattresses.

4.2

Attic Floor Radiant Panel Tests (HH-I-515D)

The results of the attic floor radiant panel tests are plotted

in figure 8 in terms of critical radiant flux versus percent chemical.

Even though the data are somewhat limited, the graph clearly shows that

the finer the grind of the chemical the lower the amount required for a given critical radiant flux. In figure 8 the least amount of boric acid was required when it was applied as a vapor and the most boric acid was required when it was applied in the granular form. The relative closeness of the data for impalpable grind and intermediate grind boric acid

suggests that there may be an optimal fineness of grind. That is, if the

grind of the chemicals is coarser than this optimal grind, the material

will have a lower critical radiant flux, and if the chemicals are ground

much finer than the optimal, then excess energy has been used for grinding

the chemicals. The tests with granular boric acid were terminated at

the 35 percent level for two reasons: (1) with this grind the chemicals

tend to separate out from the cellulose as the amount exceeds about 35

percent, and (2) this grind is not normally used in commercial mixtures

but was included to provide a comparison on the effect of grind fineness.

4.3 Recessed Light Fixture Test

The data obtained from the recessed light fixture test are shown in

table 2 for commercial cellulose insulations and in table 3 for cellulose

insulations that were made up in the laboratory.

No commercial cellulosic insulation has consistently passed this

test and the experimental insulations indicate that large amounts of

chemicals are required to pass. The finer the grind of the fire-retardant

chemicals, the lower the smoldering potential. This is shown by the

performance of the 30 percent impalpable boric acid insulation which

passed, but the 30 percent granular boric acid and the 30 percent

intermediate grind insulations both failed. To pass this test 40%-50%

of the intermediate grind boric acid is required. The results of the

recessed light fixture test strongly suggest that the cigarette smoldering

test may not represent a sufficiently severe exposure.

4.4 Divided Box Smoldering Test

The divided box test was developed as a screening procedure for the

recessed light fixture test. Any material that has passed this test has

also passed the recessed light fixture pest; the reverse is not always

true

.

Figure 9 shows maximum temperature reached during smoldering versus

percent chemical in the mix for different grinds of boric acid. The

effect of chemical fineness is shown in this figure where 35 percent

9
impalpable boric acid (85 percent passing 325 mesh) was required to pass

this test compared with 45 percent boric acid of the coarser intermediate

grind

.

Polybor, which is chemically similar to borax, failed the divided

box test over the range of 20 to 40 percent chemical in the mix (see

figure 10) . It is not surprising that the polybor failed the divided

box test, since it contains sodium. It is surprising that at the 30

percent level one of two polybor mixtures passed the recessed light

fixture test. For ease of comparison, some related information from

reference [17], is summarized in table 4, and the test data for

laboratory insulations are summarized in table 5.

4.5 Smolder Property Tests

The three tests which are being investigated as candidates to

provide heat release rate parameters were partially evaluated in terms

of ease of use. These tests are the Bowes and Townshend [5] hot plate

test, the TGA [8], and the adiabatic furnace [9,10].

For untreated ground paper, a set of runs on the hot plate test ^

gave a value of 31700 cal/mole for the activation energy and 3.2 x 10

cal/sec*cm® for the Arrhenius pre-exponential factor. A set of runs for

a similar material on a TGA apparatus gave a value of 54000 cal/mole

for the activation energy using Flynn's method [18]. Although both

these values are within the range of values for cellulosic materials

19,19], the TGA value seems high. One cause for this value would be if

the sample were overly compacted in the sample holder. In this situation

the observed reaction would be that for a higher rate reaction than the one of interest [20], hence the need for standardizing the TGA test

procedure for the particular material under test. The reduced data from

a hot plate test series are shown in figure 11.

For the untreated ground paper the adiabatic furnace gave a value

of 26400 cal/mole for the activation energy and 1.65 x 10® cal/sec*cm®

for the pre-exponential factor. A test on a treated ground paper with

30 percent impalpable boric acid gave a value of 40400 cal/mole for the

activation energy and 5.47 x 10® cal/sec-cm® for the pre-exponential

factor. The reduced data from an adiabatic furnace test series are shown in figure 12.

The particular adiabatic furnace that was used for these tests was

built in the 1950's and the data are reduced manually from a time

temperature strip chart. During tne course of the data reduction it was noted that the value of the activation energy was not very sensitive to

small errors in picking the data off the chart, but the value of the

pre-exponential factor was sensitive to these small errors; that is, a small change in the slope of dT/dt vs 1/T produces a large change in the

intercept (the pre-exponential factor) . This sensitivity is typical of

phenomena that are modeled by exponential functions.

10
The advantages of the adiabatic furnace are that a fairly large

sample is tested compared with thermal analyses, compacting the sample

to the applied density improves the test performance, the test is easy

to run, the data reduction is simple and unlike the hot plate test, a single test gives the required thermal parameters.

5. DISCUSSION

Three practical tests for evaluating the smoldering potential of

loose fill cellulosic insulation were used in this study. The cigarette

smoldering test indicated whether a smoldering wave could be generated

by a small moving high temperature source, specifically a cigarette.

The recessed light fixture test indicates whether a smoldering wave can be initiated in insulation covering an extended surface at high temperature, namely a recessed light fixture with an oversize bulb. The

divided box test indicated whether a plane smoldering wave can propagate

horizontally through the material once it is initiated. These three

tests have been mentioned in order of increasing severity.

Three additional tests that would provide material properties, i.e.,

activation energy and pre-exponential factor, were examined. These are

the Bowes and Townshend hot plate test, conventional thermal analyses,

and the adiabatic furnace. The hot plate test appears to be cumbersome

and tedious to run, and requires several tests to determine the smoldering temperature for a given thickness of insulation; thermal analyses

require skilled people and standardization of the test procedure, and use a very small sample usually only a few milligrams in weight. The

adiabatic furnace appears to be the easiest and most satisfactory. The

methods for calculating the activation energy and the pre-exponential

factor are mathematically similar for both the hot plate [5] and the

adiabatic furnace [10]. Therefore, in principle, it should be possible

to use the data from one of these tests to calculate the data derived

from the other. Following this idea, a method was developed to generate

from the adiabatic furnace data a relationship between thickness of

layer of insulation and equivalent hot plate temperature. The method is

described in appendix B at the back of this report.

The results of this analysis are compared with the results of the

hot plate tests in figure 13 and show better correlation for thicker

layers than for thinner layers. This is not surprising as the adiabatic

furnace ignition conditions approach those of the hot plate more closely

for thick layers. Fortunately in most practical applications, such as attic floors and exterior walls, the thickness of the layers of insulation would be in the range of 10 to 25 cm or larger, and for this

range of thicknesses the ignition parameters derived from the adiabatic

furnace would be satisfactory.

While a number of commercial insulations have passed the cigarette

ignition test, none has consistently passed the recessed light fixture

test or the divided box test. The amount of intermediate grind boric

acid that had to be added to untreated cellulosic insulation in order to

11
pass the cigarette smoldering test was 7.5 percent, while 45 percent was needed to pass the recessed light fixture test and the divided box test.

The addition of 10 percent borax to the insulation increased the amount

of intermediate grind boric acid needed to pass the cigarette smoldering

test to 20 percent. Since it was found that boric acid is approximately

as effective in increasing the critical radiant flux as borax and that

borax is a smolder promoter rather than a smolder inhibitor it would

appear that boric acid alone would be more effective in reducing the

overall combustion potential of loose fill cellulosic insulation.

Polybor which was obtained in a small particle size (70 percent

less than 45 microns) was found to be effective in passing the recessed

light fixture test at a concentration of 30 percent. However, it would

not pass the divided box test in concentrations as high as 40 percent.

Going to still smaller particle size the impalpable boric acid (80 percent

less than 45 microns) passed the divided box test at a concentration of

35 percent. Thus the finer the grind and dispersion of the retardant

the greater its effectiveness. The results with the polybor also support

the contention that the divided box test for smoldering propagation is

more severe than the recessed light fixture test for smoldering ignition.

Though this investigation concentrated on the smoldering phenomenon,

the overall question of fire safety posed by significant amounts of insulation in residences should also be investigated. Such an investigation

should include tests on both full size compartments and reduced scale

compartments, as well as computer simulations of various scenarios.

6. CONCLUSIONS

Based on the results of this study, the following conclusions may

be drawn:

1. Commercial loose fill cellulosic insulations examined in this study

were unable to pass the recessed light fixture test.

2. The divided box test is a good screening test and is conservative.

3. The fineness and dispersion of the fire-retardant chemical increases

both the smolder resistance and flame resistance of loose fill

cellulosic insulation.

4. Borax promoted the tendency to smolder and increased the

concentration of boric acid required to inhibit smoldering.

5. Borax and boric acid appear to be equally effective in increasing

the critical radiant flux, i.e. , limiting the extent of surface

flame spread.

6. The hot plate test is a slow and cumbersome method for deriving

kinetic reaction data.

12
7. The adiabatic furnace provided kinetic reaction data more easily

than does the hot plate apparatus. Furthermore, from this test it

is possible to derive a relationship between thickness of insulation

and equivalent hot plate temperatures.

7 . RECOMMENDATIONS

1. Continue work on developing a test method for characterizing the

smoldering potential of insulations in terms of their effective

kinetic reaction parameters.

2. Discontinue use of the hot plate apparatus for deriving kinetic

reaction data.

3. Concurrent with recommendation #1 above, investigate the overall

fire performance of insulation in residences using full size and

reduced scale model compartments and computer simulation.

8 . ACKNOWLEDGMENTS

Important help was provided by industry and government agencies on this project. In particular, I wish to acknowledge the assistance of

George Andrews of Therma-Coustics Manufacturing, Inc., who provided

a mixer /blower for preparing the cellulosic insulations, and to

Robert W. Sprague of the U.S. Borax Research Corporation, who provided

samples of impalpable ground boric acid and polybor chemicals, and

unpublished information on the chemistry of boron compounds. Other

industry sources offered insulation, chemicals, and information on processing. Nestor B. Knoepfler of the U.S. Department of Agriculture

provided information on their work on fire retardants and samples of

vapor applied boric acid cellulosic insulations. John Rockett and

Sanford Davis of the CFR suggested this version of the divided box test.

Tom Prather, Lee Dunlap, and Dennis Sullivan performed most of the tests

on this project. Roy Lindauer designed and built the frame to support

the blower/mixer. Joseph Loftus assisted in running the adiabatic

furnace. Particular thanks to William J. Parker and Dan Gross for their

review and suggestions during the preparation of this report.

9

.

REFERENCES

[1] Standard Test Method for Surface Flaming Characteristics of Building

Materials, ASTM E84-79. American Society for Testing and Materials,

Philadelphia, Pa. (1979).

[2] Federal Specification HH-I-515D Insulation Thermal (Loose Fill for

Pneumatic or Poured Application) Cellulosic or Wood Fiber, General

Services Administration, Washington, D.C. (June 1978).

13
[3] Private communication from the Oklahoma City Fire Department, 1970.

[4] Rogers, F. , Ohlemiller, T. J. , and Summerfield, M. , Studies of the

Smoldering Combustion of Flexible Polyurethane Cushioning Materials

Journal of Fire and Flammability, Vol. 9, pp. 5-13 (January 1978).

[5] Bowes, P. C. and Townshend, S. E. , Ignition of Combustible Dusts on Hot Surfaces, British Journal of Applied Physics, Vol. 13, pp. 105-

114, England (1957).

[6] Thomas, P. H. and Bowes, P. C. , Thermal Ignition in a Slab with One

Face at a Constant High Temperature, Transactions of the Faraday

Society, Vol. 57, pp. 2007-2017, London, England (1961).

17] Schaffer, E. L. , On Smolder Initiation in Cellulosics Under

Prolonged Low Level Heating, Forest Products Laboratory, Madison,

Wisconsin (1979), in preparation.

[8] Jellinek, H. H. G. , Aspects of Degradation and Stabilization of

Polymers, Elsevier Scientific Publishing Co., New York, N.Y.

(1978).

[ 9 J Gross, D. and Robertson, A. F., Self Ignition Temperatures of

Materials from Kinetic Reaction Data, J. Res. Nat. Bur. Stand.

(U.S.), Vol. 61, No. 5, pp. 413-417, (1958).

[10] Raskin, W. H. and Robertson, A. F., An Adiabatic Apparatus for the

Study of Self-Heating of Poorly Conducting Materials, The Review

of Scientific Instruments, Vol. 25, No. 6, pp. 540-544 (1944).

[11] Ohlemiller, T., private communication (1979).

[12] Carslaw, H. S. and Jaeger, J. G. , Conduction of Heat in Solids,

Oxford University Press, London, England (1959).

[13] Knoepfler, N. B. , Madacsi, J. P. and Neumeyer, J. P., Permanence

of Boron Containing Treatment for Cotton Batting Products That

Meet the Mattress Flammability Standard FF 4-72, Journal of Flame

and Flammability/Fire Retardant Chemistry, Vol. 2, p. 65 (May 1975)

[14] Day, M. and Wiles, D. M. , Combustibility of Loose Fill Cellulose

Insulation: The Role of Borax and Boric Acid, Journal of Consumer

Product Flammability, Vol. 5, pp. 113-122 (1978).

[15] Walker, P. L. , Chemistry and Physics of Carbon, London, England

(1968)

.

[16] Hawley, G. G. , Condensed Chemical Dictionary, 8th Edition,

Van Nostrand-Reinhold Co., New York, N.Y. (1972).
[17] Gross, D. , A Preliminary Study of the Fire Safety of Thermal

Insulation for Use in Attics or Enclosed Spaces in Residential

Housing, Nat. Bur. Stand. (U.S.), NBSIR 78-1497 (1978).

[18] Flynn, J. H. and Wall, L. A. , A Quick Direct Method for the

Determination of Activation Energy From Thermogravimetric Data,

Polymer Letters, Vol. 4, pp. 323-328 (1966).

[19] Min, K. , Dynamics of Pyrolysis of Cellulosic Materials. Presented

at the Joint Combustion Institute Meeting, San Antonio, Texas

(1975).

[20] Menis, 0., Status of Thermal Analysis, Nat. Bur. Stand. (U.S.),

Spec. Publ. 338 (1970).

[21] Turner, J. S. , Buoyancy Effects in Fluids, Cambridge University

Press, London, England (1973).

[22] Kreith, F. , Principles of Heat Transfer, 2nd Edition, International

Textbook Co., Scranton, Pa. (1965).

15
Table 1. Results of smolder tests HH-I-515D

Batch

no. Densitypcf

Concentration of chemical—^

Borax Boric acid

% %

Total

%

Weight

loss

%

Remarks

1 3.0 10 10 20 56 fail

2 3.0 10 15 25 54 fail

3 3.0 10 20 30 0 pass

4 3.0 10 25 35 0 pass

5 3.0 0 10 10 0 pass

6 3.0 0 7.5 7.5 0 pass

7 3.0 0 5 5 0 fail

"''Percent chemical as a fraction of the overall weight of the mixture

16
Table 2. Commercial insulation - recessed light fixture test

sterial Density

pcf

Result

C-l 2.9 F

02 2.2 F

03 2.5 F

06 2.3 F

08 2.3 F

09 3.3 F

010 2.0 F

Oil 3.1 F

015^ 2.2 P

2.3 F

3.0 F

016^ 3.0 F

P 3.7 F

Q 3.0 F

— Same material different supplier —^Wood fiber

17
Table

3.

Laboratory

insulation

-

recessed

light

fixture

test

•-s

« t *

< ’ f

4J rH a a

3 Pm P4 Pm #i a a a a pt| ** a a a a

<v PS

Po

4-1 •H <44 O o O co in in o o o

m cj • . • • • • • • • • c a, co co co CO CO CO -d- CO CO CO

<u Q

>

4-1 d d d d d d d d

d d •H •H •H •H •H •H •H •H o cd O CJ O CJ o CJ CJ CJ iH d cd cd cd cd cd cd cd cd CD P4 >4

4-1 |4 rH o O

•H cd CJ X cj CJ CJ o CJ cj CJ 43 43 43

CO 4-1 •H cd t4 •H •H •H •H •H •H Cd Po! a

o <u M U U U M >4 »4 J4 »4 a rH rH a m O O O o O o O o O rH O O

0 43 x> 43 43 43 43 43 43 43 Cd a a

O 0) a O >4 s^s S'? S'? 84? K BS B8 0 8-s 8-S •H m n O <n O <n O O O *H in O <44 rH i-H co co SI- sr in vO CO ' CM CO

d i “ s 44 •rl d >4

cd 00 nd d d

4-1 >4 CD •H d d 4-1 &« B'S 8

s? 8^8 BS <4 8-S 6«S d 4-i cd o o in O in o O 00 © in O

O CD £ 14 •H

•cl co CO co sr >d- in vO01 CO CM CO

cu a u

0 iH cd S * 3

S

18

30%

30%

boric

acid

3.0
Table

4.

Summary

of

experimental

datacommercial

cellulosic

insulations

cl

id •HT3

iduMOO

rH

(44

CM

o» <d 4J

<30 o c

0) rl (d . U U i4 3 U

0) -H T5 H"s > »-i id >

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toa

a) a o

fa o

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4J

Td 0) d 44 >4

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a) *h O .H •H

(U (44 fa

00

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CO

uV

TJ 44

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C/3

fa

44•H «44 CO O d fa

0) Q

n<o(OHn<j NNHHNfl

r>* • • i"

ID 00 • • CM

N 0 0*00 4J y n ti u

ao

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CM

O• • CM sj

O

H CN

H

m

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fa

fa fa fa fa fa fatun fa I fa fa

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u

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cod

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19
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to

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OX

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33

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60 O 3 CM 3 4J *H

QJ ri 'd rl 3X0 3 3 0

3

3

> 3 3 44 £

a 3

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0) 3 3

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CJ r-4 i-4 3 44

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05

CM H rl N • • • V

M CO H O 00 H H CM CO CO o 'J- on uo

CM CO CM CO

• • • • A

CO CO CO CO CO CO CO CO CO CO CO CO

rl rt H CO CO H H H CO >H CO CO

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CO

•Hj pH p4 P4 P4 P4 ^4 P4 P4

>N

4-1 •H

053

3O

44

cjCu

CO

00 uo uo <f

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4-1 3

3

3d3

3

4-) 3

3

3d3

3

3d 3d 3d 33 3d 3d 33 3d 33 33 3d 3d 33 33 33 33 33 3d 33 33 33 33 33

•H •H *H •H •H •H •H •H •H •H •r4 •H •H *H t4 -H cm] •3 *H •3 •H •H •H •H

cj O 0 O CJ a a a O O O a O O O CJ'.* '

b

O 0 O CJ 0 O CJ 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3.; •H 3 3 3 3 3 3 3

0 a 0 O O 0 0 0 a CJ O CJ O O O CJ 3 3 0 O O 0 O O

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3 O 0 O O O 0 O 0 O O O O O O O O •H 0 O O O O O O

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3 0

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3 T—

rH CM CM rH • 1—

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4-J I"- *y i. 3d 3 V 33 3

•H X X X X X 3 3

3d 3 3 3 3 3 1-4 60 3 3 3 3 3 3 3

0 O 0 O O 0 00 3

3 X x X X X rH 3 3 X XI

4-» S-S SN? s-s fr-5 6-e 3 3 3

3 O O 0 O X •H 0- O M rH rH rH 1 1 rH Pn rH X

3 K*» /""N a rH V

3 X 0 0

v-/ M 0-

20
Material

and

retardant

Density

Smolder

Divided

Recessed

Attic

floor

radiant

panel

test

box

light

No.

Density

Average

(515D)

screening

fixture

tests

critical

test

radiant flux %y m

OOin m in on o o o ...

V V

oa

ro m po m co n

w n w

04*

tb

tb

tb tb tb (b tb

tb 04

O

CL

00 n m n ro m m m m

V V V •y •y •y *y *y •y X

•H *H *H i-t *H •H *H -h *5 O

O O O y y y y y hi

•0 y <0 y y y y y o a •y a

y y y 0) y y y y y y

•H ft tI 4J •H tH •H *H *H •y u w u •H U U hi hi hi •H a O 0 0 OS O 0 /—V o o o y y

,0 ,0.0 O

a

«

X» £> <U

•pt Xi X X y X

MHN H K y y o m o •y f-t CM u mom •H y m n ^ • • y oo n n n hi y

<u M0 O y O hi « *y H iH .Q 00 y *h u y i r £ o oo y S>8 Q> a y •H O r“l <u c X JO

hi u « JS y

O *H hi y o a

a u y a b) H

y o O H y > u ^ 6>8 a

o s

/“N w

o •y

•-<1 CM|

(0

(0

(0a.

£

<u m

CNcn

ooc

•H

a)os

*9a. *8m

oo

a)

c

21

—

Polybor,

disodium

octoborate

tetrahydrate,

is

chemically

similar

to

borax,

approximately

70%

passing

325

sieve
I

Figure 1. Cigarette smoldering test

Figure 2. Recessed light fixture test exterior view

22
Figure 4. Divided box test

23

Figure 3. Recessed light fixture test interior view
24
Q3NIV13U %

25

Figure

6.

Average

particle

size

distribution

of

boric

acid

and

borax
SMOLDER

TEST

HH-I-515D

O

O

oz

00

00

X o

2 ^

CO o

g I

T- QQ • o

x

LO E

15

6^

CO QO

Q£O

00

ZZ

SS01 1H9I3M %

26

Figure

7.

Effect

of

borax

and

boric

acid

on

weight

loss

—

smoldering

ignition
27

Figure

8.

Effect

of

borax

and

boric

acid

and

fineness

of

grind

on

critical

radiant

flux

—

attic

floor

radiant

panel
(Go) 3dfUVd3dW31 MflMIXVN

28

Figure

9.

Divided

box

test

—

maximum

temperature

vs

%

chemical

by

weight

of

mix

for

different

grinds

of

boric

acid
o

(Go) 3»nivti3dW3i mnmxvN

29

Figure

10.

Divided

box

test

--

maximum

temperature

vs

%

chemical

by

weight

of

mix

for

polybor
z (ui3/saadap)

^

Figure

11.

Hot

plate

tests

—

untreated

cellulose
31

Figure

12.

Adiabatic

furnace

test

—

untreated

cellulose
Go - dM3i JiVld 10H 1N31VAMH

- imm GllVSVIdV

32

Figure

13.

Comparison

of

smolder

ignition

temperatures

inferred

from

adiabatic

furnace

tests

and

measured

in

hot

plate

tests
APPENDIX A

CRITERIA FOR TIME OF SMOLDERING TESTS

Ohlemiller' s criterion is that the time for the slope of temperature,

dT/dx, at the hot plate to reach a nearly constant value or quasi steady state

is the time that the smoldering test should be run. Ohlemiller calls this time

the "relaxation time". Since this time appears to be significantly less than

that observed in the recessed light fixture test, a detailed analysis of this

criterion was undertaken.

In analyzing Ohlemiller' s approach to relaxation time, the calculations

were redone using dimensionless parameters. These were the Biot number

2

(B. = LH/K) or dimensionless thickness, the Fourier number (F = at/L ) or

1 o dimensionless time, and the dimensionless temperature (T - T )/(T -T). The

o p o Ohlemiller criterion for the time to run a smoldering test is based on Carslaw

and Jaeger [12] case VI page 126, which may be written in the following form:

T =

1 + B

± (1 - x)

1 + B, 5

2

(B2 + B

2

) sin (B • x) n l n

B (B . + Bj + B

2

) n i i n

-B2 Fn o

• e ( 1 )

the dimensionless slope of the dimensionless temperature versus dimensionless

distance is then given by

dT

dx

15 i

X

1 + B.

l -E

2(B2 + B

2

) n i cos (B * x) n n -B2 Fn o

n=l

B (B, + B^ + B

z

) n i x n

( 2 )

A-l
The slope at the hot plate, x = 0, is of primary interest. Thomas

and Bowes [6] found that in their mathematical model for smoldering in a

layer heated on one side the maximum temperature occurs at a short

distance away from the hot plate, at approximately 0.012 <_ x <_ 0.052.

In the calculation for the slope, equation (2) above, the differences in

the time to reach quasi steady state at these locations were negligibly

different from those at the hot plate.

The plot of the slope of the temperature at the hot plate (in

dimensionless terms) , shown in figure A-l, indicates that for relatively

thick layers of insulation, with greater than about 10, Ohlemiller's

criterion is satisfied. That is the slope of the temperature at the hot

plate becomes almost constant after F

q

_> 0.5, approximately. For a

relatively thin layer, B^ about equal to 1, the slope becomes almost

constant only at later times, that is F^ _> 0.9, approximately.

In order to determine the range of actual thicknesses of insulation

corresponding to the range of Biot numbers, it was necessary to determine

a surface coefficient of heat transfer that is independent of the plan

size of the insulation layer. One such relation, given by Turner [21]

is

N = 0.17 u

(3)

after writing out the terms, noting that for air P = 0.7 over a large

range of temperatures [22] we have

H = 0.17

c

(4)

A2
where the material properties refer to those for air, and T

q

is in

absolute temperature. Using the properties for air tabulated by Kreith

[22] we have

H = 4.26 x 10" 5

AT1/3 cal/ (cm2 -s* °C) c

or 1.73 AT1/3 W/(m2 *°K)

The heat losses from the top surface of the layer of insulation should

also include a term for radiation heat losses. This term as given by

Carslaw and Jaeger [12] is

= oe

[T4 _ T4]

S O

T - T

s o with e = 0 . 8 we have

= 1.096 x 10

-12 - T

n

] cal/cm2 *s*°C

T - t

s o

(5)

and

H

T

- H

c +

"r ( 6 )

The results are shown in figure A-2

Equations (4) and (5) show that is a function of the ambient

temperature and the surface temperature. Thus in order to determine the

correct Biot number, or conversely the thickness corresponding to a

particular Biot number, the dimensionless surface temperature was

determined for a range of Biot numbers and Fourier numbers. This is

shown in figure A- 3.
-4

For T of 30°C, IL, = 2.078 x 10 , and for a thickness of insulation of

s 1 10 cm, the Biot number is 16.7. Since this is greater than 10, and referring

to figure 11 we can assume that for most hot plate type smoldering tests, the

layer of insulation is thick and Ohlemiller's criterion is satisfied.

A-4
Figure

A-l.

Dimensionless

slope

vs

dimensionless

time

at

hot

plate
-Olxfi

(

A6

Figure

A-2.

Surface

heat

transfer

coefficient
A7

Figure

A3.

Dimensionless

unexposed

surface

temperature

vs

dimensionless

time

APPENDIX B

RELATIONSHIP BETWEEN HOT PLATE TEST

AND ADIABATIC FURNACE

In both the hot plate test and the adiabatic furnace the activation

energy "E", and the pre-exponential factor "A" are calculated by semi-graphical

procedure.

In the hot plate tests we have

AE E . 1

KR “ R T

while in the adiabatic furnace we have

6T2 In = In ( 8 )

(9)

Both these equations are linear, i.e., are of the form y

= b + mx with the

ordinates scaled logarithmically. In application the data from the test is

plotted on semi-log paper and the activation energy is derived from the slope

and the pre-exponential factor from the intercept. The equations may be calculated by the method of least squares using a hand calculator or computer.

Though the ordinates in equations (8) and (9) have different physical

meanings, if we set the x-axis so that 1/T coincides with 1/T^, and adjust

the scale for the y-axis for equation (8) so that the intercepts for the

curves for both equation (8) and equation (9) occur at the same point, then

the two lines will coincide. The assumptions in this analysis are that the

B-l
phenomena measured in both tests are the same, that the activation energy

and pre-exponential factor are the same as measured in both tests. Though

these assumptions are only approximately satisfied the results which are

discussed in the report are satisfactory.

Determination of ordinate scale.

From equation (1) at the intercept

Equation (13) locates the intercept for the hot plate equation at the

same point as the intercept for the adiabatic furnace equation and the resulting

hot plate equation is

( 10 )

From equation (9) at the intercept (1/T = 0)

(ID

therefore

( 12 )

or

(13)

( 14 )

B-2
inserting the values from the adiabatic furnace tests give

6T2, In = 37.418 - 13273 x (15)

P

The computation method is to select a thickness of insulation layer and

assume a hot plate temperature. Next, using the Bowes-Townshend graph shown

in figure B-l determine 6 and calculate 6 T

2 /r2

. Substitute this last proc c p

duct into equation (15) and determine the corresponding T . Repeat the process

with the new value of until convergence occurs. Usually only one or two

iterations were necessary for convergence. The results are shown in

figure B-2.

B-3
I

II Q?

r

I

ii

i 1.1

m

ii

\

\

H H H H

TT

\

\

\T

\

\

^ ^ . ^ ^

TV—ir

. \

' \ » ' \ \ \

I

ii

TT

\

\

8

8

-

vo

J I I I I L J L

«©

hi

» * * « «

• « O C0 M N « N

«©

B-4

Figure

B-l.

6

as

function

ofB

and
ui3 * SS3NX3IH1 DHIQNOaSBUUOO

z (iuo/saaj3ap)

zJ

iWQ

CVJ

I CO

I

oas/saaj3ap

IP

Figure

B

2.

Correspondence

of

adiabatic

furnace

and

equivalent

hot

plate

test
NBS ' ' (REV. 0-78)

i . OEPT. OF COl* BIBLIOGRAPHIC DATA

SHEET

CATION OR REPORT NO. NBSIR 80-2085

3. Recipient's Wmm>.

mmmmmMmm

amm

4. TITLE AND SUBTITLE

Fire Performance of Loose Fill Cellulosic Insulation in

Residential Occupancies - A Progress Report

5. Publication Date August 1980

7. AUTHOR(S)

Lionel A. Issen

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

• .

•

11. Contract/Grant No.

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

Department of Energy

Washington, D.C. 20585

13. Type of Report & Period Covered Interim

15. SUPPLEMENTARY NOTES

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

16. ABSTRACT (A 200-word or leaa factual aummary of moat aignificant information. If document inctudea a aignificant bibliography or

literature aurvey, mention it here.)

The smoldering and flame spread properties

of cellulosic loose fill insulation were examined

as a function of retardant type, particle size,

and concentration to provide a basis for the development of improved fire test methods. A series of laboratory insulations was prepared

whose fire performance covered an extended range

of critical radiant flux in the attic floor radiant

panel test and weight loss in the cigarette smoldering test. These materials were evaluated in a recessed light fixture test in a simulated attic

configuration. Borax and boric acid were effective

in raising the critical radiant flux (CRF) in the attic floor radiant panel test, but borax alone,

in the cigarette smolder test, increased the smoldering potential of loose fill cellulosic

insulation. The divided box test for smoldering

propagation appears to be a more realistic test than the present test for smoldering ignition.

In the cigarette smoldering test, inclusion

of 10% borax increased the boric acid requirement

for passing from 7.5% to 20%. In the attic floor

radiant panel test, the finer the grind, the less boric acid required to meet Federal Specification

HH-I-515D. This varied from less than 10% for vapor applied boric acid to over 35% for granular

boric acid. Above the 25% level the presence of borax did not significantly affect the CRF level. Passing the recessed light fixture test required

a minimum of 30% impalpable boric acid, or 40% to 50% intermediate grind boric acid.

In order to determine fundamental parameters

which could be used to characterize smoldering

ignition potential, a number of test methods have

been investigated which can be used to determine

the pre-exponential factor and the activation

energy of ignition reaction. These include the Bowes and Townshend hot plate, thermo-gravimetric

analysis (TGA) , and the adiabatic furnace.

17. KEY WORDS (aix to twelve entries; alphabetical order; capitalize only the first letter of the lirat key word unlearn a proper name;

hv *-*~>icolona) Activation energy; borax; boric acid; cellulose; critical radiant flux; fire;

fire retardants; fire tests; loose fill insulation; smoldering ignition; thermal

analysis; thermal insulation.

18. AVAILABILITY Unlimited

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